PASOS Y PRUEBAS FSACONDICIONES GENERALES DE MEDICIN

Todas las indicaciones de prueba se refieren al paso de prueba indicado en elttulo.

Despus de finalizar la prueba, eliminar las intervenciones realizadas y, siconviene, borrar el cdigo de error introducido en la unidad de mando.

Durante la conexin de los emisores, el motor DEBE estar apagado y el encendidodesconectado.

Conectar los bornes negro y rojo del cable de conexin de la batera a labatera.

ATENCIN!

El borne negro del cable de conexin de la batera debe permanecer conectadoal borne B de la batera.

Las indicaciones de conexion son para una secuenciade ensayo aplicable en la mayora de casos.En caso dado, los sensores deben conectarse de otromodo en algunos pasos. Tener en cuenta las indicacionesde conexin de los pasos.

Cuando hay varias indicaciones al mismo puesto enchufesensor, se debe reenchufar el sensor, segn aplicacin.

Los reenchufes pueden minimizarse empleando el "conmutadorentrada CH1 y CH2" (1 687 023 356).

Con este conmutador pueden quedar enchufados, respectivamente,dos sensores en CH1 o CH2.

Con esta medicin (adaptacin completa del primario) se verificansimultneamente los lados primarios de todos los circuitos de encendido.

Usar cables adaptadores especficos del vehculo o uno de los cables adaptadoresprimarios siguientes:

Cables adaptadores primarios UNI II 1 684 461 116Cables adaptadores primarios UNI IV 1 684 462 211 (en equipamiento de serieFSA7xx)Cables adaptadores primarios UNI VIII 1 684 462 374

En los cables adaptadores primarios UNI II, IV, VIII, se conecta el borne verde("Cil. 1/A") con el borne 1 / - de la bobina de encendido para elprimer cilindro y los otros bornes verdes con las identificaciones "B", "C","D", .... al borne 1 / - de las bobinas de los cilindros 2, 3, 4, ...(adaptacin completa del primario)

En distribuciones de alta tensin rotativas, se conecta el borne verde ("Cil. 1/A") del cable primario al borne 1/- de la bobina de encendido.

Deteccin de cilindro 1, ROV, DFS y EFS con emisor de KWConectar la pinza inductiva de disparo al cable de encendido del 1er. cilindro.

Deteccin de cilindro 1, EFS con emisor de NWLa deteccin del cilindro 1 se hace o bien mediante la pinza inductiva dedisparo (conectar a travs del cable de primario hacia el borne 1/- de la bobinade encendido del cilindro 1.) o bien mediante la conexin con la identificacin"Cil. 1/A" del cable adaptador primario.Cuando se hace la unin con el cable adaptador primario, se debe tener en cuentaque la conexin "Cil. 1/A" se conecte al borne 1/- de la bobina de encendido del1er. cilindro.

En sistemas de encendido sin distribuidor (bobinas de chispa nica, bobinas dedoble chispa), los captadores secundarios (negro/- o rojo/+) se sujetan medianelos cables de encendido entre las bobinas de encendido y las bujas deencendido.

En sistemas sin cables de encendido se emplean los captadores secundariosespecficos del vehculo.

En sistemas de encendido con distribuciones de alta tensin rotativas, sujetar 1captador secundario negro/- mediante el cable de encendido entre la bobina deencendido y el distribuidor de encendido.

En las bobinas de doble chispa debe tenerse en cuenta la polaridad de la tensinde encendido.

Los transmisores de valor de medicin secundarios negro/- o rojo/+ se conectan alos diferentes cilindros de forma que las imgenes de encendido se representencon los lados correctos en el osciloscopio, con la aguja de encendido haciaarriba.

Sujetar la pinza de medicin de corriente de 1000 A (CH1) en los pasos de prueba"Batera/arrancador/compresin" y "Generador" en todos los cables a B-(flecha hacia afuera de B-) o en todos los cables a B+ (flecha hacia B+).

Apretar la pinza amperimtrica de 30 Amperios(CH1) en el paso de prueba"encendido primario", a travs de todos los cables, al borne 15/+ de la(s)bobina(s) de encendido (flecha en direccin bobina).

En el paso de prueba "corriente de reposo de la batera", se aprieta lapinza amperimtrica de 30 Amperios(CH1 o CH2), a travs de todos loscables, a B- (flecha saliendo de B-) o, a travs de todos los cables, a B+(flecha hacia B+).

Quitar varilla original de medicin de aceite. Introducir sensor de temperatura del aceite en el mango de la varilla de medicin de aceite.

Atencin! Adaptar longitud de la sonda de temperatura de aceite a longitud de varilla, empujando cono de goma fijable y hermetizar punto de medicin.

Si el mango de varilla de medicin de aceite est inaccesible para la sonda, la temperatura de motor se puede registrar tambin mediante sensor infrarrojos 1 687 230 057 (antiguo ya no sum.) 1 687 230 066 (nuevo con pointer lser).

La punta de medicin del sensor de infrarrojos y la superficie a medir deben estar libres de polvo y lquidos. Si la superficie a medir es fuertemente reflectiva, antes de la medicin, pegar cinta cobertera sobre el punto de medicin. Para la medicin, ir lo ms cerca posible a un punto del bloque motor, donde se pueda medir la temperatura de servicio confiablemente.

Conectar el cable de medicin Multi (CH1) para la medicin de la tensin o de laresistencia en el objeto a medir.

Para la medicin de tensin o bien para la emisin de seales, conectar el cableMultimess (CH2) al componente en "generador de seales".

Con el cable Multimess (CH2) no se pueden realizar mediciones de resistencias.

Para mediciones de presin, debe conectarse el tubo flexible de medicin depresin al componente respectivo.

En caso dado, debe usarse una pieza en T.

En los pasos de prueba "Batera/arrancador/compresin" y en el 2o paso de pruebaparcial de "Encendido primario" debe impedirse que el motor se ponga en marchacon las intervenciones correspondientes.

Resaltar el paso de prueba deseado y arrancar las revoluciones de pruebalentamente desde "abajo".

Todos consumidores "DESCONECTADOS"

Otras informaciones con la tecla "F1" en el paso de prueba respectivo.

Emisor para el registro del nmero de revoluciones:

- pinza de disparo inductiva- cable de conexin primario, conexin "cil. 1 / A" (borne 1, TN, TD)- cable de conexin de batera (conectarlo directamente a la batera)- pinza amperimtrica de 1000 A (en el paso de prueba batera-arrancador)

Si el n rev. de ensayo deseado no se alcanza con una limitacin del n rev. estndar especfica del motor, es necesario desactivar la limitacin estndar durante la comprobacin. Efectuar dicha desactivacin atendiendo a las especificaciones del fabricante y volver activar tras la comprobacin.

En general, la limitacin del nmero de revoluciones estndar se reactiva tras un nuevo arranque del motor.

Tener en cuenta las informaciones en ESI[tronic] y del fabricante del vehculo.

Las indicaciones de conexiones especficas del vehculo y nmeros de pedido de las diferentes adaptaciones se deben ver en el paso de ensayo especfico del vehculo "Condiciones generales de medicin".

Al respecto, seleccionar el tipo de vehculo a travs del respectivo fabricante de vehculos, y elegir el paso de ensayo "Condiciones generales de medicin".

Los valores tericos especficos del vehculo y las indicaciones de ensayo especficas del vehculo para los diferentes pasos de ensayo, se han previsto para una versin ulterior.

CORRIENTE, REPOSO, BATERIA

Electrical energy management An electrical energy management (EEM) system coordinates the interaction between alternator, voltage transformer, batteries and electrical consumers when the vehicle is in use. When the vehicle is parked,the EEM monitors the batteries, and switches standstill-draw and constant-draw equipment off as soon as the battery charge reaches a critical limit. The EEM regulates the entire electrical energy balance. It compares the power demand from the consumers with the power available within the vehicle electrical system and maintains a constant balance between supply and power output.

The basis for the EEM is the battery management. The objective of the battery management is to communicate to the EEM information about the current state of the battery and about predicted electrical behavior. Using this information, it is possible to implement operating strategies for increasing vehicle availability and profitability.

The battery management communicates to the EEM the variables relevant to the battery, e.g. the state of charge (SOC), the state of health (SOH) and the state of function (SOF) of the battery. SOF is a prediction of how the battery would react to a predefined load profile, e.g. whether a starting operation would be successful with the current battery status. These values are calculated using complex, model-based algorithms from the measurement of battery current, voltage and temperature.

Using this battery data, the EEM is able to determine the optimal charge voltage and reduce the load on the electrical system (switch off consumers) in response to a degrading state of function and/or increase power generation (e.g. by increasing the idling speed).If the batterys state of function falls below a specified threshold value despite the measures that have been implemented, the EEM can warn the driver that certain functions (e.g. engine start) will not be available with the current battery status.

Battery status recognitionThe control unit that makes battery status recognition (BSR) possible is the electronic battery sensor EBS (sometimes even EEM functions are implemented in this control unit). The sensor with integrated evaluation electronics records the fundamental battery variables of voltage, current and temperature. From these variables, it uses complex software algorithms to calculate the variables that describe the status of the car battery.

The following tasks of the electrical energy management are made possible by the use of battery status recognition:

- Assurance of startability (SOF) through compliance with defined limit values of the battery state of function and an increase in vehicle availability- Reductions in electrical load requirements and reductions in fuel consumption by means of alternator management with adaptation of alternator voltage- Greater flexibility in the design of battery and alternator size by means of superordinate energy management (optimal economic efficiency)- Extension of battery life (e.g. through prevention of exhaustive discharge)- Battery change indication.Two-battery vehicle electrical systemIn the design of a vehicle battery, which supplies both the starter and the other consumers in the vehicle electrical system, a compromise has to be found between different requirements.

During the engine starting sequence, the battery is subjected to high current loads (300...500 A). The associated voltage drop has an adverse effect on certain electrical equipment (e.g. units with microcontroller) and should be as low as possible. On the other hand, only comparatively low currents flow during vehicle operation; for a reliable power supply, the capacity of the battery is the decisive factor. Neither properties rated output nor capacity can be optimized simultaneously.

In vehicle electrical systems with two batteries (starter battery and general-purpose battery), the high power for starting and general-purpose electrical supply functions are separated by the vehicle electrical system control unit to make it possible to avoid the voltage drop during the starting process, while ensuring reliable cold starts, even when the charge level of the general-purpose battery is low.

Starter battery The starter battery must supply a high amount of current for only a limited period of time (during starting). It is therefore designed for a high power density (high power for low weight). Compact dimensions allow installation in the immediate vicinity of the starter motor with short connecting cables. The capacity is reduced.

General-purpose battery This battery only supplies the vehicle electrical system (excluding the starter). It provides currents for supplying the consumers of the vehicle electrical system (e.g. approx. 20 A for the engine-management system) but has a high cyclic capability, i.e. it can supply and store large amounts of power. Dimensioning is based essentially on the capacity reserves required for activated consumers, the consumers that operate with the engine switched off (e.g. no-load-current consumers, parking lights, hazard warning flashers, immobilizer), and the minimum permissible charge level.

Vehicle electrical system control unitThe control unit (VES ECU) in a two-battery vehicle electrical system separates the starter battery and the starter from the rest of the vehicle electrical system provided this can be supplied with sufficient power by the general-purpose battery. It therefore prevents the voltage drop that occurs during starting, affecting the performance of the vehicle electrical system. When the vehicle is parked, this prevents the starter battery from becoming discharged electrical equipment that draws current when switched on when the engine is switched off and standstill-draw devices.

By separation of the starting system from the remainder of the vehicle electrical system, there are theoretically no limits for the voltage level within the starting system. Consequently, the charge voltage can be optimally adapted to the starter battery by a DC/DC converter to minimize the charging time.

If there is no charge in the general-purpose battery, the control unit is capable of provisionally connecting both vehicle electrical systems. This means that the vehicle electrical system can be sustained using the fully-charged starter battery. In another possible configuration, the control unit for the starting operation would connect only the start-related consumers to whichever battery was fully charged.Two-battery vehicle electrical system1 Starter, 2 Starter battery, 3 Vehicle electrical system ECU, 4 Alternator, 5 Electrical loads, 6 Engine ECU, 7 General-purpose battery.

BatteryCharging and dischargingThe active materials in a lead-acid battery are lead dioxide (PbO2) on the positive plates, spongy, highly porous lead (Pb) on the negative plates, and electrolyte composed of diluted sulfuric acid (H2SO4). The electrolyte is simultaneously an ion conductor for charging and discharging. Compared with the electrolyte, PbO2 and Pb adopt typical electrical voltages (individual potentials). Their magnitudes (disregarding the electrical sign) are equal to the sum of the cell voltages measurable from the outside (Figure C). It is approximately 2V in standby. When the cell discharges, PbO2 and Pb combine with H2SO4 to form PbSO4 (lead sulfate). This conversion causes the electrolyte to lose SO4 (sulfate) ions, and its specific gravity decreases. During the charging process, the active materials PbO2 and Pb are reconstituted from the PbSO4.Electrical parameters inside and on the battery (Figure C).IE Discharge current Ri Internal resistance RV Load resistance U0 Steady-state voltage UK Terminal voltage Ui Voltage drop across internal resistance

Discharged cell before chargingPbSO4, which is made up of the ions Pb++ and SO4, is on both electrodes. The electrolyte consists of low specific-gravity H2SO4 due to previous current demand resulting in the formation of H2O.

Charging process Pb++ is converted to Pb++++ at the positive electrode due to electron stripping. This combines with O2 from H2O to form PbO2. On the other hand, Pb is formed at the negative electrode. The SO4 ions released from PbSO4 on both electrodes and H+ ions from H2O create new H2SO4 and increase the specific gravity of the electrolyte.

If the charge voltage continues to be applied after the cell has reached a state of full charge, only the electrolytic decomposition of water occurs. This produces oxygen at the positive plate and hydrogen at the negative plate (oxyhydrogen gas). The specific gravity of electrolyte can be used to indicate the state of charge of the battery (see Table 1). The accuracy of this relationship depends on battery design, electrolyte stratification, and battery wear with a certain degree of irreversible sulfating and/or a high degree of shedding of plate material.

Table 1. Electrolyte values of the dilute sulfuric acid in a typical auto starter battery

ChargestatusElectrolyte density kg/l 1)Freezing threshold C

charged1.28-68

semi-charged1.16/1.20 2)-17...-27

discharged1.04/1.12 2)-3...-11

1) At 20C: the electrolyte density drops by approximately 0.01 kg/l for every 14 K that the temperature rises and vice-versa when the temperature drops2) Low value: high electrolyte utilization. High value: low electrolyte utilizationCharged cellPbSO4 on the positive electrode is converted to PbO2, and PbSO4 on the negative diode is converted to Pb. There is no further rise in charge voltage or the specific gravity of the electrolyte.Discharging processThe direction of current flow and the electrochemical processes during discharging are reversed in relation to charging. This results in a combination of Pb++ and SO4 ions on both electrodes to form the discharge product PbSO4.

Battery voltage curves as a function of the discharge time for various discharge currents (Figure E).

Deliverable capacity as a function of discharge current and temperature (Figure F).

BATERIA / ARRANCADOR / COMPRESIN

Using the batteryChargingIn vehicle electrical systems, the battery is charged using voltage limitation. This corresponds to the IU charging method, where the battery charge current reduces automatically as the steady-state voltage rises (Figure G). The IU charging method prevents damage due to overcharging, and makes sure that the battery has a long service life.Charging using the IU characteristic curve (Figure G).1Charge voltage, 2 Charge current.

Battery chargers, on the other hand, still operate using constant current or the Wcharacteristic curve (see Figure H). In both cases, once the full state of charge has been reached, charging continues with only a slightly reduced, or possibly a constant current. This leads to high water consumption and to subsequent corrosion of the positive grid.Charging using the W characteristic curve (Figure H).1Charge voltage, 2 Charge current.

DischargingShortly after discharging begins, the voltage in the storage battery drops to a value which only changes relatively slowly if discharging continues. Only shortly before the end of the discharging process will the voltage collapse sharply due to exhaustion of one or more of the active components (positive material, negative material, electrolyte).

Self-discharge (see also Battery maintenance)Batteries discharge over a period of time even if they are not subjected to loads, i.e. when no electrical equipment is connected. Modern batteries using the lead-antimony alloy lose approximately 0.1...0.2% of their charge daily when new. As battery ages, this value can increase by up to 1% or more each day due to the migration of antimony to the negative plate and other impurities, until a point is reached when the battery finally stops functioning. A rule of thumb for the impact of temperature: the self-discharge rate doubles for every 10K rise in temperature.

Lead-calcium batteries have a considerably lower rate of self-discharge (by a factor of 1:5). This remains virtually constant throughout their entire service life.

Battery maintenanceOn low-maintenance batteries, the electrolyte level should be inspected in accordance with the manufacturers operating instructions; when required, it should be replenished to the MAX mark with distilled or demineralized water. The battery should be kept clean and dry to minimize self-discharge. It is also advisable to test the electrolytes specific gravity before the onset of winter or, if this is impossible, measure the battery voltage. The battery should be recharged when the specific gravity is below 1.20g/ml, or the battery voltage is under 12.2V. Terminal posts, terminal clamps, and fixings should be coated with acid-protection grease.

Batteries temporarily removed from service should be stored in a cool, dry place. The electrolytes specific gravity and/or the battery voltage should be checked every 3 to 4 months. The battery should be recharged whenever the electrolyte specific gravity drops below 1.20g/ml or the battery voltage is below 12.2V. Low-maintenance and maintenance-free batteries are best recharged with the IU method (see Charging) at a maximum voltage of 14.4V.This method allows adequate charging times in the order of 24hours without any risk of overcharging. If a constant-current or W-characteristic battery charger is used, the current (in A) should be reduced to max. 1/10 of the nominal capacity when gassing is first observed,i.e. at a current of 6.6 A on a 66Ah battery. The battery charger should be switched off about 1hour afterwards.

The charging area should be well ventilated (oxyhydrogen gas, risk of explosion, no naked flames, or sparks), and the operator should wear protective goggles.

Battery malfunctionsBattery failures which are traceable to internal faults (such as short-circuits caused by separator wear, or loss of active material,broken cell connectors or plate straps)can rarely be rectified by repair. The battery has to be replaced. Internal short-circuits are indicated by major fluctuations in specific-gravity readings between cells (difference between max. and min. > 0.03g/ml). When an open circuit occurs in the cell connectors, low currents can often be taken from the battery and it can also be charged, but even when fully charged, the voltage collapses when an attempt is made to start the engine.

If no defects can be found in a battery which consistently loses its charge (indication: low specific gravity in all cells, no starting power), or is overcharged (indication: high water loss), this suggests a malfunction in the vehicle electrical system (faulty alternator,electrical equipment remains on when the engine is switched off due to faulty relays for instance, voltage regulator set too high or too low, or regulator completely inoperative).

In batteries which are deeply discharged for a long period, the fine crystalline lead sulfate that occurs when the battery is discharged may turn into large crystals, making the battery more difficult to recharge.

StarterTesting directly on the vehicleFirst of all, the battery voltage must be tested under load, and the electrolyte level and specific gravity must be checked.

The following faults can be identified by listening to the sound of the starter when it is turning:- Unusual noises when starting- Starter engages but either only turns the engine slowly or fails to turn it at all- No starter-engagement sound- Starter fails to disengage or disengages too slowly

If unusual noises occur when starting, the fault can be traced to either the starter itself, the way it has been fitted, or the flywheel ring gear. Other problems require systematic electrical testing of the starting system (e.g. using an engine analyzer).

The following tests are carried out with the starter at rest:- Voltage at terminal 30- Continuity of wires or- Contact resistances of wires

The tests carried out during the starting sequence are:- Voltage at terminal 50- Voltage at terminal 30, and- Starter power consumption

Repairing startersFirst of all, the starter pinion is checked for damage (broken or worn teeth, etc.) and replaced if necessary. Various testers are then used as specified by the relevant servicing instructions. In addition, each starter type requires special tools for disassembly and reassembly, and for locating and correctly repairing faults inside the starter.

Testing the starter on the combination test benchAfter the starter has been fixed to the starter test bench on the combination test bench (see figure below), the speed sensor is adjusted, and the wires are connected to the starter.

The tests essentially consist of:- a no-load test, and - a short-circuit or load test. With more recent types of starter, the short-circuit test is no longer permissible and has therefore been replaced by a load test.Starter motor mounted on test bench1 Ring gear, 2 Starter, 3 Guard, 4 Speed sensor, 5 Handwheel, 6 Clamping bracket, 7 Clamping flange, 8 Test bench.

ALTERNADOR

Test technology for alternatorsTesting directly on the vehicleA visual inspection centers on the drive belt, wiring and the alternator indicator lamp. Basically, electrical testing is carried out using a motor tester or a voltmeter/ammeter for measuring the following measured variables:- Oscillograph of DC voltage with low harmonics component (between D+, B+ and B)- Alternator voltage (between B+ and B)- Quiescent current- Battery voltage- Continuity of wires and contact resistances of wires.Repairing alternatorsTest equipment used: alternator tester and coil-winding short-circuit testers. In addition, each alternator type requires special tools for locating the fault within the alternator and repairing it correctly.Testing the alternator on the combination test benchAfter repair, the alternator is fixed to the alternator test bench on the combination test bench (see figure on next page). Depending on the alternator type, it is normally possible to drive it directly at test speeds up to 6,000 rpm. For higher speeds, the drive is transmitted via a drive belt.After setting the position of the alternator and tensioning the drive belt on the clamping fixture, the speed sensor is adjusted. The wires are then connected to the alternator.In order to test an alternator, it is driven to two points on its output curve; in other words, at two different test speeds within its output curve, the alternator is subjected to the required load current by means of a variable load resistance. The alternator voltage must remain above a specified limit. If it does, the alternator is ready for service.Combination test bench for starters and alternators.1 Control panel for alternator and starter testing, 2 Variable load resistance (alternator testing), 3 Handwheel for test-bench vertical adjustment (alternator testing), 4 Alternator test bench, 5 Protection hood (alternator testing), 6 Storage compartment, 7 Display unit, 8 Lighting console, 9 Socket for speed sensor (starter and alternator testing), 10 Starter test bench, 11 Starter terminals, 12 Battery compartment with door, 13 Pedal for starter load (drum brake).

Alternator mounted on test bench1 Guide, 2 Clamping fixture, 3 Swivel arm, 4 Speed sensor, 5 Drive motor, 6 Drive belt, 7 Alternator, 8 Test bench.

ENCENDIDO PRIMARIO ADAPTACIN COMPLETA

Ignition systemsOn modern vehicles, the ignition systems are almost always incorporated as subsystems of the engine-management system. Autonomous ignition systems are now only used for special applications (e.g. small engines). In the case of ignition systems for automobiles, coil ignition (inductive ignition) with a separate ignition circuit per cylinder (static high-voltage distribution with single-spark coils) has come to the fore. Alongside this, but to a much lesser extent, high-voltage capacitor ignitions (capacitive ignition) or other special designs such as magnetos are used for small engines. The next section will focus on coil ignition alone.Structure of an ignition circuit with single spark coils1 Ignition driver stage, 2 Ignition coil, 3 Activation arc diode (suppression of activation spark), 4 Spark plug. 15, 1, 4, 4a Terminal designations, Triggering signal.

Coil ignition (inductive ignition)

Principle of coil ignitionThe ignition circuit of a coil-ignition system consists of: - An ignition coil with a primary and a secondary winding - An ignition driver stage to control the current by means of the primary winding (integrated in the engine control unit or in the ignition coil) - A spark plug connected to the high-voltage connection point of the secondary winding

Before the desired moment of ignition, the ignition driver stage switches a current from the vehicle electrical system through to the primary winding of the ignition coil. While the primary current circuit is closed (dwell period), a magnetic field builds up in the primary winding.

At the moment of ignition, the current through the primary winding is interrupted again, and the magnetic-field energy is discharged, mainly via the magnetic-coupled secondary winding (induction). In the process, a high voltage is produced in the secondary winding, which in turn generates the spark at the spark plug. The ignition voltage required at the spark plug (ignition voltage demand) must always be less than the maximum possible ignition voltage in the ignition system (ignition voltage supply).

After flashover, the remaining energy is converted at the spark plug while the spark is present.

Functions of an ignition system with coil ignitionThe basic functions of an inductive ignition system are:- Determining the moment of ignition- Determining the dwell period- Ignition release

Ignition system with single spark coils1 Ignition lock, 2 Ignition coil, 3 Spark plug, 4 Control unit, 5 Battery.

Determining the moment of ignitionThe current moment of ignition in each case is determined from program maps depending on the operating point and output.

Determining the dwell periodThe required ignition energy is made available at the moment of ignition. The amount of ignition energy is dependent on the amount of primary current at the moment of ignition (cutoff current) and the inductance of the primary winding. The amount of cutoff current is mainly dependent on the operating time (dwell period) and on the battery voltage at the ignition coil. The dwell periods required to achieve the desired cutoff current are contained in characteristic curves or program maps as a function of the steady-state voltage. The change in dwell period with temperature can also be compensated for.

Ignition releaseThe ignition release ensures that the ignition spark occurs at the right cylinder at the right time and with the required level of ignition energy. On electronic-controlled systems, a trigger wheel with a fixed-angle reference mark (typically 60 - 2 teeth) located on the crankshaft is usually scanned by an induction-type pulse generator (sensor system). From this, the control unit can calculate the crankshaft angle and the momentary rotational speed. The ignition coil can be switched on and off at any required crankshaft angle. An additional phase signal from the camshaft is required for the unambiguous identification of the cylinder.

For each combustion, the control unit uses the desired moment of ignition, the required dwell period and the current engine speed to calculate the switch-on time and switches on the driver stage. The moment of ignition, or the switchoff point for the driver stage, can be triggered either when the dwell period expires or when the desired angle is reached.

ENCENDIDO SECUNDARIO ADAPTACIN COMPLETA

Ignition Basic principles

On a spark-ignition (SI) engine, the combustion process is initiated by an externally supplied ignition. The ignition is responsible for igniting the compressed A/F mixture at the right time. This is done by producing an electric spark between the electrodes of a spark plug in the combustion chamber.

Consistent, reliable ignition under all conditions is essential to ensure fault-free engine operation.

Misfiring leads to: - Combustion misfires - Damage or destruction of the catalytic converter - Poor exhaust emission figures - Higher consumption - Lower engine output Ignition spark An electric spark can only occur at the spark plug if the necessary ignition voltage is exceeded. The ignition voltage is dependent on the spark-plug electrode gap and the density of the A/F mixture at the moment of ignition. After flashover, the voltage at the spark plug drops to the firing voltage. The firing voltage depends on the length of the spark plasma (electrode gap and excursion by the A/F mixture flow).

During the ignition-spark combustion time (spark duration), the ignition-system energy is converted into the ignition spark. After the spark has broken away, the voltage is damped and drops to zero.Spark-plug voltage characteristic with static or semi-static A/F mixture1 Ignition voltage, 2 Firing voltage, t Spark duration.

Mixture ignition and ignition energyThe electric spark between the spark-plug electrodes generates a high-temperature plasma. If mixture conditions at the spark plug are suitable and sufficient energy has been supplied by the ignition system, the resulting arc develops into a flame front that propagates of its own accord.

The ignition must guarantee this process under all engine operating conditions. Under ideal conditions, provided that the A/F mixture is stationary, homogeneous and stoichiometric, for each individual ignition process an energy of approx. 0.2 mJ is required to ignite the mixture by means of electric spark. In real engine operation, however, much higher energy levels are required. Some of the spark energy is converted at flashover, and the rest in the spark combustion phase.

Larger electrode gaps generate a larger arc, but require higher ignition voltages. Lean A/F mixtures or turbocharged engines need higher ignition voltages. At a given level of energy, the spark duration shortens as the ignition voltage increases. A longer spark duration generally stabilizes the combustion; lack of mixture homogeneity at the moment of ignition in the area of the spark plug can be compensated for by means of a longer spark duration. A/F-mixture turbulences such as occur in the stratified-charge mode with gasoline direct injection can divert the ignition spark to such an extent that it extinguishes. Follow-up sparks are then required to ignite the A/F mixture again.

The need for higher ignition voltages, longer spark durations, and the provision of follow-up sparks have resulted in the design of ignition systems with higher ignition energy. If not enough ignition energy is produced, ignition will not occur, resulting in combustion misses. The system must therefore deliver enough ignition energy to ensure reliable ignition of the A/F mixture under all operating conditions.

Efficient fuel atomization and good access of the A/F mixture to the ignition sparks enhance ignitability, extend spark duration and spark length, and lengthen the electrode gap. The dimensions of the spark plug determine the position and length of the spark; spark duration depends on the type and design of the ignition system, as well as on the instantaneous ignition conditions in the combustion chamber. Dependent on the engine requirements (intake-manifold injection, gasoline direct injection or turbo), the spark energy of ignition systems lies in a range from approx.30...100mJ.PUNTO DE ENCENDIDO

Moment of ignition The start of combustion in a spark-ignition (SI) engine can be controlled by selecting the moment of ignition. The moment of ignition is always referred to the top dead center of the spark-ignition (SI) engine power cycle. The earliest possible moment of ignition is determined by the knock limit, and the latest possible moment of ignition by the combustion limit or the maximum permissible exhaust-gas temperature.

The moment of ignition influences:- The delivered torque- The exhaust-gas emissions- The fuel consumption

Basic ignition pointThe speed at which the flame front propagates in the combustion chamber increases with higher cylinder charge and higher rotational speed. To deliver maximum engine torque, maximum combustion, and thus maximum combustion pressure, should occur shortly after top dead center. Ignition must therefore occur before top dead center, and the moment of ignition must be advanced as rotational speed increases or charge decreases.

Likewise, the moment of ignition must also be advanced in the case of lean A/F mixtures, because the flame front propagates more slowly. Ignition timing adjustment, therefore, essentially depends on rotational speed, charge, and the excess-air factor. The moments of ignition are determined on the engine test bench and in the case of electronic engine management systems are stored in program maps.Combustion-chamber pressure characteristic for various moments of ignition1 Ignition (Za) at the correct point in time,2 Ignition (Zb) too advanced,3 Ignition (Zc) too retarded.

Ignition timing corrections and operation-dependent moments of ignitionElectronic engine-management systems can take other effects on the moment of ignition into consideration in addition to rotational speed and charge. The basic moment of ignition can either be modified by means of additive corrections or replaced for certain operating points or ranges by special ignition timing angle or ignition timing angle program maps. Examples of ignition timing corrections are knock control, the correction angle for the gasoline direct injection homogeneous-lean operation, and warm-up. Examples of special ignition angles or ignition maps are gasoline direct injection stratified-charge operation, and starting operation. Final implementation depends on the prevailing electronic control unit concept.

Exhaust gas and fuel consumption The moment of ignition has a considerable impact on exhaust gas because it can be used to control the various untreated exhaust-gas constituents directly. However, the various optimization criteria, such as exhaust gas, fuel economy, drivability, etc., may not always be compatible, so it is not always possible to derive the ideal moment of ignition from them.

Shifts in the moment of ignition induce mutually inverse response patterns in fuel consumption and exhaust-gas emissions. Whereas more spark advance increases power and reduces fuel consumption, it also raises HC and, in particular, nitrogen-oxide emissions. Excessive spark advance can cause engine knock that may damage the engine. Retarded ignition results in higher exhaust-gas temperatures, which can also harm the engine.

Electronic engine-management systems featuring programmed ignition curves are designed to adapt the moment of ignition in response to variations in factors such as rotational speed, load, temperature, etc. They can thus be employed to achieve the optimum compromise between these mutually antagonistic objectives.

Knock control Basic principlesElectronic control of the moment of ignition offers the possibility of accurate control of the ignition angle as a function of rotational speed, load, temperature, etc. Nevertheless, if there is no knock control, there must still be some means to define a clear safety margin to the knock limit.

This margin is necessary to ensure that, even in the most knock-sensitive case with regard to engine tolerances, engine aging, environmental conditions, and fuel quality, no cylinder can reach or exceed the knock limit. The resulting engine design leads to lower compression, retarded moments of ignition, and thus worsening of fuel consumption and torque.

These disadvantages can be avoided through the use of knock control. Experience shows that knock control increases engine compression and significantly improves fuel consumption and torque. Now, however, the pilot control ignition angle no longer has to be determined for the conditions most sensitive to knocking rather for the conditions least sensitive to knocking (e.g. compression of the engine at lowest tolerance limit, best possible fuel quality, cylinder least sensitive to knocking). Each individual engine cylinder can now be operated throughout its service life in virtually all operating ranges at its knock limit, and thus at optimum efficiency.

For this type of ignition angle adjustment, a reliable method of knock detection is essential. It should detect knock for each cylinder throughout the engines operating range starting from a specified knock intensity.

Knock-control systemA knock-control system consists of:- Knock sensor- Signal evaluation- Knock detection- Ignition-angle control system with adaptation facility

Schematic of knock control

Knock sensorTypical features of knocking combustion are high-frequency vibrations in the combustion chamber that override the low-pressure development. These vibrations are best detected directly in the combustion chamber by means of pressure sensors. As fitting these pressure sensors in the cylinder head for each cylinder still involves relatively high overhead and costs, these vibrations are usually picked up using knock sensors fitted to the exterior of the engine. These piezo-electric acceleration sensors pick up the characteristic vibrations of knocking combustion and convert them into electrical signals.

There are two types of knock sensor. A wide-band sensor, with a typical frequency band of 5...20 kHz, and a resonance sensor, which preferably transmits only one knock-signal resonant frequency. When combined with the flexible signal-evaluation system in the control unit, it is possible to evaluate different or several resonant frequencies from one wide-band knock sensor. This improves knock detection performance, which is why the wide-band knock sensor is increasingly replacing the resonance sensor.

To ensure sufficient knock detection in all cylinders and across all operating ranges, the number and location of the required knock sensors must be carefully determined for each engine type. Four-cylinder in-line engines are usually fitted with one or two knock sensors, while 5- and 6-cylinder engines are fitted with two, and 8- and 12-cylinder engines with four knock sensors.

Signal evaluationFor the duration of a timing range in which knock can occur, a special signal evaluation circuit in the control unit evaluates from the wide-band signal the frequency band(s) with the best knock information and generates a representative variable for each combustion process. This extremely flexible signal-evaluation system using a wide-band sensor produces considerably better knock-detection results than a resonance knock sensor. This is because the resonance knock sensor transmits just one resonant frequency for analysis for all cylinders assigned to it and across the entire engine map.

Knock detectionThe variable produced by the signal-evaluation circuit is classified in a knock-detection algorithm as knock or no knock for each cylinder and for each combustion process. This is done by comparing the variable for the current combustion process with a variable which represents combustion without knock.

Ignition-angle control system with adaptation facilityIf combustion knock is detected in a cylinder, the moment of ignition for that cylinder is retarded. When knock stops, the moment of ignition is advanced again in stages up to the precontrol value. The knock-detection and knock-control algorithms are matched in such a way as to eliminate any knock that is audible and damaging to the engine, even though each cylinder is operated at knock limit within the optimum efficiency range.

Real engine operation produces different knock limits, and thus different moments of ignition for individual cylinders. In order to adapt precontrol values for the moment of ignition to a particular knock limit, the ignition retard values are stored for each cylinder dependent on the operating point. They are stored in non-volatile program maps in the permanently powered RAM for load and engine speed. In this way, the engine can be operated at optimum efficiency at each operating point and without audible combustion knocks, even if there are rapid load and engine-speed changes.

This adaptation even enables the use of fuels with lower antiknock properties (e.g. regular instead of premium grade petrol).INYECCIN

Mixture formation Basic principlesA/F (Air/fuel) mixtureTo be able to operate, a spark-ignition (SI) engine requires a specific A/F ratio. Ideal theoretical complete combustion is available at a mass ratio of 14.7:1. This is also termed the stoichiometric ratio, i.e. 14.7 kg of air are required to burn 1 kg of fuel. Or, expressed as a volume: 1 l fuel burns completely in roughly 9,500 l air.

The specific fuel consumption of a spark-ignition (SI) engine is essentially dependent on the mixture ratio of the A/F mixture. Excess air is required in order to ensure genuine complete combustion, and thus as low a fuel consumption as possible. However, limits are imposed due to the flammability of the mixture and the available combustion time.

The A/F mixture also has a decisive impact on the efficiency of exhaust-gas treatment systems. State-of-the-art technology is represented by the three-way catalytic converter. However, it needs a specific stoichiometric A/F ratio in order to operate at maximum efficiency. This can reduce damaging exhaust gas components by higher than 98%. The engines available today are therefore operated with a stoichiometric mixture as soon as their operating status allows this.

Certain engine operating statuses require mixture adaptation. Selective modifications to the mixture composition are required e.g. in the case of a cold engine. The mixture-formation (carburation) system must therefore be in a position to satisfy variable requirements.

Excess-air factor The excess-air factor or air characteristics (Lambda) has been chosen to indicate how far the actual A/F mixture deviates from the theoretically ideal mass ratio (14.7:1):

defines the ratio of the actually supplied air mass to the theoretical air mass required for complete (stoichiometric) combustion.

=1: The inducted air mass corresponds to the theoretically required air mass.

=1: This indicates air deficiency and therefore a rich A/F mixture. Maximum power output results at = 0.85...0.95.

>1: In this range, there is an air surplus or lean mixture. This excess-air factor is characterized by reduced fuel consumption, but also by reduced power output. The maximum value for the lean-misfire limit that can be achieved is very strongly dependent on the construction of the engine and the mixture-formation system used. The mixture is no longer ignitable at the lean-misfire limit. Combustion misses occur, and this is accompanied by a marked increase in uneven running.

Spark-ignition (SI) engines with intake-manifold fuel injection achieve the lowest fuel consumption at constant engine output dependent on the engine at 20...50% air surplus ( = 1.2...1.5).

For a typical engine with intake-manifold injection, the illustrations show the dependency of the specific fuel consumption and uneven running as well as development of pollutants on the excess-air factor at constant engine output. It can be deduced from these graphs that there is no ideal excess-air factor at which all the factors assume the most favorable value. In order to implement optimal consumption at optimal power output, excess-air factors of =0.9...1.1 have proven conducive to the achievement of objectives for engines with intake-manifold injection.

Engines with direct injection and charge stratification involve different combustion conditions so that the lean-misfire limit occurs at significantly higher lambda values. In the part-load range, these engines can therefore be operated with considerably higher excess-air factors (up to = 4).

For the catalytic exhaust-gas treatment by a three-way catalytic converter, exact adherence to =1 is obligatory with the engine at operating temperature. To achieve this, the air mass drawn in must be precisely recorded and an exactly metered fuel mass added to it.

For optimum combustion in engines with intake-manifold injection that are common today, not only is a precise injected fuel quantity necessary, but also a homogeneous A/F mixture. This requires efficient fuel atomization. If this precondition is not satisfied, large fuel droplets will precipitate on the intake manifold or the combustion-chamber walls. These large droplets cannot fully combust and will result in increased hydrocarbon emissions.Mixture-formation systemsIt is the job of fuel-injection systems, or carburetors, to provide an A/F mixture which is adapted as well as possible to the relevant engine operating status. Fuel-injection systems, especially electronic systems, are better designed to maintaining narrowly defined limits for A/F mixture composition. This helps to improve fuel consumption, drivability, and power output. Increasingly stringent emission-control legislation has meant that, in the automotive sector, fuel-injection systems have completed superseded the carburetor.

Until now, the automotive industry has almost exclusively used systems in which mixture formation takes place outside the combustion chamber. Systems with internal mixture formation, i.e. where the fuel is injected directly into the combustion chamber, are designed to reduce fuel consumption even further and are therefore becoming increasingly important.Intake-manifold injection (external mixture formation)Gasoline injection systems for external mixture formation are characterized by the fact that the A/F mixture is created outside of the combustion chamber (in the intake manifold). Although carburetor engines also utilize external mixture formation, they have been almost completely superseded by spark-ignition (SI) engines with intake-manifold injection because they feature better fuel metering and fuel management. The state of the art is represented by electronic intake-manifold injection systems where the fuel is injected intermittently for each individual cylinder, i.e. with a temporal interruption, directly ahead of the inlet valves.

Systems that are based on mechanical-continuous fuel injection or a central fuel injection arranged upstream of the throttle valve are practically no longer of any significance for new developments.

The high requirements for engine smooth running and exhaust emissions make high demands on the A/F mixture composition in each power cycle. Precise injection timing is vital as well as precise metering of the injected fuel mass as a factor of the engine intake air. In electronic multipoint fuel-injection systems, therefore, not only is each engine cylinder assigned an electromagnetic fuel injector, but this fuel injector is also activated individually for each cylinder. The control unit has the task of calculating both the required fuel mass for each cylinder and the correct start of injection for the fuel mass drawn in and the current engine operating status. The injection time required to inject the calculated fuel mass is a function of the opening cross-section of the fuel injector and the pressure differential between the intake manifold and the fuel supply system.

In intake-manifold injection systems, fuel is sent via the electric fuel pump, fuel supply lines, and filters at primary pressure to the fuel rail, which ensures that the fuel is evenly distributed to the fuel injectors. How the fuel is prepared by the fuel injectors is extremely important for the quality of the A/F mixture. It is essential that the fuel is atomized into the very fine droplets. The spray shape and spray angle of the fuel injectors are adapted to the geometric circumstances in the intake manifold or cylinder head.If the precisely metered fuel mass is injected directly upstream of the cylinder intake valve(s), most of the finely atomized fuel may evaporate. The required A/F mixture can therefore be formed at the right time using the air flowing in via the throttle valve. The amount of time available for mixture formation can be increased by injecting the fuel into the intake valves that are still closed.

A proportion of the fuel precipitates onto the wall near the intake valves and forms a film; the thickness of this film essentially depends on the pressure in the intake manifold, and thus on the engine load condition. In the case of non-stationary or dynamic engine operation, this precipitation can lead to temporary deviations in the desired lambda value ( =1), which means that the fuel mass stored in the wall film is to be kept as low as possible. Wall coating effects in the intake duct, particularly in cold start conditions, cannot be neglected either: As fuel does not evaporate sufficiently, more fuel is required initially in the starting phase in order to create an ignitable A/F mixture. When the intake-manifold pressure then drops, parts of the previously formed wall film will vaporize. This may result in increased HC emissions if the catalytic converter is not running at operating temperature. Irregular fuel injection may also result in the formation of wall films in the combustion chamber, and may in turn become critical emission sources. Defining the geometric alignment of fuel sprays (spray targeting) will allow the selection of suitable fuel injectors which will control or minimize manifold-wall fuel condensation in the area of the intake duct and the intake valves.

Compared with carburetor engines and single-point injection systems, manifold-wall fuel condensation in multipoint injection systems is reduced significantly. At the same time the intake manifolds used can be optimally adapted to the combustion air flow and the dynamic gas requirements of the engine.Mechanisms and factors influencing mixture formation in intake-manifold injection

Gasoline direct injection (internal mixture formation)In gasoline direct injection, unlike intake-manifold injection, pure air flows through the intake valves into the combustion chamber. Only then is the fuel injected into the air via an injector located directly in the cylinder head. There are basically two main operating modes. Fuel injection in the intake stroke is called homogeneous operation, while fuel injection during compression is called stratified-charge operation. There are also various special modes, which are either a mixture of the two main operating modes or a slight variation of them.

In stratified-charge operation, the air is not restricted; the A/F mixture is lean. The excess air in the exhaust gas prevents conversion of the nitrogen oxides by means of a three-way catalytic converter. These gasoline direct injection systems therefore require exhaust gas treatment with an NOX accumulator catalytic converter. For this reason, mostly gasoline direct injection systems that work exclusively in the homogeneous mode are currently being placed on the market.Homogeneous operationIn homogeneous operation, mixture formation is similar to intake-manifold injection. The mixture is formed in a stoichiometric ratio ( =1). However, from a mixture formation point of view, there are some differences. For instance, there is no flow process around the intake valve to promote mixture formation, and there is much less time available for the mixture formation process itself. Whereas injection can take place across the overall 720 crankshaft (stored and synchronous with induction) of the four operating cycles in the case of intake-manifold injection, only an injection window of 180 crankshaft remains in the case of gasoline direct injection. Fuel injection is only permitted in the induction stroke. This is because, prior to this, the exhaust valves are open and unburned fuel would otherwise escape into the exhaust-gas train. This would cause high HC emissions and catalytic converter problems. In order to deliver a sufficient quantity of fuel in this shortened period, the fuel flow through the injector must be increased for gasoline direct injection. This is achieved mainly by increasing fuel pressure. The increase in pressure brings with it an additional advantage as it increases turbulence in the combustion chamber, which in turn promotes mixture formation. The fuel and air can therefore be completely mixed, even though the fuel/air interaction time is shorter compared with intake-manifold injection.Stratified-charge operationIn stratified-charge operation, a distinction is made between several combustion strategies. All strategies have one thing in common, namely they all attempt to achieve charge stratification. This means that, instead of supplying the corresponding stoichiometric air flow rate to the fuel quantity required for a specific load point by adjusting the throttle valve, the full air flow rate is supplied to the combustion chamber, and only a portion of it interacts with the fuel before it is conveyed to the spark plug. The rest of the fresh air surrounds the stratified charge. In addition to having a cooling effect, which reduces knock tendency and makes it possible to increase compression, the dethrottling action also offers considerable fuel-saving potential.Wall-directed combustion systemIn a wall-directed combustion system, fuel is injected into the combustion chamber from the side. A recess in the piston crown deflects the fuel spray in the direction of the spark plug. Mixture formation takes place on the path from the injector tip to the spark plug. As the mixture formation time is even shorter, the fuel pressure for this system must usually be even higher than for homogeneous operation. The increased fuel pressure shortens the injection time and increases interaction with the air because pulse reflection is greater.

The disadvantage of the wall-directed combustion system is that fuel condenses on the wall, which increases HC emissions. As mixture formation time is short, the charge cloud usually contains rich mixture zones at higher loads, and this increases the risk of soot production. At low loads, the fuel pulse, which is used as a means of transporting the stratified charge cloud to the spark plug, is low. As a result, the flow must usually be restricted here so that the fuel meets with a lower density of air.Air-directed combustion systemIn principle, an air-directed combustion system works in exactly the same way as a wall-directed system. The main difference is that the fuel cloud does not interact directly with the piston recess. Instead, the charge cloud moves on a cushion of air. This solves the problem of fuel condensing on the piston recess. However, air-directed combustion systems are not as stable as wall-directed ones, as it is difficult to reproduce the air flows fully.

Often, the actual combustion processes are a mixture of wall-directed and air-directed processes, depending on the operating point in each case.

Jet-directed combustion processThe jet-directed combustion process is visually different from the other two processes in that the injector is installed at a different location. It is located at top center and injects vertically down into the combustion chamber. The spark plug is located immediately next to the injector. The fuel spray is not deflected; instead, it is ignited immediately after injection. As a result, the mixture formation time is very short. This requires an even higher fuel pressure for the jet-directed combustion process. This combustion process can eliminate the disadvantages of fuel condensing on the manifold walls, air-flow dependency, and flow restriction at low loads. It therefore has the greatest potential for fuel saving. Nevertheless, the short mixture formation time is a huge challenge for fuel-injection and ignition systems. Other operating modesIn addition to homogeneous and stratified-charge operation, there are also special operating modes. They include changeover between operating modes (homogeneous-stratified mode), catalytic converter heating, and knock protection (homogeneous-split mode), and homogeneous-lean mode.Mixture-formation systems for gasoline direct injection (assisted by swirl or tumble in each case).a) Wall-directed,b) Air-directed,c) Jet-directed.

1 Fuel injector, 2 Spark plug.

Lambda closed-loop control

The lambda closed-loop control evaluates the signals of the lambda oxygen sensors. These sensors measure the oxygen content in the exhaust gas, and thus provide information about mixture composition. All current lambda closed-loop control strategies for spark-ignition (SI) engines use the injected fuel quantity as the manipulated variable and, strictly speaking, can only compensate for fuel errors (e.g. fuel injector faults, fuel pressure faults, etc.). Here, the pilot control accuracy, based on charge calculation (dynamic charge as well) determines the amount of actuator adjustments required.

Two-step controlThe two-step lambda oxygen sensor with its voltage-jump characteristic at =1 is suitable for two-step controls. A manipulated variable, composed of the voltage jump and the ramp, changes its direction of control for each voltage jump. This indicates a change from rich/lean or lean/rich. The typical amplitude of this manipulated variable has been set in the range of 2% to 3%. The result is a limited controller dynamic, which is predominantly determined by the sum of the response times (pre-storage of fuel in the intake manifold, four-stroke principle of the spark-ignition (SI) engine, and gas travel time).Shaping the manipulated variables characteristic curve asymmetrically compensates for the two-step Lambda sensors typical false signal caused by variations in A/F mixture formation. Here, the preferred method is to hold the ramp value at the voltage jump for a controlled dwell time tV after the sensor is subjected to a voltage jump.

Continuous lambda closed-loop controlThe defined dynamic response of a two-step control can only be improved if the deviation from =1 can actually be measured. The wide-band sensor can be used to achieve continuous-action control at =1 with a stationary, very low amplitude in conjunction with high dynamic response. The control parameters are calculated and adapted as a function of the engines operating points. Above all, with this type of lambda closed-loop control, compensation for the unavoidable offset of the stationary and non-stationary pilot control is far quicker. The wide-band lambda oxygen sensor also enables adjustment to mixture compositions that deviate from =1. Continuous-action lambda control is therefore also suitable for lean and rich operation.

Two-sensor controlProtective layer systems in the lambda oxygen sensor have helped minimize interference both with an accuracy of =1 at the voltage-jump point of a two-step sensor, and with the characteristics of a wide-band sensor. Nevertheless, aging and environmental influences (poisoning) still have an effect. A sensor downstream of the catalytic converter is subjected to these influences to a much lesser extent. The principle two-step control is based on the fact that the controlled rich or lean shift, or the setpoint value of a continuous closed-loop control are changed by a slow control loop, which adds corrections. Manipulated-variable curve with closed-loop-controlled lambda shift (two-step control) tv Dwell time after sensor jump.

Three-sensor controlThe use of a third sensor downstream of the main catalytic converter is recommended both from the perspective of catalytic converter diagnosis and exhaust-gas constancy in the case of SULEVs (Super Ultra-Low-Emission Vehicles). The two-sensor control system (single cascade) is expanded to include extremely slow control with the third sensor downstream of the main catalyst and thereby facilitates faster control with the second sensor.

Individual-cylinder lambda closed-loop controlWith primary catalytic converters located near the engine, there is no guarantee that the exhaust gases in the individual cylinders will be adequately mixed before flowing through the catalytic converter. The fact that exhaust gas passes through the catalyst segments in strands, depending on the deviation from =1 of the cylinders, results in insufficient conversion. Lambda matching can considerably improve exhaust-gas performance in these conditions. Extremely high demands must be place on the dynamic response of the lambda oxygen sensor in order to obtain the lambda values for the individual cylinders from a measured lambda signal.

Torque equalizationLambda matching only results in torque equalization if no charge errors are present. If necessary, it must be replaced by torque equalization, which, particularly in the lean-burn range, compensates for cylinder-charging errors by measuring the engines smooth-running performance, and thus any fluctuations in torque.

Lambda closed-loop control with control cascade for three-step control

Basic structure of single-cylinder lambda closed-loop control

PRESIN DINAMICA DE LOS GASES DE ESCAPE

Exhaust-gas systemDesign and purpose

In compliance with legal requirements, the exhaust-gas system reduces the pollutants in the exhaust gas that are generated by an internal-combustion engine. The exhaust-gas system also helps to muffle exhaust-gas noise and to discharge the exhaust gas at a convenient point on the vehicle. Engine power should be reduced as little as possible during the process.

ComponentsA passenger-car exhaust-gas system consists of:- Manifold - Components for exhaust-gas treatment- Components for sound absorption- System of pipes connecting these components

Components for treating the exhaust gas are not always included in exhaust-gas systems for commercial vehicles and trucks. When the European EU 4 emissions-control standard comes into force for commercial vehicles, it will be necessary for all commercial vehicle exhaust-gas systems to include emissions-control facilities.Depending on engine displacement and the type of muffler used, the exhaust-gas system weighs between 8 and 40 kg. The components are generally made of high-alloy steels on account of the extreme stresses that occur in exhaust-gas systems.Exhaust-gas system (example with three mufflers).1 Manifold, 2 Near-engine catalytic converter, 3 Front pipe, 4 Front muffler, 5 Intermediate pipe, 6 Center muffler, 7 Rear muffler, 8 Exhaust-gas flap, 9 Tailpipe.

Emissions controlComponents used for treating the exhaust gas include:- The catalytic converter to break down the gaseous pollutants in the exhaust gas - The particulate filter (or soot filter) to filter out the fine, solid particulates in the exhaust gas (especially in diesel engines)

Catalytic converters are installed in the exhaust-gas system as close as possible to the engine so that they can quickly reach their operating temperature and therefore be effective in urban driving. Diesel particulate filters are also installed in the front area of the exhaust-gas system to ensure that the soot particles they have retained are burnt off more effectively at the higher exhaust-gas temperatures. Both components also assume a sound-absorbing function, especially the higher frequency components of exhaust-gas noise.

Sound absorptionMufflers dampen or absorb the noise produced by exhaust gas. In principle, they can be installed at any position in the exhaust-gas system. However, they are mostly located in the middle and rear sections of the exhaust-gas system.

Depending on the number of cylinders and engine output, generally 1 ... 3 mufflers are used in an exhaust-gas system. In V-engines, the left and right cylinder banks are often run separately, each being fitted with its own catalytic converters and mufflers.

The noise-emission limit for the complete vehicle is defined by legislation. The noise produced by the exhaust-gas system represents a substantial source of noise emission in a vehicle. This fact makes it necessary to devote particular attention and resources to the development of mufflers. Although the aim is to reduce noise in compliance with the legislation, they can also create the sound specific to the type of vehicle.

ManifoldThe manifold is an important component in the exhaust-gas system. It routes the exhaust gas out of the cylinder outlet ports into the exhaust-gas system. The geometric design of the manifold (i.e. length and cross-section of the individual pipes) has an impact on the performance characteristics, the acoustic behavior of the exhaust-gas system, and the exhaust-gas temperature. In some cases, the manifold is insulated with an air gap to achieve high exhaust-gas temperatures faster and to shorten the time taken by the catalytic converter to reach its operating temperature.MufflersMufflers (or silencers) are intended to smooth out exhaust-gas pulsations and make them as inaudible as possible. There are basically two physical principles involved: - Reflection and - Absorption.

Mufflers also differ according to these principles. However, they mostly comprise a combination of reflection and absorption. As mufflers and the exhaust-gas system pipes together form an oscillating system with its own natural resonance, the position of the mufflers is highly significant for the quality of sound-damping. The objective is to tune the exhaust-gas systems as low as possible, so that their natural frequencies do not excite bodywork resonances. To avoid structure-borne noise and to provide heat insulation for the vehicle underbody, mufflers often have double walls and an insulating layer.Muffler principles.a) Reflection muffler, b) Absorption muffler, c) Combination of a) and b).

Reflection mufflersReflection mufflers consist of chambers of varying lengths interconnected by pipes. The differences in the cross-sections of the pipes and the chambers, the diversion of the exhaust gases, and the resonators formed by the connecting pipes and the chambers produce a muffling effect which is particularly efficient at low frequencies. The more such chambers are used, the more efficient is the muffler.Reflection mufflers cause a higher exhaust-gas backpressure. As a rule, they are therefore associated with greater power loss.

Absorption mufflersAbsorption mufflers are designed with one chamber, through which a perforated pipe passes. The chamber is filled with absorption material. The sound enters the absorption material through the perforated pipe and is converted into heat by friction. The absorption material usually consists of long-fiber mineral wool with a bulk density of 100...150g/l. The level of muffling depends on the bulk density, the sound-absorption grade of the material, and on the length and coating thickness of the chamber. Damping takes place across a very broad frequency band, but only begins at higher frequencies. The shape of the perforations, and the fact that the pipe passes through the wool, ensures that the material is not blown out by exhaust-gas pulses. Sometimes the mineral wool is protected by a layer of stainless-steel wool around the perforated pipe.

Muffler designDepending on the space available under the vehicle, mufflers are produced either as spiral-wound casing or from half-shells. To produce the jacket for a spiral-wound muffler, one or several metal sheet blanks are shaped over a round mandril and joined together either by the longitudinal folds or by laser welding. The completely assembled and welded core is then installed in the jacket casing. It consists of internal tubes, baffles, and intermediate layers. The outer layers are then connected to the jacket in a folding or laser-welding process. It is often not possible to effectively accommodate a spiral-wound muffler in view of the complicated space conditions in the floor assembly. In such cases, a shell-type muffler made of deep-drawn half-shells is used as it can assume virtually any required shape.

The total volume of the mufflers in a passenger-car exhaust-gas system corresponds to approximately eight to twelve times the engine displacement.Muffler with integrated catalytic converter 1 Inlet pipe, 2 Mounting mat, 3 Ceramic monolith, 4 Tailpipe.

Connecting elementsPipes are used to connect the catalytic converters and mufflers together. Arrangements where the catalytic converter and muffler are integrated in a single housing may also be used on very small engines and vehicles.The pipes, the catalytic converter and muffler are connected to form an integrated system by means of plug-in connections and flanges. Many original-equipment systems are fully welded for faster mounting.

The entire exhaust-gas system is connected to the vehicle underbody via elastic mounting elements. The fixing points must be carefully selected, otherwise vibration may be transmitted to the bodywork and generate noise in the passenger compartment. The wrong fixing points may also create strength and therefore durability problems. In some cases, these problems are counteracted by the use of vibration absorbers. These components oscillate at the critical frequency in precisely the opposite direction of the exhaust-gas system, thereby eliminating vibration energy in the system.

The exhaust-gas system noise at the exhaust-emission point (tailpipe) as well as sound radiation from the mufflers can also cause bodywork resonance. Depending on the intensity of the engine vibrations, decoupling elements are used to insulate the exhaust-gas system from the engine block and to relieve the stress load on the exhaust-gas system.

Ultimately, the mounting arrangement of an exhaust-gas system is tuned so that it is rigid enough to withstand vibrations reliably on the one hand, and it exhibits sufficient flexibility and damping properties to reduce the transfer of forces to the bodywork effectively on the other.Decoupling element 1 Liner, 2 Corrugated sheathing, 3 Wire braiding.

Acoustic tuning devices A number of different components can be used to eliminate disturbing frequencies in the noise emitted from the tailpipe.

Helmholtz resonatorThe Helmholtz resonator consists of a pipe arranged along the side of the exhaust-gas train and a defined volume connected to it. The gas volume acts as a spring, while the gas in the pipe section acts as a mass. At its resonant frequency, this spring-mass system provides a very high degree of sound absorption but in a narrow frequency band. The resonant frequency f depends on the size of the volume V as well as the length L and cross-sectional area A of the pipe:

Quarter-wave resonatorsQuarter-wave resonators consist of a pipe branching off from the exhaust-gas system. The resonant frequency f of these resonators is derived from the length L of the pipe branch. It is expressed as f = c /(4 L). These resonators also feature a very narrowband damping range about their resonant frequency.

Exhaust-gas flapsExhaust-gas flaps are most commonly found in rear mufflers. Depending on the engine speed or exhaust-gas throughput, they close off a bypass pipe in the muffler or a second tailpipe. As a result, exhaust-gas noise can be substantially damped at lower engine speeds without the need to trade off power losses at high engine speeds. Exhaust-gas flaps can be either self-controlling based on pressure and flow, or they can be controlled externally. An interface to the engine management system must be provided for externally controlled flaps. This makes them more complex than self-controlled flaps. However, their application range is also more flexible.

PRESIN DE CARGA

Turbochargers and superchargers for internal-combustion enginesBy compressing the air inducted for combusting fuel in the internal-combustion (IC) engine, and thereby increasing its air throughput, turbochargers and superchargers increase the output obtained for a given displacement at a given engine speed. There are of generally three basic types of compressor used in IC engines: the mechanically driven supercharger, the exhaust-gas turbocharger and the pressure-wave supercharger.

Mechanical superchargers compress the air using power supplied by the engine crankshaft (mechanical coupling between engine and supercharger), while the turbocharger is powered by the engines exhaust gases (fluid coupling between engine and turbocharger).

Although the pressure-wave supercharger also derives its compression force from the exhaust gases, it requires a supplementary mechanical drive (combination of mechanical and fluid coupling).Superchargers (mechanically driven)These fall into two categories: mechanical centrifugal superchargers (MKL) and mechanical positive-displacement superchargers (MVL).

Mechanical centrifugal superchargerThe MKL compressor corresponds to the configuration of the exhaust-gas turbocharger. This type of device is very efficient, providing the best ratio between unit dimensions and volumetric flow. However, the extreme peripheral velocities required to generate the pressure mean that drive speeds must be very high. As the secondary pulley (2:1 conversion ratio relative to primary pulley) does not rotate fast enough to drive a centrifugal supercharger, a single-stage planetary gear with a 15:1 speed-increasing ratio is employed to achieve the required peripheral velocities. In addition, a transmission unit must be included to vary the rotational speeds if the pressure is to be maintained at a reasonably constant level over a wide range of volumetric flow rates (~ engine speed).

The necessity of using extreme rotational speeds, and the technical limits imposed on the transmission of drive power, mean that the centrifugal superchargers range of potential applications is limited to medium- and large-displacement diesel and gasoline passenger-car engines. This design has not been extensively employed for mechanical superchargers.

Positive-displacement superchargersPositive-displacement superchargers (MVL) operate both with and without internal compression. Internal-compression superchargers include the reciprocating-piston, the screw-type, the rotary-piston, and the sliding-vane compressor. The Roots supercharger is an example of a unit without internal compression.

All of these positive-displacement superchargers share certain characteristics as shown in the program map of a Roots supercharger:The speed curves nCOM=const in the p2/p1-V program map are very steep, i.e. the volumetric flow V decreases only slightly as the pressure ratio p2/p1 increases. The precise extent of the drop in flow volume is basically determined by the efficiency of the gap seal (backflow losses). It is a function of the pressure ratio p2/p1 and of time, and is not influenced by rotational speed.The pressure ratio p2/p1 does not depend on the rotational speed. In other words, high pressure ratios can also be generated at low volumetric flow rates.The volumetric flow V is independent of the pressure ratio and, roughly formulated, directly proportional to rotational speed.- The unit retains stability throughout its operating range. The positive-displacement compressor operates at all points of the p2/p1-V program map as determined by supercharger dimensions.

Roots superchargerThe two twin-bladed rotary pistons of the Roots supercharger operate without directly contacting each other or the housing. The size of the sealing gap thus created is determined by the design, the choice of materials and the manufacturing tolerances. An external gear set synchronizes the motion of the two rotary pistons.Cross-section through a Roots supercharger1 Housing,2 Rotary piston

Sliding-vane superchargerIn the sliding-vane supercharger, an eccentrically mounted rotor drives the three centrally mounted sliding vanes; the eccentric motion provides the internal compression. The extent of this internal compression can be varied for any given eccentricity by altering the position of the outlet edge A in the housing.Cross-section through a sliding-vane supercharger1 Housing, 2 Rotor, 3 Vane, 4 Shaft, 5 Outlet edge A.

Spiral-type superchargerThe spiral-type supercharger employs an eccentrically mounted displacer element which is designed to respond to rotation of the drive shaft by turning in a double-eccentric oscillating pattern. In sequence, the working chambers open for charging, close for transport and open once again for discharge at the hub. The spirals can be extended beyond the length shown in the figure to provide internal compression.

Cross-section through a spiral-type supercharger1 Air inlet into second working chamber, 2 Drive shaft, 3 Displacer element, 4 Air inlet into primary working chamber, 5 Housing, 6 Displacer element.

The displacer element is driven by a belt-driven, grease-lubricated auxiliary shaft, while the drive shaft is lubricated by the engines oil circuit. Radial sealing is via gaps, while lateral sealing strips provide the axial seal.

Rotary-piston superchargerThe rotary-piston supercharger incorporates a rotary piston moving about an internal axis. The driven inner rotor (rotary piston) turns through an eccentric pattern in the cylindrical outer rotor. The rotor ratio for rotary-piston superchargers is either 2:3 or 3:4. The rotors turn in opposing directions about fixed axes without contacting each other or the housing. The eccentric motion makes it possible for the unit to ingest the maximum possible volume (chamber I) for compression and discharge (chamber III). The internal compression is determined by the position of the outlet edge A.

A ring and pinion gear with sealed grease lubrication synchronizes the motion of the inner and outer rotors. Permanent lubrication is also employed for the roller bearings. Inner and outer rotors use gap seals, and usually have some form of coating. Piston rings provide the seal between working chamber and gear case.

Superchargers on IC engines are usually belt-driven (toothed or V-belt). The coupling is either direct (continuous duty) or via clutch (e.g. solenoid-operated coupling, actuation as required). The turns ratio may be constant, or it may vary according to engine speed.

Mechanical positive-displacement superchargers (MVL) must be substantially larger than centrifugal superchargers (MKL) in order to produce a given volumetric flow. The mechanical positive-displacement supercharger is generally applied to small- and medium-displacement engines, where the ratio between charge volume and space requirements is still acceptable.Cross-section through a rotary-piston supercharger1 Housing, 2 Outer rotor, 3 Inner rotor, 4 Outlet edge A, 5 Chamber III, 6 Chamber II, 7 Chamber I.

Pressure-wave superchargersThe pressure-wave supercharger exploits the dynamic properties of gases, using pressure waves to convey energy from the exhaust gas to the intake air. The energy exchange takes place within the cells of the rotor (known as the cell rotor or cell wheel), which also depends upon an engine-driven belt for synchronization and maintenance of the pressure-wave exchange process.

Inside the cell rotor, the actual energy-exchange process proceeds at the velocity of sound. This depends upon exhaust-gas temperature, meaning that it is essentially a function of engine torque, and not engine speed. Thus, the pressure-wave process is optimally tailored to only a single operating point if a constant turns ratio is employed between engine and supercharger. To get around this disadvantage, appropriately designed pockets can be incorporated in the forward part of the housings. These achieve high efficiency levels extending through a relatively wide range of engine operating conditions and provide a good overall boost curve.

The exchange of energy occurring within the rotor at the velocity of sound ensures that the pressure-wave supercharger responds rapidly to changes in engine demand, with the actual response times being determined by the charging processes in the air and exhaust pipes.

The pressure-wave superchargers cell rotor is driven by the engines crankshaft via a belt assembly. The cell walls of the rotor are irregularly spaced in order to reduce noise. The cell rotor turns within a cylindrical housing, with the fresh-air and exhaust-gas pipes feeding into the housings respective ends. On one side are low-pressure air inlet and high-pressure air, while the high-pressure exhaust and low-pressure exhaust-gas outlet are on the other side. The accompanying gas-flow and state diagrams illustrate the pressure-wave process in a basic Comprex at full load and moderate engine speed. Developing (or unrolling) rotor and housing converts the rotation to a translation. The state diagram contains the boundary curves for the four housing openings in accordance with local conditions. The diagrams for the ideal no-loss process have been drafted with the assistance of the intrinsic characteristic process.

The pressure-wave superchargers rotor is over-mounted and is provided with permanent grease lubrication, with the bearing located on the units air side. The air housing is made of aluminum, whereas the gas housing is made of NiResist materials. The rotor with its axial cells is cast using the lost-wax method. An integral governing mechanism in the supercharger regulates charge-air pressure according to demand.Pressure-wave supercharger1 Engine, 2 Cell rotor, 3 Belt drive, 4 High-pressure exhaust gas, 5 High-pressure air, 6 Low-pressure air inlet, 7 Low-pressure exhaust-gas outlet.

Exhaust-gas turbochargersOperating principleThe exhaust-gas turbocharger (ATL) consists of two turbo elements: a turbine and a compressor installed on a single shaft. The turbine uses the energy of the exhaust gas to drive the compressor. The compressor, in turn, draws in fresh air which it supplies to the cylinders in compressed form. In terms of energy, the air and the mass flow of the exhaust gases represent the only coupling between the exhaust-gas turbocharger and engine. Turbocharger speed does not depend upon engine speed, but is rather a function of the balance of drive energy between the turbine and the compressor.

Supercharging generally increases the efficiency of internal-combustion engines.Truck exhaust-gas turbocharger with twin-flow turbine housing (sectional view).1 Compressor housing, 2 Compressor wheel, 3 Turbine housing, 4 Rotor, 5 Bearing housing , 6 Exhaust-gas inflow, 7 Exhaust-gas outflow, 8 Atmospheric fresh air, 9 Precompressed fresh air, 10 Oil supply, 11 Oil return.

ApplicationsExhaust-gas turbochargers are traditionally used for the purpose of supercharging diesel engines. Originally, however, they were mainly used on heavy-duty engines for truck, marine and locomotive power plants as well as for agricultural and construction machinery applications. The mid-1970s saw the advent of the first production turbocharged diesel engines in passenger cars. In the meantime, virtually all diesel engines manufactured in Europe are now equipped with an exhaust-gas turbocharger and intercooling (charge-air cooling).

For technical reasons, supercharging of spark-ignition (SI) engines was originally the reserve of only high-output sports engines and was rarely found on the mass market. In the meantime, gasoline-engine supercharging has become an integral part of engine development, predominantly in connection with small to medium-sized engines. In addition to the improvement in efficiency, one of the main objectives of supercharging is to avoid the increases in the number of engine cylinders, thus positively influencing package space and fuel consumption.

In contrast to the diesel engine, mechanical supercharging is also employed on spark-ignition (SI) engines in addition to turbocharging, predominantly with the aim of improving the transient buildup in boost pressure. In this context, the extensive volumetric flow range of the spark-ignition (SI) engine (approximately 1:75 from idle to WOT point) has a negative effect on the behavior of the exhaust-gas turbocharger. With the introduction of spark-ignition (SI) engines with direct fuel injection, turbocharging will again become a more interesting prospect compared with other supercharging processes.

Turbocharger designThe exhaust-gas turbocharger consists of four basic components: - The bearing housing - The compressor - The turbine - The boost-pressure control facility

Bearing housingThe bearing housing accommodates the bearings and sealing elements. State-of-the-art exhaust-gas turbochargers usually feature a specially developed plain bearing both in the radial as well as the axial (thrust) bearing assembly. The radial bearings are designed either as rotating double plain bushings or as stationary plain-bearing bushings. The requirements relating to stability, power loss and noise-emission characteristics govern what type of bearing system is used. The thrust bearing is made up of a multiple-spline surface bushing that is subject to load from both sides and which is lubricated either centrally or individually for each spline surface. The lubricating oil is supplied by connecting the turbocharger to the engines oil circuit. The oil outlet is connected directly to the oil pan in the crankcase. Today, this type of bearing assembly is used to control rotational speeds of up to 300,000 rpm reliably.

The shaft is equipped with piston rings at the casing openings to seal off the oil chamber to the exterio