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Wear of Automotive Engine Valves and Seats

Tom Slatter, University of Sheffield Maik Broda, Ford Motor Company Dr Roger Lewis, University of Sheffield Dr Rob Dwyer-Joyce, University of Sheffield

The drive for reduced emissions from diesel exhausts has led to a reduction in the amount of oil present in the air stream in automotive diesel engines. This, in turn, has led to an increase in the wear of inlet valves and seat inserts in diesel engines.

Three types of valve/seat insert failure occur in internal combustion engines. These are valve recession, guttering and torching. The most prevalent failure mechanism in diesel engines is valve recession. This is caused by material removal from the valve and/or the seat insert.

Two test-rigs have been developed (bench test-rig and motorised cylinder-head) that are capable of providing a valid simulation of the wear of both inlet valves and seat inserts used in automotive diesel engines. The bench test-rig, designed to be mounted in a hydraulic test machine, is able to simulate both combustion loading and impact of the valve on the seat on valve closure. It is not possible, however, to vary the closing velocity significantly. The motorised cylinder-head can be used to investigate impact wear of valve and seats over a range of closing velocities. Test methodologies developed for the bench test-rig have isolated the effects of impact and sliding.

Investigations have shown that the valve and seat insert wear problem involves two distinct mechanisms; impact of the valve on the seat insert on valve closure and sliding of the valve on the seat insert under the action of the combustion pressure. Both have a large influence on valve recession. It is in combination, however, that they have the largest effect. In tests run on the bench test-rig using impact and sliding in combination it took a few thousand cycles to achieve wear attained in several hundred thousand cycles in the frictional sliding tests.

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Ridges and Valleys on a Valve Seating Face

The pictures illustrate; a series of ridges and valleys on a valve seating face formed by a deformation/gouging process as a result of impact on valve closure; radial indentations on an insert seating face caused by the valve sliding against

the insert under the effect of combustion loading and surface cracking and subsequent material loss on an insert seating face as a result of impact on valve

closure.

Radial Indentations on a Seat Insert Seating Face

Surface Cracking on a Seat Insert Seating Face

Wear has been shown to increase with valve closing velocity, combustion load and misalignment of the valve relative to the seat insert. Lubrication of the valve/seat interface reduced valve recession, on the material combination tested, by a factor of ten.

A semi-empirical wear model for predicting valve recession has been developed based on the fundamental mechanisms of wear determined during test work. Model predictions were compared with engine tests as shown in the graph to the right. The model can be used to give a quantitative prediction of the valve recession to be expected with a particular material pair or a qualitative assessment of how parameters need to be altered in order to reduce recession.

Software called RECESS has been developed to run the semi-empirical valve recession model.

Flow charts have also been developed, based on the review of literature, failure analysis and modelling carried out, to assist in diagnosing and rectifying valve/seat failures and to help in reducing valve recession by design.

Sponsor

We are grateful to Ford Forschungszentrum Aachen GmbH for sponsorship of this work.

Publications

1. Slatter, T., Lewis, R., 2006, “Valve Recession - The Importance of Impact Wear”, Proceedings of the IMechE Conference on Tribology 2006: Surface Engineering & Tribology for Future Engines & Drivelines.

2. Slatter, T., Lewis, R., Dwyer-Joyce, R.S., 2006, “Valve Recession Modelling”, SAE Paper 2006-01-0365. 3. Lewis, R., Dwyer-Joyce, R.S., Slatter, T.J., Brooks, A.C., 2004, “Valve Recession: From Experiment to Predictive Model”,

Proceedings of the VDI Conference on Ventriltrieb und Zylinderkopf, pp79-93. (ISBN 3 18 091813 6)

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4. Lewis, R., Dwyer-Joyce, R.S., 2002, "Design Tools for Predicting Inlet Valve Recession and Solving Valve Failure Problems", Journal of Engines, Transactions of the SAE 2001, pp105-114. (ISBN 0 7680 1099 3)

5. Lewis, R., Dwyer-Joyce, R.S., 2002, "Wear of Diesel Engine Inlet Valves and Seat Inserts", Journal of Automobile Engineering, Proceedings of the IMechE Part D., Vol. 216, pp205-216.

6. Lewis, R., Dwyer-Joyce, R.S., 2001, Automotive Engine Valve Recession, Engineering Research Series No. 8, Professional Engineering Publishing Ltd., London. (ISBN 1 86058 358 X)

7. Lewis, R., Dwyer-Joyce, R.S., 2001, "Design Tools for Predicting Inlet Valve Recession and Solving Valve Failure Problems", SAE Paper 2001-01-1987, in SP-1624, pp105-114. (ISBN 0 7680 0788 7)

8. Lewis, R., Dwyer-Joyce, R. S., and Josey, G., 2001, "An Experimental Approach to Solving Valve and Seat Wear Problems", Proceedings of the 27th Leeds-Lyon Symposium on Tribology, Elsevier Tribology Series No. 39, pp629-640. (ISBN 0 444 50581 4)

9. Lewis, R., Dwyer-Joyce, R.S., Josey, G., 2000, "Investigation of Wear Mechanisms Occurring in Passenger Car Diesel Engine Inlet Valves and Seat Inserts", Journal of Fuels and Lubricants, Transactions of the SAE 1999, pp610-618. (ISBN 0 7680 0695 3)

10. Lewis, R., (2000), "Wear of Diesel Engine Inlet Valves and Seats", University of Sheffield PhD Thesis. 11. Lewis, R., Dwyer-Joyce, R. S., and Josey, G., 1999, "Investigation of Wear Mechanisms Occurring in Passenger Car Diesel

Engine Inlet Valves and Seat Inserts", SAE Paper 1999-01-1216. (ISSN 0148 7191) 12. Lewis, R., Dwyer-Joyce, R.S., Josey, G., 1998, "Design and Development of a Bench Test-Rig for Investigating Diesel Engine

Inlet Valve and Seat Insert Wear", Proceedings of the 5th International Tribology Conference in Australia, Institution of Engineers, Australia, pp365-370. (ISBN 1 86445 001 0).

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