Experimental measurement of roller slip in end-pivoted roller follower valve train

Abstract

Direct-acting tappets and end-pivoted roller followers are the two main types of valve train configurations widely used in passenger car engines. Considerable theoretical and experimental work has been carried out on the direct-acting valve train. However, due to complex nature of the end-pivoted rollers, limited work has been carried out in this area. In roller follower valve train, the roller rotation has a direct impact on the performance in terms of component durability and friction. Roller rotation minimizes the chances of fatigue failure by even distribution of wear, improves the lubrication, and influences the valve train power loss. In this research work, the effect of lubricant rheology and operating conditions on the performance of end-pivoted roller follower has been studied experimentally in detail. Tests have been carried out on real production engine, avoiding any major modification to the components under investigation. The tests revealed presence of roller slip at certain operating conditions. Lubricant viscosity played a key role in the slippage of roller at lower temperatures, however, at high temperatures, negative slip was observed indicating that component inertia has a role to play in roller slip. High camshaft operating speeds and roller inertia increased the tendency of slippage. The study of roller slip was not possible without the development of a new method of measuring roller performance, also reported in this paper. The experimental set up, roller rotation measurement system, test procedure, and results are presented and discussed in detail.

Benefits of wonder process craft on engine valve train performance

“…During the test, no particular phenomenon of negative slip (percentage slip greater than 2.26) was encountered at all operating conditions as previously reported by the researchers. 6–8,25 The possible reason for such type of behaviour is the NEDC that follows a pattern of speed over the entire duration. The camshaft speed varies from 375 to 1412 r/min for around 20 min.…”

“…6 Relative sliding of mating surfaces operating under marginal lubrication conditions can result in deterioration of the surfaces. 7 Roller slip varies under changing engine revolutions per minute (rpm), lubrication temperature, contact loading along with the lubricant rheology as experimentally investigated by Khurram et al 1,8…”

“…The slipping behaviour in the contact patch of cam and roller increases the valve train power losses due to sliding friction, hampering of lubrication conditions and deterioration of mating surfaces. 8 The summation of power loss due to sliding friction, rolling friction power loss and power loss in roller needle bearings determines the total power loss at cam/roller interface in engine valve train. The power loss due to sliding friction is computed as follows…”

“…Both treated and untreated roller were instrumented by Giant Magneto resistive (GMR) sensor using a technique developed by Khurram et al, 8 and the instrumented rollers were installed in a real production engine head. Different tests were performed employing New European drive cycle (NEDC) to mimic the realistic conditions of vehicle run with a variation of oil inlet temperature and oil pressure inside engine head.…”

The influence of stick–slip transitions in mixed-friction predictions of heavily loaded cam–roller contacts

“…Roller slippage has been the subject of a number of theoretical and experimental studies, see for instance Duffy, 2 Khurram et al, 3 Chiu, 4 Ji and Taylor, 5 and Turturro et al 6 As explained by Chiu 4 and also demonstrated in the experiments performed by Bair and Winer, 7 the magnitude of roller slip is strongly governed by the acting contact force, i.e. the higher the contact force the lower the magnitude of experienced roller slippage due to enhanced traction to drive the roller.…”