Methodology for numerical camshaft bearing investigation of a VOLVO 4-cylinder 16 valve diesel engine: EHD Camshaft Bearing Calculation and Camshaft Stress and Durability Analysis Integrated in Complete Timing Drive Simulation

摘要

This paper presents a new methodology for camshaft bearing failure investigation of an automotive valve train system. The method is applied and demonstrated for a new design variant of a VOLVO 4-cylinder 16 valve diesel engine. Nowadays the standard for VT analysis is a classical dynamic simulation with simplified bearings because camshaft bearing failure is not often observed in valve train systems. New designs have higher loads and use camshafts with reduced diameter to reduce friction, which increases bearing loads with reduced carrying capacity. The particular design of this investigation has a high pressure injection pump mounted on the back side of the intake camshaft. In this layout the timing belt is driving the intake camshaft and the intake camshaft is driving the exhaust camshaft via a gear mounted at the back of the camshaft. The reduced camshaft diameter and the high radial load from the gear and the injection pump represent a potential danger for the intake camshaft rear bearings. High load torque that appears at the camshaft pulley results from superposition of different torques from intake camshaft, exhaust camshaft and the injection pump. The resultant high torque causes high belt forces, which represent a potential danger for the camshaft front bearing close to the belt pulley. This requires a full system approach to consider all interaction, load mechanisms and their effect on the bearing behavior. This includes full valve train, timing belt as well as detailed elasto-hydrodynamic bearing models solving Reynolds equation. The simulation model considers fully flexible Finite Element (FE) based camshaft and cylinder head structures. The timing belt is modeled as a discrete model together with the mechanical eccentric tensioner and the idlers. With the obtained results for the oil film and oil flow through the bearings it is possible to make a valid conclusion about the bearing mechanical and thermal loads and about the bearing durability and wear. In addition the stress and durability of the camshafts are investigated.