Research On Power Loss Of Engine Front End Accessory Belt Drive Systems

Understanding the power loss is one of the key steps to save energy and reduce emission with the engine front end accessory belt drive(FEAD) system. Base on experimental and computational studies on bearing friction torque and belt rolling resisting torque, a test method for belt rolling-resistance torque and a computational method for the power loss of a FEAD system are proposed in this dissertation to quantify the torque loss and power loss of a FEAD system. Analyses are conducted to reveal the variation and influential factors of the torque loss and power loss within the system. A FEAD system was taken as an example to validate both methods by comparing the computed and experimental results. The research work and output could provide a basis for the design optimization on an advanced FEAD system to achieve lower power loss.A test rig was designed for belt drives with two pulleys by which the torque loss of the drive can be measured, and dynamic models were also built for simulation on the torque loss. The orthogonal experimental design was performed to determine experiment strategies, which were achieved through physical tests using the test rig, and numerical simulation on the model. The influence of various system parameters or operational conditions were studied on the torque loss in a belt drive, from which the critical influence factors were figured out according to the range analysis.A multi-body dynamic model was constructed for a typical FEAD system using the commercial software ADAMS, where mechanical property parameters of the multi-ribbed belt used in the system were obtained by means of different experiments.Torque loss and power loss were calculated for the FEAD system under various operational conditions. Breadboard tests were conducted to verify the model and the results. Using a drum dynamometer, tests were carried out on a vehicle installed with the FEAD system according to the type 1 operational condition defined in the Euro III/IV emission standard, resulting in engine speed time history. The fuel consumption caused by the power loss of the FEAD system was evaluated according to the simulations incorporated with the engine speed profile from the dynamometer tests.Response surfaces model was constructed for the power loss of the FEAD system based on the results from simulation, and tentative optimization designs were presented withthree critical parameters.Referring to the idea of the finite element method, a quantitative approach was put forward to calculate the steady torque loss of a belt drive system with quite a few pulleys. By the method, a belt drive system is discretized into multiple pulley-belt elements. Belt rolling resistance of each pulley-belt element is determined by tests or simulations on some two-pulley belt drive systems, from which an empirical formula about the rolling resistance was derived by curve fitting. Then the torque loss of and power loss of the whole system is ultimately obtained. The method was employed to determine the torque loss and power loss of the aforementioned FEAD system, and validated by the torque loss measured during breadboard tests.Bearing friction torque is an important part of the torque loss of a belt drive. In this regard, a test method is put forward to measure the bearing friction torque. Because it effectively circumvent the eccentric interference from the radial load, the method can be used to measure the friction torque of bearings subjected to finite to high radial loads. A bearing friction torque test rig was then designed and manufactured, which is applicable to measure friction torque of a ball bearing under various combinations of radial loads,rotating speeds and environment temperature. Using the method and test rig,measurements were made with all types bearings used in the FEAD system, resulting in friction torque of the 6 types of ball bearings at various operating conditions. Base on the measured friction toque, empirical formulae were constructed by means of hypothesis tests. Statistical analyses were then performed with respect to the established formulae, which clarify the distribution of friction torque of the bearings, and estimate the contribution of bearing friction to the FEAD system torque loss.