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A simulation tool has been developed for predicting steering effort of a vehicle during steering power-assist system failure. The vehicle system is modeled with the inclusion of a system-level vehicle model and a steering system model that are linked together through the steering moment at the kingpin and front road wheel angle. A driver model has also been designed to provide closed-loop steering angular input to make the car follow a certain target path. The simulation model is correlated well with actual vehicle tests under various steering input and lateral acceleration conditions. Also illustrated are some examples of comparison between measured and simulated sensitivity study for selected factors.

This paper describes the development of a simulation technology for analyzing vehicle chassis transmissibility for the vibrations induced by tire-wheel imbalance and brake torque fluctuation. A multi-body simulation model is created for the coupled front chassis system consisting of steering, suspension, floating sub-frame, tire-wheel and a virtual excitation rig. Non-linear elements, such as frictions of joints, displacement-dependent bushings and detailed hydraulic power assist system, are considered. The simulation model is validated extensively by a unique laboratory excitation test in both frequency and time domain under different levels of excitation. Good agreement between simulation and measurement is achieved, and example results are presented.

The simulation model developed and validated by the authors [1] for vehicle chassis transmissibility of steering shimmy and brake judder is used to analyze the transmissibility mechanism and quantify the relative importance of system factors, through modal analysis around equilibrium point and a virtual DOE (design of experiment) process. Contributing chassis vibration modes are discovered, relative importance of chassis factors is efficiently determined, and potential areas for improving chassis shimmy/judder sensitivity are identified. The DOE results are further confirmed by the comparison of simulated and on-road measured shimmy/judder change with the specification change of key factors. Also presented is some successful application of the simulation technology and analysis results to vehicle development.

The transmission of fluidborne pressure and flow pulsations through a hose assembly is dominated by a four-port transfer matrix equation. The potential of pulsation attenuation in the assembly is then related to the four parameters of the matrix by the concept of “Transmission Loss”. The paper presents the development of an accurate test system, based on the “Four Sensors/Two Systems” method, for measuring the transfer matrix and transmission loss of hose assemblies. Particular attention is paid to the solutions to some technical problems encountered during the development and measurement. Then presented is the application of the system to various types of flexible hose with or without tuning cables used in power steering hydraulic systems. The measurements are very valuable for developing the best tuning cable and hose devices, quieter power steering systems as well as the hoses used similarly in other fluid power systems.

A new method, the “3 Pressures/ 2 Systems” method, is developed for determining source flow ripple and internal impedance of fluid power pumps. The method integrates exclusively an on-line measurement technique for the speed of sound in the fluid and a technique for eliminating flow disturbance effect on pressure sensors into the basic principle used in the existing “2 Pressures / 2 Systems” method. The new method has an inherent potential to yield results with higher accuracy and higher confidence. The high accuracy of the method is confirmed by the comparison of measured and predicted pressure ripple in a pump-pipe-valve system. Then, the method is applied to automotive fluid power pumps - power steering pumps. The measured results of source flow ripple and internal impedance are presented.

A tuning cable and hose device, i.e. a flexible metal tuning cable placed coaxially inside a section of hose, is usually used in power steering hydraulic circuits to reduce pressure pulsations in the circuits. To evaluate the fluidborne noise attenuation characteristics of tuning cable and hose devices correctly, a new evaluation method, based on the experimental determination of transmission loss of the tuning cables and hoses, is proposed here. The effectiveness of the method and test system are confirmed. The results obtained are valuable for design optimization and theoretical modeling of hydraulic power steering systems and other similar hydraulic systems.