Jocelyn Darling

Cylinder Pressure Transients in Oil Hydraulic Pumps with Sliding Plate Valves

This paper reports an experimental study of the cylinder pressure within an axial piston pump. This study revealed that existing theoretical models, which are based on the effects of fluid compliance within the cylinder, are highly inaccurate at high speeds or high loads. Fluid momentum at the point of port opening was found to be of considerable importance and an improved digital computer model was developed as an aid to pump design. The inclusion of fluid momentum effects resulted in a significant improvement in the agreement between theory and experiment. Cavitation within the cylinder bore was predicted at both high speed and high load conditions; this was confirmed experimentally. The theoretical approach is applicable to any sliding valve plate unit.

An Experimental Study of a Prototype Active Anti-Roll Suspension System

SUMMARY Active roll control is known to offer substantial improvements in ride and handling performance over the most sophisticated passive suspension systems. However although many different active suspension systems have been discussed and analysed through simulation little information regarding experimental performance data from a prototype active roll control system has been published. This study focuses on the design, development, commissioning and experimental evaluation of a roll control suspension based on active anti-roll bar actuation. In tests, the prototype vehicle demonstrated excellent steady state and dynamic roll cancellation within the lateral acceleration range of 0.5g. Subjective assessments of the system confirmed the benefits of a level ride together with the added benefit accrued from the elimination of roll dynamics.

DEVELOPMENT AND SIMULATION OF A NOVEL ROLL CONTROL SYSTEM FOR THE INTERCONNECTED HYDRAGAS SUSPENSION

SUMMARY The design of passive suspension systems using conventional springs and dampers is limited by the need to compromise between vehicle ride and handling functions. The Interconnected Hydragas Suspension fitted to the current Rover 100 series partially allays this compromise by reducing the vehicle pitch stiffness witfiout affecting the bounce and roll stiffnesses. However, the vehicle body is still subject to roll during cornering manoeuvres. This paper outlines the development and simulation of a sealed low bandwidth active roll control suspension based on the existing Interconnected Hydragas System. Following a brief explanation of the Hydragas suspension operating principle die paper outlines the design of a fluid displacer or ‘shuttle’. This shuttle enables control over body roll during manoeuvres by displacing fluid from one side of the car to the other. Care is taken to ensure low power consumption whilst the sealed nature of the fluid based suspension units guarantee reliable operation withou...

Steady-state steering of a tilting three-wheeled vehicle

The design of a narrow-track enclosed vehicle for urban transport was the subject of the CLEVER project. Due to its narrow track and requirement for car-like controls, an actively controlled tilting system was integrated into the chassis to allow for high lateral accelerations without rolling over. The cornering behaviour of this unique vehicle concept is investigated and compared with the ideal Ackermann response. The steer kinematics of this 1F1T (one front wheel, one wheel tilting) configuration are assessed through the use of a steady-state steering model, with attention focused on how steer parameters such as tilt axis height and inclination can be tuned to provide the required response. A prototype vehicle was designed and built and the results of experimental testing are presented to illustrate the real balancing performance of the combined steering and tilting approach used for the CLEVER vehicle. The experimental results follow the trends demonstrated in the model.

Simulation of Coupled Car and Caravan Handling Behaviour

SUMMARY Although a great deal of work has been carried out on articulated commercial vehicles, the handling behaviour of coupled cars and caravans has not been investigated to the same extent. The most sophisticated models presented in technical literature disregard important degrees of freedom and often use simplified descriptions of tyre and suspension characteristics. In this paper the equations of motion for a twenty four degree of freedom car and caravan model are developed using Lagranges equations for quasi-coordinates. These equations are combined with non-linear suspension and tyre characteristics within the simulation environment Bath fp. Caravan dimensional and suspension parameters are measured and used together with data from a fully validated car simulation model to predict high speed instability and handling behaviour. An instrumented car and caravan is tested at a range of speed conditions and good agreement between measurement and prediction is achieved. Following validation, the simulat...

Development of a tilt control method for a narrow-track three-wheeled vehicle

The space and weight savings provided by narrow tilting vehicles could make them a solution to the pollution and congestion problems seen in urban environments. The success of this new type of vehicle relies heavily on the control method used to balance the vehicle in corners. A tilting three-wheeled vehicle was developed at the University of Bath as part of an EU-funded project. The original direct tilt control method implemented on the prototype was shown to perform well in steady state, but rapid transients were shown to potentially lead to instability. A new type of controller was therefore required to reduce the load transfer across the rear axle during transient state manoeuvres. This paper presents a linearized model of the tilting vehicle system which is used to optimize a new tilt controller in the frequency domain. The controller, which uses combined steer and tilt control inputs, is shown to significantly reduce transient roll moments compared to the previous control method. This results in a much safer and more predictable handling characteristic.

An experimental investigation of car—trailer high-speed stability:

Abstract Previous work on car—trailer stability has been largely limited to theoretical studies with some reference to practical experience or accident statistics. In this study, extensive and systematic experimental investigations were carried out on a combined car—adjustable-trailer system. The influence of different trailer parameters on the system high-speed stability was examined by changing the mass, dimensions, and inertial characteristics of a fully adjustable trailer. It was found that the dominant factors affecting stability were the trailer yaw inertia, nose mass (mass distribution), and trailer axle position. The tyre pressure also affects the stability, although this effect is less significant. It is interesting to see that the trailer mass alone does not dramatically affect the high-speed stability, as this runs contrary to current guidelines relating to limits on the relative mass of the car and trailer. Experimental tests on a friction stabilizer and on car electronic stability programs demonstrate that both of these improve the high-speed stability and help to delay the onset of ‘snaking’.

The Control of an Active Seat with Vehicle Suspension Preview Information

This paper presents a novel, simple and reliable control strategy for an active seat suspension, intended for use in a vehicle, which attenuates the harmful low-frequency vertical vibration at the driver’s seat. An advantage of this strategy is that it uses measurable preview information from the vehicle suspension. The control force is calculated from this preview information and controller gains obtained by optimising an objective function using a genetic algorithm (GA) approach. The objective function optimises ride comfort in terms of the Seat Effective Amplitude Transmissibility factor, taking into account constraints on both the allowable seat suspension stroke and actuator force capacity. This new controller is evaluated using both simulation and experimental tests in both the frequency and time domains. The simulation model is based upon a linear quarter vehicle model and a single degree of freedom seat suspension. Experimental tests are performed using a multi-axis simulation table and an active seat suspension. Finally, the performance of the active seat suspension is analysed and compared to a passive system, demonstrating significant acceleration attenuation of more than 10 dB across a broad frequency range. Consequently, this has the potential to improve ride comfort and hence reduce the driver’s fatigue using a reliable and cost-effective control method.

Prediction of the pressure–flow characteristic of a Belleville washer-based damper valve

Flow control valves used in automotive suspension dampers are almost universally based upon the restriction of flow using Belleville washers. These washers can best be described as a non-flat washer of conical shape and uniform thickness. They are also known as disc springs and are commonly used for load bearing in which their compactness and ability to produce a wide range of load–deflection characteristics provide an alternative to conventional coil springs. Due to the non-linear behaviour of Belleville washers, and the complex flow paths in an automotive damper valve, it is difficult to predict the resulting pressure–flow characteristic. As a result, damper valve design is often considered to be a ‘black art’ best carried out by an experienced engineer using an experimental-based trial-and-error approach. Clearly, without the aid of an analytical tool to predict the behaviour of prototype systems it is difficult for the designer to fully exploit the functionality of a particular design. The current paper describes theoretical and experimental studies undertaken to investigate the pressure–flow characteristic of a Belleville washer-based damper valve. Existing load–deflection theory was extended to account for the hydraulic pressure acting on the surfaces of the washer. However, poor agreement was obtained between the measured pressure–flow data using a uniform pressure distribution across the washer diameter. For this reason the model was developed further to include the effect of a non-uniform pressure distribution within the valve. Computational fluid dynamics software was used to predict the pressure regime within the valve and this, in turn, was used to calculate the forces acting on the surface of the Belleville washer. The improved model was found to match the experimental behaviour with good accuracy, both for a range of spring pre-load conditions and for applications where several washers are stacked up in parallel. However further work would be required to develop a reliable simulation tool as an element of trial and error was necessary to estimate some simulation parameters.

Hardware-in-the-Loop (HIL) Simulation of a Quarter Vehicle Model using a Multi-axis Simulation Table (MAST)

The reliable and repeatable experimental testing of automotive components is a challenge, especially when human occupants are involved. In most circumstances full vehicle testing over a range of road conditions is used even though this is expensive, difficult and time-consuming. In this work an experimental platform that compensates for the vehicle motion using the principle of hardware-in-the-loop (HIL) simulation is developed using a multi-axis simulation table (MAST) available in the Center for Power Transmission and Motion Control (PTMC) laboratory at the University of Bath. The MAST was tested in both the time and frequency domains with a range of road profiles including a random and single bump in the low frequency range (0.5-25 Hz). Also, uncertainties in the vehicle suspension characteristics such as the damping coefficient, the stiffness rate and the vehicle mass are examined. The experimental results in the frequency and time domain show that the MAST can be used to reproduce the dynamic characteristics of a quarter vehicle model with an excellent degree of agreement with the simulated response.