Browsing by Author "Sharp, Robin S."
Now showing 1 - 8 of 8
Results Per Page
Sort Options
Item Open Access Controllability of road vehicles at the limits of tyre adhesion(Cranfield University, 1998-07) Kohn, Heinz Joachim; Sharp, Robin S.The research project 'Controllability of Road Vehicles at the Limits of Tyre Adhesion' (CROVLA) was established to investigate how tyre and chassis properties contribute to the handling characteristics and stability of vehicles operating at or near to the limit condition. The project involved the Department of Transport, SP Tyres UK Limited, Jaguar Cars and Cranfield University. An extensive proving ground test program of typical limit handling tests provided characteristic driver input and vehicle response data for a variety of vehicle configurations. The test data analysis was based on the concept of correlation. Cross- correlation coefficients and average response time delays were obtained for various pairs of quantities, namely steering angle and torque for the input and yaw rate and lateral acceleration for the response. The predictability of the vehicle response was evaluated by the rate by which the correlation coefficients change with severity. Analogous to the proving ground work, vehicle dynamics simulations were carried out. Two programs were employed to study the steady state performance and the transient limit handling behaviour. The `Steady State Cornering Model' was used to confirm some basic suspension design rules established for optimising the lateral adhesion of a suspension design. The importance of controlling camber and vehicle jacking by an appropriate suspension design was identified. A detailed vehicle model was built-up using the simulation code AUTOSIM. After validating the model against proving ground data, some parametric studies were conducted to quantify the effects of suspension and tyre properties on the transient limit response behaviour. Proving ground and simulation results suggest that response time lags and cross- correlation coefficients in combination with other handling parameters can be used as objective quality measures. The results quantified to what extent tyre and chassis modifications change the limit handling behaviour.Item Open Access Finite element modelling of blunt or non-contact head injuries(Cranfield University, 1997-09) Lawson, A. R.; Sharp, Robin S.Safety is an increasingly important aspect of vehicle design. Legislation requires minimum levels of safety through full scale tests. Customers are provided with information regarding the safety performance of vehicles so that they can make an informed buying decision. Vehicle crashes were responsible for 40000 fatalities and 5.2 million non fatally injured patients in the US during 1994. The direct and direct cost of head injuries in the US is estimated at $25 billion per year. Injury criteria that can predict the severity of head injuries are important engineering tools for improving vehicle safety. At present the injury that the human head is subjected to is predicted by the Head Injury Criterion (HIC). This criterion is inadequate as it is not based upon a thorough understanding of the underlying head injury mechanisms. The important blunt or non-contact head injury mechanisms are diffuse axonal injury, bridging vein disruption and surface contact contusions. The severity of these injury mechanisms is hypothesised to be related to the level of motion of the brain with respect to the skull. Finite element modelling is used to analyse these head injury mechanisms. Models are developed which include all the relevant anatomical entities and detail. Accurate material property information and boundary conditions are used in the modelling to ensure that the head injury mechanisms can be accurately simulated. Tissue failure criteria are developed to link the various field parameters monitored during the simulations with injury severity. The models are then comprehensively validated with information obtained from pathological observations, cadaver experiments, accident reconstructions and volunteer data. These models are then used to determine the biomechanics of head injury and to develop improved head injury tolerance curves. The simulations demonstrate that head injury severity is dependent upon the magnitude, pulse duration and direction of the applied translational and rotational acceleration pulses.Item Open Access Lap time simulation with transient vehicle and tyre dynamics(Cranfield University, 2008-05-07) Kelly, Daniel Patrick; Sharp, Robin S.; Harrison, M. F.; Vaughan, N. D.A numerical method is presented for the time optimal control of the race car. The method is then used to perform the role of the driver in numerical simulations of manoeuvres at the limit of race car performance. The method does not attempt to model the driver but rather replaces the driver with methods normally associated with numerical optimal control. The use of constraints on the method is then considered to represent the performance limits of the human driver. The method simultaneously finds the optimal driven line and the driver control inputs (steer, throttle and brake) to drive this line in minimum time. The method is in principle capable of operation with arbitrarily complex vehicle models as it requires only limited access to the vehicle model state vector. It also requires solution of the differential equation representing the vehicle model in only the forward time direction and is hence capable of simulating the full vehicle transient response. The impact of various vehicle parameters on minimum manoeuvre time, driven line and vehicle stability is shown for a number of representative manoeuvres using a quasi-steady state vehicle model. A similar process is then carried out to analyse the effect of suspension springs and dampers using a fully dynamic sprung vehicle model. The presented transient time optimal control method is then compared with results obtained from a traditional quasi-steady state manoeuvre time simulation method. A thermodynamic tyre model is developed and the time optimal control algorithm is used to evaluate dynamic tyre temperature effects on lap time and vehicle stability.Item Open Access Learning control of automotive active suspension systems(1997-09) Watanabe, Yukio; Sharp, Robin S.This thesis considers the neural network learning control of a variable-geometry automotive active suspension system which combines most of the benefits of active suspension systems with low energy consumption. Firstly, neural networks are applied to the control of various simplified automotive active suspensions, in order to understand how a neural network controller can be integrated with a physical dynamic system model. In each case considered, the controlled system has a defined objective and the minimisation of a cost function. The neural network is set up in a learning structure, such that it systematically improves the system performance via repeated trials and modifications of parameters. The learning efficiency is demonstrated by the given system performance in agreement with prior results for both linear and non-linear systems. The above simulation results are generated by MATLAB and the Neural Network Toolbox. Secondly, a half-car model, having one axle and an actuator on each side, is developed via the computer language, AUTOSIM. Each actuator varies the ratio of the spring/damper unit length change to wheel displacement in order to control each wheel rate. The neural network controller is joined with the half-car model and learns to reduce the defined cost function containing a weighted sum of the squares of the body height change, body roll and actuator displacements. The performances of the neurocontrolled system are compared with those of passive and proportional-plusdifferential controlled systems under various conditions. These involve various levels of lateral force inputs and vehicle body weight changes. Finally, energy consumption of the variable-geometry system, with either the neurocontrol or proportional-plus-differential control, is analysed using an actuator model via the computer simulation package, SIMULINK. The simulation results are compared with those of other actively-controlled suspension systems taken from the literature.Item Open Access Objective methods for the assessment of passenger car steering quality(Cranfield University, 2002-04-05) Harnett, Philip; Sharp, Robin S.Steering feel and quality are terms commonly used in the automotive industry when describing passenger car steering systems. However, a procedure for the quantification of these terms does not exist, let alone a concise definition of what they constitute. This thesis puts forward a hypothesis by which steering quality and feel are described by the input/output relationships of the steering system and how they are perceived by the driver. Good control properties are postulated for these relationships and an experiment is conducted, where they are altered in a manner proposed to affect quality. A methodology for the objective assessment of the control properties is developed, employing vehicle dynamic testing and representation by a mathematical model. This is put into practice to evaluate the outcome of the experiment. It was found that the methodology was successful in detecting and quantifying the alteration in the vehicle control properties. A subjective evaluation was performed to assess the experiment in terms of the quality and feel perceived by the driver. The subjective judgement delivered a result, where the deviation in quality agreed with the objective quantities hypothesised to describe quality. The thesis provides a significant step in the understanding of what is termed steering feel and quality. The methodology, successful in quantifying the experimental results with respect to quality, constitutes a scientific advancement in the current procedures for the assessment of steering quality.Item Open Access On minimum time vehicle manoeuvring: the theoretical optimal lap(Cranfield University, 2000-11) Casanova, D.; Sharp, Robin S.This work is a research on the minimum time vehicle manoeuvring problem, with a particular application to finding the minimum lap time for a Formula One racing car. The proposed method allows to solve the general problem of evaluating the vehicle lateral and longitudinal controls which yield the minimum time required to traverse a lap of a circuit. The minimum time vehicle manoeuvring problem is formulated as one of Optimal Control and is solved using mathematical programming methods. Novel techniques are employed to solve the resulting non-linear programming problem which allow to achieve effective optimisation with satisfactory accuracy, robustness and computational efficiency. Particularly, the proposed solution strategy is generally applicable to any arbitrarily complex vehicle mathematical model. Car and circuit models are set up, and the optimisation program is applied to investigate the sensitivity of the vehicle performance with respect to vehicle design parameters, such as the yaw moment of inertia, the total mass and the weight distribution. Furthermore, the minimum time manoeuvring problem is solved for very different vehicle configurations. The optimisation program accurately quantifies the vehicle performance in terms of manoeuvre time, and the nature of the optimal solution is shown to be always in excellent agreement with the dynamic properties of the vehicle model. A part of the work is devoted to the development of a strategy to obtain an initial estimate of the racing line and of the vehicle lateral and longitudinal controls to be used at the start of the optimisation. Two algorithms to compute the racing line using on board measured data from the real car are presented. A new mathematical model for the vehicle steering control is derived. The model uses multiple preview information of the intended path. Its structure derives from linear optimal preview control theory, but it is adapted to deal with non-linear vehicle operations arising from the inevitable tyre force saturation in vigorous manoeuvring. The excellent path following capability of the model is demonstrated by solving various path following tasks involving moderate manoeuvring and racing speeds.Item Open Access Pedestrian accident simulation and protection technology evaluation(2002-12) Howard, M. S.; Sharp, Robin S.; Sadeghi, M. M.Pedestrian safety is an important societal issue and as one of the stakeholders, vehicle manufacturers are attempting to improve pedestrian protection by enhancing vehicle design. In order to enhance vehicle design, first it is necessary to gain an improved understanding of the interactions between a pedestrian and a vehicle during an accident. Secondly, this knowledge needs to be transformed into vehicle design and technology changes. This thesis focuses on the construction of new models and methodologies to provide an improved understanding and the application of this understanding to design, develop and evaluate a number of pedestrian protection technologies. A review of the pedestrian safety issue and different approaches to pedestrian protection research provide the background to the chosen approach. This is described in terms of an overall methodology for any pedestrian protection technology that also provides a framework for this research. The construction and evaluation of pedestrian accident simulations with a reference C class vehicle are described in detail. The influence of accident conditions and the expected ranges of various quantitative pedestrian injury and motion measures are identified. Vehicle impact velocity, pedestrian size and stance have significant influences on these measures. Therefore it is not possible to state, for instance, that under all accident conditions, one vehicle impact location is likely to cause lower injury measures than another is. There is a clear increase in pedestrian measures (e.g. head velocity, HIC, tibia acceleration, knee bending) with a large increase in impact velocity (i.e. 25 to 40 km/h). However, some measures (e.g. HIC) do not necessarily increase with a small increase in impact velocity (e.g. 25 to 30 km/h) because of the new pedestrian motion (e.g. a new head impact location). Large differences exist between the 6 year old pedestrian and adult pedestrian model measures (e.g. larger post head impact motion but smaller HIC and tibia acceleration) and pedestrian stance has a complex influence on all measures with few overall trends. Pedestrian protection headlamp, bumper system and hood system concepts are developed in biomechanical, analytical and numerical component models. These concepts are used to construct and subsequently benchmark, with pedestrian accident simulations, two modified vehicle models that incorporate different combinations of the technologies. Both the absolute measures and ranges of the measures from the reference vehicle simulations are compared. There are large differences between the pedestrian measures from the reference and modified vehicles but much smaller differences between the modified vehicles. Impacts with the modified vehicles cause the largest differences in pedestrian motion at 40 km/h, for the 6 year old pedestrian, in stance TV, in the early (up to 20 ms) and late (after 140 ms) stages of the accident simulations. Although the modified vehicles reduce pedestrian injury measures for some of the accident conditions, neither of them reduce all measures for all of the conditions. However, significant improvements in experimental sub system measures [EEVC 1998] are achieved with a prototype modified vehicle that incorporates some of the technologies. Benchmarking is hindered by complex injury measure trends and by pedestrian and vehicle model limitations. Recommendations are made with respect to all of these factors. Further recommendations include the need for optimisation of the modified vehicle technologies in accident simulations, a more complete investigation of other technology functional requirements (e.g. low speed damageability) and accident reconstruction as a means to achieve improved model validation.Item Open Access Predictive engineering processes for motorcycle dynamics(Cranfield University, 2004-04) Styles, M. J.; Sharp, Robin S.; Harrison, M. F.This study is an investigation into the use of computer aided handling and stability analysis for motorcycles. In particular it considers Triumph Motorcycles Ltd., delving into Triumph's background, their strategy and the likelihood of them using virtual techniques for stability and handling analysis. Additionally, this work reviews current knowledge of motorcycle dynamics analysis and builds on it. A novel way of studying the steering feel has been developed by analysing the response of the steer torque equation for the Sharp 1971 [1] and 1994 [2] models. The individual contributors to this equation are identified and the important ones are investigated further. One conclusion of this study is that in reduced cornering and camber conditions the steer angle of the motorcycle, for a given steering input torque, increases when compared to standard operating conditions. The steer angle also increases further as the speed increases. An update to a previous motorcycle model [3] has been made by revising the parameter set, so that it is more applicable to a modem sports motorcycle. The rider model and relaxation length description have also been improved upon. The results show that the new motorcycle has been made more manoeuvrable by the alterations to the parameters. An optimal preview steering control system for cars [4] has been taken, improved upon and used with the newly developed motorcycle model discussed above. The results from this novel work allow a designer to alter parameters and see how this affects the motorcycles steering demands, path following, etc. It was shown that an increase in the front wheel inertia makes the motorcycle feel like the steering is heavier, and an increase in the front wheel radius and wheelbase make the steering feel lighter. Future work into non-linear analysis is recommended and improved rider and tyre modelling is also desired.