David Crolla

Road Vehicle Suspension System Design - a review

SUMMARY Based mainly on English language literature, information relating to the design of automobile suspension systems for ride comfort and control of wheel load variations for frequencies below body structure resonances is reviewed. The information is interpreted in the context of vehicles which travel through a wide speed range on roads of markedly differing quality, which do so carrying different loads and which are required to possess good handling qualities. Sections are devoted to describing road surfaces, modelling vehicles and setting up performance criteria, and to passive, active, semi-active and slow-active system types. Methods for deriving active system control laws are outlined. Strengths and weaknesses of the various systems are identified and their relative performance capabilities and equipment requirements are discussed. Attention is given to adaptation of the suspension or control system parameters to changing conditions. Remaining research needs are considered.

Coordination of active steering, driveline, and braking for integrated vehicle dynamics control:

Abstract An integrated vehicle dynamics control system which aims to improve vehicle handling and stability by coordinating active front steering (AFS) and dynamic stability control (DSC) subsystems is developed in this paper. The DSC subsystem includes driveline-based, brake-based, and driveline plus brake-based DSC subsystems. The influence of varying forward speed and lateral acceleration on the lateral vehicle dynamics is investigated first. The AFS controller, which is used to improve vehicle steerability in the low to mid-range lateral acceleration, and the DSC controller, which manages to maintain vehicle stability during extreme driving situations, are then designed by using the sliding mode control (SMC) technique and phase plane method respectively. Based on the two independently developed controllers, a rule-based integration scheme is proposed to optimize the overall vehicle performance by minimizing interactions between the two subsystems and extending functionalities of individual subsystems. Computer simulation results confirm the effectiveness of the proposed control system and the overall improvements in vehicle handling and stability.

AN OPTIMAL SELF-TUNING CONTROLLER FOR AN ACTIVE SUSPENSION

SUMMARY An optimal self-tuning control algorithm is presented for vehicle suspension design. The controller, incorporating a weighting controller, state observer and parameter estimator, is designed according to linear optimal control (LQG) theory. Based on the updated estimates of vehicle parameters and states, and the adapted weighting parameters, the LQG controller provides the optimal set of gains over different operating conditions. The feasibility and effectiveness of the proposed self-tuning system was investigated and proved by simulation studies.

Integrated Vehicle Dynamics Control —state-of-the art review

Chassis control systems have evolved dramatically over the past two decades and their impacts on vehicle dynamics can be usefully separated into the three directions, i.e. lateral, longitudinal and vertical directions. Accordingly, the state survey of chassis control systems can be reviewed in following sub-system areas, i.e. steering, driveline/braking and suspension. The developments within each of these areas have progressed at different rates and each has had different impacts on improving vehicle behavior in relation to safety, ride, handling dynamics or economy. However, the biggest challenge is in the whole chassis integration of these sub-systems to avoid their interventions and thus to improve overall vehicle dynamics performance. Hence, a hot research topic, named integrated vehicle dynamics control (IVDC) or integrated chassis control, arose. Based on the published literatures in the recent twenty years, this paper presents a comprehensive state of the art survey on IVDC. First, the roadmap and methodologies of IVDC are reviewed, and then the control strategies of coordination between the subsystems are summarized. At present, integration technique between steering and braking/traction has been most concerned, and is being researched and developed intensively both in academic and industrial aspects. It can be expected that once X-by-Wire technology and actuator hardware are further developed, more potential benefits of IVDC can be obtained.

A review of yaw rate and sideslip controllers for passenger vehicles

The development of chassis control schemes has been a major area of study for automotive control engineers over the past 30 years. The volume of published literature is large, exceeding 1000 papers. Of this literature, there are 250 examining yaw and sideslip control. Here is a comprehensive review of this field of study to identify the current state of the art and research in yaw rate and sideslip control. The survey shows that there is still a significant research effort needed to address the subjective performance of handling systems, and more research is needed to develop schemes that integrate systems to achieve high-level performance objectives.

Active Suspension Control; Performance Comparisons Using Control Laws Applied to a Full Vehicle Model

Abstract Based on a mathematical model of an actively suspended vehicle, the effects of the following issues in deriving the control laws are studied: (a)representation of the ground surface as integrated or filtered white noise. (b)cross-correlation between left and right track inputs. (c)wheelbase time delay between front and rear inputs. The third of these issues is shown to be by far the most important. Considerable improvements at the rear suspension can be obtained if the control law includes the information that the rear input is simply a delayed version of the front input. Effectively this provides feedforward terms in the control law for the rear actuator. For the full state feedback case, these improvements are indicated by reductions in the rear body acceleration and rear dynamic tyre load of around 20% and 40% respectively with no increase in suspension working space.

Integrated Active Steering and Variable Torque Distribution Control for Improving Vehicle Handling and Stability

This paper proposes an advanced control strategy to improve vehicle handling and directional stability by integrating either Active Front Steering (AFS) or Active Rear Steering (ARS) with Variable Torque Distribution (VTD) control. Both AFS and ARS serve as the steerability controller and are designed to achieve the improved yaw rate tracking in low to mid-range lateral acceleration using Sliding Mode Control (SMC); while VTD is used as the stability controller and employs differential driving torque between left and right wheels on the same axle to produce a relatively large stabilizing yaw moment when the vehicle states (sideslip angle and its angular velocity) exceed the reference stable region defined in the phase plane. Based on these stand-alone subsystems, an integrated control scheme which coordinates the control actions of both AFS/ARS and VTD is proposed. The functional difference between AFS and ARS when integrated with VTD is explained physically. The effect of the integrated control system on the vehicle handling characteristics and directional stability is studied through an open loop computer simulation of an eight degrees of freedom nonlinear vehicle model. Simulation results confirm the effectiveness of the proposed control system and the overall improvements in vehicle handling and directional stability.

The impact of hybrid and electric powertrains on vehicle dynamics, control systems and energy regeneration

The background to the development of so-called green or low-carbon vehicles continues to be relentlessly reviewed throughout the literature. Research and development (R&D) on novel powertrains – often based on electric or hybrid technology – has been dominating automotive engineering around the world for the first two decades of the twenty-first century. Inevitably, most of the R&D has focused on powertrain technology and energy management challenges. However, as new powertrains have started to become commercially available, their effects on other aspects of vehicle performance have become increasingly important. This article focuses on the review of the integration of new electrified powertrains with the vehicle dynamics and control systems. The integration effects can be discussed in terms of three generic aspects of vehicle motions, namely roll-plane, pitch-plane and yaw-plane, which however are strongly coupled. The topic on regenerative suspension is further discussed. It quickly becomes clear that this integration poses some interesting future engineering challenges to maintain currently accepted levels of ride, handling and stability performance.

The Influence of Damper Properties on Vehicle Dynamic Behaviour

This paper details a non-linear hysteretic physical shock absorber model, and the processes utilised to identify the constituent parameters. In the current paper the model parameters are extracted from experimental data for the ‘sport’ setting of a prototype front shock absorber for a vehicle in the luxury class. The model is validated by comparing simulated results to experimental data for a test damper, for three discrete frequencies of sinusoidal excitation of 1,3 and 12 Hz. Finally the shock absorber model is included in a quarter car vehicle ride model and output characteristics are compared to those obtained with classical damper representations. INTRODUCTION The detailed dynamic properties of dampers are known to influence substantially some of the subtle, and yet nevertheless hugely important, refinement aspects of vehicle ride and handling. However, damper properties are typically characterised by quasi-steady properties for vehicle simulation purposes. The classic 14 speed test [1], for example, involves subjecting a damper to 14 differing frequency levels of fixed amplitude sinusoidal excitation, and then plotting the peak force values obtained versus the relevant test velocity. Such a representation of shock absorber behaviour is clearly deficient for the purpose of vehicle simulations as only a snap shot view of the damper’s behaviour is utilised and much information is discarded. As a direct consequence the process of damper valve tuning is still carried out to a great extent via ride work. This consists of ride engineers subjectively rating the performance of the prototype vehicle(s) over a series of test tracks/ride routes. The damper valve is then possibly adjusted to improve the vehicle’s ride/handling or to obtain characteristics expected for that class of vehicle. This process is clearly open to subjective evaluation which may vary driver to driver, and even from one day to the next. A more scientific approach to the issue of damper tuning, via vehicle simulations, would offer a number of significant benefits. This is simply due to the fact that the bulk of the damper selection process could be carried out prior to the manufacture of any vehicle prototypes, and this technique would be far less subjective in nature. Such an approach would necessitate an improved method of characterising the damper, such that the important dynamic features are represented, and comprehension of the links between more subtle features of the damper response. The current paper attempts to address the aforementioned requirement for improved damper characterisation in the context of the ‘sport’ setting of a triple rate prototype adaptive shock absorber. SHOCK ABSORBER MODELLING APPROACH In order to select the optimum damper modelling strategy for a ‘virtual damper tuning environment’, the suitability of the differing approaches found within published literature were determined with respect to the following criterion: Ability to capture damper non-linearity and dynamic behaviour. Flexibility to model different shock absorber types. Ease of model generation (Experiment/Parameter identification). Suitability for use in vehicle simulations. Usefulness as a predictive tool. Clearly black box methods such as the Restoring Force Mapping method [2-5] and neural networks [6], do not satisfy the need for a predictive tool as they are inherently non-tuneable. The same applies to elementary models constructed with spring and ideal viscous damping elements [7,8]. The required need for tuneable elements for this damper model application lends itself to an explicit physical model, where the damper control force is related to physical parameters that govern the dampers internal flows and pressures. The high detail model developed by Lang [9,10], for a twin tube shock absorber, was the first physical model that actually aimed to predict damper behaviour over a wide range of operating conditions. This 87 parameter model gave good correlation with experiment, but both simulation and parameter identification processes were highly iterative. It was also very specific to the shock 2002-01-0319 The Influence of Damper Properties on Vehicle Dynamic Behaviour Adrian Simms and David Crolla Copyright

Theoretical Analysis of the Steering Behaviour of Articulated Frame Steer Vehicles

SUMMARY A theoretical analysis of the steering behaviour of articulated frame steer vehicles is presented. It includes details of the hydraulic steering system as well as the equations governing motion of the front and rear body units. Both oscillatory and exponential instabilities can occur with this type of vehicle. The most sensitive design feature is the steering system, which governs the effective torsional stiffness around the pivot. Other important features which influence stability are speed and centre of gravity positions of the bodies.