108 research outputs found
Optimisation of racing car suspensions featuring inerters
Racing car suspensions are a critical system in the overall performance of the vehicle. They must be able to accurately control ride dynamics as well as influencing the handling characteristics of the vehicle and providing stability under the action of external forces. This work is a research study on the design and optimisation of high performance vehicle suspensions using inerters. The starting point is a theoretical investigation of the dynamics of a system fitted with an ideal inerter. This sets the foundation for developing a more complex and novel vehicle suspension model incorporating real inerters. The accuracy and predictability of this model has been assessed and validated against experimental data from 4- post rig testing. In order to maximise overall vehicle performance, a race car suspension must meet a large number of conflicting objectives. Hence, suspension design and optimisation is a complex task where a compromised solution among a set of objectives needs to be adopted. The first task in this process is to define a set of performance based objective functions. The approach taken was to relate the ride dynamic behaviour of the suspension to the overall performance of the race car. The second task of the optimisation process is to develop an efficient and robust optimisation methodology. To address this, a multi-stage optimisation algorithm has been developed. The algorithm is based on two stages, a hybrid surrogate model based multiobjective evolutionary algorithm to obtain a set of non-dominated optimal suspension solutions and a transient lap-time simulation tool to incorporate external factors to the decision process and provide a final optimal solution. A transient lap-time simulation tool has been developed. The minimum time manoeuvring problem has been defined as an Optimal Control problem. A novel solution method based on a multi-level algorithm and a closed-loop driver steering control has been proposed to find the optimal lap time. The results obtained suggest that performance gains can be obtained by incorporating inerters into the suspension system. The work suggests that the use of inerters provides the car with an optimised aerodynamic platform and the overall stability of the vehicle is improved
Ride and handling assessment of vehicles using four-post rig testing and simulation
The tuning of production road car suspension parameters in the development stage of a vehicle can be a lengthy and expensive procedure and commonly relies on the subjective judgements of test drivers to assess various aspects of ride and handling. The work in this thesis aims to create a testing and tuning technique using four-post rig testing and vehicle simulation to significantly reduce the amount of physical and subjective testing required within the development stage.
A four-post rig testing technique is developed using modal sine sweep inputs to acquire the response of the vehicle in the heave, pitch, roll and warp modes of excitation. An analysis and parameter estimation method is developed based on four-post data and a 7 degree-of-freedom model, with four-post test data used to validate the parameter estimation and vehicle model simultaneously, obtaining satisfactory results in all but the roll mode of excitation.
The BS 6841 [1] discomfort acceleration weightings are applied to the modal responses, with road input PSDs representative of standardised roads and driving cycles used to produce a comfort index value for a tested vehicle or setup.
A novel performance index is created to estimate grip loss due to static and dynamic tyre properties for each axle, which allows the prediction of road input effects on the total grip and balance of the vehicle, as well as a driver requirement of steering input. MATLAB code is constructed for the parameter estimation procedure and for three general user interfaces to assist with the testing, tuning and benchmarking procedure.
An objective-subjective validation exercise is carried out using a single vehicle with four different
component setups which are tested on the four-post rig to determine comfort and performance index values, as well as recording the subjective assessments of three test drivers on two drive routes in the UK and Germany. The results show fair to good correlation for comfort measures but generally poor correlation to the performance index, mostly because of large variations between the drivers’ subjective assessment criteria
Preview-based techniques for vehicle suspension control: a state-of-the-art review
Abstract Automotive suspension systems are key to ride comfort and handling performance enhancement. In the last decades semi-active and active suspension configurations have been the focus of intensive automotive engineering research, and have been implemented by the industry. The recent advances in road profile measurement and estimation systems make road-preview-based suspension control a viable solution for production vehicles. Despite the availability of a significant body of papers on the topic, the literature lacks a comprehensive and up-to-date survey on the variety of proposed techniques for suspension control with road preview, and the comparison of their effectiveness. To cover the gap, this literature review deals with the research conducted over the past decades on the topic of semi-active and active suspension controllers with road preview. The main formulations are reported for each control category, and the respective features are critically analysed, together with the most relevant performance indicators. The paper also discusses the effect of the road preview time on the resulting system performance, and identifies control development trends
Enhancing vehicle dynamics through real-time tyre temperature analysis
Vehicle suspension optimisation is a complex and difficult task, as there are a variety of factors influencing the dynamic performance of a vehicle. During suspension development, the optimisation of a selected few of these factors is often to the detriment of others, as they are all inter-related. In addition, expertise in vehicle setup and suspension tuning is scarce, and is limited to experienced racing teams and large automotive manufacturers with extensive research and development capabilities. The motivation for this research was therefore to provide objective and user-friendly methodologies for vehicle suspension optimisation, in order to support student projects like Formula Student, while having relevance to the needs of the South African automotive industry and racing community. With the onset of digital data acquisition, it has become feasible to take real-time measurements of tyre temperatures, to provide information on how a tyre is performing at a specific point on the track. Measuring the tyre surface temperature can provide a useful indication on whether the tyre is loaded equally or not, and what suspension adjustments should be made to improve tyre load distribution
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Convolution based real-time control strategy for vehicle active suspension systems
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A novel real-time control method that minimises linear system vibrations when it is subjected to an arbitrary external excitation is proposed in this study. The work deals with a discrete differential dynamic programming type of problem, in which an external disturbance is controlled over a time horizon by a control force strategy constituted by the well-known convolution approach. The proposed method states that if a control strategy can be established to restore an impulse external disturbance, then the convolution concept can be used to generate an overall control strategy to control the system response when it is subjected to an arbitrary external disturbance. The arbitrary disturbance is divided into impulses and by simply scaling, shifting and summation of the obtained control strategy against the impulse input for each impulse of the arbitrary disturbance, the overall control strategy will be established. Genetic Algorithm was adopted to obtain an optimal control force plan to suppress the system vibrations when it is subjected to a shock disturbance, and then the Convolution concept was used to enable the system response to be controlled in real-time using the obtained control strategy. Numerical tests were carried out on a two-degree of freedom quarter-vehicle active suspension model and the results were compared with results generated using the Linear Quadratic Regulator (LQR) method. The method was also applied to control the vibration of a seven-degree of freedom full-vehicle active suspension model. In addition, the effect of a time delay on the performance of the proposed approach was also studied. To demonstrate the applicability of the proposed method in real-time control, experimental tests were performed on a quarter-vehicle test rig equipped with a pneumatic active suspension. Numerical and experimental results showed the effectiveness of the proposed method in reducing the vehicle vibrations. One of the main contributions of this work besides using the Convolution concept to provide a real time control strategy is the reduction in the number of sensors needed to construct the proposed method as the disturbance amplitude is the only parameter needed to be measured (known). Finally, having achieved what has been proposed above, a generic robust control method is accomplished, which not only can be applied for active suspension systems but also in many other fields
Investigation of a non-linear suspension in a quarter car model
This thesis presents the study of a quarter car model which consists of a two-degree-of-freedom (2 DOF) with a linear spring and a nonlinear spring configuration. In this thesis, the use of non-linear vibration attachments is briefly explained, and a survey of the research done in this area is also discussed. The survey will show what have been done by the researches in this new field of nonlinear attachments. Also, it will be shown that this topic was not extensively researched and is a new type of research where no sufficient experimental work has been applied. As an application, a quarter car model was chosen to be investigated. The aim of the Thesis is to validate theoretically and experimentally the use of nonlinear springs in a quarter car model. Design the new type of suspension and insert it in the experimental set up, built from the ground up in the laboratory. A novel criterion for optimal ride comfort is the root mean square of the absolute acceleration specified by British standards ISO 2631-1997. A new way to reduce vibrations is to take advantage of nonlinear components. The mathematical model of the quarter-car is derived, and the dynamics are evaluated in terms of the main mass displacement and acceleration. The simulation of the car dynamics is performed using Matlab® and Simulink®. The realization of vibration reduction through one-way irreversible nonlinear energy localization which requires no pre-tuning in a quarter car model is studied for the first time. Results show that the addition of the nonlinear stiffness decreases the vibration of the sprung mass to meet optimal ride comfort standards. As the passenger is situated above the sprung mass, any reduction in the sprung mass dynamics will directly have the same effect on the passenger of the vehicle. The future is in the use of a nonlinear suspension that could provide improvement in performance over that realized by the passive, semi active and active suspension. The use of a quarter car model is simple compared to a half car model or a full car model, furthermore in the more complex models you can study the heave and the pitch of the vehicle. For the initial study of the nonlinear spring the quarter car model was sufficient enough to study the dynamics of the vehicle. Obtaining an optimum suspension system is of great importance for automotive and vibration engineer involved in the vehicle design process. The suspension affects an automobile’s comfort, performance, and safety. In this thesis, the optimization of suspension parameters which include the spring stiffness and damper coefficient is designed to compromise between the comfort and the road handling. Using Genetic algorithm an automated optimization of suspension parameters was executed to meet performance requirements specified. Results show that by optimizing the parameters the vibration in the system decreases immensely
An investigation of multibody system modelling and control analysis techniques for the development of advanced suspension systems in passenger cars
The subject of this thesis is the investigation of multibody system modelling
and control analysis techniques for the development of advanced suspension
systems in passenger cars. A review of the application of automatic control to
all areas of automotive vehicles illustrated the important factors in such
developments, including motivating influences, constraints and methodologies
used. A further review of specific applications for advanced suspension systems
highlighted a major discrepancy between the significant claims of theoretical
performance benefits and the scarcity of successful practical implementations.
This discrepancy was the result of idealistic analytical studies producing
unrealistic solutions with little regard for practical constraints. The
predominant application of prototype testing methods in implementation studies
also resulted in reduced potential performance improvements.
This work addressed this gap by the application of realistic modelling and
control design techniques to practical realistic suspension systems. Multibody
system modelling techniques were used to develop vehicle models incorporating
realistic representations of the suspension system itself, with the ability to
include models of the controllers, and facilitate control analysis tasks. These
models were first used to address ride control for fully active suspension
systems. Both state space techniques, including linear quadratic regulator and
pole placement and frequency domain design methods were applied. For the
multivariable frequency domain study, dyadic expansion techniques were used
to decouple the system into single input single output systems representing
each of the sprung mass modes. Both discretely and continuously variable
damping systems were then addressed with a range of control strategies,
including analytical solutions based on the active results and heuristic rule-based
approaches. The controllers based on active solutions were reduced to
satisfy realistic practical limitations of the achievable damping force. The
heuristic techniques included standard rule-based controllers using Boolean
logic for the discretely variable case, and fuzzy logic controllers for the
continuously variable case
Control strategies of series active variable geometry suspension for cars
This thesis develops control strategies of a new type of active suspension for high
performance cars, through vehicle modelling, controller design and application, and
simulation validation. The basic disciplines related to automotive suspensions are first
reviewed and are followed by a brief explanation of the new Series Active Variable
Geometry Suspension (SAVGS) concept which has been proposed prior to the work
in this thesis. As part of the control synthesis, recent studies in suspension control
approaches are intensively reviewed to identify the most suitable control approach for
the single-link variant of the SAVGS.
The modelling process of the high-fidelity multi-body quarter- and full- vehicle
models, and the modelling of the linearised models used throughout this project are
given in detail. The design of the controllers uses the linearised models, while the
performance of the closed loop system is investigated by implementing the controllers
to the nonlinear models.
The main body of this thesis elaborates on the process of synthesising H∞ control
schemes for quarter-car to full-car control. Starting by using the quarter-car single-link
variant of the SAVGS, an H∞ -controlled scheme is successfully constructed, which
provides optimal road disturbance and external force rejection to improve comfort
and road holding in the context of high frequency dynamics. This control technique is
then extended to the more complex full-car SAVGS and its control by considering the
pitching and rolling motions in the context of high frequency dynamics as additional
objectives. To improve the level of robustness to single-link rotations and remove the
geometry nonlinearity away from the equilibrium position, an updated approach of
the full-car SAVGS H∞ -controlled scheme is then developed based on a new linear
equivalent hand-derived full-car model. Finally, an overall SAVGS control framework
is developed, which operates by blending together the updated H∞ controller and
an attitude controller, to tackle the comfort and road holding in the high frequency
vehicle dynamics and chassis attitude motions in the low frequency vehicle dynamics
simultaneously. In all cases, cascade inner position controllers developed prior to the work in this
thesis are employed at each corner of the vehicle and combined with the control systems
developed in this thesis, to ensure that none of the physical or design limitations of
the actuator are violated under any circumstances.Open Acces
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