Schalk Els

Tire-Ground Normal Force Estimation From Vehicle System Identification and Parameter Estimation

Ground vehicle stability controllers can be significantly improved through knowledge of the vehicle’s tire-ground normal force. This work demonstrates a proof-of-concept study of such an estimator. The method involves work from two previous methods that perform real-time estimation of the vehicle’s mass and horizontal CG position. Inclusion of the previous work provides the foundation for a comprehensive method that estimates the tire-ground normal load of a ground vehicle that is invariant with respect to the vehicle parameters.Copyright

Real-Time Vehicle Parameters Estimation

Parameter estimation for vehicle systems is in general a challenging topic from both sensor instrumentation and modeling perspectives. Modeling vehicle systems is a rather complex process, especially considering the numerous unknown effects on the system such as, for example, aerodynamic effects, road grade and bank angles, roll and pitch kinematics, and suspension nonlinearities. This study develops a method that is able to estimate several vehicle parameters with high accuracy for regular driving behavior. The parameter estimations are performed using the polynomial chaos-based extended Kalman filter (gPC-EKF). This method is a computationally efficient, derivative free, iterative, nonlinear regression technique which is able to estimate multiple parameters in real time. The paper presents the results obtained for estimating the location of the CG of the vehicle in the horizontal plane, and the sprung mass of the vehicle using the proposed technique. Real test data have been used for validation purposes.Copyright

Importance of Correct Validation of Simulation Models

This paper aims at demonstrating the importance of the correct validation of simulation models. Although correct model validation is often taken for granted, a large portion of published research does not pay adequate attention to this issue, resulting in models that are not adequate validated. The importance of validating the model for the correct parameters will be demonstrated by means of a case study which entails the modeling and experimental validation of a multi-leaf spring suspension system. Experimental measurements include the spring force as well as the forces acting at the suspension attachment points measured by two six component load cells. The six component load cells make it possible to validate the resultant force as well as its application point at the suspension attachment points. The result of the qualitative comparison of the experimental and model data shows the importance of validating the model against the parameters of interest. It also shows that extrapolating correlation results to other parameters may not be a good assumption in many situations.Copyright

Collaborative engineering of integrated chassis control for ground vehicle: Case study of lifelong learning technologies in automotive mechatronics

The paper introduces an approach to development and testing of integrated active chassis systems for the ground vehicle through intersectoral and interdisciplinary collaboration. The approach is illustrated by example of design of integrated control for the decoupled brake system, the active tyre pressure management and the active suspension elements. The corresponding demonstrator of sport utility vehicle is introduced. Testing procedures for the demonstrator are presented including remotely connected experiments at different locations. The paper explains how the development and testing processes are realized by way of knowledge transfer and experience sharing between academic and industrial collaborators.

Magneto-Rheological (MR) Valve for Use in Hydro-Pneumatic Suspensions

The suspension design requirements for vehicles that need both good on-road and off-road capabilities as well as vehicles where the payload changes significantly during operation is quite challenging. To overcome the ride comfort vs. handling compromise that most vehicles suffer from some suspension systems offer adjustability and control to overcome this conflict. The uptake of controllable dampers on commercial vehicles, allthough cost effective and technically feasible, have been low mainly because dampers on their own cannot significantly reduce the compromises involved with fully laden vs. empty or on-road vs. off-road use. The University of Pretoria developed a Four State Semi-Active Suspension System (4S4) that allows for the control and adjustability of the stiffness and the damping of the suspension. The 4S4 makes use of solenoid valves of which the response time unfortunately increases with an increase in flow, especially when implemented on larger vehicles, reducing the effectiveness of the control.This paper presents an alternative to the solenoid valves currently used in the 4S4 in the form of a magneto-Rheological (MR) valve that acts as a normal continuously variable MR damper, but also has the ability to virtually block the flow of fluid, thus switching between the two different spring characteristics. Experimental results show that it is indeed possible to replace the solenoid valves with a MR valve.Copyright

A Comparison of Quarter, Half and Full Vehicle Models With Experimental Ride Comfort Data

The ride comfort of a vehicle is one of the first parameters used to evaluate its performance. Ride comfort has been one of the important research topics since the dawn of the automobile. With the improvement in computational capability, vehicle engineers have modeled vehicles with increasing complexity. Initially vehicles were simplified to quarter car models, where a quarter of the vehicle was modeled with two degrees of freedom (the vertical translation of the sprung and unsprung masses). The “pitch-bounce” model has four degrees of freedom, representing the pitch rotation and vertical translation (bounce) of the vehicle body and chassis and the vertical translation of the front and rear axles and wheels. Finally, with the development of multi-body systems (MBS) software, there is the possibility to model the full vehicle with suspension kinematics and numerous degrees of freedom. The full vehicle model used for this study has 15 unconstrained degrees of freedom and experimentally determined center of mass and inertias. This paper compares the response of a quarter car, pitch-bounce and full vehicle model with the measured response of an actual vehicle.Copyright

Comparative Study of Magnetorheological Damper Models for Force Tracking

Magnetorheological (MR) dampers are controllable semi-active dampers capable of providing a range of continuous damping settings. MR dampers are often incorporated in suspension systems of vehicles where conflicting damping characteristics are required for favorable ride comfort and handling behavior. For control applications the damper controller determines the required damper current in order to track the desired damping force, often by using a suitable MR damper model. In order to utilise the fast switching time capability of MR dampers, a model that can be used to directly calculate damper current is desired. Unfortunately few such models exist and other methods, which often negatively affect the computational efficiency of the model, need to be used when implementing these models. In this paper a selection of MR damper models are developed and evaluated for both accuracy and computational efficiency while tracking a desired damping force. The Kwok model is identified as a suitable candidate for the intended suspension control application.Copyright

The Development of a Longitudinal Control System for a Sports-Utility-Vehicle

A common problem with sports-utility-vehicles is the low rollover threshold, due to a high center of gravity. Instead of modifying the vehicle to increase the rollover threshold, the aim of the control system is to prevent the vehicle from exceeding speeds that would cause the vehicle to reach its rollover threshold. The aim of the autonomous longitudinal control system, discussed here, is to improve the vehicle’s safety by controlling the vehicle’s longitudinal behavior.In order to develop a control system that autonomously controls the longitudinal degree of freedom, an experimentally validated mathematical model of the test vehicle (a 1997 Land Rover Defender 110 Wagon) was used — the model was developed in MSC.ADAMS/View. The control system was developed by generating a reference speed that the vehicle must track. This reference speed was formulated by taking into account the vehicle’s limits due to lateral acceleration, combined lateral and longitudinal acceleration and the vehicle’s performance capabilities.The MSC.ADAMS/View model of the test vehicle was used to evaluate the performance of the control system on various racetracks for which the GPS coordinates were available. The simulation results indicate that the control system performed as expected by limiting the vehicle’s acceleration vector to the prescribed limits.Copyright