Theunis R. Botha

The relationship between vehicle yaw acceleration response and steering velocity for steering control

This paper proposes a novel concept for the modelling of a vehicle steering driver model for path following. The proposed steering driver reformulates and applies the Magic Formula, used for tyre lateral force vs. slip angle modelling as a function of vertical force, to the vehicle’s yaw acceleration vs. steering velocity response as a function of vehicle speed. The path-following driver model was developed for use in gradient-based mathematical optimisation of vehicle suspension characteristics for handling. Successful application of gradient-based optimisation depends on the availability of good gradient information. This requires a robust driver model that can ensure completion of the required handling manoeuvre, even when the vehicle handling is poor. The steering driver is applied to a nonlinear full vehicle model of a sports utility vehicle, performing a severe double lane change manoeuvre. Simulation results show excellent correlation with test results. The proposed driver model is robust and well suited to gradient-based optimisation of vehicle handling.

Vehicle Motion Measurements Using Front Facing Camera and Digital Image Correlation

Modern active vehicle safety systems rely on certain vehicle motion states to function. ABS requires the vehicle longitudinal speed to calculate the tire slip. The vehicle speed is typically estimated using the speed of all the wheels and is therefore dependent on the slip states of all the wheels. Electronic stability programs can also make more informed decisions if the vehicle side-slip angle is known. Currently the side-slip angle is not measured on commercial vehicles due to the cost of the sensors. The side-slip angle can however be estimated using multiple onboard vehicle measurements. However, these estimation techniques require accurate sensors and large excitations to estimate accurately. The measurement of the vehicle motion is therefore crucial for modern vehicle safety systems. This paper proposes a method whereby all 6 vehicle velocities can be measured using inexpensive forward facing mono and stereo cameras utilizing Digital Image Correlation (DIC) algorithms.

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

Vehicle Sideslip Estimation Using Unscented Kalman Filter, AHRS and GPS

A vehicle’s sideslip angle is an important parameter for both vehicle control and tyre property estimation. This paper details the method of determining a vehicles sideslip angle using an Attitude Heading Reference System (AHRS) and a Global Position System (GPS) in conjunction with the Unscented Kalman Filter (UKF). The addition of a single GPS antenna and the AHRS provides the ability to directly estimate the sideslip angle. Incorporating this direct measurement, as well as the summation of the gravity and gyro-compensated lateral acceleration to provide lateral velocity, allows the continuous and drift free estimation of the sideslip angle. The method is evaluated in simulation, using a validated non-linear full vehicle ADAMS model with added sensor noise. The estimated sideslip angle compares well against the simulated vehicle’s sideslip angle.Copyright

Profile Optimization of Table Top Speed Hump for Speed Control

Speed bumps are the most commonly used measure to control speeding in urban areas world wide. Specifications on profiles and dimensions are largely based on road tests. Studies into speed bumps, directed at evaluating their effectiveness in reducing accidents and their environmental impact, have brought some negative aspects concerning speed bumps to light. These aspects include incidents of spinal and neck injury or loss of control while speeding over speed bumps. Observations have also shown that speeding over certain speed bumps often result in an improvement in ride comfort, thus negating the effectiveness of speed bumps as a measure to control speeding. This paper addresses these aspects by considering the optimization of a speed bump’s profile. The profile is optimized by means of a validated non-linear four degree of freedom vehicle model, as well as the gradient based LFOPC optimization algorithm. The optimized profile allows for increased ride comfort at speeds at and below the designed speed. The ride comfort decreases with an increase in vehicle speed while the vehicle response remains within boundaries set up to reduce the possibility of injury or loss of vehicle control.Copyright

Comparison of Tire Footprint Measurement Techniques

With all wheeled vehicles, the tire contact patch is the only connection between the vehicle and the road. All the forces, except for aerodynamic forces, that are acting on the vehicle are generated in the tire contact patch. The size, shape and the pressure distribution of the contact patch are important to the performance, ride qualities and handling characteristics of a vehicle. Tire footprint studies are essential in understanding tire force generation and tire wear mechanisms. It is thus important to accurately determine the tire contact patch size and dimensions. This paper discusses various methods for measuring the static tire contact patch dimensions. A set of tests are conducted on various tires and at different inflation pressures. These tests are used to discuss the suitability of the methods depending on the type, size, load and contact surface of the tire. A list of advantages and disadvantages for each method is generated and discussed. The aim of this paper is not to study the tire footprints but to discuss the various testing methods. Insight into the different methods can help to select the suitable method for future tire contact studies.Copyright

Tire Longitudinal Slip-Ratio Measurement Using a Camera

The longitudinal slip-ratio is one of several parameters that govern the magnitude of the longitudinal force generated by a tire and probably the most important. As such, the longitudinal slip-ratio of a tire is an essential measurement required in the construction of longitudinal tire models. In laboratory experimental tests the slip-ratio can typically be controlled by controlling the rotational speeds of two motors. However, in in-situ tests, where the slip-ratio needs to be measured, the slip-ratio is estimated from three other measurements namely the wheel speed, vehicle speed and the rolling radius of the tire. While the wheel speed is fairly inexpensive and easy to measure accurately, the accurate measurement of vehicle speed requires an expensive GPS or similar system. The measurement of the rolling radius is often performed statically and assumed constant or can be measured with an expensive laser displacement sensor. Errors in the all of these measurements are compounded when determining the slip-ratio. This paper proposes a method of measuring the longitudinal slip-ratio by performing image correlation techniques on consecutive images of the tire-road interface obtained from a single inexpensive camera. Since the method makes use of one measurement system the probability of inducing errors in the slip-ratio is reduced.Copyright