Active safety vehicle systems are continuously being researched to make vehicles safer to drive. Active steering is a new active safety system that involves controlling the vehicle steering angle during the vehicle's loss of stability. The steering signal, which an active steering system intervenes with, is brought to study in this thesis. Using a pulsed signal instead of a constant signal as the output of an active steering system arises new areas to study. This thesis focuses on the effect that the different pulse parameters have on the yaw and roll dynamics of a passenger vehicle. The parameters of a pulse consist of its frequency, amplitude, and pattern. Simulations were done with different vehicle models in different simulation softwares to assess the effect that each of the pulse parameters has on the vehicle dynamics. These simulation softwares include DynaFlexPro, Matlab/Simulink and Adams/Car. In addition, a whole test bed was designed and assembled to carry out Hardware-In-the-Loop (HIL) simulation experiments involving active steering systems. The test bed was used to firstly validate the results obtained from the simulations, and secondly to assess the applicability of a pulsed active steering system. Conclusions of the obtained results as well as future work are mentioned at the end of this thesis.

Active safety vehicle systems are continuously being researched to make vehicles safer to drive. Active steering is a new active safety system that involves controlling the vehicle steering angle during the vehicle's loss of stability. The steering signal, which an active steering system intervenes with, is brought to study in this thesis. Using a pulsed signal instead of a constant signal as the output of an active steering system arises new areas to study. This thesis focuses on the effect that the different pulse parameters have on the yaw and roll dynamics of a passenger vehicle. The parameters of a pulse consist of its frequency, amplitude, and pattern. Simulations were done with different vehicle models in different simulation softwares to assess the effect that each of the pulse parameters has on the vehicle dynamics. These simulation softwares include DynaFlexPro, Matlab/Simulink and Adams/Car. In addition, a whole test bed was designed and assembled to carry out Hardware-In-the-Loop (HIL) simulation experiments involving active steering systems. The test bed was used to firstly validate the results obtained from the simulations, and secondly to assess the applicability of a pulsed active steering system. Conclusions of the obtained results as well as future work are mentioned at the end of this thesis.

<p>Reversing with a trailer is very difficult and many drivers hesitate to even try it. This thesis examines if active steering, particularly AFS (Active Front Steering), can be used to provide assistance.</p><p>For analysis and controller design a simple geometric model of car and trailer is used. The model seems to be accurate enough at the low speeds relevant for trailer reversing. It is shown that the only trailer dependent model parameter can be estimated while driving. This enables use with different trailers.</p><p>Different schemes to control the system are tested. The main approach is to use the steering wheel as reference for some appropriate output signal, for example the angle between car and trailer. This makes reversing with a trailer more like reversing without a trailer. To turn left, the driver simply turns the steering wheel left and drives. Test driving, as well as theoretical analysis, shows that the resulting system is stable. Of the eight drivers that have tested this type of control, five found it to be a great advantage while two considered it more confusing than helpful.</p><p>A major problem with this control approach has to do with the way AFS is constructed. With AFS, the torque required to turn the front wheels results in a reaction torque in the steering wheel. Together with the reference tracking controllers, this makes the steering wheel unstable. Theoretical analysis implies that this problem has to be solved mechanically. One solution would be to combine AFS with electric power steering.</p><p>This thesis also presents a trajectory tracking scheme to autonomously reverse with a trailer. Starting from the current trailer position and the desired trajectory an appropriate turning radius for the trailer is decided. Within certain limits, this will stabilize the car as well. The desired trajectory can be programmed beforehand, but it can also be saved while driving forward. Both variants have been tested with good results.</p>

A superimposed steering system is the combination of a conventional steering system with an electric motor which is used to alter the steering angle imposed by the driver. The potential benefits are increased agility, automatic compensation for lateral wind forces and decreased braking distance (in combination with an electronic stability program). In this thesis we implement a model and a controller for a superimposed steering system thus achieving the first of these potential benefits. The vehicle model is based on the single-track or bicycle model. Unlike most other publications, the motor model in this thesis goes down to the level of the electrical dynamics of the motor. The model is divided into three main modules (vehicle module, steering module and friction module) as well as several submodules to ensure easy adaptability. The overall control objective consists of increasing vehicle agility by achieving a variable ratio between the steering wheel angle and the actual road wheel angle as a function vehicle velocity. We divide the controller into a torque and a current controller. The actual controller is derived in three steps starting from an analog torque controller as well as an analog current controller then moving to a digital torque controller. In doing so we use the model matching, feedback linearization and state feedback control techniques. The model and the controller are evaluated using the parameters of a small truck and different road scenarios. Finally, the Validation Square technique is applied to assess the validity of the results.

Reversing with a trailer is very difficult and many drivers hesitate to even try it. This thesis examines if active steering, particularly AFS (Active Front Steering), can be used to provide assistance. For analysis and controller design a simple geometric model of car and trailer is used. The model seems to be accurate enough at the low speeds relevant for trailer reversing. It is shown that the only trailer dependent model parameter can be estimated while driving. This enables use with different trailers. Different schemes to control the system are tested. The main approach is to use the steering wheel as reference for some appropriate output signal, for example the angle between car and trailer. This makes reversing with a trailer more like reversing without a trailer. To turn left, the driver simply turns the steering wheel left and drives. Test driving, as well as theoretical analysis, shows that the resulting system is stable. Of the eight drivers that have tested this type of control, five found it to be a great advantage while two considered it more confusing than helpful. A major problem with this control approach has to do with the way AFS is constructed. With AFS, the torque required to turn the front wheels results in a reaction torque in the steering wheel. Together with the reference tracking controllers, this makes the steering wheel unstable. Theoretical analysis implies that this problem has to be solved mechanically. One solution would be to combine AFS with electric power steering. This thesis also presents a trajectory tracking scheme to autonomously reverse with a trailer. Starting from the current trailer position and the desired trajectory an appropriate turning radius for the trailer is decided. Within certain limits, this will stabilize the car as well. The desired trajectory can be programmed beforehand, but it can also be saved while driving forward. Both variants have been tested with good results.

Hydrostatic steering systems are used in construction and agricultural machines alike. Because of their high power density, hydraulic drives are qualified for the use in vehicles with high steering loads. Conventional hydrostatic steering systems are limited in terms of steering comfort and driver assistance. For realisation of appropriate steering functions, electro-hydraulic solutions are necessary. This paper provides an overview on existing implementations and introduces a novel steering system. The presented active steering system with independent meter-in and meter-out valves fills the gap between existing active steering systems and steer-by-wire solutions. An appropriate control and safety concept provides advanced steering functions for on-road usage without the fully redundant structure of steer-by-wire systems.

Narrow tilting vehicles offer an opportunity to tackle both traffic congestion and carbon emissions having a small footprint, low weight and small frontal area. Their narrow width requires that they tilt into corners in order to maintain stability; this may be achieved by means of an automated tilt control system. A three-wheeled tilting vehicle prototype, known as the Compact Low Emission Vehicle for uRban transport (CLEVER), was constructed at the University of Bath in 2006. The vehicle was equipped with a direct tilt control system in which a pair of hydraulic actuators applied a moment between the cabin and a non-tilting base. This tilt control system provided satisfactory steady state performance but limited transient stability. High tilt rate demands associated with rapid steering inputs would lead to large tilting moments being applied to the non-tilting rear engine module; this, combined with the engine module’s own propensity to roll out of the bend, could cause the inside wheel to lift and the vehicle to capsize. This thesis details the implementation of a Steering Direct Tilt Control (SDTC) system, whereby the front wheel steer angle is used to generate some of the tilting moment, on the prototype CLEVER Vehicle. Simulation and experimental results are presented which show a 40% reduction in load transfer across the rear axle during a transient ramp steer manoeuvre. The influence of the SDTC system, and associated steer angle alteration, on the vehicle trajectory is considered. A human driver is found to be capable of adapting their steer inputs such that they can follow their chosen path. Finally, a feed-forward control strategy is shown to reduce the load transfer across the rear axle by an additional 30% in transient situations, but only if the steer input signal is sufficiently free of noise.

Hydrostatic steering systems are used in construction and agricultural machines alike. Because of their high power density, hydraulic drives are qualified for the use in vehicles with high steering loads. Conventional hydrostatic steering systems are limited in terms of steering comfort and driver assistance. For realisation of appropriate steering functions, electro-hydraulic solutions are necessary. This paper provides an overview on existing implementations and introduces a novel steering system. The presented active steering system with independent meter-in and meter-out valves fills the gap between existing active steering systems and steer-by-wire solutions. An appropriate control and safety concept provides advanced steering functions for on-road usage without the fully redundant structure of steer-by-wire systems.

No description available.

Yes / The fundamentals and preliminary analyses of an innovative future technology referred to as `semi-active steering' (SAS) are presented in this article. The proposed steering system configuration is similar to a conventional electrical power-assisted steering with the replacement of the rigid steering shaft with a low stiffness resilient shaft (LSRS), the presence of which allows `active control¿ to be performed on vehicles similar to the concept of full steer-by-wire (SBW). But, unlike SBW, the LSRS is an integral part of the system characteristics. The advantages of the semi-active system in comparison with SBWand other conventional systems are demonstrated. A mathematical model to predict the mechanical properties of the LSRS has been developed, and experiments were conducted on a medium-sized car fitted with an LSRS to verify that vehicle stability and drivability can be ensured in the event of active system failure. The results have indicated that the vehicle was stable and safe to be driven at low speeds, and is predicted to be driveable and safe at higher speeds. It is concluded that an SAS system of this type has the potential to improve the safety of SBW systems.