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Enhancement of Steering and Safety Feeling in a Steer-By-Wire Application
Abstract
A conventional way to enhance the steering features (hence optimize the vehicle dynamics) and steering feeling has been realized with EPS (Electric Power Steering) Systems. Another milestone of steering systems is the steer-by-wire steering system, which has no mechanical connection between the steering wheel and tires. Steer-by-wire systems offer many additional desirable steering characteristics. In this paper, a steer-by-wire implementation with new functions will be introduced. Furthermore first results with real-time experimental examples will be elucidated in detail.
... Therefore the importance of steering systems as an element of vehicle dynamics control has increased dramatically in recent years. [1] With the introduction of EPS (electric power steering) many new alternatives have become possible. Besides some very early mechatronic applications such as 'Servotronic', which controls the steering torque as a function of the vehicle speed, [2] EPS enabled controlling of the steering torque not only in accordance with vehicle speed, but also on driving conditions like for example oversteering and understeering. ...
... However, several challenges such as safety and cost have prevented this system to be marketable. [1] The main cost factor of this kind of steering system is to enhance the reliability of connection between the tyres and the steering wheel, which can be solved by using a fail-safe connection. Some applications of SBW systems with a fail-safe connection, have been presented in [7,8]. ...
... Stationary yawing amplification: The relationship θ stat =ψ/δ can also be written as the ratio of the yaw rate to the steering wheel angle by including the steering ratio i . 1 Therefore the Downloaded by [192.109.190 relationship between the yaw rate and steering wheel angle can be given as [10]: ...
An important development of the steering systems in general is active steering systems like active front steering and steer-by-wire systems. In this paper the current functional possibilities in application of active steering systems are explored. A new approach and additional functionalities are presented that can be implemented to the active steering systems without additional hardware such as new sensors and electronic control units. Commercial active steering systems are controlling the steering angle depending on the driving situation only. This paper introduce methods for enhancing active steering system functionalities depending not only on the driving situation but also vehicle parameters like vehicle mass, tyre and road condition. In this regard, adaptation of the steering ratio as a function of above mentioned vehicle parameters is presented with examples. With some selected vehicle parameter changes, the reduction of the undesired influences on vehicle dynamics of these parameter changes has been demonstrated theoretically with simulations and with real-time driving measurements.
... A typical VGS system is active front steering system from BMW corporation, which utilizes a double planetary gear system and an electric actuator motor to facilitate driver independent steering of the front wheels. 4,5 This system is intended to improve the steering stability at different driving speed by an optimized transmission coefficient. Because of the mechanical decoupled structure of SBW system, the steering control with variable transmission ratio can be conducted through a software, without any requirement of a hardware configuration. ...
To improve vehicle handling performance, a variable steering ratio characteristic for steer-by-wire system is designed. The steering ratio is adjusted by a compensating coefficient according to vehicle longitudinal speed and steering wheel angle. To evaluate the performance of vehicle with variable steering ratio, simulations are conducted based on an objective evaluation index, which consists of quadratic cost functions of vehicle lateral deviation, steering angular speed, vehicle lateral acceleration and roll angle. By using the optimized data from the simulation results, a Takagi-Sugeno fuzzy neural network is designed for the steering ratio control. In order to test and validate the proposed controller, a series of comparison experiments are conducted on a closed-loop driver-vehicle system, including lemniscate curve test and double lane-change test. The results demonstrate that compared with a conventional steering system with fixed steering ratio, the proposed system can not only improve steering agility at low speed and steering stability at high speed, but also reduce driver’s workload in critical driving conditions.
... If the system response is too slow, the delay might give rise to safety concern [11]. Based on the results, the overall system had achieved the accuracy between steering versus wheel with a maximum error of +/-2 degree and system response time less than a second. ...
Recent statistics shows that 93% of Malaysians own a car. This implies that enrollment to driving schools is also high and will continue to increase. Thus accidents during driving lessons are more common these days. The availability of a dual brake system for the driving instructor may not be adequate. This project aims to develop a dual steering system to enable the driving school instructor the ability to correct the vehicle steering when the need arises. A hardware structure using the already existing rack and pinion mechanism system with a DC motor assembly and a rotary encoder is proposed. Fuzzy logic is used as the control algorithm which is integrated in the microcontroller to control the proposed system. The obtained result shows that the intergrated software and hardware achieved the intended capability with the response time less than a second and steering angular error of 4 degrees.
In this paper the numerical modeling and optimization of a centrifugal pump impeller running in reverse operation is presented. The turbine operating point was determined using empirical correlations, which were also validated by the numerical performance curves obtained from multiple operating point simulations. This information is used to validate the numerical approach and assumptions in order to be used in the optimization of the impeller in turbine operation. Subsequently, a parametric study is performed comparing the relative effect in performance of various design modifications, such as the inlet edge shape, the meridional channel width, the number of vanes, and the effect of splitter blades. Using the previous results as guidelines, the numerical optimization of the runner is performed using two optimization algorithms. In the first, only the blade shape was allowed to change while the meridional contour of the runner was maintained constant in order to accommodate the available spiral casing dimensions. In the second optimization, the runner diameter was also included. From the results of the optimization, an overall increase in turbine efficiency of approximately 2.7% could be achieved.
The proportion of active chassis systems and x-by-wire applications is increasing in the current vehicle development. They represent a larger function range as well as an increased safety in the control loop "driver-vehicle- environment". At this point, especially steering systems are quite important, because the driver is adapted to the car by the steering wheel. Therefore different steering systems have been developed, starting with mechanical systems which meanwhile have been replaced by steering systems, which influence the steering torque (e.g. Servotronic, EPHS or EPS). Nowadays, active steering systems, which are also able to set an additional steering angle, conquer the vehicle industry. Dimensioning active steering systems, a realization of technical and functional requirements and a suitable safety strategy is necessary. This results in an increased comfort and active safety. On the other side, safety functions must guarantee that in case of disturbances or breakdowns of mechatronic systems, the car stays controllable. Also these malfunctions must not lead to critical driving situations in any case. This paper shows how the development process of active steering systems can be designed consequently regarding normal driver orientation. This process starts with the conception, followed by the design process and realization of the technical functions up to suitable safety concepts. Here, the maximal actuator malfunction, determined in tests with a normal driver population, are investigated and identified for safety functions.
For the first time the well known nonlinear shape of the vehicle's side force characteristics is considered to design a steering controller for automatic guidance. When applying nonlinear model predictive control, which should be the best possible controller from a mathematical point of view, it turns out that a large number of controller parameters has to be defined using heuristc methods. In this paper, however, exact linearization technique is used to determine a feedback law, that matches the performance of the model predictive controller with a much lower ammount of computing time and only two controller parameters. The position of the vehicle fixed reference point for automatic guidance significantly affects the stability properties of the control loop, which can be proven by means of mathematical stability analysis and simulation results concerning testmaneuvers at the stability limit. The capability of performing precise automatic guidance at the lateral dynamics stability limit is shown by means of a 1:5 scaled x-by-wire experimental prototype. During these test runs, the maximum lateral deviation from the desired trajectory was within a few percent of the vehicle width.
The design and analysis of steer-by-wire systems at the actuation and operational level is explored. At the actuation level, robust force feedback control using inverse disturbance observer structure and active observer algorithm is applied to enhance the robustness vs non-modelled dynamics and uncertain driver bio-impedance. At the operational level, the robustness aspects vs parameter uncertainties in vehicle dynamics and driver bio-impedance are issued and for a given target coupling dynamics between driver and vehicle the design task is converted to a model-matching problem. H
∞ techniques and active observer algorithms are used to design the steer-by-wire controller. Robustness issues at both levels are covered by mapping stability bounds in the space of physical uncertain parameters.
The well known nonlinear shape of the vehicle’s side force characteristics is considered to design a steering controller for automatic guidance. When applying nonlinear model predictive control, which should be the best possible controller from a mathematical point of view, it turns out that a large number of controller parameters has to be defined using heuristic methods. In this paper, however, exact linearization technique is used to determine a feedback law that matches the performance of the model predictive controller with a much lower amount of computing time and only two controller parameters. The position of the vehicle fixed reference point for automatic guidance significantly affects the stability properties of the control loop, which can be proven by means of mathematical stability analysis and simulation results concerning test maneuvers at the stability limit. The capability of performing precise automatic guidance at the lateral dynamics stability limit is shown by means of a race car simulation model and a 1: 5 scaled x-by-wire experimental prototype. During these simulations and test runs, the maximum lateral deviation from the desired trajectory was within a few percent of the vehicle width.
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