Steering Assistance Research Articles

Mathematical Modeling and Nonlinear Controller Design for a Novel Electrohydraulic Power-Steering System

This paper is concerned with the mathematical modeling and nonlinear controller design of a novel electrohydraulic closed-center power-steering system. After a short introduction to the requirements of modern power-steering systems, the construction of the power-steering system under consideration will be described. The main advantage of this construction is the enhancement of the overall energetic efficiency of the steering system and the possibility of a variable steering assistance while keeping the good steering feeling of traditional hydraulic steering systems. Based on a detailed mathematical model of the essential components of the system, it is shown how some of the parameters of the system can be chosen to achieve an optimal dynamic behavior of the closed-loop system. The controller design proceeds in two steps: first, a nonlinear controller for the assistance force based on the differential flatness property of the system is designed, and afterwards, a steering torque controller using an impedance matching design is derived. Finally, measurement results of a test stand show the good performance and the robust behavior of the proposed control strategy

10201 支援操舵から手動操舵への切り替え時における適応動作(生体工学)

This study examined a time driver needs to adapt to characteristic of vehicle after assisted steering is changed to manual steering. The experiment used a driving simulator. The level of driver's involvement in driving (the concerned level) was "Holding a steering wheel and front gazing (Pattern A)" and "Not holding a steering wheel and not front gazing (Pattern B)". The experimental condition was "lane change" and "side wind". As a result, in the case of Pattern A, driver needs 1 second to adapt to characteristic of vehicle in lane changing and 3 seconds in side wind. In the case of Pattern B, driver needs 2 seconds to adapt to it in lane changing and 3 seconds in side wind.

APPLICATION OF MODEL-BASED PREDICTIVE AND ROBUST LOOP SHAPING CONTROL TO AUTOMATIC CAR STEERING

The automatic steering assistance system presented in this paper takes advantage of the technique of Model-based predictive control (MPC) of systems with hard input constraints in order to compute the appropriate steering angle of the front tires. In addition the Quantitative Feedback Theory (QFT) is used to find a robust controller that maintains the key properties of the loop for the implementation of the Model-based Predictive Controller input, despite uncertainty, i.e. stability, tracking performance and disturbance rejection. The procedure involves deriving a steering angle rate from the front tire angle and applying it to the steering column. The feasibility of the proposed assistance system is evaluated in a simulation using Matlab/Simulink and a test vehicle. The results demonstrate the effectiveness of the automatic steering system in lane keeping and yaw dynamic improvement.

Active Front Steering for Passenger Cars: System Modelling and Functions

Active Front Steering is a newly developed technology for passenger cars that realises an electronically controlled superposition of an angle to the hand steering wheel angle that is prescribed by the driver. It enables functionalities such as (vehicle velocity-) variable steering ratio, steering lead, as well as it provides an interface to support vehicle dynamics control systems. This paper focuses on system modelling and derivation of both steering assistance functions and a safety / diagnostics functions. All functions described are model based. Their models are derived and their accuracy is demonstrated.

A Sensorless Optimal Control System for an Automotive Electric Power Assist Steering System

This paper considers the analysis and design of a double-pinion-type electric power assist steering (EPAS) control system. A simplified model of the augmented steering assembly-electric motor system is developed using Lagrangian dynamics, and an optimal controller structure for the model is proposed. Three main advances to the state of the art are presented in this paper. First, a state-space design model is used rather than an input-output model. A state-space formulation for a system model that incorporates motor electrical dynamics is obtained with the assist motor angular position as the output. Second, linear quadratic regulator (LQR) and Kalman filter techniques are employed to arrive at an optimal controller for the EPAS system. The selection of weighting coefficients for the LQR cost function is discussed. Finally, the authors present a control strategy that eliminates the steering column torque sensor, a critical component in existing EPAS controller designs. The proposed control strategy presents an opportunity to improve EPAS system performance and also reduce system cost and complexity.

Improvement of Steering and Vehicle Characteristics due to Electric Power Assist Steering with Disturbance Observer

Electric power assist steering (EPAS) is popular in the market due to its superior fuel economy. The electric motor inertia, friction and their fluctuations of EPAS, however, often deteriorate steering characteristics and vehicle dynamics. Elaborate parameter tuning for assist torque control based on vehicle velocity and steering wheel velocity has been made to improve them, but it is still difficult to achieve good performances in various driving situations such as load condition, road surface friction and gradual vehicle characteristics change due to time. In this paper, a feedback strategy applying the disturbance observer, “steering velocity observer”, is proposed to compensate for the adverse influences of vehicle mass change. The satisfactory effects of the proposed control strategy are observed through the simulation and field tests by using a prototype vehicle with a pinion type EPAS.

Development of the Non-Contact Torque Sensor for EPAS Using Maluss Polarization Law

Among the automotive steering systems, an Electric Power Assisted steering (EPAS) system utilizes an electronically controlled electric motor to provide steering assistance to the driver. The key components of the EPAS system are torque sensor, ECU (Electronic Control Unit), and DC Motor. The most important component of the EPAS is the torque sensor. The conventional torque sensor has complicated mechanical mechanism of torque detection. However, we suggest a non-contact torque sensor for EPAS using Maluss polarization law. It was found that the sensor exhibited not only excellent linearity but also superior characteristics of hysteresis, temperature and vibration.

Rotational sensorless scalar control of three-phase induction motors and its application to automotive electric power assist steering

A rotational position/velocity sensorless scalar control method for three-phase induction motors is described. Although voltage/frequency ( V/f) scalar control requiring such a sensor appears quite frequently in the literature, a general scheme without rotational sensors using a scalar method is not common. The method described in this work is simple in terms of algorithm and computationally less demanding, and hence can be implemented with inexpensive microprocessors. To illustrate an application, the electric actuator assisted power steering for automobiles is considered where torque is the object of control. For this particular application with near-zero or zero speed operation in general, the scalar method described in this work is considered to be a competitive alternative to the rotational sensorless field-oriented control (FOC) method for induction motors. This is particularly due to the fact that the algorithm for position sensorless FOC is computationally quite intensive for such low-speed torque tracking operations when compared with the scalar method, and in general requires expensive digital signal processors. Although this work was undertaken with automotive steering applications in mind, the methodology can also be applied to other automotive and non-automotive applications where actuators are used.

Paper 5: Power Assistance Pumps for Steering

This paper discusses the pump output problems peculiar to power assisted steering, together with the need for the flow control valve. A description of a basic combined flow control and pressure relief valve is given, and the adaptation of the flow control valve to the requirements of power assisted steering is detailed. The pump construction and operation are mentioned, with a description of a typical pump with reference to the special features incorporated for quiet operation. Some changes in design, in an attempt to keep pace with higher pressure demands, are described. The paper also presents the various types of installations and measures adopted to minimize transmitted noise, and concludes with a brief survey of pump types.