Unknown-input estimator-based controller design of electric power-assisted steering system

Abstract

In this study, the control design problem of double-pinion-type electric power assist steering (EPAS) is carefully examined. Based on a Lagrangian-based dynamical model, an optimal control approach with unknown input is formulated thereby eliminating the need for torque sensor. A new controller is developed using combination of non-linear assist curve, unknown-input estimator (UIE) and linear quadratic integral theory. It has been established that the estimation of the state, and unknown input using UIE yields a good estimate with performance compared with the well-known Kalman estimator. It is further shown that the resulting closed-loop response is able to track non-linear assist curve for different velocity. This reveals a salient feature, that is, controlling an EPAS system can be done using only single constant gain.

Parameter Estimation, Robust Controller Design and Performance Analysis for an Electric Power Steering System

“…T a = Nk e I a (7) To simply the identification of the EPS parameters, the assist motor is initially not considered. Considering Equations (1)- (3), with regard to the Laplace transformation, the following equations can be established:…”

“…Hydraulic power steering systems powered by the engine were introduced to reduce driver torque on the steering wheel. In recent years, EPS (electric power steering) systems have been widely deployed in modern vehicles due to their noticeable advantages over hydraulic power steering systems, including higher efficiency, more compact structure, better maintainability and lower fuel consumption [1][2][3][4][5]. In EPS systems, the assist torque is generated by an electric motor, which is powered by the car battery.…”

“…Wang [12] designed a robust H ∞ output-feedback yaw control algorithm based on differential steering and the complete failure of the active front-wheel steering. Moradkhani [13] introduced a loop-shaping Figure 1 illustrates the structure of a typical EPS system; the EPS consists of a steering wheel, torque sensor, vehicle velocity sensor, electronic control unit (ECU), electrical motor and rack and pinion assembly [3]. The driver torque and vehicle velocity are sent to the ECU to calculate the appropriate value of the assist torque using the desired assist torque curve.…”

“…The dynamic equations of the EPS system are also presented based on Newton's second law.Algorithms 2019, 12, 57 3 of 28 2.1. Operational Principle Figure 1 illustrates the structure of a typical EPS system; the EPS consists of a steering wheel, torque sensor, vehicle velocity sensor, electronic control unit (ECU), electrical motor and rack and pinion assembly [3]. The driver torque and vehicle velocity are sent to the ECU to calculate the appropriate value of the assist torque using the desired assist torque curve.…”