Honda Giken Kogyo Kabushiki Kaisha

Yukihiro Fujiwara

Osamu Tsurumiya

Yoshikazu Tsuchiya

Masataka Izawa

Kiyoshi Wakamatsu

Makoto Murata

Nobuyoshi Asanuma

Nobuo Sugitani

Yoshimitsu Akuta

Manabu Ikegaya

In a method for controlling a rear wheel steering device of a front and rear wheel steering vehicle, the target computed rear wheel steering angle is defined as a value smaller than the normal computed target rear wheel steering angle when the load of the steering actuator is greater than a prescribed threshold value, and which is otherwise equal to the normal computed target rear wheel steering angle, and the steering actuator is actuated according to a deviation of the actual rear wheel steering angle from the modified computed target rear wheel steering angle, typically with a duty ratio control. Thus, the rear wheel steering device can be operated in a satisfactory manner even when the output capacity of the actuator for the rear wheel steering device is limited, and the steering load is high. A high load condition typically occurs when the vehicle is stationary and when the steering wheel is turned sharply while the vehicle is traveling over a road surface having a high frictional coefficient.

Method for controlling a rear wheel steering device of a front and rear

The road friction is determined from the deviation of the estimated yaw rate under a standard condition from the actually measured yaw rate. The system for determining the road friction includes a parameter identification unit which determines a parameter of a variation term defined in the transfer function of the model for the vehicle response. The variation term may consist of a zero-th order or a first-order transfer function which would not cause any large computation load, and may not depend on the vehicle speed. The determined road friction may be used for controlling the rear wheel steering angle of a four wheel steering vehicle.

System for estimating the road surface friction

An actuator for effecting a steering action is controlled by a feed-forward variable based on a target steering angle, a state feedback control variable based on an actual steering angle, and an integral control variable given as a sum of an integrated value of a deviation between the target steering angle and the actual steering angle, and an integrated value cancelling variable based on the target steering angle. The integral control variable is disregarded when the detected load is greater than the threshold value. Typically, the integrated value cancelling variable consists of a feedback state variable based on the actual steering angle. Thus, by disregarding the integral control variable in a low speed condition that involves a high load condition but does not require a high tracking capability, the need for the output capacity of the actuator can be substantially reduced without creating substantially any ill effect. This is particularly advantageous when applied to a rear wheel steering system of a front and rear wheel steering vehicle using an electric motor for its actuator.

Method for controlling a steering system

An electric motor control system has a motor driver comprising a bridge of switching elements, a pair of failure detectors, and a microcomputer. The motor driver is connected between a battery and an electric motor that is connected between the switching elements. The switching elements are turned on and off according to drive pulse signals supplied from the microcomputer for supplying a pulsed current to the electric motor. The failure detectors monitor the electric energy supplied to the electric motor to detect a period of time in which the supplied electric energy is free of pulses, and supply a signal indicative of the detected period of time to the microcomputer. Based on the signal from the failure detectors, the microcomputer detects a failure when the detected period of time exceeds a predetermined period of time.

Electric motor control system

A four-wheel steering system on an automobile has front road wheels steerable by a steering wheel and rear road wheels steerable by an electric motor and normally biased to a neutral steering position by a spring. The electric motor is energized by a motor driver to steer the rear road wheels through an angle depending on running conditions of the automobile. The electric motor has a winding and two sets of brushes or connecting terminals connected to opposite terminals of the winding. One of the two sets of connecting terminals is connected to the motor driver. The other of the two sets of connecting terminals is connected to a short-circuiting circuit parallel to the motor driver. In the event of a failure, a controller controls the short-circuiting circuit to short-circuit the winding of the motor through the other set of connecting terminals. The short-circuiting circuit comprises a plurality of relays having respective contacts connected in series between the connecting terminals of the other set. The motor driver can also short-circuit the winding of the motor through the one set of connecting terminals in the event of a failure.

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Saitama-ken, Japan

Yukihiro Fujiwara