EP-4737273-A1 - STEER-BY-WIRE STEERING SYSTEM

Abstract

A steer-by-wire steering system including: an operation member (10) to be operated by a driver; a reaction force applying device (12) configured to apply an operation reaction force to the operation member (10); a steering device(16) including a steering motor (38) that is an electric motor as a drive source and configured to steer a wheel (14); and a controller (40, 42) configured to control the reaction force applying device (12) and the steering device (16), wherein the controller (40, 42) determines the operation reaction force including a steering-current-dependent component which is a component based on a current supplied to the steering motor (38) and a steering-speed-dependent correction component to reduce the steering-current-dependent component based on a steering speed; and wherein the controller (40, 42) determines the steering-speed-dependent correction component such that when the steering speed exceeds a set speed, the steering-speed-dependent correction component is not larger than a value at the set speed.

Inventors

• TAKEBAYASHI, Akihiro
• MIYAKE, Junya
• Namikawa, Isao
• YOSHIDA, KENJI
• KUDO, YOSHIO

Assignees

• JTEKT CORPORATION

Dates

Publication Date

20260506

Application Date

20251029

Claims (5)

1. A steer-by-wire steering system comprising: an operation member (10) to be operated by a driver; a reaction force applying device (12) configured to apply an operation reaction force to the operation member (10); a steering device (16) including a steering motor (38) that is an electric motor as a drive source and configured to steer a wheel (14); and a controller (40, 42) configured to control the reaction force applying device (12) and the steering device (16), wherein the controller (40, 42) determines the operation reaction force including a steering-current-dependent component which is a component based on a current supplied to the steering motor (38) and a steering-speed-dependent correction component to reduce the steering-current-dependent component based on a steering speed; and wherein the controller (40, 42) determines the steering-speed-dependent correction component such that when the steering speed exceeds a set speed, the steering-speed-dependent correction component is not larger than a value at the set speed.
2. The steer-by-wire steering system according to claim 1, wherein the set speed is set to a speed at which a torque that the steering motor (38) is capable of generating according to N-T characteristics falls within a range from not less than 40% to not greater than 60% of a maximum torque.
3. The steer-by-wire steering system according to claim 1 or 2, wherein the controller (40, 42) determines the operation reaction force further including a steering- acceleration-dependent correction component to reduce the steering-current-dependent component based on steering acceleration, and wherein the controller (40, 42) determines the steering-acceleration-dependent correction component such that when the steering acceleration exceeds set acceleration, the steering-acceleration-dependent correction component is not greater than a value at the set acceleration.
4. The steer-by-wire steering system according to claim 3, wherein the set acceleration is set to a value at which it is estimated that a steering operation in an emergency is performed.
5. The steer-by-wire steering system according to claim 3, wherein the set acceleration is set to a value at a time when an operation of the operation member (10) at a frequency ranging from not lower than 1.5 Hz to not higher than 2.5 Hz is performed at the set speed.

Description

TECHNICAL FIELD The present disclosure relates to a steer-by-wire steering system of a vehicle. BACKGROUND ART In a steer-by-wire type steering system (hereinafter referred to as "steer-by-wire system" where appropriate), an operation member such as a steering wheel is not mechanically connected to wheels to be steered. Therefore, the steer-by-wire system is provided with a reaction force applying device for applying an operation reaction force to the operation member. In general, the operation reaction force is preferably set to a magnitude corresponding to a load of a steering device, that is, a magnitude corresponding to a steering force for steering the wheels, and the operation reaction force may be determined based on an estimated steering force. Basically, in a case where the steering device has a steering motor, which is an electric motor, as a drive source, a current corresponding to the steering force is supplied to the steering motor. Thus, the steering force can be estimated based on the current. Therefore, the operation reaction force may be determined based on the steering force estimated based on the supply current. However, a damping force due to mechanical friction and the like is generated in the steering device. In a steer-by-wire system described in Japanese Patent Application Publication No. 2023-8890, for example, the steering force estimated based on the current supplied to the steering motor is corrected based on a steering speed. SUMMARY In view of characteristics of electric motors, the supply current has an upper limit. Even if steering of the wheels at a high speed is required, it is not always possible to supply a current corresponding to the speed. On the other hand, in the steer-by-wire system described in the above-mentioned patent document, for example, the correction based on the damping force is simply performed such that the steering force to be estimated decreases with an increase in the steering speed. Therefore, in the above-mentioned steer-by-wire system, when the steering speed increases to some extent, a difference between an actual steering force and the estimated steering force is generated, and the operation reaction force is not appropriate. This may cause an unnatural feeling in the steering operation of the driver. Thus, there is much room for improvement in determination of the operation reaction force in the steer-by-wire system. The utility of the steer-by-wire system is improved by some improvement. Accordingly, one aspect of the present disclosure relates to a steer-by-wire steering system with high utility. In one aspect of the present disclosure, a steer-by-wire steering system includes: an operation member to be operated by a driver; a reaction force applying device configured to apply an operation reaction force to the operation member; a steering device including a steering motor that is an electric motor as a drive source and configured to steer a wheel; and a controller configured to control the reaction force applying device and the steering device. The controller determines the operation reaction force including a steering-current-dependent component which is a component based on a current supplied to the steering motor and a steering-speed-dependent correction component to reduce the steering-current-dependent component based on a steering speed. The controller determines the steering-speed-dependent correction component such that when the steering speed exceeds a set speed, the steering-speed-dependent correction component is not larger than a value at the set speed. According to the steer-by-wire system of the present disclosure, since an upper limit is set for the steering-speed-dependent correction component, a component of the steering reaction force which is an index of the steering force, i.e., a steering-force-dependent component, does not become too small even when the steering speed becomes high exceeding a certain level. As a result, even when the steering speed becomes high exceeding a certain level, a proper operation reaction force is suitably maintained, thus preventing the driver from feeling unnatural with respect to steering. As will be described in detail later, the setting of the upper limit for the steering-speed-dependent correction component is particularly effective, for example, in a case of a fast steering operation to recover a wheel skid (slip) on a low-µ road. Various Forms As described above, the "steering-current-dependent component" in the present disclosure is a main component as an index of the steering force, which is a force generated by the steering device to steer the wheel. In a case where the steering device is configured such that right and left wheels are steered by moving, to the left and right, a steering rod (rack bar) connecting the right and left wheels, the steering force can be considered as a force in the axial direction, namely, an axial force, that acts on the steering rod. As explained above,