Steer-by-Wire Steering Stiffness Control via PID Feedback
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Solution Overview
Problem
Conventional steer-by-wire vehicle steering apparatuses face reduced controllability and deteriorated steering feeling due to the application of elastic support structures from link-type systems, which can lead to increased side forces, lateral slip-angles, and vehicle vibrations when used in steer-by-wire systems.
Innovation Solution
A vehicle steering apparatus with a mechanical coupling uncoupled between the steering member and steered wheels, featuring a steering actuator and a control unit that includes steering-stiffness reducing means such as a lowpass filter and PID control, allowing for reduced steering-stiffness adjustments based on road conditions, eliminating the need for elastic support structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If elastic support structures from link-type systems are applied to steer-by-wire systems, then the structure can be simplified, but controllability is reduced and steering feeling deteriorates
Solution Approach 1:
The patent replaces the mechanical elastic support structure with an electronic control system. The control unit uses feedback from steering angle sensors and steering force sensors to actively control the steering actuator, substituting passive mechanical elasticity with active electronic control. This resolves the contradiction by eliminating the need for elastic support structures while maintaining or improving controllability through electronic feedback mechanisms.
Solution Approach 2:
The patent changes the control parameters of the steering actuator dynamically based on driving conditions. The control unit adjusts steering force characteristics, response characteristics, and support force characteristics according to vehicle speed, steering angle, and road conditions. This allows the system to maintain optimal controllability without relying on fixed mechanical elastic properties.
2Ease of manufacture
If elastic support structures are used in steer-by-wire systems, then manufacturing may be easier, but side forces increase and vehicle vibrations occur
Solution Approach 1:
The patent replaces mechanical elastic support structures with an electronic control system that actively manages steering forces. The control unit processes sensor inputs and generates control signals to the steering actuator, eliminating the need for elastic bushings and rubber components. This substitution reduces manufacturing complexity while preventing harmful side forces and vibrations through precise electronic control.
Solution Approach 2:
The patent implements feedback control using steering angle sensors and steering force sensors that continuously monitor system state. The control unit uses this feedback to adjust steering actuator output in real-time, compensating for road surface irregularities and preventing the transmission of harmful vibrations and side forces to the vehicle body.
3Reliability
If rigid support is used for the steered mechanism, then steering stiffness increases and steering feeling improves, but lateral slip-angles increase and vehicle behavior changes
Solution Approach 1:
The patent implements dynamic control of steering characteristics by continuously adjusting control parameters based on driving conditions. The control unit modifies steering force characteristics, response characteristics, and support force characteristics according to vehicle speed and steering angle. This dynamic adjustment allows the system to provide firm steering feeling when needed while maintaining vehicle behavior stability under varying operating conditions.
Solution Approach 2:
The patent changes control parameters dynamically based on driving conditions such as vehicle speed, steering angle, and road surface state. The control unit adjusts gain parameters, response characteristics, and support force characteristics to optimize both steering feeling and vehicle behavior stability for each operating condition, resolving the contradiction between firm steering and stable vehicle behavior.
Data Source
AI summary
A vehicle steering apparatus in which a mechanical coupling between a steering member and steered wheels is uncoupled, includes a steering actuator for driving a steered mechanism and a control unit for drive-controlling the steering actuator. The control unit reduces steering-stiffness using a PID control portion for drive-controlling the steering actuator according to a deviation between a target steered angle and a steered-angle detected by the steered angle sensor. A gain setting portion sets gains of the PID control portion to be relatively low when a predetermined condition is satisfied.