Steer-by-Wire Rack Control Using One-Sided Brake Correction
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Solution Overview
Problem
Existing steer-by-wire steering systems face challenges in maintaining precise steering control when the servo motor's power is limited, particularly during fast steering movements, leading to significant offsets between target and actual steering angles.
Innovation Solution
A steering system with a control unit that generates a one-sided braking intervention when an offset between target and actual steering angles exceeds a threshold, utilizing data from sensors to adjust thresholds based on steering wheel velocity, and includes redundant power supplies for the servo motors to maintain control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the servo motor power is limited, then the system can operate with reduced power consumption, but the steering control precision deteriorates during fast steering movements
Solution Approach 1:
The control unit applies a counteracting braking force to the rack when detecting that the actual steering angle deviates from the target steering angle beyond a threshold value. This preliminary anti-action compensates for the insufficient servo motor power, preventing the precision deterioration that would otherwise occur during fast steering movements or when the motor is operating at power limits.
Solution Approach 2:
The rack functions as an intermediary element between the servo motor and the steerable wheels. By applying braking force directly to the rack rather than relying solely on the servo motor, the system achieves precise steering angle control without requiring increased motor power, thus resolving the contradiction between power consumption and control precision.
2Reliability
If mechanical coupling between steering handle and rack is eliminated, then system reliability improves through fail-safe operation, but steering control precision deteriorates due to offset between target and actual angles
Solution Approach 1:
The control unit continuously monitors both the target steering angle (from the steering handle sensor) and the actual steering angle (from the rack position sensor), calculates the offset between them, and uses this feedback information to determine when braking intervention is necessary. This closed-loop feedback system maintains steering angle accuracy despite the mechanical decoupling that provides fail-safe operation.
Solution Approach 2:
The patent replaces the traditional mechanical coupling between steering handle and rack with an electronic control system that uses sensors, control units, and selective braking. This substitution eliminates the mechanical connection (improving reliability through fail-safe operation) while using electronic feedback control to maintain or even improve steering angle accuracy compared to mechanical systems.
3Manufacturing precision
If offset threshold is set low, then steering angle accuracy is maintained, but braking intervention frequency increases causing wear
Solution Approach 1:
The offset threshold is not fixed but dynamically adjusted based on operating conditions such as vehicle speed, steering wheel angular velocity, and servo motor power availability. At higher speeds or during normal operation, the threshold can be relaxed to reduce braking frequency and wear. During critical maneuvers or when precision is paramount, the threshold tightens to maintain accuracy. This dynamic adaptation resolves the contradiction between maintaining accuracy and reducing wear.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances steering system availability by quickly correcting offsets and ensuring safe operation, even with reduced motor power, through proactive braking interventions and redundant power supply configurations.
Implementation Method 1
The steering system has a steering handle, at least one sensor for detecting the steering wheel angle on the steering handle
Implementation Method 2
at least one servo motor, wherein the servo motor is connected to a rack and pinion
Implementation Method 3
a control command for a one-sided braking intervention is generated to counteract the offset
Data Source
Figure 1
AI summary
The invention relates to a steering system (1) for a motor vehicle, comprising a steering handle (2), at least one sensor (3) for detecting a steering wheel angle (ϕ) on the steering handle (2), at least one control unit (4) for determining a target steering angle as a function of the steering wheel angle (ϕ), at least one servo motor (5), wherein the servo motor (5) is connected to a rack (12), and at least one sensor for detecting or determining an actual steering angle, wherein the control unit (4) is configured to control the servo motor (5) for setting the target steering angle based on at least one characteristic curve and to determine an offset between the target steering angle and the actual steering angle, wherein the steering handle (2) and the rack (12) are mechanically decoupled, wherein the control unit (4) is further configured such that, in the event of an offset greater than a threshold value, a control command (S) for a one-sided brake intervention is generated, which counteracts the offset.and a method for operating such a steering system (1).