Steer-By-Wire Rack Speed Limiting for Power-Intensive Maneuvers
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Solution Overview
Problem
Steer-by-wire steering systems experience transient response issues due to physical limitations of road wheel actuators and position controllers, leading to maneuverability problems, post-steering effects, and NVH disturbances.
Innovation Solution
A method to control steer-by-wire steering systems by limiting rack speed to a maximum value when necessary, using a position controller to calculate a target rack position based on actual and requested positions, and adjusting steering effort to maintain controllability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the road wheel actuator operates at high speed to respond quickly to steering inputs, then the settling time is reduced, but the motor torque requirements exceed physical limitations causing transient response issues
Solution Approach 1:
The system dynamically adjusts the rack speed limit based on real-time conditions. The position controller monitors the actual rack position, target rack position, and requested rack speed, and adapts the maximum rack speed value accordingly. This allows the system to operate at high speeds when power is available but reduces speed to manageable levels when motor torque limitations are detected, resolving the contradiction between speed and power requirements.
Solution Approach 2:
The invention changes the parameter of rack speed limit based on system state. By monitoring position tracking error and comparing it against predefined values, the system modifies the maximum rack speed parameter dynamically. This parameter change allows the system to maintain fast response when possible while preventing excessive speed demands that would exceed motor torque capabilities.
2Productivity
If the position controller increases the rack speed limit to improve maneuverability, then the settling time is reduced, but post-steering effects and NVH disturbances increase
Solution Approach 1:
The position controller continuously monitors the position tracking error (deviation between actual and target rack position) and uses this feedback to adjust the maximum rack speed value. When the tracking error exceeds predefined thresholds, the system reduces the rack speed limit, which prevents post-steering effects. This feedback mechanism allows the system to maintain maneuverability while preventing harmful transient effects.
Solution Approach 2:
The system takes preliminary action by monitoring position tracking behavior and detecting power limit situations before they cause harmful effects. By detecting when the road wheel actuator cannot follow the target rack position with acceptable accuracy, the system proactively reduces rack speed to prevent post-steering effects and NVH disturbances from occurring in the first place.
3Object-generated harmful factors
If the rack speed is limited to a maximum value to reduce post-steering effects, then NVH is reduced, but the settling time increases
Solution Approach 1:
The system dynamically adjusts the rack speed limit based on real-time conditions. The position controller monitors the actual rack position, target rack position, and requested rack speed, and adapts the maximum rack speed value accordingly. This allows the system to operate at high speeds when power is available but reduces speed to manageable levels when motor torque limitations are detected, resolving the contradiction between speed and power requirements.
Solution Approach 2:
The invention changes the parameter of rack speed limit based on system state. By monitoring position tracking error and comparing it against predefined values, the system modifies the maximum rack speed parameter dynamically. This parameter change allows the system to maintain fast response when possible while preventing excessive speed demands that would exceed motor torque capabilities.
4Reliability
If the road wheel actuator is in a degraded state, then the system reliability is reduced, but the settling time becomes excessively long
Solution Approach 1:
The position controller continuously monitors the position tracking error and uses this feedback to detect actuator degradation. When the tracking error exceeds predefined thresholds, the system interprets this as a power limit situation and adjusts the maximum rack speed value accordingly. This feedback mechanism allows the system to compensate for actuator degradation by reducing speed demands, thereby maintaining acceptable settling time even when the actuator is in a degraded state.
Data Source
AI summary
A method to control a steer-by-wire steering system for a road vehicle, the steer-by-wire steering system including a steering, a road wheel actuator to actuate road wheels via a rack, and a controller configured or programmed to include a position controller configured or programmed to calculate, based on an actual rack position and a rack position request, a target rack position for the road wheel actuator, the method including, in response to a requested rack speed being above a predefined maximum value, limiting the requested rack speed to a maximum rack speed value used by the position controller to calculate the target rack position for the road wheel actuator.