Steering Control Unit Virtual End Torque Limiting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric power steering systems face challenges in appropriately limiting excessive assist controlled variables with abnormal values, leading to potential self-steering issues and reduced safety due to the interaction of functions that virtually limit the steering wheel operation range and those that manage abnormal assist controlled variables.
Innovation Solution
A steering control unit comprising an assist controller, correction controller, limit calculator, and limit processor that calculates and adjusts assist controlled variables based on steering torque and angle, sets individual limits for state quantities, and incorporates a virtual end control mechanism to prevent excessive assist force generation by adjusting the assist controlled variable when the steering angle approaches its physical boundary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If virtual end control is performed to reduce assist controlled variable when steering angle reaches threshold, then steering wheel operation range is virtually limited and rack shaft end hit is prevented, but detected steering torque becomes excessively large and variation range of assist controlled variable is excessively extended
Solution Approach 1:
The patent segments the limitation process into two distinct stages: first, virtual end control reduces the assist controlled variable when steering angle reaches a threshold; second, a dedicated limitation process applies individual limits to state quantities and calculates a final limit. This segmentation resolves the contradiction by separating the virtual range limitation function from the abnormal value limitation function, ensuring each operates independently and accurately.
Solution Approach 2:
The patent applies preliminary action by first performing virtual end control to reduce the assist controlled variable, then subsequently applying the limitation process. The limitation process uses the steered wheel angle and other state quantities to calculate individual limits, which are summed to produce a final limit that is applied to the assist controlled variable. This two-stage approach ensures that the assist controlled variable is first adjusted for virtual range limitation, then properly constrained within abnormal value limits.
2Reliability
If individual limits are set for state quantities and summed to calculate final limit, then abnormal assist controlled variable is limited to appropriate value, but when virtual end control is performed the variation range of assist controlled variable is excessively extended leading to inappropriate limitation
Solution Approach 1:
The patent segments the control system into distinct functional modules: an assist controller that calculates the assist controlled variable based on state quantities, a correction controller that performs virtual end control, and a limit calculator that sets individual limits. This segmentation allows each module to perform its specific function without interference, resolving the complexity issue while maintaining reliable abnormal value limitation.
Solution Approach 2:
The patent implements feedback by continuously monitoring the steered wheel angle and other state quantities, comparing them against predetermined thresholds and limits, and adjusting the assist controlled variable accordingly. The limit calculator uses feedback from the assist controller and correction controller to dynamically calculate individual limits, which are summed to produce the final limit applied to constrain abnormal values.
Data Source
AI summary
When a steering angle reaches a first value close to a second value that defines a boundary of the maximum physical range of operation of a steering wheel, an ECU calculates a virtual end controlled variable that sharply increases a steering torque. The ECU calculates a second limit on the virtual end controlled variable and calculates a final limit (upper and lower limits) on an assist controlled variable by taking into account the second limit. When performing virtual end control, the ECU calculates the final limit on the assist controlled variable by using, as a first limit corresponding to the steering torque, a previous value held by upper and lower limit holders, instead of a present value calculated in accordance with the steering torque in a present calculation cycle.