Electric Power Steering Target Pinion Angle Computation
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Solution Overview
Problem
Conventional electric power steering systems experience deterioration in steering feel due to deviations between actual and target steered angles when the rack shaft reaches its movable range limit, leading to discomfort for drivers as excess assist torque is applied.
Innovation Solution
The system employs a target pinion angle computation unit with an ideal model that adjusts the assist torque and steering reaction force to create a virtual movable range, using a combination of PID control and spring and viscosity components to maintain alignment with the target pinion angle, preventing actual end contact and reducing steering discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback control is executed to eliminate deviation between actual and target steered angles, then steering precision is improved, but when end contact occurs the control applies excess assist torque causing driver discomfort
Solution Approach 1:
The system applies preliminary anti-action by detecting when the rack shaft is near the limit of its movable range and adjusting the target steered angle to prevent end contact before it occurs. This proactive adjustment eliminates the deviation between actual and target steered angles before excess assist torque can be applied, thereby preventing driver discomfort while maintaining steering precision.
Solution Approach 2:
The system dynamically adjusts the target steered angle based on the rack shaft position. When the rack shaft approaches the limit of its movable range, the target steered angle is modified to account for the impending end contact. This dynamic adjustment allows the feedback control to maintain precision without applying harmful excess torque, resolving the contradiction between control accuracy and driver comfort.
2Speed
If the target steered angle is increased with steering torque, then steering responsiveness is improved, but when end contact occurs the actual steered angle cannot follow causing control failure
Solution Approach 1:
The system prevents control failure by detecting the rack shaft position and adjusting the target steered angle before end contact occurs. This preliminary adjustment ensures that the target steered angle remains achievable within the physical constraints of the rack shaft movement, maintaining both steering responsiveness and feedback control reliability.
Solution Approach 2:
The system changes the target steered angle parameter dynamically based on rack shaft position. When approaching the limit of movable range, the target steered angle is adjusted to reflect the reduced available movement. This parameter change allows the feedback control to remain effective and reliable while preserving steering responsiveness within the physical limits of the system.
Data Source
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AI summary
A target pinion angle computation unit (62) computes a target pinion angle (θp*) on the basis of a basic assist component (Ta1*) and a steering torque (Th), and computes the target pinion angle (θp*) so as to rapidly increase a steering reaction force when it is determined based on the target pinion angle (θp*) that a rack shaft of a rack-and-pinion mechanism reaches a position near a limit of a movable range of the rack shaft. In an EPS, a correction component for the basic assist component (Ta1*), which is necessary to increase the steering reaction force rapidly, is computed through execution of PID control for causing an actual pinion angle to coincide with the target pinion angle (θp*). Because the correction component is added to the basic assist component (Ta1*), the steering reaction force is increased rapidly when the rack shaft reaches the position near the limit of the movable range.