Electric Power Steering Torque Difference Control
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Solution Overview
Problem
Conventional electric power steering systems experience oscillation of the steering wheel at each stroke end due to the interaction between the target steering torque and centering torque, leading to an unpleasant steering experience.
Innovation Solution
An electric power steering system that includes a steering torque difference computing means, which sets the steering torque difference to zero when the actual steering torque exceeds the target steering torque by a prescribed value, particularly at the steering stroke end, to prevent oscillation by avoiding retreating rotation of the steering wheel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback control of assist torque is performed according to steering torque difference, then steering feel impairment is reduced and steering kickback is avoided, but steering wheel oscillation occurs at each steering stroke end
Solution Approach 1:
The patent changes the control parameter from continuous steering torque difference to a conditional parameter that becomes zero when actual steering torque exceeds target steering torque by a prescribed value or more. This parameter transformation eliminates the oscillation condition while preserving the feedback control benefits for steering feel.
Solution Approach 2:
The patent segments the steering operation into two distinct conditions: normal operation where feedback control is active, and stroke-end operation where the steering torque difference is forced to zero. This segmentation prevents the harmful oscillation while maintaining beneficial control during normal steering.
2Speed
If Ackermann ratio is set to intermediate value (30-70%), then high speed turn performance is improved, but centering torque becomes extremely small at steering stroke end
Solution Approach 1:
The patent applies preliminary anti-action by detecting when actual steering torque exceeds target steering torque by the prescribed value, which indicates approaching stroke end. Before the oscillation can develop, the control system proactively sets the steering torque difference to zero, preventing the harmful effect.
Solution Approach 2:
The patent introduces an intermediary control condition that mediates between the conflicting requirements of high-speed turn performance and adequate centering torque. The prescribed value threshold acts as an intermediary parameter that triggers the transition to zero steering torque difference, resolving the contradiction.
Data Source
AI summary
Provided is an electric power steering system that prevents the oscillation of the steering wheel at each steering stroke end. If the steering stroke end flag Fse is 1 or if the determination result is Yes in step S8, the EPS-ECU (21) determines if the right steering flag (Fdrc) is 1 in step S10. If the determination result is Yes, it is then determined if the steering torque difference base value (Dtsb) is positive in step S11. If the determination result of step S11 is Yes, the EPS-ECU (21) uses the steering torque difference base value (Dtsb) as the steering torque difference (Dts) in step S12. If the determination result is No, the steering torque difference (Dts) is given by a value 0 in step S13, and the control process is concluded.