Power Steering Torque Derivative Detection for Reversal
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Solution Overview
Problem
Existing power steering systems face challenges in reliably detecting steering reversals due to long detection times and the need for additional sensors, which increase size, weight, and cost, while also being prone to false positives from slight oscillations.
Innovation Solution
A method that acquires the engine torque signal and evaluates its time derivative to detect steering reversals, eliminating the need for amplitude-based detection thresholds and reducing reliance on angular speed measurements, using signals like the torque setpoint or measured torque from the assistance motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If angular speed monitoring is used to detect steering reversal, then detection reliability is improved, but detection time increases and system complexity increases
Solution Approach 1:
Instead of monitoring angular speed to detect steering reversal, the patent inverts the approach by monitoring the time derivative of assistance torque. The assistance torque naturally peaks during steering reversal due to friction effects, so detecting this peak and its derivative provides a more direct and faster indication of reversal without requiring angular speed thresholds.
Solution Approach 2:
The power steering system's own torque signal serves the dual purpose of providing assistance and indicating steering reversal. By analyzing the time derivative of the assistance torque that the system already generates, the patent eliminates the need for separate angular speed sensors and complex threshold-based detection algorithms.
2Reliability
If high amplitude detection thresholds are used to avoid false positives, then detection reliability is improved, but detection speed decreases
Solution Approach 1:
The patent inverts the detection criterion from monitoring angular displacement amplitude to monitoring the rate of change of assistance torque. Since friction causes a characteristic peak in assistance torque during reversal, detecting the time derivative of this torque provides a reliable indicator that is independent of the magnitude of steering movements, thus avoiding false positives while maintaining fast response.
3Measurement precision
If angular speed sensors are added to improve detection accuracy, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The assistance torque signal, originally generated solely for power steering assistance, is made multi-functional by also serving as the detection signal for steering reversal. The existing torque sensor or controller that monitors assistance torque for control purposes now simultaneously provides the data needed for reversal detection, eliminating the need for dedicated angular speed sensors.
Solution Approach 2:
The power steering control system performs self-diagnosis by analyzing its own assistance torque signal. The controller that regulates assistance torque also detects steering reversal by monitoring the time derivative of this torque, making the system self-sufficient without external sensors.
Data Source
Figure 1~4
AI summary
The invention concerns a method for managing a power steering system, comprising a step (a) of detecting a reversal in the steering direction which involves acquiring a signal, referred to as a "motor torque signal" (CMot), representative of the assistance force (Cassist) delivered by the power steering motor, then evaluating the time derivative (δC Mot / δt) of said motor torque signal, then comparing said time derivative of the motor torque signal to a predefined variation threshold (Spic) in order to detect a derivative peak, greater than said variation threshold (Spic), that indicates a reversal (4) in the steering direction. Said method next comprises a friction evaluation step (b) which involves evaluating the friction from the drop, during the reversal in the steering direction, in a so-called "actuation force signal" (Caction), which is representative of the total actuation force exerted together on the power steering by the driver and by the power steering motor.