Power Steering Torque Sensor Failure Estimation
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Solution Overview
Problem
Electric power steering (EPS) systems that rely on torque sensors for driver-assist functionality may fail to provide full assist or revert to reduced assist mode when the torque sensor is faulty, leading to increased driver effort due to unavailability of driver intention data.
Innovation Solution
A power steering system that includes a rack torque estimation module to determine an estimated rack torque value based on motor angle and velocity, a driver intent detection module to compute a disturbance torque scaling factor, and a blend module to generate a motor torque assist command using the scaled rack torque value, allowing the system to continue providing assist even in the absence of a functional torque sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a torque sensor is used to determine driver-requested assist, then the system can provide full assist and accurately detect driver intention, but the system reliability deteriorates when the torque sensor fails
Solution Approach 1:
The patent introduces an intermediary estimation system that uses motor current, motor angle, and motor velocity as intermediate variables to infer driver intention when the torque sensor fails. The controller acts as a mediator by computing estimated rack torque from these intermediate measurements, thereby maintaining driver intention detection capability without direct torque sensor input.
Solution Approach 2:
The patent creates a computational copy of the torque sensor functionality by estimating rack torque from motor current and motion parameters. This virtual torque signal replicates the information that would be provided by a functional torque sensor, allowing the EPS system to continue operating in normal assist mode despite torque sensor failure.
2Ease of operation
If the torque sensor fails, then the system reverts to reduced assist mode to maintain safety, but driver effort increases and ease of operation deteriorates
Solution Approach 1:
The system performs self-diagnosis and self-compensation when the torque sensor fails. The controller automatically detects the torque sensor failure condition and switches to using motor current and motion parameters to estimate driver intention, thereby maintaining normal assist functionality without requiring external intervention or manual system reconfiguration.
Solution Approach 2:
The patent changes the input parameters used for assist calculation from direct torque sensor signals to motor current, motor angle, and motor velocity measurements. By transforming the control parameters from torque-based to current-and-motion-based, the system maintains assist functionality while adapting to the failed sensor condition.
Data Source
AI summary
A system for determining driver torque includes a rack torque estimator module that determines an estimated rack torque value based on a motor angle, and a motor velocity. The system further includes a driver intent detection module that computes a disturbance torque scaling factor based on the estimated rack torque value. The system further includes a blend module that generates a motor torque assist command based on a scaled value of the estimated rack torque value using the disturbance torque scaling factor.