Electric Power Assisted Steering Torque Signal Timing Correction
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Solution Overview
Problem
Existing electric power assisted steering systems face challenges in maintaining accurate torque control when a fault is detected, particularly with dual channel torque sensors, where it's difficult to determine which channel is faulty and ensure continued safe operation.
Innovation Solution
The system employs time stamps to correct for timing inaccuracies between processor clocks, uses interpolation to modify samples, and generates additional torque signals to verify torque measurements, incorporating multiple sensors and processing units to cross-check torque signals and ensure accurate alignment of signals in time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dual channel torque sensor is used to provide safety margin, then reliability is improved, but device complexity increases and the system cannot continue operation when one channel faults
Solution Approach 1:
The system uses feedback from the dual-channel torque sensor to continuously monitor torque measurements. When a fault is detected in one channel, the system compares the faulty channel's signal with the healthy channel's signal, uses the healthy channel's feedback to determine the correct torque value, and maintains assistance torque application throughout operation.
Solution Approach 2:
The system performs preliminary fault detection by continuously comparing torque measurements from both channels before making critical decisions. When a fault is detected, the system has already identified the healthy channel and prepared to use its signal for continued operation, ensuring seamless transition without interruption of assistance torque.
2Reliability
If dual channel torque sensor is used, then reliability is improved, but the ability to continue operation after fault is worsened
Solution Approach 1:
The system prepares for potential failures by having redundant torque measurement channels available. When one channel fails, the pre-existing healthy channel immediately provides the necessary torque information to maintain assistance, cushioning against the impact of the fault and enabling continued operation without interruption.
Solution Approach 2:
When a fault is detected in one torque sensor channel, the system discards the faulty channel's signal and recovers by using the healthy channel's signal to determine the correct torque value. This allows the system to continue normal operation using only the healthy channel, effectively recovering from the fault condition.
3Device complexity
If processor clocks are not synchronized, then device complexity is reduced, but measurement precision deteriorates due to timing inaccuracies
Solution Approach 1:
The system introduces timestamps as an intermediary element to track and compensate for timing differences between unsynchronized processor clocks. Each torque measurement sample is tagged with a timestamp indicating when it was taken, allowing the system to identify and correct timing misalignments during signal processing without requiring clock synchronization.
Data Source
Figure 1
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Figure 4~5
AI summary
An electric power assisted steering system comprising an input shaft (5) and an output shaft (3), an electric motor (2) connected to the output shaft (3), at least two sensors including one or more of: a position sensor (15), a torque sensor (6), and a motor (2) position, and a motor controller (8) that causes the motor (2) to apply an assistance torque as a function of the torque measured by the torque sensor (6), in which each of the sensors produces at least one output signal represented by a stream of digital samples captured at discrete times, and in which the apparatus further comprises: processing means arranged to process together the output signals from both processing units to produce at least one further signal. At least one sample value of each output signal is marked with a time stamp indicating the time at which the sample was created, and in which the processing means corrects each of the time stamp samples before or during the processing of the samples to reduce errors that may occur due to differences in the times at which the samples were created.