Wake-Up Circuit for Electric Power Steering Back-EMF Detection
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Solution Overview
Problem
In electric power steering systems, determining the absolute rotational position of a motor shaft during an ignition-off state is challenging, especially when abrupt steering wheel motion occurs, as existing systems struggle to accurately detect this position without continuous monitoring.
Innovation Solution
A wake-up circuit is introduced, comprising a voltage boosting circuit and a comparator circuit that increases back EMF voltage and compares it to a reference voltage, triggering the monitoring system to determine the absolute rotational position during an ignition-off state, using a microprocessor and position sensors to calculate the current absolute position based on relative rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the monitoring system is turned off during ignition off state to save power, then energy consumption is reduced, but the ability to detect abrupt steering wheel motion and determine absolute rotational position is lost
Solution Approach 1:
The wake-up circuit enables periodic sampling of back EMF voltage during ignition off state, allowing the system to remain in low-power mode while still detecting steering wheel motion events that require absolute position determination
Solution Approach 2:
The back EMF voltage generated by motor rotation during steering wheel movement serves as the detection signal itself, eliminating the need for additional power-consuming sensors or active monitoring components during ignition off state
2Measurement precision
If periodic checking of rotatable shaft position is used during ignition off state, then absolute rotational position can be determined, but abrupt steering wheel motion is difficult to detect
Solution Approach 1:
The system replaces periodic mechanical/electronic polling with a passive back EMF-based detection method, where the physical rotation of the motor shaft during steering wheel movement directly generates the detection signal, enabling immediate response to abrupt motion
Solution Approach 2:
The system changes the detection parameter from periodic position sampling to continuous back EMF voltage monitoring, which naturally responds to any rotational movement regardless of speed or abruptness, enabling detection of sudden steering wheel motions
3Device complexity
If back EMF voltage is used directly for detection, then the system is simple, but the voltage level may be insufficient for reliable detection, especially with motors having lower back-EMF constants
Solution Approach 1:
The voltage boosting circuit acts as a compensating mechanism that counteracts the insufficient back EMF voltage level, amplifying the signal to a reliable detection threshold while maintaining the simplicity of the overall back EMF-based detection approach
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables accurate determination of the absolute rotational position of the motor shaft even during ignition-off states, improving detection of abrupt steering wheel motions and supporting a wider range of motors with lower back-EMF constants, while maintaining low power consumption.
Implementation Method 1
A voltage boosting circuit of the wake-up circuit is operable to increase a back electromotive force (EMF) voltage induced on one or more of the inputs by rotation of the rotatable shaft of the motor
Data Source
AI summary
In one aspect, a wake-up circuit is provided for triggering a determination of an absolute rotational position of a rotatable shaft of a motor in an electric power steering system of a vehicle. The wake-up circuit includes a plurality of inputs coupled to separate phases of the motor. A voltage boosting circuit is operable to increase a back electromotive force (EMF) voltage induced on one or more of the inputs by rotation of the rotatable shaft of the motor and produce at least one voltage-boosted back EMF voltage. A comparator circuit is operable to compare the at least one voltage-boosted back EMF voltage to a reference voltage and trigger a monitoring system to perform the determination of the absolute rotational position of the rotatable shaft of the motor in the electric power steering system based on a result of the compare during an ignition off state of the vehicle.