Motor Shaft Position Tracking During Ignition Off State
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Solution Overview
Problem
In electric power steering systems, the microprocessor cannot accurately determine the absolute rotational position of a motor shaft when the vehicle is in an ignition off state, as it is turned off and lacks the ability to monitor the shaft position during this time.
Innovation Solution
A system and method where a microprocessor is periodically activated by a timer circuit during the ignition off state to energize position sensors, measure relative position signals, determine relative and absolute rotational positions, and store these values, allowing for accurate tracking of the motor shaft's position even when the system is not actively powered.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the microprocessor is turned off during ignition off state to save energy, then power consumption is reduced, but the ability to determine absolute rotational position of the motor shaft is lost
Solution Approach 1:
The microprocessor is activated periodically during ignition off state at predetermined time intervals rather than continuously. This periodic activation allows the system to determine absolute rotational position of the motor shaft at specific moments while maintaining power savings during intervals when the microprocessor remains inactive, directly resolving the contradiction between energy consumption and measurement capability
Solution Approach 2:
The system determines and stores the absolute rotational position of the motor shaft before the ignition is turned off. This preliminary determination ensures that position information is captured while the microprocessor is still active, allowing the system to maintain awareness of shaft position without requiring continuous microprocessor operation during ignition off state
2Measurement precision
If the microprocessor is continuously activated to monitor motor shaft position, then absolute rotational position determination accuracy is maintained, but power consumption increases
Solution Approach 1:
Instead of continuous activation, the microprocessor operates periodically at predetermined intervals during ignition off state. This approach maintains the ability to determine absolute rotational position when needed while significantly reducing overall power consumption compared to continuous operation
Solution Approach 2:
The system uses previously stored absolute position information combined with relative position changes to maintain accurate position tracking without requiring constant microprocessor intervention. The microprocessor leverages existing data and sensor inputs to update position information only when activation occurs
Data Source
AI summary
A system and a method for determining an absolute position of a motor shaft in an electric power steering system during an ignition off state are provided. The system includes a microprocessor that energizes first and second position sensors to generate first and second signals, respectively, at a first time, and third and fourth signals, respectively, at a second time. The microprocessor determines a first relative position value based on the first and second signals, and a second relative position value based on the third and fourth signals. The microprocessor determines an amount of relative rotation of the shaft during the ignition off state based on the first and second relative position values, and determines a current absolute position value based on a previously stored absolute position value and the amount of relative rotation of the rotatable shaft.