Motorized Shift Position Sensing for Accurate Rotation Counting
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Solution Overview
Problem
Existing shift devices face accuracy issues in detecting the number of motor rotations, leading to positioning errors due to external forces or power failures, as the stored number of rotations may differ from the actual count, affecting the shift position's positioning accuracy.
Innovation Solution
The shift device associates the output values of the output shaft rotational angle sensor and the rotor rotational angle sensor at predetermined positions to detect the number of motor rotations, using a stored map to correct any discrepancies upon restart, thereby ensuring accurate positioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the speed reduction ratio of the speed reduction mechanism section is set relatively high, then the positioning accuracy of the detent spring with respect to the detent plate is improved, but the motor must rotate one or more times to switch between adjacent valley parts, increasing the complexity of rotation counting
Solution Approach 1:
The output shaft rotational angle sensor acts as an intermediary that directly measures the position of the detent plate without requiring the system to track multiple motor rotations. By measuring the output shaft angle directly, the system simplifies the counting process while maintaining high positioning accuracy enabled by the high speed reduction ratio.
2Productivity
If the current motor rotational angle is detected based on the output from the motor rotational angle sensor at the time of ECU startup, then the system can operate immediately, but it is not possible to detect how many rotations the motor has made from a reference position
Solution Approach 1:
The system creates a copy of the output shaft rotational angle information and stores it in nonvolatile memory at shutdown. Upon startup, this stored copy provides the absolute position reference immediately, eliminating the need to count rotations from a reference position while maintaining accurate knowledge of the motor's rotational state.
Data Source
AI summary
A shift device includes: a shift switching member including valley parts corresponding to a shift position; a positioning member provided to establish the shift position in a state of being fitted into any one of the valley parts; a motor including a rotor and a stator and driving the shift switching member; a speed reduction mechanism section rotating the shift switching member in a state in which a rotation speed transmitted from the motor is reduced; a rotor rotational angle sensor detecting a rotational angle of the rotor; and an output shaft rotational angle sensor detecting a rotational angle of the shift switching member. The shift device detects the number of rotations of the motor based on association between output values of the output shaft rotational angle sensor and the rotor rotational angle sensor.