Shift-By-Wire Control for Parking Pawl Torque Release
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Solution Overview
Problem
Existing shift by wire systems require large and costly actuators to manage torque when shifting from a parking range to a non-parking range, especially on sloping roads, due to the need for significant force to release the parking pawl from the parking gear, which is exacerbated by the gravitational force on the vehicle.
Innovation Solution
A control device that includes a motor control unit, a shift control unit, and a torque detection unit, which cooperatively control the electric motor and actuator unit to reduce the torque required for unlocking the power transmission mechanism by adjusting the output torque based on detected torque, allowing the power transmission shaft to be unlocked with reduced force, thereby minimizing the size and cost of the actuator unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a shift by wire system is used to remove mechanical connection between shift range change mechanism and shift lever, then ease of operation is improved, but the actuator unit becomes large and costly due to high torque requirements
Solution Approach 1:
The system performs preliminary action by detecting torque on the power transmission shaft before the shift operation and controlling the electric motor to apply a counteracting torque. This preliminary torque cancellation reduces the torque burden on the actuator unit before the lock mechanism is actuated, allowing for a smaller and more cost-effective actuator design while maintaining ease of operation in the shift by wire system
2Device complexity
If torque is not managed during shift from parking range to non-parking range, then device complexity is reduced, but large actuators are required to handle gravitational force on sloping roads
Solution Approach 1:
The system implements feedback by continuously monitoring the torque applied to the power transmission shaft using a torque sensor. Based on this feedback, the control device adjusts the electric motor's output torque in real-time to counteract the torque burden during shift operations. This feedback mechanism enables precise torque management, reducing the power required by the actuator unit while maintaining the ability to handle gravitational forces on sloping roads
3Power
If electric motor controls output based on detected torque during shift from parking to non-parking range, then power required for actuator is reduced, but control system complexity increases
Solution Approach 1:
The control device achieves multi-functionality by integrating multiple functions into a single control unit. The same control device that manages the shift by wire system also controls the electric motor's torque output based on torque sensor feedback. This universal control approach reduces overall system complexity despite the added torque management functionality, as it consolidates control logic rather than adding separate dedicated control systems
Data Source
AI summary
A control device includes a motor control unit that controls an electric motor, a shift control unit that controls a shift by wire system of a movable body, and a torque detection unit that detects torque applied to a power transmission mechanism. The shift control unit drives an actuator unit so that the power transmission mechanism locked by a lock mechanism is unlocked, based on a change of a shift range of the shift by wire system from a parking range to a non-parking range. The motor control unit controls output of the electric motor depending on detected torque of the torque detection unit, based on the change of the shift range of the shift by wire system from the parking range to the non-parking range.