Variable Ratio Actuator for Shift Range Switching
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Solution Overview
Problem
The existing shift-by-wire system for automatic transmissions faces inefficiencies in switching between gear ranges, particularly when transitioning from the P range to other ranges, as it requires excessive torque, leading to slow actuation and impaired response due to a fixed gear ratio that is not optimized for all switching scenarios.
Innovation Solution
A shift range switching device with a variable reduction ratio in the actuator's reduction device, allowing for a greater reduction ratio when switching from the P range to other ranges and a smaller ratio when switching back, optimizing torque and speed for each scenario.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large reduction ratio is used in the reduction device to produce sufficient torque for switching from P range to other ranges, then the switching reliability is improved, but the switching speed becomes slow and response is impaired
Solution Approach 1:
The reduction device employs a variable reduction ratio that dynamically changes based on the shift range switching condition. When switching from P range to other ranges, a large reduction ratio is applied to provide sufficient torque for reliable parking lock mechanism operation. When switching from other ranges to P range, a small reduction ratio is used to enable fast response. This dynamic adjustment resolves the contradiction between reliability and speed by adapting the reduction ratio to the specific switching scenario.
Solution Approach 2:
The invention changes the reduction ratio parameter of the reduction device according to the switching direction. The control unit selects between a first reduction ratio (large) for P-to-other range switching and a second reduction ratio (small) for other-to-P range switching. This parameter change allows the system to optimize torque output for reliability when needed while maintaining high speed response when the parking lock mechanism does not require large torque.
2Force
If a fixed large reduction ratio is used to ensure sufficient torque for all switching scenarios, then the torque requirement is met, but the switching response becomes slow in scenarios where large torque is not necessary
Solution Approach 1:
Instead of using a fixed large reduction ratio, the invention implements a dynamic reduction ratio that adjusts based on the switching scenario. The control unit determines the appropriate reduction ratio (first or second) based on the current and target shift ranges. This dynamic approach ensures sufficient torque is provided only when necessary (during P-to-other range switching with parking lock engagement), while avoiding the torque penalty during other switching operations, thereby reducing unnecessary response time loss.
Solution Approach 2:
The invention changes the reduction ratio parameter from a fixed value to a variable value that depends on the switching condition. When the parking lock mechanism requires large torque (P-to-other range switching), the first reduction ratio is selected. When large torque is not required (other-to-P range switching), the second reduction ratio is selected. This parameter change eliminates the time loss associated with using an unnecessarily large reduction ratio in scenarios where it is not needed.
Data Source
AI summary
A shift range switching device is provided to a shift-by-wire system for an automatic transmission device. The shift range switching device includes a range switching unit for switching a shift range of the automatic transmission device between a P range and the other range. The shift range switching device further includes an actuator including an electric motor and a reduction device. The reduction device transmits driving force of the electric motor to the range switching unit for actuating the range switching unit as instructed. The reduction device has a variable reduction ratio. The reduction device transmits the driving force in switching of the shift range from the P range to the other range at a reduction ratio, which is greater than a reduction ratio in switching of the shift range from the other range to the P range.