Automatic Transmission Park Lock Control After CPU Reset
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Solution Overview
Problem
Existing control devices for automatic transmissions with park lock devices of the shift-by-wire type face issues where CPU resets, caused by power voltage drops or errors, lead to unintended park lock states, resulting in abnormal noise and safety concerns during towing or parking, as the shift range reliability is compromised.
Innovation Solution
A control device and method that maintain the locked state of the park lock mechanism after a CPU reset, ensuring the park lock device remains in its previous state, preventing unintended transitions and enhancing reliability by managing the lock mechanism's state through actuator control and hydraulic pressure management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the shift range after CPU reset is set to P-range during low vehicle speed, then the park lock device is switched to park locked state, but this causes unintended park lock activation during towing or parking, resulting in abnormal noise and safety issues
Solution Approach 1:
The control device stores the shift range information before CPU reset occurs in advance. When CPU reset happens, the control device retrieves this previously stored shift range information and uses it to determine the appropriate park lock state, rather than defaulting to P-range. This preliminary action of storing and recalling shift range information prevents unintended park lock activation during towing or parking operations.
2Reliability
If the shift range after CPU reset is constantly set to P-range, then the park lock device is activated, but this prevents smooth travel and generates abnormal noise when the previous shift range was N-range
Solution Approach 1:
The control device implements feedback by storing the shift range information before CPU reset and using this feedback to determine the appropriate park lock state after reset. Instead of constantly defaulting to P-range, the system feedbacks the previously known shift range state, allowing the park lock device to maintain its previous operational state and enabling smooth travel without unintended activation.
Data Source
AI summary
A control device for automatic transmission of the present invention includes a transmission mechanism and a park lock device. The park lock device has a rod member and a lock mechanism. The lock mechanism restricts movement of the rod member when being in a locked state. If a CPU reset (reset of a CPU constituting an ATCU) occurs, the control device maintains the locked state of the lock mechanism after a return from the CPU reset.