Automatic Transmission Fail-Safe Torque Control
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Solution Overview
Problem
Automatic transmissions in vehicles face a challenge in suppressing the rising temperature of transmission operating oil during limp-home mode while ensuring a required driving force, as fixing the transmission in a low-speed gear position can lead to increased input speed and friction, causing oil temperature to rise undesirably.
Innovation Solution
A control device with a transmission controller that includes a failure diagnosis section, a fail-safe control section, and an oil temperature rise regulation torque reduction control section, which fixes the transmission in a predetermined gear position and outputs a torque reduction request based on oil temperature conditions, setting the oil temperature condition lower for the first gear position to initiate torque reduction earlier than in other positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the automatic transmission is fixed into a low speed gear position (first gear) during fail-safe control, then the driving force required for traveling in limp-home mode is ensured, but the transmission input speed gets high and friction gets large so that the temperature of transmission operating oil tends to rise undesirably
Solution Approach 1:
The patent applies preliminary action by setting a lower oil temperature threshold specifically for when the transmission is fixed in first gear position. This allows the torque reduction control to be activated earlier (at a lower temperature) before excessive temperature rise occurs, preventing the harmful effect while maintaining the necessary driving force.
Solution Approach 2:
The patent changes the parameter of oil temperature threshold based on the gear position condition. When the transmission is fixed in first gear position, a lower temperature threshold is set compared to other gear positions. This dynamic parameter adjustment allows the system to prevent oil temperature rise in critical conditions while maintaining normal operation in other conditions.
2Temperature
If torque reduction control is activated to suppress transmission operating oil temperature, then the oil temperature rise is suppressed, but the driving force may become insufficient during vehicle restarts
Solution Approach 1:
The patent applies local quality by making the oil temperature threshold specific to the gear position condition. Different temperature thresholds are applied for different operational states (first gear fixed position vs. other positions), allowing optimized control for each specific condition rather than a uniform approach.
Solution Approach 2:
By setting a lower threshold for first gear position, the system takes preliminary action to activate torque reduction before temperature becomes critical, preventing excessive temperature rise while maintaining adequate driving force through earlier, gentler torque management.
Data Source
AI summary
A control device for an automatic transmission includes: a failure diagnosis section for diagnosing whether or not a failure has occurred in a shift control system of the automatic transmission; a fail-safe control section for fixing the automatic transmission into a predetermined gear position in response to confirmation of the failure of the shift control system of the automatic transmission; and an oil temperature rise regulation torque reduction control section for outputting a torque reduction request to suppress torque of a vehicle driving source, based on temperature of transmission operating oil of the automatic transmission, and outputting the torque reduction request in response to satisfaction of an oil temperature condition that is set lower in oil temperature when the automatic transmission is fixed in a first gear position by the fail-safe control section than when the automatic transmission is not fixed in the first gear position.