Transmission Control Device Fail-Safe for Hydraulic Actuator
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Solution Overview
Problem
Existing continuously variable transmission systems lack a fail-safe mechanism for hydraulic secondary-pressure actuators when operating under the double pressure regulation method, making it difficult to distinguish and address failure modes, which can lead to belt slippage and deteriorated vehicle performance.
Innovation Solution
A transmission control device and method that includes a failure determination unit, line command pressure control unit, primary command pressure control unit, and secondary command pressure control unit, which fix the line command pressure and secondary command pressure to predetermined values and continuously change the speed ratio of the variator to ensure a fail-safe operation during hydraulic secondary-pressure actuator failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the double pressure regulation method is used to control both primary pressure and secondary pressure, then the transmission can achieve better shifting performance and adaptability, but the system becomes more vulnerable to hydraulic actuator failures and harder to distinguish failure modes
Solution Approach 1:
The control device determines failure of the hydraulic secondary-pressure actuator before it leads to belt slippage or transmission damage. By detecting failure early and switching to the single pressure regulation method (fixing secondary pressure to line pressure), the system prevents harmful effects from developing. This preliminary detection and response mechanism ensures that the transmission can maintain safe operation even when the secondary-pressure actuator fails.
2Reliability
If the hydraulic secondary-pressure actuator fails, then the actual pressure of secondary pressure may become unpredictable, but fixing secondary command pressure to a predetermined value can suppress belt slippage in certain failure modes
Solution Approach 1:
The control device changes the control parameter strategy based on failure detection. When failure is determined, the secondary command pressure is fixed to a predetermined value that is higher than or equal to the line pressure. This parameter change ensures that sufficient secondary pressure is maintained to prevent belt slippage, regardless of the specific failure mode. The system prioritizes pressure sufficiency over precise pressure control when failure occurs.
3Device complexity
If line pressure is fixed to maximum or minimum pressure based on vehicle speed, then the transmission can simplify control in failure mode, but the system cannot adapt to different failure modes and may not prevent belt slippage
Solution Approach 1:
The control device determines failure of the hydraulic secondary-pressure actuator before it leads to belt slippage or transmission damage. By detecting failure early and switching to the single pressure regulation method with appropriately set predetermined pressures, the system prevents harmful effects from developing while maintaining relatively simple control logic.
Solution Approach 2:
The control device uses feedback from the failure determination unit to adjust the pressure control strategy. When failure is detected, the system switches from normal dual-pressure control to fail-safe single-pressure control with fixed secondary pressure. This feedback mechanism allows the system to adapt its control approach based on the actual system state, ensuring belt slippage prevention while maintaining manageable control complexity.
Data Source
AI summary
In a transmission control device for controlling a transmission, a controller determines failure of a SOL corresponding to a hydraulic secondary-pressure actuator. The controller variably controls line command pressure, and in a case where the failure is determined, fixes the line command pressure to a line pressure set value. The controller variably controls primary command pressure, and in a case where the failure is determined, continuously changes a speed ratio of a variator by variably controlling the primary command pressure. The controller variably controls secondary command pressure, and in a case where the failure is determined, fixes the secondary command pressure to a secondary pressure set value.