CVT Transmission Control Device Fail-Safe Mechanism
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing techniques lack a fail-safe mechanism for continuously variable transmissions when a hydraulic primary-pressure actuator fails, particularly during the double pressure regulation method, where distinguishing failure modes can be challenging.
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 to variably control pressures and maintain set values in case of failure, ensuring continuous speed ratio adjustment and preventing belt slippage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hydraulic primary-pressure actuator fails in a double pressure regulation system, then the transmission control system becomes more complex to handle various failure modes, but the reliability of the transmission decreases
Solution Approach 1:
The patent segments the pressure control system into three independent hydraulic actuators (line-pressure actuator, primary-pressure actuator, and secondary-pressure actuator), each controlled by dedicated command pressure signals. This segmentation allows independent failure determination and control for each actuator, simplifying the overall failure handling complexity while maintaining system reliability.
Solution Approach 2:
The patent implements preliminary failure determination by continuously monitoring the relationship between command pressure and actual pressure for the hydraulic primary-pressure actuator. When a failure is detected (discrepancy between commanded and actual pressure), the system immediately switches to a predetermined fail-safe pressure value, preventing further degradation before it affects transmission operation.
2Reliability
If command pressure is fixed to a predetermined value upon actuator failure, then belt slippage is suppressed, but speed ratio adjustment capability is reduced
Solution Approach 1:
The patent segments the pressure control into three independent channels (line pressure, primary pressure, secondary pressure), allowing selective fixing of only the failed actuator's command pressure while maintaining variable control of the other two. This enables speed ratio adjustment to continue through the functional actuators while the failed actuator is protected by a fixed predetermined value.
Solution Approach 2:
The patent changes the control parameter state dynamically: under normal operation, all command pressures are variable; upon detection of primary-pressure actuator failure, the system changes the primary command pressure from a variable parameter to a fixed predetermined value, while maintaining variability in line and secondary command pressures. This parameter state change prevents belt slippage while preserving speed ratio adjustability through the remaining functional actuators.
Data Source
AI summary
In a transmission control device for controlling a transmission, a controller determines failure of a SOL corresponding to a hydraulic primary-pressure actuator. The controller variably controls line command pressure, and in a case where the failure is determined, continuously changes a speed ratio of a variator by variably controlling the line command pressure. The controller variably controls primary command pressure, and in a case where the failure is determined, fixes the primary command pressure to a primary pressure set value. 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.