CVT Hydraulic Pressure Equalization During Switching Valve Transitions
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Solution Overview
Problem
In continuously variable transmission mechanisms, sudden changes in hydraulic pressure during switching of the switching valve can lead to unintended shifting or slippage due to differences in hydraulic pressure between oil circuits before and after switching.
Innovation Solution
A method for controlling a power transmission device that includes a continuously variable transmission mechanism with specific oil passages and an electric oil pump, where a switching valve switches between positions to maintain a hydraulic pressure difference between the third oil passage and the primary pulley oil chamber below a threshold value, thereby preventing sudden pressure changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a switching valve is used to switch between electric oil pump circuit and other actuator circuit, then the electric oil pump can be used for both shifting and source pressure functions, but sudden hydraulic pressure changes occur causing unintended shifting or slippage
Solution Approach 1:
The control device equalizes hydraulic pressure between the first oil passage and third oil passage before switching the switching valve. This preliminary pressure equalization prevents sudden pressure changes that would cause unintended shifting or slippage, while still allowing the electric oil pump to serve multiple functions.
Solution Approach 2:
The control device acts as an intermediary between the hydraulic circuits, actively managing pressure equalization through the second oil passage before valve switching occurs. This intermediary control ensures smooth transition between different operational modes of the electric oil pump without compromising transmission stability.
2Reliability
If hydraulic pressure is equalized before switching, then unintended shifting or slippage is prevented, but additional control steps and time are required
Solution Approach 1:
Pressure equalization is performed in advance before the switching valve changes position, ensuring that when switching occurs, there are no sudden pressure differential changes. This preliminary preparation prevents transmission instability while the control system manages the timing efficiently.
Solution Approach 2:
The control device monitors hydraulic pressure conditions and activates pressure equalization only when switching is anticipated or required. This feedback-based approach ensures pressure equalization occurs at the appropriate moment, preventing instability without continuously operating the equalization system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively prevents unintended shifting or slippage by ensuring the hydraulic pressure difference remains within a safe threshold during switching, ensuring stable operation of the transmission mechanism.
Implementation Method 1
an electric oil pump provided in a first oil passage that connects a primary pulley oil chamber and a secondary pulley oil chamber
Implementation Method 2
a switching valve provided at a branch point between the first oil passage and the second oil passage, and the switching valve switches between two positions
Data Source
AI summary
A method controls a power transmission device including a continuously variable transmission, an electric oil pump provided in a first oil passage connecting primary and secondary pulley oil chambers of the continuously variable transmission, and a switching valve provided at a branch point between the first oil passage and a second oil passage that branches from the first oil passage between the electric oil pump and the primary pulley oil chamber and that is connected to an oil reservoir. A third oil passage branches from the first oil passage between the electric oil pump and the secondary pulley oil chamber. The method makes a magnitude of a hydraulic pressure difference between the third oil passage and the first oil passage one the side of the primary pulley oil chamber smaller than a prescribed threshold value when the switching valve switches between a first position and a second position.