CVT Control Device Primary Pressure Stability
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Solution Overview
Problem
In continuously variable transmissions, the high limiter control operation leads to primary pressure instability and hunting due to the primary pressure entering the dead region of the solenoid, causing unstable hydraulic pressure control and transmission ratio fluctuations.
Innovation Solution
A control device with a primary pressure lower limit regulation unit that limits the decrease of primary command pressure to the primary pressure solenoid when the high limiter control is initiated, preventing the primary pressure from entering the solenoid dead region and stabilizing the hydraulic pressure control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the high limiter control decreases the primary command pressure to achieve downshift, then the transmission ratio can be reduced, but the primary pressure enters the solenoid dead region causing instability and hunting
Solution Approach 1:
The patent changes the control parameter by introducing a lower limit threshold for primary command pressure. When the primary command pressure approaches the dead region, the control system stops decreasing the pressure and maintains it at the threshold level, preventing the instability caused by operating in the dead region while still achieving the desired downshift effect.
2Stability of the object's composition
If the F/B gain is decreased to prevent hunting in normal shift control, then the control stability improves, but the shift response becomes slow or dull
Solution Approach 1:
The patent applies preliminary action by proactively limiting the primary command pressure before it enters the dead region. By predicting when the pressure will approach the unstable region and preemptively stopping the pressure decrease at the threshold, the system avoids hunting without needing to reduce the F/B gain, thereby maintaining both stability and responsive control.
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 solution effectively suppresses the hunting of the transmission ratio by maintaining primary pressure stability during high limiter control operations, ensuring smooth and controlled gear shifts.
Implementation Method 1
a hydraulic pressure control circuit having a primary pressure solenoid that controls a primary pressure supplied to the primary pulley
Data Source
AI summary
Control device for continuously variable transmission (4) with auxiliary transmission having variator (20); hydraulic pressure control circuit (11) having primary pressure solenoid (11b); and transmission ratio controller (12) controlling the transmission ratio of variator (20) by feedback control. The transmission ratio controller (12) has a high limiter control unit (FIG. 5) that, when receiving a high transmission ratio limiting request, performs a high limiter control that limits the transmission ratio to a High limit line. The transmission ratio controller (12) also has a primary pressure lower limit regulation control unit (FIG. 4) that, when operation of the high limiter control is started during a time period when the transmission ratio is present at a High transmission ratio side with respect to the high limit transmission ratio, regulates a decrease of a primary command pressure to the primary pressure solenoid up to a High limiter-operated final target primary lower limit pressure.