CVT Hydraulic Control System Pressure Stability
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Solution Overview
Problem
The existing hydraulic control systems for belt-driven continuously variable transmissions face instability and pressure hunting due to excessive changes in hydraulic pressure, which affect the control of speed ratios and torque transmitting capacity.
Innovation Solution
The system reduces the control amount of the feeding and discharging valves based on specific conditions, such as oil temperature and pressure differences, to stabilize hydraulic pressure and prevent overshooting, using balance piston valves with adjustable orifice sizes to manage oil viscosity and flow resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If feedback control is used to adjust hydraulic pressure based on pressure difference and control gain, then speed ratio and torque transmitting capacity can be controlled, but pressure hunting and instability occur due to excessive pressure changes
Solution Approach 1:
The control gain is made dynamically adjustable based on operating conditions (oil temperature, pressure difference magnitude). The system switches between different control gain values to adapt to varying conditions, preventing pressure hunting while maintaining effective control across different operating ranges
Solution Approach 2:
The control parameter (control gain) is changed based on oil temperature and pressure difference conditions. At high temperatures or large pressure differences, a smaller control gain is used to prevent excessive pressure changes, while normal conditions allow for larger control gains for more responsive control
2Speed
If larger control amount is used to respond quickly to pressure differences, then control responsiveness improves, but pressure overshooting occurs
Solution Approach 1:
The control amount is dynamically adjusted based on the magnitude of pressure difference and oil temperature. Larger pressure differences or higher temperatures result in smaller control amounts to prevent overshooting, while smaller pressure differences allow for larger control amounts for faster response
Solution Approach 2:
The control parameter (control amount) is changed based on operating conditions. The system uses different control amounts depending on whether the pressure difference is large or small, and whether the oil temperature is high or normal, achieving both responsiveness and precision
3Device complexity
If standard feedback control gain is used across all conditions, then control simplicity is maintained, but control accuracy deteriorates under varying oil temperature and viscosity
Solution Approach 1:
The control gain is made dynamically adjustable based on oil temperature and pressure difference conditions. The system switches between different control gain values to adapt to varying conditions, preventing pressure hunting while maintaining effective control across different operating ranges
Solution Approach 2:
The control parameter (control gain) is changed based on oil temperature and pressure difference conditions. At high temperatures or large pressure differences, a smaller control gain is used to prevent excessive pressure changes, while normal conditions allow for larger control gains for more 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 approach stabilizes hydraulic pressure control, preventing overshooting and hunting, while maintaining controllability even with changes in oil viscosity and temperature, ensuring efficient speed ratio and torque transmission.
Implementation Method 1
pressure in the control chamber is lowered by opening the solenoid so that the piston is withdrawn from a valve seat toward the control chamber to open the valve. By contrast, pressure in the control chamber is raised by closing the solenoid so that the piston is pushed onto the valve seat to close the outlet port thereby closing the valve
Implementation Method 2
The hydraulic chamber is connected to an opposite chamber (as will be tentatively called the 'control chamber') across the piston through a communication passage on which an orifice is formed
Data Source
AI summary
A hydraulic control system stably controls pressure in a hydraulic chamber of a pulley accommodating a belt by controlling a feeding valve and a discharging valve. The control system reduces a control amount of the feeding valve to be smaller than that calculated based on a pressure difference in a case other than one in which pressure in the hydraulic chamber is increased by delivering oil to another chamber, in case the pressure in the hydraulic chamber is increased by delivering the oil to the other chamber. The control system reduces a control amount of the discharging valve to be smaller than that calculated based on the pressure difference in a case other than one in which pressure in the hydraulic chamber is lowered by discharging the oil from the other chamber, in case the pressure in the hydraulic chamber is lowered by discharging the oil to the other chamber.