CVT Position Control with Temperature-Adaptive Gain at Cold Start
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Solution Overview
Problem
At low-temperature startup, the warm-up operation in toroidal continuously variable transmissions is limited by instability in closed-loop control due to insufficient oil fluidity, which prevents early startup of the transmission.
Innovation Solution
A position controller that adjusts the gain of the first closed-loop control to decrease sensitivity as oil temperature decreases, allowing for stable and quick initiation of closed-loop control by combining it with minor closed-loop control to reduce deviations in the transmission element's operation position, thereby preventing continuous vibration and instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the reference temperature for switching from warm-up operation to normal operation is lowered to shorten warm-up time, then the transmission can start up earlier, but the oil fluidity is insufficient and closed-loop control becomes unstable
Solution Approach 1:
The patent applies dynamics by making the control gain variable rather than fixed. The gain is adjusted dynamically based on operating conditions (temperature, transmission ratio deviation,, position deviation) to optimize control performance across different operating states. This allows the system to use higher gains when stable and lower gains when instability risk exists, resolving the contradiction between rapid response and stability.
Solution Approach 2:
The patent changes the parameter of control gain based on operating conditions. By monitoring temperature, transmission ratio deviation, and position deviation, the system adjusts the gain parameter to appropriate levels. This parameter adaptation allows the system to maintain stability during warm-up while achieving fast response during normal operation, directly addressing the contradiction.
2Speed
If the gain of closed-loop control is increased to improve responsiveness, then the transmission ratio can be controlled more quickly, but continuous vibration occurs and control becomes unstable
Solution Approach 1:
The control gain is made dynamic and adaptive rather than fixed. The system continuously monitors operating conditions and adjusts the gain accordingly - using higher gains when conditions favor stability and lower gains when vibration risk increases. This dynamic adjustment resolves the contradiction between fast response and stability.
Solution Approach 2:
The system uses feedback from multiple sensors (temperature, transmission ratio, position) to continuously monitor system state and adjust control gain accordingly. This feedback mechanism allows the system to detect early signs of instability and reduce gain before oscillations develop, maintaining both responsiveness and stability.
3Reliability
If warm-up operation is extended to ensure sufficient oil fluidity, then closed-loop control stability is improved, but the transmission startup is delayed
Solution Approach 1:
The control system transitions from static to dynamic gain adjustment. During warm-up, the gain is dynamically adapted based on temperature and deviation metrics, allowing earlier startup than traditional fixed-gain systems would permit. This dynamic approach maintains stability while reducing warm-up time.
Solution Approach 2:
The system performs preliminary adaptive gain adjustment during warm-up based on predicted operating conditions. By preparing the control parameters in advance based on temperature trends and deviation expectations, the system can transition to normal operation sooner while maintaining stability, effectively preempting potential instability issues.
Data Source
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AI summary
A position controller (140) that performs position control by outputting a drive signal to a control valve (25) of a hydraulic actuator (20) that changes an operating position of a transmission element (16) so as to change a transmission ratio of a continuously variable transmission (10), the position controller (140) comprising: an oil temperature acquisition unit (35) that acquires information of an oil temperature of the hydraulic actuator (20); an actual transmission ratio acquisition unit (44) that acquires an actual value of the transmission ratio; a position acquisition unit (42) that acquires an actual value of an operation position of the transmission element (16); a target position calculation unit (48) that calculate a target value of the operating position of the transmission element (16) by first closed-loop control (LP1) so as to reduce a deviation between a command value of the transmission ratio and the actual value of the transmission ratio; a position control unit that calculates an operation command value for the control valve by second closed-loop control (LP2) so as to reduce a deviation between the target value of the operation position of the transmission element and the actual value of the operation position of the transmission element; and a gain setting unit (160) that changes a gain (Gi) of the first closed-loop control (LP1) so that sensitivity of the first closed-loop control (LP1) decreases as the oil temperature decreases.