CVT Line Pressure Control via Dynamic Step Motor Deviation Correction
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Solution Overview
Problem
In continuously variable transmissions, excessive line pressure is generated during high load states due to overestimation of step motor deviations, leading to poor fuel economy and increased oil temperatures.
Innovation Solution
A control system that adjusts line pressure by calculating an actuator operating position deviation correction based on actual and target speed ratios, using a controller to manage oil pressure in primary and secondary pulleys, preventing excessive line pressure through precise control of the actuator's operating position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If line pressure is raised to compensate for step motor attachment error, then speed ratio control accuracy is improved, but fuel economy deteriorates and oil temperature increases in high load states
Solution Approach 1:
The patent applies dynamics by making the correction amount adaptive to operating conditions. The correction amount is dynamically adjusted based on the detected load state (engine torque), allowing the system to optimize speed ratio control accuracy while preventing excessive line pressure in high load conditions. This resolves the contradiction by transitioning from a static correction approach to a dynamic one that responds to actual operating demands.
Solution Approach 2:
The patent changes the parameter of correction amount based on load state. By detecting engine torque and adjusting the correction amount accordingly (reducing it in high load states), the system prevents excessive line pressure while maintaining adequate correction in low load states. This parameter change approach allows the system to balance control accuracy with fuel economy across different operating conditions.
2Measurement precision
If line pressure is raised to compensate for step motor attachment error, then speed ratio control accuracy is improved, but oil temperature increases in high load states
Solution Approach 1:
The system dynamically adjusts the correction amount based on detected load state, reducing excessive correction in high load conditions. This prevents unnecessary line pressure increases that would otherwise cause oil temperature rise, while maintaining adequate correction accuracy when needed. The dynamic adaptation resolves the contradiction between control accuracy and temperature management.
Solution Approach 2:
The correction amount parameter is changed based on load state detection. In high load states, the correction amount is reduced to prevent excessive line pressure and subsequent oil temperature increase. This parameter adjustment strategy maintains control accuracy when necessary while preventing harmful temperature rises during high torque operation.
3Measurement precision
If correction amount is increased to account for attachment error, then control accuracy is improved, but deviation overestimation occurs in high load states
Solution Approach 1:
The patent implements a dynamic correction strategy where the correction amount is adjusted based on detected load state. In high load states, the correction amount is reduced to prevent overestimation of deviation, while in low load states, adequate correction is applied to maintain control accuracy. This dynamic approach prevents the information loss associated with overestimation while preserving necessary correction accuracy.
Solution Approach 2:
The correction amount parameter is modified based on load state detection. By reducing the correction amount in high load conditions, the system prevents deviation overestimation and the associated control errors. This parameter change ensures that the correction remains accurate and proportional to actual attachment errors rather than being excessively large.
Data Source
AI summary
A positional deviation ERRstep of a step motor 27 is calculated on the basis of a reference model step StepMdl, an actual speed ratio-corresponding step Bstep, and an added value obtained by adding together a target deviation GTstep, calculated in accordance with a transmission input torque Ti, and a starting learned value Gstep. When the transmission input torque Ti is large, the target deviation GTstep is increased in accordance with the transmission input torque Ti. A line pressure PL is then controlled on the basis of the positional deviation ERRstep obtained as a result.