CVT Primary Pressure Control for Shift Returning to Low
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Solution Overview
Problem
Downsizing the oil pump in a continuously variable transmission (CVT) leads to slower shift speed and longer time to achieve the lowest speed ratio during deceleration, due to insufficient oil quantity balance and reduced discharge pressure, resulting in failure to return to low gear effectively.
Innovation Solution
The CVT determines a primary pressure measured lower limit value based on vehicle deceleration and speed ratio, allowing the primary pressure to be reduced below its theoretical lower limit during shift returning to low, enabling the secondary pressure to be adjusted to ensure differential thrust is maintained, even with insufficient oil quantity balance, thereby improving the shift returning to low and fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the oil pump is downsized to improve fuel efficiency, then engine power consumption and friction are reduced, but the discharge pressure decreases and shift speed slows down
Solution Approach 1:
The invention changes the control parameter from a fixed theoretical lower limit pressure to a dynamically adjusted pressure based on actual belt slip detection. By detecting actual belt slip conditions and adjusting the primary pressure lower limit accordingly, the system optimizes the balance between fuel efficiency (lower pressure) and shift speed (sufficient pressure when needed), resolving the contradiction caused by oil pump downsizing.
2Reliability
If the primary pressure lower limit is set based on theoretical torque capacity, then belt slip is prevented under normal conditions, but shift speed decreases when oil quantity balance is insufficient
Solution Approach 1:
The invention introduces feedback control by detecting actual belt slip conditions during shift operations and using this information to dynamically adjust the primary pressure lower limit. This feedback mechanism allows the system to maintain reliable belt slip prevention while optimizing shift speed, as the pressure limit is adjusted based on real-time operational conditions rather than fixed theoretical values.
Solution Approach 2:
The invention transforms the static, theory-based primary pressure lower limit into a dynamic parameter that adapts to actual operating conditions. By making the pressure limit flexible and responsive to real-time belt slip detection, the system can optimize performance for both reliability and productivity under varying oil quantity balance conditions.
3Reliability
If the target primary pressure is limited to the primary pressure lower limit value to prevent belt slip, then belt slip is avoided, but the required differential thrust becomes insufficient and shift speed decreases
Solution Approach 1:
The invention uses feedback from actual belt slip detection to dynamically adjust the primary pressure lower limit, allowing the system to maintain sufficient differential thrust for fast shifting while preventing belt slip. The feedback mechanism enables real-time optimization of the pressure-thrust-belt slip relationship.
Solution Approach 2:
The system performs preliminary detection of belt slip conditions before final pressure adjustment, allowing proactive optimization of the differential thrust while maintaining belt slip prevention. This preliminary action enables the system to prepare appropriate pressure levels based on detected conditions.
Data Source
AI summary
A transmission controller determines whether a shift returning to low, changing a speed ratio of a continuously variable transmission to the lowest when a vehicle decelerates, is being performed or not, calculates a primary pressure measured lower limit value at which a belt begins to slip actually, based on a deceleration of the vehicle and the speed ratio of the continuously variable transmission, and sets a lower limit value of a target value of the primary pressure during the shift returning to low as the primary pressure measured lower limit value.