CVT Control Unit Hydraulic Pressure Management for Belt Slip Prevention
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Solution Overview
Problem
Vehicles equipped with belt-type continuously variable transmissions and motor-generators face challenges in maintaining fuel efficiency and shift responsiveness during sudden braking, as lowering primary pressure to enhance shift responsiveness can lead to belt slip and reduced regeneration capacity.
Innovation Solution
A control method that sets target hydraulic pressures for the primary and secondary pulleys based on guaranteed capacities, including cooperative regeneration and braking capacities, to manage torque input and prevent belt slip, while optimizing differential pressure for improved shift responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the primary pressure is lowered to enhance shift responsiveness during downshift, then the shift speed is improved, but the belt sandwiching force decreases which may result in belt slip and reduced regeneration capacity
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the primary pressure based on the vehicle state and regeneration requirements. During downshift without acceleration request, the control unit sets the primary pressure to maintain sufficient belt sandwiching force while enabling adequate shift responsiveness. The system changes pressure parameters according to different operating conditions (sudden braking, gradual deceleration, acceleration requests) to optimize both shift speed and belt grip.
Solution Approach 2:
The patent implements dynamics by making the primary pressure adaptive rather than fixed. The control unit continuously monitors vehicle state and adjusts the primary pressure in real-time during downshift operations. This dynamic adjustment allows the system to maintain optimal belt sandwiching force throughout the shifting process, preventing belt slip while ensuring responsive gear changes. The secondary pressure is also dynamically coordinated with primary pressure to maintain proper differential pressure.
2Speed
If the primary pressure is lowered to improve shift responsiveness, then the differential pressure increases enhancing shift speed, but the regeneration capacity is reduced due to insufficient belt sandwiching force
Solution Approach 1:
The patent uses parameter changes to optimize the balance between shift responsiveness and regeneration capacity. The control unit adjusts primary and secondary pressure parameters based on the detected vehicle state (sudden braking, gradual deceleration, acceleration requests). During sudden braking without acceleration requests, the system sets pressures to allow rapid downshift to lowest speed ratio while maintaining sufficient belt sandwiching force for regeneration. This dynamic parameter adjustment ensures both fast shifting and energy recovery are achieved simultaneously.
Solution Approach 2:
The patent implements feedback control by monitoring the vehicle state and regeneration requirements, then adjusting the primary and secondary pressures accordingly. The control unit receives feedback about braking intensity, acceleration requests, and current speed ratio, and uses this information to determine the optimal pressure settings. This closed-loop control ensures that the belt sandwiching force is always sufficient for the required regeneration level while enabling responsive downshift when needed.
3Reliability
If the amount of regeneration is lowered to prevent belt slip, then the belt sandwiching force requirement is reduced, but fuel efficiency is lost
Solution Approach 1:
The patent applies parameter changes by setting the primary pressure to an optimal value that satisfies both belt slip prevention and regeneration requirements. Rather than reducing regeneration to prevent belt slip, the system adjusts the pressure parameter to enable full regeneration capacity while maintaining adequate belt sandwiching force. The control unit calculates the required primary pressure based on the torque input from regeneration and the current speed ratio, ensuring the belt grip is sufficient for the actual regeneration load.
Solution Approach 2:
The patent uses preliminary action by pre-setting the primary and secondary pressures before the downshift operation begins. The control unit determines the appropriate pressure values based on the detected braking state and regeneration requirements, then applies these pressures in advance of the actual speed ratio change. This preliminary pressure adjustment ensures that when downshift occurs, the belt sandwiching force is already optimized for the required regeneration capacity, preventing belt slip while maximizing fuel efficiency.
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 enhances fuel efficiency during regeneration and maintains shift responsiveness by preventing belt slip and increasing the differential pressure between primary and secondary pressures, ensuring effective torque transmission during sudden braking.
Implementation Method 1
a primary pulley whose groove width is changed by controlling a primary pressure, a secondary pulley whose groove width is changed by controlling a secondary pressure
Data Source
AI summary
The present invention is related to a vehicle including a motor-generator, a transmission, a shift hydraulic control unit, and a CVT control unit (CVTCU). When a downshift of the transmission is performed without an acceleration request from a driver, the CVTCU sets a pulley thrust at a secondary pulley on the basis of a first lower limit as a lower limit, which is a sum of a fundamental thrust and a first correction thrust. The CVTCU also sets a pulley thrust at a primary pulley on the basis of a second lower limit as a lower limit, which is a sum of the fundamental thrust and a second correction thrust.