CVT Shift Control via Wheel Slip Ratio Feedback
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Solution Overview
Problem
Conventional shift control systems for continuously variable transmissions (CVTs) during sudden braking fail to optimize belt clamping force according to road surface conditions, leading to inadequate re-accelerability and startability, and increase energy consumption due to fixed hydraulic pressure settings.
Innovation Solution
A shift control apparatus that adjusts the gear ratio and belt clamping force of a CVT based on the wheel slip ratio, calculated from wheel speed and vehicle speed, to optimize shift speed and ensure appropriate re-accelerability and startability, while minimizing energy consumption by dynamically adjusting hydraulic pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the hydraulic pressure to be supplied to the hydraulic actuator for the secondary pulley is fixedly increased to increase the shift speed toward γmax, then the belt returnability is improved, but the energy consumption increases due to excessive hydraulic pressure
Solution Approach 1:
The hydraulic pressure supplied to the secondary pulley actuator is made dynamically adjustable based on wheel slip ratio feedback. The ECU continuously monitors wheel speed and vehicle speed to calculate wheel slip ratio, and adjusts the hydraulic pressure accordingly - applying higher pressure only when wheel slip is detected (indicating need for rapid belt return), and normal pressure otherwise, thereby optimizing energy consumption.
Solution Approach 2:
The system implements a feedback control mechanism where the ECU calculates wheel slip ratio from sensor data (wheel speed and vehicle speed) and uses this information to adjust the hydraulic pressure to the secondary pulley actuator. This closed-loop control ensures hydraulic pressure is optimized based on actual driving conditions, preventing energy waste from unnecessarily high pressure application.
2Speed
If the hydraulic pressure to be supplied to the hydraulic actuator for the secondary pulley is simply set a fixed amount higher than before, then the shift speed is increased, but the belt clamping force cannot be optimized according to road surface condition
Solution Approach 1:
The system transitions from fixed hydraulic pressure adjustment to dynamic adjustment based on real-time wheel slip ratio measurement. The ECU modifies the hydraulic pressure to the secondary pulley actuator according to the calculated wheel slip ratio, enabling the CVT system to adapt its belt clamping force to actual road surface conditions rather than using a predetermined fixed pressure increase.
Solution Approach 2:
By continuously monitoring wheel speed and vehicle speed sensors, the ECU calculates wheel slip ratio and uses this feedback to adjust hydraulic pressure dynamically. This allows the system to sense road surface conditions through wheel slip detection and optimize belt clamping force accordingly, achieving adaptability that fixed-pressure systems cannot provide.
3Reliability
If the belt clamping force is increased to ensure sufficient belt returnability, then the re-accelerability is improved, but the power of the oil pump increases more than necessary
Solution Approach 1:
The oil pump power is dynamically adjusted by controlling hydraulic pressure to the secondary pulley actuator based on wheel slip ratio. The ECU applies elevated hydraulic pressure only when wheel slip detection indicates a need for enhanced belt returnability, and maintains normal pressure otherwise, thereby optimizing the balance between reliability and power consumption.
Solution Approach 2:
The system uses wheel slip ratio feedback from speed sensors to determine when increased belt clamping force is necessary. The ECU adjusts hydraulic pressure to the secondary pulley actuator based on this feedback, ensuring that oil pump power is increased only when actually needed for belt returnability, rather than continuously operating at high power.
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
The system achieves precise shift control tailored to road surface conditions, enhancing re-accelerability and startability while reducing energy consumption by optimizing belt clamping force and hydraulic pressure.
Implementation Method 1
a hydraulic actuator for the secondary pulley at the output side of the CVT is supplied with a hydraulic pressure meeting a required torque, such as typified by an engine load, to ensure a necessary amount of transmission torque (control of belt clamping force)
Implementation Method 2
a hydraulic actuator for the primary pulley at the input side of the CVT is supplied with a hydraulic pressure for a gear shift to change the winding position of the belt (control of gear ratio)
Data Source
AI summary
Disclosed is a shift control apparatus for a continuously variable transmission configured to transmit power from a drive power source of a vehicle to a drive wheel of the vehicle. The shift control apparatus is configured to change a gear ratio of the continuously variable transmission with changes in vehicle speed and, during sudden braking of the vehicle, change a rate of change of the gear ratio (a shift speed) of the continuously variable transmission in a downshift direction depending upon a wheel slip ratio calculated from a wheel speed and the vehicle speed.