CVT Shift Control for V-Belt Slippage Prevention
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Solution Overview
Problem
Conventional belt-type continuously variable transmissions experience slippage in the V-belt when re-acceleration occurs before the pulley ratio is returned to the lowest value after rapid deceleration, leading to a mismatch between the target and actual gear ratios.
Innovation Solution
A shift control system that includes speed detecting, downshift detecting, and idle state detecting means to limit the operating speed of the shift actuator when the vehicle speed is below a predetermined threshold, ensuring the actual gear ratio matches the target gear ratio by controlling the differential pressure between the primary and secondary pulley pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the shift actuator operates at high speed to quickly change the gear ratio, then the response time is improved, but V-belt slippage occurs due to rapid pulley ratio changes at low speeds
Solution Approach 1:
The patent applies dynamics by making the shift actuator's operating speed variable rather than fixed. The control device dynamically adjusts the shift speed based on detected vehicle conditions (idle state, vehicle speed, pulley ratio position). During rapid deceleration from idle state, when vehicle speed is low and pulley ratio is above the lowest value, the shift speed is limited to prevent V-belt slippage. Under normal conditions, the shift actuator operates at standard speed to maintain quick response. This dynamic speed adjustment resolves the contradiction between fast response and slippage prevention.
2Productivity
If the target gear ratio is forced to the lowest value Lo during re-acceleration, then quick acceleration is achieved, but V-belt slippage occurs because the actual gear ratio has not returned to Lo
Solution Approach 1:
The patent applies preliminary action by detecting the idle state and low vehicle speed conditions before commanding a downshift to the lowest value Lo. When these conditions are detected, the control device preemptively limits the shift actuator's operating speed to prevent slippage before it occurs. This preliminary detection and preventive speed limitation allows the system to maintain acceleration performance while avoiding the slippage that would occur if the gear ratio were forced to Lo without checking actual pulley position.
Solution Approach 2:
The patent applies feedback by using a pulley ratio detecting device to continuously monitor the actual gear ratio position. The control device compares the detected actual gear ratio with the target gear ratio and uses this feedback information to determine whether to limit the shift actuator speed. This closed-loop feedback mechanism ensures that downshift commands are executed safely, preventing V-belt slippage while maintaining the ability to achieve quick acceleration when conditions permit.
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
Prevents slippage in the V-belt during re-acceleration by limiting the shift speed of the downshift, maintaining the target gear ratio and preventing belt slippage even when the vehicle is rapidly decelerated and re-accelerated before the pulley ratio returns to the lowest value.
Implementation Method 1
a hydraulic pressure (hereinafter referred to as a primary pulley pressure) which is obtained by regulating a line pressure as an original pressure with a shift control valve is supplied to a cylinder chamber of a primary pulley
Implementation Method 2
a differential pressure is generated between the primary pulley pressure and the secondary pulley pressure to change widths of V-shaped grooves of the primary pulley and the secondary pulley
Data Source
AI summary
When a speed of a vehicle is less than 8 km/h, an upshift determination condition is established, an idle switch signal is turned off, and a downshift is detected, an operating speed of the step motor is limited. Thereby, since the operating speed of the step motor is limited even when the vehicle is rapidly decelerated and re-accelerated before a pulley ratio is returned to a lowest value Lo, a shift speed of the downshift performed in the re-acceleration is lowered, and no slippage occurs in a V-belt between pulleys.