CVT Controller Speed Ratio Switching for Startup Precision
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Solution Overview
Problem
Conventional continuously variable transmissions with two startup speed change lines face challenges in precise speed ratio control during vehicle startup and stopping, especially when switching between on-road and off-road modes, leading to imprecise speed change control.
Innovation Solution
A control device for a continuously variable transmission that includes a speed change control valve, an actuator, a controller, a shift lever position detecting switch, and a primary side pulley rotation speed sensor, which switches the speed ratio from a second speed ratio to a first speed ratio during vehicle deceleration and vice versa based on the shift lever position and primary pulley rotation speed, ensuring precise speed change control during startup and stopping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the step motor is initialized to the starting position corresponding to the biggest speed ratio, then the speed change line for off road running can be selected, but the speed ratio control precision deteriorates when switching to the speed change line for on road running
Solution Approach 1:
The control device performs preliminary initialization of the step motor to the starting position corresponding to the biggest speed ratio before normal speed change control begins. This preliminary action ensures the actuator is at a known reference position, enabling subsequent precise control when switching between different speed change lines for on-road and off-road running.
2Speed
If feedforward control is applied to the step motor during startup along the speed change line for on road running, then the vehicle can start quickly, but the speed ratio control precision deteriorates
Solution Approach 1:
The control device employs feedback control for the step motor during startup along the speed change line for on-road running, rather than feedforward control. The actual speed ratio is continuously monitored and compared with the target speed ratio, and the step motor control is adjusted based on the deviation, thereby maintaining high speed ratio control precision while enabling quick vehicle startup.
Data Source
AI summary
In a control device for a continuously variable transmission comprising a controller for controlling the speed ratio of a belt continuously variable transmission via an actuator, the continuously variable transmission is capable of selecting a first speed ratio i1 corresponding to a biggest speed ratio and a second speed ratio i2 that is smaller than the first speed ratio as a startup speed ratio. The controller switch the second speed ratio to the first speed ratio when the rotation speed of a primary side pulley falls to a predetermined rotation speed Nt during vehicle deceleration, even if the second speed ratio has been selected, and switches the first speed ratio to the second speed ratio when the rotation speed of the primary side pulley rises to the predetermined rotation speed during vehicle startup.