CVT Shift Control Reducing Gear Ratio Overshoot
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Solution Overview
Problem
Conventional belt-type continuously-variable transmissions experience gear ratio overshoot during rapid shifts, leading to inefficient acceleration response due to a gradual decrease in the rate of change of the actual pulley ratio, resulting in a larger transient target pulley ratio compared to the actual pulley ratio.
Innovation Solution
A control apparatus for an automatic transmission that includes a primary pulley, a secondary pulley, a shift control valve, a step motor, and a control section with normal and high-speed control modes. The control section uses feedback control for normal shifts and open-loop control for high-speed shifts, adjusting the hydraulic pressure to rapidly achieve the target pulley ratio, thereby reducing overshoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the shift speed is increased to improve acceleration response, then the shift response is improved, but the rate of change of the actual pulley ratio gradually decreases causing gear ratio overshoot
Solution Approach 1:
The patent applies dynamics by making the time constant variable rather than fixed. The time constant is dynamically adjusted based on the current pulley ratio and target pulley ratio, allowing the system to adapt its response characteristics during the shift process. This enables faster initial response while preventing overshoot as the target is approached.
Solution Approach 2:
The patent changes the parameter of the time constant during operation. By modifying the time constant based on the difference between actual and target pulley ratios, the system transitions from a gradual change regime to a faster response regime, thereby improving shift speed while maintaining accuracy and preventing overshoot.
2Stability of the object's composition
If feedback control with first-order delay is used to smooth the shift, then the shift is performed smoothly, but the transient target pulley ratio becomes extremely large causing overshoot
Solution Approach 1:
The patent changes the time constant parameter dynamically during the shift process. When the difference between actual and target pulley ratios is large, a larger time constant provides smooth transition. When the difference becomes small, the time constant is reduced to prevent overshoot and improve final accuracy, thus resolving the contradiction between smoothness and precision.
Solution Approach 2:
The control system transitions from static to dynamic by making the time constant adaptive. The system automatically adjusts its response characteristics based on real-time feedback, enabling it to be smooth during early stages and precise during final stages of the shift operation.
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 solution effectively decreases gear ratio overshoot and improves acceleration response by allowing for faster shifts during high-speed operations, ensuring the actual pulley ratio closely matches the target ratio, enhancing the transmission's responsiveness.
Implementation Method 1
The movable pulley of the primary pulley is arranged to move axially toward or move axially apart from the fixed pulley of the primary pulley by regulating a hydraulic pressure within a hydraulic chamber formed on a back surface (or rear surface) of the movable pulley of the primary pulley.
Implementation Method 2
The movable pulley of the secondary pulley is arranged to move axially toward or move axially apart from the fixed pulley of the secondary pulley by regulating a hydraulic pressure within a hydraulic chamber formed on a back surface (or rear surface) of the movable pulley of the secondary pulley.
Data Source
AI summary
A control apparatus for an automatic transmission includes a control section having a normal control section configured to actuate the step motor at a first speed by using a feedback control including an integral control in accordance with the target pulley ratio and the actual pulley ratio, a high speed control section configured to actuate the step motor at a second speed higher than the first speed by an open loop control based on the target pulley ratio, a judgment section configured to judge whether there is a high speed operation request, and a switch section configured to select the normal control performed by the normal control section at a normal condition, and to switch to the high speed control when a switch start condition is satisfied, the switch start condition including a first condition that the judgment section judges there is the high speed operation request.