CVT Kickdown Control With Stepwise Ratio Shift Retention
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Solution Overview
Problem
Conventional continuously variable transmission controls provide a slow sense of vehicle acceleration in the early stages, leading to driver discomfort, as they increase the target transmission ratio stepwise and fail to effectively manage the engine rotation speed increase during kickdown operations.
Innovation Solution
A control method that detects the magnitude of the acceleration request and switches from a stepless to a stepwise target transmission ratio mode when the request exceeds a threshold, executing a step-down shift and retaining the target engine rotation speed for a predetermined period to separate the engine rotation speed increase from the vehicle speed increase, thereby improving the acceleration feel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the target transmission ratio is increased stepwise in conventional continuously variable transmission control, then the engine rotation speed increases, but the vehicle speed increases slowly giving the driver a sense of discomfort
Solution Approach 1:
The patent applies dynamics by making the transmission ratio change strategy adaptable based on driving conditions. The control system dynamically switches between stepless change mode and stepwise change mode depending on the acceleration request magnitude, allowing the system to optimize between smooth acceleration and rapid engine speed increase based on real-time driver intent.
Solution Approach 2:
The patent segments the transmission ratio change process into two distinct modes: stepless change for normal acceleration and stepwise change for kickdown operations. By dividing the control strategy into these separate segments, the system can apply different control characteristics appropriate for each driving scenario, resolving the contradiction between smooth vehicle speed increase and rapid engine rotation speed increase.
2Power
If the target transmission ratio is increased along a transmission ratio fixation line from an increased operating point, then the engine rotation speed increases, but the early stage acceleration feels slow to the driver
Solution Approach 1:
The patent changes the control parameter strategy by introducing a mode switch based on acceleration request magnitude. When kickdown is detected, the system changes from continuous parameter adjustment to discrete stepwise adjustment, fundamentally altering how the transmission ratio evolves during acceleration to improve the driver's perception of acceleration response.
Solution Approach 2:
The patent applies preliminary action by detecting the kickdown operation in advance and pre-switching to the stepwise change mode before the acceleration phase fully begins. This allows the system to prepare the transmission ratio change strategy ahead of time, ensuring that the engine rotation speed increases rapidly at the appropriate moment to provide immediate acceleration feedback to the driver.
Data Source
AI summary
The control method for the continuously variable transmission in the present invention detects a magnitude of an acceleration request, and when the acceleration request exceeds a preset threshold value, the control method controls a transmission ratio by switching from a first shift mode, in which a target transmission ratio is changed steplessly, to a second shift mode, which includes a stepwise change in the target transmission ratio. Then, when executing the second shift mode, a target engine rotation speed is set according to the magnitude of the acceleration request, and a step-down shift, in which the target transmission ratio is lowered stepwise according to the target engine rotation speed, is executed at an acceleration start time, and the target engine rotation speed after executing the step-down shift is retained for a predetermined period.