CVT Control Device Stepwise Downshift Rhythm
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Solution Overview
Problem
Existing control devices for continuously variable transmissions (CVTs) on vehicles do not effectively enhance deceleration feel and drivability during braking, as they lack the ability to match the driver's intention and provide a smooth deceleration experience.
Innovation Solution
A control device that sets a target input rotational speed for the CVT to vary the speed ratio stepwise to the downshift side in response to brake pedal operation, with longer intervals between consecutive downshifts as the number of downshifts increases, thereby improving the deceleration feel by rhythmically varying vehicle states such as deceleration G and engine sound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the speed ratio is varied continuously without stepwise downshifts during braking, then the deceleration is smooth, but the deceleration feel and drivability are insufficient
Solution Approach 1:
The continuous deceleration process is segmented into multiple stepwise downshifts of the speed ratio. Instead of varying the speed ratio continuously, the control device divides the deceleration into discrete steps where the speed ratio is reduced in increments, creating a rhythmical deceleration pattern that enhances driver perception while maintaining overall smoothness.
Solution Approach 2:
The control device applies periodic action by executing multiple consecutive downshifts at predetermined intervals during braking. The speed ratio is varied stepwise a plurality of times consecutively, creating a rhythmical pattern of deceleration that matches driver expectation and improves deceleration feel, while the intervals between downshifts are controlled to maintain smooth overall deceleration.
2Speed
If the interval between consecutive downshifts is short, then the deceleration response is immediate, but the driver's intention to decelerate may not be properly matched
Solution Approach 1:
The control device applies dynamics by making the interval between consecutive downshifts variable rather than fixed. The interval is determined based on the required deceleration and driver input, allowing the system to adapt the timing of each downshift to match the driver's intention. This dynamic adjustment ensures immediate response when needed while preventing excessive deceleration that would mismatch driver intent.
Solution Approach 2:
The control device uses feedback from the brake pedal operation and vehicle state to determine the timing and magnitude of each downshift. By monitoring the required deceleration and comparing it with the actual vehicle response, the system adjusts the interval between consecutive downshifts to accurately match the driver's deceleration intention, ensuring both responsive and adaptive behavior.
3Power
If the speed ratio is increased to generate engine brake force, then the braking efficiency is improved, but the deceleration rhythmics and atmospheric feel are reduced
Solution Approach 1:
The engine brake force generation is segmented into multiple stepwise downshifts rather than a single large speed ratio increase. By dividing the total speed ratio change into several smaller consecutive steps, the system maintains engine brake force effectiveness while creating rhythmical variations in deceleration that enhance atmospheric feel and driver perception.
Solution Approach 2:
The control device applies periodic action by executing consecutive downshifts with controlled intervals during braking. This creates a rhythmical pattern of engine brake force application, where the periodic speed ratio variations generate atmospheric deceleration feel while still achieving the required braking power through cumulative engine brake force from multiple downshifts.
Data Source
AI summary
A speed change ECU for a CVT sets a target input rotational speed (Nin*) such that the speed ratio of the CVT is varied stepwise a plurality of times consecutively to the downshift side in response to an operation to depress a brake pedal by a driver, and sets the target input rotational speed (Nin*) such that the time interval between consecutive downshifts becomes longer as the number of times of execution of downshifts is increased on the basis of intershifting times (tint(1)), (tint(2)), . . . while downshifts in which the speed ratio is varied stepwise are executed consecutively.