Vehicle Control Device for Suppressing Input Shaft Overspeed
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
During a coast downshift in a vehicle with a stepped transmission, overspeeding of the input shaft can lead to decreased drivability due to increased driving force from reduced input rotation speed, especially when the vehicle decelerates and the accelerator is not operated, as existing control devices rely on engagement-side elements with higher gear ratios to suppress overspeeding, causing drivability issues.
Innovation Solution
A control device with an electronic control unit that increases the disengagement-side instructed pressure to decrease the input shaft rotation speed when overspeeding occurs, using both disengagement-side and engagement-side elements to manage clutch torque, thereby reducing the impact of decreased input rotation speed and maintaining drivability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engagement-side element with higher gear ratio is used to suppress overspeeding of the input shaft, then overspeeding is suppressed, but the driving force increases significantly causing degradation in drivability
Solution Approach 1:
Instead of using the engagement-side element (low-side gear stage) to suppress overspeeding as in conventional technology, this patent uses the disengagement-side element (high-side gear stage) to suppress overspeeding by increasing its instructed pressure. This inverted approach prevents the sudden increase in driving force that would occur with the engagement-side element, thereby maintaining drivability while still suppressing overspeeding of the input shaft.
2Reliability
If the disengagement-side instructed pressure is increased to suppress overspeeding, then overspeeding is suppressed and drivability is maintained, but the responsiveness of the pressure increase may be sluggish
Solution Approach 1:
The patent dynamically adjusts the disengagement-side instructed pressure based on the detected overspeeding state. When overspeeding is detected, the control device increases the disengagement-side instructed pressure to suppress the overspeeding. The system monitors the responsiveness and adjusts the pressure increase rate accordingly, preventing excessive pressure increases while maintaining effective overspeeding suppression.
3Reliability
If the input shaft rotation speed is decreased to suppress overspeeding, then overspeeding is suppressed, but the change in driving force affects drivability
Solution Approach 1:
The patent applies pressure control selectively to the disengagement-side element rather than uniformly to all engagement elements. By increasing the instructed pressure specifically on the disengagement-side element that forms the high-side gear stage, the system suppresses overspeeding locally at the appropriate gear stage without causing a sudden overall change in driving force transmission, thereby maintaining drivability.
Data Source
AI summary
A control device for a vehicle includes an electronic control unit configured to increase a disengagement-side instructed pressure such that an input rotation speed decreases when overspeeding of the input shaft occurs during a coast downshift of an automatic transmission. Overspeeding of the input shaft in a disengagement-side element that forms a gear stage before a downshift having a lower gear ratio than that after the downshift is suppressed.