Vehicle Control Device for Secure Low Return
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Solution Overview
Problem
The existing coast stop control systems face challenges in securely returning the variator to the lowest speed ratio, particularly when the variator is not rotating, which can worsen vehicle startability due to insufficient oil balance and quick decreases in engine and turbine rotation speeds.
Innovation Solution
A control device for a vehicle that includes a control unit configured to execute coast stop control only when specific conditions are met, including a speed ratio of the variator being lower than a threshold and the lock-up clutch being engaged, and prohibits execution if the input-output rotation speed difference exceeds a predetermined value, ensuring the variator can securely return to the lowest speed ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If coast stop control is executed without checking rotation speed difference, then fuel economy is improved, but vehicle startability deteriorates due to inability to accomplish Low return
Solution Approach 1:
The control device checks the rotation speed difference between input and output shafts of the torque converter before executing coast stop control. This preliminary check ensures that the variator can be returned to the lowest speed ratio (Low return) by confirming sufficient rotation is available, thereby preventing deterioration of vehicle startability while enabling fuel economy improvement through coast stop control execution
2Productivity
If variator speed ratio is not returned to lowest speed ratio, then coast stop control can be executed more frequently, but vehicle startability worsens
Solution Approach 1:
The control device uses feedback from the rotation speed difference detection to determine whether to execute coast stop control. By continuously monitoring the rotation speed difference between input and output shafts, the system determines if Low return is achievable, thus ensuring vehicle startability is maintained while allowing frequent coast stop control execution when conditions permit
3Power
If lock-up clutch is engaged with large rotation speed difference, then power transmission efficiency is improved, but coast stop control cannot be executed due to insufficient rotation for Low return
Solution Approach 1:
The control device performs a preliminary check of the rotation speed difference between input and output shafts before executing coast stop control. This ensures that sufficient rotation is available to return the variator to the lowest speed ratio, thereby enabling coast stop control execution while the lock-up clutch is engaged with large rotation speed difference, maintaining both power transmission efficiency and control adaptability
Data Source
AI summary
A controller includes a control unit which is configured to execute a coast stop control. The coast stop control is configured to perform automatic stopping of the drive source while the vehicle is traveling, when a permitting condition is satisfied, the permitting condition including a condition that a speed ratio R of the variator is lower than a first threshold R1 while the lock-up clutch is in an engaged phase. The control unit is configured to prohibit execution of the coast stop control in a case in which an input-output rotation speed difference of the torque converter is equal to or more than a predetermined value when the lock-up clutch is in the engaged phase.