Coast Stop Transmission Control for Acceleration Responsiveness
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Solution Overview
Problem
When a driver intends to accelerate after the engine is automatically stopped during coast stop control, the engine restarts in a state where the turbine rotation speed is higher than the engine rotation speed, leading to delayed acceleration responsiveness due to the need for the engine rotation speed to exceed the turbine rotation speed.
Innovation Solution
The transmission mechanism is controlled to a speed ratio higher than the predetermined speed ratio upon a shift request, allowing the drive source to restart in this state, thereby shortening the time to achieve vehicle acceleration and enhance acceleration responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the engine is restarted in a second gear position after automatic stop, then the vehicle can maintain a higher turbine rotation speed, but the acceleration responsiveness to driver's intention deteriorates because it takes longer for engine rotation speed to exceed turbine rotation speed
Solution Approach 1:
The transmission control unit performs a preliminary down-shift to a lower speed ratio (higher gear position) before the engine restart is completed. This preliminary action reduces the turbine rotation speed in advance, creating a larger speed differential that enables the engine rotation speed to quickly exceed the turbine rotation speed immediately after restart, thereby improving acceleration responsiveness while maintaining stability during the transition
2Force
If a down-shift command is executed immediately upon driver's acceleration request, then the turbine rotation speed increases, but the time required for engine rotation speed to exceed turbine rotation speed after restart increases, delaying acceleration
Solution Approach 1:
The system dynamically adjusts the timing and sequence of the down-shift command based on the engine restart state. Instead of executing the down-shift immediately or statically, the transmission control unit monitors the engine restart progress and performs the down-shift at the optimal dynamic moment (when the lower clutch is engaged and upper clutch is disengaged), allowing the system to adaptively balance turbine rotation speed maintenance with minimizing acceleration delay
Data Source
AI summary
A coast stop vehicle for automatically stopping a drive source when a predetermined condition holds during the travel of the vehicle includes a drive source control unit adapted to control the automatic stop and the restart of the drive source, a transmission mechanism provided between the drive source and drive wheels, and a transmission control unit adapted to control a speed ratio of the transmission mechanism. When the drive source is restarted, the transmission control unit is adapted to control the transmission mechanism to a speed ratio higher than a predetermined speed ratio in response to an input shift request to the predetermined speed ratio, and the drive source control unit is adapted to restart the drive source in a state where the speed ratio of the transmission mechanism is higher than the predetermined speed ratio.