Hybrid Vehicle Shift Control for Kick-Down Torque
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Solution Overview
Problem
Conventional hybrid vehicle shift control systems in EV mode fail to provide sufficient acceleration due to increased motor rotation speed leading to un-synchronized acceleration, and existing solutions like prohibiting kick-down shifts or delayed engine engagement result in excessive acceleration dead zones.
Innovation Solution
A shift control system and method that detects kick-down shift requests, determines motor rotation speed, and adjusts the driving mode from EV to HEV by engaging the engine clutch when necessary, ensuring required torque is met for rapid and stable acceleration, either by executing the kick-down shift in EV mode when torque is sufficient or in HEV mode when it is not.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a kick-down shift is executed in EV mode by increasing motor rotation speed, then gear ratio is increased, but torque is reduced and sufficient acceleration cannot be realized
Solution Approach 1:
The system changes the operating mode parameter from EV mode to HEV mode when kick-down shift is requested. This allows the engine to be engaged and provide torque supplementation to the motor, resolving the torque reduction issue while maintaining the speed increase benefit of the kick-down shift.
Solution Approach 2:
The system merges the power sources by engaging the engine clutch to connect the engine to the motor in HEV mode. This combines engine torque and motor torque to deliver sufficient total torque during kick-down shift, overcoming the torque limitation of motor-only operation.
2Reliability
If kick-down shift is prohibited and engine is started using ISG in conventional art, then engine clutch is engaged and HEV mode kick-down shift is executed, but excessive acceleration dead zone time occurs from kick-down request to engine start
Solution Approach 1:
The system performs preliminary engagement of the engine clutch before engine start is complete. By pre-engaging the clutch while the engine is starting, the system eliminates the acceleration dead zone and ensures immediate power transmission once the engine produces torque, rather than waiting for complete engine start.
Solution Approach 2:
The system maintains continuous acceleration capability by overlapping the engine start process with the clutch engagement and kick-down shift execution. This ensures there is no interruption or dead zone in the acceleration process, keeping the useful action of acceleration continuous throughout the mode transition.
3Speed
If motor rotation speed is increased with kick-down shift in EV mode, then gear ratio is increased, but un-synchronized acceleration happens and acceleration is deteriorated
Solution Approach 1:
The system uses feedback from the driving condition detector and hybrid control unit to monitor acceleration requests and motor rotation speed. When kick-down shift is detected, the system responds by transitioning to HEV mode and coordinating engine-motor power delivery, ensuring synchronized acceleration response based on real-time feedback.
Solution Approach 2:
The system dynamically adjusts the driving mode from EV to HEV based on acceleration requirements. This dynamic adaptation allows the system to maintain synchronized acceleration by engaging the engine when rapid acceleration is requested, rather than relying solely on motor speed increases that cause unsynchronized behavior.
Data Source
AI summary
A shift control system for a hybrid vehicle having an engine and a motor as power sources, may include a driving condition detector which detects whether a kick-down shift-request occurs, and a hybrid control unit which determines a motor rotation speed of a target shift-speed when the kick-down shift-request may be detected, determines whether the motor rotation speed satisfies a required torque, and executes a kick-down shift in EV (ElectircVehicle) mode or in HEV (Hybrid Electric Vehicle) mode according to a condition that the motor rotation speed satisfies the required torque or not.