Hybrid Vehicle LSD Control for Drivability During Mode Switch
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Solution Overview
Problem
Hybrid electric vehicles (HEVs) switching from HEV mode to EV mode can cause a decrease in drivability due to the transition from all-wheel drive to rear-wheel drive, making drivers feel strange, especially on curved roads.
Innovation Solution
A vehicle control system that includes a processor to stop the engine and engage the limited slip differential mechanism when switching from HEV mode to EV mode, maintaining the all-wheel drive state by directly coupling the front-wheel-side and rear-wheel-side output portions of the center differential, and subsequently allowing the vehicle to transition to rear-wheel drive based on road surface conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the vehicle switches from HEV mode to EV mode, then energy consumption is reduced by using only the motor, but drivability deteriorates due to transition from all-wheel drive to rear-wheel drive
Solution Approach 1:
The system dynamically adjusts the engagement state of the limited slip differential mechanism based on driving conditions. During mode switching from HEV to EV, the LSD is kept engaged to maintain torque distribution to both front and rear wheels, providing all-wheel drive characteristics. When stable in EV mode, the LSD can disengage to allow rear-wheel drive operation, optimizing energy consumption while maintaining drivability through dynamic adaptation.
Solution Approach 2:
The limited slip differential mechanism serves as an intermediary component that enables flexible torque distribution between front and rear wheels. By controlling the engagement state of this intermediary mechanism, the system can transition between all-wheel drive and rear-wheel drive configurations, allowing smooth mode switching without abrupt changes in drivetrain behavior that would degrade drivability.
2Ease of operation
If the limited slip differential mechanism is engaged during mode switching, then drivability is maintained, but mechanical complexity increases
Solution Approach 1:
The limited slip differential mechanism performs multiple functions: it enables all-wheel drive operation when engaged, allows rear-wheel drive operation when disengaged, and provides torque vectoring capabilities during transitions. This multi-functionality eliminates the need for separate mechanisms for different drive modes, reducing overall system complexity while maintaining drivability across all operating conditions.
3Use of energy by moving object
If the engine is stopped during mode switching to EV mode, then energy efficiency is improved, but torque interruption occurs affecting vehicle performance
Solution Approach 1:
The system performs preliminary engagement of the limited slip differential mechanism before stopping the engine during mode switching. This ensures that the torque path through the LSD is established beforehand, allowing smooth transition of torque delivery from the engine to the motor without interruption. The preliminary action prevents power gaps that would otherwise occur during engine shutdown.
Solution Approach 2:
The limited slip differential mechanism maintains continuous torque transmission to all wheels during the transition from engine-powered to motor-powered operation. By keeping the LSD engaged during mode switching, the system ensures uninterrupted torque delivery to the drivetrain, preventing performance degradation that would result from sudden engine shutdown while maintaining energy efficiency in EV mode.
Data Source
AI summary
A vehicle control system to be mounted in a hybrid electric vehicle includes an engine, a center differential that includes a front-wheel-side output portion and a rear-wheel-side output portion and distributes torque outputted from the engine to a front wheel and a rear wheel, a limited slip differential mechanism that limits a differential between the front-wheel-side output portion and the rear-wheel-side output portion, and a motor disposed in a drive-power transferring system that transfers drive power from the rear-wheel-side output portion to the rear wheel. The vehicle control system includes a processor. When the hybrid electric vehicle is switched from a first traveling mode to a second traveling mode, the processor stops the engine while causing the limited slip differential mechanism to limit the differential between the front-wheel-side output portion and the rear-wheel-side output portion.