Electric Four-Wheel Drive Torque Limiting for Rollback Control
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Solution Overview
Problem
Electric four-wheel drive vehicles experience discomfort due to idling wheels when motor torque is applied to reduce rollback, as the torque distribution between front and rear wheels with different road surface resistances can cause unintended wheel behavior, leading to a sense of discomfort for the driver.
Innovation Solution
A control method that acquires the driving direction and actual moving direction of the vehicle, sets a basic driving force to suppress movement in the actual moving direction for both wheels, and implements a torque limit for one wheel to ensure it generates a driving force smaller than the basic force, thereby preventing idling and discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If motor torque is applied to reduce rollback in an electric four-wheel drive vehicle, then rollback suppression is improved, but wheel idling occurs on low-resistance surfaces causing driver discomfort
Solution Approach 1:
The control device applies different torque control strategies to different wheels based on their individual road surface conditions. When one wheel is detected to be on a low-resistance surface, the control device reduces or eliminates torque application to that specific wheel while maintaining torque on the other wheel, preventing idling on the slippery surface while still suppressing rollback overall.
Solution Approach 2:
The control device dynamically adjusts torque distribution between the front and rear wheels based on real-time detection of wheel rotation states and road surface resistance. The system continuously monitors wheel speed and torque application, and adaptively modifies torque commands to prevent idling while maintaining rollback suppression effectiveness.
2Reliability
If independent motor control of front and rear wheels is implemented, then rollback suppression effectiveness is improved, but unintended wheel behavior occurs on surfaces with varying resistance
Solution Approach 1:
The control device implements a feedback mechanism that continuously monitors the rotation state of each wheel and the applied torque. When a wheel is detected to be idling (rotating without effective traction), the control device receives this feedback and adjusts torque distribution accordingly, reducing torque to the idling wheel while maintaining torque to the gripping wheel, thus stabilizing overall wheel operation consistency.
Solution Approach 2:
The control device changes the torque parameter dynamically based on detected wheel conditions. When one wheel is on a low-resistance surface, the control device modifies the torque parameter for that wheel specifically, reducing it to prevent idling, while maintaining appropriate torque on the other wheel, thereby achieving consistent operation across varying surface conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The control method effectively reduces rollback without causing discomfort to the driver by ensuring both wheels maintain traction and operate predictably, even on surfaces with varying resistances, thereby stabilizing the vehicle's operation.
Implementation Method 1
an electric vehicle including a motor as a drive source can reduce downhill movement (hereinafter, referred to as rollback) due to gravity when starting from a state of being stopped on a slope. Specifically, the electric vehicle can reduce rollback, for example, by generating a torque corresponding to a road surface gradient with a motor
Implementation Method 2
when the vehicle starts on a slope, it is assumed that a slight rollback occurs. However, in a case where one wheel of the front wheel and the rear wheel is on a road surface having a relatively low resistance, when the motor torque for reducing the rollback is generated as described above, the one wheel on the road surface having a low resistance may not grip the road surface, and may idle in a driving direction
Data Source
AI summary
A control method for an electric four-wheel drive vehicle including a front drive source for driving a front wheel and a rear drive source for driving a rear wheel independently of the front wheel includes: acquiring a driving direction of the electric four-wheel drive vehicle based on an input state of a shift lever; acquiring an actual moving direction of the electric four-wheel drive vehicle; and when the driving direction and the moving direction are different from each other, setting a basic driving force for suppressing movement in the moving direction for the front wheel and the rear wheel, and driving one wheel of the front wheel and the rear wheel with a driving force smaller than the basic driving force by implementing a limit for setting an upper limit value for a driving force generated in the one wheel.