Four-Wheel Drive Torque Control with Delay Element
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Solution Overview
Problem
Four-wheel drive vehicles experience behavior changes and track-out phenomena when the accelerator pedal is rapidly released, leading to unstable turning and reduced drivability due to uneven tire loads and lack of precise drive force control during cornering.
Innovation Solution
A drive force control method that adjusts the drive force distribution ratio between front and rear wheels and between right and left wheels by detecting lateral G signals, increasing rear wheel torque relative to front wheels and outer wheel torque relative to inner wheels, and adding a delay element to the estimated drive torque to stabilize vehicle behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drive force distribution ratio between right and left wheels is changed during accelerator release, then vehicle behavior stability deteriorates causing track-out, but maintaining fixed distribution reduces adaptability to changing driving conditions
Solution Approach 1:
The control device predicts future drive torque values and sets the drive force distribution ratio in advance based on predicted values, rather than reacting to actual torque changes. This preliminary action prevents sudden distribution changes that cause track-out while maintaining adaptability through continuous prediction updates.
Solution Approach 2:
The system adds a delay element to cushion against rapid torque changes at the trailing edge of accelerator depression. This beforehand cushioning prevents abrupt drive force distribution changes during accelerator release, stabilizing vehicle behavior while still allowing adaptive control through the delay mechanism.
2Speed
If drive force control is simplified without delay element, then response speed improves, but vehicle behavior stability deteriorates during accelerator release
Solution Approach 1:
The delay element is strategically applied only to the trailing edge of drive torque where accelerator release occurs, cushioning against harmful rapid changes. This provides stability during critical moments while maintaining fast response during normal acceleration, resolving the speed-stability contradiction.
Solution Approach 2:
The control system dynamically adjusts the delay element application based on accelerator depression state. The delay is applied selectively during accelerator release (trailing edge) rather than continuously, allowing fast response during normal operation while providing stability cushioning when needed.
3Productivity
If drive force distribution is adjusted rapidly during turning acceleration, then acceleration performance improves, but vehicle behavior becomes unstable causing track-out
Solution Approach 1:
The control device uses predicted drive torque values to adjust drive force distribution in advance, smoothing out rapid changes that would cause track-out. This maintains acceleration performance through continuous adaptation while preventing instability through predictive control.
Solution Approach 2:
The delay element cushions against rapid drive force distribution changes during accelerator release in turning conditions. This beforehand cushioning prevents track-out while allowing accelerated performance through controlled adaptation to changing torque demands.
Data Source
AI summary
In a drive force control method for a four-wheel drive vehicle using an estimated drive torque for the control, a delay element is added to a value for the estimated drive torque at the trailing edge thereof. With this control, the behavior of the four-wheel drive vehicle is stabilized when a depression force applied to an accelerator pedal is removed.