Vehicle Slip Ratio Smoothing for Four-Wheel Drive Stability
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Solution Overview
Problem
Existing control devices for four-wheel drive vehicles often experience reduced fuel efficiency and stability issues due to calculation errors in slip ratio at low speeds, leading to inappropriate driving force distribution to auxiliary wheels, regardless of road surface friction.
Innovation Solution
A control device that calculates and smooths the slip ratio of main driving wheels, using a larger time constant for filtering at low vehicle speeds to stabilize driving force transmission to auxiliary wheels, ensuring appropriate force distribution and improved stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the control device always sets the drive mode to four-wheel drive mode when vehicle body speed is equal to or lower than a predetermined value, then driving stability is improved, but fuel efficiency is reduced and tight corner braking phenomenon occurs
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the time constant for slip ratio filtering based on vehicle speed. At low speeds, a larger time constant is used to smooth out calculation errors and maintain stable four-wheel drive operation, while at higher speeds, a smaller time constant allows for more responsive control. This enables the system to maintain driving stability when needed while avoiding unnecessary four-wheel drive engagement that would waste fuel.
2Power
If the driving force transmission device is controlled based on the slip ratio when the four-wheel drive vehicle is traveling at low speeds, then the driving force is transmitted to auxiliary driving wheels, but the driving force varies significantly due to calculation error of the slip ratio
Solution Approach 1:
The patent introduces an intermediary element - a filtering process with a time constant - between the raw slip ratio calculation and the driving force control. This filter acts as a mediator that smooths out the noisy slip ratio data at low speeds, preventing direct transmission of calculation errors to the driving force control system. The filtered slip ratio is then used for stable driving force distribution to auxiliary wheels.
3Reliability
If a larger time constant is used for filtering slip ratio at low vehicle speeds, then the impact of calculation errors is minimized, but the response time of the control system increases
Solution Approach 1:
The patent applies dynamics by making the time constant adjustable rather than fixed. The system dynamically changes the filtering characteristics based on vehicle speed conditions. At low speeds where calculation errors are significant, a larger time constant provides better filtering. At higher speeds where the slip ratio calculation is more accurate, a smaller time constant allows faster response. This dynamic adjustment optimizes both reliability and response time across different operating conditions.
Data Source
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AI summary
A control device 10 mounted on a four-wheel drive vehicle 1 includes: a slip ratio calculating unit 111 that obtains a slip ratio of main driving wheels based at least on wheel speeds; a smoothing unit 112 that smooths the slip ratio by filtering; and a driving force control unit 113 that controls a driving force transmission device 2 so that a driving force that is transmitted to auxiliary driving wheels increases as the slip ratio smoothed by the smoothing unit 112 increases. The smoothing unit 112 uses a larger time constant for the filtering when a vehicle speed is less than a predetermined value than when the vehicle speed is equal to or higher than the predetermined value.