Four-Wheel Drive Speed Difference Modulation for Stability
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Solution Overview
Problem
Existing methods for controlling speed differences between the front and rear wheels of four-wheel drive vehicles, such as those disclosed in US Pat. No. 5,752,211, compromise vehicle stability due to modifications in the regulation loop for torque distribution.
Innovation Solution
A method that modulates the initial speed difference setpoint as a function of various vehicle operating parameters, including clutch temperature, turning radius, and wheel radius differences, without altering the regulation system, using intermediate blocks and filtering to adjust the final speed difference setpoint before comparison with measured values, ensuring stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the regulation loop is modified to control speed difference between front and rear axles, then speed difference control is improved, but vehicle stability is compromised
Solution Approach 1:
The control system is segmented into two independent parts: a regulation loop that maintains vehicle stability and a modulation system that adjusts speed difference setpoints. The modulation block processes multiple intermediate setpoints (clutch temperature, turning radius, wheel radius differences) separately from the regulation loop, allowing speed difference control without compromising the stability-guaranteeing regulation system.
Solution Approach 2:
A modulation block is introduced as an intermediary between the setpoint generation and the regulation system. This intermediary processes multiple intermediate speed difference setpoints based on various vehicle parameters and produces a final modulated setpoint that is fed to the regulation system, enabling flexible speed difference control while preserving the original regulation loop's stability properties.
2Adaptability or versatility
If multiple vehicle parameters are considered for speed difference control, then control flexibility is improved, but system complexity increases
Solution Approach 1:
The complex control requirements are segmented into multiple independent intermediate setpoints, each based on a specific vehicle parameter (clutch temperature, turning radius, wheel radius differences). This segmentation allows each parameter to be processed independently through separate blocks, making the overall complex system manageable and modular while maintaining high control flexibility.
Solution Approach 2:
The modulation block serves multiple functions simultaneously: it processes multiple intermediate setpoints from different vehicle parameters, applies appropriate weighting or selection logic, and generates a single final speed difference setpoint. This multi-functionality approach consolidates complex control logic into a universal block that handles all parameter considerations without requiring separate complex systems for each parameter.
Data Source
AI summary
The invention relates to a method for controlling a speed difference between the speed of the wheels of the front axle and the speed of the wheels of the rear axle of a four-wheel drive vehicle. The invention is characterised in that the method comprises the following steps: determining an initial speed difference set point (Cinitial) based on the speed of the vehicle; determining one or more intermediate speed difference set points (Ci2,Ci3,Ci4) based on one or more operational parameters of the vehicle; modulating the initial speed difference set point (Cinitial) based on the intermediate speed difference set points (Ci2,Ci3,Ci4) in order to obtain a final speed difference (Cfinal) set point; measuring the speed difference and comparing the measured speed difference with the final speed difference set point (Cfinal); and controlling the measured speed difference, so that the measured speed difference reaches the final speed difference set point (Cfinal).