Vehicle Braking Force Control With Fuel-Cut Downshift Smoothing
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Solution Overview
Problem
Existing vehicle braking/driving force control systems face challenges in achieving improved fuel efficiency and riding comfort, particularly when maintaining target vehicle speed on downhill slopes, as they often result in discontinuous changes in braking/driving force and insufficient fuel consumption reduction due to gear shifting and fuel cut cancellations.
Innovation Solution
A braking/driving force control system that includes a required acceleration calculating unit, powertrain control unit, and brake control unit, which dynamically adjusts fuel cut and gear shifting to maintain target vehicle speed by calculating and distributing the required braking/driving force between the powertrain and brake, ensuring continuous fuel cut and smooth force transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If fuel cut is performed in the engine to generate engine braking effect while maintaining target vehicle speed on downhill, then fuel consumption is reduced, but when transmission is downshifted to obtain further large engine braking effect, fuel cut is cancelled and fuel injection resumes, resulting in insufficient fuel consumption reduction
Solution Approach 1:
The control system dynamically adjusts the engine braking strategy based on vehicle speed and transmission gear stage. When vehicle speed is within a predetermined range above the downshifted gear stage speed, the system maintains fuel cut even during downshift to preserve engine braking effect and minimize fuel consumption. This dynamic adjustment resolves the contradiction by making the fuel cut state adaptive to operating conditions rather than automatically canceling during downshift.
Solution Approach 2:
The system changes the control parameter (fuel cut state) based on the relationship between vehicle speed and downshifted gear stage speed. By comparing actual vehicle speed with the speed range corresponding to the downshifted gear stage, the system determines whether to maintain or cancel fuel cut. This parameter-based control strategy enables the system to achieve both fuel consumption reduction and adequate engine braking effect by adjusting the fuel cut state according to specific operating parameters.
2Force
If transmission is downshifted to obtain larger engine braking effect, then braking force is increased, but braking/driving force changes discontinuously, deteriorating riding comfort
Solution Approach 1:
The control system dynamically manages the transition between gear stages by considering the vehicle speed relative to the downshifted gear stage speed range. When vehicle speed is within the predetermined range above the downshifted speed, the system maintains fuel cut and prevents automatic downshift, thereby avoiding discontinuous braking force changes. This dynamic control strategy smooths the transition and maintains riding comfort while still enabling adequate engine braking effect.
Solution Approach 2:
The system prepares for potential downshift by establishing a predetermined speed range buffer above the downshifted gear stage speed. This speed buffer acts as a cushion that prevents premature or inappropriate downshifts that would cause discontinuous braking force changes. By anticipating the downshift condition and maintaining fuel cut within this buffer zone, the system cushions against the harmful effect of abrupt braking force changes, thereby preserving riding comfort.
Data Source
AI summary
A braking/driving force control system, during control for maintaining a target vehicle speed, performs fuel cut and then, when a required braking/driving force for maintaining the target vehicle speed reduces, makes a downshift while fuel cut is continued. The braking/driving force control system causes a brake to generate a braking force such that the sum of a braking/driving force that a powertrain generates and the braking force that the brake generates agrees with the required braking/driving three. Thus, good fuel efficiency and riding comfort are obtained.