Vehicle Braking Force Control for Slip and Stability
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Solution Overview
Problem
When regenerative braking force is applied to steered front wheels, braking force replacement during anti-skid control can lead to understeer conditions due to insufficient lateral force, and the delay in increasing friction braking force results in decreased vehicle deceleration, causing discomfort to occupants.
Innovation Solution
A method that calculates a target braking force and controls regenerative and friction braking forces by reducing regenerative braking and increasing friction braking over time, with a provisional target regenerative braking force lower than the initial value, to manage braking slip and maintain vehicle stability and deceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If braking force replacement is carried out by decreasing regenerative braking force to 0 and gradually increasing friction braking force, then the braking slip of the wheel is alleviated, but the deceleration of the vehicle decreases causing discomfort to occupants
Solution Approach 1:
The patent applies preliminary action by increasing friction braking force in advance before regenerative braking force is completely reduced to 0. The friction braking force is increased at a rate higher than the decrease rate of regenerative braking force during the transition period, ensuring that total braking force is maintained or increased. This preliminary increase in friction braking force compensates for the delay in friction braking response and prevents deceleration loss, thereby maintaining occupant comfort while preparing for effective braking slip control.
2Reliability
If braking force replacement is carried out in preparation for anti-skid control with regenerative braking force applied to front steered wheels, then braking slip is controlled, but the vehicle falls into understeer condition due to shortage of lateral force of front wheels
Solution Approach 1:
The patent applies local quality by differentiating the braking force replacement strategy between front steered wheels and other wheels. When regenerative braking is applied to front steered wheels during turning, the system prioritizes maintaining lateral force by controlling the replacement rate. The friction braking force is increased at a moderated rate that does not exceed the decrease rate of regenerative braking force, preserving the braking slip necessary for generating lateral force. This localized adjustment prevents understeer condition while still providing effective braking slip control.
3Reliability
If friction braking force is increased from 0 with a command to increase, then the braking force replacement is executed, but the friction braking force does not increase at once due to pressure increase period in wheel cylinder and brake actuator response delay
Solution Approach 1:
The patent applies preliminary action by anticipating the delay in friction braking force increase and compensating in advance. The control system calculates the expected delay based on wheel cylinder pressure increase characteristics and brake actuator response time. Friction braking force is increased earlier and at a higher rate than the regenerative braking force decrease rate, so that the total braking force is maintained or increased during the transition. This preliminary compensation ensures that the effective braking force is not lost during the actuator response delay.
Solution Approach 2:
The patent applies feedback by continuously monitoring the actual friction braking force increase and comparing it with the commanded increase. The control system adjusts the friction braking force increase rate based on feedback from wheel cylinder pressure sensors and brake actuator status. This closed-loop control ensures that the friction braking force increases at the appropriate rate to compensate for delays while preventing excessive braking force that could cause understeer or discomfort.
Data Source
AI summary
A braking force control method that is applied to a vehicle in which regenerative braking force and friction braking force are applied to the front wheels. When the braking slip quantity of one of the front wheels that is supplied with regenerative braking force exceeds a reference value, with the instance being a reference time point, the friction braking force of the front wheels is controlled so as to increase while the regenerative braking force being controlled so as to be a provisional target regenerative braking force that is lower by a prescribed value than the regenerative braking force of the front wheels at the reference time point. When a decision is made that a prescribed period of time has passed since the reference time point, the regenerative braking force is gradually decreased and the friction braking force is gradually increased.