Fuel Cell Vehicle Braking Control for Scavenging Stability
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Solution Overview
Problem
Fuel cell vehicles equipped with regeneration-friction cooperative brakes experience a temporary decrease in regenerative braking force during the scavenging process, leading to instability in braking performance.
Innovation Solution
A control unit is implemented in the fuel cell vehicle to estimate stagnant water in the fuel cell, determine scavenging preparation conditions, and execute a responsiveness enhancement process before scavenging, ensuring stable braking force by adjusting the friction brake system's hydraulic pressure and optimizing the scavenging process timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the scavenging process is executed during braking by the regeneration-friction cooperative brake, then the stagnant water in the fuel cell is discharged, but the regenerative braking force temporarily decreases leading to unstable braking force
Solution Approach 1:
The control unit executes a responsiveness enhancement process before the scavenging process to increase the hydraulic pressure in the friction brake system. This preliminary action ensures that when the scavenging process causes regenerative braking force to decrease, the friction brake system can immediately compensate with enhanced responsiveness, thereby maintaining stable total braking force throughout the scavenging operation.
2Reliability
If the friction brake system responsiveness is enhanced by increasing hydraulic pressure before scavenging, then the braking force stability is improved, but the device complexity increases
Solution Approach 1:
The control unit integrates multiple functions into a single control system that manages both the scavenging process and the friction brake system responsiveness enhancement. By making the control unit multi-functional, the patent avoids adding separate dedicated systems for each function, thereby improving braking force stability without proportionally increasing device complexity.
3Productivity
If the scavenging process is performed during braking, then the fuel cell performance is maintained, but the regenerative braking force decreases due to increased electric power generation
Solution Approach 1:
The control unit applies preliminary anti-action by enhancing the friction brake system responsiveness before the scavenging process begins. This counter-measure is prepared in advance to offset the anticipated decrease in regenerative braking force that will occur when the fuel cell electric power generation increases during scavenging, thereby maintaining stable total braking force.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the responsiveness of the friction braking force, maintaining a stable regeneration-friction cooperative braking force even when the scavenging process is performed, thereby improving braking stability and efficiency.
Implementation Method 1
a fuel cell configured to generate electric power by electrochemical reaction between hydrogen and oxygen
Implementation Method 2
a drive motor configured to execute power running for driving the fuel cell vehicle, and regenerative operation for generating regenerative electric power to brake the fuel cell vehicle
Implementation Method 3
a master cylinder configured to generate hydraulic pressure of working fluid by a braking operation performed by a driver, wheel cylinders configured to apply braking force to wheels upon reception of the hydraulic pressure of the working fluid, and a hydraulic circuit configured to transmit the hydraulic pressure of the working fluid between the master cylinder and the wheel cylinders
Data Source
AI summary
A fuel cell vehicle includes a fuel cell, a gas supply unit, a friction brake system, a drive motor, an electric storage device, and a control unit configured to execute control of obtaining requested braking force with use of friction braking force and regenerative braking force and control of performing a scavenging process. When the fuel cell vehicle is in braking with the friction braking force and the regenerative braking force, the control unit is configured to determine whether or not a scavenging preparation condition is satisfied with use of the amount of stagnant water stagnating in the fuel cell, execute a responsiveness enhancement process when the scavenging preparation condition is executed, and execute a scavenging process when the responsiveness enhancement process is completed, and the amount of the stagnant water reaches a reference value.