05-07-2013, 12:15 PM
ELECTRO HYDRAULIC BRAKE SYSTEM
ELECTRO HYDRAULIC.ppt (Size: 908 KB / Downloads: 129)
INTRODUCTION
This is a system which senses the driver's will of braking through the pedal simulator and controls the braking pressures to each wheels
The system is also a hydraulic Brake by Wire system.
In the true sense of the definition, any EHB vehicle may be braked with an electrical “joystick” completely independent of the traditional brake pedal.
Hydraulic fluid is used to transmit energy from the actuator to the wheel brakes.
HYDRAULIC DESIGN CONSIDERATIONS
EHB supplies a braking force proportional to driver input, which reduces braking effort.
The boost characteristics also contribute to the pedal “feel” of the vehicle.
If the boost source fails, the system resorts to manual brakes where brake input energy is supplied in full by the driver.
Conventional vacuum boosted system
The conventional system utilizes a largely mechanical link all the way from the brake pedal through the vacuum booster and into the master cylinder piston.
Proportional assist is provided by an air valve acting in conjunction with the booster diaphragm to utilize the stored vacuum energy.
The piston and seal trap brake fluid and transmit the hydraulic energy to the wheel brake.
Pedal Force Emulator – Master Cylinder (PFE-MC)
The unit consists of a master cylinder with emulator piston and spring assembly.
As the driver’s foot applies the brake pedal, an input push rod displaces the primary master cylinder piston, while at the same time the isolation valves in the HCU are commanded to close.
This blocks both primary and secondary master cylinder outlet ports. The secondary piston becomes locked in place due to the trapped fluid.
The fluid contained by the primary piston is displaced into the drill path, which leads to the emulator assembly.
As pressure continues to build, the spring begins to deform under the load from the hydraulic pressure acting on the surface of the piston.
This causes the brake pedal to move in proportion to the force exerted by the driver.
Comparison of EHB & Conventional Braking System
Reduces Braking Effort in EHB
the pedal forces vs. vehicle deceleration characteristics are significantly affected in EHB
pedal force input limit of 500 N, the difference between the resulting brake line pressure is 2.5 MPa unboosted vs. 8.5 MPa boosted - vehicle deceleration is achieved easily
largely mechanical link is used in conventional
CONCLUSION
EHB design allows system flexibility, inherent accumulator precharge isolation, and the ability to tune for optimum failed system stopping performance for all vehicle classes.
A carefully designed and implemented EHB system holds the promise of enabling the new brake-by-wire features while still reliably performing the everyday task of stopping the vehicle.
ELECTRO HYDRAULIC.ppt (Size: 908 KB / Downloads: 129)
INTRODUCTION
This is a system which senses the driver's will of braking through the pedal simulator and controls the braking pressures to each wheels
The system is also a hydraulic Brake by Wire system.
In the true sense of the definition, any EHB vehicle may be braked with an electrical “joystick” completely independent of the traditional brake pedal.
Hydraulic fluid is used to transmit energy from the actuator to the wheel brakes.
HYDRAULIC DESIGN CONSIDERATIONS
EHB supplies a braking force proportional to driver input, which reduces braking effort.
The boost characteristics also contribute to the pedal “feel” of the vehicle.
If the boost source fails, the system resorts to manual brakes where brake input energy is supplied in full by the driver.
Conventional vacuum boosted system
The conventional system utilizes a largely mechanical link all the way from the brake pedal through the vacuum booster and into the master cylinder piston.
Proportional assist is provided by an air valve acting in conjunction with the booster diaphragm to utilize the stored vacuum energy.
The piston and seal trap brake fluid and transmit the hydraulic energy to the wheel brake.
Pedal Force Emulator – Master Cylinder (PFE-MC)
The unit consists of a master cylinder with emulator piston and spring assembly.
As the driver’s foot applies the brake pedal, an input push rod displaces the primary master cylinder piston, while at the same time the isolation valves in the HCU are commanded to close.
This blocks both primary and secondary master cylinder outlet ports. The secondary piston becomes locked in place due to the trapped fluid.
The fluid contained by the primary piston is displaced into the drill path, which leads to the emulator assembly.
As pressure continues to build, the spring begins to deform under the load from the hydraulic pressure acting on the surface of the piston.
This causes the brake pedal to move in proportion to the force exerted by the driver.
Comparison of EHB & Conventional Braking System
Reduces Braking Effort in EHB
the pedal forces vs. vehicle deceleration characteristics are significantly affected in EHB
pedal force input limit of 500 N, the difference between the resulting brake line pressure is 2.5 MPa unboosted vs. 8.5 MPa boosted - vehicle deceleration is achieved easily
largely mechanical link is used in conventional
CONCLUSION
EHB design allows system flexibility, inherent accumulator precharge isolation, and the ability to tune for optimum failed system stopping performance for all vehicle classes.
A carefully designed and implemented EHB system holds the promise of enabling the new brake-by-wire features while still reliably performing the everyday task of stopping the vehicle.