Power Brake Assist: Description and Operation

Description









Regeneration Brake System
During deceleration or braking of an electric vehicle or HEV, the drive motor acts as an alternator and charges the battery by converting the vehicle's kinetic energy generated during braking into electrical energy.
Regenerative braking amount depends on the vehicle speed, battery SOC, etc.
Achieves significant improvement in fuel efficiency in city driving with repeated acceleration and deceleration.

Regenerative Braking Cooperation Control (RBC)




The brake force apportion is distributed by controlling hydraulic braking and the total brake force (hydraulic + regenerative brake) output that the driver requires is generated.
In the case of regenerative brake failure, the total brake force that the driver requires is supplied by the hydraulic brake system.
The following are the details of regenerative braking cooperative control.
- The red wire in the diagram indicates hydraulic pressure change.
- "I": Braking is conducted by the regenerative braking (Initial stage of braking).
- "II": Braking is conducted by the hydraulic brake.
- "III": Regenerative braking range extends as hydraulic brake decreases.
- "IV": Rapidly increasing of hydraulic pressure to meet the required brake amount because the regenerative braking is dropping due to very low kinetic energy when the vehicle almost comes to a stop.

System Features and Components
The AHB system is composed of the hydraulic power unit, the brake actuation unit, and electric stability control.
The Hydraulic Power Unit generates the hydraulic pressure required for braking.
Similar to the boosting effect when the driver steps on the brake pedal in a system equipped with a vacuum booster, the hydraulic pressure stored in the cylinder is supplied to provide pressure throughout the entire brake line.
The brake actuation unit delivers pressure that is generated by the Hydraulic Power Unit to a caliper on each wheel via electric stability control. It is connected to the brake pedal to detect the brake force that is required by the driver, and to generate a brake feeling.
Electric stability control carries out the ABS, TCS, and ESC functions as in conventional vehicles.




AHB System Operation Principals

1. Initial Status
The internal components of the HPU include 3 Normally Open (NO) valves, 2 Normally Close (NC) valves and a motor pump. The NO VALVE 3 is connected to the Simulator Chamber of the Brake Actuation Unit and it is opened when the brake is not engaged and closed when the brake is engaged.
The NO VALVE 1 and 2 are mounted between the boosting chamber and the reservoir tank of the brake actuation unit. When they are opened, the pressure in the boosting chamber is reduced.
The NC VALVE 1 and 2 are mounted between the high pressure generating motor pump and the boosting chamber. The pressure generated by the motor pump is cut off from the boosting chamber when closed and is fed to the boosting chamber when opened.










2. Base Brake Function
During normal braking, NO VALVE 1, 2, and 3 are in the ON status and closed. The pump either turns on or off according to the chamber status.
At this point, the NC VALVE 1 and 2 become ON and opened. The pressure generated by the pump is supplied to the boosting chamber and pressure is formed in the cylinder.






NOTE:
- Motor : when charging Accumulator





3. RBCS Function
When the regenerative brake cooperation system (RBCS) is engaged, the NO VALVE 1, 2 and NC VALVE 1, 2 control the amperage to reduce or increase the pressure in the boosting chamber that operates regenerative braking.
When the hydraulic braking pressure increases, regenerative braking decreases from the total brake force (driver required brake force). When the hydraulic braking pressure decreases, regenerative braking force increases. As a result, the generated electricity also increases.






NOTE:
- Motor : when charging Accumulator





4. Back-up Brake Function: 4 Wheel Back-up / ESC Hydraulic Brake Boost
Describes brake circuit in case of Hydraulic Power Unit (HPU) failure.
As shown in the diagram, all valves are not active in the HPU. Because NO VALVE3 is not operating, the simulator chamber pressure is not generated when the brake pedal is engaged as the brake field of the simulator chamber is linked to the reservoir tank. However, when the simulator rod begins to move as the brake pedal is engaged, the boosting chamber rod is mechanically pushed. This generates pressure in the master cylinder. This pressure is transferred to the ESC, which then controls the wheels in pressurized mode to achieve braking. The ESC therefore controls braking if the HPU fails.









Circuit Diagram - HPU




HPU connector input/output