Brakes - AHB Brake System/Regenerative Braking Info.
Group: BRAKESNumber: 11-BR-001
Date: MARCH 2011
Model: SONATA HYBRID (YF HEV)
Subject
INTRODUCTION OF YF HEV AHB SYSTEM AND
REGENERATIVE BRAKING
DESCRIPTION:
This bulletin provides information about the Active Hydraulic Boost (AHB) brake system applied to YF hybrid vehicles. It also describes regenerative braking and how kinetic energy generated during braking is converted and used as electrical energy.
REGENERATIVE BRAKING
1. Principle of Regenerative Braking
Driver-required brake force = regenerative braking force + hydraulic braking force
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 into electrical energy.
This helps achieve a significant improvement in fuel efficiency in city driving with repeated acceleration and deceleration.
2. Cooperative Control of Regenerative Braking and Hydraulic Braking
Regenerative braking is a process in which kinetic energy that is generated during vehicle deceleration and braking is converted into electrical energy. This electrical energy is used to charge the battery.
Total brake demand by a driver is distributed between both the regenerative brake and hydraulic brake systems.
The regenerative braking amount is determined by the vehicle speed and battery recharge amount.
3. Regenerative Braking Cooperative Control (RBC)
*Red curve in the diagram: Hydraulic pressure change
- The brake force is distributed by controlling hydraulic braking and the total brake force (hydraulic + regenerative brake) output that the driver is required to generate.
- In the case of regenerative brake failure, the total brake force that the driver requires is supplied by the hydraulic brake system.
- "I": Braking is conducted by regenerative braking (Initial stage of braking).
- "II": Braking is conducted by the hydraulic brake.
- "III": Regenerative braking range extends as hydraulic braking decreases.
- "IV": Rapidly increasing hydraulic pressure to meet the required brake amount because regenerative braking is decreasing due to very low kinetic energy when the vehicle is almost stopped.
AHB (ACTIVE HYDRAULIC BOOST) SYSTEM
1. System Composition and Features
System Composition and Features
The AHB system is composed of the hydraulic power unit, the brake actuation unit, and electronic stability control.
- HPU (Hydraulic Power Unit)
It 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 brake lines.
- Brake Actuation Unit
It delivers pressure that is generated by the Hydraulic Power Unit to a caliper on each wheel via electronic 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.
- Electronic Stability Control
It carries out the ABS, ICS, and ESC functions as in conventional vehicles.
2. AHB system Calibration Diagnosis Service by GDS tool
SAS (Steering Angle Sensor) Offset Calibration Diagnosis Service
Absolute angle type (CAN type) steering angle sensor calculates the angle based on
the preset zero. Therefore, it requires zeroing when the SAS is first installed.
When to Conduct Zeroing Adjustment:
- After replacing SAS
- After replacing or repairing the steering column
- When the following error codes are generated
C1260 (steering wheel angle sensor signal error)
C1261 (steering wheel angle sensor not zeroed)
Zeroing Procedure/Order:
Use the GDS to input the zeroed value of the SAS into the ECU.
NOTE:
To verify that SAS calibration was successfully completed after SAS calibration, conduct a drive test (1 left turn and 1 right turn). Calibration is successful if the warning lamp does not come on.
NOTE:
Zeroing must be conducted with the front wheels aligned in a straight line with a margin of error less than +/- 5.
Yaw Rate & 2G Sensor Offset Adjustment
The yaw rate and 2G sensor are important sensors responsible for ESC control and Hill-start Assist Control (HAG). Offset occurs based on the flatness of the mount, so offset adjustment is required with the initial mount status set as the base value.
When to Conduct Zeroing Adjustment
- After changing yaw rate and 2G sensor
- After changing ESC ECU
- When the error code C1285 (offset adjustment not set) is detected
Zeroing Procedure/Order
Use the GDS to input the zeroed value of the SAS into the ECU.
NOTE:
The yaw rate and 2G sensors are important sensors responsible for ESC control and hill-start assist control (HAC). Because output is different according to the flatness of the mount, offset adjustment is necessary.
NOTE:
The yaw rate and 2G sensors are direction-sensitive. Take caution during installation.
NOTE:
The mounting location must be within 30 cm of the central weight point of the vehicle so its facing direction and mounting position must not be changed.
Brake Pedal Travel Sensor Adjustment Diagnosis Service
The brake pedal travel sensor calculates the pedal full stroke according to the preset zero. Therefore, zeroing adjustment is necessary when the brake pedal assembly is first installed.
When to Conduct Zeroing Adjustment
- After changing the brake pedal assembly
- When error codes C1380 (calibration) or C1379 (signal error) are detected.
Zeroing Procedure/Order
Use the GDS to input the zeroed value of the SAS into the HECU.
NOTE:
The brake pedal travel sensor is not a separate service part. The entire pedal assembly must be replaced in case of sensor failure. Conduct calibration after replacing the assembly.
NOTE:
The calibration must be done while the vehicle is parked without stepping on the brake pedal and while there is no vibration of the vehicle.
Pressure Sensor Adjustment Diagnosis Service
The pressure sensor mounted within the HPU calculates the pressure according to initial zeroing. Therefore, initial zeroing adjustment is required when the HPU is installed for the first time.
When to Conduct Zeroing Adjustment
- After replacing HPU
Zeroing Procedure/Order
Use the zeroing tool to input the zeroed value of the pressure sensor into the HECU.
3. AHB HPU Bleeding & Filling Process (A/S, Wet type)
NOTE:
A pressurizing device is required to supply pressure to the reservoir.
NOTE:
Bleeding and filling without using a pressurizing device is not possible.
System Bleeding & Filling Process
Air bleeding must be conducted when replacing the Hydraulic Power Unit (HPU) or the Brake Actuation Unit (BAU).
1. Disconnect the battery negative terminal from the auxiliary battery installed in the trunk.
2. Turn the ignition switch to OFF. Connect the pressurizing device (SST # S 09580-3D100 and 09580-3D200) to the reservoir tank, and then air-bleed the HPU and BAU.
3. Air-bleed wheel lines first, then the ESC module.
4. Connect the battery negative terminal to the auxiliary battery and turn the ignition switch to ON.
5. Depress the brake pedal and air-bleed the HPU and BAU.