Esp Control Brake System Against Under- or Over-Revving Phenomenon

4. Reduce pressure

Figure 31. 65. Case of pressure reduction.

- When the pressure acting on the brake pedal is relieved, the pressure of the master cylinder decreases. Then, the feedback force (to the right) of the regulator piston becomes relatively larger, causing the regulator piston to retract and the slide valve to retract. Therefore, the port “A” between the reservoir and the booster chamber opens.

- In this state, the pressure of the booster is reduced, creating a balance corresponding to the new force applied through the brake pedal. This process is repeated to reduce the pressure of the master cylinder according to the force applied through the brake pedal.

5. During a power supply failure

- If the accumulator pressure is affected by any fault, the booster chamber will not be supplied with hydraulic pressure. Therefore, no assistance can be generated for the force applied through the brake pedal and no pressure can be increased for the rear brakes.

- However, the pressure to the front brakes increases at the master cylinder piston according to the force applied to the brake pedal.

Figure 31.66. Pressure of the accumulator.

7. ELECTRONIC VEHICLE STABILITY PROTECTION SYSTEM (ESP)

Electronic Stability Program (ESP) is an active safety system that improves vehicle stability in all driving situations. This system is equipped on current cars such as Mercedes, BMW...

The ESP system (figure) works by intervening in the braking system, which can act individually on one or more wheels on the front or rear axle. ESP helps stabilize the vehicle when braking, when cornering, when starting off and accelerating. To enhance effective braking control, ESP also acts on the engine and transmission.

Figure 31. 67. ESP system diagram on Mercedes cars

1. Wheel speed sensor

2. Diagnostic connector cluster
3. ESP electronic control box	4. ESP off switch
5. ABS warning light	6. ESP indicator light
7. EPC indicator light	8. Horizontal acceleration sensor
9. Control box to slow down the vehicle's rotational torque	10. ESP fault indicator light
11. Steering angle sensor	12. Brake warning switch
13. ESP supply pump	14. Parking brake switch
15. Master cylinder pressure sensor	16. Master cylinder
17. ESP hydraulic actuator

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The ESP system includes the linkage and integration of the following systems and functions:

- The ABS system prevents the wheels from locking when braking, thus maintaining steering ability and vehicle stability while decelerating.

For example, if a particular wheel tends to lock up (the phenomenon of the wheel sliding on the road surface), the brake pressure on that wheel will be controlled. This control is controlled by the hydraulic actuator. The solenoid valves

The actuator will regulate the brake pressure through the stages of pressure increase, pressure holding and pressure reduction.

- The ASR (Acceleration Slip Regulator) system corrects the phenomenon of the driving wheels slipping when starting and accelerating suddenly. It also helps improve the stability of the vehicle by adjusting the traction of the driving wheels.

- When any active wheel is spinning, the wheel speed sensor sends this signal to the electronic controller. The electronic controller controls the hydraulic actuator to supply brake fluid to that wheel. The brake pressure is also controlled in boost, hold and depressurize modes.

- Simultaneously with brake control, the ESP system also sends a signal to the engine control box, controlling the throttle position to close or slowing the ignition timing to reduce engine torque.

The EBR (Engine Brake Regulation) system prevents the active wheels from slipping when coasting and ensures vehicle stability.

When the car coasts (for example, going downhill), the throttle valve closes, and there will be an engine brake. If the engine resistance is too great, it will cause the active wheels to slip. The ESP control box recognizes this phenomenon and sends a signal to the engine control box, increasing the engine torque to reduce the slippage of the active wheels. This process takes place without the driver being aware of it.

ESP corrects understeer or oversteer. In all situations, it ensures that the vehicle does not deviate from the driver's control direction.

Figure 31.68. ESP controls the braking system against under- or over-rotation.

When understeering or oversteering occurs, the ESP system will detect it through the steering angle sensors and lateral acceleration sensors, automatically controlling a precise braking force to the corresponding wheels on the front or rear axle to maintain the vehicle's direction of movement according to the driver's control. Figure (a) shows that when the vehicle tends to understeer, ESP controls the braking of the left rear wheel, and when the vehicle tends to oversteer, ESP controls the braking of the left rear wheel.

In the case of an excessive turn (figure b), ESP controls the braking of the right front wheel, thus helping to stabilize the vehicle when turning.

At the same time as controlling the brakes, the ESP system also sends a signal to the engine control box, controlling the reduction of engine torque. Thanks to that, the vehicle achieves high stability when turning.

8. SOME ABS BRAKE SYSTEM DIAGRAM (REFERENCE)

a. 2-position 4-way solenoid valve with priority control valve (4)

b. 2-position 6-way solenoid valve with pressure control valve

c. 2-position solenoid valve (6)

d. 2-position solenoid valve (8)

e. 3-position solenoid valve 3 with shut-off valve (1)

f. 3-position solenoid valve (5)

REVIEW QUESTIONS

Question 1. Describe the tasks and requirements of the ABS braking system.

Question 2. Describe the method of classifying ABS braking systems.

Question 3. Structure diagram and operating principle of ABS braking system. Question 4. Describe the structure and operation of wheel speed sensor.

Question 5. Describe the structure and operation of the deceleration sensor on the ABS braking system.

Question 6. Describe the structure and operation of the hydraulic actuator on the ABS braking system.

Question 7. Describe the structure and operation of the ECU on the ABS braking system. Question 8. Describe the operation of the ABS braking system with EBD support.

Question 9. Describe the operation of the BAS emergency brake assist system on the ABS braking system.

Question 10. Describe the operation of the TRC and VSC support systems.

MD 31.02. REMOVAL AND INSTALLATION OF ABS BRAKE SYSTEM

* Introduce

During the operation of the ABS braking system, it is inevitable that there will be damages. To check and fix those damages, the technician must disassemble and reassemble the system. This part of the course will equip students with the process of disassembling and reassembling the ABS braking system and the notes during the disassembling and reassembling process.

* Target:

- Choose the right disassembly tool

- Perform correct operations and technical requirements when disassembling and assembling.

- Disassemble, identify and check ABS brake drive according to technical requirements.

- Comply with procedures and regulations in automotive technology

- Train students' discipline, carefulness and meticulousness.

* content:

1. PROCEDURE FOR REMOVING, INSTALLING AND CHECKING THE ABS BRAKE SYSTEM

1.1. Prepare tools

a. Repair documents

- As automotive technology advances, new systems and features are introduced into new vehicle models. As a result, it is becoming increasingly difficult for technicians to repair highly complex vehicles based solely on their own experience.

- To inform repair personnel worldwide about proper repair procedures and new technologies, manufacturers publish various types of documents: Repair manuals, EWD (Electrical Circuit Diagram) books, SST (Special Repair Tool) lists, NCF (New Vehicle Specification) books, SDS (Repair Information Sheets), owner's manuals, and others.

b. Lubrication

Figure 31. 69. Lubricating materials

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