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Anti-lock brakes
Anti-lock brakes (ABS) controls the hydraulic pressure in the actuator brakes on all four wheels when braking and braking on a dangerous road surfaces, which prevents the wheels from locking. Cycle braking and free-wheel speed is very fast, and continues until the vehicle stops or until you release the brake pedal. At the maximum braking even under icy, the wheel is continued to some extent rotated to provide the desired retention on the vehicle trajectory. The advantages of ABS: - Provides control car with a high degree of reliability even under heavy braking; - Stops the car in case of emergency braking, while maintaining stability and controllability even in the corners. If malfunctions are provided diagnostic function and safety (backup) system. Hydraulic Electronic Control Unit (HECU) received from the wheel speed sensors signals speed and direction of the vehicle, road conditions. Based on these signals, the control unit determines the optimum value of wheel slip.
Electronic brake force distribution (EBD) The device is an electronic brake force distribution (EBD) is set in place further pressure regulator to ensure a perfect distribution of brake pressure to the brakes of the front and rear wheels. This prevents the rear wheels from locking during braking and provides improved braking performance when used. The advantages of the electronic brake force distribution: - Functional improvement of the basic braking system; - Compensation of different coefficients of traction; - No need to install a pressure regulator; - Determination of a fault with the help of the control system.
| Fig. 6.3. A comparison of the regulator pressure (A) and a system of electronic brake-force distribution (B): a - a fixed pressure distribution; b - ?�dummy" pressure distribution; to - a point of inflection; d - the starting point of the work EBD
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Compare the work and the pressure regulator of the electronic brake force distribution (EBD) is shown in Fig. 6.3.
Traction control system (TCS) Traction control system is designed to increase traction during acceleration and cornering. If the wheel speed exceeds the speed of the car at a certain predetermined value, the HECU detects that the drive wheels are slipping, and outputs a signal traction control, reducing engine power. Based on information from the wheel sensors the control unit detects bumps on the frequency of vibration of the wheel. Then it sends a signal to the starter TCS control valve system, and an electronic control unit (ECM) reduces the power of the engine, thereby improving the acceleration efficiency. Based on information from the wheel sensors control unit determines the effectiveness of tire grip, and sends a signal to the starter control valve system TCS - electronic control module (ECM) reduces the power of the engine, thereby increasing the grip.
Check the voltage at the terminals of the connector Hydraulic block HECU
| Fig. 6.4. Pin connector Hydraulic block HECU
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During the function test the anti-lock braking system is first necessary to check the voltage and resistance in the connector pins of the hydraulic block HECU (Fig. 6.4), which must conform to the values given in Table. 6.2.
Table 6.2 Voltage and resistance at connector pins Hydraulic block HECU
Removal of air from a hydraulic drive of brakes with scanner use This operation must be carried out to ensure proper venting and filling of brake fluid unit ABS, brake tubes and master cylinder. 1. Remove the lid from the tank and fill it with fresh brake fluid reservoir to the upper mark.
WARNINGS Do not spill the brake fluid on the painted surfaces of the car, otherwise wash off the brake fluid. |
When removing the air under pressure, do not press the brake pedal. Recommended brake fluid: DOT 3 or equivalent.
| Fig. 6.1. Connecting the tube to the screw to remove the air from the hydraulic circuit brake system
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2. Attach one end of a transparent plastic tube onto the bleed screw and immerse the other end of the tube into a transparent plastic container half filled with brake fluid (see. Fig. 6.1).
| Fig. 6.5. Connecting the device to the Hi-Scan diagnostic connector
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3. Connect the scanner to the diagnostic connector located under the front panel (Fig. 6.5). 4. Select the mode of operation in accordance with the instructions on the screen of the scanner.
A WARNING It is necessary to sustain maximum engine performance ABS with a scanner to prevent burnout of the motor pump. |
Select diagnostics of cars Hyundai (Hyundai vehicle diagnosis). Select the name of the car SONATA. Select the anti-lock brakes (Anti-Lock brake system). Select venting (air bleeding mode). Click ?�YES?� to start the motor pump and solenoid valve. Turning ?�ON?� and shutdown ?�OFF?� will take place automatically in order to avoid burnout of the electric pump motor. 5. Press the brake pedal a few times, and then unscrew the screw to remove the air and wait until then, until the liquid begins to flow without any air bubbles. Without releasing the pedal, tighten the screw of removal of air.
| Fig. 6.2. Sequence of removal of air from a hydraulic drive of brakes
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6. Repeat steps p. 5 for each wheel in the sequence shown in Fig. 6.2 as long as the brake fluid (for each wheel) is not air bubbles. 7. Tighten the screw to remove the air torque 7-13 Nm.
Comments on the determination of fault When the anti-lock braking system can occur phenomenon in Table. 6.3, which are normal. Conditions for diagnosis will vary depending on the diagnostic code. When checking the symptom after erasing fault diagnostic code, make sure that the conditions specified in the remarks.
Table 6.3 Is a normal phenomenon that can occur when using an anti-lock brake system
Fault codes Determining fault codes with an instrument Hi-Scan 1. Turn off the ignition.
| Fig. 6.6. Pin assignment of the diagnostic socket: 1 - connection with "weight"; 2 - wire K; 3 - ABS; 4 - "B +" (positive voltage from the battery); 5 - airbag
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2. Connect the Hi-Scan scanner to diagnostic connector located under the front panel (Fig. 6.6). 3. Turn on the ignition. 4. Use the Hi-Scan scanner, check for diagnostic codes. 5. After repair or adjustment, turn off the ignition and the reset button to erase the codes in memory. 6. Remove the scanner Hi-Scan. Codes and fault causes the brake system are given in Table. 6.4.
Table 6.4 Fault codes tomoznoy system
Check ABS sensor output voltage Lift the car and lower the parking brake lever. Remove the pin from the Hydraulic block HECU and take measurements from the connector located on the side of wires.
A WARNING Remove the double protection pin and insert the probe into the meter connector harness side (rear). When installing the probe from the contacts is difficult to ensure reliable connection. |
Rotate the wheel under test at 1 / 2-1 min -1 and check the ABS sensor output voltage with a voltmeter or oscilloscope. Pin Numbers to check the output voltage of the ABS sensors the respective wheels are shown in Table. 6.5.
Table 6.5 Pin Numbers to check the output voltage of the ABS sensors the respective wheels
Hydraulic and electronic block HECU The hydraulic unit is installed in the engine compartment and is located between the brake pipes from the master cylinder and the brake lines to the wheel brakes. In accordance with commands from the electronic control unit, a pressure applied to the wheel brake, either maintained at a constant level either decreases or increases again. However, the pressure can be higher than established in the master cylinder when the brake pedal. Control pressure distribution is carried out by solenoid valves. When the windings of the solenoid valves are not energized, the brake pressure is increased by increasing the braking of the wheels. If through the coils maximum current flows, pressure drop occurs, the wheels are released, thereby increasing the frequency of their rotation. With an average current of pressure is maintained at one level, and the deceleration of the wheels is not changed. To reduce the pressure of the brake fluid coming out of the master cylinder can not simply disappear, as the brake pedal is still fully depressed, so she pumped a powerful return pump back into the master brake cylinder. This is evident in the small pulsations of the brake pedal, which begin with the entry into force of the return pump means and the launch of ABS. If you listen carefully, you can hear the noise generated by running the pump, which is reduced by the use of sound insulation of the hydraulic unit. The electronic control unit lock system is located directly on the hydraulic unit, and based on the information from the sensors controls the solenoid valves, excluding the wheels from locking during braking. Along with the signal processing and control valves further control unit also performs the diagnostic function. The unit monitors and detects a fault in the electrical circuits or elements anti-lock system, as well as the operating voltage in the vehicle electrical system. In the event of a fault in the instrument cluster warning lamp. Withdrawal Remove the pin HECU (the hydraulic and electronic control unit) and engine. Disconnect the brake pipes from the hydraulic unit HECU.
| Fig. 6.7. Location bracket bolts and block HECU
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Remove the bracket bolts HECU block and remove the block HECU (Fig. 6.7).
WARNINGS Never dismantle the HECU. The unit to be transported and stored vertically, with the plugged holes. The liquid from the HECU block it from draining. |
Setting Installation is performed in reverse order of removal. Tighten modulator 8-10 Nm brake pipe nuts 13-17 Nm.
Wheel speed sensor Speed sensors, one at each wheel, the wheel speed is measured on the basis of their signals in the electronic control unit calculates the average speed approximately corresponding to the vehicle speed. By comparing the rotational speed of each wheel with an average speed calculation, the electronic unit detects the status of the individual wheel slippage and thus establishes a wheel is in a state of predblokirovochnom. Speed sensors consisting of a magnetic armature coils are installed with a small clearance from the toothed rotor rotating with the wheel. Each tooth of the rotor, passing the sensor, the sensor induces a short voltage pulse. Thus, the sensor generates an alternating voltage whose frequency is increased or decreased in accordance with the frequency of rotation of the wheel, and transmits it to the control unit. Withdrawal
| Fig. 6.8. Wheel speed sensor: 1 - gear; 2 - front wheel speed sensor, 8-9.5 Nm; 3 - a rear wheel speed sensor, 15,5-16,5 Nm
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Remove the mounting bolt front wheel speed sensor and then disconnect the connector, remove the sensor (Fig. 6.8). Remove the rear seat cushion. Remove the C-pillar trim. Remove the rear wheel. Remove the bolt of the rear wheel speed sensor and then disconnect the connector, remove the sensor. Check Connect an ohmmeter between contacts the wheel speed sensor and measure the resistance. Rated resistance: - The front wheel sensor - 1275-1495 Ohm; - Rear wheel sensor - 1275-1495 Ohm. If the wheel speed sensor attached to the vehicle, connect a voltmeter to terminals wheel speed sensor connector and turning the wheel, measure the voltage.
A WARNING Set the voltmeter to measure AC voltage. Nominal value means that the AC voltage is present. |
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