Scheme of the organization of the hydraulic drive of brake mechanisms
1 - GTZ; 5a - Right front brake caliper; 5b - Left front brake caliper; 6a - Right rear brake caliper; 6b - Left rear brake caliper; A7 / 3 - Hydromodulator of auxiliary systems
Brief description of the principles of operation of auxiliary electronic systems of anti-lock brakes (ABS), emergency braking amplification (BAS), brake force distribution (EBV), anti slip (ASR/4-ETS) and anti-skid (ESP) given in Chapter Controls and techniques for safe operation.
Layout of the components of the emergency braking assistance system (BAS)
1 - GTZ; 2 - Vacuum connector; A1e17 - ABS warning lamp; A1e48 - BAS / ASR indicator lamp; A7 / 7 - Vacuum brake booster; A7 / 7b1 - BAS diaphragm travel sensor; A7 / 7s1 - Sensor-switch release BAS; A7 / 7y1 - Solenoid valve BAS; N48 - BAS control module integrated in ESP control module (N47-5); Y61 - GTZ switch valve (if provided)
ASR/ETS/ESP Auxiliary Electronic Systems Layout Diagram
A1e17 - ABS warning lamp; A1e35 - ETS control lamp; A1e36 - Light indicator 4-ETS; A7 / 3 - Hydromodulator; F1 - Fuse and relay mounting block; k25 - Pressure-return pump relay; L6 / 1 - Left front wheel sensor; L6 / 2 - Right front wheel sensor; L6 / 3 - Left rear wheel sensor; L6 / 4 - Right rear wheel sensor; N47-5 - BAS/ESP control module; S9 / 1 - 4-pin brake light switch; S12 - Sensor-switch for charging the parking brake; S11 - Brake fluid level switch; X11 / 4 - Diagnostic connector DLC of the on-board self-diagnosis system
The brake fluid reservoir is located under the brake master cylinder and supplies fluid to the entire hydraulic braking system.
The brake booster stores part of the vacuum created in the engine intake pipe. Since a diesel engine does not have the necessary suction vacuum, diesel vehicles have a special vacuum pump. With the help of an appropriate valve, if necessary, the force on the brake pedals is increased due to the action of vacuum.
The pedal-actuated parking brake acts through the cables on the rear wheel brakes. Additionally, the rear brake mechanisms are equipped with drum-type parking brake units with a pedal-cable drive.
Principles of operation of auxiliary systems ABS / 4-ETS / ESP / EBV
The electro-hydraulic diagram of the auxiliary systems functioning is shown in the illustration, to which all references in the text refer.
Diagram of the hydraulic circuit of the auxiliary electronic systems ABS/4-ETS/ESP/EBV
4 - Control unit of the braking path; 5a - Right front brake caliper; 5b - Left front brake caliper; 6a - Right rear brake caliper; 6b - Left rear brake caliper; 7 - Control valve; 9 - One-way control valve of the return pump; 10 - Damper with control plate; 11 - Low-pressure accumulator; A7 / 3 - Hydromodulator for auxiliary brake systems; m1 - Pressure and return pump; p1 - Self-priming pump of the first (DK) diagonal contour; p2 - Secondary self-priming pump (SK) diagonal contour; y6 - Left front solenoid pressure holding valve (inlet); y7 - Left front solenoid pressure relief valve (high school graduation); y8 - Right front solenoid pressure holding valve (inlet); y9 - Right front solenoid pressure relief valve (high school graduation); y10 - Left rear solenoid pressure holding valve (inlet); y11 - Left rear solenoid pressure relief valve (high school graduation); y12 - Right rear solenoid pressure holding valve (inlet); y13 - Right rear e / m pressure relief valve (high school graduation); y24 - Control multi-way solenoid valve of the first (DK) diagonal contour; y25 - Control multi-way solenoid valve of the second (SK) diagonal contour; y26 - Solenoid valve for pre-filling the first (DK) diagonal contour; y27 - Solenoid valve for pre-filling the second (SK) diagonal contour; DK - First diagonal contour; SK - Second diagonal contour; VL - Left front wheel; VR - Right front wheel; HL - Left rear wheel; HR - Right rear wheel
As part of the hydraulic modulator of auxiliary brake systems (A7/3) includes components of closed-loop dynamic control systems of ABS, 4-ETS/ASR and ESP systems.
Pressure and return pump (A7/3m1)
Self-priming pressure and return pumps (p1, p2) built into the hydraulic modulator assembly (A7/3) and are switched by pulse signals during the pressurization and depressurization phases of the active control system ETS and ESP, as well as during the regulation of the return flow when ABS is activated.
Self-priming pressure and return pumps (p1, p2) run as needed to minimize noise levels.
Each brake circuit is equipped with a separate damper (10), to reduce the noise generated by the pump.
Holding solenoid valves (intake) and reset (graduation) pressure (A7/3y6 - A7/3y13)
One 2/2-way valve is used to control the pressure in the circuits of each of the wheels in the injection / hold and hold / reset phases of the ABS, ETS and ESP control modes.
Low pressure accumulator (11)
Low pressure accumulator (11) filled with brake fluid during the depressurization phase of ABS, ETS or ESP and ensures its transfer to the delivery and return pump (p1/p2).
Pilot multi-way solenoid valves (A7/3y24 and A7/3y25)
Solenoid multi-way switching valves (y24 and y25) provide a cut-off of active pressure diagonal circuits from the GTZ during the operation of ETS and ESP. Also, the valves provide pressure relief when it rises above 150 atm. The brake fluid passed through the switch valves is sent back to the GTZ.
Prefill Solenoid Valves (A7/3y26 and A7/3y27)
valves (y26, y27) open in the pressure build-up phases of the ETS/ESP.
The principle of operation of the assembly of the sensor of the withdrawal moment / transverse overloads ESP
The slip torque and transverse g-force sensors are combined into a single assembly in order to save space (B24/2). The micromechanical sensor assembly converts the lateral and vertical projections of angular accelerations into electrical signals. Working elements of various masses under the influence of those arising during the non-inertial movement of the vehicle (turning and accelerating) overloads provide varying degrees of deformation. A special electronic converter converts the received signals and transmits them via the CAN bus to the control module of the anti-slip and anti-skid systems (N47).
The sensing element of the slip torque sensor is formed from a micromechanical ring (A), equipped with eight spring jumpers (b), providing its movement and electromagnetic action. During rotation in the assembly, additional Coriolis forces arise, proportional to the speed of rotation, fixed electromagnetically and, after conversion in the ACIS module into the form of analog signals, issued to the control unit of the instrument cluster.
The design of the capacitive torque sensor of the ESP system
a - Silicon ring
b - Spring jumper
c - Electronic sensor
The principle of measuring transverse overloads is based on the use of a spring-mass element with a capacitive detector. Operating voltage is supplied from the ESP control module (N47-2).
The transverse overloads arising during the making of turns provide a displacement of the spring-mass element from the equilibrium position by an amount proportional to the value of the resulting reaction force. Any change in the position of the element results in a change in the capacitance of the detector. Further, the recorded deviation value is converted into a signal voltage that allows the ESP control module to (N47-2) to quantify the values of fixed transverse overloads.
The electronic control module ensures that the system, in the event of mechanical damage to the circuit (e.g. cable break), or if there is an excessive voltage drop, it will automatically turn off. The situation is displayed on the instrument panel by activating the ABS warning lamp. At the same time, the ESP and BAS systems are turned off, which is confirmed by the operation of the corresponding indicator (see chapter Controls and techniques for safe operation). The main braking system continues to function at the same time - during braking, the car behaves as if the ABS system was not present.
Activation of the ESP warning lamp while driving indicates a malfunction of the emergency brake booster (BAS) or anti-skid system (ESP), - the corresponding systems are also switched off while maintaining the ability of the main braking system to function.
When the red warning lamp of the brake system is activated while driving, it is necessary to stop immediately and try to find out the cause of the violation, which may in particular be a drop in the brake fluid level, or an incompletely released parking brake lever.
Procedure for the operation of the ABS warning lamp while driving
Stop the car, turn off the engine and start it again.
Check the voltage level of the battery - if the measurement is less than 10.5 V, recharge the battery.
Note. If the ABS warning lamp comes on at the beginning of the movement and then goes out after a while, this indicates a low battery voltage, which rises after the generator starts.
Make sure that the wire ends are securely fastened to the battery terminals, tighten the fasteners if necessary.
Jack up the car and put it on supports, remove the wheels and check the condition of the wiring of the wheel sensors.
More detailed diagnostics should be performed in a service station using special equipment to read fault codes stored in the memory of the control module (DTC).
Security measures
- Brake fluid is one of the highly toxic and chemically aggressive compounds and, in contact with body panels, destroys the paintwork!
- Brake dust generated during the wear of brake pads may contain asbestos, which is harmful to human health - in no case should you inhale it when cleaning the brake mechanisms!
- Working with the brake system requires special cleanliness and strict adherence to instructions. In the absence of the necessary experience, it is advisable to contact the service station.
Note. When driving on wet roads, periodically press the brake pedal to remove moisture from the brake discs
- In the process of wheel rotation, moisture is discharged from the brake discs under the action of centrifugal force, but a silicone film, rubber abrasion products, grease and other contaminants that reduce braking efficiency remain!
- After installing new brake pads, the latter should run in - try to avoid sudden braking for the first 200 km after the replacement!
- Corroded disc brakes create a shaking effect during braking that does not disappear over time - replace the discs!
- Dirt sticking to the surface of the brake pads leads to the formation of grooves on the surface of the brake discs, which leads to a decrease in braking efficiency!