Audi A4

since 1994 of release

Repair and car operation



A4 Audi
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ exhaust System
+ cooling System
+ Fuel tank and fuel pump
+ Air filter and absorption channels
+ injection System
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
- Brakes
   Independent work on brake system
   So the brake system works
   Check of brakes
   Brake liquid
   Check of level of brake liquid
   Check of brake system on tightness and existence of damages
   Replacement of brake liquid
   Disk brakes
   Measurement of thickness of overlays of forward disk brakes
   Check of a condition of brake disks
   Replacement of overlays of disk brakes
   Back disk brakes
   Measurement of overlays of back disk brakes
   Hand brake
   Check of idling of the lever of the hand brake
   Main brake cylinder
   Brake amplifier
   Check of the brake amplifier
   Works on hydraulics of brake system
   Pumping of brake system
   The help at malfunctions
   ABS and EDS
   What does ABS?
   Function of separate knots
   Electronic system of distribution of brake effort (EBV)
   Violations in ABS system work
   Electronic blocking of differential (EDS)
+ Wheels and tires
+ Electrotechnical equipment
+ ignition System
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ body Details
+ Salon
Search of malfunctions
Technical characteristics





Function of separate knots

Hydraulic module

The hydraulic module (1) system of anti-blocking takes place ahead at the left in an impellent compartment. It is connected by the central socket (2) with the control unit under a back seat.

It is ahead at the left in an impellent compartment: the module is built in between brake pipelines of the main brake cylinder and the brake tubes conducting to brakes of wheels. According to orders of the electronic control unit pressure in contours of brake system remains or to constants, or goes down, or again raises. But pressure cannot be higher than what you create, pressing a brake pedal. Pressure is regulated by four quickly being switched electromagnetic valves – on one on each wheel.

If electromagnetic valves are disconnected, pressure raises. If the maximum current arrives, there is a pressure decline, at an average current pressure remains at one level. The particular interest is represented by a phase of removal of pressure: as for pressure decline it is impossible to let out somewhere simply brake liquid (for this purpose the brake pedal would need to be wrung out completely), arriving here from the main brake cylinder, brake liquid pump out the powerful return pump back to the main brake cylinder. You notice it on behavior of a pedal of a brake which starts to pulse slightly when the return pump works, i.e. ABS starts to work. If attentively to listen, noise of the working pump is audible. In the hydraulic module this noise chokes with special dampers a little.

Sensors of number of turns

Such sensors of number of turns (2) are established on all four wheels in openings (1) suspension bracket of an axis. Behind them according to frequency of rotation of wheels gear elastic washers rotate.

Only four sensors fix speed of rotation of each wheel and hand over this information in the electronic control unit. On its basis the electronic control unit regulates operation of the hydraulic module.

Sensors of number of turns consist of the magnetic core and the coil and are mounted at small distance from a gear disk – a rotor. The rotor – its name speaks for itself – rotates together with a wheel and forces to rotate zubtsevidny cambers on its perimeter by the sensor quicker or more slowly depending on speed. Each tooth passing under the sensor, induces short lifting of tension in the sensor. In such a way in the sensor the alternating voltage which changes the frequency according to speed of rotation of a wheel is created. The signal arising thus is processed by the electronic control unit as information on number of turns of a wheel.

In Audi A4 rotors take place on two or on four (quattro) driving wheels on the external hinge of a power shaft and on naves of not driving back wheels.

Electronic control unit

The combined control unit (shooter) system of anti-blocking and electronic blocking of differential is approximately in the middle of the car under a back seat.

The electronic control unit is under a back seat and processes information arriving from sensors of number of turns.

At the same time it operates the hydraulic module so that wheels were not blocked. Along with processing of signals and the subsequent logic part, the control unit still has the blocking scheme. By means of it the device can check, distinguish itself failures and supervise working tension. If malfunctions are fixed, it switches off ABS and the control bulb in the combined device lights up.