[4matic] funkcjonowanie elektroniki.pdf

28-030

Electronics

Electronic components

A1e17

ABS warning lamp

Rear axle speed sensor

A1e24

ASD/4MATIC warning lamp

L6/1/2

Left and right front axle speed sensor

A1e25

ASD/4MATIC function indicator lamp

N30

ABS control unit

A7/2

4MATIC valve control unit

N30/3

4MATIC control unit

K1/2

Overvoltage protection relay 87E/87L/30a, (9-pin)

(series K1/1)

N49

Steering angle sensor

S9/1

Stop lamp switch (4MATIC/ASD)

X11/4

Test coupling for diagnosis, pulse readout (8-pin)

Electronics function

The electronics control the engagement and

disengagement of the four-wheel drive and

differential locks. They switch the solenoid valves in

the 4MATIC valve control unit (A7/2).

The electronics consist of the following components:

- Voltage supply

- Rear axle speed sensor (L6)

- Left and right front axle speed sensors (L6/1/2)

- Steering angle sensor (N49)

- Stop lamp switch (4MATIC/ASD) (S9/1)

- 4MATIC control unit (N30/3)

Voltage supply

The voltage supply for the electronics is via the

overvoltage protection relay (K1/2). It is in the right

of the components compartment.

K1/2 Overvoltage protection relay 87E/87L/30a (9-

pin) (series K1/1)

Battery voltage is continuously supplied to terminal

30. A 10 A fuse is installed between terminal 30 and

30a. The fault memory is continuously supplied with

voltage via terminal 30a. When the ignition is

switched on, the relays are controlled by electronics

via terminal 15. In this way the ABS (N30) and

4MATIC (N30/3) control units are supplied with

voltage via terminal 87E and additional equipment

via terminal 87L.

Overvoltage protection is achieved by means of a

22 volt Zener diode. Voltage peaks above 22 volts

which occur upstream of the overvoltage protection

are switched directly to ground by the Zener diode.

An overload is prevented by fuses. Terminals 87E

and 87L are fused separately.

Wheel speed sensors (L6, L6/1/2)

The wheel speed sensors (L6, L6/1/2) comprise a

magnet core and a coil. A toothed rotor moves in

the magnetic field of the wheel speed sensor. The

teeth of the rotor interrupt the magnetic field when

turning. Each tooth induces a voltage pulse in the

coil of the wheel speed sensor. The pulses are

transmitted to the 4MATIC control unit (N30/3)

which determines the speed from the number of

pulses.

Front axle wheel speed sensors (L6/1/2)

The front axle wheel speed sensors (L6/1/2) are

located in the steering knuckle. The rotor toothing

(43) is machined in the front axle drive shaft (44) in

the case of the 4MATIC.

43 Rotor

44 Front axle drive shaft

L6/1/2 Left/right front axle speed sensor

Rear axle wheel speed sensor (L6)

The rear axle speed sensor (L6) is located in the

rear axle casing (45). The rotor (43) is pressed on to

the bevel pinion (44).

Asuitable rotor with a different number of teeth is

required for each rear axle ratio. The mean speed of

both rear wheels is determined via the speed sensor

(L6) on the rear axle.

Rotor

Rear axle casing

Rear axle speed sensor

Steering angle sensor(N49)

The steering angle sensor (N49) is located

beneath the steering wheel. It senses the steering

movements and transmits them to the 4MATIC

control unit (N30/3).

The magnets are embedded in a plastic slip ring

(a) on the underside of the impact absorber. The

two Hall-effect sensors (b) are offset. Thus

different signals arise between left and right

steering lock.

The steering angle sensor (N49) comprises 72

magnets (c) and two Hall-effect sensors (b). Hall-

effect sensors are semi-conductor elements

whose electrical characteristics are influenced by

magnetic fields.

The 4MATIC control unit (N30/3) compares the

input signals to specified values and engages the

four-wheel drive in the event of lateral skid.

Bevel pinion

N49

Steering angle sensor

Hall-effect sensor

Plastic slip ring

Magnets

Stop lamp switch (4MATIC/ASD) (S9/1)

The stop lamp switch (4MATIC/ASD) (S9/1) has an

additional contact (arrow) for the 4MATIC. The stop

lamp contact has one plug connection of 4 mm Q

and an auxiliary contact of 2.5 mm Q .

When the service brake is operated, the stop lamp

contact is closed and the auxiliary contact is opened.

S9/1 Stop lamp switch (4MATIC/ASD)

When the service brake is operated, the 4MATIC

control unit (N30/3) receives a signal via a cable (d)

whereby the 4MATIC is switched off. The second

cable de-energizes the ABS control unit (N30).

The effect of the auxiliary contact is that when the

brake pedal is operated, the rear axle differential

lock valve (A7/2y3) is switched off in each case and

the rear axle lock releases even if there is a fault in

the stop lamp contact or 4MATIC control unit

(N30/3).

S9/1 Stop lamp switch (4MATIC/ASD)

X20 Intermediate plug connector, stop lamp switch (2-pin)

Stop lamp

Fuse box, fuse 5 (terminal 15)

4MATIC control unit (N30/3) and ABS control unit (N30)

Rear axle differential lock valve (A7/2y3)

4MATIC control unit (N30/3)

The 4MATIC control unit (N30/3) is located in the

right of the components compartment. It processes

all input signals and controls the solenoid valves

(A7/2y) in the 4MATIC valve control unit (A7/2).

The entire signal conditioning and processing is

performed digitally.

N30/3 4MATIC control unit

Overvoltage protection (terminal 87L)

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