BMW 7 Series: System Components

DSC Components

DSC Unit

The DSC unit on the F01/F02 essentially uses the same technology as on the E70/E71.

Versions

The DSC unit comprises the DSC control unit and the hydraulic modulator. The two are attached to one another in such a way as to form a waterproof unit.

The repair kits available are either

• the complete DSC unit with pre-filled hydraulic modulator or
• the DSC control unit on its own.

There is a seal integrated in the casing of the DSC control unit at precisely the point where it joins the hydraulic modulator. That is the reason why the DSC control unit can be replaced separately (seal is replaced at the same time). The hydraulic modulator, by contrast, can not be replaced separately because the seal would be damaged when the two parts were separated. The required degree of waterproofing would then no longer be provided.

There are two versions of the DSC unit which differ by virtue of the number of pressure sensors fitted.

DSC VERSION DESCRIPTION CHART

The DSC unit with only one pressure sensor uses a computation model to determine the pressures in the front and rear brake circuits. The degree of accuracy obtained is sufficient for the functions of the dynamic handling systems and the cruise control with braking function. The optional extras ACC and ACC Stop&Go require a higher degree of accuracy for determining the brake pressure generated and modulated by the Dynamic Stability Control. Therefore, the two additional brake sensors are fitted in the front and rear brake circuits.

Hydraulic modulator

With its highly advanced pump design, the hydraulic modulator also offers an enhanced degree of control accuracy. There are 2 groups of 3 pump elements with a diameter of 6.5mm and intake-optimized units. This pump design produces, firstly, substantially improved pressure generation dynamics. And secondly, the pressure increments during pressure generation are smaller. Together with the improved design of the valves, the overall effect is less pedal feedback during brake modulation.

For the driver this is noticeable in as far as the pedal pulsation can now only be felt very slightly during ABS braking. There is a pressure sensor for detecting the pressure applied by the driver in the hydraulic modulator.

DSC control unit

Like the hydraulic modulator, the DSC control unit on the F01/F02 is also based on the one used on the E70/E71.

Specifically, the following special features and differences should be noted:

• FlexRay connection
• Wiring of the new DTC button
• Wheel-speed signals for electromechanical parking brake, Car Access System and Telematic Control Unit

Fig. 58: Overview Of Connections On DSC Control Unit

INDEX REFERENCE CHART

1. DSC control unit
2. FlexRay input with terminal resistor
3. DF_TCU_L, front left wheel-speed signal for Telematic Control Unit (TCU)
4. DF_TCU_R, front right wheel-speed signal for TCU
5. WUP, wake-up line
6. DFA_EMF, wheel-speed signal for Car Access System (CAS)
7. DFA_EMF, wheel-speed signal for electromechanical parking brake (EMF)
8. Power supply for DSC module (Terminal 30F)
9. Power supply for valves (Terminal 30)
10. Power supply for pump motor (Terminal 30)
11. Ground for DSC module
12. Ground for valves and pump motor

The DSC control unit on the F01/F02 is connected to the FlexRay and not, as on previous vehicles, to the PTCAN and F-CAN.

The FlexRay is brought to the DSC control unit (from the ZGM) and ends there. The DSC control unit is thus the terminal node of the FlexRay. Accordingly, it contains a terminal resistor for the FlexRay.

On previous vehicles, the DTC button was electrically analyzed by the IHKA control unit, for instance (E70/E71). On those vehicles, the button operation signal is transmitted via bus systems to the DSC control unit.

The new DTC button on the F01/F02 is connected to the ICM control unit instead. The DTC button and the associated function is part of the "dynamic handling control" function on the F01/F02. As that, in turn, is computed on the ICM control unit, the DTC button has been connected to the ICM control unit. The ICM control unit then signals the appropriate vehicle handling mode via the FlexRay. The DSC control unit analyses the signalled mode and adapts its function accordingly.

For the EMF and CAS control units, the information about vehicle standstill is of particular importance. For those two systems, the DSC control unit provides the DFA_EMF signal. It is a calculated signal computed from the speeds of the two rear wheels. It is transmitted as a pulse-width modulated signal on a dedicated line to the EMF and CAS control units.

If there is a Telematic Control Unit (TCU) fitted on the vehicle but no navigation system, the TCU control unit has to take on the task of determining vehicle location. That is necessary for the manual and automatic emergency call functions. The signals from the GPS aerial are insufficient for that purpose as it has to be possible to determine the vehicle's location even if the GPS signals are temporarily unavailable. In that case, the TCU control unit uses the speed signals from the two front wheels to calculate the road speed and changes of direction when cornering. The wheel-speed signals are provided by the DSC control unit and transmitted to the TCU control unit by a directly wired connection (DF_TCU_L and DF_TCU_R).

The power supply for the DSC unit is split into three: control unit, valves and pump motor are supplied by separate leads. That prevents interference from the load circuits (inductive loads) being transferred to the electronic circuitry.

The DSC control unit is also connected to the wake-up line. The wake-up line is used to wake up the DSC control unit.

Location and repair

The DSC unit is located in the vehicle underbody, set back somewhat from the wheel arch. That location applies to both left and right-hand-drive vehicles.

Fig. 59: Identifying DSC Unit Location, F01/F02

INDEX REFERENCE CHART

1. Quick-release hydraulic pipe unions, 4 off
2. Screw-fit hydraulic pipe unions, 6 off
3. DSC control unit
4. DSC valve manifold
5. DSC pump motor
6. DSC unit mounting bracket
7. Bolt fixing with vibration damper for DSC unit
8. Screw-fit hydraulic pipe unions, 2 off

Six short lengths of hydraulic pipe are connected to the DSC unit by screw-fit unions.

Four of those hydraulic pipes run upwards from the hydraulic modulator and terminate at a block with quickrelease unions. They are connected by those quick-release unions to the pipes running off to other parts of the vehicle. Specifically, that is the two pipes to the left and right front brakes and the two pipes to the tandem master cylinder.

The two remaining hydraulic pipes run to the rear. They are connected by quick-fit unions to the pipes running off to other parts of the vehicle. In this case, they lead to the left and right rear brakes.

If the DSC unit has to be replaced, first of all the vehicle underbody trim has to be removed in the appropriate places. When the DSC unit is removed, the six short lengths of hydraulic pipe referred to above are removed with it. Therefore, before removal, the four quick-release unions (4) and the two screw-fit unions (8) have to be disconnected. The short lengths of hydraulic pipe subsequently have to be removed and fitted to the new DSC unit.

Only after the DSC unit has been removed can the DSC control unit be separated from the hydraulic modulator, if necessary, and new one fitted.

The braking system must always be bled whenever the DSC unit has been removed and refitted/replaced.

The precise procedures for the individual repair operations in connection with the DSC unit are described in the Repair Instructions.

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