BMW 7 Series: Service Function

Installation Mode

EMF installation mode is required for the purposes of replacing the EMF actuator unit or the brake cables. The EMF can be set to installation mode with the aid of the BMW diagnosis system. This mode is comprised of two subfunctions:

• Setting the EMF actuator unit to the installation position
• Preventing the EMF parking brake function.

To set the unit to the installation position, the brake cables are extended to the maximum length. That is the essential requirement for being able to remove and refit the cables.

While work is being carried out on the actuator unit, the brake cables or the duo-servo parking brake, the EMF must not be inadvertently or deliberately applied. Doing so would risk causing injury. Installation mode prevents the EMF parking brake function.

That means that pulling out the parking brake button as if to apply the parking brake has no effect.

Installation mode is indicated on the instrument cluster by the parking brake indicator lamp flashing yellow.

Fig. 69: Instrument Cluster Display - Parking-Brake Installation Mode

Installation mode can be cancelled in two ways:

• By the performing the service function "Reset installation mode" using the BMW diagnosis system
• By driving the vehicle; when doing so, a minimum speed must be exceeded.

Once installation mode has been successfully cancelled, the parking-brake indicator lamp on the instrument panel goes out.

Running-in the Brakes

The function for running-in the parking brakes only has to be carried out if

• the linings of the duo-servo parking brakes have been replaced or
• the rear brake discs have been replaced.

In either case, a material/surface pairing then initially exists which does not yet have the optimum frictional properties. That means that the required braking forces could not be achieved.

The brake running-in function removes play between the two surfaces forming the frictional pairing, i. e. the brake linings and the inside of the brake disc recess. It also wears-in the surfaces. Both operations are essential to achieving the required frictional coefficient between the two surfaces.

The brake running-in function is prepared with the aid of the BMW diagnosis system. It is started by pulling out the parking brake button once. The parking brake indicator lamp flashes red throughout the entire sequence.

While running-in the parking brakes, the EMF applies a defined force to the duo-servo parking brakes. That force is substantially lower than the brake force required to hold the vehicle stationary. The rear wheels are then rotated either on a brake dynamometer or by driving the vehicle on the road.

NOTE: The precise procedure for running-in the parking brakes is described in the Repair Instructions under the heading "Adjusting the parking brake". The instructions given there must be followed exactly.

EMF Components

This section deals only with the special features of the actuator unit and the controls for the electromechanical parking brake. On the F01/F02, as on numerous other BMW models, the braking force for the parking brake is produced by the familiar duo-servo parking brakes on the two rear wheels.

EMF Actuator Unit

The complete EMF actuator unit and especially the electric motor and gearing have been optimized for use on the F01/F02. That is noticeable in particular by quieter operation during actuation.

The EMF actuator unit is made up of the following main components:

• EMF control unit
• Electric motor
• Gearbox
• Force sensor

Those components are housed in a plastic casing that can not be opened. In the event of a fault, the EMF actuator unit can only be replaced as a complete unit.

Fig. 70: Identifying EMF Actuator Unit Components

INDEX REFERENCE CHART

1. Spindle
2. Gearbox
3. Splined shaft
4. Emergency release mechanism
5. Force sensor
6. Sleeve nut for right brake cable
7. Connector
8. Electric motor
9. Control unit circuit board
10. Entry/exit for emergency release cable
11. Sleeve nut for left brake cable

EMF control unit

As on the E70, the EMF control unit on the F01/F02 is integrated in the actuator unit casing and is also identical in design to the one on the E70. It is the actuation controller for the EMF functions. It therefore controls the electric motor and reads the signals from the force sensor.

The most important control signal from outside is that from the parking brake button. The parking brake button is directly wired to the EMF control unit.

The EMF control unit is connected to the PTCAN. Integrated in the EMF control unit is one of the two terminal resistors for the PT-CAN. The EMF control unit communicates via the PT-CAN with its most important partner, the DSC control unit. As the DSC control unit is only connected to the FlexRay, the central gateway module is required to transfer the signals between the PT-CAN and the FlexRay.

A special place among the input signals is occupied by the information relating to vehicle standstill. The EMF actuator unit must not be activated while the vehicle is moving but rather only when it is stationary. Otherwise, the vehicle handling would become unstable due to the rear wheels locking up. The EMF control unit detects vehicle standstill on the basis of the following three input signals:

• Road speed (provided by Integrated Chassis Management via bus systems)
• Rear axle speed (provided by engine management via PT-CAN)
• Wheel-speed signal "DFA_EMF" (calculated by Dynamic Stability Control and transmitted via direct wired link to EMF control unit).

Only when those three signals definitively indicate vehicle standstill does the EMF control unit allow operation of the actuator unit.

Fig. 71: Overview Of Connections On EMF Actuator Unit

INDEX REFERENCE CHART

1. Electric motor
2. Force sensor
3. EMF control unit
4. Signal leads for parking brake button and function indicator lamp
5. DFA_EMF, wheel-speed signal from DSC
6. WUP, wake-up line
7. PT-CAN input with terminal resistor
8. Power supply for EMF control unit (Terminal 30)
9. Power supply for electric motor (Terminal 30)
10. Earth for EMF control unit
11. Earth for electric motor

Force sensor

Technically speaking, the force sensor is a travel sensor that operates according to the Hall effect. Between the two brake cables there is a spring with a defined strength. That strength is stored on the EMF control unit.

Therefore, it can determine the force acting on the cables from the change in the length of the spring.

The force acting on the brake cables is an important input variable for the control algorithm on the EMF control unit. When the parking brake is applied, the EMF control unit has to ensure that a specific required force is applied to the brake cables. The EMF control unit calculates that required force on the brake cables directly from the legally required holding force on the wheels. The latter has to be great enough to safely keep the vehicle stationary on an uphill or downhill gradient of up to 20 %.

Over the life of the cables, a slight degree of stretching can occur. However, that does not corrupt the force-sensor signal. The spring does not, of course, start to compress until a force is acting on the cables. If, due to stretching, the cables are initially loose when in the released position, then no force is acting on the spring. Only when a force is applied to the cables, and, therefore, to the spring by operation of the electric motor does the spring compress. Then the force sensor sends the appropriate signal to the EMF control unit.

Bracket

To attach the EMF actuator unit to the vehicle's structural components, a multi-angled bracket is used. That design allows the EMF actuator unit itself to remain virtually identical in dimensions (to the one on the E70/E71). Adaptation to the geometry of the surrounding components on the different vehicles is achieved by the specific design of the mounting bracket.

The bracket for the EMF actuator unit locates at the top on a boss on the rear suspension subframe. Fixing of the bracket at the bottom differs according to whether the vehicle is fitted with Integrated Active Steering or not.

Vehicles with Integrated Active Steering have an actuator for the rear-wheel steering on the rear suspension.

The bracket for the EMF actuator then rests on the rear-wheel steering actuator bracket. The two brackets are joined by two bolts.

Fig. 72: Identifying EMF Actuator Unit Bracket And HSR Actuator Components

INDEX REFERENCE CHART

1. Left brake cable
2. Sleeve nut for left brake cable
3. Boss on rear suspension subframe
4. EMF actuator unit
5. Bolt joining EMF actuator and HSR actuator brackets
6. HSR actuator bracket
7. EMF actuator unit bracket
8. Emergency release cable

On vehicles without Integrated Active Steering, the bracket for the EMF actuator unit is attached to the rear suspension subframe by the same two bolts.

Fig. 73: Identifying EMF Actuator Unit Bracket Without HSR Actuator Components

INDEX REFERENCE CHART

1. Bowden cable, emergency release
2. Left brake cable
3. Sleeve nut for left brake cable
4. EMF actuating unit
5. Bolt fixing EMF actuator to mounting bracket
6. Bolt fixing EMF actuator to rear suspension subframe
7. EMF actuator unit bracket
8. Rear suspension subframe
9. Track rod

The bracket and the EMF actuator unit itself are also attached to one another by bolts. If replacement is necessary, both the bracket and the EMF actuator unit itself can be ordered as separate parts.

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