BMW 7 Series: Overview Of EMF Functions

Normal Operation

Parking brake application

The driver can activate the EMF parking brake function by pulling on the parking brake button. Thus the way in which the parking brake button is operated emulates the action of a handbrake lever.

The signal from the parking brake button is read by the EMF control unit and transmitted to the DSC control unit as a bus signal. The DSC control unit then decides whether to use the DSC hydraulic modulator or the EMF actuator unit to implement the parking brake function. If the engine is running, the vehicle is held stationary by using the DSC hydraulic modulator; otherwise the EMF actuator unit is used.

The parking brake function is possible at any logical terminal status, i. e. at:

• Terminal 0
• Terminal R
• Terminal 15 (and Terminal 50)

Parking brake application at Terminal 0 is specifically made possible by the fact that the EMF control unit is supplied by Terminal 30 and the parking brake button is connected directly to the EMF control unit. If the driver operates the parking brake button at Terminal 0, the EMF control unit is woken up. The EMF control unit in turn wakes up the other control units on the vehicle. Only then can the EMF control unit receive the important signals relating to vehicle standstill. In addition, the changed status of the parking brake can be displayed after the system has been woken up.

The status "parking brake on" is indicated by a red LED on the parking brake button and an indicator lamp on the instrument cluster.

The driver does not have to operate any other controls to apply the parking brake.

Once the parking brake is on, pulling the parking brake button again has no effect.

Fig. 66: Instrument Cluster Display - Parking Brake ON

INDEX REFERENCE CHART

1. Function indicator lamp on parking brake button
2. Indicator lamp on instrument cluster

Roll-away monitoring

The roll-away monitoring function is computed on the DSC control unit. It is active while the vehicle is being held stationary by:

• the DSC hydraulic modulator or
• the EMF actuator unit.

The condition for activation of roll-away monitoring is thus that either the EMF parking brake function or the Automatic Hold function is active.

Roll-away monitoring observes the signals from the wheel-speed sensors. If any of the wheel-speed sensors signals movement of the wheel, that indicates that the vehicle is rolling. Since, however, the vehicle is supposed to be stationary by virtue of the brake pressure applied by the hydraulic system or the EMF actuator, the rollaway monitoring function has to intervene. The hydraulic brake pressure is increased by control signals to the DSC hydraulic modulator or EMF electric motor in order to increase the braking force. In that way the rolling is counteracted.

Release

In similar fashion to the operation of a handbrake lever, the EMF is released by pushing the parking brake button in.

But in order that the parking brake function is actually cancelled, Terminal 15 must also be on and one of the following conditions must be met:

• Brake pedal depressed or
• Automatic transmission parking lock engaged.

That prevents the vehicle rolling away if another occupant of the vehicle apart from the driver presses in the parking brake button (child safety feature).

Once the parking brake is released, the function indicator lamp on the parking brake button and the indicator lamp on the instrument cluster go out.

Fig. 67: Instrument Cluster Display - Parking Brake Released

INDEX REFERENCE CHART

1. Function indicator lamp on parking brake button
2. Indicator lamp on instrument cluster

Dynamic braking

The law requires that vehicles have two means of applying the brakes. On the F01/F02, the second means (the brake pedal being the first) is the parking brake button on the center console.

If the parking brake button is pulled out while the vehicle is in motion, a defined degree of braking is applied by the DSC system. That function is intended for emergency situations in which the driver is unable to apply the brakes by pressing the brake pedal. Other occupants of the vehicle can also bring the vehicle to a standstill in that way if, for example, the driver suddenly loses consciousness.

Dynamic braking hydraulically applies brake pressure at all four brakes. The stabilization functions of Dynamic Stability Control remain fully functional and the brake lights are switched on. That represents a major advantage over a manual parking brake.

Braking takes place only while the parking brake button is pulled out. The degree of deceleration set by the DSC is increased progressively from initially 3 m/s2 to 5 m/s2.

During dynamic braking, the parking brake indicator light on the instrument cluster comes on. In addition, a Check Control message and an audible warning signal are issued to make the driver aware of the critical situation.

If the driver uses the brake pedal and the parking brake button at the same time to slow down, the DSC control unit prioritizes. The greater braking requirement is put into effect.

If dynamic braking is continued to the point of standstill, the vehicle continues to be held stationary after the parking brake button is released. The indicator lamp on the instrument cluster remains on. The driver can then release the parking brake (as described above).

Emergency release

A mechanical emergency release facility is provided in order to be able to release the parking brake in the event of the electromechanical actuator unit failing or insufficient power supply.

NOTE: Caution: secure vehicle to prevent it rolling before operating the emergency release!

NOTE: After a power supply failure, it may still not be possible to move the vehicle even after releasing the brake with the emergency release facility. The automatic transmission parking lock may still be engaged.

In that case, the parking brake must first be released with the emergency release facility. Then the automatic transmission parking lock must be released using the emergency release facility. To do so, the appropriate tool must remain engaged in the parking lock emergency release.

The parking brake emergency release status is indicated on the instrument cluster.

The parking brake indicator lamp shows yellow.

Fig. 68: Instrument Cluster Display - Parking Brake Emergency Release/Fault

The driver is shown the same indication (together with a check control message) if the parking brake has a fault.

When the parking brake is to be used again after an emergency release, that can not be done mechanically but only electrically. It requires pushing in the parking brake button once as if to release the parking brake. The familiar conditions for releasing the parking brake must also be met.

READ NEXT: