Part 1
00 01 07 (149)
Electrical systems
E70, E71
Introduction
For the new BMW X5 (E70) the following objectives have been set by Marketing and Design:
- Clear positioning in the MCL+ vehicle class (size, price)
- Development of the BMW interpretation of a SAV, based on driving dynamics, handling, agility, design and passion
- Installation of additional 3rd seating row without compromising other vehicle characteristics (weight, exterior, proportion)
- Increase of the variability and practicality compared with E53 so that multiple uses can be supported
- Extension of the accessory equipment programme to meet the increased customer expectations in the MCL+ (e.g. Active Steering, adaptive drive, tailgate lift, reversing camera)
The X6 (E71) besides being the sportiest BMW X model, also opens up a completely new vehicle segment: the Sport Activity Coupe segment.
The X6 features the following innovations:
- Conceptual innovation of the world's first Sports Activity Coupe
- Sportiest development of a BMW X model with special emphasis on the active driving potential
- Lavish body styling
- Worldwide first vehicle with Dynamic Performance Control (marketing designation) for unique forward driving stability
- Generous ground clearance and capacious wheel housings
This BMW Service Technical bulletin gives an overview of the electrical systems in the new BMW X5. The electrical systems are arranged as follows:
- Drive [system overview ...]
- Chassis [system overview ...]
- Body [system overview ...]
The overviews of the electrical systems can be accessed from this main document by clicking the hotspots.
Electrical systems
The most important technical details are briefly described below.
- Electrical system
- Drive
- Chassis
- Body
Electrical system
The new X5 is equipped with the Electrical System 2000. For the first time ever the FlexRay databus will be introduced in a BMW vehicle. FlexRay is a new bus standard.
The Electrical System 2000 is made up of the following databuses:
- Body CAN K-CAN
- Media Oriented System Transport: MOST
- Powertrain CAN PT-CAN
- FlexRay: Databus with a data transmission rate of 10 Mbit/s
- Chassis CAN F-CAN
- CAN interface for diagnosis: D-CAN (diagnosis-on CAN)
Between the diagnosis socket and the Junction Box Electronics (JBE) there is now a CAN that acts as the diagnosis interface. The D-CAN interface has a higher data transfer rate (500 kbit/s). D-CAN is a twin-wire connection. D-CAN stands for: Diagnosis-on-CAN.
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Important: Automatic terminal cutoff of Terminal 15 from 03/07.
Terminal 15 is automatically switched off by the signal from the door contact when the driver's door is opened or closed. Terminal 15 is permanently reactivated if the START/STOP button is then pressed. Perform this operation before programming or diagnosing a vehicle.
Drive
With BMW EfficientDynamics, the Sports Activity Vehicle in the model year 2008 sets new standards in drive dynamics and wear reduction.
The comprehensive programme for the optimization of wear and emission performance includes intelligent alternator control as well as requirement-based control of auxiliary units (e.g. coolant pump).
In addition the belt drive for the A/C compressor is equipped with a clutch. If the climate control system is switched off, the A/C compressor is automatically disconnected. In this way the drag torque of the A/C compressor is reduced to a minimum.
The scope of equipment includes roll-resistance reduced tires, a friction-minimized rear axle transmission and a modified drive assistance pump. The pressure- and volume-dependent adjustment of the cam ring prevents transmission losses increasing in proportion to engine speed.
The vehicle is also equipped with active aerodynamic features. The vent flaps open and close depending on the driving situation. In this way as soon as the cooling requirement of the engine falls, the air resistance of the vehicle can be reduced.
The X5 contains the following advanced engineering features in the powertrain area:
- Spark-ignition engines
For the market launch the familiar N52B30O1 and N62B48O1 spark-ignition engines will be used. However the engines shall be adapted in certain respects.
The exhaust system, the cooling system and the fuel supply system are specific to the vehicle.
The belt drive has been adapted to the increase in the number of optional extras. On the power takeoff side, the transfer case has been redesigned.
In addition, a modified rear axle transmission is used in the X5 4.8i and 3.0d. The way in which the drive shaft and power takeoff shafts are coupled with the rear axle is new.
The N52B30O1 will be equipped from 10/07 with a map-controlled oil pressure regulator. The coolant temperature sensor at the cooler outlet has been omitted.
With the E71, the new N63B44O0 8-cylinder spark-ignition engine will be introduced to the market. In addition, the N54B30O0 6-cylinder spark-ignition engine with 2 turbo chargers will also be used in the E71.
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- Diesel engines
The vehicle contains the 2 familiar diesel engines:
- M57D30O2 (turbo charged)
- M57D30T2 (2-level turbo charging)
A new exhaust system has been developed for these diesel engines that satisfies the high expectations on this vehicle (e.g. with respect to exhaust emissions, noise). These diesel engines comply as standard with the exhaust norm EURO 4. The oxidation catalyst is installed close to the engine. The diesel particle filter is accommodated in the same housing.
The M57D30T2 is equipped with a pressure-controlled fuel low pressure system.
A fuel-pressure-temperature sensor measures the pressure and the temperature in the fuel low-pressure system. The signals are received by the Digital Diesel Electronics (DDE).
The DDE actuates the fuel pump controller (EKPS control unit).
The EKPS control unit in turn actuates the fuel pump.
This enables very precise and responsive fuel delivery.
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- Intelligent alternator regulation
The intelligent alternator regulation is a function of the engine controller.
The intelligent alternator regulation represents a refinement of the recharging strategy for the vehicle battery.
The vehicle battery is no longer completely recharged but charged to a certain degree depending on various external conditions (ambient temperature, battery age etc.).
In contrast to conventional recharging strategies, the battery is only recharged when the vehicle is coasting. In the process the alternator receives maximum stimulus, electrical energy is produced and fed into the vehicle battery.
No fuel is consumed in the process. The kinetic energy from the coasting vehicle drives the alternator via the wheels and engine. Electrical energy is generated.
The alternator is not actuated during acceleration phases of the vehicle. This means no energy and more specifically no fuel is used to generate electrical energy.
- Automatic transmission
The GA6HPTU automatic transmission has been revised in the following respects:
- Torque moment converter with torsion damper
- Adjusted electronic transmission control (EGS)
- More responsive hydraulics thanks to new pressure regulator
- Electric switching via gear selector switch (GMWS)
The EGS control unit is located in the automatic transmission. The electronic immobilizer (EWS) is integrated in the EGS control unit. This increases the degree of theft protection.
The gear selector switch (GWS) is a separate control unit.
The gear selector switch (GWS) acts to select a drive level of the automatic transmission with Steptronic mode and sport program. The transmission selector switch is located at the front of the center console of the vehicle and is a separate control unit. With the gear selector switch, instead of being actuated mechanically, the transmission is now actuated electronically.
The gear selector switch (GWS) consists of the control electronics and the selector lever.
The sensors for recording the selector lever position and for inhibiting inadvertent gearshifts are integrated in the control electronics.
The E71 is available with rocker switches.
- xDrive
xDrive is an all-wheel drive system that links Dynamic Stability Control (DSC) system to an electronically controlled multi-plate clutch in the transfer case.
The electronically controlled multi-plate clutch smoothly distributes the drive torque as required to the front axle. The rear axle is always powered.
All of the input torque is applied to the rear axle when the multi-plate clutch is separated.
xDrive constantly communicates with the DSC. The drive-dynamic input information is computed in the DSC control unit.
Important items of information are:
- Gas pedal position
- Engine torque
- Drive-dynamic state
The DSC calculates the necessary locking torque. The locking torque is communicated to xDrive. This allows xDrive to determine whether the vehicle is able to follow the driver's commands.
If the wheels exhibit a tendency to spin or there is a risk of over- or understeering, xDrive cuts in with a corrective effect.
xDrive adjusts the drive torque between the two axles in response to requirements.
Only if xDrive cannot maintain the vehicle's course on its own will DSC also intervene. Engine output is reduced and individual wheels are specifically braked.
The drive torque is delivered to the axle that has better traction when road conditions change, due for example to snow, ice or a loose road surface.
- Transverse torque distribution (only E71)
The rear axle transverse torque distribution is fitted as standard and is offered by Marketing under the name "Dynamic Performance Control".
The rear axle transverse torque distribution specifically distributes the drive torque between both wheels on the rear axle.
With the new development, the rear axle transmission of the conventional design is supplemented by 2 planetary gearboxes with override function. These planetary gearboxes can if required by integrated in the powertrain via a disc set. Independently of the required drive torque of the engine, a differential moment of up to 1800 Nm can be actively set between the left and right rear wheel.
Benefits:
- Optimum directional stability as well as reduced steering effort
- Improved traction
- Increased driving safety
The chassis control systems are still interconnected, even if they function largely independent of each other.
The innovative architecture of the Integrated Chassis Management (ICM) takes over the role of a superordinate control unit, opening up new potentials in driving dynamics. The ICM as the central controller in the vehicle compiles all the available individual items of information and distributes these in a coordinated and concerted manner to the chassis control systems.
On the basis of a comprehensive analysis of the driving status derived from a wide variety of information, the ICM can decide: Which servo interventions in the respective driving context are most likely to harmonize driver wishes and vehicle reaction. By means of networking via ICM, new functions are also created that are only made possible by the interaction of several control systems.
Thus the Dynamic Performance Control ( rear axle transverse torque distribution) interacts dynamically with Dynamic Stability Control, Active Steering and dynamic drive.
Chassis
From an electrical point of view, the chassis has been modified with respect to the following systems:
- Dynamic Stability Control
The vehicle is equipped as standard with Dynamic Stability Control (DSC).
DSC is a development of the DSC 8Plus.
For ease of identification this chassis control system is known as "Premium".
The control functions of DSC have been further optimized. The improvements have been achieved through the use of a return pump with 6 pistons as well as more efficient electronics. The extended functions of the DSC are:
- Brake standby by preemptive application of brake shoes in case of need (creation of low anticipatory brake pressure)
- "Dry braking" of the brake discs on wet roads when wiper switched on
- Detection of fading and increase in brake pressure during fading
- Start-off assistant
- Cruise control with brake function (option 544)
- Parking brake (electromechanical and hydraulic parking brake)
> from 09/07: additionally with automatic-hold function
New from 10/07:
The DSC is equipped with the function "Drive dynamic brake intervention". To this end, the software in the DSC has been changed. No additional hardware is required.
Drive dynamic brake intervention increases agility and reduces understeering. This improves the handling characteristics of the vehicle.
As soon as the front wheels push unduly outward, the rear wheel on the inside of the curve will be specifically braked by the DSC.
The resulting loss in forward drive is compensated for by an increase in engine power. Thus even on slippery roads, curves can be taken more precisely.
Whether and to what extent intervention of this kind is required, is determined with the data on yaw rate, steering angle and engine power.
- Active front steering
For the 3rd generation of Active Steering the following features are new:
- Yawing moment compensation has been fully integrated as a function in the Active Steering control unit
- Cumulative steering angle sensor withdrawn
- Digital motor position sensor
- Commissioning exclusively via service function in BMW diagnosis system
On the X5, Active Steering is available for the first time on an all-wheel drive vehicle.
The variable steering transmission ratio offer the optimum gear ratio for every speed. With speeds of up to approx. 100 km/h, a very direct and agile vehicle performance is realized in conjunction with a small steering angle.
It is hardly necessary for the driver to span the steering wheel with his hands. This means that the controls on the steering wheel are easier and safer to control. Thus for parking you can steer from the left stop to the right stop with only two turns of the steering wheel.
At high speeds, steering becomes increasingly indirect, thus improving the straight-running stability and the general driving comfort.
The road speed dependent Servotronic adjusts the force required to turn the steering wheel to a reasonable degree, while the Active Steering influences the steering angle requirement. Thus Active Steering and Servotronic have different effects and perfectly complement each other. For this reason Active Steering is only offered in combination with the Servotronic.
Drive stability functions:
The possibilities of Active Steering are also exploited to stabilize the vehicle in oversteering situations.
The Active Steering can countersteer more rapidly and precisely that the average driver and stabilizes the car largely automatically. Another function increases vehicle stability during braking maneuvers on non-uniform road surfaces (split braking). The differences in frictional coefficients result in vehicle reactions and the driver has to compensate for these with conventional systems by countersteering.
Active Steering takes over this function and stabilizes the vehicle automatically. On one hand, it is easier to stay in control in this kind of situation and, on the other, the braking distance is reduced. This produces a tangible increase in safety compared with an identical vehicle without Active Steering.
- Adaptive Drive
With the optional extra Adaptive Drive the following are functionally combined:
Active Roll Stabilization Dynamic Drive (ARS = Dynamic Drive) and variable Impact Damping Adjustment (VDM = Vertical Dynamic Management).
The integration of both systems maximizes safety, comfort and responsiveness and is not available with any other SAV.
> Vertical Dynamic Management
The Vertical Dynamic Management offers the following advantages:
- Increased driving comfort
- Increased vehicle agility
- Improved independent steering performance and response to changing loads
The VDM increases driving comfort. Increased driving comfort is attained when the vertical movement of the vehicle body is reduced to the minimum: whether this is due to agitation of the vehicle by the road surface (unevenness, joints) or on curves.
The VDM controls the damper satellites in the actuation of the shock absorbers (impact force for individual wheel). To this end, the VDM control unit is connected with the damper satellites via the very high speed FlexRay databus. With a data transfer rate of 10 Mbit/s, FlexRay is significantly faster than the databuses employed on comparable vehicles (in the areas of body and powertrain/suspension).
In addition to the higher bandwidth, FlexRay supports a real-time data time transmission. FlexRay can be configured to be error-tolerant.
The damper satellites (= control units) electronically regulate the impact forces.
The damper satellites and the EDC valves are directly connected to the shock absorbers. Each damper satellite contains its own vertical acceleration sensor.
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> Active Roll Stabilization (Marketing designation Dynamic Drive)
Dynamic Drive provides active stabilizers on the front and rear axles. These active stabilizers support continuous adaptation to the current driving situation.
There is thus no necessity to make compromises between the basic attunement of the chassis to sporty or comfortable driving. When you are driving straight ahead Dynamic Drive is "sensitively" activated, thus offering the greatest possible degree of suspension comfort. Depending on the lateral acceleration, the lateral inclination when taking cures or avoiding obstacles will be minimized by a "sporty" setting of the stabilizers. The active stabilizers are vertically distributed in the center. The active stabilizer consists of the oscillating motor and the stabilizer halves mounted on the oscillating motor.
As one stabilizer half is connected with the shaft and the other with the housing, the stabilizer halves counter-rotate. The torque thus produced exerts a stabilizing effect on the rolling motion. The maximum system pressure is 180 bar.
The most important control variable is the lateral acceleration. In addition the following signals are evaluated on the PT-CAN:
- Lateral acceleration
- Yaw rate
- Vehicle road speed
- Steering wheel angle
- Electronic height control (simple level control)
Ride height is controlled by air being fed into or withdrawn from the air springs. The EHC control unit receives information about the ride height on the left and right-hand sides of the vehicle from the level sensors.
If the ride height is outside defined tolerances, the system will automatically activate the air supply unit to regulate to the specified level.
The system is activated and starts to regulate whenever a door or the tailgate is opened. The system is deactivated after a certain time (approx. 20 minutes).
The signals from the level sensors are filtered to distinguish between changes in load and other disturbances such as an uneven road surface. For correct use, two signals filtered at different frequencies are computed for each signal (low-pass filter with fast and slow filtering).
Fast filtering is always employed when regulation is in progress. This prevents the regulated height from exceeding the specified level. Slow filtering is employed when the vehicle is in motion. This mode of filtering eliminates oscillations induced by the road surface.
Both sides of the vehicle are regulated independently.
In other words, the comparison of specification to actual value is performed separately for each side (Exception: testing the minimum height and the control function "Intermeshing".)
With these control functions, the mean values of the left and right-hand sides of the vehicle are taken into account. The EHC control unit recognizes the different operating conditions from the incoming signals and messages. Depending on operating conditions, appropriately adapted control functions are activated.
- Parking brake (electromechanical parking brake = EMF)
The vehicle is equipped as standard with an electromechanical parking brake (EMF). The parking brake acts as a hand brake. The parking brake is actuated via the parking brake button in the central console.
- Exclusion of all safety-critical conditions
- Optimum functionality
- Highest availability
- Highest degree of comfort
The parking brake is designed to secure the parked vehicle against rolling away. When the engine is turned off, the EMF takes over braking: electromechanically via the servo unit.
When the engine is running, braking is control by the Dynamic Stability Control (DSC): hydraulically via the 4 disc brakes.
New from 10/07:
The vehicle has an automatic-hold function. The automatic-hold function is activated by a button behind the parking brake switch. The switch is linked to the EMF.
When the function is selected, the vehicle is hydraulically braked from the first application of the brake by the DSC until it comes to a complete halt. Stepping on the gas pedal releases the disc brakes and the vehicle continues in motion. The automated braking and release process supports driving in city traffic or in jams, for example.
The start assistant for starting on uphill slopes is integrated in the DSC (via signal longitudinal acceleration sensor).
- Tire pressure control (US version only)
The tire pressure control (RDC) is a system for monitoring the tire pressure when driving.
To this end, the tire pressure and the tire air temperature are measured at certain intervals on request by the RDC control device and telemetrically transmitted to the RDC aerial via a high-frequency transmission path.
The RDC aerial relays the signal back to the RDC control device via a sub-bus. The control device evaluates the received data.
Then the RDC control device forwards the data if necessary to the instrument cluster (KOMBI).
The driver can thus be informed about any correction required to the tire pressure or about a flat tire (check-control message).
The RDC monitors the tire pressure throughout the journey.
The driver sets the tire pressure to be monitored. He instructs the system via the control function in iDrive or via the RDC button to save the current tire pressure as the target pressure value (Reset).
The RDC control unit tests the target value for plausibility before saving it (axle by axle comparison of target pressures, minimum pressures).
A reset is only possible when the air pressure in all wheels is at least 1.6 bar. If the tire pressure of a wheel is under this limit, a check-control message will be issued immediately.
If the pressure difference between the wheels on an axle is > 0.4 bar, the reset will be rejected after the plausibility test. A check-control message will be issued. Remedy: Set the tire pressures to the correct values and repeat the reset.