Electrical systems: Drive

With BMW Efficient Dynamics  , the Sports Activity Vehicle in the model year 2008 sets new standards in drive dynamics and wear reduction.

The comprehensive program 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 10/2007 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.

• 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 catalyzator 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.

• 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 under steering, 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.