BMW X5: Convenient-Start System - System Functions

The convenient-start system allows the engine to be started in a user-friendly manner as the starter motor automatically remains engaged until the engine is running.

When the START-STOP button is pressed, the CAS control unit first activates terminal 15. The relief relay for the ignition coils is activated.

When the START-STOP button is pressed, the CAS control unit checks that the brake pedal is depressed and the selector lever is in P or N.

The engine start process runs as follows:

• First, the EWS is checked via the EWS data wire.
• If the data is correct, the DME enables the ignition and the fuel injection.
• The CAS control unit switches battery voltage to the DME control unit via terminal 50E. This gives the signal for the required engine start.
• The CAS control unit switches battery voltage to the starter motor via terminal 50L. The starter motor is switched on by the DME via the starter inhibitor relay.

> E65, E66 and E70

The DME switches the starter motor on.

• The starter motor continues to turn until the CAS control unit receives the "engine running" signal from the DME through the data bus. The terminals 50 are then switched off by the CAS control unit.

  If the engine does not start, the terminals 50L and 50E will be switched off after a maximum of 20 seconds. The engine start is thus aborted.

Air supply: 2-stage differentiated air intake system "DISA"

The intake strokes of the pistons generate cyclic pressure waves in the inlet pipe.

These pressure waves travel along the inlet pipe and are reflected by the closed inlet valves.

A precise matching of the inlet pipe length with the valve response time produces the following effect: Shortly before the inlet valve is closed, a pressure maximum of the reflected air wave reaches the inlet valve.

This has a supercharging effect which pumps a higher proportion of fresh air into the cylinder.

The differentiated air intake system also makes use of the inherent benefits of both short and long inlet pipes.

• The effect of short inlet pipes or inlet pipes with a large diameter is a high efficiency in the upper engine speed range (and also low torque in the medium engine speed range).
• Long inlet pipes or inlet pipes with a small diameter make high torque in the medium engine speed range possible.

A front intake pipe is installed upstream of each resonating pipe. When the sliding sleeves are closed, the combined effect of the front intake pipe and resonating pipe is similar to that of a long inlet pipe.

The pulsating air column inside it increases torque in the medium engine speed range considerably.

To increase performance in the higher engine speed range, the sliding sleeves are opened. This largely reduces the dynamics in the front intake pipes. The short resonating pipes which are now effective can make high performance figures in the upper engine speed range possible.

The DME control unit adjusts the sliding sleeves via the two DISA servomotors (12 volts) with integrated transmission. Each DISA servomotor has one output stage. The information as to whether a downwards or upwards gearshift was made is saved by the DME control unit.

When the value falls below 4700 RPM, the DME control unit closes the sliding sleeve with the assistance of the DISA servomotors. When the value of 4800 RPM is exceeded, the sliding sleeves are opened again (N62B40TU: 4800 and 4900 RPM). At changeover, these engine speeds are displaced reciprocally (hysteresis) to prevent the sleeves opening and closing in rapid succession.

In the event of system failure, the sliding sleeves remain in their respective positions. The driver will be aware of system failure through a loss of power and reduction in the final speed.

Once the engine has been switched off (terminal 15 OFF), the sliding sleeves are run once to their limit position.

This prevents deposits accumulating and blockage of the sliding sleeve during longer journeys at low engine speeds.

Charge monitoring

The following input variables are used to monitor the charge state of the DME:

• Throttle-valve angle
• Valvetronic lift
• Air intake pressure
• Intake air-mass

From these 4 input variables on the inlet side, the DME calculates the charge state for all operating conditions.

"Valvetronic" variable valve gear

Valvetronic was developed to reduce fuel consumption.

The quantity of air supplied to the engine when Valvetronic is active is adjusted by the variable valve lift on the inlet valve and not the throttle-valve actuator.

An electrically-adjustable eccentric shaft changes the action of the camshaft on the roller cam follower via an intermediate lever. The result of this is variable valve lift.

With Valvetronic, the throttle-valve actuator is activated for the following functions:

• Engine start (warm-up)
• Idle speed control
• Full load operation
• Emergency operation

In all other operating conditions, the throttle valve only remains open far enough to induce a slight low pressure.

This low pressure is required to ventilate the tank, for example.

The DME control unit calculates the associated setting of Valvetronic using the position of the accelerator pedal and other variables.

The DME control unit activates the Valvetronic actuator motor on the cylinder head via the Valvetronic control unit. The Valvetronic actuator uses a worm gear to drive the eccentric shaft in the cylinder head oil chamber.

The eccentric shaft sensor records the current position of the eccentric shaft. The eccentric shaft sensor is equipped with 2 angle sensors.

The Valvetronic control unit adjusts the current position of the eccentric shaft via the Valvetronic actuator until the nominal position is reached.

For safety reasons, 2 angle sensors are used with characteristic curves which have opposing directions. Both signals are digitally transmitted to the DME control unit. The DME control unit supplies 5 volts to both angle sensors.

Both signals from the eccentric shaft sensors are continuously monitored by the DME control unit.

Checks are made as to whether the signals are plausible in their own right and also in relation to one another.

The signals may not differ. Where a short circuit or fault develops, the signals lie outside the measuring range.

The DME control unit continuously checks whether the actual position of the eccentric shaft corresponds with its nominal position. This makes it possible to detect any stiff movements in the mechanics.

In the event of a fault, the valves are opened as wide as possible. The air supply is controlled by the throttle valve.

If the actual position of the eccentric shaft cannot be detected, the valves are opened to the maximum extent without regulation (controlled emergency operation).

In order to achieve the correct valve opening, an adaptation must be made to balance all tolerances in the valve gear. During this adaptation process, the mechanical stops on the eccentric shaft are adjusted.

The positions registered are subsequently saved. These positions are used as the basis for calculating the actual valve lift at any point during operation.

The adaptation process is automatic: Each time the engine is restarted, the position of the eccentric shaft is compared with the values registered. If following a repair, for example, a different position of the eccentric shaft is detected, the adaptation process is carried out. In addition, the adaptation can be initiated via the BMW diagnosis system.

"VANOS" variable camshaft control

The variable camshaft control improves torque in the low and medium engine speed range.

Due to a larger valve overlap, the volume of residual fumes at idle speed is reduced. A recirculation of internal exhaust gas in the part-load range reduces the volume of nitrogen oxide.

The following is also achieved:

• Faster heating of catalytic converters
• Reduced exhaust emissions following a cold start
• Reduced fuel consumption

A controlled VANOS adjustment unit is mounted at both intake and exhaust camshafts (controlled using oil pressure).

A VANOS solenoid valve is used to control the VANOS adjustment unit. The required position of the intake and exhaust camshaft is calculated using the engine speed and load signal (dependent on intake temperature and engine temperature). The DME control unit activates the VANOS adjustment unit accordingly.

The control of the intake and exhaust camshaft is variable within their maximum adjustment range.

Once the correct camshaft position has been reached, the VANOS solenoid valves ensure that the oil volume in the servo control cylinders in both chambers remains constant. This keeps the camshafts in this position.

To perform the adjustment, the variable camshaft control requires information on the current position of the camshaft. Camshaft sensors on the intake and exhaust end record the position of the camshafts.

When the engine is started, the inlet camshaft is in the end position ("retarded" position). When the engine is started, the exhaust camshaft is pretensioned by a spring and held in the "advanced" position.

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