BMW X5: Oil Supply - System Functions

The oil condition sensor reports the engine oil level and engine oil quality back to the DME control unit. A temperature sensor in the oil condition sensor indicates the engine oil temperature. The engine oil temperature is used together with the coolant temperature to calculate the engine temperature.

The oil pressure is indicated by the oil-pressure switch.

The oil level is also measured for the electronic oil level check. The 2nd capacitor in the upper part of the oil condition sensor registers the oil level. The capacitor is at the same level as the oil level in the oil sump.

As the oil level falls, the capacitance of the capacitor falls. The electronic evaluation unit creates a digital signal from this. The DME then calculates the engine oil level.

The DME control unit activates the warning and indicator lamp in the instrument cluster via the PT-CAN (red: oil pressure low; yellow: oil level low).

Electronic oil level check:

The dipstick now has a black handle. The engine oil level is measured by the oil condition sensor.

The measured value is displayed in the Central Information Display (CID).

The signal from the oil condition sensor is evaluated in the DME. Besides the oil level, the thermal oil level sensor also indicates the engine oil temperature.

Condition Based Service:

In addition, the engine oil quality is measured for the Condition Based Service (CBS).

The electrical material properties of the engine oil change as the engine oil wears and ages. The changed electrical properties of the engine oil (dielectrics) cause the capacity of the capacitor in the oil condition sensor to change.

The electronic evaluation unit converts the measured capacity into a digital signal.

The digital sensor signal is transmitted to the DME as a statement about the condition of the engine oil

The DME uses this to calculate the next engine oil change as part of Condition Based Service (CBS).

Engine cooling

The opening and closing of the mapped thermostat is controlled by a characteristic map. This regulating operation can be split into 3 operating ranges:

• Mapped thermostat closed:
  The coolant only flows through the engine and the coolant circuit is closed.
• Mapped thermostat open:
  The entire coolant volume flows through the radiator. This results in maximum use of the available cooling output.
• Control range of the mapped thermostat:
  A proportion of the coolant flows through the radiator. The mapped thermostat maintains a constant coolant temperature within the control range at the engine inlet.

  In this operating range, the coolant temperature can now be selectively controlled with the assistance of the mapped thermostat. This means that a high coolant temperature can be set in the part-load range of the engine. High operating temperatures in the part-load range result in improved combustion. This in turn leads to reduced consumption and exhaust emissions.

  During full load operation, certain disadvantages are associated with higher operating temperatures (retarding of ignition due to knock).

  A lower coolant temperature is therefore specifically set during full load operation with the assistance of the mapped thermostat.

Knock control

The engine is equipped with a cylinder-selective adaptive knock control.

4 knock sensors detect combustion knock (cylinders 1 and 2, cylinders 3 and 4, cylinders 5 and 6, cylinders 7 and 8). The sensor signals are evaluated in the DME control unit.

If the engine is operated with combustion knock for longer periods of time, this can cause serious damage.

Knock is encouraged by:

• Increased compression ratio
• High cylinder fill levels
• Inferior fuel grade (RM/MM)
• High intake-air and engine temperature

The value of the compression ratio can also become too high due to spread due to deposits or the manufacturing process. On engines without knock control, these unfavorable influences must be taken into account. The design of the ignition system must include a safety gap to the anti-knock limit. This makes reduced efficiency in the upper load range unavoidable.

The knock control prevents knock. The firing point of the relevant cylinder (cylinder-selective) is set as far as possible in the retarded direction only when a knocking risk is present.

This means that the ignition control grid can be designed around ideal consumption values (without having to take the anti-knock limit into account). A safety margin is no longer necessary.

The knock control performs all the necessary corrections to the firing point due to knock and also makes trouble free driving with regular grade petrol (minimum RM 91) possible. The knock control provides:

• Protection from damage caused by knock (also in unfavorable conditions)
• Reduced consumption and increased torque throughout the entire upper load range (according to the quality of fuel used)
• High economic efficiency through optimum use of the available fuel quality and by taking the specific engine condition into account

The knock control self-diagnosis performs the following checks:

• Check for signal interference, e.g. breaks in wiring or defective connector
• Self-test for evaluating circuit
• Check of engine noise level recorded by the knock sensor

If a fault is identified during one of these checks, knock control is deactivated. An emergency program assumes control of the ignition angle. A fault is simultaneously registered in the fault memory. The emergency program guarantees damage-free operation from a minimum of RON 91. The emergency program depends on the load, engine speed and engine temperature.

Tank ventilation

The fuel evaporation control valve controls the regeneration of the activated carbon filter with scavenging air.

Scavenging air drawn through the activated carbon filter is enriched with hydrocarbons (HC) depending on the loading of the activated carbon. The scavenging air is subsequently fed to the engine for combustion.

The formation of hydrocarbons in the fuel tank is dependent on:

• Fuel temperature and ambient temperature
• Air pressure
• Fill level in the fuel tank

In a current-free state, the fuel evaporation control valve is closed. This prevents the ingress of fuel vapor from the activated carbon filter into the inlet pipe when the engine is switched off.

Closed-loop Lambda control system

Optimum efficiency of the catalytic converter can only be achieved if an ideal fuel/air ratio is used for combustion. Oxygen sensors are used upstream and downstream of the catalytic converter.

The oxygen sensors upstream of the catalytic converter have a steady characteristic output curve (measure oxygen content in rich and lean ranges.) The measurement method employed by this oxygen sensor is different to an oxygen sensor with an erratic characteristic output curve. The oxygen sensor is therefore connected using 6 pins instead of 4.

• Oxygen sensors upstream of catalytic converter
  The oxygen sensors upstream of the catalytic converter (control sensors) are used to assess the composition of the exhaust gas.

  The control sensors are screwed into the exhaust manifold.

  The oxygen sensors measure the residual oxygen content in the exhaust fumes. The voltage values determined are relayed to the DME control unit. The DME control unit corrects the mixture composition by adjusting the injection period.

  Values which are greater or less than l = 1 are aimed at depending on the operating condition.

• Oxygen sensors downstream of catalytic converter
  The oxygen sensors downstream of the catalytic converter (monitoring sensors) are used to monitor the control sensors. In addition to this, the function of the catalytic converter is monitored.

To ensure full operational reliability of the oxygen sensors upstream of the catalytic converter, a temperature of approximately 750 ºC is required (350 ºC for oxygen sensors downstream of the catalytic converter). For this reason, all oxygen sensors are heated.

The oxygen sensor heating is controlled by the DME control unit. When the engine is cold, the oxygen sensor heating remains switched off, as condensation which is present would otherwise destroy a hot oxygen sensor due to thermal strain.

This means that the closed-loop Lambda control only becomes active a short time after the engine has started, once the catalytic converters have warmed up. The oxygen sensor is initially warmed up using a reduced heating power, to avoid imposing unnecessary loads on it due to thermal strain.

Torque monitoring

The DME monitors the torque required.

The following systems may request torque data from the DME control unit:

• Active Steering
• Servotronic
• Alternator
• Cruise control
• Dynamic Stability Control
• Transmission management
• Internal monitoring against "self-acceleration"

Evaluation of road speed signal

The road speed signal is required by the DME control unit in order to perform several functions:

• Speed limiting function:
  Once the maximum road speed has been reached, the fuel injection and ignition are adjusted. If required, individual ignition and injection signals are suppressed. A "soft" speed limiting function is thus carried out.
• Control of A/C compressor:
  When the air-conditioning system is switched on, the A/C compressor is switched off during full-load acceleration, provided that: the car's road speed is less than 13 km/h.
• Idle speed control:
  If the car's road speed is 0 km/h, the idle speed is adjusted (depends on A/C compressor ON, selected drive position for automatic transmission, light ON).
• Poor-road-surface detection:
  At low road speeds, the check for smooth engine operation is switched off.

A/C compressor activation

The DME control unit supplies the signal to actuate the A/C compressor.

The A/C compressor is switched off under the following conditions:

• Full engine load
• car's road speed under 13 km/h
• Engine overheating

The IHKA actuates the A/C compressor. The DME sends the signal on the bus system.

Intelligent alternator regulation

Intelligent alternator regulation systematically controls the battery charge state.

The battery is predominantly charged in overrun mode.

Depending on the battery charge state, the battery will not be charged during an acceleration phase.

Active air flap control

Active air flap control regulates the air supply for the engine and assemblies cooling system by only opening the air flaps as they are needed.

READ NEXT: