Oil Sensor, Function

Oil Sensor, Function




B40 Oil sensor (oil level, temperature and quality)
2 Temperature sensor (PT1000)
A Capacitive measuring range
C1 Top condenser
CL Capacitive air
COIL Capacitive engine oil
C2 Bottom condenser
h Fill level

The sensor is used to detect oil data concerning oil level, temperature and quality (B40). The data is passed on by the engine control unit over CAN to the instrument cluster and used there to calculate the individual service intervals. Oil top-ups are automatically recognised and extend the service interval. The data can be displayed on the instrument cluster. Overfilling of engine oil, error messages, overheating of engine oil and an upcoming oil change are automatically displayed.

The measuring principle of the oil sensor is a capacitance measurement, whereby the capacitance is dependent upon the oil level. The measuring system consists of two cylinder condensers which possess a metal pipe as a common external electrode. Both other electrodes are arranged over each other as an inner pipe.
The dielectric constant of the engine oil is determined by the lower condenser (C2) which is always full of oil
( approximately 2.3 to 4.0).

The fill level (h) is then determined by the upper condenser (C1) using the dielectric constant. The capacitance of the upper condenser (C1) is calculated on the basis of a parallel connection with two condensers which have air and engine oil
as a dielectric material.

The condensers are located in a plastic housing which serves as a damping cup. The engine oil flows through the feed bore holes into the housing between the condensers.
The measures capacitances are transmitted over screened cables to integrated electronics.
A temperature sensor on the base of the oil sensor detects the engine oil temperature for switching of a cylinder.
All results of measurement are prepared by the electronics as a PWM - signal (pulsewidthmodulated).
The engine control unit calculates the oil level based on the capacitance values received.