Oil Level Sensor: Description and Operation
Oil Level Indicator
The engine on the Cayenne S Hybrid is equipped with an oil level sensor that operates according to the ultrasonic measuring principle (PULS = Packaged Ultrasonic Level Sensor) to display the oil level in the instrument cluster.
Operating principle
The transmitted ultrasonic impulses are reflected by the oil/air boundary layer. The oil level is calculated from the time difference between the transmitted impulse and the return impulse, taking into account the speed of the sonic signal.
Sensor electronics integrated in the oil level sensor housing process the measured signal and then output a PWM signal (PWM = pulse width modulation).
Advantages of the ultrasonic sensor:
- Sensor signal available almost immediately (after approx. 100 ms)
- Low current consumption < 0.5 A
The signal from the oil level sensor is evaluated in the engine control unit, which then transmits the calculated values to the CAN Drive. The diagnostic interface for the data bus (Gateway) forwards the signals to the corresponding bus systems.
The indicator used in the Cayenne S Hybrid displays a realistically calculated oil level. The oil dipstick is therefore omitted. The customer still has the option of checking the oil level via the indicator on the instrument cluster. The pipe that usually holds the oil dipstick is still installed in the vehicle as it can be used in the workshop to extract oil from the engine. The end of the pipe is closed off with a plug.
Calculating the oil level
Two methods are used to calculate the oil level: dynamic and static measurement. Dynamic measurement takes place while the vehicle is driving. Key measurement factors here are:
- Engine speed
- Axial and lateral acceleration from the PSM control unit
- Engine cover contact (bonnet must be closed)
- Engine temperature (engine must be at operating temperature)
- Driving cycle since the engine cover was last opened > 30 miles (50 km)
- A certain number of values must have been measured during the driving cycle The dynamic measurement method is more accurate and is used most of the time.
However, there are some instances where dynamic measurement cannot be used.
Measurement is interrupted if:
- Acceleration values exceed 3 m/s2,
- Oil temperature exceeds 284° F. (140° C.) and
- Contact switch for the engine cover is actuated.
Static measurement is used where dynamic measurement is not possible such as the instances mentioned above. Static measurement is used if the:
- Ignition is "on". The measuring process is initiated as soon as the driver's door is opened in order to obtain a measured result as quickly as possible.
- Engine oil temperature > 104° F. (40° C.),
- Engine speed < 100 rpm and
- Engine is off > 60 sec.
The acceleration values from the PSM control unit are also included here in case the vehicle is parked on an incline. The signal from the parking brake is also used. A low level warning is issued if the oil reaches a level where the engine could become damaged (value below minimum level). A high level warning is issued if the oil reaches a level where the engine could become damaged (value above maximum level).
Example of when static measurement is required
The vehicle is refuelled at a service station and the bonnet is opened to refill the washer fluid. Dynamic measurement is interrupted when the contact switch for the engine cover is actuated. The signal from the oil level sensor is read via CAN. In this instance, the oil level would only be displayed again after a driving cycle of 30 miles (50 km). The customer would not be able to check the oil level at the service station as a result. Mechanics must also be able to check the oil level via the indicator when the vehicle is parked in the workshop.