April 15, 2008
Daimler developing advanced oil-change sensor
Who wouldn’t want to change their oil less often?
Researchers from Daimler AG have developed a practical system that allows oil quality to be monitored directly onboard a vehicle. This helps reduce operating costs, especially in commercial vehicles. The sensor is being developed first for large trucks, and is projected to cut oil-change frequencies by 25%.
The longer engine oil remains in use, the more it is susceptible to impurities. Its quality is impaired, and it gradually loses its lubricating effect — ultimately leading to engine damage. With up to 40 liters of oil in a truck’s diesel engine, an oil change should take place as early as necessary, but as late as possible.
In view of the many external conditions to be taken into account, calculating the precise maximum service interval on the basis of mathematical models alone is difficult. A software solution must combine and assess various parameters: the engine oil temperature, the frequency with which the engine is started, mild or harsh conditions of use, and the particular circumstances of the vehicle’s operation and environment.
In order to determine the ideal moment for the next servicing, Daimler researchers are using a special sensor that provides clear readings. This sensor, which is integrated into the oil circuit and registers the characteristic parameters, allows the engine oil to be monitored directly.
To evaluate the quality of the oil, its so-called permittivity is calculated by means of an AC potential applied between the interior and exterior pipes of the oil-filled sensor. This parameter is a measure of the extent to which the oil can transmit the applied electric field. If the engine oil is contaminated by water or soot particles, it polarizes to a greater extent and its permittivity increases.
However, not all impurities can be registered with sufficient precision via the electric field. The researchers are using viscosity as a further quality marker to detect any diesel fuel that may have found its way into the oil. In the laboratory, they use an orifice viscometer (a container with a small opening through which the oil flows out). The time required for this process (the “efflux time,” which is dependent on the oil’s flow characteristics), is a direct measure of its viscosity. This in turn gives an indication of the oil’s remaining lubricating quality.
The Daimler researchers are also measuring viscosity while the vehicle is in motion by observing the oil’s side-to-side motion in the sump. The more slowly the oil moves, the higher its viscosity. The oil sensor registers this movement, and the viscosity calculated on this basis.
One single sensor, and the intelligently processed information, which is already available onboard the vehicle, is sufficient to determine the various parameters of the engine oil.
Source: Daimler AG
