Rail pressure sensor

The rail-pressure sensor is threaded into the end of the fuel-distribution rail.

This sensor furnishes the DME digital engine electronics system with a measurement of the fuel pressure downstream from the high-pressure pump.

The rail-pressure sensor supports the rail-pressure control process. The rail-pressure sensor's signal serves as a vital input signal for the DME, which employs it in defining how it controls the quantity-control valve. The quantity-control valve is a component within the high-pressure pump.

Strain gauges are employed to monitor the rail pressure. A membrane equipped with strain-gauge strips is deflected by the applied pressure. The changes in resistance in the strain gauge are electronically detected by a Wheatstone bridge and evaluated. The measured voltage is then included as an actual value for closed-loop control of rail pressure.

Fig 1: Identifying Rail Pressure Sensor Components

Courtesy of BMW OF NORTH AMERICA, INC.

A signal wire relays the rail-pressure information back to the DME digital engine electronics control unit. The effective signal for rail pressure fluctuates according to pressure levels. The measurement range of approximately 0.5 - 4.5 volts corresponds to rail pressures extending from 0 MPa (0 bar) to 25 MPa (250 bar).

Fig 2: Rail Pressure Characteristic Curve

Courtesy of BMW OF NORTH AMERICA, INC.