Gas injection system function

P07.54-2118-79

Phantom view

1 Gas cylinder 1

2 Gas cylinder 2

3 Gas cylinder 3

4 Gas fill line

5 Gas filler connection with check valve

Y58/1 Purge control valve

Y107/1y1 Gas cylinder 1 gas shutoff valve

Y107/1y2 Gas cylinder 2 gas shutoff valve

Y107/1y3 Gas cylinder 3 gas shutoff valve

Y107/2 Pressure control unit

45 Fuel filler neck

75 Fuel tank

N3/10 ME-SFI [ME] control unit

N118/2 CNG control unit

Function requirements for gas injection system - general points

 Circuit 87M (engine control ON)

 Engine running

Gas injection system - general points

The CNG control unit in combination with the gasoline injection and ignition system and in electrical connection with the sensors and actuators for engine 270 DE creates the engine timing.

The abbreviation CNG stands for:

C = Compressed

N = Natural

g = Gas

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The engine 270 DE CNG can preferably be refilled with a so-called
H-gas (H=High) with a high gross calorific value or L-gas (L=Low) with a low gross calorific value.

It can, however, also be filled with appropriately prepared biogas (biomethane), which meets the requirements of DIN 51624.

LPG (Liquefied Petroleum Gas) should not be used in this vehicle.

The engine 270 DE CNG is based on the engine 270.920. It allows both gasoline operation and gas operation.

The CNG control unit is connected electrically with the ME-SFI [ME] control unit to control the fuel and gas injection. To do this, it is networked via the drive train sensor CAN (CAN I) and over four direct lines with the ME-SFI [ME] control unit. The CNG control unit CNG also controls and monitors the complete gas system in the vehicle.

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The vehicle and the engine 270 DE were extended by the following components due to gas injection:

- CNG control unit

- Gas filler connection, located behind the fuel filler door

- 3 gas reservoirs with the respective gas reservoir 1 to 3 gas shutoff valve

- pressure regulating unit with a gas high-pressure sensor (Y107/2b1) and pressure regulating valve (Y107/2y1), which reduces the system high pressure from about 200 bar to the system lower pressure of 2.5 to 4 bar

- gas distribution rail with gas injection valves gas of cylinders 1 to 4 (Y106/1 to 4) and the low pressure and temperature sensor GAS (B18/6)

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Gas injection system function sequence

The basic operating mode is natural gas operation. The driver does not have any option to to select between the operating modes.

The CNG control unit switches autonomously into gasoline operation for:

- empty gas reservoirs

- in case of errors in the gasoline system (hydraulic)

- in case of errors in the natural gas system

- for short-time after each refilling

The ME-SFI [ME] control unit calculates the individual injection signals (valve opening time, valve opening duration) for each of the gas injection valves gas (Y106).

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The ME-SFI [ME] control unit transmits the injection signals directly to the CNG control unit and this actuates the gas injection valves gas directly.

Data are exchanged continuously between the ME-SFI [ME] control unit and CNG control unit over the drive train sensor CAN.

After each gas refueling, the opening time of the gas injection valves gas is adapted to the available gas quality (energy content). The gas quality is determined over the mixture adaptation. The possible range depends greatly on the gas quality.

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The CNG interface control unit detects when gas refueling has taken place from the pressure difference in the gas reservoirs (before and after refueling).

For an engine start switching takes place for a short time into gasoline operation. The gasoline operation is maintained until various temperature-dependent parameter values are reached or until the is oxygen regulation release. Only then can natural gas operation be selected.

If a predefined remaining fuel level is reached in gasoline operation, and there is a sufficient gas reserve, then gas operation is selected automatically. If the gas reserve is then used up, then gasoline operation is selected again.

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Limp-home mode function

System errors detected in the gas system can cause the gas system to be shut off.

It may become necessary for the gas system to be activated with the aid of Xentry Diagnostics through deletion of the errors in the fault memory.

If the ME-SFI [ME] control unit receives a "crash signal" indirectly via the chassis CAN (CAN E) or directly from the supplemental restraint system control unit (N2/10), the signal is passed on via the drive train sensor CAN to the CNG control unit and both of the gas/gasoline systems are switched off.

In this case, the natural gas system can only be performed over Xentry Diagnostics.

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All work on the gas injection and ignition system must be carried out only by specially trained service personnel.

More information concerning requirements on personnel and measuring equipment (for example: General information concerning leak testing of natural gas system) is available in the WIS under the information "Model testing and repair work (AR)" and "General information (AH)".