Description and Operation
System Operation
The null (liquefied petroleum gas) gas system is a completely self-contained fuel system which is present in addition to the petrol fuel system. The two fuel systems are independent of each other. The null fuel system is exclusively controlled by the gas control module.
Refuelling the vehicle
4
Hose, gas pressure release valve
When the vehicle is refueled, the non-return valve in the gas tank filler neck is opened against the spring force by the pressure applied from the forecourt fuel pump. The liquid null flows through the gas tank filler neck line and the gas valve unit non-return valve into the gas tank. The rising null level moves the float upwards. When the float reaches the 80% fill level limit, a piston retaining rod engages in a cut-out in the float link. This causes the piston to be pressed downwards and close the filler hole in the gas fill level limiting valve. The result is that there is a rise in pressure in the forecourt fuel pump, which then stops. After it has stopped, a spring lifts the piston retaining rod out of the cut-out again, so that the float can operate normally again. A gear transmits the movement of the float via a shaft onto the float magnet. The fuel gauge magnetic follower, which has gas-tight separation from the tank interior, moves the slider over the resistance board. Above the gas operation switch, a voltage is created at the resistance board. As the slider ring moves over the resistance board, the resistance changes. The resulting change in voltage is evaluated in the gas operation switch. The gas fill level null (light emitting diode)s are actuated in accordance with the evaluated signal.
Gas fill level display
2
Gas fill level
null for reserve and 1/4 full
Comments:
Flashes when reserve is reached.
3
Gas fill level
null for 1/2 full
4
Gas fill level
null for 3/4 full
5
Gas fill level
null for full
The gas fill level nulls only light up when gas operation is requested or activated. When the gas tank is full, all four nulls illuminate. As soon as the level falls below the minimum fill level set for an null, that null is switched off. If the permitted maximum gas fill level of 80% is exceeded, all four gas fill level nulls flash simultaneously. This may happen if the null expands because of a temperature rise after the tank is filled, or the gas fill levels are set incorrectly. If the gas level reaches or goes below the fill quantity set as reserve, the gas fill level null for reserve will start to flash.
The signal from the gas fill level sensor is not used for engine management.
Safeguarding against loss of gas with a high pressure loss: Thanks to the non-return valve at the gas tank filler neck and the non-return valve at the gas tank, the refueling process is doubly safeguarded. If the gas filler neck line becomes damaged, the non-return valve in the gas valve unit prevents gas from escaping from the gas tank. This does not protect against low quantity gas losses.
Pressure limitation in the ring-shaped gas tank
When the tank is refueled to capacity, the pressure in the gas tank rises to about 20 bar. The pressure depends on the setting of the forecourt fuel pump. Because of increasing ambient temperatures, the pressure in the gas tank can rise further. The gas pressure release valve opens as soon as the pressure in the gas tank rises above the maximum permitted pressure of 28 bar. The null flows from the exhaust valve and is routed outwards via the two gas tank ventilations.
Driving
Safeguarding against loss of gas with a sudden pressure loss: During petrol operation, the front and rear gas shut-off valves are closed. This limits any occurring loss of gas between the gas valve unit and the gas shut-off valve. If a heavy loss of gas occurs in this area during null operation, the pressure drops in the gas distributor. The gas pressure and temperature sensor for the gas distributor sends a signal to the gas control module. The gas control module closes the front and rear gas shut-off valves and switches to petrol operation. Further gas escape is prevented. The petrol operation warning buzzer notifies the driver of the switch-over to petrol operation. Operation using null can no longer be activated as the preconditions for it are not met. Gas loss between the front gas shut-off valve and the gas distributor is prevented in the same manner. This does not protect against low quantity gas losses.
Further information on driving can be found in section 303-14.
Component Description
Gas fill level sensor and display unit
The gas fill level sensor and display unit comprises a resistance board and a magnet with slider and pointer which is moved by the magnetic field of the float magnet. The pointer shows the fill level on the scale.
Front and rear gas shut-off valves
The gas shut-off valves are electromagnetically operated valves. In their currentless state the gas shut-off valves are closed. The solenoid coil is outside the gas system, the valve is inside it.
High pressure gas filter
The high-pressure gas filter is a fine filter with a specified direction of flow.
Gas vaporizer
The gas vaporizer controls the pressure by means of a spring-loaded membrane. The spring pre-load is steplessly adjustable. A vacuum connection on the rear of the membrane permits additional manipulation using vacuum. The evaporator needs the heat from the engine coolant to evaporate the nullwithout any ice forming.
Low pressure gas filter
The low-pressure gas filter is a fine filter with a specified direction of flow.
