Audi A4

since 1994 release

Manual of the car

The coordinated work of separate details

When the engine works, the pistons rising and falling in cylinders soak up air. If you completely wring out the accelerator pedal, then the engine soaks up the maximum quantity of air as in this case both butterfly valves are completely open. It is necessary for neat job of the engine that with the soaked-up air fuel in an exact proportion mixed up. For definition of a proportion of air and gasoline in working mix in MPI the mass of the soaked-up air is used. In MPFI as comparative size serves information on pressure in an inlet collector and temperature.

Now the control unit can give the correct signals for opening and closing of valves of injection. Long opening is provided for big amount of fuel, short time — at the need for a small amount of fuel.

Start

For start of the cold engine more saturated is necessary, i.e. working mix rich with fuel as the set of droplets of fuel settles on walls in the field of absorption on their way to combustion chambers and does not participate in combustion process any more. Therefore the fuel share in fuel-air mix has to be raised.

During management of start of the cold engine injection duration valves increases. Such factors as temperature of cooling liquid and frequency of rotation of the engine, influence injection duration. After a certain speed of the engine the amount of fuel necessary for start of the cold engine, slowly decreases and begins to correspond to standard.

Heated-up engine

After start the engine some time needs the enriched working mix as still certain amount of fuel is condensed in the field of absorption. For this purpose there is "a poststarting increase". Depending on temperature some time moves more fuel. The control unit obtains the necessary information on engine temperature from the sensor of temperature of cooling liquid.

Engine oil, quite viscous at the cold engine, causes the increased internal friction in the car. The increased effort to hold engine turns is necessary. Already mentioned idling stabilization valve is intended for ensuring giving of this increased amount of working mix.

Idling

At the closed butterfly valve via the roundabout channel around a butterfly valve a small amount of air is carried out. This air is fixed by the air stream measuring instrument, or pressure sensor and therefore in working mix for idling it is supplemented with necessary amount of fuel. In general working mix idling contains more gasoline, than at usual operation in order that the engine worked exactly and trouble-free in ignition.

The amount of air passing the roundabout channel (and, therefore, engine speed idling), is defined by the idling stabilization valve.

Partial loading

At partial loading the engine receives standard amount of fuel. At the same time significance is attached to minimization of fuel consumption.

Accelerations

If the accelerator pedal is suddenly wrung out, then the enrichment of fuel-air mix necessary for acceleration when the gain of the soaked-up amount/weight of air in a second exceeds a certain size is caused. Also the potentiometer of a butterfly valve gives a signal of acceleration. At the cold engine accelerations require bigger amount of fuel. Therefore the control unit estimates each impulse of the measuring instrument of a stream of fresh air or a sensor of pressure and a potentiometer of a butterfly valve as a signal of acceleration and increases fuel supply.

Full loading

The potentiometer of a butterfly valve shows to the control unit that the driver completely wrung out the accelerator pedal. To develop the maximum power, the engine receives more enriched working mix now (enrichment of working mix at full loading).

Mode of compulsory idling

At the movement downhill with the released accelerator pedal it is not necessary to give fuel to the engine. The car itself slides at the expense of the weight or dispersal. (From its potentiometer) the control unit recognizes by high turns of the engine and the provision of a butterfly valve when there is a mode of compulsory idling, and can "save fuel".

Restriction of speed

The system of injection compares the frequency of rotation of the engine to the maximum speed of 6500 rpm at present and at their excess just closes "the crane with fuel".