Fuel dispenser-distributor of the K-Jetronic system (BMW 5 Series E12)

The metering distributor regulates the amount of fuel supplied to the injectors in proportion to the amount of air supplied.

The fuel metering distributor consists of a pressure regulator, a distribution plunger, differential pressure valves and a control pressure circuit.

Pressure regulator

The pressure regulator regulates the fuel supply pressure within the range of 4.5-5.2 kg/cm². Excess fuel returns to the tank through the drain pipe.

When the engine is stopped, the pressure regulator reduces the fuel pressure in the system to a value slightly less than 3.3 kg/cm², i.e. the opening pressure of the injectors. This eliminates the possibility of spontaneous combustion of the working mixture.

Distribution plunger

The amount of fuel supplied to the engine cylinders changes depending on the position of the distribution plunger, in the walls of which there are rectangular slots, the flow cross-section of which changes as the plunger moves relative to the windows (one window per cylinder), made in the plunger sleeve.

Fuel dosed in this way (proportional to air flow) is supplied to the upper chambers of the differential pressure valves.

Differential pressure valves

Four differential pressure valves (one per cylinder) have two chambers separated by a diaphragm. Regardless of the amount of fuel supplied, they maintain a constant pressure drop at the level of the distribution plunger slots. Due to this, the fuel pressure in the system and the pressure of the fuel supplied to the injectors are maintained at a constant level.

As the fuel supply to the upper chambers increases, the pressure increases, the diaphragm bends downward, completely opening the fuel supply holes to the injectors.

When the fuel supply to the upper chambers decreases, the diaphragm bends upward, reducing the flow area of the fuel supply holes to the injectors.

Control pressure circuit

The pressure in the control circuit is regulated by a pressure regulator and can vary within the range from 0.5 kg/cm² on a cold engine to 3.4-3.8 kg/cm² on a warm engine. With the throttle valve fully open, the control pressure decreases to 2.9 kg/cm², causing enrichment of the working mixture at full engine load.

To prevent uncontrolled beating of the air flow meter pressure disk under the influence of air flow pulsations (at low crankshaft speed or at full engine load) a shock-absorbing throttle restriction is provided.

(Examine the original source using the link on the website: «BMWMan.ru»)