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D-Jetronic




Function

In 1967 the D-Jetronic was the first electronically controlled multi-point injection. This also resulted in the first analogue control device (1) that was used in the automobile. The complexity of the mixture processing led to an electronically controlled system with sensors, control device and actuators.

How it works

Per cylinder, one injector (2) respectively, is arranged just before the intake valve (inlet manifold injection). Through a distributor pipe, and 3 volts (!) of operating voltage, these injectors are supplied by pump and filter with fuel. The pressure control valve at the end of the distributor pipe is adjusted to 2 bar injection pressure and can be corrected by the workshop accordingly. The injection amount is dependent on the injection pulse timing. The fuel injection start is controlled by a special contact (5) in the ignition distributor (4). Afterwards the contact-breaker points take over this function.

The equipment got its name from the pressure sensor (3). Two air correctors, filled to normal pressure, are surrounded by the pressure ratios in the inlet manifold. If these ratios change, the air correctors shift an iron core in a magnetic field. They are registered, together with the full load position, by the control device. In addition, it is informed by a transducer in the throttle valve about acceleration processes and about their idling or full load position. For cold starting, an additional cold start valve is mounted, which is not controlled by the control device, but by a separate, (dependent on temperature and time) thermo time switch and is supplied with current through terminal 50. The warming up is regulated by an auxiliary air valve (7). A bi-metal, switched on by the ignition, slowly blocks, time-wise and also motor temperature dependent, the bypass channel around the throttle valve (6).

Sensors

Pressure sensor (3), temperature sensor (coolant), thermo time switch, throttle switch, ignition signal (terminal 1)

Actuators

Injection valve (2), relay (fuel pump)

Next subject

L-Jetronic


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