The invention is based on a fuel injection pump for internal combustion engines as set forth hereinafter. With the increasing use of the diesel engine, particularly in vehicles, the demand on the performance of a piece of injection equipment has also correspondingly risen. Not only are the exhaust gas values of the engine to be improved, but the combustion noises are to be reduced and a more advantageous driving characteristic is demanded, for example a largely uniform idling speed under changed driving conditions which occur when an air-conditioning system is additionally switched on or the engine is still cold. Such an idling load can lead, for example with a cold engine without additional facilities, to the stalling of the engine as the injected idling fuel quantity is too small. Thus, the injected quantity required for maintaining an adequate idling speed with a cold engine with additional idling load can be greater than the injected quantity required with a hot engine and full loading. On the other hand, the degree of nonuniformity during idling is high at the relatively low speeds so that differences of engine characteristics which affect the idling have a relatively great effect. In this connection, tolerances in the force of the idling spring or even pump frictions have a considerable effect on the quality of regulation of the idling so that it would be necessary to adjust the idling spring.
In a known fuel injection pump (German Offenlegungsschrift 35 00 341), the idling spring of the speed regulator is therefore suspended to be fixed to the pump housing with its end facing away from the regulator levers, the respective spring pretension being adjustable via an adjusting lever. This mainly achieves that the idling can be adjusted separately and very finely independently of the other regulator variables. The idling spring can be constructed to be very soft for its spring travel, which results in a lower degree of nonuniformity and it, above all, can be achieved that in overrun operation, when the vehicle pushes the engine and the gas peddle is in its zero position, a small quantity is always injected, that is to say the injected idling quantity is not also controlled to be zero. The main advantage of this is that when power is applied again, no "hole" occurs in the fuel supply which has an unpleasant effect, particularly in a diesel engine, since, due to the high compression of the diesel engine, a correspondingly high braking effect is produced by the engine on the vehicle when no fuel is supplied. This arrangement of the idling spring does not, however, eliminate the problem of increasing the injected quantity during cold idling.
In another known fuel injection pump of a similar type (German Offenlegungsschrift 28 44 910), the fuel injection pump regulation is acted upon via a temperature transmitter, the control variable of which is the cooling-water temperature of the internal combustion engine, the idling speed being regulated in such a manner that it decreases with increasing temperature. For this purpose, the pretension of the idling spring is changed by a stop, which determines the spring pretension, being changed by the temperature transmitter. Since the idling spring and the actual regulating spring in this regulator are connected in series, with appropriate limitation to the travel of the idling spring, either the initial position of a rotating lever, which engages the tension lever via a starting lever and is used for shutoff, or the point of suspension of the regulating spring or the initial position of the adjusting lever pretensioning the regulating spring can be changed via the temperature transmitter. Whilst the possible lever travel of the shut-off lever is reduced with increasing temperature, this travel is increased with increasing temperature in the case of the adjusting lever. As a result, the idling spring is relieved more with increasing temperature by the latter in the zero position. Due to the greater relief, the cut-off speed is set to a lower speed in idling and, respectively, causes a reduction in the fuel quantity to be injected.
This latter known regulating system, however, has the disadvantage, initially mentioned, of a high proportionality factor with a relatively hard spring (very short spring travel) and with fuel delivery which is interrupted in overrun operation.