Pumps – Expansible chamber type – Pumping member position controlled port
Patent
1987-10-13
1989-07-25
Smith, Leonard E.
Pumps
Expansible chamber type
Pumping member position controlled port
F02M 5924, F02M 5944
Patent
active
048508225
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a fuel injection pump. With such lifting slide-valve pumps, the volume control or the beginning of injection control is effected by the control of ports via which the pump working space can be connected to the suction space of the pump, namely by the assignment of control edges lying on the pump piston to the control edges lying in the control slide valve. For this reason, the rotational position of the control slide valve with respect to the cylinder liner must be fixed, with the result that, on the one hand, the control slide valve maintains a certain fixed rotational position in relation to the twistable pump piston and that, on the other hand, during basic adjustment, which is effected by slight twisting of the cylinder liner, which is subsequently clamped, the control slide valve is turned with it.
According to the object of such a control slide valve, the latter executes very many lifting cycles, with the result that a high wear load occurs at the guide surfaces of the anti-twist device. Added to this is the fact that, owing to the fuel control performed by twisting of the pump piston, the control slide valve must be guided very exactly in twisting direction, so that a twisting backlash between control slide valve and cylinder sleeve has a great effect on the metering and injection timing accuracy of the fuel, it being possible for even a small backlash to lead to considerable deviations of the actual control from the setpoint control.
In the case of a known fuel injection pump of the generic type (EP-A-0 181 402), a pin is arranged on the wall of the clearance of the cylinder liner, which pin engages in a longitudinal guide groove of the control slide valve, with the result that, upon the axial displacement of the control slide valve, the latter is secured against twisting by pin and guide groove. Disregarding the fact that the distance between pin and piston axis is relatively small, whereby the lever distance preventing the twisting is also relatively short, the pin has only line contact or, with slight inclined position, point contact toward the groove wall, which leads to a relatively rapid wear, with the consequence of the disadvantageous twisting backlash and corresponding deterioration in the control accuracy of the fuel. A further disadvantage consists in that such a pin can be fixed relatively poorly in the wall of the clearance, whereby during a loosening of this pin considerable damages directly on the pump and indirectly on the engine were possible.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved fuel injection pump.
The fuel injection pump according to the invention has, in comparison, the advantage that the distance of the twisting guide point from the pump piston axis is increased, so that wear effects and thus backlash at the guide points have a lesser effect on the pump with respect to the associated twisting error of the control slide valve. The greater is the distance of the twisting guide from the piston axis, the smaller is the control error with a certain twisting backlash. With twice as long "lever guidance", the control error is only half as large with the same twisting backlash. A further advantage consists in that the anti-twist device according to the invention can be produced very inexpensively and is extremely sturdy and can be performed in terms of the precision working of this fit between lug and guide groove with simple customary working methods. A working loose of the lug from the control slide valve is not possible, with the result that no consequential damages in this respect can arise either. A further advantage consists in that the control slide valve is not additionally weakened by a groove or subjected to dimensional changes in heat treatment and during production on account of a groove, so that the "dynamic" slide valve durability is very good.
According to an advantageous development of the invention, the guide groove is designed as a slit-shaped perforation in t
REFERENCES:
patent: 4661051 (1987-04-01), Nakamura
Guntert Josef
Hafele Walter
Warga Johann
Robert & Bosch GmbH
Smith Leonard E.
Striker Michael J.
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