Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1999-02-22
2000-08-15
Moulis, Thomas N.
Internal-combustion engines
Charge forming device
Fuel injection system
123467, F02M 3704
Patent
active
061020060
DESCRIPTION:
BRIEF SUMMARY
The invention is concerned with a fuel injection assembly, in each case for one cylinder of a diesel engine, said assembly consisting of a housing, of a controllable piston pump and of an injection nozzle adjoining the latter and having a nozzle chamber, the housing possessing a fuel supply chamber fed from outside and a return orifice leading outward, the piston pump possessing a pump piston bush which is mounted longitudinally displaceably and is guided on a coaxial pin fixed relative to the housing and which has at least one control orifice, and the pin containing a first longitudinal bore leading from the interior of the pump piston bush to the injection nozzle.
In generic injection assemblies, also referred to as "injector units", which are known from DE 33 25 479 C2, the pump piston bush is rotatable, for example for the purpose of controlling the injection quantity; in order to control the start of injection, said pump piston bush is additionally also positively displaceable in the axial direction. Located between the pump piston bush and the housing is a fuel inflow chamber which has to be separated by means of a seal from the chamber located above it and containing the adjusting members and lubricating oil. This seal presents problems, since it must be absolutely leaktight, even under the highly pulsating fuel pressure which occurs when the feed stroke is cut off. The seal therefore experiences wear and frictional losses which increase the actuating force. Moreover, gas bubbles or air bubbles may form in the inflow chamber, but also in the nozzle chamber below it, at locations of low flow velocity, particularly in upwardly closed pockets and at locations of higher temperature. The result is irregular pump conveyance and, as a consequence, uneven engine running. Furthermore, this design requires impact protection in order to protect the inner wall of the housing against erosion.
The object on which the invention is based is, therefore, to eliminate these defects and to improve the sealing and throughflow of an injector unit.
This is achieved, according to the invention, in that, firstly, the pump piston bush is sealingly surrounded by a sealing sleeve which forms, with the outer wall of the pump piston bush, a closed sealing space, into which the control orifice opens at the top and a first transverse bore of the pump piston bush opens at the bottom, in that, secondly, the pin possesses a second longitudinal bore which is flow-connected, on the one hand, to the fuel supply chamber and, on the other hand, via the first transverse bore, to the sealing space, and in that, thirdly, the sealing space is flow-connected to the return orifice via a second transverse bore and a third longitudinal bore in the pin.
The fuel thus flows from the fuel supply chamber through the second longitudinal bore in the pin and the sealing space into the working chamber in the pump piston bush. The fuel jet occurring during cutoff flows from the connecting chamber via the second transverse bore and a third longitudinal bore in the pin to the return orifice. As a result, the seal which presents problems between the pump piston bush and the housing is avoided and its function is performed by the high pressure seal which exists in any case between the inner surface of the pump piston bush and the pin. This high pressure seal is a cylindrical surface of small diameter, without sealing rings and with a long guide length, which, in addition to this, is lubricated hydrodynamically by a leakage flow, the quantity of which is insignificant. The forces which occur are therefore low. Another advantage is that along the flow path described there are no longer any dead zones where vapor bubbles or air bubbles could form. Moreover, the fluctuating pressure in the return can no longer exert any disturbing forces on the displaceable pump piston bush.
In an advantageous development of the invention, the third longitudinal bore in the pin opens into the nozzle chamber which is connected to the return by means of an orifice in the housing (c
REFERENCES:
patent: 5299738 (1994-04-01), Genter et al.
patent: 5638791 (1997-06-01), Tsuzuki
Moulis Thomas N.
Steyr-Daimler-Puch Aktiengesellschaft
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