GB2088948A

GB2088948A - Fuel Injection Pump and and Fuel Injector Combination

Info

Publication number: GB2088948A
Application number: GB8126793A
Authority: GB
Original assignee: Vysoke Uceni Technicke V Brne
Current assignee: Vysoke Uceni Technicke V Brne
Priority date: 1980-12-09
Filing date: 1981-09-04
Publication date: 1982-06-16
Also published as: CS215203B1; JPS5797062A; GB2088948B; DE3129916A1; DD207475A3; FR2495694B3; FR2495694A1

Abstract

The biasing spring 21 in the chamber 22 which is pressurised by fuel leaking past the injector needle 51 provides a force such that, in combination with the constant volume suck-back delivery valve 1321 of the injection pump 1, the residual pressure in the chamber 22 and the connecting pipe 6 between injections is constant under any steady state conditions of operation of the pump and injector combination. <IMAGE>

Description

SPECIFICATION An Injection Device for a Fuel Injection Engine The invention relates to an injection device for a fuel injection engine, the device comprising a piston injection pump, an injector, and a delivery piping interconnecting the outlet of the pump with the inlet of the injector, the pump being provided with a device for equivolume relieving of fuel pressure in the delivery piping, e.g. with an equivolume relieving delivery valve, the injector being provided with a holder and an injection nozzle, the latter including a body accommodating a differential needle forced into a seat in the body by a prestressed spring and by the pressure of fuel contained in a closed space in the holder above the differential needle, in which space is situated the spring. This injection device will hereinafter be referred to as "an injection device of the kind hereinbefore specified".The invention also relates to an engine incorporating the injection device and to a method of adjusting the injection device.

One known design of an injection device provided with injectors, in which the space in the holder above the differential needle of the injection nozzle, where a steel spring is seated, is sealed against outer surroundings and filled with fuel, use in the injection pump so called equipressure relieving delivery valves, which enable the fuel to expand from the said closed space in the holder through a clearance between the differential needle and the body of the injection nozzle into the delivery piping. A drawback of these devices resides in the fact that if their revolutions drop, at a constant position of the control bar of the injection pump, a relatively strong increase of cycle delivery of fuel takes place, which increases the smoking of the engine in the range of low operation revolutions.

Another known design of an injection device provided with an injector of the described type uses in the injection pump a so called equivolume relieving delivery valve, the relieving volume of which is dimensioned so that overrelieving of the delivery piping is ensured in the whole operating range of the engine, including idle running and starting of the engine. In such an overrelieved injection device, a cavity filled with fuel vapour appears in the delivery piping after each injection, and this cavity must first be filled with fuel during the next delivery, before fuel pressure in the delivery piping starts increasing. A relatively extensive overrelieving of the delivery piping, which is needed for the said type of the injection device, affects sometimes disadvantageously the beginning of the fuel injection.

The aim of the invention is to avoid, or at least to mitigate said disadvantages.

The invention provides an injection device of the kind hereinbefore specified in which the spring is prestressed so as to exert on to the differential needle, when the latter bears onto the seat, a pressure such that when the engine, equipped with the injection device, operates at a steady state, in any revolutions and stresses in the whole operating mode thereof, including idling and starting, neither the value of the residual pressure of the fuel in the delivery piping, nor the value of the residual pressure of the fuel in the closed space, varies. The invention also provides a fuel injection engine comprising said injection device, and a method of adjusting the device.

In order that the invention may be clearly understood and readily carried into effect, a preferred embodiment thereof is, by way of example, hereinafter more fully described and illustrated in the accompanying drawing showing a sketch of the injection device.

An injection pump 1 has a cylinder 11 accommodating a lapped piston 12, provided with at least one control edge 121 of a known design, working opposite to at least one radial channel 111 1 1 in 111 inthecylinderll.Abodyl3lofan equivolume relieving delivery valve is fixed to the upper face of the cylinder 11 by means of an outlet branch 14. A cone 132 of the said valve is provided with a relieving piston 1 321.

The outlet branch 14 of the injection pump 1 communicates with an inlet branch of a holder 2 by means of a delivery piping 6. To the lower face of the holder 2 is fixed a washer 3, and to it a body 52 of the injection nozzle by means of a cup nut 4. A differential needle 51 is lapped into a body 52 of the injection nozzle. The differential needle 51 is forced, with its conical end 511, by a prestressed steel spring 21, via a disk 23, and by the pressure of fuel filling a closed space 22 in the holder 2, into a seat 521 in the body 52 of the injection nozzle, below which jet holes 522 are arranged.

The function of the described injection device is well known and will not be described in detail here. With each jet a small quantity of fuel passes through a clearance between the differential needle 51 and the body 52 of the injection nozzle into the closed space 22 in the holder 2, whereby the pressure of fuel filling this space is increased.

In the interval between each two successive injections, fuel expands out of the said space 22 through said clearance in the opposite direction into delivery channels 523,31,24,25, into the delivery piping 6 and into the cavity 141 above the body 1 31 of the relieving delivery valve closed by the cone 132 pushed by a spring 133, which increases the fuel pressure in this area.

During the operation of the said injection device, in the engine, at its steady state, gradual increase of the residual pressure in the delivery piping 6 takes usually place, as well as an increase of the residual pressure in the closed space 22. In this way, in the same position of a control member, the quantity of the cycle fuel delivery drops step by step, until the differential needle 51 is locked in the closed space 22 by the fuel pressure, and the cycle fuel delivery drops to zero.

As was shown by the results of research, the described increase of the residual fuel pressure in the delivery piping 6 and in the closed space 22 above the differential needle 51 is strongly affected by the value of the force F0 exerted by prestressed steel spring 21 acting onto the differential needle 51 when the latter bears on to the seat 521. By reducing this force, the increase of the two mentioned residual pressures is reduced.For injection devices of the kind hereinbefore specified for a given engine working in a given range of revolutions and loads, it is possible to find for this range, in an experimental way, such a valve of the force F,, at which, at a steady state of the engine at any point of its operating mode, both the residual pressure in the delivery piping 6 and the residual pressure in the closed space 22 above the differential needle 51 are kept at the same value. In this way a constant cycle fuel delivery is secured. The value of the force F0 may be varied e.g. by changing the washer 26.

Although the invention is iilsutrated and described with reference to one preferred embodiment thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a preferred embodiment, but it is capable of numerous modifications within the scope of the appended claims.

Claims

1. An injection device of the kind hereinbefore specified in which the spring is prestressed so as to exert on to the differential needle, when the latter bears onto the seat, a pressure such that when the engine, equipped with the injection device, operates at a steady state, in any revolutions and stresses in the whole operating mode thereof, including idling and starting, neither the value of the residual pressure of the fuel in the delivery piping, nor the value of the residual pressure of the fuel in the closed space, varies.

2. An injection device of the kind hereinbefore specified constructed, arranged, and adapted to operate substantially as herein described with reference to, and as shown in, the accompanying drawing.

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3. Afuel injection engine comprising an injection device according to claim 1 or 2.

4. A method of adjusting an injection device of the kind hereinbefore specified substantially as herein described with reference to the accompanying drawing.