GB2140505A

GB2140505A - Injector for fuel-injection equipment

Info

Publication number: GB2140505A
Application number: GB08408230A
Authority: GB
Inventors: John Noraberg; Robert Kolitsch
Original assignee: AVL List GmbH; AVL Gesellschaft fuer Verbrennungskraftmaschinen und Messtechnik mbH
Current assignee: AVL List GmbH
Priority date: 1983-03-31
Filing date: 1984-03-30
Publication date: 1984-11-28
Also published as: DE3409924A1; GB8408230D0

Abstract

An injector needle 8 is subjected, jointly with a by-pass piston 16 to a bias load in the valve-closing direction applied by a spring 9. The injector needle 8 and the by-pass piston 16 are displaced by the fuel pressure in opposition to the spring loading when a certain pressure level is exceeded resulting, in the first instance, in fuel injection and then a sudden increase in the piston surface area to which fuel pressure is applied and in the opening-up of a storage volume. By appropriate co-ordination of the surface areas of the injector needle 8 and the by-pass piston 16 exposed to fuel-pressure, the start of the opening stroke of the by-pass piston 16 is shifted in time relative to that of the injector needle 8 so that the needle 8 temporarily closes the orifice while the pressure builds up. A longer fuel flow-path 40,41,44 is provided for the piston 16 than the corresponding path 33,34,35 for needle-lifting to achieve a delayed response during pilot injection at higher engine speeds. <IMAGE>

Description

SPECIFICATION Injector for fuel-injection equipment The invention relates to an injectorforfuel-injection equipment having an injector needle which controls at least one nozzle orifice and is biased in the direction of closing the orifice by a nozzle spring, and having a by-pass piston arranged coaxiallywith the injector needle at the opposite end of the spring and also biased by the spring, the piston and the injector needle being slidingly displaceable against the action of the spring by fuel fed under pressure through a pressure line, the piston area to which fuel pressure is applied increasing suddenly when a specified pressure level is exceeded, and the by-pass piston and the injector needle being connected in parallel as regards the application of fuel pressure thereto.

In a known construction, for example as disclosed, in German PS 686.943, of an injector for fuel-injection equipment the application of fuel under pressure to the injector needle is designed to occur after the application of fuel pressure to the by-pass piston, that is to say, it can happen only when the piston, in the manner of a valve, has lifted at least very slightly off its seat in the injector. This arrangement has an influence on the injection characteristic in the sense that for low engine speeds and pressure gradients of the fuel, there will be a form of pilot injection of a quantity of fuel which is reduced by the lift of the by-pass piston, and with increasing speed, due to the increased back pressure of the fuel caused to leak by the by-pass piston, the pressure head progressively earlier assumes a value which is enough to lift the injector needle off its seat.For this reason, in the case of this known device the main fuel injection starts earlier at high speeds than at low speeds and in the extreme case the pilot injection feature disappears completely.

The drawback of this known arrangement resides particularly in that it no longer actually provides a distinct division of the injection process into main and pilot injection in which the pilot injection is completely separate from the main injection with the injector needle closing between the two injection stages, and in that, the pilot injection stage in particular, which is extremely favourable from the point of view of reducing combustion noise, cannot be retained at all at high speeds.

There are also known fuel injection systems in which the by-pass piston, for the purpose of storing a quantity of fuel provisionally retained after completed pilot injection, is arranged on the injection pump or on a distributor pump and subjected to fuel pressure in parallel with the injector needle. In this manner a relatively free choice can be made in respect of the design parameters of the piston and/or the injector needle which influence the injection characteristic. However, there is this drawback that tuning becomes very difficult, if not impossible, due to the relatively large distances between the by-pass piston and the injector needle particularly when dealing with multi-cylinder engines with long fuel injection lines of different lengths.

Also known, for example from German OS 23 01 628, is a device of the kind specified in which fuel pressure is applied in parallel to the by-pass piston and the injector needle. The disadvantage in this arrangement resides in that with increasing speed, that is to say with increasing pumping speed of the fuel and steeper pressure rise in the corresponding cycle, there is an increasingly earlier response on the part of the piston with the consequence that again, as in the previously discussed known arrangement, the pilot injection quantity decreases with rising speed thereby preventing the desired reduction of combustion noise generated by an abrupt start of the combustion process.

It is the aim of the present invention to avoid the disadvantages appertaining to known injectors of the kind hereinbefore mentioned and preferably to improve the same by providing the facility of a pilot injection stage distinctly separate from the main injection stage in every speed range of the engine.

The present invention consists in an injector for fuel injection equipment having an injector needle which controls at least one nozzle orifice and is biased in the direction of closing the orifice by an injector spring, and having a by-pass piston arranged coaxiallywith the injector needle at the opposite end of the spring and also biased by the spring, the piston and the injector needle being slidingly displaceable against the action of the spring by fuel fed under pressure through a pressure line, the piston area to which fuel pressure is applied increasing suddenly when a specified pressure level is exceeded, and the by-pass piston and the injector needle being connected in parallel as regards the application of fuel pressure thereto, characterised in that the path which must be travelled by a pressure wave in the pressure line to the point of pressure application to the by-pass piston is longer than the corresponding path to the point of pressure application to the injector needle.

The invention is based on the following considerations which are known in the field of hydraulics: The bias force in the common spring provides, on the one hand, an opening pressure for the injector needle of

in which: Poo opening pressure of the injector needle PF bias force in spring dN needle diameter ds seat diameter of needle F1D initial effective area of the injector needle, and, on the other hand it provides an opening, or response pressure for the by-pass piston of PF 4 PF PoA= =- dl2 sr F1A in which: d1 diameter of initial effective area of the bypass piston F1A initial effective area of the bypass piston It is therefore possible by co-ordination of F1A with the given effective injector needle area F1D to shift the start of opening of the piston relative to that of the injector needle in time in such a way that the piston responds only after a certain quantity has already been injected by the injector needle. On further pressure increase beyond a pressure level which is set by the pre-applied tension of the common spring the piston will lift off its seat and the pressure is then effectively applied to the piston area which has been increased to d 2 F2A (or-: in which ..... the effective diameter of the piston after lift-off.Due to the excess effective force the lifting speed and the actual lift of the by-pass piston increase relatively fast. Due to the high speed of release, the final fuel pressure drops so strongly that the injector needle will temporarily close again.

This process is further assisted by the increasing spring force corresponding to APF = AS.CF in which: cF stiffness of spring s lift of by-pass piston The injector needle remains in the closed position until fuel pressure has risen once more to injector opening pressure which is now PF + S CF ~PF +S.CF F1D At this point the main injection takes place which is terminated in known manner by means of spill ports in the pump. By making the correct choice for the values of d1,d2 and it is thus possible to arrange for an optimum quantity of fuel at the pilot injection stage as well as for an optimum time lag between the start of the pilot injection stage and the start of the main injection stage.

The present invention avoids the previously described drawbacks appertaining to known constructions due to the fact that the distance which must be travelled by a pressure wave in the pressure line to the point of application to the by-pass piston is greater than the corresponding distance to the point of application to the injector needle.A pressure wave in the fuel coming from the injection pump arrives at the point at which pressure is applied to the injector needle or to the by-pass piston with a time delay corresponding to the length L of the respective pressure line and to the speed of sound a in the fuel: L At a Since, moreover, the pressure rise in the fuel gets steeper with increasing speed, as in the construction known for example from the cited German OS 23 01 628, which clearly shows a shorter pressure line to the point of pressure application to the piston by comparison with the pressure line to the point of pressure application to the injector needle, there is an increasingly earlier piston response with increasing speed, as has in fact been observed in practice.Now according to the present invention the effect of the difference in the distance which the pressure wave has to travel is used precisely for the opposite effect, namely to retard the piston response with increasing speed, so that, if required, even an increase in the quantity of fuel injected in a pilot injection stage, which is distinctly separate from the main injection stage, can be obtained with rising speed.

In an injector with a fuel feed alongside the by-pass piston, and in which the pressure line is routed past the piston and the injector spring, the invention, according to a further embodiment thereof, provides that a common pressure line for piston and injector needle extends up to the region of the injector needle and only :in this region divides into a shorter branch leading to the injector needle seat and a longer branch leading to the by-pass piston. In these circumstances the branch of the pressure line which leads to the piston may, in an extremely attractive embodiment, consist simply of an additional bore extending parallel to the common pressure feed line and provided merely with appropriate connecting passages.If the length differential obtained by this arrangement of the two branches of the pressure line downstream of the branching point should not be long enough for the purposes of the invention, the branch which leads to the by-pass piston may very easily be arranged to include, for example, two further bores also extending parallel to the common section of the pressure feed line and adapted to be appropriately connected via interconnecting passages. Such an arrangement raises no particular problems in view of the fact that in injectors of this kind inhere is already provided a relatively thick wall section in the region of the injector spring to accommodate the existing pressure feed line to the injector needle.

According to a further, particularly attractive embodiment of the invention the ratio of the two branches of Whe pressure line may be adjustable which affords the facility of accurately timing the effect of the pressure-wave retardation on the injection characteristic.

A furthar development of the invention provides an arrangement in the branch of the pressure line which leads to the by-pass piston of length-increasing inserts, for example of spiral or labyrinth configuration, which permits many applications of the basic principle of the invention even under conditions of confined space. With the aid of exchangeable inserts it is also possible, under certain circumstances, to obtain a different injection characteristic for different engine types.

The invention is hereinafter more particularly described, by way of example, with reference to embodiments shown in the drawings in which: Figure 1 its a longitudinal section taken on line I-I in Figure 3 of an embodiment of the invention, Figure 2 is a longitudinal section taken on line ll-ll in Figure 3, Figure 3 is å cross section taken on line Ill-Ill in Figure 2, Figure 4shows an example of an injector utilizing merely the parallel application of pressure to the by-pass piston and injector needle which is in itself known in connection, for example, with injection pumps ior distributor pumps, and Figure 5 is a part-sectional view corresponding to Figure 1 of another embodiment of the invention.

The injector 1 according to Figures 1 to 3 comprises a locating sleeve 2 into the front end 3 of which is inserted, together with a seal 6, the body 5 of a nozzle which has blind bore 38 leading to a nozzle orifice 4.

The body 5 has a bore 7 at that end thereof which is remote from the nozzle orifice 4 which provides axial guidance for an injector needle 8 biased by a spring 9 in the direction of closing the needle valve in which its pointed end part 10 sealingly engages a conical seat 11 of the body 5.

The spring 9 bears, at one end, on a flange 12 coacting with the injector needle 8 and, at the other end, on a flange 13 which coacts with a pin 14 on a by-pass piston 16 arranged co-axially with the needle 8 for axial sliding displacement in a bore 15. The lift of piston 16 which is of the order of, for example, approximately 0.2 to 0.7 mm is limited in one direction by abutment of its front end face 17 against a gasket 19 which is provided with a feed bore 18 and in the other direction by a shoulder 20 forming a seat on the rim of a bore 21 in the spring housing 22. The stroke of the injector needle 8 is limited in one direction by the sealing engagement of its pointed end 10 with the seat 11 and in the other direction by the engagement of a shoulder .23 with the edge of a bore 24 in a further gasket 25.These limitations in stroke also determine the extremes .of travel for the spring 9 which merely bears on flanges 12 and 13.

Fuel which is pressurised by an injection pump, not shown, is fed, and the leakage fuel discharged, through a connector piece 26 which in the illustrated embodiment is screwed by a screw thread 27 into the locating sleeve 2 and thereby also tightens with respect to one another and in a sealing manner the gasket 19, the spring housing 22, the gasket 25, the nozzle body 5 and the seal 6. Fuel supply to the high-pressure side is obtained through a nipple 28 starting from which the pressure feed line 29 leads first in a bore 30 of the connector piece 26, then in a bore 31 of gasket 19, a bore 32 of spring housing 22, an oblique bore 33 in gasket 25 and finally a bore 34 in the body 5. Bore 34 terminates in a pressure chamber 35 whence the fuel passes through an annular gap 36 around the injector needle 8 to arrive at the valve seat 11.As soon as the force applied by fuel pressure to a shoulder 37 or also the pointed end 10 of the injector needle 8 exceeds the respective effective force of spring 9, the pointed end 10 of the injector needle 8 is lifted off the seat 11 and fuel is injected through the bore 38 and the nozzle orifice 4 into the combustion chamber of an internal combustion engine, not particularly shown.

As will be noted particularly from Figures 2 and 3, the pressure line 29 had a branch 40 at the front end of spring housing 22 facing the injector needle 8, which branch communicates, through a part-annular passage 39, bores 41,42 and 43 extending parallel with bore 32 and a groove-like recess 44, with the feed or inlet bore 18 to the end face 17 of the by-pass piston 16.

Also clearly visible, particularly in Figure 1, is the provision of a discharge line 45 for leakage fuel, which communicates via bore 46 with the interior space 47 of the spring housing 22 in which the injector spring is accommodated, and conducts the fuel escaping from the high-pressure part through bores 7,24 or 15,21 into a leak-collector line connection 48.

In order to prevent relative rotational movement of the parts which are adjacent the gaskets 19 and 25, causing misalignment relative to the corresponding passage bores in the gaskets, sleeves 49 are inserted in corresponding bores.

Considering the fact that the pressure effectively applied from the spring chamber to the by-pass piston 16 and the pressure applied to the injector needle 8, which is composed of the pressure applied by spring 9 and the fluid pressure of leaked fuel, are equal it is possible initially, that is to say at low engine speed and therefore relatively low fuel supply rates and pressure gradients in the fuel, to influence the instants at which the injector needle 8 opens and/or the piston 16 and therefore its end face 17, lifts off the gasket 19. This is achieved primarily by controlling the size of the areas which are subjected to the respective pressures.In order to obtain a pilot injection stage which is clearly distinct from the actual main injection stage, that is to say initially indicated by a closed injector needle, and which is desirable for the purpose of reducing combustion noise, the area which is exposed to fuel pressure through feed bore 18 when the end face 17 of piston 16 engages with gasket 19, which area in this case corresponds to the cross section of bore 18, is made smaller by a specified amount than the corresponding surface area on the injector needle 8 exposed to fuel pressure and which is effective in the direction of opening the injector needle-valve. This means that as fuel pressure builds up along pressure line 29 the injector needle 8 will open first and start pilot injection.As soon as the steadily increasing fuel pressure has reached the value needed to displace piston 16, the piston face 17 is lifted off gasket 19 with the result that suddenly and abruptly a drastically enlarged effective surface area corresponding to the actual cross section area of the piston 16 itself and a correspondingly drastically increased volume in bore 15 become available. Due to such sudden onset of fuel pressure drop in pressure line 29 there is a shortfall in fuel pressure relative to that which is required for keeping the injector needle valve open so that the needle 8 returns to the closed position of the valve and the pilot injection is terminated.

The injector valve needle 8, now once more in closed position, and the by-pass piston 16, the shoulder 20 of which now engages with the edge of bore 21, now permit pressure to rise once more which eventually leads to renewed opening of the injector needle valve 8 and thus to the main injection stage.

In the illustrated example the pressure line 29 is routed past the by-pass piston 16 and the injector spring 9 into the region of the injector needle 8 as a common feed line for fuel to the piston and the injector needle and it is only in this region that it divides at junction 40 into a shorter branch, essentially comprising bores 33, 34, which leads to the injector 8 and a longer branch, comprising essentially the line parts 39,41,42, 43, 44 and 18 which leads to the by-pass piston.Due to the relatively different length of the two branches of pressure line downstream of junction 40 the invention achieves the result that a pressure wave coming via line 29 from the injection pump arrives at the end face 17 of piston 16 after a specific time-delay which, in association with the more steeply increasing pressure in the fuel following increasing engine speed, causes an increasingly later response on the part of the by-pass piston with increasing engine speeds. This has the direct result that the pilot-injection quantity of fuel increases with increasing engine speed by a measure which can be easily controlled by the value of the length differential in the two branches of the pressure line, and this results in a very advantagous injection characteristic.

The injector 1' shown in Figure 4 is constructed similarly to that shown in Figures 1 to 3; like parts carry like reference numbers. The most important difference by comparison with the embodiment hereinbefore described in detail resides in that in this case the junction or branching point 40' in the pressure line 29 is arranged upstream of the gasket 19' which results in a substantially shorter path for a pressure wave to travel through the line 29 to the point of application to the by-pass piston 16 as compared with the path of such a pressure wave travelling to the point of pressure application to the injector needle, notshown in this Figure.This arrangement therefore haste undesirable and adverse result that with increasing engine speed a pressure wave from the injection pump arrives at the injector needle with a time delay depending on the difference in the length of the paths which results in an increasingly earlier response of the piston with increasing engine speeds. However, this is highly undesirable because it means that the quantity of fuel injected in the pilot stage decreases with increasing engine speed.

Apart from the arrangement shown in Figures 1 to 3 which may be adopted to ensure a longer path for the pressure wave to the by-pass piston it would also be possible, as schematically shown in Figure 5, to achieve this kind of extended path by means of inserts 50, for example of spiral or labyrinth configuration fitted in that part of the pressure line which leads to the piston 16 or by known alternative means of a similar nature.It is also conceivable, for example in application to test engines, to make the length ratio of the two branches of pressure line downstream of the branching point adjustable, for example by means of exchangeable inserts 50 having flow-paths of different lengths or by means of spring housings 22 provided with different numbers of successively arranged longitudinal bores, or by known provisions for infinitely variable adjustment of flow paths for the fuel which could allow the most favourable conditions to be ascertained directly by monitoring the injection characteristic. It would further be possible by deliberate influential design provisions to modify leak-fuel pressure in the interior space 47 of the spring housing and via leak-line connection 48 to alter the response time of the injector needle and by-pass piston in relation to operative parameters of the internal combustion engine, for example engine load or engine speed.

Claims

1. An injector for fuel injection equipment having an injector needle which controls at least one nozzle orifice and is biased in the direction of closing the orifice by an injector spring, and having a by-pass piston arranged coaxially with the injector needle at the opposite end of the spring and also biased by the spring, the piston and the injector needle being slidingly displaceable against the action of the spring by fuel fed under pressure through a pressure line, the piston area to which fuel pressure is applied increasing suddenly when a specified pressure level is exceeded, and the by-pass piston and the injector needle being connected in parallel as regards the application of fuel pressure thereto, characterised in that the path which must be travelled by a pressure wave in the pressure line to the point of pressure line to the point of pressure application to the by-pass piston is longer than the corresponding path to the point of pressure application to the injector needle.

2. An injector according to claim 1 with a fuel feed to one end of the by-pass piston, in which the pressure line is routed past the by-pass piston and the injector spring, characterised in that a common pressure line is provided for by-pass piston and injector needle up to the region of the injector needle and only in this region divides at a fork into shorter branch leading to the seat for the injector needle and a longer branch leading to the by-pass piston.

3. An injector according to claim 1 or 2, characterised in that the length ratio of the two paths is adjustable.

4. An injector according to any of claims 1 to 3, characterised in that inserts, for example of spiral or labyrinth configuration, which extend the length of the path the fuel must travel are provided in the branch of the pressure line which leads to the point of pressure application to the by-pass piston.

5. An injector for fuel injection equipment substantially as described herein with reference to, and as illustrated by, Figures 1 to 3 of the accompanying drawings.

6. An injector for fuel injection equipment substantially as described herein with reference to, and as illustrated by, Figures 1 to 3 as modified by Figure 5 of the accompanying drawings.