GB2074234A - Multi-outlet I.C. engine fuel injector - Google Patents

Abstract

A nozzle body (12) has a nozzle needle (10), which extends as far as a blind recess (16) and is urged against a seat (13) by spring force. One outlet (14) extends from the region of the seat (13) and has a larger diameter than a further outlet (15) extending from the recess (16). The outlets (14, 15) provide for an increasing proportion of the fuel flow through the one outlet (14) with increasing needle lift. <IMAGE>

Description

SPECIFICATION Fuel injector The present invention relates to a fuel injector, preferably for direct injection in a Diesel engine having a combustion chamber in the form of a rotary body in the piston, particularly with air movement rotating around the longitudinal axis of the combustion chamber and with fuel accumulation on or in the region of the combustion chamber wall.

A number of constructional variants of the multi-hole injector mode of construction are known, by which different relationships between the injected quantities of the nozzles are provided in dependence on engine speed and injection quantity.

It is known from US-PS 3 559 892 to provide a valve needle of an injector with a conical portion and a control extension guided sealingly in a blind bore, wherein a spray nozzle of small cross-section is arranged to start from a conical valve seat of the injector body and a further, larger spray nozzle starts from the blind bore. In this construction, the relationships of the injection quantities of the two nozzles are influenced in dependence on engine speed and injection quantity, for which the needle stroke in this case has a controlling effect.

It is also known from DE-OS 2 434 339 and FR-PS 1 256474 for the influencing of the distribution of the fuel, particularly at idling and low engine speeds, to provide injectors with several controlling seat or mount cross-sections, each of which is respectively associated with one or more spray nozzles.

Thus, in injectors of the kind described in DE - OS 2434399 and DDR - PS 133 a series of spray nozzles is arranged to open out into an annular space arranged downstream of the conical seat portion of the needle. A further series of spray nozzles starts from the blind recess, the spray behaviour of the latter series being influenced at the nozzle needle by a control spigot fitted to the nozzle body. In that case, the needle can be subject to a variable spring force and spring stiffness in dependence on stroke.

In the injector of FR-PS 1 256 474, a double valve seat is provided by means of a conical needle point with an annular recess in the region of the middle of the conical surface, in which double seat the conical profile cooperates with a seat in the nozzle body at the lower and upper ends of the needle.

A spray nozzle of small cross-section is arranged in the conical surface of the needle starting from the region of the annular recess, while further spray nozzles open out in the blind bore at the cone point below the second seat.

It is disadvantageous in all the afore-described constructions that two mutually adapted seat profiles or seat and fit profiles must be produced on the needle and in a blind bore in the nozzle body.

It is also known from DE-OS 2 147 719 and DD-PS 102 198 to arrange for the two series of nozzles to become effective at different pressures.

For this purpose, the needle is contructed in two parts, wherein each part is individually loaded by a spring force so that two sealing cross-sections open one after the other at different pressures to cause the nozzles to become effective differently in their characteristics at different engine speeds and injection quantities. This two-part construction is expensive and complicated to manufacture, because several parts must be interfitted and must provide adequate sealing by virtue of their fit.

It is also known from GB-PS 1 41 8 574 to act, starting from the conical valve seat, on a number of spray nozzles distributed around the periphery. With this construction, a differential jet condition is effected, which occurs at different needle strokes.

There is accordingly a need for an injector wherein a differential quantity distribution characteristic between a plurality of nozzles thereof is provided in dependence on engine speed and injection quantity, such that at a lower speed and load range of an engine the fuel preferably issues through a subsidiary nozzle and, on increase in engine speed and load, issues through a main nozzle. A simple construction of the injector facilitating manufacture and providing good durability is also desirable.Such an injector - should preferably avoid double guidance for a valve needle and.nozzle body between valve seats According to the present invention there is provided a fuel injector for an engine and comprising nozzle body provided with a bore defining a valve seat and with a first outlet nozzle communicating with the bore at-a blind end portion thereof and a second outlet nozzle communicating with the bore in the region of the seat, the diameter of the second nozzle being larger than that of the first nozzle, and a valve needle engaged in the bore to extend as far as the blind end portion, the needle having a generally conical and portion and being resiliently urged towards the seat.

Due to the geometrical relationships of the nozzles and their arrangement, and the flow conditions to the nozzles resulting thereform at different needle strokes, a control spigot on the needle for control of injection quantity relationships between the two nozzles may be redundant. Due to the flow conditions at the valve seat at relatively low flow speeds, for example at starting and idling, the issue of fuel from the larger nozzle is largely inhibited. An excess pressure at the valve seat, so that the larger nozzle provides a proportionally greater injection quantity, occurs only at higher engine speeds. Consequently, the injection quantity is increased in the upper load and speed range mainly at the large nozzle.

Preferably, the ratio of the diameter of the larger nozzle to that of the smaller nozzle is 1.5 to 2.3:1.

By virtue of the afore-mentioned features, the desired distribution of the injection quantity over the nozzles, of which more than two can be provided, is achieved in dependence on engine speed and the injection quantity. This ensures an advantageous adaptation of the injection to the operating conditions of a Diesel engine of the previously mentioned mode of construction for the attainment of low exhaust gas emission.

Advantageously, the axis of the smaller nozzle approximately coincides with the injector axis, while the two nozzles may extend at an angle of 20 to 400 relative to each other. This arrangement allows favourable incorporation of the injector in a cylinder head with due consideration of the necessary jet positions.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a schematic cross-section of the cylinder head of a Diesel engine fitted with an injector embodying the present invention, showing the arrangement of the injector and the position in the combustion chamber of the injection jets from the injector nozzles, Fig. 2 is a longitudinal section of the injector, Figs. 3a and 3b are diagrams showing fuel quantity distribution with equally sized nozzle diameters and differently sized needle diameters at different fuel pump speeds of 300 rpm (Fig. 3a) and 1400 rpm (Fig. 3b), and Fig. 4 is a diagram showing throughflow quantities of injector nozzles atdifferent strokes of an injector valve needle.

Referring now to the drawings, in Figs. 1 and 2 there is shown a multi-nozzle injector 1 fitted to a Diesel engine to provide direct injection. The injector 1 has two fuel outlet nozzles 14 and 1 5 which provide jets St 14 and St 1 5 directed in different directions into a rotationally symmetrical combustion chamber 2 in a piston 3 of the engine.

It can be seen that the jet St 15 of the smaller nozzle 1 5 passes through the centre of the combustion chamber 2, which results in predominantly air-distributed fuel. Thereagainst, the jet St 14 of the nozzle 14 extends in the proximity of the wall of the combustion chamber 2 and is preferably directed perpendicularly to the block swirl flow 4 or slightly inclined towards this flow. The fuel is atomised in the proximity of the wall and subsequently burnt uniformly under the effect of the swirl.

The essentiai details of the injector are evident in Fig. 2. A valve needle 10 is slidably guided in a bore in a nozzle body 12. The needle 10 has a conical seat 11 which co-operates with a conical seat 13 in the nozzle body 12.

The larger nozzle 14, which provides the main jet at normal operating conditions, opens out in the seat 1 3 in the nozzle body 12 and is concealed from the needle seat 11 at the lowest setting of the needle. The smaller nozzle 15, which preferably delivers fuel in start conditions in idling and the lower load range, opens out in a blind hole 16 at the end of the bore in the nozzle body 12. It is to be emphasized that the blind hole 16 is of relatively small volume, this being achieved either through low depth or else through being partially occupied by a conical projection at the end of the needle 10 below the seat 11.

Figs. 3a and 3b show injection quantity characteristics by the nozzle arrangement according to Fig. 2. The lefthand diagram, Fig. 3a, applies to a rotational speed of the pump of 300 revolutions per minute and the righthand diagram, Fig. 3b, to 1400 revolutions per minute. In both diagrams, the spray quantities issuing from the nozzles 14 and 1 5 are recorded on the ordinate and the entire quantity is recorded on the abscissa. The diameter ratio of the nozzles is 1.5:1 for the solid lines and 1:1 for the dashed lines, i.e.

in the latter case the nozzles are of the same diameter.

At 300 pump revolutions per minute and idling quantity, the fuel issues almost exclusively from the nozzle 1 5. At larger total quantity, the quantities from nozzles with a diameter of d14:d15 equal to 1.5:1 then become approximately equal, whilst substantially more fuel constantly issues out of the nozzle 15 when the two nozzles are of the same diameter.

At 1400 pump revolutions per minute, when dl 4:d1 5 is 1.5:1, an equal quantity output from the two nozzles 14 and 15 takes place at a smaller total quantity and, for nozzles of equal diameter, the spray quantity QSt 1 5 clearly predominates here as well.

Stationary throughflow measurements on an injector with nozzles of equal diameter according to Fig. 4 again clearly illustrate the effects of the different flow conditions to both nozzles 1 4 and 1 5 on the effective cross-sections thereof.

Virtually no fuel issues from the nozzle 14 opening out into the seat 1 3 up to a needle stroke of about 0.06 miliimetres and the effective throughflow cross-section of the nozzle 15 opening out into the blind hole 1 6 again clearly predominates at full needle stroke. The injection quantity distribution at 1 400 revolutions per minute according to Fig.

3b nearly corresponds to the ratio of the effective throughflow cross-sections in Fig. 4.

Claims (11)

1. A fuel injector for an engine and comprising a nozzle body provided with a bore defining a valve seat and with a first outlet nozzle communicating with the bore at a blind end portion thereof and a second outlet nozzle communicating with the bore in the region of the seat, the diameter of the second nozzle being larger than that of the first nozzle, and a valve needle engaged in the bore to extend as far as the blind end portion, the needle having a generally conical end portion and being resiliently urged towards the seat.

2. An injector as claimed in claim 1, wherein the diameter of the second nozzle is 1.5 to 2.3 times that of the first nozzle.

3. An injector as claimed in either claim 1 or claim 2, wherein the first and second nozzles are so inclined relative to each other as to include an angle of 20 to 400 therebetween.

4. An injector as claimed in any one of the preceding claims, wherein the angle between the axis of the second nozzle and the axis of the bore is substantially greater than the angle between the axis of the first nozzle and the axis of the bore.

5. An injector as claimed in claim 4, wherein the first nozzle is substantially coaxial with the bore.

6. A fuel injector substantially as hereinbefore described with reference to the accompanying drawings.

7. An engine provided with an injector as claimed in any one of the preceding claims, the injector being mounted for direct injection into a cylinder of the engine.

8. An engine as claimed in claim 7, wherein the combustion of said cylinder is provided by a rotationally symmetrical recess in the crown of a piston associated with the cylinder.

9. An engine as claimed in claim 8, the engine being provided with air intake means to promote an air current rotating about the axis of symmetry of the combustion chamber thereby to cause fuel from the injector to collect on or in the region of the combustion chamber wall.

10. An engine as claimed in any one of the claims 7 to 9, the engine being a Diesel engine.

11. An engine as claimed in claim 7 and substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.