GB2118624A - >I.C. engine liquid fuel injector - Google Patents

Abstract

The injector needle (16) includes a seat section at one end, a guide section (20) mounting the needle for axial sliding movement in the housing and a plunger section (15) at the other end. A pump sleeve (13) and a spring seat (21) are mounted about the plunger section and there is a compression spring (17) for urging the spring seat into contact with said shoulder and the pump sleeve away from said shoulder and into contact with a servo piston (11). A one way valve (12) is provided in the servo piston for allowing liquid fuel to enter a pump chamber (14) between the servo piston and the pump sleeve during a metering stroke of the piston. A passage (18) in the injector needle communicates the pump chamber to an annular space (19) in the housing where fuel pressure acts on an annular region of the needle to lift the needle off the seat and to communicate the annular chamber with the orifices (24) during a pumping stroke. The pump chamber is vented to prevent secondary injection between successive pumping strokes by lifting of the servo piston (11) from the sleeve (13), by a permanently open bleed (29), Fig. 2 (not shown), from the pumping chamber or by passage (31), Fig. 2, which aligns with a piston passage (30). The spring chamber is vented through a valve (32). <IMAGE>

Description

SPECIFICATION A liquid fuel injector The invention relates to a servo-operated liquid fuel injector for internal combusiqn engines.

In conventional servo-operated injectors, the nozzle closes only after pressure of fuel oil in the nozzle has fallen to a level set by a spring. This causes the final stage of injection to occur at reduced pressure. Hence, atomisation is poor and this is bad regarding smoke and hydrocarbon emissions, and fuel economy. Moreover, kinetic energy is acquired by the liquid fuel in the distribution pipe to the injector during injection and then on abrupt termination of the pumping or injection stroke this causes a succession of high pressure surges and negative waves. These negative waves can be of sufficiently low pressure that the pump chamber filling mechanism can operate with the result that the succeeding positive wave causes a harmful secondary injection.

It is an object of the present invention to provide an improved liquid fuel injector.

The invention provides a servo-operated liquid fuel injector for an internal combustion engine, constructed and arranged so as to enable the attainment of high peak pressure at the termination of injection by using and attenuating kinetic energy in pressure surges in the piping to the injector, and having means for preventing re-opening of the injector, with consequent secondary injection, due to the high pressure trapped in the injector at the termination of injection.

The invention further provides a servo-operated liquid fuel injector for an internal combustion engine, comprising an injector housing provided at one end with a nozzle having one or more injection orifices and a set for an injection needle, the needle including a seat section at one end, a guide section mounting the needle for axial sliding movement in the housing and a plunger section at the other end, the cross-sectional area of the guide section being greater than the cross sectional area of the plunger section with a shoulder therebetween, a pump sleeve and a spring seat mounted about the plunger section and a compression spring between the pump sleeve and spring seat for urging the spring seat into contact with the shoulder and the pump sleeve away from the shoulder and into contact with a servo piston mounted for axial movement in the housing, valve means in the servo piston for allowing liquid fuel to enter a pump chamber between the servo piston and the pump sleeve during a metering stroke of the piston, a passage in the injector needle communicating the pump chamber to )an annular space in the housing where liquid fuel pressure acts on an annular region of the needle between the guide and seat sections thereof to lift the needle off said seat and to communicate the annular chamber with the injection orifices during a pumping stroke of the injector, and means for venting the pump chamber to avoid movement of the needle away from the seat between successive pumping strokes and thereby prevent secondary injection.

With the above described injector it is possible to achieve needle seating at peak injection pressure and to prevent secondary injection. It is also possible to increase injection pressure in the later stages of injection by utilising the kinetic energy of the liquid fuel in the distributor pipe to the injector.

The spring provides motive force for both nozzle closing and the piston return or metering stroke.

Preferably, there is a one way valve communicating with the space occupied by the spring to prevent accumulation of fuel oil in said space.

The injector may, for example, be used with a control system as described in our British Patent No. 830963 or its derivatives.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through one embodiment of an injector according to the invention; Figure 2 is a section through another embodiment of an injector according to the invention; Figure 3 is a spray diagram from a conventional injector showing the low pressure ending; Figure 4 is a spray diagram from the injector of Figure 1; Figure 5 is a spray diagram from the injector of Figure 2.

When the fuel oil at servo pressure reaches the injector it enters at connection 10, Figure 1, and bears on top of a servo piston 11, which has a one way valve 1 2 therein, causing the piston 11 to bear downwards on a pump sleeve 1 3. This in turn causes a pump chamber space 1 4 to decrease with a consequent increase of pressure therein dependent on the relative areas of the piston 11 and a plunger section 1 5 of a needle 1 6 and on the force of a main spring 1 7. The pressure generated in the pump chamber is transmitted via passage 18 to an annular space 1 9 between a guide section 20 of the needle and a seat 21.The guide section 20 has a frusto-conical region 22 at that end thereof adjacent to the seat 10 and the dimensions are selected so that the area of the region 22 is greater than the cross-sectional area of the plunger section 1 5, hence the nett hydraulic force on the needle 1 6 is upwards, tending to lift it away from its seat 21. When this hydraulic force exceeds the force of spring 1 7 acting through a spring seat 23 the needle lifts off its seat and injection commences via orifices 24. Selection of dimensions to give a small difference of area between the frusto-conical region 22 and the plunger section 1 5 enables the use of very high opening pressure with moderate force of spring 1 7. This is the first phase of injection.

Once the needle lifts, a space 25 underneath the seat 21 is pressurised so the lifting force is increased causing an upward acceleration of the needle and a consequent lessening of the injection pressure in the spaces 1 9 and 25. The magnitude of the pressure change can be controlled by selection of dimensions of the plunger section 1 5, guide, section 20 and seat 21 and by selection of the force of spring 1 7. Downward movement of the piston 11 and sleeve 1 3 causes the sleeve to contact the spring seat 23 and then the whole assembly of piston, sleeve, spring and seat and the needle to move downwards. Because the guide section 20 of the needle has a larger area than the plunger section 1 5 the rate of oil displacement for an increment of stroke is increased.The pressure intensification ratio is decreased but actual pressure levels are increased by kinetic effects.

During the first phase of injection, oil in distributor pipe 26 accelerates towards the injector, so gaining kinetic energy. With the deceleration of the pumping assembly in the second phase the oil column is also decelerated with a consequent increase of pressure acting on the piston 11, hence a further increase of injection pressure occurs in the spaces 1 9 and 25. The increase of oil pressure above the servo piston 11 due to deceleration of the piston is less abrupt, hence of lower magnitude than it would be if the piston 11 were stopped suddenly from its maximum velocity by hitting a stop. Subsequent pressure oscillations are also greatly reduced.It is possible to select dimensions of the injector components and distributor piping so that the peak injection pressure occurs as the needle 1 6 reaches its seat 21 or at any other desired moment during the injection pericJ.

Needle seating at peak injection pressure gives an advantage in the last phase of injection which occurs after needle seating. Conventional injection nozzles close after the fuel oil pressure has dropped to a relatively low level, and part of the fuel oil displaced by the needle during its closing motion may be discharged at relatively low velocity, 35 (Figure 3), causing poor atomisation, and there is the possibility of some oil remaining on the nozzle surface, leading to carbon formation and nozzle fouling. With the injector of Figure 1 the needle seats at peak injection pressure, 36, Figure 4, and the oil in the orifices 24 has its maximum velocity so it is ejected and finely atomised by its own momentum, without spreading over the outer surface of the nozzle tip.

The combined mass of the needle 1 6, spring seat 23, sleeve 13, spring 17 and piston 11 is greater than that of the needle, stalk, etc., of a conventional injector, but impact damage on seating is prevented by the low velocity at which contact occurs. This is due to the large area of the guide section 20 relative to the nozzle orifices 24 which limits the needle velocity, and the fact that the needle cannot be accelerated freely towards the seat 21 because of the opposing action of high pressure oil in the spaces 19, 25.

After termination of injection at peak pressure, fuel oil at this high pressure level is trapped in the space 1 9 and when pressure acting on the piston 11 is relieved the whole assembly might move upwards away from the seat 21 to re-open the nozzle. This may be avoided by several methods. A simple method is to use greater clearances than are normal for conventional fuel injection equipment around the cylindrical portions 1 5 and 20 of the needle 1 6 so that pressure in the spaces 1 4 and 1 9 can decay before pressure above the piston 11 is reduced. Because the volume of the spaces 14 and 19 is small the amount of oil required to leak away is minute.Definite venting of the high pressure spaces 14 and 19, may be achieved by making the effective diameter of the seal 28 between the piston 11, and the sleeve 1 3, larger than the diameter of the plunger 1 5. This provides a hydraulic downward force on the sleeve which can overcome the force of the spring 1 7, only at high pressure. Moreover, the iarger effective diameter of the seal 28 increases the area of the piston 11 which is subject to nozzle pressure. Thus, when the peak of servo pressure acting on the piston 11 decays, the piston only may lift momentarily to allow fuel oil to escape across the seal 28 between the piston 11 and the sleeve 13 and the nozzle is prevented from re-opening.The annular area between the seal 28 and the sleeve bore must be small to be effective only at high pressure and to prevent parting of the sleeve 13 and piston 11 during normal injection.

Alternative methods of relieving the high pressure spaces are a by-pass jet 29, Figure 2, in the piston 11 a which bleeds off fuel oil throughout the injection period or a by-pass passage 30, Figure 2, in the piston which aligns with the passage 31 only when the needle seats.

Oil leakage past either part of the needle 1 5, 20 or the piston 11 into the housing of the spring 1 7 is discharged through a vent valve 32 as the piston moves downwards during injection. During a later upward stroke of the piston 11 the valve 32 closes to prevent oil being drawn back inside the injector from the leak-off passage.

Injection quantity is controlled by a metering period between injections. The pipe 26 is connected to a low pressure source for a finite number of degrees of each engine cycle. During this low pressure phase the main spring 17, can lift the servo piston 11, whilst reacting against the seat 21, to hold the nozzle shut. As the servo piston 11 lifts fuel oil passes the valve 12 to fill the pump chamber 14. The rate of piston lift is controlled by a driver operated throttle so that the total lift in the period available is adjustable.

Controlled lift of the nozzle needle may be provided. A simple method to achieve this is to include a shoulder on the spring seat, or a separate collar 33, Figure 2, which abuts against a shoulder 34, in the injector body. There will be then three stages of injection as shown in the spray diagram of Figure 5, which are nozzle opening 37, nozzle against stop 38, and nozzle closing 39. The feature of maximum pressure at the end of injection with an extremely sharp cutoff is retained.

Claims (10)

1. A servo-operated liquid fuel injector for an internal combustion engine, constructed and arranged so as to enable the attainment of high peak pressure at the termination of injection by using and attenuating kinetic energy in pressure surges in the piping to the injector, and having means for preventing re-opening of the injector, with consequent secondary injection, due to the high pressure trapped in the injector at the termination of injection.

2. A servo-operated liquid fuel injector for an internal combustion engine, comprising an injector housing provided at one end with a nozzle having one or more injection orifices and a set for an injection needle, the needle including a seat section at one end, a guide section mounting the needle for axial sliding movement in the housing and a plunger section at the other end, the crosssectional area of the guide section being greater than the cross-sectional area of the plunger section with a shoulder therebetween, a pump sleeve and a spring seat mounted about the plunger section and a compression spring between the pump sleeve and spring seat for urging the spring seat into contact with the shoulder and the pump sleeve away from the shoulder and into contact with a servo piston mounted for axial movement in the housing, valve means in the servo piston for allowing liquid fuel to enter a pump chamber between the servo piston and the pump sleeve during a metering stroke of the piston, a passage in the injector needle communicating the pump chamber to an annular space in the housing where liquid fuel pressure acts on an annular region of the needle between the guide and seat sections thereof to lift the needle off said seat and to communicate the annular chamber with the injection orifices during a pumping stroke of the injector, and means for venting the pump chamber to avoid movement of the needle away from the seat between successive pumping strokes and thereby prevent secondary injection.

3. The injector of claim 2, wherein a one way valve communicates with the space occupied by the spring to prevent accumulation of fuel oil in this space.

4. The injector of claim 2 or claim 3, wherein means are provided to limit lift of the nozzle needle.

5. The injector of any one of claims 2--4, wherein the means for venting the pump chamber comprises the provision of ciearances around the plunger and guide sections of the needle such that the pressure in the pump chamber can decay before pressure above the servo piston is reduced.

6. The injector of any one of claims 2-4, wherein the means for venting the pump chamber comprises a by-pass passage in the servo piston for bleeding off fuel from the pump chamber during an injection period.

7. The injector of any one of claims 2-4, wherein the means for venting the pump chamber comprises a bypass passage in the piston which registers with a bleed passage in the injector housing only when the needle seats.

8. The injector of any one of claims 2-4, wherein the means for venting the pump chamber comprises the provision that the effective diameter of the seal between the servo piston and the pump sleeve is larger than the diameter of the plunger section of the needle such that the piston and pump sleeve will separate momentarily when the peak of servo pressure acting on the piston decays to allow fuel to escape across said seal whilst the nozzle is prevented from re-opening.

9. A servo-operated liquid fuel injector substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

10. An internal combustion engine having at least one injector as claimed in any one of the preceding claims.