DK171216B1 - Fuel injector for an internal combustion engine - Google Patents

Description

in DK 171216 B1

BACKGROUND OF THE INVENTION This invention relates to a fuel injector for an internal combustion engine, in particular a large two-stroke diesel engine, with an outer housing for mounting in a cylinder cover and with a through-passage fuel passage which opens into a nebulizer and with a slidable longitudinally adjustable valve slider, against its valve seat by a biased compression spring and in the opposite direction of the fuel pressure in the fuel passage, where at the one end of the compression spring there is a first piston displaceable in the housing having a first surface facing away from the spring which together with a stationary component defines a first pressure chamber which communicates through a duct with the fuel passage and wherein the compression spring affects the first piston in the direction towards an outer position with minimal fuel volume in the first pressure chamber.

In such an injector known from Danish patent no.

152 619, the duct from the fuel passage to the first pressure chamber is designed as a throttle channel so that the pressure in the chamber 20 with a time delay follows the instantaneous pressure in the fuel passage. As the fuel pressure rises during an injection period, the pressure also rises in the pressure chamber, so that the first piston is pressed against the closing spring and increases the force by which the spring 25 exerts the valve slider towards its seat, which raises the closing pressure of the injector.

This eliminates the problem that the closing pressure, ie. the pressure at which the valve slider moves toward its seat at the end of the delivery period, usually 30 is less than the opening pressure, i.e. the pressure in the fuel passage at which the valve slider is lifted from its valve seat at the beginning of a delivery period. The lower closing pressure is due to the fact that, in the closed position of the injector, the fuel pressure acts on an effective area 35 of the valve slide, which is smaller than when the valve slide DK 171216 B1 2 is in the open position, where the pressure also acts on the slide area below the seat surface.

In the injector known from the Danish patent, the first piston makes continuous adjusting movements during and immediately after the delivery period of the injector, which can cause a not insignificant wear on the piston's control surface with consequent increased leakage from the pressure chamber. At the end of each delivery period, the compression spring pushes the first piston back to the outer position with minimal fuel volume in the pressure chamber so that the injector opening pressure is not affected by the hydraulic tension of the compression spring.

It is known that the compression pressure in the engine cylinder depends on the engine load such that the pressure at full load is substantially higher than at low load. For example, at full load the compression pressure may be approx. 120 bar, while the compression pressure at idle load is approx. 40 bar.

20 When the valve slider is in the closed position, the pressure in the engine cylinder moves into the nebulizer holes and further up to the sliding area under the seat surface, ie. the sliding section located on the nebulizer side of the valve seat. The instantaneous compression pressure therefore affects the valve slider with a force in the opening direction. Thus, the compression pressure increasing with the motor load causes the opening pressure of the known injectors to decrease with increased motor load. For example, in a typical fuel injector for a 30 large two-stroke diesel engine, the opening pressure can drop from 400 bar at the idle load to 325 bar at full engine load. The lower opening pressure at full load is not conducive to fuel atomization at the start of the injection period.

DK 171216 B1 3

At low engine load, the fuel pressure in the injector is determined by its opening pressure, since the fuel pumps here deliver such a small amount of fuel that the flow resistance in the nebulizer does not affect the fuel pressure. In contrast, the fuel quantities delivered from the pumps at higher engine load are so large that the flow resistance of the nebulizer determines the fuel pressure in the injector, ie. in this case, the fuel pressure is substantially greater than the opening pressure of the injector.

The opening pressure of the known injectors is determined by the bias of the compression spring. The manufacture of the springs is subject to certain production tolerances, which means that the fuel injectors in an internal combustion engine are not necessarily all set to exactly the same opening pressure. The variations in the opening pressure of the injectors are often more pronounced after prolonged operation of the motor, the springs settling during operation, ie. loses some of the bias. Thus, there are 20 timed changes in the opening pressures of the injectors, necessitating regular checking and tightening of the compression springs at regular intervals to maintain satisfactory operation of the engine. This is labor intensive and undesirable.

The invention has for its object to provide a fuel injector which has increasing opening pressure with increasing engine load and which requires less maintenance.

To this end, the fuel injector according to the invention is characterized in that the spring is in force-transmitting connection with a second piston with a second surface facing away from the spring, which constitutes the end wall of a second pressure chamber, that the first piston moves in movement away from said piston. outer position allows for a flow connection between the first and the second pressure chamber, that the second pressure chamber has greater cross-sectional area than the first chamber, and that a limited drainage passage connects the second pressure chamber with a drain.

With increasing engine load, the pressure in the fuel passage increases as mentioned above due to the flow resistance in the nebulizer. Thus, the pressure in the first pressure chamber also increases, which causes a displacement of the first piston so that the flow connection between the first and the second pressure chamber 10 is opened and a quantity of fuel flows into the second pressure chamber. Since this pressure chamber has a greater effective cross-sectional area than the first chamber, the pressure build-up in the second chamber will result in a return of the first piston to the outer position with a minimum fuel volume while at the same time blocking the amount of fuel in the second pressure chamber, the first piston interrupting the flow connection between the the chambers. Since the second piston is in power transmitting connection with the spring, it is shortened as the filling 20 of the combs, whereby the spring bias grows. Except for a small amount of drained fuel, the fuel is kept confined in the pressure chamber until the fuel injector has to be actuated again for fuel injection, thus maintaining the increased pre-tension of the spring, which gives the spring higher opening pressure and higher closing pressure.

If the greatest pressure in the fuel passage during the next injection period is greater because the engine load increases, the fuel pressure in the first pressure chamber will produce a force on the first piston which is greater than the opposite compressive force from the spring, leading to a displacing the first piston so that the flow connection between the chambers is opened until the pressure build-up in the second pressure chamber has produced an increased spring force which is slightly greater than the fuel pressure on the effective cross-sectional area of the first pressure chamber. The increased spring force will then again return the first piston to the outer position with blocked flow connection 5 between the chambers.

The limited drainage passage allows for continuous drainage of a small amount of fuel from the second pressure chamber. This ensures that the spring bias is also reduced when the engine load and thus the maximum 10 pressure in the fuel passage is decreasing. If the load is not decreasing, the amount of drained fuel is replaced with new fuel at the next injection period, the fuel drain causing a small pressure drop in the second pressure chamber so that the first piston can again open the flow connection.

The opening pressure of the fuel injector at a particular load in the upper load range of the engine depends on the effective cross-sectional area of the first chamber. Since such an area can be manufactured with very fine tolerances, all the fuel injectors in the engine will adjust with equal opening and closing pressures, the various manufacturing-specific variations of the spring springs and varying sentences during the operating period being offset by compression of the 25 springs. until they provide a uniform compressive force which adjusts to the greatest fuel pressure in the injectors.

This setting occurs automatically during engine operation, thus eliminating a significant portion of the need for periodically manual adjusting of the injectors.

It is possible to form the flow connection with a lateral opening which may be covered or exposed by the first piston upon its displacement, but it is preferred that the first piston has a seat portion which, when abutting against a corresponding seat portion, on the stationary component interlocks the flow connection DK 171216 B1 6 between the first and the second pressure chamber. Such seat sections have for many years proved to be very reliable in fuel injectors, and they produce a well-defined shut-off which can withstand large pressure differences.

The drainage passage may conveniently be of such a limited size that the drained volume at full engine load during a motor cycle is in the range of one half to one-twentieth of the fuel volume of the second pressure chamber. If the drained amount becomes greater than half, especially at lower engine loads it will be difficult to achieve the desired increase in the opening pressure, and in addition, the piston movements become large and frequent, the second pressure chamber having to be filled after each injection period, even when the engine load is constant. If the drained volume becomes less than one-twentieth, the opening pressure will drop inconveniently slowly by abruptly reducing the engine load. The mentioned 20 drainage conditions apply at full engine load.

The effective cross-sectional area of the first pressure chamber may in one embodiment be smaller than the opening area of the valve slide. This causes the first piston to remain in the above-mentioned outer position at low engine load, the fuel pressure being determined by the injector's opening pressure generated solely by the mechanically preset bias of the spring. Only when the fuel pressure increases with increasing engine load will the pressure on the effective cross-sectional area of the first chamber produce a force capable of overcoming the spring force and moving the first piston away from the outer position.

It is preferred that the second pressure chamber has several times greater effective cross-sectional area than the first chamber. As a result, the pressure in the second pressure chamber is correspondingly times less than the pressure in the first chamber when the force of the second piston on the spring and thus on the first piston balances the opposite force effect of the fuel on the first piston. Thus, the large effective cross-sectional area of the second chamber causes a shut-off of the second chamber at an advantageously low chamber pressure, which results in a relatively small pressure drop across the drain passage, with consequent small drainage of the fuel from the second pressure chamber. Furthermore, the large area of the second chamber 10 gives the advantage that the chamber is filled with a large volume of fuel at a certain displacement of the second piston and a corresponding compression of the spring. These two conditions both help the spring bias to change only slightly, while the injector is in the closed position between two injection periods.

It is possible to place both pistons at the end of the nebulizer facing the nebulizer, the stationary component being then constituted by the valve slider relative to the first piston. Such a design results in the pistons participating in the valve slider setting movements. In this case, the pistons will act as an increase in the mass of the slider, which will give the injector more sluggish adjusting movements. As this is usually considered a disadvantage, the first piston may alternatively be formed at the opposite end of the spring. This gives the disadvantage that the flow connection between the two pressure chambers becomes elongated and relatively cumbersome to manufacture. In a preferred embodiment, which both avoids these drawbacks and is easy to manufacture, the fuel injector is designed such that the compression spring is mounted in a manner known per se between two spring controllers which are longitudinally displaceable on a centrally located central pressure piece that the second piston is formed in the upper spring guide opposite the nebulizer DK 171216 B1 8, which has a lower tubular wall, which pressurally encloses the pressure piece, and a larger internal diameter than the lower wall, designed to pressurally enclose it. 5, a first plunger, and an intermediate piece connecting the walls and with its upper side, the second surface constitutes the first plunger, which is annular and is enclosed between the printing piece and the upper wall of the second plunger, and has a lower inwardly collar which, with its upper side 10, constitutes the first face extending inwardly into the seat section and the corresponding seat section of the pressure piece facing downwards o g is located between a channel passing through to the fuel passage and a lower area of reduced diameter which constitutes the flow connection 15 between the two chambers.

The drainage passage may be formed as an independent element, for example in the form of a small bore through the second piston into the second chamber, but it is preferred that the drainage passage consists of the pressure-sealing ring gaps between the two walls of the second piston and the first piston respectively. pressure ring, since these ring slots are already difficult to close completely. The amount of drained fuel will simultaneously lubricate the sliding surfaces against each other.

An example of an embodiment of the invention will now be explained in more detail with reference to the drawing, in which fig. 1 is a partial longitudinal section through a fuel injector according to the invention; FIG. 2 shows on a larger scale a section of FIG. 1 showing the compression spring with associated elements, and FIG. 3 is a diagram of the relationship between the engine load and the opening pressures of injectors of known type and according to the invention, respectively.

DK 171216 B1 9 In fig. 1, there is generally shown a fuel injector 1 designated as having an outer housing 2 for mounting in a cylinder cover. The housing is elongated and has at its upper end a laterally projecting mounting piece 3 which, by means of bolts fastened in the cover, presses a contact surface 4 at the lower end of the housing against a corresponding contact surface formed in the cover. A fuel pump or similar source for periodically delivering high-pressure fuel is connected through a pressure line 10 at a fuel supply 5 at the top of the injector, from which a fuel passage 6 passes centrally through the injector down to an atomizer 7 with a central cavity 8, from which nebulizer holes for injecting fuel into the engine-15 cylinder.

The fuel passage may have a valve which allows circulation of preheated fuel in the injector between the injection periods. The fuel passage passes through a pressure piece 9 which faces upwardly against a stationary element 10 in the housing and downwards towards an intermediate piece 11 which is pressed against an in-house slider guide 12. A valve slider 13 is longitudinally slidably accommodated in a central control bore 12 'in the slide guide and with one end encloses a projecting cylindrical portion 11' of the spacer. The guide bore centers the slide so that an annular tapered seat surface 14 at the lower end of the valve slide, which is shaped like a needle, is coaxial with a corresponding valve seat on the slide guide 12. When the valve slide is in the closed position with the seat surface pressed against the valve seat on the slide guide the needle tip down into the central nebulizer of the nebulizer and is here subjected to the pressure in the engine cylinder which propagates through the nebulizer holes into the cavity and affects the valve slider with a force in the opening direction.

The lower end of the valve slide and the slide guide 12 define 10 a pressure chamber 15, which communicates with the fuel passage 6 via inclined bores 16. The downwardly flushing annular end face of the valve slide, which is delimited inwardly by the needle, is affected by the fuel pressure in the chamber 15. the fuel pressure affecting the valve slider with an opening force. The opening area of the valve slider is mainly determined by the diameter difference between the outer diameter of the cylindrical portion 11 'and the inner diameter of the guide bore 12'.

The valve slider is further loaded in the closure, i. in a downward direction towards the valve seat, by means of a compression spring 17, the upper end of which abuts against an upper spring guide 18, which is slidably mounted on the pressure piece 9, and whose lower end via a lower 15 spring guide 19, which is also slidably controlled on the pressure piece 9, is supported by a slotted pressure bushing whose lower end face abuts an upwardly extending chest on the valve slide 13. The spring force is thus transferred through the spring guide 19 and the pressure bushing 20 to the valve slide 13.

An annular first piston 21 is mounted axially displaceable about the upper portion of the pressure member 9. The inner diameter of the piston sliding surface 22 (Fig. 2) is adapted to the opposite guide surface 23 of the pressure piece in such a way that the annular gap between the surfaces is sufficiently narrow that the piston pressurally encloses the pressure piece. The guide surface 23 is terminated downwardly in a circular recess incorporated in the pressure piece, which communicates through a channel 24 with the central fuel passage 6 in the pressure piece. The recess extends downwardly into a cylindrical section 25 having a smaller outer diameter than the guide surface 23. Under section 25, the thrust member has an annular, tapered downward-facing seat portion 26.

The first piston 21 has a lower, inwardly facing collar 27 with a tapered, upwardly extending seat portion 26 ', which may be pressure-tight against the seat portion 26. The first piston and pressure portion define in the region adjacent to the recess and cylindrical portion 25 a first pressure chamber 28 having an effective cross-sectional area determined at the 5 diameter gap between the section 25 and the guide surface 23.

The effective cross-sectional area is located on the upper side of the collar 27, ie. on a first surface facing away from the spring so that the fuel pressure applied through the channel 24 in the first pressure chamber affects the first piston with a downward force.

A second piston 29 is formed integrally with the upper spring guide 18 and comprises an annular spacer 30 which carries a lower tubular wall 31 and an upper tubular wall 32. The inside of the lower wall 31 lies pressure-sealing and longitudinally displaceable against a cylindrical , second guide surface 33 on the pressure member 9, and the inside of the upper wall 32 abuts pressure-sealing and axially displaceable against the outside of the first piston 21. The first and the second piston define together with the pressure member 9 a second pressure chamber 34 with an effective cross-sectional area determined by the diameter difference between the cylindrical interiors of the lower wall 31 and the upper wall 32. A cylindrical recess located immediately below the seat section 26 in the outside of the pressure member forms a flow connection 35 between the two pressure chambers when the first piston is moved away from the seat section 26.

The underside of the collar 27 may have one or more projections or a circumferential projection with intersections holding the portion radially outside the projection 30 of the second pressure chamber 34 in flow communication with the flow connection 35 when the projection abuts the upper side of the intermediate piece 30.

In an alternative embodiment not shown, the projection may be circumferential, and the inside of the lower wall 31 may have a smaller diameter than the inside of the collar 27, so that the portion of the second pressure chamber 35 adjacent the flow connection 35 has an upwardly effective cross-sectional area. which is open to the flow connection 35 when the protrusion of the collar 27 abuts 5 towards the upper side of the spacer 30 and interlocks the connection to the remaining part of the pressure chamber 34. By appropriate pressure rise in the flow connection 35, this effective area causes the second piston 29 to move away. from the first piston 21 while simultaneously exposing the full effective cross-sectional area of the second pressure chamber.

The second pressure chamber 34 is sustained in connection with a limited drainage passage which consists of a pressure-sealing ring gap between the inside of the upper wall 32 and the cylindrical outer surface of the first piston, and of the pressure-sealing ring gap between the inside of the lower wall 31 and the guide surface 33 of the pressure piece. .

Next, it is described how the two pistons automatically produce the desired biasing force in the compression spring 17. When the engine is stopped and the fuel passage 6 is not pressurized, the two pistons occupy the position shown in the drawing, where the compression spring 17 presses the second piston 29 with its preset bias. abutting against the first piston 21, which 25 transmits through the seat sections 26 and 26 'the spring force to the pressure member 9.

As the engine is started and the load increased, the pressure in the fuel passage 6 increases during each injection period to a maximum pressure which corresponds to the injector opening pressure at low load and at higher load is determined by the flow resistance in the nebulizer holes. Thus, the maximum pressure in the fuel passage increases with increasing engine load.

The pressure in the fuel passage 6 propagates through the conduit 24 to the first pressure chamber 28 and when the pressure DK 171216 B1 13 reaches a magnitude where the downward force on the first piston overcomes the preset spring bias, the first piston moves towards the spring which compressed between the spring guides 18 and 5 19, and at the same time the fuel flows via the flow connection 35 into the second pressure chamber, where the pressure builds up to a level which returns the first piston 21 to abutment against the seat section 26, while the second piston 29 remains in it. position where the spring 10 is provided with the extra bias.

If the pressure in the fuel duct 6 increases during the subsequent injection periods to a higher level, the piston movements are repeated so that the spring 17 is given a bias which depends linearly on the maximum pressure in the fuel passage 6.

Through the pressure-sealing ring slots, a small amount of fuel is continuously drained from the second pressure chamber, the fuel being passed through the internal cavity of the housing 2 to a drain opening (not shown).

In this way, the fuel injector according to the invention achieves a spring bias and thus an opening pressure which grows with increasing engine load, as shown in FIG. 3. This makes it possible to lower the opening pressure at low engine load, the injector automatically generating the high opening pressure required at full load. The compression spring can thus be prefabricated with a bias which gives an opening pressure at low load of about 200 bar, which promotes stable engine operation at partial load, while the opening pressure at full load is higher than at the known injectors, which promotes good atomization. of the fuel at the start of the injection period.

Instead of the central process described above, the fuel passage 6 may in a well-known manner comprise a number of 35 channels extending in a stationary intermediate part on the outside of the spring and which via slanting channels in the sliding guide end into the pressure chamber 15. In this embodiment, the opening area of the valve slide is determined by the downwardly annular end face surrounding the needle.

Claims (7)

1. A fuel injector (1) for an internal combustion engine, in particular a large two-stroke diesel engine, with an outer housing (2) for mounting in a cylinder cover and having a through-flow 5 fuel passage (6) which opens into an atomizer (7) and with a in a sliding guide (12) longitudinally displaceable valve slider (13) actuated in the direction towards its valve seat by a biased compression spring (17) and in the opposite direction of the fuel pressure in the fuel passage, where at one end of the compression spring there is an axially displaceable in the housing a first piston (21) having a first surface facing away from the spring which, together with a stationary component (9), defines a first pressure chamber (28) which communicates through a channel (24) with the fuel passage and where the pressure spring affects the first piston towards an outer position with minimal fuel volume in the first pressure chamber, characterized in that the spring is in power-transferring connection with a second piston (29) with one removed from the spring. ending second surface constituting the end wall of a second pressure chamber (34) that the first piston (21), when moving in a direction away from said outer position, opens a flow connection (35) between the first and the second pressure chamber, that the second pressure chamber (34) has a greater effective cross-sectional area than the first chamber (28), and that a limited drainage passage connects the second pressure chamber to a drain. Fuel injector according to claim 1, characterized in that the first piston (21) has a seat section (26 ') which, upon abutment against a corresponding seat section (26) on the stationary component, blocks the flow connection (35) between the first and the second pressure chamber. DK 171216 B1 16 3. A fuel injector according to claim 1 or 2, characterized in that the drainage passage is of such a limited size that during a motor cycle the drained volume is in the range of half to 5 one-twentieth of the fuel volume in the second pressure chamber (34) at full engine load. Fuel injector according to any one of claims 1-3, characterized in that the effective cross-sectional area of the first pressure chamber (28) is smaller than the opening area of the valve slide. Fuel injector according to one of claims 1 to 4, characterized in that the second pressure chamber (34) has several times greater effective cross-sectional area than the first chamber (28). Fuel injector according to one of claims 1 to 5, characterized in that the compression spring (17) is mounted in a manner known per se, between two spring guides (18, 19), which are longitudinally displaceable on a central pressure piece (9) stationary in the housing (9). ) that the second piston (29) is formed in the upper spring guide (18) located opposite the nebulizer (7), which has a lower tubular wall (31) which pressurally encloses the pressure piece and one with a larger internal diameter than the a lower wall formed upper tubular wall (32) which pressurally seals 25 the first piston (21), and an intermediate piece (30) connecting the walls and with its upper surface the second piston, the first piston (21) being annular and is enclosed between the pressure member and the upper wall of the second piston, and has a lower inwardly facing collar (27) which, with its upper side, constitutes the first surface which faces inwardly into the seat portion (26 ') and that the corresponding seat portion (26) faces downwards and is situated those between a duct (24) passing through to the fuel passage (6) and a lower area of reduced diameter which constitutes the flow connection (35) between the two chambers. Fuel injector according to claim 6, characterized in that the drainage passage consists of the pressure-sealing ring gaps between the two walls (31, 32) of the second piston and the first piston (21) and the pressure piece (9), respectively.