DE19820264A1 - High-pressure piston cylinder unit for internal combustion engine - Google Patents

Abstract

The high-pressure piston cylinder unit has a piston(5), guidable through a cylinder bore(3), and coupled to an actuating device. There are fine grooves(10), in at least one part of the guiding surface of the piston, which run close to one another. The grooves have a width of at least between 10-40 micrometers. An Independent claim is included for a method of making the above high-pressure piston cylinder unit.

Description

The invention relates to a high-pressure piston-cylinder unit, in particular one Injection pump or an injection valve for an internal combustion engine, in particular for high number of lifting cycles, as provided in the preamble of claim 1.

In such a high-pressure piston-cylinder unit, which has a large number of Lift cycles is exposed, as is particularly the case with an injection pump or a Injector for an internal combustion engine is generally a piston available, which is guided in a cylinder bore, and which a high Pressure difference is exposed. The piston guided in the cylinder bore serves either the delivery of the fuel to be injected into the combustion chamber of the internal combustion engine, as in the case of an injection pump, or in the case of an injection valve, below Exposure to the fuel to be injected under high pressure Open the injector, typically by having the piston coupled or Nozzle needle formed in one piece from the valve seat of a needle valve takes off and thus an injection cross section for injecting the fuel into the Releases the combustion chamber of the internal combustion engine.

With such a high-pressure piston-cylinder unit, there is the fact that ultimately unavoidable manufacturing tolerances a deaxing of the piston in the Cylinder bore occurs, which has the consequence that the pressure distribution over the Piston circumference because of the different setting over the piston circumference Gap widths is not uniform, and this results in a resulting radial force that  acts in the direction of deaxing. The resulting one-sided pressure of the Piston in its guide leads to wear in the contact surface.

In the case of a common rail fuel injection system, in which the one to be injected Fuel is stored in a storage tank under high pressure and is kept permanently fuel injected by the high pressure fuel into the Combustion chamber of the internal combustion engine is injected, the risk of wear is special high. With permanently acting high pressures comes namely add to the stress that the resulting from the compressive forces Radial forces act in full during the entire lifting phase, unlike one conventional injection system, in which the stroke is still partially in the Pressure build-up phase, i.e. when the injection pressure is lower than the maximum Pressing takes place. The fact that the actuation of the injection valve of a common rail Piston fuel injector, typically with the valve needle of the Injector coupled or integrally formed with this, the is exposed to the high fuel pressure that arises during deaxing the nozzle needle guide to the nozzle needle seat or the piston in the cylinder bore permanent leakage flow asymmetrical over the piston circumference. Also act due to the high pressures high, the deaxing increasing radial forces during the entire lifting phase are available, in particular also at the beginning of the Lifting phase. These radial forces can cause starting or rubbing and strong Wear of the nozzle needle in the nozzle needle guide or the piston in the Lead cylinder bore.

An injection valve for an internal combustion engine is known from DE 38 24 467 C2, at which the valve needle in two parts by a hollow needle and one in an inner bore the hollow needle guided valve needle is formed. The hollow needle points in the area of Point a number of circumferential grooves, which in Longitudinal direction of the valve needle by a distance of about the order of magnitude  Diameter of the valve needle are spaced and have a width and depth that correspond to about one tenth of the valve needle diameter.

Furthermore, from MTZ 55 (1994) 9, page 502, column 3 and page 511, column 1 Use of titanium nitride coatings for the pistons of Fuel injection pumps for large diesel engines are known to "seize" the To prevent piston.

EP 0 565 742 A1 describes methods for the fine machining of workpiece surfaces, in particular of walls of the bores in the cylinder of an internal combustion engine known in which the surface by blasting, in particular by means of a Lasers arranged according to a predetermined pattern are generated, which as Lubricant reservoir should serve.

Finally, EP 0 419 999 B1 describes a method for processing by friction highly stressed surfaces in internal combustion engines, especially the cylinder surfaces known from piston engines, in which the surface is honed and additionally one Laser beam treatment is subjected, the laser treatment for the evaporation of outstanding roughness peaks or scaling is used to make it smoother To reach surface.

The object of the invention is a high-pressure piston-cylinder unit, in particular to specify an injection pump or an injection valve for an internal combustion engine, at which has a lower risk of wear on a guided in a cylinder bore Piston exists by deaxing.

Furthermore, the invention is intended to provide a method for producing such High pressure unit can be specified.  

This task is accomplished by the high pressure Piston cylinder unit or by the method specified in the claims for Manufacture of such a solution, the respective advantageous embodiments in the Subclaims are specified.

The invention provides a high-pressure piston-cylinder unit, in particular a Injection pump or an injection valve for an internal combustion engine, in particular for created a high number of lifting cycles, in which a guided in a cylinder bore Piston on one side a high pressure and thus a high pressure difference is exposed, according to the invention at least in a part of the guide surface of the Pistons are formed at a small distance from each other fine grooves.

An advantage of the guide surface of the piston designed according to the invention is that that there is a hydraulic pressure equalization on the circumference of the guide through the grooves and so that the one-sided contact of the piston in the cylinder bore is prevented or at least the contact forces are reduced. Another advantage is that the Leakage flow after central alignment of the piston in the longitudinal direction of the Guide surface of the piston is reduced and thus the hydraulic efficiency of the Unity is improved. A reduction in the leakage flow is also coming only because the grooves running transverse to the direction of the leakage flow act like a labyrinth seal. Another advantage is that this is in the grooves fluid present wets the contact surfaces, whereby a lubrication effect is achieved.

The grooves formed in the guide surface advantageously have a width b of between 5 to 100 microns, preferably between 10 to 40 microns.

The depth t of the grooves is advantageously between 3 to 50 μm, preferably between 10 to 30 µm.  

The distance a of the grooves is advantageously between 0.05 to 1 mm, preferably between 0.1 to 0.5 mm, preferably between 0.1 to 0.3 mm.

According to an advantageous embodiment, the width b corresponds to a groove in the essentially their depth t.

It is also advantageous if the ratio of the depth t of the groove to Nominal diameter D of the guide surface is between 1/200 and 1/1000.

According to one embodiment of the invention, the grooves in the circumferential direction are Guide surface designed to run.

According to a further development thereof, the grooves can also be provided in the longitudinal direction Guide surface varying distance a be formed.

According to another embodiment of the invention, it is provided that the grooves in Longitudinal direction of the guide surface are formed.

According to another embodiment of the invention, it is provided that the grooves under are formed at an angle to the longitudinal direction of the guide surface.

According to a further development, the grooves can be arranged in the longitudinal direction of the Guide surface have varying slope.

According to another embodiment of the embodiment which is very advantageous in terms of production technology Invention it is provided that the grooves are formed by a helix.

This can be further developed in that the helix is multi-start.  

The helix can have a gradient varying in the longitudinal direction of the guide surface to have.

According to yet another embodiment of the invention, it is provided that the grooves at different angles to the longitudinal direction of the guide surface crosswise are progressive.

This can be further developed in that the grooves in the longitudinal direction of the Guide surface of varying slope are formed.

In the aforementioned embodiments, it may be advantageous to set the distance a Grooves in the longitudinal direction of the guide surface so that it is essentially the Operating stroke of the piston in the cylinder bore corresponds.

According to a further embodiment of the invention, several of the aforementioned can Patterns can be combined to form the grooves.

According to one embodiment of the invention it is provided that the grooves in one the high pressure side of the piston adjoining area of the guide surface are trained.

Alternatively, the grooves can extend over the entire area of the guide surface be trained.

According to one embodiment of the invention, the grooves are in the guiding surface serving outer surface of the piston.

Alternatively or additionally, it can be provided that the grooves in the To provide the guide surface serving cylinder bore.  

The invention is of particular value in the case of a high-pressure piston-cylinder unit which Part of a fuel injector of a common rail injection system, in which the Piston is used to actuate the injector of the fuel injector, and wherein the Pressure difference permanently applied to the piston. With such a permanent from The component subjected to fuel pressure can undergo constant deaxing, i.e. from the beginning the movement of the piston in the cylinder bore occur, which is why Invention here achieved a significant reduction in wear with particular advantage can be.

In such a, serving as part of a common rail injection system High pressure unit, the piston is advantageously made of one piece of material on the nozzle needle of the injection valve, wherein the piston has a shoulder that is permanent is acted upon by the fuel pressure of the common rail injection system.

According to the invention, the grooves on which the fuel pressure is advantageous are advantageous applied shoulder adjoining lateral surface of the Pistons trained.

The inventive method for manufacturing a high pressure unit of the invention it provides that the grooves are created by fine turning.

An alternative method, which is particularly advantageous, provides for the grooves to generate by beam processing.

Such beam processing is advantageously carried out in particular by laser engraving.

An advantageous development of the method according to the invention provides that the Creation of the grooves takes place after the finishing of the guide surface and after that lapping or fine grinding of the guide surface is carried out.  

Exemplary embodiments of the invention are explained below with reference to the drawing. Show it:

Figure 1 is a partially sectioned side view of the injection valve of a fuel injector of a common rail injection system, which is designed according to an embodiment of the invention, wherein the cutout A shows the fine grooves provided in the guide surface of a piston of the injection valve.

FIG. 2 is an enlarged view of the nozzle needle of the injection valve of the fuel injector shown in FIG. 1;

. Fig. 3 is a greatly enlarged cross-section through the guide surface of the piston of the formed shown in Figure 2 the nozzle needle fine grooves; and

Fig. 4 is a Fig. 2 corresponding view of the nozzle needle of the injection valve with four embodiments a) to d) the arrangement of the grooves on the outer surface serving as a guide surface of the nozzle needle piston.

Fig. 1 shows a view, partly in cross section, of the injection nozzle of a fuel injector for a common rail fuel injection system. The injection nozzle designated by reference number 1 has a needle housing 2 , in which a cylinder bore 3 is provided. In this cylinder bore 3 , a piston 5 is guided, which is integrally formed with a nozzle needle 4 . The nozzle needle 4 has a needle tip 8 which interacts with a valve seat 9 . An injection cross section 11 in the form of injection openings is formed in the area of the valve seat 9 . At the transition from the piston 5 to the nozzle needle 4 , a shoulder 6 is formed, which lies in the area of an annular space 12 formed in the needle housing, into which a fuel channel 7 opens. The fuel channel 7 leads to a high-pressure accumulator of the common rail system, in which fuel to be injected is held under high pressure. To control the injector 1 , the fuel injector has an electromechanical or hydraulic actuating element, not shown in FIG. 1, as is well known per se, by means of which the piston 5 is released in the sense of an upward movement, so that it is in the annular space 12 acting on the shoulder 6 of the piston 5 fuel pressure causes a lifting of the nozzle needle 4 and thus the needle tip 8 from the valve seat 9 and thus a release of the injection cross section 11 .

As can be seen in the enlarged section labeled A, fine grooves 10 are formed in the lateral surface of the piston 5 at a short distance from one another. On the one hand, these grooves 10 bring about a hydraulic pressure equalization over the circumference of the piston 5 in the guide formed by the cylinder bore 3 and thus prevent the piston 5 from one-sided contact due to the gap between the outer surface of the piston 5 and the cylinder bore due to the annular space 12 3 entering fuel under high pressure when the nozzle needle guide is deaxed. At the same time, an asymmetrical and thus increased leakage flow in the longitudinal direction of the guide between the outer surface of the piston 5 and the cylinder bore 3 is reduced, and thus the hydraulic efficiency of the fuel injector is improved.

In FIG. 2, the materially in one provided with the piston 5 nozzle needle 4 is shown enlarged. The piston 5 has a nominal diameter D, which is 6.8 millimeters in the illustrated embodiment. From the shoulder 6 and thus from the side of the piston 5 acted upon by the fuel under high pressure in the annular space 12, the grooves 10 are formed on the lateral surface of the piston 5 in a circumferential direction over a length l. In the illustrated embodiment, this length l, over which the grooves 10 are provided, is approximately 22 mm.

In Fig. 3 is a greatly enlarged cross-section through the surface of the skirt of the piston 5, which shows two grooves 10. The cross section of the grooves 10 has a substantially triangular shape in the illustrated embodiment. The width b of a groove is, for example, 5 to 100 μm, preferably between 10 to 40 μm. In the illustrated embodiment, the groove width b is 30 microns. The groove depth t can be 3 to 50 μm, preferably between 10 to 30 μm. In the illustrated embodiment, the depth t is 15 microns. The distance a between two grooves can be between 0.05 to 1 mm, preferably between 0.1 to 0.5 mm, preferably between 0.1 to 0.3 mm. In the illustrated embodiment, the distance a is 0.2 mm.

The ratio of the depth t of the groove 10 to the nominal diameter D of the guide surface or of the piston 5 is advantageously between 1/200 and 1/1000. In the illustrated embodiment, the ratio mentioned is around 1/450, which has proven to be very advantageous.

FIG. 4 again shows a representation corresponding to FIG. 2 and examples a) to d) of the structuring of the outer surface of the piston 5 .

According to the example of FIG. 4a), the grooves 10 are formed in the circumferential direction of the piston 5 , as shown above in the side view and also in FIG. 2. In the exemplary embodiment, the grooves are formed with the same distance a in the longitudinal direction, alternatively the grooves 10 can also be formed with a distance a varying in the longitudinal direction of the guide surface.

According to the exemplary embodiment in FIG. B), the grooves 10 are designed to run in the longitudinal direction of the guide surface.

According to the exemplary embodiment of FIG. 4c), the grooves 10 are designed to run at an angle to the longitudinal direction of the guide surface. In the illustrated embodiment, the grooves 10 all have the same slope. Alternatively, the grooves 10 can also be provided with an incline that varies in the longitudinal direction of the guide surface.

As a borderline case of the arrangement of the grooves 10 in the circumferential direction as in FIG. 4a) and the arrangement of the grooves at an angle to the longitudinal direction as in FIG. 4c), the grooves 10 can be formed by a helical line. This helix can be single-start or multi-start. The helix may have a constant gradient in the longitudinal direction of the guide surface or, alternatively, a gradient varying in the longitudinal direction of the guide surface. The formation of the grooves as a helix is particularly advantageous in terms of production technology.

According to FIG. 4d), the grooves 10 can be designed to run crosswise at different angles to the longitudinal direction of the guide surface, the angles being opposite, but the same in amount or different in amount. While in the illustrated embodiment the slope of the grooves 10 in the longitudinal direction of the guide surface is the same, the grooves 10 can alternatively also be formed with a gradient varying in the longitudinal direction of the guide surface.

The structuring patterns according to FIGS. 4a) to 4d) are basic patterns, but different patterns are also possible. Furthermore, several patterns can be combined in accordance with the type described with reference to FIGS. 4a) to 4d).

According to a special embodiment of the invention, the distance a of the grooves 10 in the longitudinal direction of the guide surface is selected so that it essentially corresponds to the operating stroke of the piston 5 in the cylinder bore 3 . This has the advantageous effect that the remaining guide surface on the jacket of the piston 5 between the grooves 10 is constantly moving on wetted surfaces of the guide, thus largely preventing the guide from running dry. In the case of a single-start thread, the distance a between the grooves 10 then corresponds to the thread pitch.

In the exemplary embodiments shown with reference to FIGS. 1 to 4, the grooves 10 are formed in the outer surface of the piston 5 in their function as a guide surface. Alternatively or optionally in addition, the grooves 10 can also be formed in the cylinder bore 3 as a guide surface.

In the application shown in Fig. 1 of an injection valve for a common rail fuel injection injector, the fuel pressure provided by the pre-store via the fuel channel 7 and the annular space 12 is permanently applied to the shoulder 6 of the piston 5 , so that the piston 5 is permanently one-sided Pressure difference is exposed. Here, the advantage of the hydraulic pressure equalization caused by the grooves 10 and the reduction of the leakage flow particularly come into play. However, even in the case of other high-pressure piston-cylinder units in which a piston is exposed to a high pressure difference on one side, as is the case in particular with other injection valves and injection pumps for internal combustion engines, the invention leads to a corresponding advantage.

The grooves 10 in the guide surface of the piston, that is to say in the outer surface of the piston 5 or in the surface of the cylinder bore 3, can be produced, for example, by fine turning. As an alternative to this, the grooves, in particular on the lateral surface of the piston 5, can be produced by beam machining, the method of laser engraving being particularly advantageous. Preferably, the generating of the grooves 10 is performed after the fine machining of the guide surface, and after the creation of the grooves 10 nor a lapping or fine grinding is preferably carried out of the guide surface, to produce the final surface of the guide surface.

Reference list

1

Injector

2nd

Needle housing

3rd

Cylinder bore

4th

Nozzle needle

5

piston

6

shoulder

7

Fuel channel

8th

Needle point

9

Valve seat

10th

groove

11

Injection cross section

12th

Annulus

Claims (29)

1.High-pressure piston-cylinder unit, in particular injection pump or injection valve for an internal combustion engine, in particular for high number of strokes, with a piston ( 5 ) guided in a cylinder bore ( 3 ) and coupled to an actuating element, which is exposed to a high pressure difference, characterized in that at least In some of the guide surface of the piston ( 5 ) there are fine grooves ( 10 ) running a short distance apart. 2. High-pressure unit according to claim 1, characterized in that the grooves ( 10 ) have a width b of between 5 to 100 microns, preferably between 10 to 40 microns. 3. High pressure unit according to claim 1 or 2, characterized in that the grooves ( 10 ) have a depth t of between 3 to 50 microns, preferably between 10 to 30 microns. 4. High pressure unit according to claim 1, 2 or 3, characterized in that the grooves ( 10 ) a distance a of between 0.05 to 1 mm, preferably between 0.1 to 0.5 mm, preferably between 0.1 to 0 , 3 mm. 5. High-pressure unit according to one of claims 1 to 4, characterized in that the width b of a groove ( 10 ) corresponds substantially to the depth t. 6. High-pressure unit according to one of claims 1 to 5, characterized in that the ratio of the depth t of the groove ( 10 ) to the nominal pressure meter D of the guide surface is between 1/200 and 1/1000. 7. High-pressure unit according to one of claims 1 to 6, characterized in that the grooves ( 10 ) are formed extending in the circumferential direction of the guide surface. 8. High-pressure unit according to claim 7, characterized in that the grooves ( 10 ) are formed with a distance a varying in the longitudinal direction of the guide surface. 9. High-pressure unit according to one of claims 1 to 6, characterized in that the grooves ( 10 ) are designed to extend in the longitudinal direction of the guide surface. 10. High-pressure unit according to one of claims 1 to 6, characterized in that the grooves ( 10 ) are formed at an angle to the longitudinal direction of the guide surface. 11. High-pressure unit according to claim 10, characterized in that the grooves ( 10 ) have a varying gradient in the longitudinal direction of the guide surface. 12. High-pressure unit according to one of claims 1 to 6, characterized in that the grooves ( 10 ) are formed by a left-hand or right-hand helix. 13. High-pressure unit according to claim 12, characterized in that the Helix is multi-start. 14. High pressure unit according to claim 12 or 13, characterized in that the Helix has a gradient varying in the longitudinal direction of the guide surface.   15. High-pressure unit according to one of claims 1 to 6, characterized in that grooves ( 10 ) are formed crosswise at different angles to the longitudinal direction of the guide surface. 16. High-pressure unit according to claim 15, characterized in that the grooves ( 10 ) are formed with a gradient varying in the longitudinal direction of the guide surface. 17. High-pressure unit according to one of claims 7 to 16, characterized in that the distance a of the grooves ( 10 ) in the longitudinal direction of the guide surface corresponds essentially to the operating stroke of the piston ( 5 ) in the cylinder bore ( 3 ). 18. High-pressure unit according to one of claims 1 to 6, characterized in that the grooves ( 10 ) are formed by combining several patterns according to claims 7 to 16. 19. High-pressure unit according to one of claims 1 to 18, characterized in that the grooves ( 10 ) are formed in a region of the guide surface adjoining the high pressure of the piston ( 5 ). 20. High-pressure unit according to one of claims 1 to 18, characterized in that the grooves ( 10 ) are formed over the entire area of the guide surface. 21. High-pressure unit according to one of claims 1 to 20, characterized in that the grooves ( 10 ) in the outer surface of the piston ( 5 ) are designed as a guide surface. 22. High-pressure unit according to one of claims 1 to 21, characterized in that the grooves ( 10 ) in the cylinder bore ( 3 ) are designed as a guide surface. 23. High-pressure unit according to one of claims 1 to 22, characterized in that the high-pressure piston-cylinder unit is part of a fuel injector of a common rail injection system, in which the piston ( 5 ) is used to actuate the injection valve of the fuel injector and the pressure difference is permanently on the piston ( 5 ). 24. High-pressure unit according to claim 23, characterized in that the piston ( 5 ) is integrally formed on the nozzle needle ( 4 ) of the injection valve, the piston ( 5 ) having a shoulder ( 6 ) which is permanently from the fuel pressure of the common rail Injection system is acted upon. 25. The high-pressure unit according to claim 24, characterized in that the grooves ( 10 ) on the shoulder ( 6 ) acted upon by the fuel pressure and which serve as a guide surface of the piston ( 5 ) are formed. 26. A method for producing a high-pressure unit according to one of claims 1 to 25, characterized in that the grooves ( 10 ) are produced by fine turning. 27. A method for producing a high-pressure unit according to one of claims 1 to 25, characterized in that the grooves ( 10 ) are produced by blasting. 28. The method according to claim 27, characterized in that the grooves ( 10 ) are produced by laser engraving. 29. The method according to claim 26, 27 or 28, characterized in that the production of the grooves ( 10 ) takes place after the fine machining of the guide surface and then a lapping or fine grinding of the guide surface is carried out.