Injector of a fuel injection system of an internal combustion engine

An injector with a double-switching control valve in which a valve body is guided in the housing of the control valve in a way that reduces the wear on a valve cone of the valve body and on a first valve seat in the housing of the control valve.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 35 USC 371 application of PCT/EP 2005/056138 filed on Nov. 22, 2005.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to an injector for an internal combustion engine, having a control valve for opening and closing a nozzle needle; the control valve has a valve body with a valve cone that cooperates with a valve seat of a housing of the control valve. In this injector, a closing spring presses the valve body against a plunger of an actuator and is centered by means of the valve seat.

In an injector for an internal combustion engine, having a control valve for opening and closing a nozzle needle—where the control valve includes a housing and an actuator, the housing contains a stepped bore with a spring chamber for accommodating a valve body, one section of the stepped bore is embodied as an inlet, and another section of the stepped bore is embodied as an outlet—and having a first valve seat, where the valve body is equipped with a valve cone that cooperates with the first valve seat and the valve body is pressed against the plunger of an actuator by a closing spring contained in the spring chamber, according to the invention, the valve body is guided in at least one section of the stepped bore and in this section, one or more passages is/are provided for the control quantity of the injector.

SUMMARY AND ADVANTAGES OF THE INVENTION

The fact that the valve body of the injector of the invention is guided in at least one section of the stepped bore assures that the valve cone of the valve body always comes into contact with the valve seat of the housing in an approximately centered, low-slippage fashion. This avoids local overstressing of the valve cone and valve seat and also reduces wear on the valve cone and valve seat. Both effects result in the fact that the valve stroke changes only slightly during operation of the internal combustion engine so that the operating behavior of the engine remains approximately the same over the entire service life. In this connection, the play between the stepped bore and the guide section of the valve body should be selected to be large enough that in the closed position of the control valve, the valve body is centered in relation to the valve seat of the housing because only then does the control valve close tightly.

In advantageous variants of the injector according to the invention, an inlet of the control valve communicates with a control chamber of the injector while an outlet of the control valve communicates with a fuel return.

In another advantageous embodiment of the invention, the closing spring acts on the valve body in the direction opposite from the actuating direction of the actuator. This assures that the valve body always assumes a definite position and the control valve is closed when the actuator is switched into the currentless state.

It has turned out to be advantageous if the closing spring is supported at least indirectly against the housing and a spring plate of the valve member.

Preferably, the guidance of the valve body occurs in the region of the outlet and/or in the region of the spring chamber. It is alternatively possible for the valve body to be guided on the spring plate or for a sleeve to be provided in the spring chamber and for the valve body to be guided by the sleeve.

In order for the control quantity of the control valve according to the invention to be able to flow through despite the guidance of the valve body in the housing, the passages can alternatively be embodied as grooves, flattened regions, and/or longitudinal bores extending in the longitudinal direction of the valve body. This can reduce the flow resistance of the control valve in the open state to such an extent that the function of the injector is not impaired by the guidance of the valve body in the stepped bore.

In order to simplify manufacturing and assembly, the housing can be comprised of two parts. In this case, the control valve can be either embodied as a separate component or can be integrated into the injector. In the latter instance, the housing of the control valve is simultaneously also the housing of the injector.

The control valve can be advantageously embodied in the form of a ⅔-way control valve. This makes it easier to implement multiple injections and offers additional possibilities for shaping the injection curve.

In order to make the best use of the advantages of the injector equipped with the control valve according to the invention, it is possible for the valve body to be actuated by a piezoelectric actuator. This permits extremely rapid control movements. Because the seat in the housing and the valve cone on the valve body do not experience any appreciable wear thanks to the structural design of the control valve according to the invention, the function of the control valve is assured over the entire service life of the internal combustion engine despite the short adjusting paths of a piezoelectric actuator.

Preferably, the injector according to the invention is used in common rail fuel injection systems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows an injector with a control valve15according to the invention. By means of a high-pressure connection1, fuel is conveyed through an inlet conduit5to an injection nozzle7and through an inlet throttle9to a control chamber11. The control chamber11is connected to a fuel return17via an outlet conduit12and an outlet throttle13. A bypass14produces a hydraulic connection between the inlet conduit5and an inlet of the control valve15.

A control piston19delimits the control chamber11. The control piston19is adjoined by a nozzle needle21that prevents the pressurized fuel from flowing into the combustion chamber, not shown, between injections. The control piston19and nozzle needle21can also be integrally joined to each other. The nozzle needle21has a cross-sectional change from a larger diameter25to a smaller diameter27. The nozzle needle21is guided with its larger diameter25in a sleeve28.

When the outlet throttle13is closed, the hydraulic force acting on an end surface33of the control piston19is greater than the hydraulic force acting on the cross-sectional change because the area at the end of the control piston19is greater than the annular area of the cross-sectional change. As a result, the nozzle needle21is pressed into a nozzle needle seat35and seals the inlet conduit5off from the combustion chamber, not shown.

If the high-pressure pump, not shown, of the fuel injection system is not driven because the engine is not running, then a nozzle spring39, which acts on the shoulder37of the nozzle needle21, presses the injection nozzle7against the nozzle needle seat35so that the injector is closed.

If, through a suitable triggering of the control valve15, a hydraulic connection is produced between the outlet throttle13and the fuel return17, then this reduces the pressure in the control chamber11and therefore also the hydraulic force acting on the end surface33of the control piston19. As soon as this hydraulic force is less than the hydraulic force acting on the cross-sectional change, the nozzle needle21opens so that the fuel3can travel through the injection ports, not shown, into the combustion chamber. This indirect triggering of the nozzle needle21via a hydraulic power boosting system is necessary because the forces required to rapidly open the nozzle needle21cannot be produced directly with the control valve15. The so-called “control quantity”, which is required in addition to the fuel quantity injected into the combustion chamber, travels into the fuel return17via the inlet throttle9, the control chamber11, and the control valve15. Between the injections, the control valve15closes the outlet throttle13. The control valve15can be actuated by means of electromagnetic or piezoelectric actuators.

FIG. 2is an enlarged depiction of a first exemplary embodiment of a control valve15according to the invention. The two-part housing, which is comprised of the parts29aand29b, has a stepped bore41. A first section41aof the stepped bore constitutes the bypass14of the control valve15. This bypass14is hydraulically connected to the inlet conduit5of the injector (not shown). A second section41bconstitutes a spring chamber, while a third section41cof the stepped bore41constitutes the outlet of the control valve15. This outlet is hydraulically connected to the fuel return17(seeFIG. 1).

The second section41bof the stepped bore is connected to the outlet conduit12, which is equipped with an outlet throttle13. The outlet conduit12starts in the control chamber11of the injector.

A first valve seat43is embodied between the sections41band41cof the stepped bore41. A valve body45is provided with a valve cone47that cooperates with the first valve seat43. Above the valve cone47, the valve body45has a stump49whose end surface rests against a plunger51of a piezoelectric actuator (not shown). Below the valve cone47, the valve body45is provided with a spring plate53. Between the spring plate53and the housing part29b, a closing spring55is clamped, which presses the valve body45against the first valve seat43and/or against the plunger51of the piezoelectric actuator, not shown. In the first switched position of the control valve15shown inFIG. 2, the piezoelectric actuator (not shown) is not supplied with current so that the valve cone47of the valve body45rests against the first valve seat. As a result, the control valve15is closed. The valve body45is thus clamped between the plunger51and the closing spring55.

The exemplary embodiment of a control valve15according to the invention shown inFIG. 2is embodied in the form of a double-switching control valve. To this end, at the transition between the first section41aand section41bof the stepped bore41, a second valve seat57is provided, embodied in the form of a flat seat. This second valve seat57cooperates with an end surface59of the valve body45. In the switched position of the control valve15shown inFIG. 2, there is a hydraulic connection between the inlet conduit5and the control chamber11via the bypass14, the outlet conduit12, and the outlet throttle13.

When the piezoelectric actuator, not shown is supplied with current, the plunger51moves downward inFIG. 2so that the valve cone47of the valve body45lifts away from the first valve seat43and, during the switching phase, a hydraulic connection is temporarily produced between the section41aof the stepped bore and the fuel return17. If the valve body45is then moved toward the second valve seat57until the end surface59of the valve body45comes into contact with the second valve seat, then the hydraulic connection between the section41aof the stepped bore, i.e. the bypass14, and the fuel return17is closed again. When the first valve seat43is open and the second valve seat57is closed, the outlet throttle13is open.

If the valve body45is kept in this second switched position (not shown), then the hydraulic connection between the outlet throttle13and the fuel return17is opened. As long as this hydraulic connection exists, the nozzle needle21of the injector lifts away from its nozzle needle seat so that fuel is injected into the combustion chamber of the engine.

If the first valve seat43is closed again, then a hydraulic connection exists between the section41aof the stepped bore, i.e. the bypass14, and the outlet conduit12, as a result of which the control chamber11is filled with fuel from both the inlet throttle9and the bypass14. This achieves a rapid closing of the nozzle needle41.

In the control valve15according to the invention, the diameter of the spring plate53, for example, is matched to the diameter of the second section41bof the stepped bore41so that a very small gap s remains between the spring plate53and the second section41bof the stepped bore. This gap s is dimensioned so that the valve body45is laterally guided in such a way that the valve cone47always comes into contact with the valve seat43in the same place when the control valve15is closed. This significantly reduces slippage and therefore wear on the valve cone47and the first valve seat43.

On the other hand, the gap s must be dimensioned as large enough so that the valve cone47centers itself in the first valve seat43. The guidance of the valve body45on the outer diameter of the spring plate53should only prevent the valve body45from appreciable lateral deflection. If such a lateral deflection were to occur during operation of the engine, then the valve cone47would contact the valve seat43in an off-center fashion, which could result in local overstressing. The force of the closing spring55would then center the valve body45in the first valve seat43. The relative movement thus occurring between the first valve seat43and the valve cone47(slippage) generates wear on the components involved so that the stroke of the valve body45between the first switched position and the second switched position changes significantly over the service life of the engine. This results in an impaired operating behavior and possibly even malfunctions since, as is known, the adjusting path of piezoelectric actuators is relatively small. In concrete embodiments, a thickness of the gap s of less than 0.1 mm has turned out to be advantageous.

FIG. 2ashows a top view of the spring plate53along the line A-A inFIG. 2. It is clear from this depiction that the gap s is not present over the entire circumference of the spring plate, but instead, the spring plate53has three flattened regions61. These flattened regions61make it possible for the control quantity to flow out past the spring plate53.FIGS. 2band2cshow other embodiment forms of passages according to the invention. In the exemplary embodiment shown inFIG. 2b, the spring plate53is provided with four radially oriented grooves63, while in the exemplary embodiment shown inFIG. 2e, the spring plate53is provided with four bores65.

In the exemplary embodiment shown inFIG. 3, the valve body45is guided in the third section41cof the stepped bore41. This means that the diameter of the plunger49is selected so that once again a gap is formed, this time between the plunger49and the third section41cof the stepped bore41. Here, it has turned out to be advantageous if the gap s is smaller than 0.05 mm.

In this exemplary embodiment as well, passages must be provided in the valve body45in the region in which the valve body45is guided in the stepped bore41.FIGS. 3aand3bshow sectional depictions along the line B-B ofFIG. 3of two different embodiments of a plunger49according to the invention. In the exemplary embodiment shown inFIG. 3a, flattened regions61are provided, while in the exemplary embodiment shown inFIG. 3b, grooves63are provided, which extend over the entire length of the guide section between the plunger49and the third section41cof the stepped bore41. Naturally, the invention is not limited to the forms of the flattened regions61, grooves63, and bores65that are explicitly shown.

FIG. 4shows another exemplary embodiment of a control valve15according to the invention. In this exemplary embodiment, the valve body45is guided by means of a sleeve67in the region of the section41bof the stepped bore41.

On the right side ofFIG. 4, the sleeve67is embodied in the form of ring with an approximately square cross section, while on the left side, the sleeve67has an L-shaped cross section. The essential difference between these two embodiments lies in the overlap H1and H2between the valve body45and the sleeve67.

In order to be able to drain off the control quantity when the control valve15is open, despite the narrow gap s between the inner diameter of the sleeve67and the outer diameter of the valve body45, longitudinal grooves63are provided in the sleeve67and/or the valve body45. The detail views4aand4bshow two different cross-sectional forms of the grooves63. Which of these forms is preferable depends on the available space and the control quantity to be drained off.

FIG. 5shows another exemplary embodiment of a control valve15according to the invention. In this exemplary embodiment, the sleeve67is situated between the spring plate53and the closing spring55. InFIG. 5as well, two different forms of sleeve67are shown on the right and left side. The common trait shared by the two embodiments is that the passages are embodied in the form of grooves63. In the embodiment shown on the right side inFIG. 5, grooves63are also provided in the valve body45. The spring plate53also has bores65that likewise permit the control and leakage quantity coming from the injector (not shown) to drain out through the control valve15and into the fuel return17.

The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.