EP2275666B1 - Fuel injector with pressure-equalised control valve - Google Patents

Abstract

The injector (1) has a control valve element (26) adjustable between two switching positions. The valve element is formed and arranged such that no or reduced resulting hydraulic force is exerted in an axial direction on the valve element by pressure in a control chamber (17) when a hydraulic connection between the chamber and a low pressure region (10) is disconnected in one of the switching positions. The valve element sealingly lies at a guiding sleeve (32) in the other switching position for sealing a hydraulic connection between a control valve chamber (24) and a high pressure region (8).

Description

State of the art

The invention relates to a fuel injector for injecting fuel into a combustion chamber of an internal combustion engine, in particular a common rail injector, according to the preamble of claim 1.

From the DE 10 2004 030 445 A1 a fuel injector is known which has a control valve (servo valve). The control valve is designed as a so-called 3/2-way valve and controls the connection between a directly from an injection valve element control space and a low pressure area (leakage oil space) of the fuel injector. The control valve has a control valve element, which can be adjusted axially by means of an actuator, for example an electromagnetic or piezoelectric actuator, within a control valve chamber and thus cooperates with a first control valve seat and with a second control valve seat. If the control valve element is in contact with the first (upper) control valve seat, the connection between the control space bounded by the injection valve element and the low-pressure region of the fuel injector is blocked. At the same time, a bypass throttle is opened, via which the control chamber is refilled. When the control valve element is in contact with the second (lower) control valve seat, the bypass throttle is closed and the hydraulic connection between the control chamber and the low pressure region of the fuel injector is established, whereby the pressure in the control valve chamber drops, which in turn causes the injection valve element to move from its position Injector valve seat lifts and thus releases the flow of fuel through a nozzle hole arrangement in the combustion chamber of the internal combustion engine. A disadvantage of the axially not pressure balanced control valve is that the load of the actuator with increasing rail pressure continues to increase. As a result, given a known actuator with the known principle, there is no potential for a further system pressure increase.

From the present application at the time of filing not yet disclosed DE 10 2008 001 330 The applicant is aware of an alternative injector concept with a pressure compensated control valve (servo valve). As a matter of principle, this new servo principle does not switch against rail pressure, but it is structurally guided by a low-pressure connection under the control valve element. This means that the opening force of the control valve, depending on the degree of pressure compensation, less and less dependent on the rail pressure. Thus, the new injector concept offers the potential of a further system pressure increase without unduly increasing the actuator load. The control valve member of the control valve is disposed in a control valve space which is bounded radially outwardly by a single plate member, to the axially below a throttle plate and axially above an actuator space limited component abuts. The new injector seems to be optimized in terms of shortened Rückbefüllbarkeit the control room.

Disclosure of the invention

The invention has for its object to provide a fuel injector, on the one hand has sufficient potential for system pressure increases and in the other hand, a minimized Rückbefüllzeit is realized for refilling the control chamber.

This object is achieved with a fuel injector having the features of claim 1. Advantageous developments of the invention are specified in the subclaims.

The invention is based on the idea, a second, in particular lower control valve seat on which the control valve element of the control valve (servo valve) sealingly abuts in the second switching position to the immediate hydraulic Interrupt connection between the high-pressure region of the fuel injector and the control valve chamber on a guide sleeve for the control valve, which leads, preferably not sleeve-shaped, in particular bolt-shaped, control valve element on its outer circumference. In other words, in the second switching position of the control valve, which is preferably formed of a 3/2-way valve, the control valve element bears directly against the guide sleeve in a sealing manner. In this way, a large cross-sectional area is released in the first switching position in which the control valve element is not sealingly against the guide sleeve, through which the control valve space and thus preferably via an outlet throttle, the control chamber can be refilled. This in turn results in a much faster closing of the one- or multi-part injection valve element with a turn resulting greater robustness of the fuel injector. Due to the closeability of the hydraulic connection between the high-pressure region of the fuel injector, preferably between a pressure chamber of the fuel injector and the control valve element, also during the injection, a significantly lower control amount than in conventional pressure-balanced fuel injectors can be realized with permanently acting Fülldrossel in a designed according to the concept of the invention, the fuel injector preferably designed as a throttle connection hydraulic connection between the high-pressure region of the fuel injector and the control valve chamber through the second, preferably lower, control valve seat can be separated. This advantage is so important because with pressure balanced fuel injectors due to the existing permanent leakage anyway very large and therefore expensive high-pressure pumps are needed and due to the invention, the possibility is created to use smaller and thus cheaper high-pressure pumps, whereby the system costs are reduced overall. In addition, the minimized control valve volume results in a significantly lower characteristic slope, which makes it possible to use nozzles that rapidly decompress, whereby the engine output can be increased without impairing the fuel injector's small-capacity capability. The fuel injector according to the invention has particularly good hydraulic properties by the simultaneous presence of a bypass (hydraulic connection between the high-pressure region and the control valve chamber) and a minimum control valve chamber volume, which in combination to an extreme quick refilling the control valve chamber and thus the control chamber and thus in turn leads to a very quick reversal of the injection valve element with said flat map.

The refilling time, which is required to refill the control chamber, can be reduced in the invention by a minimum, in which instead of a helical compression spring, a plate spring is used as a valve spring for the control valve. Preferably, the plate spring is arranged such that the control valve element in the direction of the first switching position, i. Federkraftbeaufschlagt in the direction of the first control valve seat, so that the control valve member against the spring force of the spring plate must be moved from the first switching position to the second switching position. Due to the design of the spring as a plate spring, the control valve volume can be reduced to a minimum, resulting in the first switching position of the control valve, an accelerated pressure increase in the control valve chamber and thus also in the control room. The combination of the formation of the second control valve seat on the guide sleeve for the control valve member with the design of the control valve spring as a Belleville spring brings minimal Rückbefüllzeiten, resulting in an extremely fast reversal, i. Closing the injection valve element results.

Particularly useful is an alternative embodiment of the fuel injector, wherein the hydraulic connection between the high-pressure region, for example, a pressure chamber surrounding the control chamber radially outside and the control valve chamber is designed as a throttle connection. This can be realized in a simple manner in that in the hydraulic connection, a throttle bore is integrated, which is particularly preferably, as will be explained later, is arranged in a throttle plate, which bears axially against the guide sleeve for the control valve element.

Particularly expedient with a view to minimizing the control valve volume, it is the spring, in particular the plate spring, against the spring force, the control valve element must be adjusted on its way from the first switching position to the second switching position one end axially on the control valve element, in particular on a peripheral collar of the control valve element and the other end is supported on the guide sleeve for the control valve element. Prefers the spring is arranged such that it is not completely flattened even in the second switching position of the control valve.

With regard to the specific design of the hydraulic connection between the high-pressure region of the fuel injector and the control valve chamber, there are different possibilities. Very particularly preferred is a variant in which the hydraulic connection comprises a gap, which is bounded radially outwardly directly from the guide sleeve and radially inwardly directly from the control valve member. In this case, the space formed as an annular space is preferably contoured and arranged such that resulting from the fuel under high pressure in the space no resulting axial forces on the control valve element.

In a further development of the invention is advantageously provided that the aforementioned gap is at least one introduced into the guide sleeve sleeve bore hydraulically permanently connected to an annular space which is bounded radially inwardly of the guide sleeve and preferably radially outwardly from the inner periphery of an end-side recess in a throttle plate is limited. By arranging an annular space filled with high-pressure fuel radially outside the guide sleeve, comparatively fuel-tight guide gaps can be ensured between the control valve element and the guide sleeve, whereby leakage losses from the above-described interspace are limited in a radially outward direction of the guide sleeve and in the axial direction by the control valve element minimized to low pressure.

It is particularly preferred if the annular space arranged radially outside the guide sleeve is connected via a channel in a throttle plate on which the guide sleeve rests in the axial direction to the high-pressure region, preferably to a pressure chamber surrounding the control chamber radially on the outside. Particularly preferably, this channel is designed as a throttle bore.

Particularly useful is an embodiment of the fuel injector, in which the control valve element on the outer circumference leading guide sleeve, in particular on a, in particular piezoelectric actuator facing Side has a biting edge for sealing cooperation with the control valve element in the second switching position. By providing a biting edge a good fuel-tightness can be ensured, whereby a fuel outlet is prevented via the hydraulic connection in the control valve chamber in the second switching position of the control valve.

In principle, the fuel can be actuated with an electromagnetic actuator. However, an embodiment variant with a piezoelectric actuator is particularly preferred, wherein a coupler is preferably provided between the piezoelectric actuator and the control valve element, with which a force path transmission can be realized and compensated for with the expansion effects due to heat.

In a further development of the invention is advantageously provided that the hydraulic connection between the control chamber and the control valve chamber, so the hydraulic connection through which in the second switching position of the control valve fuel from the limited by the injection valve element control chamber can flow into the low pressure region, at least two, Having in different injector components extending sections. Most preferably, a section extends in a previously explained throttle plate and another section in a control valve space radially outwardly bounding plate.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing.

Fig. 1

eine schematische Darstellung eines Kraftstoff-Injektors mit in axialer Richtung druckausgeglichenem Steuerventil und mit einem piezoelektri- schen Aktuator zum Betätigen des Steuerventils.

This shows in the only one

Fig. 1

a schematic representation of a fuel injector with pressure compensated in the axial direction control valve and with a piezoelectric actuator for actuating the control valve.

In Fig. 1 is a designed as a common rail injector fuel injector 1 for injecting fuel in a combustion chamber, not shown, of a likewise not shown internal combustion engine of a motor vehicle in a schematic Illustration shown. A high pressure pump 2 delivers fuel from a reservoir 3 in a high-pressure fuel storage 4 (Rail). In this fuel, especially diesel or gasoline, under high pressure, stored in this embodiment about 2000 bar. To the high-pressure fuel accumulator 4, the fuel injector is connected via other, not shown, injectors via a supply line 5. The supply line 5 opens into a supply channel 6 within the fuel injector 1, which in turn opens into a pressure chamber 7, which, like the supply channel 6, belongs to the high-pressure region 8 of the fuel injector 1. The fuel flowing into the pressure chamber 7, which is bounded radially on the outside by a nozzle body 9, flows directly into the combustion chamber of the internal combustion engine during an injection process. The fuel injector 1, more precisely a low-pressure region 10 of the fuel injector 1, is connected to a return line 11 via an injector return port (not shown). Via the return line 11, a control quantity of fuel, which will be explained later, can flow into the fuel injector 1 to the storage container 3 and be fed back from there to the high-pressure circuit.

Within the nozzle body 9, a one-piece injection valve element 12 designed as a nozzle needle is arranged axially adjustable. This can also be made in several parts instead of the one-piece training and, for example, consist of a control rod and a coupled with this nozzle needle. In any case, the preferred one-piece injection valve element 12 protrudes in the drawing plane down to an injection valve element seat 13, with which it cooperates in a sealing manner in a conventional manner. When the injection valve member 12 abuts its injection valve member seat 13, i. is in a closed position, the fuel outlet from a plurality of injection openings comprehensive nozzle hole assembly 14 is locked. If, on the other hand, it is lifted from its injection valve element seat 13, fuel can be injected from the pressure chamber 7 into a region below the injection valve element 12 and from there through the nozzle hole arrangement 14, substantially under high pressure (rail pressure) into the combustion chamber.

From an upper end face 15 of the injection valve element 12 and a spring-loaded in the drawing plane sleeve 16 is a control chamber 17th limited, which is supplied via a in a throttle plate 18, on which the sleeve 16 is supported in the axial direction, introduced inlet throttle 19 with high-pressure fuel from the high-pressure region 8, here the supply channel 6. Alternatively, the inlet throttle 19 may also be provided as a radial bore in the sleeve 16. The sleeve 16 with the control chamber 17 enclosed therein is enclosed radially on the outside by fuel under high pressure, so that an annular guide gap between the sleeve 16 and the injection valve element 12 is comparatively fuel-tight.

The sleeve 16 is supported in the axial direction from below on the aforementioned throttle plate 18, in which in addition to the inlet throttle 19, a flow restrictor 20 exhibiting flow channel 21 is introduced. The drainage channel 21 as well as an aligned in the flow direction with this channel 22, which is introduced in an axially adjacent to the throttle plate 18 plates 23 to a hydraulic connection between the control chamber 17 and a radially outwardly of the plate 23 limited control valve chamber 24. The control valve chamber 24 is inserted in a lower portion of a stepped bore 25 in the plate 23. Axially adjustable within the control valve chamber 24 is a bolt-shaped control valve element 26 of a control valve 27 which is connected by means of a piezoelectric actuator 29 via a hydraulic coupler 29 between an upper first switching position, i. between an upper first control valve seat 30 and a lower, i. second switching position, ie a second control valve seat 31 is adjustable. The control valve 27 is a 3/2-way valve.

When the control valve element 26 is in the second (lower) switching position, that is, the control valve element 26 abuts the second control valve seat 31 formed on a later to be explained guide sleeve 32 for the control valve element 26, fuel from the provided with a minimum volume control valve chamber 24 on first control valve seat 30 pass into the low-pressure region 10 and from there to the return line 11. By in this switching position on the existing from the channel 22 and the drain passage 21 hydraulic connection from the control chamber 17 fuel flowing down the fuel pressure in the control chamber 17 decreases rapidly. This is due to the fact that the flow area of the outlet throttle 20 is larger as that of the inlet throttle 19, so that when located in the second switching position control valve 27, a net outflow of fuel (fuel control amount) from the control chamber 17 results. Due to the pressure drop in the control chamber 17, the injection valve element 12 lifts off from the injection valve element seat 13 so that fuel can flow through the nozzle hole arrangement 14 into the combustion chamber of the internal combustion engine.

If the control valve element 26 is moved upward in the plane of the drawing into the first switching position, so that the control valve element 26 bears against the first control valve seat 30 formed on the plate 23, the hydraulic connection between the control chamber 17 and the low-pressure region 10 is closed. At the same time, a hydraulic connection 33 to be explained later between the high-pressure region 8, more precisely the pressure chamber 7 and the control valve chamber 24, so that fuel via this hydraulic connection 33 and the channel 22 and the drain channel 21 flow into the control chamber 17 and there an increase in pressure can cause. In addition, fuel continues to flow via the inlet throttle 19, which leads to a total rapid increase in pressure in the control chamber 17, whereby the injection valve element 12 is moved in the drawing plane down to the injection valve element seat 13 and thus the injection process is terminated.

The hydraulic connection between the high pressure region 8 and the control valve chamber 24 includes a throttle bore 35 in the throttle plate 18, wherein the throttle bore 35 hydraulically connects the pressure chamber 7 with an annular space 36, wherein the annular space 36 radially outward from the inner periphery of a frontal bore in the throttle plate 18 and is bounded radially inwardly from the outer periphery of the guide sleeve 32 for the control valve element 26. The annular space 36 is connected via a sleeve bore 37 in permanent hydraulic connection with a gap 38, which is bounded radially outwardly from the inner circumference of a central bore in the guide sleeve 32 and radially inwardly from the outer periphery of the control valve element 26. In the second (lower) switching position of the control valve 27 of the intermediate space 38 is separated from the control valve chamber 24 via a formed on the guide sleeve 32 biting edge 39 which cooperates sealingly with the underside of a peripheral collar 40 of the control valve element 26. The biting edge 39 is located on the front side of an axial, The extension 41 creates axial space for accommodating a plate spring 42 (control valve spring), against the spring force, the control valve member 26 must be moved in energizing the piezoelectric actuator 28 in the drawing plane down to the second switching position. By providing a plate spring 42 as a control valve spring, the volume of the control valve chamber 24 can be minimized as shown. The plate spring 42 is supported in the axial direction on an upper end side of the guide sleeve 32 and in the other axial direction from below on the peripheral collar 40 of the control valve element 26.

The control valve element 26 is an at least approximately pressure-balanced control valve element 26 in the axial direction; this means that when the control valve element 26 is in the upper (first) switching position, no (or possibly only small) resulting hydraulic forces act in the axial direction. This is achieved in that the control valve element 26 is acted upon at a lower end face 43 with low pressure. The lower end face 43 bounded in the axial direction upwards a compensation chamber 44, which belongs to the low pressure region 10 of the fuel injector 1 and is hydraulically connected via a low pressure passage 45 to the injector return port. The compensation chamber 44 is bounded radially on the outside by the guide sleeve 32, which limits the control valve chamber 24 in the axial direction downwards. The guide sleeve 32 is received over a majority of its axial extent in a frontal bore in the throttle plate 18 and is sealingly connected to an upper portion of its outer periphery to a lower portion of the inner periphery of the stepped bore 25, so that the annular space 36 is sealed relative to the control valve chamber 24.

Claims (10)

1. Fuel injector for injecting fuel into a combustion chamber of an internal combustion engine, in particular common rail injector, comprising a single-part or multi-part injection valve element (12) for opening and closing at least one injection opening, wherein the injection valve element (12) is assigned a control valve (27) having a control valve element (26) which can be adjusted between a first and a second switching position and which is arranged in a control valve chamber (24), wherein in the first switching position, a hydraulic connection between a control chamber (17), which is operatively connected to the injection valve element (12), and a low-pressure region (10) of the fuel injector (1) is blocked and a hydraulic connection (33) between a high-pressure region of the fuel injector (1) and the control valve chamber (24) is open, and wherein in the second switching position, the hydraulic connection between the control chamber (17) and the low-pressure region (10) is open and the hydraulic connection between the high-pressure region (8) and the control valve chamber (24) is blocked,
   characterized
   in that the control valve element (26) is designed and arranged such that the pressure in the control valve chamber (24) does not cause a resultant hydraulic force to act, or causes only a small resultant hydraulic force to act, in the axial direction on the control valve element (26) when the hydraulic connection (33) between the control valve chamber (24) and the low-pressure region (10) is blocked in the first switching position of the control valve element (26), and that the control valve element (26), in the second switching position, in order to seal the hydraulic connection (33) between the high-pressure region (8) and the control valve chamber (24), bears sealingly against a guide sleeve (32) which guides the control valve element (26) at its outer circumference.
2. Fuel injector according to one of the preceding claims,
   characterized
   in that a spring is arranged so as to be supported at one side axially on a circumferential collar (40) of the control valve element (26) and at the other side axially on the guide sleeve (32) for the control valve element (26).
3. Fuel injector according to either of Claims 1 and 2,
   characterized
   in that the hydraulic connection (33) between the high-pressure region (8) and the control valve chamber (24) is designed as a throttle connection, preferably by means of the provision of a throttle bore (35).
4. Fuel injector according to Claim 2,
   characterized
   in that the spring is designed as a plate spring (42).
5. Fuel injector according to one of the preceding claims,
   characterized
   in that the hydraulic connection (33) comprises an intermediate space delimited radially at the outside by the guide sleeve (32) and radially at the inside by the control valve element (26).
6. Fuel injector according to Claim 5,
   characterized
   in that the intermediate space is connected via at least one sleeve bore (37) in the guide sleeve (32) to an annular space (36) delimited radially at the inside by the guide sleeve (32).
7. Fuel injector according to one of the preceding claims,
   characterized
   in that the guide sleeve (32) axially adjoins a throttle plate (18) in which is formed a bore, designed preferably as a throttle bore (35), as a partial section of the hydraulic connection (33) between the high-pressure region (8) and the control valve chamber (24).
8. Fuel injector according to Claim 7,
   characterized
   in that the guide sleeve (32) has a biting edge for sealingly interacting with the control valve element (26) in the second switching position.
9. Fuel injector according to one of the preceding claims,
   characterized
   in that a piezoelectric actuator (28) is provided for actuating the control valve (27).
10. Fuel injector according to one of the preceding claims,
    characterized
    in that the hydraulic connection (20, 21, 22) between the control chamber (17) and the control valve chamber (24) runs through two components which axially adjoin one another.

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