WO2004063553A1 - Fuel injection device - Google Patents

Abstract

A fuel injection device (24), comprising a housing (30), at least one outer valve element (34) and at least one inner valve element (42) which is guided at least partially in a fluid-tight manner in the outer valve element (34). Both elements are respectively impinged against a housing-side valve seat (39,48). An inflow area is arranged downstream from the valve seat (39) of the outer valve element (34). In order to ensure that the inner valve element (42) can be switched in a simple and reliable manner, a pressure channel (58) is provided in the inner valve element (42), said channel leading into a lateral surface (44) of the inner valve element (42) and being connected to a pressure chamber (62) which is defined by a pressure surface (60) of the inner valve element (42) acting in the direction of opening, whereby the mouth of the pressure channel (58) provided in the outer lateral surface (44) is covered thereby when the outer valve element (34) is closed and is released thereby once a specific opening lift (h) of the outer valve element (34) is achieved.

Description

Fuel injector

State of the art

The invention relates to a fuel injection device with a housing, with at least one outer valve element and with at least one inner valve element which is guided in a fluid-tight manner in the outer valve element, each of which is acted upon by an actuating device against a valve seat on the housing side, with one existing upstream from the valve seat of the outer valve element Inflow space, and each with at least one fuel outlet channel assigned to the respective valve element.

Such a fuel injection device is known from DE 40 23 223 AI. This shows an injector with two coaxial valve needles. The valve needles are each against a by a helical compression spring

Valve seat pressed. From this they are pushed away against the force of the helical compression springs when the pressure of the fuel is increased in the area of the valve seat. In addition to this “pressure-controlled” fuel injection device, “stroke-controlled” fuel injection devices are also known in which a comparatively high pressure is constantly applied in the area of the valve seat. By temporarily reducing one in

Force acting in the closing direction then lifts the corresponding valve element from its valve seat.

The object of the present invention is to develop a fuel injection device of the type mentioned at the outset in such a way that it can be produced as simply and inexpensively as possible. Furthermore, the control should be as simple and reliable as possible

This object is achieved in a fuel injection device of the type mentioned at the outset in that a pressure channel is present in the inner valve element, which on the one hand opens into a lateral surface of the inner valve element and on the other hand is connected to a pressure chamber which extends from a pressure surface acting in the opening direction inner valve element is limited, the mouth of the pressure channel present in the outer surface being covered by the closed outer valve element and being released from a certain opening stroke of the outer valve element.

Advantages of the invention

In the fuel injection device according to the invention, the inner valve element can only be switched when - the outer valve element has performed a correspondingly sufficient opening stroke. If there is no such opening stroke of the outer valve element, the inner valve element remains reliably closed. This is possible with simple hydraulic measures without the need for complex mechanical drivers or the like. The movement of the outer valve element can be adjusted either by the fluid pressure correspondingly acting in the opening direction or by the duration of the application of the force acting in the opening direction of the outer valve element. A combination of both effects is also possible. Such control is easy to implement.

Advantageous developments of the invention are specified in the subclaims.

In a first further development it is proposed that the ^'inner valve member has only one radially inwardly located from the sealing seat printing surface. This measure has two positive effects: Firstly, it is ensured that after opening the outer valve element no force acting in the opening direction initially acts on the inner valve element. This therefore remains reliably closed.

In addition, however, the manufacturing costs of the fuel injection device are also reduced, since only one pressure surface has to be produced at the axial end of the inner valve element, since there is a “pressure stage”, that is to say two pressure surfaces, which differ from one another in terms of their angle with respect to the longitudinal axis of the inner valve element , is not required. This is very cost-saving in production, especially considering the fact that the inner valve element usually has extremely small dimensions (outer diameter approximately 1-2 mm).

It is also possible that the inner valve element in an end blind bore of the outer valve element is included. In this way, the assembly of the fuel injector is simplified and the manufacturing cost of the fuel injector is reduced because a blind hole can be drilled faster than a through hole.

The proposal in which the inner valve element is acted on by a helical compression spring against the valve seat assigned to it also has a cost-reducing effect. This is particularly advantageous in connection with the end blind bore in the outer valve element proposed further above.

A further cost reduction in the manufacture of the fuel injection device according to the invention is achieved in that the pressure channel in the inner valve element has a section running essentially parallel to the longitudinal axis and at least one section running essentially in the radial direction. Such channels can still be introduced without any problems, even taking into account the extremely small dimensions of the inner valve element.

drawing

A particularly preferred exemplary embodiment of the present invention is explained in detail below with reference to the accompanying drawing. The drawing shows:

Figure 1 is a schematic representation of a

Fuel system with multiple fuel injection devices;

Figure 2 is a partial section through one of the Fuel injectors of Figure 1; and

FIG. 3 shows a detail III of the fuel injection device from FIG. 2.

Description of the embodiment

A fuel system bears the overall reference number 10 in FIG. 1. It belongs to an internal combustion engine 12 and comprises a fuel tank 14, from which an electric fuel pump 16 (pre-feed pump) delivers the fuel to a high-pressure fuel pump 18. The high-pressure fuel pump 18 is mechanically driven by the internal combustion engine, compresses the fuel to a very high pressure, and delivers it to a fuel manifold 20 (rail). The fuel is stored under very high pressure.

To the fuel rail 20 are over

High pressure lines 22 connected to several injectors 24. These inject the fuel directly into their respective combustion chambers 26. A low-pressure fuel line 28 leads from the injectors 24 back to the fuel tank 14.

An injector 24 is shown in detail in FIGS. 2 and 3. However, for reasons of clarity, not all reference numerals are entered in FIG. 2. The injector 24 comprises a housing 30 in which a stepped blind bore 32 is present. In this an outer valve element 34 is arranged, which tapers conically in two stages in a lower area in FIG. The radially outer conical surface forms a pressure surface 36 which is delimited by a sealing edge 38. This works with a housing-side sealing seat 39 together.

In the lower end region of the outer valve element 34 in FIGS. 2 and 3 there is an axial blind bore 40. An inner valve element 42 is guided in this in a sliding and fluid-tight manner. An outer circumferential surface 44 of the inner valve element 42 is delimited downwards in FIGS. 2 and 3 by a circumferential sealing edge 46. This lies in the closed state of the interior shown in FIGS. 2 and 3

Valve element 42 on a housing-side valve seat 48. In this position, the inner valve element 42 is acted upon by a helical compression spring 50, which is clamped between a circumferential shoulder 52 of the inner valve element 42 and a bottom 54 of the blind bore 40. The helical compression spring 50 is guided by a pin-like section 56 of the inner valve element 42.

In the inner valve element 42 there is a pressure channel 58 which is coaxial with the longitudinal axis of the inner one

Includes valve element 42 extending portion 58a and a portion 58b transverse to the longitudinal axis of the inner valve member 42. The transverse section 58b opens into the outer circumferential surface 44 of the inner valve element 42 at two diametrically opposite locations. The longitudinally extending section 58a of the pressure channel 58 opens into a conical pressure surface 60 arranged radially inward from the sealing edge 46 at the lower end of the inner valve element 42 ,

Between the lower end of the inner valve element 42 in FIGS. 2 and 3 and the housing 30 there is a pressure chamber 62, from which inner fuel outlet channels 64 arranged distributed over the circumference lead to the outside. The same is true of a position which is located somewhat radially inward from the sealing seat 39, outer fuel outlet channels 66 arranged distributed over the circumference.

The upper region of the valve element 34 in FIGS. 2 and 3 corresponds to the customary configuration in the case of so-called “stroke-controlled” injectors. Therefore, only the essential elements of this area are dealt with below:

A support ring 70 is supported on a circumferential shoulder 68 of the valve element 34. This is supported in turn by a helical compression spring 72 which acts on an annular sleeve 74 against a housing section 76. The upper end of the valve element 34 in FIG. 2 is delimited by a pressure surface 78. Together with the sleeve 74 and the housing section 76, this in turn delimits a control chamber 80.

The control chamber 80 can be connected to the high-pressure line 22 via a high-pressure duct 82 and an inflow throttle 84.

The inflow throttle 84 is introduced as a bore in the wall of the sleeve 88. An outlet throttle 86 leads from the control chamber 80 to a switching valve 88 with which the control chamber 80 can be connected to the low-pressure fuel line 28. Via the high pressure channel 82 and one between the

Valve element 34 and the stepped blind bore 32 in the annular space 90 present in the housing 30, the pressure surface 36 at the lower end of the valve element 34 in FIGS. 2 and 3 is constantly connected to the high-pressure line 22.

The injector 24 works as follows:

In operation, the high fuel pressure prevailing in the fuel rail 20 is via the high-pressure line 22, the high-pressure channel 82 and the inflow throttle 84 are transmitted into the control chamber 80. The high fuel pressure also prevails in this, which also prevails in the fuel collecting line 20. The same also applies to the annular space 90 between the valve element 34 and the housing 30. The corresponding high fluid pressure is therefore also present on the pressure surface 36 of the valve element 34.

The compression spring 72 and the hydraulic force acting on the pressure surface 78 at the upper end of the valve element 34 press the valve element 34 with its sealing edge 38 in the closing direction against the valve seat 39. Overall, the hydraulic force acting on the annular pressure surface 36 of the valve element 34 in the opening direction is not yet sufficient to achieve this

Lift off valve element 34 or sealing edge 38 from valve seat 39. The fuel connection between the high-pressure duct 82 and the outer fuel outlet ducts 66 is therefore interrupted by the valve element 34.

If the injector 24 is to inject fuel into the combustion chamber 26 assigned to it, the switching valve 88 is opened briefly. Thus, the fuel present under high pressure in the control chamber 80 can flow out to the fuel tank 14 via the outlet throttle 86 and the low-pressure fuel line 28. As a result, there is a pressure drop in the control chamber 80 and the hydraulic force acting on the pressure surface 78 is weakened. As a result, the hydraulic force acting on the pressure surface 36 of the valve element 34 in the opening direction exceeds the forces acting overall in the closing direction, so that the sealing edge 38 of the valve element 34 lifts off the valve seat 39. The valve element 34 is now the Free fuel connection in the direction of the fuel outlet channels 66.

At the same time, the mouth of the section 58b of the pressure channel 58 remains covered by the outer valve element 34, so that the pressure chamber 62 is separated from the flow chamber 90 and the inner valve element is further pressed by the spring 50 with the sealing edge 46 against the gas back pressure in the combustion chamber 26 against the valve seat 48 becomes. No fuel can thus initially escape through the fuel outlet channels 64.

Only when the valve element 34 has moved away from the corresponding valve seat 39 by a certain minimum stroke h with its sealing edge 38, the orifices of the transverse section 58b of the pressure channel 58 come free from the outer valve element 34. The high fuel pressure prevailing in the annular space 76 can thus be transmitted to the pressure space 62 via the transverse portion 58b and the longitudinal portion 58a of the pressure channel 58. The channel sections 58b are so small in diameter that transmission of the static pressure is possible, but not a relevant amount of fluid.

As a result, a force acting in the opening direction builds up on the pressure surface 60 of the inner valve element 42, which force causes the inner valve element 42 with its sealing edge 46 to lift off the valve seat 48 against the force of the compression spring 50. The resulting gap between the sealing edge 46 and the valve seat 48 allows the fuel to pass from the annular space 90 into the pressure space 62 and now also to exit into the combustion chamber 26 via the inner fuel outlet channels 64. Whether the outer valve element 34 moves by the distance h can be set either via the pressure prevailing in the annular space 90 and / or via the duration of the actuation of the switching valve 88. In this way it can be controlled by means of a simple one-stage control whether only the outer valve element 34 opens or both valve elements 34 and 42 open. It can easily be seen that the production of the inner valve element 42 is comparatively simple since the conical pressure surface 60 is evenly inclined and since the sections 58a and 58b of the pressure channel 58 can also be easily introduced into the inner valve element 42, which has a comparatively small diameter ,

Injection is ended by switching valve 88 being closed again. High-pressure fuel can flow back into control chamber 80 via inflow throttle 84, so that the pressure in control chamber 80 rises again. The hydraulic force acting on the pressure surface 78, which acts in the closing direction of the outer valve element 34, also increases accordingly. When the valve element 34 again moves with its sealing edge 38 in the direction of the valve seat 39, it again covers the mouth of the transverse section 58b of the pressure channel 58 in the outer lateral surface 44 of the inner valve element 42.

Thus, the pressure in the pressure chamber 62 drops and the inner valve element 42 moves due to the closing force of the helical compression spring 50 with its sealing edge 46 back towards the valve seat 48. As soon as both sealing edges 38 and 46 rest against the corresponding sealing seats 39 and 48, the connection between the annular space 90 and the fuel outlet channels 64 and 66 is interrupted, so that no more fuel can escape into the combustion chamber 26.

Claims

Expectations 1. Fuel injection device (24) with a housing (30), with at least one outer valve element (34) and with at least one in the outer valve element (34) at least partially fluid-tightly guided inner valve element (42), each against a housing-side valve seat (39, 48) are acted upon, with an inflow space (90) present upstream of the valve seat (39) of the outer valve element (34), and with at least one fuel outlet channel (64, 66) assigned to the respective valve element (34, 42) , characterized in that in the inner valve element (42) there is a pressure channel (58) which on the one hand opens into a lateral surface (44) of the inner valve element (34) and on the other hand is connected to a pressure chamber (62) which is separated from a Pressure area (60) of the inner valve element (42) acting in the opening direction is limited, the opening of the pressure channel (44) in the outer lateral surface (44) 58) is covered by the latter when the outer valve element (34) is closed and is released by the outer valve element (34) from a certain opening stroke (h). 2. Fuel injection device (24) according to claim 1, characterized in that the inner valve element (34) only has a pressure surface (60) lying radially inward from the valve seat (48). 3. Fuel injection device (24) according to one of claims 1 or 2, characterized in that the inner valve element (42) in a blind bore (40) of the outer valve element (34) is received. 4. Fuel injection device (24) according to one of the preceding claims, characterized in that the inner valve element (42) is acted upon by a helical compression spring (50) against the valve seat (48) assigned to it. 5. Fuel injection device (24) according to one of the preceding claims, characterized in that the pressure channel (58) in the inner valve element (42) has a section running parallel to the longitudinal axis (58a) and at least one section running essentially in the radial direction (58b).