EP1654454A1

EP1654454A1 - Fuel injection device for a combustion engine

Info

Publication number: EP1654454A1
Application number: EP04738751A
Authority: EP
Inventors: Peter Boehland; Sebastian Kanne; Godehard Nentwig
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-08-08
Filing date: 2004-06-22
Publication date: 2006-05-10
Anticipated expiration: 2024-06-22
Also published as: ATE348260T1; DE10336411A1; JP4291369B2; KR20060060679A; US20060255173A1; DE502004002330D1; WO2005014996A1; JP2007506898A; EP1654454B1

Abstract

A fuel injection device (20) for a combustion engine comprises a first valve element (36) with a pressure surface (38) that acts in an opening direction. An impinging device (50) acts in a closing direction. A second valve element (34) comprises a hydraulic control surface (58), which acts in the closing direction and which delimits a hydraulic control space (60). A corresponding impinging device acts in an opening direction. In addition, a high-pressure connection (24) is provided. The invention provides that the fuel injection device (20) has an additional valve device (66) that, in a first final position, connects the pressure space (40) only to the low pressure connection (28) and connects the control space (60) only to the high pressure connection (24). In a second final position, the additional valve device (66) connects the pressure space (40) only to the high pressure connection (24) and separates the control space (60) essentially from the high pressure connection (24). In an intermediate position, the pressure space (40) is connected only to the high pressure connection (24), and the control space (60) is simultaneously connected to the high pressure connection (24) and to the low pressure connection (28).

Description

Fuel injection device for an internal combustion engine

State of the art

The invention relates to a fuel injection device for an internal combustion engine, in particular with direct fuel injection, with at least two valve elements, of which one valve element has a pressure surface acting in the opening direction, which delimits a pressure chamber, and an acting device acting in the closing direction, and of which another Valve element a hydraulic control surface acting in the closing direction, which delimits a hydraulic control chamber which is at least temporarily connected to a high-pressure connection, and one which acts in the opening direction

Acting device, and with a control valve which can connect the control chamber with a low pressure connection.

A fuel injection device of the type mentioned is known from DE 100 58 130 AI. This shows an injection nozzle for internal combustion engines with two coaxially arranged and separately controllable valve elements. The outer valve element is pressure-controlled, that is to say, by increasing an injection pressure which acts on a pressure surface acting in the opening direction, it lifts off its valve seat against a spring force and thereby releases corresponding outlet openings. The inner valve element is stroke controlled. That said, it opens when the pressure of a hydraulic fluid in a control room is reduced. The force of the inner valve element acting in the opening direction is provided by the injection pressure acting on a corresponding pressure surface. At least two pressure accumulators with different pressure levels and at least two control valves are required to control the known fuel injection device.

The reasons for realizing fuel injectors with multiple valve elements are as follows:

In particular in the case of diesel internal combustion engines, in order to reduce the emissions and increase the efficiency, it is necessary to atomize the fuel as finely as possible into the corresponding combustion chambers of the internal combustion engine. This can be achieved either by increasing the injection pressure at which the fuel enters the fuel injector, or by increasing and increasing the number of fuel outlet openings from which the fuel exits the fuel injector into the combustion chamber at the same time the individual cross section of a fuel outlet opening is reduced. These measures make it possible to improve the atomization quality of the injected fuel jets while at the same time reducing the drop diameter of the fuel spray produced (“spray”).

By using a plurality of valve elements, each of which releases a certain number of fuel outlet openings, good atomization quality can be achieved even if only a small amount of fuel is to be injected. It must be in that Case in which a large amount of fuel is to be injected, an excessively long injection period and / or an excessively high injection pressure are not accepted.

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 controlled as simply as possible and yet operates reliably. At the same time, it should be possible to achieve good emission and consumption behavior when used on the corresponding internal combustion engine.

These tasks are solved in a power injection device of the type mentioned at the outset in that it comprises an additional valve device which in a first end position connects the pressure chamber only to the low pressure connection and the control chamber to the high pressure connection, in a second end position the pressure chamber at least predominantly connects to the high pressure connection and essentially separates at least one area of the control chamber from the high pressure connection, and in an intermediate position connects the pressure chamber at least predominantly to the high pressure connection and the control chamber also to the high pressure connection.

Advantages of the invention

In the fuel injection device according to the invention, only a high-pressure and a low-pressure connection are required. A plurality of pressure reservoirs with different pressure levels can be dispensed with. The opening and closing of the valve elements can be controlled independently of one another. In the first end position of the additional valve device, there is a low pressure in the pressure chamber, so that the first valve element can be pressed into the closed position by the loading device. At the same time, there is high pressure in the control room, which also pushes the second valve element into the closed position.

In the second end position of the valve device, there is high pressure in the pressure chamber, which causes a corresponding hydraulic opening force on the pressure surface, by means of which the first valve element opens. At the same time, the hydraulic control chamber is essentially separated from the high-pressure connection and can therefore only be connected to the low-pressure connection via the control valve. The pressure in the spreading space therefore drops significantly and quickly and the second valve element can be opened by the actuating device acting in the opening direction. In this second end position, both valve elements are open.

In the intermediate position provided according to the invention, the pressure chamber is connected to the high-pressure connection, so there is a high pressure in the latter, by means of which the first valve element is opened. The control room, on the other hand, is also connected to the high pressure connection. If it is connected to the low pressure connection via the control valve at the same time, an "intermediate pressure" is established in the control room. The actuating device acting on the second valve element in the opening direction is designed such that the second valve element remains reliably closed even at such an intermediate pressure in the hydraulic control chamber. In this intermediate position only the first valve element is open to the valve device.

Ultimately, all of this is only possible with the high-pressure and high-pressure devices already present in conventional devices

Low pressure connections enables, so that the fuel injection device according to the invention is inexpensive and simple to build. The pressure-controlled opening of the first valve element achieves a ramp-shaped pressure increase with the second valve element closed at the same time. This leads to favorable emission and consumption behavior, particularly when the internal combustion engine is under low load. If, on the other hand, the valve device is immediately brought into the second end position, both valve elements open very quickly, which enables a rectangular injection profile to be implemented in the full-load operation at high engine speeds. As a result, the entire injection period at high speeds can be limited.

The actuation principle can also be implemented very easily in existing fuel injection devices, since no changes are necessary, for example, to the valve elements themselves. In addition, the fuel injector according to the invention has the typical advantages of fuel injectors with two valve elements. This includes the fact that, for example, in the part-load operation of the internal combustion engine, small injection quantities can be realized even at a comparatively high pressure. This is because when only the first valve element opens, only a few outlet openings are "active", and therefore longer injection times can be realized. As a result, atomization similar to that achieved in full load operation is achieved even with small quantities to be injected. A hard combustion with strong noise is avoided.

In addition, the accuracy requirements for maintaining a very short switching time in the injection of very small quantities, such as are present in a pre-injection, decrease. As a result, the quantity spread from one injection to another injection can be reduced.

Advantageous developments of the invention are specified in the subclaims.

First, it is proposed that the additional valve device has a cylindrical switching body, which has a first valve edge, which separates the pressure chamber from the low-pressure connection, and a second valve edge, which connects the pressure chamber to the high-pressure connection, and a hydraulic control surface that delimits the hydraulic control chamber , The

In this case, the additional valve device is a hydraulic servo valve. This is technically easy to implement and works reliably. Additional control lines are not required.

It is particularly advantageous if a fluid channel is formed in the switching body, which at least temporarily connects the high-pressure connection to the control chamber. Such a fluid channel can simply be drilled into the switch body and reduces the machining work to be carried out, for example, on a housing of the fuel injection device to a minimum. Ultimately, this saves costs during production. A flow restrictor can be present in the fluid channel, or it can be designed as a flow restrictor overall. Such a flow restrictor is also referred to as an "inlet restrictor" or "Z restrictor". The dimensioning of the inlet throttle influences the pressure drop, the pressure build-up and also the level of the intermediate pressure when the additional valve device is in the intermediate position. As a result, the switching behavior of the entire fuel injection device can be adjusted overall.

That further development of the fuel injection device according to the invention is also very easy to manufacture, in which there is a sealing section on an axial boundary surface of the control chamber, on which the switching body comes into contact in the second end position, and which in this second end position of the switching body is one of the Control surface of the second valve element delimited and connectable to the low-pressure connection area of the control chamber from a connected to the fluid channel

Separates the area of the control room. In this way, in the second end position of the switching body, the hydraulic pressure acting on the control surface of the second valve element is lowered very quickly, since the inflow of fuel from the fluid channel is greatly restricted or even largely prevented. When the switch body has reached the second end position, the second valve element therefore opens at high speed, which favors the formation of the desired rectangular injection profile. It should be expressly pointed out here that the sealing section can be present, for example, on the switch body itself as well as on a housing surface opposite the switch body. It can also be provided that the one acting in the closing direction on the first valve element

Actuation device is designed so that the first valve element opens at a comparatively low pressure at the high pressure connection. In this case, a very flat pressure rise at low pressure at the high-pressure connection is made possible, which can be the case when the internal combustion engine is under low load. At the same time, a steep increase in pressure is guaranteed at high loads, at which there is usually a high pressure at the high pressure connection.

It is further proposed that the switching body has a central through opening, in which a section of the second valve element is guided. As a result, the dimensions of the fuel injection device according to the invention are kept very small.

drawing

A particularly preferred exemplary embodiment of the present invention is explained in more detail below with reference to the accompanying drawing, in which:

Figure 1 is a schematic representation of a fuel system of an internal combustion engine with several fuel injection devices

FIG. 2 shows a partial section through one of the fuel injection devices from FIG. 1;

Figure 3 shows a detail III of the fuel injection device of Figure 2; FIG. 4 shows a detail IV of the fuel injection device from FIG. 2; and

Figure 5 is a diagram showing the course of injection upon actuation of the fuel injection device of Figure 2 in different operating cases.

Description of the embodiment

A fuel system of an internal combustion engine bears the overall reference number 10 in FIG. 1. It comprises a fuel tank 12, from which an electric fuel pump 14 delivers the fuel to a high-pressure pump 16. This further delivers the fuel to a fuel collecting line 18 (“rail”), in which the fuel is stored under very high pressure. A plurality of fuel injection devices 20 are connected to the fuel collecting line 18 and inject the fuel directly into combustion chambers 22 assigned to them.

The fuel injection devices 20 are connected to the fuel collecting line 18 via high pressure connections 24. A low pressure line 26 connects the fuel injection devices 20 to the fuel tank 12. For this purpose 20 low pressure connections 28 are provided on the fuel injection devices. The operation of the fuel injection devices 20 is controlled or regulated by a control and regulating device 30.

FIG. 2 shows a fuel injection device 20 in greater detail: it comprises a housing 32, in which two to each other in a step-shaped longitudinal bore 33 coaxial valve elements 34 and 36 are guided. The outer valve element 36 is pressure-controlled, the inner valve element 34 is stroke-controlled.

For this purpose, the outer valve element 36 has a pressure surface 38 at approximately half its length, the resultant force of which points in the opening direction. The pressure surface 38 delimits a pressure chamber 40 which, as will be shown in detail below, via a channel 42 either with the low-pressure connection 28 or the

High pressure connection 24 can be connected. An annular space 43 leads from the pressure space 40 to the lower end of the fuel injection device 20 which projects into the combustion chamber 22 in the installed position and which is shown in detail in FIG.

There is a further pressure surface 38b on the outer valve element 36. A sealing edge 44 of the outer valve element 36 works together with a conical housing surface 46. If the sealing edge 44 lifts off the housing surface 46, fuel outlet channels 48, which are arranged distributed over the circumference of the fuel injection device 20, are connected to the annular space 43. A compression spring 50 presses the outer valve element 36 into the closed position, in which the sealing edge 44 abuts the housing surface 46.

The inner valve element 34 is guided in regions in the outer valve element 36. At its lower end in FIG. 2, it likewise has a pressure surface 51 which acts in the opening direction and a sealing edge 52 which, in the closed state, also bears on the housing surface 46. The inner valve element 34 includes fuel outlet channels 54, which are likewise distributed over the circumference of the fuel injection device 20 are arranged. The inner valve element 34 has a push rod section 56 (see FIG. 2) which has a slightly larger diameter than the section (without reference number) on which the sealing edge 52 is present.

The push rod section 56 is delimited at its upper end in FIG. 2 (also compare FIG. 4) by a hydraulic control surface 58 which acts in the closing direction of the inner valve element 34. The hydraulic control surface 58 delimits a hydraulic control chamber 60. From this, an outlet throttle 62 leads to an electromagnetic 2/2-way switching valve 64 (but this can also be designed as a piezo valve). The outlet throttle 62 can be connected to the low-pressure connection 28 via this.

The opening and closing of the two valve elements 34 and 36 is ultimately influenced by an additional valve device 66, which is designed as a hydraulic servo valve. Its structure will now be explained in particular with reference to FIG. 4:

The servo valve 66 comprises a cylindrical switching body 68. This has a central through bore 70 through which the push rod section 56 of the inner one

Valve element 34 is passed. The switch body 68 has a total of four sections 68a, 68b, 68c, and 68d, which have different diameters. The two sections 68a and 68b are received in a section 33a of the longitudinal bore 33, whereas the two sections 68c and 68d are arranged in a section 33b of the longitudinal bore. Section 33b has a larger diameter than section 33a. The outer diameter of the lowest section 68a of the switching body 68 in FIG. 4 has approximately the same diameter as the section 33a of the longitudinal bore 33, the section 68d of the switching body 68 has approximately the same diameter as the section 33b of the longitudinal bore 33.

These two sections are therefore guided in the longitudinal bore 33 in a fluid-tight manner. The section 68b of the switching body 68 has a smaller diameter than the section 68a. Section 68c has a larger diameter than section 68a, but a smaller diameter than section 68d.

In this way, a slide edge 72 is formed between the sections 68a and 68b of the switching body 68. A channel 74, which is connected to the low-pressure connection 28, can be released or closed by this. Between the sections 68b and 68c, a sealing edge 76 is formed, which cooperates with a slightly conical shoulder 78, which is present between the section 33a and 33b of the longitudinal bore 33. If the sealing edge 76 abuts the shoulder 78, an annular space 80, which is present between the section 68b of the switching body 68 and the section 33a of the longitudinal bore 33, is of an annular space 82, which is between the section 68c of the switching body 68 and the section 33b Longitudinal bore 33 is present, separated. If, however, the sealing edge 76 is raised from the shoulder 78, the two annular spaces 80 and 82 are connected to one another. The channel 42, which starts from the pressure chamber 40, opens into the section 33a of the longitudinal bore 33, specifically in FIG. 4 axially above the mouth of the channel 74. A high-pressure channel 84, which is connected to the high-pressure connection 24, branches off from the annular chamber 82 , A throttle point 86 is present in the high-pressure channel 84. In section 68d of the switch body 68 there is a fluid channel 88 running in the axial direction, in which in turn an inlet throttle 90 is formed. The fluid channel 88 connects the annular space 82 to the hydraulic control space 60. The annular end face of the switching body 68 facing the control space 60 forms a hydraulic control surface 92. The housing-side boundary surface (without reference number) of the control space 60 opposite the control surface 92 of the control space 60 has an annular sealing section 94 on. This is arranged in the radial direction between the mouth of the fluid channel 88 in the control chamber 60 and the control surface 58 of the inner valve element 34.

The fuel injection device 20 shown in FIGS. 2 to 4 operates as follows:

When the 2/2-way switching valve 64 is closed, the connection between the control chamber 60 and the low-pressure connection 28 is interrupted. At the same time, however, the control chamber 60 is connected to the high-pressure connection 24 via the high-pressure duct 84, the annular space 82, and the fluid duct 88. A high fluid pressure therefore prevails in the control chamber 60. Due to the corresponding hydraulic force acting on the hydraulic control surface 58 of the inner valve element 34 in the closing direction, the inner valve element 34 is pressed with the sealing edge 52 against the housing surface 46.

Due to the hydraulic force also acting on the control surface 92 of the switching body 68, the latter is pressed with the sealing edge 76 against the shoulder 78. In this position of the switch body 68, the slide edge 72 releases the channel 74. Pressure chamber 40 is thus ultimately connected to low-pressure connection 28 via channel 42 and annular space 80. The on the printing areas 38a and 38b acting hydraulic forces are comparatively low, so that the outer valve element 36 is pressed by the compression spring 50 with the sealing edge 44 against the housing surface 46. The outer valve element 36 is therefore also closed. No fuel is emitted from the fuel injector 20.

If the 2/2 switching valve 64 is opened, the hydraulic control chamber 60 is connected to the low pressure connection 28. As a result, the pressure in the control chamber 60 drops. Due to the high pressure prevailing in the annular chamber 82 (which is constantly connected to the high-pressure connection 24 via the high-pressure duct 84), the switching body 68 now lifts off from the shoulder 78 with the sealing edge 76. This means that on the one hand the slide edge 72 of the switching body 78 covers the mouth of the channel 74, so that the annular space 80 is now separated from the low pressure connection 28. On the other hand, the two annular spaces 80 and 82 are hereby connected to one another, so that a correspondingly high fluid pressure also builds up in the annular space 80 and in the channel 42 and the pressure space 40 and the annular space 43.

The hydraulic forces acting on the pressure surfaces 38a and 38b in the opening direction exceed the force acting in the closing direction by the compression spring 50, so that the outer valve element 36 with the sealing edge 44 lifts off the housing surface 46. Fuel is now released through the outlet channels 48. This results in the pressure curve typical of pressure-controlled valve elements, which bears the reference symbol 96 in FIG. 5, with a ramp-shaped pressure increase. The control chamber 60 remains connected to the high-pressure connection 24 overall via the fluid channel 88. There is therefore still a comparatively high intermediate pressure in the hydraulic control chamber 60, which prevents the inner valve element 34 opens. Fuel is therefore only released through the outlet channels 48.

When the control surface 92 of the switch body 68 comes into abutment in the “upper” end position on the housing-side sealing section 94, the connection of the region of the control chamber 60 lying radially inward from the sealing section 94 becomes largely or even ultimately with the high-pressure connection 24 completely interrupted. Now the pressure in this radially inner region of the control chamber 60 drops further, which leads to a corresponding reduction in the hydraulic force acting on the control surface 58 of the inner valve element 34 in the closing direction.

Since the outer valve element 36 with its sealing edge 44 has lifted off the housing surface 46, hydraulic forces acting in the opening direction now act on the pressure surface 51 of the inner valve element 34. This leads to the inner valve element 34 now opening.

Fuel can also escape through the outlet channels 54. This results in a pressure curve which is shown in dashed lines in FIG. 5 and bears the reference symbol 98.

To end the injection process, the 2/2 switching valve 64 is closed again. As a result, the pressure in the control chamber 60 rises again. Because of the force acting on the control surface 92 of the switching body 68, the latter moves back into its starting position, in which it rests with the sealing edge 76 on the shoulder 78 and in which the slide edge 72 again opens the channel 74. The pressure chamber 40 is thereby separated from the high-pressure connection 24 and connected to the low-pressure connection 28, so that the pressure in the annular space 80 and subsequently also in the channel 42 and in the pressure space 40 drops.

The outer valve element 36 can therefore be pressed by the compression spring 50 back into the closed position in which the sealing edge 44 abuts the housing surface 46. As a result, the hydraulic force acting on the pressure surface 51 of the inner valve element 34 decreases, and at the same time the hydraulic force acting on the control surface 58 of the inner valve element 34 increases. This pushes it back into its closed position.

If only the outer valve element 36 is to open during an injection, the 2/2 switching valve is closed again before the switching body 68 comes into contact with the control surface 92 on the sealing section 94. In this case, the control chamber 60 is simultaneously connected to the low-pressure connection 28 and to the high-pressure connection 24 via the fluid channel 88. This results in an “intermediate pressure” (possibly very briefly) in the control chamber 60, at which the switching body 68 does not open fully and the inner valve element 34 remains reliably closed. It is true that the pressure chamber 43 is also connected in a certain way to the low-pressure connection 28 via the inlet throttle 90, the corresponding one

However, the pressure drop in the pressure chamber 43 is so small that this does not yet lead to the outer valve element 36 being closed. The outer valve element 36 is only closed when the slide edge 72 opens the channel 74 again.

A return spring for the inner valve element 34 can be dispensed with, since it is moved reliably in normal operation by the prevailing pressure forces. Incidentally, even if the 2/2 switching valve 64 is defective, it is independent of the pressure in the fuel rail 18 ensures that no fuel is injected, since the outer valve element 36 is closed by the compression spring 50 and thus also prevents the inflow to the fuel outlet channels 54.

It should also be pointed out that the ramp of the pressure curve (reference symbol 96 in FIG. 5) depends on the pressure in the fuel collecting line 18 when the outer valve element 36 is opened. At a high pressure in the fuel manifold 18, as is usually set at high load and high engine speeds, a comparatively steep ramp can be realized, so the outer valve element 36 opens correspondingly quickly. At low load and correspondingly low pressure in the fuel rail 18, however, a comparatively flat ramp is realized.

Claims

Expectations

1. Fuel injection device (20) for an internal combustion engine, in particular with direct fuel injection, with at least two valve elements (34, 36), of which one valve element (36) has a pressure surface (38) acting in the opening direction, which has a pressure chamber (40, 43), and has an actuating device (50) acting in the closing direction, and of which another valve element (34) is one in

Hydraulic control surface (58) acting in the closing direction, which delimits a hydraulic control chamber (60), which is at least temporarily connected to a high-pressure connection (24) and has an admission device (51) acting in the opening direction, and with a control valve (64), which controls the Control room (60) can connect to a low pressure connection (28), characterized in that it comprises an additional valve device (66) which, in a first end position, the pressure chamber (40, 43) only with the low pressure connection (28) and the

Connects control chamber (60) to high pressure connection (24), in a second end position connects pressure chamber (40, 43) at least predominantly to high pressure connection (24) and essentially separates at least one area of control chamber (60) from high pressure connection (24), and in an intermediate position connects the pressure chamber (40, 43) at least predominantly to the high-pressure connection (24) and the control chamber (60) also to the high-pressure connection (24).

2. Fuel injection device (20) according to claim 1, characterized in that the additional valve device (66) has a cylindrical switching body (68) which has a first valve edge (72) which separates the pressure chamber (40, 43) from the low pressure connection ( 28), and a second valve edge (76), which connects the pressure chamber to the high pressure connection (24), and has a hydraulic control surface (92), which delimits the hydraulic control chamber (60).

3. Fuel injection device (20) according to claim 2, characterized in that in the switching body (68) a fluid channel (88) is formed which at least temporarily connects the high pressure connection (24) to the control chamber (60).

4. Fuel injection device (20) according to claim 3, characterized in that the fluid channel (88) comprises a flow restrictor (90).

5. Fuel injection device (20) according to one of claims 3 or 4, characterized in that on an axial boundary surface of the control chamber (60)

Sealing section (94) is present, against which the switching body (68) comes into contact in the second end position, and which, in this second end position of the switching body (68), defines one of the control surfaces (58) of the second valve element (34) and with it the

Separates the low-pressure connection (28) of the control chamber (60) from an area of the control chamber (60) connected to the fluid channel (88).

6. Fuel injection device (20) according to one of the preceding claims, characterized in that the acting in the closing direction on the first valve element (36) acting device (50) is designed so that the first valve element (36) opens at a comparatively low pressure at the high-pressure connection (24).

7. Fuel injection device (20) according to one of claims 2 to 6, characterized in that the switching body (68) has a central through opening (70) in which a section (56) of the second valve element (34) is guided.