EP1476655A1

EP1476655A1 - Fuel injection system for an internal combustion engine

Info

Publication number: EP1476655A1
Application number: EP02792635A
Authority: EP
Inventors: Peter Boehland
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2002-02-12
Filing date: 2002-12-06
Publication date: 2004-11-17
Anticipated expiration: 2022-12-06
Also published as: US20040144365A1; EP1476655B1; WO2003069154A1; US7025284B2; JP2005517859A; DE50203434D1; DE10205750A1

Abstract

The invention relates to a fuel injection system comprising a high pressure fuel pump (10) and a fuel injection valve (12) connected to said pump, for each cylinder of the internal combustion engine. A pump piston (18) of the high pressure fuel pump (10) defines a pump working area (22) which is connected to a pressure chamber (40) of the fuel injection valve (12). Said fuel injection valve comprises an injection valve element (28) which is used to control injection openings (32) and can be displaced against a closing force in an opening direction by means of the pressure in the pressure chamber (40). A connection (66) between the pump working area (22) and a discharge chamber (24) is controlled by a first control valve (68), and a connection (64) between a control pressure chamber (52) associated with the pump working area (22) and a discharge chamber (24) is controlled by a second control valve (70). A throttle point (63, 65) is respectively provided in connections (62, 64) between the control pressure chamber (52) and the pump working area (22) and between the control pressure chamber and the discharge chamber (24). Another pressure chamber (54) is connected to the pump working area (22) and is defined by a pressure surface (53) by which means another force is exerted on the injection valve element (28) in the closing direction.

Description

Fuel injection device for an internal combustion engine

State of the art

The invention is based on one

Fuel injection device for an internal combustion engine according to the preamble of claim 1.

Such a fuel injection device is known from EP 0 987 431 A2. This

Fuel injection device has a high-pressure fuel pump and a fuel injection valve connected to this for each cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston which is driven by the internal combustion engine in a stroke movement and delimits a pump working space. The fuel injection valve has a pressure chamber connected to the pump working chamber and an injection valve member, through which at least one injection opening is controlled and which through the

Pressure chamber prevailing pressure is movable against a closing force in the opening direction to release the at least one injection opening. A first electrically operated control valve is provided, by means of which a connection of the pump work space to a relief space is controlled. A second electrically actuated control valve is also provided, by means of which a connection of a control pressure chamber to a relief chamber is controlled. The control pressure chamber is limited by a control piston, the control piston from the

Control pressure chamber prevailing pressure acts in a closing direction on the injection valve member and is movable together with the injection valve member. The Control pressure chamber has a connection to the pump work chamber. For a fuel injection, the first control valve is closed and the second control valve is opened, so that no high pressure can build up in the control pressure chamber and the fuel injection valve can open. When the second control valve is open, however, fuel flows out of the pump work chamber via the control pressure chamber, so that the quantity of fuel available for injection is reduced from the quantity of fuel delivered by the pump piston, and the pressure available for injection is also reduced. It follows from this that the efficiency of the fuel injection device is not optimal.

Advantages of the invention

The fuel injection device according to the invention with the features according to claim 1 has the advantage that the end face of the control piston, which is acted upon by the pressure in the control pressure chamber, can be kept small, so that the fuel flow that flows off when the second control valve is open can be kept small with the minimum flow cross-sections of the throttle points required for the function and thus the efficiency of the fuel injector is improved.

Advantageous refinements and developments of the fuel injection device according to the invention are specified in the dependent claims. The embodiment according to claim 3 enables the arrangement of the further printing surface in a simple manner. The embodiment according to claims 4 and 5 enables a simple construction of the fuel injection device.

drawing An embodiment of the invention is shown in the drawing and explained in more detail in the following description. 1 shows a

Fuel injection device for an internal combustion engine in a schematic representation, FIG. 2 shows a section of FIG

3 shows detail II of the fuel injection device according to a further modified embodiment, and FIG. 4 shows a course of a pressure at injection openings of a fuel injection valve of the fuel injection device.

Description of the embodiment

In Figures 1 to 3 is one

Fuel injection device for an internal combustion engine of a motor vehicle shown. The internal combustion engine is preferably a self-igniting internal combustion engine. The fuel injection device is preferably designed as a so-called pump-nozzle unit and has for each cylinder of the internal combustion engine a high-pressure fuel pump 10 and a fuel injection valve 12 connected to it, which form a common structural unit. Alternatively, the

Fuel injection device can also be designed as a so-called pump-line-nozzle system, in which the high-pressure fuel pump and the fuel injection valve of each cylinder are arranged separately from one another and are connected to one another via a line. The high-pressure fuel pump 10 has a pump body 14 with a cylinder bore 16, in which a pump piston 18 is tightly guided, which is lifted at least indirectly by a cam 20 of a camshaft of the internal combustion engine against the force of a return spring 19 is driven. The pump piston 18 delimits a pump working chamber 22 in the cylinder bore 16, in which fuel is compressed under high pressure during the delivery stroke of the pump piston 18. The pump working chamber 22 is supplied with fuel from a fuel tank 24 of the motor vehicle.

The fuel injection valve 12 has a valve body 26 which is connected to the pump body 14 and which can be constructed in several parts and in which an injection valve member 28 is guided so as to be longitudinally displaceable in a bore 30. The valve body 26 has at least one, preferably a plurality of injection openings 32 at its end region facing the combustion chamber of the cylinder of the internal combustion engine. The injection valve member 28 has at its end region facing the combustion chamber an, for example, approximately conical sealing surface 34 which interacts with a valve seat 36 formed in the valve body 26 in its end region facing the combustion chamber, from or after which the injection openings 32 lead away. in the

Valve body 26 has an annular space 38 between injection valve member 28 and bore 30 toward valve seat 36, which, in its end region facing away from valve seat 36, merges into a pressure chamber 40 surrounding injection valve member 28 by radial expansion of bore 30. The injection valve member 28 has a pressure shoulder 42 at the level of the pressure chamber 40 by reducing the cross section. At the end of the injection valve member 28 facing away from the combustion chamber, a prestressed closing spring 44 engages, by means of which the injection valve member 28 is pressed toward the valve seat 36. The closing spring 44 is arranged in a spring chamber 46 of the valve body 26, which adjoins the bore 30.

A further bore 48 connects to the spring chamber 46 at its end facing away from the bore 30 in the valve body 26 in which a control piston 50 is tightly connected, which is connected to the injection valve member 28. The bore 48 is stepped in diameter and has a section 148 with a large diameter arranged towards the spring chamber 46 and a section 248 with a small diameter arranged remote from the spring chamber 46. The control piston 50 is also correspondingly stepped in diameter and has an area 150 with a large diameter that is tightly guided in the bore section 148 and an area 250 with a small diameter that is tightly guided in the bore section 248. A control pressure chamber 52 is delimited in the bore section 248 by the end face of the region 250 of the control piston 50 as a movable wall. At the transition between the areas 150, 250, an annular pressure surface 53 is formed on the area 150 of the control piston 50, with which the area 150 of the control piston 50 delimits a further pressure space 54 in the bore section 148. The control piston 50 is connected to the injection valve member 28 via a piston rod 51 which is smaller in diameter than this. The control piston 50 can be formed in one piece with the injection valve member 28, but is preferably connected to the injection valve member 28 as a separate part for reasons of assembly.

A channel 60 leads from the pump work chamber 22 through the pump body 14 and the valve body 26 to the pressure chamber 40 of the fuel injection valve 12. A channel 62 leads from the pump work chamber 22 or from the channel 60 to the control pressure chamber 52. A channel 64 also opens into the control pressure chamber 52, which connects to form a relief space than that at least indirectly can serve the fuel reservoir 24 or another area in which a low pressure prevails. A connection 66 leads from the pump work chamber 22 or from the channel 60 to a relief chamber 24, which is controlled by a first electrically operated control valve 68. The control valve 68 can be as shown in Figure 1 be designed as a 2/2-way valve. The connection 64 of the control pressure chamber 52 to the relief chamber 24 is controlled by a second electrically operated control valve 70, which can be designed as a 2/2-way valve. In the connection 62 of the control pressure chamber 52 with the

Pump work chamber 22, a throttle point 63 is provided and a throttle point 65 is provided in the connection of the control pressure chamber 52 with the relief chamber 24. The inflow of fuel from the pump work chamber 22 into the control pressure chamber 52 and the outflow of fuel from the control pressure chamber 52 can be adjusted to a required extent by suitable dimensioning of the throttle points 63, 65. A sufficient inflow of fuel into the control pressure chamber 52 is required for a quick closing of the fuel injection valve 12 and a sufficient outflow of fuel from the control pressure chamber 52 is required for a quick opening of the fuel injection valve 12. The control valves 68, 70 can have an electromagnetic actuator or a piezo actuator and are controlled by an electronic control device 72.

The further pressure chamber 54 has a connection 56, for example in the form of a duct, to the pump working chamber 22, which can open into the duct 60, for example. There is no throttle point in connection 56. The further pressure chamber 54 is thus directly bypassing the throttle point 63 of the connection 62 of the control pressure chamber 52 with the pump work chamber 22 to the pump work chamber 22 and the same pressure acts on the pressure surface 53 of the control piston 50 as in the pump work chamber 22 and in the pressure chamber 40 pressure prevailing in further pressure chamber 54, a force which supports the closing spring 44 is generated in the closing direction on the injection valve member 28 via the pressure surface 53 and the control piston 50. Through the im Control pressure chamber 52 prevailing pressure is generated via the end face of the control piston 50 also a force supporting the closing spring 44 in the closing direction on the injection valve member 28. The pressure in the control pressure chamber 52 is controlled by the second control valve 70, wherein when the control valve 70 is closed, at least approximately the same pressure is established in the control pressure chamber 52 as in the pump work chamber 22 and as in the further pressure chamber 54, while when the control valve 70 is open due to the connection to the relief chamber 24 sets a lower pressure in the control pressure chamber 52. The total closing force acting on the injection valve member 28 is therefore dependent on the force of the closing spring 44, on the pressure prevailing in the control pressure chamber 52, which is controlled by the second control valve 70, and on the pressure prevailing in the further pressure chamber 54, which is the same like the pressure prevailing in the pump working chamber 22, which in turn is dependent on the delivery stroke of the pump piston 18.

FIG. 2 shows a detail of a modified version of the fuel injection device, in which the basic structure is the same as described above, but the pressure surface 53 is formed on a piston 55 separate from the control piston 50. The control piston 50 only has the control piston region 250 which is tightly guided in the bore section 248 and which limits the control pressure chamber 52 with its end face. The control piston 50 is connected to the injection valve member 28 via the piston rod 51. The piston 55 replaces the control piston region 150 of the embodiment according to FIG. 1 and is likewise connected to the injection valve member 28 via a piston rod 57, the piston rod 51 of the control piston 50 passing through the piston 55 and its piston rod 57. FIG. 3 shows a detail of a modified version of the fuel injection device, in which the basic structure is again the same as in the embodiment according to FIG. 1, but the design of the control piston and the connection of the control pressure chamber 52 to the

Pump work space 22 is modified. The control piston 50 in turn has the region 150 which is tightly guided in the bore section 148 with a larger diameter and the region 250 which is tightly guided in the bore section 248 with a smaller diameter. The control pressure chamber 52 is delimited by the end face of the control piston region 250 and the further pressure chamber 54 is delimited by the annular pressure surface 53 of the control piston region 150. The further pressure chamber 54 is connected to the channel 60 via the connection 56 and via this to the

Pump work room 22 connected. A connection 162, for example in the form of a bore, is formed in the control piston region 250, through which the control pressure chamber 52 is connected to the further pressure chamber 54. A throttle point 163 is provided in the connection 162, which can be formed by the connection 162 itself if it is designed with a correspondingly small cross section. The connection 64 leads from the control pressure chamber 52 to the relief chamber 24, which is controlled by the second control valve 70 and in which the throttle point 65 is provided. 1, the bore section 148 has the same diameter as the spring chamber 46. To separate the bore section 148 and the spring chamber 46, an intermediate disk 58 is provided, on which the closing spring 44 is supported in the spring chamber 46. Between the piston rod 51 and the injection valve member 28, a shim 59 can be arranged, with which the distance between the control piston 50 and the injection valve member 28 can be adjusted. The function of

Fuel injector explained. FIG. 4 shows the course of the pressure p at the injection openings 32 of the fuel injection valve 12 over the time t during an injection cycle. During the suction stroke of the pump piston 18, fuel is supplied to it from the fuel reservoir 24. During the delivery stroke of the pump piston 18, the fuel injection begins with a pre-injection, the first control valve 68 being closed by the control device 72, so that the pump working chamber 22 is closed

Relief chamber 24 is separated. The control device 72 also opens the second control valve 70 so that the control pressure chamber 52 is connected to the relief chamber 24. In this case, no high pressure can build up in the control pressure chamber 52, since this is relieved towards the relief chamber 24. However, a small amount of fuel can flow out of the pump work chamber 22 via the throttling points 63 and 65 to the relief chamber 24, so that the full high pressure cannot build up in the pump work chamber 22 as it would build up when the second control valve 70 is closed. In the further pressure chamber 54 there is the same pressure as in the pump work chamber 22 and in the pressure chamber 40. If the pressure in the pump work chamber 22 and thus in the pressure chamber 40 of the fuel injection valve 12 is so great that the pressure on the pressure shoulder 42 on it

Injection valve member 28 pressure force is greater than the sum of the force of the closing spring 44, the pressure force acting on the control piston 50 by the residual pressure acting in the control pressure chamber 52 and the pressure force generated by the pressure prevailing in the further pressure chamber 54 via the pressure surface 53, this moves

Injection valve member 28 in the opening direction 29 and releases the at least one injection opening 32. To end the pilot injection, the second control valve 70 is closed by the control device, so that the control pressure chamber 52 is separated from the relief chamber 24. The first control valve 68 remains in its closed position. High pressure builds up in the control pressure chamber 52 as in the pump work chamber 22, so that a large pressure force acts on the control piston 50 in the closing direction. In addition, when the second control valve 70 is closed, the pressure in the pump work chamber 22 and thus also in the further pressure chamber 54 increases, so that an increased force in the closing direction on the injection valve member 28 is also generated via the pressure surface 53. Since now that acting on the injection valve member 28 in the opening direction 29

Force is less than the sum of the force of the closing spring 44, the pressure force on the control piston 50 and the pressure force on the pressure surface 53 closes the fuel injection valve 12. The pre-injection corresponds to an injection phase designated I in FIG.

For a subsequent main injection, which corresponds to an injection phase designated II in FIG. 4, the second control valve 70 is opened by the control device 72, so that the pressure in the control pressure chamber 52 drops. The fuel injection valve 12 then opens due to the reduced pressure force on the control piston 50 and the injection valve member 28 moves over its maximum opening stroke. To limit the opening stroke movement of the injection valve member 28 and the control piston 50, the pressure surface 53 can come to rest on the annular shoulder formed at the transition between the bore sections 148 and 248. However, another stroke stop can be provided for the injection valve member 28 to limit its opening movement. With the second open

Control valve 70 flows a small amount of fuel via the throttling points 63, 65 to the relief chamber 24, however, the throttling points 63, 65 can be designed with a small flow cross-section, so that the outflowing fuel amount and the reduction in pressure in the pump work chamber 22 are small. To end the main injection, the first control valve 68 is brought into its open switching position by the control device 72, so that the pump working chamber 22 is connected to the relief chamber 24 and only a small compressive force acts on the injection valve member 28 in the opening direction 29 and the fuel injection valve 12 is caused by the force of the closing spring 44, which closes on the control piston 50 due to the residual pressure prevailing in the control pressure chamber 52 and the force generated on the pressure surface 53 in the further pressure chamber 54. The second control valve 70 may be in its open or closed position to complete the main injection.

In the embodiments of the fuel injection device explained above, it can additionally be provided that the flow cross section from the control pressure chamber 52 to the relief chamber 24 is variably controlled by the control piston 50 depending on its stroke. A large flow cross section is released by the control piston 50 in a stroke position corresponding to the closed position of the injection valve member 28 and in a stroke position corresponding to the open position of the

Injection valve member 28 released a small flow cross section.

Claims

Expectations

1. Fuel injection device for an internal combustion engine with a high-pressure fuel pump (10) and a fuel injection valve (12) connected thereto for each cylinder of the internal combustion engine, the high-pressure fuel pump (10) having a pump piston (18) driven by the internal combustion engine in a stroke movement, which has a pump work space (22), to which fuel is supplied from a fuel reservoir (24), the fuel injection valve (12) having a pressure chamber (40) connected to the pump working chamber (22) and an injection valve member (28) through which at least one injection opening (32) is controlled, which is acted upon by the pressure prevailing in the pressure chamber (40) against a closing force in an opening direction (29) to release the at least one injection opening (32), with a first control valve (68) through which a connection (66) the pump work space (22) with a relief space (24) is controlled and with a second control valve (70) through which a connection (64) of a control pressure chamber (52) with a relief chamber (24) is controlled, the control pressure chamber (52) being delimited by a control piston (50) which is controlled by the Control pressure chamber (52) acting pressure acts in a closing direction on the injection valve member (28) and which is movable together with the injection valve member (28), the control pressure chamber (52) having a connection (62) to the pump work chamber (22), characterized that in the connections (62,64) of the control pressure chamber (52) with A throttle point (63, 65) is provided in each case for the pump work chamber (22) and with the relief chamber (24), that a further pressure chamber (54) is provided, which is connected to the pump work chamber (22) and which is connected by a pressure surface (53) is limited, via which a further force is generated in the closing direction on the injection valve member (28).

2. Fuel injection device according to claim 1, characterized in that the pressure surface (53) on one

Control piston (50) surrounding separate piston (55) is designed as an annular surface.

3. Fuel injection device according to claim 1, characterized in that the pressure surface (53) on the control piston

(50) is formed, which is stepped in cross section, that the control piston (50) with the end face of an area (250) with a small cross section the control pressure chamber

(52) and that the pressure surface (53) is formed as a ring-shaped surface on a region (150) of the control piston (50) with a large cross-section at the transition to the region (250) with a small cross-section.

4. Fuel injection device according to one of claims 1 to 3, characterized in that the further pressure chamber

(54) with the pump work space (22) directly bypassing the throttle point (63) of the connection (62) of the control pressure chamber (52) with the pump work space (22).

5. Fuel injection device according to one of claims 1 to 3, characterized in that the control pressure chamber (52) via the further pressure chamber (54) with the pump work chamber

(22) is connected and that the throttle point (163) is arranged in the connection (162) between the control pressure chamber (52) and the further pressure chamber (54).

6. Fuel injection device according to claim 5, characterized in that the connection (162) of the control pressure chamber (52) with the further pressure chamber (54) via at least one channel in the control piston (50).