DE10311522A1 - Fuel injection device for an internal combustion engine - Google Patents

Abstract

The fuel injection device has a high-pressure fuel pump (10) and a fuel injection valve (12) for a cylinder of the internal combustion engine. The high-pressure fuel pump (10) has a pump work space (22) and the fuel injection valve (12) has an injection valve member (28) through which at least one injection opening (32) is controlled and of which a connection (48) to the pump work space (22) having pressure chamber (40) prevailing pressure against the force of a closing spring (44) can be moved in an opening direction (29), the closing spring (44) being supported on the one hand on the injection valve member (28) and on the other hand on a displaceable storage piston (50) which, with its side facing away from the closing spring (44), delimits a storage space (52) which has a connection (54) to the pump working space (22) and which can be moved into a spring space (46) against the force of the closing spring (44). The spring chamber (46) has a connection formed by a channel (76) with a low-pressure region (62) which extends along the spring chamber (46), the spring chamber (46) via a throttle point (78) with an end region of the channel (76) is connected and the channel (76) opens at its opposite end into the low-pressure region (62).

Description

State of technology

The invention is based on one Fuel injector for an internal combustion engine according to the preamble of claim 1.

Such a fuel injector is due to the DE 198 44 891 A known. This fuel injection device has a high-pressure fuel pump and a fuel injection valve for a cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston which is driven by the internal combustion engine and delimits a pump work space, a connection of the pump work space to a relief region being controlled by an electrically controlled valve. The fuel injection valve has an injection valve member, through which at least one injection opening is controlled and which can be moved in an opening direction against the force of a closing spring arranged in a spring chamber by the pressure prevailing in a pressure chamber having a connection to the pump working chamber. The closing spring is supported on the one hand at least indirectly on the injection valve member and on the other hand at least indirectly on a storage piston. The storage piston delimits a storage space on its side facing away from the closing spring, which has a connection to the pump working space and can be moved into the spring space against the force of the closing spring. The spring chamber has a connection to a low-pressure area via a throttle point, the low-pressure area being connected to a fuel inlet. The accumulator piston enables fuel to be pre-injected by moving it into the spring chamber as the pressure in the pump work chamber rises due to the pressure prevailing in the accumulator chamber. When the pressure in the pump work chamber and thus in the pressure chamber of the fuel injector increases, its injector member first opens for the pre-injection. When the accumulator piston moves into the spring chamber, the bias of the closing spring and the pressure prevailing in the spring chamber are increased, so that the injection valve member closes again. If the pressure in the pump work chamber and in the pressure chamber continues to rise, the injection valve member opens against the increased pretension of the closing spring and a main injection of fuel takes place. The amount of fuel that is injected during the pre-injection is predetermined in a map as a function of the operating parameters of the internal combustion engine, in particular the speed. It was found that the amount of fuel injected during the pre-injection is significantly influenced by pressure fluctuations in the spring chamber, which in turn are caused by pressure fluctuations in the low pressure range. These pressure fluctuations are triggered by fluctuations in the inlet pressure and by the closing process of the control valve when the pump work space is separated from the relief area. Since the connection between the spring chamber and the low-pressure area is very short and opens directly into the low-pressure area, the pressure fluctuations in the low-pressure area are transmitted almost undiminished into the spring area. The pressure fluctuations in the spring chamber make it difficult to achieve the fuel injection quantity specified in the map during the pre-injection.

The fuel injection device according to the invention with the features according to claim 1 has in contrast the advantage that pressure fluctuations in the spring chamber due to the connection of the spring chamber with the low-pressure area of great length is reduced and thus the fuel injection quantity during the pre-injection can be adhered to more precisely.

In the dependent claims are advantageous refinements and developments of the fuel injection device according to the invention specified. The training according to claims 2 to 4 enables a big Length of Channel connecting the spring chamber with the low pressure area.

An embodiment of the invention is shown in the drawing and explained in more detail in the following description. Show it 1 a fuel injection device for an internal combustion engine in a first longitudinal section, 3 the fuel injector in a second longitudinal section and 3 the fuel injector in a cross section along line III-III in 1 ,

Description of the embodiment

In the 1 to 3 shows a fuel injection device for an internal combustion engine of a motor vehicle. The internal combustion engine has one or more cylinders, with a fuel injection device with a high-pressure fuel pump for each cylinder 10 and a fuel injector 12 is provided. The high pressure fuel pump 10 and the fuel injector 12 are combined into a so-called pump-nozzle unit. The high pressure fuel pump 10 has a pump body 14 on in which in a cylinder 16 a pump piston 18 is tightly guided by a cam 20 a camshaft of the internal combustion engine against the force of a return spring 19 driven in one stroke becomes. The pump piston 18 limited in the cylinder 16 a pump work room 22 , in the delivery stroke of the pump piston 18 Fuel is compressed under high pressure. The pump work room 22 becomes during the suction stroke of the pump piston 18 Fuel from a fuel tank 24 supplied, for example by means of a feed pump 21 , The pump work room 22 has a connection to a relief area, such as a return to the fuel tank 24 can serve, and that of an electrically operated control valve 23 is controlled. The control valve 23 is with an electronic control device 25 connected.

The fuel injector 12 has a valve body 26 on, which can be formed in several parts, and that with the pump body 14 , for example with the interposition of at least one intermediate body 27 , connected is. Between the intermediate body 27 and the pump body 14 can still have a disc 15 be arranged. In the valve body 26 is in a hole 30 an injector member 28 guided longitudinally. The hole 30 runs at least approximately parallel to the cylinder 16 of the pump body 14 , but can also be inclined to it. The valve body 26 has at least one, preferably a plurality of injection openings at its end region facing the combustion chamber of the cylinder of the internal combustion engine 32 on. The injector member 28 has, for example, an approximately conical sealing surface on its end region facing the combustion chamber 34 on that with one in the valve body 26 in its end region, which for example is also approximately conical in shape and faces the combustion chamber 36 cooperates, from or after which the injection openings 32 dissipate.

In the valve body 26 is between the injection valve member 28 and the hole 30 to the valve seat 36 towards an annulus 38 present in its the valve seat 36 end area facing away from the radial expansion of the hole 30 in one the injector member 28 surrounding pressure chamber 40 transforms. The injector member 28 points to the level of the pressure chamber 40 by reducing the cross-section to the valve seat 36 pointing pressure shoulder 42 on. At the end of the injection valve member facing away from the combustion chamber 28 grips a preloaded closing spring 44 through which the injector member 28 to the valve seat 36 is pressed down. The closing spring 44 is in a through a hole 47 formed spring chamber 46 a spring holding body 45 arranged which is part of the valve body 26 forms and attaches to the hole 30 followed. Between the valve body 26 and the spring holding body 45 can have one or more slices 43 be arranged. The pressure room 40 points like in 2 represented one by the valve body 26 , the disks 43 , the spring retainer 45 , the intermediate body 27 , the disc 15 and the pump body 14 ongoing connection 48 with the pump work room 22 on.

The closing spring 44 is supported on the one hand at least indirectly, for example via a spring plate, on the injection valve member 28 and on the other hand at least indirectly, for example also via a spring plate, on a storage piston 50 from. The accumulator piston 50 is coaxial with the spring chamber 46 subsequent drilling 51 in the intermediate body 27 tightly guided and limited with its closing spring 44 facing end in the hole 51 a storage space 52 , The storage space 52 has one through the intermediate body 27 , the disc 15 and the pump body 14 ongoing connection 54 with the pump work room 22 on.

The valve body 26 and the pump body 14 are by means of a clamping nut 60 with the spring holder body in between 45 , of the intermediate body 27 as well as the disc 15 connected and tense. The tension nut 60 overlaps the valve body 26 and is on one on the pump body 14 trained external thread screwed on. Between the tension nut 60 and the valve body 26 is at the level of the pressure chamber 40 and the hole 30 in which the injector member 28 is tight, an annulus 62 educated. The tension nut 60 points in the area of the annulus 62 a large number of openings in its circumference 64 each with a small cross-section, which form filter openings. The tension nut 60 is in the area of the annulus 62 on the outside of another annulus 66 surrounded that between the tension nut 60 and a hole 68 is formed in a cylinder head of the internal combustion engine, in which the fuel injection device is inserted. In the annulus 66 a fuel inlet from the feed pump opens 21 ago. The one through the feed pump 21 supplied fuel passes through the filter openings 64 in the annulus 62 and out of this through channels 70 in the slices 43 , in the spring retainer 45 , in the intermediate body 27 , in the disc 50 as well as in the pump body 14 into a valve room 72 of the control valve 23 , Through a control valve member 74 is the valve space 72 optionally with the pump work area depending on the switching position 22 connectable and from the pump work room 22 separable. The valve room 72 also has a connection with a return to the fuel tank 24 on.

The annulus 62 forms a low pressure area with which the spring chamber 46 connected is. In the spring retainer 45 is like in 1 shown a channel 76 , for example in the form of a bore, which extends along the spring chamber 46 extends. The channel 76 settles through the panes 43 away and flows into the annulus 62 , The channel 76 on the other hand, ends at the intermediate body 27 , The spring chamber 46 is with the channel 76 via a throttling point 78 connected that close to the storage piston 50 facing end of the spring chamber 46 is arranged. The channel 76 thus extends from the accumulator piston 50 facing end region of the spring chamber 46 to the annulus 62 and has one great length on. The low pressure area 62 is in the direction of the longitudinal axis 13 of the fuel injector 12 at a distance from the spring chamber 46 arranged. The spring chamber 46 is thus over the long channel 76 with the annulus forming the low pressure area 62 connected, the channel 76 forms a damping space in which pressure fluctuations in the annular space 62 are weakened so that they only cause slight pressure fluctuations in the spring chamber 46 to lead.

The function of the fuel injection device is explained below. The pump work room 22 becomes during the suction stroke of the pump piston 18 with open control valve 23 filled with fuel. The gets through the feed pump 21 delivered fuel into the annulus 66 , passes through the filter openings 64 through into the annulus 62 and from there it goes through the channels 70 in the valve room 72 and from this into the pump workspace 22 , During the delivery stroke of the pump piston 18 is the control valve 23 initially opened so that it is in the pump work room 22 no high pressure can build up. When the fuel injection should start, the control valve 23 by the control device 25 closed so that the pump work space 22 from the valve room 72 and thus from the fuel inlet and from the return to the fuel tank 24 is separated and builds up in this high pressure. When the pressure in the pump work space 22 and in the pressure room 40 is so high that over the pressure shoulder 42 on the injector member 28 force acting in the opening direction 29 is greater than the force of the closing spring 44 , the injection valve member moves 28 in the opening direction 29 and gives the at least one injection port 32 free, through which fuel is injected into the combustion chamber of the cylinder. The accumulator piston 50 is in a starting position in which it is closest to the target 15 is arranged. The pressure in the pump work space 22 subsequently rises according to the profile of the cam 20 further on.

If through the in the pump work room 22 prevailing pressure on the accumulator piston 50 force exerted is greater than that by the closing spring 44 on the accumulator piston 50 exerted force, so the storage piston leads 50 an evasive stroke movement and moves from the disc 15 away in the spring chamber 46 into it, with the storage space 52 is enlarged. This will increase the pressure in the spring chamber 46 caused because of this because of the throttle point 78 fuel can only escape with a delay, and also the preload of the closing spring 44 increases, which is on the accumulator piston 50 supported. The one in the spring chamber 46 prevailing pressure generated over the spring plate, over which the closing spring 44 on the injection valve member 28 supports, one in the closing direction on the injection valve member 28 Acting force. Due to the pressure increase in the spring chamber 46 and increasing the bias of the closing spring 44 there is an increased force in the closing direction on the injection valve member 28 , so that it is moved again in the closing direction with its sealing surface 34 at the valve seat 36 comes to the plant and the injection openings 32 closes so that the fuel injection is interrupted. The fuel injector 12 is only open for a short period of time and only a small amount of fuel is injected into the combustion chamber as a pre-injection. The amount of fuel injected is, among other things, that in the spring chamber 46 prevailing pressure, which, as stated above, in the closing direction on the injection valve member 28 acting force generated. When closing the control valve 23 at the beginning of the high pressure delivery of the pump piston 18 it occurs in the annulus forming the low pressure area 62 to an increase in pressure, however, due to the long channel 76 and the throttling point 78 not or only to a small extent to an increase in pressure in the spring chamber 46 leads and thus affects the amount of fuel injected during the pre-injection only slightly. With a direct connection of the spring chamber 46 with the low pressure area 62 as in the prior art, the pressure increase would be in the low pressure range 62 to a sharp increase in pressure in the spring chamber 46 lead, which leads to a sharp reduction in the amount of fuel injected during the pre-injection, so that the amount of fuel specified in the map cannot be injected.

The opening stroke of the injector member 28 during the pre-injection can be hydraulically limited by a damping device. The injector member 28 dives with a pressure pin 80 into a fuel-filled damping room 82 by one through an end face of the disc 43 formed fixed paragraph 84 is limited, which is a stroke stop for a ring shoulder 86 on the injection valve member 28 forms. It is between the wall of the damping room 82 and the pressure pin 80 a throttle cross-section is formed, which is ground as a surface 88 is formed and over which the damping space 82 with the spring chamber 46 connected is. The surface grinding 88 on the pressure pin 80 has an axial distance from the ring shoulder 86 on the injection valve member 28 in the area of the pressure pin 80 the diameter of the hole in the disc 43 corresponds so that a control edge 90 is formed, the running over the paragraph 84 the control of the hydraulic damping chamber 82 controls. The injection valve member passes through during the pre-injection 28 only a partial opening stroke caused by passing the control edge 90 on the injection valve member 28 about the paragraph 84 the disc 43 is limited, as a result of which the damping space 82 is controlled so that the closing force on the injection valve member 28 elevated.

The pressure in the pump work space 22 subsequently continues to rise according to the profile of the cam 20 so that the on the injector member 28 compressive force acting in the opening direction 29 increases again and that due to the increased bias of the closing spring 44 and the increased pressure in the spring chamber 46 increased closing force exceeds, so that the fuel injector 12 opens again. A larger amount of fuel is injected over a longer period of time than during the pre-injection. The length of time and the amount of fuel injected during this main injection are determined by the time at which the control valve 23 by the control device 25 is opened again. After opening the control valve 23 is the pump workspace 22 again with the return to the fuel tank 24 connected so that it is relieved and the fuel injector 12 closes. The accumulator piston 50 is by the force of the closing spring 44 moved back to its original position.

Claims (6)

Fuel injection device for an internal combustion engine with a high-pressure fuel pump ( 10 ) and a fuel injector ( 12 ) for a cylinder of the internal combustion engine, the high-pressure fuel pump ( 10 ) a pump work space driven by the internal combustion engine ( 22 ) limiting pump piston ( 18 ) with an electrically operated control valve ( 23 ), through which at least indirectly a connection of the pump work space ( 22 ) with a relief area ( 24 ) is controlled with the fuel injection valve ( 12 ) at least one injection valve member ( 28 ) through which at least one injection opening ( 32 ) is controlled by a connection ( 48 ) with the pump workspace ( 22 ) pressure room ( 40 ) prevailing pressure against the force of a spring chamber ( 46 ) arranged closing spring ( 44 ) in an opening direction ( 29 ) is movable, the closing spring ( 44 ) on the one hand at least indirectly on the injection valve member ( 28 ) and on the other hand at least indirectly on a displaceable storage piston ( 50 ) which supports the closing spring ( 44 ) facing away from a connection ( 54 ) with the pump workspace ( 22 ) having storage space ( 52 ) limited by the in the storage space ( 52 ) prevailing pressure against the force of the closing spring ( 44 ) in the spring chamber ( 46 ) is movable, the spring chamber ( 46 ) via a throttling point ( 78 ) a connection ( 76 ) with a low pressure area ( 62 ) with a fuel inlet and with the relief area ( 24 ), characterized in that the connection of the spring chamber ( 46 ) with the low pressure area ( 62 ) through a channel ( 76 ) is formed, which extends along the spring space ( 46 ) extends, the spring chamber ( 46 ) via the throttle point ( 78 ) with an end portion of the channel ( 76 ) is connected and the channel ( 76 ) at its opposite end in the low pressure area ( 62 ) flows out. Fuel injection device according to claim 1, characterized in that the channel ( 76 ) from the storage piston ( 50 ) facing end of the spring chamber ( 46 ) up to at least that of the accumulator piston ( 50 ) opposite end of the spring chamber ( 46 ) extends. Fuel injection device according to claim 1 or 2, characterized in that the low pressure region ( 62 ) as a one valve body ( 26 ) of the fuel injection valve ( 12 ) surrounding and in the direction of the longitudinal axis ( 13 ) of the fuel injection valve ( 12 ) at a distance from the spring chamber ( 46 ) arranged annular space is formed. Fuel injection device according to claim 3, characterized in that the low pressure region ( 62 ) at least approximately at the level of the pressure chamber ( 40 ) of the fuel injection valve ( 12 ) is arranged. Fuel injection device according to claim 3 or 4, characterized in that the low pressure region ( 62 ) as one between the valve body ( 26 ) and a clamping nut surrounding it ( 60 ) is formed, with the clamping nut ( 60 ) the valve body ( 26 ) with a pump body ( 14 ) the high pressure fuel pump ( 10 ) is connected and the clamping nut ( 60 ) several openings in their circumference ( 74 ) over which the low pressure area ( 62 ) is connected to the fuel supply. Fuel injection device according to one of the preceding claims, characterized in that the channel ( 76 ) is so long that in the low pressure range ( 62 ) occurring pressure fluctuations are so strongly damped that there are no or only slight pressure fluctuations in the spring chamber ( 46 ) to lead.