DE10233101A1 - 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 ratio (lambda) of the length (11) of the connection (48) of the pressure space (40) to the pump work space (22) to the length (12) of the connection (54) of the storage space (52) to the pump work space (22) is between 1 , 5 and 4.

Description

State of the art

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 39 00 763 A1 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 chamber 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 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 is 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 dependent on the operating parameters of the internal combustion engine, in particular the speed, in a map. It was found that the amount of fuel injection during the pre-injection is significantly influenced by pressure waves in the fuel injection device between the pump work space and the pressure space and the storage space. These pressure waves are triggered by the closing process of the control valve when the pump work space is separated from the relief area. The running times of these pressure waves, which are dependent on the length of the connections between the pressure space or the storage space and the pump work space, are therefore of great importance for the fuel injection quantity during the pre-injection and these are not optimal in the known fuel injection device.

Advantages of invention

The fuel injection device according to the invention with the features according to claim 1 has in contrast the advantage that the Fuel injection quantity in the pre-injection in the map optimal is set. This is done by tuning the lengths of the Connections of the pressure space and the storage space with the pump work space, the determine the transit times of the pressure waves in the specified in claim 1 relationship reached.

In the dependent claims are advantageous refinements and developments of the fuel injection device according to the invention specified. The training according to claim 2 enables a further optimization of the fuel injection quantity in the pre-injection in the map. The training according to claim 4 enables easily a great one Length of Connection of the storage space with the pump work space, which is used for Achievement of the specified ratio of lengths of connections is necessary because of the length of the connection of the pressure chamber with the pump workspace is difficult due to the structural conditions shortened can be.

drawing

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 simplified schematic representation, 2 one in 1 with II marked section in an enlarged view and 3 a course of the stroke of an injection valve member of the fuel injector during an injection cycle.

Description of the embodiment

In the 1 and 2 is a fuel injector for an internal combustion engine 10 shown 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 is driven in one stroke. 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 the fuel reservoir, for example, at least indirectly 24 can serve, and that of an electrically operated control valve 23 is controlled. The control valve 23 is with a 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 an 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 of the intermediate body 27 arranged, which is attached to the bore 30 followed. The spring chamber 46 is preferably with a relief area, for example at least indirectly the fuel tank 24 , connected. The pressure room 40 has one through the valve body 26 , the intermediate body 27 , the disc 15 and the pump body 14 ongoing connection 48 with the pump work room 22 on. The connection 48 has a length 11 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 51 , on a storage piston 50 from. The accumulator piston 50 is in the spring chamber 46 forming bore 47 tightly guided and limited in the bore with its end facing away from the closing spring 47 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 connection 54 has a length 12 on. To be as long as possible 12 the connection 54 to reach the connection runs 54 not directly along the shortest route between the storage space 52 and the pump work room 22 but has at least one deflection. As in 2 the connection is shown 54 starting from that of the disc 15 facing end area of the storage space 52 for example initially at least approximately radially to the longitudinal axis of the intermediate body 27 , which is the same as the longitudinal axis of the injection valve member 28 , outward. Here is in the disc 15 facing end face of the intermediate body 27 , or alternatively in the intermediate body 27 facing end of the disc 15 , a groove 56 educated. The groove 56 is through the disc 15 closed, so that a closed channel is formed. To the groove 56 closes as another part of the connection 54 a hole 58 in the intermediate body 27 at, for example, at least approximately parallel to the longitudinal axis of the intermediate body 27 runs. The hole 58 opens onto the valve body 26 facing side of the intermediate body 27 in one in the the valve body 26 facing end face of the intermediate body 27 trained further groove 60 , The groove 60 can alternatively also in the the intermediate body 27 facing end of the valve body 26 be trained. The groove 60 runs, for example, at least approximately radially outwards. From the radially outer end of the groove 60 leads another hole 62 through the intermediate body 27 from, for example, at least approximately parallel to the bore 58 runs and that on the disc 15 facing end face of the intermediate body 27 empties. In the disc 15 and the pump body 14 close further holes as part of the connection 54 on. The length 12 the connection is the sum of the lengths of the grooves 56 . 60 , the holes 58 . 60 in the intermediate body 27 and the holes in the disc 15 and the pump body 14 to the pump work room 22 ,

According to the invention, the ratio λ is the length 11 the connection 48 of the pressure room 40 of the fuel injector 12 with the pump work room 22 divided by the length 12 the connection 54 of the storage space 52 with the pump work room 22 between 1.5 and 4. The ratio λ is in particular between 2 and 2.5, preferably at least approximately 2.1. The length 11 the connection 48 of the pressure room 40 of the fuel injector 12 with the pump work room 22 is structurally determined by the structure of the fuel injection device and can therefore not be reduced arbitrarily.

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 filled with fuel. During the delivery stroke of the pump piston 18 is the control valve 23 first 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 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 causes a pressure drop in the pump work space 22 causes and also the bias of the closing spring 44 increases, which is on the accumulator piston 50 supported. Due to the pressure drop in the pump workspace 22 and in the pressure room 40 there is less force in the opening direction 29 on the injector member 28 and due to the increase in the bias of the closing spring 44 there is an increased force in the closing direction on the injection valve member 28 , so that this 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. In 3 is the opening stroke of the injection valve member 28 plotted over time during an injection cycle, the stroke during the pre-injection in 3 is denoted by I. The amount of fuel injected is essentially the opening pressure of the accumulator piston 50 determined, that is the pressure in the pump workspace 22 where the accumulator piston 50 its evasive stroke begins. By closing the control valve 23 during the delivery stroke of the pump piston 18 pressure waves are caused, which arise from the pump work space 22 about the connection 48 to the pressure room 40 and about the connection 54 to the storage room 52 spread. Through the choice of length explained above 11 the connection 48 and the length 12 the connection 54 To achieve the ratio λ in the specified range are the transit times of the pressure waves in the connections 48 and 54 matched to one another in such a way that, under different operating conditions, in particular different speeds of the internal combustion engine, an optimum fuel injection quantity is achieved during the pre-injection.

The opening stroke of the injector member 28 during the pre-injection can be hydraulically limited by a damping device. Such a damping unit is due to the DE 39 00 762 A1 as well as the corresponding US-5,125,580 and the DE 39 00 763 A1 and the corresponding US Pat. No. 5,125,581, the content of which is hereby expressly incorporated by reference.

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 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 stroke of the injector member 28 during the main injection is in 3 marked with II. 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 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. The time offset between the pre-injection and the main injection is mainly due to the evasive stroke of the accumulator piston 50 certainly.

Claims (4)

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 work space ( 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, characterized in that the ratio (λ) of the length ( 11 ) the connection ( 48 ) of the pressure chamber ( 40 ) with the pump workspace ( 22 ) divided by the length ( 12 ) the connection ( 54 ) of the storage space ( 52 ) with the pump workspace ( 22 ) is between 1.5 and 4. Fuel injection device according to claim 1, characterized in that this relationship (λ) between 2 and 2.5, preferably at least approximately 2.1. Fuel injection device according to Claim 1 or 2, characterized in that the high-pressure fuel pump ( 10 ) a pump body ( 14 ) and the fuel injection valve ( 12 ) a valve body ( 26 ) which, with the interposition of at least one intermediate body ( 27 ) are interconnected so that the storage space ( 52 ) in the intermediate body ( 27 ) and that the connection (54) of the storage space ( 52 ) with the pump workspace ( 22 ) at least partially through the intermediate body ( 27 ) runs. Fuel injection device according to claim 3, characterized in that the connection ( 54 ) of the storage space ( 52 ) with the pump workspace ( 22 ) in the intermediate body ( 27 ) at least one redirection to extend the connection ( 54 ) having.