Patent Publication Number: US-6705551-B1

Title: Common rail injector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 00/02580 filed on Aug. 2, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a common rail injector for injecting fuel in a common rail injection system of an internal combustion engine, which system has an injector housing with a fuel inlet that is in communication with a central high-pressure fuel reservoir outside the injector housing and with a pressure chamber inside the injector housing, from which fuel subjected to high pressure is injected as a function of the position of a control valve that assures that a nozzle needle movable back and forth and received in a longitudinal bore of the injector axially counter to the prestressing force of a nozzle spring that is received in a nozzle spring chamber, lifts from a seat when the pressure in the pressure chamber is greater than the pressure in a control chamber that communicates with the fuel inlet via an inlet throttle. 
     2. Description of the Prior Art 
     In common rail injection systems, a high-pressure pump pumps the fuel into the central high-pressure fuel reservoir, which is called a common rail. From the high-pressure fuel reservoir, high-pressure lines lead to the individual injectors, which are assigned to the engine cylinders. The injectors are triggered individually by the engine electronics. The rail pressure prevails in the pressure chamber and at the control valve. When the control valve opens, fuel subjected to high pressure reaches the combustion chamber, past the nozzle needle that is lifted counter to the prestressing force of the nozzle spring. 
     In conventional injectors of the kind known for instance from German Patent Disclosures DE 197 24 637 A1 or DE 197 32 802 A1, relatively long nozzle needles are used. In operation, because of the high pressures and the rapid load changes, very strong forces act on the nozzle needle. These forces cause the nozzle needle to be stretched and compressed in the longitudinal direction. This in turn means that the nozzle needle stroke varies as a function of the forces acting on the nozzle needle. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to furnish a common rail injection system with a small structural volume that is simple in design and can be produced economically. In particular, even at a high nozzle needle speed, good closing performance should be assured. 
     In a common rail injector for injecting fuel in a common rail injection system of an internal combustion engine, which system has an injector housing with a fuel inlet that is in communication with a central high-pressure fuel reservoir outside the injector housing and with a pressure chamber inside the injector housing, from which fuel subjected to high pressure is injected as a function of the position of a control valve that assures that a nozzle needle movable back and forth and received in a longitudinal bore of the injector axially counter to the prestressing force of a nozzle spring that is received in a nozzle spring chamber, lifts from a seat when the pressure in the pressure chamber is greater than the pressure in a control chamber that communicates with the fuel inlet via an inlet throttle, this object is attained in that the control chamber is defined by a bush that is displaceable, causing a sealing action, on the end of the nozzle needle remote from the combustion chamber and that is kept in contact against the injector housing with the aid of the nozzle spring. The bush offers the advantage that the control chamber and the nozzle spring chamber can be combined on the end remote from the combustion chamber of the nozzle needle, without the volume of the control chamber depending on the structural space of the nozzle spring. It is therefore possible to build in a nozzle spring with high spring rigidity, which assures good closure of the nozzle needle. As a result, the injection time and the instant of injection can be defined exactly. Furthermore, the control chamber can be made quite small, which leads to a rapid response behavior of the injector of the invention. There is also a relationship between the maximum attainable nozzle needle speed and the nozzle needle diameter. To achieve elevated nozzle needle speeds, which is important especially upon needle closure, the nozzle needle diameter must be reduced. For a closing speed of 1 m/s, a needle diameter below 3.5 mm is required, for an acceptable control quantity. This is technologically quite complicated and therefore expensive. According to the present invention, the nozzle needle diameter can be selected freely and is not dependent on the dimensions of the nozzle spring. In comparison to convention nozzle needles, the length can be reduced considerably, which contributes to an exact stroke stop. 
     One particular type of embodiment of the invention is characterized in that a biting edge is embodied on the face of the bush that is in contact with the injector housing. As a result, it is attained that the control chamber embodied in the interior of the bush remains separated from the nozzle spring chamber that surrounds the bush. 
     A further particular type of embodiment of the invention is characterized in that the inside diameter of the bush is less than or equal to a guide diameter at the nozzle needle. The smaller the control chamber volume can be selected to be, the more readily the injector reacts. According to the present invention, the inside diameter of the bush and the corresponding outside diameter at the nozzle needle can be made much smaller than in conventional injectors. 
     Another particular type of embodiment of the invention is characterized in that the fuel inlet communicates with the pressure chamber via the nozzle spring chamber, and that the nozzle needle is guided between the nozzle spring chamber and the pressure chamber. This offers the advantage that the nozzle needle guide no longer has any sealing function. This makes the demands in terms of quality of the guide less stringent, leading to economies in production. Since the same pressure prevails on both sides of the guide, guide leakage no longer occurs. 
     A further particular type of embodiment of the invention is characterized in that the nozzle spring chamber communicates with the pressure chamber via a bore. As a result, the entire circumference of the nozzle needle can be utilized for guide purposes. 
     A further particular type of embodiment of the invention is characterized in that at least one flat face, past which fuel from the nozzle spring chamber can reach the pressure chamber, is embodied on the nozzle needle between the nozzle spring chamber and the pressure chamber. This type of embodiment offers advantages especially with regard to the high-pressure strength. 
     Further particular types of embodiment of the invention are characterized in that the inlet throttle is integrated with the bush, the nozzle needle or the injector housing. The inlet throttle serves to prevent pressure surges in operation. 
     A further particular type of embodiment of the invention is characterized in that the bush has a collar on its end remote from the combustion chamber. The collar forms a first abutment for the nozzle spring. 
     A further particular type of embodiment of the invention is characterized in that a step that forms a stop for a spring plate is formed on the nozzle needle. The spring plate forms a second abutment for the nozzle spring. 
     A further particular type of embodiment of the invention is characterized in that a circumferential groove is recessed out of the nozzle needle, and in this groove a retaining ring which forms a stop for a spring plate is braced. In this type of embodiment, the outside diameter of the nozzle needle in the control chamber and the guide diameter of the nozzle needle between the nozzle spring chamber and the pressure chamber can be the same size. This is advantageous in production, for instance by means of lapping. 
     A further particular type of embodiment of the invention is characterized in that the retaining ring is in two parts, and in the assembled state it is fixed by the spring plate. As a result, loosening of the spring plate in operation is prevented in a simple way. 
     A further particular type of embodiment of the invention is characterized in that the nozzle needle stroke is defined by the spacing between the bush and the spring plate. This purely mechanical nozzle needle stroke end stop offers the advantage that the nozzle needle stroke is exactly replicable. As a result, the course of injection can be shaped reliably. So-called hydraulic sticking is avoided. 
     A further particular type of embodiment of the invention is characterized in that the nozzle needle stroke and the nozzle spring prestressing can be adjusted with the aid of spacer elements, which are disposed between the spring plate and the stop for the spring plate, and between the nozzle spring and the abutments for the nozzle spring. As a result, the closing performance of the injector can be improved. 
     A further particular type of embodiment of the invention is characterized in that the nozzle needle stroke is defined by the spacing between the end face, remote from the combustion chamber, of the nozzle needle and the injector housing. This type of embodiment has the advantage of being especially simple to achieve in terms of production technology. 
     A further particular type of embodiment of the invention is characterized in that recesses, whose dimensions are adapted to the volume of the control chamber, are provided in the end face, remote from the combustion chamber, of the nozzle needle and/or in the opposed face of the injector housing. In order in injector operation to achieve the most linear possible quantity performance graph, it is useful not to embody the nozzle needle stroke purely hydraulically. In a purely hydraulic nozzle needle stroke stop, it can happen that the nozzle needle “floats” on a pressure cushion in the open position. This can cause vibration of the nozzle needle. The vibration in turn leads to nonlinear quantity performance graphs. Since this is a dynamic motion, the result is a greater tolerance dependency. The vibration of the nozzle needle can depend on the inlet throttle and the outflow throttle, the friction of the nozzle needle guide, the control chamber volume, and so forth. In a purely mechanical stop, although vibration of the nozzle needle is indeed avoided, still a somewhat greater control quantity is required for the purpose. This has an unfavorable effect on the efficiency of the injector. The recesses, which can for instance take the form of cross-shaped slots, creates a “semi-hydraulic” stop. The flow cross section that remains upon impact is selected to be precisely large enough that while vibration of the nozzle needle is avoided, still the control quantity at the end stop is lowered as far as possible. In this respect it is advantageous that the injector of the invention has no leakage; that is, without triggering of the injector, no return quantity is generated. 
     A further particular type of embodiment of the invention is characterized in that in the end face, remote from the combustion chamber, of the nozzle needle at least one axial bore is provided, which communicates with at least one radial bore in the nozzle needle. This type of embodiment has the advantage of being insensitive to mechanical running-in; that is, the flow cross section does not change over the service life. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages, characteristics and details of the invention will become apparent from the ensuing description, in which various exemplary embodiments of the invention are described in detail in conjunction with the drawings, in which: 
     FIG. 1 is a fragmentary sectional view of a first exemplary embodiment of the injector with a bore between the nozzle spring chamber and the pressure chamber; 
     FIG. 2 is a view similar to FIG. 1 showing a second exemplary embodiment in longitudinal section through the injector, with a flat face on the nozzle needle between the nozzle spring chamber and the pressure chamber; 
     FIG. 3 shows a further exemplary embodiment in longitudinal section through the injector, with the inlet throttle integrated with the nozzle needle or with the injector housing; 
     FIG. 4 shows a further exemplary embodiment in longitudinal section through the injector, in which the guide diameter is equal to the control diameter; 
     FIG. 5 shows a variant of the exemplary embodiment shown in FIG. 4, with a two-part retaining ring; 
     FIG. 6 is a section taken along the line VI—VI in FIG. 5; 
     FIG. 7 shows a further exemplary embodiment in longitudinal section through the injector with spacer elements for adjusting the nozzle needle stroke and the nozzle spring prestressing force; 
     FIG. 8 shows a further exemplary embodiment in longitudinal section through the injector, with cross-type slots in the end face, remote from the combustion chamber, of the nozzle needle; 
     FIG. 9 shows the end face, remote from the combustion chamber, of the nozzle needle of FIG. 8, in plan view; 
     FIG. 10 shows a further exemplary embodiment in longitudinal section through the injector, with bores in the end face remote from the combustion chamber; and 
     FIG. 11 is a further exemplary embodiment in longitudinal section through the injector, with a groove in the injector housing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The first exemplary embodiment of the injector of the invention, shown in longitudinal section in FIG. 1, has an injector housing identified overall by reference numeral  1 . The injector housing  1  includes a nozzle body  2 , which protrudes with its lower, free end into the combustion chamber of the internal combustion engine to be supplied. With its upper end face, remote from the combustion chamber, the nozzle body  2  is axially braced by a lock nut  5  against a valve body  3  and an injector body  4 . 
     An axial guide bore  6  is recessed out of the nozzle body  2 . A nozzle needle  8  is guided axially displaceably in the guide bore  6 . A sealing face is embodied on the tip  9  of the nozzle needle  8 , and this face cooperates with a sealing seat that is embodied on the nozzle body  2 . When the tip  9  of the nozzle needle  8  is located with its sealing face in contact with the sealing seat, two injection ports  10  and  11  in the nozzle body  2  are closed. When the nozzle needle tip  9  lifts from its seat, fuel subjected to high pressure is injected through the injection ports  10  and  11  into the combustion chamber of the engine. 
     Beginning at the tip  9 , the nozzle needle  8  has three regions of different diameters d 1 , d 2  and d 3 . The diameter d 2  is the largest and serves to guide the nozzle needle  8  in the nozzle body  2 . The diameter d 1  is the smallest. In the portion having the diameter d 1 , a collar  16  with a flat face  17  is embodied on the outer circumferential surface of this portion. The collar  16  forms a second guide for the nozzle needle  8 . By means of the flat face  17  in the collar  16 , a flow connection is made possible in the longitudinal direction of the nozzle needle  8  from one side of the collar  16  to the other. The diameter d 3  is larger than the diameter d 1  but smaller than the diameter d 2 . The diameter d 3  is also the diameter of the control diameter. 
     The nozzle needle  8  is prestressed against the nozzle needle seat in the region of the injection ports  10  and  11  with the aid of a nozzle spring  19 . The nozzle spring  19  is disposed in a nozzle spring chamber  20 , into which a fuel inlet  21  discharges. An arrow  22  indicates that the fuel inlet  21  is supplied from a rail (not shown) with fuel that is subjected to high pressure. Via a bore  23 , the fuel subjected to high pressure flows out of the nozzle spring chamber  20  into a pressure chamber  24 . The pressure chamber  24  communicates with the injection ports  10  and  11  via an annular chamber  25 , when the nozzle needle  8  has lifted from its seat counter to the prestressing force of the nozzle spring  19 . 
     Because of the difference in size between the diameter d 2  and the d 3 , a step is created on the nozzle needle  8 , which forms a stop for a spring plate  26 . Via the spring plate  26 , the prestressing force of the nozzle spring  19  is transmitted to the nozzle needle  8 . The other end of the nozzle spring  19  is braced against a collar  27 , which is embodied on a bush  28 . The inside diameter of the bush  28  is slightly greater than the control diameter d 3  of the nozzle needle  8 . The respective diameters are selected such that the bush  28  is displaceable relative to the nozzle needle  8 , with a sealing effect. As a consequence of the prestressing force of the nozzle spring  19 , the bush  28  is pressed with a biting edge  29  against the valve body  3 . As a result, a control chamber  30 , which is provided in the interior of the bush  28  and is defined by the end face, remote from the combustion chamber, of the nozzle needle  8 , is sealed off from the nozzle spring chamber  20 . 
     The control chamber  30  communicates with the nozzle spring chamber  20  via an inlet throttle  31 . The control chamber  30  furthermore communicates with a relief chamber (not shown) via an outflow throttle  32 . The communication of the control chamber  30  with the relief chamber depends on the position of a control valve member  33 . 
     The injector shown in FIG. 1 functions as follows: 
     Via the fuel inlet  21 , fuel subjected to high pressure reaches the nozzle spring chamber  20 . From there, the fuel subjected to high pressure reaches the control chamber  30  on the one hand, via the inlet throttle  31 , and the pressure chamber  24  on the other, via the bore  23 . The ratios of the diameters are selected in a known way, such that as a consequence of the high pressure in the control chamber  30 , the nozzle needle  8  is located with its tip  9  in contact with the nozzle needle seat. When the control valve member  33  opens, the control chamber  30  is pressure-relieved, and the nozzle needle tip  9  lifts from its seat. Then, fuel subjected to high pressure is injected through the injection ports  10  and  11  into the combustion chamber of the engine until such time as the control valve member  33  closes again. The consequence of that is that the pressure in the control chamber  30  rises again, and the nozzle needle  8  is pressed by its tip  9  back against the associated nozzle needle seat. 
     The second exemplary embodiment, shown in FIG. 2, is quite extensively equivalent to the first exemplary embodiment of the invention shown in FIG.  1 . For the sake of simplicity, the same reference numerals are used to designate identical parts. In addition, to avoid repetition, reference is made to the above description of the first exemplary embodiment. Below, only the distinctions between the two exemplary embodiments will be addressed. The procedure will be analogous for the extensive description of the exemplary embodiments shown in FIGS. 3-11. 
     In the second exemplary embodiment shown in FIG. 2, a connecting bore between the nozzle spring chamber  20  and the pressure chamber  24  is lacking. Instead, a flat face  36  is embodied in the portion of the nozzle needle  8  that has the diameter d 2 . The flat face  36  provides a communication between the nozzle spring chamber  20  and the pressure chamber  24 . Otherwise, there are no distinctions between the two exemplary embodiments. 
     The third exemplary embodiment shown in FIG. 3 differs from the second exemplary embodiment in that the inlet throttle is not disposed in the bush  28 . Reference numeral  38  in FIG. 3 indicates that the inlet throttle can be integrated with the nozzle needle  8  in the form of bores of different orientations and different dimensions. Reference numeral  39  indicates that the inlet throttle can also be integrated with the valve body  3 . 
     In the fourth exemplary embodiment shown in FIG. 4, the spring plate  26  is not braced directly on the nozzle needle  8  but rather only indirectly, via a resilient retaining ring  42  of rectangular cross section. To enable insertion of the retaining ring  42  into a circumferential groove embodied in the nozzle needle  8 , the retaining ring  42  is embodied in split form. 
     In FIGS. 5 and 6, it is shown that instead of a single-part retaining ring that can be clipped on, a two-part retaining ring  46  can also be used. The retaining ring  46  comprises two ring halves, which are placed in the associated groove in the nozzle needle  8  and are fixed with the aid of the spring plate  26 . 
     In the exemplary embodiment shown in FIG. 7, the stroke is not, as in the exemplary embodiment shown in FIG. 1, defined by the spacing H 1  of the end face, remote from the combustion chamber, of the nozzle needle  8  and the opposed face of the valve body  3 , but rather by the spacing H 2  between the bush  28  and the spring plate  26 . It can also be seen in FIG. 7 that the stroke H 2  can be adjusted by means of a spacer disk  51 . To that end, the spacer disk  51  is disposed between the shoulder, which results from the difference in diameter between d 2  and d 3 , and the spring plate  26 . The spring prestressing force of the nozzle spring  19  can also be adjusted with the aid of a spacer disk  50 . To that end, the spacer disk  50  is disposed between the nozzle spring  19  and the collar  27  of the bush  28 . Because of these adjustment capabilities, hydraulic sticking or a complete exertion of pressure on the nozzle needle  8  in the control chamber  30  can be prevented. The result is better closing performance of the injector. 
     In the exemplary embodiments shown in FIGS. 8-11, the nozzle needle stroke is obtained, as in the exemplary embodiment shown in FIG. 1, from the spacing H 1  between the nozzle needle  8  and the valve body  3 . To prevent the nozzle needle  8  in the open position from floating on a pressure cushion, the following proposals are offered: 
     In the exemplary embodiment shown in FIGS. 8 and 9, two grooves  55  and  56  are disposed intersecting one another in the end face  54  of the nozzle needle  8 . As a result, a purely mechanical stop of the nozzle needle is achieved. If the dimensions of the grooves  55  and  56  are adapted to the injector, this can become a “semi-hydraulic stop”. The open cross section that remains in the stop is selected to be precisely large enough that while vibration of the nozzle needle  8  is avoided, still the control quantity at the end stop is lowered as much as possible. 
     In the exemplary embodiment shown in FIG. 10, a throttle bore  58  is disposed, parallel to the longitudinal axis of the nozzle needle  8 , in the end face  54  of the nozzle needle  8 . The throttle bore  58  discharges into a bore  59  that extends transversely to the longitudinal axis of the nozzle needle  8 . The bore  59  is a blind bore, which is open toward frustoconical end, remote from the combustion chamber, of the nozzle needle  8 . This exemplary embodiment has the advantage of being insensitive to mechanical running-in. 
     In the exemplary embodiment shown in FIG. 11, a groove  61  is recessed not in the end face  54  of the nozzle needle  8  remote from the combustion chamber but rather in the opposed face  62  of the valve body  3 . The groove  61  has the same function as the grooves  55  and  56  in the exemplary embodiment shown in FIGS. 8 and 9. 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.