Abstract:
The present invention relates to a control valve, especially for fuel injection devices for internal combustion engines, preferably diesel engines, with a valve housing within which at least one piston is displaceable and which comprises stops for the piston, wherein at least one of the stops is axially displaceable.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a control valve for fuel injection devices for internal combustion engines, preferably Diesel engines, with a valve housing within which at least one piston is displaceable and which comprises stops for the piston. 
     Today&#39;s internal combustion engines, Diesel engines, in particular, require an injection process consisting of several individual injection actions for a reliable and clean mixture formation within the combustion chamber of the engine. These injection processes are divided into one or more pre-injections, a main injection and, perhaps one or more subsequent injections of the fuel. For producing the pre-injection fuel quantity, a control unit is employed which requires a high-cost electronic control system and which shows energy losses. Frequently, a damper is employed for producing the pre-injection fuel quantity. This damper, however, cannot be fully utilized in each step of the operation and shows severe deviating depending on the operational location. The reason for this is that the switching time of the control hydraulic is too long in the event of small injection quantities due to the design of the control elements and a small pre-injection quantity can, therefore, be produced only with the help of a significant control-technical structural design and expenditure. 
     Therefore, it is an object of the present invention to provide a control valve of the aforementioned kind such that a small pre-injection quantity of fuel can be produced at all operational locations without a high control-technical structural design and expenditure 
     SUMMARY OF THE INVENTION 
     This object is solved by the inventive control valve by providing at least one of the stops to be axially adjustable. 
     With the inventive control valve, at least one of the stops for the piston is axially displaceable. This determines the stroke of the piston and the time period in the respective end positions corresponding to the closed or opened up control valve. Because of the possibility to adjust the stop, the piston stroke can be varied, depending on what the requirements are. Thereby, the smallest injection quantities, particularly for the pre-injection, and, if necessary, also for a subsequent injection, can be precisely controlled in a simple way without negatively affecting the main injection. It is also possible to reduce leakage losses by correspondingly adjusting the position of the stop. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The object and advantages of the present invention will appear more clearly from the following specification in conjunction with the accompanying schematic drawings in which: 
     FIG. 1 shows a longitudinal section of a injection device with an inventive control valve; 
     FIG.  2  and 
     FIG. 3 show an enlarged view of a longitudinal section of the inventive control valve at various valve lift positions; 
     FIG. 4 to 
     FIG. 6 show various embodiments of the control valve at various valve lift positions; 
     FIG.  7  and 
     FIG. 8 show further embodiments of the control valve in simplified illustrations. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with the aid of several specific embodiments utilizing FIGS. 1 through 8. 
     The fuel injection device is utilized in motor vehicles and its purpose is to supply fuel to an internal combustion engine, a Diesel engine, in particular. The fuel injection device has a control piston  1  which is provided in a housing  2 . The pressure medium is supplied to the control piston  1  by a control valve  3  which is connected to a control unit  4 . The control valve  3  is disposed on the housing  2  and projects with a projection  5  of a valve housing/valve body  6  into a recess  7  provided at the end face of the housing  2 . At least one annular seal  8  is provided at the external wall of the projection  5  and seals the projection  5  against the housing  2 . An annular cavity  9  is provided within the projection  5  and is line-connected to working connections A, B of the control valve  3 . The control valve  3  is controlled and monitored by the control unit  4 . Coils  10 ,  11  of the control valve  3  can be supplied with current by means of the control unit  4 . A piston  12  of the control valve  3  is embodied as an anchor and can be displaced by the coils  10 ,  11  in the desired direction. The piston  12  is axially displaceable between two stops  13 ,  14  which are inserted into the end faces of the valve body  6 . 
     If the control valve  3  is closed, the control piston  1  abuts the projection  5  of the valve body  6  under the force of a compression spring  15 . FIG. 1 shows the control piston  1  in its starting position, displaced by the spring  15 , in which an injection valve body  16  of an injection valve  17  closes off nozzle openings  18  by means of which the fuel is fed to the combustion chamber of the internal combustion engine (not illustrated). 
     The control piston  1  is provided with a piston surface  19  which is acted upon by the system pressure p   1   . A central projection  20  is provided in the piston surface  19 . In the starting position, the control piston  1  abuts with the central projection  20  an axial central projection  21  the projection  5 . 
     At its opposite end, the control piston  1  is provided with a recess bore  22  at the bottom surface  23  of which a pressure transferring or intensifying piston  24  abuts. The pressure intensifying piston  24  has a smaller diameter than the control piston  1  and projects into a bore  25  of the housing  2 . The system pressure p   1   is intensified by the pressure intensifying piston  24  creating the larger pressure p   2   which acts on the injection valve  17 . 
     The compression spring  15  abuts the bottom surface of a shoulder  26  at an end of the pressure intensifying piston  24 . The compression spring  15  surrounds the pressure intensifying piston  24  and abuts with its other end the bottom  27  of a bore hole  28  of the housing  2 , whereby this bore hole  28  receives the control piston  1 . 
     When the internal combustion engine is operated the piston  12  of the control valve  3  is displaced by means of the control unit  4  that provides current to the coil  11  such that the hydraulic medium which is fed by a line  29  within the valve body  6  is pressurized. The hydraulic medium reaches the annular cavity  9  and acts with the system pressure p   1   upon the piston surface  19  of the control piston  1 . The recess bore  22  positioned opposite the piston surface  19  is relieved of pressure and is connected to the atmosphere by a bore opening  30  penetrating the housing  2 . Due to this design, the control piston  1  can be displaced against the force of the compression spring  15  by the system pressure p   1   . Thereby, the pressure intensifying piston  24  abutting the bottom surface  23  of the recess bore  22  is also displaced whereby the fuel within the bore  25  is pressed into a bore channel  32  by a fixedly connected distribution plate  31 . The bore channel  32  is provided within an insertion member  33  which is received by a threaded socket member  34 . The threaded socket member  34  is screwed onto the housing  2  and receives the injection valve  17  which projects out of the threaded socket member  34 . The distribution plate  31  is clamped by means of the threaded socket member  34  between the insertion member  33  and the housing  2 . The threaded socket member  34  extends under the insertion member  33  so that the insertion member  33  is pressed in the direction of the housing  2  when the threaded socket member  34  is screwed on. 
     The bore channel  32  extends from the distribution plate  31  through the insertion member  33  to an injection chamber  35  which is provided within the insertion member  33  and which is penetrated by the injection valve body  16 . An axial bore  36  is provided, adjoining the injection chamber  35  and leading to the nozzle openings  18 . The axial bore  36  has a larger diameter than the portion of the injection valve body  16  which projects into the axial bore  36 . The injection valve body  16  projects into a central receiving cavity  37  of the insertion member  33 . The central receiving cavity  37  is closed off at the opposite side by the distribution plate  31 . One end of a second compression spring  38  is supported on the distribution plate  31  and its other end rests on a shoulder member  39 . The shoulder member  39  is provided at the end portion of the injection valve body  16  that is positioned within the central receiving cavity  37  and the shoulder member  39  has a central projection  40  for centering the second compression spring  38 . The injection valve body  16  is axially guided with an enlarged portion  41  within the injection valve  17  and projects with this enlarged portion  41  into the injection chamber  35 . Within the injection chamber  35  the enlarged portion  41  goes over into a thinner end portion  42 . 
     The fuel reaching the injection chamber  35  by passing through the bore channel  32  exerts pressure upon the enlarged valve portion  41 , whereby the injection valve body  16  is pushed back against the force of the second compression spring  38 . The nozzle openings  18  are thus released from the injection valve body  16  so that the fuel can enter the combustion chamber. 
     Subsequent to the injection process, the piston  12  is displaced by activating the control valve  3  by means of the control unit  4 , in such a way as to relieve the pressure in the annular cavity  9  into the tank. A back pressure valve  43  provided within the distribution plate  31  is opened up by the low pressure that is created on the return stroke of the pistons  1 ,  24 , whereby fuel is taken in from a fuel container (not illustrated) through an opening  44  within the threaded socket member  34  and through an adjoining channel  45  within the insertion member  33 . The fuel reaches the bore  25  via the distribution plate  31  so that the fuel can be conveyed to the nozzle openings  18  during the next stroke of the pressure intensifying piston  24  in the manner described. The channel  45  also opens into the central receiving cavity  37  of the insertion member  33 . 
     When the piston  12  of the control valve rests against the stop  13 , the two working connections A, B of the control valve  3  are separated from the line  29  by the piston  12 . The piston  12  takes this position when the two pistons  1 ,  24  are pushed back into the starting position illustrated in FIG. 1 by the spring force in the described manner. The hydraulic medium in the annular cavity  9  is pushed toward the tank connection T via the line connecting the annular cavity  9  and the tank connection T, as is indicated by the flow arrows in FIG.  2 . When the injection process takes place, the piston  12  is displaced to such an extent that it rests against the opposite stop  14 . In this position, the working connections A, B are connected to the line  29  while the tank connection T is separated from the bores leading into the annular cavity  9 . Thereby, the hydraulic medium can enter the annular cavity  9  via the working connections A, B and the bores. 
     The injection process is controlled by the control valve  3  which is a solenoid valve in the illustrated embodiment. However, also other types of valves, for example, piezo valves, can be utilized as control valves. The control valve according to FIGS. 2 to  4  is provided with the opposite stop  14  to be axially adjustable in order to vary the displacement distance of the piston member depending on what the requirements are. A precise control of the injection with respect to timing and quantity is possible by means of the piston stroke. The opposite stop  14  is embodied as an anchor which is surrounded by a valve coil  46  provided within the valve body  6 . The valve coil  46  is connected to the control unit  4 . The opposite stop  14  has a socket portion  47  which is guided to be axially displaceable within a valve bore  48  of the valve body  6 . The socket portion  47  is provided with a radially outwardly facing flange  49  at its end facing away from the piston  12 . 
     In FIG. 2, the opposite stop  14  is positioned such that the piston  12  can perform a large stroke. The piston  12  is displaced in the described manner by the coils  10  or  11  in order to convey the hydraulic medium through the line  29  into the annular cavity  9 , respectively, in order to relieve the annular cavity  9  to the tank. The stop  13  of the control valve  3  is axially fixedly connected to the valve body  6 . 
     FIG. 3 shows the opposite stop  14  in its inwardly displaced position in which it abuts with its flange  49  the end face of the valve body  6 . The socket portion  47  is inwardly displaced into the valve body  6  to such an extent that it is spaced only slightly from the piston  12 . Thus, only a shortened piston stroke is available for the piston  12 . For displacing the opposite stop  14 , the valve coil  46  is provided with current, controlled by the control unit  4 . The control valve  3  can be embodied such that the displaceable opposite stop  14  is continuously displaceable relative to the piston  12 . 
     FIGS. 2 to  4  show the valve position in its opened stage. A varying opening diameter can be achieved by varying the position of the opposite stop  14  so that the valve can be excellently adjusted to the various requirements of pre-injection, main injection and subsequent injection. Furthermore, the response time of the control valve  3  is reduced by a shorter valve lift; this is also advantageous with respect to an improved control of the fuel amounts. 
     FIG. 5 shows a closed position of the control valve  3 . Also in this closed position of the control valve  3 , the position of the piston  12  can be changed. For this purpose, the stop  13  can be displaced by a coil  50  which is arranged in the valve body  6  and is also connected to the control unit  4 . The stop  13  is also provided with a socket portion  51  having a radially outwardly facing flange  52  at one end face. By supplying the coil  50  with current, this stop  13  can be displaced into any desired position. The stop  13  can, for example, be shifted into a position in which the piston  12  creates a larger overlap of the valve control edges, thereby achieving a reduction of oil leakage. In order to avoid that the fuel injection is affected, the stop  13  can be displaced outwardly into its original position shortly before the injection starts. 
     In order to shift the piston  12  into different positions when the control valve  3  is closed off, only the stop  13  is provided to be axially displaceable. In contrast to the previous embodiment, the opposite stop  14  is fixedly connected; thus its position cannot be changed. In the resting position of the piston  12  and when the control valve  3  is closed off, the piston  12  is positioned at a distance from the opposite stop  14  so that the piston  12  can be displaced for the injection process into the direction of the opposite stop  14  to the extent desired by supplying the coils  10  or  11  with current. 
     As is shown in FIG. 6, it is also possible, however, to provide both stops  13 ,  14  to be axially displaceable. In that event, the valve body  6  is provided with the two coils  46  and  50  by which the stops  13 ,  14  can be displaced to the desired extent. In this embodiment, a combination of the variation of the piston stop is, therefore, ensured when the control valve  3  is opened and when it is closed. 
     FIG. 7 shows a schematic view of a portion of the piston  12  of the control valve  3 . A position of the piston  12  is illustrated in which it exposes an opening cross section  53  (hatched area) of a bore. This bore is provided with a constant width in the displacing direction  54  of the piston  12  so that the opening cross section  53  is constantly enlarged when the piston  12  is displaced. In such an embodiment, it is not possible to influence the travel-volume characteristic line of the control valve  3 . 
     FIG. 8 illustrates the possibility to influence this characteristic line by a particular special design of the bore. It has a T-shaped cross section. If the piston  12  is located in the position illustrated in FIG. 8, it overlaps the wider portion  55  of the bore and only exposes the narrower opening cross section  56  (hatched area). Thereby, only a small quantity of hydraulic medium is initially conveyed. As soon as the control edge  57  of the piston  12  reaches the area of the significantly wider portion  55 , the flow quantity of the hydraulic medium is immediately increased. 
     With the control valves  3  described herein, a control of the smallest injection quantities for the pre-injection and, if provided for, also for a subsequent injection is possible without having a negative impact on the main injection. By displacing the piston  12  when the control valve  3  is closed, leakage losses can be reduced. The stops can be adjusted irrespective of the type of valve employed. The stops can be continuously adjusted to reach any desired position so that the control valve  3  can be designed according to the most different requirements. The control valve described herein can be utilized in any area in which varying opening cross sections are required, e.g., in adjustment devices for cam shafts. 
     The specification incorporates by reference the disclosure of German priority document 199 16 658.7 of Apr. 14, 1999. 
     The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.