Abstract:
The invention relates to a unit injector system for internal combustion engines, in particular diesel engines, having a pump element for subjecting fuel in a pump chamber to high pressure, having an injection element for injecting the pressurized fuel into the combustion chamber of the engine, and having a control valve, which opens and closes a connection between the pump chamber and a low-pressure chamber. To make a preinjection possible, a throttle device ( 13 ) is disposed in the connection between the pump chamber and the low-pressure chamber, and there is a flow through the throttle device as a function of the position of the control valve.

Description:
FIELD OF THE INVENTION 
     This invention relates to a unit injector system for internal combustion engines, and more particularly to such a system for diesel engines having a pump element for subjecting fuel in a pump chamber to high pressure, an injection element for injecting the pressurized fuel into the combustion chamber of the engine, and a control valve which opens and closes a connection between the pump chamber and a low-pressure chamber. 
     BACKGROUND OF THE INVENTION 
     One such unit injector system, or UIS for short, is described in German Patent Disclosure DE 198 35 494, which had not been published by the priority date of the present application. In a UIS, the pump element and the injection element form a unit, and one such unit is typically built into each cylinder head of the engine. The drive of the UIS is done either via a tappet or indirectly from the camshaft via rockers. 
     A 2/2-way valve can be used as the control valve. In the first position of the 2/2-way valve, the connection between the pump chamber and the low-pressure chamber is open. Then filling of the pump chamber is possible during the intake stroke, and during the pumping stroke a return flow of fuel to the low-pressure chamber is possible. In the second position of the 2/2-way valve, the connection between the pump chamber and the low-pressure chamber is interrupted. Then, the pressure required for injecting the fuel is built up in the pump chamber. Once the pressure exceeds a predetermined opening pressure, the injection element opens, and the pressurized fuel is injected into the engine combustion chamber. The closing time of the control valve thus determines the injection onset. The injection quantity depends on the closing duration of the control valve. To reduce fuel consumption and pollutants, a so-called preinjection of a slight fuel quantity can be performed before the actual main injection. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to furnish a unit injector system of the type described at the outset, with preinjection, that is simple in structure and can be produced economically. 
     In a unit injector system for internal combustion engines, in particular diesel engines, having a pump element for subjecting fuel in a pump chamber to high pressure, having an injection element for injecting the pressurized fuel into the combustion chamber of the engine, and having a control valve, which opens and closes a connection between the pump chamber and a low-pressure chamber, this object is attained in that a throttle device is disposed in the connection between the pump chamber and the low-pressure chamber, and there is a flow through the throttle device as a function of the position of the control valve. 
     The throttle limits the fuel quantity that flows through the connection between the pump chamber and the low-pressure chamber and thus in a simple way makes it possible to define a preinjection. 
     One embodiment of the invention is characterized in that the control valve includes a first valve body with a first valve seat face and a second valve body with a second valve seat face, which are received, capable of reciprocation, in a housing. The cooperation of the two valve bodies enables a precise setting of different strokes of the valve bodies. 
     A further embodiment of the invention is characterized in that the control valve is a 3/3-way valve. In the first position of the 3/3-way valve, the connection between the pump chamber and the low-pressure chamber is interrupted. In the second position of the 3/3-way valve, because of the throttle device, less fuel flows through the connection between the pump chamber and the low-pressure chamber than in the third valve position. The lesser fuel quantity is used for the preinjection. In the third position of the 3/3-way valve, a connection, provided parallel to the throttle device, to the low-pressure chamber enables normal filling of the pump chamber. 
     A further embodiment of the invention is characterized in that in a first valve position, the first valve body is spaced apart from the second valve body, and both the first valve body having the first valve seat face and the second valve body having the second valve seat face rest on their associated valve seat edges, as a result of which the connection between the pump chamber and a low-pressure chamber is closed; 
     that in a second valve position, the first valve body comes to rest on the second valve body, and the first valve body having the first valve seat face lifts from its associated valve seat edge, as a result of which fuel can flow to a throttle in the second valve body, which throttle communicates with the low-pressure chamber; 
     and that in a third valve position, the second valve body comes to rest on a stroke end stop, and both the first valve body having the first valve seat face and the second valve body having the second valve seat face are lifted from their associated valve seat edges, as a result of which a connection without a throttle is opened up to the low-pressure chamber. The first valve body can be kept in contact, with the first valve seat face, on the associated valve seat edge by a first valve closing spring. The actuation of the first valve body can be done by means of a magnet or a piezoelectric actuator. The second valve body can be kept in contact, with the second valve seat face, on the associated valve seat edge by means of a second valve closing spring. As a result, it is assured that in the unactuated state, the control valve is closed. 
     A further embodiment of the invention is characterized in that a groove is recessed out of the end face, toward the second valve body, of the first valve body. The groove assures that fuel can reach the throttle in the second valve body when the two valve bodies are in contact with one another. 
     A further embodiment of the invention is characterized in that a groove is embodied on the stroke end stop. The groove prevents the formation of a pressure cushion during operation between the second valve body and the stroke end stop, that could unfavorably affect the injection performance. 
     A further embodiment of the invention is characterized in that the control valve is a 2/3-way valve. In the first position of the 2/3-way valve, the connection between the pump chamber and the low-pressure chamber is interrupted. In the first position of the 2/3-way valve, the connection between the pump chamber and the low-pressure chamber is interrupted. In the second position of the 2/3-way valve, because of the throttle device, less fuel flows through the connection between the pump chamber and the low-pressure chamber than in the third valve position. The lesser fuel quantity is used for the preinjection. In the third position of the 2/3-way valve, a connection, provided parallel to the throttle device, to the low-pressure chamber enables normal filling of the pump chamber. 
     A further embodiment of the invention is characterized in that the first valve body has a central bore, in which part of the second valve body is displaceably received; 
     that in a first valve position, the first valve body is spaced apart from a stroke stop on the second valve body, and both the first valve body having the first valve seat face and the second valve body having the second valve seat face rest on their associated valve seat edges, as a result of which the connection between the pump chamber and the low-pressure chamber is closed; 
     that in a second valve position, the first valve body comes to rest on the stroke stop of the second valve body, and the first valve body having the first valve seat face lifts from its associated valve seat edge, as a result of which fuel can flow to a throttle in the second valve body, which throttle communicates with the low-pressure chamber; 
     and that in a third valve position, the second valve body comes to rest on a stroke end stop, and both the first valve body having the first valve seat face and the second valve body having the second valve seat face are lifted from their associated valve seat edges, as a result of which a connection to the low-pressure chamber without a throttle is opened up. The first valve body can be kept in contact, with the first valve seat face, on the associated valve seat edge by a first valve closing spring. The actuation of the first valve body can be done by means of a magnet or a piezoelectric actuator. The second valve body can be kept in contact, with the second valve seat face, on the associated valve seat edge by means of a second valve closing spring. As a result, it is assured that in the unactuated state, the control valve is closed. 
     A further embodiment of the invention is characterized in that the second valve body in the built-in state is substantially balanced in terms of force. As a result, it is attained that a closing spring of small dimensions can be used for the second valve body. 
     A further embodiment of the invention is characterized in that the throttle has a constant flow diameter. The throttle can be manufactured as an independent component with high precision. As a result, it is possible to achieve a preinjection quantity with highly accurate replicability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings, in which: 
     FIG. 1 is a sectional view of a control valve in a first embodiment of the invention; and 
     FIG. 2 is a sectional view of a control valve in a second embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, the control valve of a unit injector system according to the invention is shown in section. The unit injector system is used to deliver fuel to the combustion chamber of direct-injection internal combustion engines. The unit injector system includes a pump element for building up the injection pressure and an injection nozzle for injecting the fuel into the combustion chamber. The course of injection is controlled by the control valve. 
     The control valve shown in FIG. 1 includes a valve housing  1 , and a bore  2  is recessed out of the valve housing  1 . Discharging into the bore  2  is a connecting conduit  3  to the pump chamber (not shown), where the injection pressure is built up. A first connecting conduit  4  and a second connecting conduit  5  also extend from the bore  2  in the valve housing  1  to a low-pressure chamber (not shown). In the intake stroke, fuel from the low-pressure chamber reaches the pump chamber. In the pumping stroke, the low-pressure chamber serves to receive returning fuel and leakage. The low-pressure pressure chamber can for instance be a line system that communicates with a fuel tank. 
     A first valve body  6  is received, in a manner capable of reciprocation, in the bore  2  in the valve housing  1 , in the region where the connecting conduit  3  discharges into the pump chamber. On the first valve body  6 , a first valve seat face  7  is formed, which is in contact with a first valve seat edge  8  that is embodied in the valve housing  1 . One end  9  of the first valve body  6  is shown in cutaway form. The end  9 , shown cut away, of the first valve body  6  is coupled with an actuating device (not shown). The actuating device can for instance be a magnet or a piezoelectric actuator. A groove  10  is formed in the end face on the other end of the first valve body  6 . 
     The first valve body  6  is spaced apart with its free end from a second valve body  11  by a spacing or stroke h 1 . A second valve seat face  17  is embodied on the second valve body  11 ; it is in contact with a second valve seat edge  18  that is embodied in the valve housing  1 . The second valve body  11  furthermore has a central through bore  12 , in which a throttle  13  is embodied. The second valve body  11  is kept in contact with the second valve seat edge  18  by a closing spring  14 . A stroke end stop  15  with a groove  16  is spaced apart from one end face of the second valve body  11  by a spacing or stroke h 2 . 
     The position shown in FIG. 1 of the control valve according to the invention will be called the first switching position. In the first switching position, the connection between the pump chamber and the low-pressure chamber is interrupted. When the first valve body  6  is moved by the stroke h 1 , for instance by magnet actuation, and put into contact with the second valve body  11 , the first valve seat face  7  lifts from the associated first valve seat edge  8 . The position, not shown in FIG. 1, of the control valve of the invention will be called the second switching position. In the second switching position of the control valve, a connection between the low-pressure chamber and the pump chamber is opened up via the connecting conduit  3 , the groove  10 , the through bore  12 , the throttle  13 , and the second connecting conduit  5 . 
     When the first valve body  6  together with the second valve body  11  is moved onward by the stroke h 2 , the second valve seat face  17  now also lifts up from the associated second valve seat edge  18 . This position of the control valve of the invention will be called the third switching position. In the third switching position, an additional connection is opened between the low-pressure chamber and the pump chamber, via the connecting conduit  3  and the first connecting conduit  4 . 
     In the first switching position of the control valve according to the invention, the connection between the pump chamber and the low-pressure chamber is interrupted and the main injection takes place. In the second switching position of the control valve of the invention, the fuel flows through the throttle  13 , and a so-called preinjection is effected. 
     In FIG. 2, a second embodiment of a control valve of a unit injector system according to the invention is shown in section. The control valve has a valve housing  21 . A bore  22  is recessed out of the valve housing  21 . Discharging into the bore  22  are a connecting conduit  23  to the pump chamber and a connecting conduit  24  to the low-pressure chamber of the unit injector system of the invention. In the region where the connecting conduit  23  discharges into the pump chamber, a first valve body  26  is received, in a manner capable of reciprocation, in the bore  22 . On the first valve body  26 , a first valve seat face  27  is embodied, which is in contact with a first valve seat edge  28  embodied in the valve housing  21 . An end  29 , shown cut away, of the first valve body  26  is actuated by a magnet. A central bore is recessed out of the first valve body  26 . The central bore in the valve body  26  includes one bore segment  30  with a large diameter and one bore segment  39  with a small diameter. The bore segment  39  with the small diameter is used for removing leaking fuel. The bore segment  30  with the large diameter is used for receiving a portion of a second valve body  31  in a manner capable of reciprocation. On the second valve body  31 , there is a second valve seat face  37 , which is in contact with a second valve seat edge  38  in the valve housing  21 . A central longitudinal bore  32 , which discharges into a transverse bore  40 , is disposed in the end of the second valve body  31  facing away from the first valve body  26 . 
     The position shown in FIG. 2 of the control valve of the invention will be called the first switching position. In the first switching position, the connection between the low-pressure chamber and the pump chamber is interrupted. When the first valve body  26  is moved toward the second valve body  31  by a stroke h 1 , the first valve seat face  27  lifts away from the first valve seat edge  28 , and a flow course is opened up from the connecting conduit  23 , past the first valve seat face  27 , through the transverse bore  40  and the longitudinal bore  32  in the second valve body  31 , to the connecting conduit  24  to the low-pressure chamber. A throttle  33 , which assures that a so-called preinjection occurs, is embodied in the longitudinal bore  32  in the second valve body  31 . When the first valve body  26  together with the second valve body  31  is moved by a stroke h 2  as far as a stroke end stop  35 , counter to the prestressing force of a closing spring  34 , the second valve seat face  37  lifts away from the associated valve seat edge  38  as well. A connection between the connecting conduit  23  to the pump chamber and the connecting conduit  24  to the low-pressure chamber is then opened up, which bypasses the throttle  33  in the second valve body  31 . 
     By the introduction of the supplementary throttle  13 ,  33 , it is possible in the case of short strokes to define a preinjection with highly accurate replicability from one UIS to another. 
     In FIGS. 1 and 2, the strokes h 1 , and h 2  are shown larger than in reality, for the sake of clarity. In actuality, the strokes h 1 , and h 2  are markedly shorter. 
     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.