Abstract:
The invention relates to an injector for reservoir (common rail) injection systems for direct-injection internal combustion engines in which a nozzle needle which is surrounded by a nozzle chamber is guided in an injector housing. The inlet of the nozzle chamber is closable and openable via an externally actuatable closing element. From the nozzle inlet, inlets branch off to control parts. The inlets are embodied as throttle elements, one of which is closable on the outlet side via a closing element.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    In direct-injection internal combustion engines, reservoir injection systems (common rail systems) are increasingly being used, and the following demands are made of them: The injection pressure and the injection quantity should be definable independently of one another for every operating point of the direct-injection internal combustion engine, thus affording one additional degree of freedom for mixture formation. In addition, at the onset of injection the injection quantity should be as slight as possible, so that during the ignition delay between the onset of injection and the onset of combustion, not too much fuel will be introduced into the combustion chamber of a direct-injection internal combustion engine. In reservoir (common rail) injection systems with preinjection and main injection and having a modular design, the following components are used: Controlled injectors, which are screwed in in the region of the cylinder head of the engine, pressure reservoir systems, and high-pressure pumps. The injectors communicate with the high-pressure reservoir via short lines and essentially include an injection nozzle and a triggering unit. The injected fuel quantity, for a given pressure, is proportional to the ON time of the actuating unit and is independent of the rpm of the engine and of the pump rpm. The requisite short switching times of the valve actuating units can be attained by designing them appropriately for triggering with high currents and voltages.  
           [0003]    2. Description of the Prior Art  
           [0004]    From German Patent Disclosure DE 198 35 494 A1, a unit fuel injector is known. It serves to deliver fuel to a combustion chamber of direct-injection internal combustion engines with a pump unit for building up an injection pressure and for injecting the fuel via an injection nozzle into the combustion chamber. A control unit with a control valve is also included; the control valve is embodied as an outward-opening A-valve. A valve actuating unit is provided for controlling the pressure buildup in the pump unit. To create a unit fuel injector with a control unit that has a simple design, is small in size, and especially has a short response time, this reference proposes that the valve actuating unit be embodied as a piezoelectric actuator.  
           [0005]    From German Patent DE 37 28 817 C2, a fuel injection pump for an internal combustion engine is known. A control valve member comprises a valve shaft, which forms a guide sleeve and slides in a conduit, and a valve head connected to it and oriented toward the actuating device. The sealing face of the valve head is embodied to cooperate with the face of the control bore that forms the valve seat. The valve shaft, on its circumference, has a recess whose axial length extends from the discharge point of the fuel delivery line to the beginning of the sealing face on the valve head that cooperates with the valve seat. A face subjected to the pressure of the fuel delivery line is embodied in the recess and is equal in size to a face of the valve head that in the closed state of the control valve is exposed to the pressure of the fuel delivery line. As a result, in the closed state the valve is pressure-equalized, and a spring urging the control valve toward its open position is received in the guide sleeve.  
           [0006]    It has been found that in injector designs that are used in reservoir (common rail) injection systems and that execute nozzle needle strokes of only a few tenths of a millimeter, throttle bores cannot be cleanly closed at such short strokes. As a result, unwanted leaks occur in the vertical motion of a control part in an injector housing and adversely affect the efficiency of an injector used in reservoir injection systems.  
         SUMMARY OF THE INVENTION  
         [0007]    With the designed proposed according to the invention of an injector for injecting fuel, which is at high pressure, into the combustion chambers of a direct-injection internal combustion engine, it is possible instead of a 3/2-way valve to use a 2/2-way valve. The incident leakage losses are significantly reduced by splitting the closing or relief throttle into two throttle elements. The reduction in leakage during the injection is achieved by closing the inlet of the second throttle element by means of a valve ring on a valve bolt. The valve ring can be embodied as a component surrounding a control part piston and including a plane end face and a conical jacket face. Both faces are acted upon via spring elements, which can be embodied as spiral springs. The spiral springs can be disposed in hollow chambers inside the injector housing. When the valve ring is moved into an annular chamber in the injector housing, the conical jacket face of the valve ring closes off the second throttle element from the leaking oil outlet. As a result, reduced leakage can be attained, which favorably affects the efficiency of the injector.  
           [0008]    As the nozzle needle moves upward to enable the injection of the fuel into the combustion chambers of a direct-injection internal combustion engine, or in other words during the injection phase, the second throttle element is closed off on the outlet side, so that the pressure from the high-pressure collection chamber (common rail), which prevails in the nozzle inlet, is maximally maintained. Thus the injection pressure course and the injection pressure level can be adhered to as calculated in advance, so that an injection pressure course corresponding to the course of combustion can be achieved.  
           [0009]    The term “injection pressure course” means the varying fuel flow rate during one injection cycle (from the onset to the end of an injection). The course of injection determines the fuel mass pumped during the injection delay between the onset of injection and the onset of combustion. It affects the distribution of fuel in the combustion chamber and thus the air utilization upon combustion in the cylinder of a direct-injection internal combustion engine. The course of injection must rise slowly, so that as little fuel as possible will be injected during the ignition delay. With the onset of combustion, that is, after the development of a complete flame front, this fuel burns fiercely; a term also used is premixed combustion, which adversely affects noise production and NO X  emissions. At the end of combustion, the course of injection must drop off sharply, to prevent poorly atomized fuel in the final phase from causing major emissions of hydrocarbons and soot and increased fuel consumption in the direct-injection internal combustion engine. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0010]    The invention will be described in further detail below in conjunction with the sole drawing figure which shows a longitudinal section through an injector configured according to the invention, whose nozzle needle can be acted upon by a control part piston which in turn is surrounded by a valve ring that closes off a second throttle element. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    The injector  1  shown in FIG. 1 for injecting fuel, which is at high pressure, into the combustion chambers of a direct-injection internal combustion engine includes an injector housing  2 . An inlet  3  arriving from the high-pressure collection chamber (common rail) is let into the injector housing. The discharge point of the inlet  3  from the high-pressure collection chamber is above what in this case is a spherically embodied closing element  5 , which is actuatable via a final control element, whether it is a piezoelectric actuator, an electromagnet, or a hydraulic/mechanical booster. The final control element  4  is designed to be externally actuated.  
         [0012]    The spherically embodied closing element  5  is surrounded by a disklike ring, on which a sealing spring  6  is based. The space surrounding the closing element  5  is equipped with two sealing seat faces  7  and  8 , against which the spherically embodied closing element  5  can be positioned in two positions. If the spherically embodied closing element  5  is placed in the upper seat  7 , then the inlet  3 , arriving from the high-pressure collection chamber, is closed off from the nozzle inlet  9 . From the nozzle inlet  9 , which discharges into a nozzle chamber  12  that surrounds a nozzle needle  13 , two throttle elements  10  and  11  branch off. The first throttle element  10  discharges into the hollow chamber  29  provided in the injector housing, in which chamber a sealing spring  28  is received. The sealing spring  28  is braced by one side on a boundary front of the hollow chamber  29  of the injector housing  2  and by the opposite face end on a platelike element  27 , which is embodied on a control part bolt  19 . From the hollow chamber  29 , a first branch extends into an outlet line  26 , which discharges into the tank of the motor vehicle.  
         [0013]    From the nozzle inlet  9 , a further throttle element  11  extends into an annular chamber  24 , embodied in the injector housing  2  and extending annularly around a valve ring  23 . The control part bolt  19  is surrounded by the valve ring  23 , which includes a plane annular end face on its lower end and in its upper region is equipped with a conically extending jacket face region. The end face of the valve ring  23  is acted upon by a spring element  22 , which is braced on one side on the end face of the valve ring  23  and on the other rests on the end face of a pressure piece  17  on the nozzle needle  13 . The top side, that is, the conically embodied region, of the valve ring  23  is acted upon via a spring  25 , which is braced on an annularly embodied face of the injector housing  2 . The spring element  22 , which rests on the face end of the valve ring  23 , is in turn surrounded by a stop ring  20  received in a hollow chamber  21 . The stop ring  20  serves as a stop face for limiting the pressure piece  17  of the nozzle needle  13 . Upon opening of the nozzle needle  13  or  17  and enabling of the injection at the injection port  16 , the end face of the pressure piece  17  is positioned against the stop ring  20 . Thus the spring element  22 , also acted upon by the end face, is pressed against the valve ring  23 , which is supported displaceably on the control part bolt  19  and which in turn moves into the annular chamber  24  in the injector housing  2  and closes the second outlet to the leaking oil line  26 . Thus the second throttle element  11  in the nozzle inlet  9  is sealed off on the outlet side from a direct short circuit to the leaking oil line  26  via the annular chamber  24 .  
         [0014]    The mode of operation of the injector proposed according to the invention is as follows: Upon actuation of the valve actuating unit  4 , which may be a piezoelectric actuator, electromagnet, or hydraulic/mechanical final control element, the inlet  3  from the high-pressure collection chamber (common rail) to the nozzle inlet is opened. Depending on the dimensioning of the sealing spring  6  that acts on the closing element  5 , which element as designed here is spherical, a fuel flow rate is established in the nozzle inlet  9  into the nozzle chamber  12 . Inside the nozzle chamber  12 , by application of the pressure in the nozzle inlet  9  from the high-pressure collection chamber, the nozzle needle  13  and pressure piece  17  are opened. As a result, by vertical upward motion of the nozzle tip  15  out of its seat face, the injection port  16  is uncovered, and a metered quantity of fuel which is at high pressure can be injected into the combustion chamber of a direct-injection internal combustion engine. When the nozzle needle  13  or the pressure piece  17  moves upward as a result of pressure exerted on the pressure shoulder  14  in the nozzle chamber  12 , the end face of the pressure piece  17  moves into the hollow chamber  21  in the injector housing  2 , far enough that the end face rests on the stop ring  20 . As a result, the control part bolt  19  likewise moves vertically upward, as a result of which the valve ring  23 , received on it, moves into an annular chamber  24  inside the injector housing  2 . By the upward vertical motion of the control part bolt  19 , the sealing spring  28  in the hollow chamber  29  inside the injector housing  2  is compressed, since the spring plate  27  connected to the control part bolt  19  also moves vertically upward into the valve chamber  29 . The valve chamber is acted upon in turn, via the first throttle element  10 , with the fuel at high pressure located in the nozzle inlet  9 , and this fuel is likewise present in the hollow chamber  29  in the injector housing  2 . The fuel at high reinforces the action of the sealing spring  28 , located there, on the plate element  27  of the control part bolt  19 . Upon upward motion of the valve ring  23  into the annular hollow chamber  24  in the injector housing  2 , counter to the action of the sealing spring  25 , a lower branch of a leaking oil line  26  is closed. This prevents a short circuit between the further throttle element  11 , branching off from the nozzle inlet  9 , to the leaking oil line  26  via the annular chamber  24 , so that an outflow of fuel which is at high pressure directly via such a short circuit into the fuel tank of a motor vehicle can be prevented.  
         [0015]    This improves the efficiency of the injector proposed according to the invention considerably. This improvement is attained in that with the nozzle stroke, the valve ring  23  can be moved, which seals off the outlet precisely at the instant when the injection nozzle at the injection port  16  opens out of its seat  15 . The vertical upward motion of the nozzle needle  13  or pressure piece  17 , which is effected via a pressure shoulder  14  between the nozzle needle  13  and the pressure piece  17 , causes the vertical displacement motion of the valve ring  23  that trips the sealing. Upon nozzle closure, that is, when the spherically embodied closing element  5  moves against its upper seat  7  or its lower seat  8 , a pressure relief of the nozzle inlet  9  to the nozzle chamber  12  which surrounds the nozzle needle  13  takes place, initially via the throttle element  11 .  
         [0016]    The high pressure prevailing in the hollow chamber  29  in the injector housing  2 , reinforced by the sealing spring  28 , causes a downward motion of the spring plate  27 , so that the control part bolt  19  and thus the pressure piece  17  and the nozzle needle  13  are pressed into the nozzle needle seat  15 , so that the injection port  16  is closed. With the vertically downward motion of the control part bolt  19 , the conically embodied face on the valve ring  23  moves out of the annular chamber  24  and allows a pressure relief of the nozzle inlet  9  via the annular chamber  24  into the lower is branch of the leaking oil line  26 . The downward motion of the nozzle needle  13  or  17  is effected as a result of the high pressure, still prevailing in the hollow chamber  29 , in the nozzle inlet  9  and the sealing spring  28  received there, on the one hand, and on the other via a pressure relief of the nozzle inlet  9 , effected by the further throttle element  11 , into the leaking oil line  26  via the annular chamber  24 . Leakage that is merely slight can be attained by splitting up the closing throttle (relief throttle) into two throttle elements, since precisely at the instant of injection, the second throttle element  11  on the downstream side is closed by the upward motion of the valve ring  23  into the annular chamber  24  occurring upon opening of the nozzle needle  13  or  17 , the communication between the second throttle element  11  and the leaking oil line  26 , is closed by upward motion of the valve ring  23 . The closing face embodied conically on the valve ring  23  moves into its opposite seat in the injector housing  2  and seals off the annular chamber  24 , so that at this instant, that is, during the injection phase, a leakage loss can now occur only via the first throttle element  10 , which discharges into the hollow chamber  29  provided on the housing.  
         [0017]    The foregoing relates to preferred exemplary embodiment 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.