Abstract:
An injector for injection a fuel under high pressure into a combustion chamber of an internal combustion engine, the injector has an injector housing, a control chamber, a primary-side inlet to the control chamber, a control valve which controls the primary-side inlet to the control chamber, a pressure multiplier movable in the injector housing, the pressure multiplier being formed as a two-part piston arrangement.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to injectors with subdivided pressure convertors or multipliers. 
     Injectors are utilized in fuel injection system for injection of fuel under high pressure into combustion chambers of internal combustion engines with direct injection. The injection start and the injection quantity are adjusted with the injectors. The injectors are located at the position of the previously utilized nozzle holder combinations. The injectors can be used without significant modifications of cylinder heads of the internal combustion engines. The injectors can have pressure multipliers, with which a primary pressure at the inlet side can be significantly increased. 
     German patent document DE 198 35 494 A1 discloses a pump-nozzle unit. It supplies the combustion chamber of an internal combustion engine with fuel under high pressure. A pump unit serves for building up an injection pressure, so that the fuel can be injected via an injection nozzle into combustion chamber of an internal combustion engine. Furthermore, a control valve connected with a control unit is provided, which can be formed as an outwardly open A-valve. A valve actuating unit controls the pressure buildup in the pump unit. For providing a pump-nozzle unit with a control unit which has a simple construction, is small and has in particular a short response time, it is proposed to form a valve actuating unit as a piezo-electric actuator. In this pump-nozzle unit, a valve actuating unit is associated with a single-part hydraulic multiplier. It serves in a corresponding design for transmission of a small expansion movement of the actuator into a great valve actuating movement. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an injector with a subdivided pressure convertor or multiplier which is a further improvement of the existing injectors. 
     In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in an injector with a subdivided pressure multiplier in which the pressure multiplier is formed as a two-part piston arrangement. 
     With the inventive two-part design of the pressure multiplier, a simple construction can be provided, so that a cost-favorable production is guaranteed. When the pressure multiplier which is composed of two piston elements, is formed so that a radial play is provided with respect to the opening of the injector housing which receives the piston, then an expensive manufacture of a one-part piston which requires high manufacturing tolerances can be avoided. The subdivision of the piston element into two individual pistons allows, due to a subdivision of the housing which receives the pistons, a cost favorable manufacture both of the individual pistons which operates as a pressure multiplier, as well as two-part housing. 
     The both pistons, of which one piston forms limiting surface of a control chamber in which a control pressure acts, while the other piston extends with an end side into a pressure chamber, are spread or in other words pre-tensioned for making difficult the separation at the contact surfaces by a spring element. It is therefore guaranteed that the pistons do not separate during an axially extending stroke movement. 
     The individual pistons of the piston arrangement are pretensioned relative to one another in an axial direction, to avoid separation of the pistons during the stroke on their contact surfaces. For compensation of mounting tolerances, to the contrary the individual pistons are received with a play relative to one another. In other words the outer individual piston is guided in the upper housing half, while the inner piston is guided in its lower housing half with a plate. Thereby the housing tolerances and manufacturing tolerances of the components are compensated, so that the manufacture of the pressure multiplier together with the housing can be achieved in a substantially most cost-favorable manner. 
     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The single FIGURE of the drawing is a view illustrating an injector with a subdivided pressure multiplier in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An injector in accordance with the present invention has a 3/2-way control valve  3 . The control valve  3  is arranged inside an injector housing  2 . A valve body  7  is movably received in an opening  4  in the injector housing  2 . A inlet  5  is provided in the housing and connected with a high pressure collecting chamber (common rail). The valve body  7  in the region of the inlet  5  is provided with a constriction  6 . 
     The constriction  6  on the valve body  7  extends over a conical region  10 , on which a seat diameter is formed and cooperates with a seat surface  9  provided in the housing. It releases or closes an inlet  12  to a control chamber  13 . The control body  7  is surrounded by a valve chamber  8 , and the valve chamber opens into a leakage oil opening  11  at the side of the injector housing which faces away from the high pressure collecting chamber  5 . 
     An outer piston  14  of a pressure multiplier is received in an opening in the injection housing  2 . It extends with its upper ring-shaped end surface into a control chamber  13  in the injector housing  2 , which can be loaded with a control chamber volume through the above mentioned control chamber inlet  12 . The outer piston  14  as shown in the drawings is cup-shaped and provided with screw-in element  15 . The screw-in element  15  provided with an outer thread  17  can be screwed into the outer piston  14 . For this purpose it is provided with a tool projection  16  which can be formed for example as a hexagonal surface. The screw-in surface element  15  which can be screwed into the outer piston  14  has a ring  19  on its lower end surface  18 . It serves for centering a spring element  20 . 
     The spring element  20  shown in the drawings is formed as a flat spring. It abuts on the one hand against the lower end surface  18  of the screw-in element  15  and abuts with its outer edge regions against the upper end surface  23  of an inner piston  22 . The inner piston  22  abuts with its head region against a ring shaped surface which extends around the lower opening in the outer piston  14 . The spring element  20  received by the lower end surface  18  of the screw-in element  15  and the upper end surface  23  of the inner piston  22  produces a pretensioning between the outer piston  14  and the inner piston  22  in an axial direction. 
     The head region of the inner piston  22  is guided with a radial plate  21  relative to the opening of the outer piston  14 . The plate or gap  25  is provided also between the shaft region  24  of the inner piston  22  and the opening in the bottom of the outer piston  14 . The outer piston  14  is closed substantially by an upper housing half of the injector housing  22 . The shaft  24  of the inner housing  22  substantially extends into a lower housing half of the injector housing  22 . The both housing halves of the injector housing  22  abut against one another along a separation joint  26 . 
     The outer piston  14  abuts at the housing side against a spring element  27  which can be formed for example as a spiral spring. In the illustration of FIG. 1 it is compressed approximately to a blocking length. The spiral spring is supported against a bottom surface  37  provided in the injector housing  2 . A branch  29  extends from the hollow chamber in which the spiral-shaped spring element  27  is supported. It opens into an opening  28  in the lower housing half of the injector housing  22 . A ventilation valve  30  is loaded through it. It fills a pressure chamber  34  with a fuel under high pressure with interposition of a throttle element. 
     The ventilating valve  30  includes substantially a sealing element which is as a spherical body  31  and is pretensioned via a spring element  33 . With the spring element the opening pressure of the sealing body  31  in the ventilation valve  30  can be fixed. With the constant loading of the pressure chamber  34  with fuel under high pressure via the ventilation valve  30  and supply opening  28 , it is guaranteed that a sufficient fuel value is provided in the pressure chamber  34  at all times. With pressure loading of the control chamber  13  through the outer piston  14  which moves downwardly and the positive guidance of the inner piston  22 , a compression by the lower end surface  35  of the inner piston  22  which moves in the pressure chamber  34 . Because of the adjusting pressure increase in the pressure chamber  34 , a fuel volume flows through the nozzle inlet  36  in direction toward the injection nozzle. 
     An axial pretensioning of the outer piston  14  and the inner piston  22  relative to one another can be obtained with the spring element  30  which in the embodiment shown in the drawings is shown as a plate spring. The spring element  20  is adjustable by the screw-in element  15  or its screw-in depth with an outer thread  17  in the outer piston  14 . Also, the spring force can be adjusted by the arrangement of several plate springs, whether in the same direction-or in the opposite direction, between the lower end surface  18  of the screw-in element  15  and the upper end surface  23  of the inner piston  22 . The solution shown in the drawings is characterized first of all in that, the housing tolerances or the pressure multiplier tolerances can be selected in a substantially cost-favorable manner, since with the radial play or gap  21  and  25  provided in the head region of the inner piston or its shaft  24  relative to the outer piston  14 , housing tolerances of a preferably two-part housing can be compensated. The tolerances of the outer piston  14  as well as the inner piston  22  can be selected favorably for the manufacturing process, when the injector housing  2  is formed as two-part housing, whose surfaces abut against one another on the separation joint  26 . 
     In addition to controlling the control chamber volume of the control chamber  13  via the 3/2-way valve  3  in its inlet  12 , the piston arrangement  14 ,  22  or in other words the pressure multiplier also allows to control through the lower chamber in which in the shown embodiment the spring element  27  is received. This can be performed when at the secondary side of the pressure multiplier, or in other words at the end surface  35  of the inner piston  22 , also a control pressure is provided. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in injector with subdivided pressure multiplier, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.