Abstract:
A plug assembly is provided for a high-pressure valve of the type with a tubular body extending along a longitudinal axis and in which, under the action of a piloted actuator, a needle moves longitudinally between a closed position and an open position. The plug assembly includes a plug having a flat part able to be fixed onto the body transversally to the longitudinal axis, and a spring intended to apply to the needle a force biasing it axially towards the closed position. The spring is fixed to the plug forming with it an integrated assembly.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a high-pressure valve for a diesel injection circuit and more particularly to the process of assembling such a valve. 
       TECHNOLOGICAL BACKGROUND OF THE INVENTION 
       [0002]    Circuits for direct fuel injection in internal combustion engines include a pilot operated valve which can be directly connected to a common rail distributing the pressurised fuel to injectors. The valve is normally closed and can be actuated to open a passage and allow egress of the fuel thus allowing the pressure in the injection circuit to be constantly controlled. 
         [0003]    Valves are known inter alia comprising a tubular body in which a needle piloted by an electromagnetic actuator obturates or opens the fuel outlet passage. On the opposite side to the passage, a plug is welded to the body and closes it in sealed manner. In normal operation the passage is closed and its closure is ensured by the piloted actuator which applies a closing force to the needle opposing the opening force applied to the needle by the pressurised fuel. It has proved necessary to ensure the closure of the passage in case of malfunction of the actuator for any reason. A compression spring has therefore been arranged in the body, on the opposite side to the passage, the spring permanently acting between the plug and the needle applying to the latter a force for closure of the passage. The spring is calculated so that in case of malfunction of the actuator, the force applied by the spring is sufficient to overcome the opening force applied by the fuel, and thus the pressurised fuel continues to supply the injectors. Valves are known inter alia in which the needle is attached to the magnetic core of the actuator, the spring being compressed between the plug and the said core. 
         [0004]    When the valves are assembled, the multiple components must be handled individually and placed in position one after the other. Inter alia, the assembly of the spring and the holding of it in place between the core, the body and the plug is a source of considerable difficulties and requires a large assembly cycle time. 
         [0005]    It has become an urgent matter to facilitate the assembly of the valves and reduce the time necessary for it. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention resolves the problem mentioned above by proposing a plug assembly for a high-pressure valve forming part of the common rail injection circuit of an internal combustion engine. The valve is of the type with a tubular body extending along a longitudinal axis and in which, under the action of a piloted actuator, a needle moves longitudinally between a closed position and an open position. The plug assembly comprises a plug having a flat part able to be fixed onto the body transversally to the longitudinal axis, and a spring intended to apply to the needle a force biasing it axially towards the closed position. Moreover, the spring is advantageously fixed to the plug forming with it an easily handled integrated assembly. In addition the plug includes an annular protuberance which extends axially from the flat part so as to form a bearing intended for longitudinal guidance of the needle. The spring is fixed onto the annular protuberance. 
         [0007]    The spring is preferably of the helical type and the annular protuberance includes a first jamming section the external diameter of which is slightly greater than the internal diameter of the spring. Thus the spring is fixed by jamming of a turn of the spring around the jamming section. The jamming section is arranged at the base of the protuberance close to the flat part of the plug. The annular protuberance includes a second guiding section which extends beyond the jamming section and the external diameter of which is less than the internal diameter of the spring. Thus, during assembly, the second guiding section acts as a guide for the spring, without hampering the movements of the spring during compression and expansion phases. 
         [0008]    The guiding section and the jamming section can be formed by a surface in the form of a truncated cone which has the advantage of facilitating the placing in position of the spring during assembly. The protuberance is formed in one piece with the plug. 
         [0009]    Alternatively, the spring can be fixed to the plug by welding or sticking or any other means in particular using an intermediate piece such as a flange. This fixing method can be selected to replace or be added to the jamming method described above. 
         [0010]    In addition, the plug is provided with a tubular jacket extending axially from the circumference of the flat part to a distal end. The plug is able to be fixed to the body at this distal end. Thus, the plug defines an internal space able to house and guide a movable part of the piloted actuator such as the magnetic core of an electromagnet. 
         [0011]    The invention also relates to a high-pressure valve forming part of the common rail injection circuit of an internal combustion engine. The valve comprises a tubular body, a passage known as low-pressure, for the fuel being formed at a first end of the body. A needle is arranged axially in the body and is displaced under the action of a piloted actuator between an open position of the passage and a closed position of the passage, The valve comprises in addition a plug assembly in accordance with the description above. The plug is fixed to a second end of the body opposite to the first end and the spring is arranged between the plug and the needle and applies to the latter a force biasing it towards the closed position. 
         [0012]    The invention lastly relates to a process for assembly of a high-pressure valve intended to be part of the common rail injection circuit of an internal combustion engine. The process comprises the following steps:
   providing a tubular body extending along a longitudinal axis, a passage being formed at one end of the body,   providing a needle and a piloted actuator,   providing a plug having a flat part able to be fixed onto the body transversally to the axis of the body, the plug being provided with a bearing intended to guide the needle along the longitudinal axis,   providing a spring,   arranging the needle and the piloted actuator in the body,   fixing the spring to the plug so as to form an integrated plug assembly in accordance with the preceding description. This step of the process can advantageously be performed in parallel with the other steps which saves time. In addition the handling of the plug assembly is facilitated by means of this step of the process.   arranging the plug assembly so that the spring applies a force to the needle,   fixing the plug assembly to the body.   
 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0021]    An embodiment of the invention is now described by means of the following figures. 
           [0022]      FIG. 1  is a view in axial section of a high-pressure valve in accordance with the invention. 
           [0023]      FIG. 2  is a detail of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]      FIG. 1  shows a valve  10  arranged at the end of the common rail  11  of a high-pressure direct injection circuit fitted to an internal combustion engine. The valve  10  comprises a cylindrical and tubular body  12  extending along a longitudinal axis A. A needle  14  is arranged in the body  12  and can be displaced in it along the longitudinal axis A. The displacements of the needle  14  are controlled by an electromagnetic actuator  16  the core  18  of which is attached to the needle  14 . A weld, or any other permanent fixing means can be used to attach the needle  14  and the core  18  together. The needle  14  extends between a first end  20 , here shown pointed and to the left in  FIG. 1 , and a second end  22  shown flat. The first end  20  cooperates with a seat  24  attached to the body  12 , the seat  24  being provided with a central hole. When the actuator  16  forces the needle  14  so that the first end  20  is in circumferential contact with the seat  24 , the fuel under high pressure circulates in the rail  11  towards the injectors not shown, the valve being in a closed state. Conversely when the actuator  16  causes the needle  14  to be displaced distancing the first end  20  from the seat  24 , then the pressurised fuel in the rail  11  leaves the rail  11  through the central hole of the seat  24  and reaches a low-pressure outlet passage BP. The valve  10  has switched from the closed state to the open state. Many constructions exist to produce this cooperation between the needle  14  and the seat  24  for the closure of the valve  10 . In particular the addition is known of a ball between the first end  20 , the ball being of a sufficient diameter to plug the central hole of the seat  24  without passing it or jamming in it. It will be understood moreover that when the valve  10  is in the closed state the pressurised fuel in the rail  11  applies to the needle  14  a force which tends to repel it and open the low-pressure outlet BP. On the opposite side to the seat  24 , on the side of the second end  22  of the needle  14 , the body  12  is closed in sealed manner by a plug  26 . The plug  26  is permanently fixed to the body  12 . This fixing effected by welding can also be effected by other means. The plug  26  includes a flat part  27  the inner face  28  of which turned towards the body  12 , which face is called the inner face  28 , is transversal to the axis A of the body  12 . At the centre of the inner face  28  axially extends a protuberance  30  provided with an outer face  32  and with a hollow housing the internal face of revolution  34  of which forms a bearing for guiding the second end  22  of the needle  14  which can slide in it along the longitudinal axis A. 
         [0025]    As shown in the Figures, the plug  26  comprises a cylindrical jacket  29  which extends axially from the peripheral circumference of the flat part  27 . The plug  26  is fixed to the body  12  by welding at the end of the jacket  29 . Thus placed in position and fixed to the body  12 , the plug  26  defines an internal volume in which the core  18  is housed and displaced axially. Alternatively to this construction of a plug provided with a jacket, the jacket can be associated with the body, the plug only comprising the flat part. 
         [0026]    To ensure that in the case of malfunction of the actuator  16  the valve  10  remains in the closed state and the low-pressure outlet passage BP remains obturated by the first end  20  of the needle  14 , a helical spring  36  is compressed between the inner face  28  of the plug  26  and the core  18  of the actuator  16 . Thus arranged the spring  36  constantly applies to the needle  14 , via the core  18 , a closing force which biases the needle  14  so as to keep the valve  10  in the closed state. The spring  36  is so dimensioned that the closing force applied to the needle  14  is greater than the opening force applied to this same needle  14 , but in the opposite direction to the closing force, by the pressurised fuel. The valve  10  is therefore kept in the closed state even in case of malfunction of the actuator  16 . 
         [0027]    In order to facilitate the assembly of the valve  10 , the outer face  32  of the protuberance  30  includes a base section  38  situated at the junction with the inner face  28  and a guiding section  40 . The base section  38  is cylindrical of revolution of a diameter slightly greater than the internal diameter of the last turn  42  of the spring  36 . Conversely the guiding section  40  is of a diameter less than the internal diameter of the spring  36 . 
         [0028]    Thus, on assembly of the valve  10 , the spring  36  is easily fixed to the plug  26  by firstly slipping it around the guiding section  40  until the last turn  42  is jammed around the base section  38 . The plug  26  and the spring  36  thus form an integrated plug assembly  44  which is very easy to handle. 
         [0029]    Many modified embodiments of the plug assembly  44  can be created by giving various methods of fixing the spring  36  to the plug  26 . The base  38  and guiding  40  sections detailed in  FIG. 2  are cylindrical of revolution and joined one to the other by an intermediate surface in the form of a truncated cone. They could also only form a single surface slightly in the form of a truncated cone, wider at the base than at the top. Also the protuberance  30  could have no guiding section and only comprise a base section  38  for jamming the spring  36 . The protuberance  30  shown here and described as being of complete revolution could be formed of a plurality of separate sections together forming the guiding bearing and the jamming base. 
         [0030]    The jamming and guiding of the spring  36  have been described as interior to the spring. A plug  26  could be envisaged not provided with a protuberance but with a hollow housing in which the spring jams by its external diameter, the guiding, if it is present being able to be interior or exterior to the spring. 
         [0031]    Lastly, fixing of the spring  36  by means of welding or sticking could also be envisaged.