FR2750172A1 - ELECTROMAGNETIC INJECTOR FOR INTERNAL COMBUSTION ENGINES - Google Patents

Abstract

On the rear end of an injector needle act, on the one hand, a control piston subjected to the pressure of the fuel in a control chamber and, on the other hand, a needle closing spring. The other end of the closing spring (17) rests directly on the control piston (3) or on an intermediate element which can be connected to this piston. The closing spring (17) has a position and / or a length such that its effect is suppressed in the open state of the injector needle (11) by the direct application of the control piston (3) against the barrel (10) of the needle. Applicable in particular to fuel injection systems having a high pressure distribution rail.

Description

The invention relates to an injector for internal combustion engines,

  comprising an injector needle, an electromagnet-controlled valve, a control chamber connected to an inlet pipe for pressurized fuel and, when the valve is open, to a pressure relief pipe, the pressure fuel in the control chamber acting via a control piston on the rear end of the injector needle, together with a needle closing spring, which allows the application of the needle against a valve seat of the injector, the needle closing spring pressing, at one end, directly

  on the rear end of the injector needle or on an in-

  intermediate in connection with this needle.

  An injector of this type is described in European Patent Application 0 615 064 A1. It is also called "injector fed from a common rail injector" ("common rail injector"). This

  injector is also exposed to high pressure in the resting state, that is,

  ie in the state where the injector needle is closed and a fuel injection does not take place. The needle is then held in the closed position by the needle spring on the one hand and by the application of pressure to a control chamber communicating with the inlet pipe under high pressure on the other hand. When the engine is stopped and there is no more high pressure in the system, the needle spring alone holds the needle in the closed position, which prevents fuel from entering the cylinder. During operation, ie when fuel is to be injected, the activation of an electromagnet results in the control chamber being connected to a pressure relief line. Due to the prefixed relationships of pressures and diameters, the high pressure produces the opening of the injector needle against

  the closing force of the needle spring.

  In the case of the injector according to the European patent application 0 615 064, the needle closing spring is supported by one end on the rear end of the needle, while it is supported by its other end on a fixed part of the body of the injector. This known injector has the disadvantage that the needle closing spring acts not only in the idle state of the injector, but also during operation and that, as a result, it is permanently subjected to a dynamic solicitation. . This means that the spring is subject to increased sensitivity to disturbances,

  for example as a result of wear, and a reduction in its service life.

  before going to break the spring. Another disadvantage is that the vibrations of the spring can occur during operation, which modifies the behavior accordingly.

fuel supply.

  German Patent Application 38 24 467 A1 discloses an injector

  for large engines and having a closing spring which can be pre-

  constrained more or less by different pistons. Two pistons are provided for this purpose. This injector does not relate to a distribution ramp system. The injector needle is held in the closed position by a spring. In addition, several injection ports are provided, which can

  be put into action independently, in a targeted way.

  German Patent 38 11 885 C2 discloses an injection device which pre-injects and injects and has a spring-loaded piston. This device is as a whole of another construction and does not relate to a system with a distribution ramp. Patent Application 41 15 103 A1 describes an injection device comprising a high pressure pump according to a distribution ramp system. This injector does not have a closing piston or

  command. Its function is ensured by the barrel of the injector needle.

  The object of the invention is to create an injector, of the type mentioned at the beginning, whose construction is simpler and which is especially less

sensitive to disturbances.

  According to the invention, this result is achieved by the fact that the needle closing spring is supported by its other end directly on the control piston or on an intermediate element which can be connected to this piston. Needle closure

  a position and / or length such that it is "short-circuited", that is,

  to say that the effect of this spring is suppressed, in the open state of the needle of

  ejector. Thanks to the arrangement and the embodiment according to the invention of the needle closing spring, this spring is ineffective, therefore not subjected to dynamic stresses, to the operating state, that is to say when the injector needle is open and fuel is injected into the coordinated cylinder. Because the needle closing spring

  is then "short-circuited", the control piston acts directly, mechanically

  only on the injector needle. The needle closing spring according to the invention is practically used only, or between only in function, when necessary, namely in the idle state of the injector, in order to prevent the flow of fuel. in the cylinder. In all other cases, that is to say when a pressure reigns in the system, it is immobile. Another advantage of the solution according to the invention is that, with this embodiment of the injector, a relatively short overall length is obtained because the needle closing spring is arranged, take up little space, between the piston control and the injector needle. Compared with solutions according to the state of the art, the solution according to the invention also eliminates sealing surfaces and provides a simple construction of the injector, which

  leads to a corresponding cost saving.

  An embodiment of the invention provides for at least one guiding element to be placed between the control piston and the injector needle, which element is made as a guide for the needle closing spring, the guiding element being connected to the piston of

  command or injector needle.

  Other features and advantages of the invention will emerge

  more clearly from the following description of several examples not

  and in the accompanying drawing, in which: - Figure 1 is a schematic axial section of an injector according to the invention; FIG. 2 shows a detail of an injector with a different disposition of the needle closing spring; and FIG. 3 shows a detail of an injector presenting a

  third arrangement of the needle closing spring.

  The injector whose description will follow has a structure and

  a mode of operation whose principles are known (see for example the European patent application 0 615 064 A1), reason why only the essential parts of the invention will be described in more detail. The injector comprises an injector body 1 in which is formed an inlet channel 2 connected under high pressure to a ramp system of

  common distribution. A bore of the injector body 1 contains a pis-

  control tone 3 behind which is a control chamber 4. This chamber is connected by a branch pipe 2a containing

  a throttling point 5, at the fuel inlet under high pressure.

  The control chamber 4 is further connected through a flow point 6, which can be closed by an electromagnetically controlled valve 7 constituting a two-way valve, to a pressure relief line 8. . The valve 7 can be controlled in known manner by an electromagnet 9. When the valve is actuated by the electromagnet 9, which causes the opening of the flow throat 6, the control chamber 4 can thus be

discharged under pressure.

  Due to the pressure in the control chamber 4, the control piston 3 exerts a force on the rear side of the barrel 10 of an injector needle 11. If the needle 11 is not in the closed position , in which it is pressed against a valve seat 12 in the injector body 1, it unmasks injection channels 13 leading to

  the interior space of a cylinder not shown.

  An annular space 14, connected to the side of the control piston 3, directed towards the needle 11 is connected by a leakage line 15

  fuel return for the escape of fuel.

  The control piston 3 is provided with a central bore 16 which opens towards the needle 11. A needle closing spring 17 is placed in the bore 16. This spring has a size and a length such that in the compressed state, when the high pressure prevails in the inlet channel 2 and the branch pipe 2a, it is

  completely inside the bore 16.

  As can be seen in FIG. 1, the control piston 3 thus applies directly, by its frontal side directed towards the needle 11,

  against the rear end of the barrel 10 of the injector needle.

  The injector according to the invention operates as follows: During operation, that is to say when the pressure of the system is permanently applied, the needle closing spring 17 is "short-circuited" and its effect is removed. The control piston 3 and

  the barrel 10 of the needle are applied directly against each other.

  Depending on whether the electromagnet 9 holds the valve 7 and consequently the flow restriction 6 in the open position or in the closed position, the injector needle 11 is in known manner in the open state or in the state closed. It is only in the state of rest, in the absence of high pressure in the inlet channel 2 and consequently also in the bypass channel 2a, that the closing spring 17 of the injector needle between in action. Due to the absence of a back pressure from a high-pressure space 18, from which the injection ports 13 leave, the spring force acts in this case on the rear end of the barrel 10. the needle and

  thus presses the needle 11 on the seat 12.

  In the exemplary embodiment according to FIG. 2, the needle 11 is basically of the same structure as that described with reference to FIG. 1. In place of the bore 16 formed in the control piston 3, provision is made for here, for guiding and also for establishing a direct mechanical connection or a direct application of the piston 3 against the barrel 10 of the injector needle during operation, a rod 19 as a guide element. The needle closing spring 17 is threaded onto the rod 19 and

guided by her.

  FIG. 3 represents an equivalent solution with regard to the guiding of the needle closing spring 17. In place of a rod 19, a bushing 20 is provided here as a guide element. The sleeve 20 is also arranged, like the rod 19, as a spacer between the control piston 3 and the rear end of the barrel of the needle. The rod 19 according to Figure 2 and the sleeve according to Figure 3

  are connected either to the control piston 3 or else to the barrel 10 of the

  guille of injector. During operation, the sleeve 20, like the rod 19, is applied by a frontal side against the other part, that is to say against the piston 3 or the barrel 10 of the needle, depending on whether it is connected to one or the other. This means that even in the cases according to FIGS. 2 and 3, the needle closing spring 17 is "short circuited", that is to say without effect in this state. It is only in the absence of high pressure in the system that the spring force acts between the control piston 3 and the barrel 10 of the needle, with the result that the injector needle 11 is pressed on

the valve seat 12.

Claims (5)

  1. Injector for internal combustion engines, comprising an injector needle, an electromagnet-controlled valve, a control chamber connected to an inlet pipe for pressurized fuel and, when the valve is open, to a pressure discharge line, the fuel pressure in the control chamber acting through a control piston on the rear end of the injector needle, together with a needle closing spring, which allows the needle to be applied against a valve seat of the injector, the needle closing spring being supported at one end directly on the rear end of the injector needle or an intermediate element in connection with this needle, characterized in that the needle closing spring (17) is supported by its other end directly on the control piston (3) or on an intermediate element which can be connected to the plunger, the needle closing spring (17) having a position and / or length such that it is "short-circuited", i.e. the effect of this spring   is removed, in the open state of the injector needle (11).   2. Injector according to claim 1, characterized in that the needle closing spring (17) is arranged in a bore (16) in the control piston (3), a bore which opens towards the needle d injector (11). Injector according to Claim 1, characterized in that at least one guide element (19, 20) is placed between the control piston (3) and the injector needle (11), which element is produced as a guide for the needle closing spring (17), the guide element (19, 20) being connected   to the control piston (3) or to the injector needle (11).   Injector according to claim 3, characterized in that the guide element is in the form of a central rod (19) on which is   threaded the needle closing spring (17).   Injector according to claim 3, characterized in that the guide element is in the form of a sleeve (20) inside the   which is guided the needle closing spring (17).