FIELD OF THE INVENTION

The present invention concerns an improvement to injectors such as fuel injectors comprising a control valve having a stem moveable in a sleeve for circuit pressure operation.

BACKGROUND OF THE INVENTION

In injectors such as described in document EP2620632 A1 in the name of the applicant which is hereby incorporated by reference, the injector comprises an injector body, an injector nozzle and a movably mounted injector needle. A spring is provided in a spring chamber for biasing the injector needle towards a seated position in which the nozzle holes are closed. The injector comprises a control valve assembly for controlling the injector needle. The control valve assembly comprises a control valve body and a control valve member mounted in a control chamber. The control valve member comprises a guide barrel and a stem having a smaller diameter.

In such injectors, as per the prior art design according to figure 1 , a sleeve 2 in which the stem 41 of the control valve member 4 may move axially is provided in a fluid chamber. The sleeve 2 is held in the control valve body 1. The sleeve is a fixed part to prevent deposit and contamination. To allow fuel flow of the pressure circuit, a fluid passage 11 in the control valve body provides fluid F in a chamber 3 and the sleeve 2 comprises two holes 5 to let the fluid enter a space 6 around the reduced diameter stem to allow said fluid to be extracted from said space 6 and escape through an upper passage 8 when the control valve member is lifted together with seal cap 7 in the direction A. In this design, potential failure by sleeve deformation and deposit may arise because of an uneven pressure distribution on the sleeve outer diameter as represented with the arrows since there is less fuel between the sleeve and stem than on the outer side of the sleeve. SUMMARY OF THE INVENTION

The present invention provides an improved control valve design to reduce the pressure difference between an outer side and an inner side of the sleeve and more precisely concerns: In a first aspect, a control valve assembly for an injector comprising a control valve body housing a longitudinal tubular sleeve in which is received a reduced diameter stem of a control valve member which may move axially in a longitudinal direction between a fluid receiving position and a fluid expelling position, wherein said control valve body is provided with a fluid passage delivering fluid in a chamber around a medium part of said sleeve, wherein said sleeve comprises at least one fluid distribution hole within the chamber to let the fluid enter a space around the reduced diameter stem when said control valve member is in said fluid receiving position, characterized in that said sleeve comprises at least one pressure relief hole spaced in the longitudinal direction from the or each fluid distribution hole and from said space.

In one embodiment, the sleeve may comprise two fluid distribution holes.

In one embodiment, the sleeve may comprise two pressure relief holes spaced in the longitudinal direction from the or each fluid distribution hole and from said space.

The pressure relief hole(s) reduces pressure strain on the tubular sleeve and provides bending of such sleeve.

The cylindrical valve member may comprise a proximal part attached to a seal cap. The cylindrical valve member may include an intermediate part comprising said reduced diameter stem and a distal part forming a guiding rod. Said pressure relief hole(s) may be located in front of said guiding rod.

The pressure relief hole(s) position may be optimized to avoid bending of the sleeve.

A size and location of said pressure relief hole(s) may be adapted to keep said pressure relief hole(s) in front of said guiding rod in both the fluid receiving position and the fluid expelling position of said control valve member.

In consequence, the pressure relief holes do not produce leaks during movements of the control valve member. A fluid path may be provided between at least one fluid distribution hole and at least one pressure relief hole on both sides of a tubular wall of said sleeve so that pressure is equilibrated on both sides of the sleeve wall. In other words, a fluid path exits on opposing sides of the sleeve so that the pressure is equilibrated on both sides of the sleeve. In a second aspect, the invention also concerns an injector comprising a pressure control system provided with a control valve according to the invention.

The injector may be an electromechanical injector, said pressure control system comprising an electromechanical actuator for driving movements of said control valve.

It will be appreciated that preferred and/or optional features of the first aspect of the invention may be incorporated alone or in appropriate combination within the second aspect of the invention also.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of exemplary embodiments of the invention will be discussed hereunder in reference to the attached drawings where:

Figure 1 A is a cut lateral view of an injector of the prior art; Figure 1b is a cut lateral view of a control valve assembly of an injector as in figure 1 A;

Figure 2A and 2B are cut lateral views of an embodiment of the present invention in a fluid receiving position and a fluid expelling position, respectively; and Figure 3 is an enlarged view of a detail of figure 2. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention concerns injectors such as electromagnetically driven fuel injectors 100 used in common rail fuel injection systems as depicted in figure 1A.

Such injectors comprise an electromagnetic actuator 130 actuating a control valve member 4 of a valve 1 and comprise a nozzle 110 and a needle 120 for injecting fuel.

In these systems, the regulation valve 4 is embedded in the injectors, and the valve controls communication between a high-pressure fuel passage and low-pressure fuel return line of the common rail system which in turn controls injection of fuel through the nozzle of the injector as described in EP 2 620 632 A1 .

In the present invention an improved control valve as described in figure 2A comprising a control valve body 1 housing a longitudinal tubular sleeve 2. The longitudinal direction is the vertical direction in the drawing and the electromechanical actuator 130 is above the control valve while the needle and nozzle system not shown are under the control valve in the injector.

The control valve comprises further a cylindrical valve member 4 which comprises a proximal part attached to a seal cap 7, an intermediate part comprising a reduced diameter stem 41 to form a fluid receiving space 6 and a distal part forming a guiding rod 42. The control valve member may move axially in the longitudinal direction A between the fluid receiving position of figure 2A and the fluid expelling position of figure 2B. Fluid received in the space 6 around the reduced diameter stem 41 is expelled from such space in an upper passage as shown in figure 2B.

The tubular sleeve 2 houses part of the valve member 4 including the reduced diameter stem 41 of the control valve member 4 and provides a sidewall for the space 6 and fluid distribution holes 5a, 5b for the fluid to enter the space 6.

For feeding the control valve, the control valve body 1 is provided with a fluid passage 11 delivering fluid F in a chamber 3 around a medium or middle part of the tubular sleeve 2 and the fluid distribution holes 5a, 5b within the chamber 3 let the fluid enter the space 6 around the reduced diameter stem 41 when said control valve member is in the fluid receiving position.

In the present invention, the sleeve 2 comprises at least two pressure relief holes 9a, 9b spaced in the longitudinal direction from said fluid distribution holes 5a, 5b and from said space 6. These pressure relief holes 9a, 9b equilibrate pressure around the tubular wall of the sleeve 2 as shown on figure 3 where pressure P1 on the inner side of the sleeve 2 equilibrates pressure P2 on the outer side of the sleeve 2.

In the present design the pressure relief holes 9a, 9b are located in front of the guiding rod 42 and a size and location of the pressure relief holes 9a, 9b is adapted to keep said pressure relief holes in front of said guiding rod 42 in both the fluid receiving position and fluid expelling position of said control valve member 4.

Due to the pressure relief holes 9a, 9b, a fluid path 10a, 10b is provided between at the fluid distribution holes 5a, 5b and the pressure relief holes 9a, 9b on both sides of the tubular wall of said sleeve 2. Alternate designs may include one hole or more than two holes (i.e. not necessarily two pressure relief holes). This fluid path also improves lubrification between the sleeve 2 and the moving control valve member guiding rod 42 in addition to balancing the pressure on both sides of the sleeve wall.

The invention solves problems of potential deformation and deposit on the sleeve 2 with the additional pressure distribution path provided by the pressure relief holes 9a, 9b.

Contrary to the design of figure 1 where stress P is distributed only on the outside surface of the sleeve 2, and where deformation by concentrated stress can occur on a middle part of the sleeve wall, the design of the invention reduces stress on such middle part of the sleeve 2.

The invention is not limited to the above example and in alternate embodiments, a different number of fluid distribution holes and pressure relief holes may be provided. Part numbering: control valve body 1 longitudinal tubular sleeve 2 chamber 3 control valve member 4 fluid distribution holes 5a, 5b space 6 seal cap 7 upper passage 8 pressure relief holes 9a, 9b fluid path 10a, 10b fluid passage 11 reduced diameter stem 41 guiding rod 42 injector 100 nozzle 110 needle 120 electromechanical actuator 130