Abstract:
A filter for a fuel injection device, comprising a plurality of filter elements arranged within a housing such that, in use, fluid is directed through clearances of predetermined size between respective mutually adjacent ones of the elements for preventing the passage of oversized contaminant particles carried in the fluid.

Description:
TECHNICAL FIELD 
     This invention relates to a filter and more particularly, but not exclusively, to a final stage filter for a fuel injection device. 
     BACKGROUND OF THE INVENTION 
     Devices commonly known as “edge filters” are typically disposed in a fuel injector or injector adapter to protect the finely dimensioned final stage conduits of an injection device, which may be as small as around 25 μm in diameter, from contamination by undesirably large particles. Such particles may, for example, be the residue of the combustion process, internal deterioration debris, service-induced debris, or matter that has penetrated the main filter. A fuel injection device having an edge filter typically defines a narrow passageway between a surface of the edge filter and a housing of the device in which the edge filter is disposed, for removing particles above a predetermined size from fuel that must flow through the passageway towards an outlet of the injector. 
     SUMMARY OF THE INVENTION 
     The inventor has identified two main problems with such edge filters. Firstly, the housing that partially forms the passageway has been found to elastically extend so as to dilate away from the surface of the edge filter when subjected to fuel under high pressure, thereby temporarily widening the passageway and permitting oversize contaminant particles to pass. Secondly, an oversize particle is continually re-presented to the passageway&#39;s entrance so that the particle is inevitably either reshaped by the high pressure fuel entering the passageway until it is small enough in at least one dimension to fit through the passageway, or the particle passes through the passageway as the wall of the injector dilates. These problems can lead to an edge filter passing contaminant particles having dimensions of significantly larger than the nominal spacing of the wall of the passageway from the surface of the edge filter. 
     An object of the invention is to mitigate or overcome at least one of the above-mentioned problems. 
     Accordingly, the invention provides a filter for a fuel injection device, comprising a plurality of filter elements arranged within a housing such that, in use, fluid is directed through clearances of predetermined size between respective mutually adjacent ones of the elements for preventing the passage of oversized contaminant particles carried in the fluid. 
     Preferably, the elements are arranged side by side in a loop such that, in use, force exerted on one side of one of the elements by pressurized fluid in a respective one of the clearances is opposed by force exerted on another side of this element by pressurized fluid in a next adjacent one of the clearances. 
     In this manner, the effects of high pressure in the filter clearances can be balanced and any significant increase in the size of the clearances due to the fuel pressure can be alleviated. 
     The invention also includes a fuel injection device having a housing, a 3 filter disposed in the housing for rejecting oversized contaminant particles, and a particle collection zone, the filter being configured and arranged relative to the housing such that, in use, fluid flowing through the filter directs rejected particles away from the filter into the particle collection zone. 
     This reduces time spent by a particle in contact with the filter, and reduces the opportunity for high-pressure pulses in the fluid to reshape the particle and force it through the filter. 
     The filter is conveniently of the type described hereinbefore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be well understood, by way of example only, two embodiments thereof will now be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a cross-sectional view through a fuel injection device in accordance with the invention; 
     FIG. 2 is a view taken along line AA in FIG. 1; 
     FIG. 2A is a full view of an inner surface of a transversely extending wall of a housing of the fuel injecction device of FIG. 1 with protrusions formed thereon for spacing apart the filter elements; 
     FIG. 2B is a full view of an inner surface of a transversely extending wall of a housing of the fuel injection device of FIG. 1 with reliefs machined therein for spacing apart the filter elements; 
     FIG. 2C is a partial side view of a collector formed of sintered metal; 
     FIG. 2D is a partial side view of a collector formed of mesh; and 
     FIG. 2E is a partial side view of a collector formed of segment-shaped elements. 
     FIG. 3 is a cross-sectional view of another fuel injection device in accordance with the invention; and 
     FIG. 4 is a view taken on line BB in FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a portion of a fuel injection device is shown including a housing  1 , a filter  2  disposed within the housing  1  and a collector  3 . The filter  2  is formed as a segmented hollow generally frusto-conical arrangement formed of sixteen segments or elements  4 . Each of the sixteen elements  4  of the filter  2  is separated by a clearance  4   a  of approximately 15 μm from its neighboring elements  4 . 
     The collector  3  comprises a hollow body closed at one end. The open end of the collector  3  is sealingly fitted around the narrower end of the filter  2  in an annular recess  5  provided therein for receiving the collector  3 . As best seen in FIG. 1, the collector forms a chamber  6  and the inner periphery of the narrow end of the filter  2  provides a relatively small inlet opening  7  to the chamber  6 . 
     The housing  1  comprises an inlet portion  8 , an outlet portion  9  and an intermediate portion  10  between the portions  8  and  9 . The intermediate portion  10  is provided with a support wall  11  which extends radially inwardly of the housing  1  and engages and supports the collector  3 . The collector  3  is relatively rigid and is thus able to locate and support the narrow end of the filter  2  in the position shown in FIG.  1 . The wide end of the filter  2  engages an inner surface of a transversely extending wall  12  of the housing  1 . This inner surface is provided with means  40  for engaging the axial ends of the elements  4  for maintaining the peripheral spacing between the ends of the elements  4 . With reference to FIGS. 2A and 2B, the engaging means could, for example, be provided by protrusions  41  on the inner surface of the wall  12  or alternatively by reliefs  43  machined in the inner surface of the wall  12 . 
     In use, fuel is driven through the inlet portion  8  in the direction of the arrows shown in FIG.  1  and into the wide end of the filter  2 . Because of the greatly restricted flow through the orifice  7  at the narrow end of the filter  2  and the presence of the collector  3 , most of the fuel is directed through the clearances  4   a  of the filter  2 . Any particle having a minor dimension greater than the 15 μm filter clearance will not be able to pass through the clearances  4   a  and will engage the inner peripheral surface  13  of the filter  2 . Because fuel passing through the filter  2  has a flow component directed parallel to the inner peripheral surface  13 , filtered contaminant particles are swept through the narrow end of the filter and into the chamber  6 . Filtered fuel passes through perforations  14  in support wall  11  and through the outlet portion  9  of the housing  1  for injection into an engine cylinder (not shown). Contaminant particles are retained in the chamber  6  so that there is little opportunity for them to be shaped and forced through the clearances  4   a  by high pressure fuel pulses. It will be appreciated that the chamber  6  acts as a collection zone. 
     The collector  3  may be impermeable, particles being retained in chamber  6  by virtue of the relatively small entry orifice  7 . Alternatively, the walls of the chamber may be permeable to permit a relatively low rate of flow through the chamber  6 . The collector  3  may, for example, be made from a sintered material (FIG. 2C) or a mesh (FIG.  2 D), or comprise segment-shaped elements (FIG. 2E) arranged in a manner similar to the elements  4  of the filter  2  to provide clearances of a size equal to or smaller than the size of the clearances  4   a.  Such through-flow may be beneficial in some circumstances in reducing excitation of particles in the chamber  6  due to reverberation during operation of the fuel injection device. The size of the chamber  6  should be commensurate with the expected number of particles likely to be collected in the planned service period for any particular application. Accumulation of particles in the chamber does not prevent flow-through significantly since the force of the flow is insufficient to reshape the particles. 
     Peripherally directed forces exerted by high pressure fluid in the clearances  4   a  on the sides of the elements  4  tend to balance each other out so that these forces do not significantly increase the size of the clearances  4   a  during high pressure operation. Furthermore, as should be clear from the above description, contaminant particles which are unable to pass through the clearances  4   a  are immediately directed into the chamber  6  remote from the filter  2  where they are no longer subject to significant reshaping forces which might otherwise force them through the filter clearances  4   a.    
     The filter  2  provides a flow area of about 7 mm 2 , but it should be apparent that the dimensions of the filter  2  and the number of elements  4  can be adjusted to suit a desired application. 
     Referring now to FIGS. 3 and 4, a portion of another fuel injection device is shown. The device comprises a housing  20  having an inlet portion  21 , an outlet portion  22  and an intermediate portion  23 . The intermediate portion  23  is considerably wider than the inlet and outlet portions  21 , 22  and houses a filter  24 . The filter  24  takes the form of a thick walled tube defining a central hole  24   a.  The tube comprises sixteen segment-shaped elements  25 . Each element  25  is separated from its adjacent elements  25  by a predetermined clearance  26 . The filter  24  is fitted snugly within the housing  20  so as substantially to prevent the flow of fuel between an outer peripheral surface  27  of the filter and an inner peripheral surface  28  of the housing  20 . 
     One end (the upper end as shown in FIG. 3) of the filter&#39;s central hole  24   a  is blocked by a closure  29 . The other end of the filter&#39;s central hole  24   a  (the lower end as shown in FIG. 3) is stepped and receives an inwardly extending tube  30  which provides fluid communication between the central hole  24   a  of the filter and the outlet portion  22  of the housing  20 . 
     The axial end faces and outer peripheral surface of the filter are provided with recesses which form channels  31 . Each channel  31  bridges a respective one of the clearances  26  and extends axially along the entire dirty-side surface of the filter  24 . 
     In use, fuel is driven in the direction of the arrows shown in FIG.  3  through the inlet portion  21  of the housing  20 . Fuel enters the channels  31  and flows over a first, downwardly sloping, section  32  of each channel, through a second, vertical, section  33  to a third, horizontal, section  34 . As shown by the arrows in FIG. 3, some of the fuel flows through the clearances  26  as it progresses along the channels  31 . Particles which are unable to pass through the clearances  26  are swept along the sloping section  32  of each channel  31 , down the vertical section  33  and along the horizontal section  34  by the fuel as it flows through the filter. The particles will come to rest in the general proximity of a collection zone  35  of relatively undisturbed flow at the bottom of each channel  31 . The particles tend to settle in the undisturbed zone  35  and are not subject to any significant shaping forces. The elements  25  are pressure balanced in a manner similar to the elements  4  described in relation to FIGS. 1 and 2 and thus the clearances  26  are not prone to dilation effects. 
     Although in the description hereinbefore, the filter is intended for use in a system of the type in which fuel is driven through the filter, for example by a pump located upstream of the filter or by the fuel pressure within a common rail, it will be appreciated that the invention is also applicable to arrangements in which fuel is drawn through the filter, for example by a fuel pump located downstream of the filter.