Abstract:
A solenoid for use with a fuel injector, the solenoid comprising a housing able to be attached to an injector; a core able to be located within the housing; a coil able to be located within the core; and an electrical cable electrically connected to the coil wherein at least the coil and the electrical cable connection to the coil is encapsulated by encapsulant.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a solenoid. In particular, the invention resides in a solenoid for use with a diesel injector for an engine used in underground coal mining machinery and therefore will be described in this context. However, it should be appreciated that the solenoid may be used for other purposes. 
       BACKGROUND OF THE INVENTION 
       [0002]    Methane is stored under pressure within coal until. mining activities release the methane into the atmosphere. This is a well known phenomenon which all coal mining operations cater for in order to provide safe working conditions for miners. If methane concentrations in an underground mine&#39;s atmosphere exceeds 2%, operations are suspended because of the dangerous conditions. This danger is mitigated by strictly enforced mine ventilation safety regulations. Still, methane accumulation in underground mines is responsible for thousands of deaths worldwide every year related to underground mine explosions. 
         [0003]    For an underground coal mining explosion to occur, there must be an ignition source. If there is no ignition source, then an explosion cannot occur. However, only a small spark is required to create a methane explosion in an underground coal mine. Accordingly, all machines that operate in an underground coal mine must be designed to prevent the creation of an ignition source of methane. 
         [0004]    The majority of machines that are designed to work in an underground coal mine are primarily operated mechanically. That is, the type of electrical components that are used in underground coal mine machinery is regulated to minimise the risk that failure or mal-operation could supply the ignition energy to potentially ignite combustible gases and dusts. The problem is that many engines today are electrically controlled for increased performance and lower emissions. Lower emissions and increased performance are good for underground coal mining machines. However, electrical control increases the risk of an unwanted ignition source often to unacceptable levels. 
       OBJECT OF THE INVENTION 
       [0005]    It is an object of the invention to overcome and/or alleviate one or more of the above disadvantages and/or provide the consumer with a useful and/or commercial choice. 
       SUMMARY OF THE INVENTION 
       [0006]    In one form, the invention relates to a solenoid which has a reduced risk of an unwanted ignition source. 
         [0007]    In another form, the invention resides in a solenoid for use with a fuel injector, the solenoid comprising: 
         [0000]    a housing able to be attached to an injector;
 
a core able to be located within the housing;
 
a coil able to be located within the core; and
 
an electrical cable electrically connected to the coil.
 
         [0008]    Preferably, the housing is made from a non-magnetic material. For example, the housing may be made of brass or non-magnetic stainless steel or high performance non-metallic compounds or the like materials. 
         [0009]    Preferably, the housing, coil and core are all flush with each other at one end of the solenoid. Normally, housing, core and coil are machined to so that the housing, coil and core are all flush with each other. 
         [0010]    Normally, at least the coil is encapsulated with encapsulant. The core may have a least one slot for the purpose of encapsulation. Preferably, the core has two slots to assist with encapsulation via encapsulant. The core is typically made from a magnetic material. 
         [0011]    A printed circuit board may be used to electrically connect the electrical cable to the coil. The printed circuit board may be formed with at least one track that may substantially mirror the temperature of the coil. A thermal fuse may be mounted to the printed circuit board and connected to tracks of the printed circuit board. Normally, the thermal fuse is located adjacent to the at least one track of the printed circuit board that substantially mirrors the temperature of the coil. 
         [0012]    Encapsulant may also be used to encapsulate the printed circuit board, thermal fuse and electrical cable terminations. 
         [0013]    A strain relief may be attached to the housing with the electrical cable passing through the housing. 
         [0014]    In another form, the invention resides in a method of producing a solenoid including the steps of: 
         [0000]    locating a coil within a core;
 
locating a core within a housing; and
 
connecting the coil to an electrical cable.
 
         [0015]    The method may further include one or more of the steps of: 
         [0000]    encapsulating the coil with encapsulant;
 
connecting the coil to an electrical cable via a printed circuit board;
 
attaching a thermal fuse to the printed circuit board;
 
locating the thermal fuse adjacent the printed circuit board;
 
locating the electrical cable through a strain relief and/or
 
encapsulating the printed circuit board, thermal fuse and electrical cable with encapsulant.
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    An embodiment, by way of example only, will be described with reference to the accompanying drawings in which: 
           [0017]      FIG. 1  is an exploded perspective view of a solenoid according to an embodiment of the invention; 
           [0018]      FIG. 2  is a further exploded perspective view of a solenoid according to  FIG. 1 ; 
           [0019]      FIG. 3  is a front view of a solenoid according to  FIG. 1 ; 
           [0020]      FIG. 4  is a sectional view of a solenoid according to  FIG. 1 ; 
           [0021]      FIG. 5  is a sectional view of a coil; 
           [0022]      FIG. 6  is a front view of a bobbin; 
           [0023]      FIG. 7  is a sectional view of a bobbin; 
           [0024]      FIG. 8  is a schematic view of a printed circuit board; 
           [0025]      FIG. 9  is a schematic view of a printed circuit board attached to a thermal fuse, electrical cable and winding ends; 
           [0026]      FIG. 10  is a perspective view of a core; 
           [0027]      FIG. 11  is a further perspective view of a core; 
           [0028]      FIG. 12  is an exploded perspective view of a solenoid attached to a diesel injector; and 
           [0029]      FIG. 13  is a perspective view of a solenoid attached to a diesel injector. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0030]      FIGS. 1 to 4  show a solenoid  10  for use with a diesel injector. The solenoid  10  includes a housing  20 , a core  30  and a coil  40 . 
         [0031]    The housing  20  is used to house the core  30  and the coil  40 . The housing  20  is hollow, substantially cylindrical in shape, and made of brass. As the housing  20  is hollow, the housing  20  has a housing outer wall  21  and a housing inner wall  22 . Four bolt holes  23  extend through the housing  20  and are used to attach the housing  20  to a diesel injector. The four bolt holes  23  penetrate the housing inner wall  22 . A strain relief hole  24  is located adjacent the top of the housing  20  extending from the housing outer wall  21  to the housing inner wall  22 . 
         [0032]    The core  30 , shown in more detail in  FIGS. 10 and 11 , is made from magnetic material, such as magnetic steel. The core  30  is cylindrical in shape with four bolt grooves  31  that extend down a core outer wall  32 . A coil recess  33  is located at one end of the core  30 . A wire slot  34  extends the length of the core  30  and is in communication with the coil recess  33 . Similarly, an encapsulation slot  35 , which is diametrically opposed to the wire slot  34 , extends partially down the core outer wall  32  of the core  30 . An encapsulation hole (not shown) extends between the encapsulation slot  35  and the coil recess  33 . A pin aperture  36  extends through the core  30 . 
         [0033]    The coil  40 , as shown in more detail in  FIGS. 5 to 7 , is used to create a magnetic field. The coil  40  includes a hollow plastic bobbin  41  with a copper winding  42  extending around the bobbin  41 . An insulating tape  43  is wrapped around the copper winding  42 . The insulating tape  43  is typically made from fibreglass but may be made from other materials common in the art. The winding ends  44  extend upwardly into the housing  20 . The winding ends  44  are fitted with additional insulating sleeves  45 . 
         [0034]    A printed circuit board  50 , shown in more detail in  FIG. 8 , having a series of electrical tracks  51  is electrically connected to the winding ends  44  as shown in  FIG. 9 . A thermal fuse  60  is also electrically connected to the tracks  51  of printed circuit board  50  and located adjacent the printed circuit board  50 . Electrical cable wires  71  of an electrical cable are also connected to the tracks  51  of printed circuit board  50  as well as a controller (not shown). 
         [0035]    The printed circuit board  50  guarantees the physical clearance between the connections of the thermal fuse  60 , cable wires  71  and winding ends  44  and the housing  20 . Further, the cross-section of a track  51  on the printed circuit board  50  mirrors the cross section of the winding  42  of the coil  40 . Hence, the track  51  of the printed circuit board  50  reflects the physical properties of the winding  42  of the coil  40 . According, if the temperature of the winding  42  of the coil  40  becomes too high, the temperature of the track  51  on the printed circuit board  50  will mirror the high temperature. This causes the thermal fuse  60  to break preventing operation of the solenoid  10  by disconnection of the supply current provided by the electrical cable  70 . 
         [0036]    A strain relief  80  is located through the strain relief hole  24  in the housing  20  and extends outwardly from the housing  20 . The strain relief  80  is typically made from non-metallic stainless steel. 
         [0037]    A thrust plug  90  is located in the pin aperture  36  which extends through the core  30 . The thrust plug  90  is threaded to fit in a top threaded portion of the pin aperture  36 . The thrust plug  90  is made from non-metallic stainless steel. 
         [0038]    In order to produce the solenoid  10 , the first step is to fit the core  30  to the housing  20 . Loctite™  620  is applied to the outer wall of the core  30  and the inner wall  22  of the housing  20 . The core  30  is then located within the housing  20  using a device such as a bench press. The Loctite ™ is again allowed to cure. 
         [0039]    The next step is to fix the coil  40  to the core  30 . The coil  40  is located within the coil recess  33  of the core  30  ensuring that the winding ends  44  extend through the wire slot  34  in the core  30 . Interference between the bobbin  41  and the core recess  33  ensures that the bobbin  41  (with the associated winding  42 ) are fixed for the purposes of encapsulation. Again, a bench press may be used for this process. 
         [0040]    After the coil  40  has been located within the core  30 , the core  30  must be encapsulated by encapsulant (not shown). The encapsulant is Arathane™ although it should be appreciated that other suitable encapsulants may be used. The assembled housing  20 , core  30  and coil  40  are all heated in another oven between 60 and 70 degrees Celsius for one hour. The Arathane™ is mixed and then applied to an inside of the housing  20  whilst the core  30  and coil  40  are hot. The viscosity of the applied Arathane™ is reduced by the heated assembly which facilitates the flow of encapsulant through the wire slot  34 , the encapsulant slot  35  and the coil recess  33 . The housing  20 , core  30  and coil  40  and encapsulant are then placed into a vacuum chamber. This ensures that the coil  40  is impregnated with encapsulant. Once encapsulation has been achieved, the housing  20 , core  30  and coil  40  are removed from the vacuum chamber and the encapsulant is allowed to cure. 
         [0041]    The next step is to ensure the end of the housing  20 , core  30  and coil  40  are flush with one another. This is due to the low tolerances that are often associated with the movement that the solenoid  10  is required to initiate. Accordingly, the end of the solenoid  10  is faced ensuring that the bobbin  41  thickness is not less than one millimetre. A lathe is typically used for this process. 
         [0042]    The next step is to fit the thrust rod into the coil aperture. Loctite™ is applied to the thrust rod and screwed in to the coil aperture using a set position using a distance setting tool as is known in the art. 
         [0043]    The next step is to fit the strain relief  80  to the housing  20 . The strain relief  80  is pressed into the strain relief hole  24  of the housing  20 . The strain relief  80  is deformed where it protrudes into the housing  20 . The method typically uses a punch. The combination of a close fit and the deformed end ensures that the stain relief  80  is securely fixed to the housing  20 . 
         [0044]    The next step is to connect the thermal fuse  60  of the printed circuit board  50 . Insulation (not shown) is provided over leads of the thermal fuse  60  which are then fitted to the tracks  51  of the printed circuit board  50  and soldered into place. The thermal fuse  60  is temporarily immersed in a bath of water to limit the heating of the thermal fuse  60  under the soldering process. 
         [0045]    The winding ends  44  are then soldered to the tracks  51  of the printed circuit board  50 . The electrical cable  70  is then threaded through the strain relief  80 . The cable wires  71  of the electrical cable  70  are then connected to the tracks  51  of the printed circuit board  50 . The cable wires  71  are bent over where they penetrate the printed circuit board  50  to increase the strain tolerance. 
         [0046]    The next step is to encapsulate a top of the housing  20  covering the thermal fuse  60 , winding ends  44 , printed circuit board  50  and electrical cable  70 . The encapsulant is again Arathane™ which is mixed. Before being applied, the Arathane™ may be degassed using a vacuum and/or heated to about 50 deg C to improve its flow and penetration properties. The top of the housing is then filled with the prepared encapsulant and topped up as required. The stain relief  80  is filled with encapsulant to bind the cable to the stain relief  80  and housing  20 . The encapsulant is then allowed to cure. 
         [0047]    The solenoid  10  can now be used with a diesel injector as shown in  FIG. 12  and  FIG. 13 . In this embodiment, the diesel injector is a Caterpillar™ diesel injector for a caterpillar engine. A spring  110 , alloy spacer  120 , spring spacer  130  and valve  140  are all located between the solenoid  10  and the diesel injector  100 . Four screws  25  are used to hold the solenoid  10  and the diesel injector  100  together and the spring  110 , the alloy spacer  120 , the spring spacer  130  and the valve  140  in their desired locations. The solenoid  10  operates the diesel injector  100  as is known in the art. 
         [0048]    It should be appreciated that various other changes and/or modifications may be made to the embodiment described without departing from the spirit or scope of the invention.