Abstract:
A fuel pump, for an internal combustion engine, has a housing accommodating a pump and a motor. The motor is arranged to drive the pump so as to pump fuel through the housing. The motor has a wound stator having a plurality of inwardly directed teeth about which a stator winding is wound, and a radially outer surface in contact with an inner surface of the housing. One or more pathways are formed between the inner surface of the housing and the outer surface of the stator, for the flow of fuel there through. Each pathway is formed by an axially extending recess formed in the outer surface of the stator and aligned with a selected tooth of the stator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 200810141851.2 filed in The People&#39;s Republic of China on Sep. 3, 2008. 
     FIELD OF THE INVENTION 
     This invention relates to a fuel pump for an internal combustion engine and in particular to a fuel pump driven by a brushless direct current (BLDC) motor. 
     BACKGROUND OF THE INVENTION 
     Fuel pumps are used in motor vehicles to transfer liquid fuel, typically gasoline or diesel from a fuel tank to an internal combustion engine. The pump is driven by a small DC motor and to minimize fuel leakage through bearing seals etc, the fuel passes through the interior of the motor. This works very well even with motors having commutators, with the fuel cooling the motor and eliminating sparking between the brushes and the commutator. However, with the advent of high alcohol fuels, chemical reactions between the commutator and the fuel has become problematic leading to the use of graphite commutators and renewed interest in brushless motors to drive the fuel pumps. There are many advantages of brushless motors, especially in automobile applications, such as longer life by eliminating the use of brushes and a commutator. 
     One problem with the use of BLDC motors in fuel pumps is that the fuel has a very restricted pathway through the motor which causes a severe restriction to the free flow of fuel. One reason for this is that BLDC motors have a wound stator and due to the aggressive nature of the fuel it is desirable to protect the stator windings. This is usually done by over moulding the stator, core and windings, with over mould material such as a plastics material or a resinous material, preferably using an insert moulding technique. This technique, unfortunately, transforms the stator into a solid mass, closing off the various gaps between the stator core and the windings. As the stator core is usually pressed into the pump housing, the only remaining pathway for the fuel is through the small gap between the stator and the rotor. However, this gap is intentionally made as small as possible to increase the efficiency of the motor. Fuel in this small gap is caught between the rotating rotor on one side and the stationary stator on the other side causing frictional heating of the fuel as well as causing considerable drag on the rotor, resulting in a significant lowering of the motor efficiency. This problem does not exist in the PMDC motors having a stator formed with segment magnets due to the channels existing between the individual magnets. 
     The term brushless direct current motor is used in this specification is used in its widest sense and is intended to include those special BLDC motors known as BLAC motors which have a similar physical structure but are designed to operate with sinusoidal power signals from the motor controller. 
     SUMMARY OF THE INVENTION 
     Hence there is a desire for a BLDC motor driven fuel pump which does not restrict the flow of fuel passed the motor while maintaining the efficiency of the motor. 
     This is achieved in the present invention by fuel passageways between the motor stator and the fuel pump housing. 
     Accordingly, in one aspect thereof, the present invention provides a fuel pump for an internal combustion engine, comprising: a housing; a pump accommodated within the housing; a motor accommodated within the housing, the motor having a wound stator having a plurality of inwardly directed teeth about which a stator winding is wound, and an outer surface in contact with an inner surface of the housing; and at least one pathway formed between the inner surface of the housing and the outer surface of the stator, for the flow of fuel there through. 
     Preferably, the or each pathway is formed by an axially extending trough formed in the outer surface of the stator. 
     Preferably, the or each trough is aligned with a selected tooth of the stator. 
     Preferably, the or each selected tooth of the stator is unwound. 
     Preferably, the stator is over molded with material to protect the winding from chemical reaction with the fuel. 
     Preferably, the motor is a brushless direct current motor. 
     Preferably, the stator of the motor is encased in a plastics or resin material. 
     Preferably, there are three pathways and the motor has four rotor poles and nine stator poles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labelled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
         FIG. 1  is a sectional view of a fuel pump, according to a preferred embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the fuel pump of  FIG. 1  viewed along lines A-A; 
         FIG. 3  is a perspective view of a motor of the fuel pump of  FIG. 1 ; and 
         FIG. 4  is a schematic diagram of a stator core and rotor for the motor of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a complete fuel pump  40  in sectional view. The fuel pump has a housing  42  of cylindrical form with two open ends which are sealed by end caps  44 ,  45  which connect the fuel pump to the fuel lines. The housing has a pump section  46  and a motor section  50  accommodating a motor. The pump section  46  includes an impeller  47  arranged to be rotated by the motor within a volute  48  to draw fuel into the pump section from a fuel inlet  49  in the first end cap  44  and force the fuel through the motor section  50  and out a fuel outlet  51  in the second end cap  45 . The motor section  50  houses the motor which includes a stator  12  which is pressed into the housing  42 , and the rotor  16  with the rotor core  17  located within the stator  12  and a rotor shaft  19  which is journalled in bearings in the pump volute  48  at one end and in the second end cap  45  at the other end. The stator  12  supports a stator winding  20  and is over molded with material, such as a plastics material or a resin material, to protect the winding from chemical reaction with the fuel being pumped. The second end cap is shown being of two parts, a first part sealing the housing  42  and forming the fuel outlet  51  and the connector for the electrical power to operate the motor, and a second part supporting the bearing for the rotor shaft. The second end cap  45  may include an electronics module to accommodate the electronics for operating the BLDC motor. However, in this embodiment the electronics module is provided outside of the fuel pump. 
     The fuel flow path through the fuel pump is: in through the inlet  49  in the first end cap  44 ; into the pump volute  48 , where it is forced out by the impeller  47  into the interior of the housing  42 ; passed the motor by passing through the fuel pathways  52  between the stator core  13  and the housing  42  (although some fuel may still pass between the rotor core  17  and the stator core  13 ); into the second end cap  45 ; and out of the pump though the fuel outlet  51  of the second end cap  45 , as illustrated by block arrows  60 . 
       FIG. 2  is a transverse sectional view through the fuel pump, viewed along section lines A-A of  FIG. 1 .  FIG. 2  illustrates the fuel pathways  52  between the stator  12  and the housing  42 . Three fuel pathways  52  are provided in the preferred embodiment.  FIG. 2  also shows how the gaps  130  (as shown in  FIG. 4 ) in the stator have been filled by the over mould material such that the end face of the stator presents as a solid wall. 
     The stator  12  and rotor  16  set is illustrated in  FIG. 3 . After the stator winding is formed on the stator core  13 , the stator  12  is over molded with a plastics material or resin material  30 , preferably by an insert molding operation. Preferably, the pole faces  18  and the radially outer surface  34  of the stator core  13  are not covered with the over mould material. This ensures a good transfer of magnetic flux between the pole faces  18  of the stator and the rotor and also allows a good fit with the motor housing in which the stator core is preferably a press fit. 
     The stator winding may be connected to stator terminals for connection to a controller or directly to motor terminals and where used the terminals would also have exposed parts (not shown) not covered by the over molding for making further electrical connections. The rotor core  17  is also shown as being over molded to protect the rotor core from the fuel and to assist retention of the magnets on the rotor. The over mould material also helps the efficiency of the fuel pump by making a smooth path for the flow of the fuel and by smoothing the outer surface of the rotor to reduce windage, the resistance created by rotating body. 
       FIG. 4  is a schematic winding diagram for a 3-phase BLDC motor for a first preferred embodiment.  FIG. 4  also illustrates the configuration of the stator core of the preferred embodiment. The stator  12  has a stator core  13  with six teeth  14 ,  15  forming the stator poles as will be described later. The winding  20  has only three coils  22  formed about alternate teeth  14 . The winding  20  is a 3-phase Delta winding having three legs, one leg for each phase, with each end of each leg being connected to two of the three stator terminals A,B,C, with each terminal being connected to two of the legs, such that the ends of each leg is electrically connected to the other two legs. Thus each leg has only one coil  22 . However, the wound teeth  14  have a larger circumferential extent than the unwound teeth  15  and have a deep groove  26  in the pole face which extends axially for the length of the tooth  14  and radially outwardly into the tooth, dividing the pole face into two, preferably equal, portions. The groove  26  has the effect of dividing the tooth  14  into two stator poles and forming a dummy slot. Thus the stator effectively has 9 slots or 9 stator poles. The grooves  26  are referred to as dummy slots as no coils are wound into the dummy slots, giving the stator a simple winding. 
     Indeed, a Delta winding configuration does offer some advantages by simplifying the winding connections as shown in  FIG. 4 . As shown, in the Delta configuration of a three phase winding, each phase winding is connected to the other two phase windings. Thus, during winding the wire is connected to a first stator terminal A, wrapped about a first stator tooth to form the first phase winding, connected to a second stator terminal B, wrapped about a second stator tooth to form the second phase winding, connected to a third stator terminal C, wound about a third stator tooth to form the third phase winding and finally connected back to the first stator terminal A. The wire is only cut after being connected to the first stator terminal for the second time, simplifying the winding by eliminating the common Star connection point. 
       FIG. 4  also shows the shape of the stator core. The stator core  13  has a circular construction to mate with the inner surface of the housing  42  of the fuel pump, with the exception that the radially outer surface  34  of the stator core  13  has a number of axially extending recesses  28 . Recesses  28  form fuel pathways between the stator core  13  and the housing  42  allowing the fuel to flow through passed the motor. The recesses  28  are shown aligned with the non-wound teeth  15 . This is thought to have no negative impact on the magnetic circuit of the stator while allowing maximum space for the coils  22  formed on the wound teeth  14 . 
     The stator core  13  is a laminated structure formed by stamping and stacking a plurality of steel laminations. The laminations may be held together by suitable means such as interlocking or welding. In the preferred embodiment the laminations are welded together. This is preferably done by using a laser welder to weld together a small nub  32  formed on each lamination for this purpose in a cut-out  33  in the outer surface  34  of the stator core aligned with the wound teeth  14 , as shown in  FIG. 4 . During over molding, this cut-out  33  is filled with mould material to protect the weld. This over mould material forms the strip  31 , which can be seen in  FIG. 3  on the outer surface  34  of the stator core connecting the ends of the stator. 
     Thus the present invention provides a novel construction for a fuel pump. This structure is well suited to use of a BLDC motor in the pump for driving the pump. For the fuel pump, the provision of fuel pathways between the stator and the housing is considered an advantage. The use of a BLDC motor, especially a BLDC motor with reduced cogging torque is an added advantage. Certain embodiments are ideally suited to mass production. 
     While the housing of the fuel pump has been described as ‘cylindrical’ and the example shown is a right circular cylinder, it is intended that this term is not limited to a cylinder with a right circular cross-section but covers any tubular structure having a constant cross-section, with ends which may or may not be formed perpendicular to the longitudinal axis of the cylinder. 
     Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow. 
     In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items.