This invention relates to an electric motor and more particularly
but not exclusively to such a motor for use in conjunction with a fuel pump.
It is known from US5788210 to provide a motor which is
mounted on an external device by fitting an exposed section of a radial bearing
of the motor into an engaging recess of the external device to thus align the motor
and the external device. However, electronic circuitry is not separated from a potential
flow path defined between the external device and the motor.
The document US 5053664 discloses a motor-driven fuel pump
including a brushless motor, a motor having for enclosing the brushless motor and
a pump section adapted to be driven by the motor. The housing also contains a control
According to the present invention there is provided a
motor comprising a stator, a rotor, a sleeve at one end of the motor for supporting
or defining a bearing for the rotor and for attachment to a fuel pump by fitting
into a hole in a housing of the fuel pump, windings on the stator, sensors for sensing
the position of the rotor relative to the stator, electronic circuitry for switching
the current in the windings in response to outputs from the sensors so as to cause
the rotor to rotate relative to the stator, and a housing containing the rotor,
the stator, the sensors and the electronic circuitry, the sensors and at least part
of the electronic circuitry being encapsulated in an electrically insulating and
fuel resistant material in a container within the housing, characterized in that
the container has an internal sleeve through which a shaft of the rotor extends
and through which fuel from the fuel pump can flow when the fuel pump is connected
to the motor.
Preferred and/or optional features of the invention are
set forth in claims 2 to 7 inclusive.
The invention will now be more particularly described,
by way of example only, with reference to the accompanying drawings, wherein:
- Figure 1 is a perspective view of one embodiment of an electric motor according
to the present invention,
- Figure 2 is a cut away view of the motor shown in Figure 1,
- Figure 3 is a perspective exploded view of the container for containing electronic
circuitry of the motor shown in Figures 1 and 2,
- Figure 4 is a perspective view of the container of Figure 3 mounted on the stator
and containing the electronic circuitry.
- Figure 5 is a perspective underneath view of the container shown in Figure 3,
- Figure 6 is a perspective view of a front insulator of the motor,
- Figure 7 is a perspective view of the rotor of the motor,
- Figure 8 is a partly broken away view of the rotor shown in Figure 7,
- Figure 9 is a plan view showing the rotor and stator laminations of the motor,
- Figure 10 is a plan view of a second example of a modified rotor lamination,
- Figure 11 is a plan view of another modified rotor lamination,
- Figure 12 is a perspective fragmentary view of an alternative stator,
- Figure 13 is a perspective view of the stator shown in Figure 11 with the flux
pieces added, and
- Figure 14 is a sectional view of another embodiment of a motor according to
the invention in combination with a fuel pump.
Referring now to the drawings, the brushless direct current
motor shown therein comprises a deep drawn housing 10, a rotor 11 including a shaft
12 having a flat 12a at the end projecting from the closed end of the housing
10, a wound stator 13 surrounding the rotor 11, an end cap 14 closing the open end
of the housing 10, and a container 16 within the housing 10 for sensors and electronic
circuitry. The wound stator 13 comprises a stator winding 19 wound about a stack
of stator laminations 30.
The motor has an overall appearance similar to that of
a conventional permanent magnet direct current motor having commutating parts comprising
a commutator and brush/leaf system. The motor has particular application as a fuel
pump motor, but also has other uses.
Referring now to Figures 3 to 5, the container 16 comprises
a cylindrical bowl 17 having an integral sleeve 18 upstanding from the base of the
bowl. The container is typically formed of Polyacetal (POM) and contains sensors,
typically in the form of Hall-effect sensors, for sensing the position of the rotor
11 relative to the stator 13 and electronic circuitry mounted on an annular printed
circuit board 20 which fits over the upstanding sleeve 18. Ideally the Hall-effect
sensors lie flat on the printed circuit board 20. This is advantageous as compared
to conventional "standing" hall sensors because it is easier to assemble and more
reliable against fuel and vibrations after full encapsulation. Also, it allows a
reduction in distance between the sensors and the planar top surface of the permanent
magnet rotor. The circuitry switches the current in the stator windings in known
manner in response to outputs from the sensors to cause the rotor to rotate relative
to the stator. The sensors and electronic circuitry are then encapsulated in electrically
insulating material, typically epoxy resin, which fills or substantially fills the
container 16. The sleeve 18 is dimensioned such as to allow the rotor shaft 12 to
extend therethrough and to allow fuel from the fuel pump to flow therethrough.
The sensors and most of the electronic components, including
all electrically conductive parts thereof, are fully encapsulated. Only such parts
as, for example, electrical terminals and/or large capacitors will not be encapsulated
As shown in Figure 5, the underside of the base of the
bowl 17 has four insulation displacement connectors 21 for direct connection to
windings of the stator 13.
The thermal conductivity of the encapsulating material
may not be too important because of the cooling effect of fuel passing through the
Figure 6 shows in detail a front insulator 22 which is
placed on the stator and which has the same number of slots 23 (four in this example)
for receiving the stator windings and the insulation displacement connections 21
on the container 16.
Instead of mounting the sensors and the electronic circuitry
on a printed circuit board, the internal bottom surface of the container 16 could
have an electrically conductive pattern imprinted thereon. This can take the form
of a heat-press foil applied with a heat-press stamp. All electronic components
can then be automatically assembled on the bowl's inner surface and subsequently
encapsulated. Another advantage of this technique is a further reduction in the
distance between hall sensors and the planar top surface of rotor's magnet resulting
in increased magnet field strength for position detection.
The motor also has a rear insulator 24 similar to but not
identical to the front insulator 22.
The end cap 14 is connected to the housing 10 such as by
crimping the rim of the housing 10 on the end cap at e.g. two positions. This end
cap 14 supports or defines a bearing for the rotor shaft 12 and also includes integral
features needed for a customer's fuel pump. A termination 26 is provided on the
end cap 14 for connection to an external supply.
A sleeve 15 is provided at the other end of the motor.
The sleeve 15 is typically formed of Polyphenylensulfide (PPS). This material has
a high heat dimensional stability, low elongation and extremely good resistance
against all kinds of aggressive fuels. The sleeve 15 supports or defines a bearing
for the rotor shaft 12 and is also for attachment to a customer's fuel pump by press
fitting into a hole in the fuel pump housing. Conventionally, the sleeve 15 has
been part of the pump housing. It is now a part of the motor and serves the duel
purpose of supporting or defining a bearing for the rotor shaft 12 and as a connecting/aligning
element for the pump housing and allows the motor to be fully tested before supply
to a customer. The sleeve 15 is the sole means of aligning the pump impeller and
the rotor 11 of the motor.
The use of a brushless direct current motor as opposed
to a conventional commutator motor makes a radial and axial reduction of motor dimensions
Referring now to Figures 7 to 11, the rotor comprises a
rotor shaft 12 and a laminated core 27 overmoulded with material 33 magnetised subsequent
The laminated core 27 comprises a plurality of rotor laminations
29. As shown in Figure 9, these laminations are stamped from sheet metal and maybe
stamped at the same time as stator laminations 30. The rotor laminations 29 have
three equi-angularly spaced, radially inwardly extending, slots 31 and a central
aperture 32 for mounting the laminations on the rotor shaft 12. A stack of these
laminations 30 are overmoulded with magnetisable material 33, typically thermoplastical
bonded NdFeB compound and this (isotropic) material 33 is magnetised (as shown in
Figure 7) subsequent to moulding. The overmoulding may also include an integral
ring 34 which can be charged like an encoding disc to give a higher magnetic field
strength in the axial direction (necessary for the Hall sensors).
A rotor formed in this manner does not require any glue
and is simple to assemble. Also no balancing is needed. The moulding material 33
also fills the slots 31.
Figure 10 shows an alternative rotor lamination having
six apertures 35 therein. These apertures 35 are equi-angularly spaced and three
of the apertures are larger than the others. This reduces the weight of the rotor
core 27 although, preferably, in order to avoid fuel pump rotor punch losses (i.e.
losses due to turbulences of rotor in the fluid) the end laminations preferably
have no such apertures 35.
Figure 11 shows yet a further rotor lamination having no
slots 31 but an uneven, knurled peripheral surface and six apertures 35' of equal
The stator laminations 30 shown in Figure 9 are stamped
at the same as the rotor laminations and comprise an outer ring 36, four equi-angularly
spaced, radially inwardly extending pole pieces 37 around which windings (not shown)
are wound and four flux pieces between the pole pieces 37. A stack of these laminations
is difficult to wind because of the small gaps between the pole shoes 37 and the
flux pieces 38. Also, external coil winding around pole pieces with subsequent insertion
onto outer ring is not recommended for small-sized motors.
In one aspect of the invention, and as shown in Figures
12 and 13, an alternative stator 13', has an outer ring 36', a plurality of angularly
spaced pole pieces 37' extending radially inwardly from the outer ring 36' and a
plurality of flux pieces 38' between the pole pieces 37'. The flux pieces 38' are
separate from the ring 36' and pole pieces 37' and are slidable into slots 39 defined
by the outer ring 36' subsequent to winding of the pole pieces 37'. This simplifies
the winding process and allows the flux pieces 38 to be optimally shaped.
The ring 36' and pole pieces 37' are integrally formed
and could be formed of stamped laminations secured together such as by laser welding/package
punching or more preferably are formed in a unitary construction by moulding soft-magnetic
Figure 14 shows another embodiment of a motor in combination
with a fuel pump 40 having an impeller 41. In this case, the motor is a conventional
PMDC motor having a commutator 42 and brush system 43. As shown in Figure 14 there
is an outer housing 45 accommodating the motor and the fuel pump 40. There is a
gap between the motor and the outer housing to allow the motor to be aligned with
the pump 40 solely by sleeve 15. The pump body is press fitted into one end of the
outer housing 45 to form a seal at the pump end of the outer housing and there is
an O-ring seal 46 at the other end between an output cap 47 and the outer housing
45. There will be a similar arrangement accommodating the brushless motor of Figures
1 to 13 and the fuel pump.
The embodiments described above are given by way of example
only and various modifications will be apparent to persons skilled in the art without
departing from the scope of the invention as defined in the appended claims. For
example, the rotor could surround the stator, more particularly when used as fan
motors or storage drives.