Note: Descriptions are shown in the official language in which they were submitted.
CA 02622790 2008-03-14
03L006781A
1
PROGRAMMABLE ELECTRIC MOTOR AND METHOD OF ASSEMBLY
This application is a division of Canadian Serial No.
2,329,073 filed March 27, 2000.
Background of the Invention
This invention relates generally to electric motors and
more particularly to an electric motor having a simplified,
easily assembled construction.
Assembly of electric motors requires that a rotor be
mounted for rotation relative to a stator so that magnets on
the rotor are generally aligned with one or more windings on
the stator. Conventionally, this is done by mounting a shaft
of the rotor on a frame which is attached to the stator. The
shaft is received through the stator so that it rotates about
the axis of the stator. The frame or a separate shell may be
provided to enclose the stator and rotor. In addition to
these basic motor components, control components are also
assembled. An electrically commutated motor may have a
printed circuit board mounting various components. Assembly
of the motor requires electrical connection of the circuit
board components to the winding and also providing for
electrical connection to an exterior power source. The
circuit board itself is secured in place, typically by an
attachment to the stator with fasteners, or by welding,
soldering or bonding. Many of these steps are carried out
manually and have significant associated material labor costs.
The fasteners, and any other materials used solely for
connection, are all additional parts having their own
associated costs and time needed for assembly.
Tolerances of the component parts of the electric motor
must be controlled so that in all of the assembled motors, the
rotor is free to rotate relative to the stator without
contacting the stator. A small air gap between the stator and
the magnets on the rotor is preferred for promoting the
transfer of magnetic flux between the rotor and stator, while
permitting the rotor to rotate. The tolerances in the
dimensions of several components may have an effect on the
,
CA 02622790 2008-03-14
03L006781A
2
size of the air gap. The tolerances of these components are
additive so that the size of the air gap may have to be larger
than desirable to assure that the rotor will remain free to
rotate in all of the motors assembled. The number of
components which affect the size of the air gap can vary,
depending upon the configuration of the motor.
Motors are commonly programmed to operate in certain ways
desired by the end user of the motor. For instance certain
operational parameters may be programmed into the printed
circuit board components, such as speed of the motor, delay
prior to start of the motor, and other parameters. Mass
produced motors are most commonly programmed in the same way
prior to final assembly and are not capable of re-programming
following assembly. However, the end users of the motor
sometimes have different requirements for operation of the
motor. In addition, the end user may change the desired
operational parameters of the motor. For this reason, large
inventories of motors, or at least programmable circuit
boards, are kept to satisfy the myriad of applications.
Electric motors have myriad applications, including those
which require the motor to work in the presence of water.
Water is detrimental to the operation and life of the motor,
and it is vital to keep the stator and control circuitry free
of accumulations of water. It is well known to make the
stator and other components water proof. However, for mass
produced motors it is imperative that the cost of preventing
water from entering and accumulating in the motor be kept to a
minimum. An additional concern when the motor is used in the
area of refrigeration is the formation of ice on the motor.
Not uncommonly the motor will be disconnected from its power
source, or damaged by the formation of ice on electrical
connectors plugged into the circuit board. Ice which forms
between the printed circuit board at the plug-in connector
can push the connector away from the printed circuit board,
CA 02622790 2008-03-14
03L006781A
3
causing disconnection, or breakage of the board or the
connector.
Summary of the Invention
Among the several objects and features of the present
invention may be noted the provision of an electric motor
which has few component parts; the provision of such a motor
which does not have fasteners to secure its component parts;
the provision of such a motor which can be accurately
assembled in mass production; the provision of such a motor
having components capable of taking up tolerances to minimize
the effect of additive tolerances; the provision of such a
motor which can be re-programmed following final assembly; the
provision of such a motor which inhibits the intrusion of
water into the motor; and the provision of such a motor which
resists damage and malfunction in lower temperature
operations.
Further among the several objects and features of the
present invention may be noted the provision of a method of
assembling an electric motor which requires few steps and
minimal labor; the provision of such a method which minimizes
the number of connections which must be made; the provision of
such a method which minimizes the effect of additive
tolerances; the provision of such a method which permits
programming and testing following final assembly; and the
provision of such a method which is easy to use.
In one form, the invention comprises an electric motor.
A stator includes a stator core having a winding thereon. A
rotor includes a shaft received in the stator core for
rotation of the rotor relative to the stator about the
longitudinal axis of the shaft. A housing connected together
with the stator and rotor forms an assembled motor, the
housing being adapted to support the stator and rotor. A
printed circuit board having programmable components thereon
03LO06781A CA 02622790 2008-03-14
4
controls operation of the motor, the printed circuit board
having contacts mounted thereon for use in programming the
programmable components, the printed circuit board being
received in the housing. The housing has a port therein
generally in registration with the contacts on the printed
circuit board, the port being sized and shaped to receive a
probe connected to a microprocessor into connection to the
contacts inside the housing for programming the motor.
In another form, the invention comprises a method of
assembling an electric motor comprising the steps of:
forming a stator including a stator core and a winding
thereon;
forming a rotor including a rotor shaft;
forming a housing adapted to support and at least
partially enclose the stator and rotor;
connecting a printed circuit board having a programmable
component thereon to the winding;
assembling the stator, rotor and housing such that the
printed circuit board is enclosed in the housing;
inserting a probe through a port in the housing into
connection with contacts on the printed circuit board
subsequent to said step of assembling the stator, rotor and
housing; and
programming the programmable component through the probe
connection to the printed circuit board.
Other objects and features of the present invention will
be in part apparent and in part pointed out hereinafter.
Brief Description of the Drawings
FIG. 1 is an exploded elevational view of an electric
motor in the form of a fan;
FIG. 2 is an exploded perspective view of component
parts of a stator of the motor;
CA 02622790 2008-03-14
03L006781A
FIG. 3 is a vertical cross sectional view of the
assembled motor;
FIG. 4 is the stator and a printed circuit board exploded
from its installed position on the stator;
FIG. 5 is an enlarged, fragmentary view of the shroud of
Fig. 1 as seen from the right side;
FIG. 6 is a side elevational view of a central locator
member and rotor shaft bearing;
FIG. 7 is a right end elevational view thereof;
FIG. 8 is a longitudinal section of the locator member
and bearing;
FIG. 9 is an end view of a stator core of the stator with
the central locator member and pole pieces positioned by the
locator member shown in phantom;
FIG. 10 is an opposite end view of the stator core;
FIG. 11 is a section taken in the plane including line
11-11 of Fig. 10;
FIG. 12 is a greatly enlarged, fragmentary view of the
motor at the junction of a rotor hub with the stator;
FIG. 13 is a section taken in the plane including line
13-13 of Fig. 5, showing the printed circuit board in phantom
and illustrating connection of a probe to a printed circuit
board in the shroud and a stop;
FIG. 14 is a section taken in the plane including line
14-14 of Fig. 5 showing the printed circuit board in phantom
and illustrating a power connector plug exploded from a plug
receptacle of the shroud;
FIG. 15 is an enlarged, fragmentary view of the motor
illustrating snap connection of the stator/rotor subassembly
with the shroud;
FIG. 16 is a block diagram of the microprocessor
controlled single phase motor according to the invention;
FIG. 17 is a schematic diagram of the power supply of the
motor of Figure 16 according to the invention. Alternatively,
CA 02622790 2008-03-14
03L006781A
6
the power supply circuit could be modified for a DC input or
for a non-doubling AC input.
FIG. 18 is a schematic diagram of the low voltage reset
for the microprocessor of the motor of Figure 16 according to
the invention.
FIG. 19 is a schematic diagram of the strobe for the Hall
sensor of the motor of Figure 16 according to the invention.
FIG. 20 is a schematic diagram of the microprocessor of
the motor of Figure 16 according to the invention.
FIG. 21 is a schematic diagram of the Hall sensor of the
motor of Figure 16 according to the invention.
FIG. 22 is a schematic diagram of the H-bridge array of
switches for commutating the stator of the motor of Figure 16
according to the invention.
FIG. 23 is a flow diagram illustrating the operation of
the microprocessor of the motor of the invention in a mode in
which the motor is commutated at a constant air flow rate at a
speed and torque which are defined by tables which exclude
resonant points.
FIG. 24 is a flow diagram illustrating operation of the
microprocessor of the motor of the invention in a run mode
(after start) in which the safe operating area of the motor is
maintained without current sensing by having a minimum off
time for each power switch, the minimum off time depending on
the speed of the rotor.
FIG. 25 is a timing diagram illustrating the start up
mode which provides a safe operating area (SOA) control based
on speed.
FIG. 26 is a flow chart of one preferred embodiment of
implementation of the timing diagram of Figure 25 illustrating
the start up mode which provides a safe operating area (SOA)
control based on speed.
CA 02622790 2008-03-14
03L006781A
7
FIG. 27 is a timing diagram illustrating the run up mode
which provides a safe operating area (SOA) control based on
speed.
FIG. 28 is a flow diagram illustrating the operation of
the microprocessor of the motor of the invention in a run mode
started after a preset number of commutations in the start up
mode wherein in the run mode the microprocessor commutates the
switches for N commutations at a constant commutation period
and wherein the commutation period is adjusted every M
commutations as a function of the speed, the torque or the
constant air flow rate of the rotor.
Corresponding reference characters indicate corresponding
parts throughout the several views of the drawings.
Detailed Description of the Preferred Embodiment
Referring now to the drawings, and in particular to Figs.
1 and 3, an electric motor 10 constructed according to the
principles of the present invention includes a stator 22, a
rotor 24 and a housing 26 (the reference numerals designating
their subjects generally). In the illustrated embodiment, the
motor 10 is of the type which the rotor magnet is on the
outside of the stator, and is shown in the form of a fan.
Accordingly, the rotor 24 includes a hub 28 having fan blades
30 formed integrally therewith and projecting radially from
the hub. The hub 28 and fan blades 30 are formed as one piece
of a polymeric material. The hub is open at one end and
defines a cavity in which a rotor shaft 32 is mounted on the
axis of the hub (Fig. 3). The shaft 32 is attached to the hub
28 by a insert 34 which is molded into the hub, along with the
end of the shaft when the hub and fan blades 30 are formed. A
rotor magnet 35 exploded from the rotor in Fig. 1 includes a
magnetic material and iron backing. For simplicity, the rotor
magnet 35 is shown as a unitary material in the drawings. The
03L006781A CA 02622790 2008-03-14
8
back iron is also molded into the hub cavity at the time the
hub is formed.
The stator, 22 which will be described in further detail
below, is substantially encapsulated in a thermoplastic
material. The encapsulating material also forms legs 36
projecting axially of the stator 22. The legs 36 each have a
catch 38 formed at the distal end of the leg. A printed
circuit board generally indicated at 40, is received between
the legs 36 in the assembled motor 10, and includes components
42, at least one of which is programmable, mounted on the
board. A finger 44 projecting from the board 40 mounts a Hall
device 46 which is received inside the encapsulation when the
circuit board is disposed between the legs 36 of the stator
22. In the assembled motor 10, the Hall device 46 is in close
proximity to the rotor magnet 35 for use in detecting rotor
position to control the operation of the motor. The stator 22
also includes a central locator member generally indicated at
48, and a bearing 50 around which the locator member is
molded. The bearing 50 receives the rotor shaft 32 through
the stator 22 for mounting the rotor 24 on the stator to form
a subassembly. The rotor 24 is held on the stator 22 by an E
clip 52 attached to the free end of the rotor after it is
inserted through the stator.
The housing 26 includes a cup 54 joined by three spokes
56 to an annular rim 58. The spokes 56 and annular rim 58
generally define a shroud around the fan blades 30 when the
motor 10 is assembled. The cup 54, spokes 56 and annular rim
58 are formed as one piece from a polymeric material in the
illustrated embodiment. The cup 54 is substantially closed on
the left end (as shown in Figs. 1 and 3), but open on the
right end so that the cup can receive a portion of the
stator/rotor subassembly. The annular rim 58 has openings 60
for receiving fasteners through the rim to mount the motor in
a desired location, such as in a refrigerated case (not
03L006781A CA 02622790 2008-03-14
9
shown). The interior of the cup 54 is formed with guide
channels 62 (Fig. 5) which receive respective legs 36. A
shoulder 64 is formed in each guide channel 62 near the closed
end of the cup 54 which engages the catch 38 on a leg to
connect the leg to the cup (see Figs. 3 and 16). The diameter
of the cup 54 narrows from the open toward the closed end of
the cup so that the legs 36 are resiliently deflected radially
inwardly from their relaxed positions in the assembled motor
to hold the catches 38 on the shoulders 64. Small openings
66 in the closed end of the cup 54 (Fig. 5) permit a tool (not
shown) to be inserted into the cup to pry the legs 36 off of
the shoulders 64 for releasing the connection of the
stator/rotor subassembly from the cup. Thus, it is possible
to nondestructively disassemble the motor 10 for repair or
reconfiguration (e.g., such as by replacing the printed
circuit board 40). The motor may be reassembled by simply
reinserting the legs 36 into the cup 54 until they snap into
connection.
One application for which the motor 10 of the illustrated
in the particular embodiment is particularly adapted, is as an
evaporator fan in a refrigerated case. In this environment,
the motor will be exposed to water. For instance, the case
may be cleaned out by spraying water into the case. Water
tends to be sprayed onto the motor 10 from above and to the
right of the motor in the orientation shown in Fig. 3, and
potentially may enter the motor wherever there is an opening
or joint in the construction of the motor. The encapsulation
of the stator 22 provides protection, but it is desirable to
limit the amount of water which enters the motor. One
possible site for entry of what is at the junction of the hub
28 of the rotor and the stator 22. An enlarged fragmentary
view of this junction is shown in Fig. 12. The thermoplastic
material encapsulating the stator is formed at this junction
to create a tortuous path 68. Moreover, a skirt 70 is formed
03L006781A CA 02622790 2008-03-14
which extends radially outwardly from the stator. An outer
edge 72 of the skirt 70 is beveled so that water directed from
the right is deflected away from the junction.
The openings 66 which permit the connection of the
stator/rotor subassembly to be released are potentially
susceptible to entry of water into the cup where it may
interfere with the operation of the circuit board. The
printed circuit board 40, including the components 42, is
encapsulated to protect it from moisture. However, it is
still undesirable for substantial water to enter the cup.
Accordingly, the openings 66 are configured to inhibit entry
of water. Referring now to Fig. 15, a greatly enlarged view
of one of the openings 66 shows a radially outer edge 66a and
a radially inner edge 66b. These edges lie in a plane Pl
which has an angle to a plane P2 generally parallel to the
longitudinal axis of the rotor shaft of at least about 45 .
It is believed that water is sprayed onto the motor at an
angle of no greater than 45 . Thus, it may be seen that the
water has no direct path to enter the opening 66 when it
travels in a path making an angle of 45 or less will either
strike the side of the cup 54, or pass over the opening, but
will not enter the opening.
The cup 54 of the housing 26 is also constructed to
inhibit rnotor failures which can be caused by the formation of
ice within the cup when the motor 10 is used in a refrigerated
environment. More particularly, the printed circuit board 40
has power contacts 74 mounted on and projecting outwardly from
the circuit board (Fig. 4). These contacts are aligned with
an inner end of a plug receptacle 76 which is formed in the
cup 54. Referring to Fig. 14, the receptacle 76 receives a
plug 78 connected to an electrical power source remote from
the motor. External controls (not shown) are also connected
to the printed circuit board 40 through the plug 78. The
receptacle 76 and the plug 78 have corresponding, rectangular
CA 02622790 2008-03-14
03L006781A
11
cross sections so that when the plug is inserted, it
substantially closes the plug receptacle.
When the plug 78 is fully inserted into the plug
receptacle 76, the power contacts 74 on the printed circuit
board 40 are received in the plug, but only partially. The
plug receptacle 76 is formed with tabs 80 (near its inner end)
which engage the plug 78 and limit the depth of insertion of
the plug into the receptacle. As a result, the plug 78 is
spaced from the printed circuit board 40 even when it is fully
inserted in the plug receptacle 76. In the preferred
embodiment, the spacing is about 0.2 inches. However, it is
believed that a spacing of about 0.05 inches would work
satisfactorily. Notwithstanding the partial reception of the
power contacts 74 in the plug 78, electrical connection is
made. The exposed portions of the power contacts 74, which
are made of metal, tend to be subject to the formation of ice
when the motor 10 is used in certain refrigeration
environments. However, because the plug 78 and circuit board
40 are spaced, the formation of ice does not build pressure
between the plug and the circuit board which would push the
plug further away from the circuit board, causing electrical
disconnection. Ice may and will still form on the exposed
power contacts 74, but this will not cause disconnection, or
damage to the printed circuit board 40 or the plug 78.
As shown in Fig. 13, the printed circuit board 40 also
has a separate set of contacts 82 used for programming the
motor 10. These contacts 82 are aligned with a tubular port
84 formed in the cup 54 which is normally closed by a stop 86
removably received in the port. When the stop 86 is removed
the port can receive a probe 88 into connection with the
contacts 82 on the circuit board 40. The probe 88 is
connected to a microprocessor or the like (not shown) for
programming or, importantly, re-programming the operation of
the motor after it is fully assembled. For instance, the
03L00 67 81A CA 02622790 2008-03-14
12
speed of the motor can be changed, or the delay prior to
starting can be changed. Another example in the context of
refrigeration is that the motor can be re-programmed to
operate on different input, such as when demand defrost is
employed. The presence of the port 84 and removable stop 86
allow the motor to be re-programmed long after final assembly
of the motor and installation of the motor in a given
application.
The port 84 is keyed so that the probe can be inserted in
only one way into the port. As shown in Fig. 5, the key is
manifested as a trough 90 on one side of the port 84. The
probe has a corresponding ridge which is received in the
trough when the probe is oriented in the proper way relative
to the trough. In this way, it is not possible to incorrectly
connect the probe 88 to the programming contacts. If the
probe 88 is not properly oriented, it will not be received in
the port 84.
As shown in Fig. 2, the stator includes a stator core (or
bobbin), generally indicated at 92, made of a polymeric
material and a winding 94 wound around the core. The winding
leads are terminated at a terminal pocket 96 formed as one
piece with the stator core 92 by terminal pins 98 received in
the terminal pocket. The terminal pins 98 are attached in a
suitable manner, such as by soldering to the printed circuit
board 40. However, it is to be understood that other ways of
making the electrical connection can be used without departing
from the scope of the present invention. It is envisioned
that a plug-in type connection (not shown) could be used so
that no soldering would be necessary.
The ferromagnetic material for conducting the magnetic
flux in the stator 22 is provided by eight distinct pole
pieces, generally indicated at 100. Each pole piece has a
generally U-shape and including a radially inner leg 100a, a
radially outer leg 100b and a connecting cross piece 100c.
CA 02622790 2008-03-14
03L006781A
13
The pole pieces 100 are each preferably formed by stamping
relatively thin U-shaped laminations from a web of steel and
stacking the laminations together to form the pole piece 100.
The laminations are secured together in a suitable manner,
such as by welding or mechanical interlock. One form of
lamination (having a long radially outer leg) forms the middle
portion of the pole piece 100 and another form of lamination
forms the side portions. It will be noted that one pole piece
(designated 100' in Fig. 2) does not have one side portion.
This is done intentionally to leave a space for insertion of
the Hall device 46, as described hereinafter. The pole pieces
100 are mounted on respective ends of the stator core 92 so
that the radially inner leg 100a of each pole piece is
received in a central opening 102 of the stator core and the
radially outer leg 100b extends axially along the outside of
the stator core across a portion of the winding. The middle
portion of the radially outwardly facing side of the radially
outer leg 100b, which is nearest to the rotor magnet 35 in the
assembled motor, is formed with a notch 100d. Magnetically,
the notch 100d facilitates positive location of the rotor
magnet 35 relative to the pole pieces 100 when the motor is
stopped. The pole pieces could also be molded from magnetic
material without departing from the scope of the present
invention. In certain, low power applications, there could be
a single pole piece stamped from metal (not shown), but having
multiple (e.g., four) legs defining the pole piece bent down
to extend axially across the winding.
The pole pieces 100 are held and positioned by the stator
core 92 and a central locator member, generally indicated at
104. The radially inner legs 100a of the pole pieces are
positioned between the central locator member 104 and the
inner diameter of the stator core 92 in the central opening
102 of the stator core. Middle portions of the inner legs
100a are formed from the same laminations which make up the
03L006781A CA 02622790 2008-03-14
14
middle portions of the outer legs 100b, and are wider than the
side portions of the inner legs. The radially inner edge of
the middle portion of each pole piece inner leg 100a is
received in a respective seat 104a formed in the locator
member 104 to accept the middle portion of the pole piece.
The seats 104a are arranged to position the pole pieces 100
asymmetrically about the locator member 104. No plane
passing through the longitudinal axis of the locator member
104 and intersecting the seat 104a perpendicularly bisects the
seat, or the pole piece 100 located by the seat. As a result,
the gap between the radially outer legs 100b and the permanent
magnet 35 of the rotor 24 is asymmetric to facilitate starting
the motor.
The radially outer edge of the inner leg 100a engages
ribs 106 on the inner diameter of the stator core central
opening 102. The configuration of the ribs 106 is best seen
in Figs. 9-11. A pair of ribs (106a, 106b, etc.) is provided
for each pole piece 100. The differing angulation of the
ribs 106 apparent from Figs. 9 and 10 reflects the angular
offset of the pole pieces 100. The pole pieces and central
locator member 104 have been shown in phantom in Fig. 9 to
illustrate how each pair is associated with a particular pole
piece on one end of the stator core. One of the ribs 106d' is
particularly constructed for location of the unbalanced pole
piece 100', and is engageable with the side of the inner leg
100a' rather than its radially outer edge. Another of the
ribs 106d associated with the unbalanced pole piece has a
lesser radial thickness because it engages the radially outer
edge of the wider middle portion of the inner leg 100a'.
The central locator member 104 establishes the radial
position of each pole piece 100. As discussed more fully
below, some of the initial radial thickness of the ribs 106
may be sheared off by the inner leg 100a upon assembly to
accommodate tolerances in the stator core 92, pole piece 100
03L00 67 8lA CA 02622790 2008-03-14
and central locator member 104. The radially inner edge of
each outer leg 100b is positioned in a notch 108 formed on
the periphery of the stator core 92. Referring now to Figs.
6-8, the central locator member 104 has opposite end sections
which have substantially the same shape, but are angularly
offset by 45 about the longitudinal axis of the central
locator member (see particularly Fig. 7). The offset
provides the corresponding offset for each of the four pole
pieces 100 on each end of the stator core 92 to fit onto the
stator core without interfering with one of the pole pieces
on the opposite end. It is apparent that the angular offset
is determined by the number of pole pieces 100 (i.e., 360
divided by the number of pole pieces), and would be different
if a different number of pole pieces were employed. The
shape of the central locator member 104 would be
corresponding changed to accommodate a different number of
pole pieces 100. As shown in Fig. 8, the central locator
member 104 is molded around a metal rotor shaft bearing 110
which is self lubricating for the life of the motor 10. The
stator core 92, winding 94, pole pieces 100, central locator
member 104 and bearing 110 are all encapsulated in a
thermoplastic material to form the stator 22. The ends of
the rotor shaft bearing 110 are not covered with the
encapsulating material so that the rotor shaft 32 may be
received through the bearing to mount the rotor 24 on the
stator 22 (see Fig. 3).
Method of Assembly
Having described the construction of the electric motor
10, a preferred method of assembly will now be described.
Initially, the component parts of the motor will be made. The
precise order of construction of these parts is not critical,
and it will be understood that some or all of the parts may be
made a remote location, and shipped to the final assembly
site. The rotor 24 is formed by placing the magnet 35 and the
03L006781A CA 02622790 2008-03-14
16
rotor shaft 32, having the insert 34 at one end, in a mold.
The hub 28 and fan blades 30 are molded around the magnet 35
and rotor shaft 32 so that they are held securely on the hub.
The housing 26 is also formed by molding the cup 54, spokes
56 and annular rim 58 as one piece. The cup 54 is formed
internally with ribs 112 (Fig. 5) which are used for securing
the printed circuit board 40, as will be described. The
printed circuit board 40 is formed in a conventional manner
by connection of the components 42 to the board. In the
preferred embodiment, the programming contacts 82 and the
power contacts 74 are shot into the circuit board 40, rather
than being mounted by soldering (Fig. 4). The Hall device 46
is mounted on the finger 44 extending from the board and
electrically connected to components 42 on the board.
The stator 22 includes several component parts which are
formed prior to a stator assembly. The central locator member
104 is formed by molding around the bearing 110, which is made
of bronze. The ends of the bearing 110 protrude from the
locator member 104. The bearing 110 is then impregnated with
lubricant sufficient to last the lifetime of the motor 10.
The stator core 92 (or bobbin) is molded and wound with magnet
wire and terminated to form the winding 94 on the stator core.
The pole pieces 100 are formed by stamping multiple, thin,
generally U-shaped laminations from a web of steel. The
laminations are preferably made in two different forms, as
described above. The laminations are stacked together and
welded to form each U-shaped pole piece 100, the laminations
having the longer outer leg and wider inner leg forming middle
portions of the pole pieces. However, one pole piece 100' is
formed without one side portion so that a space will be left
for the Hall device 46.
The component parts of the stator 22 are assembled in a
press fixture (not shown). The four pole pieces 100 which
will be mounted on one end of the stator core 92 are first
CA 02622790 2008-03-14
03L006781A
17
placed in the fixture in positions set by the fixture which
are 90 apart about what will become the axis of rotation of
the rotor shaft 32. The pole pieces 100 are positioned so
that they open upwardly. The central locator member 104 and
bearing 110 are placed in the fixture in a required
orientation and extend through the central opening 102 of the
stator core 92. The radially inner edges of the middle
portions of the inner legs 100a of the pole pieces are
received in respective seats 104a formed on one end of the
central locator member 104. The wound stator core 92 is set
into the fixture generally on top of the pole pieces
previously placed in the fixture. The other four pole pieces
100 are placed in the fixture above the stator core 92, but
in the same angular position they will assume relative to the
stator core when assembly is complete. The pole pieces 100
above the stator core 92 open downwardly and are positioned
at locations which are 45 offset from the positions of the
pole pieces at the bottom of the fixture.
The press fixture is closed and activated to push the
pole pieces 100 onto the stator core 92. The radially inner
edges of the inner legs 100a of the pole pieces 100 engage
their respective seats 104a of the central locator member.
The seat 104a sets the radial position of the pole piece 100
it engages. The inner legs 100a of the pole pieces 100 enter
the central opening 102 of the stator core 92 and engage the
ribs 106 on the stator core projecting into the central
opening. The variances in radial dimensions from design
specifications in the central locator member 104, pole pieces
100 and stator core 92 caused by manufacturing tolerances are
accommodated by the inner legs 100a shearing off some of the
material of the ribs 106 engaged by the pole piece. The
shearing action occurs as the pole pieces 100 are being passed
onto the stator core 92. Thus, the tolerances of the stator
core 92 are completely removed from the radial positioning of
CA 02622790 2008-03-14
03L006781A
18
the pole pieces. The radial location of the pole pieces 100
must be closely controlled so as to keep the air gap between
the pole pieces and the rotor magnet 35 as small as possible
without mechanical interference of the stator 22 and rotor 24.
The assembled stator core 92, pole pieces 100, central
locator member 104 and bearing 110 are placed in a mold and
substantially encapsulated in a suitable fire resistant
thermoplastic. In some applications, the mold material may
not have to be fire resistant. The ends of the bearing 110
are covered in the molding process and remain free of the
encapsulating material. The terminal pins 98 for making
electrical connection with the winding 94 are also not
completely covered by the encapsulating material (see Fig. 4).
The skirt 70 and legs 36 are formed out of the same material
which encapsulates the remainder of the stator. The legs 36
are preferably relatively long, constituting approximately one
third of the length of the finished, encapsulated stator.
Their length permits the legs 36 to be made thicker for a more
robust construction, while permitting the necessary resilient
bending needed for snap connection to the housing 26. In
addition to the legs 36 and skirt 70, two positioning tangs
114 are formed which project axially in the same direction as
the legs and require the stator 22 to be in a particular
angular orientation relative to the housing 26 when the
connection is made. Still further, printed circuit board
supports are formed. Two of these take the form of blocks
116, from one of which project the terminal pins 98, and two
others are posts 118 (only one of which is shown).
The encapsulated stator 22 is then assembled with the
rotor 24 to form the stator/rotor subassembly. A thrust
washer 120 (Fig. 3) is put on the rotor shaft 32 and slid down
to the fixed end of the rotor shaft in the hub 28. The thrust
washer 120 has a rubber-type material on one side capable of
absorbing vibrations, and a low friction material on the other
CA 02622790 2008-03-14
03L006781A
19
side to facilitate a sliding engagement with the stator 22.
The low friction material side of the washer 120 faces axially
outwardly toward the open end of the hub 28. The stator 22 is
then dropped into the hub 28, with the rotor shaft 32 being
received through the bearing 110 at the center of the stator.
One end of the bearing 110 engages the low friction side of
the thrust washer 120 so that the hub 28 can rotate freely
with respect to the bearing. Another thrust washer 122 is
placed on the free end of the bearing 110 and the E clip 52 is
shaped onto the end of the rotor shaft 32 so that the shaft
cannot pass back through the bearing. Thus, the rotor 24, is
securely mounted on the stator 22.
The printed circuit board 40 is secured to the
stator/rotor subassembly. The assembly of the printed circuit
board 40 is illustrated in Fig. 4, except that the rotor 24
has been removed for clarity of illustration. The printed
circuit board 40 is pushed between the three legs 36 of the
stator 22. The finger 44 of the circuit board 40 is received
in an opening 124 formed in the encapsulation so that the Hall
device 46 on the end of the finger is positioned within the
encapsulation next to the unbalanced pole piece 100', which
was made without one side portion so that space would be
provided for the Hall device. The side of the circuit board
40 nearest the stator 22 engages the blocks 116 and posts 118
which hold the circuit board at a predetermined spaced
position from the stator. The terminal pins 98 projecting
from the stator 22 are received through two openings 126 in
the circuit board 40. The terminal pins 98 are electrically
connected to the components 42 circuit board in a suitable
manner, such as by soldering. The connection of the terminal
pins 98 to the board 40 is the only fixed connection of the
printed circuit board to the stator 22.
The stator/rotor subassembly and the printed circuit
board 40 are then connected to the housing 26 to complete the
CA 02622790 2008-03-14
03L006781A
assembly of the motor. The legs 36 are aligned with
respective channels 62 in the cup 54 and the tangs 114 are
aligned with recesses 128 formed in the cup (see Figs. 5 and
14). The legs 36 will be received in the cup 54 in only one
orientation because of the presence of the tangs 114. The
stator/rotor subassembly is pushed into the cup 54. The free
ends of the legs 36 are beveled on their outer ends to
facilitate entry of the legs into the cup 54. The cup tapers
slightly toward its closed end and the legs 36 are deflected
radially inwardly from their relaxed configurations when they
enter the cup and as they are pushed further into it. When
the catch 38 at the end of each leg clears the shoulder 64 at
the inner end of the channel 62, the leg 36 snaps radially
outwardly so that the catch engages the shoulder. The leg 36
is still deflected from its relaxed position so that it is
biased radially outwardly to hold the catch 38 on the shoulder
64. The engagement of the catch 38 with the shoulder 64
prevents the stator/rotor subassembly, and printed circuit
board 40 from being withdrawn from the cup 54. The motor 10
is now fully assembled, without the use of any fasteners, by
snap together construction.
The printed circuit board 40 is secured in place by an
interference fit with the ribs 112 in the cup 54. As the
stator/rotor assembly advances into the cup 54, peripheral
edges of the circuit board 40 engage the ribs 112. The ribs
are harder than the printed circuit board material so that the
printed circuit board is partially deformed by the ribs 112 to
create the interference fit. In this way the printed circuit
board 40 is secured in place without the use of any fasteners.
The angular orientation of the printed circuit board 40 is set
by its connection to the terminal pins 98 from the stator 22.
The programming contacts 82 are thus aligned with the port 84
and the power contacts 74 are aligned with the plug receptacle
76 in the cup 54. It is also envisioned that the printed
CA 02622790 2008-03-14
03L006781A
21
circuit board 40 may be secured to the stator 22 without any
interference fit with the cup 54. For instance, a post (not
shown) formed on the stator 22 may extend through the circuit
board and receive a push nut thereon against the circuit board
to fix the circuit board on the stator.
In the preferred embodiment, the motor 10 has not been
programmed or tested prior to the final assembly of the motor.
Following assembly, a ganged connector (not shown, but
essentially a probe 88 and a power plug 78) is connected to
the printed circuit board 40 through the port and plug
receptacle 76. The motor is then programmed, such as by
setting the speed and the start delay, and tested. If the
circuit board 40 is found to be defective, it is possible to
non-destructively disassemble the motor and replace the
circuit board without discarding other parts of the motor.
This can be done be inserting a tool (not shown) into the
openings 66 in the closed end of the cup 54 and prying the
catches 38 off the shoulders 64. If the motor passes the
quality assurance tests, the stop 86 is placed in the port 84
and the motor is prepared for shipping.
It is possible with the motor of the present invention,
to re-program the motor 10 after it has been shipped from the
motor assembly site. The end user, such as a refrigerated
case manufacturer, can remove the stop 86 from the port 84 and
connect the probe 88 to the programming contacts 82 through
the port. The motor can be re-programmed as needed to
accommodate changes made by the end user in operating
specifications for the motor.
The motor 10 can be installed, such as in a refrigerated
case, by inserting fasteners (not shown) through the openings
60 in the annular rim 58 and into the case. Thus, the housing
26 is capable of supporting the entire motor through
connection of the annular rim 58 to a support structure. The
motor is connected to a power source by plugging the plug 78
CA 02622790 2008-03-14
03L006781A
22
into the plug receptacle 76 (Fig. 14). Detents 130 (only one
is shown) on the sides of the plug 78 are received in slots on
respective sides of a tongue 132 to lock the plug in the plug
receptacle 76. Prior to engaging the printed circuit board
40, the plug 78 engages the locating tabs 80 in the plug
receptacle 76 so that in its fully inserted position, the plug
is spaced from the printed circuit board. As a result, the
power contacts 74 are inserted far enough into the plug 78 to
make electrical connection, but are not fully received in the
plug. Therefore, although ice can form on the power contacts
74 in the refrigerated case environment, it will not build up
between the plug 78 and the circuit board 40 causing
disconnection and/or damage.
Figure 16 is a block diagram of the microprocessor
controlled single phase motor 500 according to the invention.
The motor 500 is powered by an AC power source 501. The motor
500 includes a stator 502 having a single phase winding. The
direct current power from the source 501 is supplied to a
power switching circuit via a power supply circuit 503. The
power switching circuit may be any circuit for commutating the
stator 502 such as an H-bridge 504 having power switches for
selectively connecting the dc power source 501 to the single
phase winding of the stator 502. A permanent magnet rotor 506
is in magnetic coupling relation to the stator and is rotated
by the commutation of the winding and the magnetic field
created thereby. Preferably, the motor is an inside-out motor
in which the stator is interior to the rotor and the exterior
rotor rotates about the interior stator. However, it is also
contemplated that the rotor may be located within and internal
to an external stator.
A position sensor such as a hall sensor 508 is positioned
on the stator 502 for detecting the position of the rotor 506
relative to the winding and for providing a position signal
via line 510 indicating the detected position of the rotor
CA 02622790 2008-03-14
03L006781A
23
506. Reference character 512 generally refers to a control
circuit including a microprocessor 514 responsive to and
receiving the position signal via line 510. The
microprocessor 514 is connected to the H-bridge 504 for
selectively commutating the power switches thereof to
commutate the single phase winding of the stator 502 as a
function of the position signal.
Voltage VDD to the microprocessor 514 is provided via
line 516 from the power supply circuit 503. A low voltage
reset circuit 518 monitors the voltage VDD on line 516 and
applied to the microprocessor 514. The reset circuit 518
selectively resets the microprocessor 514 when the voltage VDD
applied to the microprocessor via line 516 transitions from
below a predetermined threshold to above the predetermined
threshold. The threshold is generally the minimum voltage
required by the microprocessor 514 to operate. Therefore, the
purpose of the reset circuit 518 is to maintain operation and
re-establish operation of the microprocessor in the event that
the voltage VDD supplied via line 516 drops below the preset
minimum required by the microprocessor 514 to operate.
Optionally, to save power, the hall sensor 508 may be
intermittently powered by a hail strobe 520 controlled by the
microprocessor 514 to pulse width modulate the power applied
to the hail sensor.
The microprocessor 514 has a control input 522 for
receiving a signal which affects the control of the motor 500.
For example, the signal may be a speed select signal in the
event that the microprocessor is programmed to operate the
rotor such that the stator is commutated at two or more
discrete speeds. Alternatively, the motor may be controlled
at continuously varying speeds or torques according to
temperature. For example, in place of or in addition to the
hall sensor 508, an optional temperature sensor 524 may be
provided to sense the temperature of the ambient air about the
CA 02622790 2008-03-14
03L006781A
24
motor. This embodiment is particularly useful when the rotor
506 drives a fan which moves air through a condenser for
removing condenser generated heat or which moves air through
an evaporator for cooling, such as illustrated in Figures 1-
15.
In one embodiment, the processor interval clock
corresponds to a temperature of the air moving about the motor
and for providing a temperature signal indicating the detected
temperature. For condenser applications where the fan is
blowing air into the condenser, the temperature represents the
ambient temperature and the speed (air flow) is adjusted to
provide the minimum needed air flow at the measured
temperature to optimize the heat transfer process. When the
fan is pulling air over the condenser, the temperature
represents ambient temperature plus the change in temperature
(Lt) added by the heat removed from the condenser by the air
stream. In this case, the motor speed is increased in
response to the higher combined temperature (speed is
increased by increasing motor torque, i.e., reducing the power
device off time PDOFFTIM; see Fig. 26). Additionally, the
speed the motor could be set for different temperature bands
to give different air flow which would be distinct constant
air flows in a given fan static pressure condition. Likewise,
in a condenser application, the torque required to run the
motor at the desired speed represents the static load on the
motor. The higher static loads can be caused by installation
in a restricted environment, i.e., a refrigerator installed as
a built-in, or because the condenser air flow becomes
restricted due to dust build up or debris. Both of these
conditions may warrant an increased air flow/speed.
Similarly, in evaporator applications, the increased
static pressure could indicate evaporator icing or increased
packing density for the items being cooled.
CA 02622790 2008-03-14
03L006781A
In one of the commercial refrigeration applications, the
evaporator fan pulls the air from the air curtain and from the
exit air cooling the food. This exhaust of the fan is blown
through the evaporator. The inlet air temperature represents
air curtains and food exit air temperature. The fan speed
would be adjusted appropriately to maintain the desired
temperature.
Alternatively, the microprocessor 514 may commutate the
switches at a variable speed rate to maintain a substantially
constant air flow rate of the air being moved by the fan
connected to the rotor 506. In this case, the microprocessor
514 provides an alarm signal by activating alarm 528 when the
motor speed is greater than a desired speed corresponding to
the constant air flow rate at which the motor is operating.
As with the desired torque, the desired speed may be
determined by the microprocessor as a function of an initial
static load of the motor and changes in static load over time.
Figure 23 illustrates one preferred embodiment of the
invention in which the microprocessor 514 is programmed
according to the flow diagram therein. In particular, the
flow diagram of Figure 23 illustrates a mode in which the
motor is commutated at a constant air flow rate corresponding
to a speed and torque which are defined by tables which
exclude resonant points. For example, when the rotor is
driving a fan for moving air over a condenser, the motor will
have certain speeds at which a resonance will occur causing
increased vibration and/or increased audio noise. Speeds at
which such vibration and/or noise occur are usually the same
or similar and are predictable, particularly when the motor
and its associated fan are manufactured to fairly close
tolerances. Therefore, the vibration and noise can be
minimized by programming the microprocessor to avoid operating
at certain speeds or within certain ranges of speeds in which
the vibration or noise occurs. As illustrated in Figure 23,
CA 02622790 2008-03-14
03L006781A
26
the microprocessor 514 would operate in the following manner.
After starting, the microprocessor sets the target variable I
to correspond to an initial starting speed pointer defining a
constant air flow rate at step 550. For example, I=O. Next,
the microprocessor proceeds to step 552 and selects a speed
set point (SSP) from a table which correlates each of the
variable levels 0 to n to a corresponding speed set point
(SSP), to a corresponding power device off time (PDOFFTIM=Pmin)
for minimum power and to a corresponding power device off time
(PDOFFTIM=PmaX) for maximum power.
It is noted that as the PDOFFTIM increases, the motor
power decreases since the controlled power switches are off
for longer periods during each commutation interval.
Therefore, the flow chart of Fig. 23 is specific to this
approach. Others skilled in the art will recognize other
equivalent techniques for controlling motor power.
After a delay at step 554 to allow the motor to stabilize,
at step 556 the microprocessor 514 selects a PDOFFTIM for a
minimum power level (Pmin) from the table which provides
current control by correlating a minimum power level to the
selected level of variable I. At step 558 the microprocessor
selects a PDOFFTIM for a maximum power level (Pmax) from the
table which provides current control by correlating a maximum
power level to the selected variable level I.
At step 560, the microprocessor compares the actual
PDOFFTIM representing the actual power level to the minimum
PDOFFTIM (Pmin) for this I. If the actual PDOFFTIM is greater
than the minimum PDOFFTIM (PDOFFTIM > Pmin), the microprocessor
proceeds to step 562 and compares the variable level I to a
maximum value n. If I is greater or equal to n, the
microprocessor proceeds to step 564 to set I equal to n.
Otherwise, I must be less than the maximum value for I so the
microprocessor 514 proceeds to step 566 to increase I by one
step.
03L006781A CA 02622790 2008-03-14
27
If, at step 560, the microprocessor 514 determines that
the actual PDOFFTIM is less than or equal to the minimum
PDOFFTIM (PDOFFTIM :< Pmin), the microprocessor proceeds to step
568 and compares the actual PDOFFTIM representing the actual
power level to the maximum PDOFFTIM (Pmax) for this I. If the
actual PDOFFTIM is less than the maximum PDOFFTIM (PDOFFTIM <
Pmax), the microprocessor proceeds to step 570 and compares the
variable level I to a minimum value 0. If I is less or equal
to 0, the microprocessor proceeds to step 572 to set I equal
to 0. Otherwise, I must be greater than the minimum value for
I so the microprocessor 514 proceeds to step 574 to decrease I
by one step.
If the actual PDOFFTIM is less than or equal to the
minimum and is greater than or equal to the maximum so that
the answer to both steps 560 and 568 is no, the motor is
operating at the speed and power needed to provide the desired
air flow so the microprocessor returns to step 552 to maintain
its operation.
Alternatively, the microprocessor 514 may be programmed
with an algorithm which defines the variable rate at which the
switches are commutated. This variable rate may vary
continuously between a preset range of at least a minimum
speed Smin and not more than a maximum speed Smax except that a
predefined range of speeds Sl +/- S2 is excluded from the
preset range. As a result, for speeds between Sl - S2 and Sl,
the microprocessor operates the motor at Sl - S2 and for
speeds between Sl and Sl + S2, the microprocessor operates the
motor at speeds S1 + S2.
Figure 22 is a schematic diagram of the H-bridge 504
which constitutes the power switching circuit having power
switches according to the invention, although other
configurations may be used, such as two windings which are
single ended or the H-bridge configuration of U.S. Patent No.
5,859,519, incorporated by reference herein. The dc input
CA 02622790 2008-03-14
03L006781A
28
voltage is provided via a rail 600 to input switches Q1 and
Q2. An output switch Q3 completes one circuit by selectively
connecting switch Q2 and stator 502 to a ground rail 602. An
output switch Q4 completes another circuit by selectively
connecting switch Ql and stator 502 to the ground rail 602.
Output switch Q3 is controlled by a switch Q5 which receives a
control signal via port BQ5. Output switch Q4 is controlled
by a switch Q8 which receives a control signal via port BQ8.
When switch Q3 is closed, line 604 pulls the gate of Q1 down
to open switch Ql so that switch Q1 is always open when switch
Q3 is closed. Similarly, line 606 insures that switch Q2 is
open when switch Q4 is closed.
The single phase winding of the stator 502 has a first
terminal F and a second terminal S. As a result, switch Q1
constitutes a first input switch connected between terminal S
and the power supply provided via rail 600. Switch Q3
constitutes a first output switch connected between terminal S
and the ground rail 602. Switch Q2 constitutes a second input
switch connected between the terminal F and the power supply
provided via rail 600. Switch Q4 constitutes a second output
switch connected between terminal F and ground rail 602. As a
result, the microprocessor controls the first input switch Ql
and the second input switch Q2 and the first output switch Q3
and the second output switch Q4 such that the current through
the motion is provided during the first 90 of the commutation
period illustrated in Figure 27. The first 90 is significant
because of noise and efficiency reasons and applies to this
power device topology (i.e., either Ql or Q2 is always "on"
when either Q3 or Q4 is off, respectively. PDOFFTIM is the
term used in the software power control algorithms. When the
first output switch Q3 is open, the first input switch Q1 is
closed. Similarly, the second input switch Q2 is connected to
and responsive to the second output switch Q4 so that when the
second output switch Q4 is closed, the second input switch Q2
CA 02622790 2008-03-14
03L006781A
29
is open. Also, when the second output switch Q4 is open, the
second input switch Q2 is closed. This is illustrated in
Figure 27 wherein it is shown that the status of Ql is
opposite the status of Q3 and the status of Q2 is opposite
the status of Q4 at any instant in time.
Figure 26 is a timing flow chart illustrating the start
up mode with a current maximum determined by the setting of
PDOFFTIM versus the motor speed. In this mode, the power
devices are pulse width modulated by software in a continuous
mode to get the motor started. The present start algorithm
stays in the start mode eight commutations and then goes into
the RUN mode. A similar algorithm could approximate constant
acceleration by selecting the correct settings for PDOFFTIM
versus speed. At step 650, the value HALLIN is a constant
defining the starting value of the Hall device reading. When
the actual Hall device reading (HALLOLD) changes at step 652,
HALLIN is set to equal HALLOLD at step 654 and the PDOFFTIM is
changed at step 656 depending on the RPMs.
Figure 25 illustrates the microprocessor outputs (BQ5 and
BQ8) that control the motor when the strobed hall effect
output (HS3) changes state. In this example, BQ5 is being
pulse width modulated while HS3 is 0. When HS3 (strobed)
changes to a 1, there is a finite period of time (LATENCY) for
the microprocessor to recognize the magnetic change after
which BQ5 is in the off state so that BQ8 begins to pulse
width modulate (during PWMTIM).
Figure 24 illustrates another alternative aspect of the
invention wherein the microprocessor operates within a run
mode safe operating area without the need for current sensing.
In particular, according to Figure 24, microprocessor 514
controls the input switches Ql-Q4 such that each input switch
is open or off for a minimum period of time (PDOFFTIM) during
each pulse width modulation period whereby over temperature
protection is provided without current sensing. Specifically,
CA 02622790 2008-03-14
03L006781A
the minimum period may be a function of the speed of the rotor
whereby over temperature protection is provided without
current sensing by limiting the total current over time. As
illustrated in Figure 24, if the speed is greater than a
minimum value (i.e., if A < 165), A is set to 165 and SOA
limiting is bypassed and not required; if the speed is less
than (or equal to) a minimum value (i.e., if A? 165), the
routine of Fig. 24 ensures that the switches are off for a
minimum period of time to limit current. "A" is a variable
and is calculated by an equation that represents a PDOFFTIM
minimum value at a given speed (speed is a constant multiplied
by l/TINPS, where TINPS is the motor period). Then, if
PDOFFTIM is < A, PDOFFTIM is set to A so that the motor
current is kept to a maximum desired value at the speed the
motor is running.
As illustrated in Figure 18, the motor includes a reset
circuit 512 for selectively resetting the microprocessor when
a voltage of the power supply vdd transitions from below a
predetermined threshold to above a predetermined threshold.
In particular, switch Q6 disables the microprocessor via port
MCLR/VPP when the divided voltage between resistors R16 and
R17 falls below a predetermined threshold. The microprocessor
is reactivated and reset when the voltage returns to be above
the predetermined threshold thereby causing switch Q6 to
close.
Figure 19 illustrates one preferred embodiment of a
strobe circuit 520 for the hall sensor 508. The
microprocessor generates a pulse width modulated signal GP5
which intermittently powers the hall sensor 508 as shown in
Figure 21 by intermittently closing switch Q7 and providing
voltage VB2 to the hall sensor 508 via line HS1.
Figure 17 is a schematic diagram of the power supply
circuit 503 which supplies the voltage Vin for energizing the
stator single phase winding via the H-bridge 504 and which
CA 02622790 2008-03-14
03L006781A
31
also supplies various other voltages for controlling the H-
bridge 504 and for driving the microprocessor 514. In
particular, the lower driving voltages including VB2 for
providing control voltages to the switches Ql-Q4, VDD for
driving the microprocessor, HS2 for driving the hall sensor
508, and VSS which is the control circuit reference ground not
necessarily referenced to the input AC or DC voltage are
supplied from the input voltage Vin via a lossless inline
series capacitor Cl.
Figure 20 illustrates the inputs and outputs of
microprocessor 514. In particular, only a single input GP4
from the position sensor is used to provide information which
controls the status of control signal BQ5 applied to switch Q5
to control output switch Q3 and input switch Q1 and which
controls the status of control signal BQ8 applied to switch Q8
to control output switch Q4 and input switch Q2. Input GP2 is
an optional input for selecting motor speed or other feature
or may be connected for receiving a temperature input
comparator output when used in combination with thermistor
524.
Figure 28 illustrates a flow chart of one preferred
embodiment of a run mode in which the power devices are
current controlled. In this mode, the following operating
parameters apply:
MOTOR RUN POWER DEVICE (CURRENT) CONTROL
= At the end of each commutation, the time power devices will
be off the next time the commutation period is calculated.
OFFTIM = TINP/2. (The commutation period divided by 2 = 90 ).
While in the start routine, this is also calculated.
= After eight commutations (1 motor revolution) and at the
start routine exit, PWMTIM is calculated:
PWMTIM = OFFTIM/4
03L006781A CA 02622790 2008-03-14
32
=At the beginning of each commutation period, a counter
(COUNT8) is set to five to allow for four times the power
devices will be turned on during this commutation:
PWMSUM = PWMTIM
PDOFFSUM = PWMTIM-PDOFFTIM
TIMER = 0
(PDOFFTIM is used to control the amount of current in the
motor and is adjusted in the control algorithm (SPEED, TORQUE,
CFM, etc.).
=Commutation time set to 0 at each strobed hall change,
HALLOLD is the saved hall strobe value.
During motor run, the flow chart of Fig. 28 is executed during
each commutation period. In particular at step 702, the
commutation time is first checked to see if the motor has been
in this motor position for too long a period of time, in this
case 32mS. If it has, a locked rotor is indicated and the
program goes to the locked rotor routine at step 704.
Otherwise, the program checks to see if the commutation time
is greater then OFFTIM at step 706; if it is, the commutation
period is greater than 90 electrical degrees and the program
branches to step 708 which turns the lower power devices off
and exits the routine at step 710. Next, the commutation time
is compared at step 712 to PWMSUM. If it is less than PWMSUM,
the commutation time is checked at step 714 to see if it is
less or equal to PDOFFSUM where if true, the routine is exited
at step 716; otherwise the routine branches to step 708 (if
step 714 is yes).
For the other case where the commutation time is greater
or equal to PWMSUM, at step 718 PWMSUM and PDOFFSUM have
PWMTIM added to them to prepare for the next pulse width
modulation period and a variable A is set to COUNT 8-1.
03L006781A CA 02622790 2008-03-14
33
If A is equal to zero at step 720, the pulse width
modulations (4 pulses) for this commutation period are
complete and the program branches to step 708 to turn the
lower power devices off and exit this routine. If A is not
equal to zero, COUNT8 (which is a variable defining the number
of PWMs per commutation) is set to A at step 722; the
appropriate lower power device is turned on; and this routine
is exited at step 716. More PWM counts per commutation period
can be implemented with a faster processor. Four (4) PWMs per
commutation period are preferred for slower processors whereas
eight (8) are preferred for faster processors.
The timing diagram for this is illustrated in Figure 27.
In the locked rotor routine of step 704, on entry, the lower
power devices are turned off for 1.8 seconds after which a
normal start attempt is tried.
In view of the above, it will be seen that the several
objects of the invention are achieved and other advantageous
results attained.
As various changes could be made in the above
constructions without departing from the scope of the
invention, it is intended that all matter contained in the
above description or shown in the accompanying drawings shall
be interpreted as illustrative and not in a limiting sense.
