U.S. patent application number 12/250884 was filed with the patent office on 2009-02-12 for dc brushless motor for electrical power steering and the production method thereof.
This patent application is currently assigned to HITACHI, LTD. Invention is credited to Toshiyuki Innami, Takashi Ishigami, Masashi Kitamura, Osamu Koizumi, Mitsuaki Mirumachi, Masamichi Yagai.
Application Number | 20090039729 12/250884 |
Document ID | / |
Family ID | 34937214 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090039729 |
Kind Code |
A1 |
Innami; Toshiyuki ; et
al. |
February 12, 2009 |
DC Brushless Motor for Electrical Power Steering and the Production
Method Thereof
Abstract
The stator core of a motor comprises an annular back core, and a
plurality of tees created separately from the back core and secured
onto the inner periphery of the back core. A stator coil is wound
on each of the tees by a distributed or concentrated winding
method. The stator core and stator coil are formed by molding.
Inventors: |
Innami; Toshiyuki; (Mito,
JP) ; Mirumachi; Mitsuaki; (Hitachinaka, JP) ;
Koizumi; Osamu; (Higashiibaraki, JP) ; Yagai;
Masamichi; (Hitachinaka, JP) ; Kitamura; Masashi;
(Mito, JP) ; Ishigami; Takashi; (Hitachinaka,
JP) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
HITACHI, LTD
Tokyo
JP
|
Family ID: |
34937214 |
Appl. No.: |
12/250884 |
Filed: |
October 14, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11756210 |
May 31, 2007 |
7453179 |
|
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12250884 |
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|
11136423 |
May 25, 2005 |
7242128 |
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11756210 |
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Current U.S.
Class: |
310/254.1 ;
29/596 |
Current CPC
Class: |
H02K 3/28 20130101; H02K
11/33 20160101; H02K 1/148 20130101; H02K 1/185 20130101; Y10T
29/49009 20150115; B62D 5/0403 20130101; H02K 5/1732 20130101; H02K
5/225 20130101; H02K 29/06 20130101; H02K 11/00 20130101 |
Class at
Publication: |
310/254 ;
29/596 |
International
Class: |
H02K 1/18 20060101
H02K001/18; H02K 15/02 20060101 H02K015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2004 |
JP |
2004-165345 |
Claims
1. A DC brushless motor for electrical power steering for
outputting the steering torque, controlled by a power conversion
apparatus for converting the power obtained from an on-board power
source, into polyphase a.c. power and for outputting the power,
said DC brushless motor for electrical power steering comprising: a
frame; a stator secured on said frame; a rotor arranged opposite to
said stator through an air gap; a flange for blocking both ends of
the frame in the axial direction; and a sensor for checking the
magnetic pole position of the rotor said stator comprising; a
stator core; and a polyphase stator coil built in said stator core;
said stator core, formed by connecting a plurality of split core
pieces, comprising: an annular back core; and a plurality of tee
cores projected radially from said back core; wherein a slot is
formed on said tee core adjacent to said stator core, and said
stator coil is composed of a plurality of unit coils, and is
incorporated in said slot; said rotor comprising: a shaft; a rotor
core provided on the shaft; and a plurality of magnets fixed onto
the surface of the outer periphery of the rotor core; said DC
brushless motor for electrical power steering further characterized
in that said stator core and stator coil are molded by a molding
agent, with the stator coil incorporated in the stator core, said
shaft being rotatably supported by a bearing, said bearing being
arranged on the flange, one side of said flange being provided with
a recess, said recess, as a cylindrical member concentric with the
shaft, being located inward of the axial end of the frame and
extending to the position opposed to the coil end, and one side of
said bearing being arranged on the position of the recess radially
opposite to the coil end.
2. The DC brushless motor for electrical power steering described
in claim 1, wherein the sensor is arranged on the axial end of the
frame, and the flange with the recess arranged thereon blocks one
of the axial ends of the frame, equipped with the sensor.
3. The DC brushless motor for electrical power steering described
in claim 2, wherein one end of said shaft in the axial direction
expends further in the axial direction than one side of the bearing
and reaches said recess, and said sensor is arranged in the air gap
between the outer peripheral surface of the shaft and the
peripheral surface of the recess.
4. The DC brushless motor for electrical power steering described
in claim 3, said sensor comprising: a census tester with a coil
wound on the core; and a sensor rotor arranged opposite to the
census tester; wherein said census tester is secured on the
peripheral surface of the recess, while the sensor rotor is secured
on the outer peripheral surface of the shaft so as to be positioned
opposite to the census sensor through the air gap.
5. The DC brushless motor for electrical power steering described
in claim 1, wherein a plurality of unit coils are electrically
connected for each phase by the connection member arranged on one
side of the coil end, and the flange equipped with said recess
blocks the end on the side axially opposite to the coil end
equipped with said connection member.
6. The DC brushless motor for electrical power steering described
in claim 1, wherein the other end of the flange has a recess on the
side axially opposite to the coil end, said recess on the other end
of the flange being engaged with the tip of the coil end.
7. The DC brushless motor for electrical power steering described
in claim 1, wherein the coil end opposite axially to the other end
of the flange is covered with said molding agent so that an air gap
is formed between the frame and air space; the other end of said
flange provided with an annular protrusion extending in the axial
direction, and said protrusion being engaged with the air gap when
the other end of the flange is secured on the frame.
8. A DC brushless motor for electrical power steering manufacturing
method, driven by polyphase alternating current power, for
outputting steering torque, said manufacturing method comprising: a
first step of assembling a stator coil into a stator core; a
subsequent second step of press-fitting into the frame a plurality
of positions of the stator core incorporating the stator coil in
the circumferential direction, and obtaining a structure composed
of the stator core incorporating the stator coil, secured to the
frame; a subsequent third step of mounting a jig on said structure
in such a way that the jig and frame will enclose the stator core
and the coil end of the stator coil protruding axially from the
axial end of the stator core; a subsequent fourth step of injecting
the molding agent into the space enclosed by the jig and frame,
thereby filling the molding agent into the air gap between the coil
end and stator core, the air gap of the stator coil, the air gap
between stator core and stator coil, and the air gap between the
stator core and frame; a subsequent fifth step of solidifying the
molding agent; and a subsequent sixth step of removing the jig.
9. The DC brushless motor for electrical power steering
manufacturing method described in claim 8, further comprising the
steps of preparing a plurality of serrated coil pieces with coil by
winding a coil on the serrated core piece; and connecting a
plurality of serrated coil pieces with coil, to annular core
pieces, thereby obtaining said stator core incorporating the stator
coil.
10. The DC brushless motor for electrical power steering
manufacturing method described in claim 8, further comprising the
steps of: preparing a plurality of T-shaped core pieces with coil,
by winding the coil on the protruded portion of the T-shaped core
piece; and connecting a plurality of T-shaped core pieces in the
circumferential direction, thereby obtaining said stator core
incorporating the stator coil.
11. The DC brushless motor for electrical power steering
manufacturing method described in claim 8, further comprising the
steps of: electrically connecting one side of the coil end to a
plurality of unit coils constituting the stator coil using a
connection member; electrically connecting said connection member
to a cable extending outside from the frame; and molding one side
of the coil end with said molding agent in such a way that the
connection member and part of the cable are molded together with
one side of the coil end by the molding agent.
Description
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/756,210, filed May 31, 2007, which is a
divisional of U.S. patent application Ser. No. 11/136,423, filed
May 25, 2005, now U.S. Pat. No. 7,242,128, issued Jul. 10, 2007,
the entire disclosure of which is incorporated herein by reference,
which in turn claims priority under 35 U.S.C. .sctn.119 of prior
Japanese application no. 2004-165345, filed Jun. 3, 2004.
FIELD OF THE INVENTION
[0002] The present invention relates to a DC brushless motor for
electrical power steering and production method thereof.
BACKGROUND OF THE INVENTION
[0003] In the prior art DC brushless motor for electrical power
steering, the need for reducing the torque pulsation is known, as
described in the Japanese Patent Laid-open No. 2001-275325 and
Japanese Patent Laid-open No. 2003-250254.
SUMMARY OF THE INVENTION
[0004] Efforts have been made to reduce the torque pulsation,
without satisfactory reduction of torque pulsation having been
achieved so far. One of the problems to be solved in the DC
brushless motor for electrical power steering is how to achieve a
further reduction in torque pulsation.
[0005] The DC brushless motor for electrical power steering is
required to reduce torque pulsation and to generate a large torque
as required. For example, when the vehicle is stopped or is slowly
running close to the stopped state, if the steering wheel is
turned, the aforementioned motor is required to provide a large
torque due to the friction coefficient between the steering wheel
and ground surface.
[0006] To be more specific, another problem of the DC brushless
motor for electrical power steering is to find out a way for
meeting both requirements for reduction of torque pulsation and
production of a large torque, so that torque pulsation can be
reduced and a large torque can be produced, whenever required.
[0007] The embodiments described below solve various problems found
in the DC brushless motor for electrical power steering. These
solutions will be described each of the following embodiments:
[0008] The present invention provides a DC brushless motor for
electrical power steering capable of more effective reduction of
torque pulsation.
[0009] The DC brushless motor for electrical power steering is most
typically characterized in that a stator core is formed by
connecting split core pieces, and the stator core and the stator
coil built in this stator core are molded by a molding agent, with
the stator coil built in this stator core.
[0010] The present invention provides a further reduction in torque
pulsation.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a transverse cross sectional view representing the
configuration of the DC brushless motor for electrical power
steering as an embodiment of the present invention;
[0012] FIG. 2 is a cross sectional view taken along line A-A of
FIG. 1;
[0013] FIG. 3 is an explanatory diagram representing the
relationship between the numbers of poles P and slots S in an AC
motor;
[0014] FIG. 4 is an explanatory diagram representing the actual
measurements of the cogging torque in the DC brushless motor for
electrical power steering of an embodiment in the present
invention;
[0015] FIG. 5 is a connection diagram of stator coils in the DC
brushless motor for electrical power steering according to the
present embodiment of an embodiment in the present invention;
[0016] FIG. 6 is a side view representing the electrical connection
of the stator coils in the DC brushless motor for electrical power
steering according to an embodiment in the present invention;
[0017] FIG. 7 is a view in the direction of the arrow A-A in FIG.
1, showing the configuration of another stator;
[0018] FIG. 8 is a system configuration diagram representing the
configuration of a steering system using the DC brushless motor for
electrical power steering according to an embodiment in the present
invention;
[0019] FIG. 9 is a function block diagram representing the
configuration of the controller for controlling the DC brushless
motor for electrical power steering of an embodiment in the present
invention;
[0020] FIG. 10 is a perspective exploded view representing the
configuration of the controller of the DC brushless motor for
electrical power steering of an embodiment in the present
invention;
[0021] FIG. 11 is a circuit diagram representing the circuit
configuration of the controller for controlling the DC brushless
motor for electrical power steering of an embodiment in the present
invention;
[0022] FIG. 12 is a perspective bottom view showing the
configuration of conductor module of the controller for controlling
the DC brushless motor for electrical power steering of an
embodiment in the present invention;
[0023] FIG. 13 is a perspective view representing the configuration
of the controller for controlling the DC brushless motor for
electrical power steering of an embodiment in the present
invention;
[0024] FIG. 14 is a cross sectional view of the controller for
controlling the DC brushless motor for electrical power steering of
an embodiment in the present invention;
[0025] FIG. 15 is a cross sectional view representing the major
portions of the controller for controlling the DC brushless motor
for electrical power steering of an embodiment in the present
invention;
[0026] FIG. 16 is a cross sectional view representing the major
portions of the controller for controlling the DC brushless motor
for electrical power steering of an embodiment in the present
invention; and
[0027] FIG. 17 is a perspective view representing another
configuration of the controller for controlling the DC brushless
motor for electrical power steering of an embodiment in the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] The DC brushless motor for electrical power steering of the
present invention is most typically characterized as follows:
[0029] The present invention provides a DC brushless motor for
electrical power steering, driven by polyphase alternating current
power, for outputting steering torque, the aforementioned DC
brushless motor for electrical power steering comprising a frame, a
stator secured on the aforementioned frame and a rotor arranged
opposite to the aforementioned stator through an air gap. This
stator comprises a stator core and a polyphase stator coil built in
the aforementioned stator core. The stator core, formed by
connecting a plurality of split core pieces, comprises an annular
back core, and a plurality of tee cores projected radially from the
aforementioned back core. A slot is formed on the aforementioned
tee core adjacent to the aforementioned stator core, and the
aforementioned stator coil is incorporated in the aforementioned
slot. The rotor comprises a rotor core, and a plurality of magnets
fixed onto the surface of the outer periphery of the rotor core.
The stator core and stator coil being molded by a molding agent,
with the stator coil incorporated in the stator core.
[0030] The method for manufacturing a DC brushless motor for
electrical power steering of the present invention is most
typically characterized as follows:
[0031] The present invention provides a DC brushless motor for
electrical power steering manufacturing method, driven by polyphase
alternating current power, for outputting steering torque. This
manufacturing method comprises a first step of assembling a stator
coil into a stator core; a subsequent second step of press-fitting
into the frame a plurality of positions of the stator core
incorporating the stator coil in the circumferential direction, and
obtaining a structure composed of the stator core incorporating the
stator coil, secured to the frame; a subsequent third step of
mounting a jig on the aforementioned structure in such a way that
the jig and frame will enclose the stator core and the coil end of
the stator coil protruding axially from the axial end of the stator
core; a subsequent fourth step of injecting the molding agent into
the space enclosed by the jig and frame, thereby filling the
molding agent into the air gap between the coil end and stator
core, the air gap of the stator coil, the air gap between stator
core and stator coil, and the air gap between the stator core and
frame; a subsequent fifth step of solidifying the molding agent;
and a subsequent sixth step of removing the jig.
[0032] Referring to FIGS. 1 through 9, the following describes the
configuration and operation of the DC brushless motor for
electrical power steering as an embodiment of the present
invention.
[0033] In the first place, the following describes the
configuration and operation of the DC brushless motor for
electrical power steering of the present embodiment with reference
to FIGS. 1 and 2:
[0034] FIG. 1 is a transverse cross sectional view representing the
configuration of the DC brushless motor for electrical power
steering of the present embodiment of the present invention. FIG. 2
is a cross sectional view taken along line A-A of FIG. 1. FIG. 2
(A) is an overall cross sectional view and FIG. 2 (B) is a cross
sectional view representing the major portions.
[0035] The DC brushless motor for electrical power steering
(hereinafter referred to as "EPS motor") 100 is a surface magnet
type synchronous motor comprising a stator 110 and the rotor 130
rotatably supported inside this stator 110. The EPS motor 100 is
driven by an on-board power source equipped with a battery namely,
by power supplied from a 14-volt power source (12-volt battery
output voltage), a 24-volt power source a 42-volt power source
(36-volt battery output voltage), or a 48-volt power source, for
example.
[0036] The stator 110 comprises a stator core 112 formed of a
magnetic substance laminated with a silicon steel plate and a
stator coil 114 held inside the slot of the stator core 112. The
stator core 112 is composed of an annular back core and a plurality
of tees created separately from this back core and mechanically
fixed onto the back core thereafter, as will be described later
with reference to FIG. 2. Each of the tees is wound with a stator
coil 114. The stator coil 114 is wound by a distributed or
concentrated winding method.
[0037] The stator coil 114 wound according to the distributed
winding method is characterized by excellent field weakening
control and occurrence of reluctance torque. Downsizing of the
motor and reduction of winding resistance are very important for
the EPS motor. The length of the coil end of the stator coil 114
can be reduced by concentrated winding of the stator coil 114. This
arrangement reduces the length of the EPS motor 100 in the
direction of rotary axis. Further, since the length of the coil end
of the stator coil 114 can be reduced, the resistance of the stator
coil 114 can be reduced, and rise in motor temperature can also be
reduced. Reduction in coil resistance minimizes the motor copper
loss. Thus, the percentage of the energy consumed by copper loss
relative to the entire energy inputted into the motor can be
reduced and the efficiency of the output torque relative to input
energy can be improved.
[0038] As described above, the EPS motor is driven by the power
source mounted on a vehicle. The output voltage of the
aforementioned power source is often low. A series circuit is
equivalently formed by the switching device with an inverter formed
across the power source terminal, the aforementioned motor and
other current supply circuit connecting means. In the
aforementioned circuit, a total of the terminal voltage of the
circuit constituent devices becomes the terminal voltage of the
aforementioned power source. Thus, the terminal voltage of the
motor for supplying power to the motor is lowered. To ensure the
current flowing into the motor under this condition, it is crucial
to keep the copper loss of the motor low. For this reason, a
low-voltage system of 50 volts or less is often used as the power
source mounted on a vehicle. The concentrated winding method is
preferably applied to the stator coil 114. This is very important
especially when a 12-volt power source is used.
[0039] The power steering motor is placed close to the steering
column or close to a rack-and-pinion mechanism. Downsizing is
required in either case. In the downsized structure, the stator
winding must be fixed in position. It is also important to make
winding work easy. Concentrated winding ensures easier winding work
and fixing work than distributed winding.
[0040] The end of the stator coil 114 is molded. The EPS motor
preferably keeps the torque fluctuation such as cogging torque to a
very low level. After the stator section has been assembled,
machining may be performed again inside the stator. Chips will be
produced by such machining operation. Means must be provided to
prevent these chips from entering the end of the stator coil. The
coil end is preferably molded. The coil end refers to the position
protruding in the axial direction from both axial ends of the
stator core 112. In the present embodiment, an air gap is provided
between the mold resin covering the end of the stator coil 114 and
a frame 150. The molding agent can be filled up to the position
coming in contact with the frame 150, a front flange 152F and a
rear flange 152R. This arrangement ensures that heat generated from
the stator coil 114 is transferred from the coil end through the
mold resin directly to the frame 150, front flange 152F and rear
flange 152R, and is released to the outside. As compared with heat
transmission through air, this method reduces temperature rise of
the stator coil 114 effectively.
[0041] The stator coil 114 is composed of three phases; U, V and W
phases. Each coil is made up of a plurality of unit coils. These
unit coils are connected for each phase by a connection ring 116
arranged on the left of the drawing, as will be described with
reference to FIG. 3.
[0042] The EPS motor is required to provide a large torque. For
example, when the vehicle is stopped or is running close to the
stopped state, if the steering wheel is turned at a high speed, the
aforementioned motor is required to provide a large torque due to
the friction coefficient between the steering wheel and ground
surface. In this case, a large current is supplied to the stator
coil. This current can be 50 amperes or more, although it depends
on conditions. Further, it can be 70 or 150 amperes. To ensure safe
supply of such a large current and reduce generation of heat by the
aforementioned current, it is important to use the connection ring
116. Current is supplied to the stator coil through the connection
ring 116, whereby the connection resistance is lowered and voltage
drop resulting from copper loss is minimized. This arrangement
provides easy supply of a large current and reduces the time
constant for current startup caused by the operation of the
inverter device.
[0043] The stator core 112 and stator coil 114 are molded by resin
(electrically insulating type) together to form an integral piece,
and constitutes a stator subassembly. This integral stator
subassembly is press-fitted into the cylindrical yoke 150 formed of
metal such as aluminum and is fixed therein; this integral stator
subassembly is molded under this condition. The integral stator
subassembly can be molded, with the stator coil 114 built in the
stator core 112, and can be press-fitted in position
thereafter.
[0044] The EPS on board a vehicle is subjected to various forms of
vibration, as well as the impact from the wheel. Further, it is
used under the condition of a drastic temperature change. It may be
exposed to the temperature of 40.degree. Celsius below zero, or
100.degree. C. or more due to temperature rise. Further, means must
be taken to prevent water from entering the motor. In order for the
stator to be fixed to the yoke 150 under these conditions, the
stator subassembly is preferably press-fitted into a cylindrical
metal free of any hole such as a screw hole, on the outer periphery
of at least the stator core of the cylindrical frame. After
pressing fitting, screws may be used to fix it in position, from
the outer periphery of the frame. In addition to press fitting,
locking is preferably provided.
[0045] The rotor 130 comprises a rotor core 132 formed of a
magnetic substance laminated with a silicon steel plate; magnets
134 as a plurality of permanent magnets bonded on the surface of
the rotor core 132 by adhesive; and a magnet cover 136 composed of
non-magnetic substance provided on the outer periphery of the
magnets 134. The magnet 134 is a rare-earth magnet and is composed
of neodymium, for example. The rotor core 132 is fixed on the shaft
138. A plurality of magnets 134 are bonded on the surface of the
rotor core 132 by adhesive. At the same time, the outer periphery
is covered with a magnet cover 136, whereby the magnet 134 is
prevented from being thrown away. The aforementioned magnet cover
136 is made stainless steel (commonly known as SUS). It can be
wound with tape. Use of the stainless steel provides easier
production. As described above, the ESP motor is suited to hold the
permanent magnet that is subjected to severe vibration and thermal
change, and is easy to break down. Even if it breaks down, it is
prevented from being thrown away, as described above.
[0046] A front flange 152F is arranged on one end of the
cylindrical frame 150. The frame 150 and front flange 152F are
fixed together by a bolt B1. A rear flange 152R is press-fit into
the on the end of the frame 150. A bearing 154F and a bearing 154R
are mounted on the front flange 152F and rear flange 152R,
respectively. A shaft 138 and a stator 110 fixed on this shaft 138
are rotatably supported by these bearings 154F and 154R.
[0047] The front flange 152F is provided with an annular protrusion
(or extension). The protrusion of the front flange 152F is extended
in the axial direction from the coil end side of the front flange
152F. When the front flange 152F is secured to the frame 150, the
tip of the protrusion of the front flange 152F is inserted into the
air gap formed between the molding agent of the coil end on the
side of the front flange 152F and the frame 150. To encourage heat
radiation, the protrusion of the front flange 152F is preferably
kept in close contact with the molding agent of the coil end on the
side of the front flange 152F.
[0048] The rear flange 152R is provided with a cylindrical recess.
The recess of the rear flange 152R is concentric with the center
axis of the shaft 138, and is located axially inwardly (on the side
of the stator core 112) from the axial end of the frame 150. The
tip of the recess of the rear flange 152R extends toward the inner
diameter side of the coil end on the side of the rear flange 152R,
and is located radially opposite to the coil end on the side of the
rear flange 152R. A bearing 154 is held by the tip of the recess of
the rear flange 152R. The axial end of the shaft 138 on the side of
the rear flange 152R extends further inwardly (opposite to the
rotor core 132 side) from the bearing 154 to reach the position
close to the opening of the recess of the rear flange 152R, or the
position protruding slightly outwardly from the opening in the
axial direction.
[0049] A resolver 156 is arranged in the air gap formed between the
inner peripheral surface of the recess of the rear flange 152R and
the outer peripheral surface of the shaft 138. The resolver 156 is
provided with a resolver stator 156S and is located outwardly
(opposite to the rotor core 132 side) from the bearing 154R in the
axial direction. The resolver rotor 156R is secured on one end
(left end in the drawing) of the shaft 138 by a nut N1. When the
resolver holding plate 156B is secured on the rear flange 152R by a
screw SC1, the resolver stator 156S is secured on the inner
periphery of the recess of the rear flange 152R, and is arranged in
opposite position through the resolver rotor 156R and air gap. The
resolver 156 is composed of the resolver stator 156S and resolver
rotor 156R. The rotation of the resolver rotor 156R is detected by
the resolver stator 156S, whereby the positions of a plurality of
magnets 134 can be detected. To put it more specifically, the
resolver comprises a resolver rotor 156R having a concavo-convex
pattern on the outer peripheral surface (e.g. elliptical or
petal-shaped), and a resolver stator 156S wound with two output
coils (displaced 90.degree. electrically) and exciting coil. When
a.c. voltage is applied to the exciting coil, a.c. voltage
conforming to the variation in the length of the air gap between
the resolver rotor 156R and resolver stator 156S occurs to two
output coils, wherein this a.c. voltage has a phase difference in
proportion to rotary angle. Thus, the resolver is intended to
detect two output voltages having a phase difference. The magnetic
pole position of the rotor 130 is detected by finding out the phase
angle from the phase angle of the two output voltage having been
detected.
[0050] Power is supplied from an external battery to each of the U,
V and W phases through a power cable 162. The power cable 162 is
mounted on the frame 150 by a grommet 164. The magnetic pole
position signal detected from the resolver stator 156S is taken out
by the signal cable 166. The signal cable 166 is mounted on the
rear holder 158 by the grommet 168. The connection ring 116 and
part of the power cable 1 are molded together with the coil
end.
[0051] The following describes the configuration of the stator 110
and rotor 130 more specifically with reference to FIG. 2. FIG. 2 is
a view in the direction of the arrow A-A in FIG. 1. FIG. 2 (B) is
an enlarged cross sectional view of the section P in FIG. 2 (A).
The same reference numerals as those in FIG. 1 indicate the same
parts.
[0052] The stator 110 will be described first. The stator core 112
shown in FIG. 1 is composed of an annular back core 112B and a
plurality of tees 112T provided separately from this annular back
core 112B. The annular back core 112B is made of a lamination of
magnetic sheet metals such as silicon steel plate stamped out by
press molding.
[0053] The tee 112T is composed of twelve independent tees 112T
(U1+), 112T (U1-), 112T (U2+), 112T (U2-), 112T (V1+), 112T (V1-),
112T (V2+), 112T (V2-), 112T (W1+), 112T (W1-), 112T (W2+), and
112T (W2-). The tees 112T (U1+), 112T (U1-), 112T (U2+), 112T
(U2-), 112T (V1+), 112T (V1-), 112T (V2+), 112T (V2-), 112T (W1+),
112T (W1-), 112T (W2+), and 112T (W2-) are wound with stator coils
114 (U1+), 114 (U1-), 114 (U2+), 114 (U2-), 114 (V1+), 114 (V1-),
114 (V2+), 114 (V2-), 114 (W1+), 114 (W1-), 114 (W2+), and 114
(W2-), respectively in a concentrated winding mode.
[0054] Here the stator coil 114 (U1+) and the stator coil 114 (U1-)
are wound in such a way that current flows in the opposite
directions. The stator coil 114 (U2+) and the stator coil 114 (U2-)
are also wound in such a way that current flows in the opposite
directions. The stator coil 114 (U1+) and the stator coil 114 (U2+)
are wound in such a way that current flows in the same directions.
The stator coil 114 (U1-) and the stator coil 114 (U2-) are also
wound in such a way that current flows in the same directions. The
relation of the directions of current flow for the stator coil 114
(V1+), stator coil 114 (V1-), stator coil 114 (V2+) and stator coil
114 (V2-), and the relation of the directions of current flow for
the stator coil 114 (W1+), stator coil 114 (W1-), stator coil 114
(W2+) and stator coil 114 (W2-) are also the same as those in the
case of U phases.
[0055] Twelve tees 112T and stator coils 114 are manufactured in
the same manner. The tee 112T (U1+) and stator coil 114 (U1+) will
be taken as an example to explain the assembling process. The
stator coil 114 (U1+) is a molded coil formed in such a way as to
wind the tees 112T (U1+). The stator coil 114 (U1+) is a pre-molded
coil so as to be wound on the tee 112T (U1+). The stator coil 114
(U1+) as the molded coil is molded together with a bobbin 112BO. An
integrated piece consisting of the stator coil 114 (U1+) and bobbin
112BO is fitted into the tee 112T (U1+) from its rear. The tip end
of the tee 112T (U1+), namely, the side facing the rotor 130 is
expanded in the circumferential direction. The bobbin 112BO and
stator coil 114 (U1+) serve as stoppers in this expanded section,
and are anchored therein. The convex portion 112BK formed on the
inner periphery of the back core 112B and a concave portion 112TT
shaped for fitting are formed on the rear of the tee 112T (U1+).
The concave portion 112TT of the tee 112T (U1+) wound with the
molded stator coil 114 (U1+) is press-fitted into the convex
portion 112BK of the back core 112B so that the tee 112T (U1+) is
fastened on the back core 112B. The above description applies also
to the process of mounting the stator coil 114 (U1-) through 114
(W2-) on the other tees 112T (U1+) through 112T (W2-), and the
process of mounting the other tees 112T (U1-) through 112T (W2-) on
the back core 112B.
[0056] Twelve tees 112T equipped with stator coils 114 are secured
on the back core 112B, and a plurality of positions on the outer
periphery of the back core 112B are press-fitted with the inner
periphery of the frame 150. Under this condition, the stator core
112 and stator coil 114 are integrally molded by thermosetting
resin MR to form a stator subassembly. In the present embodiment,
the stator coil 114 built in the stator core 112 is press-fitted
with the frame 150. Under this condition, the stator core 112 and
stator coil 114 are integrally molded. This procedure has been
described so far. It is also possible to make such arrangements
that, with the stator coil 114 is built in the stator core 112, the
stator core 112 and stator coil 114 are integrally molded and the
stator core 112 is press-fitted with the frame 150
subsequently.
[0057] In the processing of molding with molding agent, the jig
(not illustrated) is mounted on the structure composed of the
stator core 112 and frame 150 in such a way that the stator core
112 and the coil end of the stator coil 114 protruding axially from
the axial end of the stator core 112 will be enclosed by the jig
(not illustrated) and frame 150. Liquid molding agent is poured
into the space enclosed by the jig (not illustrated) and the frame
150, thereby filling the molding agent into the air gap between the
core end and stator core 112, the air gap of the stator coil 114,
the air gap between stator core 114 and stator coil 114, and the
air gap between the stator core 112 and frame 150. Then the molding
agent is solidified. After it has solidified, the jig (not
illustrated) is removed.
[0058] The inner peripheral surfaces of the molded stator
subassembly, namely, the tips of the tees 112T (U1-) . . . 112T
(W2-) as the surfaces radially opposite to the rotor 130 are
provided with machining. This arrangement reduces the variation of
the air gap between the stator 110 and rotor 130, and further
improves the roundness in the inner diameter of the stator 110.
Further, integral molding ensure effective release of the heat
generated by electric conduction of the stator coil 114, as
compared to the case where integral molding is not adopted.
Further, the molding process protects the stator coil and tee
against vibration.
[0059] For example, when the air gap between the outer periphery of
the rotor core of the rotor 130 and the inner periphery of the tee
of the stator 110 is 3 mm (3000 .mu.m), the roundness of the inner
diameter of about .+-.30 .mu.m will occur due to the production
error of the back core 112B and tee 112T, and assembling error of
the back core 112B and tee 112T at the time of press fitting and
assembling. The roundness is equivalent to 1% (=30 .mu.m/3000
.mu.m) of the air gap, and therefore a cogging torque is produced
by the roundness of inner diameter. However, after molding, the
inner diameter is machined. This process reduces the cogging torque
resulting from the roundness of the inner diameter. Reduction of
the cogging torque improves the steering comfort.
[0060] Concave portions 150T are arranged inside the frame 150.
Concave portions 112BO2 are arranged on the outer periphery of the
back core 112B so as to be engaged with the concave portions 150T.
The details are shown in FIG. 2 (B). The concave portions 150T and
concave portions 112BO2 constitute an engagement section IP having
a mutually different curvature rate for engagement with each other.
They are continuously formed in the axial direction. Eight of these
portions are arranged at a predetermined interval in the
circumferential direction. The engagement section also serves as a
press-fit section. To be more specific, when the stator core 112 is
secured on the frame 150, the concave portions 112BO2 of the back
core 112B are press-fitted into the concave portions 150T of the
frame 150 to ensure that the tips of the concave portions 150T of
the frame 150 and the bottoms of the concave portions 112B pressed
against each other. As can be seen, in the present embodiment, the
stator core 112 is secured on the frame 150 by partial
press-fitting. This press-fitting process forms a fine air gap
between the frame 150 and stator core 112. In the present
embodiment, when the stator core 112 and stator coil 114 are molded
by a molding agent, the molding agent is filled into the air gap
formed between the frame 150 and stator core 112 at the same time.
The engagement section serves as a locking section to prevent the
stator core 112 from turning in the circumferential direction with
respect to the frame 150.
[0061] As described above, in the present embodiment, the stator
core 112 is partially press-fitted into the frame 150. This
arrangement increases the sliding property between the frame 150
and stator core 112 and reduces the rigidity. In the present
embodiment, this improves the effect of damping the noise between
the frame 150 and stator core 112. In the present embodiment, the
air gap between the frame 150 and stator core 112 is filled with
the molding agent, whereby the noise damping effect is further
improved.
[0062] It is also possible to arrange such a configuration that the
concave portions 150T and concave portions 112BO2 are formed in a
non-contact structure and are used only for locking purposes, and
the outer peripheral surface of the back core 112B is press-fitted
into the inner peripheral surface of the frame 150 other than the
concave portions 150T and concave portions 112BO2.
[0063] The stator coil 114 (U1+) and stator coil 114 (U1-), and
stator coil 114 (U2+) and stator coil 114 (U2-) are positioned
symmetrically, relative to the center of the stator 110. To be more
specific, the stator coil 114 (U1+) and stator coil 114 (U1-) are
located adjacent to each other, and the stator coil 114 (U2+) and
stator coil 114 (U2-) are also located adjacent to each other.
Further, the stator coil 114 (U1+) and stator coil 114 (U1-), and
stator coil 114 (U2+) and stator coil 114 (U2-) are positioned
symmetrically with respect to a line, relative to the center of the
stator 110. To put it another way, the stator coil 114 (U1+) and
stator coil 114 (U2+) are placed symmetrically with respect to a
line, relative to the broken line C-C passing through the shaft
138. Further, the stator coil 114 (U1-) and stator coil 114 (U2-)
are placed symmetrically with respect to a line.
[0064] Similarly, the stator coil 114 (V1+) and stator coil 114
(V1-), and stator coil 114 (V2+) and stator coil 114 (V2-) are
positioned symmetrically with respect to a line. The stator coil
114 (W1+) and stator coil 114 (W1-), and stator coil 114 (W2+) and
stator coil 114 (W2-) are also positioned symmetrically with
respect to a line.
[0065] Further, adjacent stator coils 114 of the same phase are
continuously wound in the form of one wire; namely, the stator coil
114 (U1+) and stator coil 114 (U1-) form one wire; namely, the
stator coil 114 (U1+) and stator coil 114 (U1-) form one wire,
which constitutes two winding coils. They are each inserted into
the tees, and are wound on the tees. Similarly, the stator coil 114
(U2+) and stator coil 114 (U2-) are continuously wound in the form
of one wire. Similarly, the stator coil 114 (V1+) and stator coil
114 (V1-); stator coil 114 (V2+) and stator coil 114 (V2-); the
stator coil 114 (W1+) and stator coil 114 (W1-); and stator coil
114 (W2+) and stator coil 114 (W2-) are continuously wound in the
form of one wire, respectively.
[0066] Such a symmetric layout with respect to a line and winding
of two adjacent coils of the same phase in the form of one wire
provide a simplified connection link structure, when the same or
difference phases are connected by the connection ring, as will be
described later with reference to FIG. 4.
[0067] The following describes the configuration of the rotor 130.
The rotor 130 comprises:
[0068] a rotor core 132 composed of a magnetic substance;
[0069] ten magnets 134 (134A, 134B, 134C, 134D, 134E, 134F, 134G,
134H, 134I and 134J) bonded on the surface of the rotor core 132 by
adhesive; and
[0070] a magnet cover 136 arranged on the outer periphery of the
magnets 134. The rotor core 132 is secured on the shaft 138.
[0071] When the surface (side opposite to the tee 112T of the
stator) is an N-pole, the magnets 134 are energized in the radial
direction to ensure that the back side thereof (side bonded to the
rotor core 132) will be an S-pole. Further, when the surface (side
opposite to the tee 112T of the stator) is an S-pole, the magnets
134 are energized in the radial direction in some cases to ensure
that the back side thereof (side bonded to the rotor core 132) will
be an N-pole. The adjacent magnets 134 are energized in such a way
that the energized poles will alternate with each other in the
circumferential direction. For example, if the surface of the
magnet 134A is attracted by the N-pole, the surfaces of the
adjacent magnets 134B and 134J are attracted by the S-pole. To put
it another way, when the surfaces of the magnets 134A, 134C, 134E,
134G and 134I are attracted by the N-pole, the magnets 134B, 134D,
134F, 134H and 134J are attracted by the S-pole.
[0072] The magnets 134 have a semicylindrical cross section. The
semicylindrical shape can be defined as a structure wherein the
radial thickness of the right and left in the radial direction is
smaller than that at the center in the circumferential direction.
Such a semicylindrical structure allows the magnetic flux to be
distributed in the form of a sinusoidal wave. Then the induced
voltage waveform resulting from the rotation of the EPS motor can
be changed into a sinusoidal wave, and the amount corresponding to
pulsation can be reduced. Reduction in the amount corresponding to
pulsation improves the steering comfort. When a magnet is formed by
attraction to the ring-like magnetic substance, by control of the
energizing force, the magnetic flux can be distributed in the form
similar to the sinusoidal wave, in some cases.
[0073] The rotor core 132 is provided with ten large-diameter
through-holes 132H formed on the concentric circle and five
small-diameter recesses 132K with protruded inner periphery. The
rotor core 132 is composed of a lamination of the sheet metal of
magnetic substance such as SUS having been stamped out by press
molding. The recesses 132K are formed by crimping the sheet metal
at the time of press molding. When a plurality of sheet metals are
laminated, the recesses 132K are fitted with each other, whereby
positioning is performed. The through-hole 132H is intended to cut
down the inertia. The rotor balance can be improved by the
through-hole 132H. The outer periphery of the magnet 134 is covered
by the magnet cover 136 to prevent the magnet 134 from being thrown
away. The back core 112B and rotor core 132 can be formed
simultaneously from the same sheet metal by stamping out by a
press.
[0074] As described above, the rotor 130 of the present embodiment
has ten magnets 134 and ten poles. Also as described above, twelve
tees 112T are provided. The number of slots formed between adjacent
tees is 12. To put it another way, the EPS motor of the present
invention is a 10-pole 12-slot surface magnetic type synchronous
motor.
[0075] Referring to FIG. 3, the following describes the
relationship between the numbers of poles P and slots S in an AC
motor.
[0076] FIG. 3 is an explanatory diagram representing the
relationship between the numbers of poles P and slots S in an AC
motor.
[0077] In FIG. 3, a combination given by hatching using horizontal
lines indicates the relationship between the numbers of poles P and
slots S that can be used in a three-phase AC motor (brushless
motor). Namely, the available combinations include 2 poles and 3
slots, 4 poles and 3 slots, 4 poles and 6 slots, 6 poles and 9
slots, 8 poles and 6 slots, 8 poles and 9 slots, 8 poles and 12
slots, 10 poles and 9 slots, 10 poles and 12 slots, and 10 poles
and 15 slots. Of these combinations, a 10-pole/12-slot combination
provided with right and left oblique lines indicates the numbers of
motors and slots in the present embodiment. The 8-pole/9-slot and
10-pole/9-lot combinations shown by left oblique lines will be
described later. The EPS motor shown in FIG. 1 is a small-sized
motor having an outer diameter of 85 mm. Such a small-sized motor
cannot be achieved if the number of poles N is 12 or more, and is
therefore not illustrated.
[0078] The motors having 2 poles and 3 slots, 4 poles and 3 slots,
4 poles and 6 slots, 6 poles and 9 slots, 8 poles and 6 slots, 8
poles and 12 slots, and 10 poles and 15 slots are provided with
similar characteristics. The motor having 6 poles and 9 slots will
be take up as an typical example in the following explanation:
[0079] The 10-pole/12-slot motor of the present embodiment provides
a higher usage rate of the magnetic flux of a magnet than the
6-pole/9-slot AC motor. To be more specific, the 6-pole/9-slot
motor has a winding factor (usage rate) (kw) of 0.87 and a skew
factor ks of 0.96. The usage rate (kwks) of the magnetic flux of
the magnet is 0.83. In the meantime, the 10-pole/12-slot motor of
the present embodiment has a winding factor (usage rate) (kw) of
0.93 and a skew factor ks of 0.99. Thus, it has a usage rate of
0.92. This means that the 10-pole/12-slot motor of the present
embodiment improves the usage rate of the magnetic flux of a magnet
(kwks).
[0080] The period of the cogging torque corresponds to the least
common multiple of the numbers of poles P and slots S, and
therefore the period of the cogging torque in the 6-pole/9-slot AC
motor is 18. Thus, the period of the cogging torque in the
10-pole/12-slot motor of the present embodiment can be reduced to
60. This shows that a reduction of cogging torque is ensured.
[0081] Further, the cogging torque resulting from poor roundness of
inner diameter can also be reduced. To be more specific, assuming
that the cogging torque resulting from the out-of-roundness of
inner diameter in the 6-pole/9-slot AC motor is 3.7, that in the
10-pole/12-slot motor of the present embodiment can be 2.4, with
the result that the cogging torque resulting from the
out-of-roundness of inner diameter can be reduced. Further, in the
present embodiment, machining is applied to the inner diameter of
the molded stator subassembly to improve the roundness of the inner
diameter. This leads to further reduction in the cogging torque
resulting from the poor roundness of inner diameter.
[0082] Referring to FIG. 4, the following describes the actual
measurements of the cogging torque in the DC brushless motor for
electrical power steering.
[0083] FIG. 4 is an explanatory diagram representing the actual
measurements of the cogging torque in the DC brushless motor for
electrical power steering of the present embodiment.
[0084] FIG. 4 (A) shows the cogging torque measured for the angle
(mechanical) ranging from 0 through 360.degree.. FIG. 4 (B) shows
the peak value (mNm) by separating the high frequency component of
the cogging torque shown in FIG. 4 (A) for each time order. As
described above, time order "60" indicates the period of the
cogging torque in a 10-pole/12-slot motor and the cogging torque
having occurred is almost zero. Time order "12" is the result of
variation in the magnetic field force of the 10-pole magnet. As
described above, use of a semicylindrical magnet reduces the
cogging torque resulting from variation in magnetic field force
down to 1.4. The time order "10" is the result of the variation of
each tee of a 12-slot stator. Since the roundness of the inner
diameter by cutting subsequent to molding is improved, the cogging
torque resulting from variation of the tee is also reduced to
2.6.
[0085] Time order "0" indicates a DC component, so-called a loss
torque (friction coefficient produced at a speed of zero). The loss
torque can also be lowered to 26.3 mNm. Even when a driver has
released the steering wheel, the loss torque is smaller as compared
to the restoring force of steering wheel to get back to the
original position, with the result that the restoring force of the
steering wheel is improved.
[0086] As described above, each cogging component can be reduced,
the cogging torque can be reduced to 9 mNm, as shown in FIG. 4 (A).
The maximum torque of the EPS motor is 4.5 mNm, and therefore the
cogging torque can be reduce as low as 0.2% (=9 mNm/4.5 Nm) (3/1000
or less of the rated level). The loss torque can also be reduced to
0.57% (=26.3 mNm/4.5 Nm).
[0087] The EPS motor 100 of the present embodiment is a motor using
an on-board battery (e.g. output voltage of 12 volts) as the power
source thereof. The EPS motor 100 is mounted close to the steering
system or the rack of a rack/pinion mechanism for transmitting the
power of the steering system to the wheel. This requires downsizing
due to the limited installation space. In the meantime, a large
torque (e.g. 4.5 Nm) is required for power assistance of the
steering system.
[0088] When an attempt is made to deliver the required torque from
the AC servo motor powered by a 100 VAC power source, the motor
current of about 5 amperes is sufficient. However, when 14 VAC
obtained by DC-to-AC conversion of the 14 VDC is used for driving,
as in the present embodiment, the motor current must be 70 through
100 amperes in order to get about the same torque with about the
same volume. To get such a large current, the diameter of stator
coil 114 must be increased to as large as 1.6 mm. In this case, the
number of turns of the stator coil 114 is 14 (T). The number of
turns of the stator coil 114 is in the range from 9 through 21,
although it depends on the diameter of the stator coil 114. When
the diameter of the stator coil 114 is 1.8 mm, the number of turns
is 9. Here if the coil having a diameter of 1.6 mm instead of the
coil having a diameter of 1.8 is used for winding, coil space
factor can be improved by 75%, for example. Since the coil space
factor can be improved, the current density can be reduced in
relative terms. This arrangement reduces the copper loss and keeps
down motor temperature rise. Further, it improves the rpm/torque
characteristics. Some of the recent powered vehicles are equipped
with a 42-volt battery. In this case, this arrangement reduces the
motor current. The number of turns of the stator coil 114 is in the
range from 20 through 30.
[0089] In the adjacent tees 112T, the space W1 (e.g. tee 112T (U1-)
of the expanded section of the tip (side facing the rotor 130) of
the tee 112T and the space W1 (circumferential space at the
position closest to the circumferential direction) of the expanded
section of the tip tee 112T (W1-) are 1 mm. Reducing the tee space
in this manner decreases the cogging torque. Even if vibration is
applied to the motor, the line of the stator coil 114 is larger
than the space W1, and this prevents stator coil 114 from being
dropped out on the rotor side. The appropriate space W1 between
adjacent tees is 0.5 through 1.5 mm, for example, which is smaller
than the diameter of the stator coil 114. As described above, in
the present embodiment, the space W1 of the adjacent tees is
smaller than the diameter of the stator coil 114.
[0090] Referring to FIGS. 5 and 6, the following describes the
connection of stator coils in a DC brushless motor for electrical
power steering in the present embodiment:
[0091] FIG. 5 is a connection diagram of stator coils in the DC
brushless motor for electrical power steering according to the
present embodiment. FIG. 6 is a side view representing the
electrical connection of the stator coils in the DC brushless motor
for electrical power steering according to the present embodiment
of the present embodiment. FIG. 6 is a view in the direction of the
arrow B-B in FIG. 1. The same reference numerals as those in FIG. 2
indicate the same parts.
[0092] In FIG. 5, coil U1+ denotes a stator coil 112T (U1+) shown
in FIG. 2. Coils U1-, U2+, U2-, V1+, V1-, V2+, V2-, W1+, W1-, W2+,
W2- indicate the stator coils 112T (U1-) . . . 112T (W2-) of FIG.
2.
[0093] In the stator coil of the present embodiment, a delta
connection is used for U, V and W phases. Each phase constitutes a
parallel circuit. To be more specific about the U phase, a parallel
connection of coil U2+ and coil U2- is provided for the series
connection of coil U1+ and coil U1-. Here as described above, the
coil U1+ and coil U1- are formed by continuous winding of a wire.
This is also applicable to the V and W phases.
[0094] A star-connection method can also be used for this
connection. The delta connection allows the lower terminal voltage
than the star connection. For example, assuming that the voltage
across the series/parallel circuit of the U phase is E. The
terminal voltage is E, but this is {square root over (3)} E in the
star connection. Since the terminal voltage can be reduced, the
number of turns of the coil can be increased and a small-diameter
wire can be utilized. Further, as compared to the case of four
coils in series, a parallel circuit reduces the current flowing to
each coil, and this allows use of a smaller-diameter wire and
improves the coil space factor, with the result that better bending
properties and easier in production are ensured.
[0095] Referring to FIGS. 5 and 6, the following describes the
connection method for three phases and each phase, using a
connection ring.
[0096] As shown in FIG. 5, coils U1-, U2-, V1+ and V2+ are
connected by the connection ring CR (UV); coils V1-, V2+, W1+ and
W2+ are connected by the connection ring CR (VW); and coils U1+,
U2+, W1- and W2- are connected by the connection ring CR (UW).
Through these connections, a three-phase delta connection is
made.
[0097] As shown in FIG. 6, three connection rings CR (UV), CR (VW)
and CR (UW) are used. The connection rings CR (UV), CR (VW) and CR
(UW) are formed by bending and machining the bus bar type
connection board bent in a circular arc so as to feed a large
current. Each of the connection rings has the same shape. For
example, the connection ring CR (UV) is formed by a connection
between a circular arc of a small radius and a circular arc of a
large radium. Other connection rings CR (VW) and CR (UW) are made
in the same structure. These connection rings CR (UV), CR (VW) and
CR (UW) are retained by the holders H1, H2 and H3 in the state
displaced 120.degree. in the circumferential direction. The
connection ring CR and holders H1, H2 and H3 are molded together
with the coil end using a molding agent.
[0098] In the meantime, in FIG. 6 the stator coil terminal T (U1+)
is one terminal of the stator coil 114 (U1+) wound with the stator
coil 112T (U1+). The stator coil terminal T (U1+) is one terminal
of the stator coil 114 (U1-) wound with the stator coil 112T (U1-).
As described above, the stator coil 114 (U1+) and stator coil 114
(U1-) are form a continuous coil in the form of one wire. Two
terminals T (U1+) and T (U1-) are present for two coils, stator
coil 114 (U1+) and stator coil 114 (U1-). The stator coil terminals
T (U2+), T (U2-), T (V1+), T (V1-), T(V2+), T(V2-), T (W1+), T
(W1-), T (W2+) are T (W2-) are the terminals on one side of the
stator coil 114 (U2+), . . . (W2+).
[0099] The stator coil terminals T (U1-), (U2-), (V1+) and (V2+)
are connected by the connection ring CR (UV), whereby the coils
U1-, U2-, V1+ and V2+ shown in FIG. 5 are connected by the
connection ring CR (UV). The stator coil terminal T (V1-), T (V2-),
T (W1+) and T (W2+) are connected by the connection ring CR (VW),
whereby the coils V1-, V2-, W1+ and W2+ shown in FIG. 5 are
connected by the connection ring CR (UW).
[0100] Referring to FIG. 7, the following describes another example
of the configuration of the stator 110. FIG. 7 is a view in the
direction of the arrow A-A in FIG. 1. The same reference numerals
as those in FIG. 2 indicate the same parts.
[0101] In the stator 110 shown in FIG. 2, the stator core 112 is
composed of an annular back core 112B and a plurality of tees 112T
provided separately from this annular back core 112B. By contrast,
in the present example, it is composed of twelve T-shaped
tee-integrated split back cores; 112 (U1+), 112 (U1-), 112 (U2+),
112 (U2-), 112 (V1+), 112 (V1-), 112 (V2+), 112 (V2-), 112 (W1+),
112 (W1-) and 112 (W2+), 112 (W2-). To be more specific, the
annular back core 112B of FIG. 2 is split into twelve pieces in the
circumferential direction. A tee is integrated with each of the
split back core piece. The tee-integrated split back cores 112
(U1+) . . . 112 (W2-) are composed of a lamination of the sheet
metal of magnetic substance such as a silicon steel plate having
been stamped out by press molding. The rotor 130 is formed as shown
in FIG. 2.
[0102] Stator coils 114 (U1+), 114 (U1-), 114 (U2+), 114 (U2-), 114
(V1+), 114 (V1-), 114 (V2+), 114 (V2-), 114 (W1+), 114 (W1-), 114
(W2+) and 114 (W2-) are wound on the tees of the tee-integrated
split back cores 112 (U1+) . . . 112 (W2-), namely, on twelve
independent tees 112T (U1+) . . . 112T (W2-), in a concentrated
winding. The stator coil 114 (U1+) . . . 114 (W2-) is wound in the
direction shown in FIG. 2.
[0103] The stator coils 114 (U1+) . . . 114 (W2-) are wound on the
tee-integrated split back cores 112 (U1+) . . . 112 (W2-),
respectively. Then the fitting type convex portions are
press-fitted into the concave portions formed on the end faces of
the tee-integrated split back cores 112 (U1+) . . . 112 (W2-) in
the circumferential direction, whereby assembling of the stator 110
terminates. A plurality of positions on the outer periphery of the
back core 112B are press-fitted with the inner periphery of the
frame 150. Under this condition, the stator core 112 and stator
coil 114 are integrally molded by thermosetting resin MR to form a
stator subassembly. In the present embodiment has referred to the
case where the stator coil 114 built in the stator core 112 is
press-fitted with the frame 150. Under this condition, the stator
core 112 and stator coil 114 are integrally molded. This procedure
has been described so far. It is also possible to make such
arrangements that, with the stator coil 114 is built in the stator
core 112, the stator core 112 and stator coil 114 are integrally
molded and the stator core 112 is press-fitted with the frame 150
subsequently.
[0104] In the processing of molding with molding agent, the jig
(not illustrated) is mounted on the structure composed of the
stator core 112 and frame 150 in such a way that the stator core
112 and the coil end of the stator coil 114 protruding axially from
the axial end of the stator core 112 will be enclosed by the jig
(not illustrated) and frame 150. Liquid molding agent is poured
into the space enclosed by the jig (not illustrated) and the frame
150, thereby filling the molding agent into the air gap between the
core end and stator core 112, the air gap of the stator coil 114,
the air gap between stator core 114 and stator coil 114, and the
air gap between the stator core 112 and frame 150. Then the molding
agent is solidified. After it has solidified, the jig (not
illustrated) is removed.
[0105] The inner peripheral surfaces of the molded stator
subassembly, namely, the tips of the tees of the tee-integrated
split back cores 112 (U1+) . . . 112 (W2-) as the surfaces radially
opposite to the rotor 130 are provided with machining. This
arrangement reduces the variation of the air gap between the stator
110 and rotor 130, and further improves the roundness in the inner
diameter of the stator 110. Further, integral molding ensure
effective release of the heat generated by electric conduction of
the stator coil 114, as compared to the case where integral molding
is not adopted. Further, the molding process protects the stator
coil and tee against vibration. Further, machining of the inner
diameter subsequent to molding reduces the cogging torque resulting
from the roundness of the inner diameter. Reduction of the cogging
torque improves the steering comfort of the steering system.
[0106] Concave portions 150T are arranged inside the frame 150.
Concave portions 112BO2 are arranged on the outer periphery of the
back core 112B so as to be engaged with the concave portions 150T.
The concave portions 150T and concave portions 112BO2 constitute an
engagement section IP having a mutually different curvature rate
for engagement with each other. They are continuously formed in the
axial direction. Eight of these portions are arranged at a
predetermined interval in the circumferential direction. The
engagement section also serves as a press-fit section. To be more
specific, when the stator core 112 is secured on the frame 150, the
concave portions 112BO2 of the back core 112B are press-fitted into
the concave portions 150T of the frame 150 to ensure that the tips
of the concave portions 150T of the frame 150 and the bottoms of
the concave portions 112B pressed against each other. As can be
seen, in the present embodiment, the stator core 112 is secured on
the frame 150 by partial press-fitting. This press-fitting process
forms a fine air gap between the frame 150 and stator core 112. In
the present embodiment, when the stator core 112 and stator coil
114 are molded by a molding agent, the molding agent is filled into
the air gap formed between the frame 150 and stator core 112 at the
same time. The engagement section serves as a locking section to
prevent the stator core 112 from turning in the circumferential
direction with respect to the frame 150.
[0107] As described above, in the present embodiment, the stator
core 112 is partially press-fitted into the frame 150. This
arrangement increases the sliding property between the frame 150
and stator core 112 and reduces the rigidity. In the present
embodiment, this improves the effect of damping the noise between
the frame 150 and stator core 112. In the present embodiment, the
air gap between the frame 150 and stator core 112 is filled with
the molding agent, whereby the noise damping effect is further
improved.
[0108] It is also possible to arrange such a configuration that the
concave portions 150T and concave portions 112BO2 are formed in a
non-contact structure and are used only for locking purposes, and
the outer peripheral surface of the back core 112B is press-fitted
into the inner peripheral surface of the frame 150 other than the
concave portions 150T and concave portions 112BO2.
[0109] Referring to FIG. 8, the following describes the
configuration of a steering system using the DC brushless motor for
electrical power steering of the present invention.
[0110] FIG. 8 is a system configuration diagram representing the
configuration of a steering system using the DC brushless motor for
electrical power steering of the present embodiment.
[0111] When the steering ST is turned, the rotation drive force is
decelerated by a manual steering gear STG through the rod RO and is
transmitted to right and left tie rods TR1 and T2 to steer the
right and left wheel WH1 and WH2.
[0112] The EPS motor 100 of the present embodiment is mounted close
to the manual steering gear STG. The drive force is transmitted to
the manual steering gear STG through a gear GE. The rod RO is
equipped with a torque sensor TS, which detects the rotation drive
force (torque) applied to the steering ST. Based on the torque
sensor TS, the controller 200 controls the current supplied to the
motor in such a way that the output torque of the EPS motor 100
will be the target torque. The controller 200 and EPS motor 100 is
supplied with power from a battery BA.
[0113] The aforementioned configuration indicates a rack type power
steering system with the EPS motor mounted close to the rack/pinion
mechanism. The EPS motor 100 of the present invention is also
applicable to a column type power steering system with the EPS
motor mounted close to the steering system.
[0114] Referring to FIG. 9, the following describes the
configuration of a controller for controlling the DC brushless
motor for electrical power steering of the present embodiment.
[0115] FIG. 9 is a function block diagram representing the
configuration of the controller for controlling the DC brushless
motor for electrical power steering of the present invention.
[0116] The controller 200 comprises a power module 210 having a
function as an inverter; and a control module 220 for controlling
the power module 210. The DC voltage from the battery BA is
converted to the 3-phase AC voltage by the power module 210 having
a function as an inverter, and is supplied to the stator coil 114
of the EPS motor 100.
[0117] The torque control 221 in the control module 220 calculates
the torque Te based on the torque Tf of the steering ST detected by
the torque sensor TS and the target torque Ts, and outputs the
torque command, i.e. current command Is and rotary angle .theta.1
of the rotor 130 thereto by the PI control (P: proportional item;
I: integration item).
[0118] The phase shift circuit 222 outputs the pulse from the
encoder E, i.e. the position information .theta. of the rotor by
shifting the phase thereof, in response to the command of the
rotary angle .theta.1 from the torque control circuit (ASR) 221.
Based on the position information .theta. of the resolver 156 for
detecting the position of the pole of permanent magnet and the
rotor with its phase shifted by the phase shift circuit 222, a
sine/cosine wave generator 2223 outputs the sinusoidal wave
obtained by shifting the phase of the induction voltage of each of
the windings (three-phase in this case) of the stator coil.
[0119] The 2-phase/3-phase conversion circuit 224 outputs the
current commands Isa, Isb and Isc to respective phases in response
to the current command Is from the torque control circuit (ASR) 221
and the output from the sine/cosine wave generator 223. These
phases are separately provided with current control systems 225A,
225B and 225C, respectively. The 2-phase/3-phase conversion circuit
224 sends the signals conforming to the current commands Isa, Isb
and Isc, and current detection signals Ifa, Ifb and Ifc from the
current detector CT, to the inverter 210 to control the currents of
these phases.
[0120] The aforementioned description refers to the 10-pole/12-slot
EPS motor. The following describes the 8-pole/9-slot EPS motor and
10-pole/9-slot EPS motor with reference to the hatched area in FIG.
3.
[0121] The 8-pole/9-slot and 10-pole/9-slot motors provide a higher
usage rate of the magnetic flux of a magnet than the 6-pole/9-slot
AC motor. To be more specific, the 6-pole/9-slot AC motor has a
usage rate of the magnetic flux of a magnet (kwks) of 0.83. In the
meantime, the 8-pole/9-slot and 10-pole/9-slot motors have a
winding factor (kw) of 0.95 with a skew factor (ks) of 1.00. Thus,
the 8-pole/9-slot and 10-pole/9-slot motors have a usage rate
(kwks) of 0.94. This means that the 8-pole/9-slot motor and
10-pole/9-slot motors improve the usage rate of the magnetic flux
of a magnet (kwks).
[0122] The period of the cogging torque corresponds to the least
common multiple of the numbers of poles P and slots S, and
therefore the period of the cogging torque in the 6-pole/9-slot AC
motor is 18. Thus, the period of the cogging torque in the
8-pole/9-slot and 10-pole/9-slot motors can be reduced to 72. This
shows that a reduction of cogging torque is ensured.
[0123] Further, the cogging torque resulting from poor roundness of
inner diameter can also be reduced. To be more specific, assuming
that the cogging torque resulting from the out-of-roundness of
inner diameter in the 6-pole/9-slot AC motor is 3.7, that in the
8-pole/9-slot and 10-pole/9-slot motors can be 1.4, with the result
that the cogging torque resulting from the out-of-roundness of
inner diameter can be reduced. Further, machining is applied to the
inner diameter of the molded stator subassembly to improve the
roundness of the inner diameter. This leads to further reduction in
the cogging torque resulting from the poor roundness of inner
diameter.
[0124] In the 8-pole/9-slot and 10-pole/9-slot motors, parallel
connection of the series circuit of the coil U2+ and coil U2-
cannot be configured as viewed from the U phase, with respect to
the series circuit of the coil U1+ and coil U1-, as in the
10-pole/12-slot EPS motor described above with reference to FIG. 5.
This requires a series connection of the coil U1+, coil U1-, coil
U2+ and coil U2-.
[0125] Referring to FIGS. 10 through 16, the following describes
the controller of the DC brushless motor for electrical power
steering of the present embodiment.
[0126] FIG. 10 is a perspective exploded view representing the
configuration of the controller of the DC brushless motor for
electrical power steering of the present embodiment.
[0127] As shown in FIG. 10, the motor controller 200 comprises a
power module 210, a control module 220, a conductor module 230, a
case 240 and a shield cover 250.
[0128] In the power module 210, a wiring pattern is formed on a
metallic substrate through an insulator. A semiconductor switching
device SSW such as a MOSFET (metal oxide semiconductor field-effect
transistor) described with reference to FIG. 9 is mounted on the
wiring pattern. The power module 210 is fixed with one end of each
of multiple lead frames 210 LF by soldering. The lead frames 210 LF
is used for electrical connection of the power module 210 and
control module 220.
[0129] In the control module 220, a CPU and driver circuit are
mounted on the PCB substrate. In the illustrated state, the CPU and
driver circuit are mounted on the lower surface of the substrate.
The signal connector 220C is mounted on the control module 220.
[0130] The conductor module 230 is integrally connected with the
bus bar 230B as a power line by molding. At the same time, it is
connected integrally with the motor connector 230 SC as a terminal
for supplying motor current to the motor and the power connector
230 PC by molding. The parts 230P such as a relay coil and a
capacitor are mounted in advance on the conductor module 230. The
terminal of the parts 230P and bus bar 230B are secured by TIG
welding (arc welding).
[0131] The case 240 is made of aluminum. At the time of assembling,
the power module 210 and conductor module 230 are fixed by screws
in the case 240. The control module 220 is also fixed by screws on
the power module 210 and conductor module 230. The multiple ends of
the lead frames 210 LF is connected with the terminal of the
control module 220 by soldering. The shield cover 250 is fixed by
screws in the final step, whereby the motor controller 200 is
manufactured.
[0132] FIG. 11 is a circuit diagram representing the circuit
configuration of the controller for controlling the DC brushless
motor for electrical power steering of the present embodiment. The
same reference numerals as those in FIG. 10 indicate the same
parts.
[0133] The motor controller 200 comprises a power module 210,
control module 220 and conductor module 230.
[0134] The conductor module 230 is integrally molded with the bus
bar 230B. In the drawing, the bold solid line indicates the bus
bar. In the conductor module 230, the common filter CF, normal
filter NF, capacitors CC1 and CC2, and relay RY1 are connected to
the bus bar for connecting the collector terminal of the
semiconductor switching device SSW, as shown in the drawing.
[0135] The portion indicated by a double circle denotes the welded
connection. For example, the four terminals of the common filter CF
are connected to the bus bar terminal by welding. Two terminals of
the normal filter, two terminals of each of ceramic capacitors CC1
and CC2 and two terminals of the relay RY1 are also connected to
the terminals of the bus bar by welding. The common filter CF and
normal filter NF are provided to avoid radio noise.
[0136] A bus bar is also used for the wire for supplying motor
current to the motor 100 from the power module 210. Relays RY2 and
RY3 are connected by welding to the bus bar wire leading from the
power module 210 to the motor 100. Relays RY1, RY2 and RY3 are used
for the fail safe system to cut off power to the motor in the event
of motor failure or control module trouble.
[0137] The control module 220 is provided with a CPU 222 and driver
circuit 224. Based on the torque detected by the torque sensor TS
and the rotary position of the motor 100 detected by the resolver
156, the CPU 222 outputs to the driver circuit 224 the control
signal for controlling on-off operation of the semiconductor
switching device SSW of the power module 210. Based on the control
signal from the CPU 222, the driver circuit 224 controls the on-off
drive of the semiconductor switching device SSW of the power module
210. The motor current supplied from the power module 210 to the
motor is detected by the motor current detection resistors (shunt
resistors) DR1 and DR2 and is amplified by the amplifiers AP1 and
AP2. Then the current is inputted into the CPU 222. The CPU 222
provides feedback control to ensure that the motor current will be
the target. The CPU 222 is connected by the external engine control
ECU, CAN and others, whereby information is exchanged.
[0138] The .DELTA. (inverted delta symbol) in the drawing indicates
the portions connected by welding using the lead frame. Use of the
lead frame reduces the stress. The configuration of the lead frame
will be described with reference to FIG. 15. Welding using the lead
frame is utilized for electrical connection between the control
module 220 and power module 210 or conductor module 230.
[0139] The power module 210 comprises six semiconductor switching
devices SSW such as IGBT. The semiconductor switching device SSW is
serially connected to the upper 56- and lower arms for each of
three phases. In the drawing, a cross "x" denotes an electrical
connection by wire bonding. To be more specific, motor current is
supplied to the motor 100 from the power module 210 through the bus
bar of the conductor module 230, but this is a large current.
Accordingly, connection is made by wire bonding that allows a large
current to run, and reduces the stress. The details will be
described later with reference to FIG. 16. The power supply line
and earth line for the semiconductor switching device SSW are also
connected wire bonding.
[0140] Referring to FIG. 12, the following describes the
configuration of the conductor module 230 of the controller for
controlling the DC brushless motor for electrical power steering of
the present embodiment.
[0141] FIG. 12 is a perspective bottom view showing the
configuration of conductor module of the controller for controlling
the DC brushless motor for electrical power steering. The same
reference numerals in FIGS. 10 and 11 indicate the same parts. FIG.
12 shows the bottom view of the conductor module 230 shown in FIG.
10.
[0142] The conductor module 230 is formed by molding, and is
provided with holes for inserting the terminals of electrical parts
such as the common filter CF, normal filter NF, capacitors CC1 and
CC2, and relays RY1, RY2 and RY3. Electrical parts are arranged on
these positions, and the terminals of the electrical parts and
terminals of the bus bar are connected by welding on the
illustrated bottom surface side.
[0143] FIG. 13 is a perspective view representing the configuration
of the controller for controlling the DC brushless motor for
electrical power steering of the present embodiment.
[0144] In FIG. 13, the power module 210 and conductor module 230
are arranged in the case 240. The control module 220 is not yet
mounted in position.
[0145] The conductor module 230 and a plurality of bus bars BB1,
BB2, BB3, BB4, BB5, BB6 and BB7 are formed by molding. The bus bar
terminals and terminals of the electrical parts such as the common
filter CF, normal filter NF, capacitors CC1 and CC2, and relays
RY1, RY2 and RY3 are connected by welding.
[0146] The power module 210 is provided with a plurality of
semiconductor switching device SSW. Electrical connections are
provided by wire bonding WB1, WB2, WB3, WB4 and WB5 at five
positions between the power module 210 and conductor module 230.
For wire bonding WB1, for example, five aluminum wires having a
diameter of 500 .mu.m are connected in parallel.
[0147] The power module 210 and conductor module 230 are arranged
opposite to each other on one and the same flat plane. To be more
specific, the power module 210 is mounted on one side of the case
240, and the conductor module 230 is located on the other side of
the case 240. This arrangement ensures easier wire bonding
work.
[0148] FIG. 14 is a cross sectional view of the controller for
controlling the DC brushless motor for electrical power steering of
the present embodiment. It shows the cross sectional configuration
at position X1-X1 of FIG. 13. The same reference numerals in FIGS.
10 through 13 indicate the same parts.
[0149] The power module 210 and conductor module 230 are fixed by
screws on the inner bottom surface of the case 240. As shown in
FIG. 11, the conductor module 230 are provided with electrical
parts and is welded together with the bus bar, thereby forming an
integral module, which is fixed by screws. Then electrical
connection between the power module 210 and conductor module 230 is
provided by wire bonding WB.
[0150] The lower end of the lead frames LF is secured on the power
module 210 by soldering. Under this condition, the control module
220 is placed thereon and is secured the other end of the lead
frames LF by soldering. The control module 220 is secured on the
case 240 by screws. A shield cover 250 is then fixed on the case
240 by screws.
[0151] FIG. 15 is a cross sectional view representing the major
portions of the controller for controlling the DC brushless motor
for electrical power steering of the present embodiment. The same
reference numerals as those in FIG. 14 indicate the same parts.
[0152] FIG. 15 indicates a detailed structure of the connections
between the power module 210 and conductor module 230.
[0153] The power module 210 is provided with a semiconductor
switching device SSW. A metal substrate MP (e.g. aluminum (Al) and
copper (Cu)) is used to release the heat thereof. Heat conduction
grease HCG is applied between the metal substrate MP and case 240.
Thus, the heat generated from the semiconductor switching device
SSW is released from the aluminum case 240 through therebetween
heat conduction grease HCG. A wiring pattern WP is formed on the
metal substrate MP through the insulation film 1M. An insulation
layer of low elasticity is used to produce the insulation film 1M.
The wiring pattern WP is obtained by etching and patterning a 175
.mu.m-thick copper (Cu) foil. An aluminum pad PD used for
electrical connection is formed on the wiring pattern WP. A nickel
film is formed on the back of the aluminum pad PD.
[0154] For the conductor module 230, in the meantime, a bus bar BB
is formed. On the end of the bus bar BB, a nickel film is formed on
the surface of the connection with the power module 210.
[0155] Wire bonding WB is used for connection between the bus bar
BB of the power module 210 and the aluminum pad PD of the conductor
module 230 by means of an aluminum wire.
[0156] As described above, the metallic substrate is used as a
conductor module 230. This arrangement causes expansion coefficient
to be increased. Since expansion and compression are repeated in
conformity to the temperature change of the conductor module 230,
stress is applied to the electrical connection with the power
module 210. Because a large current runs between the power module
210 and conductor module 230, such a conductor as a bus bar is
preferably utilized for connection. However, this may cause
separation of the connection due to thermal stress. To solve this
problem, an aluminum wire susceptible to reversible change is used,
as in the present embodiment. This allows thermal deformation of
the conductor module 230 to be absorbed by the aluminum wire, with
the result that stress is not applied to the electrical connection.
This provides a stress-free structure. However, to allow a large
current to flow, five aluminum wires having a diameter of 500 .mu.m
are connected in parallel.
[0157] A wire pattern is obtained by etching and patterning a 175
.mu.m-thick copper (Cu) foil. If the thickness is in the range from
105 through 200 .mu.m, for example, resistance can be reduced, and
the amount of heat generation can also be reduced in the face of a
large current. It is more preferably to use a wire pattern having a
thickness of 145 through 175 .mu.m. Use of a wire pattern having a
thickness of 145 .mu.m or more allows the resistance to be reduced
as compared to the thickness of 105 .mu.m. The amount of heat
generation can also be reduced in the face of a large current.
Further, when a copper foil having a thickness of 200 .mu.m is
patterned by etching, the pattern pitch will be increased and a
small chip resistor or chip capacitor may not be installed in some
cases. If the thickness is 175 .mu.m or more, smaller chip parts
can be utilized.
[0158] FIG. 16 is a cross sectional view representing the major
portions of the controller for controlling the DC brushless motor
for electrical power steering of the present embodiment. The same
reference numerals as those in FIG. 14 indicate the same parts.
[0159] The power module 210 and control module 220 are connected by
the lead frames LF. The lead frames LF used in the present
embodiment is made of a brass sheet material having a thickness of
0.15 mm, for example, and has a bend at some midpoint as shown in
the drawing. As described above, the metal substrate MP is used as
the substrate of the power module 210. Accordingly, the
aforementioned lead frames LF is used to prevent thermal stress
from being applied to the electrical connection between the power
module 210 and control module 220 by thermal stress. Soldering is
used for connection between the power module 210 and one end of the
lead frames LF, and between the control module 220 and the other
end of the lead frames LF. This arrangement provides signal line
connection with a stress-free structure.
[0160] Referring to FIG. 17, the following describes another
configuration of the controller for controlling the DC brushless
motor for electrical power steering of the present embodiment.
[0161] FIG. 17 is a perspective view representing another
configuration of the controller for controlling the DC brushless
motor for electrical power steering of the present embodiment. The
same reference numerals in FIGS. 10 through 16 indicate the same
parts.
[0162] Basically, the structure of the present embodiment is the
same as shown in FIGS. 10 and 12, and the circuit configuration is
the same as shown in FIG. 11. FIG. 17 shows the power module 210
and conductor module 230A mounted in the case 240, where the
control module 220 is not yet mounted.
[0163] In this example, the configuration of the conductor module
230A is slightly different from that of the conductor module 230
illustrated in FIG. 13. To be more specific, the conductor module
230A is L-shaped in its planer geometry, as compared with the
conductor module 230 shown in FIG. 13 being rectangular. The
terminals of the electrolytic capacitor and ceramic capacitor are
fixed to the bus bar by welding at the portion Y1. At another
portion Y2, the terminals of the relay, normal filter and common
filer are secured to the bus bar by TIG welding (arc welding), as
in FIG. 13.
[0164] As described above, according to the present embodiment,
welding is used for connection between the power module 210 and
conductor module 230. Connection between the control module 220 and
power module 210 is provided by soldering. According to this
method, the portion exposed to a large current is connected by
welding, whereby melting of welding connection is avoided and the
reliability is improved. Other positions are connected by
soldering, thereby improving the manufacturability
[0165] Connection between the power module 210 and conductor module
230 is provided by wire bonding. This arrangement reduces the
stress on a large current line. Further, parallel connection of a
plurality of wires allows a large current to run.
[0166] The power module 210 and conductor module 230 are arranged
on the same plane opposed to each other. To be more specific, the
power module 210 and conductor module 230 are arranged on one side
of the case 240. The conductor module 230 is placed on the other
side of the case 240. This arrangement ensures easier wire bonding
work.
* * * * *