U.S. patent application number 12/044553 was filed with the patent office on 2008-09-11 for drive motor for use in variable valve operating device for internal combustion engine.
This patent application is currently assigned to Keihin Corporation. Invention is credited to Hideki Furuta, Yoshihiro Suzuki, Masashi Ueda.
Application Number | 20080216781 12/044553 |
Document ID | / |
Family ID | 39678195 |
Filed Date | 2008-09-11 |
United States Patent
Application |
20080216781 |
Kind Code |
A1 |
Furuta; Hideki ; et
al. |
September 11, 2008 |
DRIVE MOTOR FOR USE IN VARIABLE VALVE OPERATING DEVICE FOR INTERNAL
COMBUSTION ENGINE
Abstract
An actuator of a variable valve operating device includes an
electric motor for varying the distance by which an intake valve of
an internal combustion engine is lifted. The electric motor has a
hollow cylindrical magnet assembly disposed around a hollow
cylindrical holder, and a shaft rotatably supported in a housing,
with a hollow region being defined between the shaft and the
holder. The magnet assembly is skew-magnetized at a predetermined
angle to the axis of the magnet assembly.
Inventors: |
Furuta; Hideki; (Kakuda-shi,
JP) ; Suzuki; Yoshihiro; (Natori-shi, JP) ;
Ueda; Masashi; (Natori-Shi, JP) |
Correspondence
Address: |
LAHIVE & COCKFIELD, LLP;FLOOR 30, SUITE 3000
ONE POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Assignee: |
Keihin Corporation
Shinjuku-Ku
JP
|
Family ID: |
39678195 |
Appl. No.: |
12/044553 |
Filed: |
March 7, 2008 |
Current U.S.
Class: |
123/90.16 ;
464/29 |
Current CPC
Class: |
H02K 1/2733 20130101;
H02K 7/116 20130101; Y10T 464/30 20150115; F01L 13/0021
20130101 |
Class at
Publication: |
123/90.16 ;
464/29 |
International
Class: |
F01L 1/344 20060101
F01L001/344 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2007 |
JP |
2007-059566 |
Claims
1. A drive motor for use in a variable valve operating device
disposed in a cylinder head of an internal combustion engine for
controlling an angular displacement of a camshaft which is
angularly movably supported in the cylinder head, comprising: a
housing; a rotor including a shaft rotatably supported in said
housing and a hollow cylindrical magnet assembly disposed around
said shaft; and a stator disposed around said rotor and including a
wound coil; said magnet assembly comprising a Nd--Fe--B magnet.
2. A drive motor according to claim 1, wherein said magnet assembly
has skewed magnetic poles.
3. A drive motor according to claim 2, wherein said rotor has a
hollow region defined between said magnet assembly and said
shaft.
4. A drive motor according to claim 3, wherein said hollow region
is defined between a holder disposed around said shaft and holding
said magnet assembly and a slender shaft portion of said shaft
which faces said holder.
5. A drive motor according to claim 4, wherein said holder has a
breather hole through which said hollow region is held in fluid
communication with the exterior of said holder.
6. A drive motor according to claim 2, wherein said magnet assembly
comprises a pair of magnets held by said holder, said magnets being
arrayed along an axial direction of said holder.
7. A drive motor according to claim 6, wherein said magnets are
skew-magnetized at a predetermined angle to an axis of the
magnets.
8. A drive motor according to claim 7, wherein said predetermined
angle is 15.degree..
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a drive motor for use in a
variable valve operating device in an internal combustion engine
for controlling the angular displacement of a control shaft
angularly movably supported in the cylinder head of the internal
combustion engine thereby to control the distance by which a valve
is lifted in response to the displacement of a cam shaft.
[0003] 2. Description of the Related Art
[0004] As disclosed in Japanese Laid-Open Patent Publication No.
2006-307713, for example, there is known a variable valve operating
device including a drive motor for angularly moving a cam shaft
that is angularly movably supported in the cylinder head of an
internal combustion engine. In recent years, drive motors for use
in variable valve operating devices for internal combustion engines
have been required to be more responsive and smaller in size.
SUMMARY OF THE INVENTION
[0005] It is a general object of the present invention to provide a
drive motor for use in a variable valve operating device in an
internal combustion engine, which drive motor is more responsive
when energized, can smoothly be operated, and is small in size.
[0006] The above and other objects, features, and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings in which a preferred embodiment of the present invention
is shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a front elevational view, partly omitted from
illustration, of an internal combustion engine incorporating a
variable valve operating device which includes a drive motor
according to an embodiment of the present invention;
[0008] FIG. 2 is an enlarged side elevational view of a lift
varying mechanism and nearby parts of the variable valve operating
device shown in FIG. 1;
[0009] FIG. 3 is an exploded perspective view of the lift varying
mechanism shown in FIG. 2;
[0010] FIG. 4 is a vertical cross-sectional view of an actuator of
the variable valve operating device shown in FIG. 1;
[0011] FIG. 5 is an enlarged cross-sectional view of an electric
motor and nearby parts of the actuator shown in FIG. 4;
[0012] FIG. 6 is a perspective view of a rotor of the electric
motor of the actuator shown in FIG. 4;
[0013] FIG. 7 is an exploded perspective view of the rotor shown in
FIG. 6; and
[0014] FIG. 8 is a side elevational view of the rotor shown in FIG.
6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] As shown in FIG. 1, a variable valve operating device 10
which includes a drive motor according to an embodiment of the
present invention is incorporated in an internal combustion
engine.
[0016] As shown in FIGS. 1 through 3, the variable valve operating
device 10 is mounted in a cylinder head 14 fixedly mounted on a
cylinder block 12 of the internal combustion engine which has a
plurality of cylinders. The cylinder head 14 houses therein an
intake valve 16 openably and closably disposed in an intake port of
each of the cylinders. The intake valve 16 is opened and closed by
the variable valve operating device 10.
[0017] For each of the cylinders, the variable valve operating
device 10 comprises a camshaft 20 having a valve operating cam 18,
a rocker arm 22 swingably displaceable in response to movement of
the valve operating cam 18 for operating the intake valve 16, and a
lift varying mechanism 24 for continuously varying the distance by
which the intake valve 16 is lifted to open the intake port. The
variable valve operating device 10 further comprises an actuator 26
for actuating the lift varying mechanism 24.
[0018] As shown in FIG. 2, an upper holder 28a is fastened to the
cylinder head 14 and disposed on both sides of the cylinders. The
camshaft 20 is rotatably supported by a cap 30 mounted on an upper
surface of the upper holder 28a.
[0019] The rocker arm 22 is of a substantially V-shaped cross
section bent through a predetermined angle. A tappet screw 34 held
in abutment with a stem 32 of the intake valve 16 is axially
adjustably threaded through an end of the rocker arm 22. A roller
40 is rotatably supported by a substantially central portion of the
rocker arm 22 through a first coupling shaft 36 and a needle
bearing 38. The roller 40 is held in rolling abutment against the
outer circumferential surface of the valve operating cam 18 on the
camshaft 20.
[0020] As shown in FIGS. 2 and 3, the lift varying mechanism 24
includes a first link arm 44 having an end angularly movably
coupled to the substantially central portion of the rocker arm 22
and another end angularly movably supported by a fixed shaft 42.
The lift varying mechanism 24 also includes a second link arm 46
having an end angularly movably coupled to another end of the
rocker arm 22 and another end angularly movably supported by a
movable shaft 45. The lift varying mechanism 24 further includes a
control shaft 48 engaged by the movable shaft 45 and angularly
displaceable through a predetermined angle about the axis of the
movable shaft 45.
[0021] The end of the first link arm 44 is of a substantially
U-shaped cross section sandwiching the substantially central
portion of the rocker arm 22 at its opposite sides, and is
angularly movably supported by the first coupling shaft 36 by which
the roller 40 is rotatably supported on the substantially central
portion of the rocker arm 22. The fixed shaft 42 by which the other
end of the first link arm 44 is angularly movably supported is
supported by the upper holder 28a.
[0022] The second link arm 46 is disposed below the first link arm
44. The end of the second link arm 46 is sandwiched by the other
end of the rocker arm 22, and is angularly movably supported on the
rocker arm 22 by a second coupling shaft 50 which extends through
the other end of the rocker arm 22.
[0023] The control shaft 48 comprises a pair of webs 52 disposed
one on each side of the rocker arm 22, a shaft 54 extending
perpendicularly to the webs 52 and interconnecting pairs of webs
52, and a joint 56 interconnecting the webs 52. The movable shaft
45, which is disposed substantially parallel to the shaft 54,
extends through the control shaft 48 across the webs 52 and is held
thereby.
[0024] The shaft 54 of the control shaft 48 is angularly movably
supported by the upper holder 28a and a lower holder 28b which is
fastened to a lower surface of the upper holder 28a (see FIG.
2).
[0025] When the intake valve 16 is placed in a closed state, the
second coupling shaft 50 which connects the second link arm 46 to
the rocker arm 22 is coaxial with the shaft 54 of the control shaft
48. When the control shaft 48 is angularly displaced about the
shaft 54, the movable shaft 45 held by the control shaft 48 moves
along an arcuate path about the axis of the shaft 54.
[0026] Specifically, when the control shaft 48 is angularly
displaced to lower the movable shaft 45, and the roller 40 is
pressed by the valve operating cam 18 of the camshaft 20, a
four-link mechanism interconnecting the fixed shaft 42, the first
coupling shaft 36, the second coupling shaft 50, and the movable
shaft 45 is deformed to angularly displace the rocker arm 22
downwardly. The tappet screw 34 mounted on the end of the rocker
arm 22 presses the stem 32 of the intake valve 16, lifting the
intake valve 16 by a small distance to open the intake port.
[0027] When the control shaft 48 is angularly displaced to elevate
the movable shaft 45, and the roller 40 is pressed by the valve
operating cam 18 of the camshaft 20, the four-link mechanism is
deformed to angularly displace the rocker arm 22 downwardly. The
tappet screw 34 presses the stem 32 of the intake valve 16, lifting
the intake valve 16 by a large distance to open the intake
port.
[0028] The shaft 54 has an end portion projecting as a slightly
long coupling shaft 58 laterally of the cylinder head 14. The
coupling shaft 58 is inserted into a casing 60 (see FIG. 4) of the
actuator 26 which is mounted on a side wall of the cylinder head
14.
[0029] As shown in FIG. 4, the actuator 26 comprises the casing 60,
an electric motor 62 disposed in the casing 60 and having a drive
shaft rotatable when the electric motor 62 is energized, a drive
power transmitting mechanism 64 for transmitting drive power from
the electric motor 62 to the control shaft 48, and a default
mechanism 66 for holding the control shaft 48 in a predetermined
angular position when the electric motor 62 is de-energized.
[0030] A first cover 68 is mounted on a side wall of the casing 60
by a plurality of bolts 70 in covering relation to the drive power
transmitting mechanism 64. The casing 60 and the first cover 68
define a speed reducer mechanism housing chamber 72 therebetween.
The speed reducer mechanism housing chamber 72 houses therein a
speed reducer mechanism 74 of the drive power transmitting
mechanism 64.
[0031] A second cover 76 is mounted on an opposite side wall of the
casing 60 in covering relation to the default mechanism 66. The
casing 60 and the second cover 76 define a default mechanism
housing chamber 78 therebetween. The default mechanism housing
chamber 78 houses therein the default mechanism 66.
[0032] As shown in FIGS. 4 and 5, the electric motor 62 is disposed
in a motor housing hole 80 defined in a lower portion of the casing
60. The electric motor 62 comprises a housing 82, a rotor 84
rotatably held in the housing 82, and a stator 88 disposed around
the rotor 84 and including a wound coil 86.
[0033] The rotor 84 comprises a shaft 90 rotatably supported in the
housing 82, a hollow cylindrical holder 92 disposed around the
shaft 90, and a magnet assembly 94 disposed around the holder
92.
[0034] The shaft 90 has both ends supported respectively by
bearings 96a, 96b. A drive gear 98 is mounted on an end of the
shaft 90 which is closer to the drive power transmitting mechanism
64. The drive gear 98 is held in mesh with a driven gear 100 of the
drive power transmitting mechanism 64. A disk plate 102 is coupled
to the other end of the shaft 90 which is closer to the default
mechanism 66. The shaft 90 includes a slender shaft portion 104
having a radially inwardly reduced diameter in a substantially
axially central position. The shaft 90 also includes a flange 106
having radially outwardly increased diameter between the slender
shaft portion 104 and the end of the shaft 90 which is supported by
the bearing 96a.
[0035] The holder 92 comprises a large-diameter portion 108
disposed coaxially with the shaft 90 in covering relation to the
slender shaft portion 104 of the shaft 90 and having a
substantially constant diameter, and a small-diameter portion 110
disposed on an end of the large-diameter portion 108 and smaller in
diameter than the large-diameter portion 108.
[0036] The large-diameter portion 108 extends up to the flange 106
in covering relation to the slender shaft portion 104 and a portion
of the shaft 90 near the end of the shaft 90 which is supported by
the bearing 96a. The large-diameter portion 108 has an end held
against the flange 106 to limit axial displacement of the shaft 90.
The holder 92 is thus positioned with respect to the shaft 90.
[0037] The small-diameter portion 110 is disposed near the other
end of the shaft 90 and holds an outer circumferential surface of
the shaft 90. The small-diameter portion 110 is fitted over and
held on the shaft 90, e.g., the small-diameter portion 110 is
lightly press-fitted over the other end of the shaft 90.
[0038] An annular hollow region 112 having a given radial clearance
is defined between the large-diameter portion 108 and the slender
shaft portion 104. The annular hollow region 112 is held in fluid
communication with the exterior of the holder 92 through a breather
hole 114 defined in the junction between the large-diameter portion
108 and the small-diameter portion 110. Stated otherwise, the
annular hollow region 112 is defined as a cylindrical space between
the inner circumferential surface of the holder 92 and the outer
circumferential surface of the slender shaft portion 104.
[0039] A flange 116 which projects slightly radially outwardly is
disposed on the end, near the small-diameter portion 110, of an
outer circumferential surface of the large-diameter portion 108.
The flange 116 serves to position the magnet assembly 94 disposed
around the holder 92.
[0040] The magnet assembly 94 comprises an Nd--Fe--B bonded magnet
formed by mixing a powder of neodymium magnet with a plastic
material and compression-molding or injection-molding the mixture,
or an Nd--Fe--B sintered magnet formed by compression-molding a
powder of neodymium magnet in a magnetic field and sintering the
molded body. The magnet assembly 94 is in the form of a hollow
cylinder whose diameter remains substantially constant in the axial
direction. The magnet assembly 94 has an inside diameter which is
substantially the same as the outside diameter of the
large-diameter portion 108 of the holder 92 (see FIG. 5).
[0041] As shown in FIGS. 6 through 8, the magnet assembly 94
comprises a pair of coaxial magnets 94a, 94b, which have
substantially the same axial lengths, arrayed along the axial
direction of the holder 92. The magnets 94a, 94b are placed axially
onto the large-diameter portion 108, and then secured to the holder
92. Specifically, the magnets 94a, 94b are bonded to the holder 92
by an adhesive applied to either the inner circumferential surfaces
of the magnets 94a, 94b or the outer circumferential surface of the
holder 92, so that the magnets 94a, 94b and the holder 92 are
integrally combined with each other.
[0042] The magnet assembly 94 has an axial length which is
essentially the same as the axial length of the large-diameter
portion 108. Therefore, the magnet assembly 94 is mounted on the
large-diameter portion 108 in covering relation to substantially
the entire outer circumferential surface of the large-diameter
portion 108.
[0043] The magnet assembly 94 is skew-magnetized, i.e., has skewed
magnetic poles, at a given angle .theta. to the axis D of the
magnets 94a, 94b (see FIG. 8). The magnetizing angle .theta. is
optimally set to 15.degree., for example, with respect to the axis
D of the magnets 94a, 94b.
[0044] The magnet assembly 94 is not limited to being made up of
the magnets 94a, 94b, but may be of a three-piece structure made of
three magnets having substantially the same shape disposed around
the holder 92 or a one-piece structure made up of a single magnet
disposed around the holder 92.
[0045] The drive power transmitting mechanism 64 is disposed
between the coupling shaft 58 of the control shaft 48 and the
electric motor 62. The drive power transmitting mechanism 64
transmits drive power from the electric motor 62 to the lift
varying mechanism 24 including the control shaft 48.
[0046] The drive power transmitting mechanism 64 comprises a worm
wheel 118 fixed to the coupling shaft 58, a worm gear 120 held in
mesh with the worm wheel 118, and the speed reducer mechanism 74
disposed between the worm gear 120 and the electric motor 62.
[0047] The worm gear 120 is housed in a worm gear housing chamber
122 defined in the casing 60 above the motor housing hole 80. The
worm gear 120 is disposed coaxially on a worm gear shaft 144 which
has an end rotatably supported in the casing 60 by a ball bearing
124 and another end rotatably supported in the casing 60 by a
needle bearing 126.
[0048] The end of the worm gear shaft 144 which is rotatably
supported by the ball bearing 124 extends into the speed reducer
mechanism housing chamber 72 housing therein the speed reducer
mechanism 74. The speed reducer mechanism 74 includes a driven gear
100 mounted on the end of the worm gear shaft 144. The other end of
the worm gear shaft 144 which is rotatably supported by the needle
bearing 126 supports thereon a small-diameter gear 130 held in mesh
with a large-diameter gear 128 of the default mechanism 66.
[0049] A worm wheel housing chamber 132 connected to the worm gear
housing chamber 122 is provided at the upper of the casing 60. The
worm wheel housing chamber 132 houses therein the worm wheel 118.
The coupling shaft 58 has an end inserted into the worm wheel
housing chamber 132, and the worm wheel 118 is coaxially fixed to
the inserted end of the coupling shaft 58 by a bolt 70.
[0050] The speed reducer mechanism 74 comprises the drive gear 98
mounted on the end of the shaft 90 and the driven gear 100 held in
mesh with the drive gear 98. The speed reducer mechanism 74 is
housed in the speed reducer mechanism housing chamber 72 that is
defined between the casing 60 and the first cover 68. The speed
reducer mechanism 74 reduces the speed of drive power from the
electric motor 62 at a ratio depending on the drive gear 98 and the
driven gear 100, and transmits the reduced-speed drive power to the
worm gear 120.
[0051] The default mechanism 66, which is housed in a default
mechanism housing chamber 78 formed in the casing 60, comprises a
default shaft 134 rotatably supported in the casing 60, the
large-diameter gear 128 mounted on the default shaft 134 and held
in mesh with the small-diameter gear 130 of the drive power
transmitting mechanism 64, and a spring holder 136 disposed
coaxially with the large-diameter gear 128.
[0052] The default mechanism 66 also comprises a first default
spring 138 for normally urging the large-diameter gear 128 to move
in a direction to abut against the spring holder 136, and second
and third default springs 140, 142 for normally urging the spring
holder 136 to move in a direction opposite to the direction in
which the first default spring 138 normally urges the
large-diameter gear 128, while the large-diameter gear 128 and the
spring holder 136 are being held in abutment against each
other.
[0053] The default shaft 134 is disposed substantially parallel to
the worm gear shaft 144 and has both ends supported respectively by
the casing 60 and the second cover 76. The large-diameter gear 128
is mounted on one of the ends of the default shaft 134, and held in
mesh with the small-diameter gear 130 on the other end of the worm
gear shaft 144. Therefore, the large-diameter gear 128 is
operatively connected to the electric motor 62 through the
small-diameter gear 130, the worm gear shaft 144, and the speed
reducer mechanism 74.
[0054] The spring holder 136 is supported on the other end of the
default shaft 134 and positioned adjacent to the large-diameter
gear 128. The spring holder 136 is rotatable relatively to the
large-diameter gear 128.
[0055] Engaging pins 146 project respectively from confronting end
faces of the spring holder 136 and the large-diameter gear 128. The
engaging pins 146 abut against each other upon angular movement of
the large-diameter gear 128. When the large-diameter gear 128 is
angularly moved to change the distance by which the intake valve 16
is lifted between a predetermined lifted distance and a minimum
lifted distance, the spring holder 136 is angularly moved in unison
with the large-diameter gear 128 about the default shaft 134 by the
abutting engagement between the engaging pins 146.
[0056] The second and third default springs 140, 142 comprise
helical springs, respectively, disposed around the spring holder
136. Each of the second and third default springs 140, 142 has an
end engaging the spring holder 136 and another end engaging the
casing 60.
[0057] Specifically, the second default spring 140 is disposed
radially inwardly closely to the radially inner portion of the
spring holder 136. The third default spring 142 is disposed
radially outwardly in spaced relationship to the second default
spring 140. The second and third default springs 140, 142 normally
urge the spring holder 136 to move in the same direction from a
minimum lifted distance position toward a predetermined lifted
distance position.
[0058] As shown in FIG. 3, a tubular spring holder 148 is fixedly
mounted on the coupling shaft 58 in surrounding relation thereto.
The first default spring 138 is disposed around the spring holder
148. The first default spring 138 has an end engaging the cylinder
head 14 and another end engaging the spring holder 148.
[0059] The variable valve operating device 10 incorporating the
drive motor according to the present embodiment is basically
constructed as described above. Operation and advantages of the
variable valve operating device 10 will be described below.
[0060] When the electric motor 62 of the actuator 26 is
de-energized, the worm gear 120 is angularly moved under the
resiliency of the second and third default springs 140, 142,
turning the worm wheel 118 through a predetermined angle. The
control shaft 48 of the lift varying mechanism 24 which is coupled
to the worm wheel 118 is turned to cause the movable shaft 45 to be
angularly displaced to change the relative positions of the first
and second link arms 44, 46, thereby angularly displacing the
rocker arm 22 upwardly. As a result, the intake valve 16 pressed by
the tappet screw 34 on the end of the rocker arm 22 is lifted by
the predetermined lift distance to open the inlet port.
[0061] According to the present embodiment, the magnet assembly 94
of the electric motor 62 is in the form of a hollow cylinder, and
is fitted over and secured to the holder 92 of the rotor 84. Even
when the rotor 84 is rotated at a high speed upon energization of
the electric motor 62, the magnet assembly 94 is prevented from
being spaced radially outwardly from the holder 92. The magnet
assembly 94 is therefore rotated in unison with the shaft 90 and
the holder 92 at all times.
[0062] The magnet assembly 94 which comprises an Nd--Fe--B magnet
is capable of producing greater magnetic forces than if the magnet
assembly 94 comprises a ferrite magnet. In other words, if the
magnet assembly 94 is to produce the same magnetic forces as a
ferrite magnet, then the magnet assembly 94 may be smaller in size
than the ferrite magnet.
[0063] If the magnet assembly 94 is reduced in size, then the rotor
84 including the magnet assembly 94 is reduced in weight. The
moment of inertia of the rotor 84 is thus reduced, allowing the
electric motor 62 to have an improved response, to reduce its power
consumption, and to permit the rotor 84 to rotate more
smoothly.
[0064] The magnet assembly 94 which comprises an Nd--Fe--B magnet
tends to increase the cogging torque when the electric motor 62 is
de-energized. However, since the magnet assembly 94 is
skew-magnetized, as described above, the cogging torque is reduced,
and the electric motor 62 including the magnet assembly 94 is
reduced in size.
[0065] Inasmuch as the shaft 90 includes the slender shaft portion
104 with the hollow region 112 defined between the slender shaft
portion 104 and the inner circumferential surface of the holder 92,
the rotor 84 including the shaft 90 and the holder 92 is reduced in
weight. Accordingly, the moment of inertia of the rotor 84 can be
reduced. As a result, the electric motor 62 has an improved
response and allows the rotor 84 to rotate more smoothly.
[0066] Since the hollow region 112 is defined between the slender
shaft portion 104 and the holder 92, the weight of the rotor 84 is
reduced in weight efficiently due to absence of materials between
the holder 92 and the shaft 90.
[0067] Although a certain preferred embodiment of the present
invention has been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
* * * * *