U.S. patent application number 09/933714 was filed with the patent office on 2002-04-04 for variable valve timing apparatus.
Invention is credited to Imamura, Fumihiko, Mae, Yosuke.
Application Number | 20020038639 09/933714 |
Document ID | / |
Family ID | 18773274 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020038639 |
Kind Code |
A1 |
Mae, Yosuke ; et
al. |
April 4, 2002 |
Variable valve timing apparatus
Abstract
A variable valve timing apparatus has a rotational torque
transmission path that changes the relative phases of a camshaft
that moves an engine valve and a rotary crank body that is coupled
to the crankshaft. The rotational torque transmission path has uses
an electromagnetic brake delay rotation of a drum, which is coupled
to the rotary crank body by a biasing member and a moving member.
When rotation of the drum is delayed, the moving member changes the
angular orientation between the drum and the rotary crank body
against the biasing force of the biasing member. The
electromagnetic brake is coupled to a cover by two protrusions and
two concavities. The protrusions are arranged to prevent contact
between the electromagnetic brake and the drum due to tension of
the chain.
Inventors: |
Mae, Yosuke; (Yokohama-shi,
JP) ; Imamura, Fumihiko; (Yokohama-shi, JP) |
Correspondence
Address: |
SHINJYU GLOBAL IP COUNSELORS, LLP
1233 20TH STREET, NW, SUITE 700
WASHINGTON
DC
20036-2680
US
|
Family ID: |
18773274 |
Appl. No.: |
09/933714 |
Filed: |
August 22, 2001 |
Current U.S.
Class: |
123/90.17 ;
123/90.15 |
Current CPC
Class: |
F02B 2275/18 20130101;
Y10T 74/2102 20150115; F01L 2001/3522 20130101; F01L 1/34406
20130101; F01L 1/024 20130101; F01L 2001/0537 20130101 |
Class at
Publication: |
123/90.17 ;
123/90.15 |
International
Class: |
F01L 001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2000 |
JP |
2000-289976 |
Claims
What is claimed is:
1. A variable valve timing apparatus for an internal combustion
engine, comprising: a rotary crank body adapted to be coaxially
coupled with a camshaft, and to be operatively rotated by a
crankshaft; a moving member operatively coupling said rotary crank
body to the camshaft along a rotational torque transmission path
that transmits torque from said rotary crank body to the camshaft;
a drum operatively coupled to said moving member to move said
moving member in an axial direction relative to said drum upon
relative rotational movement between said drum and said moving
member; a biasing member elastically coupling said drum to said
rotary crank body to apply a biasing force on said drum in a
direction of rotation of the camshaft relative to said rotary crank
body; an electromagnetic brake disposed opposite an axial side
surface of said drum to attract said axial side surface of said
drum towards said electromagnetic brake with a magnetic force upon
energizing said electromagnetic brake to delay rotation of said
drum about the camshaft and to change a phase of the camshaft
relative to a phase of said rotary crank body due to an axial
movement of said moving member; a cover fixed to an engine main
body side of said electromagnetic brake to cover said
electromagnetic brake; and a rotation regulation mechanism
operatively coupled between a wall portion of said electromagnetic
brake and a wall portion of said cover to regulate relative
rotation of said electromagnetic brake about the camshaft relative
to said cover, said rotation regulation mechanism including first
and second protrusions provided on one of said wall portions and
first and second concavities provided on the other of said wall
portions, said wall portions being opposing each other with said
first and second protrusions being coupled to said first and second
concavities, respectively, said first and, second protrusions lying
on a base line passing substantially through a center of said
drum.
2. The variable valve timing apparatus as set forth in claim 1,
wherein said rotary crank body includes a driven member engaged by
a drive member that is wound onto of said driven member to receive
a rotational torque from the crankshaft; and said base line is
arranged substantially perpendicular to a direction of a resultant
force of tension applied from said drive member to said driven
member.
3. The variable valve timing apparatus as set forth in claim 2,
further comprising an elastic member arranged between said wall
portion of said electromagnetic brake and said wall portion of said
cover to urge said electromagnetic brake toward said drum.
4. The variable valve timing apparatus as set forth in claim 3,
wherein said elastic member applies an urging force that at least
exceed a predetermined axial vibration input applied to said
electromagnetic brake.
5. The variable valve timing apparatus as set forth in claim 4,
wherein said biasing force of said biasing member and said urging
force of said elastic member are set such that said drum is
maintained at a position most rotated in a direction of rotation of
the camshaft relative to said rotary crank body when said
electromagnetic brake is in an initial state in which said
electromagnetic brake is not electrified.
6. The variable valve timing apparatus as set forth in claim 1,
further comprising an elastic member arranged between said wall
portion of said electromagnetic brake and said wall portion of said
cover to urge said electromagnetic brake toward said drum.
7. The variable valve timing apparatus as set forth in claim 6,
wherein said elastic member applies an urging force that at least
exceed a predetermined axial vibration input applied to said
electromagnetic brake.
8. The variable valve timing apparatus as set forth in claim 6,
wherein said biasing force of said biasing member and said urging
force of said elastic member are set such that said drum is
maintained at a position most rotated in a direction of rotation of
the camshaft relative to said rotary crank body when said
electromagnetic brake is in an initial state in which said
electromagnetic brake is not electrified.
9. The variable valve timing apparatus as set forth in claim 1,
wherein said biasing member is a torsion spring having a first end
coupled to said drum to and a second end coupled to said rotary
crank body.
10. The variable valve timing apparatus as set forth in claim 1,
wherein said rotary crank body is movably coupled to said moving
member for relative axial movement by a first helical spline
arrangement formed therebetween.
11. The variable valve timing apparatus as set forth in claim 10,
wherein said moving member is movably coupled to said drum by for
relative axial movement by a thread arrangement formed
therebetween.
12. The variable valve timing apparatus as set forth in claim 11,
further comprising a splined shaft adapted to be coaxially to
coupled said rotary crank body with the camshaft, said splined
shaft being coupled to said moving member for relative axial
movement by a second helical spline arrangement formed
therebetween.
13. The variable valve timing apparatus as set forth in claim 12,
wherein said drum is rotationally supported on said splined
shaft.
14. The variable valve timing apparatus as set forth in claim 12,
wherein said splined shaft has a center bore that is adapted to
receive a fastener to secure said splined shaft to the
camshaft.
15. The variable valve timing apparatus as set forth in claim 12,
wherein said biasing member is a torsion spring having a first end
coupled to said drum to and a second end coupled to said rotary
crank body.
16. A variable valve timing apparatus for an internal combustion
engine, comprising: rotary crank means for coaxially coupling with
a camshaft, and for being operatively rotated by a crankshaft;
moving means for operatively coupling said rotary crank means to
the camshaft along a rotational torque transmission path that
transmits torque from said rotary crank means to the camshaft; drum
means for moving said moving means in an axial direction relative
to said drum means upon relative rotational movement between said
drum means and said moving means; biasing means for elastically
coupling said drum means to said rotary crank means to bias said
drum means in a direction of rotation of the camshaft relative to
said rotary crank means; electromagnetic brake means for disposed
opposite an axial side surface of said drum means to attract said
axial side surface of said drum means towards said electromagnetic
brake means with a magnetic force upon energizing said
electromagnetic brake means to delay rotation of said drum means
about the camshaft and to change a phase of the camshaft relative
to a phase of said rotary crank means due to an axial movement of
said moving means; cover means for covering said electromagnetic
brake means; and rotation regulation means for regulating relative
rotation of said electromagnetic brake means about the camshaft
relative to said cover means, said rotation regulation means being
disposed between said electromagnetic brake means and said cover
means to regulate relative rotation of said electromagnetic brake
means about the camshaft relative to said cover means.
17. The variable valve timing apparatus as set forth in claim 16,
wherein said rotation regulation means including first and second
protrusions and first and second concavities, said first and second
protrusions being coupled to said first and second concavities,
respectively, said first and second protrusions lying on a base
line passing substantially through a center of said drum means.
18. The variable valve timing apparatus as set forth in claim 17,
wherein said rotary crank means includes a driven member engaged by
a drive member that is wound onto of said driven member to receive
a rotational torque from the crankshaft; and said base line is
arranged substantially perpendicular to a direction of a resultant
force of tension applied from said drive member to said driven
member.
19. The variable valve timing apparatus as set forth in claim 18,
further comprising elastic means for urging said electromagnetic
brake toward said drum.
20. The variable valve timing apparatus as set forth in claim 16,
further comprising elastic means for urging said electromagnetic
brake toward said drum.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to an improvement of
a variable valve timing apparatus for an internal combustion
engine. More specifically, the present invention relates a variable
valve timing apparatus that changes the valve timing of the intake
and exhaust valves by changing the phase of the camshaft relative
to that of the crankshaft.
[0003] 2. Background Information
[0004] Japanese Laid-Open Patent Publications H4-272411 and
H10-153105 disclose variable valve timing apparatuses for an
internal combustion engine that change the valve timing of the
intake and exhaust valves. The variable valve timing apparatuses
disclosed by these publications are of a type that uses an
electromagnetic brake.
[0005] In other words, this type of variable valve timing apparatus
has a moving member in a rotational torque transmission path that
transmits torque from a rotary crank body to a camshaft. The rotary
crank body rotates in sync with a crankshaft. A drum that is
coupled to the moving member is biased toward a rotational
direction of the camshaft by a biasing means such as a torsional
spring. By attracting an axial surface of the drum toward the
electromagnetic brake with a magnetic force, the electromagnetic
brake is attracted (biased) toward the drum. By delaying rotations
of the drum and displacing the moving member in the axial
direction, the phase of the camshaft relative to that of the rotary
crank body is changed. This electromagnetic brake is housed within
a cover that is fixed to the engine main body side while the
electromagnetic brake is in a state in which rotation relative to
the engine main body is restricted.
[0006] There exists a need for an improved variable valve timing
apparatus for an internal combustion engine. This invention
addresses this need in the prior art as well as other needs, which
will become apparent to those skilled in the art from this
disclosure.
SUMMARY OF THE INVENTION
[0007] It has been discovered that in variable valve timing
apparatus using an electromagnetic brake, a stable braking torque
cannot be generated unless surfaces of the electromagnetic brake
and the drum, which axially oppose each other, uniformly face and
contact each other.
[0008] However, during the operation of the system, tension from a
timing chain or timing belt is applied to a sprocket or pulley,
which is a part of the rotary crank body. Due to this tension, a
center axis of the drum that is coupled to the rotary crank body
becomes inclined. Accordingly, the surfaces of the electromagnetic
brake and the drum that are opposite each other may stop uniformly
facing and contacting each other. Moreover, as a result of this
inclination of the center axis of the drum, the opposing surfaces
of the electromagnetic brake and the drum may partially contact
each other. In such case, a desired frictional resistance cannot be
obtained. Therefore, the phase adjustment will be negatively
affected.
[0009] Alternatively, a bearing can be provided on an end of the
camshaft, such that the electromagnetic brake can be rotatably
supported by the camshaft via the bearing. However, the structure
becomes very complicated in this case. Accordingly, this
arrangement is not desirable from the point of view of cost and
layout.
[0010] Also, where a certain clearance is secured between the
opposing surfaces of the electromagnetic brake and the drum, such
that excessive friction will not be generated between the opposing
surfaces of the electromagnetic brake and the drum due to
inconsistency in size of members, as axial vibrations are inputted
into the electromagnetic brake, the electromagnetic brake may
vibrate axially or collide into the cover or the drum, causing
noises.
[0011] Furthermore, as such clearance is enlarged, the amount of
power of the electromagnetic brake that is required to attract the
drum becomes greater. Accordingly, the electromagnetic brake may
need to be larger, power to be consumed may increase, and
accordingly the fuel efficiency may be worsened.
[0012] Additionally, as such clearance becomes larger, the behavior
of the electromagnetic brake becomes unstable during the operation.
Accordingly, it is difficult for the electromagnetic brake to
attract the surface of the drum with a stable uniform force.
[0013] The present invention has been conceived in view of the
aforementioned problems. In other words, a variable valve timing
apparatus for an internal combustion engine is provided that
includes a rotary crank body, a moving member, a drum, a biasing
member, an electromagnetic brake, a cover and a rotation regulation
mechanism. The rotary crank body is adapted to be coaxially coupled
with a camshaft, and to be operatively rotated by a crankshaft. The
moving member operatively couples the rotary crank body to the
camshaft along a rotational torque transmission path that transmits
torque from the rotary crank body to the camshaft. The drum is
operatively coupled to the moving member to move the moving member
in an axial direction relative to the drum upon relative rotational
movement between the drum and the moving member. The biasing member
elastically couples the drum to the rotary crank body to bias the
drum in a direction of rotation of the camshaft relative to the
rotary crank body. The electromagnetic brake is disposed opposite
an axial side surface of the drum to attract the axial side surface
of the drum towards the electromagnetic brake with a magnetic force
upon energizing the electromagnetic brake to delay rotation of the
drum about the camshaft and to change a phase of the camshaft
relative to a phase of the rotary crank body due to an axial
movement of the moving member. The cover is fixed to an engine main
body side of the electromagnetic brake to cover the electromagnetic
brake. The rotation regulation mechanism is operatively coupled
between a wall portion of the electromagnetic brake and a wall
portion of the cover to regulate relative rotation of the
electromagnetic brake about the camshaft relative to the cover. The
rotation regulation mechanism includes first and second protrusions
provided on one of the wall portions and first and second
concavities provided on the other of the wall portions. The wall
portions are arranged to oppose each other with the first and
second protrusions being coupled to the first and second
concavities, respectively. The first and second protrusions lying
on a base line passing substantially through a center of the
drum.
[0014] These and other objects, features, aspects and advantages of
the present invention will become apparent to those skilled in the
art from the following detailed description, which, taken in
conjunction with the annexed drawings, discloses a preferred
embodiment of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Referring now to the attached drawings which form a part of
this original disclosure:
[0016] FIG. 1 is a cross sectional view of a variable valve timing
apparatus for an internal combustion engine in accordance with one
embodiment of the present invention;
[0017] FIG. 2 is an exploded perspective view of the variable valve
timing apparatus illustrated in FIG. 1, with portions broken away
for purposes of illustration;
[0018] FIG. 3 is a front elevational view of a V-type internal
combustion engine in which the variable valve timing apparatus
illustrated in FIGS. 1 and 2 is utilized;
[0019] FIG. 4 is a front elevational view of another V-type
internal combustion engine in which the variable valve timing
apparatus illustrated in FIGS. 1 and 2 is utilized;
[0020] FIG. 5 is an explanatory cross sectional view showing the
inclination of the drum relative to the electromagnetic brake when
the protrusions lie on a base line that is parallel to the
direction (the vertical upward direction) of the total tensions
apply to the drum via the timing belt or timing chain;
[0021] FIG. 6 is an explanatory cross sectional view showing the
electromagnetic brake being inclined to uniformly face and contact
the drum in accordance with the present embodiment since the
protrusions lie on a base line that is substantially perpendicular
to the direction (the vertical upward direction) of the total
tensions apply to the drum via the timing belt or timing chain;
[0022] FIG. 7 is a partial cross sectional view of a selected
portion of a first example of the elastic member in accordance with
the present invention;
[0023] FIG. 8 is a partial cross sectional view of a selected
portion of a second example of the elastic member in accordance
with the present invention; and
[0024] FIG. 9 is a partial cross sectional view of a selected
portion of a third example of the elastic member in accordance with
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Selected embodiments of the present invention will now be
explained with reference to the drawings. It will be apparent to
those skilled in the art from this disclosure that the following
description of the embodiments of the present invention is provided
for illustration only, and not for the purpose of limiting the
invention as defined by the appended claims and their
equivalents.
[0026] Referring initially to FIGS. 1 and 2, a variable valve
timing apparatus is illustrated to explain a first embodiment of
the present invention. The variable valve timing apparatus has a
rotational torque transmission path that changes the relative
phases of a camshaft 2 that moves a plurality of engine valve (not
shown) and a rotary crank body 18 that is coupled to a crankshaft 1
(See FIGS. 3 and 4).
[0027] The variable valve timing apparatus is disposed on an end of
a camshaft 2. The camshaft 2 drives the intake and/or exhaust
valves (not shown) in a conventional manner. The variable valve
timing apparatus basically includes a rotary crank body 18, a cover
7, an electromagnetic brake 8, a substantially cylindrical moving
member 11, a drum 9, a coil torsion spring 10, a cylindrical
splined shaft 13, and a rotation regulation mechanism 30. As
disscussed below, the variable valve timing apparatus uses the
electromagnetic brake 8 to delay rotation of the drum 9, which is
coupled to the rotary crank body 18 by the torsion spring 10 and
the moving member 11.
[0028] The rotational torque or power transmission path between the
rotary crank body 18 and the camshaft 2 is basically formed by the
moving member 11, the drum 9, the torsion spring 10, and the
splined shaft 13. The rotary crank body 18 rotates in sync with a
crankshaft 1 (See FIGS. 3 and 4) during the non-energized state of
the electromagnetic brake 8. During the non-energized state of the
electromagnetic brake 8, the moving member 11 is disposed on the
rotational torque transmission path that directly transmits torque
from the rotary crank body 18 to the splined shaft 13 connected to
the camshaft 2. The drum 9 engages an axial side (left hand side in
FIG. 1) of the moving member 11. The coil torsion spring 10
functions as a biasing means that biases the drum 9 in the
direction of rotation of the camshaft 2 relative to the rotary
crank body 18. The electromagnetic brake 8 is disposed opposite an
outer axial side surface 9a (left hand side in FIG. 1) of the drum
9. The cover 7 is fixedly coupled to a sprocket cover 6 on an
engine main body side so as to cover the electromagnetic brake 8.
The rotation regulation mechanism 30 regulates relative rotation of
the electromagnetic brake 8 relative to the cover 7 about the
camshaft 2.
[0029] As will be described later, the electromagnetic brake 8
attracts the surface 9a of the drum 9. Accordingly, rotation of the
drum 9 about the camshaft 2 is delayed. As a result, the moving
member 11 moves axially to change the phase of the camshaft 2
relative to those of the rotary crank body 18 and the crankshaft 1.
In other words, when rotation of the drum 9 is delayed, the moving
member 11 changes the angular orientation between the drum 9 and
the rotary crank body 18 against the biasing force of the coil
torsion spring 10. More specifically, the cylindrical splined shaft
13 is fixed to an end of the camshaft 2 via a fixing bolt 3 and a
positioning pin 21. Thus, the splined shaft 13 rotates together
with the camshaft 2.
[0030] In the embodiments shown in FIGS. 3 and 4, two examples of
timing arrangements are illustrated to explain the present
invention. For instance, as shown in FIG. 3, a V-type internal
combustion engine has a main drive member 4A that is wound onto the
crankshaft 1 and a pair of driven members or intake sprockets 5A
that are disposed on inner sides of a V bank. Two sub drive members
4B are wound onto the driven members or intake sprockets 5A and two
additional driven members or exhaust sprockets 5B that are adjacent
each other in each bank. Alternatively, as shown in FIG. 4, a
single drive member 4 can be wound onto the intake sprockets 5A,
the exhaust sprockets 5B, and the crankshaft 1 in each bank. While
the drive member 4 is illustrated as a timing chain that engages
the sprockets SA and SB, the drive member 4 can be either a timing
chain or a timing belt. If the drive member 4 is a timing belt,
then the driven members 5A and 5B are pulleys, instead of
sprockets. In any event, the V-type internal combustion engines
shown in FIGS. 3 and 4 each utilizes four variable valve timing
apparatuses in accordance with the present invention.
[0031] Referring again to FIG. 1, the rotary crank body 18
basically includes a sprocket or driven member 5, a spring case 12,
a spring cover 22 and a plurality of bolts 17. The timing chain or
drive member 4 engages the sprocket 5 and other the sprockets to
transmit rotational torque from the crankshaft 1 to the camshaft 2.
The spring cover 22 covers a portion of an outer periphery of the
coil torsion spring 10. The spring case 12 is fixedly coupled to a
first end of the coil torsion spring 10. These members 5, 12, and
22 are fixedly coupled together by jointly tightening the bolts 17.
The rotary crank body 18 is rotatably coupled to an outer periphery
of the splined shaft 13 so as to be relatively rotatable.
[0032] An inner peripheral surface of the moving member 11 and the
outer peripheral surface of the splined shaft 13 have helical
splines that are meshed together to form a helical or spiral spline
arrangement 27. An outer peripheral surface of the moving member 11
and an inner peripheral surface of the spring case 12 have helical
splines that are meshed together to form a helical or spiral spline
arrangement 28. Therefore, as the moving member 11 moves in the
direction of the axis of the camshaft 2 (left-right direction in
FIG. 1), the splined shaft 13 and the spring case 12 rotate
relative to each other. Accordingly, the phase of the camshaft 2
changes relative to that of the rotary crank body 18.
[0033] The drum 9 is coupled to the outer periphery of the splined
shaft 13 via bearings 14 so as to be relatively rotatable. The
inner periphery of the drum 9 has a stopping ring 23 that abuts on
one of the axial surfaces of bearings 14. The inner peripheral
surface of the drum 9 and the outer peripheral surface of the
moving member 11 each has a spiral square thread or spline that
meshes with the other to form a square thread arrangement 29 or a
spiral spline arrangement. Accordingly, as the drum 9 rotates
relative to the moving member 11, the moving member 11 moves
axially relative to the drum 9.
[0034] A disk-shaped flange 9b that extends in a radially outward
direction is formed on an axial end of the drum 9. The flange 9b
has a pin 24 that receives one end of the coil torsion spring 10 to
fix that end of the torsion spring 10 to the drum 9. The flange 9b
also has a surface 9a that opposes a surface 8a of the
electromagnetic brake 8.
[0035] The electromagnetic brake 8 is a substantially annular
member that includes an electromagnetic coil 25 and a housing 26
that houses the electromagnetic coil 25. The electromagnetic coil
25 is electrified and controlled in response to an engine
operational state signal that is sent from a controller (not shown
in the Figure). A thin plate-shaped friction member 8b is provided
on the axially inner surface 8a that is opposite and slideably
adjacent to the surface 9a of the drum 9.
[0036] The rotation regulation mechanism 30 includes a first
protrusion 31 and a second protrusion 32, and a first concavity 33
and a second concavity 34. The first and second protrusions 31 and
32 are fixed to an axial end wall portion of the housing 26 of the
electromagnetic brake 8. The first protrusion 31 and the second
protrusion 32 are cylindrical and extend axially outward from the
end wall portion of the housing 26. The first and the second
concavities 33 and 34 are concavely provided in an inner wall
portion of the cover 7. Preferably, the first and the second
concavities 33 and 34 are substantially circular holes to which the
first protrusion 31 and the second protrusion 32 loosely coupled
therein, respectively. In other words, the first and second
concavities 33 and 34 are designed so as to have a larger diameter
and a longer dimension than those of the protrusions 31 and 32,
such that slight displacement of the electromagnetic brake 8
relative to the cover 7 can be accommodated in both the axial
direction and the circumferential direction.
[0037] In view of possible assembling errors, the axial dimension
of a space between the drum 9 and the cover 7, in which the
electromagnetic brake 8 is housed, is sized so as to be slightly
greater than the axial dimension of the electromagnetic brake 8,
such that a small gap D1 is formed in between the electromagnetic
brake 8 and the cover 7, in view of possible assembling errors.
[0038] In the rotation regulation mechanism 30, the first and
second protrusions 31 and 32 lying on a base line P passing
substantially through a center (axis of rotation) of the drum 9.
The base line P is set so as to be substantially perpendicular to a
direction of a tension or a resultant force of tension applied from
the chain or belt 4 to the sprocket or pulley 5. By virtue of the
rotation regulation mechanism 30, the relative rotation of the
electromagnetic brake 8 relative to the cover 7 is regulated. At
the same time, inclination of the electromagnetic brake 8 relative
to the cover 7 about the base line P can be adequately tolerated.
Therefore, even when the drum 9 becomes inclined relative to the
base line P due to the aforementioned tension of a resultant force
of tension, the electromagnetic brake 8 also becomes inclined as
seen in FIG. 6, compensating for the inclination of the drum 9.
Therefore, partial contact between the opposing surfaces 8a and 9a
of the drum 9 and the electromagnetic brake 8, respectively, can be
effectively prevented.
[0039] In the cover 7, a guide 7b is formed as a cup-shaped
protrusion. The guide 7b opposes the inner peripheral surface of
the electromagnetic brake 8 with an adequate gap therebetween. In
other words, the cover 7 covers the electromagnetic brake 8 from
three directions in order to regulate excessive displacement of the
electromagnetic brake 8.
[0040] The above-described rotary crank body 18, the moving member
11 and the electromagnetic brake 8 are disposed coaxially about the
center axis L1 of the camshaft 2 in the normal state. Also, several
lubricant supply grooves 36, 37 and 38 are formed on splined shaft
13 in order to supply lubricant to various bearing portions.
[0041] In the embodiments shown in FIGS. 3 and 4, a base line P is
defined so as to lie along a predetermined diameter of the
electromagnetic brake 8 (or the camshaft 2). The base line P
connects the first protrusion 31 and the second protrusion 32 when
viewed along the axial direction such that the base line P passes
through the center (axis of rotation) of the drum 9. In other
words, the first and second protrusions 31 and 32 are disposed
opposite each other (180.degree. apart) with the center axis L1 of
the camshaft 2 therebetween. Similarly, the concavities 33 and 34
are also disposed opposite each other with the center axis L1
therebetween.
[0042] Due to this structure, in an initial state (non-operating
state) in which the electromagnetic brake 8 is not electrified, the
drum 9 is kept at the initial position due to the biasing force of
the coil torsion spring 10. The initial position of the drum 9 is
the position most rotated in the direction of rotation of the
camshaft 2 relative to the rotary crank body 18. In this state, the
rotary crank body 18, the moving member 11, the drum 9 and the
camshaft 2 rotate in sync.
[0043] In this initial state, as the controller electrifies the
electromagnetic brake 8, the magnetic force that is generated
between the electromagnetic brake 8 and the drum 9 makes the
electromagnetic brake 8 attract the axial side surface 9a of the
drum 9. In this manner, the electromagnetic brake 8 is attracted
and biased toward the drum 9. Frictional force is generated in
between the opposing surfaces 8a and 9a of the electromagnetic
brake 8 and the drum 9. Then, rotation of the drum 9 about the
camshaft 2 is adequately delayed due to the spring force of the
coil torsion spring 10. Accordingly, the drum 9 relatively rotates
with respect to the moving member 11, which makes the moving member
11 move axially via the square thread arrangement 29. The spring
case 12 and the splined shaft 13 relatively rotate via the helical
or spiral spline arrangement 27 and 28. As a result, the phase of
the camshaft 2 changes relative to that of the rotary crank body
18. Accordingly, the valve timing of the intake and/or exhaust
valves is adequately changed.
[0044] By controlling the attraction force of the electromagnetic
brake 8, the attraction force and the biasing force of the coil
torsion spring 10 can be balanced. In this way, the amount of delay
of the drum 9 can be freely controlled within a predetermined
control range. Accordingly, the valve timing can be controlled
continuously.
[0045] Tension force is applied from the chain 4 to the sprocket 5.
Although the magnitude of each tension force varies depending on
the variation of the driving torque or burning torque of the
camshaft 2 during the engine operation, its direction is mostly
constant. In other words, direction of each tension force
substantially equals to a direction from the center of the meshed
portion between the chain 4 and the sprocket 5 toward the center of
the sprocket 5.
[0046] For instance, as shown in FIG. 3, in the case of a V-shaped
internal combustion engine, the main chain 4A is wound onto the
crankshaft 1 and a pair of intake sprockets 5A that are disposed on
inner sides of a V bank, while a sub chains 4B are wound onto the
intake sprockets 5A and exhaust sprockets 5B that are adjacent each
other in each bank. The intake sprockets 5A receive tension force
Fa from the main chain 4A, and tension force Fb from the sub chain
4B, which create a resultant force Fc. On the other hand, the
exhaust side sprocket SB receives tension force Fb' from the sub
chain 4B.
[0047] Alternatively, as shown in FIG. 4, a single chain 4 can be
wound onto the intake sprockets 5A, the exhaust sprockets SB, and
the crankshaft 1 in each bank. In this case, tension Fd and Fe are
applied from the chain 4 to the sprockets 5A and 5B,
respectively.
[0048] Due to the total tension (tension or resultant of tensions)
from the chain 4 to the sprocket 5, the center axis L2 of the drum
9 that engages the sprocket 5 via the moving member 11 sometimes
becomes inclined relative to the center axis L1 of the camshaft
2.
[0049] Now, as seen in a comparative example in FIG. 5, when the
base line that connects the protrusions 31 and 32 is set in
parallel with the direction in which the aforementioned total
tensions apply (the vertical upward direction in FIG. 5), the
electromagnetic brake 8 cannot become inclined to compensate for
the inclination of the drum 9 in a preferable manner. As a result,
the center axis L2 of the drum 9 and the center axis (L1) of the
electromagnetic brake 8 become offset from each other as seen in
FIG. 5. Accordingly, the opposing surfaces 8a and 9a of the
electromagnetic brake 8 and the drum 9 only partially contact each
other. As a result, the frictional force that is applied to the
sliding surfaces 8a and 9a becomes unstable. Therefore, desired
phase adjustment cannot be obtained.
[0050] In this embodiment, as seen in FIGS. 3 and 4, the base lines
P that connect the first protrusion 31 and the second protrusion 32
are set so as to be substantially perpendicular to the direction of
total tensions (Fc and Fb' in FIG. 3 and Fd and Fe in FIG. 4)
applied from the rotation torque transmission the chain 4 to the
sprockets 5. In this way, as shown in FIG. 6, even if the center
axis L2 of the drum 9 becomes inclined due to the chain tension as
described above, the electromagnetic brake 8 can also become
inclined about the base line P, compensating for the inclination of
the center axis L2. Accordingly, the opposing surfaces 8a and 9a of
the electromagnetic brake 8 and the drum 9 can uniformly face and
contact each other. As a result, the sliding surfaces 8a and 9a do
not partially contact each other. The friction torque generated in
the sliding surfaces 8a and 9a becomes stable. Therefore, desired
valve timing adjustment can be obtained.
[0051] More preferably, as seen in FIGS. 7-9, an elastic member
39A, 39B or 39C is disposed in between the axial opposing surfaces
of the outer wall portions of the electromagnetic brake 8 and the
inner wall of the cover 7. The elastic member 39A, 39B or 39C urges
the electromagnetic brake 8 axially toward the drum 9. More
specifically, the elastic member 39A can be a rubber element as
shown in FIG. 7, or a wave spring (plate spring) 39B as shown in
FIG. 8, or a plurality of coil springs 39C as shown in FIG. 9. In
the structure shown in FIGS. 6 and 7, in order to avoid conflict
with the protrusions 31 and 32, adequate cut out portions (omitted
in Figure) are created for the annular elastic members 39A and 39B,
or a plurality of elastic members 39A are placed intermittently
around the periphery.
[0052] By providing one or more elastic members 39A, 39B or 39C in
this manner, the surface 8a of the electromagnetic brake 8 and the
surface 9a of the drum 9 are kept so as to always uniformly contact
each other even in the initial state, in which electric power is
not supplied to the electromagnetic brake 8. Therefore, due to the
axial gap D1 secured between the electromagnetic brake 8 and the
cover 7, inadvertent axial vibrations and rattling of the
electromagnetic brake 8 can be restrained. Also, even if rattling
occurs, it is reduced quickly by the damping effect of the elastic
member 39A, 39B or 39C. Therefore, vibrations and noises that
result from such rattling can be certainly reduced.
[0053] In other words, in order to reduce vibrations of the
electromagnetic brake 8 securely, the urging force of the elastic
member 39A, 39B or 39C is set in advance so as to be greater than a
predetermined axial vibration input that is applied to the
electromagnetic brake 8.
[0054] However, if the urging force of the elastic member 39A, 39B
or 39C is set excessively great, then the drum 9 can rotate from
the initial phase inadvertently due to the biasing force of the
coil torsion spring 10 even in the initial state, in which the
electromagnetic brake 8 is not electrified. Therefore, in such
initial state, the biasing force of the coil torsion spring 10 and
urging force of elastic member 39A, 39B or 39C should be set
adequately such that the drum 9 is maintained at a position most
rotated in the rotational direction of the camshaft 2 relative to
the rotary crank body 18.
[0055] Therefore, preferably, by setting the urging force of the
elastic member 39A, 39B or 39C sufficiently great, but not greater
than the biasing force of the coil torsion spring 10, the
attraction force can be sufficiently limited. In other words, the
electric power to be consumed of the electromagnetic brake 8 that
is necessary for phase changing can be sufficiently limited. In
this manner, the electromagnetic brake 8 requires less electric
power and also can be reduced in size. In this case, at the time of
shifting from the electrified state to the electrification stopping
state, the drum 9 can quickly return to the initial phase by the
biasing force of the coil torsion spring 10 that exceeds the urging
force of the elastic member 39A, 39B or 39C.
[0056] Although the shapes of the aforementioned protrusions 31 and
32 and the concavities 33 and 34 are cylindrical and circular holes
in the aforementioned embodiment, other shapes such as key and key
groove and shapes having width across flats can also be
utilized.
[0057] Additionally, although the chain 4 and sprockets 5 are
utilized in the rotational torque transmission path of rotational
torque of the crankshaft 1 in the aforementioned embodiment, this
structure can be substituted with other structures such as one that
has timing belt and pulley, or one in which a gear is partially
utilized.
[0058] Furthermore, with regard to the layout of the chain 4, other
multi-level structures and one-level structures can be utilized,
other than the ones shown in FIGS. 3 and 4.
[0059] Moreover, terms that are expressed as "means-plus function"
in the claims should include any structure that can be utilized to
carry out the function of that part of the present invention. The
terms of degree such as "substantially", "about" and
"approximately" as used herein mean a reasonable amount of
deviation of the modified term such that the end result is not
significantly changed. For example, these terms can be construed as
including a deviation of at least .+-.5% of the modified term if
this deviation would not negate the meaning of the word it
modifies.
[0060] This application claims priority to Japanese Patent
Application No. 2000-289976. The entire disclosure of Japanese
Patent Application No. 2000-289976 is hereby incorporated herein by
reference.
[0061] While only selected embodiments have been chosen to
illustrate the present invention, it will be apparent to those
skilled in the art from this disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. Furthermore,
the foregoing description of the embodiments according to the
present invention are provided for illustration only, and not for
the purpose of limiting the invention as defined by the appended
claims and their equivalents. Thus, the scope of the invention is
not limited to the disclosed embodiments.
* * * * *