U.S. patent application number 13/318870 was filed with the patent office on 2012-03-08 for variable valve actuation apparatus for internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Akio Kidooka.
Application Number | 20120055428 13/318870 |
Document ID | / |
Family ID | 42732715 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120055428 |
Kind Code |
A1 |
Kidooka; Akio |
March 8, 2012 |
VARIABLE VALVE ACTUATION APPARATUS FOR INTERNAL COMBUSTION
ENGINE
Abstract
A variable valve actuation apparatus for an internal combustion
engine includes a first link arm which has a projected portion that
is engageable with and disengageable from a guide rail, and which
is displaceable in the axis direction of a camshaft, and a link
shaft linked to the first link arm in such a manner as to allow
rotation but constrain movement in the axis direction. When an
electro-magnetic solenoid is electrified, the first link arm
rotates about the link shaft so that the projected portion engages
with the guide rail. In association with the displacement of the
link arms that occurs during the engagement, the state of motion of
second rocker arms changes, so that the opening characteristic of
valves provided for each cylinder is switched.
Inventors: |
Kidooka; Akio;
(Ashigarakami-gun, JP) |
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
TOYOTA-SHI, AICHI-KEN
JP
|
Family ID: |
42732715 |
Appl. No.: |
13/318870 |
Filed: |
May 26, 2010 |
PCT Filed: |
May 26, 2010 |
PCT NO: |
PCT/IB10/01237 |
371 Date: |
November 4, 2011 |
Current U.S.
Class: |
123/90.16 |
Current CPC
Class: |
F01L 2013/0052 20130101;
F01L 1/267 20130101; F01L 2820/031 20130101; F01L 13/0005 20130101;
F01L 13/0036 20130101; F01L 1/185 20130101 |
Class at
Publication: |
123/90.16 |
International
Class: |
F01L 1/34 20060101
F01L001/34 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2009 |
JP |
2009-129481 |
Claims
1. A variable valve actuation apparatus for an internal combustion
engine comprising: transfer members that are disposed between cams
and valves and that transfer operating force of the cams to the
valves; a camshaft on which the cams are provided; a guide rail
provided on an outer peripheral surface of a cylindrical portion
that is provided on the camshaft; a main displacement member which
has an engagement portion that is engageable with and disengageable
from the guide rail and which is displaceable in an axis direction
of the camshaft; a member-linked shaft which is linked to the main
displacement member in such a manner that, relative to the
member-linked shaft, the main displacement member is allowed to
rotate and is constrained from moving in the axis direction; and an
actuator that produces drive force for engaging the engagement
portion of the main displacement member with the guide rail,
wherein when the actuator operates, the main displacement member
rotates about the member-linked shaft so that the engagement
portion engages with the guide rail, and in association with
displacement of the main displacement member and the member-linked
shaft that occurs when the engagement portion and the guide rail
are engaged, state of motion of the transfer member changes so that
opening characteristic of the valves that are provided for at least
two cylinders is switched.
2. The variable valve actuation apparatus according to claim 1,
wherein the main displacement member, the guide rail and the
actuator are provided corresponding to at least one but not all of
the cylinders of the internal combustion engine, and the variable
valve actuation apparatus further comprising: a subsidiary
displacement member which is provided for at least one other
cylinder that is not provided with the main displacement member,
and which is displaced in operative connection with the main
displacement member via the member-linked shaft, wherein the state
of motion of the transfer member provided for the cylinder that is
provided with the main displacement member changes in association
with the displacement of the main displacement member that occurs
when the engagement portion and the guide rail are engaged, and the
state of motion of the transfer member provided for the at least
one other cylinder that is provided with the subsidiary
displacement member changes in association with the displacement of
the subsidiary displacement member which is in operative connection
with the displacement of the main displacement member.
3. The variable valve actuation apparatus according to claim 2,
wherein the transfer member, for each of the at least two
cylinders, includes a first rocker arm that is oscillatable
synchronously with the cams, and a second rocker arm that is able
to push the valves, the variable valve actuation apparatus further
comprising: a switch pin that is disposed movably in a pin hole
formed in the first rocker arm and in a pin hole formed in the
second rocker arm, wherein the switch pin for the cylinder provided
with the main displacement member is displaced in operative
connection with the displacement of the main displacement member,
and the switch pin for the at least one other cylinder that is
provided with the subsidiary displacement member is displaced in
operative connection with the displacement of the subsidiary
displacement member, and wherein for the cylinder provided with the
main displacement member, the first rocker arm and the second
rocker arm are switched via the switch pin between a linked state
in which the first rocker arm and the second rocker arm are linked
together and an unlinked state in which linkage between the first
rocker arm and the second rocker arm is removed, in operative
connection with the displacement of the main displacement member,
and for the at least one other cylinder provided with the
subsidiary displacement member, the first rocker arm and the second
rocker arm are switched via the switch pin between the linked state
in which the first rocker arm and the second rocker arm are linked
together and the unlinked state in which the linkage between the
first rocker arm and the second rocker arm is removed, in operative
connection with the displacement of the subsidiary displacement
member.
4. The variable valve actuation apparatus according to claim 3,
wherein the member-linked shaft is disposed within a rocker shaft
that supports the first rocker arms and the second rocker arms.
5. The variable valve actuation apparatus according to claim 3,
wherein the second rocker arm is used for a plurality of the valves
that are provided for a cylinder.
6. The variable valve actuation apparatus according to claim 1,
wherein an outer peripheral surface of the member-linked shaft is
provided with a groove that has an annular or arcuate shape, and
the member-linked shaft penetrates an interior of the main
displacement member, and the variable valve actuation apparatus
further comprising: a pin that penetrates the main displacement
member and that engages with the groove.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a variable valve actuation
apparatus for an internal combustion engine.
[0003] 2. Description of the Related Art
[0004] Japanese Patent Application Publication No. 6-33714
(JP-A-6-33714), for example, discloses a variable valve actuation
apparatus for an internal combustion engine. This related-art
variable valve actuation apparatus includes an intake or exhaust
valve, a low-speed cam, a high-speed cam, a main rocker arm that is
drivable by the low-speed cam and that drives the intake valve or
the exhaust valve, and a sub-rocker arm that is driven by the
high-speed cam. Furthermore, the variable valve actuation apparatus
includes a hydraulic piston mechanism as mode switch means for
switching between a non-coordination mode in which the sub-rocker
arm is not coordinated with the main rocker arm and a coordination
mode in which the sub-rocker arm is coordinated with the main
rocker arm.
[0005] By the way, in the variable valve actuation apparatus of an
internal combustion engine, when the opening characteristic of
valves is switched in association with an motion performed by an
actuator, the actuator's drive force needed in order to drive a
member that is driven by the actuator becomes inconveniently large
if the inertia of the member is large, or if the friction force
that occurs on the member when the actuator drives the member is
large. Therefore, in order to switch the opening characteristic of
valves while minimizing the required power, it is desirable that
the inertia of the foregoing member be small and that the friction
force that occurs on the member be small.
SUMMARY OF THE INVENTION
[0006] The invention provides a variable valve actuation apparatus
for an internal combustion engine which reduces the inertia of a
member that is driven by an actuator and reduces the friction that
occurs on the member, and which favorably switches the opening
characteristic of valves that are provided for at least two
cylinders of the engine in association with motion performed by the
actuator.
[0007] A variable valve actuation apparatus for an internal
combustion engine in accordance with a first aspect of the
invention includes: transfer members that are disposed between cams
and valves and that transfer operating force of the cams to the
valves; a camshaft on which the cams are provided; a guide rail
provided on an outer peripheral surface of a cylindrical portion
that is provided on the camshaft; a main displacement member which
has an engagement portion that is engageable with and disengageable
from the guide rail and which is displaceable in an axis direction
of the camshaft; a member-linked shaft which is linked to the main
displacement member in such a manner that, relative to the member
linked shaft, the main displacement member is allowed to rotate and
is constrained from moving in the axis direction; and an actuator
that produces drive force for engaging the engagement portion of
the main displacement member with the guide rail, wherein when the
actuator operates, the main displacement member rotates about the
member-linked shaft so that the engagement portion engages with the
guide rail, and in association with displacement of the main
displacement member and the member-linked shaft that occurs when
the engagement portion and the guide rail are engaged, state of
motion of the transfer member changes so that opening
characteristic of the valves that are provided for at least two
cylinders is switched.
[0008] According to the first aspect of the invention, since the
main displacement member and the member-linked shaft is linked
together in such a manner that relative rotation therebetween is
possible, the main displacement member rotates alone without
involving rotation of the member-linked shaft, when the actuator
operates so as to engage the engagement portion of the main
displacement member with the guide rail. Therefore, according to
the first aspect, it becomes possible to reduce the inertia of the
member that is driven by the actuator and reduce the friction force
that occurs on the member, and to favorably switch the opening
characteristic of valves that are provided for at least two
cylinders in association with motion performed by the actuator.
[0009] Besides, in the foregoing construction, the main
displacement member, the guide rail and the actuator may be
provided corresponding to at least one but not all of the cylinders
of the internal combustion engine, and the variable valve actuation
apparatus may further include a subsidiary displacement member
which is provided for at least one other cylinder that is not
provided with the main displacement member, and which is displaced
in operative connection with the main displacement member via the
member-linked shaft, and the state of motion of the transfer member
provided for the cylinder that is provided with the main
displacement member may change in association with the displacement
of the main displacement member that occurs when the engagement
portion and the guide rail are engaged, and the state of motion of
the transfer member provided for the at least one other cylinder
that is provided with the subsidiary displacement member may change
in association with the displacement of the subsidiary displacement
member which is in operative connection with the displacement of
the main displacement member.
[0010] Therefore, due to the construction provided in the first
aspect, the inertia of the member that is driven by the actuator
can be reduced, and the friction force that occurs on the member
can be reduced. Besides, the state of motion of the transfer member
of each cylinder can be changed through the utilization of the
displacement of the main displacement member and the displacement
of the subsidiary displacement member that is in operative
connection with the displacement of the main displacement
member.
[0011] In the foregoing construction, the transfer member, for each
of the at least two cylinders, may include a first rocker arm that
is oscillatable synchronously with the cams, and a second rocker
arm that is able to push the valves, and the variable valve
actuation apparatus may further include a switch pin that is
disposed movably in a pin hole formed in the first rocker arm and
in a pin hole formed in the second rocker arm, and the switch pin
for the cylinder provided with the main displacement member may be
displaced in operative connection with the displacement of the main
displacement member, and the switch pin for the at least one
cylinder that is provided with the subsidiary displacement member
may be displaced in operative connection with the displacement of
the subsidiary displacement member, and for the cylinder provided
with the main displacement member, the first rocker arm and the
second rocker arm may be switched via the switch pin between a
linked state in which the first rocker arm and the second rocker
arm are linked together and an unlinked state in which linkage
between the first rocker arm and the second rocker arm is removed,
in operative connection with the displacement of the main
displacement member, and for the at least one cylinder provided
with the subsidiary displacement member, the first rocker arm and
the second rocker arm may be switched via the switch pin between
the linked state in which the first rocker arm and the second
rocker arm are linked together and the unlinked state in which the
linkage between the first rocker arm and the second rocker arm is
removed, in operative connection with the displacement of the
subsidiary displacement member.
[0012] According to the foregoing construction, in a variable valve
actuation apparatus of a type that switches between the state in
which the first rocker arm and the second rocker arm are linked
together and the unlinked state in which the linkage therebetween
is removed, by utilizing the displacement of the switch pin, it
becomes possible to reduce the inertia of the member that is driven
by the actuator and reduce the friction force that occurs on the
member and to switch between the foregoing linked state and the
unlinked state.
[0013] In the foregoing construction, the member-linked shaft may
be disposed within a rocker shaft that supports the first rocker
arms and the second rocker arms.
[0014] According to this construction, by effectively utilizing the
space present over the cylinder head of the internal combustion
engine, it is possible to improve the mountability of the variable
valve actuation apparatus on the internal combustion engine, in
comparison with a construction in which the member-linked shaft is
supported by a member that is separate from the rocker shaft.
[0015] Besides, in the foregoing construction, the second rocker
arm may be used for a plurality of the valves that are provided for
a cylinder.
[0016] According to this construction, a mounting space for the
main displacement member and the subsidiary displacement member can
be secured by utilizing the unoccupied space obtained as a result
of the use, of the second rocker arm for two or more valves
provided for a cylinder, in comparison with a construction in which
one valve is driven by one second rocker arm.
[0017] Besides, in the foregoing construction, an outer peripheral
surface of the member-linked shaft may be provided with a groove
that has an annular or arcuate shape, and the member-linked shaft
may penetrate an interior of the main displacement member, and the
variable valve actuation apparatus may further include a pin that
penetrates the main displacement member and that engages with the
groove.
[0018] According to the foregoing construction, due to the
engagement between the groove formed in the member-linked shaft and
the pin that penetrates the main displacement member, it is
possible to favorably realize the linkage between the main
displacement member and the member-linked shaft in a manner that
allows relative rotation between the main displacement member and
the member-linked shaft but constrains relative movement
therebetween in the axis direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The features, advantages, and technical and industrial
significance of this invention will be described in the following
detailed description of example embodiments of the invention with
reference to the accompanying drawings, in which like numerals
denote like elements, and wherein:
[0020] FIG. 1 is a perspective view showing a variable valve
actuation apparatus for an internal combustion engine according to
an embodiment of the invention;
[0021] FIG. 2A and FIG. 2B are sectional views of portions of the
variable valve actuation apparatus shown in FIG. 1, except a
camshaft, which are taken on a plane that includes the axis of a
rocker shaft shown in FIG. 1 and the axis of a switch pin also
shown in FIG. 1;
[0022] FIG. 3 is an exploded perspective view of characteristic
component elements of the variable valve actuation apparatus shown
in FIG. 1; and
[0023] FIG. 4 is a view of the variable valve actuation apparatus
of FIG. 1 which is taken in an axis direction of the camshaft (and
the rocker shaft) (more specifically, the direction indicated by an
arrow 4A in FIG. 2A).
DETAILED DESCRIPTION OF EMBODIMENTS
[0024] EMBODIMENT 1. Hereinafter, Embodiment 1 of the invention
will be described with reference to FIG. 1 to FIG. 4. [CONSTRUCTION
OF VARIABLE VALVE ACTUATION APPARATUS] (BASIC
[0025] CONSTRUCTION OF VARIABLE VALVE ACTUATION APPARATUS) FIG. 1
is a perspective view showing a variable valve actuation apparatus
10 for an internal combustion engine 1 according to Embodiment 1 of
the invention. Incidentally, in FIG. 1, the illustration of a
later-described camshaft 18 is omitted. Besides, although FIG. 1
shows only two cylinders (cylinders No. 1 and No. 2) while omitting
the illustration of other cylinders and the like, the internal
combustion engine 1 of Embodiment 1 is, for example, an in-line
four-cylinder engine that has four cylinders (No. 1 to No. 4).
Besides, each cylinder of the internal combustion engine 1 is
provided with two intake valves and two exhaust valves. The
variable valve actuation apparatus 10 functions as an apparatus
that drives two intake valves or two exhaust valves that are
disposed on each cylinder.
[0026] As shown in FIG. 1, each cylinder of the internal combustion
engine 1 is provided with a first rocker arm 12 and a second rocker
arm 14 that are adjacent to each other. The rocker arms 12 and 14
of each cylinder are rotatably (oscillatably) supported by one
rocker shaft 16.
[0027] FIG. 2A and FIG. 2B are sectional views of portions of the
variable valve actuation apparatus 10 excluding a camshaft 18,
which are taken on a plane that includes the axis of the rocker
shaft 16 shown in FIG. 1 and the axis of a switch pin 38 described
below. FIG. 2A shows the variable valve actuation apparatus 10 in a
linked state described below, and FIG. 2B shows the variable valve
actuation apparatus 10 in an unlinked state described below. The
camshaft 18 is linked to a crankshaft (not shown) by a timing chain
or a timing belt so as to rotate at half the speed of the
crankshaft. As shown in FIG. 2A and FIG. 2B, the camshaft 18 is
provided with a main cam 20 and a subsidiary cam 22 for each
cylinder. Besides, the rocker shaft 16 is disposed parallel to the
camshaft 18.
[0028] The main cams 20 are each constructed as a cam that has an
arcuate base circle portion that is coaxial with the camshaft 18
(i.e., a lift cam), and a nose portion formed so that a portion of
the base circle portion is expanded radially outward. Besides, in
Embodiment 1, the subsidiary cams 22 are each constructed as a cam
that has only a base circle portion (i.e., a zero-lift cam).
[0029] As shown in FIG. 1, FIG. 2A and FIG. 2B, with regard to each
cylinder, the first rocker arm 12 has a first roller 24 that is
rotatably attached at such a position on the first rocker arm 12
that the first roller 24 can contact the main cam 20. The first
rocker arm 12 is urged so that the first roller 24 is always in
contact with the main cam 20, by a coil spring (not shown) that is
attached to the rocker shaft 16. The first rocker arm 12
constructed as described above oscillates about the rocker shaft 16
that serves as a fulcrum, through cooperation of the operating
force of the main cam 20 and the force of the aforementioned coil
spring.
[0030] Besides, with regard to each cylinder, the second rocker arm
14 has a second roller 26 that is rotatably attached at such a
position on the second rocker arm 14 that the second roller 26 can
contact the subsidiary cam 22. Besides, at a rocker shaft 16-side
end portion of the second rocker arm 14, the rocker shaft 16 is
supported by a cam carrier 27 (or a cylinder head or the like) that
is a stationary member of the internal combustion engine 1, via a
lash adjuster (not shown). The second roller 26 provided on the
second rocker arm 14 is urged toward the subsidiary cam 22 as the
second roller 26 receives upward force from the lash adjuster.
[0031] Besides, an opposite end portion of the second rocker arm 14
from the rocker shaft side thereof is provided with a contact
portion 14a that contacts two valves 28. Specifically, the second
rocker arm 14 is used for both valves 28. More specifically, the
second rocker arm 14 is disposed so as to be at an intermediate
position between the two valves 28 that are provided for each
cylinder. Besides, each valve 28 is urged in the closing direction
by a valve spring 30 as shown in FIG. 1.
[0032] (CONSTRUCTION OF SWITCHING MECHANISM) The variable valve
actuation apparatus 10 includes a switching mechanism 32 that
switches between the linked state in which the first rocker arm 12
and the second rocker arm 14 are linked together (see FIG. 2A) and
the unlinked state in which the linkage between the first rocker
arm 12 and the second rocker arm 14 is removed. Due to the
provision of the switching mechanism 32, the opening characteristic
of the valves 28 is switched by switching between the state in
which the operating force of the main cam 20 is transferred to the
second rocker arm 14 via the first rocker arm 12 (the foregoing
linked state) and the state in which the operating force of the
main cam 20 is not transferred to the second rocker arm 14 (the
foregoing unlinked state).
[0033] Hereinafter, the construction of the switching mechanism 32
will be described in detail with reference to FIG. 3 and FIG. 4 as
well as FIG. 1 and FIGS. 2A and 2B. As shown in FIG. 2A and FIG.
2B, a first pin hole 34a concentric with the first roller 24 is
formed within a spindle 34 of the first roller 24. Likewise, a
second pin hole 36a concentric with the second roller 26 is formed
within a spindle 36 of the second roller 26.
[0034] The centers of the pin holes 34a and 36a are disposed on an
arc whose center is the rocker shaft 16, which is the rotation
center of the rocker arms 12 and 14. Then, when the first roller 24
is in contact with the base circle portion of the main cam 20 and
the second roller 26 is in contact with the base circle portion of
the subsidiary cam 22, the position of the first pin hole 34a
coincides with the position of the second pin hole 36a in a view in
the axis direction.
[0035] Furthermore, a cylindrical switch pin 38 is slidably
disposed in the pin holes 34a and 36a. Besides, an opposite end
portion of the first pin hole 34a from the second rocker arm 14 is
closed, and a second rocker arm 14-side end portion of the first
pin hole 34a is open. The first pin hole 34a contains therein a
return spring 40 that urges the switch pin 38 in the direction to
the second rocker arm 14 (hereinafter, referred to as "advancement
direction of the switch pin"). More specifically, the return spring
40 is constructed so as to always urge the switch pin 38 to the
second rocker arm 14 side when it is actually mounted.
[0036] Besides, the second pin hole 36a is a penetration hole in
which a cylindrical piston 42 is slidably inserted. Furthermore,
for the cylinder No. 1, a first link arm 44 that has an arm portion
44a that contacts the piston 42 is disposed at a side surface of
the second rocker arm 14 opposite the first rocker arm 12-side
surface thereof. The first link arm 44 is attached to the rocker
shaft 16.
[0037] On another hand, for the cylinder No. 2, a second link arm
46 that has an arm portion 46a that contacts the piston 42 is
disposed at a side surface of the second rocker arm 14 opposite the
first rocker arm 12-side surface thereof. The second link arm 46 is
attached to the rocker shaft 16.
[0038] The first link arm 44 is different from the second link arm
46 in the following respects. That is, a distal end of the arm
portion 44a of the first link arm 44 is provided with a projected
portion 44b that is projected toward a peripheral surface of the
camshaft 18. Besides, an opposite end portion of the first link arm
44 from the arm portion 44a is provided with a pressurization
surface 44c that is pressurized by an electromagnetic solenoid 54
(described below). Incidentally, the link arms provided for the
cylinders No. 3 and No. 4 are the same as the second link arm 46 of
the cylinder No. 2.
[0039] FIG. 3 is an exploded perspective view of characteristic
component elements of the variable valve actuation apparatus 10
shown in FIG. 1. Incidentally, FIG. 3 omits the first roller 24,
the second roller 26, the switch pin 38 disposed in the first and
second rollers, etc. Besides, FIG. 4 shows a view of the variable
valve actuation apparatus 10 of FIG. 1 which is taken from the axis
direction of the camshaft 18 (and of the rocker shaft 16) (more
specifically, from the direction indicated by the arrow 4A in FIG.
2A).
[0040] As shown in FIGS. 3 and 4, the rocker shaft 16 has a hollow
shape. Inside the rocker shaft 16, a link shaft 48 is inserted
slidably relative to the rocker shaft 16. The link shaft 48 is
provided for enabling the first link arm 44 disposed for the
cylinder No. 1 and the second link arms 46 disposed for the
cylinders No. 2 to No. 4 to be simultaneously displaced in the axis
direction of the rocker shaft 16.
[0041] The link shaft 48 is provided with four annular grooves 48a
that correspond to the placement sites of the link arms 44 and 46
of the four cylinders, as shown mainly in FIG. 3. Besides, a
peripheral surface of the rocker shaft 16 is provided with four
penetration holes 16a that correspond to the annular grooves 48a of
the link shaft 48.
[0042] Besides, as shown in FIG. 4, the link shaft 48 and the
rocker shaft 16 in which the link shaft 48 is inserted penetrate an
interior of each link arm 44, 46. The link arms 44 and 46 have
press-fit pin holes 44d and 46b, respectively, each of which
receives a press-fit pin 50 that is press-fitted thereinto, as
shown in FIG. 3. The press-fit pins 50, each penetrating a wall of
a corresponding one of the link arms 44 and 46 through its
pressure-fit hole 44d, 46b, are engaged with the corresponding
annular grooves 48a, as shown in FIG. 4.
[0043] The width of the annular grooves 48a is set so as to be
substantially equal to the diameter of the press-fit pins 50.
Besides, each penetration hole 16a of the rocker shaft 16 has such
a generous size as to avoid causing interference between the
press-fit pin 50 and the electromagnetic solenoid 54 and therefore
avoid impeding the rotation of the first link arm 44 (or the second
link arm 46) when the first link arm 44 (or the second link arm 46)
rotates in association with motion of the electromagnetic solenoid
54. Furthermore, each penetration hole 16a has such an elongated
hole shape as to avoid causing interference between the penetration
hole 16a and the press-fit pin 50 and therefore avoid impeding the
movement of the link shaft 48 when the link shaft 48 moves in the
axis direction thereof in association with motion of the
electromagnetic solenoid 54.
[0044] Since the foregoing construction is adopted, the first link
arm 44 is linked to the link shaft 48 in such a manner that the
first link arm 44 is allowed to freely rotate but is constrained
from moving in the axis direction of the link shaft 48. Likewise,
the second link arms 46 are also linked to the link shaft 48 in
such a manner that the second link arms 46 are allowed to freely
rotate but are constrained from moving in the axis direction.
[0045] Besides, as shown in FIG. 2A, FIG. 2B and FIG. 4, a
cylindrical portion 18a that has a cylindrical shape is provided on
an outer peripheral surface of the camshaft 18 which faces a
projected portion 44b that is provided on the arm portion 44a of
the first link arm 44. An outer peripheral surface of the
cylindrical portion 18a is provided with a helical guide rail 52
that extends in a circumferential direction. In this construction,
the guide rail 52 is formed as a helical groove.
[0046] Besides, the switching mechanism 32 includes an
electromagnetic solenoid 54 as an actuator that produces drive
force for causing the projected portion 44b to be engaged with
(inserted into) the guide rail 52. The electromagnetic solenoid 54
is duty-controlled on the basis of commands from an electronic
control unit (ECU) 56. The ECU 56 is an electronic control unit
that controls the state of operation of the internal combustion
engine 1.
[0047] Besides, the electromagnetic solenoid 54 is fixed to a
stationary member, such as the cam carrier 27 or the like, at such
a position that a drive shaft 54a of the solenoid 54 is able to
pressurize the pressurization surface 44c of the first link arm 44
toward the guide rail 52.
[0048] Besides, the orientation of the helix of the guide rail 52
is set such that when the camshaft 18 rotates in a predetermined
rotation direction shown in FIG. 4 while the projected portion 44b
is inserted in the helical groove, the first link arm 44, the link
shaft 48 that moves in operative connection with the first link arm
44, and the second link arms 46 that are driven by the link shaft
48 are displaced in the leftward direction in FIG. 2. More
concretely, the leftward direction in FIG. 2 is the direction in
which each of the first link arm 44 and the second link arms 46
approaches its adjacent rocker arms 12 and 14 while pushing the
switch pin 38 in the withdrawal direction thereof (that is opposite
the foregoing advancement direction of the switch pin) against the
force of the return spring 40.
[0049] The position of the first link arm 44 in FIG. 2A, that is,
the position of the first link arm 44 at which the switch pin 38 is
inserted in both the first pin hole 34a and the second pin hole 36a
due to force of the return spring 40, is referred to as
"displacement end Pmax1". When the first link arm 44 is positioned
at the displacement end Pmax1, the first rocker arm 12 and the
second rocker arm 14 assume the foregoing linked state. The
position of the first link arm 44 in FIG. 2B, that is, the position
of the first link arm 44 at which the switch pin 38 and the piston
42 are inserted only in the first pin hole 34a and the second pin
hole 36a, respectively, as the switch pin 38 receives from the link
arm 44 the force that is caused by torque of the camshaft 18, is
referred to as "displacement end Pmax2". That is, when the first
link arm 44 is positioned at the displacement end Pmax2, the first
rocker arm 12 and the second rocker arm 14 assume the foregoing
unlinked state.
[0050] In Embodiment 1, the position of a beginning end 52a of the
guide rail 52 in the axis direction of the camshaft 18 is set so as
to coincide with the position that the projected portion 44b
assumes when the first link arm 44 is positioned at the
displacement end Pmax1. The position of a terminating end 52b of
the guide rail 52 in the axis direction of the camshaft 18 is set
so as to coincide with the position that the projected portion 44b
assumes when the first link arm 44 is positioned at the
displacement end Pmax2. That is, Embodiment 1 is constructed so
that the first link arm 44 is displaced between the displacement
end Pmax1 and the displacement end Pmax2, in a range determined by
the guide rail 52 guiding the projected portion 44b.
[0051] Furthermore, as shown in FIG. 4, the guide rail 52 is
provided with a shallow bottom portion 52c in which the guide rail
52 gradually becomes shallower with rotation of the camshaft 18, as
a predetermined section of the guide rail 52 on a terminating end
52b side which is used after the first link arm 44 reaches the
displacement-end Pmax2. Incidentally, the depth of the guide rail
52 except the shallow bottom portion 52c is constant.
[0052] Besides, the first link arm 44 is provided with a cut-out
portion 44e that is formed in a recess shape by cutting out a
portion of the pressurization surface 44c. The pressurization
surface 44c is provided so that contact thereof with the drive
shaft 54a is maintained while the first link arm 44 is displaced
from the displacement end Pmax1 to the displacement end Pmax2.
Then, the cut-out portion 44e is provided at such a site on the
first link arm 44 as to be engageable with the drive shaft 54a when
the projected portion 44b is taken out from the guide rail 52 to
the surface of the cylindrical portion 18a due to operation of the
shallow bottom portion 52c during a state in which the first link
arm 44 is positioned at the displacement end Pmax2.
[0053] The cut-out portion 44e is formed so as to engage with the
drive shaft 54a in a manner such that the engagement of the cut-out
portion 44e with the drive shaft 54a can restrict the first link
arm 44 from rotating in such a direction that the projected portion
44b is inserted into the guide rail 52, and such that the
engagement can restrict the first link arm 44 from moving in the
advancement direction of the switch pin 38.
[0054] As described above, the switching mechanism 32 is
constructed of the switch pin 38, the return spring 40, the piston
42, the first link arm 44, the second link arm 46, the link shaft
48, the press-fit pin 50, the guide rail 52, and the
electromagnetic solenoid 54 whose electrification is controlled by
the ECU 56.
[0055] [MOTIONS OF VARIABLE VALVE ACTUATION APPARATUS] (DURING
VALVE ACTING STATE) During a valve acting state, the driving of the
electromagnetic solenoid 54 is off. Therefore, the first link arm
44 is apart from the camshaft 18, and is positioned at the
displacement end Pmax1 due to the force that the first link arm 44
receives from the return spring 40. In this state, the first rocker
arm 12 and the second rocker arm 14 are linked together via the
switch pin 38 (the foregoing linked state), with regard to each
cylinder, as shown in FIG. 2A. As a result, the operating force of
the main cam 20 is transferred from the first rocker arm 12 to the
two valves 28 via the second rocker arm 14. Therefore, in
accordance with the profile of the main cams 20, normal lift motion
of the valves 28 is performed.
[0056] (DURING VALVE STOP CONTROL) A valve stop motion is performed
when the ECU 56 detects a demand for executing a predetermined
valve stop motion, for example, a demand for the fuel-cut of the
internal combustion engine 1, and the like. Firstly, the
electrification of the electromagnetic solenoid 54 is started at a
predetermined timing. As a result, the first link arm 44 rotates
about the rocker shaft 16 (the link shaft 48) clockwise in FIG. 4.
As stated above, the first link arm 44 is linked to the link shaft
48 in such a manner as to be rotatable. Therefore, the link shaft
48 does not rotate while the first link arm 44 rotates.
[0057] If the first link arm 44 rotates as described above, the
projected portion 44b engages with the guide rail 52. As a result,
since the projected portion 44b is guided by the guide rail 52,
torque of the camshaft 18 is utilized to produce a force to move
the first link arm 44 toward the displacement end Pmax2. Then, the
drive force of the first link arm 44 engaged with the guide rail 52
is transferred to the second link arms 46 via the press-fit pins 50
thereof and the link shaft 48. Therefore, the link shaft 48 linked
to the first link arm 44, and the second link arms 46 linked to the
link shaft 48 are displaced in operative connection with the first
link arm 44.
[0058] When the first link arm 44 reaches the displacement end
Pmax2, the switch pin 38 is returned into the first pin hole 34a,
so that the first rocker arm 12 and the second rocker arm 14 assume
the unlinked state. As a result, the operating force of the main
cam 20 discontinues being transferred from the first rocker arm 12
to the second rocker arm 14. Besides, the subsidiary cams 22 that
is in contact with the second rollers 26 of the second rocker arms
14 are zero-lift cams. Therefore, after the transfer thereto of the
operating force of the main cam 20 discontinues, the second rocker
arms 14 are no longer given force for driving the valves 28. As a
result, irrespective of the rotation of the main cam 20, the second
rocker arm 14 is in a stationary state, and the lift motion of the
valves 28 is stopped at the closed valve position.
[0059] (MOTION FOR MAINTAINING THE VALVE STOPPED STATE) Besides,
after the first link arm 44 reaches the displacement end Pmax2, the
first link arm 44 is rotated in such a direction as to separate
from the camshaft 18 (the guide rail 52) due to operation of the
shallow bottom portion 52c of the guide rail 52. Then, when the
first link arm 44 is further rotated so that the cut-out portion
44e of the first link arm 44 coincides with the drive shaft 54a
that continues being driven by the electromagnetic solenoid 54, the
contact site of the first link arm 44 with the drive shaft 54a
switches from the pressurization surface 44c to the cut-out portion
44e. As a result, since the drive shaft 54a engages with the
cut-out portion 44e, the first link arm 44 is held in a state in
which the projected portion 44b is apart from the camshaft 18 and
in which the drive shaft 54a bears the force of the return spring
40. Therefore, the state in which the first rocker arm 12 and the
second rocker arm 14 are unlinked from each other, that is, the
valve stopped state, is maintained. Besides, according to the
motion of the drive shaft 54a holding the first link arm 44 through
the utilization of the cut-out portion 44e, it is possible to
maintain the valve stopped state while avoiding occurrence of
friction and abrasion of the drive shaft 54a associated with the
sliding between the drive shaft 54a and the camshaft 18 when the
camshaft 18 rotates.
[0060] (DURING VALVE RETURNING MOTION) A valve returning motion for
returning the valve state from the valve stopped state to the valve
acting state is performed when the ECU 56 detects a demand for
executing a predetermined valve returning motion, for example, a
demand for return from the fuel-cut (a demand for discontinuation
of the fuel-cut), or the like. This valve returning motion is
started by turning off the electrification of the electromagnetic
solenoid 54 at a predetermined timing. When the electrification of
the electromagnetic solenoid 54 is turned off, the engagement
between the cut-out portion 44e of the first link arm 44 and the
drive shaft 54a of the electromagnetic solenoid 54 is removed. As a
result, the force for retaining the switch pin 38 within the first
pin hole 34a against the force of the return spring 40 disappears.
Due to this, the force of the return spring 40 moves the switch pin
38 in the advancement direction, bringing back the state in which
the first rocker arm 12 and the second rocker arm 14 are linked
together via the switch pin 38, that is, the state in which the
lift motion of the valves 28 can be carried out by the operating
force of the main cams 20. Besides, as the switch pin 38 moves in
the advancement direction due to the force of the return spring 40,
the first link arm 44 (as well as the link shaft 48 and the second
link arm 46 that is operatively connected to the first link arm 44)
is returned from the displacement end Pmax2 to the displacement end
Pmax1 by the piston 42.
[0061] According to the variable valve actuation apparatus 10 of
Embodiment 1 constructed as described above, the position of the
first link arm 44 in the axis direction is moved between the
displacement end Pmax1 and the displacement end Pmax2 by utilizing
the turning on and off of the electrification of the
electromagnetic solenoid 54, the torque of the camshaft 18, and the
force of the return spring 40. Therefore, as for the cylinder No. 1
equipped with the first link arm 44, it becomes possible to switch
the motion state of the valves 28 between the valve acting state
and the valve stopped state. Furthermore, as for the other
cylinders (No. 2 to No. 4), too, it becomes possible to switch the
motion state of the valves 28 between the valve acting state and
the valve stopped state, via the link shaft 48 and the second link
arms 46 that are operatively connected to the first link arm 44.
Thus, according to the variable valve actuation apparatus 10, the
motion state of the valves 28 disposed for the four cylinders of
the internal combustion engine 1 can be switched by using one
electromagnetic solenoid 54. Besides, according to the variable
valve actuation apparatus 10 having the foregoing construction, the
valve stopped state can be brought about with high response during
one rotation of the camshaft 18, by utilizing the torque of the
camshaft 18.
[0062] Besides, in the foregoing variable valve actuation apparatus
10, the first link arm 44 is linked to the link shaft 48 in such a
manner that, relative to the link shaft 48, the first link arm 44
is allowed to freely rotate but is constrained from moving in the
axis direction. According to this linking method, the first link
arm 44 will rotate alone without involving rotation of the link
shaft 48, when the electromagnetic solenoid 54 presses the first
link arm 44. Unlike this construction, in a construction in which
the first link arm is fixed to the link shaft, when the first link
arm is rotated due to electrification of the electromagnetic
solenoid, the link shaft will rotate together therewith. As a
result, when the projected portion is engaged with the guide rail,
the inertia of the member that is driven by the electromagnetic
solenoid increases by an amount that corresponds to the link shaft,
and the friction that occurs on the members at the time of driving
of the electromagnetic solenoid increases by an amount that
corresponds to the sliding between the link shaft and the rocker
shaft that occurs during rotation of the link shaft. Therefore, the
required thrust force of the electromagnetic solenoid increases,
and a large-side electromagnetic solenoid becomes necessary.
[0063] In Embodiment 1, however, the first link arm 44 and the link
shaft 48 are constructed so as to be rotatable relative to each
other. Therefore, the inertia of the member that is driven by the
electromagnetic solenoid 54 in order to engage the projected
portion 44b with the guide rail 52 can be made small, and the
friction force that occurs on the member can be made small.
Therefore, the required thrust of the electromagnetic solenoid 54
can be favorably reduced, and the size of the electromagnetic
solenoid 54 can be reduced.
[0064] Besides, in the variable valve actuation apparatus 10, the
first link arm 44 and the second link arms 46 are mounted on the
rocker shaft 16 that functions as a support shaft for the first
rocker arms 12 and the second rocker arms 14. Besides, the two
valves 28 of each cylinder are simultaneously driven by the second
rocker arm 14 that has the contact portion 14a that contacts the
two valves 28. This construction, in comparison with a construction
in which one valve is driven by one second rocker arm, makes it
possible to utilize the unoccupied space obtained as a result of
the use of a second rocker arm 14 for two valves in order to mount
the first link arm 44 and the second link arms 46 for switching the
motion state of the valves 28. Due to this, by effectively
utilizing the space present over the cylinder head of the internal
combustion engine 1, it is possible to improve the mountability of
the variable valve actuation apparatus 10 on the internal
combustion engine 1.
[0065] Besides, in the foregoing variable valve actuation apparatus
10, the link shaft 48 that transfers the drive force of the first
link arm 44 engaged with the guide rail 52 to the second link arms
46 of the other cylinders is disposed within the rocker shaft 16.
This construction, in comparison with a construction in which the
link shaft is supported by a member apart from the rocker shaft,
makes it possible to effectively utilize the space present over the
cylinder head of the internal combustion engine 1 in order to
improve the mountability of the variable valve actuation apparatus
10 on the internal combustion engine 1. Besides, the construction
eliminates the need for component parts for supporting the link
shaft. Besides, in a construction in which a rocker arm is directly
supported by a link shaft, unlike the construction of Embodiment 1,
friction force occurs between the link shaft and the rocker arm
that receives the operating force of the cams when the link shaft
is displaced in the axis direction thereof. On the other hand,
according to the construction of Embodiment 1, since the link shaft
48 is disposed within the rocker shaft 16, the operating force of
the main cams 20 does not directly act on the link shaft 48 via the
first rocker arms 12 and the second rocker arms 14, and therefore
the friction force that occurs when the link shaft 48 is displaced
in the axis direction can be reduced.
[0066] By the way, in Embodiment 1 described above, in association
with displacement of the first link arm 44 and the link shaft 48
(as well as the displacement of the second link arms 46 that occurs
during the engagement between the projected portion 44b of the
first link arm 44 and the guide rail 52, the switch pin 38 of each
cylinder is displaced. Then, as the first rocker arm 12 and the
second rocker arm 14 of each cylinder are switched between the
linked state and the unlinked state by displacement of the switch
pin 38, the opening characteristic of the valves 28 of each
cylinder is switched between the valve acting state and the valve
stopped state. However, the variable valve actuation apparatus of
the invention is not limited to the foregoing constructions as long
as the opening characteristic of valves that are provided for at
least two cylinders is switched as the motion state of a transfer
member is switched in association with displacement of a main
displacement member and a member-linked shaft which occurs when the
engagement portion and the guide rail are engaged.
[0067] Concretely, the member that is displaced so as to switch the
state of motion of the transfer member in association with
displacement of the main displacement member and the member-linked
shaft which occurs when the engagement portion and the guide rail
are engaged is not limited to the switch pin 38. That is, for
example, in a construction in which a rocker arm corresponding to
the transfer member is rotatably supported by a rocker shaft, the
foregoing member may also be a member that causes an operation in
which in association with the movement of the main displacement
portion and the member-linked shaft, the rocker arm is displaced on
the rocker shaft in the axis direction of the rocker shaft, so that
the cam that contacts the rocker arm is switched to another cam and
therefore the state of motion of the rocker arm is switched.
Alternatively, for example, in a construction that includes a
rocker arm that has a roller that contacts cams, the foregoing
member may also be a member that causes an operation in which in
association with the displacement of the main displacement member
and the member-linked shaft, the roller is displaced on the rocker
arm in the axis direction of the spindle of the roller, so that the
cam that contacts the roller is switched to another cam and
therefore the state of motion of the rocker arm (transfer member)
is switched. Also alternatively, for example, in a construction in
which a rocker arm corresponding to the transfer member is
rotatably supported by a rocker shaft, the foregoing member may
also be a member that causes an operation in which in association
with displacement of the main displacement member and the
member-linked shaft, the rocker shaft itself is displaced in its
own axis direction, so that the cam that contacts the rocker shaft
is switched to another cam and therefore the state of motion of the
rocker arm is switched. Furthermore, for example, in a construction
in which a member equipped with two kinds of cams is mounted on a
camshaft so as to be movable in the axis direction of the camshaft,
the foregoing member may also be a member that causes an operation
in which in association with displacement of the main displacement
member and the member-linked shaft, the member equipped with two
kinds of cams is displaced in the axis direction of the camshaft,
so that the cam that contacts the transfer member is switched to
another cam and therefore the state of motion of the transfer
member is switched.
[0068] Besides, Embodiment 1 is described above with reference to
an example that is the variable valve actuation apparatus 10 that
drives the two valves that are disposed on each one of the four
cylinders of the internal combustion engine 1. However, the
variable valve actuation apparatus of the invention is not limited
to the foregoing constructions but may have any construction as
long as the opening characteristics of the valves provided for at
least two cylinders are switched. That is, the variable valve
actuation apparatus of the invention may be, for example, an
apparatus constructed so as to drive the valves of all the
cylinders of the internal combustion engine that has two or more
cylinders, or may also be an apparatus constructed so as to drive
the valves of at least two cylinders of an internal combustion
engine that has three or more cylinders.
[0069] Besides, in Embodiment 1 described above, only the cylinder
No. 1 of the four cylinders is equipped with the cylindrical
portion 18a that has the guide rail 52, and with the
electromagnetic solenoid 54 and the first link arm 44. However, in
the invention, the cylinder equipped with elements that correspond
to the foregoing components is not limited so, but may be any one
or more of the cylinders of the engine as long as the foregoing
cylinder does not correspond to each one of the cylinders.
Alternatively, it is also permissible to adopt a construction in
which the foregoing elements are provided separately from an
arbitrary one of the cylinders and each cylinder is equipped with a
subsidiary displacement member such as the second link arm 46 that
does not have the projected portion 44b.
[0070] Besides, in Embodiment 1 described above, the first link arm
44 and the second link arms 46 are rotatably supported by utilizing
the rocker shaft 16 that is provided for supporting the first
rocker arm 12 and the second rocker arms 14. However, the member
that supports the main displacement member or the subsidiary
displacement member in the invention is not limited to the rocker
shaft. That is, the member that supports the main displacement
member and the subsidiary displacement member in the invention may
be, for example, a shaft that is provided separately from the
rocker shaft. Alternatively, the main displacement member and the
subsidiary displacement member in the invention may be supported
only by a member that functions as a member-linked shaft in the
invention (for example, by the ring shaft 48).
[0071] Besides, in Embodiment 1 described above, the link shaft 48
is disposed within the rocker shaft 16. However, the technique of
disposing the member-linked shaft in the invention is not limited
to this disposal, but it is also permissible to adopt, for example,
a construction in which a shaft that functions as the member-linked
shaft is provided at an outer peripheral side of the rocker
shaft.
[0072] Besides, in Embodiment 1 described above, the link shaft 48
is provided with the annular grooves 48a that engage with the
press-fit pins 50, in order to link the first link arm 44 (and the
second link arms 46 as well) to the link shaft 48 in such a manner
that the first link arm 44 is allowed to rotate relative to the
link shaft 48, and is constrained from moving in the axis direction
of the link shaft 48. However, in the invention, the element
provided for realizing the function of linking the main
displacement member in such a manner that the main displacement
member is allowed to freely rotate and is constrained from moving
in the axis direction does not need to be the annular grooves 48a.
That is, for example, in the case where there is provided a
construction in which the press-fit pins are press-fit into the
first link arms as in the construction of Embodiment 1 and where
the link shaft has grooves that engage with the press-fit pins, it
is not altogether necessary that the grooves be annular if the
grooves are provided so that the press-fit pins will move without
rotating the link shaft when the first link arm is rotated by the
electromagnetic solenoid. For example, the grooves may be arcuate
grooves.
[0073] Besides, although in Embodiment 1 described above, the
subsidiary cams 22 are zero-lift cams, the subsidiary cam in the
invention is not limited to a zero-lift cam. That is, in a
construction as in the foregoing variable valve actuation apparatus
10, the subsidiary cams may have a nose portion that achieves a
smaller lift than the nose portion of the main cams 20.
[0074] Besides, Embodiment 1 described above includes the
electromagnetic solenoid 54 as an actuator that produces drive
force for engaging the projected portion 44b with the guide rail
52. Therefore, the opening characteristic of the valves 28 can be
switched by utilizing the actuator that is excellent in
responsiveness. However, in the invention, the actuator is not
limited so, but may also be, for example, a hydraulically driven
actuator.
[0075] Incidentally, in Embodiment 1 described above, the main cams
20 function as a "cam" in the first aspect of the invention, and
the first rocker arms 12 and the second rocker arms 14 each
function as a "transfer member" in the first aspect, and the
projected portion 44b functions as an "engagement portion" in the
first aspect, and the first link arm 44 functions as a "main
displacement member" in the first aspect, and the link shaft 48
functions as a "member-linked shaft" in the first aspect, and the
electromagnetic solenoid 54 functions as an "actuator" in the first
aspect. Besides, in Embodiment 1 described above, the second link
arms 46 each function as a "subsidiary displacement member" in the
first aspect. Besides, in Embodiment 1 described above, the annular
grooves 48a function as a "groove" in the first aspect, and the
press-fit pins 50 function as a "pin" in the first aspect.
* * * * *