U.S. patent application number 12/310974 was filed with the patent office on 2010-04-15 for variable valve apparatus.
This patent application is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Shuichi Ezaki, Akio Kidooka.
Application Number | 20100089348 12/310974 |
Document ID | / |
Family ID | 39467676 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100089348 |
Kind Code |
A1 |
Kidooka; Akio ; et
al. |
April 15, 2010 |
Variable Valve Apparatus
Abstract
A motor 30 or the like is used to drive a camshaft 22 or the
like having a cam 18 or the like to push a valve 12 biased in the
closing direction of the valve by a valve spring 17. Between the
cam 18 or the like and the valve 12 is present a valve lifter 16
that abuts the cam 18 or the like. The valve lifter 16 includes a
top face 16a formed so that when viewed from the axial direction of
the camshaft 22 or the like, a tangential direction to the nose tip
18c of the cam 18 or the like inclines with respect to the
direction perpendicular to the axial line of a valve stem 14.
Inventors: |
Kidooka; Akio;
(Ashigarakami-gun, JP) ; Ezaki; Shuichi;
(Susono-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
Toyota Jidosha Kabushiki
Kaisha
Toyota-shi
JP
|
Family ID: |
39467676 |
Appl. No.: |
12/310974 |
Filed: |
November 13, 2007 |
PCT Filed: |
November 13, 2007 |
PCT NO: |
PCT/JP2007/071997 |
371 Date: |
March 13, 2009 |
Current U.S.
Class: |
123/90.16 |
Current CPC
Class: |
F01L 9/22 20210101; F01L
1/143 20130101; F01L 1/0532 20130101 |
Class at
Publication: |
123/90.16 |
International
Class: |
F01L 1/34 20060101
F01L001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2006 |
JP |
2006-320350 |
Claims
1.-8. (canceled)
9. A variable valve apparatus that uses a motor to drive a camshaft
including a cam for pushing a valve biased in the closing direction
thereof by a valve spring, the variable valve apparatus, further
comprising: a valve lifter which abuts the cam between the cam and
the valve; wherein the valve lifter includes a top face formed such
that when viewed from an axial direction of the camshaft, the
direction of a tangential line to a nose tip of the cam inclines
with respect to the direction perpendicular to the axial line of a
valve stem; and wherein the inclining direction of the tangential
line is a direction in which the distance between the tangential
line and a bottom face of the valve lifter decreases as the
inclination goes in the traveling direction of a contact point
between the cam during forward rotation thereof and the valve
lifter.
10. A variable valve apparatus that uses a motor to drive a
camshaft including a cam for pushing a valve biased in the closing
direction thereof by a valve spring, the variable valve apparatus,
further comprising: a valve lifter which abuts the cam between the
cam and the valve; wherein the valve lifter includes a top face
formed such that when viewed from an axial direction of the
camshaft, the direction of a tangential line to a nose tip of the
cam inclines with respect to the direction perpendicular to the
axial line of a valve stem; and wherein the top face, when viewed
from the axial direction of the camshaft, is formed into a
convexedly curved shape to be convex toward the cam.
11. The variable valve apparatus according to claim 10, wherein on
the top face formed into the convexedly curved shape to be convex
toward the cam, an apical point whose height above the bottom face
of the valve lifter is maximized, and the contact point between the
nose tip and the valve lifter are spaced from each other when
viewed from the axial direction of the camshaft.
12. The variable valve apparatus according to claim 10, wherein the
top face having the convexedly curved shape to be convex toward the
cam is formed to have a maximum achievable height above the bottom
face of the valve lifter, on a central axis of the valve lifter;
and the camshaft is disposed such that a central axis thereof and
the central axis of the valve lifter do not intersect with each
other when viewed from the axial direction of the camshaft.
13. The variable valve apparatus according to claim 10, wherein the
camshaft is disposed such that a central axis thereof intersects
with the central axis of the valve lifter when viewed from the
axial direction of the camshaft; and the top face having the
convexedly curved shape to be convex toward the cam is formed such
that when viewed from the axial direction of the camshaft, an
apical point whose height above the bottom face of the valve lifter
is maximized takes up an offset position relative to the axial line
of the valve stem.
14. The variable valve apparatus according to claim 9, wherein the
top face, when viewed from the axial direction of the camshaft, is
an inclined surface having a constant gradient.
15. The variable valve apparatus according to claim 9, further
comprising: electric power supply control means for stopping supply
of electric power to the motor when a command value assigned to the
motor to drive the camshaft reaches a predetermined value.
16. The variable valve apparatus according to claim 9, further
comprising: a torque reduction mechanism that generates a reduced
torque for reduction in a driving torque of the camshaft; wherein
the torque reduction mechanism is constructed such that the reduced
torque is small in comparison with a camshaft torque based upon a
biasing force of the valve spring.
17. The variable valve apparatus according to claim 10, further
comprising: electric power supply control means for stopping supply
of electric power to the motor when a command value assigned to the
motor to drive the camshaft reaches a predetermined value.
18. The variable valve apparatus according to claim 10, further
comprising: a torque reduction mechanism that generates a reduced
torque for reduction in a driving torque of the camshaft; wherein
the torque reduction mechanism is constructed such that the reduced
torque is small in comparison with a camshaft torque based upon a
biasing force of the valve spring.
Description
TECHNICAL FIELD
[0001] The present invention relates to a variable valve apparatus
that drives a valve of an internal combustion engine.
BACKGROUND ART
[0002] Referring to conventional techniques, Patent Document 1, for
example, discloses an internal combustion engine that includes a
valve-driving system using a motor to drive the opening and closing
of a valve. If an error in the synchronous control of camshaft and
crankshaft speeds occurs in this conventional valve-driving system,
evacuation driving becomes possible by stopping the opening/closing
of the valve by use of a lost-motion mechanism or by switching to a
low-lift cam for driving the valve at a smaller amount of lift.
[0003] Including the above-mentioned document, the applicant is
aware of the following documents as a related art of the present
invention. [0004] [Patent Document 1] Japanese Laid-open Patent
Application Publication No. 2005-54732 [0005] [Patent Document 2]
Japanese Laid-open Utility Model Application Publication No. Hei
6-87605 [0006] [Patent Document 3] Japanese Laid-open Patent
Application Publication No. 2004-225562 [0007] [Patent Document 4]
Japanese Laid-open Patent Application Publication No. 2004-225610
[0008] [Patent Document 5] Japanese Patent No. 3359524
DISCLOSURE OF INVENTION
Problem To Be Solved By the Invention
[0009] The type of variable valve apparatus that uses a cam to
drive a valve via a valve lifter is known as one form of apparatus
that conducts motor driving of a camshaft, as with the conventional
valve-driving system discussed above. In such a type of variable
valve apparatus, if the variable valve apparatus becomes abnormal
and motor driving is stopped with the cam having its nose tip
abutted upon the valve lifter, this stoppage could leave the valve
open with the amount of valve lift maximized. If this situation
happens, interference is likely to occur between the valve
remaining stopped in the maximum lift state, and the piston
continuing a reciprocating motion.
[0010] In the type of variable valve apparatus that uses a motor to
rotationally drive a camshaft, if the evacuation control mechanism
as used in the above conventional valve-driving system, that is,
the mechanism for stopping the opening/closing of the valve or for
switching to the low-lift cam, is equipped only to avoid the above
interference, this will complicate the system configuration
uselessly. In addition, in the type that employs the above
evacuation control mechanism, after the error in the synchronous
control of the camshaft and crankshaft speeds, the valve-piston
interference could occur during the period of switching to the
evacuation control.
[0011] The present invention was made for solving the foregoing
problems, and an object of the invention is to provide a variable
valve apparatus that uses a motor to rotationally drive a camshaft
including a cam to push a valve biased to close by a valve spring,
the apparatus being adapted for valve-piston interference in case
of an abnormality to be reliably resolved using a simple
configuration.
Means For Solving the Problem
[0012] A first aspect of the present invention for achieving the
above first object is a variable valve apparatus that uses a motor
to drive a camshaft including a cam for pushing a valve biased in
the closing direction thereof by a valve spring, the variable valve
apparatus, further comprising:
[0013] a valve lifter which abuts the cam between the cam and the
valve;
[0014] wherein the valve lifter includes a top face formed such
that when viewed from an axial direction of the camshaft, the
direction of a tangential line to a nose tip of the cam inclines
with respect to the direction perpendicular to the axial line of a
valve stem.
[0015] A second aspect of the present invention is the variable
valve apparatus according to the first aspect of the present
invention,
[0016] wherein the inclining direction of the tangential line is a
direction in which the distance between the tangential line and a
bottom face of the valve lifter decreases as the inclination goes
in the traveling direction of a contact point between the cam
during forward rotation thereof and the valve lifter.
[0017] A third aspect of the present invention is the variable
valve apparatus according to the first or second aspect of the
present invention,
[0018] wherein the top face, when viewed from the axial direction
of the camshaft, is formed into a convexedly curved shape to be
convex toward the cam.
[0019] A fourth aspect of the present invention is the variable
valve apparatus according to the third aspect of the present
invention,
[0020] wherein on the top face formed into the convexedly curved
shape to be convex toward the cam, an apical point whose height
above the bottom face of the valve lifter is maximized, and the
contact point between the nose tip and the valve lifter are spaced
from each other when viewed from the axial direction of the
camshaft.
[0021] A fifth aspect of the present invention is the variable
valve apparatus according to the third or fourth aspect of the
present invention,
[0022] wherein the top face having the convexedly curved shape to
be convex toward the cam is formed to have a maximum achievable
height above the bottom face of the valve lifter, on a central axis
of the valve lifter; and
[0023] the camshaft is disposed such that a central axis thereof
and the central axis of the valve lifter do not intersect with each
other when viewed from the axial direction of the camshaft.
[0024] A sixth aspect of the present invention is the variable
valve apparatus according to the third or fourth aspect of the
present invention,
[0025] wherein the camshaft is disposed such that a central axis
thereof intersects with the central axis of the valve lifter when
viewed from the axial direction of the camshaft; and
[0026] the top face having the convexedly curved shape to be convex
toward the cam is formed such that when viewed from the axial
direction of the camshaft, an apical point whose height above the
bottom face of the valve lifter is maximized takes up an offset
position relative to the axial line of the valve stem.
[0027] A seventh aspect of the present invention is the variable
valve apparatus according to the first or second aspect of the
present invention,
[0028] wherein the top face, when viewed from the axial direction
of the camshaft, is an inclined surface having a constant
gradient.
[0029] An eighth aspect of the present invention is the variable
valve apparatus according to any one of the first to seventh aspect
of the present invention, further comprising:
[0030] electric power supply control means for stopping supply of
electric power to the motor when a command value assigned to the
motor to drive the camshaft reaches a predetermined value.
[0031] A ninth aspect of the present invention is the variable
valve apparatus according to any one of the first to eighth aspect
of the present invention, further comprising:
[0032] a torque reduction mechanism that generates a reduced torque
for reduction in a driving torque of the camshaft;
[0033] wherein the torque reduction mechanism is constructed such
that the reduced torque is small in comparison with a camshaft
torque based upon a biasing force of the valve spring.
Advantages of the Invention
[0034] According to the first aspect of the present invention, even
if the driving of the camshaft by the motor is stopped with the cam
nose tip abutting upon the top face of the valve lifter, the
biasing force of the valve spring acts to rotate the cam as well as
to push the cam upward. The invention, therefore, allows the valve
to be properly prevented from remaining open in case of the
abnormality, thus valve-piston interference to be avoided
reliably.
[0035] According to the second aspect of the present invention,
even if the driving of the camshaft by the motor is stopped with
the cam nose tip abutting upon the top face of the valve lifter,
the cam is returned in its forward rotational direction. After the
occurrence of the abnormality, therefore, the invention allows easy
cam-piston synchronization during a restart, and hence, reduction
of likelihood of valve-piston interference. A reduction in the
amount of electric power required immediately after the restart is
additionally anticipated.
[0036] According to the third to seventh aspects of the present
invention, even if the driving of the camshaft by the motor is
stopped with the cam nose tip abutting upon the top face of the
valve lifter, the biasing force of the valve spring acts to rotate
the cam as well as to push the cam upward. The invention,
therefore, allows the valve to be properly prevented from remaining
open in case of the abnormality, thus valve-piston interference to
be avoided reliably.
[0037] According to the eighth aspect of the present invention,
even if an abnormality that leaves a driving force of the camshaft
with respect to the motor occurs in the variable valve apparatus,
the biasing force of the valve spring is permitted to be converted
into a torque that rotates the cam. Accordingly, valve-piston
interference can be avoided reliably.
[0038] According to the ninth aspect of the present invention, a
sufficient biasing force of the valve spring in the variable valve
apparatus with the torque reduction mechanism for reducing the
driving torque of the camshaft can be obtained as a torque that
rotates the cam, and thus, valve-piston interference can be avoided
reliably.
BRIEF DESCRIPTION OF DRAWINGS
[0039] FIG. 1 is a perspective view showing the configuration of
the variable valve apparatus according to the first embodiment of
the present invention.
[0040] FIG. 2 is an axial view of the camshaft for a further
detailed description of its configuration shown in FIG. 1.
[0041] FIGS. 3(A) and 3(B) are schematic diagrams showing the way
the valve lifter is driven by the cam.
[0042] FIG. 4 is a reference diagram for structural comparison of a
variable valve apparatus A having a valve lifter of a general
shape, with respect to the variable valve apparatus according to
the first embodiment of the present invention.
[0043] FIG. 5 is an explanatory diagram of the characteristic
configuration according to the first embodiment of the present
invention.
[0044] FIG. 6 is a diagram showing a first variant relating to a
top-face shape of a valve lifter and an arrangement relationship
between the valve lifter and the camshaft.
[0045] FIG. 7 is a diagram showing a second variant relating to the
top-face shape of a valve lifter.
[0046] FIG. 8 is a flowchart illustrating a routine that is
executed in the second embodiment of the present invention.
[0047] FIGS. 9(A) and 9(B) are diagrams illustrating a
configuration of a torque reduction mechanism in a variable valve
apparatus according to the third embodiment of the present
invention.
[0048] FIG. 10 is a diagram that illustrates general settings of
the reduced torque in a torque reduction mechanism having
substantially the same configuration as that of the torque
reduction mechanism shown in FIG. 9.
[0049] FIG. 11 is a diagram illustrating the settings of the
reduced torque stemming from the torque reduction mechanism in the
third embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
[Variable Valve Apparatus Configuration]
[0050] Hereinafter, a basic configuration of a variable valve
system 10 according to a first embodiment of the present invention
will be described referring to FIGS. 1 to 3.
[0051] FIG. 1 is a perspective view showing the configuration of
the variable valve apparatus 10 according to the first embodiment
of the present invention. The variable valve apparatus 10 shown in
FIG. 1 is an apparatus for driving a valve of an internal
combustion engine. The system configuration here assumes that the
internal combustion engine is constructed as a straight
four-cylinder engine. Reference numbers #1 to #4 in FIG. 1 denote
first to fourth cylinders, respectively, of the internal combustion
engine. The system also assumes that as in a general internal
combustion engine, the explosion stroke of the internal combustion
engine is sequentially performed in cylinders #1, #3, #4, and #2 in
the order named. In addition, the present embodiment assumes that
the variable valve apparatus 10 functions as an apparatus to drive
air intake valves of each cylinder, and the configuration of the
variable valve apparatus 10 on the exhaust valve side is omitted in
FIG. 1. The variable valve apparatus 10, however, may be
constructed as an apparatus for driving the exhaust valves of each
cylinder, in place of or in addition to the intake valves.
[0052] The configuration shown in FIG. 1 includes two valves 12 for
each cylinder, the valves each functioning as an intake valve. Each
valve 12 has a valve stem 14 fixed thereto. The valve stem 14 has a
valve lifter 16 at its upper end. A biasing force of a valve spring
17 (see FIG. 5) is acting upon the valve stem 14, which is biased
to close by the biasing force. The variable valve apparatus 10 of
the present-embodiment characterized by the shape of a top face 16a
of the valve lifter 16 and by the arrangement relationship between
the valve lifter 16 and cams 18 and 20 described later herein.
These sections characterizing the apparatus will be described later
with reference to FIG. 5.
[0053] Each valve lifter 16 has a corresponding cam 18 or 20 at its
upper section. As shown in FIG. 1, the cams corresponding to the
valve lifters 16 disposed above the #1 and #4 cylinders, and the
cams corresponding to the valve lifters 16 disposed above the #2
and #3 cylinders are termed the cams 18 and 20, respectively, for
distinction in the present embodiment. The cams 18 corresponding to
the #1 and #4 cylinders are each fixed to a camshaft 22. The cams
20 corresponding to the #2 and #3 cylinders are each fixed to a
camshaft 24 rotatable with respect to the camshaft 22 and disposed
coaxially therewith. That is to say, the configuration shown in
FIG. 1 shares the camshafts for each cylinder that is 360.degree.
CA different in explosion timing. The two camshafts, namely, the
camshaft 22 corresponding to the #1 and #4 cylinders, and the
camshaft 24 corresponding to the #2 and #3 cylinders are both
constructed to be able to rotate or swing in a circumferential
direction independently of each other. The camshafts 22 and 24 are
rotatably supported by a support member such as a cylinder head not
shown.
[0054] A first driven gear 26 is coaxially fixed to the camshaft
22. The first driven gear 26 has a first output gear 28 meshed
therewith. The first output gear 28 is fixed to an output shaft of
a first motor 30. The first motor 30 is a servomotor controllable
in rotational speed and in the amount of rotation. For example, a
brushless motor or the like is preferably used as the first motor
30. The first motor 30 contains a rotational angle detection sensor
such as a resolver or rotary encoder to detect the rotational
position (rotational angle) of the motor. This configuration allows
a torque of the first motor 30 to be transmitted to the camshaft 22
via the gears 26 and 28.
[0055] A second driven gear 32 is coaxially fixed to the camshaft
24. The second driven gear 32 has a second output gear 36 meshed
therewith via an intermediate gear 34. The second output gear 36 is
fixed to an output shaft of a second motor 38. A detailed
configuration of the second motor 38 is substantially the same as
that of the first motor 30. This configuration allows a torque of
the second motor 38 to be transmitted to the camshaft 24 via the
gears 32, 34, and 36.
[0056] The system shown in FIG. 1 includes an electronic control
unit (ECU) 40. Sensors not shown, such as a crank angle sensor and
a cam angle sensor, and actuators such as the first motor 30 and
the second motor 38 are connected to the ECU 40. The ECU 40 can use
outputs of these sensors to control the rotational speeds of the
first motor 30 and the second motor 38, and the respective amounts
of rotation. More specifically, the ECU 40 can rotate the camshaft
22 or the like by assigning a driving command to the motor 30 or
the like for continuous unidirectional driving of the camshaft 22.
The ECU 40 can also swing the camshaft 22 or the like by assigning
another driving command to the motor 30 or the like for reversal of
the rotational direction thereof during an opening period of the
valve 12.
[0057] FIG. 2 is an axial view of the camshaft 22 for a further
detailed description of its configuration shown in FIG. 1. As
described above, the cams 18 (#1) and the cams 18 (#4) are fixed to
the camshaft 22. As shown in FIG. 2, each cam 18 (#1) for the #1
cylinder has two cam faces, 18a and 18b, that differ in profile.
The circular base 18a, one of the two cam faces, is formed to be
constantly distanced from a center of the camshaft 22. The nose
18b, the other cam face, is formed so that the distance from the
center of the camshaft 22 increases progressively and so that once
a top portion 18c (nose tip 18c) has been overstepped, the distance
diminishes progressively. Each cam 18 (#4) for the #4 cylinder also
has substantially the same circular base 18a and nose 18b as those
of the cam 18 (#1). The top portion 18c of the cam 18 (#1) and the
top portion 18c of the cam (#4) are arranged to have an offset of
180.degree. from each other in the circumferential direction of the
camshaft 22. Although detailed description is omitted herein, the
present embodiment assumes that the cams 20 (#2) and cams (#3) on
the camshaft 24 corresponding to the #2 and #3 cylinders are each
constructed similarly to those of the camshaft 22.
[0058] FIGS. 3(A) and 3(B) are schematic diagrams showing the way
the valve lifter 16 is driven by the cam 18. The description given
below will use a configuration of the cam 18. The same also applies
to a configuration of the cam 20. In addition, in this description,
if there is no essential difference between the configuration of
the cam 18 and that of the cam 20, only either one of the
configurations will be described per FIG. 3 and subsequent
drawings, and the other configuration may be omitted.
[0059] As shown in FIG. 3, the valve lifter 16 that abuts the cam
18 is disposed between the cam 18 and the valve 12 (see FIG. 1).
The valve lifter 16 has a top face 16a that abuts the cam 18. When
the circular base 18a of the cam 18 and the valve lifter 16 abut
each other, the biasing force of the valve spring 17 brings the
valve into firm contact with a valve seat (not shown), thus closing
the valve.
[0060] When a rotary motion of the first motor 30 is transmitted to
the camshaft 22 via the gears 26, 28, the cam 18 rotates integrally
with the camshaft 22 and while the nose 18b gets over the valve
lifter 16, the valve lifter 16 is pushed downward to lift (open)
the valve 12 in defiance of the biasing force of the valve spring
17.
[0061] FIGS. 3(A) and 3(B) show two driving modes of the cam 18. A
forward driving mode that is one of the driving modes rotates the
first motor 30 continuously in one direction so that as shown in
FIG. 3(A), the cam 18 continuously rotates forward in excess of a
maximum lifting position, that is, the position at which the nose
tip 18c of the cam 18, the top 18c, abuts the valve lifter 16. A
swinging mode that is the other driving mode reciprocates the cam
18 as shown in FIG. 3(B), by changing the rotational direction of
the first motor 30 before the maximum lifting position in the
forward driving mode is reached.
[0062] In the forward driving mode, the rotational speed of the cam
18 is controlled, whereby the operating angle of the valve is
controlled. In the swinging mode, the operating angle and maximum
lift amount of the valve 12 can be controlled by controlling the
rotational speed of the cam 18 and the swinging angle range
thereof.
Feature Sections of the Present Embodiment
[0063] Next, feature sections of the present embodiment are
described below referring to FIGS. 4 and 5.
[0064] FIG. 4 is a reference diagram for structural comparison of a
variable valve apparatus A having a valve lifter of a general
shape, with respect to the variable valve apparatus 10 of the
present embodiment, and shows the apparatus A existing when viewed
from an axial direction of a camshaft. The variable valve apparatus
A compared with the variable valve apparatus 10 of the present
embodiment includes the valve lifter having a general top face
formed to be planar for perpendicularity to an axial line of a
valve stem as shown in FIG. 4.
[0065] Some abnormality associated with the variable valve
apparatus A, such as a loss of rotational synchronization between
its camshaft and crankshaft, may result in a stoppage of a motor.
Under the stopped motor state, despite such factors resisting the
rotation of the camshaft as friction between the cam and the valve
lifter, friction between the motor and the camshaft, and inertia of
the motor, the camshaft itself is basically in a rotatable state.
If the variable valve apparatus A becomes abnormal, therefore, when
a nose portion other than a tip of the nose is in contact with the
valve lifter (e.g., when the state shown in FIG. 3(B) occurs), the
cam is rotated by valve spring repulsion force and the valve is
returned to its closed state.
[0066] However, in the case that the top face of the valve lifter
is of such a planar shape as described above, the valve is likely
to remain open with the maximum amount of lift if, as shown in FIG.
4, the driving of the camshaft by the motor is stopped with the cam
nose tip abutting the top face of the valve lifter.
[0067] The above situation occurs because, in the configuration
shown in FIG. 4, when the nose tip of the cam abuts the top face of
the valve lifter, a tangential direction that connects the nose tip
and the top face becomes perpendicular to the axial line of the
valve stem, with the result that the valve spring repulsion force
marked with an arrow in FIG. 4 acts only in the upward pushing
direction of the camshaft and does not act in the rotational
direction of the cam. In addition, the above situation structurally
occurs not only in the case that top face of the valve lifter is
planar. The same will also occur in the case of the top face not
being planar, provided that the tangential direction with the nose
tip of the cam and the top face of the valve lifter abutting each
other becomes perpendicular to the axial line of the valve
stem.
[0068] The occurrence of the above situation could cause
interference between the valve that will remain open and a piston
that will continue reciprocating. In the present embodiment,
therefore, the configuration shown in FIG. 5 is used to prevent the
valve from stopping in its maximum lifting state.
[0069] FIG. 5 is an explanatory diagram of the characteristic
configuration of the present embodiment and shows the apparatus
existing when viewed from an axial direction of the camshaft 22. As
shown in FIG. 5, in order that when viewed from the axial direction
of the camshaft 22 in the present embodiment, a tangential
direction connecting the nose tip 18c of the cam 18 and the top
face 16a of the valve lifter 16 inclines with respect to the
direction perpendicular to the axial line of the valve stem 14, the
shape of the top face 16a of the valve lifter 16 is determined and
the arrangement relationship between the valve lifter 16 and the
camshaft 22 is adjusted.
[0070] Additionally, in order that the inclining direction of the
tangent line matches a direction in which the distance between the
tangent line and a bottom face 16b of the valve lifter 16 decreases
as the tangent line extends in the traveling direction of the
contact point between the forward rotating cam 18 and the valve
lifter 16 (i.e., a leftward direction in FIG. 5), the shape of the
top face 16a of the valve lifter 16 is determined and the
arrangement relationship between the valve lifter 16 and the
camshaft 22 is adjusted.
[0071] In the present embodiment, the top face 16a of the valve
lifter 16, when viewed from the axial direction of the camshaft 22
as shown in FIG. 5, is formed into a convexedly curved shape to be
convex with respect to the cam 18, and more specifically, into a
cylindrical shape, as a more specific example showing the
above-described shape of the top face 16a and the above arrangement
relationship. In addition, the camshaft 22 is disposed with its
central axis offset with respect to that of the valve lifter 16 so
that an apical point on the top face 16a, that is, the highest
point above the bottom 16b, and the contact point P between the
nose tip 18c and the top face 16a become spaced from each other
when viewed from the axial direction of the camshaft 22.
Furthermore, in the present embodiment, the top face 16a that has
been formed into the convexedly curved shape is formed for the
valve lifter 16 to have a maximum achievable height on its central
axis, and the camshaft 22 is disposed for the central axis thereof
to be distant from that of the valve lifter 16 when viewed from the
axial direction of the camshaft 22.
[0072] Furthermore, in the configuration of FIG. 5, the disposition
of the camshaft 22 with respect to the valve lifter 16 is adjusted
so that the offset direction of the central axis of the camshaft 22
with respect to that of the valve lifter 16 matches the traveling
direction of the contact point P between the forward rotating cam
18 and the valve lifter 16.
[0073] Furthermore, the present embodiment has a swirl-stopping
mechanism to prevent the valve lifter 16 from rotating with respect
to the cam 18 so that during actual operation of the variable valve
apparatus, the above tangential direction is always maintained in
the foregoing direction. Such a swirl-stopping mechanism, although
details are omitted in FIG. 5, can be realized in, for example, the
configuration described below. That is to say, a pin that faces
perpendicularly to an axial line of the valve stem is made to
penetrate the valve lifter. In addition, a guide groove for the pin
to extend in the axial-line direction of the valve stem is formed
in a cylinder head that is a peripheral member of the valve lifter,
and the pin is engaged with the guide groove.
[0074] As described above, in the configuration of FIG. 5, in order
that when viewed from the axial direction of the camshaft 22, the
tangential direction connecting the nose tip 18c of the cam 18 and
the top face 16a of the valve lifter 16 inclines with respect to
the direction perpendicular to the axial line of the valve stem 14,
the shape of the top face 16a of the valve lifter 16 is determined
and the arrangement relationship between the valve lifter 16 and
the camshaft 22 is adjusted. According to this configuration, even
if the nose tip 18c of the cam 18 abuts the top face 16a of the
valve lifter 16 during the stopped state of the motor, the
repulsion force of the valve spring acts to rotate the cam 18 as
well as to push the cam 18 upward.
[0075] This means that according to the above configuration, not
only a component of the axial-line direction of the valve stem 14
but also a decomposition component (marked with an arrow in FIG. 5)
that is inclined to the axial-line direction of the valve stem 14
exists in the valve spring repulsion force acting upon the cam 18.
As a result, the cam 18 rotates to actuate the valve in the closing
direction thereof.
[0076] By virtue of this, according to the configuration of the
present embodiment, interference between the valve 12 and the
piston during the occurrence of an abnormality can be avoided
reliably in a mechanical manner using a simple configuration,
without relying upon such evacuation control mechanism as provided
in the conventional technology. If an error in the synchronous
control of the camshaft and crankshaft speeds is detected,
interference between the valve and the piston can also be avoided
during the period of switching to such evacuation control.
[0077] Furthermore, in the foregoing configuration that FIG. 5
shows, in order that the inclining direction of the tangent line
matches the direction in which the distance between the tangent
line and the bottom face 16b of the valve lifter 16 decreases as
the tangent line extends in the traveling direction of the contact
point between the forward rotating cam 18 and the valve lifter 16
(i.e., the leftward direction in FIG. 5), the shape of the top face
16a of the valve lifter 16 is determined and the arrangement
relationship between the valve lifter 16 and the camshaft 22 is
adjusted. More specifically, such a configuration is realized by
adjusting the disposition of the camshaft 22 with respect to the
valve lifter 16 so that the offset direction of the central axis of
the camshaft 22 with respect to that of the valve lifter 16 matches
the traveling direction of the contact point P between the forward
rotating cam 18 and the valve lifter 16.
[0078] According to such a configuration, if the motor is stopped
with the nose tip 18c of the cam 18 abutting upon the top face 16a
of the valve lifter 16, the cam 18 is made to escape in the forward
rotational direction. As a result, the final stopping position of
the cam 18 after the escape operation thereof has been conducted
becomes the position that the normal valve 12 occupies immediately
after the lifting operation thereof has ended. If this
consideration is given to the escape direction of the cam 18, the
excellent effects described below can be yielded.
[0079] That is to say, in the configuration with the two motors, 30
and 38, that share the driving of all cylinders' air intake valves,
as in the present embodiment, when the cam 18 is rotated during the
restart following the occurrence of an abnormality, a cam angle
margin of about 60.degree. will be created until the lifting of the
valve is started next time. If a phase of the cam angle is
discriminated in the section of about 60.degree., synchronization
with a piston phase can be implemented and the likelihood of
valve-piston interference can be reduced. In addition, since
kinetic energy can be given to the cam 18 by raising the rotational
speed thereof to a sufficiently high level in the section of about
60.degree., a reduction in the amount of electric power required
immediately after the restart is anticipated.
[0080] Meanwhile, in the above-described first embodiment, the top
face 16a of the valve lifter 16, when viewed from the axial
direction of the camshaft 22, is formed into a convexedly curved
shape to be convex with respect to the cam 18, and more
specifically, into a cylindrical shape. Additionally, the top face
16a formed into the convexedly curved shape is formed for the valve
lifter 16 to have the maximum achievable height on its central
axis, and the camshaft 22 is disposed for the central axis thereof
to be distant from that of the valve lifter 16 when viewed from the
axial direction of the camshaft 22. However, if the top-face shape
of the valve lifter in the present invention and the arrangement
relationship between the valve lifter and the camshaft incorporate
the consideration needed to ensure that when viewed from the axial
direction of the camshaft, the tangential direction connecting the
nose tip of the cam and the top face of the valve lifter inclines
with respect to the direction perpendicular to the axial line of
the valve stem, application of the invention is not limited to the
above configuration shown in FIG. 5, and the invention can be
applied to, for example, such configurations as shown in FIG. 6 or
7.
[0081] FIG. 6 is a diagram showing a first variant relating to a
top-face shape of a valve lifter and an arrangement relationship
between the valve lifter and the camshaft. In the configuration
that FIG. 6 shows, the camshaft 22 is disposed so that when an
axial line of the valve stem 14 (i.e., a central axis of the valve
lifter 42) is viewed from the axial direction of the camshaft 22,
the central axis thereof is positioned on an extension line of the
axial line of the valve stem 14. In addition, the top face 42a of
the valve lifter 42, when viewed from the axial direction of the
camshaft 22, is formed into a convexedly curved shape to be convex
with respect to the cam 18, and more specifically, into a
cylindrical shape.
[0082] However, unlike the above-described configuration shown in
FIG. 5, the top face 42a formed into the convexedly curved shape is
formed so that when viewed from the axial direction of the camshaft
22, an apical point on the top face 42a, that is, the highest point
from a bottom face 42b, takes up an offset position with respect to
the axial line of the valve stem 14 (i.e., the central axis of the
valve lifter 42).
[0083] Furthermore, in the configuration of FIG. 6, the shape of
the top face 42a is determined so that the offset direction of the
apex of the top face 42a with respect to the central axis of the
valve lifter 42 becomes the opposite of the traveling direction of
a contact point Q between the forward rotating cam 18 and the valve
lifter 16, that is, becomes a rightward direction in FIG. 6. In
such an offset direction, the cam 18 is made to escape in its
forward rotational direction, if the motor is stopped with the nose
tip 18c of the cam 18 abutting upon the top face 42a of the valve
lifter 42.
[0084] The valve lifter 42 can have substantially the same
swirl-stopping mechanism as used in the configuration of the first
embodiment.
[0085] FIG. 7 is a diagram showing a second variant relating to the
top-face shape of a valve lifter. In the configuration that FIG. 7
shows, the top face 44a of the valve lifter 44, when viewed from
the axial direction of the camshaft 22, is formed to be an inclined
surface having a constant gradient. In addition, the top face 44a
is inclined to a direction in which the distance to a bottom face
44b of the valve lifter 44 diminishes as the inclination of the top
face 44a goes in the traveling direction of a contact point R
between the forward rotating cam 18 and the valve lifter 44. In
such an inclined direction, the cam 18 is made to escape in its
forward rotational direction, if the motor is stopped with the nose
tip 18c of the cam 18 abutting upon the top face 44a of the valve
lifter 44.
[0086] The valve lifter 44 can have substantially the same
stopping-stopping mechanism as used in the configuration of the
first embodiment.
Second Embodiment
[0087] Next, a second embodiment of the present invention is
described below referring to FIG. 8.
[0088] An apparatus according to the present embodiment can be
implemented by using the hardware configurations shown in FIGS. 1
to 3 and 5, and making the ECU 40 execute the routine shown in FIG.
8 described later herein.
Feature Sections of the Second Embodiment
[0089] If an abnormality that has been caused to the variable valve
apparatus 10 is of a mode that completely powers off the motor,
adoption of the above-described configuration shown in FIG. 5
allows interference between the valve 12 and the piston to be
avoided reliably, since the cam 18 or the like is rotated by valve
spring repulsion. The mode of the abnormality, however, could be
such that instead of the motor being completely powered off, the
force for driving the cam 18 remains in the motor. If this state
actually happens, the valve 12 will stop in a lifted condition
since the driving torque of the camshaft 22 by the motor and the
torque upon the camshaft 22, based upon the biasing force of the
valve spring 17, will be balanced while the cam 18 is holding down
the valve 12 from above.
[0090] Consequently, interference between the valve 12 and the
piston is likely. In the present embodiment, therefore, in order to
ensure reliable avoidance of valve-piston interference even in the
event of the abnormality of the above mode, supply of electric
power to the motor is stopped when the driving repulsion force for
motor driving of the cam 18 reaches or exceeds a predetermined
level, and more specifically, when a current command value (torque
command value) assigned from the ECU 40 to the motor reaches a
predetermined value.
[0091] FIG. 8 is a flowchart of the routine which the ECU 40
executes to implement the above function. In the routine of FIG. 8,
whether the camshaft 22 is in a stopped state is first
discriminated in accordance with an output of the cam angle sensor
(step 100). As a result, if the camshaft 22 is judged to be in a
stopped state, then the current command value that the ECE 40
assigns to the motor is acquired (step 102).
[0092] Next, whether the current command value that was acquired in
above step 102 is in excess of the predetermined value is
discriminated (step 104). If the camshaft 22 is in a stopped state
and the electric power is supplied to the motor, the position of
the cam 18 is maintained with the valve 12 remaining lifted by the
cam 18. If the amount of lift at this time increases above a
certain level, interference is likely to occur between the valve 12
and the piston that is continuing the reciprocating motion. The
driving repulsion force due to the valve-spring repulsion force
existing when the cam 18 presses the valve 12 increases with
increases in the amount of lift of the valve 12, since the valve
spring repulsion force increases. The current command value that
has been assigned to the cam 18, therefore, increases with the
increases in the amount of lift of the valve 12. The predetermined
value in step 104 is set to be a value allows discrimination of
whether the amount of lift of the valve 12 has increased to such a
level that causes valve-piston interference.
[0093] If, in step 104, the current command value is judged to be
in excess of the predetermined value, supply of the electric power
to the motor is stopped (step 106).
[0094] According to the above-described routine shown in FIG. 8,
if, under the stopped state of the camshaft 22, the current command
value assigned thereto is in excess of the predetermined value and
the valve 12 is judged to be liable to interfere with the piston,
supply of the electric power to the motor is stopped. In other
words, the biasing force of the valve spring 17 is permitted to be
converted into a torque that rotates the cam 18. The variable valve
apparatus is also constructed so that the shape of the valve lifter
16 in the present embodiment and the arrangement relationship
between the valve lifter 16 and the camshaft 22 are substantially
the same as in FIG. 5. Provided that supply of the electric power
to the motor is stopped, therefore, the valve 12 can be prevented
from being maintained in a lifted state, irrespective of the
position of the contact point existing between the nose 18b of the
cam 18 and the top face 16a when the motor is stopped. In this way,
the control function of the present embodiment allows interference
between the valve 12 and the piston to be avoided reliably,
regardless of the mode of the abnormality of the variable valve
apparatus 10.
[0095] In the second embodiment, which has been described above,
the "electric power supply control means" in the earlier
description of the eighth aspect of the present invention herein
will be realized when the routine process shown in FIG. 8 is
executed by the ECU 40.
Third Embodiment
[0096] Next, a third embodiment of the present embodiment is
described below with reference to FIGS. 9 to 11.
[0097] FIGS. 9(A) and 9(B) are diagrams illustrating a
configuration of a torque reduction mechanism 52 in a variable
valve apparatus 50 according to the third embodiment of the present
invention. More specifically, FIG. 9(A) shows the variable valve
apparatus 50 existing when viewed from the axial direction of the
camshaft 22, and FIG. 9(B) shows the variable valve apparatus 50
existing when viewed from the direction of arrow A in FIG. 9(A). In
FIG. 9, the same constituent elements as those shown in FIG. 1, are
each assigned the same reference number, with their description
omitted or simplified.
[0098] The variable valve apparatus 50 of the present embodiment is
constructed similarly to the variable valve apparatus 10 of the
first embodiment, except that the apparatus 50 includes the torque
reduction mechanism 52 shown in FIG. 9. The torque reduction
mechanism 52 is a reduced-torque generator for reducing the torque
generated when the motor 30 or the like drives the camshaft 22 or
the like. The torque reduction mechanism 52 includes an antiphase
cam 54 and a biasing mechanism 58 that imparts a biasing force of a
spring 56 to the antiphase cam 54. The torque reduction mechanism
52 is provided at ends of two camshafts 22 and 24 each in the
variable valve apparatus 50. Since such configuration of the torque
reduction mechanism 52 is known, detailed description of the
configuration is omitted herein.
[0099] FIG. 10 is a diagram that illustrates general settings of
the reduced torque in a torque reduction mechanism having
substantially the same configuration as that of the torque
reduction mechanism 52 shown in FIG. 9. The waveform denoted by a
solid line in FIG. 10 indicates how the driving torque of the
camshaft changes while the camshaft rotates through one full turn
in a configuration not using such a torque reduction mechanism.
Except for factors such as cam-valve lifter friction, the torque
upon the camshaft, based upon the biasing force of the valve
spring, constitutes a principal part of the driving torque of the
camshaft. For this reason, the driving torque of the camshaft
increases gradually as the cam rotates and pushes the valve
downward in defiance of the valve spring force, and exhibits a
maximum value in immediate front of a maximum lifting position. The
driving torque of the camshaft subsequently decreases and
instantaneously becomes zero at the maximum lifting position. After
the maximum lifting position has been overstepped, the valve spring
repulsion force assists the cam rotation. This changes the camshaft
torque into a minus value, and after a minus peak has been reached,
the camshaft torque approaches zero with the valve being
closed.
[0100] As represented using a waveform denoted by a broken line in
FIG. 10, in order to reduce such driving torque of the camshaft as
discussed above, the reduced torque stemming from the torque
reduction mechanism is generally given as a torque oriented in a
direction reverse to that of the camshaft torque based upon the
biasing force of the valve spring. That is to say, these torques
counteract each other as shown in FIG. 10. The profile of the
antiphase cam 54 and the biasing force of the spring 56 are
adjusted appropriately to achieve those settings of the reduced
torque. When the reduced torque is applied, a final driving torque
of the camshaft is, theoretically, cleared to zero (except for
friction) with the cam present at any rotary position.
[0101] As a result, when the torque reduction mechanism is used at
such general settings as described above, even if contact with the
valve lifter is occurring at whatever position of the cam nose,
that is, even except when the nose tip of the cam comes into
contact with the valve lifter, the torque that rotates the cam in
the closing direction of the valve is not exerted upon the
camshaft. Therefore, the cam is likely to stop with the valve in a
lifted state. This is liable to cause valve-piston
interference.
[0102] FIG. 11 is a diagram illustrating the settings of the
reduced torque stemming from the torque reduction mechanism 52 in
the present embodiment. In the present embodiment, in order to
solve the above problem, the reduced torque stemming from the
torque reduction mechanism 52 is set to be as shown in FIG. 11.
More specifically, as shown in FIG. 11, the reduced torque stemming
from the torque reduction mechanism 52 is set to be smaller than
the torque exerted upon the camshaft 22 on the basis of the biasing
force of the valve spring 17. If the reduced torque is set to have
such a value, the torque that is a resultant value of the camshaft
torque and the reduced torque (i.e., the waveform denoted by a
thick broken line in FIG. 11) acts in a counter direction with
respect to the rotation of the cam 18. This means that sufficient
biasing force of the valve spring 17 can be obtained as the torque
that rotates the cam 18.
[0103] Additionally, the reduced torque that the torque reduction
mechanism 52 assigns is determined so that the resulting
differential torque is slightly greater than a sum of cam-valve
lifter friction, meshing friction of gears arranged between the
motor and the camshaft, motor inertia, and other factors resisting
the rotation of the camshaft.
[0104] Even when the settings shown in FIG. 11 are adopted,
sections with the above differential torque becoming zero near the
maximum lifting position will exist. Accordingly, in the present
embodiment, the variable valve apparatus is constructed so that as
in the first embodiment, the shape of the top face 16a of the valve
lifter 16 and the arrangement relationship between the valve lifter
16 and the camshaft 22 are as shown in FIG. 5. Even at the sections
where the differential torque becomes zero, the valve spring
repulsion force can be distributed into the torque that rotates the
cam 18.
[0105] According to the above-described configuration of the
present embodiment, even in the variable valve apparatus 50 having
the torque reduction mechanism 52 intended to reduce the driving
torque of the camshaft 22 or the like, interference between the
valve 12 and the piston can be reliably avoided using a simple
configuration, irrespective of the stopping position of the cam 18
or the like in case of an abnormality.
* * * * *