U.S. patent application number 15/244224 was filed with the patent office on 2017-04-13 for valve operating apparatus for internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Akio KIDOOKA, Yoshiaki MIYAZATO, Hiroki MURATA.
Application Number | 20170101906 15/244224 |
Document ID | / |
Family ID | 58405370 |
Filed Date | 2017-04-13 |
United States Patent
Application |
20170101906 |
Kind Code |
A1 |
MIYAZATO; Yoshiaki ; et
al. |
April 13, 2017 |
VALVE OPERATING APPARATUS FOR INTERNAL COMBUSTION ENGINE
Abstract
A valve operating apparatus includes: a first intermediate arm
and a first rocker arm that are interposed between a first cam unit
and a first valve; a second intermediate arm and a second rocker
arm that are interposed between a second cam unit and a second
valve; and hydraulic lash adjusters that rockably support the
rocker arms. The intermediate arms are rockably supported by a
rocker shaft. In the axial direction of the rocker shaft, the
distance between the first transmission part and a bearing nearest
thereto is shorter than the distance between the first pressure
receiving part and a bearing nearest thereto, and likewise, the
distance between the second transmission part and a bearing nearest
thereto is shorter than the distance between the second pressure
receiving part and a bearing nearest thereto.
Inventors: |
MIYAZATO; Yoshiaki;
(Shizuoka-ken, JP) ; MURATA; Hiroki; (Gotemba-shi,
JP) ; KIDOOKA; Akio; (Kanagawa-ken, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
58405370 |
Appl. No.: |
15/244224 |
Filed: |
August 23, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01L 1/181 20130101;
F01L 2250/04 20130101; F01L 2250/02 20130101; F01L 2305/00
20200501; F01L 2001/0473 20130101; F01L 1/053 20130101; F01L
13/0063 20130101; F01L 2001/186 20130101; F01L 1/2405 20130101;
F01L 13/0021 20130101; F01L 13/0036 20130101; F01L 1/185 20130101;
F01L 1/2411 20130101; F01L 2013/0068 20130101; F01L 2013/0052
20130101 |
International
Class: |
F01L 13/00 20060101
F01L013/00; F01L 1/24 20060101 F01L001/24; F01L 1/18 20060101
F01L001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 8, 2015 |
JP |
2015-200403 |
May 18, 2016 |
JP |
2016-099738 |
Claims
1. A valve operating apparatus for an internal combustion engine,
comprising: a first cam unit and a second cam unit configured to
respectively drive a first valve and a second valve that are
installed in a cylinder; a first intermediate arm interposed
between the first cam unit and the first valve, and including a
first pressure receiving part that is pressed by the first cam unit
and a first transmission part that transmits a pressing force of
the first cam unit to a side of the first valve; a second
intermediate arm interposed between the second cam unit and the
second valve, and including a second pressure receiving part that
is pressed by the second cam unit and a second transmission part
that transmits a pressing force of the second cam unit to a side of
the second valve; a rocker shaft configured to support the first
intermediate arm and the second intermediate arm to be rockable
between bearings that are respectively installed at both sides of
the cylinder; a first rocker arm interposed between the first
intermediate arm and the first valve, and configured to transmit a
pressing force from the first transmission part to the first valve;
a second rocker arm interposed between the second intermediate arm
and the second valve, and configured to transmit a pressing force
from the second transmission part to the second valve; a first
hydraulic lash adjuster configured to rockably support the first
rocker arm, and act to eliminate a gap between the first valve and
the first rocker arm, and a gap between the first rocker arm and
the first intermediate arm; and a second hydraulic lash adjuster
configured to rockably support the second rocker arm, and act to
eliminate a gap between the second valve and the second rocker arm,
and a gap between the second rocker arm and the second intermediate
arm, wherein, in an axial direction of the rocker shaft, a distance
between the first transmission part and the bearing that is nearest
to the first transmission part is shorter than a distance between
the first pressure receiving part and the bearing that is nearest
to the first pressure receiving part, and a distance between the
second transmission part and the bearing that is nearest to the
second transmission part is shorter than a distance between the
second pressure receiving part and the bearing that is nearest to
the second pressure receiving part.
2. The valve operating apparatus according to claim 1, wherein the
first pressure receiving part and the second pressure receiving
part, and the first transmission part and the second transmission
part are disposed on a same side with respect to the rocker shaft,
seen from an axial direction of the cylinder.
3. The valve operating apparatus according to claim 1, wherein the
first cam unit is configured by a first cam group including a
plurality of cams having different profiles, and wherein the valve
operating apparatus further comprises a device that switches a cam
that gives a pressing force to the first intermediate arm among the
cams of the first cam group.
4. The valve operating apparatus according to claim 1, wherein the
second cam unit is configured by a second cam group further
includes a plurality of cams having different profiles, and wherein
the valve operating apparatus further comprises a device that
switches a cam that gives a pressing force to the second
intermediate arm among the cams of the second cam group.
Description
BACKGROUND
[0001] Technical Field
[0002] Embodiments of the present disclosure relate to a valve
operating apparatus for an internal combustion engine.
[0003] Background Art
[0004] For example, JP 2001-263015 A discloses a variable valve
operating apparatus for an internal combustion engine. The variable
valve operating apparatus is an apparatus that can continuously
change the lift amount and the operating angle of a valve (an
intake valve or an exhaust valve).
[0005] More specifically, the variable valve operating apparatus
includes an intermediate drive mechanism in a transmission path for
the pressing force which is transmitted from a cam to valves. The
intermediate drive mechanism includes an input part and rocking
cams which are rockably supported by a support pipe that is
disposed in parallel with a camshaft. The rocking cams are provided
for the respective two valves included in the same cylinder. The
input part and the rocking cams are configured to rock integrally.
The input part receives a pressing force from the cam, and the
rocking cams transmit the pressing force from the cam to the valves
via rocker arms.
[0006] Further, the above described variable valve operating
apparatus includes an actuator that displaces, in an axial
direction of a control shaft, the control shaft which is disposed
in the support pipe. The intermediate drive mechanism is configured
to be able to change a relative phase difference of the input part
and the rocking cams in accordance with a position in the axial
direction of the control shaft. According to the variable valve
operating apparatus having the above configuration, the relative
phase difference of the input part and the rocking cams is changed
by adjusting the position in the axial direction of the control
shaft, and as a result, the lift amount and the operating angle of
each of the valves can be changed.
[0007] JP 2010-019126 A and JP 2003-201814 A also show the state of
the art at the date of filing of this application.
Technical Problem
[0008] The variable valve operating apparatus disclosed in JP
2001-263015 A is configured to transmit the pressing force of a
single cam to two valves via the input part and the two rocking
cams of the intermediate drive mechanism. Meanwhile, a valve
operating apparatus for an internal combustion engine is known, in
which a cam unit, an intermediate arm (a member interposed between
the cam unit and a valve) that is rockably supported by a rocker
shaft, a rocker arm that is interposed between the intermediate arm
and the valve, and a hydraulic lash adjuster that operates to
eliminate a gap between the valve and the rocker arm and a gap
between the rocker arm and the intermediate arm are included
independently for each valve. Here, in the intermediate arm, a part
which is pressed by the cam unit is referred to as a "pressure
receiving part", and a part which transmits the pressing force of
the cam unit to a valve side (that is, the rocker arm) is referred
to as a "transmission part".
[0009] In the valve operating apparatus, it sometimes becomes
necessary to offset the position of the transmission part in the
axial direction of the locker shaft with respect to the position of
the pressure receiving part in the same direction, for a reason,
such as a constraint on the layout of the cam unit. When such an
offset is provided, the position where the locker shaft receives a
load from the cam side, and the position where the rocker shaft
receives a load from the valve side differ in the axial direction.
When these loads become large, a deflection occurs to the rocker
shaft at a time of valve opening. When the offset is provided, if
the positional relation of the pressure receiving part and the
transmission part in the axial direction of the rocker shaft is not
proper, the displacement amount of the transmission part (more
specifically, a contact position with the rocker arm in the
transmission part) becomes large when a deflection occurs to the
rocker shaft.
[0010] When a deflection of the rocker shaft which supports the
intermediate arm occurs at a time of valve opening, a very small
gap sometimes is produced between the intermediate arm and the
rocker arm. The hydraulic lash adjuster acts to eliminate the gap
instantly. At a time of valve closing, the load to the intermediate
arm from the rocker arm becomes small, and therefore, the
deflection of the rocker shaft is eliminated or becomes small.
However, even when the deflection of the rocker shaft becomes
small, it takes time until oil drains out of the hydraulic lash
adjuster. Consequently, if the positional relation between the
pressure receiving part and the transmission part in the axial
direction of the rocker shaft is not appropriate, a closing failure
of the valve may occur.
SUMMARY OF THE INVENTION
[0011] Embodiments of the present disclosure address the
above-described problem and have an object to provide a valve
operating apparatus for an internal combustion engine that can
improve a closing failure of a valve due to the displacement of a
transmission part accompanying the deflection of a rocker shaft, in
the internal combustion engine that includes a cam unit and an
intermediate arm for each valve, and adopts a configuration in
which the position of the transmission part in the axial direction
of the rocker shaft is offset to the position of a pressure
receiving part in the same direction.
[0012] A valve operating apparatus for an internal combustion
engine according to the present disclosure includes: a first cam
unit and a second cam unit configured to respectively drive a first
valve and a second valve that are installed in a cylinder; a first
intermediate arm interposed between the first cam unit and the
first valve, and including a first pressure receiving part that is
pressed by the first cam unit and a first transmission part that
transmits a pressing force of the first cam unit to a side of the
first valve; a second intermediate arm interposed between the
second cam unit and the second valve, and including a second
pressure receiving part that is pressed by the second cam unit and
a second transmission part that transmits a pressing force of the
second cam unit to a side of the second valve; a rocker shaft
configured to support the first intermediate arm and the second
intermediate arm to be rockable between bearings that are
respectively installed at both sides of the cylinder; a first
rocker arm interposed between the first intermediate arm and the
first valve, and configured to transmit a pressing force from the
first transmission part to the first valve; a second rocker arm
interposed between the second intermediate arm and the second
valve, and configured to transmit a pressing force from the second
transmission part to the second valve; a first hydraulic lash
adjuster configured to rockably support the first rocker arm, and
act to eliminate a gap between the first valve and the first rocker
arm, and a gap between the first rocker arm and the first
intermediate arm; and a second hydraulic lash adjuster configured
to rockably support the second rocker arm, and act to eliminate a
gap between the second valve and the second rocker arm, and a gap
between the second rocker arm and the second intermediate arm. In
an axial direction of the rocker shaft, a distance between the
first transmission part and the bearing that is nearest to the
first transmission part is shorter than a distance between the
first pressure receiving part and the bearing that is nearest to
the first pressure receiving part, and a distance between the
second transmission part and the bearing that is nearest to the
second transmission part is shorter than a distance between the
second pressure receiving part and the bearing that is nearest to
the second pressure receiving part.
[0013] The first pressure receiving part and the second pressure
receiving part, and the first transmission part and the second
transmission part may be disposed on a same side with respect to
the rocker shaft, seen from an axial direction of the cylinder.
[0014] The first cam unit may be configured by a first cam group
including a plurality of cams having different profiles. The valve
operating apparatus may further include a device that switches a
cam that gives a pressing force to the first intermediate arm among
the cams of the first cam group.
[0015] The second cam unit may be configured by a second cam group
further includes a plurality of cams having different profiles. The
valve operating apparatus may further include a device that
switches a cam that gives a pressing force to the second
intermediate arm among the cams of the second cam group.
[0016] According to the valve operating apparatus for an internal
combustion engine of the present disclosure, in the configuration
including a cam unit and an intermediate arm for each of valves,
the positions of the respective transmission parts in the axial
direction of the rocker shaft are offset with respect to the
positions of the respective pressure receiving parts in the same
direction, in the following form. That is, in the axial direction
of the rocker shaft, the distance between the first transmission
part and the bearing that is the nearest to the first transmission
part is configured to be shorter than the distance between the
first pressure receiving part and the bearing that is the nearest
to the first pressure receiving part. Similarly, in the axial
direction of the rocker shaft, the distance between the second
transmission part and the bearing that is the nearest to the second
transmission part is configured to be shorter than the distance
between the second pressure receiving part and the bearing that is
the nearest to the second pressure receiving part. According to the
offsets in the form like this, the transmission parts are nearer to
the bearings which are the fixed ends as compared with the pressure
receiving parts, and therefore, the displacement amounts of the
transmission parts at the time of the pressing forces of the cams
acting on the intermediate arms can be restrained to be small. The
gaps which should be adjusted by the hydraulic lash adjusters
thereby become small, and therefore, a closing failure of the
valves can be improved, which is caused by the hydraulic lash
adjusters pushing the rocker arms excessively when the pressing
forces of the cams do not act on the intermediate arms (that is, at
the time of valve closing).
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a view of the outline of a valve operating
apparatus for an internal combustion engine according to a first
embodiment of the present disclosure, seen from the axial direction
of a cylinder;
[0018] FIG. 2A and FIG. 2B are sectional views of the valve
operating apparatus cut along a line A-A in FIG. 1;
[0019] FIG. 3 is a perspective view of a pair of intermediate
arms;
[0020] FIG. 4A and FIG. 4B are views for explaining an example of a
specific configuration of a cam switching device included by the
valve operating apparatus shown in FIG. 1;
[0021] FIG. 5A to FIG. 5C are views for explaining switch
operations of a cam unit which are performed by the cam switching
device;
[0022] FIG. 6A and FIG. 6B are views which relate to the first
embodiment of the present disclosure, and are for explaining a
difference of influence of deflection of a rocker shaft due to a
difference in the form of offsets;
[0023] FIG. 7 is a view of a main part of a valve operating
apparatus for an internal combustion engine according to a second
embodiment of the present disclosure, seen from the axial direction
of a cylinder, and shows a configuration included by each of the
cylinders in the valve operating apparatus;
[0024] FIG. 8 is a view of cam units, intermediate arms, rocker
arms, hydraulic lash adjusters and valves seen from the axial
direction of a rocker shaft; and
[0025] FIG. 9A and FIG. 9B are views that relate to the second
embodiment of the present disclosure, and are for explaining a
difference in influence of deflection of the rocker shaft due to
difference in the manner of offsets.
DETAILED DESCRIPTION
First Embodiment
Configuration of Valve Operating Apparatus According to First
Embodiment
(Entire Configuration)
[0026] FIG. 1 is a view of the outline of a valve operating
apparatus 10 for an internal combustion engine according to a first
embodiment of the present disclosure, seen from the axial direction
of a cylinder. FIG. 2A and FIG. 2B are sectional views of the valve
operating apparatus 10 cut along a line A-A in FIG. 1. More
specifically, FIG. 2A is a view at a time of a first valve 12a
being in a valve closed state. FIG. 2B is a view at a time of the
first valve 12a being in a valve open state. FIG. 3 is a
perspective view of a pair of intermediate arms 20 (20a, 20b).
[0027] Each cylinder of the internal combustion engine is equipped
with two intake valves and two exhaust valves. The valve operating
apparatus 10 is an apparatus for driving two valves (the two intake
valves or the two exhaust valves) 12 which are disposed in each
cylinder of the internal combustion engine. When the two valves 12
need to be distinguished from each other, the two valves are
referred to as a first valve 12a and a second valve 12b (this
similarly applies to the components other than the valves 12). For
the valve operating apparatus 10, FIG. 1 shows a configuration
which is equipped for each of the cylinders.
[0028] The valve operating apparatus 10 includes a camshaft 14. The
camshaft 14 is connected to a crankshaft (not illustrated) via a
timing pulley and a timing chain (or a timing belt) which are not
illustrated, and is configured to rotate at a half of the speed of
the crankshaft by the rotational force of the crankshaft.
[0029] As shown in FIG. 1, a first cam unit 16a and a second cam
unit 16b for each cylinder are attached to the camshaft 14. The
first cam unit 16a drives the first valve 12a via a first
intermediate arm 20a and a first rocker arm 22a which will be
described later. The second cam unit 16b drives the second valve
12b via a second intermediate arm 20b and a second rocker arm 22b
which will be described later. In the present embodiment, as an
example, the first cam unit 16a is configured by a first cam group
including three cams 16a1, 16a2 and 16a3, and the second cam unit
16b is configured by a second cam group including three cams 16b1,
16b2 and 16b3. A configuration around the camshaft 14 will be
described later with reference to FIGS. 4A and 4B and FIGS. 5A to
5C. Furthermore, as described below, the valve operating apparatus
10 includes a rocker shaft 18, an intermediate arm 20, a rocker arm
22 and a cam switching device 24 (see FIG. 4A) as main
components.
[0030] As shown in FIG. 1, the rocker shaft 18 is disposed in
parallel with the camshaft 14. The rocker shaft 18 is supported by
a plurality of bearings 26. More specifically, each of the bearings
26 is configured by a bearing part which is formed at a cylinder
head (or a cam carrier which is attached to the cylinder head), and
a cam cap (a camshaft support member) which is combined with the
bearing part, and only the cam caps are illustrated in FIG. 1. A
journal of the rocker shaft 18 is supported by the bearing part and
the cam cap. In order to allow the intermediate arm 20 to rock
freely, a clearance for forming an oil film is provided between the
journal, and the bearing part and the cam cap.
[0031] As shown in FIG. 1, the bearings 26 are respectively
installed at both sides of the cylinder. The first intermediate arm
20a and the second intermediate arm 20b for the same cylinder are
rockably supported by the rocker shaft 18 between a pair of
bearings 26 which are installed in this way. As long as the
intermediate arms 20a and 20b for the same cylinder are disposed
between the pair of bearings 26, the two bearings 26 do not have to
be always included on a cylinder to cylinder basis. That is, one or
both of the pair of bearings 26 may be shared by adjacent
cylinders.
[0032] The first intermediate arm 20a is interposed between the
first cam unit 16a and the first valve 12a. More specifically,
since the first rocker arm 22a is interposed between the first
intermediate arm 20a and the first valve 12a, the first
intermediate arm 20a is interposed between the first cam unit 16a
and the first rocker arm 22a. In the first intermediate arm 20a, a
first cam roller 28a is rotatably attached to a position facing the
first cam unit 16a (more specifically, at a position facing the
first cam 16a2 in an operation state shown in FIG. 1 and FIGS. 2A
and 2B). The first cam roller 28a corresponds to a "first pressure
receiving part" which is pressed by the first cam unit 16a (to be
more specific, 16a1 or 16a2).
[0033] Further, in the first intermediate arm 20a, a first
transmission part 32a is provided at a position facing a rocker
roller 30 of the first rocker arm 22a. The first transmission part
32a is a part that transmits the pressing force of the first cam
unit 16a to the first valve 12a via the first rocker arm 22a. The
first transmission part 32a is formed as a non-working surface 32a1
and a working surface 32a2. The non-working surface 32a1 is a
surface (a base circle part) in a circular-arc shape which is
formed so that the distance from the center of rocking (that is,
the axial center of the rocker shaft 18) of the first intermediate
arm 20a is constant. The working surface 32a2 is a surface which is
provided so as to continue from the non-working surface 32a1, and
is formed so that the distance from the center of rocking (the axis
of the rocker shaft 18) of the first intermediate arm 20a becomes
gradually longer as the working surface 32a2 is away from the
non-working surface 32a1.
[0034] The second intermediate arm 20b which is interposed between
the second cam unit 16b and the second valve 12b is configured
similarly to the aforementioned first intermediate arm 20a, except
that a point which will be described in detail later (that is, a
positional relation between the pressure receiving part and the
transmission part) is different. That is, the second intermediate
arm 20b includes a second cam roller 28b corresponding to the
"second pressure receiving part" which is pressed by the second cam
unit 16b. Further, the second intermediate arm 20b is provided with
a second transmission part 32b which transmits a pressing force of
the second cam unit 16b to the second valve 12b via the second
rocker arm 22b. The second transmission part 32b is formed as a
non-working surface 32b1 and a working surface 32b2, similarly to
the first transmission part 32a.
[0035] As above, the valve operating apparatus 10 of the present
embodiment includes the cam unit 16 and the intermediate arm 20
independently for each valve 12. Further, in order to be able to
keep contact of the cam unit 16 and the cam roller 28 at all times
during rotational operation of the cam unit 16, the intermediate
arm 20 is urged to the cam unit 16 by a spring 34 (see FIG. 2A and
FIG. 2B). An end part which is located at an opposite side of an
end part at the intermediate arm 20 side in the spring 34 is
provided at the cylinder head or the cam carrier not
illustrated.
[0036] Further, one end of the rocker arm 22 is supported by a
valve shaft end of the valve 12, and the other end is supported by
a hydraulic lash adjuster 36 (see FIG. 2A and FIG. 2B). More
specifically, the valve operating apparatus 10 includes a first
hydraulic lash adjuster 36a for the first valve 12a, and a second
hydraulic lash adjuster 36b for the second valve 12b. The first
hydraulic lash adjuster 36a rockably supports the first rocker arm
22a, and acts to eliminate a gap between the first valve 12a and
the first rocker arm 22a and a gap between the first rocker arm 22a
and the first intermediate arm 20a. The second hydraulic lash
adjuster 36b rockably supports the second rocker arm 22b, and acts
to eliminate a gap between the second valve 12b and the second
rocker arm 22b and a gap between the second rocker arm 22b and the
second intermediate arm 20b. Further, the valve 12 is urged, by a
valve spring 38 (see FIG. 2A and FIG. 2B), in a closing direction,
that is, a direction to push up the rocker arm 22.
[0037] Next, an opening and closing action of the valve 12 will be
described with the second valve 12b taken as an example. As shown
in FIG. 2A, in a state where a pressing force of the second cam
16b2 is not given to the second intermediate arm 20b, the
non-working surface 32b1 of the second transmission part 32b abuts
on the rocker roller 30 of the second rocker arm 22b. In this
state, the second rocker arm 22b is not pressed down by the second
intermediate arm 20b, and therefore, the second valve 12b keeps a
valve closed state.
[0038] Meanwhile, when a pressing force of the second cam 16b2 is
given to the second intermediate arm 20b, the second intermediate
arm 20b rocks with the rocker shaft 18 as a center as shown in FIG.
2B, and the part of the second transmission part 32b which contacts
the rocker roller 30 is switched from the non-working surface 32b1
to the working surface 32b2. As a result, the second rocker arm 22b
is pressed down by the second intermediate arm 20b, and the second
valve 12b lifts. In this way, the second cam 16b2 rotates, the
second intermediate arm 20b thereby rocks, and with this, the
second rocker arm 22b rocks, whereby the second valve 12b opens and
closes.
(Cam Switching Device)
[0039] FIG. 4A and FIG. 4B are views for explaining an example of a
specific configuration of the cam switching device 24 included by
the valve operating apparatus 10 shown in FIG. 1. More
specifically, FIG. 4A is a view showing a configuration around the
cam switching device 24 provided for each of the cylinders of the
internal combustion engine. FIG. 4B is a view of a cam unit 40 seen
from the direction of an arrow B (the axial direction of the
camshaft 14) shown in FIG. 4A.
[0040] The first cam unit 16a and the second cam unit 16b described
above are provided as components of the cam unit 40. The cam unit
40 is supported by the camshaft 14 in a form in which the cam unit
40 is movable in the axial direction of the camshaft 14 and
movement in the rotational direction thereof is restricted.
[0041] The cam switching device 24 switches the cam which is to be
mechanically connected to each of the valves 12 (that is, gives the
pressing force to the cam roller 28 of the intermediate arm 20)
among the three cams (16a1 to 16a3, or 16b1 to 16b3) having
different profiles. The cam switching device 24 may include a
configuration other than the configuration which will be described
below as long as the cam switching device is a device that can
switch a plurality of cams which the cam unit 16 has.
[0042] Here, an example of profiles of the three cams 16a1, 16a2
and 16a3 of the first cam group will be described. The following
explanation similarly applies to profiles of the three cams 16b1,
16b2 and 16b3 of the second cam group. The profile of the cam 16a2
which is disposed in the center of the first cam group (16a1, 16a2
and 16a3) is set as a large cam for obtaining a relatively large
lift amount and operating angle as a lift amount and an operating
angle of the first valve 12a. The cam 16a1 is disposed adjacently
(the right side of the cam 16a2 in FIG. 4A) to the cam 16a2. The
profile of the cam 16a1 is set as a small cam which obtains a
smaller lift amount and operating angle than the lift amount and
the operating angle obtained by the cam 16a2. The cam 16a3 is
disposed adjacently to the cam 16a2 (the left side of the cam 16a2
in FIG. 4A) at an opposite side of the cam 16a1. The profile of the
cam 16a3 is set as a cam that only includes a base circle part in
which the distance from the axis of the camshaft 14 is equal, that
is, a zero lift cam which does not give a pressing force to the
first valve 12a.
[0043] Further, the cam unit 40 includes a guide groove 42.
Although a location of the guide groove 42 on the cam unit 40 is
not specially limited, and in the present embodiment the guide
groove 42 is formed on an outer peripheral surface of the cam unit
40, next to (at the left side of the second cam 16b3 in FIG. 4A)
the second cam 16b3. The guide groove 42 is formed to extend in a
Y-shape in the circumferential direction. More specifically, the
guide groove 42 has a pair of branch parts 42a and 42b which is
branched into a Y-shape, and a junction part 42c which is a
location where the pair of branch parts 42a and 42b join each
other.
[0044] At a position facing the guide groove 42, an electromagnetic
solenoid type actuator 44 having three cylindrical movable elements
44a, 44b and 44c capable of engaging with and disengaging from the
guide groove 42 is disposed. The actuator 44 is electrically
connected to an electronic control unit (ECU) 46 for controlling
the internal combustion engine including the valve operating
apparatus 10. Energization of the actuator 44 is controlled on the
basis of an instruction from the ECU 46. The actuator 44 is
configured to be able to push out a movable element of the three
movable elements 44a, 44b and 44c toward the guide groove 42 in a
state where electric power is turned on.
[0045] More specifically, each of the movable elements 44a, 44b and
44c is urged, by a spring not illustrated, in a direction to
separate from the guide groove 42. The actuator 44 is configured so
that the thrust force of a solenoid which is generated as a result
of energization surpasses the force of the spring, and thereby the
movable element 44a, 44b or 44c can protrude (advance) to the guide
groove 42. Further, the actuator 44 is attached to the cylinder
head or the cam carrier not illustrated. The cam switching device
24 is equipped with a stopper device (not illustrated) between the
cam unit 40 and the camshaft 14, in order to keep an axial position
of the cam unit 40 on the camshaft 14, in a state where none of the
movable elements 44a, 44b and 44c is engaged with the guide groove
42.
[0046] Further, as shown in FIG. 4A, the distance between groove
center lines of the first branch part 42a and the junction part 42c
in the guide groove 42, and the distance between groove center
lines of the second branch part 42b and the junction part 42c are
configured to be equal to the distance between cam center lines in
the width direction of the adjacent cams in the cam unit 16.
Further, each of distances between center lines of the respective
movable elements 44a, 44b and 44c of the actuator 44 is configured
to be equal to the above described distance between the groove
center lines.
[0047] FIG. 5A to FIG. 5C are views for explaining switch
operations of the cam unit 16 which are performed by the cam
switching device 24. FIG. 5A shows an operation state (state using
the large cams) where the cam 16a2 of the first cam group and the
cam 16b2 of the second cam group respectively contact the first cam
roller 28a and the second cam roller 28b, similarly to FIG. 4A. The
cam switching device 24 is configured so that in this operation
state, the groove center line of the first branch part 42a
coincides with the center line of the first movable element 44a,
and the groove center line of the second branch part 42b coincides
with the center line of the third movable element 44c.
[0048] When the actuator 44 is operated so that the first movable
element 44a is inserted into the first branch part 42a during use
of a common base circle part concerning the first cam unit 16a and
the second cam unit 16b in the operation state shown in FIG. 5A,
the guide groove 42 slides the cam unit 40 in a direction shown in
FIG. 5B by using a rotational force of the camshaft 14. As a
result, the cams respectively contacting the cam rollers 28a and
28b are switched to the cams 16a3 and 16b3 from the cams 16a2 and
16b2 as a result of rotation of the camshaft 14. In this way, with
the operation of the actuator 44, the operation state of the cam
switching device 24 is switched to an operation state shown in FIG.
5B (a valve stopped state). When a state where the position of the
first movable element 44a coincides with the position of the
junction part 42c in the axial direction of the camshaft 14 is
brought about as a result of the aforementioned slide operation,
energization of the actuator 44 is stopped quickly. As a result,
the first movable element 44a is removed from the guide groove 42.
In addition, the axial position of the cam unit 40 is kept by the
aforementioned stopper device. This similarly applies to switch of
other operation states which will be described below.
[0049] In the operation state shown in FIG. 5B, the groove center
line of the second branch part 42b of the guide groove 42 coincides
with the center line of the second movable element 44b. When the
actuator 44 operates in this operation state so that the second
movable element 44b is inserted into the second branch part 42b
during use of the common base circle part concerning the first cam
unit 16a and the second cam unit 16b, the guide groove 42 switches,
by using the rotational force of the camshaft 14, the cams which
respectively contact the cam rollers 28a and 28b to the cams 16a2
and 16b2 from the cams 16a3 and 16b3 as a result of rotation of the
camshaft 14. The operation state of the cam switching device 24 is
thereby switched (is returned) to the operation state shown in FIG.
5A again as a result of the operation of the actuator 44.
[0050] Meanwhile, when the actuator 44 operates in the operation
state shown in FIG. 5A so that the third movable element 44c is
inserted into the second branch part 42b during use of the common
base circle part concerning the first cam unit 16a and the second
cam unit 16b, the guide groove 42 slides the cam unit 40 in a
direction shown in FIG. 5C by using the rotational force of the
camshaft 14. As a result, the cams which respectively contact the
cam rollers 28a and 28b are switched to the cams 16a1 and 16b1 from
the cams 16a2 and 16b2 as a result of rotation of the camshaft 14.
The operation state of the cam switching device 24 is thereby
switched to the operation state (a state using small cams) shown in
FIG. 5C as a result of the operation of the actuator 44.
[0051] In the operation state shown in FIG. 5C, the groove center
line of the first branch part 42a of the guide groove 42 coincides
with the center line of the second movable element 44b. When the
actuator 44 operates in this operation state so that the second
movable element 44b is inserted into the first branch part 42a
during use of the common base circle part concerning the first cam
unit 16a and the second cam unit 16b, the guide groove 42 switches,
by using the rotational force of the camshaft 14, the cams which
respectively contact the cam rollers 28a and 28b to the cams 16a2
and 16b2 from the cams 16a1 and 16b1 as a result of rotation of the
camshaft 14. The operation state of the cam switching device 24 is
thereby switched (is returned) to the operation state shown in FIG.
5A again as a result of the operation of the actuator 44.
[0052] The above described cam switching device 24 is configured by
the aforementioned components (that is, the cam unit 40 which is
attached to the camshaft 14 in a form that the cam unit 40 is
movable in the axial direction of the camshaft 14 and the movement
thereof is restricted in the rotational direction, the guide groove
42 and the actuator 44).
[0053] As described above, according to the valve operating
apparatus 10 of the present embodiment, the lift amounts and the
operating angles of the valves 12 can be changed stepwise, which
includes realization of the valve stopped state where the valves 12
are kept in a closed state, by switching, with the cam switching
device 24, the cams which give the pressing forces to the cam
rollers 28 of the intermediate arms 20 among the plurality of cams
which the cam units 16 have. In this way, the valve operating
apparatus 10 of the present embodiment is configured as a variable
valve operating apparatus capable of changing the valve opening
characteristics of the valves 12. In the configuration so far, the
cams 16a3 and 16b3 are both zero lift cams, but the present
disclosure is not limited to this. If only either one of the cam
16a3 and the cam 16b3 is, for example, a zero lift cam, an
operation of stopping only one of the valves 12 can be
implemented.
Characteristic Configuration of Valve Operating Apparatus According
to First Embodiment and Effect by the Configuration
[0054] The valve operating apparatus which is mounted in an
internal combustion engine is requested to be established in a
limited mounting space in the cylinder head. For the configuration
of the intermediate arms 20, the valve operating apparatus 10 of
the present embodiment has a feature that will be described as
follows. As a result, in the configuration in which each of the
valves 12 includes the cam unit 16 and the intermediate arm 20
which is rockably supported by the rocker shaft 18, occurrence of a
negative effect which is caused by displacement of the transmission
part accompanying deflection of the rocker shaft 18 can be
restrained while a space necessary to mount the valve operating
apparatus 10 is reduced to be small, as described in detail
below.
(Saving Space in Height Direction of Cylinder Head)
[0055] According to the valve operating apparatus 10 of the present
embodiment described above, the intermediate arms 20 are configured
so that the first cam roller 28a (the first pressure receiving
part) and the second cam roller 28b (the second pressure receiving
part), and the first transmission part 32a and the second
transmission part 32b are located on the same side with respect to
the rocker shaft 18, seen from the axial direction of the cylinder
(see FIG. 1). Hereinafter, the disposition like this will be
referred to as a "disposition A" for convenience. To add to that,
in the intermediate arms 20, the position of the first transmission
part 32a in the axial direction of the rocker shaft 18 is offset
with respect to the position of the first cam roller 28a (the first
pressure receiving part), and the position of the second
transmission part 32b in the axial direction of the rocker shaft 18
is similarly offset with respect to the position of the second cam
roller 28b (the second pressure receiving part). If the above
described offsets are adopted in an example where the above
described disposition A is adopted, the mounting position of the
camshaft can be restrained to be low as compared with an example
without offsets. As a result, the height of the cylinder head can
be restrained to be low. In other words, a space in the height
direction of the cylinder head (that is, the axial direction of the
cylinder) shown in FIG. 3 can be saved.
(Restraint on Displacement of Transmission Part Due to Deflection
of Rocker Shaft)
[0056] In addition, the above described offsets in the intermediate
arms 20 are set with the following form (hereinafter, referred to
as a "form A" for convenience of explanation). That is, according
to the form A mentioned here, in the axial direction of the rocker
shaft 18, the distance between the first transmission part 32a and
the bearing 26 (the bearing 26 at the right side in FIG. 1) which
is the nearest to the first transmission part 32a is set to be
shorter than the distance between the first cam roller 28a (the
first pressure receiving part) and the bearing 26 (the same bearing
26 at the right side in FIG. 1) which is the nearest to the first
cam roller 28a. Further, according to the form A, in the axial
direction of the rocker shaft 18, the distance between the second
transmission part 32b and the bearing 26 (the bearing 26 at the
left side in FIG. 1) which is the nearest to the second
transmission part 32b is set to be shorter than the distance
between the second cam roller 28b and the bearing 26 (the same
bearing 26 at the left side in FIG. 1) which is the nearest to the
second cam roller 28b (the second pressure receiving part). An
effect obtained by providing the offsets in the form A like this
will be described below with reference to FIG. 6A and FIG. 6B.
[0057] FIG. 6A and FIG. 6B are views which relate to the first
embodiment of the present disclosure, and are for explaining a
difference of influence of deflection of the rocker shaft due to a
difference in the form of offsets. More specifically, FIG. 6A is a
view of an example where offsets in the form A which is adopted in
the present embodiment are provided. FIG. 6B is a view showing a
comparative example which is referred to for the purpose of being
compared with the configuration of the present embodiment. As a
form that can be adopted as the above described offsets, there is a
form that is adopted in the comparative example shown in FIG. 6B,
other than the form A. That is, the offsets can also be provided in
this form in which the positions where loads from the cams are
received are nearer to the bearings as compared with the positions
where loads from the rocker arms (valve side) are received,
contrary to the form A.
[0058] First, as shown in the respective views in FIG. 6A and FIG.
6B, if the pressing force of each cam is given to the intermediate
arm, the load from the cam acts on the pressure receiving part of
the intermediate arm. In addition, if the pressing force is given,
a load which is caused by a valve spring reaction force that is
produced by receiving the aforementioned pressing force and the
magnitude of which is equivalent to the load from the cam, acts on
the transmission part of the intermediate arm from the valve side
(acts via the rocker arm 22 in the example of the valve operating
apparatus 10). If the offsets are provided, in the axial direction
the position where the rocker shaft receives the load from the cam
side differs from the position where the rocker shaft receives the
load from the valve side, even though either form of the forms in
FIG. 6A and FIG. 6B is adopted. As a result, a deflection occurs to
the rocker shaft.
[0059] In the comparative example shown in FIG. 6B, at the position
where the load from each rocker arm (each valve side) is received,
the distance from the bearing which is nearer to the intermediate
arm out of the pair of bearings is longer than that at the position
where the load from the cam is received. Consequently, the moment
which is produced with the bearing as the center and which is of
the load from each rocker arm (each valve side) becomes larger than
the moment of the load from each cam. FIG. 6B shows a state where
the rocker shaft deflects in a manner where the rocker shaft is
pushed toward the cam side (in the upward direction in FIG.
6B).
[0060] Meanwhile, the configuration of the present embodiment shown
in FIG. 6A adopts offsets in the opposite form (that is, form A) to
the comparative example shown in FIG. 6B as described above.
Consequently, concerning the moment with, as the center, the
bearing 26 nearer to the intermediate arm 20 to which attention is
paid, the moment of the load from each rocker arm 22 (each valve 12
side) is smaller than the moment of the load from each cam unit 16.
FIG. 6A shows a state where the rocker shaft deflects in a manner
where the rocker shaft is pushed toward the valve side (in the
downward direction in FIG. 6A).
[0061] In the example where the form A is used, the position of
each transmission part becomes nearer to the bearing (the bearing
nearer to the intermediate arm to which attention is paid) which is
a fixed end, as compared with the example where the form in which
the positional relation of the pressure receiving part and the
transmission part are opposite to the form A is used. Consequently,
as is understandable when FIG. 6A and FIG. 6B are compared, when
attention is paid to the position of each transmission part in the
axial direction of the rocker shaft, the deflection amount .delta.
of the rocker shaft in the position of each transmission part
becomes smaller in the configuration shown in FIG. 6A, as compared
with the configuration shown in FIG. 6B. Accordingly, the
displacement amount of each transmission part (more specifically,
the displacement amount of each contact position with a mating
member (in the valve operating apparatus 10, the rocker roller 30
corresponds to this) in each transmission part) at the time of the
pressing force of each cam acting on the intermediate arm becomes
smaller in the configuration shown in FIG. 6A, as compared with the
configuration shown in FIG. 6B. A straight line L1 in each of FIG.
6A and FIG. 6B represents the center axis of the rocker shaft at a
time of no deflection occurring to the rocker shaft, and straight
lines L2 and L2' in FIG. 6A and FIG. 6B represent center axes of
the rocker shafts at a time of deflection occurring. This similarly
applies to FIG. 9A and FIG. 9B which will be described later.
[0062] When the rocker shaft which supports the intermediate arms
deflects in the upward direction in FIG. 6A at a time of opening of
the valves, very small gaps are generated between the intermediate
arms and the rocker arms. More specifically, gaps are generated
between the rocker rollers of the rocker arms and the non-working
surfaces (the base circle parts) of the intermediate arms. The
hydraulic lash adjusters act to eliminate the gaps instantly.
Meanwhile, the loads to the intermediate arms from the rocker arms
become small at a time of valve closing, and therefore, the
deflection of the rocker shaft is eliminated or decreases. However,
even though the deflection of the rocker shaft becomes small, it
takes time until oil drains from the hydraulic lash adjusters.
Consequently, when deflection decreases in the state where the
positions of support points of the rocker arms at the hydraulic
lash adjuster side become high as a result of the hydraulic lash
adjusters acting to eliminate the gaps, there is a possibility that
the valves may be pressed by the rocker arms due to the fact that
the positions of the support points have become high (that is, the
fact that the gaps have been eliminated), even during a time period
in which the pressing forces from the cams do not act on the
intermediate arms. Consequently, if the displacement amounts of the
transmission parts of the intermediate arms due to deflection of
the rocker shaft are large, a closing failure of the valves may
occur.
[0063] However, according to the configuration of the intermediate
arms 20 of the present embodiment, the displacement amounts of the
transmission parts 32 can be reduced when deflection occurs to the
rocker shaft 18 due to adoption of offsets. As a result, the
closing failure of the valves 12 due to the influence of the action
of the aforementioned hydraulic lash adjusters 36 can be
improved.
(Saving of Space in Axial Direction in Example of Having
Configuration of Making Opening Characteristics of Valves Variable
by Using Slide Operations of Cams)
[0064] The offsets in the form A of the present embodiment also
provides the following effect when the offsets in the form A are
applied to a valve operating apparatus having the configuration in
which the opening characteristics of the valves are made variable
by switching the cams which press the valves by sliding a plurality
of cams in the axial direction of the camshaft as in the valve
operating apparatus 10. That is, in the example of having the
configuration in which a plurality of cams are slid in the axial
direction of the camshaft, a large space is required in the axial
direction of the camshaft in order to establish the slide
operation. The issue becomes more remarkable as the number of cams
to be slid is larger.
[0065] For the above described issue, according to the offsets in
the form A, in other words, the form in which the pressure
receiving parts (that is, the cam rollers 28) are disposed at inner
sides of the first valve 12a and the second valve 12b in the axial
direction of the rocker shaft 18, a space between the first valve
12a and the second valve 12b in the axial direction of the rocker
shaft 18 can be more effectively used for the slide operations of
the cam units 16, as compared with the form in which the positional
relation of the pressure receiving parts and the transmission parts
is opposite to that in the form A. The reason is that the first and
second cam units 16a and 16b are disposed near to the center side
of the cylinders, so that the variable device for changing the
opening characteristics of the valves 12 is easily disposed at
outer sides of the cylinder relative to the first and second cam
units 16a and 16b. As a result, the space in the axial direction
(the axial direction shown in FIG. 3) of the camshaft 14 can be
saved, and therefore, the configuration which makes the opening
characteristics of the valves variable can be easily established by
using the slide operation of the cams.
(Saving Space in Width Direction of Cylinder Head)
[0066] In the intermediate arms 20, the first cam roller 28a (the
first pressure receiving part) and the second cam roller 28b (the
second pressure receiving part), and the first transmission part
32a and the second transmission part 32b are disposed on the same
side with respect to the rocker shaft 18 seen from the axial
direction of the cylinder (see FIG. 1). According to the
disposition A, even where the space ensured to mount the valve
operating apparatus is small for the reason that bore diameters of
the cylinders are small, for example, the valve operating apparatus
can be easily established in the limited space. More specifically,
the space can be saved in the width direction of the cylinder head
shown in FIG. 3 (that is, a direction that is orthogonal to each of
the axial direction of the cylinders and the axial direction of the
camshaft 14).
Modified Example of First Embodiment
[0067] In the first embodiment described above, explanation is made
by taking, as an example, the valve operating apparatus (that is,
the variable valve operating apparatus) 10 including, as the first
cam unit 16a which drives the first valve 12a, the first cam unit
16a configured by the first cam group formed of a plurality (three
as an example) of the cams 16a1 to 16a3 having different profiles,
and also including the similar configuration concerning the second
cam unit 16b. However, the first cam unit and the second cam unit
included by the valve operating apparatus of the internal
combustion engine which is the object of the present disclosure may
be each configured by a single cam. More specifically, the valve
operating apparatus to be the object of the present disclosure may
be, for example, configured as a valve operating apparatus which
does not have the function of making variable the opening
characteristics of the valves by adopting, for each intermediate
arm 20, the configuration which drives, via the intermediate arm 20
and the rocker arm 22, a valve by a single fixed cam.
Alternatively, the valve operating apparatus to be the object of
the present disclosure may be configured as a variable valve
operating apparatus having the function of making variable the
opening characteristics of the valves by adopting, for each
intermediate arm, a configuration that includes a known variable
device which makes the operation of the intermediate arms variable
while including, for each of the intermediate arms, the
configuration that drives a valve by a single cam via the inter
mediate arm and the rocker arm.
[0068] Further, in the first embodiment described above,
explanation is made by taking, as an example, the valve operating
apparatus 10 including the first cam roller 28a and the second cam
roller 28b respectively as the first pressure receiving part and
the second pressure receiving part. However, the parts
corresponding to the first pressure receiving part and the second
pressure receiving part in the present disclosure are not limited
to the parts that contact the cams with rolling contact as in the
example of using the cam rollers 28, but may be parts using slide
contact similarly to a valve operating apparatus 50 which will be
described later. That is, the above described parts may be formed
at the intermediate arms as pads having curved surfaces or flat
surfaces which contact the cams. Further, the pressure receiving
part in the present disclosure is not necessarily limited to the
part that directly contacts the cam itself as long as the part is
pressed by the cam, and may be configured to be pressed by the cam
via a member, for example.
[0069] Further, in the first embodiment described above,
explanation is made by taking, as an example, the valve operating
apparatus 10 including the single cam-switching device 24 for each
of the cylinders. However, the single cam-switching device in the
present disclosure may be included for each of the valves. If the
single cam-switching device is included for each of the valves,
single valve control (for example, single valve stop control of
bringing only one of the valves into a stopping state, for example)
that causes the opening characteristic of one of the first valve
and the second valve to differ from the opening characteristic of
the other one can be performed. Alternatively, the device which
switches the cam in the present disclosure may be shared among a
plurality of cylinders which share the base circle part of the
cams.
Second Embodiment
[0070] Next, a second embodiment of the present disclosure will be
described with reference to FIG. 7 to FIG. 9B.
Configuration of Valve Operating Apparatus According to Second
Embodiment
[0071] In the first embodiment described above, explanation is made
by taking, as an example, the valve operating apparatus 10, which
adopts the disposition A (that is, the disposition in which the
first cam roller 28a (the first pressure receiving part) and the
second cam roller 28b (the second pressure receiving part), and the
first transmission part 32a and the second transmission part 32b
are included on the same side with respect to the rocker shaft 18
seen from the axial direction of the cylinder). Here, in the valve
operating apparatus for an internal combustion engine, disposition
as follows, that is, a disposition (hereinafter, referred to as a
"disposition B" for convenience of explanation) is sometimes used
in which a pressure receiving part is provided at an opposite side
of a transmission part with respect to a rocker shaft, seen from
the axial direction of a cylinder, other than the aforementioned
disposition A. Even in the valve operating apparatus adopting the
disposition B like this, it is sometimes necessary to offset the
positions of the transmission parts in the axial direction of the
rocker shaft with respect to the positions of the pressure
receiving parts in the same direction, for the reason, such as a
constraint on the layout of the cam units. The valve operating
apparatus 50 of the present embodiment which will be described
below is preferable in restraining occurrence of the harmful effect
due to displacement of the transmission parts accompanying a
deflection of the rocker shaft when the disposition B is
adopted.
[0072] FIG. 7 is a view of a main part of the valve operating
apparatus 50 for an internal combustion engine according to the
second embodiment of the present disclosure, seen from the axial
direction of a cylinder, and shows a configuration included by each
of the cylinders in the valve operating apparatus 50. FIG. 8 is a
view of cam units 56, intermediate arms 54, the rocker arms 22, the
hydraulic lash adjusters 36 and the valves 12 seen from the axial
direction of a rocker shaft 58. In FIG. 7 and FIG. 8, the same
components as the components shown in FIG. 1 described above will
be assigned with the same reference signs and explanation thereof
will be omitted or simplified.
[0073] As shown in FIG. 7, for each cylinder, a first cam unit 56a
which drives the first valve 12 via a first intermediate arm 54a
and the first rocker arm 22a, and a second cam unit 56b which
drives the second valve 12b via a second intermediate arm 54b and
the second rocker arm 22b are attached to a camshaft 52. In the
example of the valve operating apparatus 50 of the present
embodiment, the first cam unit 56a and the second cam unit 56b are
each configured by a single cam. The first intermediate arm 54a and
the second intermediate arm 54b are rockably supported by the
rocker shaft 58.
[0074] The first intermediate arm 54a includes a first pressure
receiving part 60a which is pressed by the first cam unit 56a, and
a first transmission part 62a which transmits the pressing force of
the first cam unit 56a to the first valve 12a side (the first
rocker arm 22a). Similarly, the second intermediate arm 54b
includes a second pressure receiving part 60b which is pressed by
the second cam unit 56b, and a second transmission part 62b which
transmits the pressing force of the second cam unit 56b to the
second valve 12b side (the second rocker arm 22b).
[0075] As shown in FIG. 7, the valve operating apparatus 50 adopts
the disposition B in which the pressure receiving parts 60a and 60b
are provided at the opposite side of the transmission parts 62a and
62b with respect to the rocker shaft 58, seen from the axial
direction of the cylinder. In addition to that, in the intermediate
arms 54 of the present embodiment, offsets concerning the pressure
receiving parts 60 and the transmission parts 62 are set in a
manner as follows (hereinafter, referred to as a "manner A'" for
convenience of explanation). That is, in the manner A' mentioned
here, in the axial direction of the rocker shaft 58, the distance
between the first transmission part 62a and the bearing 26 (the
bearing 26 at the right side in FIG. 7) which is the nearest to the
first transmission part 62a is set to be shorter than the distance
between the first pressure receiving part 60a and the bearing 26
(the same bearing 26 at the right side in FIG. 7) which is the
nearest to the first pressure receiving part 60a. Further, in the
manner A', the distance between the second transmission part 62b
and the bearing 26 (the bearing 26 at a left side in FIG. 7) which
is the nearest to the second transmission part 62b the second
transmission part 62b is set to be shorter than the distance
between the second pressure receiving part 60b and the bearing 26
(the same bearing 26 at the left side in FIG. 7) which is the
nearest to the second pressure receiving part 60b. An effect by
providing offsets in the manner A' like this will be described
below with reference to FIG. 9A and FIG. 9B.
[0076] FIG. 9A and FIG. 9B are views that relate to the second
embodiment of the present disclosure, and are for explaining a
difference in influence of deflection of the rocker shaft due to
difference in the manner of offsets. More specifically, FIG. 9A is
a view of a configuration where offsets in the mariner A' which is
adopted in the present embodiment are provided. FIG. 9B is a view
showing a comparative example which is referred to for the purpose
of being compared with the configuration of the present
embodiment.
[0077] First, when the disposition B is adopted, loads from the
cams and loads from the valves are both act onto the rocker shaft
58 in substantially the same direction as shown in FIG. 8, unlike
the disposition A described in the first embodiment. As a result,
the rocker shaft deflects in such a manner as to be pressed to the
upward direction in FIG. 9A and FIG. 9B, in both configurations in
FIG. 9A and FIG. 9B.
[0078] As described above, in the manner A' of the present
embodiment, the distances between the transmission parts 62a and
62b and the bearings 26 which are the nearest to them are set to be
shorter than the distances between the pressure receiving parts
(cam rollers) 60a and 60b and the bearings 26 which are the nearest
to them. According to the configuration like this, the deflection
amount .delta. of the rocker shaft in each of the positions of the
transmission parts becomes smaller as shown in FIG. 9A, as compared
with the comparative example (FIG. 9B) which adopts the
configuration opposite from this. Accordingly, by the valve
operating apparatus 50 of the present embodiment which adopts the
offsets in the manner A', the harmful effect (more specifically, a
closing failure of the valves 12) due to displacements of the
transmission parts 62a and 62b accompanying the deflection of the
rocker shaft 58 can also be restrained, similarly to the valve
operating apparatus 10 of the first embodiment.
* * * * *