Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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60724-1719
VALVE OPERATING MECHANISM
FOR INTERNAL coMsusTIoN ENGINE
BACKGROUND OF THE INVENTION
The present invention relates to a valve operating
mechanism for an internal combustion engine, including a cam-
shaft rotatable in synchronism with the rotation of the inter-
nal combustion engine and having integral cams for operating an
intake or exhaust valve, and rocker arms or cam followers
angularly movably supported on a rocker shaft for opening and
closing the intake or exhaust valve in response to rotation
of the cams.
Valve operating mechanisms used in internal combus-
tion engines are generally designed to meet requirements for
high-speed operation of the engines. The valve diameter and
valve lift are selected to efficiently introduce an air-fuel
mixture required to produce maximum engine power in a certain
engine speed range.
If an intake valve is actuated at constant valve
timing and valve lift throughout a full engine speed range from
low to high speeds, then the speed of flow of an airfuel mix-
ture into the combustion chamber varies from engine speed to
engine speed since the amount of air-fuel mixture varies from
engine speed to engine speed. At low engine speeds, the speed
of flow of the air-fuel mixture is lowered and the air-fuel
mixture is subject to less turbulence in the combustion cham-
ber, resulting in slow combustion therein. Therefore, the
combustion efficiency is reduced and so is the fuel economy,
and the knocking prevention margin is lowered due to the slow
combustion.
One solution to the above problems is disclosed in
-- 1 --
'' ~ : ~ ` ' - -
.
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60724-171g
Japanese Laid-Open Patent Publication No. 59(1984)-226216.
According to the disclosed arrangement, some of the intake or
exhaust valves remain closed when the engine operates at a low
speed, whereas all of the intake or exhaust valves are
operated, i.e., alternately opened and closed, during high-
speed operation of the engine. Therefore, the valves are
controlled differently in low- and high-speed ranges. However,
if the valve control were effected in different modes in more
speed ranges, the engine output power would be increased and
the fuel economy would be improved. Furthermore, if the intake
or exhaust valve of a particular engine cylinder of a multi-
cylinder internal combustion engine could be kept inoperative
in order to make the particular engine cylinder substantially
inactive, fuel consumption would be reduced by stopping the
operation of the intake or exhaust valve of the particular
engine cylinder while the engine operates in a low-speed range.
However, no satisfactory devices have been available in the
past to achieve such a task.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a
valve operating mechanism for an internal combustion engine,
which controls a valve in low-, medium-,
fj () 7 2 4 - l. 7
and high-speed ranges for increased engine power and fuel
economy~
Anotller ob~ect of the present invention ls to provide
a valve operatincl mechanism for an internal combustion engine,
which is of a relatively simple structure, for making the
intake or exhaus~ valve of a particular engine cylinder
inoperative for better fuel economy.
According to the present invention, there is provided
a valve operating mechanism for operating a single valve of a
particular cylinder of an internal combustion engine,
comprising: a camshaft rotatable in synchronism with rotation
of the internal combustion engine; a plurality of cams on said
camshaft with each of said cams bearing a different cam
profile; a plurality of cam followers, each of which slidably
engages one of said cams for selectively operating the valve
according to the profile of the selected cam and one of which
engages said valve; and means for selectively interconnecting
and disconnecting the respective cam followers to operate the
valve differently in different speed ranges of the internal
combustion engine.
The camshaft has an annular raised portion and low-
and high-speed cams, or low-, medium-, and high-speed cams, or
a single high-speed cam, and the cam followers are held in
sliding contact with these raised portion and cams. The valves
are selectively kept inoperative by the raised portion and
operated in low- and high-speed ranges by the low- and high-
speed cams, or selectively operated in low-, medium-, and high-
speed
~''.
2 ~
60724-1719
ranges by the low-, medium-, and high-speed cams, or selective-
ly kept inoperative by the raised portion and operated in a
high-speed range by the single high-speed cam.
The above and other objects, features and advantages
of the present invention will become more apparent from the
following description when taken in conjunction with the
accompanying drawings in which preferred embodiments of the
present invention are shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l is a vertical cross-sectional view of a valve
operating mechanism according to an embodiment of the present
invention, the view being taken along line I - I of FIG. 2;
FIG. 2 is a plan view of the valve operating mecha-
nism shown in FIG. l; :~
FIG. 3 is a cross-sectional view taken along line
III - III of FIG. 2;
FIG. 4 is a cross-sectional view taken along line IV :
- IV of FIG. l, showing first through third cam followers dis-
connected from each other;
FIG. 5 is a cross-sectional view similar to FIG. 4,
showing the first and second cam followers connected to each
other;
FIG. 6 is a cross-sectional view similar to FIG. 4,
showing the first through third cam followers connected to each
other;
FIG. 7 is a plan view of a valve operating mechanism
according to another embodiment of the present invention;
FIG. 8 is a cross-sectional view similar to FIGS. 4
through 6, showing a mode of operation for actuating the valve
operating mechanism of FIG. 7,
-- 4 --
- . :.
~ 8 60724~1719
FIG. 9 is a plan view of a valve operating mechanism
according to still another embodiment o~ the present inven-
tion;
FIG. 10 is a cross-sectional view taken along line X
- X of FIG. 9;
FIG. 11 is a plan view of a valve operating mechanism
according to a still further embodiment of the present inven-
tion;
FIG. 12 is a plan view of a valve operating mechanism
according to a yet still further embodiment of the present
invention;
FIG. 13 is a cross-sectional view taken along line
XIII - XIII of FIG. 12,
FIG. 14 is a cross-sectional view taken along line
XIV - XIV of FIG. 13, illustrating first and second cam
followers connected to each other; and
FIG. 15 is a cross-sectional view similar to FIG. 14,
showing the first and second cam followers disconnected from
each other.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Like or corresponding parts are denoted by like or
corresponding reference characters throughout several views.
FIGS. 1 and 2 show a valve operating mechanism
according to an embodiment of the present invention. The valve
operating mechanism is incorporated in a particular engine
cylinder of an internal combustion engine including a single
intake valve 1 for introducing an air-fuel-mixture into a
combustion chamber defined in an engine body.
The valve operating mechanism comprises a camshaft 2
rotatable in synchronism with rotation of the engine at a speed
-- 5 --
X
.
~ 60724-1719
ratio of ~ with respect to the speed of rotation of the engine.
The camshaft 2 has an annular raised portion 3, a low-speed cam
4, and a high-speed cam 5 which are integrally disposed on the
circumference of the camshaft 2. The valve operating mechanism
also has a rocker shaft 6 extending parallel to the camshaft 2,
and first through third rocker arms or cam followers 7, 8, 9
angularly movably supported on the rocker shaft 6 and held
against the raised portion 3, the low-speed cam 4, and the
high-speed cam 5, respectively, on the camshaft 2. The intake
valve 1 is selectively operated by the first through third cam
followers 7, 8, 9 actuated by the low- and high-speed cams 4,
5.
The camshaft 2 is rotatably disposed above the engine
body. The raised portion 3 is disposed in a position above the
intake valve 1. The low-speed cam 4 and the high-speed cam 5
are disposed one on each side of the raised portion 3. The
raised portion 3 has a circumferential profile in the shape of
a circle corresponding to the base circles 4b, 5b of the low-
and high-speed cams 4, 5. The low-speed cam 4 has a cam lobe
4a projecting radially outwardly Erom the base circle 4b, and
the high-speed cam 5 has a cam lobe 5a projecting radially
outwardly from the base circle 5b to a greater extent than the
cam lobe 4a, the cam lobe 5a having a larger angular extent
than the cam lobe 4a.
The rocker shaft 6 is fixed below the camshaft 2.
The first cam follower 7 pivotally supported on the rocker
shaft 6 is aligned with the raised portion 3, the second cam
follower 8 pivotally supported on the rocker shaft 6 is aligned
with the low-speed cam 4, and the third cam follower 9 pivotal-
ly supported on the rocker shaft 6 is aligned with the high-
-- 6
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60724-1719
speed cam 5. The cam followers 7, 8, 9 have on their upper
surfaces cam slippers 7a, 8a, 9a, respectively, held in sliding
contact with the raised portion 3 and the cams 4, 5, respecti-
vely. The first cam follower 7 has a distal end positioned
above the intake valve 1. A tappet screw 12 is threaded
through the distal end of the first cam follower 7 and has a
tip engageable with the upper end of the valve stem of the in-
take valve 1.
A flange 14 is attached to the upper end of the
valve stem of the intake valve 1. The intake valve 1 is
normally urged to close the intake port by a compression coil
spring 16 disposed under compression around the valve stem
between the flange 14 and the engine body.
As shown in FIG. 3, a bottomed cylindrical lifter 19
is disposed in abutment against a lower surface of the second
cam follower 8. The lifter 19 is normally urged upwardly by a
compression sprin~ 20 of relatively weak resiliency interposed
between the lifter 19 and the engine body for resiliently bias-
ing the cam slipper 8a of the second cam follower 8 slidably
against the low-speed cam 4.
As illustrated in FIG. 4, the first and second cam
followers 7, 8 have confronting side walls held in sliding
contact with each other. A first selective coupling 21 is
operatively disposed in and between the first and second cam
followers 7, 8 for selectively disconnecting the cam followers
7, 8 from each other for relative displacement and also for
interconnecting the cam followers 7, 8 for their movement in
unison. Likewise, the first and third cam followers 7, 9 have
confronting side walls held in sliding contact with each other.
X
~.2~ 8 60724-1719
A second selective coupling 22 is operatively disposed in and
between the first and third cam followers 7, 9 for selectively
disconnecting the cam followers 7, 9 from each other for
relative displacement and also for interconnecting the cam
followers 7, 9 for their movement in unison.
The first and second selective couplings 21, 22 are
of an identical construction, and hence only the first selec-
~ tive coupling 21 will hereinafter be described in detail.
- The first selective coupling 21 comprises a piston 23
movable between a position in which it interconnects the first
and second cam followers 7, 8 and a position in which it dis-
connects the first and second cam followers 7, 8 from each
other, a circular stopper 24 for limiting the movement of the
piston 23, and a coil spring 25 for urging the stopper 24 to
move the piston 23 toward the position to disconnect the first
and second cam followers 7, 8 from each other.
The first cam follower 7 has a first guide hole 26
opening toward the second cam follower 8 and extending parallel
to the rocker shaft 6. The first cam follower 7 also has a
smaller-diameter hole 28 near the closed end of the Eirst guide
hole 26, with a step or shoulder 27 being defined between the
smaller-diameter hole 28 and the first guide hole 26. The
piston 23 is slidably fitted in the first guide hole 26. The
piston 23 and the closed end of the smaller-diameter hole 28
define therebetween a hydraulic pressure chamber 29.
The first cam follower 7 has a hydraulic passage 30
~ defined therein in communication with the hydraulic pressure
; chamber 29. The rocker shaft 6 has a hydraulic passage 31
defined axially therein and coupled to a source (not shown) of
hydraulic pressure through a suitable hydraulic pressure
-- 8 --
. ~ ,
`
~X~ 8 60724-1719
control mechanism. The hydraulic passages 30, 31 are held in
communication with each other through a hole 32 defined in a
side wall of the rocker shaft 6, irrespective of how the first
cam follower 7 is angularly moved about the rocker shaft 6.
The second cam follower 8 has a second guide hole 35
opening toward the first cam follower 7 in registration with
the first guide hole 26 in the first cam follower 7. The
circular stopper 24 is slidably fitted in the second guide hole
35. The second cam follower 8 also has a smaller-diameter hole
37 near the closed end of the second guide hole 35, with a step
or shoulder 36 defined between the second guide hole 35 and the
smaller-diameter hole 37 for limiting movement of the circular
stopper 24. The second cam follower 8 also has a through hole
38 defined coaxially with the smaller-diameter hole 37. A
guide rod 39 joined integrally and coaxially to the circular
stopper 24 extends through the hole 38. The coil spring 25 is
disposed around the guide rod 39 between the stopper 24 and the
clcsed end of the smaller-diameter hole 37.
The piston 23 has an axial length selec-ted such that
when one end of the piston 23 abuts against the step 27, the
other end thereof is positioned just between and hence lies
flush with the sliding side walls oE the first and second cam
~ollowers 7, 8, and when the piston 23 is moved into the second
guide hole 35 until it displaces the stopper 24 into abutment
against the step 36, said one end of the piston 23 remains in
the first guide hole 26 and hence the piston 23 extends between
the first and second cam followers 7, 8.
The hydraulic passages 31 communicating with the
first and second selective couplings 21, 22 are isolated from
each other by a steel ball 33 forcibly fitted and fixedly
:
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60724-1719
positioned in the rocker shaft ~. Therefore, the first and
second selective couplings 21, 22 are operable under hydraulic
pressure independently of each other.
Operation of the valve operating mechanism will be
described with reference to FIGS. 4 through 6. When the engine
is to operate in an ultralow-speed range, the first and second
selective couplings 21, 22 are actuated to disconnect the first
through third cam followers 7, 8, 9 from each other as
illustrated in FIG. 4. More specifically, the hydraulic
pressure is released by the hydraulic pressure control mecha-
nism from the hydraulic pressure chamber 29, thus allowing the
stopper 24 to move toward the first cam follower 7 under the
resiliency of the spring 25 until the piston 23 abuts against
the step 27. When the piston 23 engages the step 27, the
mutually contacting ends of the piston 23 and the stopper 24 of
the first selective coupling 21 lie flush with the sliding side
walls of the first and second cam followers 7, 8. Likewise,
the mutually contacting ends of the piston 23 and the stopper
24 of the second selective coupling 22 lie flush with the slid-
ing side walls of the first and third cam followers 7, 9.Thus, the first, second, and third cam followers 7, 8, 9 are
held in mutually sliding contact for relative angular move-
ment.
With the first through third cam followers 7, 8, 9
being thus disconnected, the first cam follower 7 is not affec-
ted by the angular movement of the second and third cam
followers 8, 9 in sliding contact with the low- and high-speed
cams 4, 5. The first cam follower 7 does not swing as the
raised portion 3 imposes no camming action thereon. Any
frictional loss of the valve operating mechanism is relatively
-- 10 --
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60724-1719
low because the second cam follower 8 is held in slidiny
contact with the low-speed ca~ 4 under the relatively small
resilient force of the spring 20.
During ultralow-speed operation of the engine, there-
fore, the intake valve 1 remains closed, thus reducing fuel
consumption.
For low-speed operation of the engine, the first and
second cam followers 7, 8 are interconnected by the first
selective coupling 21, with the first and third cam followers
7, 9 remaining disconnected from each other, as shown in FIG.
5. More specifically, the hydraulic pressure chamber 29 of the
first selective coupling 21 is supplied with hydraulic pressure
to cause the piston 23 to push the stopper 24 into the second
guide hole 35 against the resiliency of the spring 25 until the
stopper 24 engages the step 36. The first and second cam
followers 7, 8 are now connected to each other for angular
movement in unison.
Therefore, the intake valve 1 alternately opens and
closes the intake port at the valve timing and valve lift
according to the profile of the low-speed cam 4. The air-fuel
mixture now flows into the combustion chamber at a rate suit-
able for the low-speed operation of the engine, resulting in
good fuel economy and knocking prevention.
When the engine is to operate at a high speed, the
first and third cam followers 7, 9 are interconnected by the
second selective coupling 22, as shown in FIG. 6, by supplying
hydraulic pressure into the hydraulic-pressure chamber 29 of
the second selective coupling 22. At this time, the first and
second cam followers 7, 8 may remain connected by the first
selective coupling 21 or may be disconnected thereby. At any
-- 11 --
1.~R~
60724-1719
rate, the first cam follower 7 is caused to swing with the
third cam followe~ 9. As a consequence, the intake valve l
alternately opens and closes the intake port at the valve tim-
ing and valve lift according to the profile of the high-speed
cam 5. The intake efficiency is increased to enable the engine
to produce higher output power and torque.
FIG. 7 shows another embodiment of the present inven-
tion in which the low-speed cam 4 is disposed between the high-
speed cam 5 and the raised portion 3. The first and second cam
followers 7, 8 are held in sliding contact with the low- and
high-speed cams 4, 5, respectively, whereas the third cam
follower 9 slidingly contacts the raised portion 3, the third
cam follower 9 being engageable with the intake valve 1. In
the ultralow-speed range, the first and second selective coup-
lings 21, 22 are operated as shown in FIG. 4, and hence the cam
followers 7, 8, 9 are independently pivotable, allowing the
intake valve l to remain closed. In the low-speed range, the
first and third cam followers 7, 9 are interconnected and the
first and second cam followers 7, 8 remain di~connected by
operating the first and second selective couplings 21, 22 as
shown in FIG. 8. Therefore, the intake valve l is controlled
according to the cam profile of the low-speed cam 4. In the
high-speed range, the cam followers 7, 8, 9 are interconnected
as shown in FIG. 6 to cause the intake valve l to operate
according to the cam profile of the high-speed cam 5.
FIGS. 9 and lO show still another embodiment of the
present invention. The camshaft 2 supports thereon a low-speed
cam 3',a medium-speed cam 4, and a high-speed cam 5 which have
cam lobes 3a, 4a, 5a, respectively. The cam lobe 5a is larger
in radial projection and angular extent than the cam lobe 4a,
- 12 -
X
~1 2~
60724-1719
which in turn is larger in radial projection and angular extent
than the cam lobe 3a. ~he first cam follower 7, which is
engageable with the intake valve 1, is held in sliding contact
with the low-speed cam 3', while the second and third cam
followers 8, 9 are held in sliding contact with the medium- and
high-speed cams 4, 5. In the low-speed range, the cam
followers 7, 8, 9 are disconnected from each other, as shown in
FIG. 4, and the intake valve 1 is operated according to the cam
profile of the low-speed cam 3 . In the medium-speed range,
the first and second cam followers 7, 8 are interconnected and
the first and third cam followers 7, 9 remain disconnected, as
shown in FIG. 5, causing the intake valve 1 to be operated by
the medium-speed cam 4. In the high-speed range, the cam
followers 7, 8, 9 are interconnected, as shown in FIG. 6, or
only the first and third cam followers 7, 9 are interconnected,
as shown in FIG. 8, for thereby enabling the intake valve 1 to
be controlled by the high-speed cam 5.
According to a still further embodiment illustrated
in FIG. 11, the medium-speed cam 4 is positioned between the
low- and high-speed cams 3',5. The Eirst and second cam
followers 7, 8 are kept in sliding contact with the medium- and
high-speed cams 4, 5. The low-speed cam 3' is slidingly
engaged by the third cam follower 9 which is engageable with
the intake valve 1. During low-speed engine operation, the cam
followers 7, 8, 9 are disconnected, as shown in FIG. 4, and the
intake valve 1 is controlled by the low-speed cam 3'. In the
medium-speed range, the first and third cam followers 7, 9 are
interconnected, and the fi.rst and second cam followers 7, 8
remain disconnected,as shown in FIG. 8, to operate the intake
valve 1 according to the cam profile of the medium- speed cam
~ 60724-1719
4. In the high-speed range, all of the cam followers 7, 8, 9
are interconnected, as shown in FIG. 6, to control the intake
valve 1 according to the cam profile of the high-speed cam 5.
FIGS. 12 and 13 illustrate a valve operating mecha-
nism according to a yet still further embodiment of the present
invention. The camshaft 2 has an annular raised portion 3 and
a cam 5 which are integrally disposed on the circumference of
the camshaft 2. First and second cam followers 7, 8 are angu-
larly movably supported on the rocker shaft 6 and held against
the cam 5 and the raised portion 3 respectively, on the cam-
shaft 2. The intake valve 1 remains closed or inoperative by
the raised portion 3 in a low-speed range of the engine.
The camshaft 2 is rotatably disposed above the engine
body. The raised portion 3 is disposed in a position above the
intake valve 1. The raised portion 3 has a circumferential
profile in the shape of a circle corresponding to the base
circle 5b of the cam 5. The cam 5 has a cam lobe 5a projecting
radially outwardly from the base circle 5b.
The rocker shaft 6 is fixed below the camshaft 2.
The first cam follower 7 pivotally supported on the rocker
shaft 6 is aligned with the cam 5, and the second cam follower
8 pivotally supported on the rocker shaft 6 is aligned with the
raised portion 3. The cam followers 7, 8 have on their upper
surfaces cam slippers 7a, 8a, respectively, held in sliding
contact with the cam 5 and the raised portion 3, respectively.
The second cam follower ~ has a distal end positioned above the
intake valve 1. A tappet screw 12 is threaded through the
distal end of the second cam follower 8 and has a tip engage-
able with the upper end of the valve stem of the intake valve
1.
- 14 -
X
"
~.2R~ 8
60724-1719
A flange 14 is attached to the upper end of the valve
stem of the intake valve 1. The intake valve 1 i5 normally
urged to close the intake port by a compression coil spring 16
disposed under compression around the valve stem between the
flange 14 and the engine body.
A bottomed cylindrical lifter 19 is disposed in abut-
ment against a lower surEace of the first cam follower 7. The
lifter 19 is normally urged upwardly by a compression spring 20
of relatively weak resiliency interposed between the lifter 19
and the engine body for resiliently biasing the cam slipper 7a
of the first cam follower 7 slidably against the cam 5.
~ s illustrated in FIG. 14, the first and second cam
followers 7, 8 have confronting side walls held in sliding
contact with each other. A selective coupling 21 is operative-
ly disposed in and between the first and second cam followers
7, 8 for selectively disconnecting the cam followers 7, 8 from
each other for relative displacement and also for interconnect-
ing the cam followers 7, 8 for their movement in unison.
The selective coupling 21 comprises a piston 23 mov-
able between a position in which it interconnects the first andsecond cam followers 7, 8 and a position in which it discon-
nects the first and second cam followers 7, 8 from each other,
a circular stopper 24 for limiting the movement of the piston
23, and a coil spring 25 for urging the stopper 24 to move the
piston 23 toward the position to disconnect the first and
second cam followers 7, 8 from each other.
The second cam follower 8 has a first guide hole 26
opening toward the first cam follower 7 and extending parallel
to the rocker shaft 6. The second cam follower 8 also has a
smaller-diameter hole 28 near the closed end of the first guide
~ - 15 -
3.~
60724-1719
hole 26, with a step or shoulder 27 being defined between the
smaller-diameter hole 28 and the first guide hole 26. The
piston 23 is slidably fitted in the first guide hole 26. The
piston 23 and the closed end of the smaller-diameter hole 28
define therebetween a hydraulic pressure chamber 29.
The second cam follower 8 has a hydraulic passage 30
defined therein in communication with the hydraulic pressure
cham~er 29. The rocker shaft 6 has a hydraulic passage 31
defined axially therein and coupled to a source (not shown) of
hydraulic pressu.re through a suitable hydraulic pressure
control mechanism. The hydra~lic passages 30, 31 are held in
communication with each other through a hole 32 defined in a
side wall of the rocker shaft 6, irrespective of how the second
cam follower 8 is angularly moved about the rocker shaft 6.
The first cam follower 7 has a second guide hole 35
opening toward the second cam follower 8 in registration with
the first guide hole 26 in the second cam follower 8. The
circular stopper 24 is slidably fitted in the second guide hole
35. The first cam follower 7 also has a smaller-diameter hole
37 near the closed end of the second guide hole 35, with a step
or shoulder 36 defined between the second guide hole 35 and the
smaller-diameter hole 37 for limiting movement of the circular
stopper 24. The first cam follower 7 also has a through hole
38 defined coaxially with the smaller-diameter hole 37. A
guide rod 39 joined integrally and coaxially to the circular
stopper 24 extends through the hole 38. The coil spring 25 is
disposed around the guide rod 39 between the stopper 24 and the
closed end of the smaller-diameter hole 37.
The piston 23 has an axial length selected such that
when one end of the piston 23 abuts against the step 27, the
- 16 -
6072~-1719
other end thereof i9 positioned just between and hence lies
flush with the sliding side walls of the first and second cam
followers 7, 8, and when the piston 23 is moved into the second
guide hole 35 until it displaces the stopper 24 into abutment
against the step 36, said one end of the piston 23 remains in
the first guide hole 26 and hence the piston 23 extends between
the first and second cam followers 7, 8. The piston 23 is
normally urged toward the first cam follower 7 under the resi-
liency of a coil spring 33 disposed in the hydraulic pressure
chamber 29 and acting between the piston 23 and the closed
bottom of the smaller-diameter hole 28. The resilient force of
the spring 33 set under compression in the hydraulic pressure
chamber 29 is selected to be smaller than that of the spring 25
set in place under compression.
- 17 -
~1.2f~
60724-1719
~ peration of the valve operating mechanism will be
described Wit}l reference to FIGS. 14 and 15. When the engine
is to operate in a low-speed range, the selective coupling 21
is actuated to disconnect the first and second cam follower 7,
8 from each other as illustrated in FIG. 15. More specifical-
ly, the hydraulic pressure is released by the hydraulic
pressure control mechanism from the hydraulic pressure chamber
29, thus allowing the stopper 24 to move toward the second cam
follower 8 under the resiliency of the spring 25 until the
piston 23 abuts against the step 27. When the piston 23
engages the step 27, the mutually contacting ends of the piston
23 and the stopper 24 lie flush with the sliding side walls of
the first and second cam followers 7, ~. Therefore, the first
and second cam followers 7, 8 are held in mutually sliding
contact for relative angular movement.
- 18 -
60724-171g
With the first and second cam followers 7, 8 being
thus disconnected, the first cam follower 7 is angularly moved
in sliding contact with the cam 5, whereas the second cam
follower 8 is held in sliding contact with the raised portion
3. Since the raised portion 3 does not impose any camming
action on the second cam follower 8, the intake valve 1
remains closed. The swinging movement oE the first cam
follower 7 which is caused by the cam 5 does not affect the
intake valve 1 as the first cam follower 7 is disconnected from
the second cam follower 8 at this time. Any frictional loss of
the valve operating mechanism is relatively low because the
first cam follower 7 is he].d in sliding contact with the cam 5
under the relatively small resilient force of the spring 20.
During low-speed operation of the engine, therefore,
the intake valve 1 remains closed or inoperative for reducing
fuel consumption.
-- 19 --
X
~.2~
60724-1719
For high-speed operation of the engine, the first and
second cam followers 7, 8 are interconnected by the selective
coupling 21, as shown in FIG. 14. More specifically, the
hydraulic pressure chamber 29 of the selective coupling 21 is
supplied with hydraulic pressure to cause the piston 23 to push
the stopper 24 into the second guide hole 35 again~t the resi-
liency of the spring 25 until the stopper 24 engages the step
36. The first and second cam followers 7, 8 are now connected
to each other for angular movement in unison.
At this time, the second cam follower 8 is caused to
swing with the first cam follower 7. Therefore, the intake
valve 1 alternately opens and closes the respective intake
ports at the valve timing and valve lift according to the pro-
- 20 -
X
~.2~ 8
60724-1719
file of the cam 5.
While the intake valve 1 is shown as being operated
by each of the valve operating mechanisms, an exhaust valve may
also be operated by the valve operating mechanisms according to
the present invention. In such a case, unburned components due
to exhaust gas turbulence can be reduced in low-speed operation
of the engine, whereas high engine output power and torque can
be generated by reducing resistance to the flow of an exhaust
gas from the co~bustion chamber in high-speed operation of the
engine.
~ - 21 -
~.2f~
60724-1719
Although certain preferred embodiments have been
shown and described, it should be understood that many changes
and modifications may be made therein without departing from
the scope of the appended claims.
. - 22 -
