U.S. patent application number 09/927618 was filed with the patent office on 2002-02-21 for valve drive mechanism for engine.
Invention is credited to Asanomi, Kouji, Harada, Setsuo, Matsuura, Hirokazu, Oda, Hiroyuki, Saiki, Masayuki.
Application Number | 20020020380 09/927618 |
Document ID | / |
Family ID | 18735619 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020020380 |
Kind Code |
A1 |
Harada, Setsuo ; et
al. |
February 21, 2002 |
Valve drive mechanism for engine
Abstract
A valve drive mechanism includes a generally cylindrically
shaped tappet assembly (24) comprising a center tappet (41 ) and a
side tappet (42). The center tappet (41 ) has a circular-arcuate
side walls (41c) formed with vertical side shrouds (41d) at
opposite sides of each side wall (41c) which overlap and slide
contact with opposite end guide walls (42h) of the side tappet
(42), respectively. When the tappet assembly (24) is in an unlocked
state so as to transmit rotation of the side cams (25, 27), the
vertical side shroud (41d) of the center tappet (41 ) slide on the
vertical side walls (42h) of the side tappet 42 so as thereby to
guide slide movement of the center tappet (41 ) relative to the
side tappet (42).
Inventors: |
Harada, Setsuo; (Hiroshima,
JP) ; Oda, Hiroyuki; (Hiroshima, JP) ;
Matsuura, Hirokazu; (Hiroshima, JP) ; Asanomi,
Kouji; (Hiroshima, JP) ; Saiki, Masayuki;
(Hiroshima, JP) |
Correspondence
Address: |
RALPH E. SMITH
Brooks & Kushman P.C.
22nd Floor
1000 Town Center
Southfield
MI
48075-1351
US
|
Family ID: |
18735619 |
Appl. No.: |
09/927618 |
Filed: |
August 10, 2001 |
Current U.S.
Class: |
123/90.48 ;
123/90.27; 123/90.53; 123/90.55 |
Current CPC
Class: |
F01L 1/14 20130101; F01L
13/0036 20130101; F01L 1/024 20130101; F01L 2001/0537 20130101;
F02B 2275/18 20130101 |
Class at
Publication: |
123/90.48 ;
123/90.27; 123/90.53; 123/90.55 |
International
Class: |
F01L 001/02; F01L
001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 11, 2000 |
JP |
2000-245022 |
Claims
What is claimed is:
1. A valve drive mechanism having one center cam (26) having a
center cam lobe and a pair of side cams (25, 27) having side cam
lobes different from said center cam lobe for one valve (39, 40),
said side cams (25, 27) being arranged on a camshaft (15, 16) on
opposite sides of said center cam (26) in an axial direction of
said camshaft (15, 16), a generally cylindrically shaped tappet
assembly (24), which is movable in a direction of valve lift,
comprising two mating parts, and locking/unlocking means (41e, 42e,
43-46) for mechanically coupling and uncoupling said two mating
parts together so as to selectively transmit rotation of said
center cam (26) and said side cams (25, 27) as reciprocating
movement to said valve (39, 40), said valve drive mechanism
comprising: a center tappet (41) forming one of said two mating
parts (41, 42) and driven by said center cam (26); said center
tappet (41) being formed with opposite circular-arcuate vertical
side walls (41c) in a rotational direction of said camshaft (15,
16); a side tappet (42) forming another one of said two mating
parts and driven by said side cams (25, 27), said side tappet (42)
being divided into two side tappet parts in said axial direction of
said camshaft (15, 16) between which said center tappet (41) is
received for slide movement relative to said side tappet (42) in
said direction of valve lift, said side tappet (42) at said side
tappet parts being formed with opposite circular-arcuate vertical
end walls (42c), respectively, such that said circular-arcuate
vertical side walls (41c) of said center tappet (41) and said
circular-arcuate vertical end walls (42c) of said side tappet (42)
form a generally cylindrical configuration of said tappet assembly
(24); and guide means for guiding said slide movement of said
center tappet (41) relative to said side tappet (42), said guide
means comprising a vertical flat side wall (42h) extending
continuously from each of opposite sides of each said
circular-arcuate end wall (42c) of said side tappet (42) in said
rotational direction of said camshaft (15, 16) and a vertical
shroud (41d) extending continuously from each of opposite ends of
each said circular-arcuate side wall (41c) of said center tappet
(41) in said axial direction of said camshaft (15, 16) and forming
thereon a vertical flat side surface (41f), said vertical shroud
(41d) at said vertical flat side surface (41f) being slidable on
said vertical flat side wall (42h) so as thereby to guide said
slide movement of said center tappet (41) relative to said side
tappet (42).
2. A valve drive mechanism as defined in claim 1, wherein said
center cam has a high lift cam lobe and each said side cam has a
low lift cam lobe.
3. A valve drive mechanism as defined in claim 1, wherein said two
side tappet parts are joined by a connecting bridge at which said
tappet assembly is engaged by a valve stem of said valve, said
connecting bridge being formed with a spring receiving recess in
which a return spring is received so as to force said center tappet
to return when said center tappet slides relatively to said side
tappet.
4. A valve drive mechanism as defined in claim 3, wherein said
connecting bridge has an oil spill port formed in a bottom of said
spring receiving recess.
5. A valve drive mechanism as defined in claim 3, and further
comprising a shim disposed between said connecting bridge and said
valve stem.
6. A valve drive mechanism as defined in claim 3, wherein said
vertical guide shroud extends along almost the entire vertical
length of said center tappet.
7. A valve drive mechanism as defined in claim 3, wherein said
locking/unlocking means comprises guide bores formed in each said
center tappet and each said side tappet part of said side tappet
and being in alignment with one another in said direction of said
rotational axis of camshaft, a locking/unlocking pin received for
slide movement in said guide bore of said center tappet, a plunger
received for slide movement in said guide bore of one of said two
side tappet parts of said side tappet, a spring loaded receiver
received for slide movement in said guide bore of another of said
two side tappet parts of said side tappet, and an oil channel
formed in said one side tappet part of said side tappet so as to
communicate with said guide bore of said one of said two side
tappet parts of said side tappet, through which hydraulic oil is
intpinuced into and removed from said guide bore of said one of
said two side tappet parts of said side tappet.
8. A valve drive mechanism as defined in claim 7, and further
comprising means for supplying said hydraulic oil into said guide
bore of said one of said two side tappet parts through said oil
channel so as to force said plunger and said locking/unlocking pin
to slide against said spring loaded receiver and to partly enter
said guide bores of said center tappet and said other side tappet
part of said side tappet, respectively, thereby mechanically
coupling said center tappet to said side tappet together and for
removing said hydraulic oil from said guide bore of said one of
said two side tappet parts through said oil channel so as to cause
said plunger and said locking/unlocking pin to slide back by said
spring loaded receiver, thereby mechanically uncoupling said center
tappet from said side tappet.
9. A valve drive mechanism as defined in claim 7, wherein said
locking/unlocking pin is formed with a circumferential recess.
10. A valve drive mechanism as defined in claim 1, an further
comprising an oil gallery extending along each of an intake
camshaft and an exhaust camshaft, a branch oil channel branching
off from said oil gallery and extending between two said tappet
assemblies for each twins of twin intake valves and twin exhaust
valves per cylinder, an oil channel formed in an outer wall of said
side tappet and being in communication with said branch oil
channel, and a plunger as a part of said locking/unlocking means
incorporated within said tappet assembly, wherein said plunger
operates to bring said center tappet and said side tappet into a
locked condition when pressure of hydraulic oil is supplied to said
plunger from said oil gallery through said oil channel via said
branch oil channel and into an unlocked condition when pressure of
said hydraulic oil is removed from said plunger.
11. A valve drive mechanism as defined in claim 10, wherein branch
oil channel extends such as to partly overlap outer peripheries of
said each twins of said tappet assemblies and said oil channel has
a length sufficient to remain communicated with said branch oil
channel during up and down movement of said tappet assembly.
12. A valve drive mechanism as defined in claim 11, wherein said
branch oil channel is formed by drilling a cylinder head to said
oil gallery from one side of said cylinder head and plugged at said
one side of said cylinder head.
13. A valve drive mechanism as defined in claim 11, wherein said
side tappet of said tappet assembly is formed with a guide bore in
which said plunger is received for slide movement, said guide bore
being provided with a stopper operative to limit said slide
movement of said plunger in said guide bore and to close said guide
bore at one end and being in communication with said oil channel
through a connecting oil channel.
14. A valve drive mechanism as defined in claim 11, and further
comprising a member operative to prevent said tappet assembly from
turning relative to said cylinder head, said member being provided
on an outer wall of said side tappet at one of opposite sides of
said tappet assembly remote from said branch oil chamber.
15. A valve drive mechanism as defined in claim 3, and further
comprising retaining means provided between said center tappet and
said side tappet for preventing said center tappet from moving up
beyond a top of said side tappet by said return spring and however
for allowing down movement of said center tappet with respect to
said side tappet against said return spring.
16. A valve drive mechanism as defined in claim 15, wherein said
retaining means comprises a retaining pin extending between said
center tappet and said side tappet, a supporting bore in which said
retaining pin is removably received and a limiting recess
engageable with said retaining pin which limits said down movement
of said center tappet, said supporting bore being formed in either
one of said center tappet and said side tappet and said limiting
recess being formed in another one of said center tappet and said
side tappet.
17. A valve drive mechanism as defined in claim 3, an further
comprising an oil gallery extending along each of an intake
camshaft and an exhaust camshaft, a branch oil channel branching
off from said oil gallery and extending between twins of said
tappet assemblies for each twins of twin intake valves and twin
exhaust valves per cylinder, an oil channel formed in said side
tappet and being in communication with said branch oil channel, and
a plunger as a part of said locking/unlocking means incorporated
within said tappet assembly, wherein said plunger operates to bring
said center tappet and said side tappet into a locked condition
when pressure of hydraulic oil is supplied to said plunger from
said oil gallery through said oil channel via said branch oil
channel and into an unlocked condition when pressure of said
hydraulic oil is removed from said plunger.
18. A valve drive mechanism as defined in claim 17, wherein branch
oil channel extends such as to partly overlap outer peripheries of
said each twins of said tappet assemblies and said oil channel has
a length sufficient to remain communicated with said branch oil
channel during up and down movement of said tappet assembly.
19. A valve drive mechanism as defined in claim 18, wherein said
branch oil channel is formed by drilling a cylinder head to said
oil gallery from one side of said cylinder head and plugged at said
one side of said cylinder head.
20. A valve drive mechanism as defined in claim 19, wherein said
side tappet of said tappet assembly is formed with a guide bore in
which said plunger is received for slide movement, said guide bore
being provided with a stopper operative to limit said slide
movement of said plunger in said guide bore and to close said guide
bore at one end and being in communication with said oil channel
through a connecting oil channel.
21. A valve drive mechanism as defined in claim 19, and further
comprising a member operative to prevent said tappet assembly from
turning relative to said cylinder head, said member being provided
on an outer wall of said side tappet at one of opposite sides of
said tappet assembly remote from said branch oil chamber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a valve drive mechanism for
an engine which is variable in valve lift and has a valve lifter or
tappet which selectively transmits rotation of different cams of
different lift cams.
[0003] 2. Description of Related Art
[0004] There has been known various valve drive mechanisms which
can drive valves with variable valve lifts. For example in U.S.
Pat. No. 5,287,830 a valve drive mechanism has a center tappet and
a side tappet arranged coaxially with each other and couples them
together by a hydraulically operated locking/unlocking pin for high
speed engine operation with a high lift cam and uncoupled from one
another by the hydraulically operated locking/unlocking pin for low
speed engine operation with low lift cams. In Japanese Unexamined
Patent Publication No. 10-141030 a cylindrically shaped tappet is
divided into three parts in a rotational direction of cams.
Further, in Japanese Unexamined Patent Publication No. 7-71213 a
shim is divided into three parts.
[0005] The tappet disclosed in U.S. Pat. No. 5,287,830 comprises a
cylindrical center tappet and a side tappet which coaxially
surrounds the cylindrical center tappet. This cylindrical
configuration of the tappet has restraints on the length of the
center tappet as a cam follower. In order to avoid such a
restraint, it is proposed to incorporate a center tappet having an
elongated top. However, this alternative center tappet increases
the height of the tappet. The tappet disclosed in Japanese
Unexamined Patent Publication No. 10-141030 or Japanese Unexamined
Patent Publication No. 7-71213 has the drawback that, since a
circumferential outer wall at an edge of an interface of the side
tappet with the center tappet causes contact slide on a wall of a
tappet guide bore formed in a cylinder head in other words, since
the center tappet is not subjected to a force by the cam, while the
side tappet is driven by side cams, there occurs a rise in pressure
between the side tappet and tappet guide bore, which results in
uneven abrasion of the tappet and tappet guide.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the present invention to
provide a valve drive mechanism which enables a large cam follower
length of a tappet and lowers a force that is caused due to an
inclination of the tappet and is exerted on a tappet guide from the
tappet.
[0007] The above object of the present invention is accomplished by
a valve drive mechanism including one center cam which has a center
cam lobe per valve and a pair of side cams which have side cam
lobes, respectively, different from the center cam lobe per valve
and are arranged on a camshaft on opposite sides of the center cam
in an axial direction of the camshaft, a generally cylindrically
shaped tappet assembly which is movable in a direction of valve
lift and comprises two mating parts, and locking/unlocking means
for mechanically coupling the two mating parts together and
uncoupling the two mating parts from each other so as to
selectively transmit rotation of the center cam and the side cams
as reciprocating movement to the valve. The valve drive mechanism
comprises a center tappet, forming one of the two mating parts and
driven by the center cam; which is formed with opposite
circular-arcuate vertical side walls in a rotational direction of
the camshaft, a side tappet, forming another one of the two mating
parts and driven by the side cams, which is divided into two side
tappet parts in the axial direction of the camshaft between which
the center tappet is received for slide movement relative to the
side tappet in said direction of valve lift and is formed at the
side tappet parts with opposite circular-arcuate vertical end
walls, respectively, such that the circular-arcuate vertical side
walls of the center tappet and the circular-arcuate vertical end
walls of the side tappet form a generally cylindrical configuration
of the tappet assembly, and guide means for guiding the slide
movement of the center tappet relative to the side tappet which
comprises a vertical flat side wall extending continuously from
each of opposite sides of each circular-arcuate end wall of the
side tappet in the rotational direction of the camshaft and a
vertical shroud extending continuously from each of opposite ends
of each circular-arcuate side wall of the center tappet in the
axial direction of the camshaft and forming thereon a vertical flat
side surface. The vertical shroud at the vertical flat side surface
is slidable on the vertical flat side wall so as thereby to guide
the slide movement of the center tappet relative to the side
tappet.
[0008] In the valve drive mechanism which preferably includes the
center cam having a high lift cam lobe and the side cam having a
low lift cam lobe, the two side tappet parts are joined by a
connecting bridge at which the tappet assembly is engaged by a
valve stem of the valve. This connecting bridge is formed with a
spring receiving recess in which a return spring is received so as
to force the center tappet to return when the center tappet slides
relatively to the side tappet. Further, the connecting bridge may
be provided with at least one oil spill port formed at a bottom of
the spring receiving recess. A shim may be disposed between the
connecting bridge and the valve stem.
[0009] The locking/unlocking means may preferably comprise guide
bores which are formed in each the center tappet and each the side
tappet part of the side tappet and are in alignment with one
another in the direction of the rotational axis of camshaft, a
locking/unlocking pin received for slide movement in the guide bore
of the center tappet, a plunger received for slide movement in the
guide bore of one of the two side tappet parts of the side tappet,
a spring loaded receiver received for slide movement in the guide
bore of another of the two side tappet parts of the side tappet,
and an oil channel formed in the one side tappet part of the side
tappet so as to communicate with the guide bore of the one of the
two side tappet parts of the side tappet, through which hydraulic
oil is introduced into and removed from the guide bore of the one
side tappet part of the side tappet. The hydraulic oil is supplied
into the guide bore of the one side tappet part of the side tappet
through the oil channel so as to force the plunger and the
locking/unlocking pin to slide against the spring loaded receiver
and to partly enter the guide bores of the center tappet and the
other side tappet part of the side tappet, respectively, thereby
mechanically coupling the center tappet to the side tappet together
and is removed from the guide bore of the one side tappet part of
the side tappet through the oil channel so as to cause the plunger
and the locking/unlocking pin to slide back by the spring loaded
receiver, thereby mechanically uncoupling the center tappet from
the side tappet. The locking/unlocking pin is preferably formed
with a circumferential recess.
[0010] The tappet assembly may includes a stopper in the guide bore
in which the plunger is received so as to limit the slide movement
of the plunger in the guide bore and to close the guide bore at one
end. In this case, the guide bore is communicated with the oil
channel through a connecting oil channel.
[0011] The valve drive mechanism includes oil supply means
comprising oil galleries which extend along the intake camshaft and
the exhaust camshaft, respectively, branch oil channels which
branch off from the oil galleries, respectively and extend between
two tappet assemblies for twin intake valves and two tappet
assemblies for twin exhaust valves for each cylinder, oil channels
each of which is formed in an outer wall of the side tappet and is
in communication with the branch oil channel. The plunger in the
guide bore of the one side tappet part of the side tappet operates
to bring the center tappet and the side tappet into a locked or
mechanically coupled condition when pressure of hydraulic oil is
supplied to the plunger from the oil gallery through the oil
channel via the branch oil channel and into an unlocked or
mechanically uncoupled condition when the pressure of hydraulic oil
is removed from the plunger.
[0012] The branch oil channel preferably extends such as to partly
overlap outer peripheries of the two tappet assemblies for the twin
intake valves or the twin exhaust valves, and the oil channel has a
length sufficient to remain communicated with the branch oil
channel during up and down movement of the tappet assembly.
[0013] The branch oil channel may be formed by drilling a cylinder
head to the oil gallery from one side of the cylinder head and
plugged at the one side of the cylinder head.
[0014] The valve drive mechanism may further comprise a member
operative to prevent the tappet assembly from turning relative to
the cylinder head during installing the tappet assembly in the
valve drive mechanism. The member is provided on an outer wall of
the side tappet at one of opposite sides of the tappet assembly
remote from the branch oil chamber.
[0015] The valve drive mechanism may further comprises retaining
means provided between the center tappet and the side tappet for
preventing the center tappet from moving up beyond a top of the
side tappet by the return spring and however for allowing down
movement of the center tappet with respect to the side tappet
against the return spring. Specifically, the retaining means
comprises a retaining pin extending between the center tappet and
the side tappet, a supporting bore in which the retaining pin is
removably received and a limiting recess engageable with the
retaining pin which limits the down movement of the center tappet,
the supporting bore being formed in either one of the center tappet
and the side tappet and the limiting recess being formed in another
one of the center tappet and the side tappet.
[0016] According to the valve drive mechanism, the tappet assembly
has the vertical shroud which extends, preferably along almost the
entire vertical length of the center tappet, continuously from each
of opposite sides of each circular-arcuate vertical side wall of
the center tappet in the axial direction of the camshaft, slide
movement of the center tappet relative to the side tappet is guided
by the vertical shrouds sliding on the vertical flat side wall of
the side tappet, respectively. This structure of the tappet
assembly enables a large cam follower length of the tappet
assembly. In addition, the tappet assembly thus structured
disperses a force, which presses the side tappet against the guide
wall of the tappet guide, toward the center tappet through the
vertical shrouds while the side tappet is driven by the side cams,
so that the side tappet slides on the tappet guide through the
outer wall of the center tappet that is perpendicular to a
direction in which the force presses the side tappet against the
wall of the tappet guide. As a result, there is no concentration of
pressing force that occurs at circumferential outer edges of an
interface with the center tappet in the conventional valve drive
mechanisms. In addition, the force that is caused due to an
inclination of the tappet and is exerted on the tappet guide from
the tappet is lowered.
[0017] The valve drive mechanism has the cam arrangement in which
the high lift center cam is disposed between the low lift side cams
enables a large cam follower length of the tappet assembly. This
cam arrangement is quite advantageous to high lift operation. In
addition to the cam arrangement, the valve drive mechanism has the
side tappet structure in which the two side tappet parts are joined
by the connecting bridge engageable with the valve stem and the
return spring is received in the recess formed in the connecting
bridge so as to force the center tappet to return. This side tappet
arrangement keeps the center tappet ridden on the center cam while
the center tappet is uncoupled from the side tappet. This prevents
an occurrence of rattling noises due to repeated collisions of the
center tappet with the center cam during floating action of the
center tappet and, in addition, provides the tappet assembly with
compactness.
[0018] The locking/unlocking means that comprise guide bores formed
in the center tappet and the side tappet, a locking/unlocking pin
received for slide movement in the guide bore of the center tappet,
a plunger received for slide movement in the guide bore of one of
the two side tappet parts, a spring loaded receiver received for
slide movement in the guide bore of another one of the two side
tappet parts, and an oil channel formed in the one side tappet part
so as to communicate with the guide bore of the one side tappet
part through which hydraulic oil is introduced into and removed
from the guide bore of the one side tappet part. This
locking/unlocking means operates such that, when hydraulic oil is
supplied into the guide bore of the one side tappet part through
the oil channel, the locking/unlocking means forces the plunger and
the locking/unlocking pin to slide against the spring loaded
receiver and to partly enter the guide bores of the center tappet
and the other side tappet part, respectively, thereby mechanically
coupling the center tappet to the side tappet together and, when
the hydraulic oil is removed from the guide bore of the one side
tappet part through the oil channel, the locking/unlocking means
causes the plunger and the locking/unlocking pin to slide back by
the spring loaded receiver, thereby mechanically uncoupling the
center tappet from the side tappet. This hydraulically operated
mechanism of the locking/unlocking means can couple the center
tappet to the side tappet together in a state where the engine
operates at a high speed and, in consequence, a high hydraulic
pressure is provided assuredly. This prevents an occurrence of
unstable mechanical coupling of the center tappet to the side
tappet due to an insufficient hydraulic pressure.
[0019] The locking/unlocking pin formed with a circumferential
recess decreases an area of contact surface with the guide bore, so
as to lower frictional resistance between the locking/unlocking pin
and the guide bore.
[0020] The valve drive mechanism includes the oil channel
arrangement for the tappet assembly which comprises the oil
galleries extending along the intake camshaft and the exhaust
camshaft, respectively, branch oil channels branching off from the
oil galleries, respectively and extending between the two adjacent
tappet assemblies for the twin intake valves and the two adjacent
tappet assemblies for the twin exhaust valves for each cylinder,
oil channels each of which is formed in an outer wall of the side
tappet and is in communication with the branch oil channel.
Further, in the oil channel arrangement, the branch oil channel
extends such as to partly overlap outer peripheries of the two
tappet assemblies for the twin intake valves or the twin exhaust
valves, and the oil channel has a length sufficient to remain
communicated with the branch oil channel during up and down
movement of the tappet assembly. The oil channel arrangement has
one branch oil channel used commonly to both the two adjacent
tappet assemblies. This avoids drilling the branch oil channel per
the tappet guide, which leads to a reduction in man-hour for
forming the branch oil channel. In addition, the oil channel
arrangement is easily formed.
BRIEF DESCRIPTION OF DRAWINGS
[0021] The foregoing and other objects and features of the present
invention will become more apparent from the following description
in connection with the preferred embodiments thereof when
considering0 in conjunction with the accompanying drawings, in
which the same reference numerals have been used to denote same or
similar parts throughout the accompanying drawings, and
wherein:
[0022] FIG. 1 is an end view of an engine equipped with a valve
drive mechanism in accordance with n embodiment of the present
invention;
[0023] FIG. 2 is a top view of the engine with a cylinder head
cover removed;
[0024] FIG. 3 is a cross-sectional view of the engine taken along
line III-III of FIG. 2;
[0025] FIG. 4 is a cross-sectional view of the engine taken along
line IV-IV of FIG. 2;
[0026] FIG. 5 is a cross-sectional view of the engine taken along
line V-V of FIG. 2;
[0027] FIG. 6 is a perspective view of a center tappet;
[0028] FIG. 7 is a perspective view of a side tappet;
[0029] FIG. 8 is a plane cross-sectional view of a tappet
assembly;
[0030] FIG. 9 is cross-sectional view of the tappet assembly;
[0031] FIG. 10 is a cross-sectional view of an essential part of a
cylinder head with the tappet assembly installed thereto;
[0032] FIG. 11 is a plan view partly showing the cylinder head;
[0033] FIG. 12 is an end view of the tappet assembly;
[0034] FIG. 13 is a plane cross-sectional view of the tappet
assembly taken along line XIII-XIII of FIG. 12;
[0035] FIG. 14 is an end view of the center tappet;
[0036] FIG. 15 is a cross-sectional view of the side tappet taken
along line XV-XV of FIG. 8; and
[0037] FIG. 16 is a plane cross-sectional view of an variant of the
tappet assembly shown in FIG. 8.
DETAILED DESCRIPTION OF THE INVENTION
[0038] In the following description the terms "front end" and "rear
end" shall mean and refer to front and rear ends of an engine,
respectively, as viewed in a direction in which a row of cylinders
is arranged, and the terms "front side" and "rear side" of the
engine shall mean and refer to the front and rear sides,
respectively, as viewed in a lengthwise direction of a vehicle
body.
[0039] Referring to the drawings in detail, and in particular to
FIG. 1 which shows an internal combustion engine 1 equipped with a
valve drive mechanism according to the present invention, the
engine 1 is of an in-line four cylinder type that has double
overhead camshafts. The engine 1, which is mounted in an engine
compartment so that the camshafts extend in a transverse direction
of the engine compartment, has an engine body comprising a cylinder
block 11, a cylinder head 12 and a head cover 13. A crankshaft 14
is disposed at the bottom of the cylinder block 14 and axially
extends beyond a front end of the cylinder block 11. Camshafts,
namely an intake camshaft 15 and an exhaust camshaft 16 are
disposed over the cylinder head 12 and axially extend beyond the
front end of the cylinder head 12. The crankshaft 14 is provided
with a crankshaft pulley 17 secure to one end thereof. The intake
camshaft 15 is provided with a camshaft pulley 18 secure to one end
thereof extending beyond the front end of the cylinder head 12.
Similarly, the exhaust camshaft 16 is provided with a camshaft
pulley 19 secure to one end thereof extending beyond the front end
of the cylinder head 12. The cylinder block 11 is provided with a
tension pulley 20 and an idle pulley 21 pivotally mounted to the
front end thereof. The intake camshaft 15 and the exhaust camshaft
16 are turned by a timing belt 22. The tension pulley 20 is
adjustable in position so as to apply desired tension to the timing
belt 22. The camshafts 15 and 16 turn one-half crankshaft
speed.
[0040] Referring to FIGS. 2 to 5 which show a top of the cylinder
head 12, a vertical cross-section of the cylinder head 12 as viewed
along line III-III of FIG. 2, a vertical cross-section of the
cylinder head 12 as viewed along line IV-IV of FIG. 2, and a
vertical cross-section of the cylinder head 12 as viewed along line
V-V of FIG. 2, respectively, the camshafts 15 and 16 extend in
parallel with each other in the transverse direction. There is one
spark plug 23 on the cylinder head 12 for each cylinder A in the
engine 1. The engine 1 has four valves, namely two intake valves 39
and two exhaust valves 40, per cylinder A. These valves 39 and 40
are driven at appropriate timings by the camshafts 15 and 16 to
open and close intake ports 34 and exhaust ports 35, respectively.
The valve train includes a valve lifter or tappet assembly 24
installed between a cam lobe of the camshaft 15, 16 and a valve
stem 81 of the valve 39, 40. The lower end of the tappet assembly
24 is in contact with the cam lobe and slid up and down when the
camshaft 15, 16 turns.
[0041] The intake camshaft 15 has two low lift side cams 25 and 27
and one high lift center cam 26 for each intake valve 39.
Similarly, the exhaust camshaft 16 has two low lift side cams 25
and 27 and one high lift center cam 26 for each exhaust valve 40.
The low lift side cams 25 and 27 have the same shape of lobes. The
high lift center cam 26 has a lobe different in shape from those of
the low lift side cams 25 and 27 and is interposed between the low
lift side cams 25 and 27. The cam lobe of high lift center cam 26
is in contact with a center portion of the tappet assembly 24
(which is hereafter referred to as a center tappet 41 and will be
described in detail later) The cam lobes of low lift side cams 25
and 27 are in contact with side portions of the tappet assembly 24
(which are hereafter referred to as a side tappet 42 and will be
described in detail later) at opposite sides of the center portion.
The low lift side cam 25, 27 has a smaller lobe lower than that of
the high lift center cam 26.
[0042] The cylinder head 12 comprises a base portion 30 and front
side, rear end and rear side shrouds 31, 32 and 33 extending
vertically from the front side, rear end and rear side peripheries
of the base portion 30. The front side, rear end and rear side
shrouds 31, 32 and 33 are formed as a continuous wall. The engine 1
has a front cover 28 that covers front ends of the cylinder block
11, the cylinder head 12 and the head cover 13 so as to protect a
camshaft drive mechanism including the crankshaft pulley 17 the
camshaft pulleys 18 and 19, the tension pulley 20, the idle pulley
21 and the timing belt 22. The cylinder head 12 is formed with an
upper portion of combustion chamber B, the intake ports 34, the
exhaust ports 35 and a plug hole 36 per cylinder A all of which are
bored in the cylinder head base portion 30. The cylinder head 12 at
opposite sides is provided with an intake manifold 37 and an
exhaust manifold 38 mounted to the cylinder head base portion
30.
[0043] There is a cam carrier 50 on the cylinder head base portion
30. The cam carrier 50 comprises a horizontal base plate 51
disposed in a space that is formed over the cylinder head base
portion 30 by the continuous shrouds 31, 32 and 33 and a peripheral
shroud 52 extending along the almost entire periphery of the
horizontal base plate 51 such as to provide a box-shaped
configuration. Journal bearings 57 are located such that the
journal bearings 57 are on each of the opposite sides of a straight
row of the cylinder A as viewed in the longitudinal direction of
the vehicle body and that there is one journal bearing 57 per
camshaft behind each cylinder A as viewed in the transverse
direction of the vehicle body. The journal bearings 57 support the
intake camshaft 15 and the exhaust cam shaft 16 at their journals
15a and 16a, respectively, for rotation. The journal bearing 57
comprises a bearing lower block 53 formed as an integral part of
the horizontal base plate 51 and a bearing upper block 55 secured
to the bearing lower block 53 by fastening bolts 56 and 56a. The
each pair of bearing lower blocks 53 for the intake camshaft 15 and
the exhaust camshaft 16 are interconnected by a bridge 72 formed as
an integral part of the horizontal base plate 51. In this instance,
the journal bearings 57 are basically identical in configuration
and arranged at regular intervals. However, the foremost journal
bearings 57a are slightly different in configuration from the
remaining journal bearings 57 and located closely to the camshaft
pulleys 18 and 19, respectively.
[0044] There is one tappet guide 54 formed in the horizontal base
plate 51 per cylinder A in which the tappet assembly 24 is received
for slide movement therein. The tappet guide 54 is such an inclined
cylindrical bore as to extend through the horizontal base plate 51.
The tappet assembly 24 slides up and down in the tappet guide 54
following rotation of the cams 25-27 so as to lift up and down the
intake valve 39 or the exhaust valve 40. There is further a guide
bore 58 formed in the horizontal base plate 51 as a guide way for
the spark plug 23 when the spark plug 23 is fixedly mounted in the
plug hole 36. Specifically, the spark plug guide bore 58, except
the foremost one, is formed such as to pass through a cylindrical
column 59 vertically extending above the center of each cylinder A
from the horizontal base plate 51. As seen in FIG. 2, the spark
plug guide bore 58 associated with the foremost cylinder A is
formed in a cocoon-shaped column 62. A bore 61 is also formed in
the column 62 so as to receive a hydraulic oil supply control valve
60 operative to supply hydraulic oil to the tappet assembly 24.
[0045] The head cover 13 is brought into contact with the cylinder
head 12 along the top surfaces of shrouds 13-33 extending
vertically from the base portion 30, and the top surfaces of the
columns 59 and 62 vertically extending from the horizontal base
plate 51 and fixedly attached to the cylinder head 12.
[0046] The horizontal base plate 51 has ribs 63 and 64 extending in
a direction from the front end to the rear end of the engine 1. The
rib 63, which is formed as an integral part of the horizontal base
plate 51, is located between a straight row of the tappet guide 54
associated with the intake camshaft 15 and a straight row of spark
plug guide bores 58 and extends in parallel to the intake camshaft
15 in a direction from the front to the back of the engine 1. An
oil gallery 65 is formed in the rib 63. Similarly, the rib 63,
which is formed as an integral part of the horizontal base plate
51, is located between a straight row of the tappet guide 54
associated with the exhaust camshaft 16 and the straight row of
spark plug guide bores 58 and extends in parallel to the exhaust
camshaft 16 in a direction from the front to the back of the engine
1. An oil gallery 66 is formed in the rib 64.
[0047] As clearly shown in FIG. 3, the horizontal base plate 51 is
formed with a plurality of circular-shaped recesses 70 at the front
side thereof and a plurality of circular-shaped projections 71 (see
FIG. 2) at the rear side thereof. Further, the horizontal base
plate 51 has a cylindrical column 72 with a through bore 73 formed
at the center thereof. The cylinder head 12 has cylindrical columns
75 correspondingly in position to the circular-shaped recesses 70,
circular-shaped projections 71 and bridge 73. In securing the cam
carrier 50 to the cylinder head 12, the cam carrier 50 is placed on
the cylinder head by bringing these circular-shaped recesses 70,
circular-shaped projections 71 and bridge 73 into contact with the
columns 75, respectively and then fixedly secured to the cylinder
head 12 by fastening bolts 74 into the columns 75. The cylinder
head 12 at the base portion 30 has further cylindrical columns 76
correspondingly in position to the columns 59 and 62 of the cam
carrier 50. These cylindrical columns 76 are such that when the cam
carrier 50 is secured to the cylinder head 12, the columns 76 are
abutted against by the columns 59 and 62 of the cam carrier 50,
this is advantageous to stably fix the cam carrier 50 to the
cylinder head 12.
[0048] Some of the fastening bolts 56, namely the fastening bolts
56a that are used to fixedly secure the bearing upper block 55 to
the bearing lower block 53 for supporting the intake camshaft 15,
are sufficiently long in length differently from the remaining
fastening bolts 56 so as to extend passing through both bearing
lower block 53 and horizontal base plate 51, thereby fixedly
securing the cam carrier 50 to the cylinder head 12 while fixedly
securing the bearing upper block 55 to the both bearing lower block
53. In this instance, the cam carrier 50 has cylindrical columns 77
extending downward from the horizontal base plate 51 at locations
corresponding to these fastening bolts 56a, and the cylinder head
12 is formed with cylindrical columns 78 extending upward from the
cylinder head base portion 30 as counterparts of the cylindrical
columns 77. When the cam carrier 50 is secured to the cylinder head
12, the cylindrical columns 78 of the cylinder head 12 are abutted
against by the cylindrical columns 77 of the cam carrier 50, this
is advantageous to stably fix the cam carrier 50 to the cylinder
head 12.
[0049] As clearly shown in FIG. 3, the cylinder head 12 is fixedly
secured to the cylinder block 11 by fastening bolts 80. The
fastening bolts 80 are located such that the fastening bolts 80 are
on each of the opposite sides of the straight row of the cylinder A
as viewed in the longitudinal direction of the vehicle body and
that there is one fastening bolt 80 per camshaft behind each
cylinder A as viewed in the transverse direction of the vehicle
body. This arrangement of fastening bolts 80 causes the fastening
bolts 80 receive explosion force generated in the respective
cylinders 1 equally.
[0050] As described above, in the structure associated with
camshaft drive mechanism, the cam carrier 50, that is provided
separately from the cylinder head 12, has the bearing lower blocks
53 forming part of the journal bearings 57 and the tappet guides
54. This structure enables the bearing lower blocks 53 of the
journal bearings 57 and the tappet guides 54 to be assembled to the
cylinder head 12 all at once by fixing the cam carrier 50 to the
cylinder head 12 only, so as to prevent aggravation of assembling
performance and serviceability of the engine 1 that is caused due
to possible mechanical interference between the fastening bolts 80
and the camshafts 15 and 16. In addition, this structure provides
significant improvement of layout and, as a result of which, the
cylinder head 12 is improved in assembling performance and enabled
to be compact. The cam carrier 50 is constructed by means of mutual
combinations of various parts stretching or extending in different
directions such as the horizontal base plate 51, the peripheral
shroud 52, the bearing lower block 53, the tappet guides 54 and the
like and, in consequence, these parts are complementary to each
other. As a result, the cam carrier 50 is given a high stiffness
and leads to stable support of the camshafts 15 and 16, the tappet
assemblies 24 and the hydraulic oil supply control valve 60.
Further, because the cam carrier 50 is provided separately from the
cylinder head 12, there occurs no possible mechanical interference
between the fastening bolts 80 and the bearings 57 comprising the
upper and lower bearing blocks 53 and 55, so that the layout of
bolts 80 causes no constraints on the degree of freedom in
arranging the bearings 57. This permits both the bearing 57 and
fastening bolt 80 to clash in position with each other such that
they are located in an intermediate position between two adjacent
cylinders 2 on one of the opposite sides of a straight row of the
cylinder A as viewed in the lengthwise direction of the vehicle
body.
[0051] FIGS. 6 through 9 shows the tappet assembly 24 in detail. It
is to be noted that while the same tapped assembly 24 is installed
to each of valve trains for the intake valve 39 and the exhaust
valve 40, respectively, in the embodiment shown in FIG. 10, it may
be installed either one of the valve trains.
[0052] As shown in FIG. 10, the tappet assembly 24 is almost
touched by the upper end of valve stem 81 through a shim 90. The
tapped assembly 24 has a valve spring retainer 92. On the other
hand, the cylinder head 12 has an annular recess 93 per valve. A
valve spring 82 is mounted on the valve stem 81 between the valve
spring retainer 92 and the annular recess 93 of the cylinder head
12 so as to force the tappet assembly 24 to the cam lobe of the
cams of the camshaft 15, 16. A branch oil channel 95 branches off
from the oil gallery 65 at a right angle. Similarly, a branch oil
channel 95 branches off from the oil gallery 66 at a right angle.
The branch oil channel 95 is made by drilling a channel in the
cylinder head 12 from the front side thereof or the rear side
thereof so as to reach the oil gallery 65 or 66. The oil channel at
the front side of the cylinder head 12 or at the rear side of the
cylinder head 12 is stopped up by a ball 95a (see FIG. 11). The
branch oil channel 95 is formed so as to partly overlap the outer
peripheries of each adjacent tappet assemblies 24 (see FIG. 11).
Oil flows in the oil gallery 65, 66, enters the branch oil channel
95, and then enters in the interior of the bore as the tappet guide
54.
[0053] As shown in FIG. 11, the tappet guide 54 is formed with a
recess 54a in the interior wall thereof. As will be described, the
side tappet 24 has a ball retainer 421 fixedly fitted in a side
surface 42c on a side remote from the oil gallery 65, 66 with
respect to the center tappet 41. The ball retainer 421 is located
so as to face the recess 54a of the tappet guide 54. A ball 94 is
in the ball retainer 421. W hen installing the tappet assembly 24
into the tappet guide 54, the ball 94 is interposed between the
ball retainer 421 of the tappet assembly 24 and the recess 54a of
the tappet guide 54. The ball 94 prevents the tappet assembly 24
from turning in the tappet guide 54 during insertion of the tappet
assembly 24 into the tappet guide 54.
[0054] The tappet assembly 24 comprises a side tappet 42 attached
to the valve stem 81 of the valve 39 40 and the center tappet 41.
The side tappet 42 the side tappet 42 has two tappet heads 42a
separated apart from each other. The center tappet 41 is received
for slide movement between the tappet heads 42a of the side tappet
42. As describe later, the tappet assembly 24 has a coupling
mechanism between these center tappet 41 and side tappet 42 which
mechanically couples them together so as to allow the center tappet
41 to slide up and down relative to the side tappet 42. The side
tappet 42 at the tappet heads 42a rides on the lobes of the low
lift side cams 25 and 27 so as to slide up and down, thereby
opening and closing the valve 39, 40 when the camshaft 15, 16
turns. The center tappet 41 at a tappet head 41a rides on the lobe
of the high lift center cam 26. The center tappet 41 is slid up and
down relatively to the side tappet 42 while it is mechanically
uncoupled from the side tappet 42. Accordingly, the center tappet
42 is not contributory to opening and closing the valve 39, 40 even
though the camshaft 15, 16 turns. On the other hand, while the
center tappet 41 is mechanically coupled to the side tappet 42, the
center tappet 41 is slid up and down integrally with the side
tappet 42 by the high lift center cam 26. The low lift side cam 25,
27 is used as a slow speed cam, and the high lift center cam 27 is
used as a fast speed cam.
[0055] More specifically describing, the tappet assembly 24, having
a generally cylindrical configuration, is made up of two mating
parts, namely a center tappet 41 and a side tappet 42. The tappet
assembly 24 is divided into three tappet head sections in an axial
direction of the camshaft 15, 16, namely the center tappet head 41a
and the side tappet heads 42a on opposite side of the center tappet
had 41a. Each tappet head 41a, 42a has a length greater in the
direction perpendicular to the axis of rotation of the cam 25, 26,
27 than a width in the direction of the axis of rotation of the cam
25, 26, 27. The center tappet 41, that has a generally inverted
U-shaped configuration, is formed with flat end walls 41b at
opposite sides thereof in the direction of the axis of rotation of
the cam 25, 26, 27. Each end wall 41b extends perpendicularly to a
flat top wall of the tappet head 41a which is perpendicular to the
axis of the valve stem 81. The center tappet 41 is further formed
with circular-arcuate side walls 41c at opposite sides thereof in
the direction perpendicular to the axis of rotation of the cam 25,
26, 27. In addition, the center tappet 42 is formed with a vertical
flat side shroud 41d extending as an extension of the side wall
41c. These circular-aruate side wall 41c and vertical side shrouds
41d form parts of an outer shell of the tappet assembly 24. The
vertical side shroud 41d forms a vertical flat side surface facing
a vertical side wall 42h formed on the side tappet 42 (which will
be described later). The center tappet 41 is further formed with a
guide bore 41e passing through the end walls 41b. This guide bore
41e extends at the center of the end walls 41b in the direction
parallel to the axis of rotation of the cams 39, 40.
[0056] The side tappet 42 has a generally U-shaped configuration
complementary to the inverted U-shaped configuration of the center
tappet 41. The center tappet 41 and the side tappet 42 form a
complete cylindrical configuration when they are assembled to each
other as the tappet assembly 24. The side tappet 42 is formed with
flat inner end walls 42b separated from each other and
circular-arcuate outer end walls 42c at opposite sides thereof in
the direction of the axis of rotation of the cam, 25, 26, 27. The
opposite circular-arcuate end walls 42c of the side tappet 41 and
the opposite circular-arcuate side walls 41c form a generally
cylindrical configuration of an outer shell of the tappet assembly.
The inner end walls 42b are parallel to each other and extend
perpendicularly to flat top walls of the tappet head 42a which are
perpendicular to the axis of the valve stem 81. The distance
between the inner end walls 42b is such that the center tappet 41
is received for slide movement between the inner end walls 42b. The
side tappet 42 is further formed with vertical flat side walls 42h
as guide surfaces at opposite sides thereof in the direction
perpendicular to the axial direction of the cam 25, 26, 27 so that
each side wall 42h connects each adjacent inner and outer end walls
42b and 42c. The circular-arcuate end walls 42c form parts of the
outer shell of the tappet assembly 24 and cooperate with the
circular-arcuate end walls 41c of the center tappet 41 so as to
complete the generally cylindrically configuration of the outer
shell of the tappet assembly 24. The flat side walls 42h mate with
the flat side surfaces 41f of the vertical flat side shrouds 41d,
respectively, when the center tappet 41 is installed to the side
tappet 42. These shroud 41d formed with the guide surface 41f an
the side walls 42h form guide means for guiding reciprocal slide
movement of the center tappet 41 relative to the side tappet 42.
The side tappet 42 further has a bridge 42d interconnecting lower
portions of the flat inner end walls 42b. The bridge 42d is formed
with a spring receiving recess 42g in which a tappet spring 49 is
received. As shown in FIG. 9, there are oil spill ports 42j formed
at the bottom of the spring receiving bore 42g so as to drain away
oil trapped at the bottom of the inner end walls 42b.
[0057] The side tappet 42 is further formed with first and second
guide bores 42e, each of which passes through the inner and outer
end walls 42b and 42c. These guide bores 42e extend at the center
of the inner and outer end walls 42b and 42c in the direction
parallel to the axis of rotation of the cams 39, 40 so as to be
brought into alignment with the guide bore 41e when the center
tappet 41 is installed to the side tappet 42. There is an oil
channel 42f extending in parallel to the axis of the valve stem 81
from the first guide bore 42e in the outer end wall 41b of the side
tappet 42.
[0058] When the center tappet 41 is installed to the side tappet
42, the vertical side shrouds 41d of the center tappet 41 are
brought into slide contact with the vertical side walls 42h of the
side tappet 42, respectively. Accordingly, during relative movement
of the center tappet 41, the center tapped 41 is guided through
slide contact between the vertical side shrouds 41d and the
vertical side walls 42h. The tappet assembly 24 thus structured
disperses and transmits a force that is exerted on the side tappet
41 by the side cams 25 and 26 to the center tappet 41 through the
slide contact between the vertical side shrouds 41d and the
vertical side walls 42h while the valve is driven by side cams 25
and 25 through the side tappets 42 uncoupled from the center tappet
41. As a result, not only the side tappet 42 but also the center
tappet 41 are pressed against the tappet guide 54 at their opposite
circular-arcuate walls 41c and 42c. This leads to a decrease in
interface resistance between the center and side tappets 41 and 42
and the tappet guide 54, which provides improvement of wear-restant
properties of the center and side tappets 41 and 42 and the tappet
guide 54.
[0059] The center tappet 41 and the side tappet 42 mate with each
other to form a generally cylindrically-shaped tappet assembly 24
when they are installed to each other. When the center tappet 41 is
installed in the side tappet 42 the tappet heads 41a and 42a of the
center tappet 41 and the side tappet 42 are brought even with one
another, and the guide bores 41e and 42e of the center tappet 41
and the side tappet 42 are brought into alignment with one another.
This state is such that the cams 25-27 at their base ride on the
tappet heads 41a and 42a, respectively.
[0060] There is a lock mechanism in the tappet assembly 24 which
cooperates with the guide bore 41e of the center tappet 41 and the
guide bores 42e of the side tappet 42 so as to mechanically couple
the center and side tappets 41 and 42. Specifically, the lock
mechanism comprises a locking/unlocking pin 43, a plunger 44 and a
cup-shaped receiver 46 having a flange 46a. The locking/unlocking
pin 43 is received for slide movement in the guide bore 41e of the
center tappet 41. The locking/unlocking pin 43 has the same axial
length as the guide bore 41e of the center tappet 41 and is formed
with circumferential recess 43c so as to reduce a contact area with
the guide bore 41e. The plunger 44 is received for slide movement
in the first guide bore 42e of the side tappet 42. The receiver 46
is received for slide movement in the second guide bore 42e of the
side tappet 42 and forced against the locking/unlocking pin 44 by a
receiver spring 45 received in the second guide bore 42e of the
side tappet 42. As shown in FIG. 9 in detail, the plunger 44 is
shorter in the axial direction of the camshaft 15, 16 than the
first guide bore 42e and stopped by an annular stopper ring 48 so
as to provide an oil chamber in the first guide bore 42e at the
outer end of the plunger 44. The plunger 44 is such that, when the
plunger 44 is stopped by the annular stopper ring 48, the plunger
44 places the locking/unlocking pin 43 in a neutral position where
the opposite end surfaces 43a and 43b of the locking/unlocking pin
43 are even with opposite end walls 41b of the center tappet 41,
respectively. Pressurized oil is supplied to the plunger 4 in the
guide bore 42e through the oil channel 42f of the side tappet 42
extending from the first guide bore 42e of the side tappet 42. The
oil channel 42f is sufficiently long in the vertical direction so
that the first guide bore 42e always remains in communication with
the branch oil channel 95 while the side tappet 42 moves up and
down.
[0061] The plunger 44 is operated by hydraulic oil that is
generated by the hydraulic oil supply control valve 60 (see FIG.
2). The hydraulic oil is supplied into the oil chamber in the first
guide bore 42e through the oil channel 42f through the branch oil
channel 95 branching off from the oil gallery 65, 66 and then acts
on the outer end of the plunger 44 so as to always force the
plunger 44 against the locking/unlocking pin 43 in a direction
opposite to the direction in which the plunger 44 is forced by the
spring loaded receiver 46. The receiver spring 45 is retained in
the second guide bore 42e by an annular retainer ring 47. The
second guide bore 42e of the side tappet 42 is formed with a
shoulder 42i so that the flange 46a of the receiver 46 abuts
against the shoulder 42i for restriction of axial movement of the
receiver 46. The receiver 46 is such that, when the flange 46a of
the receiver 46 abuts against the shoulder 42i, the receiver 46
places the locking/unlocking pin 43 in the neutral position where
the opposite end surfaces 43a and 43b of the locking/unlocking pin
43 are even with opposite end walls 41b of the center tappet 41,
respectively.
[0062] When applying controlled hydraulic oil in the oil chamber in
the first guide bore 42e of the side tappet 42 to the plunger 44,
the plunger 44 is forced to enter the guide bore 41e of the center
tappet 41 pushing the locking/unlocking pin 43 against the receiver
spring 45 and, in consequence, the locking/unlocking pin 43 is
forced to enter the second guide bore 42e of the side tappet 42
pushing the receiver 46 against the receiver spring 45. As a
result, the center tappet 41 and the side tappet 42 are
mechanically coupled together by the plunger 44 and the
locking/unlocking pin 43, respectively. On the other hand, when
removing the control hydraulic oil in the oil chamber in the first
guide bore 42e of the side tappet 42, the receiver 46 is pushed by
the receiver spring 45 so as to force the locking/unlocking pin 43
and the plunger 44 to return into their neutral positions,
respectively. As a result, the center tappet 41 is mechanically
uncoupled from the side tappet 42.
[0063] The branch oil channel 95 is in communication with a lower
portion of the oil channel 42f extending from the first guide bore
42e of the side tapped 42. This oil channel 95 is formed in the
base portion 30 of the cylinder head 12 by boring or drilling the
front side and rear end shrouds 31 and 32 aiming at the oil gallery
65, 66 after forming the cylinder head 12 such that it partly
overlaps the inner wall of the recess 54a of the adjacent tappet
guide 54 and is brought into communication with the oil channel 42f
when the side tappet 24 is assembled. This avoids drilling the
branch oil channel per the tappet guide, which leads to a reduction
in man-hour for forming the branch oil channel.
[0064] FIGS. 12 to 15 shows various aspects of the tappet assembly
24. FIG. 12 shows one end of the tappet assembly 24. FIG. 13 shows
a cross-section of the tappet assembly 24 taken along line
XIII-XIII of FIG. 12. FIG. 14 shows one end of the center tappet
41. FIG. 15 shows a vertical-section of the tappet assembly 24
taken along line XV-XV of FIG. 8.
[0065] As shown in FIGS. 6, 7, 10 and 12 to 15, the center tappet
41 is formed with retaining pin supporting bores 41g passing
through the center tappet 41 for receiving retaining pins 101,
respectively. Specifically, two retaining pin supporting bores 41g
are arranged in alignment with each other in the axial direction of
the camshaft 15, 16 on each side of the guide bore 41e. These
retaining pin supporting bores 41g are arranged symmetrical with
the vertical center axis of the center tappet 41. The side walls
42h of the side tappet 42 at opposite sides are formed with
limiting recesses 42m facing the retaining pin supporting bores
41g, respectively, and extending vertically. Each limiting recess
42m is located such that the retaining pin supporting bore 41g
exposes the exterior of the tappet assembly 24 through the limiting
recess 42m when the center tappet 41 is installed to the side
tappet 42. This enables insertion of the retaining pins 101 into
the retaining pin supporting bores 41g after installation of the
center tappet 41 to the side tappet 42. Since the structure of the
tappet assembly 24 is such that the center tappet 41 is forced by
the tappet spring 49 so as to always abut against the high lift
center cam 26, the locking/unlocking pin 43 possibly comes off from
the guide bore 41e due to upward movement of the center tappet 42
that is caused by the tappet spring 49 in the course of assembling
the center tappet 41 to the side tappet 42. The structure of the
tappet assembly 24 prevents the locking/unlocking pin 43 from
coming off from the guide bore 41e by inserting the retaining pins
101 into the retaining pin supporting bores 41g and engaging
opposite ends of the retaining pins 101 by upper ends of the
limiting recesses 42m. Specifically, the limiting recess 42m is
such as to bring the retaining pin 101 into engagement with the
upper end of the limiting recess 42m when the tappet head 41a of
the center tappet 41 is substantially even with the tappet heads
42a of the side tappet 42 and to have a vertical length H greater
than a distance by which the center tappet 41 and the side tappet
42 are allowed to move relatively to each other. Otherwise, these
retaining pin support bore 41g and limiting recesses 42m may be
replaced with each other.
[0066] FIG. 16 shows a tappet assembly 24 in accordance with
another embodiment of the present invention. The tappet assembly 24
is different from that of the previous embodiment described above
in that a guide bore 42e of a side tappet 42 in which a plunger 44
is received is closed by a stopper block 108 which is provided in
place of the annular stopper ring 48 of the previous embodiment so
as a stopper member for limiting axial slide movement of the
plunger 44 and that the guide bore 42e is in communication with an
oil channel 42f formed in an outer end wall 41b of the side tappet
42 through a connecting oil channel 42k.
[0067] In operation of the valve drive mechanism equipped with the
tappet assembly 24, when it is intended to drive the valve 39, 40
for low lift valve operation for low speed operation of the engine
1, the hydraulic oil supply control valve 60 is operated to remove
hydraulic oil from the oil chamber of the first guide bore 42e of
the side tappet 42. The locking/unlocking pin 43, and hence the
plunger 44, is moved in the axial direction by the spring loaded
receiver 46 until the plunger 44 is stopped by the annular stopper
ring 48 or the stopper block 108. When the plunger 44 is brought
into abutment against the annular stopper ring 48 or the stopper
block 108, the locking/unlocking pin 43 comes out of the second
guide bore 42e of the side tappet 42 and is fully accepted in the
first guide bore 41e of the side tappet 42, so that the center
tappet 41 is mechanically uncoupled from the side tappet 42 and, in
consequence, permitted to move relatively to the side tappet 42.
Therefore, when the camshaft 15, 16 rotates, although the cams
25-27 cause reciprocating movement of the center and side tappets
41 and 42, the center tappet 41 reciprocally moves up and down
relatively to the side tappet 42, so that rotation of the camshaft
15, 16 is not transmitted to the valve 39, 40 through the high lift
center cam 26. As a result, rotation of the camshaft 15, 16 is
transmitted to the valve 39, 40 by both the low lift side cams 25
and 27.
[0068] On the other hand, when it is intended to drive the valve
39, 40 for high lift valve operation for high speed operation of
the engine 1, the hydraulic oil supply control valve 60 is operated
to supply hydraulic oil into the oil chamber of the first guide
bore 42e of the side tappet 42 so as to force the plunger 44, and
hence the locking/unlocking pin 43 against the return spring 45. As
a result, the plunger 44 partly enters the guide bore 41e of the
center tappet 41, and hence, the locking/unlocking pin 43 partly
enters the second guide bore 42e of the side tappet 42, so that the
center tappet 41 is mechanically coupled to the side tappet 42
together. Therefore, when the camshaft 15, 16 rotates, rotation of
the camshaft 15, 16 is transmitted to the valve 39, 40 by the high
lift center cam 26 only through the center tappet 41 mechanically
coupled to the side tappet 42.
[0069] Coupling the center tappet 41 to the side tappet 42 or
uncoupling the center tappet 41 from the side tappet 42 is
performed while the center and side tappets 41 and 42 at their
tappet heads 41a and 42a ride on the base of the lobes of the
center and side cams 25, 26 and 27.
[0070] According to the valve drive mechanism equipped with the
tappet assembly described above, since the center tappet 41 can
cause large reciprocating movement relative to the side tappet 42,
a valve lift difference between low lift and high lift operation of
the valve 39, 40.
[0071] In the case where the tappet assembly 24 is used in order to
cause a swirl of intake air in the combustion chamber of the engine
1, the valve drive mechanism employs low lift side cams 25 and 27
having substantially circular profiles for either one of two intake
valves for each combustion chamber so that the one intake valve is
not lifted during high speed operation of the engine 1. In this
case, it is necessary for the side cams 25 and 27 to have an
effective valve lift of approximately 2 mm in order to force out
fuel collected in the intake port and to intpinuce it into the
combustion chamber.
[0072] The tappet assembly can be incorporated in a valve drive
mechanism in which two intake valves or two exhaust valves per
cylinder are driven by cams having cam profiles that are different
and variable.
[0073] It is to be understood that although the present invention
has been described in detail with regard to preferred embodiments
thereof, various other embodiments and variants may occur to those
skilled in the art, which are within the scope and spirit of the
invention, and such embodiments and variants are intended to be
covered by the following claims.
* * * * *