Information
-
Patent Grant
-
6276320
-
Patent Number
6,276,320
-
Date Filed
Wednesday, November 3, 199924 years ago
-
Date Issued
Tuesday, August 21, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Armstrong, Westerman, Hattori, McLeland & Naughton, LLP
-
CPC
-
US Classifications
Field of Search
US
- 123 9015
- 123 9016
- 123 9017
- 123 9022
- 123 9027
- 123 9039
- 123 9042
- 123 9044
- 123 906
- 123 198 F
- 123 308
-
International Classifications
-
Abstract
In a valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, the number of operation modes of the air-intake valves in accordance with engine operation region is increased to improve combustion nature in a combustion chamber and engine output and to miniaturize the valve mechanism. The valve mechanism comprises first and second drive rocker arms operatively connected with the respective air-intake valves, first, second and third free rocker arms coming into contact with first, second and third operation cams having profiles for making the air-intake valve perform opening-closing motion. The drive rocker arms are connected and disconnected with the free rocker arms in accordance with engine operation states, thereby a state in which both the air-intake valves are closed for pause, a state in which one of the air-intake valves performs opening-closing motion with a small lift and another air-intake valve is closed for pause, a state in which both the air-intake valves perform opening-closing motion with a small lift, or a state in which both the air-intake valves perform opening-closing motion with a large lift is obtained. Pipe members with fan-shaped cross-section are inserted in a rocker arm shaft to form oil-pressure supply passages for switching over the connection states.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a valve mechanism of a multi-cylinder internal combustion engine, particularly such a valve mechanism in which a pair of air-intake valves provided on a cylinder can be closed together to make the cylinder pause and lift, of each air-intake valve can be changed independently in accordance with engine operation regions.
Hitherto, a valve mechanism of a multi-cylinder internal combustion engine in which a pair of air-intake valves provided on a cylinder can be closed together to make the cylinder pause and lift of each air-intake valve can be changed independently in accordance with engine operation regions is known (see Japanese Laid-Open Patent Publication No. 8-61031.
The above-mentioned valve mechanism comprises first and second drive rocker arms which are operatively connected to the respective air-intake valves and contacted with circular pause sections of a cam shaft, a first free rocker arm contacted with a substantial pause cam enabling the air-intake valve to open slightly, a second free rocking arm contacted with a low-speed cam for making the air-intake valve open with a small lift, and a third free rocker arm contacted with a high-speed cam for making the air-intake valve open with a large lift.
The first and second drive rocker arms and the first, second and third free rocker arms are connected or disconnected with each other suitably by switchover means so that the operation mode of the air-intake valves can be switched over. Namely, both the air-intake valves are closed by the pause sections in an engine pause state, one of the air-intake valves is made to perform opening-closing motion by the low-speed cam while another air-intake valve is made to substantially pause by the substantial pause cam in an engine low-speed operation region to produce swirl within a combustion chamber for improvement of combustion, and both the air-intake valves are made to perform opening-closing motion by the high-speed cam in an engine high-speed operation region to improve engine output.
In a rocker arm shaft of the valve mechanism are formed two switching oil-pressure supply passages of circular cross sections for supplying oil-pressure to the connection switchover means.
In the above valve mechanism, the operation mode of the air-intake valves is shifted from a state that one air-intake valve is made to perform opening-closing motion by the low-speed cam as well as another air-intake valve is made to substantially pause by the substantial pause cam in an engine low-speed operation region, to a state that both the air-intake valves are made to perform opening-closing motion by the high-speed cam in an engine high-speed operation. Accordingly, in a part of the engine low-speed operation region near the high-speed region where only one air-intake valve opens with the small lift, sufficient engine output cannot be obtained.
Since a plurality of the switching oil-pressure supply passages, which are usually formed by mechanical work and of relatively small diameter, must be provided within the rocker arm shaft, the working takes much time. Further, since each of the two switching oil-pressure supply passages formed in the rocker arm shaft has a circular cross section, the inner space of the rocker arm shaft is not necessarily utilized efficiently. Therefore, in order to ensure a necessary passage area of the switching oil-pressure supply passage, sometimes the diameter of the rocker arm shaft must be enlarged and it obstructs miniaturization of the valve mechanism.
The present invention has been accomplished in order to overcome the above difficulties, and a subject of the invention is to improve the nature of combustion in the combustion chamber and output of the engine, by increasing the number of operation modes of the air-intake valves depending on engine operation regions, in a valve mechanism of a multi-cylinder internal combustion engine having a cylinder provided with a pair of air-intake valves. Another subject of the invention is cost reduction and miniaturization of the valve mechanism.
SUMMARY OF THE INVENTION
The present invention provides a valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, comprising: a cam shaft having a pair of pause sections for holding the air-intake valves substantially in closing pause states, a first operation cam with a profile capable of causing the air-intake to perform opening-closing motion, a second operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, and a third operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion with a larger lift compared to the first and second operation cams; a first drive rocker arm operatively connected to one of the air-intake valves and contacted with one of the pause sections of the cam shaft; a second drive rocker arm operatively connected to another air-intake valve and contacted with another pause section of the cam shaft; a first free rocker arm contacted with the first operation cam; a second free rocker arm contacted with the second operation cam; a third free rocker arm contacted with the third operation cam; a first connection switchover means for connecting and disconnecting the first drive rocker arm with the first free rocker arm; a second connection switchover means for connecting and disconnecting the second drive rocker arm with the second free rocker arm; and a third connection switchover means for connecting and disconnecting the first drive rocker arm and the second drive rocker arm with the third free rocker arm.
According to the invention, the air-intake valves provided on one cylinder can take a first state in which both the air-intake valves are substantially closed to pause, a second state in which one air-intake valve is made to perform opening-closing motion substantially by the first or second operation cam as well as another air-intake valve is substantially closed to pause, a third state in which one air-intake valve is made to perform opening-closing motion substantially by the first operation cam as well as another air-intake valve is made to perform opening-closing motion substantially by the second operation cam, and a fourth state in which both the air-intake valves are made to perform opening-closing motion substantially by the third operation cam. Therefore, desirable operation modes of the air-intake valves can be set according to engine operation regions, in view of cylinder pause, swirl generation in the combustion chamber to improve combustion nature or improvement of engine output.
More concretely, in the first state, the engine can be operated with the cylinder pausing. In the second state, only one air-intake valve is made to perform opening-closing motion to cause a vortex or a swirl in the combustion chamber so that combustion nature is improved and circulation of a large amount of exhaust gas and lean mixture combustion become possible. In the third state, since both the air-intake valves are made to perform opening-closing motion with a lift smaller than that in the fourth state, engine output can be improved compared to prior art in a transition region between an engine operation region by the second state and an engine operation region by the fourth state. Further, since profiles of the first and second operation cams can be made identical or different, formation of the swirl in the combustion chamber and amount of intake air into the combustion chamber can be set with increased freedom. In the fourth state, since both the air-intake valves are made to perform opening-closing motion with the largest lift, a high engine output can be obtained.
The above valve mechanism may be provided with a control means by which in an engine operation region with the cylinder pausing, the first, second and third connection switchover means are in disconnecting states; in an engine operation region with a small amount of intake air, the first connection switchover means is in a connecting state and the second and third connection switchover means are in disconnecting state; in an engine operation region with a middle amount of intake air, the first and second connection switchover means are in connecting states and the third connection switchover means is in a disconnecting state; and in an engine operation region with a large amount of intake air, the third connection switchover means is in a connecting state.
According the valve mechanism, both the air-intake valves can be closed for enabling the engine to operate with the cylinder pausing. In the engine operation region with a small amount of intake air, one air-intake valve is opened with a lift smaller than that of the third operation cam and another air-intake valve is closed to pause, therefore vortex or swirl can be produced in the combustion chamber to improve combustion nature, and circulation of a large amount of exhaust gas or lean mixture combustion in an engine low-speed or low-load operation region become possible to improve emission or fuel consumption. Further, in the engine operation region with a middle amount of intake air, both the air-intake valves are opened with a lift smaller than that of the third operation cam so that engine output can be improved in a transition engine operation region between an engine low-speed or low-load operation region and an engine high-speed or high-load operation region. In the engine operation region with a large amount of intake air, both air-intake valves are opened with large lift so that a high engine output necessary in this operation region can be obtained.
The above-mentioned valve mechanism may be provided with pipe members of fan-shaped cross section provided in an axial hole of a rocker arm shaft pivotally supporting the rocker arms. The pipe members communicate with the first, second and third connection switchover means to constitute first, second and third switching oil-pressure supply passages respectively.
According to such a valve mechanism, since the switching oil-pressure supply passages are formed easily only by inserting three pipe members into an axial hole of the rocker arm shaft, for example into a hollow portion of a pipe-shaped rocker arm shaft, cost can be reduced. Moreover, since each of the pipe members has a fan-shaped cross section, the entire shape of the three pipe members inserted into the axial hole of the rocker arm shaft can be made cylindrical, therefore, the space of the axial hole can be utilized effectively. Three switching oil-pressure supply passages having necessary passage areas can be arranged within the shaft compactly so that the valve mechanism can be miniaturized.
In the aforementioned valve mechanism, the air-intake valves may be operatively connected to the first and second drive rocker arms through hydraulic tappets respectively, a hydraulic tappet holder for holding the hydraulic tappets may have respective hydraulic tappet holding sections, and a recess maybe formed between the hydraulic tappet holding sections for receiving a roller of the third free rocker arm contacted with the third operation cam.
According to the valve mechanism, the roller of the third free rocker arm can be received in the recess between the hydraulic tappet holding sections when the third free rocker arm closely approaches the hydraulic tappet holder, therefore both horizontal and vertical distances between the hydraulic tappet holding section and the rocker arm shaft can be set short; that is, the hydraulic tappet holding section can be disposed at a place near the rocker arm shaft to miniaturize the valve mechanism. And freedom of layout of valve mechanism component members in a limited valve mechanism chamber is increased.
In this specification, the substantial closed pause state of the air-intake valve means a state that the air-intake valve is made not to perform opening-closing motion at all, or a state that the air-intake valve is made to perform opening-closing motion with a slight lift, but air flowing into the combustion chamber when the air-intake valve opens is so little that combustion in the combustion chamber is not affected by the air. The expression that the air-intake valve performs opening-closing motion substantially means that the air-intake valve performs opening-closing motion with a lift such that air flowing into the combustion chamber when the air-intake valve opens participates in the combustion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a sectional view of a valve mechanism of a multi-cylinder internal combustion engine according to a preferred embodiment of the present invention;
FIG. 2
is a section taken along the line II—II of
FIG. 3
;
FIG. 3
is a plan view of the valve mechanism of
FIG. 1
with a cylinder head cover removed and some parts of rocker arms and rocker arm shafts omitted;
FIG. 4
is a perspective view showing arrangement of rocker arm shaft holders and oil passages;
FIG. 5
is a perspective view showing an arrangement of hydraulic tappet holders;
FIG.
6
(A) to FIG.
6
(D) are views showing modes of connection and disconnection of connection switchover means;
FIG.
7
(A) and FIG.
7
(B) are views for explaining movement of a timing plate of the connection switchover means;
FIG. 8
is a plan view of the hydraulic tappet holder;
FIG. 9
is a view of the hydraulic tappet holder viewed in the direction of the arrow IX of
FIG. 8
; and
FIG. 10
is a sectional view showing the positional relation between a rocker arm shaft and a first fastening member in another embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to
FIGS. 1
to
9
.
The internal combustion engine
1
shown in
FIG. 1
is a four stroke cycle V-type eight cylinder (four cylinders in one side) overhead valve internal combustion engine. In each cylinder of a cylinder block
2
is fitted a piston (not shown) so as to slide, and on an upper surface of the cylinder block
2
is connected a cylinder head
3
forming a combustion chamber together with the piston. Namely, as shown in
FIG. 4
, the cylinder head
3
is formed with bolt holes
40
arranged surrounding the combustion chamber. The cylinder block
2
is also formed with bolt holes
41
along downward extension lines of the bolt holes
40
and bolts
42
passing through the bolt holes
40
are screwed into the bolt holes
41
to combine the cylinder head
3
with the cylinder block
2
.
At every cylinder of the cylinder head
3
is provided a pair of air-intake valve openings and a pair of exhaust valve openings which open toward the combustion chamber. As shown in
FIG. 1
, the air-intake valve openings communicate with an intake port
4
opening on a side surface (inside of V-bank) of the cylinder head
3
, and the exhaust valve openings communicate with an exhaust port
5
opening on another side surface (outside of V-bank) of the cylinder head. At the air-intake valve openings are provided respective air-intake valves
6
so as to perform opening-closing motion separately, and at the exhaust valve openings are provided respective exhaust valves
7
so as to perform opening-closing motion separately. Further, on one side surface of the cylinder head
3
is connected an intake manifold communicating with the intake port
4
, and on another side surface is connected an exhaust manifold communicating with the exhaust port
5
.
At each upper end of valve guides
8
of the air-intake valves
6
and the exhaust valves
7
is provided a valve spindle seal
9
, and a valve spring retainer
10
is attached to an end of the valve spindle. A valve spring
12
is inserted between the valve spring retainer
10
and a valve spring retaining section
11
of the cylinder head
3
. The air-intake valve
6
and the exhaust valve
7
are energized by spring force of the valve spring
12
so as to always close the air-intake valve opening and the exhaust valve opening, respectively.
For each cylinder, an hydraulic tappet holder
13
is attached to the cylinder head
3
by bolts
46
(FIG.
3
). The hydraulic tappet holder
13
has hydraulic tappet holding sections
112
in which respective hydraulic tappets
15
of known construction are fitted for sliding motion. Upper ends of the air-intake valves
6
and the exhaust valves
7
are contacted with lower ends of the hydraulic tappets
15
. Detailed construction of the hydraulic tappet holder
13
will be described later.
An air-intake valve drive apparatus
18
for transforming rotative motion of an air-intake cam shaft
16
into opening-closing motion of the air-intake valve
6
is provided between the air-intake valve
6
and the air-intake cam shaft
16
. Between the exhaust valve
7
and an exhaust cam shaft
17
is provided an exhaust valve drive apparatus
19
for transforming rotative motion of the exhaust cam shaft
17
into opening-closing motion of the exhaust valve
7
. The air-intake valve drive apparatus
18
has an air-intake rocker arm
22
fitted to a air-intake rocker arm shaft
20
so as to rock, and the exhaust valve drive apparatus
19
has an exhaust rocker arm
23
fitted to an exhaust rocker arm shaft
21
so as to rock. The air-intake rocker arm shaft
20
and the exhaust rocker arm shaft
21
penetrate a rocker arm shaft holder (lower cam holder)
24
and is fixed thereto.
As shown in
FIG. 4
, the rocker arm shaft holders
24
are arranged in a row so that each cylinder is positioned between neighboring rocker arm shaft holders, and attached to the cylinder head
3
by bolts
43
penetrating the rocker arm shaft holder
24
downward from above. The air-intake cam shaft
16
positioned above the air-intake rocker arm
22
is held between the rocker arm shaft holder
24
and an air-intake cam shaft holder (air-intake upper cam holder)
25
so as to rotate, the exhaust cam shaft
17
positioned above the exhaust rocker arm
22
is held between the rocker arm shaft holder
24
and an exhaust cam shaft holder
26
so as to rotate. The cam shaft holders
25
,
26
are fixed to the rocker arm shaft holder
24
by means of bolts
44
. On the one hand, the air-intake cam shaft
16
and the exhaust cam shaft
16
are connected with a crankshaft by means of a sprocket and a chain (not shown) so as to rotate once during the period the crankshaft rotates twice.
As shown in
FIG. 1
, the rocker arm shaft holder
24
has a low middle connecting portion
24
a
formed between respective portions holding the air-intake cam shaft
16
and the exhaust cam shaft
17
. A cylinder head cover
27
is attached to the cylinder head
3
along outlines of the rocker arm shaft holder
24
and both the cam shaft holders
25
,
26
with a slight gap. A breadthwise middle portion of the cylinder head cover
27
is shaped in a hollow corresponding to the middle connecting portion
24
a
of the rocker arm shaft holder
24
.
The cylinder head cover
27
is pressed against the cylinder head
3
by a coil spring
30
through a rubber bush
29
. The coil spring
30
is compressed to apply spring force to the cylinder head cover
27
by a bolt
28
which penetrates the middle bottom portion
27
a
of the cylinder head cover
27
and is screwed into a head of a bolt
45
provided at the middle connecting portion
24
a
.
Next, referring to
FIG. 3
, mechanisms for driving the air-intake valve
6
and the exhaust valve
7
will be described. The air-intake cam shaft
16
has journals (not shown) to be rotatively supported between the rocker arm shaft holder
24
and the cam shaft holder
25
disposed at regular intervals axially. The air-intake cam shaft
16
has also a first air-intake valve operation cam
51
, an air-intake cam pause section
50
, a third air-intake valve operation cam
53
, an air-intake valve pause section
50
, and a second air-intake valve operation cam
52
arranged between neighboring journals in this order from above in FIG.
3
. Similarly the exhaust cam shaft
17
has a first exhaust valve operation cam
51
′, an exhaust valve pause section
50
′, a third exhaust valve operation cam
53
′, an exhaust valve pause section
50
′, and a second exhaust valve operation cam
52
′.
The first air-intake valve operation cam
51
has a profile consisting of a circular base section surrounding the axis of the cam shaft as a center and a cam nose section projecting radially outward from the circular base section to make the air-intake valve
6
perform opening-closing motion substantially. The second air-intake valve operation cam
52
has the same profile as the first air-intake valve operation cam
51
. The third air-intake valve operation cam
53
also has a profile consisting of a circular base section surrounding the axis of the cam shaft as a center and a cam nose section projecting radially outward from the circular base section. However, the cam nose section of the third air-intake valve operation cam is higher than those of the first and second air-intake valve operation cams
51
,
52
. The air-intake valve pause section
50
is formed in a circular surrounding the axis of the cam shaft with the same radius as that of the circular base section of the first air-intake valve operation cam
51
. However, the air-intake valve pause section
50
may have a profile consisting of a circular base section surrounding he axis of the cam shaft as a center and a cam nose section which makes the air-intake valve in a pause state substantially but slightly open. The above is the same regarding the operation cams for the exhaust valve
7
.
As shown in
FIGS. 1 and 2
, the air-intake valve drive apparatus
18
comprises first and second air-intake valve drive rocker arms
54
,
55
(FIG.
3
), first, second and third air-intake valve free rocker arms
56
,
57
,
58
(FIG.
3
), and the air-intake rocker arm shaft
20
which is fixed to the rocker arm shaft holder
24
at a position obliquely under the air-intake cam shaft
16
and supports the rocker arms
54
,
55
,
56
,
57
,
58
so as to rock.
The air-intake rocker arm shaft
20
has a hole of circular cross-section in which three pipe members
31
are inserted together. Each pipe members
31
has a fan-shaped cross-section which is not changed in the axial direction. The three pipe members
31
are put together in a cylindrical shape having a circular outer periphery, and inserted in the hole of the rocker arm shaft
20
in a state that the outer periphery is contacted with an inner wall of the hole.
The pipe members
31
constitute switching oil-pressure supply passages
32
for supplying oil-pressure to first, second and third connection switchover means
61
,
62
,
63
respectively. Namely, the passages
32
always communicate with oil-pressure chambers
72
,
75
,
84
(
FIG. 6
) of the first, second and third connection switchover means
61
,
62
,
63
through communication passages
73
,
76
,
85
(
FIG. 6
) formed within the first, second and third air-intake valve free rocker arms
56
,
57
,
58
respectively. The switching oil-pressure supply passages
32
are connected with an oil-pressure source through respective control valves (not shown). The control valves are controlled by a control means (not shown) in accordance with engine operation regions (a region with small amount of intake air, a region with middle amount of intake air and a region with large amount of intake air, for example) which is judged based on a cylinder pause direction signal or signals from means for detecting engine rotative speed, engine load, amount of intake air and the like.
As shown in
FIG. 4
, the rocker arm shaft holder
34
or the lower cam holder, in other words, has a hole
20
a
for supporting the air-intake rocker arm shaft
20
. The hole
20
a
is formed just under one of the bolts
44
(the second fastening member) for fixing the air-intake cam shaft holder
25
or the air-intake upper cam holder, in other words, to the lower cam holder
24
, which is positioned outside.
The lower cam holder
24
has a hole
21
a for supporting the exhaust rocker arm shaft
21
. The hole
21
a
is formed just under one of the bolts
44
(the second fastening member) for fixing the exhaust cam shaft holder
26
or the exhaust upper cam holder, in other words, to the lower cam holder
24
, which is positioned outside.
Therefore, the rocker arm shafts
20
,
21
can be supported utilizing spaces under the bolts
44
, an air-intake valve
6
and an exhaust valve
7
forming a narrow angle between them can be adopted, and the cylinder head
3
can be miniaturized.
The air-intake rocker arm shaft
20
and the exhaust rocker arm shaft
21
are disposed tangentially crossing the respective bolts (the first fastening member)
43
. Therefore, the bolts
43
can be positioned inside to the utmost to contribute to miniaturization of the cylinder head
3
or the internal combustion engine
1
.
As shown in
FIG. 10
, the air-intake rocker arm shaft
20
and the exhaust rocker arm shaft
21
may be arranged so as to be contacted with the bolts
43
more closely. According to such an arrangement, rotations of the rocker arm shafts
20
,
21
can be prevented by the bolts
43
.
In this case, the rocker arm shafts
20
,
21
are disposed so that the bolt
43
penetrates only one of three switching oil-pressure supply passages
32
to prevent mutual communication of the switching oil-pressure supply passages.
As shown in
FIG. 3
, each of the first and second air-intake valve drive rocker arms
54
,
55
has an end contacted with an upper end of the tappet
15
of the air-intake valve
6
and another end contacted with the air-intake valve pause section
50
. The first air-intake valve free rocker arm
56
has a roller
56
a
coming into rolling contact with the first air-intake valve operation cam
51
, the second air-intake valve free rocker arm
57
has a roller
57
a
coming into rolling contact with the second air-intake valve operation cam
52
, and the third air-intake valve free rocker arm
58
has a roller
58
a
coming into rolling contact with the third air-intake valve operation cam
53
. The first air-intake valve free rocker arm
56
, the first air-intake valve drive rocker arm
54
, the third air-intake valve free rocker arm
58
, the second air-intake valve drive rocker arm
55
and the second air-intake valve free rocker arm
57
are arranged on the air-intake rocker arm shaft
20
at respective positions corresponding to the first air-intake valve operation cam
51
, the air-intake valve pause section
50
, the third air-intake valve operation cam
53
, the air-intake valve pause section
50
and the second air-intake valve operation cam
52
.
Springs
33
(
FIG. 2
) are provided between the cylinder head
3
and the respective first, second and third air-intake valve free rocker arms
56
,
57
,
58
. The rocker arms
56
,
57
,
58
are forced by the springs
33
so as to always come into contact with the first, second and third air-intake valve operation cams
51
,
52
,
53
.
The air-intake valve drive apparatus
18
has the first connection switchover means
61
for connecting and disconnecting the first air-intake valve drive rocker arm
54
with the first air-intake valve free rocker arm
56
, the second connection switchover means
62
for connecting and disconnecting the second air-intake valve drive arm with the second air-intake valve free rocker arm
57
, and the third connection switchover means
63
for connecting and disconnecting the first and second air-intake valve drive rocker arms
54
,
55
with the third air-intake valve free rocker arm
58
.
As shown in
FIG. 6
, the first connection switchover means
61
comprises a piston
65
fitted in a cylinder room
64
of the first air-intake valve free rocker arm
56
so as to slide, a pressing member
66
fitted in the piston
65
so as to slide, a pressing spring
67
compressed between the piston
65
and the pressing member
66
, a switching pin
69
which is contacted with the pressing member
66
and adapted to be fitted in the cylinder room
68
of the first air-intake valve drive rocker arm
54
so as to slide, a regulating member
70
which is contacted with the switching pin
69
at a side opposite to the pressing member
66
and fitted in the cylinder room
68
, and a return spring
71
compressed between the regulating member
70
and a bottom of the cylinder room
68
. Set load of the return spring
71
is larger than that of the pressing spring
67
.
The oil-pressure chamber
72
is formed between an end of the piston
65
and a bottom of the cylinder room
64
. The oil-pressure chamber
72
always communicates with the first switching oil-pressure supply passage
32
in the air-intake rocker arm shaft
20
through the communication passage
73
formed in the first air-intake valve free rocker arm
56
. The pressing member
66
disposed in the piston
65
is formed in a bottomed cylinder and has an open end facing a closed end of the piston
65
. The pressing spring
67
is compressed between the closed end of the piston
65
and a bottom of the pressing member
66
. The switching pin
69
can slide between a position in which it exists in both the cylinder rooms
64
,
68
and extends over the first air-intake valve drive rocker arm
54
and the first air-intake valve free rocker arm
56
, and another position in which it exists in the cylinder room
68
with its contact surface to the pressing member
66
positioned between the first air-intake valve drive rocker arm
54
and the first air-intake valve free rocker arm
56
. The regulating member
70
is formed in a bottomed cylinder having the bottom on a side contacted with the switching pin
69
. At an open end of the regulating member
70
are projected radially outward a flange
70
a
for coming into sliding contact with the cylinder room
68
. In the cylinder room
68
is fitted a retaining ring
74
for regulating movement of the regulating member
70
toward the switching pin
69
.
The first connection switchover means
61
is provided with a timing plate
90
(
FIG. 7
) for regulating timing of connection and disconnection of the first air-intake valve drive rocker arm
54
and the first air-intake valve free rocker arm
56
. The timing plate
90
is pivotally supported by a pin
91
to the first air-intake valve free rocker arm
56
so that the timing plate
90
can rock between a position in which it engages with an engage groove
65
a
of the piston
65
or an engage groove
65
b
provided between the piston
65
and the switching pin
69
for regulating movement of the piston
65
, and a position in which it comes out of the engage groove
65
a
or the engage groove
65
b
for allowing movement of the piston
65
. The timing plate
90
is forced by a spring
92
so as to engage with the engage grooves
65
a
,
65
b
. An extent of rocking motion of the timing plate
90
is regulated by that the timing plate comes into contact with a stopper face
93
which is a flat bottom surface of a groove formed on an outer periphery of the air-intake rocker arm shaft
20
.
In a state that oil-pressure in the oil-pressure chamber
72
is released, the switching pin
69
extends over the first air-intake valve free rocker arm
56
and the first air-intake valve drive rocker arm
54
to connect the rocker arms
54
,
56
with each other due to spring force of the return spring
71
. In this state, when the first air-intake valve free rocker arm
56
is contacted with the base circle section of the first air-intake valve operation cam
51
, the timing plate
90
engages with the engage groove
65
b
. At this time, the timing plate
90
is contacted with the stopper face
93
and a slight gap is formed between the timing plate
90
and the bottom of the engage groove (FIG.
7
(A)). When the first air-intake valve free rocker arm
56
is depressed by the cam nose section of the first air-intake valve operation cam
51
, rocking motion of the timing plate
90
is limited as the timing plate
90
is contacted with the stopper face
93
and the plate
90
comes out of the engage groove
65
b
(FIG.
7
(B)).
In a state that oil-pressure is applied into the oil-pressure chamber
72
, when the timing plate
90
comes out of engage groove
65
b
, the piston
65
moves until it comes into contact with the switching pin
69
compressing the pressing spring
67
. However, because the switching pin
69
extends over the first air-intake valve drive rocker arm
54
and the first air-intake valve free rocker arm
56
, the switching pin
69
is subjected to shearing force, and due to the force, the piston
65
is prevented from moving until the switching pin
69
is completely pushed into the first air-intake valve drive rocker arm
54
. When the first air-intake valve free rocker arm
56
begins to come into sliding contact with the base circle section of the first air-intake valve operation cam
51
and the above-mentioned shearing force becomes small, the piston
65
moves until the switching pin
69
is completely pushed into the first air-intake valve drive rocker arm
54
to disconnect the rocker arms
54
,
56
with each other.
In a state that the first air-intake valve drive rocker arm
54
and the first air-intake valve free rocker arm
56
are disconnected, when the first air-intake valve free rocker arm
56
is in contact with the base circle section of the first air-intake valve operation cam
51
, the timing plate
90
engages with the engage groove
65
a
. When the first air-intake valve free rocker arm
56
is depressed by the cam nose section of the first air-intake valve operation cam
51
, the timing plate
90
comes into contact with the stopper face
93
by which rocking motion of the timing plate
90
is limited and it comes out of the engage groove
65
a
.
In the state that oil-pressure in the oil-pressure chamber
72
is released in order to connect the rocker arms
54
,
56
, when the first air-intake valve free rocker arm
56
is depressed by the cam nose section of the first air-intake valve operation cam
51
and the timing plate
90
comes out of the engage groove
65
a
, the piston
65
is moved by spring force of the pressing spring
67
to a position for minimizing the volume of the oil-pressure chamber
72
. Then the first air-intake valve free rocker arm
56
begins to come into sliding contact with the base circle section of the first air-intake valve operation cam
51
, and when axes of the cylinder rooms
64
,
68
coincide with each other, the switching pin
69
is moved by spring force of the return spring
71
to a position in which the switching pin
69
extends over the rocker arms
54
,
56
to connect the both.
The second connection switchover means
62
for connecting and disconnecting the second air-intake valve drive rocker arm
55
and the second air-intake valve free rocker arm
57
is basically identical with the above-mentioned first connection switchover means
61
. However, in a state that oil-pressure in the oil-pressure chamber
75
is released, the switching pin is positioned within the second air-intake valve free rocker arm
57
and the rocker arms
55
,
57
are disconnected with each other. When oil-pressure is applied to the oil-pressure chamber
75
, the switching pin moves to a position in which the switching pin extends over the second air-intake valve drive rocker arm
55
and the second air-intake valve free rocker arm
57
to connect the rocker arms
55
,
57
. The oil-pressure chamber
75
formed between an end of the piston and the cylinder room always communicates with the second switching oil-pressure supply passage
32
through the communication passage
76
in the second air-intake free rocker arm
57
.
The third connection switchover means
63
for connecting and disconnecting the first air-intake valve drive rocker arm
54
, the second air-intake valve drive rocker arm
55
and the third air-intake valve free rocker arm
58
with each other comprises a switching pin
80
adapted to be fitted slidingly in a cylinder room
77
formed in the second air-intake valve drive rocker arm
55
and a cylinder room
78
formed in the third air-intake valve free rocker arm
58
, a switching pin
81
adapted to be fitted slidingly in the cylinder room
78
and a cylinder room
79
formed in the first air-intake valve drive rocker arm
54
and contacted with the switching pin
80
, a regulating member
82
contacted with an end of the switching pin
81
opposite to the switching pin
80
and fitted in the cylinder room
79
so as to slide, and a return spring
83
compressed between the regulating member
82
and a bottom of the cylinder room
79
.
An oil-pressure chamber
84
is formed between an end of the switching pin
80
and the cylinder room
77
. The oil-pressure chamber
84
always communicates with the third switching oil-pressure supply passage
32
through a communication passage
85
provided in the second air-intake valve drive rocker arm
55
. Since the first, second and third switching oil-pressure supply passages
32
are independent of each other, the first, second and third connection switchover means
61
,
62
,
63
can perform switching operation independently of each other.
An end of the switching pin
81
comes into contact with the switching pin
80
and another end of the switching pin
81
comes into contact with a bottom part of the regulating member which is shaped in a bottomed cylinder. At an open end of the regulating member
82
is projected radially outward a flange
82
a
which comes into sliding contact with the cylinder room
72
. A retaining spring
86
fixedly fitted to the cylinder room
79
comes into contact with the flange
82
a
to regulate movement of the regulating member
82
toward the switching pin
81
.
In the third connection switchover means
63
, when oil-pressure in the oil-pressure chamber
84
is released, the contact surface of the switching pins
80
,
81
exists between the second air-intake valve driver rocker arm
55
and the third air-intake valve free rocker arm
58
, and the contact surface of the switching pin
81
and the regulating member
82
exists between the third air-intake valve free rocker arm
58
and the first air-intake valve driver rocker arm
54
, to bring the rocker arms
54
,
55
,
58
into disconnected states. When oil-pressure is applied to the oil-pressure chamber
84
, the switching pin
80
moves until an end of the pin
80
opposite to the chamber
84
is positioned in the cylinder room
78
, and the switching pin
81
moves until an end of the pin
81
opposite to the pin
80
is positioned in the cylinder room
79
. Thus the rocker arms
54
55
,
58
are connected with each other.
Next, the hydraulic tappet holder
13
for holding the hydraulic tappet
15
will be described. As shown in
FIG. 8
, the hydraulic tappet holder
13
comprises a pair of attachment legs
110
, a pair of attachment legs
111
, four hydraulic tappet holding sections
112
for holding the respective hydraulic tappets
15
so as to slide, a cylindrical ignition plug holding section
113
, frame members
114
a
,
114
b
,
114
c
and
114
d
forming together a hexagonal plan and integrally combining the attachment legs
110
,
111
and the hydraulic tappet holding sections
112
, a connecting part
115
positioned on a side of the ignition plug holding section
113
toward the air-intake valve
6
and connecting the attachment legs
110
to each other, and a thin part
116
formed among the attachment legs
110
,
111
, the hydraulic tappet holding sections
112
, and ignition plug holding section
113
, the frame members
114
a
,
114
b
,
114
c
,
14
d ad the connecting part
115
. The frame members
114
a
,
114
b
connecting the hydraulic tappet holding sections
112
for the air-intake valves
6
and the hydraulic tappet holding sections
112
for the exhaust valves
7
, respectively, have the same thickness as the thin part
116
and are curved to join with the thin part
116
(FIG.
2
). The frame members
114
c
,
114
d
connecting the attachment legs
110
to the respective hydraulic tappet holding sections
112
are inclined downward toward the hydraulic tappet holding sections
112
. The ignition plug holding section
113
has an insertion hole
117
in which a pipe
14
b
receiving an ignition plug
14
a
is inserted, the ignition plug
14
a
is held by the cylinder head
3
through the pipe
14
b
.
On a side of each of the hydraulic tappet holding sections
112
for the air-intake valve
6
facing toward the air-intake rocker arm shaft
20
is formed a cut dent
112
a
which receives a part of the first air-intake valve drive rocker arm
54
or the second air-intake valve rocker arm
55
when the air-intake valve
6
is opened. Similarly, on a side of each of the hydraulic tappet holding sections
112
for the exhaust valve
7
facing toward the exhaust rocker arm shaft
21
is formed a cut dent
112
a
which receives a part of the first exhaust valve drive rocker arm
54
′ or the second exhaust valve drive rocker arm
55
′.
A reinforcement rib
118
formed on an upper surface of the thin part
116
extends radially from the ignition plug holding section
113
to join with the hydraulic tappet holding section
112
for the exhaust valve
7
. The rib
118
prevents the hydraulic tappet holding section
112
from having reduced strength due to formation of the cut dent
112
a
. On the one hand, between the ignition plug holding section
113
and the hydraulic tappet holding section
112
for the air-intake valve
6
is formed a reinforcement rib
119
(FIG.
9
), which is formed on a lower surface of the thin part
116
and extends radially from the ignition plug holding section
113
to join with the hydraulic tappet holding section
112
the air-intake valve
6
similarly to the rib
118
.
In the cylinder head
3
is formed a bolt hole
121
along a lower extension line of the bolt hole
120
of the hydraulic tappet holder
13
. The bolt
46
(
FIG. 3
) screwed in the cylinder head
3
passing through the bolt hole
120
for fixing the hydraulic tappet holder
13
to the cylinder head
3
passes through the hole
121
. As shown in
FIG. 5
, a pair of right and left openings of the bolt holes
121
disposed on respective sides of the rocker arm shaft holder
24
communicate with each other through a V-shaped oil communication passage
122
formed in the cylinder head
3
.
The diameter of the bolt hole
120
is larger than that of the bolt
46
so that oil can pass through the attachment leg
110
. Oil communication passages
123
a
,
123
b
are formed in the frame members extending obliquely downward from the bolt hole
120
toward the hydraulic tappet holding section
112
, and an oil communication passage
124
connecting the oil communication passages
123
a
of the air-intake valve side with each other is formed in the connecting part
115
. The hydraulic tappets
15
are supplied with oil through openings
123
c
provided on respective ends of the oil communication passages
123
a
,
123
b
.
An oil supply system to the hydraulic tappet holder
13
will be described. Oil delivered from an oil pump connected to a crankshaft of the engine
1
is led through an oil filter to a main gallery
125
(
FIG. 4
) which is formed in the cylinder block
2
in parallel with the crankshaft. Between an end of the main gallery
125
near a cam chain chamber
126
and one of the bolt holes
41
in the cylinder head
3
near the cam chain chamber
126
is formed an oil passage hole
127
to supply the oil to the bolt hole
41
.
As shown in
FIGS. 4
,
5
, a bolt hole
128
for the bolt
45
is formed in the middle connecting portion
24
a
of the rocker arm shaft holder
24
neighboring the cam chain chamber
126
, and a bolt hole
129
is formed in the cylinder head
3
along a lower extension line of the bolt hole
128
. An oil communication hole
130
is extended from an opening of the bolt hole
129
to the bolt hole
40
in which the bolt
42
for fixing the cylinder head
3
to the cylinder block
2
is inserted. Further, an oil communication passage
131
is extended from an opening of the bolt hole
121
neighboring the cam chain chamber
126
to the oil communication hole
130
.
Oil communication holes
132
extend from the bolt hole
128
of the rocker arm shaft holder
24
obliquely upward toward bearing sections of the air-intake cam shaft
16
and the exhaust cam shaft
17
. Also in the air-intake cam shaft
16
and the exhaust cam shaft
17
themselves, oil communication holes
133
communicating with the oil communication holes
132
are formed penetrating circumferential walls of the cam shafts
16
,
17
. Similar oil communication holes
132
,
133
are formed also at other bearing sections of the air-intake cam shaft
16
and the exhaust cam shaft
17
.
Next, positional relations of the first and second air-intake valve drive rocker arms
54
,
55
and the first, second and third air-intake valve free rocker arms
56
,
57
,
58
to the hydraulic tappet holder
13
will be described.
As shown in
FIG. 2
, at each end of the frame member
114
a
between the hydraulic tappet holding sections
112
for the air-intake valves
6
, a side of the frame member
114
a
facing toward the air-intake rocker arm shaft
20
is tangent to a plane including the axis of the cylindrical hydraulic tappet holding section
112
, and an upper end of the frame member
114
a
is positioned in the neighborhood of an axial middle of the cylindrical hydraulic tappet holding section
112
. Therefore, as shown in
FIG. 8
, a recess
135
facing toward the air-intake rocker arm shaft
20
is formed in the hydraulic tappet holder
13
by the hydraulic tappet holding sections
112
for the air-intake valves
6
and the frame member
114
a
. The hydraulic tappet holder
113
, the air-intake rocker arm shaft
20
and the air-intake cam shaft
116
are arranged so that the roller
58
a
of the third air-intake valve free rocker arm
58
pivotally supported on the air-intake rocker arm shaft
20
is received in the recess
135
. That the roller
58
a
is received in the recess
135
means that the hydraulic tappet holding section
112
and the roller
58
a
are overlapped when viewed in an axial direction of the crankshaft (direction perpendicular to the surface of
FIGS. 1
or
2
).
The roller
58
a
of the third air-intake valve free rocker arm
58
may be received in the recess
135
when the roller
58
a
is in sliding contact with the base circle section of the third air-intake valve operation cam
53
, or the roller
58
a
may be received in the recess
135
when the third air-intake valve free rocker arm
58
is in sliding contact with the cam nose section of the third air-intake valve operation cam
53
and has rotated by a predetermined angle. Anyway, the roller
58
a
should be received in the recess
135
in at least a part of rocking range of the third air-intake valve free rocking arm
58
. Therefore, the roller
58
a
may be positioned near the frame member
114
a
with a slight gap when lift of the air-intake valve
6
is maximum.
The attachment legs
110
of the hydraulic tappet holder
13
are arranged on a line parallel with the crankshaft and a distance between the attachment legs
110
is larger than that between the hydraulic tappet holding sections
112
for the air-intake valves
6
. An outside face of the frame member
114
c
connecting the attachment leg
110
with the hydraulic tappet holding section
112
for the air-intake valve
6
is positioned toward a center of the hydraulic tappet holder
13
with regard to a plane tangential to both cylindrical surfaces of the attachment leg
110
and the hydraulic tappet holding section
112
. Therefore, the hydraulic tappet holder
13
has a pair of recesses
136
formed by the attachment legs
110
, the hydraulic tappet holding sections
112
for the air-intake valves
6
and the outside faces of the frame members
114
c
. The hydraulic tappet holder
13
, the air-intake rocker arm shaft
20
and the air-intake cam shaft
16
(see
FIG. 2
) are arranged so that the rollers
56
a
,
57
a
of the first and second air-intake valve free rocker arms
56
,
57
are received in the recesses
136
respectively.
The meaning of receiving the rollers
56
a
57
a
in the recesses
136
is the same as in the case regarding the recess
135
and the third air-intake valve free rocker arm
58
.
Regarding the exhaust valve
7
, arrangement of the hydraulic tappet holder
13
, the exhaust rocker arm shaft
21
and the exhaust cam shaft
17
is basically the same as the foregoing. That is, the roller
58
′
a
of the third exhaust valve free rocker arm
58
′ is received in the recess
135
formed between the hydraulic tappet holding sections
112
for the exhaust valve
7
, and the rollers
56
′
a
,
57
′
a
of the first and second exhaust valve free rocker arms
56
′,
57
′ are received in the recesses
136
formed between the respective attachment legs
110
and the respective hydraulic tappet holding sections
112
for the exhaust valve
7
.
The above-mentioned embodiment of the present invention acts as follows.
During operation of the internal combustion engine
1
, if a cylinder pause instruction signal is made, the aforementioned control valve controls oil-pressure of the switching oil-pressure supply passage
32
on the basis of the signal so that all of the first, second and third connection switchover means
61
,
62
,
63
of the air-intake valve drive apparatus
18
are made in a disconnected state and similarly, all of the three connection switchover means of the exhaust valve drive apparatus
19
are made in disconnected states. Therefore, the first and second air-intake valve drive rocker arms
54
,
55
and the first and second exhaust valve rocker arms
54
′,
55
′ come into contact with the pause sections
50
,
50
′ of the air-intake cam shaft
16
and the exhaust cam shaft
17
to bring the air-intake valves
6
and the exhaust valves
7
in substantially closed pause states and the engine is brought into a cylinder pause state (FIG.
6
(A)).
When the engine
1
is operated in a operation region with a small amount of intake air, such as a low rotative speed region or a low load region, in the air-intake valve drive apparatus
18
, the first connection switchover means
61
is connected and the second and third connection switchover means
62
,
63
are disconnected, on the one hand, and in the exhaust valve drive apparatus
19
, the first connection switchover means is connected and the second and third connection switchover means are disconnected. Thus, the first air-intake valve drive rocker arm
54
is connected with the first air-intake valve free rocker arm
56
, and the first exhaust valve drive rocker
54
′ is connected with the first exhaust valve free rocker arm
56
′, therefore, the first air-intake valve driver rocker arm
54
and the first exhaust valve drive rocker arm
54
′ are driven by the first air-intake operation cam
51
of the exhaust cam shaft
17
, respectively, and one of the air-intake valves
6
and one of the exhaust valves
6
of a cylinder are made to perform opening-closing motion in accordance with the profiles of the respective operation cams
51
,
51
′ with smaller lifts than those of the third air-intake valve operation cam
53
and the third exhaust valve operation cam
53
, while the second air-intake valve driver rocker arm
55
and the second exhaust valve drive rocker arm
55
′ are in contact with the pause sections
50
,
50
′ of the air-intake cam shaft
16
and the exhaust cam shaft
17
to bring another air-intake valve
6
and another exhaust valve
7
of the cylinder in substantially closed pause states. Since only one air-intake valve
6
performs opening-closing motion to produce vortex or swirl in the combustion chamber, the nature of combustion is improved, circulation of a large amount of exhaust gas or lean combustion in engine low-speed or low-load operation region is possible, and emission and fuel consumption can be improved (FIG.
6
(B)).
When the engine
1
is operated in an operation region with an intermediate amount of intake air, such as a middle rotative speed region or a middle load region, in the air-intake valve drive apparatus
18
, the first and second connection switchover means
61
,
62
are connected and the third connection switchover means
63
is disconnected, on the one hand. And in the exhaust valve drive apparatus
19
, the first and second connection switchover means are connected and the third connection switchover means is disconnected to connect the first and second air-intake valve drive rocker arms
54
,
55
with the first and second air-intake valve free rocker arms
56
,
57
, respectively, and the first and second exhaust valve free rocker arms
56
′,
57
′, respectively. Therefore, the first and second air-intake valve operation cams
51
,
52
of the air-intake cam shaft
16
, and the first and second exhaust valve drive rocker arms
54
′,
55
′ are driven by the first and second exhaust valve drive rocker arms
54
,
55
are driven by the first and second air-intake valve operation cams
51
′,
52
′ of the exhaust cam shaft
17
. Accordingly, one of the air-intake valves
6
and one of the exhaust vales
7
in one cylinder are made to perform opening-closing motions in accordance with the profiles of the first air-intake valve operation cam
51
and the first exhaust valve operation cam
51
′ with smaller lifts than those of the third air-intake valve operation cam
53
and the third exhaust valve operation cam
53
′, while another air-intake valve
6
and another exhaust valve
7
are made to perform opening-closing motion in accordance with profiles of the second air-intake operation cam
52
and the second exhaust operation cam
52
′ with lifts smaller than those of the third air-intake valve operation cam
53
and the third exhaust valve operation cam
53
′. Since both the air-intake valves
6
are made to perform opening-closing motion in an engine operation region with a middle amount of intake air, engine output in an engine operation region between a low speed or low load region and a high speed or high load region can be improved (FIG.
6
(C)).
When the engine
1
is operated in an operation region with a large amount of intake air, such as high rotative speed or high load region, in the air-intake valve drive apparatus
18
, the third connection switchover means
63
is connected, on the one hand, in the exhaust valve drive apparatus
19
, the third connection switchover means is connected to connect the first and second air-intake valve drive rocker arms
54
,
55
with the third air-intake valve free rocker arm
58
and the first and second exhaust valve drive rocker arms
54
′,
55
′ with the third exhaust valve free rocker arm
58
′. Therefore, the first and second air-intake valve drive rocker arms
54
,
55
are driven by he air-intake valve operation cam
53
of the air-intake cam shaft
16
, and the first and second exhaust valve drive rocker arms
54
′,
55
′ are driven by the exhaust valve operation cam
53
′ of the exhaust cam shaft
17
. Accordingly, both the air-intake valves
6
and both the exhaust valves
7
are made to perform opening-closing motion in accordance with the profiles of the third air-intake valve operation cam
53
and the third exhaust vale operation cam
53
′ with a large lift, so that a high engine output required in an operation region with a large amount of intake air can be obtained. At that time, the first and second connection switchover means
61
,
62
, . . . may be connected or may be disconnected. In the latter case, since the first and second free rocker arms
56
,
57
,
56
′,
57
′ are cut off from the drive system of the air-intake valves
6
and the exhaust valves
7
, weight of the rocker arms driving the valves
6
,
7
is small so that the critical rotative speed can be raised (FIG.
6
(D)).
Each of the switching oil-pressure supply passages
32
is formed by the pipe member
31
and it is necessary only to insert these pipe members
31
in the hole of circular section formed in the respective rocker arm shafts
20
,
21
, so that three switching oil-pressure supply passages are formed easily and cost can be reduced. Each of the pipe members
31
has a fan-shaped cross-section unchanged axially, and three pipe members
31
are combined together in a circular cylindrical shape and inserted in the hole of the respective rocker arm shafts
20
,
21
in a state that the periphery of the combined pipe members
31
is in contact with the peripheral wall of the hole in the respective rocker arm shafts
20
,
21
. Therefore, the space in the hole can be utilized efficiently, and three switching oil-pressure supply passages each having a necessary passage area can be disposed in the shaft compactly. Thus, the valve mechanism can be miniaturized.
Even when the third air-intake valve free rocker arm
58
and the third exhaust valve free rocker arm
58
′ approach the hydraulic tappet holders
13
most closely, the roller
58
a
,
58
′
a
of the free rocker arms
58
,
58
′ can be received in the recess
135
formed between the hydraulic tappet holding sections
112
, and to the extent, horizontal and vertical distances between the air-intake and exhaust rocker arm shafts
20
,
21
and the respective hydraulic tappet holding sections
112
can be made small. Therefore, the valve mechanism can be miniaturized and freedom of layout of the valve mechanism component members in the valve mechanism chamber increases.
Even when the first and second air-intake valve free rocker arms
56
,
57
and the first and second exhaust valve free rocker arms
56
′,
57
′ approach the hydraulic tappet holder
13
to the utmost, the rollers
56
a,
57
a
,
56
′
a
,
57
′
a
of the free rocker arms
56
,
57
,
56
′,
57
′ can be received in the recesses
136
formed between the attachment legs
110
,
111
and the hydraulic tappet holding sections
112
, and to the extent, distances between both the air-intake rocker arms
22
and between both the exhaust rocker arms
23
in an axial direction of the rocker arm shaft at every cylinder can be made small. Therefore, the air-intake rocker arms
22
and the exhaust rocker arms
23
can be made compact and the valve mechanism can be miniaturized.
As mentioned above, the cut recesses
112
a
are formed at a side of each hydraulic tappet holding section
112
of the hydraulic tappet holder
13
facing toward the rocker arm shaft
20
or
21
for receiving a part of the first or second air-intake valve drive rocker arm
54
(
55
) or the first or second exhaust valve drive rocker arm
54
(
55
′) therefore, vertical distances between the hydraulic tappet holding sections
112
and the rocker arm shafts
20
,
21
can be made small to miniaturize the valve mechanism. Since the reinforcement ribs
118
,
119
are formed between the cylindrical ignition plug holding section
112
and the respective hydraulic tappet holding sections
112
, lowering of strength of the hydraulic tappet holding section
112
due to formation of the cut recess
112
a
can be prevented.
In the aforementioned embodiment, the profile of the second air-intake valve operation cam
52
is the same as that of the first air-intake valve operation cam
51
. However, both of the profiles may be made different to set opening times, closing times or opening lifts of the first and second air-intake valves differently from each other. The pipe members
31
constituting the switching oil-pressure supply passages
32
have the same cross-sectional areas usually, but, if necessary, the cross-sectional areas may be made different from each other.
Claims
- 1. A valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, comprising;a cam shaft having a pair of pause sections for holding the air-intake valves substantially in closing pause states, a first operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, a second operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, and a third operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion with a larger lift compared to the first and second operation cams; a first drive rocker arm operatively connected to one of the air-intake valves and contacted with one of the pause sections of the cam shaft; a second drive rocker arm operatively connected to another air-intake valve and contacted with another pause section of the cam shaft; a first free rocker arm contacted with the first operation cam; a second free rocker arm contacted with the second operation cam; a third free rocker arm contacted with the third operation cam; a first connection switchover means for connecting and disconnecting the first drive rocker arm with the first free rocker arm; a second connection switchover means for connecting and disconnecting the second drive rocker arm with the second free rocker arm; a third connection switchover means for connecting and disconnecting the first driver rocker arm and the second driver rocker arm with the third free rocker arm; and at least one of the drive rocker arms being pivotally supported on a rocker arm shaft and operatively connected to the air-intake valve through a hydraulic tappet which is held by a hydraulic tappet holder fixed to a cylinder head of the engine, and the hydraulic tappet holder being formed with a recess positioned within a rocking range of the drive rocker arm and capable of receiving the drive rocker arm partially.
- 2. A valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, comprising;a cam shaft having a pair of pause sections for holding the air-intake valves substantially in closing pause states, a first operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, a second operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, and a third operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion with a larger lift compared to the first and second operation cams; a first drive rocker arm operatively connected to one of the air-intake valves and contacted with one of the pause sections of the cam shaft; a second drive rocker arm operatively connected to another air-intake valve and contacted with another pause section of the cam shaft; a first free rocker arm contacted with the first operation cam; a second free rocker arm contacted with the second operation cam; a third free rocker arm contacted with the third operation cam; a first connection switchover means for connecting and disconnecting the first drive rocker arm with the first free rocker arm; a second connection switchover means for connecting and disconnecting the second drive rocker arm with the second free rocker arm; a third connection switchover means for connecting and disconnecting the first driver rocker arm and the second driver rocker arm with the third free rocker arm; and the first and second drive rocker arms being pivotally supported on a rocker arm shaft and operatively connected to the air-intake valves through respective hydraulic tappets which are held by respective hydraulic tappet holding sections of a hydraulic tappet holder fixed to a cylinder head of the engine, and the hydraulic tappet holding sections being formed with recesses positioned within rocking ranges of the first and second drive rocker arms and capable of receiving the drive rocker arms partially.
- 3. A valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, comprising:a cam shaft having a pair of pause sections for holding the air-intake valves substantially in closing pause states a first operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, a second operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, and a third operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion with a larger lift compared to the first and second operation cams; a first drive rocker arm operatively connected to one of the air-intake valves and contacted with one of the pause sections of the cam shaft; a second drive rocker arm operatively connected to another air-intake valve and contacted with another pause section of the cam shaft; a first free rocker arm contacted with the first operation cam; a second free rocker arm contacted with the second operation cam; a third free rocker arm contacted with the third operation cam; a first connection switchover means for connecting and disconnecting the first drive rocker arm with the first free rocker arm; a second connection switchover means for connecting and disconnecting the second drive rocker arm with the second free rocker arm; a third connection switchover means for connecting and disconnecting the first drive rocker arm and the second drive rocker arm with the third free rocker arm wherein, in an engine operation region with the cylinder pausing, the first, second and third connection switchover means are in disconnecting states; in an engine operation region with a small amount of intake air, the first connection switchover means is in a connecting state and the second and third connection switchover means are in disconnecting states; in an engine operation region with a middle amount of intake air, the first and second connection switchover means are in a connecting state and the third connection switchover means is in a disconnecting state; and in an engine operation region with a large amount of intake air, the third connection switchover means is in a connecting state; and pipe members of fan-shaped cross section being provided in an axial hole of a rocker arm shaft pivotally supporting the rocker arms, the pipe members communicating with the first, second and third connection switchover means to constitute first, second and third switching oil-pressure supply passages, respectively.
- 4. A valve mechanism of an internal combustion engine as claimed in claim 3, wherein the air-intake valves are operatively connected to the first and second drive rocker arms through hydraulic tappets respectively, and a hydraulic tappet holder for holding the hydraulic tappets has respective hydraulic tappet holding sections between which a recess is formed for receiving a roller of the third free rocker arm contacted with the third operation cam.
- 5. A valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, comprising:a cam shaft having a pair of pause sections for holding the air-intake valves substantially in closing pause states, a first operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, a second operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, and a third operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion with a larger lift compared to the first and second operation cams; a first drive rocker arm operatively connected to one of the air-intake valves and contacted with one of the pause sections of the cam shaft; a second drive rocker arm operatively connected to another air-intake valve and contacted with another pause section of the cam shaft; a first free rocker arm contacted with the first operation cam; a second free rocker arm contacted with the second operation cam; a third free rocker arm contacted with the third operation cam; a first connection switchover means for connecting and disconnecting the first drive rocker arm with the first free rocker arm; a second connection switchover means for connecting and disconnecting the second drive rocker arm with the second free rocker arm; a third connection switchover means for connecting and disconnecting the first drive rocker arm and the second drive rocker arm with the third free rocker arm; and pipe members of fan-shaped cross section being provided in an axial hole of a rocker arm shaft pivotally supporting the rocker arms, the pipe members communicating with the first, second and third connection switchover means to constitute first, second and third switching oil-pressure supply passages respectively.
- 6. A valve mechanism of an internal combustion engine as claimed in claim 5, wherein the air-intake valves are operatively connected to the first and second drive rocker arms through hydraulic tappets respectively, and a hydraulic tappet holder for holding the hydraulic tappets has respective hydraulic tappet holding sections between which a recess is formed for receiving a roller of the third free rocker arm contacted with the third operation cam.
- 7. A valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, comprising;a cam shaft having a pair of pause sections for holding the air-intake valves substantially in closing pause states, a first operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, a second operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, and a third operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion with a larger lift compared to the first and second operation cams; a first drive rocker arm operatively connected to one of the air-intake valves and contacted with one of the pause sections of the cam shaft; a second drive rocker arm operatively connected to another air-intake valve and contacted with another pause section of the cam shaft; a first free rocker arm contacted with the first operation cam; a second free rocker arm contacted with the second operation cam; a third free rocker arm contacted with the third operation cam; a first connection switchover means for connecting and disconnecting the first drive rocker arm with the first free rocker arm; a second connection switchover means for connecting and disconnecting the second drive rocker arm with the second free rocker arm; a third connection switchover means for connecting and disconnecting the first driver rocker arm and the second driver rocker arm with the third free rocker arm; and air-intake valves operatively connected to the first and second drive rocker arms through hydraulic tappets respectively, and a hydraulic tappet holder for holding the hydraulic tappets having respective hydraulic tappet holding sections between which a recess is formed for receiving a roller of the third free rocker arm contacted with the third operation cam.
- 8. A valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, comprising;a cam shaft having a pair of pause sections for holding the air-intake valves substantially in closing pause states, a first operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, a second operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, and a third operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion with a larger lift compared to the first and second operation cams; a first drive rocker arm operatively connected to one of the air-intake valves and contacted with one of the pause sections of the cam shaft; a second drive rocker arm operatively connected to another air-intake valve and contacted with another pause section of the cam shaft; a first free rocker arm contacted with the first operation cam; a second free rocker arm contacted with the second operation cam; a third free rocker arm contacted with the third operation cam; a first connection switchover means for connecting and disconnecting the first drive rocker arm with the first free rocker arm; a second connection switchover means for connecting and disconnecting the second drive rocker arm with the second free rocker arm; a third connection switchover means for connecting and disconnecting the first driver rocker arm and the second driver rocker arm with the third free rocker arm; and a valve mechanism supporting structure comprising an air-intake cam shaft bearing section for supporting an air-intake cam shaft, an exhaust cam shaft bearing section for supporting an exhaust cam shaft, a lower cam holder common to the both cam shaft bearing sections, an air-intake upper cam holder cooperating with the lower cam holder to form the air-intake cam shaft bearing section, and an exhaust upper cam holder cooperating with the lower cam holder to form the air-intake cam shaft bearing section, and an exhaust upper cam holder cooperating with the lower cam holder to form the exhaust cam shaft bearing section, both ends of the lower cam holder being fixed to a cylinder head of the engine by first fastening members, and both ends of the air-intake upper cam holder and both ends of the exhaust upper cam holder being fixed to the lower cam holder at positions inside of the first fastening members by second fastening members having diameters smaller than that of the first fastening member.
- 9. A valve mechanism of an internal combustion engine as claimed in claim 8, wherein the lower cam holder supports an air-intake rocker arm shaft and an exhaust rocker arm shaft so as not to rotate, the air-intake rocker arm shaft is disposed under one of the second fastening members for the air-intake upper cam holder positioned outside, and the exhaust rocker arm shaft is disposed under one of the second fastening members for the exhaust upper cam holder positioned outside.
- 10. A valve mechanism of an internal combustion engine as claimed in claim 9, wherein the each rocker arm shaft is disposed crossing the corresponding first fastening member.
- 11. A valve mechanism of an internal combustion engine as claimed in claim 8, wherein the each rocker arm shaft is disposed crossing the corresponding first fastening member.
- 12. A valve mechanism of an internal combustion engine as claimed in claim 11, wherein pipe members of fan-shaped cross section are provided in an axial hole of a rocker arm shaft pivotally supporting the rocker arms, the pipe members communicate with the first, second and third connection switchover means to constitute first, second and third switching oil-pressure supply passages respectively, and the first fastening member penetrates only one of the switching oil-pressure supply passages.
Priority Claims (1)
Number |
Date |
Country |
Kind |
10-314281 |
Nov 1998 |
JP |
|
US Referenced Citations (5)
Foreign Referenced Citations (1)
Number |
Date |
Country |
8-61031 |
Mar 1996 |
JP |