Information
-
Patent Grant
-
6279529
-
Patent Number
6,279,529
-
Date Filed
Friday, September 8, 200023 years ago
-
Date Issued
Tuesday, August 28, 200122 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 123 1935
- 123 1933
- 123 9027
- 123 9048
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International Classifications
-
Abstract
A cylinder head constructions wherein the cylinder head is comprised of a main cylinder head member that slidably supports the valves for the engine, and which has an upper peripheral edge that defines a cam chamber. At least one camshaft and the tappets associated thereby are supported by a separate cam and tappet carrier member that is affixed to the main cylinder head member. The bearing surfaces for the camshaft are formed at longitudinally spaced points and the valves for the corresponding cylinder are disposed between those points and are in parallel relation but have a large diameter and their actuating tappets have a large diameter but do not encroach on the bearing surfaces for the camshaft.
Description
This invention relates to a valve actuating mechanism for an internal combustion engine and, more particularly, to an improved cylinder head and valve actuating system for an overhead camshaft internal combustion engine.
It is well recognized that the performance of internal combustion engines can be improved through the use of overhead valves operated by overhead mounted camshafts. When an overhead camshaft arrangement is employed, the cylinder head assembly trends to become much more complicated than with a conventional pushrod operated engine. This is because the cylinder bead must, in addition to supporting the valves and the valve springs, provide support for the camshaft and for the actuators for the valves. Frequently, the valves are directly operated and this means that an arrangement must be provided for slidably supporting the thimble tappets that operate the individual valves from the camshaft.
If all of these functions are performed primarily by the cylinder head, then the cylinder head casting becomes extremely complicated. In addition, since it is necessary to machine the bearings for the camshaft provided by the cylinder head, and the bores for slidably supporting the tappets, than machining operations also add significantly to the cost of the cylinder head. Furthermore, there is the problem of assembly of all of components into such a unitary cylinder head assembly, and the problems of accessibility the various fasteners for securing the cylinder head to the cylinder block and the bearing caps to the cylinder head for journaling the camshaft. Of course, the problems mentioned above are complicated when the engine employs twin overhead camshafts.
It has been proposed, therefore, to employ a construction wherein the main cylinder head member itself does not have to perform all of these functions. For example, in U.S. Pat. No. 4,612,885, entitled “Camshaft Bearing Arrangement For Overhead Cam Engine”, issued Sep. 23, 1986, in the name of Masaaki Yoshikawa, and assigned to the assignee hereof, there is depicted a cylinder head arrangement wherein the main cylinder head assembly only supports the poppet valves for their movement and the return springs for the poppet valves. The camshafts and valve actuating tappets are supported in a separate cam carrier that is affixed to the cylinder head and thus can be machined and cast separately simplifying the aforenoted problems. However, with the arrangement shown in that Patent, the cam carrier forms the outer periphery of the cylinder head and the cam cover must sealingly engage it. In addition, the cam carrier must have a sealing arrangement around its outer periphery with the upper surface of the cylinder head to afford sealing. Hence, substantial addition machining operations are required.
Another arrangement has been proposed which offsets or avoids certain of the difficulties in connection with the structure shown in U.S. Pat. No. 4,612,885 and which problems are noted in the preceding paragraph. This construction is described in co-pending application Ser. No: 09/624,709, which application is a continuation of co-pending application of the same title, filed Jun. 7, 1995, which application is a division of co-pending application Ser. No. 08/145490, filed Oct. 29, 1993, now issued as U.S. Pat. No. 5,522,354, all assigned to the assignee hereof.
In connection with the constructions shown in that co-pending application, there is provided a cam and tappet carrier member that is comprised of a plurality of longitudinally spaced bearing portions which provide bearings for the camshaft and which are interconnected by longitudinally extending bridging portions that define bores that slidably receive the tappets for actuating the associated valves. In all instances shown in that application where the bearing members are spaced at the opposite sides of the cylinder bore, there are provided three intake valves that are staggered relative to the cylinder bore and hence, the size of the valve and size of the tappets can be maintained quite large without minimizing or requiring cut-outs in the bearing area. However, when there are employed only two valves per cylinder or where two valves having parallel axes are disposed adjacent each other, it is more difficult to maintain large valve areas and also large tappet bearing areas without encroachment to and reduction in the size of the camshaft bearing surface.
It is, therefore, a principal object of this invention to provide an improved cylinder head assembly for an overhead camshaft internal combustion engine.
It is a further object of this invention to provide an improved cylinder head assembly for an overhead cam internal combustion engine wherein at least some of the valve actuating tappets and at least one of the camshafts are supported by a separate cam carrier member that is affixed to the cylinder head but in such a way that this cam carrier member need perform no sealing functions for the overall cylinder head assembly.
It is a further object of this invention to provide an improved and simplified cylinder head assembly for an internal combustion engine having an overhead camshaft wherein machining and assembly operations are considerably simplified.
It is yet a further object to this invention to provide an improved cam and tappet carrier member where the bearing surfaces for the camshaft are formed at longitudinally spaced points and the valves for the corresponding cylinder are disposed between those points and are in parallel relation but have a large diameter and their actuating tappets have a large diameter but do not encroach on the bearing surfaces for the camshaft.
SUMMARY OF THE INVENTION
This invention is adapted to be embodied in a cam and tappet carrier member that is associated with cylinder head member to form a cylinder head assembly for an overhead camshaft engine. The cam and tappet carrier member is affixed to the cylinder head member within the cam chamber and defines at least a pair bearing surfaces for journaling a camshaft on opposite sides of a cylinder bore axis. These bearing surfaces are integrally connected by a bridging member that defines at least a pair of tappet bores each of which receives a respective tappet actuated by the camshaft for operating a respective one of a pair of valves supported by the main cylinder head member and serving the cylinder bore. The bridging member defines at least two parallel bores having their axes lying in a common plane for reciprocally supporting thimble tappets. The thimble tappets are associated with valves that are mounted in the cylinder head and associated with the respective cylinder. The axes of the stems of the valves are offset from the axes of the tappet receiving bores in a direction spaced outwardly toward the cam bearing surfaces so as to permit a large valve size and also to permit a large tappet diameter without encroaching upon the cam bearing surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a cross sectional view of a cylinder head assembly constructed in accordance with an embodiment of the invention and taken along the line
1
—
1
of FIG.
2
.
FIG. 2
is a partial top plan view of the cylinder head assembly with the cam cover, camshaft bearing caps and other members removed so as to more clearly show the construction.
FIG. 3
is a cross sectional view taken along the line
3
—
3
of
FIG. 1
showing the offsetting of the tappet bores relative to the valves to show this feature of the invention.
FIG. 4
is a partial, perspective view of the cam and tappet carrier member.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
In the drawings, only a portion of the cylinder head assembly of an internal combustion engine is depicted and this portion of the cylinder head assembly is not shown attached to the cylinder block, piston and remaining portions of the engine, which may be considered to be conventional. Also, it is not believed necessary to show all cylinders of the engine because those skilled in the art will readily understand how the invention may be employed in conjunction with multiple cylinder engines. In addition, it is to be understood that the cylinder head assembly depicted may be the cylinder head assembly for an in-line engine or for one bank of a V-type or opposed engine. Again, it is believed that those skilled in the art can readily understand how the invention can be applied to such engines.
Referring now in detail to the drawings, a cylinder head assembly constructed in accordance with this embodiment is identified generally by the reference numeral
11
. The cylinder head assembly
11
includes a number of parts, to be described including a main cylinder head member
12
which is formed conveniently as a casting and may be made from a light weight material such as aluminum, aluminum alloys or the like.
The main cylinder head member
12
has a lower sealing surface
13
that is adapted to be affixed to an associated cylinder block by means such as socket headed screws
14
or the like. The socket headed screws
14
are disposed around a depressed central area
15
(
FIGS. 3 and 3
) of the cylinder head surface
13
that is adapted to cooperate with the associated cylinder bore to form the combustion chamber thereof, along with the piston and cylinder bore.
The main cylinder head member
12
is also provided with an upper peripheral sealing surface
16
, which surrounds a cam chamber
17
in which a valve actuating mechanism (to be described) is contained.
The cylinder head assembly
11
is of the twin overhead cam type embodying a cross flow pattern. To this end, one side, the left side, of the cam chamber
17
comprises the intake side and the other side of the cam chamber
17
comprises the exhaust side.
A plurality of intake valves
18
are supported for reciprocation in the main cylinder head member
12
by means of valve guides
19
that are pressed in place. In the illustrated embodiment, there are provided two intake valves for each combustion chamber recess
15
. It should be readily apparent to those skilled in the art, however, that the invention can be employed with engines having different numbers of intake valves. The invention, however, has particular utility with multiple valve engines because it easily facilitates the use of actuating mechanisms for such multiple valves.
Each intake valve
18
is biased toward its closed position by means of a coil compression spring
21
that bears against machined surfaces
22
of the main cylinder head member
12
. The other ends of the coil springs
21
acts against keeper retainer assemblies
23
that are affixed to the upper ends of the stems of the valves
18
. As a result of this construction, the intake valves
18
are all biased to a closed position, as is well known in this art. The intake valves
18
are opened in a manner, which will be described.
The heads of the intake valves
18
cooperate with valve seats
24
that are pressed or otherwise held in place in the cylinder head member
12
and which are formed at the termination of intake ports
25
that extend through the intake side of the main cylinder head member
12
. The intake ports
25
may be either individual for each intake valve
18
or may be Siamese in a desired grouping, as shown in the illustrated embodiment.
Turning now to the exhaust side of the main cylinder head member
12
, this includes a plurality of poppet type exhaust valves
26
which have there stems slidably supported in valve guides
27
that are pressed into the main cylinder head members
12
. In the illustrated embodiment, there are two exhaust valves per cylinder, but, like the intake valves
18
, it is to be understood that the invention may be employed in conjunction with engines having any number of exhaust valves. As with the intake valves, however, the invention has particular utility with multiple valve engines.
Coil compression springs
28
encircle the stems of the exhaust valves
26
and engage at one end machined surfaces
29
of the main cylinder head member
12
. The opposite sides of these springs
28
are retained to the stems of the exhaust valves
26
by keeper retainer assemblies
31
. Single or Siamese exhaust ports
32
extend from the valve seats to an exhaust system (not shown).
The area between the intake and exhaust sides of the main cylinder head member
12
is provided with a plurality of spark plug wells
33
, one for each combustion chamber recess
15
to accommodate a spark plug
34
that is threaded into a tapped opening formed at the base of the well
33
so that the gap of the spark plug
34
will be disposed substantially centrally in the combustion chamber recess
15
.
The mechanism for actuating the intake valves
18
will now be described, and this includes a combined cam and tappet carrier member, indicated generally by the reference numeral
35
. The carrier member
35
embodies important features of the invention and may be formed as a casting from a lightweight material such as aluminum or aluminum alloy. The carrier member
35
has tappet supporting, bridging portions
36
that are provided with machined bores
37
for receiving a tumble type tappets
38
associated with each of the intake valves
18
. Since the carrier member
35
is a separate piece, these tappet receiving bores
37
may be easily machined.
The carrier member
35
is also provided with camshaft lower bearing portions
39
which are disposed between adjacent cylinders and which provide bearing surfaces
41
(
FIG. 1
) for the rotatably journaling the bearing portions of an intake camshaft
42
which has individual cam lobes
43
(
FIG. 1
) that cooperates with the thimble tappets
38
for opening the intake valves
18
in a well known manner.
Individual bearing caps
44
are affixed to the carrier member
35
and also affixed to this assembly to the cylinder head member
12
by means of bolts
45
. Locating pins (not shown) may be provided at spaced locations to facilitate alignment. The rotational axis thus defined for the intake camshaft lies in a common plane containing the axes of reciprocation of both the tappets
38
and the intake valves
18
and is perpendicular to these axes.
It should be noted that the cam bearing portions
39
, and, specifically, the bearing surfaces
41
overly the cylinder head hold down bolts
14
. In order to permit retorqueing of these bolts
14
without removing the engine carrier assembly, the carrier member bearing surfaces
41
may be provided with through bores (not shown) through which a tool may be passed so as to torque down the cylinder head fastener
14
on the intake side.
It should be readily apparent that the intake side of the cylinder head assembly
11
can be easily assembled by placing the intake valves
18
in place with their springs
21
and retainers
23
before the carrier member
35
is installed. Although the upper lower and bearing surfaces
41
of the carrier member are parallel to the lower sealing surface
13
of the cylinder head while the tappet bores
37
are disposed at an angle, this later assembly presents no problem because the tappets
38
can be sized so that they can be in place in the carrier member
35
either before or after the carrier member
35
is placed on the cylinder head member
12
. The bores
37
are adequate in size so as to clear the valve spring assemblies during this installation. It should also be noted that the carrier member
35
is disposed inwardly of the cylinder head upper sealing surface
16
within the cam cavity
17
and does not extend above this surface.
It should be readily apparent that since the bridging portions
36
in which the tappet receiving bores
37
are formed are disposed between the camshaft bearing portions
39
, the diameter for the tappets
38
is somewhat limited unless the cam bearing portions
39
are cut away to provide a larger diameter. However, this reduces the effective surface of the bearing portions
41
and may not be desired.
Therefore, an while still maintaining a large size for the heads of the intake valves
18
, the tappet receiving bores
37
of the bridging members
36
are offset slightly relative to the center of the valve stems of the intake valves
18
as best seen in
FIGS. 2 and 3
. In these figures, the center of the valve stem is indicated by the dimension Vc while the center of the tappet
38
and, accordingly, the cam lobe
43
is indicated at Lc. This offsetting “F” in the direction of the length of the engine permits the tappets
38
to be disposed further from the camshaft bearing portions
39
for each cylinder than the valves. Thus, a large tappet area is provided without minimizing the effect that this would have if the valves were equally displaced.
This would provide a small bridging surface in the cylinder head between the heads of the valves
18
, which is not desirable, because cracking might occur in this area. Thus, by offsetting the tappet bores relative to the valve stem axes it is possible to maximize bearing areas for the camshaft
42
while at the same time maintaining a large valve diameter without a narrow area in the cylinder head between the intake valve seats
24
which could cause the possibility of cracking.
Finally, it should be noted that the area of the bridging portions
36
surrounding each tappet receiving bore
37
is formed with a slotted area, indicated at
46
in
FIG. 1
that permits lubricant to collect around the bores
37
and insure that the tappets are well lubricated.
Turning now to the exhaust side valve of the cylinder head assembly
11
and the actuation for the exhaust valves
26
, this is of the conventional type wherein the exhaust camshaft, to be described, and valve actuating thimble tappets are supported within the main cylinder member
12
.
The cylinder head member
12
on the exhaust side is provided with pairs of bosses
48
that are bored as at
49
so as to receive thimble tappets
51
. These thimble tappets
51
engage the keeper retainer assemblies
31
for operating the exhaust valves
26
.
An exhaust camshaft
52
having lobes
53
is journalled in the cylinder head member
12
by bearing portions
54
formed integrally with the exhaust side of the cylinder head assembly between the pairs of bosses
48
for the tappets
51
for each cylinders. Bearing caps
55
are affixed to each of these bosses
54
by threaded fasteners
56
for engaging corresponding bearing surfaces on the exhaust camshaft
52
between the lobes
53
for journaling the exhaust camshaft.
The cam chamber
17
is covered by a cam cover
57
which carriers a sealing gasket
58
around its periphery and which sealingly engages the surface
16
of the cylinder head member
12
to close the cam chamber
17
.
It should be readily apparent from the foregoing description of the described embodiment of the invention is very effective in providing a cylinder head assembly that can be easily machined and assembled and, nevertheless, will accommodate a large number of parallel tappets and support the associated actuating camshaft. Also large valve and tappet diameters are possible without reducing the cam bearing surface area. Of course, the embodiment described is only preferred embodiment of the invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.
Claims
- 1. A cam and tappet carrier member for association with a cylinder head member to form a cylinder head assembly for an overhead camshaft engine, said cam and tappet carrier member being adapted to be affixed to the cylinder head member within a cam chamber and defining at least a pair of bearing surfaces for journaling a camshaft on opposite sides of a cylinder bore axis, said bearing surfaces are integrally connected by a bridging member defining at least a pair of tappet bores each of which receives a respective tappet actuated by the camshaft for operating a respective one of a pair of valves supported by the main cylinder head member and serving the cylinder bore, said bridging member defining at least two parallel bores having their axes lying in a common plane for reciprocally supporting thimble tappets, the thimble tappets being associated with valves that are mounted in the cylinder head member and associated with the respective cylinder bore, the axes of the stems of the valves being offset from the axes of the tappet receiving bores in a direction spaced outwardly toward the cam bearing surfaces so as to permit a large valve size and also to permit a large tappet diameter without encroaching upon said bearing surfaces.
- 2. A cam and tappet carrier member as set forth in claim 1 wherein the bearing surfaces define a rotational axis for the camshaft that is generally perpendicular to the tappet bore axes.
- 3. A cam and tappet carrier member as set forth in claim 1 wherein the bearing surfaces define a rotational axis for the camshaft that is generally perpendicular to the valve axes.
- 4. A cam and tappet carrier member as set forth in claim 3 wherein the bearing surfaces define a rotational axis for the camshaft that is generally perpendicular to the tappet bore axes and lies in the plane containing the tappet bore axes.
- 5. A cylinder head assembly for an overhead camshaft engine comprising a main cylinder head member defining a lower sealing surface for sealing engagement with a cylinder block and at least one portion of said lower surface cooperating with a cylinder bore of the cylinder block to define a combustion chamber, said cylinder head member having an uppermost peripheral surface surrounding a cam chamber and adapted to sealingly engage with a cam cover for enclosing said cam chamber, and a cam and tappet carrier member as set forth in claim 1 affixed to said main cylinder head member within said cam chamber inwardly of said uppermost peripheral surface and below said uppermost peripheral surface so that said uppermost peripheral surface only absorbs the sealing force of said cam cover.
- 6. A cylinder head assembly for an overhead camshaft engine as set forth in claim 5 wherein the main cylinder head member has a plurality of longitudinally spaced portions each cooperating with a respective cylinder bore and forming a respective combustion chamber, the cam and tappet carrier member providing a plurality of transversely extending members forming a plurality of longitudinally spaced bearing surfaces for the camshaft each formed between adjacent cylinder bores.
- 7. A cylinder head assembly for an overhead camshaft engine as set forth in claim 6, further including a plurality of bearing caps each affixed to a respective transversely extending member of the cam and tappet carrier member and fastening means for affixing at least partially said bearing caps and said cam and tappet carrier member to said main cylinder head member.
- 8. A cylinder head assembly as set forth in claim 7 wherein the bearing surfaces define a rotational axis for the camshaft that is generally perpendicular to the tappet bore axes.
- 9. A cylinder head assembly as set forth in claim 7 wherein the bearing surfaces define a rotational axis for the camshaft that is generally perpendicular to the valve axes.
- 10. A cylinder head assembly as set forth in claim 9 wherein the bearing surfaces define a rotational axis for the camshaft that is generally perpendicular to the tappet bore axes and lies in the plane containing the tappet bore axes.
Priority Claims (1)
Number |
Date |
Country |
Kind |
11-272200 |
Sep 1999 |
JP |
|
US Referenced Citations (5)