Internal-combustion engines – Particular piston and enclosing cylinder construction – Cylinder head
Reexamination Certificate
2000-09-08
2001-08-28
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Particular piston and enclosing cylinder construction
Cylinder head
C123S090270
Reexamination Certificate
active
06279529
ABSTRACT:
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.
REFERENCES:
patent: 5080057 (1992-01-01), Batzill et al.
patent: 5094197 (1992-03-01), Rosa
patent: 5522354 (1996-06-01), Sakamoto et al.
patent: 5651337 (1997-07-01), Regueiro
patent: 5921210 (1999-07-01), Regueiro
Fujita Hideo
Kageyama Hidetoshi
Komatsu Kenji
Beutler Ernest A.
McMahon Marguerite
Yamaha Hatsudoki Kabushiki Kaisha
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