Internal-combustion engines – Poppet valve operating mechanism – Overhead camshaft
Reexamination Certificate
2002-03-27
2003-09-09
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Overhead camshaft
C123S090390, C123S090430, C123S090450
Reexamination Certificate
active
06615781
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an overhead camshaft type valve train for an internal combustion chamber which includes rocker arms for driving engine valves, and more particularly to an overhead camshaft type valve train including biasing means for biasing the rocker arms to either a cam side or an engine valve side.
2. Description of the Related Art
Conventionally, as an overhead camshaft type valve train including rocker arms for driving engine valves, Japanese Utility Model Publication No. 34563/1994 discloses an overhead camshaft type valve train for an internal combustion engine having biasing members for biasing the rocker arms to a cam side. This overhead camshaft type valve train includes intake side and exhaust side valve trains having the same construction. The intake side valve train for each cylinder includes a pair of drive rocker arms, a free rocker arm and a connection switching mechanism. The pair of drive rocker arms are brought into sliding contact with two low-speed cams, respectively, provided on a camshaft rotatably supported by cam holders fastened to a cylinder head and are interlockingly connected to a pair of intake valves, respectively. The free rocker arm is situated between the two drive rocker arms to be brought into sliding contact with a high-speed cam. The connection switching mechanism switches over the connection and release of connection of the drive rocker arms and the free rocker arm. Since the free rocker arm moves idly irrespective of the intake valve when the engine is driven at low speeds, in order to prevent the rough action thereof, a lost motion mechanism (corresponding to the biasing member) is provided on the intake side valve train for biasing the free rocker arm to the high speed cam side, and the lost motion mechanism is held in a holding portion having a recessed portion formed in the cylinder head.
Incidentally, according to the related art, since the holding portion for the lost motion mechanism is formed in the cylinder head, the construction of the cylinder head becomes complicated in which fixing portions for valve guides for slidingly guiding the intake valve and the exhaust valve and accommodation cylinders for accommodating spark plugs are formed, and there is caused a problem that productivity is decreased. In addition, since a space for the holding portion needs to be secured, the compact layout of the fixing portions, the accommodating cylinders and moreover valve springs becomes difficult, and this causes a further problem that the cylinder head is enlarged, this leading to the enlargement of the valve train chamber and eventually the internal combustion engine. To cope with this, in order to simply the construction of the cylinder head without forming the holding portions in the cylinder head so as to improve the productivity and realize a compact layout of the fixing portions, the accommodating cylinders and the valve springs, it is contemplated that a member is separately prepared in which a holding portion is formed for attachment to the cylinder head. However, the valve train chamber and hence the internal combustion engine are enlarged to such an extent that the additional member is attached thereto, and in the event that the internal combustion engine is enlarged, the weight thereof is increased. Moreover, the number of components is increased and hence the assembling man hours are also increased, leading to the deterioration of assembling performance.
On the other hand, a load is exerted to the holding portion for holding the lost motion mechanism, from the free rocker arm which is rocked when brought into sliding contact with the high speed cam. Therefore, it is desirable that the deformation of the cylinder head in which the holding portions are formed due to the load so exerted is made as small as possible and that a biasing force which is stable in a certain direction is exerted to the free rocker arm. Accordingly, the thickness of a peripheral portion of the member where the holding portion is formed needs to be increased, or reinforcement ribs are formed in such a manner as to connect to the holding portion in the peripheral portion of the holding portion so that the rigidity can be increased. As a result of such efforts, the cylinder head is made large in size and heavy in weight, thus causing a problem increasing the size and weight of the internal combustion engine.
Further, U.S. Pat. No. 5,297,506 discloses a valve operating system in which a holding portion for holding a spring is provided in a cam holder. However, according to U.S. Pat. No. 5,297,506, the holding portion is protruded from the cam holder, thus causing a problem increasing the size of the internal combustion engine.
SUMMARY OF THE INVENTION
The invention was made in view of the situations, and an object of the invention is to reduce the size and weight of a cylinder head on which an overhead camshaft type valve train having biasing members held at holding portions is provided, leading eventually to provision of an overhead camshaft type valve train for an internal combustion engine which can reduce the size and weight of the internal combustion engine.
With a view to attaining the object, according to a first aspect of the invention, there is provided an overhead camshaft type valve train for an internal combustion engine including: a camshaft supported by a plurality of holders provided on an cylinder head; rocker arms mockingly supported on a rocker shaft for driving engine valves to open; cams provided on the camshaft for regulating the rocking action of the rocker arms; and biasing members for biasing the rocker arms to either a cam side or an engine valve side, wherein at least one of the plurality of holders is fastened to the cylinder head with fastening members at two fastening portions spaced apart from each other in an orthogonal direction which intersects at right angles with an axial direction of the rocker shaft when viewed from a plane, and wherein the at least one of holders includes a holding portion for holding the biasing member, which is integrally formed on at least one of the two fastening portions.
According to the first aspect of the invention, the following advantage can be provided. Namely, the holding member for holding the biasing member is formed on the holder fastened to the cylinder head for supporting the shaft member which is a constituent component of the valve train, the construction of the cylinder head is simplified to improve the productivity of cylinder heads. Moreover, since there is no need to prepare a separate member for forming the holding portion for attachment to the cylinder head, the number of components is reduced to improve the assembling efficiency of internal combustion engines, and at the same time the size and weight of an internal combustion engine so produced can be reduced. Furthermore, since the fastening portion where the holding portion is formed integrally is a portion where the holder with the holding portion is fastened to the cylinder head with the fastening member, the deformation generated in the fastening portion where the holding portion is formed by virtue of a load exerted from the rocker arm to the holding portion via the biasing member is extremely small, and the biasing force which is stable in the certain direction can be exerted to the rocker arm. Thus, since the deformation amount of the holder with the holding portion due to the load exerted to the holding portion is made as mall as possible by making use of the fastening portion, there is almost no need to form a thicker portion on the holder or reinforcement ribs that would otherwise be needed due to the formation of the holding portion on the holder, whereby the holder with the holding portion can be made small in size and light in weight, this leading to an internal combustion chamber which is small in size and light in weight. Moreover, since the holding portion is integrally formed on the fastening portion, the rigidity thereof can be improved f
Sato Toshiyuki
Takahara Naoki
Tanaka Shigekazu
Arent Fox Kintner Plotkin & Kahn
Corrigan Jaime
Denion Thomas
Honda Giken Kogyo Kabushiki Kaisha
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