Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2001-03-13
2002-10-29
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090330, C123S090160, C123S090270, C123S090340
Reexamination Certificate
active
06470840
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an internal combustion engine for automobiles or the like, more particularly to a cylinder head structure defining the upper part of an engine body of an internal combustion engine.
BACKGROUND OF THE INVENTION
Typically, in a combustion chamber for each cylinder of an internal combustion engine, an intake port is provided with an intake valve for opening/closing the intake port to induct an air or mixture into the combustion chamber, while an exhaust port is provided with an exhaust port for opening/closing the exhaust port to discharge an expanded combustion gas from the combustion chamber. Currently, for valve mechanisms for driving and/or controlling the opening/closing motions of such intake and exhaust valves, there are widely used various types including an overhead-valve (OHV) type wherein a camshaft is arranged in the side region of a crankcase, a single overhead camshaft (SOHC) type wherein a camshaft is arranged in the upper region of a cylinder head and the intake and exhaust valves are driven by a single camshaft, or a double overhead camshaft (DOHC) type wherein a camshaft is arranged in the upper region of a cylinder head and the intake and exhaust valves are driven separately by individual camshafts.
As compared to the OHV engine, the SOHC and DOHC engines are superior in high-speed performance. Conversely, relatively long distance between the camshaft and crankshaft of the SOHC and DOHC engines can lead to a complicated driving arrangement of the camshaft and a complicated cylinder head structure.
The valves of the SOHC engine are driven indirectly by the camshaft through a rocker arm. In contrast, the valves of the DOHC engine are driven directly by the camshaft. In the DOHC engine, a tappet or lifter is employed as a follower element which is contacted continuously with the cam surface of the camshaft so as to convert the rotational motion of the cam into the reciprocating motion to be transferred to the valves. As a carrying element for containing and guiding the tappet, a tappet guide or lifter guide is formed integrally with the cylinder head by casting, or otherwise is separately formed and then incorporated in the cylinder head.
On the other hand, each of bearing portions each having a journal portion for supporting the camshaft is comprised of a vertical wall portion protruding vertically from the base portion of the cylinder head and a cam cap coupled with the vertical wall portion. The vertical wall portion is formed integrally with the cylinder head by casting, or otherwise is separately formed and then incorporated in the cylinder head. In order to assure the supporting rigidity of the camshaft, the bearing portion is arranged close to the cam located for each valve.
Taking a four-valve type engine having a pair of intake ports and intake valves and a pair of exhaust ports and exhaust valves for each cylinder as an example, a pair of intake valve driving cams or a pair of exhaust valve driving cams are aligned on the camshaft. Two adjacent bearing portions are located on both sided of the pair of intake valve cams or the pair of exhaust valve cams with interposing these cams between the bearing portions, and more specifically each bearing portion is located in the outboard region of a cylinder and between said cylinder and another cylinder adjacent to said cylinder. Otherwise, each bearing portion is located between the pair of intake valve cams or the pair of exhaust valve cams with being interposed between these cams, and more specifically the bearing portion is located in the outboard region of a cylinder and at a position corresponding to the center of said cylinder.
However, in case that a variable valve timing (VVT) control and/or variable valve lift (VVL) control device for varying the valve timing and/or valve-lift amount of the intake and/or exhaust valves in response to driving conditions is applied to improve fuel consumption and output power, a plurality of cams each having a different cam profile in valve-opening timing or valve-lift amount, for example, are provided for each valve, and this results in the increased number of cams for each cylinder. For example, in the above-exemplified engine, the bearing portion may be hardly to be arranged at the position corresponding to the center of the cylinder, and thereby will be arranged between adjacent cylinders. In this case, if the number of cams for each valve is not more than two, the bearing portion is not required to locate excessively far from the position corresponding to the center of the cylinder. However, if the number of cams for each valve is increased, for example, up to 3 or more, the bearing portion is required to locate far from the position corresponding to the center of the cylinder and consequently locates at approximately middle position between the cylinder and another cylinder adjacent to the cylinder.
Unfortunately, in the middle portion between adjacent cylinders, a cylinder head bolt for securing the cylinder head to a cylinder block is necessarily located to evenly receive the stress due to the combustion pressure in the cylinder, which leads to the interference between the cylinder head bolt and the bearing portion. For measures to this problem, the cylinder head may be fastened to a cylinder block by using in common a bolt for uniting the cam cap with the vertical wall portion. However, this undesirably results in a lengthened cylinder head bolt and excessively enlarged bearing portion.
On the other hand, separately mounting the vertical wall portion or tappet guide to the cylinder head leads to the increased number of parts, a complexified cylinder head structure, and a lowered flexibility of cylinder head layout. This causes problems, such as the significantly increased volume and height of the cylinder head. Further, in the engine having the variable valve control device, the cylinder head is required to firmly support associated components including an oil pressure control valve for supplying an operating oil to a movable portion of the device.
A technique for reducing the number of parts of the cylinder head is, for example, disclosed in Japanese Patent Laid-Open Publication No. Hei 7-103068 wherein a cam cap for supporting the upper portion of a camshaft reliably secures a plug tube for an ignition plug to a cylinder head by pressing the plug tube in its axial direction with constraining the plug tube in its radial direction. Japanese Patent Laid-Open Publication No. Hei 5-86813 also discloses a related technique wherein an ignition-plughole is comprised of a lower ignition-plug hole formed in a cam carrier for supporting the lower portion of a camshaft and an upper ignition-plug hole formed in a cam cap for supporting the upper portion of the camshaft. However, these techniques cannot solve the above problems all at once.
It is known that a carrier member integrally including a vertical wall portion defining a bearing portion for a camshaft and a tappet guide for containing a tappet is formed separately to a cylinder head. For example, Japanese Patent Laid-Open Publication No. Hei 6-146822 discloses a related technique wherein a cam carrier integrally including at least a camshaft journal and a lifter guide portion is formed separately to a cylinder head, and the cam carrier is integrally fastened to a cylinder head body. Japanese Patent Laid-Open Publication No. Hei 8-74540 also discloses a related technique wherein a cam carrier having a plurality of cam bearing portions integrally connected with each other by guide bosses formed with lifter guide holes is prepared as respective intake and exhaust cam carriers to be mounted separately to a cylinder head.
Further, Japanese Patent No. 259735 discloses a related technique wherein a camshaft bearing pedestal doubling as a support member of a tappet is connected to a cylinder head. Japanese Patent Laid-Open Publication No. Hei 4-91351 also discloses a related technique wherein a carrier supporting a camshaft and formed with a tappet-carrying device is m
Asanoumi Kouji
Deguchi Hiroaki
Ebesu Hidesaku
Harada Setsuo
Matsuura Hirokazu
Denion Thomas
Mazda Motor Corporation
Nixon & Peabody LLP
O'Brien Sean
Studebaker Donald R.
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