Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2001-08-10
2002-06-04
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090170, C123S090500
Reexamination Certificate
active
06397804
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a valve drive mechanism for an engine which is variable in valve lift and has a valve lifter or tappet which selectively transmits rotation of different cams of different lift cams.
2. Description of Related Art
There has been known various valve drive mechanisms which can drive valves with variable valve lifts. For example in U.S. Pat. No. 5,287,830 a valve drive mechanism has a center tappet and a side tappet arranged coaxially with each other and couples them together by a hydraulically operated locking/unlocking pin for high speed engine operation with a high lift cam and uncoupled from one another by the hydraulically operated locking/unlocking pin for low speed engine operation with low lift cams. In Japanese Unexamined Patent Publication No. 10-141030 a cylindrically shaped tappet is divided into three parts in a rotational direction of cams. Further, in Japanese Unexamined Patent Publication No. 7-71213 a shim is divided into three parts.
The tappet disclosed in U.S. Pat. No. 5,287,830 comprises a cylindrical center tappet and a side tappet which coaxially surrounds the cylindrical center tappet. This cylindrical configuration of the tappet has restraints on the length of the center tappet as a cam follower. In order to avoid such a restraint, it is proposed to incorporate a center tappet having an elongated top. However, this alternative center tappet increases the height of the tappet. The tappet disclosed in Japanese Unexamined Patent Publication No. 10-141030 or Japanese Unexamined Patent Publication No. 7-71213 has the drawback that, since a circumferential outer wall at an edge of an interface of the side tappet with the center tappet causes contact slide on a wall of a tappet guide bore formed in a cylinder head in other words, since the center tappet is not subjected to a force by the cam, while the side tappet is driven by side cams, there occurs a rise in pressure between the side tappet and tappet guide bore, which results in uneven abrasion of the tappet and tappet guide.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a valve drive mechanism which enables a large cam follower length of a tappet and lowers a force that is caused due to an inclination of the tappet and is exerted on a tappet guide from the tappet.
The above object of the present invention is accomplished by a valve drive mechanism including one center cam which has a center cam lobe per valve and a pair of side cams which have side cam lobes, respectively, different from the center cam lobe per valve and are arranged on a camshaft on opposite sides of the center cam in an axial direction of the camshaft, a generally cylindrically shaped tappet assembly which is movable in a direction of valve lift and comprises two mating parts, and locking/unlocking means for mechanically coupling the two mating parts together and uncoupling the two mating parts from each other so as to selectively transmit rotation of the center cam and the side cams as reciprocating movement to the valve. The valve drive mechanism comprises a center tappet, forming one of the two mating parts and driven by the center cam; which is formed with opposite circular-arcuate vertical side walls in a rotational direction of the camshaft, a side tappet, forming another one of the two mating parts and driven by the side cams, which is divided into two side tappet parts in the axial direction of the camshaft between which the center tappet is received for slide movement relative to the side tappet in said direction of valve lift and is formed at the side tappet parts with opposite circular-arcuate vertical end walls, respectively, such that the circular-arcuate vertical side walls of the center tappet and the circular-arcuate vertical end walls of the side tappet form a generally cylindrical configuration of the tappet assembly, and guide means for guiding the slide movement of the center tappet relative to the side tappet which comprises a vertical flat side wall extending continuously from each of opposite sides of each circular-arcuate end wall of the side tappet in the rotational direction of the camshaft and a vertical shroud extending continuously from each of opposite ends of each circular-arcuate side wall of the center tappet in the axial direction of the camshaft and forming thereon a vertical flat side surface. The vertical shroud at the vertical flat side surface is slidable on the vertical flat side wall so as thereby to guide the slide movement of the center tappet relative to the side tappet.
In the valve drive mechanism which preferably includes the center cam having a high lift cam lobe and the side cam having a low lift cam lobe, the two side tappet parts are joined by a connecting bridge at which the tappet assembly is engaged by a valve stem of the valve. This connecting bridge is formed with a spring receiving recess in which a return spring is received so as to force the center tappet to return when the center tappet slides relatively to the side tappet. Further, the connecting bridge may be provided with at least one oil spill port formed at a bottom of the spring receiving recess. A shim may be disposed between the connecting bridge and the valve stem.
The locking/unlocking means may preferably comprise guide bores which are formed in each the center tappet and each the side tappet part of the side tappet and are in alignment with one another in the direction of the rotational axis of camshaft, a locking/unlocking pin received for slide movement in the guide bore of the center tappet, a plunger received for slide movement in the guide bore of one of the two side tappet parts of the side tappet, a spring loaded receiver received for slide movement in the guide bore of another of the two side tappet parts of the side tappet, and an oil channel formed in the one side tappet part of the side tappet so as to communicate with the guide bore of the one of the two side tappet parts of the side tappet, through which hydraulic oil is introduced into and removed from the guide bore of the one side tappet part of the side tappet. The hydraulic oil is supplied into the guide bore of the one side tappet part of the side tappet through the oil channel so as to force the plunger and the locking/unlocking pin to slide against the spring loaded receiver and to partly enter the guide bores of the center tappet and the other side tappet part of the side tappet, respectively, thereby mechanically coupling the center tappet to the side tappet together and is removed from the guide bore of the one side tappet part of the side tappet through the oil channel so as to cause the plunger and the locking/unlocking pin to slide back by the spring loaded receiver, thereby mechanically uncoupling the center tappet from the side tappet. The locking/unlocking pin is preferably formed with a circumferential recess.
The tappet assembly may includes a stopper in the guide bore in which the plunger is received so as to limit the slide movement of the plunger in the guide bore and to close the guide bore at one end. In this case, the guide bore is communicated with the oil channel through a connecting oil channel.
The valve drive mechanism includes oil supply means comprising oil galleries which extend along the intake camshaft and the exhaust camshaft, respectively, branch oil channels which branch off from the oil galleries, respectively and extend between two tappet assemblies for twin intake valves and two tappet assemblies for twin exhaust valves for each cylinder, oil channels each of which is formed in an outer wall of the side tappet and is in communication with the branch oil channel. The plunger in the guide bore of the one side tappet part of the side tappet operates to bring the center tappet and the side tappet into a locked or mechanically coupled condition when pressure of hydraulic oil is supplied to the plunger from the oil gallery through the oil channel via the branch oil channel and into an unlocked or
Asanomi Kouji
Harada Setsuo
Matsuura Hirokazu
Oda Hiroyuki
Saiki Masayuki
Brooks & Kushman
Lo Weilun
Mazda Motor Corporation
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