Internal-combustion engines – Poppet valve operating mechanism – Plural valve trains – single actuator
Reexamination Certificate
2000-04-25
2001-05-29
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Plural valve trains, single actuator
C123S090280, C123S090400
Reexamination Certificate
active
06237553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrangement for actuating valves employed in an internal combustion engine.
2. Description of the Related Art
A four-valve engine that has two intake valves and two exhaust valves per each cylinder is known in the art. In some of the four-valve engines, the two intake valves for each cylinder are bridged to each other by a valve bridge and the two exhaust valves are also bridged by another valve bridge. Upper surfaces of these valve bridges are pressed by ends of rocker arms respectively such that the two intake valves are forced downwards (or in a valve opening direction) simultaneously and the two exhaust valves are also forced downwards (or in a valve opening direction) simultaneously.
The end of each rocker arm performs a pivot movement about an associated shaft. Thus, the rocker arm end slides on the upper surface of the valve bridge while the rocker arm pushes the valve bridge downwards. This sliding movement of the rocker arm takes place in a certain small area on the valve bridge upper surface. Thus, this area is only subjected to wear. In order to prevent this local wear, Japanese Utility Model Application Laid Open Publication No. 2-126006 provides an improvement. Specifically, a rotatable chip member is located on the valve bridge top surface such that it contacts the rocker arm. Since the chip member rotates, the contact between the rocker arm and chip member varies. Accordingly, the wear of the chip member is less concentrated.
In this improvement, however, the pivot movement of the rocker arm draws an arcuate orbit that passes through a rotation center of the chip member when it slides in contact with the chip member. As a result, the rocker arm cannot apply a sufficiently large rotational moment onto the chip member due to the drag between the rocker arm and chip member. Thus, the chip member does not rotate very much, and the local wear is not prevented as much as expected.
Another known arrangement for actuating valves of an engine is an over head cam arrangement that allows a camshaft to directly contact and drive the intake and exhaust valves. A rotatable lifter is sometimes located at a top of each valve stem such that it contacts the associated cam. By offsetting the lifter center from the cam contact point (press center), the cam can apply a rotational moment to the lifter and causes the lifter to rotate. The drag exerted by the cam in this case positively forces the lifter to rotate so that the wear is not concentrated in a particular area.
This arrangement may be utilized in the engine having rocker arms. Specifically, the rocker arm contact point (press center) may be offset from the chip member rotation center. However, the center lines of the two intake valves (or exhaust valves) lie in the same plane as the chip member center. Thus, if the rocker arm press center were offset relative to this plane, a couple of force would act on the entire valve bridge including the chip member from the rocker arm and valves. This would cause lateral pressure to apply between the valve bridge and intake valves (or exhaust valves). If large lateral pressure were generated, gall would occur.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the above described problems.
According to one aspect of the present invention, there is provided a valve drive arrangement for use in an engine having a pair of intake valves and a pair of exhaust valves for each cylinder, with each pair of intake valves being coupled to each other by a valve bridge and forced downwards simultaneously by a single rocker arm, and each pair of exhaust valves being coupled to each other by another valve bridge and forced downwards simultaneously by another single rocker arm, characterized in that a contact member is rotatably provided on an upper surface of each valve bridge such that it contacts the associated rocker arm, the press center (contact point) of the rocker arm to the associated contact member and center lines of the associated valves lie in a single plane, and a rotation center of the associated contact member is offset from this single plane.
For the sake of easier understanding, the following description only deals with the two intake valves for a particular cylinder. Since the press center of the rocker arm to the contact member and the center lines of the intake valves lie in the same plane, no couple of force acts on the valve bridge including the contact member. Accordingly, no lateral pressure acts between the valve bridge and the valves. Thus, gall is prevented. Further, since the press center of the rocker arm to the contact member does not coincide with the rotation center of the contact member, the rotation of the contact member is promoted. Accordingly, local wear does not occur in the contact member.
Each contact member may have a relatively large head and a stem extending from the head, and the stem may be rotatably received in a recess formed in the associated valve bridge. Each rocker arm may have a chip made from a wear-resistive material, and the chip may contact the head of the associated contact member. The stem of each contact member may be loosely fitted in the recess of the associated valve bridge. Each contact member may be made from a wear-resistive material. No bridge guide is required for supporting movement of the valve bridge.
REFERENCES:
patent: 5410995 (1995-05-01), Bentz et al.
patent: 5626110 (1997-05-01), Regueiro
patent: 5699762 (1997-12-01), Horiuchi
patent: 5921209 (1999-07-01), Regueiro
patent: 2-126006 (1990-10-01), None
Isuzu Motors Limited
Lo Weilun
McCormick Paulding & Huber LLP
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