Internal-combustion engines – Poppet valve operating mechanism – Overhead camshaft
Reexamination Certificate
1999-10-12
2001-08-21
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Overhead camshaft
C123S090280, C123S193500, C123S090220
Reexamination Certificate
active
06276323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to multi-valve double-over-head-camshaft engines (referred to as “DOHC engines”), and more particularly to DOHC engines which have relatively large space for installation of a functional part (e.g., injector) along the center line of each of cylinder bores.
2. Description of the Related Art
One of known DOHC engines is a four-valve DOHC engine which has two intake valves and two exhaust valves for each of cylinders and which is equipped with a functional part such as injector or spark plug arranged along the center line of each of the cylinder bores. In this type of DOHC engine, when viewed from the top, intake valves are arranged generally linearly in parallel to the longitudinal center line of the engine, and the exhaust valves are also arranged linearly in parallel to the longitudinal center line of the engine on the opposite side.
In a conventional valve drive mechanism for such a four-valve DOHC engine, when viewed from the top, the center line of a camshaft for the intake valves extends right above the mutual center line of the linearly arranged intake valves, and likewise the center line of the other camshaft for the exhaust valves lies right above the mutual center line of the linearly arranged exhaust valves. Further, the center line of each cam (or cam lobe) lies right above the center of associated valve.
If an engine has relatively small bores, the distance between the intake camshaft and exhaust camshaft is relatively small, and the distance between each two cams (cam lobes) on each camshaft for each cylinder is relatively small. Therefore, the space for a functional part such as injector or spark plug to be installed along the center line of each cylinder bore is also relatively small. Similarly, if the included angle (i.e., an angle between the intake valve and exhaust valve) is small, the spacing between the intake and exhaust camshafts is small so that the installation space for the functional part is small.
An engine having five valves for each cylinder is disclosed in, for example, EP 0 444 562 A1, entitled “Timing System, Particularly For An Internal Combustion Engine With A Number Of Valves Per Cylinder” published on Sep. 4, 1991.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a valve drive mechanism for a DOHC engine which leaves sufficient installation space for a functional part to be arranged along the center line of each of cylinder bores even if each cylinder bore is relatively small and/or the included angle is relatively small.
According to one aspect of the present invention, there is provided a valve drive mechanism for a DOHC engine, the engine having a plurality of intake valves and exhaust valves for each cylinder and a functional part located at a central portion of each cylinder bore, characterized in that when viewed from the top, the center line of the intake camshaft is offset from a mutual center line of the linearly arranged intake valves in a transverse direction of the engine, i.e., to an outward direction of the cylinder bore, such that the intake camshaft center line is apart from the longitudinal center line of the engine and the center line of the exhaust camshaft is offset in the opposite outward direction from a mutual center line of the linearly arranged exhaust valves, with the parallel relationship between the intake and exhaust camshafts being maintained. In short, the distance between the intake camshaft and exhaust camshaft is enlarged as compared with a conventional arrangement. Therefore, larger installation space is ensured for a functional part to be located along the center line of each cylinder.
According to another aspect of the present invention, there is provided a valve drive mechanism for a DOHC engine, the engine having two intake valves and two exhaust valves for each cylinder and a functional part located at a central portion of each cylinder bore, characterized in that when viewed from the top, the center lines of each pair of cams (cam lobes) on each camshaft for each cylinder are offset from the centers of associated valves in the opposite directions in the longitudinal direction of the camshaft. The opposite directions in the longitudinal direction of the camshaft may be defined as follows: to an outside direction of the associated cylinder bore along the associated camshaft.
According to still another aspect of the present invention, there is provided a valve drive mechanism for a DOHC engine which combines the above two aspects of the invention. Specifically, provided is a valve drive mechanism for an engine having two intake valves and two exhaust valves for each cylinder and a functional part arranged along the center line of each cylinder, characterized in that when viewed from the top, the center line of the intake camshaft is offset from the mutual center line of the linearly arranged intake valves to an outside direction of the cylinder bore and the center line of the exhaust camshaft is offset from the mutual center line of the exhaust valves to an (opposite) outside direction of the cylinder bore, with the parallel relationship between the intake and exhaust camshafts being maintained, and the center lines of each pair of cams (cam lobes) on each camshaft for each cylinder are offset from the centers of associated valves to an outside direction of the cylinder bore along the camshaft.
REFERENCES:
patent: 5099812 (1992-03-01), Yamada
patent: 5148779 (1992-09-01), Okuse et al.
patent: 5535710 (1996-07-01), Zoschke et al.
patent: 5570669 (1996-11-01), Regueiro
patent: 5606942 (1997-03-01), Tsuzuku et al.
patent: 5752479 (1998-05-01), Kinoshita et al.
patent: 0 262 250 A1 (1988-04-01), None
patent: 0 444 562 A1 (1991-09-01), None
patent: 0 499 601 A1 (1992-08-01), None
patent: 0 692 613 A1 (1996-01-01), None
patent: 8-128308 (1996-05-01), None
Isuzu Motors Limited
Lo Weilun
McCormick Paulding & Huber LLP
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