Internal-combustion engines – Poppet valve operating mechanism – Tappet
Reexamination Certificate
1999-10-11
2001-01-09
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Tappet
C123S090650, C074S569000
Reexamination Certificate
active
06170450
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority, under 35 U.S.C. 119, of earlier-filed Italian Application MI98A002190, filed Oct. 13, 1998.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE DISCLOSURE
The present invention concerns an improved hydraulic tappet, which besides being especially suitable for application to diesel engines also proves advantageous for normal internal combustion engines.
As is known, in some diesel engines the distribution shaft (cam shaft), in addition to having cams acting by sliding against the disk of the hydraulic tappet associated with each poppet valve head (or stem), also has a second series of cams. Each cam of this second series of cams is rotationally displaced relative to the respective cam for controlling the engine poppet valve. The second cams indirectly control the diesel fuel injectors at the proper time by means of a rocker arm.
The actuation of the diesel fuel injectors constitutes a further load on the camshaft, subjecting it to a downward deflection, which also influences the functioning of the cam that is supposed to actuate the cylinder poppet valves arranged on the same shaft. Such a deflection of the cam shaft results in an irregular opening of the valves and, consequently, a poor functioning of the engine.
In fact, the conventional hydraulic tappet, by its construction, is unable in certain cases to follow, with sufficient speed, the “lift loss” of the hydraulic tappet which, instead of causing the valve to open, collapses by virtue of the size of the deflection of the camshaft. It should be understood that as used herein and in the appended claims, the term “lift loss” will mean and include the lost motion which occurs within the tappet as a result of the deflection of the injector cam, so that the engine poppet valve doesn't open.
BRIEF SUMMARY OF THE INVENTION
The purpose of the invention is to guarantee that the engine poppet valves do not open by virtue of the deflection of the camshaft, but only under the command of the valve control cams.
According to the invention, in a conventional hydraulic tappet of the type formed by an inverted cylindrical cup, closed at the top by the cam contact disk, it is proposed to insert, directly beneath the contact disk itself, an additional elastic device comprised of two different elements, of which:
the first element, directly supported on the internal surface of the disk of the tappet, is comprised of a flat ring equipped with peripheral spacing elements which keep it centered within the internal cylindrical wall of the tappet itself; and
the second element, placed beneath the preceding one and having the function of a leaf spring, is formed by preferably three elastic arms (or spokes), arranged in a rosette at equal distance from each other and combined with a central junction disk with a central borehole. The central junction disk is supported against the rim of the low-pressure oil reservoir portion so as to form a cushioning element between the disk of the tappet and the valve stem, the disk being placed in series in the normal kinematic force path of the hydraulic tappet.
The diameter of the central disk joining the elastic leaf arms of the second element is much less than the inner diameter of the ring comprising the first element. Consequently, when the two elements are pressed against each other, the central disk of the second element can go completely inside the ring itself, causing a bending of the leaf arms which strike against the inner edge of the circular ring formed by said first element. This generates an elastic force tending to flatten the second element (elastic leaf element), centrally supported on the low-pressure oil reservoir portion of the hydraulic tappet and, peripherally, on the ring of the first element, ensuring a prompt axial recovery of the travel of the tappet by an amount equal to the thickness of the ring comprising the first element.
In fact, the cushioning assembly comprised of the first and second elements is active until such time as the arms of the leaf spring comprising the second element are parallel to the surface of the first element and close against it, producing a recovery of lift loss equal to the thickness of the first element.
Specifically, the thickness of the first element should be calibrated so as to be at least equal in magnitude to the loss of recovery of the tappet, or the “lift loss”, which is estimated or experimentally deduced with respect to a tappet used in a particular type of engine. The invention is intended to produce a repeatable total lift loss equal to the injector cam deflection which is imparted to the tappet while it is on the valve cam base circle. The total lift loss is equal, in turn, to the lost motion which occurs within the tappet plus the leakdown which occurs within the hydraulic element of the tappet.
REFERENCES:
patent: 4470381 (1984-09-01), Buente et al.
patent: 4924825 (1990-05-01), Speil
patent: 6021751 (2000-02-01), Spath
patent: 6076491 (2000-06-01), Allen
Eaton Corporation
Kasper L. J.
Lo Weilun
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