Internal-combustion engines – Vibration compensating device – Balancing arrangement
Reexamination Certificate
2000-08-30
2001-10-23
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Vibration compensating device
Balancing arrangement
C074S603000
Reexamination Certificate
active
06305339
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a balance shaft, and in particular to a balance shaft provided with a counter weight for canceling the unbalance force produced in reciprocating engines.
BACKGROUND OF THE INVENTION
Engine balancing devices are known. For instance, Japanese UM publication No. 5-39233 discloses a balancing device in which a pair of balance shafts each provided with a counter weight for canceling the unbalance force of the second order produced by pistons of an engine are disposed under the crankshaft in the oil pan, and the rotation of the crankshaft is transmitted to the balance shafts via a chain/sprocket mechanism or a gear mechanism. A similar balancing device is disclosed in U.S. Pat. Nos. 4,703,724 issued Nov. 3, 1987 to C. Candea et al. and 4,703,725 issued Nov. 3, 1987 to W. L. Weertman.
In such a balancing device, because the vibration control diminishes in effectiveness if the balance shafts deflect, the journal portion for rotatably supporting each balance shaft is desired to have as high a rigidity as possible. Therefore, the journal portion of a balance shaft generally consists of a solid structure having a fully circular cross section.
However, it is desired to minimize the overall weight of the balance shaft because of the increasing demand for the weight reduction of engines. Also, the balance shaft is required to have a certain unbalance mass. Therefore, the mass of the balance shaft is desired to be allocated to the unbalance mass as much as possible, and the mass which does not contribute to the generation of unbalance for canceling that of the engine, such as the mass found in the journal portion is desired to be minimized.
Such an effort to reduce the mass or weight of the various parts of a balance shaft should be implemented without compromising the required properties of the balance shaft such as the adequate bending rigidity and the load bearing capability of the journal.
Also, because the balance shaft is required to be installed in a relatively limited recess within the confine of an engine, it is important that the assembly of the various components of the balancing device can be executed in a simple manner.
BRIEF SUMMARY OF THE INVENTION
In view of such problems of the prior art, a primary object of the present invention is to provide an improved balance shaft which can minimize the size and overall weight of the counter weight without reducing the bending rigidity of the balance shaft.
A second object of the present invention is to provide a balance shaft which can minimize the weight of the balance shaft without sacrificing the load bearing capability of its journal portion.
A third object of the present invention is to provide a balance shaft which can minimize the weight of the balance shaft without unduly increasing the rotational resistance of its journal portion.
A fourth object of the present invention is to provide a balance shaft which is easy to assemble.
A fifth object of the present invention is to provide a balance shaft which is suited for compact design.
According to the present invention, such objects can be accomplished by providing a balance shaft for an engine balancing system for canceling an unbalance force of an engine, comprising: an counter weight portion having a gravitational center offset from a rotational center thereof; and a journal portion for rotatably supporting the balance shaft in a bearing bore defined in a fixed part of the engine; the journal portion being provided with a recess on a side remote from the gravitational center of the counter weight.
The recess reduces the weight or mass of the balance shaft, and this recess does not diminish the performance of the bearing because the bearing load is essentially due to the unbalanced mass of the counter weight portion, and the recessed part of the bearing portion receives a significantly smaller part of the bearing load than the opposite side of the bearing portion. The recessing also contributes to increasing the eccentricity of the gravitational center of the associated part. Typically, the journal portion is provided with a full circular part having a full circular cross section, preferably on each axial end thereof, to ensure the load bearing capability of the journal portion under all circumstances.
To compensate for any reduction in the bending rigidity of the balance shaft due to the recessing of a part of the bearing portion, the journal portion may be provided with a first rib extending across the recess axially along a radial plane between the full circular axial end portions of the journal portion.
The counter weight portion typically comprises a radially offset lobe. The rigidity of the balance shaft against bending can be significantly and easily improved by providing a second rib which extends axially along a radial plane on a side of the balance shaft diagonally opposite the lobe. It is particularly preferable if the the first and second ribs extend along a common radial plane and merge at one of the full circular axial end portions.
The first rib may be provided with an outer profile which is common to an outer profile of the full circular part of the journal portion. However, in view of reducing the resistance against rotation due to the deposition of lubricating oil in the recessed part of the journal portion may be provided with an outer profile which is recessed radially inward with respect to an outer profile of the full circular part of the journal portion. For the same reason, the outer profile of the first rib may be defined by a rounded edge. Additionally or alternatively, the first rib may be provided with an opening passed therethrough, preferably in a part of the rib adjacent to an axial center of the balance shaft.
In view of maximizing the reinforcing effect of the second rib, the second rib may extend substantially over an entire length of the counter weight portion. To reduce the weight of the rib without detracting from its reinforcing performance, the second rib may be provided with a radial height which progressively diminishes away from the journal portion.
Preferably, the journal portion has a substantially smaller rotational diameter than the counter weight portion. Thereby, the overall eccentricity of the balance shaft is maximized. In such a case, the housing for the balance shaft should consist of an upper and lower housing halves which jointly define a bearing bore for the journal portion so that the counter weight portion which is desired to have a relatively large rotational diameter is not required to be passed through the bearing bore for the balance shaft.
According to a particularly preferred embodiment of the present invention, the counter weight portion is provided on each axial end of the journal portion. Thus, the bending rigidity of the balance shaft against the unbalance force of the unbalance mass portions of the engine can be maximized for a given amount of the material for the balance shaft. Often, a pair of balance shafts rotating in opposite directions are required, and such a synchronizing motion may be accomplished by a gear such as a spur gear or helical gear attached to each balance shaft. To support such balance shafts in a stable fashion, each balance shaft may be provided with a gear attached thereto at a part adjacent to an end of one of the counter weight portion remote from the journal portion, and a second journal portion on an axial side of the gear remote from the counter weight portion.
REFERENCES:
patent: 4523553 (1985-06-01), Backlund
patent: 4703724 (1987-11-01), Candea et al.
patent: 4703725 (1987-11-01), Weertman
patent: 5253547 (1993-10-01), Yoneyama et al.
patent: 0 243 683 (1990-05-01), None
patent: 5-39233 (1993-10-01), None
Iwata Kazuyuki
Yoshida Keiko
Armstrong Westerman Hattori McLeland & Naughton LLP
Honda Giken Kogyo Kabushiki Kaisha
Kamen Noah P.
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