Endless belt power transmission systems or components – Means for adjusting belt tension or for shifting belt,... – Tension adjuster or shifter driven by electrical or fluid motor
Reexamination Certificate
1999-06-09
2001-05-22
Bonck, Rodney H. (Department: 3681)
Endless belt power transmission systems or components
Means for adjusting belt tension or for shifting belt,...
Tension adjuster or shifter driven by electrical or fluid motor
C474S138000
Reexamination Certificate
active
06234929
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the priority of German Patent Application, Serial No. 198 28 309.1, filed Jun. 25, 1998, the subject matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a tensioner for traction means, in particular belts.
Tensioners of this type are frequently used in belt drives of motor vehicles. For example, German Pat. No. DE 196 09 420 A1 discloses a tensioner having a housing which receives a cylinder for guiding a hydraulically dampened plunger in longitudinal direction. The interior space of the housing forms a reservoir for hydraulic oil, whereby hydraulic oil under pressure migrates out of the cylinder into the interior space, and whereby hydraulic oil is drawn from the interior space into the high pressure chamber of the cylinder. The interior space of the housing is closed by a cover which has a guide opening for passage of the plunger. The housing has a cylindrical receptacle for forming a seat for the cover, and a seal which is positioned outside of the cover, and thus is mounted in place following an installation of the cover. When mounting the seal, the distance between the cover and the seal becomes smaller, so that a gas cushion trapped between the cover and the seal is compressed. As a consequence of the thus-generated overpressure exerted by the gas cushion, the conventional tensioner suffers the drawback that the seal is pushed out of its seat again, and thus out of the cylindrical receptacle.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved tensioner, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved tensioner, which realizes a secure seat of the seal and is so configured as to prevent a gas cushion trapped between the cover and the seal from urging the seal out of its seat.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing the cover with a vent passageway in communication with the interior space for release of a gas cushion formed between the seal and the cover via the vent passageway into the interior space. The provision of a vent passageway enables a reduction of excess gas pressure trapped between the seal and the cover. Normally, the interior space, which is approximately at atmospheric pressure, is sufficiently sized so that the generated rise in pressure in the interior space due to intake of gas is negligible.
When providing the housing with a cylindrical receptacle for forming a seat for the cover and for the seal, the risk of an unintended pressure rise of trapped gas cushion can be eliminated through the arrangement of a vent passageway. Suitably, the cover and the seal have each an outer peripheral area which tightly or substantially tightly bears upon the inside wall surface of the cylindrical receptacle. Without provision of a vent passageway according to the present invention, the space in which the gas cushion builds up is effectively hermetically sealed off and thus poses the problems described above.
A further advantage of the tensioner according to the present invention, is the ability of hydraulic oil to migrate from the interior space via the vent passageway to the seal. As during reciprocating movements of the plunger in longitudinal direction, the seal and the plunger slide on one another, hydraulic oil can thus lubricate the seal in the sliding contact area with the plunger so that the service life of the seal can be significantly enhanced.
According to another feature of the present invention, the vent passageway may be formed by bores provided about the outer circumference of the cover. These bores may be configured, for example, of U shape. Suitably, the cover is made of sintered material by a sintering process so that the bores can be formed easily in a sintering mold.
According to still another feature of the present invention, the cylindrical receptacle forms a counterbore so as to define a radial shoulder for placement of the cover which thus is securely fixed in axial direction. When being provided at the outer circumference of the cover, the vent passageway projects radially inwards beyond the radial shoulder.
Oftentimes, the plunger supports a spring plate for support of one end of a helical compression spring whose other end rests against a housing bottom. When the plunger moves out of the cylinder, the spring plate impacts upon the cover. Suitably, the vent passageway is so configured as to have a cross sectional area of a size sufficient to extend, at least partially outside the impact zone between the spring plate and the cover so as to communicate with the interior space.
REFERENCES:
patent: 4790801 (1988-12-01), Schmidt et al.
patent: 4950209 (1990-08-01), Kawashima et al.
patent: 5482262 (1996-01-01), Hayakawa et al.
patent: 5547429 (1996-08-01), Hirabayashi et al.
patent: 5607368 (1997-03-01), Hida et al.
patent: 5833563 (1998-11-01), Takeda et al.
patent: 6036612 (2000-03-01), Katogi et al.
patent: 41 24 500 C2 (1993-01-01), None
patent: 196 09 420 A1 (1997-09-01), None
patent: 197 46 034 A1 (1998-04-01), None
patent: 405321994 (1993-12-01), None
JP 09166190 A, Jun. 24, 1997, Tsubakimoto Chain Co., Hydraulic Tensioner, In: Patent Abstracts of Japan.
Bonck Rodney H.
Feiereisen Henry M.
Ho Ha
Ina Walzlager Schaeffler OHG
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