Machine element or mechanism – Elements – Pawls and ratchets
Reexamination Certificate
2002-04-23
2004-05-18
Bucci, David A. (Department: 3682)
Machine element or mechanism
Elements
Pawls and ratchets
C403S374100
Reexamination Certificate
active
06736027
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to devices for arresting an element on a shaft. More particularly, the present invention pertains to an attachment mechanism intended for arresting a machine member, such as a pulley, a sheave, a sprocket or the like, on a cylindrical shaft.
BACKGROUND OF THE INVENTION
The mounting of elements such as sheaves, sprockets or the like on a cylindrical shaft so that the element is arrested against circumferential and/or axial movements relative to the shaft can be affected in different ways. One example is to provide a keyway in the shaft and/or in the boss or hub of the machine member, and a key inserted in the keyway for preventing relative circumferential movement. However, this arresting mechanism requires a more expensive machining of the keyway in the shaft, reduces the strength of the shaft and is not well suited to being used together with relatively light and inexpensive hollow shafts.
Similar limitations can be seen with use of threaded joints as this requires thread cutting of the shaft and inner surface of the bore in the machine member.
Cylindrical shaft and hub joints can also be obtained with a press fit affected with or without the use of a pressure oil arrangement. However, with these mechanisms, it is also difficult to use hollow shafts due to large radially inwardly directed forces.
Swedish Patent Application No. 9901711-3 discloses an attachment mechanism intended for arresting a machine member having a substantially cylindrical bore on a cylindrical shaft. The bore has a larger inner diameter than the outer diameter of the shaft to provide an annular space between the machine member and the shaft. In this space is inserted a pair of elements having mating, cooperating taper surfaces facing each other, with the elements being intended at mutual displacement to change their overall radial size, thereby increasing or reducing the clamping force between the machine member and the shaft. The elements are in the form of a first thin-walled sleeve member having a smooth inner surface arranged to enclose a portion of the shaft, and a second thin-walled sleeve member having a smooth outer surface arranged to engage the bore of the machine member, with the second sleeve member enclosing the first sleeve member. The first and second sleeve members in their surfaces that face each other have a plurality of saw-tooth-shaped consecutive axially tapering sections. In addition, one of the end edges of the second sleeve member abuts against a stop provided in the machine member, and the first sleeve member projects outside the opposite end edge of the second sleeve member for being readily accessible to receive an external pushing force causing such mutual displacement between the first and second sleeve members.
This generally described attachment mechanism is able to function relatively well, but suffers from the drawback that the size relationship between the shaft and bore of the sheave is very important for allowing proper attachment to be obtained. This makes it necessary to provide a substantial number of differently sized sleeve members.
FIG. 1
shows in cross-section an attachment device similar to that described above and disclosed in Swedish patent application No. 9901711-3. In this known device, a machine member
11
is secured to a portion of a hollow shaft
10
. The machine member
11
is shown only partially and is in the form of a sheave. As shown, the hollow shaft
10
has a cylindrical external peripheral surface and the machine member
11
has an inner bore of cylindrical shape, with the inner diameter of the bore in the machine member
11
exceeding the outer diameter of the shaft
10
. A shoulder
12
is provided at one axial side of the bore in the machine member
11
. This shoulder
12
has a diameter slightly larger than the outer diameter of the shaft
10
, thereby providing a clearance so that the machine member
11
can be easily pushed up the shaft
10
to a desired arresting position. The annular space
13
formed between the inner surface of the bore in the machine member
11
and the outer peripheral surface of the shaft
10
has a certain radial dimension x. In this space is inserted the primary part of the attachment mechanism which is in the form of the two-piece sleeve
15
.
This two-piece sleeve
15
includes a first or inner sleeve piece
15
a
having a cylindrical inner surface and an external surface provided with a continuous axially arranged series of tapering, substantially saw-tooth-shaped surface elements, in which a first surface element b tapers from a larger diameter to a smaller diameter, followed by a consecutive second surface element c connected to the first surface element b via a substantially radial wall member d so that the end of the second surface element c adjacent the narrower end of the first surface element b has substantially the same outer diameter as that of the first surface element b at its largest end, i.e. at the end remote from the second surface element c. The second surface element c is related to and connected to the consecutive next surface element e in the same manner as the relationship between the first and second surface elements b, c, with this same relationship continuing along the length of the exterior surface of the inner sleeve piece.
The second or outer sleeve piece
15
′ of the two-piece sleeve is designed as a reverse image of the first inner sleeve piece
15
a
. Thus, the outer second sleeve piece
15
′ has a cylindrical outer peripheral surface and an inner surface provided with saw-tooth-shaped surface elements that are complementary to those of the first sleeve piece
15
a
. The outer second sleeve piece
15
′ is arranged to enclose the inner sleeve piece
15
a
, with a short section f of the inner sleeve
15
a
projecting axially beyond the interior of the outer second sleeve piece
15
′ as shown in FIG.
1
.
This known attachment mechanism also incorporates a ring member
16
arranged around the shaft
10
on the side of the machine member
11
facing away from the shoulder
12
. This ring member
16
is provided with a number of axially extending through-holes
16
a
, each of which receives a bolt
17
projecting through the through-hole
16
a
and screwed into a corresponding one of several threaded bores
18
in the machine member
11
. This ring member
16
abuts the projecting sleeve portion f of the inner sleeve
15
a
. By tightening the bolts
17
, it is possible to axially move the inner sleeve piece
15
a
relative to the outer sleeve piece
15
′ to cause the cooperating tapering surfaces of the inner and outer sleeve pieces
15
a
,
15
′ to slide against each other, thereby first reaching the radial measure x of the space
13
, and thereafter upon continued tightening of the bolts increasing the grip between the attachment mechanism and the shaft
10
as well as between the attachment mechanism and the interior of the machine member
11
until a firm grip is obtained in the circumferential as well as in the axial direction.
By virtue of the consecutive saw-tooth-shaped taper portions being made in an integral unit, the attachment mechanism is centered in its seat without risk of misalignment. In addition, the handling and stock-keeping of the attachment mechanism is somewhat simplified.
The known attachment mechanism described above and illustrated in
FIG. 1
provides very good and reliable attachment results. However, the arresting of sheaves of various bore diameters requires stock-keeping a large variety of sizes of the attachment mechanisms. Alternatively, this requires separate manufacture for different relationships between the bore and shaft diameter.
A need thus exists for an improved attachment mechanism of the type mentioned above which is not as susceptible to the drawbacks mentioned above, and which is useful for a wide variety of sheave bore diameters with only a few different sizes
SUMMARY OF THE INVENTION
One aspect of the invention involves an attachment device
Axelsson Uno
Östling Sture
Aktiebolaget SKF
Bucci David A.
Burns Doane , Swecker, Mathis LLP
Van Pelt Bradley J.
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