Harvesters – Motorized harvester – With condition-responsive operation
Reexamination Certificate
2002-08-19
2004-01-13
Kovács, Árpád F (Department: 3671)
Harvesters
Motorized harvester
With condition-responsive operation
C056S006000
Reexamination Certificate
active
06675563
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to mechanisms for protecting mechanical drive components from overloads, and more particularly relates to a shear device coupled between components of an agricultural disc mower that protects the various components of the mower in the event a cutterhead strikes an object and creates an overload condition.
BACKGROUND OF THE INVENTION
Typical disc cutterbars used in agriculture include an elongated housing containing a train of meshed idler and drive spur gears, or a main power shaft coupled by respective bevel gear sets, for delivering power to respective drive shafts for cutterheads spaced along the length of the cutterbar. The cutterheads each comprise a cutting disc including diametrically opposed cutting blades (though configurations with three or more blades are known) and having a hub coupled to an upper end of a drive shaft, the lower end of the drive shaft carrying a spur gear in the case where a train of meshed spur gears is used for delivering power, and carrying a bevel gear of a given one of the bevel gear sets in the case where a main power shaft is used. In either case, bearings are used to support the various shafts. The cutterheads are rotated at a relatively fast speed making the drive components, such as gears, bearings and shafts, vulnerable to damage in the event that the unit strikes a foreign object. For background information on the structure and operation of some typical disc cutterbars, reference is made to U.S. Pat. No. 4,815,262, issued to E. E. Koch and F. F. Voler, the descriptive portions thereof being incorporated herein in full by reference.
In order to minimize the extent of such possible damage to the drive components, it is known to incorporate a shear device somewhere in the drive of each unit that will “fail” upon a predetermined overload being imposed on the device. As used herein with reference to shear devices, the terms “fail” or “failing” are intended to cover the actual function of such devices, i.e., shearing, fracturing, breaking and the like. Several different such shear devices and arrangements are shown in U.S. Pat. Nos. 4,999,981, 4,497,161 and 5,715,662.
The '981 patent shows a shear mechanism that comprises a shaft with a weakened portion created by a cut groove, or break zone
41
(seen, for example, in
FIG. 3
thereof) in driven shaft
20
. Upon overload, the shaft breaks at zone
41
that is located outside the support bearing such that there is a clean and complete break in the shaft. This structure is intended to eliminate the input of kinetic energy to the cutterhead after failure of the shear mechanism, thereby eliminating damage to the drive system and gearing. While this structure may in fact eliminate the input of further kinetic energy, it does not stop rotation of the cutterhead or prevent the damage that continued rotation would generate.
A somewhat different shear mechanism is disclosed in
FIGS. 2 and 3
of the '161 patent. Cutting disc
3
is connected by a series of shear bolts
26
to the vertical shaft
8
. Upon impact of the cutterhead with an obstruction, the shear bolts fail, stopping the input of rotational force to the cutterhead.
FIG. 4
shows a slightly different embodiment where a resilient cover plate
28
depresses balls
30
arranged in holes of the disc
3
and fitting into recesses
31
of the disc
27
. An overload impact is intended to cause balls
30
to snap out of the recesses
31
so that the direct rotary joint between shaft
8
and cutting disc
3
is interrupted. It is stated that the connection can be reestablished by continuing to rotate disc
3
with respect to the disc
27
so that the balls
30
again snap into the recesses
31
. The embodiments set forth in this patent exhibit the same shortcomings as seen in the '981 patent, i.e., standard shear mechanisms do not stop rotation of the cutterhead, and thus do not prevent additional damage thereby encountered.
The shear mechanisms shown in the '662 patent each employ shearable splines. In a first embodiment the shear device is in the form of either a collar or clamping member having internal splines received on a splined upper end of the drive shaft and having shearable cylindrical drive lugs engaged with complementary shaped openings provided in an upper surface of a disk hub. Referring more specifically to
FIG. 2
thereof, the upper end of drive shaft
26
has a splined section
86
. Shear collar
88
establishes a drive connection between shaft
26
and hub
80
. The collar
88
includes internal splines
90
engaged with the splined section
86
of shaft
26
just above hub
80
. Shearable cylindrical drive lugs
92
project downwardly from the bottom of collar
88
and are received in complementary holes
94
in hub
80
. An overload situation causes the lugs
92
to shear and the continuing transfer of rotational power to cease.
FIGS. 4 through 6
show another embodiment where shaft
34
has a splined upper end section
110
. Instead of a shear collar, a shear device in the form of a cap-like clamping member
114
is used for transferring torque from shaft
34
to hub
80
. Clamping member
114
has an annular lower portion
116
provided with interior splines
118
engaged with the splined section
110
of shaft
34
. A plurality of shearable lugs
120
extend downwardly from lower portion
116
and are received in complementary shaped cylindrical openings
94
in hub
80
, whereby torque is transferred from shaft
34
to hub
80
. Again, when an overload occurs, lugs
120
shear, and torque is no longer transmitted. The final embodiment shown in the '662 patent is shown in
FIGS. 7 through 9
. Instead of a disk hub
80
, a disk hub
127
is used which has a central splined opening
128
disposed in spaced concentric relationship t the splined upper end section
110
of shaft
34
. A ring-like shear insert
130
is received on the upper end of the drive shaft
34
and has inner splines
132
engaged with the splined upper end section of the shaft and has outer splines
134
engaged with the splined opening
128
of hub
126
. Splines
132
are designed to shear upon overload.
Similar to the devices discussed above, the embodiments of the '662 patent do not stop the cutterhead from rotating, even after power is cut off by a shear device. The third embodiment shown in this patent exhibits an additional shortcoming in that upon failure of the shearable splines, the broken pieces tend to become temporarily “jammed” in among the other parts and components, resulting in even further, though short lived, torque to be transferred, and the resultant additional damage to the cutterheads.
Particularly in its preferred embodiment, the instant invention overcomes the drawbacks and shortcomings of the prior art. A two-piece hub design, with a spring mounted ball and detent as a shear mechanism therebetween will fail with substantially no residual transfer of torque. The use of this unique shear mechanism results in no broken pieces to become “jammed” in among the other parts and components, and can be easily repaired by simply realigning the top and bottom hubs so that the spring-loaded ball in the top disc hub fits into the detent in the lower disc hub. Upon failure, the two-piece hub, one of which is driven directly by the drive shaft, separates and the upper disc hub is driven up a specially threaded retaining bolt and separates from the lower hub and drive shaft. This upward movement separates the upper disc hub from the drive train and removes the affected cutting implement from the path of the other cutterheads on the cutterbar. The upper disc hub continues to rotate upward until it reaches a threadless portion of the retaining bolt. There, the upper disc hub is permitted to rotate freely until the absence of drive train inertia causes it to stop.
Clearly, the concept of a shear mechanism is not new, however the use of a spring-mounted ball and detent instead of a pin, lug, or bolt, as well as the utilization of a specially threaded retai
Ehrhart Philip J.
Hess David A.
Hoffman Charles H.
McLean Kenneth W.
Kovács Árpád F
Maurer Brant T.
New Holland North America, Inc
Stader John William
Webb Collin A.
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