Annular groove in a shock protection device

A shock protection device having opposing pluralities of frangible splines separated by an annular groove disposed in an internal splined opening in a drive hub, the splines for intermeshing engagement with a splined end of a drive shaft for transferring rotary motion to a cutter head from a driveline. Variation in the width of the annular groove enables precise adjustment of the fracture torque for the shock protection device beyond the adjustment possible through variation in the number or configuration of the individual splines.

BACKGROUND 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 in the driveline.

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 or a series of shafts 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, as would be expected, 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.

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 which 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.

One known type of shear mechanism employs frangible splines engaged on an interfacing splined shaft. The shear device is in the form of either a collar or clamping member having internal splines received on a splined end of the drive shaft. An overload situation preferably causes the splines in the shear device to shear and the continuing transfer of rotational power to cease. Variation of the overload situation (shear torque) at which the internal splines shear is accomplished through variation in the number, profile (height), length, or material of the splines. Such means often lack the precision necessary to achieve the desired shear torque needed for optimal rotary cutter shock protection or cause other operational problems when a low shear torque threshold is required. For example, use of spline length as a means for shear torque variation can result in a shock hub that is unstable when mounted on a shaft due to insufficient spline engagement length. Variations in the number of splines increase production costs as unique tooling may be necessary to provide the desired variations.

It would be advantageous to have a driveline shock protection device having improved capability to precisely establish a pre-determined shear torque value without compromising the operation or production cost of a driveline shock hub that overcomes the above problems and limitations.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a shock protection device for a driveline that will prevent the transfer of power along the driveline in the event of an overload.

It is a further object of the present invention to provide a driveline shock protection device having capability to establish a selectively pre-determined overload torque value with improved precision.

It is a further object of the present invention to provide a driveline shock protection device incorporating an annular groove in the internal splines that allows for precise variation in strength of the frangible spline elements.

It is a further object of the present invention to provide a driveline shock protection device in which an annular groove in the internal splines enables precise adjustment of the effective spline length with no change required to external mating components.

It is a further object of the present invention to provide a driveline shock protection device in which an annular groove in the internal splines enables precise adjustment of the effective spline length with no tooling changes required.

It is a still further object of the present invention to provide an annular groove in a shock protection device that enables greater precision in effective spline length than is provided by varying the number of splines in the device.

It is a still further object of the present invention to provide an improved shock protection device incorporating an annular grove in an internal spline that is durable in construction, inexpensive of manufacture, carefree of maintenance, easily assembled, and simple and effective to use

These and other objects are achieved in accordance with the instant invention by providing a shock protection device having opposing pluralities of frangible splines separated by an annular groove in the internal splined opening in a hub, the splines for intermeshing engagement with a splined end of a drive shaft for transferring rotary motion to a cutter head from a drive line, variation in the width of the annular groove enabling precise adjustment of the fracture torque for the shock protection device.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Many of the fastening, connection, processes and other means and components utilized in this invention are widely known and used in the field of the invention described, and their exact nature or type is not necessary for an understanding and use of the invention by a person skilled in the art, and they will not therefore be discussed in significant detail. Also, any reference herein to the terms “left” or “right” are used as a matter of mere convenience, and are determined by standing at the rear of the machine facing in its normal direction of travel. Likewise, “forward” and “rearward” are determined by the normal direction of travel. “Upward” and “downward” orientations are relative to the ground or operating surface as are any references to “horizontal” or “vertical” planes. Furthermore, the various components shown or described herein for any specific application of this invention can be varied or altered as anticipated by this invention and the practice of a specific application of any element may already be widely known or used in the art by persons skilled in the art and each will likewise not therefore be discussed in significant detail. When referring to the figures, like parts are numbered the same in all of the figures.

Referring now to the drawings and particularly toFIG. 1, wherein a plan view of a typical modular rotary disc mower5having a cutterbar10featuring a plurality of individual disc cutterhead modules20, each module incorporating the principles of the present invention is presented. Cutterbars of this type are used on hitch-mounted, pull-behind, and self-propelled mowers and are generally well-known in the art. For background information on the structure and operation of an exemplar rotary disc cutterbar, reference is made to U.S. Pat. No. 4,815,262, issued to Koch, and U.S. Pat. No. 5,761,890, issued to Lehman et al., the descriptive portions thereof being incorporated herein in full by reference.

Modular cutterbar10is formed from alternating cutterhead modules20and spacer modules29. Each cutterhead module20, as best seen inFIG. 2, includes a hollow cast housing21having a shape to retain a low profile and to establish an oil reservoir therewithin. Cutterheads20are gear driven and assembled in such a manner as to establish a specific timing relationship between adjacent units. More particularly, the cutterheads are arranged such that the knives33on adjacent units have overlapping cutting paths, but do not come into contact with each other. Failure to maintain this timed relationship during operation will result in one unit hitting the adjacent unit(s), damaging the cutterheads (and possibly initiating a chain reaction that damages all cutterheads), the drive train of the cutterbar and/or connected prime mover.

Now referring toFIGS. 2 through 4, each cutterhead module20features a stationary base21which allows the module to be mounted on the cutterbar and houses an interconnecting driveline to provide motive power to each module. Each module20includes a generally vertically oriented drive shaft22interconnecting the driveline for driving the individual rotating head32and connected knives33of each module. The drive shaft22is positioned along a rotational centerline100which serves as the principal reference axis for the module20and shock hub40. Drive shaft22features external splines23for engagement with shock hub40which rotationally interconnects drive shaft22and rotating head32. While involute splines are shown, square splines or similar structures may be utilized to provide a torque-transferring interaction between the drive member, namely drive shaft22, and the driven member, namely rotating head32, through interconnecting shock hub40and are contemplated within the scope of this invention. The shock hub40provides an easily replaceable apparatus in the driveline to prevent shock impact loads caused when the cutter knives33impact a rock or other immovable object from damaging the cuterbar driveline or other portions of the power transfer apparatus. Establishing an overload or breakaway torque for the shock hub40that is lower than the torque at which damage to the external splines23or other portions of the driveline occurs and is a well known method for protecting drivelines from momentary torque increases (shock or impact) commonly occurring as a cutter blade strikes an immovable object or a heavy movable object such as a rock. The breakaway torque may be varied through material selection for the shock hub, the size of each spline, the number of internal splines, or the effective (engaged) length of the splines.

Shock hub40is a generally flat, disk-like structure having an internal opening41for receiving drive shaft22and an outer periphery which includes mounting structures50for connecting the rotating cutting head32. It is also advantageous to provide a protective debris cover60to reduce accumulation of debris near the driveline components. Debris cover60may also be connected by mounting structures50. The internal opening41of shock hub40includes a plurality of frangible engagement structures42, hereinafter referred to as splines42. The splines42are arranged about the interior circumference or base perimeter of the opening41and extend radially inwardly from the base perimeter for a height. The splines42are generally uniformly positioned about the circumference so as to evenly distribute drive stresses within the hub40. The number of internal splines42may be varied to provide a desired breakaway torque for the hub, that is, the torque which will shear the internal splines from the interior surface of opening41. Variation in material, alteration of the spline configuration, including the number of splines, additionally allow for variation of the desired breakaway torque. However, it is not always practical to achieve the desired breakaway torque for the shock hub within the constraints of these design parameter variations.

The solution is to incorporate an annular groove45in the internally splined portion of the hub40so that the effective length of the frangible internal splines42engaging the drive shaft22may be varied while still providing sufficient hub support width (dimension L1inFIG. 3) to resist bending in the spline-shaft interface. Annular groove45is machined into the internal splines42to reduce the effective engagement length of the internal and external splines. Preferrably, the depth of the groove will be at least as much as the projection height of the splines from the base perimeter surface of opening41. The depth of annular groove may also be greater than the spline protrusion above the base perimeter surface of opening41thereby creating a groove which extends outwardly radially beyond the base perimeter surface of the opening into the surrounding hub material thereby providing a space for receiving fragments of the frangible splines and limiting the potential for damage to the shaft external splines. In either case, the purpose of the groove is to limit the effective spline length and thus the interaction between the interfacing splines. The width of annular groove, shown as L2inFIG. 3, allows the overall length of the internal splines42to be easily adjusted as the effective spline length of the internal splines42is length L1less length L2. Additionally, it is permissible to provide a groove in only a portion of the inner circumference of the opening so that the groove is not fully annular, though machine operations of such a configuration would be more complex that those to create an annular groove.

The effective spline length is comprised of two portions44,46, one on either side of the annular groove45. Resistance to bending at the shaft-hub interface is necessary to prevent the hub40from rocking on the drive shaft22as this interface supports the hub40. By positioning the engaged portions of the frangible internal splines42on either side of the annular groove45, an effective hub support width is provided which is capable of preventing rocking of the hub on the drive shaft22. Both portions44,46must engage the external splines23of the drive shaft22to provide the necessary stability for the hub40and the desired overload torque capability.

Using the present invention allows spline configurations (e.g., number, profile) common for a wide array of applications to be used, thereby simplifying machining operations (broaching). A common shock hub wherein the number of internal splines is selected to withstand a breakaway torque in excess of the desired breakaway torque can be produced. The breakaway torque capability is thus reduced by reducing the effective engaging length of the splines42through addition of the annular groove45, in essence removing a portion of the spline length. The width of the annular groove45can be easily varied using standard machining processes allowing the effective engaging length of the splines to be easily varied.

An added benefit of the annular groove45is that fragments of the splines42that are generated when the shock hub40shears in response to an impact by the cutters may migrate into the groove rather than being retained in the shaft splines where they might damage the external splines of the drive shaft. Furthermore, providing an annular groove45that extends radially beyond the base perimeter of opening41for a distance at least as great as the anticipated fragment size assures that the fragments generated by the frangible splines42can fully migrate out of the drive shaft/shock hub interface further reducing the potential for damage. As the shock hub is designed to be the weak link in the drive line, features that further protect the integrity of remaining components are beneficial in controlling component damage and thereby overall operating costs of the machine.