Self-Cleaning Sprocket

This application is related to application Ser. No. 690,813, filed May 27, 1976, by Edward A. Fritz and Peter Sammarco, and assigned to the assignee hereof.

This invention relates to sprockets used with an endless belt of the type having internal drive lugs and, more particularly, to a self-cleaning sprocket for use with a crop gathering belt in a forage harvester row crop gathering unit.

The use of endless crop gathering belts having internal drive lugs in a forage harvester gathering unit is well known. Examples of this can be found in U.S. Pat. Nos. 3,853,016, 3,854,272, 3,888,132, and 3,940,913. Cage-like, tang, or flanged sprockets are utilized in these references.

A problem which occurs with the use of these belts and sprockets in crop gathering is that crop debris in the form of small pieces of crop can accumulate behind the belts on or in the sprockets. Debris in longer pieces can become wrapped around the sprocket or its mounting spindle. In either case, a sufficient accumulation of debris can throw the belts off the sprocket, especially driving sprockets, or at least lift the belt far enough from its driving sprocket to cause the sprocket to slip beneath the belt, defeating its purpose. Such a debris accumulation could also stretch the belt thus shortening its life or, indeed, break it. Wrapping of crops on the sprocket or spindle tends to feed upon itself and adversely affect bearing life. In extreme cases, the flow of crop through the gathering passages could be obstructed.

In U.S. Pat. No. 3,472,563 a self-cleaning belt and sprocket are taught for use on snowmobiles. The sprocket is similar in some respects to that taught herein. A major exception is that the belt lug pockets formed by the sprocket teeth have no bottoms which extend to the center hub producing a cage-like structure. Our experience in removing crop debris, especially moist and sticky debris or mud, from belt sprockets indicates that the debris must be forced out of the pocket. Without a complete pocket, including a bottom which closely fits the belt lug, this type of crop debris is not easily expelled. In U.S. Pat. No. 3,948,110 complete pockets are provided. However, the inner portion of the pocket and bottom portion meet at nearly right angles creating a corner. Drier debris can become lodged or wedged in this area and moist material would stick in the corner and build an accumulation.

Another aspect of cleaning sprockets is providing a side to side cleaning action by having the pitch of the tangs exceed slightly the pitch of the belt as will be explained below. Sprockets of the type shown in U.S. Pat. No. 3,853,016 have been so designed. However, if the pocket bottom does not closely fit the belt lug, debris cleaning action can be lost.

Accordingly, it is the major object of the invention described and claimed herein to provide a self-cleaning sprocket for use with an endless belt having internal drive lugs wherein debris accumulating in the lug pockets of the sprocket may be easily removed therefrom primarily by the action of the lug in the pocket.

It is further an object of the invention to provide a sprocket and belt combination wherein wrapping of crops about the sprocket or its mounting spindle is minimized.

These and other objects of the invention are specifically met in a self-cleaning sprocket for use with an endless gathering belt having internal drive lugs wherein the sprocket comprises a body of material having a disk-like base portion and a plurality of radial ribs extending axially from the base portion and converging to a hub portion, thereby forming a plurality of circumferentially-spaced, lug-receiving pockets axially adjacent the base portion, the pockets having open axial ends. The base portion slopes toward the open axial end from the periphery of the base portion toward the hub portion and the hub portion slopes radially inwardly from the base portion to the open axial end, the intersection between the hub portion and base portion being filletted to facilitate the flow of debris from said base portion to said hub portion. The axial end of the sprocket is preferably flat and without obstructions to prevent wrapping. In the preferred embodiment, the aforementioned pockets comprise the upper set of pockets for a double lugged belt and a second set of pockets extends downwardly from the base portion to accommodate the lower belt lugs and are of similar shape except that the sloped hub portion of the pockets is unnecessary. In the preferred embodiment, the sprocket would be mounted to its associated structure from beneath the sprocket.

In a further aspect of the invention, the pitch of the lug pockets is slightly greater than the root pitch of the belt lugs and the pockets are of considerably larger size circumferentially than the belt lugs while the pocket bottoms closely fit the belt lugs. This produces a change of circumferential position of the belt lug in the pocket with each succeeding rotation of the sprocket when the belt is under no load or light loads. Under normal loads, the lugs move back in the pockets to be driven by the ribs causing a sideward cleaning action. Since this action, as well as the axial expulsion action described herein, which is apparently more effective on moist and sticky debris, are both desirable, the preferred embodiment includes these latter features. However, if the sideward cleaning action were not desired, the lug pockets would be only slightly larger than the belt lugs to enhance the axial expulsion action.

Other objects and advantages of the invention will become apparent upon reference to the detailed description of the invention and to the drawings, in which:

FIG. 1 is a pictorial view of a row crop gathering unit incorporating the invention, portions of the surrounding sheet metal being removed for clarity;

FIG. 2 is a pictorial view of a portion of an endless belt entrained on one embodiment of a sprocket in accordance with the invention;

FIG. 3 is a top view of an endless belt and a second embodiment of the sprocket in accordance with the invention; and,

FIG. 4 is a sectional view of the belt and sprocket of FIG. 3 taken along the line 4--4 thereof.

Turning to FIG. 1, there is shown a row crop gathering unit, generally designated 10, of the type described in detail in the aformentioned copending application Ser. No. 690,813, which is incorporated by reference herein. For purposes of the present invention, the row crop unit 10 is adapted to be mounted to the basic processing unit (not shown) of a forage harvester and comprises left and right outer dividers 11 and 12 which together with the center divider 14 define a pair of crop gathering passageways 15. A crop cutting means in the form of a pair of cooperating rotary knives 17 is located at the forward end of each of the passageways 15. The passageways converge rearwardly to an open feed throat 19 whereat the crop stalks are transferred to the forage harvester (not shown). To move the crop stalks through the passageways 15 after cutting, a pair of rearwardly moving elastomeric endless belts 20 are disposed along the sides of the passageways 15, the belts 20 having external lugs 21 which aid the gripping of the stalk butts between the belts 20.

The belts are further provided with generally pyramidal-shaped internal drive lugs 22 in a pair of equally longitudinally spaced rows of a given pitch, the lugs of one row being in lateral alignment with the lugs of the other row. Each of the belts 20 is entrained about a generally vertically oriented driving sprocket 24 located adjacent the rear ends of the crop passageways 15, the internal drive lugs 22 entering upper lug pockets 25 and lower lug pockets 37 in the sprockets 24 as will hereinafter be seen. The forward end of the belts 20 are entrained on forward sprockets (not shown) mounted on the rotational axes of the rotary knives 17 and transmit power thereto, suitable means, such as shown in the copending application, maintaining the belts in tension.

Referring now to FIGS. 2, 3, and 4, it will be observed that the only difference between the sprocket 24A of FIG. 2 and the sprocket 24 of FIG. 3 is in the configuration of the outer periphery. Both sprockets are formed from a body material, such as high density, polyethylene, and have a disk-like center or base portion 30, 30A having a generally cylindrical outer periphery. In the case of the sprocket 24A of FIG. 2, the cylindrical outer periphery of the base portion 30A is circular. In the case of the sprocket 24, the cylindrical outer periphery of the base portion 30 is more hexagonal, being formed by chordal lines across the openings of the six pockets 25 therein. The latter sprocket form is preferred since it apparently increases belt life.

The sprocket 24 further comprises a plurality of equally spaced ribs 32, preferably six in number, extending axially upwardly from the center or base portion 30, the ribs 32 extending radially inwardly from the outer periphery of the base portion 30 and converging to form a hub portion 34 by the blending of a relatively large radius between the ribs. The diameter of the outer periphery of the base portion 30 is sized such that, in operation, the circumferential spacing or pitch of the ribs 32 will be slightly greater than the pitch between the bases of the lugs 22 on the belt 20. The ribs 32, hub portion 34, and base portion 30 thus define the lug receiving pockets 25 of the sprocket 24, the axial or upper ends of the pockets 25 being open.

The side faces 26 of the pockets 25, which drivingly engage the internal lugs 22 of the belt 20, lie in a plane parallel to a radial plane bisecting the adjacent rib 32, the nondriving side faces 27 being on the opposite sides of the ribs 32 from the driving side faces 26. The thickness of the ribs 32 combined with the orientation of the side faces should produce the same angle of the side faces 26 relative to the axis of the sprocket as the face of the drive lug 22 which may engage it. By proper sizing and a limited number of ribs, this should also produce the result that the pockets 25 are considerably larger than the belt lugs 22 and have relatively large subtended angles, on the order of 60.degree., as shown in FIG. 3. The bottom face 31 of the pocket 25 formed by the base portion 30 lies in a plane sloping upwardly, preferably at an angle of about 10.degree., coinciding with the angle of the face of the belt lug 22 which engages it, from the periphery of the base portion 30 to its intersection with the hub portion 34. The hub portion 34, forming the radially inner face 35 of the pocket 25, slopes radially inwardly, preferably at an angle of about 10.degree., from its intersection with the base portion 30 to its upper axial end. The obtuse angle thus formed between the base portion and hub portion and the relatively large subtended angle of the pockets also prevents drier materials from lodging in the inner portion of the pocket. The intersection between the base portion 30 and hub portion 34 is generously filletted as at 36 to permit material flow from the bottom face 31 of the pocket 25 to the inner face 35 thereof.

Thus, when debris, especially moist and sticky debris, is present in a pocket 25, the action of the belt lug 22 entering the pocket will cause debris laying on the bottom face 31 to be pushed inwardly toward the center and, as more material is added, to move around the fillet 36 and up on the inner face 35 or hub portion 34 of the pocket 25 and ultimately out the open axial end of the pocket. It can be seen that the coincidence of angles between the bottom face 31 of the pocket 25 and the belt lug face and the obtuse angle between the hub 34 or inner face 35 and the base portion 30 or bottom face 31 aids this action. Similarly the close fit and angular coicidence between the driving side face 26 of the pocket 25 and that of the belt lug 22 will tend to move material from this area which will also be pushed toward the hub portion 35 and upwardly thereon.

As mentioned above, the pitch or circumferential distance between the ribs 32 or lug-driving side faces 26 is designed to be slightly greater, on the order of about 0.020 inch, or about 1% of the pitch, than the pitch of the belt lugs 22 along the line of contact of the belt 20 with the sprocket 24, that is, at the bases of the lugs 22. The lug pockets 25 are of considerably large size circumferentially than the lugs as shown in FIG. 3. When the belt 20 is operated under no load or light crop loads, the belt is driven by the frictional engagement of the portion between the rows of lugs with the outer periphery of the base portion 30 of the sprocket 24. Since the slight difference in pitch between the belt and sprocket creates an out of phase condition which is accumulative, as each pocket rotates to receive a belt lug, the position of the lug relative to the pocket will be further away from the lug driving side face 26 until it nears the face 27 on the other side of the pocket whereat it will tend to remain unless a load is imposed on the belt. As a sufficient amount of load is applied to the belt, as by crops being cut and moved through the passageway 15, the frictional dirving of the belt is overcome and the lug slides back in the pocket toward the driving side face 26, the belt stretching a little to overcome the slight difference in pitch, and the belt is then driven by the side faces 26 of the sprocket acting through the lugs 22. This produces the result that, as the loading on the belt fluctuates, the lug moves back and forth in the pocket and, since the bottom face 31 of the pocket fits the lug surface relatively closely, dislodges debris which can be thrown off the sprocket by centrifugal force.

It will be appreciated that although the sprocket 24 has been described as having specific portions, the sprocket is in fact one body of molded material and that the hub portion is formed by a blend radius between the ribs 32. The intersections of the side faces 26, 27 and the bottom and inner faces 31, 35 of the pockets 25 are filletted to prevent material from catching in the corners.

As indicated, the foregoing discussion has concerned itself with the set of pockets 25 located above the base portion 30. As will be seen from FIG. 4, a lower set of pockets 37 are formed below the center or base portion 30 by the extension of the ribs 32 and hub portion 34 therethrough. These pockets are the same as the upper pockets except that the radially inward slope of the hub portion 34A is not necessary since debris pushed inwardly in the lower pockets 37 by the belt lugs will fall out by gravity. It is also noted that the axial thickness of the base portion 30 should be sized to produce a relatively close fit between the base portion and the upper and lower lugs 22 of the belt 20. This aids proper belt tracking as well as the removal of debris.

The top surface 39 of the sprocket 24 is perpendicular to the sprocket axis and ends beyond the lateral edge of the belt 20 so that the debris forced upwardly out of the pockets by the lugs 22 will be thrown off the sprocket. The top surface 39 further is flat and without obstructions to prevent wrapping of longer material thereabout. To accomplish this, the sprocket 24 is provided with a metal core 40 having a hexagonal shaft 41 which extends from a location flush with the top face 39 of the sprocket and out the bottom face thereof to a rotational mounting (not illustrated) in a casting, a portion of which is shown at 42, mounted on the frame of the row crop unit 10. The sprocket 24 is retained on the hexagonal shaft 41 by a roll pin 44 extending therethrough. It will observed from FIG. 4 that the lower end of the hub portion 34 is provided with an annular recess 45 to receive the end of the casting 42, thereby preventing wrapping of crops around the rotating hexagonal shaft 41. The details related to driving the sprocket 24 are beyond the scope of this invention, but may be found in the referenced copending application.

Thus it is apparent that there is provided, in accordance with the invention, a self-cleaning sprocket especially for use with harvester gathering belts that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in the light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.