DRIVE SPROCKET DEVICE WITH FLANGES

Abstract: Drive sprocket device for holding a saw chain tensioned on a chain saw with downwardly directed drive shaft, comprising a rim type drive sprocket and a loose drive ring rolling on the periphery of the sprocket, the drive links of the saw chain entering recesses on the sprocket through orifices in the drive ring, where the drive ring has on the upper edge an inwardly directed flange to keep the ring from falling off the sprocket, and on the lower edge an outwardly directed flange to keep the chain from falling off the drive ring.

Description: DRIVE SPROCKET DEVICE WITH FLANGES Background In patent application SE 9302842-1 was shown a drive sprocket device for automatic tensioning of saw chain on chain saws, where the saw chain runs around a loose outer drive ring rolling against an inner drive sprocket of traditional rim sprocket type. The rim sprocket is characterized by having a periphery with a row of recesses where the drive links of the saw chain can enter, the width of the recesses being only slightly larger than the thickness of the drive links, and the row of recesses bordering to cylindrical surfaces on both sides. The axial alignement between the drive ring and the drive sprocket is kept by either two inward flanges on the drive ring, or two outward flanges on the drive sprocket. This prevents such displacements that could make the drive links climb out of the recesses. A device with two flanges in the same direction works well for any direction of the drive sprocket shaft, up or down. In many applications it is not relevant to consider upwardly directed shafts, either because the cutting heads of vehicle-born chain saws can not be turned upside down, or because handheld chain saws are rarely operated with upwardly directed shaft and never laid down with upwardly directed shaft except for service. The present invention concerns a drive sprocket device where a drive ring is rolling around a drive sprocket, and the drive ring has a new type of flanges to prevent axial displacement when the shaft is pointing downwards, and to make it easier to replace saw chain and drive ring. Description The invention is described with reference to figures 1 - 2, CONFIRMATION where figure 1 shows a cross section of a rim sprocket (11) and a drive ring (12) rollingly supported by cylindrical surfaces (13) on the rim sprocket and carrying a saw chain comprising drive links (16) and side links (17) . The drive links (16) of the chain penetrate orifices (20) in the drive ring to enter recesses in the rim sprocket, and tangential forces are transmitted from the sprocket to the chain in the recesses . The rim sprocket may be fastened directly to a downwardly pointing drive shaft, as on vehicle-born chain saws, or supported with a limited axial mobility on a spline shaft adjacent to a clutch drum, as is common on handheld chain saws. The drive ring (12) is according to the invention made at one edge with an inwardly directed flange (14) with an inner diameter smaller than the outer diameter of the sprocket (11) . This prevents it from falling off when the shaft is pointing downwards, even before the saw chain is mounted. At the other edge there is one outwardly directed flange (15) which facilitates mounting of a saw chain and serves to hold the chain in place when the chain is not yet running or not yet under tension. At the same edge that has the outwardly directed flange (15) there may also be a low inwardly directed flange (18) , with an inner diameter larger than the diameter of the sprocket (11) , in order not to obstruct mounting of the sprocket later than and separately from the drive ring. This will improve the axial rolling precision of the drive ring against the rim sprocket, especially if saw dust has become caught between drive ring and sprocket. As rim sprockets are commonly provided with clearing holes (19) on the lower side for emptying of oil and sawdust brought into the recesses by the drive links, the low inward flange (18) must be low enough not to block these clearing holes. To keep the drive ring from climbing onto the cylindrical surfaces of the sprocket the low inward flange should preferably have a rounded or tapered inner edge.

Claims: CLAIMS 1. Drive ring for chain saws, loosely placed between a saw chain and a drive sprocket, where the drive ring (12) has an inner cylindrical surface with larger diameter than the outer diameter of the sprocket (11) and a row of generally rectangular orifices (20) through which the drive links of the chain- enter a row of recesses in the sprocket, characterized by the drive ring having at a first edge one inwardly directed flange (14) and at a second edge at least one outwardly directed flange (15) . 2. Drive ring according to claim 1, characterized by having at the second edge one outwardly directed flange (15) and one lower inwardly directed flange (18) . 3. Drive ring according to claim 2, characterized by the lower inwardly directed flange (18) at the second edge being rounded or tapered on the side facing the chain.

Inventors: SUNDSTROEM ERIK, SUNDSTROEM, ERIK
Applicants: SANDVIK AB
Application year: 1995
Main classification: B27B17
IPC codes: B27B17