In the construction of quality rotary lawn mowers, or like devices having a working element powered by a rotating shaft, it is desirable to provide integration between the driving and braking operations. Particularly, it is desirable to effect positive braking of the working element when the driving action is terminated, and vice versa.
According to the present invention, apparatus is provided that allows desirable integration of the driving and braking functions described above, in a simple yet effective manner. The apparatus according to the present invention may be constructed utilizing a subassembly which is easy to build and easy to install and/or maintain and/or replace. There are a minimum of components, especially movable structures, and in particular the frictional surfaces providing braking and clutching are rigidly attached to a component that is rotatable and linearly movable, but need not bend or flex.
The high friction material braking and clutching elements utilized according to the present invention are annular. The annular members may be solid, having sides tapering together from a plate to which each is connected toward a point spaced from the plate. Alternatively, each annular member may comprise a pair of bands of high friction material attached to tapering surfaces. Either provides an effective substantially truncated V cross-section. The friction members have a wedging engagement with a stationary housing portion (to provide braking) or a rotatable drive plate (to provide clutching), and the construction thereof minimizes the amount of normal force necessary to perform a driving or braking action.
According to one aspect of the present invention, a power tool (such as a rotary lawn mower) comprising a housing mounting an engine, the engine powering a rotatable shaft, and a working element adapted to be driven by the rotatable shaft, is provided. A combination clutch and brake means for selectively effecting driving or braking of the working element is provided, the clutching and brake means comprising a drive plate attached to the rotatable shaft for rotation therewith and having a clutching portion; a braking portion of the housing; and adaptor plate attached to the working element and having friction material disposed on either surface thereof, the adaptor disposed between the drive plate and the housing braking portion and having a central bore therein coaxial with the rotatable shaft; and means for selectively moving the adaptor plate parallel to the axis of the rotatable shaft from a first position wherein the friction material engages the housing braking portion to effect braking of the working element, to a second position wherein the friction material engages the clutching portion to effect driving of the working element by the drive plate.
According to another aspect of the present invention, a subassembly for a power tool is provided for operatively connecting a powered rotary shaft of the power tool to a working element (such as a rotary lawn mower blade). The subassembly includes an elongated adaptor tube adapted to be operatively disposed on the powered rotary shaft of the power tool, a drive plate, releasable means (such as screws) for operatively rigidly connecting the drive plate and the adaptor tube so that they are concentric, an adaptor plate for connection to the working element and an actuation plate to cooperatively engage the adaptor plate and the drive plate. The working element may be connected to the adaptor plate as part of the subassembly. The subassembly further comprises a pair of friction members connected to the adaptor plate, one extending from each surface of the adaptor plate and one adapted to operatively engage surface means formed on the drive plate. Spring means are disposed between the adaptor plate and the drive plate to bias them apart, and a central bore is formed in the adaptor plate through which the adaptor tube passes. A collar formed on the adaptor tube and disposed on the opposite side of the actuation plate, the adaptor plate and the drive plate is dimensioned so that it cannot pass through the central bore in the actuation plate and the adaptor plate. The friction members of the subassembly preferably each comprise an annular member of high friction material having substantially a truncated V cross-section. The friction members may be integral, with one member formed as a plurality of annular segment teeth which extend through openings formed in the adaptor plate to stand proud of opposite surfaces of the adaptor plate.
According to another aspect of the apparatus according to the invention, an assembly for effecting driving or braking of a rotatable working element adapted to be driven by a powered rotatable shaft is provided. The assembly includes a housing stationary with respect to the shaft and having stationary first surface means associated therewith; a working element; means for operatively mounting the working element with respect to the rotatable shaft so that in a first position the working element operatively engages the rotatable shaft for rotation therewith, and in a second position the working element operatively engages the housing and remains stationary with respect to the shaft; and means for actuating the working element operatively mounting means for moving between the first and second positions thereof. The operatively mounting means comprises a drive plate fixed to and coaxial with the rotatable shaft and having a second surface means associated therewith; an adaptor plate fixed to the working element and coaxial with the rotatable shaft and having third and fourth surface means associated therewith, the adaptor plate mounted between the housing first surface means and the drive plate along the axis of the rotatable shaft with the third surface means aligned with the first surface means, and the fourth surface means aligned with the second surface means; and means for mounting the adaptor plate for movement parallel to the axis of the rotatable shaft in response to actuation by the actuation means, from the first position wherein the first and third surface means operatively frictionally engage each other while the second and fourth surface means operatively engage each other, to the second position wherein the first and third surface means are not operatively engaged and the second and fourth surface means operatively frictionally engage each other.
It is the primary object of the present invention to provide for simple, yet effective, driving or braking of a rotatable working element adapted to be driven by a powered rotatable shaft. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.