Marine Propeller and Hub Assembly

FIG. 1 is a vertical cross-sectional view taken through a marine propeller incorporating a coupling hub constructed in accordance with the invention;

FIG. 2 is a transverse cross-sectional view of the propeller of FIG. 1 taken generally along line 2--2 of FIG. 1; and

FIG. 3 is a cross-sectional view of another coupling hub constructed in accordance with the invention and connecting a pair of shafts.

Referring to the drawing and to FIG. 1 in particular, shown therein and generally designated by the reference character 10 is a marine propeller mounted on a drive shaft 12 extending from the stern 14 of a boat or the like (not shown). The shaft 12 includes a plurality of splines 16 along a portion thereof and has threads 18 mating with a nut 20 utilized to retain the propeller 10 on the shaft 12. The propeller hub assembly includes a driver member 22 fitted over the shaft 12.

The driver member 22 includes a splined portion 24 mating with the splines 16 on the shaft 12 for transmission of torque from the shaft 12 to the driver member 22 as more clearly illustrated in FIG. 2. The exterior of the driver member 22 is

provided with a plurality of circumferentially spaced full semi-circular grooves 26 extending generally parallel with the rotational axis 28 of the shaft 12.

The propeller hub assembly also includes a driven member or propeller hub 30 which carries on its exterior a plurality of circumferentially spaced, radially extending propeller blades 32 which may be of any desired configuration to provide the desired force to drive the boat 14.

The interior surface of hub 30 defines a plurality of circumferentially spaced axially extending full semi-circular grooves 34. It will be noted that the semi-circular grooves 34 are arranged to image the semi-circular grooves 26 in the driver member 22, thus forming a plurality of spaced radially disposed and axially aligned cylinders with each having its inner half formed by the driver member 22 and its outer half formed by the hub or driven member 30.

An elastomeric member 36 may be inserted into each or only selected one of the cylinders. Each member 36 is generally circular in cross-section in its smallest dimension and large enough so that it fits closely within the full diameter of the cylinder formed by the mating semi-circular grooves 26 and 34.

The elastomeric member 36 may be, for example, a rod having a diameter and length equal to the dimensions of the cylinder. Thus, with each cylinder filled with an elastomeric rod, torque is transmitted from the driver to the driven hub member across the full diameter of the entire length of all rods simultaneously. The compressibility of the material of the rod thus determines the degree of relative movement between the driver and the driven member available to compensate for shock. The total length of all the rods determines the total torque load available before shearing occurs. It will thus be noted that maximum shear load can be varied by filling less than the full length of each cylinder with elastomeric rod. For example, short rods having lengths less than the length of the cylinders can be used to lower maximum shear load capacity while maintaining full rotational arc shock resistance. Alternatively, elastomeric rods may be placed in less than all of the cylinders to accomplish similar results.

It will be noted that the closest adjacent portions of the driven hub 30 and the driver member 22 are disposed near the diameter of the elastomeric members 34 so that the maximum thickness is provided by the members 34 to resist shear or relative rotation between the driver member 22 and the hub 30. It will also be noted that each of the members 36 is independent and thus can be simply made from a rod of elastomeric material having a diameter essentially the same as the diameter of the cylinders. Thus, no special molds are required and the elastomeric members 34 can be manufactured easily and inexpensively and the replacement thereof can be easily obtained.

An unexpected discovery resulting from the structure of the invention is that the rate of compression of the elastomeric member 36 can be varied as desired to permit the compression load to rapidly increase with relative movement of the driver with respect to the driven member. This permits vastly increased shock absorbing characteristics while maintaining resistance over the full arc of relative movement and maximum shear resistance. To accomplish this effect, spherical bodies having a circular cross-section as their smallest dimension which is equal to the diameter of the cylinders are used as the elastomeric member 36. To acheive the greatest compression from minimum load to maximum load, round balls or spheres are used. It will be noted that when a ball which has a diameter equal to the diameter of the cylinder is used, only the edge of the ball is initially compressed. Thus, compression is permitted with relatively light loads. However, as the relative rotational arc of the driver to the driven member is increased, the portion of the ball which is subject to compression is increased because the portion of ball lying in the axial direction of the cylinder is increased. Thus resistance increases along a curve relative to the curved surface of the ball. The rate of movement versus resistance will be greatest when the elastomeric body is a round ball and will be the least when the elastomeric body is a continuous rod. Various rates between these two extremes can be achieved by using ellipsoid bodies of various lengths.

As when rods are used, maximum shear load can be varied as desired by using fewer spherical or ellipsoid bodies than necessary to fill the full length of all the cylinders. Furthermore, the rate of compression can be even more infinitely varied between the two extremes by using combinations of short sections of rods and spheres or ellipsoids.

A particularly unique advantage of using balls instead of rods is that the balls may rotate 360.degree. in any plane. Thus, wear on the surface of the balls is greatly minimized when compared to wear on rods which is confined to 360.degree. in only one plane.

While virtually any compressible material can be utilized to form the members 34, it is desired that the members be formed from a material such as neoprene and preferably from a neoprene having a hardness durometer of about 60-90. The preferred durometer is about 80. A hardness durometer of 80 provides excellent shearing strength while at the same time providing for deformation of the member to some extent to absorb shock loads should the propeller blades 32 strike an object in the water. It will also absorb shock loads imposed as a result of extremely high torque being applied through the shaft 16 to the propeller 10.

To utilize the coupling described herein, the driver member 22, when off the shaft 12, is provided with the elastomeric members 34 which are placed in the grooves 26. The hub 30 is then slipped thereover with the grooves 34 therein aligned to receive the members 36. Once the initial subassembly of the driver 22, elastomeric members 36 and hub 30 has taken place, the assembled propeller 10 is slipped over the shaft 12 with the splines 16 and 24 in mating relationship. The nut 20 is then screwed onto the thread 18 and provided with suitable locking pins or keys (not shown) to prevent inadvertent dislodgment of the propeller 10 from the shaft 12.

It can be seen then that when the engine or boat 14 is in operation, torque is transmitted through the shaft 12, the driver member 22, and elastomeric members 36 to the propeller 10. Should an object in the water be struck or excess torque imposed by the engine, the hub 30 and driver member 22 may move slightly relative to each other due to the resiliency of the members 36, but the operation of the propeller 10 will not be impaired until the force imposed is sufficiently great to shear all the elastomeric members 36 across their full diameters simultaneously.

It will be observed that the semi-circular grooves 26 in the driver member 22 and the semi-circular grooves 34 in the hub 30 are equal in number and spaced in parallel arrangement about the outer and inner surfaces of the driver and hub, respectively. Accordingly, the cylinders formed by the aligned grooves are disposed radially within the coupling with the geometric central axis of each cylinder lying on the circumference defined by the maximum diameter of the driver which, of course, is approximately equal to the minimum internal diameter of the hub 30. Accordingly, without the elastomeric members 36 in place, the driver 22 would rotate freely within the hub 30. However, with elastomeric members 36 positioned within each of the cylinders, torque is transmitted from the driver 22 to the hub 30 across the full diameter of each elastomeric member 36. Since the members 36 are individual bodies, they may each rotate within their individual cylinders. Thus, the expected life of each member 36 should be substantially lengthened since compression stresses are not always applied at the same points on the circumference of the member 36.

The size and number of cylinders to be formed will depend, of course, upon the torque to be transmitted and the physical characteristics of the elastomeric members 36. However, because each elastomeric member 36 can be removed and replaced individually, the maximum torque to be transmitted to the hub 30 can be adjusted as desired by removing some of the elastomeric members 36 entirely, reducing the length of some or all of the elastomeric members 36 and/or substituting elastomeric members with differing physical characteristics or shapes as described above.

It should be understood that while the invention has been described hereinabove in connection with its use as a coupling for joining a marine propeller to a shaft for driving the propeller, many other uses can be envisioned for the coupling. The coupling may, of course, be used for various other shaft couplings for various other purposes. For example, FIG. 3 illustrates in simplified form a coupling 100 which can be utilized to couple a first shaft 102 with a second shaft 104. As illustrated, shaft 104 has an enlarged portion 106 which is provided with a plurality of circumferentially spaced semi-circular grooves 108. The enlarged portion 106 is large enough to receive in telescoping relationship an enlargement 110 on shaft 102. The exterior of the enlargement 110 is also provided with a plurality of semi-circular recesses 112.

The recesses 108 and 112 are arranged as described above to form a plurality of cylinders which are sized to receive a plurality of elastomeric members 114. The elastomeric members 114 prevent relative rotation between the shaft 102 and 104 and thus transmit torque therethrough. Due to their elasticity, they also absorb shock transmitted by the shafts 102 or 104.

The coupling described hereinabove can be relatively easily and simply constructed, can be maintained easily and inexpensively, and will provide the desired torque transmission as well as shock absorption between the drive and driven members.

While the coupling hub assembly of the invention has been described in detail hereinabove with respect to certain preferred embodiments, it will be understood that various changes and modifications can be made thereto without departing from the spirit and scope of the invention as defined by the appended claims.