Many mechanical systems contain power transmission devices whose typical role is transmission of mechanical energy, usually rotation from an electrical internal combustion, etc., motor to the working organ, such as wheels in surface vehicles.
In many instances, the mechanical rotation must be transmitted between rotatably mounted components whose axes of rotation intersect and are at an angle with each other, either by design such as in steel mills, or due to specifics of operation of the mechanical system. For example, even if the driveshaft of a rear-wheel-drive vehicle is coaxial with the output shaft of its transmission when the vehicle is moving along an ideally flat surface, this changes when the driven rear wheels change their level relative to the front wheels due to an uneven road.
Transmission of rotational motion between two mechanical components (shafts) with intersecting axes can be smoothly performed when the shafts are connected by a universal or cardan joint. In a typical commercially available universal cardan joint there are two yokes, attached to connected shafts, and an intermediate cross-shaped member having four legs extended ouwardly at 90 deg. to each other in the plane perpendicular to the axis of the cross-shaped member, with the free end of each leg being trunnion-shaped. The trunnions are connected with bores in the yokes by means of sliding or rolling bearings. If the shafts connected by the universal joint are inclined at angle α to each other, then continuous rotation of these shafts is accompanied by oscillatory rotations of the trunnions in their bearings with angular amplitude α, while the torque acting along the shaft system is transmitted by tangential forces acting as radial forces on the trunnion bearings. It is known that such an oscillatory regime of heavily loaded bearings is associated with reduced load ratings of both sliding and rolling bearings, especially for small magnitudes of α. As a consequence, relatively large bearings and thus, large universal joints are required for a given transmitted torque. Such universal joints require good lubrication and are very sensitive to dirt and other contamination, thus requiring elaborate seals.
Most of commercially available universal joints have trunnions being supported in relation to yokes by journal (radial) bearings. However, there are cases wherein some axial forces might be generated in the trunnion-yoke connection, and such forces have to be accommodated by thrust bearings. Since the thrust bearings are also exposed to oscillating motions, both sliding and rolling thrust bearings have to be derated for the universal joint applications. Use of the enlarged sliding or rolling thrust bearings on each trunnion may significantly contribute to size, weight, and cost of the joint.
It is long known that so-called “thin-layered rubber-metal laminates” comprising thin layers of an elastomeric (rubber-like) material alternating with and bonded to thin layers of a rigid material, such as metal, woven fiber mat, etc., can accommodate very high compressive forces, up to and exceeding 250 MPa (˜37,000 psi) while retaining very low resistance to shear deformation (low shear stiffness) in the direction perpendicular to the compression force. As a result, such laminates can be used as bearings for limited displacements, e.g see E. I. Rivin, “Properties and Prospective Applications of Ultra Thin Layered Rubber-Metal Laminates for Limited Travel Bearings,” Tribology International, 1983, Vol. 16, No. 1, pp. 17-25.
Since conditions in the universal joints require bearings for limited displacements, there are several teachings of universal joint designs using rubber-metal laminated bearing sleeves, e.g. see the prior art design in FIGS. 1 and 2 from the above-quoted article. This prior art universal joint 11 connects shafts 19 and 20 and comprises yokes 12, 13, intermediate cross-shaped member 14 with trunnions 15a,b and 16a,b and rubber-metal laminated bearing sleeves 17a,b and 18a,b. In operation, the tangential force is accommodated by radial compression of the rubber-metal laminated bearing sleeves, while the oscillatory motions of the trunnions in the bores of the yokes are accommodated by shear deformations of the laminated bearing sleeves. Obviously, such a design does not require lubrication and is insensitive to contamination since it is, essentially, the solid-state design. However, use of bearing sleeves as shown in FIGS. 1 and 2 requires relatively large shear forces in order to deform the sleeves for oscillating within angles ±α. In the same time, compression forces which can be safely accommodated by these sleeves are much larger than forces transmitted by a given size joint, due to quoted above extremely high allowable compression forces on thin-layer rubber-metal laminates.
Radial precompression (preloading) of thin-layered rubber-metal laminates is very important for enhancing radial stiffness of the bearing sleeves (thus, providing for high torsional stiffness of the joint), as well as for better fatigue properties of the laminated sleeves. However, the radial preload of the bearing sleeves is difficult if at all possible to achieve in the design in FIGS. 1, 2.
Another disadvantage of the design in FIGS. 1 and 2 is a potential difficulty of its assembly and, especially, disassembly. The assembly should involve interference fits of bearing sleeves 17, 18 in the annular clearances between trunnions 15 and 16 and the bores in the respective yokes 12 and 13. Since looseness of the bearing sleeves is highly undesirable, the interference fits should be achieved simultaneously between the sleeves and the bores and between the sleeves and the trunnions. This combination requires a complex manufacturing sequence with high accuracies of the fitting components. Disassembly of such a connection would be very difficult.
The rubber-metal laminated bearing sleeves with solid rubber layers as shown in FIGS. 1 and 2 as 17, 18 have very high compression stiffness and very high allowable compression forces. However, there are cases wherein much lower torsional stiffness of the joint is desirable, even at the price of a reduced torque rating.
The proposed invention allows to eliminate the above shortcomings and to comply with the diverse specifications, e.g. relative to the torsional stiffness, while retaining the positive features of the prior art design as shown in FIGS. 1 and 2.
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