Patent Publication Number: US-5289737-A

Title: Elastic clutch

Description:
This is a continuation of application Ser. No. 07/748,827, filed Aug. 22, 1991 and now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention concerns an elastic clutch of disk design, particularly suited for a split flywheel for an internal combustion engine. A clutch for this type is known from the German patent disclosure 38 41 639. 
     The prior clutch features mutually engaging clutch halves between which a helical spring is inserted that is relatively long and extends across a large angular area, i.e., is installed in a curved condition. For that purpose, the one clutch half features for the radial and axial guidance an outer area that is round and adapted to the spring windings. Such a spring arrangement is characterized in that for specific operating conditions there are favorable spring properties achieved, namely when large amplitudes of torsional oscillation are to be absorbed and damped with low spring stiffness. But due to its curved installation, the spring is heavily forced outward in a radial direction during the twisting of the two clutch halves. Despite the lubricant contained in the clutch, this leads to heavy frictional damping in the outer winding area and to an uncontrollable adverse effect on the spring characteristic. Additionally, wear occurs on the bearing surface and on the spring, and the curved spring itself is unfavorably stressed on its radially inner windings. In terms of manufacture, it is expensive to produce a high-precision curved spring. 
     The problem underlying the invention consists is a clutch of the type discussed above where a spring that can be produced at low cost is arranged in such a manner that it is protected from wear and also favorably stressed, while the known is favorable spring properties are retained. 
     SUMMARY OF THE INVENTION 
     The above problems are solved, according to the invention, by providing an oblong spring that is subdivided in the axial direction into portions separated by at least one wedge-shaped cup member inserted between adjacent windings in the outer winding area. 
     Provided is an oblong spring in the radially outer windings of which there is at least one wedge-shaped member inserted, so that the spring itself is subdivided into at least two sub-sections, with angular alignment being imparted to the longitudinal axes of these partial areas relative to one another. This angling occurs through spreading adjacent spring windings, so that overall a form of the entire spring curved in polygon fashion is created. 
     The advantage of this arrangement is constituted by the fact that, in the preferred embodiment, the spring itself is integral and can be produced with an essentially straight-line longitudinal axis in its unstressed condition, with an adaptation to the curvature of the cutout in the coupling being effected just before installation by insertion of wedge-shaped spring cups. As the spring is stressed, the wedge-shaped spring cups move along with the windings along the housing enveloping the spring because the wedge-shaped spring cups are not fastened to the surrounding housing, but are free to move. Therefore, the sub-sections of the spring are essentially stretched sections and are thus subject to a favorable load. 
     The spring arrangement may be of a design such that each section of the spring is curved less than the entire spring, based on its total length. Each spring section between two spring cups may also be of a straight-line design, i.e., with an infinite radius of curvature. The wedge type spring cup may be fashioned as a radial guide of the spring at the point of buckle as a lateral guide within the cutout in the coupling halves. What is achieved thereby is that the windings of the spring have no metal-to-metal contact with the surrounding parts, so that neither friction nor wear will occur. The spring may be provided with spring plates at its ends and, as is known, guide pieces may be inserted loosely between the radially outer winding area of the sections and the outer definition of the cutout, in order to prevent a buckling under load. The wedge-shaped spring cup may preferably consist of a material which is resistant to temperature and wear as well as lubricants. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     An embodiment of the invention will be more fully described hereafter with the aid of the drawing, wherein: 
     FIG. 1 is a longitudinal sectional view of an elastic coupling in accordance with an embodiment of the invention; and 
     FIG. 2 is a cross sectional view of the spring area along the section line II--II in FIG. 1. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows half of a longitudinal section through an elastic coupling comprising a first coupling half 1 and a second coupling half 2 forming the two masses of a dual-mass flywheel of disk design. Coupling half 1 is connected with an internal combustion engine (not shown), whereas the second coupling half 2 is connected by way of a friction clutch with a gear box of a vehicle drive (not illustrated). The first coupling half 1 features two side disks 4 into which plunges a center disk 5 pertaining to the second coupling half 2 and which, in turn, is rotatably mounted on the first coupling half 1, in the hub area, by way of an anti-friction bearing 3. Arranged between center disk 5 and side disks 4 is an elastic coupling element fashioned as a helical spring 7. Both center disk 5 and also side disks 4 feature for that purpose corresponding cutouts 6 in which spring 7 is received and is oriented in the circumferential direction. 
     FIG. 2 shows a schematic cross section through the spring area, along line II--II in FIG. 1. Visible is the cutout 6 in center disk 5 as well as spring 7. Contained in the outer winding areas 13 of spring 7 are two wedge-shaped spring cups 8. These subdivide spring 7 into three partial areas 9, 10, which through the radially outer spreading between two adjacent windings assume a buckled position to one another. Supporting spring plates 14 are located at the two ends of spring 7 in cutout 6. 
     The wedge-shaped spring cups 8 are so arranged between the outer windings 13 of spring 7 and the outer limit of cutout 6 that a support of spring 7 will ensue, without the spring itself making metallic contact with the parts of the spring. Not connected with the center disk 5, i.e., the cutout 6, the wedge-shaped spring cups 8 are capable of moving along with spring 7. In the process, while spring 7 is stressed, they maintain the buckled position of the longitudinal axes 16 of the individual partial areas 9, 10 of spring 7 relative to one another. Accomplished thereby is that the radius of curvature R of each section 9, 10 remains very large, or each area even retains the stretched position (radius of curvature R/infinity) and yet, the entire spring arrangement between the two spring plates 14 has a much smaller radius of curvature, the center point of which coincides normally with the axis of rotation 15 of the coupling. This makes it possible to provide an overall curved spring 7 which, however, is composed of favorably stressed stretched partial areas 9, 10. 
     In each partial area 9, 10, of the spring, a loosely inserted guide piece 12 may be provided between the outer winding area 13 and the inner definition of the cutout 6, which guide piece 12 additionally prevents a radially outward buckling. 
     The wedge type spring cup is preferably made of a non-metallic material which is light-weight, resistant to abrasion, high temperature and to the lubricant that is normally contained in the coupling, under retention of good sliding properties. For example, a plastic such as polyethylene is acceptable. Furthermore, the wedge-shaped spring cup may be so designed that it extends from outside up to the radially inner winding area of the spring. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.