Abstract:
A shaft coupling having two attachment elements that are rotatable relative to one another and that are connected to one another by a rotationally resilient assembly, and further having a dampening device which is active between the attachment elements for the purpose of suppressing torsional vibrations of the rotationally resilient assembly is disclosed. The rotationally resilient assembly comprises two ramp discs that are rotatable relative to one another and that support one another at least indirectly. One disc is supported in a rotationally fixed and rigid manner on one of the attachment elements and the other disc is supported in a rotationally fixed and axially resilient manner on the other one of the attachment elements by a spring. The dampening device is a viscous coupling having a hub connected to one of the attachment elements and a housing connected to the other one of the attachment elements.

Description:
This is a divisional application of the prior application Ser. No. 09/320,293 filed May 26, 1999 and is now U.S. Pat. No. 6,296,096B1 which issued on Oct. 2, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a shaft coupling having two attachment elements that are rotatable relative to one another and that are connected to one another by rotationally resilient assembly, and further having a dampening device which is active between the attachment elements for the purpose of suppressing torsional vibrations of the rotationally resilient assembly. 
     In the drivelines of motor vehicles there occur torsional vibrations which, especially in high-performance vehicles and four wheel drive vehicles, cannot be suppressed by conventional vibration dampening means at the clutch disc. Likewise, vibration dampening means additionally attached to the propeller shaft, for example, resiliently arranged absorber masses, often are not sufficient to prevent such vibrations from occurring. 
     It is therefore the object of the present invention to provide a shaft coupling that is incorporated into the driveline, has a high torque transmitting capacity and includes a highly effective dampening means. 
     SUMMARY OF THE INVENTION 
     According to a first embodiment, the rotationally resilient assembly comprises two ramp discs that are rotatable relative to one another and that support one another at least indirectly. One disc is supported in a rotationally fixed and rigid manner on one attachment element. The other disc is supported in a rotationally fixed and axially moveable manner on the other attachment element by a spring. The dampening device is a viscous coupling having a hub connected to one of the attachment elements and a housing connected to the other one of the attachment elements. The torsion spring and the torsion damper are systematically switched in parallel relative to one another. 
     In a preferred embodiment, the ramp discs include circumferential grooves having variable depths, in which balls are guided. Each circumferential groove has a deepest point and the depth of the groove decreases symmetrically from the deepest point towards both ends. Furthermore, the circumferential grooves of the discs are preferably arranged opposite one another as are the discs to thereby jointly accommodate a plurality of balls between them. The decrease in the groove depth as a function of the angle of rotation from the deepest point can be linear or progressive. 
     In a further preferred embodiment the spring comprises a plurality of plate springs. To achieve uniform load conditions, there are preferably provided three circumferentially distributed balls in the respective grooves to permit the ramp discs to rotate relative to one another in a low-friction way. The rotation of the ramp discs, which is converted into compression of the plate spring, can lead to a very high shaft stiffness of the coupling while at the same time achieving a short coupling length. To ensure effective dampening, there is provided a viscous coupling with suitable plates for generating a high dampening effect, i.e. there is provided an assembly which consists of a hub and a housing, which is filled with a highly viscous medium and which carries axially alternatingly arranged plates. 
     According to a further preferred embodiment, the ramp discs and the plate spring are arranged in the housing of the viscous coupling. 
     According to a second embodiment the rotationally resilient assembly comprises a torsion bar having one end connected in a rotationally fixed manner to one of the attachment elements and the other end connected in a rotationally fixed manner to the other one of the attachment elements. The dampening device is a viscous coupling whose hub is connected in a rotationally fixed manner to one of the attachment elements and whose housing is connected in a rotationally fixed manner to the other one of the attachment elements. The torsion bar needs to have a certain length because a hub-shaped attachment element can, at the same time, form the hub of the viscous coupling, i.e. as the torsion bar is arranged concentrically inside the viscous coupling, in this case, too, the overall assembly length is relatively small. The assembly has a very simple design. To ensure effective dampening, there is provided a viscous coupling with suitable plates for generating a high dampening effect, i.e. an assembly which consists of a hub and a housing, which is filled with a highly viscous medium and which carries axially alternatingly arranged plates. 
     According to a preferred embodiment the rotationally resilient assembly furthermore comprises a torsion tube spring arranged concentrically relative to the torsion bar. One end of the torsion tube spring is connected in a rotationally fixed manner to one of the attachment elements and that the other end of the torsion tube spring is freely rotatable relative to the other attachment element up to a limited rotational angle. In this way it is possible, from a certain angle of rotation onwards, to achieve a high degree of torsional stiffness, without the design of the shaft coupling becoming particularly complicated. In this embodiment also, the torsion bar, the torsion tube spring and the viscous coupling are arranged coaxially relative to one another to reduce the length of the assembly. 
     Preferred embodiments of the invention will be described below in greater detail with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view through a shaft coupling having a plate spring, ramp discs and a separately arranged viscous coupling, with the shaft coupling shown in two positions. 
     FIG. 2 a  is a longitudinal cross-sectional view through a shaft coupling having rotary ramps, plate springs and an integrated viscous coupling. 
     FIG. 2 b  is a cross-sectional view between the ramp discs along line  2 — 2  of FIG. 2 a.    
     FIG. 3 a  is a longitudinal cross-sectional view of a shaft coupling with a torsion bar and a separate viscous coupling. 
     FIG. 3 b  is an axial view of FIG. 3 a.    
     FIG. 4 a  is a longitudinal cross-sectional view of a shaft coupling with a torsion bar and an additional tube spring along with a viscous coupling. 
     FIG. 4 b  is a cross-sectional view along line  4 — 4  of FIG. 4 a  through the end of the tube spring. 
     FIG. 5 is a graph of the characteristic spring curve of the shaft coupling designed according to FIGS. 4 a  and  4   b.    
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 an inventive shaft coupling is shown generally at  10 . Shaft coupling  10  includes a flange  11  which constitutes the first attachment element and a flange  12  constituting the second attachment element. Flange  11  is secured by bolts  13  to a counter flange (not shown). Flange  12  is provided with bolt holes  14  for securing another counter flange (not shown) by means of bolts. To the flange  11  there is secured a substantially torsionally stiff shaft journal  15  which extends into the region of flange  12 . A first end  9  of the shaft journal  15  and the flange  12  are rotatably supported relative to one another by a ball bearing  16 . At first end  9 . the journal  15  includes shaft teeth  17 . 
     A first ramp disc  18 , by means of counter teeth  19 , engages shaft teeth  17  so as to be rotationally fixed to first end  9  and axially displaceable along shaft journal  15 . A second ramp disc  20  is connected to the flange  12  in a rotationally fixed and axially supported manner. Second ramp disc  20  is pressed into a protective tube  21  that is directly welded to flange  12 . 
     First ramp disc  18  includes circumferential grooves  22  whose depth varies across the circumference and which accommodate a plurality of balls  23 . Second ramp disc  20  is provided with corresponding circumferential grooves  24  which are symmetrical mirror images of the grooves  22 . The plurality of balls  23  are held by a cage  25  so as to be at a constant circumferential distance from one another and aligned with the circumferential grooves ( 22  and  24 ). The first ramp disc  18  and The second ramp disc  20  are arranged opposite each other and comprise a rotationally resilient assembly. 
     First ramp disc  18  is supported by an axial bearing  26  on an axially displaceable pressure ring  27  which is held under pre-tension by a plurality of plate springs  28 . Plate springs  28  are supported on a cover  29  which is threaded at the end of the protective tube  21  into a set of internal threads  42 . Cover  29  is held so as to be rotationally secured by a plurality of worm screws  30 . 
     When no torque acts on the shaft coupling  10  the balls  23 , under the influence of the plate springs  28  acting via the pressure ring  27  and the axial bearing  26  on the first ramp disc  18 , assume a neutral position at the deepest point in the base of the circumferential grooves  22 ,  24 , as shown in the lower half of FIG.  1 . However, under the influence of torque, the ramp discs  18  and  20  are rotated relative to one another against the force of the plate springs  28 , with the balls  23  running into the flatter regions of the circumferential grooves  22 ,  24  as shown in the upper half of FIG.  1 . By rotating the flanges  11  and  12  relative to one another, the ramp discs  18  and  20  can be rotated relative to one another until the plate springs  28  cannot be compressed any further, as shown in the upper half of FIG.  1 . Thereafter the shaft coupling  10  is torsion-proof. 
     The dampening device is in the form of a viscous coupling  8  having a hub  31  arranged on a second set of teeth  32  on the shaft journal  15  by means of a corresponding set of counter teeth  33  on hub  31 . A multi-part housing  34  is connected in a rotationally fixed way to the above-mentioned protective tube  21  by means of worm screws  30 . The viscous coupling  8  is filled with a viscous medium through a set of bores  35 . A plurality of inner plates  36  of the viscous coupling  8  are held on a set of teeth  37  of the hub  31  in a rotationally fixed way. A plurality of outer plates  38  of the viscous coupling  8  are arranged in a rotationally fixed way on a set of inner teeth  39  of the housing  34 . The hub  31  and the housing  34  are sealed relative to one another by seals  40 ,  41 . 
     The movements of the flanges  11  and  12  relative to one another are dampened by the viscous coupling  8  as a result of the corresponding relative movement of the hub  31  connected to the journal  15  and of the housing  34  connected to the protective tube  21 , so that any torsional vibrations are thereby suppressed. 
     FIG. 2 a  shows an inventive shaft coupling  100  having a hub  111  constituting the first attachment element and a flange  112  constituting the second attachment element. The hub  111  is connectable to a flange (not shown) by means of a set of teeth  113 . The flange  112  is provided with threaded holes  114  for threading on a counter flange (not shown) by means of bolts. Hub  111  is in the form of a substantially torsionally stiff hollow shaft which extends into the region of flange  112 . 
     A first end  109  of the hub  111  and the flange  112  are supported by a ball bearing  116  so as to be rotatable relative to one another. Hub  111  is provided with a set of shaft teeth  117  that engage a set of counter teeth  119  on a first ramp disc  118 . Thus, first ramp disc  118  is rotationally fixed and axially displaceable on hub  111 . A second ramp disc  120 , that is integral with the flange  112 , is pressed into a protective tube  121  which is welded directly to the flange  112 . 
     The first ramp disc  118  includes circumferential grooves  122  whose depth and width varies across the circumference and which accommodate a plurality of balls  123 . The second ramp disc  120  is provided with corresponding circumferential grooves  124  which are symmetrical mirror images of circumferential grooves  122 . The plurality of balls  123  are held by a cage  125  so as to be at a constant circumferential distance from one another and aligned with circumferential grooves ( 122  and  124 ). The first ramp disc  118  and the second ramp disc  120  are arranged opposite each other and comprise a rotationally resilient assembly. 
     The first ramp disc  118  is held under pre-tension directly by a plurality of plate springs  128  supported on an inner step  129  formed in the protective tube  121 . 
     When no torque acts on the shaft coupling  100  the balls  123 , under the influence of the plate springs  128  acting on the first ramp disc  118 , assume a neutral position at the deepest point in the base of the circumferential grooves  122 ,  124 , as shown in FIG. 2 a . However, under the influence of torque, the ramp discs  118 ,  120  are rotated relative to one another against the force of the plate springs  128 , with the balls  123  running into the flatter regions of the circumferential grooves  122 ,  124  as described above for FIG.  1 . By rotating the hub  111  relative to the flange  112 , the ramp discs  118 ,  120  can be rotated relative to one another until the plate springs  128  cannot be compressed any further. Thereafter, the shaft coupling  100  is torsion-proof. 
     The dampening device is in the form of a viscous coupling  108  having a hub  131  formed directly by hub  111  and a multi-part housing  134  comprising the second ramp disc  120 , the above-mentioned protective tube  121  and a cover  107 . The multi-part housing  134  is thus connected to the flange  112  in a rotationally fixed way. The viscous coupling  108  is filled with a viscous medium through a set of closed bores  135 . A set of inner plates  136  of the viscous coupling  108  are held in a rotationally fixed way on the shaft teeth  117  of the hub  111 . A set of outer plates  138  of the viscous coupling  108  are arranged in a rotationally fixed way on a set of inner teeth  139  of the protective tube  121 . The hub  111  and the housing  134  are sealed relative to one another by seals  140 ,  141 . Movements of the hub  111  relative to the flange  112  are dampened by the corresponding relative movements of the inner plates  136  relative to the outer plates  138 , so that torsional vibrations are suppressed. 
     In FIG. 2 b  it is possible to see the circumferential grooves  124  which extend in a symmetrically constant, circular-arch-shaped way and become narrower and shallower from their deepest point toward their ends. FIG. 2 b  also shows the balls  123  in their deepest position in circumferential grooves  124 . 
     FIG. 3 a  shows an alternative embodiment having a first attachment element in the form of a hub  51  and a second attachment element in the form of a flange  52 . The hub  51  carries a set of outer teeth  53  which are connectable to a flange (not shown). The flange  52  includes threaded holes  54  for threading on a counter flange (not shown). The end of the hub  51  positioned opposite the outer teeth  53  and the flange  52  are rotatably supported relative to one another by a ball bearing  56 . 
     The hub  51  and the flange  52  are rotationally resiliently connected to one another by a torsion bar  55  which has a first square end  57  that directly engages a square opening  58  in the hub  51  and a second square end  59  that engages a square opening  60  in an intermediate plate  69 . The intermediate plate  69 , in turn, is externally square and engages a corresponding square inner aperture  70  of the flange  52 . 
     The hub  51  is integral with a hub  71  of a viscous coupling  72  which carries a set of inner plates  76  on a set of outer teeth  77 . The flange  52 , an outer tube  61  and a cover  62  form a housing  74  of the viscous coupling  72 . Housing  74  includes a set of inner teeth  79  that hold a set of outer plates  78  of the viscous coupling  72 . The housing  74  and the hub  71  are sealed relative to one another by seals  80 ,  81 . 
     When the hub  51  rotates relative to the flange  52  under torsion of the torsion bar  55 , the housing  74  of the viscous coupling  72  simultaneously rotates relative to the hub  71  of same, so that any rotational vibrations of the torsion bar  55  are dampened. At one end, the hub  71 , on the outer teeth  77 , carries a stop disc  82  which, with rotational play, engages circumferential recesses  86  in the outer tube  61  with stop cams  85 . Only after the torsion bar  55  has rotated by a certain angle, do the stop cams  85  become effective and limit the rotation. 
     FIG. 4 a  shows an alternative embodiment having a first attachment element in the form of a flange  151  and a second attachment element in the form of a flange  152 . The flange  151  is provided with bolt holes  153  for threading on a first counter flange (not shown). The flange  152  is provided with bolt holes  154  for threading on a second counter flange (not shown). The flange  151  is connected in a rotationally fixed way to a hub  171 . The end of the hub  171  positioned opposite flange  151  and flange  152  are rotationally supported relative to one another by a friction bearing  156 . 
     The flange  151  and the flange  152  are rotationally resiliently connected to one another by a torsion bar  155  having a set of teeth  157  on one end that directly engage a set of inner teeth  158  in the flange  151  and a set of second teeth  159  at the other end that directly engage a set of teeth  160  of the flange  152 . 
     Inside the hub  171  there is concentrically arranged a rotary tube spring  183  which is directly secured to the flange  151  at one end by driving elements  184  but which, otherwise, is positioned at a radial distance between the hub  171  and the torsion bar  155 . At the opposite end of the tube spring  183  there are provided stop elements  185  which, with rotational play, engage circumferential slots  186  in the flange  152 . Only after the torsion bar  155  has been rotated by a certain angle do the stop elements  185  become effective, with the tube spring  183  becoming active in addition to the torsion bar  155 . The hub  171  directly forms the hub of a viscous coupling  200 . A set of outer teeth  177  on hub  171  carries a set of inner plates  176 . The flange  152  is connected to a housing  174  of the viscous coupling  200 . Housing  174  is formed by the flange  152 , an outer tube  161  and a cover  162 . Housing  174  includes inner teeth  179  that carry a set of outer plates  178  of the viscous coupling  200 . The housing  174  and the hub  171  are sealed relative to one another by seals  180 ,  181 . 
     When the flange  151  rotates relative to the flange  152  under the influence of torsion of the torsion bar  155  and, possibly, relative to the tube spring  183 , the housing  174  of the viscous coupling  200  rotates simultaneously relative to the hub  171 , so that any rotational vibrations of the torsion bar  155  and, possibly, of the tube spring  183  are dampened. 
     FIG. 4 b  shows a cross-sectional view along line  4 — 4  of FIG. 4 a.    
     FIG. 5 shows a graph of the characteristic spring curve of the viscous coupling  200  designed according to FIGS. 4 a  and  4   b,  which, up to an angle of rotation α1, due to the sole function of the torsion bar  155  resilience extends linearly with a first flatter inclination and which, above the angle of rotation α1, due to the joint effect of the torsion bar  155  resilience and the tube spring  183 , extends linearly with a second steeper inclination.