Abstract:
In a damper, in particular for spin-drying cylinder washing machines, it is provided, with a view to obtaining low-noise and low-wear guidance of a tappet in a casing, that the damper comprises a guiding damping unit which damps any deflections of the tappet in the radial direction and centers the tappet in the casing.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a damper comprising a flexible guiding damping unit in particular for spin-drying washing machines.  
         [0003]     2. Background Art  
         [0004]     Dampers of the generic type are known for example from DE 196 15 010 A1. Owing to low-cost manufacture, there is undesired play between the tappet and casing in those dampers. Upon operation of a washing machine that comprises those dampers, undesired noise develops by the tappet hitting against the casing. Moreover, the lifetime of those dampers is reduced as a result of increased wear between the tappet and the casing.  
       SUMMARY OF THE INVENTION  
       [0005]     It is an object of the invention to develop a damper of the type mentioned at the outset in such a way that low-noise and low-wear guidance of the tappet in the casing is ensured, accompanied with manufacture at a low cost.  
         [0006]     This object is attained by the features including a substantially tubular casing which has a central longitudinal axis and an end on the side of a tappet and a free end; a tappet which is displaceably guided in the casing and projects from the end on the side of the tappet, having a central longitudinal axis and an end inside the casing and a free end; fastening elements which are mounted on the free end of the casing and on the free end of the tappet; a frictional damping unit for producing a given frictional damping effect between the casing and the tappet; and a guiding damping unit for damping and centering any deflection of the tappet crosswise of the central longitudinal axis of the casing. The gist of the invention resides in providing the damper with a guiding damping unit that will attenuate any radial deflections of the damper and center the tappet in the casing.  
         [0007]     Additional features and advantages of the invention will become apparent from the ensuing description of five exemplary embodiments of the invention, taken in conjunction with the drawing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]      FIG. 1  is a diagrammatic elevation of a first embodiment of a cylinder washing machine with dampers;  
         [0009]      FIG. 2  is a longitudinal sectional view of a damper of  FIG. 1 ;  
         [0010]      FIG. 3  is a perspective illustration of a guiding damping unit of the damper of  FIG. 2 ;  
         [0011]      FIG. 4  is a plan view of the guiding damping unit of  FIG. 3 ;  
         [0012]      FIG. 5  is a longitudinal sectional view of a second embodiment of a damper;  
         [0013]      FIG. 6  is a perspective view of a guiding damping unit of the damper of  FIG. 5 ;  
         [0014]      FIG. 7  is a plan view of the guiding damping unit of  FIG. 6 ;  
         [0015]      FIG. 8  is a plan view of a third embodiment of a guiding damping unit;  
         [0016]      FIG. 9  is a perspective view of the guiding damping unit of  FIG. 8 ;  
         [0017]      FIG. 10  is a plan view of a fourth embodiment of a guiding damping unit;  
         [0018]      FIG. 11  is a perspective view of the guiding damping unit of  FIG. 10 ;  
         [0019]      FIG. 12  is a perspective view of a fifth embodiment of a guiding damping unit; and  
         [0020]      FIG. 13  is a plan view of the guiding damping unit of  FIG. 12 . 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]     The following is a detailed description of a damper comprising a guiding damping unit according to a first embodiment, taken in conjunction with FIGS.  1  to  4 . A cylinder washing machine comprises a vibratory washing aggregate  2  with a driving motor  3  which actuates a washing cylinder (not shown in detail) via a belt drive  4 . By way of two dampers  5 , which are going to be described in detail, the vibratory washing aggregate  2  supports itself on a basic machine frame  6  on the ground. Additionally, the washing aggregate  2  is vibratorily suspended on the machine frame  6  by means of helical extension springs  7 . Consequently, the washing aggregate  2  combines with the dampers  5  and the helical extension springs  7 , constituting a spring-damper system vibratorily lodged in the machine frame  6  for damping any imbalances during spin-drying jobs of the washing cylinder.  
         [0022]     Each damper  5  comprises a substantially tubular casing  8  with a central longitudinal axis  9 . Tubular casings are understood to be casings of round as well as noncircular, in particular rectangular cross-sectional shape. The free end  10  of the tubular casing  8  is closed by a bottom  11 . A first fastening element  12  is fixed to the outside of the bottom  11 , including a first bearing  13  and a bearing bush  14  which is fixed inside the bearing  13 . By means of the first fastening element  12 , the damper  5  is mounted on the machine frame  6  for pivotability in relation to the washing aggregate  2  about a pivoting axis  15  which is parallel to the cylinder axis of rotation  16 .  
         [0023]     The damper  5  further comprises a tappet  17  which possesses a central longitudinal axis  18  and, on its free end  19 , a second fastening element  20  with a second bearing  21 . The second fastening element  20  is inserted into the free end  19  of the tubular tappet  17 , where it is fixed by positive fit so that the second fastening element  20  closes the free end  19 . By way of the second fastening element  20 , the damper  5  is mounted on the washing aggregate  2  in such a way that the damper  5  is rotatable about a second pivoting axis  22  which is also parallel to the cylinder axis of rotation  16 .  
         [0024]     By its end  23 , inside the casing  8 , the tappet  17  is inserted into the end  24  of the casing  8  on the side of the tappet  17 . Upon ideal guidance of the tappet  17  inside the casing  8 , the central longitudinal axis  9  of the casing  8  and the central longitudinal axis  18  of the tappet  17  coincide. In the direction of the central longitudinal axes  9 ,  18 , the motion of the tappet  17 , which is displaceably mounted in the casing  8 , is damped by a frictional damping unit  26 . The frictional damping unit  26  is disposed inside a casing cup  27 . The casing cup  27  has a bottom  28  which is pierced by the end  24  of the casing  8  on the side of the tappet  17 , the cup  27  and the casing  8  being one piece. The end  24  on the side of the tappet  17  extends as far as approximately to the middle of the casing cup  27 .  
         [0025]     The frictional damping unit  26  comprises an annular frictional damping lining  29 , a contact-pressure-piston component  30 , a fastening-piston component  31  and a first spring  32  as well as a second spring  33 . The annular frictional damping lining  29  rests on the outside wall of the tappet  17 ; it is pressed against the outside wall of the tappet  17  by the contact-pressure-piston component  30  and held in the direction of the free end  19  of the tappet  17 . In the direction of the end  23 , inside the casing  8 , of the tappet  17 , the frictional damping lining  29  is held by the fastening-piston component  31 . In the direction of the central longitudinal axes  9 ,  18 , the end of the fastening-piston component  31  that is turned towards the inside wall of the casing cup  27  comprises an annular locking projection  34  which combines with the end of the contact-pressure-piston component  30  that is turned towards the end  23 , inside the casing  8 , of the tappet  17 , forming a rear recess of positive fit and fixing the fastening-piston component  31  and the contact-pressure-piston component  30 . The first spring  32  is pre-loaded between a stop  35  of the fastening-piston component  31  and an annular stop  36  on the inside wall of the casing cup  27  in vicinity to the bottom  28  thereof. By contrast, the second spring  33  is pre-loaded between a stop  37  of the contact-pressure-piston component  30  and a stop  38  of a cap  39 .  
         [0026]     The cap  39  is cup-shaped too, on its bottom  40  having a guiding damping unit  41  which the free end  19  of the tappet  17  passes through and which serves for damping any deflection of the tappet  17  crosswise of the central longitudinal axis  9  of the casing  8  and for centering the tappet  17 . The cap  39  has a greater diameter than the cup  27 ; it is pushed over the cup  27  in the direction of tappet insertion  42  and fixed thereto. Fixing takes place by means of locking noses  43  which combine with the outer wall of the cup  27 , forming rear recesses.  
         [0027]     The following is a detailed description of the cap  39  and the guiding damping unit  41 . The cap  39  comprises a basic cap structure  44  which tapers in the direction of the bottom  40  of the cap  39 , having ventilation apertures  45  uniformly distributed along the circumference. The guiding damping unit  41  is disposed inside the bottom  40 , having a tappet inlet  46 ; the unit  41  and the basic cap structure  44  are integral. From the non-tapered end of the basic cap structure  44 , fastening ribs  48  extend in the direction of a central longitudinal axis  47  of the cap  39  which is identical with the central longitudinal axis  9  of the casing  8 ; they are regularly distributed along the circumference and, by their free ends, joined to a fastening ring  49 , possessing the locking noses  43  on their inside wall in proximity to their free ends.  
         [0028]     The guiding damping unit  41  is comprised of several annularly disposed damping elements  50  which are formed in one piece with the cap  39 . The unit  41  is integrally injection-molded from plastic material, in particular POM or polyamide. The damping elements  50  are regularly distributed along the circumference, related to the central longitudinal axis  47  of the cap  39 , two of the damping elements  50  at a time facing each other diametrically as related to the central longitudinal axis  47  of the cap  39 . Each damping element  50  has a U-shaped profile with an inner rib portion  51  and an outer rib portion  52  which is longer than the inner rib portion  51 , the outer rib portion  52  being curved in accordance with an outside radius and the inner rib portion  51  being curved in accordance with an inside radius as related to the central longitudinal axis  47  of the cap  39  and the outside radius being greater than the inside radius. The inner rib portion  51  and the outer rib portion  52  are interconnected by a curved connecting rib portion  53  and jointly enclose a chamber  66  which is open only in the axial direction. The outer rib portion  52  additionally possesses a radially inward stop  55  in the shape of a wedge which defines the mobility of the inner rib portion  51  radially outwards. It is also possible to define the radial motion of the rib portions without a stop. To this end, the stability and geometry of the rib portions must be selected suitably. The guiding damping unit  41  is rotationally symmetrical of the central longitudinal axis  47  of the cap  39  by an angle of 360° divided by the number of damping elements  50 . The spring characteristic of the damping elements  50  is adjustable by way of their geometry. Owing to the one-piece design of the damping elements  50 , the inner rib portions  51  thereof form a closed inner ring  67  and the outer rib portions  52  an outer ring, both rings being interconnected by the connecting rib portions  53 . The tappet  17  slides on the ring  67  by some play.  
         [0029]     The following is a detailed description of the mode of operation of the damper  5  with the guiding damping unit  41 . Upon operation of the cylinder washing machine  1 , loads act on the damper  5  as a result of imbalances of the washing cylinder of the washing aggregate  2  in the direction of its central longitudinal axes  9 ,  18 ,  47  and crosswise thereof. The ensuing description proceeds from a sudden rise in the stimulation of load on the tappet  17  in the direction of tappet insertion  42 . A first case of stimulation of load on the tappet  17  precisely in the direction of the central longitudinal axis  9  of the casing  8  is differentiated from another case in which stimulation does not take place precisely in the direction of the central longitudinal axis  9  i.e., there is a transverse-load component.  
         [0030]     Proceeding from the position of rest of the damper  5  seen in  FIG. 2 , the tappet  17  moves precisely in the direction of the central longitudinal axis  9  of the casing  8  in the direction of tappet insertion  42  in the first case of actuation of the tappet  17  by load. Upon insertion, the central longitudinal axis  18  of the tappet  17  is identical with the central longitudinal axis  9  of the casing  8 , there being no transverse-load component. As a result of the friction between the frictional damping lining  29  and the outside wall of the tappet  17 , the frictional damping lining  29 , together with the contact-pressure-piston component  30  and the fastening-piston component  31 , is being entrained by the motion of insertion of the tappet  17  in the direction of tappet insertion  42 . During this motion of insertion, the fastening-piston component  31  slips over the end  24  of the casing  8  on the side of the tappet  17 , loading the first spring  32 . If the spring load of the increasingly loaded first spring  32  exceeds the frictional force that acts between the frictional damping lining  29  and the tappet  17 , the result is reversion of the motion of the frictional damping lining  29  and the contact-pressure-piston component  30  and the fastening-piston component  31  so that the first spring  32  relaxes partially. The frictional damping lining  29  now moves counter to the direction of tappet insertion  42  and, as a result of the frictional force, brakes the motion of the tappet  17  in the direction of tappet insertion  42  until there is a reversion of motion of the tappet  17 . As the motion of the tappet  17  and of the frictional damping lining  29  proceeds counter to the direction of tappet insertion  42 , the first spring  32  relaxes more and more, whereas the second spring  33  is being loaded increasingly. If the spring load of the second spring  33  exceeds the frictional force that acts between the frictional damping lining  29  and the tappet  17 , there will be a renewed reversion of the motion of the frictional damping lining  29  together with the contact-pressure-piston component  30  and the fastening-piston component  31 , with the second spring  33  again relaxing. As a result of the frictional force that acts between the frictional damping lining  29  and the tappet  17 , the motion of the tappet  17  counter to the direction of tappet insertion  42  is again being braked until there is also a reversion of motion of the tappet  17 .  
         [0031]     That motional process is repeated several times. Consequently, the tappet  17  performs damped vibration within the casing  8 . Upon stimulation of load precisely in the direction of the central longitudinal axis  9  of the casing  8 , the guiding damping unit  41  only has the function of additional guidance of the tappet  17 . The damping elements  50  are not active in that case.  
         [0032]     As regards the second case of load stimulation not precisely in the direction of the central longitudinal axis  9  of the casing  8 , the stimulation of load can be divided into a component in the direction of the central longitudinal axis  9  of the casing  8  and into another component crosswise of the central longitudinal axis  9 . As for the load component in the direction of the central longitudinal axis  9  of the casing  8 , the mode of operation of the damper  5  is the same as described in the first case. The load component crosswise of the central longitudinal axis  9  of the casing  8  leads to deflection of the free end  19  of the tappet  18  crosswise of the central longitudinal axis  9  of the casing  8 , the central longitudinal axis  18  of the tappet  17  no longer coinciding with the central longitudinal axis  9  of the casing  8 . The deflection of the tappet  17  crosswise of the central longitudinal axis  9  of the casing  8  is damped by the guiding damping unit  41  so that centering of the tappet  17  takes place in such a way that the central longitudinal axis  18  of the tappet  17  again coincides with the central longitudinal axis  9  of the casing  8 .  
         [0033]     The ensuing description of the mode of operation of the guiding damping unit  41  proceeds from the assumption that the transverse-load component works on a plane that intersects the central longitudinal axis  47  of the cap  39  and two opposed stops  55  of two diametrically opposed damping elements  50 . As a result of the transverse load component, the inner rib portion  51  of the damping element  50  moves radially outwards. In doing so, the connecting-rib portion  53  is loaded such that spring load originates in the direction of the central longitudinal axis  47  of the cap  39 . This spring load brakes any radial deflection of the tappet  17  and leads to a reversion of motion of the tappet  17  in the direction of the central longitudinal axis  47  of the cap  39 . In the moving process specified, the inner rib portion  51  of the diametrically opposed damping element  50  is first being moved in the direction of the central longitudinal axis  47  of the cap  39 , with the connecting-rib portion  53  also building up spring load, however of radially outward action. This also results in that the motion of the tappet  17  in the transverse direction is being braked and damped. The friction losses that are responsible for the damping effect primarily originate in the material structure of the damping elements  50  as a result of lossy flexible deformation. What imports is the reduction of energy of motions in the radial direction. Consequently, the guiding damping unit  41  serves for damping any deflection of the tappet  17  crosswise of the central longitudinal axis  9  of the casing  8  and for simultaneously centering the tappet  17  after disappearance of the transverse-load component. In case of transverse-load components of great amplitude, any deflection of the tappet  17  is defined by the wedge-shaped, projecting stops  55 . Consequently, the damper  5  and the guiding damping unit  41  lead to clearly reduced noises of the damper  5  during operation of the cylinder washing machine  1  and to clearly reduced wear of the damper  5  as a result of the tappet  17  being permanently centered.  
         [0034]     The following is a description of a second embodiment of the invention, taken in conjunction with FIGS.  5  to  7 . Parts of identical construction have the same reference numerals as in the first embodiment, to the description of which reference is made. Parts that differ in construction, but are functionally identical, have the same reference numerals with an a annexed. The decisive difference from the first embodiment resides in that the frictional damping coating  29   a  passes by friction along the inside wall of the casing  8   a.  To this end, the tappet  17   a  is of two-piece design, with the first tappet component  56  being integral with the second fastening element  20   a  and a blind hole  57  that is concentric of the central longitudinal axis  18  of the tappet  17   a  varying in diameter for connection to a second tappet component  58  by positive fit and frictional engagement. The precise design of the blind hole  57  is not going to be explained in detail. The second tappet component  58  is substantially tubular, having a diameter inferior to that of the first tappet component  56 . The end  23   a,  inside the casing  8   a,  of the second tappet component  58  is provided with an annular tappet stop  59  of enlarged diameter which supports the guiding damping unit  41   a.  The end  60  of the first tappet component  56  has an annular stop  61  which is recessed in the shape of a wedge. Between the end  60  and the end  23   a,  inside the casing  8   a,  of the tappet  17   a,  provision is made for the contact-pressure component  30   a  with the frictional damping lining  29   a.  The contact-pressure-piston component  30   a  is a U-shaped ring, bilaterally holding the frictional damping lining  29   a.  On the wall of the contact-pressure-piston component  30   a  that is turned towards the central longitudinal axis  9  of the casing  8   a,  a contact-pressure-piston stop  37   a  is provided, which projects radially. The first spring  32   a  is pre-loaded between the tappet stop  59  and the wall of the contact-pressure-piston stop  37   a  which is turned towards the end  23   a  of the tappet  17   a  inside the casing  8   a.  As opposed to this, the second spring  33   a  is pre-loaded between the stop  61  of the tappet component  56  and the wall of the contact-pressure-piston stop  37   a  turned towards the end  60  of the tappet component  56 . The first fastening element  12   a  and the casing  8   a  form two pieces, the fastening element  12   a  being united with the free end  10   a  of the casing  8   a  by positive fit.  
         [0035]     Consequently, the first fastening element  12   a  constitutes the bottom  11   a  of the casing  8   a.  The second tappet component  58  and the guiding damping unit  41   a  are going to be described in detail below. The second tappet component  58  has a tubular basic tappet structure  62 , the end  63  of which tapers, with two fastening projections  64  being disposed thereon, which extend in the direction of the central longitudinal axis  18  of the tappet  17   a,  each having a fastening nose  65 . The disk-shaped tappet stop  59  is integral with the basic tappet structure  62  and the guiding damping unit  41   a.  Various reinforcing elements are provided inside the basic tappet structure  62 , which are not going to be explained in detail.  
         [0036]     The guiding damping unit  41 a is composed of six damping elements  50   a  of annular arrangement, which face each other diametrically and are spaced from, and uniformly distributed relative to, the central longitudinal axis  18   a  of the tappet  17   a.  Each damping element  50   a  comprises an inner rib portion  51   a  and an outer rib portion  52   a,  the outer rib portion  52   a  being bent by an outside radius and the inner rib portion  51   a  by an inside radius, and the inside radius exceeding the outside radius. The inner rib portion  51   a  centrally comprises a stop  55   a  that projects radially in the direction of the outer rib portion  52   a.  Each damping element  50   a  is symmetrical of a plane that intersects the central longitudinal axis  18  of the tappet  17   a  and the tip of the stop  55   a  which belongs to the damping element  50   a.  The outer rib portion  52   a  is bilaterally connected to the inner rib portion  51   a  via a connecting-rib portion  53   a  such that the individual rib portions pass seamlessly into each other. The portions  51   a,    52   a  and  53   a  enclose a double-reniform chamber  66  which is open only in the axial direction. The outside diameter DSA of the guiding damping unit  41   a  is defined as the maximal distance from each other of two opposed outer rib portions  52   a  in the relaxed condition seen in  FIGS. 6 and 7 . The casing  8   a  has an inside diameter D GI . D SA &lt;D GI  applies, which means that there is always some play between the portions  52   a  and the inside wall of the casing  17   a.    
         [0037]     The mode of operation of the damper  5   a  is analogous to that of the first embodiment. In the case of actuation of the tappet  17   a  by suddenly rising load in the direction of the central longitudinal axis  9  of the casing  8   a,  the only difference resides in that the frictional damping lining  29   a  bears by friction against the inside wall of the casing  8   a  and guidance of the guiding damping unit  41   a  takes place on the inside wall of the casing  8   a.  In the second case of an existing transverse-load component, the deflection of the tappet  17   a  is also damped by the guiding damping unit  41   a  and the tappet  17   a  is centered relative to the central longitudinal axis  9  of the casing  8   a.  Assuming that the transverse-load component acts on the plane that intersects the central longitudinal axis  18  of the tappet  17   a  and the tip of the stop  55   a  of a damping element  50   a,  the outer rib portion  52   a  of the respective damping element  50   a  is being moved flexibly in the direction of the central longitudinal axis  18  of the tappet  17   a  so that spring load builds up, counteracting the transverse-load component. As a result, the deflection of the tappet  17   a  crosswise of the central longitudinal axis  18  is being braked until there is reversion of the motion of the tappet  17   a.  The outer rib portion  52   a  now moves from the central longitudinal axis  18  radially outwards. Owing to friction losses in the material of the damping elements  50   a  and friction losses between the guiding damping unit  41   a  and the inside wall of the casing  8   a,  the vibratory operation crosswise of the central longitudinal axis  18  that is performed by the tappet  17   a  is being damped so that the tappet  17   a  is again centered relative to the central longitudinal axis  9  of the casing  8   a  after disappearance of the transverse-load component. In case of a transverse-load component of great amplitude, the motion of the outer rib portion  52   a  is defined by the stop  55   a.    
         [0038]     The following is a description of a third embodiment of the invention, taken in conjunction with  FIGS. 8 and 9 . Identical parts have the same reference numerals as in the first embodiment, to the description of which reference is made. Parts that differ in construction, but are functionally identical, have the same reference numerals with a b annexed. The substantial difference from the first embodiment resides in the configuration of the guiding damping unit  41   b.  Like in the first embodiment, the guiding damping unit  41   b  is fixed to the cap  39   b.  Unlike the first embodiment, the cap  39   b  is not pushed over the casing cup  27  but into it so that the locking noses  43   b  that are disposed on the cap  39   b  stand out radially, snap-engaging from inside with corresponding recesses in the casing cup  27 . The cap  39   b  comprises four damping elements  50   b  which are uniformly distributed along the circumference and project inwards from an annular edge  68 . The inner rib portion  51   b  as well as the connecting rib portions  53   b  constitute a flexibly compressible spring arm or bow which projects inwards in the shape of a bow. It encloses a chamber  66   b  of oval cross-sectional shape which is open only in the axial direction. Between two adjacent damping elements  50   b,  provision is made for a guide rib  69  which projects inwards from the edge  68  and the inner surfaces  70  of which that are turned towards the axis  47  have the cross-sectional shape of a radius around the axis  47 . The diameter in the vicinity of two opposed inner rib portions  51   b  is designated by D BI . The diameter in the vicinity of two opposed guide ribs  69  is designated by D FI . D FI &gt;D BI  applies, which means that the inner rib portions  51   b  stand out further in the direction towards the axis  47  than the inner surfaces  70  of the guide ribs  69 . The tappet  17  has some play towards the portions  51   b.  Consequently, the tappet  17 , when tilted, first rests on the inner rib portions  51   b.  If it is more strongly tilted, guidance of the tappet  17  is ensured by the inner surfaces  70 . A groove  71  of substantially radial extension is arranged between a damping element  50   b  and a guide rib  69 , freeing the curved connecting rib portion  53   b  and offering sufficient space for deformation of the rib portion  53   b  upon compression.  
         [0039]     As regards the mode of operation of the guiding damping unit  41   b,  reference is made to the explanations of the first embodiment. Advantages reside in that the damping elements  50   b  are able to take deformations more easily, because they are not connected by a joint inner ring  67  as in the first embodiment. Moreover, the guide ribs  69  provide for stable guidance in the case of stronger tilting.  
         [0040]     A fourth embodiment of the invention will be described below, taken in conjunction with  FIGS. 10 and 11 . Identical parts have the same reference numerals as in the first embodiment, to the description of which reference is made. Parts that differ in construction, but are functionally identical, have the same reference numerals with a c annexed. The cap  39   c  has the same design as the cap  39   b  of the third embodiment with only one exception. The only difference consists in that, in the middle, the inner rib portions  51   c  are interrupted by a gap  72 . In other words, the damping element  50   c  is formed by two arcs  73  of the cross-sectional shape of quarter circles which are turned towards each other and the free ends of which define the gap  72 . An advantages of this arrangement resides in that less force is needed for compressing the arcs  73  in the radial direction. Consequently, more solid materials which are advantageous for the rest of the cap  39   c,  such as POM, can be used without any change in the damping behaviour.  
         [0041]     As regards the mode of operation of the fourth embodiment, reference is made to the third embodiment and thus also to the first embodiment.  
         [0042]     The following is a description of a fifth embodiment of the invention, taken in conjunction with  FIGS. 12 and 13 . Identical parts have the same reference numerals as in the first embodiment, to the description of which reference is made. Parts that differ in construction, but are identical functionally, have the same reference numerals with a d annexed. The fifth embodiment has substantially the same design as the second embodiment according to FIGS.  5  to  7 . The only difference resides in that the outer rib portion  52   d  is centrally interrupted by a gap  72   d,  as a result of which the two parts of the rib portion  52   d  become more flexible, offering the same advantages as in the fourth embodiment according to  FIGS. 10 and 11 . Like in the second embodiment, a groove  71   d  is provided between adjacent damping elements  50   d,  the groove  71   d  being defined by adjacent rib portions  53   d.  Unlike the second embodiment, the stop  55   d  is flattened, meaning that it possesses a saddle  74  which the free ends of the parts of the rib portions  52   d  will rest on in case of strong compression. As regards the mode of operation, reference is made to the description of the second embodiment.