Abstract:
In a damper for spin-drying washing machines, it is provided, with a view to amplitude-dependent damping behaviour being obtained accompanied with manufacture at a low cost, that a frictional damping unit, which is disposed inside a casing, comprises an at least sectionally bare and elastic frictional damping lining for producing a given frictional damping effect, and at least one stop element which is stationary in relation to the casing and turned towards the at least one frictional damping lining, with the at least one stop element being designed for direct cooperation with the at least one frictional damping lining.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a damper for spin-drying washing machines. 
     2. Background Art 
     Dampers of the generic type are used for vibration damping in cylinder washing machines, ensuring smooth and vibrationless operation of the cylinder washing machine. Known dampers, at varying speeds of the washing cylinder, exhibit a damping behaviour that depends on the vibration amplitude. A reduced damping effect of the dampers is desirable in the range of small amplitudes, whereas great amplitudes require as strong as possible a damping effect. This amplitude-dependent damping behaviour leads to a constructionally complicated design of the dampers. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to improve a damper of amplitude-dependent damping behaviour in such a way that it is easy to manufacture at a low cost. 
     This object is attained by a damper for spin-drying washing machines comprising a tubular casing which has a central longitudinal axis; a tappet which is guided for displacement in the casing and projects from an end thereof; fastening elements which are mounted on a free end of the casing and of the tappet, respectively; and a frictional damping unit, which is disposed inside the casing, comprising at least one elastic frictional damping lining which is displaceable in relation to the casing and the tappet along the central longitudinal axis and which lies bare at least sectionally in a lengthwise axial direction, producing a given frictional damping effect, and at least one stop element which is stationary in relation to the casing and turned towards the at least one frictional damping lining, defining the motion of the at least one frictional damping lining, with the at least one stop element being configured such that, for motion damping, it directly cooperates with the at least one frictional damping lining. The gist of the invention resides in that the elastic frictional damping lining lies open at least sectionally in the axial direction so that the stop element, in the case of great vibration amplitudes, cooperates directly with the frictional damping lining. Thus, the frictional damping lining simultaneously fulfills the task of a stop buffer, this leading to constructional simplicity of design and to manufacture of the damper at a low cost. 
     Further features, details and advantages of the invention will become apparent from the ensuing description of several exemplary embodiments, taken in conjunction with the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a diagrammatic side view of a cylinder washing machine with a damper according to a first embodiment; 
         FIG. 2  is an elevation of the cylinder washing machine according to  FIG. 1 ; 
         FIG. 3  is an axial sectional view of the damper of  FIG. 1 ; 
         FIG. 4  is a perspective view of a contact-pressure piston of the damper of  FIG. 1 ; 
         FIG. 5  is a perspective view of a cap of the damper of  FIG. 1 ; 
         FIG. 6  is an elevation of the cap of  FIG. 5 ; 
         FIG. 7  is a side view of the cap of  FIG. 5 ; 
         FIG. 8  is an axial sectional view of a damper according to a second embodiment; 
         FIG. 9  is an axial sectional view of a damper according to a third embodiment; 
         FIG. 10  is a perspective view of a contact-pressure piston of the damper of  FIG. 9 ; 
         FIG. 11  is a plan view of the contact-pressure piston of  FIG. 10 ; 
         FIG. 12  is an axial sectional view of a damper according to a fourth embodiment; and 
         FIG. 13  is a perspective view of a contact-pressure piston of the damper according to  FIG. 12 . 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A first embodiment of the invention is going to be described below, taken in conjunction with  FIGS. 1 to 7 . A cylinder washing machine seen in  FIGS. 1 and 2  with a horizontal or inclined cylinder axis  1  comprises a vibratory washing aggregate  2  with a drive motor  3  which, via a belt drive  4 , actuates a washing cylinder, details of which are not shown. To simplify matters, further components that are connected to the washing aggregate  2 , for instance a transmission, are not shown. By means of helical extension springs  5 , the vibratory washing aggregate  2  is suspended from a washing-machine casing  6  which is supported on, and connected to, a machine frame  8  that stands on the ground  7  and constitutes a base frame. On the one hand, the helical extension springs  5  are fixed to eyelets  9  which are disposed in the top area of the washing aggregate  2 . On the other hand, they are suspended from eyelets  10  which are formed on the washing-machine casing  6 . The casing  6  is covered by a cover plate  11 . 
     Two frictional dampers  12 , details of which will be described below, are mounted centrically on the bottom side of the washing aggregate  2 ; they are connected to the machine frame  8 . Each frictional damper  12  comprises a tubular casing  13  with a central longitudinal axis  14 , with a tappet  15  being coaxially displaceable therein. At its free end, the tappet  15  comprises a first fastening element  16 , by means of which the frictional damper  12  is fixed to a bearing  17  on the washing aggregate  2  for the frictional damper  12  to be able to pivot in relation to the washing aggregate  2  about a pivoting axis  18  that is parallel to the cylinder axis  1 . Mounted on the free end of the casing  13  is a second fastening element  19 , by means of which the frictional damper  12  is fixed to a bearing  20  on the machine frame  8  in such a way that the frictional damper  12  is able to pivot in relation to the machine frame  8  about a pivoting axis  21  that is parallel to the cylinder axis  1 . A flap  22  which is disposed on the washing aggregate  2  serves for laundry to be put in and taken out. 
     The design of the frictional damper  12  will be described in detail in the following, taken in conjunction with  FIGS. 3 to 7 . The tubular casing  13  of the frictional damper  12  comprises a guiding section  23  and a take-up section  24  which forms one piece therewith. The guiding section  23  is disposed downstream of the take-up section  24  in a direction of insertion  25 . The free end of the guiding section  23 , which is simultaneously the free end of the casing  13 , is closed by means of a bottom  26 . The bottom  26  and the fastening element  19  are one piece. The guiding section  23  has an inside diameter selected for the tappet  15  to have as little play as possible in the direction of insertion  25  and to be displaceable without static friction. 
     The take-up section  24  is disposed upstream of the guiding section  23  in the direction of insertion  25 . The take-up section  24  has an inside diameter which is greater than that of the guiding section  23 . The take-up section  24  is fixed to the end, on the side of the tappet, of the guiding section  23  by means of an annular stop collar  27 . 
     At its end turned away from the guiding section  23 , the take-up section  24  is closed by means of a cap  28 . The cap  28  possesses an annular collar  29  and a tubular fastening section  30  fixed thereto, the fastening section  30  extending in the direction of the central longitudinal axis  14  and encompassing the take up section  24 . The end, turned away from the guiding section  23 , of the take-up section  24  bears against the cap collar  29 , and the cap  28  is safeguarded against displacement in the vicinity of the fastening section  30  by means of a locking mechanism (not shown). The annular cap collar  29  forms a cap aperture  31  where the tappet  15  is guided with as little play as possible. 
     Within the casing  13 , a frictional damping unit  32  is provided in the vicinity of the take-up section  24 . The frictional damping unit  32  comprises a contact-pressure piston  33  which is displaceable along the central longitudinal axis  14 . The contact-pressure piston  33  is substantially tubular, comprising a centric contact-pressure section  34  where an encircling annular groove  35  is provided which is turned towards the tappet  15 . The annular groove  35  holds an annularly encircling, elastic frictional damping lining  36  which bears against side walls  37  of the annular groove  35  so that it is safeguarded against displacement in relation to the contact-pressure piston  33 , when rubbing against the tappet  15 . The side walls  37  of the annular groove  35  are embodied in such a way that the contact-pressure piston  33  is guided along the central longitudinal axis  14  on the tappet  15 . 
     A first stop section  38  which forms one piece with the contact-pressure section  34  proceeds from the side wall  37  that is turned towards the casing  13 . The first stop section  38  is tubular and does not bear against the take-up section  24  of the casing  13  as it is spaced apart from section  24 . The stop section  38 , on its inside circumference, comprises several longitudinal grooves  39  which are regularly spaced and extend along the central longitudinal axis  14  and which taper in the direction of the frictional damping lining  36 ; the grooves  39  extend as far as to the frictional damping lining  36 . Thus the frictional damping lining  36  is bare in the vicinity of the grooves  39  in the axial direction as  FIG. 4  shows the opposite ends  36 ′ of the lining facing open ends  39 ′ of grooves  39  are uncovered. Two grooves  39  at a time face each other diametrically. A wedge  40  is located between two side by side grooves  39 , tapering in a direction opposite to the grooves  39  and extending in the form of a ramp in the direction of the side wall  37  with which it forms one piece. Each wedge  40  has side walls  41 , each of which define a bottom  42  of an adjacent groove  39 . Each bottom  42  also extends in the form of a ramp in the direction of the frictional damping lining  36 . 
     A second stop section  43 , corresponding to the first stop section  38 , proceeds from the side wall  37  that is turned towards the tappet  15 . The second stop section  43  corresponds in design to the first stop section  38  and forms one piece with the contact-pressure section  34 . The grooves  39  and  10  wedges  40  of the second stop section  43  are displaced in relation to the first stop section  38 . This means that a wedge  40  of the first stop section  38  is located opposite a groove  39  of the second stop section  43  and vice versa. For simplicity of mounting of the frictional damping lining  36 , the contact-pressure piston  33  may also be embodied in several pieces. 
     For the motion of the contact-pressure piston  33  with the frictional damping lining  36  to be defined and for damping operation to be obtained, the frictional damping unit  32  comprises a first stop element  44  on the side of the casing  13  and a second stop element  45  on the side of the tappet  15 . The first stop element  44  comprises several stop pins  46  which, proceeding from the stop collar  27  of the casing  13 , extend along the central longitudinal axis  14 . The stop pins  46  of the first stop element  44  form one piece with the stop collar  27  and the guiding section  23  of the casing  13 . A two-piece design, possibly of various materials, is just as well conceivable. The stop pins  46  are disposed and embodied for prolonging the guiding section  23  so that the tappet  15  is additionally guided by the stop pins  46  of the first stop element  44 . The stop pins  46  are further embodied and disposed for the contact-pressure piston  33 , by the grooves  39  of the first stop section  38 , to be able to encompass the stop pins  46  so that the contact-pressure piston  33  is movable into a first annular space  47  between the take-up section  24  and the stop pins  46 . A detailed description of the stop pins  46  and the arrangement thereof will follow, taken in conjunction with the description of the second stop element  45 . 
     The second stop element  45  also comprises several stop pins  46  which form one piece with the collar  29  of the cap  28  and extend along the central longitudinal axis  14 . A two-piece design, possibly of various materials, is also conceivable. The stop pins  46  are disposed in a circle around the central longitudinal axis  14 , forming a flush prolongation of the cap aperture  31  so that the tappet  15  is additionally guided by the stop pins  46 . To this end, the stop pins  46  are embodied as ring segments, with a guide wall  48  that is turned towards the tappet  15  being arched, corresponding to the periphery of the tappet  15 . Proceeding from the cap collar  29 , each stop pin  46  tapers towards the frictional damping lining  36 , having two side walls  49  and a front wall  50 . On its side turned away from the tappet  15 , each stop pin  46  additionally comprises an outside wall  51  which extends in the form of a ramp in the direction of the cap collar  29 . Two stop pins  46  at a time oppose each other diametrically, these two stop pins  46  being of uniform length along the central longitudinal axis  14 , but deviating in length as compared to the remaining stop pins  46 . A different arrangement is possible too. The stop pins  46  of the second stop element  45  combine with the take-up section  24  of the casing  13  to form a second annular space  52  into which to move the second stop section  43  of the contact-pressure piston  33 . 
     The detailed design of the first stop element  44  corresponds to that of the second stop element  45 , with the stop pins  46  of the second stop element  45  being displaced as compared to those of the first stop element  44  so that they may engage with the displaced grooves  39  of the second stop section  43 . 
     Fundamentally, any design of the stop pins  46 , in particular of the length and shape thereof, is possible as long as the stop pins  46  correspond in length and shape to the corresponding grooves  39  so that the stop pins  46  are able to cooperate with the frictional damping lining  36 . Pins of varying lengths are preferred, ensuring continuous, progressive damping. 
     Within the casing  13 , the tappet  15  is guided for displacement along the central longitudinal axis  14  by means of the guiding section  23  and the aperture  31  of the cap collar  29 . The tappet  15  is tubular and has a tapering end. 
     In the following, the mode of operation of the frictional damper  12 , upon operation of the cylinder washing machine, will be described in detail. At first, a load of laundry is being put into the washing aggregate  2  and the washing cylinder is being set rotating by means of the drive motor  3  and the belt drive  4 . The damping behaviour of the frictional damper  12  in the case of small vibration amplitudes is going to be described first. These small vibration amplitudes occur in the case of so-called uncritical speeds, for example with the cylinder washing machine spinning. In this case, the motion of the tappet  15  in relation to the casing  13  along the central longitudinal axis  14  is so insignificant that the contact-pressure piston  33 , together with the frictional damping lining  36 , does not touch the first and second stop element  44 ,  45 . Owing to the static friction of the frictional damping lining  36 , there is no motion of the contact-pressure piston  33  in relation to the tappet  15  so that the frictional damping lining  36  does not rub against the tappet  15 . This status is termed friction-less idle stroke. In this condition, the frictional damper  12  exhibits insignificant damping behaviour which is characterized by the other friction losses upon the motion of the tappet  15 . In this condition, the casing  13  and the tappet  15  are un-coupled as far as possible. 
     If however the speed of the cylinder washing machine is in the range of a so-called critical speed or should there be significant imbalance, then there are important vibration amplitudes of the tappet  15  in relation to the casing  13 . This is when the contact-pressure piston  33 , together with the frictional damping lining  36 , and the stop elements  44 ,  45  start interacting and the contact-pressure piston  33  moves in relation to the tappet  15  so that the frictional damping lining  36  rubs against the tappet  15 . If, proceeding from the position seen in  FIG. 3 , the tappet  15  moves in the direction of insertion  25 , then the contact-pressure piston  33  starts being entrained in the direction of insertion  25  because of the static friction between the frictional damping lining  36  and the tappet  15 . As the depth of insertion grows, the first stop section  38  is being guided by its grooves  39  encompassing the stop pins  46  of the first stop element  44 . When the stop pins  46 , by their front wall  50 , touch the frictional damping lining  36  which is bare in the vicinity of the grooves  39 , then the motion of the contact-pressure piston  33  is being braked, with motion of the frictional damping lining  36  relative to the tappet  15  occurring. The frictional damping lining  36  rubs against the tappet  15 , producing damping behaviour. The damping behaviour is dependent on the speed of the relative motion and independent of the depth of penetration of the stop pins  46  into the frictional damping lining  36 . In the frictional damper  12 , the elastic frictional damping lining  36  has the additional task of a stop buffer. Owing to their varying lengths, the stop pins  46  penetrate successively into the frictional damping lining  36 , there being no abrupt impact of the contact-pressure piston  33  and, consequently, no abrupt increase of load on the machine frame  8 . With two opposite stop pins  46  at a time having an identical length, the contact-pressure piston  33  is safely precluded from getting tilted on the tappet  15 . 
     Upon return of motion of the tappet  15 , the contact-pressure piston  33  is at first being entrained counter to the direction of insertion  25  because of the static friction between the frictional damping lining  36  and the tappet  15 , the contact-pressure piston  33  not moving in relation to the tappet  15 . As the motion counter to the direction of insertion  25  continues, the second stop section  43  is being moved with the grooves  39  encompassing the stop pins  46  of the second stop element  45 . By the stop pins  46  penetrating into the frictional damping lining  36 , the motion of the contact-pressure piston  33  is being braked so that the frictional damping lining  36  makes a motion relative to the tappet  15  and rubs against the tappet  15 . The cooperation of the second stop element  45  with the frictional damping lining  36  corresponds to the above-mentioned penetration behaviour of the first stop element  44 . The cap collar  29  serves as a final stop of the contact-pressure piston  33 . Upon renewed return of motion of the tappet  15 , the contact-pressure piston  33  is again being entrained in the direction of insertion  25  because of the static friction between the frictional damping lining  36  and the tappet  15 . The described motion cycle recurs. 
     With the frictional damping lining  36  additionally working as a stop buffer, the frictional damper  12  is of simple design and can be manufactured at a low cost. Moreover, the idle stroke without friction can be adjusted arbitrarily by simple constructional modifications. 
     A second embodiment of the invention will be described below, taken in conjunction with  FIG. 8 . Constructionally identical parts have the same reference numerals as in the first embodiment, to the description of which reference is made. Parts that differ constructionally, but are identical functionally, have the same reference numerals with an “a” suffixed. The essential difference from the first embodiment resides in that the contact-pressure piston  33 a and the stop elements  44 a,  45 a are designed in such a way that at least one of the stop pins  46 a is disposed at least sectionally in one of the grooves  39 a. Such a design of the contact-pressure piston  33 a and the stop elements  44 a,  45 a ensures that either at least one stop pin  46 a of the first stop element  44 a or at least one stop pin  46 a of the second stop element  45 a will be in engagement with one of the grooves  39 a of the contact-pressure piston  33 a, this providing for a safeguard against rotation of the contact-pressure piston  33 a in relation to the stop elements  44 a,  45 a. Preferably the stop elements  44 a,  45 a have four stop pins  46 a each. Such a number of stop pins  46 a helps optimize the constructional implementation while ensuring invariable functionality of the frictional damper  12 a. As regards the further mode of operation, reference is made to the first embodiment. 
     A third embodiment of the invention will be described below, taken in conjunction with  FIGS. 9 to 11 . Constructionally identical parts have the same reference numerals as in the first embodiment, to the description of which reference is made. Parts that differ constructionally, but are identical functionally, have the same reference numerals with a “b” suffixed. The essential difference from the preceding embodiments resides in that stop buffers  53  are provided, preventing the contact-pressure piston  33 b from hitting hard against the stop collar  27  or the cap collar  29  in the case of extreme vibration amplitudes. The stop sections  38 b,  43 b of the contact-pressure piston  33 b each have four grooves  39 b and wedges  40 b which are disposed between the grooves  39 b. Each stop section  38 b,  43 b further comprises two stop buffers  53  which are formed on the front walls  54  of two wedges  40 b that face each other. The stop buffers  53  of the first stop section  38 b are displaced in relation to the stop buffers  53  of the second stop section  43 b about the central longitudinal axis  14 . 
     The stop buffers  53  are identical, only one stop buffer  53  being described in the following. The stop buffer  53  comprises two flexible stop-buffer elements  55  which are formed in one piece with the wedge  40 b, having the shape of bent tongues that proceed from the wedge side walls  41  towards each other. The stop-buffer elements  55  in the form of tongues project over the front walls  54  of the adjoining wedges  40 b along the central longitudinal axis  14  and, as seen along the central longitudinal axis  14 , they taper proceeding from the side walls  41 . The stop-buffer elements  55  and the associated wedge front wall  54  substantially define a stop-buffer recess  56  which extends sectionally into the contact-pressure piston  33 b so that the wedge front wall  54  that is allocated to the stop-buffer elements  55  stands back from the front walls  54  of the adjacent wedges  40 b. The stop-buffer elements  55  are flexibly extensible into the stop-buffer recess  56 . A stop-buffer opening  57  is formed between the stop-buffer elements  55  that run towards each other so that the stop-buffer elements  55  are spaced apart centrically and do not touch each other. A convex stop-buffer limit  58 , which is integral with the wedge front wall  54 , is disposed opposite the stop-buffer opening  57  as related to the stop-buffer recess  56 . For defined flexion of the stop-buffer elements  55 , the stop-buffer limit  58  proceeds from the wedge front wall  54  along the central longitudinal axis  14  into the stop-buffer recess  56 . By alternative, the stop-buffer limit  58  can be dropped, the flexion of the stop-buffer elements  55  being defined by the associated wedge front wall  54 . 
     The following is a description of the mode of operation of the frictional damper  12 b in the case of extreme vibration amplitudes. Upon motion of the tappet  15  in the direction of insertion  25 , the stop pins  46 b of the first stop element  44 b penetrate into the frictional damping lining  36  so that the contact-pressure piston  33 b, entrained by the tappet  15 , makes a motion relative to the tappet  15  and rubs against the tappet  15 . As a result of the stop pins  46 b penetrating, the elastic frictional damping lining  36  counteracts the motion of the contact-pressure piston  33 b, buffering the impact of the stop pins  46 b on the frictional damping lining  36 . If the vibration amplitude of the frictional damper  12 b is such that the buffering action of the frictional damping lining  36  does not sufficiently define the motion of the contact-pressure piston  33 b, then the stop buffers  53  start working. In the case of extreme vibration amplitudes, the stop-buffer elements  55  of the stop buffers  53  hit against the stop collar  27  of the guiding section  23 . As the motion of the contact-pressure piston  33 b continues in the direction of insertion  25 , the flexible stop-buffer elements  55  bend in a direction towards the stop-buffer limit  58 , buffering the motion of the contact-pressure piston  33 b. When the motion of the contact-pressure piston  33 b stops, then the flexible stop-buffer elements  55  rebound, moving the contact-pressure piston  33 b back against the direction of insertion  25  until they relax. In the case of extreme vibration amplitudes, the flexion of the stop-buffer elements  55  is defined by them hitting on the stop-buffer limit  58  or, should there be not stop-buffer limit  58 , by them hitting on the associated wedge front wall  54 . Simultaneously, the front walls  54  of the wedges  40 b that adjoin the stop buffers  53  hit on the stop collar  27 . Upon return motion of the tappet  15 , the contact-pressure piston  33 b is entrained counter to the direction of insertion  25 , the described process repeating when the contact-pressure piston  33 b hits on the cap collar  29 . Alternatively, the stop buffers  53  may also be formed on the stop collar  27  and the cap collar  29 . As for the further mode of operation, reference is made to the preceding embodiments. 
     A fourth embodiment of the invention will be described below, taken in conjunction with  FIGS. 12 and 13 . Constructionally identical parts have the same reference numerals as in the preceding embodiments, to the description of which reference is made. Parts that differ constructionally, but are identical functionally, have the same reference numerals with a “c” suffixed. The essential difference from the preceding embodiments resides in that the stop buffers  53 c each have a continuous, convex stop-buffer element  55 c which narrows centrically, entirely defining the stop-buffer recess  56  on the side opposite the wedge front wall  54 . A stop-buffer opening is not provided. Alternatively, the stop buffers  53 c may also be disposed on the stop collar  27  and the cap collar  29 . As regards the mode of operation of the frictional damper  12 c, reference is made to the preceding embodiments.