Damper and washing machine having the damper

Abstract

A damper includes a cylinder; a piston rod disposed to be movable linearly in the cylinder; a friction unit disposed to be movable in a radial direction inside the cylinder and generating a damping force by rubbing on an inner circumferential surface of the cylinder; and a damping force control unit mounted at the piston rod and controlling a damping force by moving the friction unit in the radial direction. A desired damping force is generated at a desired point such that a strong damping force can be generated at an interval where excessive vibration is generated and zero or a weak damping force can be generated at a normal interval, to thereby reduce vibration and noise of a washing machine.

1 . A damper comprising: 
 a cylinder;    a piston rod disposed to be movable linearly in the cylinder;    a friction unit disposed to be movable in a radial direction inside the cylinder and generating a damping force by rubbing on an inner circumferential surface of the cylinder; and    a damping force control unit mounted at the piston rod and controlling a damping force by moving the friction unit in the radial direction.    
     
     
         2 . The damper of  claim 1 , wherein the friction unit comprises: 
 holders disposed at equal intervals in a circumferential direction inside the cylinder;    a friction member fixed at an outer circumferential surface of the holders and rubbed on the inner circumferential surface of the cylinder according to radial movement of the holders; and    an elastic member connected between holders and providing an elastic force in a direction that a radius of the holders is diminished.    
     
     
         3 . The damper of  claim 2 , wherein the holder includes a sloped portion at its inner circumferential surface and a fixing recess to which the friction member is insertedly fixed.  
     
     
         4 . The damper of  claim 3 , wherein the friction member is made of a material which can be expanded and contracted in a radial direction within a certain range.  
     
     
         5 . The damper of  claim 2 , wherein the friction member is formed of a grease-absorbed sponge.  
     
     
         6 . The damper of  claim 2 , wherein the elastic member is formed as an elastic body made of a rubber material.  
     
     
         7 . The damper of  claim 2 , wherein the damping force control unit comprises: 
 an operation unit disposed at an inner circumferential surface of the holders and pressing the holders so as to be expanded in a radial direction; and    a driving force generating unit mounted at an upper end of the piston rod and driving the operating unit.    
     
     
         8 . The damper of  claim 7 , wherein the operating unit comprises: 
 a first operating member fixed at the driving force generating unit; and    a second operating member mounted to be movable in a vertical direction on the first operating member  84 , and a sloped surface is formed at at least one of the first and second operating members and slidably contacts with the sloped portion of the holder.    
     
     
         9 . The damper of  claim 8 , wherein the first and second operating members are made of a magnetic material.  
     
     
         10 . The damper of  claim 8 , wherein the driving force generating unit comprises: 
 a core formed at an upper surface of the piston rod and integrally formed with the first operating member; and    a coil wound on an outer circumferential surface of the core and generating a magnetic force by making the core an electromagnet when power is applied thereto.    
     
     
         11 . A washing machine comprising: 
 a cabinet;    a tub installed in the cabinet and storing washing water;    a drum rotatably disposed inside the tub and washing and dewatering the laundry;    a plurality of support springs mounted between an upper portion of the tub and an upper inner wall of the cabinet; and    a plurality of dampers installed between a lower portion of the tub and a lower inner wall of the cabinet,    wherein the damper comprises: 
 a cylinder connected with one of the tub and the cabinet;  
 a piston rod disposed to be movable linearly in the cylinder and connected with the other of the tub and cabinet;  
 a friction unit disposed to be movable in a radial direction inside the cylinder and generating a damping force by rubbing on an inner circumferential surface of the cylinder; and  
 a damping force control unit mounted at the piston rod and controlling a damping force by moving the friction unit in the radial direction.  
   
     
     
         12 . The washing machine of  claim 11 , wherein the friction unit comprises: 
 holders disposed at equal intervals in a circumferential direction inside the cylinder;    a friction member fixed at an outer circumferential surface of the holders and rubbed on the inner circumferential surface of the cylinder according to radial movement of the holders; and    an elastic member connected between holders and providing an elastic force in a direction that a radius of the holders is diminished.    
     
     
         13 . The washing machine of  claim 12 , wherein the holder includes a sloped portion at its inner circumferential surface and a fixing recess to which the friction member is insertedly fixed.  
     
     
         14 . The washing machine of  claim 12 , wherein the friction member is made of a material which can be expanded and contracted in a radial direction within a certain range.  
     
     
         15 . The washing machine of  claim 12 , wherein the friction member is formed of a grease-absorbed sponge.  
     
     
         16 . The washing machine of  claim 12 , wherein the elastic member is formed as an elastic body made of a rubber material.  
     
     
         17 . The washing machine of  claim 12 , wherein the damping force control unit comprises: 
 an operation unit disposed at an inner circumferential surface of the holders and pressing the holders so as to be expanded in a radial direction; and    a driving force generating unit mounted at an upper end of the piston rod and driving the operating unit.    
     
     
         18 . The washing machine of  claim 17 , wherein the operating unit comprises: 
 a first operating member fixed at the driving force generating unit; and    a second operating member mounted to be movable in a vertical direction on the first operating member  84 , and a sloped surface is formed at at least one of the first and second operating members and slidably contacts with the sloped portion of the holder.    
     
     
         19 . The washing machine of  claim 18 , wherein the first and second operating members are made of a magnetic material.  
     
     
         20 . The washing machine of  claim 18 , wherein the driving force generating unit comprises: 
 a core formed at an upper surface of the piston rod and integrally formed with the first operating member; and    a coil wound on an outer circumferential surface of the core and generating a magnetic force by making the core an electromagnet when power is applied thereto.