Piston seal and disc brake using the piston seal

Abstract

A piston seal of a disc brake can stabilize the amount of rollback of a piston by reducing thermal expansion and a decrease in modulus of elasticity of the piston seal caused by an increase in temperature, thereby preventing a driver from feeling that the brake operation is unnatural. The piston seal is formed of a rubber composition in which at least 100 parts by weight or more of carbon black is added to 100 parts by weight of ethylene propylene rubber.

1 . A piston seal used for a caliper body for a disc brake, 
 wherein the piston seal fluid-tightly and slidably maintains a piston in a cylinder bore, the piston sliding inside the cylinder bore, and the piston is rolled back,    wherein the piston seal is formed of an ethylene propylene rubber composition comprising at least 100 parts carbon black per hundred parts rubber.    
   
   
       2 . The piston seal according to  claim 1 , wherein the carbon black has an average particle diameter of 40 nm to 500 nm.  
   
   
       3 . The piston seal according to  claim 1 , wherein the carbon black has a nitrogen adsorption specific surface area of 70 m 2 /g or less.  
   
   
       4 . The piston seal according to  claim 1 , wherein the rubber composition has a coefficient of linear expansion of 1.6×10 −4  (/K) or less.  
   
   
       5 . The piston seal according to  claim 1 , being used for a caliper body for a disc brake.  
   
   
       6 . A disc brake, comprising: 
 the piston seal and piston as defined in  claim 1;  and    a cylinder having a cylinder bore including a ring-shaped groove formed in an inner surface of the cylinder bore,    wherein the piston seal is fitted into the ring-shaped groove, and    wherein the piston, when inserted into the cylinder bore, is fluid-tightly and movably in contact with the cylinder, and the piston that has been moved forward by applying hydraulic pressure is rolled back.    
   
   
       7 . A disc brake comprising: 
 the piston seal and piston as defined in  claim 2;  and    a cylinder having a cylinder bore including a ring-shaped groove formed in an inner surface of the cylinder bore,    wherein the piston seal is fitted into the ring-shaped groove, and    wherein the piston, when inserted into the cylinder bore, is fluid-tightly and movably in contact with the cylinder, and the piston that has been moved forward by applying hydraulic pressure is rolled back.    
   
   
       8 . A disc brake comprising: 
 the piston seal and piston as defined in  claim 3;  and    a cylinder having a cylinder bore including a ring-shaped groove formed in an inner surface of the cylinder bore,    wherein the piston seal is fitted into the ring-shaped groove, and    wherein the piston, when inserted into the cylinder bore, is fluid-tightly and movably in contact with the cylinder, and the piston that has been moved forward by applying hydraulic pressure is rolled back.    
   
   
       9 . A disc brake comprising: 
 the piston seal and piston as defined in  claim 4;  and    a cylinder having a cylinder bore including a ring-shaped groove formed in an inner surface of the cylinder bore,    wherein the piston seal is fitted into the ring-shaped groove, and    wherein the piston, when inserted into the cylinder bore, is fluid-tightly and movably in contact with the cylinder, and the piston that has been moved forward by applying hydraulic pressure is rolled back.    
   
   
       10 . A disc brake comprising: 
 the piston seal as defined in  claim 5;     a cylinder having a cylinder bore; and    a piston which is inserted into the cylinder bore,    wherein the piston seal is fitted into a ring-shaped groove formed in an inner surface of the cylinder bore, and    wherein the piston inserted into the cylinder bore is fluid-tightly and movably in contact with the cylinder, and the piston that has been moved forward by applying hydraulic pressure is rolled back.    
   
   
       11 . The piston seal according to  claim 1 , 
 wherein the rubber composition comprises 120 to 250 parts carbon black per hundred parts rubber.    
   
   
       12 . The piston seal according to  claim 1 , 
 wherein the rubber composition includes no process oil.    
   
   
       13 . A piston seal used for caliper body for a disc brake, 
 wherein the piston seal fluid-tightly and slidably maintains a piston in a cylinder bore, the piston sliding inside the cylinder bore,    wherein the piston seal is formed of a rubber composition in which at least 100 parts by weight or more of carbon black is added to 100 parts by weight of ethylene propylene rubber.    
   
   
       14 . A piston seal in which a cylinder bore and piston sliding inside the cylinder bore fluid-tightly and slidably come in contact with each other, and the piston is rolled back, 
 wherein the piston seal is formed of a rubber composition in which at least 100 parts by weight or more of carbon black is added to 100 parts by weight of ethylene propylene rubber.