Patent Publication Number: US-2012037465-A1

Title: Braking device and method for manufacturing friction material

Description:
TECHNICAL FIELD 
     The present invention relates to a braking device and a method for manufacturing a friction material, and particularly, to a braking device provided with a pair of friction materials having a friction surface, and a method for manufacturing a friction material used for the braking device. 
     BACKGROUND ART 
     A braking device consisting of a pad and a rotor (disc) of a conventional brake for an automobile is a combination of a relatively hard component and a relatively soft component. Therefore, the conventional braking device has a problem in that the effect of the brake is poor or either of the hard and soft components is apt to wear out. For example, in a braking device in which a non-steel pad consisting of a soft resin-based component, and a harder cast-iron rotor are combined together, and a frictional force is generated by adhesion friction, there is a problem in that the effect of the brake is poor. Additionally, in a braking device in which a low steel pad consisting of hard steel fibers, and a softer cast-iron rotor are combined together, and a frictional force is generated by abrasive friction, there is a problem in that there is a lot of wear on the rotor. 
     Thus, for example, Patent Literature 1 discloses a brake pad, which is manufactured by arranging and forming a composite material portion consisting of at least silicon carbide and metal silicon in a predetermined ratio and having excellent wear resistance, on the surface of a base material of a C/C composite which is a composite carbon fiber, a brake disc, and a brake consisting of the brake pad, in order to improve wear resistance. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2002-257168 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the braking device in which hard materials are arranged on both the pad and the disc as described above, there is an advantage that wear is very slight on both the pad and the disc. However, in the braking device in which hard materials are arranged on both the pad and the disc as described above, the frictional force (frictional coefficient) between the pad and the disc is not necessarily made to be high. 
     The invention has been made in consideration of such circumstances, and the object thereof is to provide a braking device and a method for manufacturing a friction material which can obtain a higher frictional force, without sacrificing wear resistance. 
     Solution to Problem 
     The invention is a braking device including a first friction material having a first hard member on a first friction surface; and a second friction material having a second hard member on a second friction surface which moves with respect to the first friction surface. Any one of the first hard member and the second hard member includes a groove portion along a movement direction of the second friction surface with respect to the first friction surface. The other one of the first hard member and the second hard member includes a protruding portion which abuts on the groove portion. 
     According to this configuration, in a braking device including a first friction material having a first hard member on a first friction surface; and a second friction material having a second hard member on a second friction surface which moves with respect to the first friction surface, any one of the first hard member and the second hard member includes a groove portion along a movement direction of the second friction surface with respect to the first friction surface, and the other one of the first hard member and the second hard member includes a protruding portion which abuts on the groove portion. Therefore, the actual contact area between the friction surfaces having the hard members is increased, and a higher frictional force can be obtained without sacrificing wear resistance. 
     In this case, preferably, a force acting on an abutting portion between the groove portion and the protruding portion includes a component in a direction which is perpendicular to the movement direction of the second friction surface with respect to the first friction surface and parallel to either the first friction surface or the second friction surface. 
     According to this configuration, a force acting on an abutting portion between the groove portion and the protruding portion includes a component in a direction which is perpendicular to the movement direction of the second friction surface with respect to the first friction surface and parallel to either the first friction surface or the second friction surface. Therefore, the force acting per unit area of the abutting portion between the groove portion and the protruding portion becomes the same as that of the conventional flat friction surface due to the resultant force with the force of the component (a force which presses the first friction material and the second friction material against each other) in the direction perpendicular to the movement direction of the second friction surface with respect to the first friction surface and perpendicular to any of the first friction surface and the second friction surface. As a result, the area of the abutting portion increases, so that a higher frictional force can be obtained. 
     Additionally, it is preferable that any one of the first hard member and the second hard member includes a plurality of the groove portions, and the other one of the first hard member and the second hard member includes protruding portions which abut the plurality of groove portions, respectively. 
     According to this configuration, any one of the first hard member and the second hard member includes a plurality of the groove portions, and the other one of the first hard member and the second hard member includes protruding portions which abut the plurality of groove portions, respectively. Therefore, a higher frictional force can be obtained by the plurality of groove portions and protruding portions. 
     Additionally, it is preferable that the groove portion and the protruding portion form wavelike shapes which abut on each other, in a sectional view through a section perpendicular to the movement direction of the second friction surface with respect to the first friction surface. 
     According to this configuration, the groove portion and the protruding portion form wavelike shapes which abut on each other, in a sectional view through a section perpendicular to the movement direction of the second friction surface with respect to the first friction surface. Therefore, the actual contact area between the frictional surfaces is increased, and a higher frictional force can be obtained. 
     In this case, preferably, the groove portion and the protruding portion form wavelike shapes having mutually different amplitudes, in a sectional view through a section perpendicular to the movement direction of the second friction surface with respect to the first friction surface. 
     According to this configuration, the groove portion and the protruding portion form wavelike shapes having mutually different amplitudes, in a sectional view through a section perpendicular to the movement direction of the second friction surface with respect to the first friction surface. Therefore, places where the groove portion and the protruding portion abut on each other are limited. Therefore, the actual contact area between the friction surfaces can be stabilized, and a stable frictional force can be obtained. 
     Additionally, it is preferable that the protruding portion consists of a spherical body and a portion of the spherical body. 
     According to this configuration, the protruding portion consists of a spherical body and a portion of the spherical body. Therefore, places where the groove portion and the protruding portion abut on each other are limited. Therefore, the actual contact area between the friction surfaces can be stabilized, and a stable frictional force can be obtained. 
     In this case, preferably, the groove portion forms a V shape which abuts on the spherical body of the protruding portion at two points, in a sectional view through a section perpendicular to the movement direction of the second friction surface with respect to the first friction surface. 
     According to this configuration, the groove portion forms a V shape which abuts on the spherical body of the protruding portion at two points, in a sectional view through a section perpendicular to the movement direction of the second friction surface with respect to the first friction surface. Therefore, places where the groove portion and the protruding portion abut on each other are further limited. Therefore, the actual contact area between the friction surfaces can be further stabilized, and a more stable frictional force can be obtained. 
     Additionally, as the second friction material rotates, the second friction surface may move with respect to the first friction surface. 
     According to this configuration, the braking device of the invention can be applied to an automobile, for example, using the first friction material as a brake pad and using the second friction material as a brake disc or a brake drum. 
     Additionally, it is preferable that at least any one of the first hard member and the second hard member includes a foreign matter removing portion which discharges foreign matter which has entered between the groove portion and a recessed portion. 
     According to this configuration, at least any one of the first hard member and the second hard member includes a foreign matter removing portion which discharges foreign matter which has entered between the groove portion and a recessed portion. Therefore, even in prolonged use, the foreign matter which has entered between the groove portion and the recessed portion can be discharged, and a stable frictional force can be obtained. 
     Additionally, it is preferable that the first hard member and the second hard member are made of any of a material of a hardness at which wear does not occur when the second friction surface moves with respect to the first friction surface and a material with a Mohs hardness which is greater than or equal to 9. 
     According to this configuration, the first hard member and the second hard member are made of any of a material of a hardness at which wear does not occur when the second friction surface moves with respect to the first friction surface and a material with a Mohs hardness which is greater than or equal to 9. Therefore, the wear resistance of the friction material can be enhanced. 
     Additionally, it is preferable that the first hard member and the second hard member are made of either the same material or materials having the same Mohs hardness. 
     According to this configuration, the first hard member and the second hard member are made of either the same material or materials having the same Mohs hardness. Therefore, the first hard member and the second hard member are mutually resistant to wear, and the wear resistance of the friction material can be enhanced. 
     Meanwhile, the invention is a method for manufacturing a first friction material in a friction material for braking including the first friction material having a first hard member on a first friction surface; and a second friction material having a second hard member on a second friction surface which moves with respect to the first friction surface. The second hard member includes a groove portion along a movement direction of the second friction surface with respect to the first friction surface, and the first hard member includes a protruding portion which abuts on the groove portion. The method includes arranging spherical hard members on the first friction surface so as to make rows along the movement direction of the second friction surface with respect to the first friction surface; and fixing the hard member to the first friction surface. 
     According to this configuration, in a method for manufacturing a first friction material in a friction material for braking including the first friction material having a first hard member on a first friction surface; and a second friction material having a second hard member on a second friction surface which moves with respect to the first friction surface, the second hard member includes a groove portion along a movement direction of the second friction surface with respect to the first friction surface, and the first hard member includes a protruding portion which abuts on the groove portion. The method includes arranging spherical hard members on the first friction surface so as to make rows along the movement direction of the second friction surface with respect to the first friction surface; and fixing the hard member to the first friction surface. Therefore, a desired friction material can be manufactured with comparative ease and at low cost. 
     Additionally, the invention is a method for manufacturing a second friction material in a friction material for braking including a first friction material having a first hard member on a first friction surface; and the second friction material having a second hard member on a second friction surface which moves with respect to the first friction surface. The second hard member includes a groove portion along a movement direction of the second friction surface with respect to the first friction surface, and the first hard member includes a protruding portion which abuts on the groove portion. The method includes arranging a grinding member capable of grinding the second hard member at the same position as the protruding portion of the first friction material instead of the protruding portion of the first friction material; and moving the second friction surface with respect to the first friction surface along a movement direction of the second friction surface with respect to the first friction surface, thereby grinding the second hard member with the grinding member. 
     According to this configuration, in a method for manufacturing a second friction material in a friction material for braking including a first friction material having a first hard member on a first friction surface; and the second friction material having a second hard member on a second friction surface which moves with respect to the first friction surface, the second hard member includes a groove portion along a movement direction of the second friction surface with respect to the first friction surface, and the first hard member includes a protruding portion which abuts on the groove portion. The method includes arranging a grinding member capable of grinding the second hard member at the same position as the protruding portion of the first friction material instead of the protruding portion of the first friction material; and moving the second friction surface with respect to the first friction surface along a movement direction of the second friction surface with respect to the first friction surface, thereby grinding the second hard member with the grinding member. Therefore, the groove portion of the second friction surface can be manufactured in the state where the groove portion corresponds to the protruding portion of the first friction material with higher precision. 
     Advantageous Effects of Invention 
     According to the braking device of the invention, a high frictional force can be obtained without sacrificing wear resistance, and according to the method for manufacturing a friction material of the invention, a friction material which can obtain a higher frictional force can be manufactured without sacrificing wear resistance. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a pad and a disc related to a first embodiment. 
         FIG. 2  is a sectional view taken along a line A-A of  FIG. 1  in the pad and disc related to the first embodiment. 
         FIG. 3X  is a sectional view showing a force which acts on the friction surface of a conventional disc, and  FIG. 3Y  is a sectional view showing a force which acts on the friction surface of a disc of the present embodiment. 
         FIG. 4  is a sectional view taken along the line A-A of  FIG. 1  in a pad and a disc related to a second embodiment. 
         FIG. 5  is a sectional view taken along the line A-A of  FIG. 1  in a pad and a disc related to a third embodiment. 
         FIG. 6  is a perspective view showing a pad and a disc related to a fourth embodiment. 
         FIG. 7  is a sectional view taken along the line A-A of  FIG. 1  in a pad and a disc related to a fifth embodiment. 
         FIG. 8  is an enlarged view of  FIG. 7 . 
         FIGS. 9X and 9Y  are views showing a manufacturing process of the pad of the fifth embodiment. 
         FIG. 10  is a perspective view showing forces which are applied to a conventional pad and disc. 
         FIG. 11  is a view showing a force which is applied to the conventional pad. 
         FIG. 12  is a view showing a force which is applied to the conventional pad. 
         FIG. 13  is a perspective view showing forces which are applied to the pad and disc of the first embodiment. 
         FIG. 14  is a view showing a force which is applied to the pad of the first embodiment. 
         FIG. 15  is a perspective view showing a pad and a disc related to a sixth embodiment. 
         FIG. 16  is a perspective view showing a pad and a disc related to a seventh embodiment. 
         FIG. 17  is a perspective view showing a manufacturing process of a pad of an eighth embodiment. 
         FIG. 18  is a perspective view showing the manufacturing process of the pad of the eighth embodiment. 
         FIG. 19  is a perspective view showing the manufacturing process of the pad of the eighth embodiment. 
         FIG. 20  is a perspective view showing a friction surface of the pad of the eighth embodiment. 
         FIG. 21  is a flow diagram showing a manufacturing process of a disc related to a ninth embodiment. 
         FIG. 22  is a perspective view showing a grinding instrument related to the ninth embodiment. 
         FIG. 23  is a flow diagram showing a manufacturing process of a disc related to a tenth embodiment. 
         FIG. 24  is a perspective view showing a pad and a drum related to an eleventh embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a braking device and a method for manufacturing a friction material related to embodiments of the invention will be described with reference to the drawings. 
     In the first embodiment of the invention, the braking device related to the invention is applied to a disc brake of an automobile. As shown in  FIG. 1 , the disc brake generates a frictional force as two pads  100   a  are pressed against both sides of a disc  200   a  which rotates. As shown in  FIG. 2 , the pad  100   a  has a wavelike friction surface  101 , in a sectional view (sectional view in the line A-A of  FIG. 1 ) in a plane perpendicular to the rotational direction of the disc  200   a . The disc  200   a  has a wavelike friction surface  201  corresponding to the wavelike friction surface  101  of the pad  100   a . Therefore, as shown in  FIG. 1 , the disc  200   a  has a shape in which wavelike grooves are provided in concentric circles, on both sides thereof. In addition, the wavelike friction surfaces  101  and  201  can be formed into any shape of a sinusoidal wave and a saw-tooth wave in a sectional view in a plane perpendicular to the rotational direction of the disc  200   a.    
     Hard particles  102  made of ceramics, such as Si 3 N 4 , Al 2 O 3 , and ZrO 2 , are embedded in the wavelike friction surface  101  of the pad  100   a . The diameter of the hard particles  102  is 0.1 mm to several millimeters. Additionally, the surface layer portion of the wavelike friction surface  201  of the disc  200   a  has a hard layer  203  formed through a nitriding treatment by thermal spraying or the like, adhesion, or the like. The wavelength and amplitude of the wavelike friction surfaces  101  and  201  are such that one or more hard particles  102  enter, and are about 0.1 mm to 5 mm It is preferable that the hard particles  102  of the pad  100   a  and the hard layer  203  of the disc  200   a  have the hardness at which wear does not occur at the time of braking, or a Mohs hardness greater than or equal to 9. Additionally, it is preferable that the hard particles  102  of the pad  100   a  and the hard layer  203  of the disc  200   a  be made of the same kind of material, or made of materials having the same Mohs hardness. 
     Hereinafter, the working effects of the braking device of the present embodiment will be described. Generally, two kinds of factors of adhesion friction and thermal conversion by attenuation have a great influence on a dry-friction phenomenon between hard members with little difference in hardness. In addition, the above-described abrasive friction is a principle that one hard friction material shaves off another softer friction material, and has little influence on the dry-friction phenomenon between hard members with little hardness difference. 
     The adhesion friction is based on an attractive force acting between the substances of hard members, for example, an intermolecular force. The frictional force due to the adhesion friction depends greatly on (1) the magnitude of an intermolecular force depending on the crystal structure or the like of a substance itself, (2) the distance (as the distance is shorter, the frictional force is larger) between substances (for example, molecules), and (3) the actual contact area between hard members. As for the actual contact area of (3), that the distance between substances (for example, molecules) of hard members is short in many portions means that the actual contact area is large, and the frictional force is increased. 
     However, even if the area of a pad is simply increased in a disc brake, since the pressing force (pressure) per unit area decreases if the force from a piston which pushes the pad against a disc is the same, the frictional force does not increase. Thus, in the present embodiment, the friction surfaces of the pad  100   a  and the disc  200   a  are made into the wavelike friction surfaces  101  and  201 , respectively. Thereby, even when the force from the piston is the same, the actual contact area is increased such that the pressing force per unit area does not change. 
     As shown in  FIG. 3X , in a pad  10  and a disc  20  which have conventional flat friction surfaces  104  and  204 , respectively, the force with which the pad  10  pushes the disc  20  in a perpendicular direction V of the friction surfaces becomes F per unit area A. On the other hand, as shown in  FIG. 3Y , in the pad  100   a  and the disc  200   a  of the present embodiment, the area of the unit area A projected on the wavelike friction surfaces  101  and  201  is A/cos α. Here, α is an angle that the normal of the wavelike friction surfaces  101  and  201  makes with the perpendicular direction V. 
     If the force (pushing force of the piston) with which the overall pad  100   a  pushes the disc  200   a  in the perpendicular direction V is not different from the force in which the overall pad  10  pushes the disc  20  in the perpendicular direction V, the component of a force which acts in the perpendicular direction V of a portion whose area is A/cos α is similarly F. At this time, in the wavelike friction surfaces  101  and  201 , the component of a force which acts in a direction H parallel to the friction surfaces causes a reaction force f between the wavelike friction surfaces  101  and  201 , thereby achieving a balance. Accordingly, the load of the portion whose area is A/cos α in a direction truly perpendicular to the wavelike friction surfaces  101  and  201  becomes a resultant force of F and f, and becomes F/cos α. 
     In this case, since the force acting on the area A/cos α becomes F/cos α, the force per the unit area A is F, and becomes the same as for the pad  10  and disc  20  which have the conventional flat friction surfaces  104  and  204 , respectively. Accordingly, in the pad  100   a  and the disc  200   a  of the present embodiment, since the actual contact area is increased by the wavelike friction surfaces  101  and  201  irrespective of whether the pressing force per unit area remains unchanged, the frictional force can be increased. 
     In the present embodiment, in the braking device including the pad  100   a  having the hard particles  102  on the wavelike friction surface  101 , and the disc  200   a  having the hard layer  203  on the wavelike friction surface  201  which slides on the wavelike friction surface  101 , the wavelike friction surface  201  has groove portions along a sliding direction between the wavelike friction surfaces  101  and  201 , and the wavelike friction surface  101  has protruding portions which abut on the grooves. Therefore, the actual contact area between the friction surfaces having the hard members is increased, and a higher frictional force can be obtained without sacrificing wear resistance. 
     Additionally, in the present embodiment, the abutting area between the wavelike friction surfaces  101  and  201  increases compared to the conventional flat friction surface  104  and  204 . In addition, since the force f of the component in the direction H parallel to the wavelike friction surfaces  101  and  201  is included in the force acting on the abutting portion between the wavelike friction surfaces  101  and  201 , the force acting per unit area of the abutting portion between the wavelike friction surfaces  101  and  201  becomes the same due to the resultant force with the force F of the component in the direction V perpendicular to the wavelike friction surfaces  101  and  201 . As a result, a higher frictional force can be obtained. 
     Additionally, in the present embodiment, since the wavelike friction surfaces  101  and  201  have a plurality of groove portions and protruding portions and abut on each other, a higher frictional force can be obtained. Particularly, in the present embodiment, the wavelike friction surfaces  101  and  201  form wavelike shapes which abut on each other, in a sectional view through a section perpendicular to the direction of sliding between the wavelike friction surfaces  101  and  201 . Therefore, the actual contact area between the friction surfaces is increased, and a higher frictional force can be obtained. In addition, in the present embodiment, a braking device for an automobile including the pad  100   a  and the disc  200   a  can be provided. 
     Additionally, in the present embodiment, the hard particles  102  and the hard layer  203  are made of any of a material of a hardness at which wear does not occur at the time of braking and a material with a Mohs hardness which is greater than or equal to 9. Therefore, the wear resistance of the friction material can be enhanced. Additionally, in the present embodiment, the hard particles  102  and the hard layer  203  are made of any of the same material and materials having the same Mohs hardness. Therefore, the hard particles and the hard layer are mutually resistant to wear, and the wear resistance of the friction material can be enhanced. 
     Additionally, by setting the depth of the wavelike friction surfaces  101  and  201  shown in  FIG. 3Y  to 0.5 mm to 1.5 mm, and satisfying α=60°, a double frictional force is obtained on the whole compared to the flat friction surface  104  and  204  shown in  FIG. 3X . As shown in a pad  100   b  and a disc  200   b  of a second embodiment of  FIG. 4 , in the case of α=60°, the pushing force per unit area A is F, and the frictional coefficient μ is the same as the conventional one. In this case, as for the frictional force in the length L perpendicular to the rotational direction of the disc, the frictional force in the flat friction surface  104  and  204 =μF/A×L=μL/A is obtained, whereas the frictional force in the wavelike friction surfaces  101  and  201 =μF/A×L/cos 60°=2 μL/A. As a result, a double frictional force can be obtained. 
     In addition, as shown in  FIG. 4 , in order to prevent the wavelike friction surfaces  101  and  201  from not separating from each other when biting into each other, it is preferable to provide R portions  105  and  205  at angled portions of the wavelike friction surfaces  101  and  201 , respectively. Since the frictional force decreases at the R portions  105  and  205 , it is preferable that the size of the R portions  105  and  205  be a requisite minimum. Specifically, it is preferable that the radius of curvature of the R portions  105  and  205  be greater than the radius of the hard particles  102 . It is more preferable that the radius of curvature of the R portions  105  and  205  be 1.5 or more times the radius of the hard particles  102 . 
     Hereinafter, a third embodiment of the invention will be described. As shown in  FIG. 5 , in the present embodiment, spherical hard particles  112  of such a size that the hard particles exactly enter and abut on groove portions, respectively, of a wavelike friction surface  201  of a disc  200   c  are arranged in a flat friction surface  104  of a pad  100   c . The spherical hard particles  112  are arranged so as to be aligned along the grooves of the wavelike friction surface  201  of the disc  200   c . It is preferable that the wavelike friction surface of the disc  200   c  assumes a sawtooth wave shape in a sectional view in a plane perpendicular to the rotational direction of the disc  200   c . Similarly to the above first embodiment, by setting the angle α of the wavelike friction surface  201  to 60°, a double frictional force can be obtained compared to a case where the hard particles  112  of the same number are arranged in the conventional flat friction surface  104 , and are made to abut on the disc  20  having the flat friction surface  204 . 
     In the present embodiment, each of the hard particles  112  arranged in the flat friction surface  104  of the pad  100   c  necessarily touches the wavelike friction surface  201  with a sawtooth wave shape 
     (V-shape), of the disc  200   c  at two points. Therefore, the overall pad  100   c  stably touches the disc  200   c  at points of twice the number of the hard particles  112 . Therefore, it is possible to stabilize a frictional force. 
     Particularly, in the present embodiment, the wavelike friction surface  201  of the disc  200   c  forms a V shape which abuts on the spherical hard particles  112  at two points, in a sectional view through a section perpendicular to the direction of sliding between the flat friction surface  104  and the wavelike friction surface  201 . Therefore, places where the hard particles  112  and the wavelike friction surface  201  abut on each other are further limited. Therefore, the actual contact area between the friction surfaces can be further stabilized, and a more stable frictional force can be obtained. 
     Additionally, in a pad  100   d  and a disc  200   d  of a fourth embodiment shown in  FIG. 6 , the hard particles  112  are not fixed to the pad  100   d  side. In the present embodiment, hemispherical or conical hole portions  106  of a size which is slightly greater than or slightly smaller than the hard particles  112  are provided on the pad  100   d  side. The hard particles  112  are sandwiched between the hole portions  106  of the pad  100   d  and the wavelike friction surface  201  of the disc  200   d . In the present embodiment, there is an advantage that it is not necessary to take fixation of the hard particles  112  to the pad  100   d  or separation of the hard particles  112  from the pad  100   d  into consideration. 
     Hereinafter, a fifth embodiment of the invention will be described. As shown in  FIG. 7 , in the present embodiment, a wavelike friction surface  101  of a pad  100   e  and a wavelike friction surface  201  of a disc  200   e  form wavelike shapes having mutually different amplitudes, in a sectional view through a section perpendicular to the direction of sliding between the wavelike friction surfaces  101  and  201 . That is, in the present embodiment, the concavo-convex shape of the wavelike friction surfaces  101  and  201  is slightly changed on the pad  100   e  side and the disc  200   e  side. The curvature of apex portions  107  of the wavelike friction surface  101  of the pad  100   e  is made smaller than that of groove portions of the wavelike friction surface  201  of the disc  200   e . Hard layers  103  and  203  formed by a nitriding treatment through thermal spraying or the like, adhesion, or the like are provided in the surface layer portions of the wavelike friction surfaces  101  and  201 . 
     As shown in  FIG. 8 , in a sectional view through a section perpendicular to the direction of sliding between the wavelike friction surfaces  101  and  201 , the wavelike friction surfaces  101  and  201  come into contact with each other at two frictional force generating portions F 1  for every irregularity. At least one of the wavelike friction surfaces  101  and  201  has the structure in which the hard layers  103  or  203  of such a thickness that at least a portion can be elastically deformed are formed on the surface of an elastic body. Lubricant  300  is interposed between the wavelike friction surfaces  101  and  201 . 
     When the above pad  100   e  is manufactured, as shown in FIG.  9 X, the same wavelike friction surface  101  as the wavelike friction surface  201  of the disc  200   e  is formed on the pad  100   e . The hard layer  103  is provided on the wavelike friction surface  101  with equal thickness by a technique, such as a nitriding treatment through thermal spraying, adhesion, or the like. Next, as shown in  FIG. 9Y , by grinding the hard layer  103  at the apex portions  107  by a grinding instrument  400 , it is possible to manufacture the pad  100   e  which has the wavelike friction surface  101  having concavo-convex shape which is different from that of the wavelike friction surface  201  of the disc  200   e.    
     In the present embodiment, the wavelike friction surface  101  of the pad  100   e  and the wavelike friction surface  201  of the disc  200   e  form wavelike shapes having mutually different amplitudes, in a sectional view in a section perpendicular to the direction of sliding between the wavelike friction surfaces  101  and  201 . Therefore, places where the wavelike friction surfaces  101  and  201  abut on each other are limited. Therefore, the actual contact area between the wavelike friction surfaces  101  and  201  can be stabilized, and a stable frictional force can be obtained. Additionally, in the present embodiment, since the distance between the wavelike friction surfaces  101  and  201  is stable, a stable frictional force can be obtained. Moreover, the pad  100   e  and the disc  200   e  of the present embodiment have also an advantage of being comparatively easy to manufacture. 
     The braking devices of the above first to fifth embodiments exhibit further secondary effects. As shown in  FIG. 10 , in the pad  10  and disc  20  which have the conventional flat friction surface  104  and  204 , a rotational force R to rotate the pad  10  in the radial direction of the disc  20  acts from an action between a braking force B and a reaction force f at a reaction force receiving portion of a caliper at the time of braking. For example, even in a case where the number of reaction force receiving portions  501  of a caliper  500   a  is one as shown in  FIG. 11 , and even in a case where the number of the reaction force receiving portions  501  of a caliper  500   b  is two as shown in  FIG. 12 , the rotational force R acts on the pad  10  similarly. 
     This rotational force R is an unstable force which fluctuates, for example, at the time of turning of an automobile, or due to the partial wear or the like influenced by the traveling history. Therefore, the contact state of a portion of suppressing the rotation of the pad  10  changes unstably between the calipers  500   a  and  500   b  and the pad  10 . When the contact state between the calipers  500   a  and  500   b  and the pad  10  changes in this way, the resonant frequency tuned for a reduction in squeaking (key sound: squeal) may change, and squeaking may be generated. 
     On the other hand, as shown in  FIG. 13 , in the above first embodiment, the pad  100   a  and the disc  200   a  include the wavelike friction surfaces  101  and  201  with little wear, and the rotational force R as in the conventional pad  10  does not act on the pad  100   a . Therefore, in the above first embodiment, as shown in  FIG. 14 , the reaction force receiving portion  501  is eliminated from a caliper  500   c , and a floating receiving portion  502  which does not constrain the pad  100   a  in the radial direction of the disc  200   a  is used. 
     Although the floating receiving portion  502  is a recessed portion with a large clearance from the pad  100   a  for preventing the pad  100   a  from coming off the caliper  500   c , during normal use, there is no case where the pad  100   a  moves in the radial direction of the disc  200   a , and comes into contact with side faces of the recessed portion of the floating receiving portion  502 . That is, the side faces of the recessed portion of the floating receiving portion  502  do not function during normal use, but function to prevent the pad  100   a  from coming off only at the time of abnormality such that the pad  100   a  may come off. 
     As described, in the braking devices of the first to fifth embodiments, the load of the floating receiving portion  502  may change due to the braking forces B. However, since a place where the contact state between the caliper  500   c  and the pad  100   a  changes according to conditions is eliminated, a state where the performance of preventing squeaking has been tuned does not change. As a result, in the braking devices of the first to fifth embodiments, it is difficult for squeaking to be generated. 
     Hereinafter, sixth and seventh embodiments of the invention will be described. When the wavelike friction surface  201  of the disc  200   a  or the like is clogged with foreign matter, such as dust, the wavelike friction surface  101  of the pad  100   a  or the like will ride on the foreign matter. Therefore, a decrease in the actual contact area may decrease or the distance between the pad  100   a  and the disc  200   a  may increase. As a result, there is a possibility that a desired braking force is not obtained. 
     Thus, as shown in  FIG. 15 , in the present embodiment, the end of a pad  100   f  in the sliding direction is provided with a scraper  108   a  which protrudes along the shape of the wavelike friction surface  201  and which can peel off the foreign matter adhering to the wavelike friction surface  201  from the wavelike friction surface  201 . In the present embodiment, the foreign matter which clogs the wavelike friction surface  201  of the disc  200   f  can be removed above the wavelike friction surface  201  of the disc  200   f  by the scraper  108   a  during rotation of the disc  200   f.    
     Additionally, in a pad  100   g  of a seventh embodiment shown in  FIG. 16 , the end of the pad  100   g  in the sliding direction is provided with a scraper  108   b  which protrudes along the shape of the wavelike friction surface  201  and which can scrape off the foreign matter which clogs the wavelike friction surface  201  in a direction parallel to the wavelike friction surface. In the present embodiment, the foreign matter which clogs the wavelike friction surface  201  of the disc  200   g  can be scraped off and removed in the direction parallel to the wavelike friction surface  201  of the disc  200   g  by the scraper  108   b  during rotation of the disc  200   g.    
     According to the above sixth and seventh embodiments, since the scraper  108   a  or  108   b  for discharging the foreign matter which has entered between the wavelike friction surfaces  101  and  201  is included in the pads  100   f  or  100   g , even in prolonged use, the foreign matter which has entered between the wavelike friction surfaces  101  and  201  can be discharged, and a stable frictional force can be obtained. 
     Hereinafter, a method for manufacturing the pad  100   c  of the above third embodiment in an eighth embodiment of the invention will be described. As shown in  FIG. 17 , first, a base  109  in which the groove portions of the wavelike friction surface  201  on the disc  200   c  side become the groove portions  110  is fabricated in accordance with the concentric wavelike friction surface  201  on the disc  200   c  side. Next, as shown in  FIG. 18 , the hard particles  112  are arranged side by side in the groove portions  110  of the base  109 . Next, as shown in  FIG. 19 , resin (an admixture having a resin-based organic ingredient of 50% or more)  111  is made to flow into the groove portions  110 . A jig  600  for improving dimensional precision is pressed against hard particles  112 , and is fixed thereto. 
     In practice, the hard particles  112  are arranged in the flat friction surface  104  of the pad  100   c  so as to be aligned on the circles with the same curvature as the concentric circles of the wavelike friction surface  201  on the disc  200   c  side. Additionally, in the process of  FIG. 19 , the distance between the base  109  and the hard particles  112  can be controlled by controlling the distance between the jig  600  and the base  109  and press-fitting the resin  111  in a half-cured state. Additionally, the characteristics of the portion of the resin  111  used as an elastic body can be controlled by controlling the distance between the jig  600  and the base  109  and press-fitting the resin  111  in a half-cured state. 
     According to the present embodiment, since the hard particles  112  are arranged in the flat friction surface  104  so as to make rows along the direction of sliding between the flat friction surface  104  and the wavelike friction surface  201 , and the hard particles  112  are fixed to the flat friction surface, a desired friction material can be manufactured at a comparatively low cost. 
     Hereinafter, an example of a method for manufacturing the discs  200   a  to  200   g  of the above first to seventh embodiments in a ninth embodiment of the invention will be described. For example, if the deviation between the concavo-convex shape of the wavelike friction surface  101  on the pad  100   a  side and the concavo-convex shape of the wavelike friction surface  201  on the disc  200   a  side is too large, it is not possible to cope with the deviation in the elastic deformation of the pad  100   a  and the disc  200   a , the contact points between the wavelike friction surfaces  101  and  201  may decrease, and the frictional force may be insufficient. 
     Thus, in the present embodiment, the discs  200   a  to  200   g  are manufactured by the following technique. As shown in  FIG. 21 , the caliper  500   c , a knuckle, a hub, and the disc  200   a  other than the pad  100   a  are assembled to a suspension of an automobile (S 11 ). 
     Next, a grinding instrument  700  matched with the shape of the wavelike friction surface  101  of the pad  100   a  as shown in  FIG. 22  is assembled to the part of the pad  100   a  of the suspension of the automobile (S 12 ). As for the grinding instrument  700 , specifically, diamond grinding powder or the like is arranged on the surface of the wavelike friction surface  101  of the pad  100   a . Next, as braking pressure is applied to press the grinding instrument  700  against the disc  200   a , and the disc  200   a  is rotated, final grinding of the disc  200   a  is performed (S 13 ). The grinding instrument  700  is removed and the regular pad  100   a  is assembled (S 14 ). Shipping is performed in a state where the caliper  500   c , a knuckle, a hub, and the disc  200   a  are assembled (S 15 ). 
     According to the present embodiment, the grinding instrument  700  capable of grinding the wavelike friction surface  201  of the disc  200   a  is arranged at the same position as the pad  100   a  instead of the pad  100   a , and the disc  200   a  is made to slide on the disc  100   a  along the direction of sliding between the wavelike friction surfaces  101  and  201 , thereby grinding the disc  200   a  with the grinding instrument  700 . Therefore, the groove portions of the wavelike friction surface  201  of the disc  200   a  can be manufactured in the state where the groove portions correspond to the protruding portions of the pad  100   a  with higher precision. Additionally, the wavelike friction surface  201  of the disc  200   a  of a customer&#39;s automobile can be refreshed by using the grinding instrument  700  in an automobile dealership. 
     A method for manufacturing the disc  200   a  of a tenth embodiment also includes the following technique. As shown in  FIG. 23 , the caliper  500   c  to which the pad  100   a  is attached, a knuckle, a hub, and the disc  200   a  are assembled to a suspension of an automobile (S 21 ). In this case, in an automobile dealership, all of the caliper  500   c , the knuckle, the hub, and the disc  200   a  are already in an assembled state. 
     Abrasive agent is applied to the wavelike friction surface  201  of the disc  200   a  (S 22 ). As braking pressure is applied to press the pad  100   a  against the disc  200   a , and the disc  200   a  is rotated, grinding of the disc  200   a  is performed (S 23 ). The abrasive agent is washed away, or the abrasive agent is scattered and disappears during multiple braking operations during traveling (S 24 ). In a case where an automobile has not yet been delivered to a selling point, the caliper  500   c  to which the pad  100   a  is attached, the knuckle, the hub, and the disc  200   a  are shipped in the state of being assembled to a suspension of the automobile. 
     According to the present embodiment, any deviation in irregularities between the wavelike friction surfaces  101  and  201  can be eliminated as final grinding is performed in a state where the caliper  500   c  to which the pad  100   a  is attached, the knuckle, the hub, and the disc  200   a  are assembled to the suspension of the automobile. Additionally, the wavelike friction surface  201  of the disc  200   a  of a customer&#39;s automobile can be refreshed by using in an automobile dealership. 
     Hereinafter, an eleventh embodiment of the invention will be described. The invention can be applied not only to the disc brakes described in the above first to tenth embodiments but also to a drum brake as shown in  FIG. 24 . In this case, a braking force is generated as a pad  100   h  is pressed against the inner surface of a drum  800 . The pad  100   h  and the drum  800  can be formed into a shape shown in  FIGS. 2 to 8 ,  15 , and  16  in a sectional view in the line A-A of  FIG. 24 . 
     Although the embodiments of the invention have been described above, the invention is not limited to the above embodiments, and various modifications thereof can be made. 
     INDUSTRIAL APPLICABILITY 
     The invention can provide a braking device and a method for manufacturing a friction material which can obtain a higher frictional force, without sacrificing wear resistance. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10 : PAD 
               20 : DISC 
               100   a  to  100   h : PAD 
               101 : WAVELIKE FRICTION SURFACE 
               102 : HARD PARTICLE 
               103 : HARD LAYER 
               104 : FLAT FRICTION SURFACE 
               105 : R PORTION 
               106 : HOLE 
               107 : APEX PORTION 
               108   a ,  108   b : SCRAPER 
               109 : BASE 
               110 : GROOVE PORTION 
               111 : RESIN 
               112 : HARD PARTICLE 
               200   a  to  200   g : DISC 
               201 : WAVELIKE FRICTION SURFACE 
               203 : HARD LAYER 
               204 : FLAT FRICTION SURFACE 
               205 : R PORTION 
               300 : LUBRICANT 
               400 : GRINDING INSTRUMENT 
               500   a ,  500   b ,  500   c : CALIPER 
               501 : REACTION FORCE RECEIVING PORTION 
               502 : FLOATING RECEIVING PORTION 
               600 : JIG 
               700 : GRINDING INSTRUMENT 
               800 : DRUM