Title of Invention

MECHANICAL DISC BRAKE FOR VEHICLES

Abstract

A mechanical disc brake for vehicles comprises a caliper body (40) comprising an acting portion (41) which has a receiving bore (46) and a sleeve nut (100) disposed along a disc axis. The receiving bore (46) accommodates a piston (80). A screw member (110) is screwed into the sleeve nut (100), and an output shaft (140) is disposed between the screw member (110) and the piston (80). The output shaft (140) has a large-diameter portion (144) having a spherical abutment surface (145) which is adapted to abut against a spherical abutment surface (84) of the piston (80). The output shaft (140) is fitted with a stopper (170) at its tip so that a bottom wall (81) of the piston (80) can be resiliently held by the stopper (170) and the large-diameter portion (144). Thus, the wear and tear of the output shaft and the screw member can be minimized and their durability can be improved, while preventing the interference with a braking operation due to a biased load on the output shaft and the screw member.

Full Text

BACKGROUND OF THE INVENTION 1. Technical Field The present invention relates to a mechanical disc brake apparatus for use in vehicles including automobiles, two-or three wheeled motorcycles, three- or four-wheeled dune buggies and golf carts and the like. 2. Background Art An example of a conventional mechanical disc brake for vehicles is shown in Japanese Utility Model Publication No. Hei 1-30662. In Japanese Utility Model Publication No. Hei 1-30662 (Sho 64-30662), the output shaft and the portion corresponding to the piston are integrally formed, which causes the biased load at the screw member and interferes with operation. While the feature of the present invention is that the piston and the output shaft are separately formed and the abutment surfaces is formed in the shape of a spherical concave or convex, thereby the biased load is prevented at the screw member. In this disc brake apparatus, a brake lever or pedal is operated to rotate an input lever attached to a caliper body. The rotating force of the input lever is converted into a propulsion force along the disc axis, thereby effecting a braking action. More specifically, in this mechanical disc brake system, as the input lever is rotated, a cam plate is moved toward a disc rotor. At the same time, a piston and an output shaft are moved toward the disc rotor, thereby causing a pad pressing portion at the tip of the output shaft to press friction pads against the sides of the disc rotor. The output shaft is in screwed into a screw member concentrically supporting the input lever and the cam plate. As the linings on the friction pads wear and the braking gap between the sides of the disc rotor and the friction pads increases above a predetermined amount, the output shaft is advanced out of the screw member toward the disc rotor so that the braking gap can be set to a predetermined value. In this type of mechanical disc brake, in addition to a normal braking operation, i.e., when the vehicle is stopped for a duration of time by using the brake on a slope, for example, the disc rotor creates a dragging torque in the friction pads pressing the disc rotor therebetween, due to the force dragging the vehicle down the slope. The dragging torque is transmitted via the output shaft abutted with the friction pads to the parts including the piston and screw member, thereby causing those parts as a whole to be inclined toward a disc rotation direction with respect to the disc axis. This not only adversely affects the braking operation but may also cause wear and tear of the internal or external screws connecting the output shaft and the screw member. It is an object of the present invention to provide a mechanical disc brake apparatus in which the dragging torque produced in the friction pads during braking is prevented as much as possible from being transmitted to the output shaft and the screw member, in order to effectively prevent the wear and tear of the threads of the output shaft and the screw member and thus improve durability, while preventing the biased load on the output shaft and the screw member from affecting the braking operation. It is another object of the present invention to provide a mechanical disc brake apparatus for vehicles in which the dragging of the friction pads is minimized by forcibly bringing back the piston when the braking operation is released. According to the present invention there is provided a mechanical disc brake (10) for vehicles comprising: a caliper body (40) having a receiving bore formed in an acting portion (41) disposed on one side of a disc rotor (50)/ a bottomed cylindrical piston (80) housed in said receiving bore on the side facing said disc rotor (50) such that said piston can move along the disc axis; a screw member (110) screwed into an inner wall of said receiving bore on the side away from said disc rotor (50); and an output shaft (140) disposed between said screw member (110) and said piston (80), wherein said output shaft and said screw member are integrally moved in the direction of said disc rotor (50) by the rotation of an input lever so that a friction pad (60) is pressed against one side of said disc rotor with the pressing motion of said piston abutting said output shaft, and of the abutment surfaces (83) of said output shaft (140) and said piston (80) , one abutment surface having the shape of a convex with a spherical surface, while the other is having in the shape of a concave or convex with a spherical surface. DISCLOSURE OF THE INVENTION A mechanical disc brake for vehicles according to the present invention comprises: a caliper body comprising an acting portion disposed at one side of a disc rotor, the acting portion having a receiving bore formed therein; a bottomed cylindrical piston received in the receiving bore to be movable along the disc axis at a position proximate to the disc rotor; a screw member screwed into an inner wall of the receiving bore at the position distant from the disc rotor; and an output shaft disposed between the screw member and the piston, wherein: the output shaft and the screw member are advanced together toward the disc rotor as an input lever is rotated, so that a friction pad is pressed against a side of the disc rotor by the piston abutting the output shaft thus effecting a braking action. In the first aspect of the present invention, one of the abutment surfaces of the output shaft and the piston which are in abutment engagement with each other is formed in the shape of a spherical convex, and the other abutment surface is formed in the shape of a spherical concave or convex. In the second aspect of the present invention, the output shaft has a large-diameter portion formed at a position on the distal side of the bottom wall of the piston with respect to the disc rotor and the large-diameter portion is provided with a protruding portion. The opposed surfaces of the large-diameter portion and the piston bottom wall are provided with the abutment surfaces. A through hole is formed in the bottom wall of the piston along the disc axis, through which the protruding portion passes and protrudes beyond the piston toward the disc rotor. The protruding portion is fitted with a resilient stopper such that the bottom wall of the piston can be resiliently held by the stopper and the large-diameter portion of the output shaft. According to the thus constructed disc brake apparatus, the dragging torque created in the friction pad can be prevented by the piston from being transmitted to the output shaft and the screw member as much as possible, thereby preventing the tilting of thereof toward the direction of disc rotation. This minimizes the wear and tear of the connecting portions between, the output shaft and the screw member while improving their durability. The adverse effect on braking action by the biased load put on the output shaft and the screw member can also be prevented. Since the resilient stopper fitted at the tip of the screw member acts to forcibly bring the piston away from the disc rotor when the braking operation is released, the uneven wear of the friction pad lining being dragged by the disc rotor can be minimized. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially sectional front view of a mechanical disc brake according to an embodiment of the present invention; FIG. 2 is a cross section taken along Line 2-2 of FIG. 1 according to an embodiment of the present invention; FIG. 3 is a cross section taken along Line 3-3 of FIG 1 according to an embodiment of the present invention; and FIG. 4 is a sectional side elevation of a mechanical disc brake according to another embodiment of the present invention. BEST MODE OF CARRYING OUT THE INVENTION One embodiment of the present invention will be described referring to the attached figures. A mechanical disc brake 10 comprises a caliper body 40. The caliper body 40 is supported on a bracket 20 by a pair of slidable pins 30. The caliper body 40 is slidable in a disc axis direction. The bracket 20 is mounted on a vehicle body. The caliper body 40 comprises an acting portion 41, a reacting portion 42 and a bridge portion 43. The acting portion 41 is disposed on one side of a disc rotor 50. The reacting portion 42 is disposed on the other side of the disc rotor 50. The bridge portion 43 connects the acting portion 41 and the reacting portion 42 while straddling the periphery of the disc rotor 50. A pair of friction pads 60 is suspended by a hanger pin 70 such that the disc rotor 50 is sandwiched between the friction pads 60. The friction pads 60 are movable along the disc axis. Supporting arms 44, 44 extend from either side of the acting portion 41. The supporting arms 44, 44 have the slidable pins 30, 30 passed therethrough, the pins extending away from the bracket 20. One of the supporting arms 44, 44 has a retaining arm 45 extending therefrom. The retaining arm 45 is used for having a brake wire 150 passed therethrough, as will be described later. The acting portion 41 has a receiving bore 46 formed on the side of the disc rotor 50. The receiving bore 46 accommodates a piston 80 slidably along the disc axis. The piston 80 is formed in the shape of a bottomed cylinder with a thick bottom wall 81. A through hole 82 is formed on a center axis of the bottom wall 81. The bottom wall 81 has a spherically concave abutment surface 83 formed on the side facing away from the disc rotor 50. The abutment surface 83 encircles the through hole 82. The acting portion 41 has disposed on the side away from the disc rotor 50 a piston actuating mechanism 90 for actuating the piston 80. The piston actuating mechanism 90 comprises a sleeve nut 100, a screw member 110, an input lever 130 and an output shaft 140. The sleeve nut 100 is cast-in bonded with the caliper body 40. The screw member 110 is screwed into the sleeve nut 100 from the side away from the disc rotor 50. The input lever 130 is integrally fixed to the external tip of the screw member 110 by means of a lock nut 120. The output shaft 140 is screwed into the screw member 110 and engaged with the piston 80 such that the piston 80 can be pushed toward the disc rotor 50. The sleeve nut 100, which is coaxial with the receiving bore 46, has multiple internal threads 101 formed on the inside thereof. The screw member 110 is a cylinder formed with multiple external threads 111 on the disc rotor side and multiple internal threads 112 on the side away from the disc rotor 50. The screw member 110 has one of its ends away from the disc rotor 50 protruding beyond the sleeve nut 100. The external threads 111 of the screw member 110 are screwed into the internal threads 101 of the sleeve nut 100, so that the disc-rotor side of the screw member 110 is held by the sleeve nut 100. Since the internal threads 101 of the sleeve nut 100 and the external threads 111 of the screw member 110 each have a multi-start thread with a large lead angle, the screw member 110 can be advanced greatly along the axis by a small amount of rotation of the input lever 130. The tip of the input lever 130 is coupled with one end of the brake wire 150, which is passed through the holding arm 45. The other end of the brake wire 150 is coupled with a brake pedal or lever (not shown) located near the driver's seat. A return spring 160 is assembled under compression between the tip of the input lever 130 and the holding arm 45 and encasing one end of the brake wire 150. When not in operation, the return spring 160 biases the input lever 130, the screw member 110 and the output shaft 140 into the solid line positions shown in FIGs. 1-3. The output shaft 140 comprises a shaft portion 141 with a smaller diameter extending across the piston 80 and the sleeve nut 100. The output shaft 140 also comprises an external thread 142 with a larger diameter which protrudes beyond the sleeve nut 100 away from the disc rotor 50 and which is continuous with the shaft portion 141. The external thread 142 has a knob 143 integrally formed therewith at its external end. The shaft portion 141 of the output shaft 140 forms at about the center thereof a flange-shaped large-diameter portion 144. One face of the larger-diameter portion 144 on the disc rotor side has an abutment surface 145 which expands spherically. The shaft portion 141 is continuous with a tip portion 146 extending from the large-diameter portion 144 toward the disc rotor 50. The tip portion 146 is slightly smaller in diameter than a through hole 82 of the piston 80. The tip portion 146 of the output shaft 140 is passed through the through hole 82 and protrudes beyond the bottom wall 81 of the piston 80 toward the disc rotor 50. At the same time, the abutment surface 145 abuts on the abutment surface 83 of the piston 80. The tip of the protruding tip portion 146 is fitted with a stopper 170 comprising a wave washer. Thus, the bottom wall 81 of the piston 80 is resiliently held between the stopper 170 and the large-diameter portion 144, thereby connecting the piston 80 and the output shaft 140 along the disc axis. Accordingly, either the piston 80 or the output shaft 140 thus connected can be independently inclined laterally because of the resilience provided by the spherical shapes of the abutment surfaces 83 and 145 and the stopper 170. When the braking operation is released and the output shaft 140 is moved away from the disc rotor 50, the piston 80 is also forcibly moved back. The external thread 142 of the output shaft 140 is about half way screwed into the internal thread 112 of the screw member 110. The remaining half of the external thread 142 protruding beyond the screw member 110 away from the disc rotor 50 is screwed into the above-mentioned lock nut 120, thereby locking the screw member 110, the input lever 130 and the output shaft 140 integrally. Consequently, as the brake wire 150 is pulled by a braking operation, the input lever 130, the screw member 110 and the output shaft 140 are rotated together. This causes the output shaft 140, together with the input lever 130 and the screw member 110, to be advanced toward the disc rotor 50 due to the screwed engagement between the external thread 111 and the internal thread 101, thus pushing the piston 80 at the end of the output shaft 140. The lock nut 120 is also used for the adjustment of the braking gap as required by the wear of the lining of the friction pads 60, as well as for adjusting the tension of the brake wire 150. For example, when the tension of the brake wire 150 is adjusted, the lock nut 120 is once loosened, the input lever 130 is moved in either direction along its rotation path by using the screw member 110 as a fulcrum, and then the lock nut 120 is re-fastened. In the event that the braking gap between either side of the disc rotor 50 and the lining of either of the friction pads 60 increased beyond a predetermined amount due to repeated braking operations, the lock nut 120 is similarly loosened once. Then, only the output shaft 140 is pushed toward the disc rotor 50 by manipulating the knob 143 in order to advance the friction pad 60 at the end of the output shaft 140 and properly set the braking gap. The lock nut 120 is finally re-fastened. Thus, in the above-described embodiment, as the brake wire 150 is pulled by the driver's braking operation, the input lever 130 is rotated away from the solid line position to the imaginary line position in FIG. 1. Simultaneously the screw member 110 and the output shaft 140 are rotated and thus advanced toward the disc rotor 50. This causes the piston 80 to be pushed toward the disc rotor, until the friction pad 60 at the acting portion side is pressed against one side of the disc rotor 50. This results in a reaction force which advances the caliper body 40 toward the acting portion 41 while being guided by the slidable pins 30, 30. As a result, the reacting portion 42 presses the friction pad 60 at the reacting portion side against the other side of the disc rotor 50, thereby effecting a braking action. When the braking operation is released, the individual members operate in the opposite sequence from that of the braking operation, until the pressure applied to the friction pads 60, 60 is released. Specifically, at the side of the acting portion 41, the screw member 110, the output shaft 140 and the input lever 130 are together moved away from the disc rotor 50. This is followed by a forcible returning of the piston 80 locked by the stopper 170 away from the disc rotor 50. As a result, the disk rotor 50 starts rotation and a side force arises between the both sides of the disk rotor 50 and the friction pads 60, 60 opposing to the both sides of the disk rotor 50 so that the friction pads 60, 60 are moved away from the disc rotor 50. Thus, the uneven wear of the linings of the friction pads 60,60 can be minimized as much as possible, since the side force prevents them from being dragged on the disc rotor 50. In addition to the normal braking operation as described above, a case is considered in the following where the vehicle is stopped continuously on a slope, for example. In this case, a dragging torque is created by the disc rotor 50 which acts on the friction pads 60, 60 in the direction of the vehicle being pulled down the slope. At the same time, the dragging torque acts on the piston 80 abutted with the friction pad 60 at the acting portion side, thus tilting the piston 80 in the direction of the rotation of the disc with respect to the disc axis. However, as the piston 80 is abutted against the output shaft 140 via the abutment surfaces 83 and 145 and resiliently locked with the stopper 170, the tilting of the piston 80 in the direction of the disc rotation occurs while compressing and deforming the stopper 170 and having its abutment surface 83 sliding on the abutment surface 145 of the output shaft 140. Thus, the dragging torque acting on the friction pad 60 only tilts the piston 80, while the posture of the output shaft 140 and screw member 110 is maintained along the disc axis. Therefore, the chances are eliminated of putting too much load on and thus wearing the internal thread 112 and the external thread 142, by which the screw member 110 is connected with the output shaft 140. The same goes for the multi-start internal and external threads 101 and 111, by which the sleeve nut 100 is connected with the screw member 110. Accordingly, the durability of the sleeve nut 100, the screw member 110 and the output shaft 140 can be improved. Furthermore, the interference with the braking operation which may occur when the biased load is put on the output shaft 140 or the screw member 110 can be prevented. In the following, another preferred embodiment of the present invention will be described by referring to FIG. 4, where explanations are omitted for similar or identical elements or components shown in FIGs. 1-3 by putting the same numerals. In the present embodiment, the portion of the output shaft 140 extending from the large-diameter portion 144 to its tip shown in FIGs. 1-3 is cut off, with the resultant omission of the stopper 170 at the tip of the shaft. Specifically, a piston 200 axially movably accommodated in the receiving bore 46 along the disc axis is formed by a bottomed cylinder with a bottom wall 201. The bottom wall 201 has a spherically concave abutment surface 202 formed on the side farther from the disc rotor. An output shaft 210 for pushing the piston 200 toward the disc rotor 50 comprises an shaft portion 211 extending from a sleeve nut 100 to the piston 200. The output shaft 210 also comprises an external thread 212 with a larger diameter which is continuously formed with the shaft portion 211 and which extends from the sleeve nut 100 away from the disc rotor 50. The external thread 212 has formed on its external end a knob 213. The shaft portion 211 has a flange-shaped large-diameter portion 214 formed at its tip. One side of the large-diameter portion 214 at the side facing the disc rotor is provided with an abutment surface 215 which spherically expands. Thus, the piston 200 is adapted to engage with the output shaft 210 via only the abutment between the abutment surface 202 of the piston 200 and the abutment surface 215 of the output shaft 210. Thus, in the present embodiment, the dragging torque acting on the friction pad 60 only tilts the piston 200 while leaving the output shaft 210 and the screw member 110 aligned with the disc axis. Accordingly, the chances are eliminated of putting too much load on and thus wearing the internal thread 112 of the screw member 110 and the external thread 212 of the output shaft 210, or the internal thread 101 of the sleeve nut 100 and the external thread 111 of the screw member 110. In the embodiment of FIG. 4, the abutment surface of the output shaft may be formed by grinding its end face in a spherical shape while leaving the diameter of the shaft as it is. Furthermore, the spherical abutment surfaces of the piston and the output shaft may be reversed from the above embodiment. Namely, the abutment surface of the piston may be formed in the shape of a convex, while forming that of the output shaft in a concave shape. Alternatively, both of the spherical abutment surfaces may be formed in the shape of a convex. The stopper fitted at the tip of the output shaft may comprise not only the wave washer as described in connection with the embodiments but spring washers or other types of resilient material such as a flexible or rigid resin and rubber. In the above-described embodiments, the sleeve nut continuously provided with the receiving bore for accommodating the piston constitutes a part of the receiving bore as designated by the present invention. Accordingly, the sleeve nut described in the above embodiments may be omitted, and the screw member to be disposed inside the receiving bore may directly screwed into the receiving bore. Also, the receiving bore (or the sleeve nut) does not necessarily have to be screwed into the screw member by means of the multi-start threads. WE CLAIM ;- 1. A mechanical disc brake (10) for vehicles comprising: a caliper body (40) having a receiving bore formed in an acting portion (41) disposed on one side of a disc rotor (50) / a bottomed cylindrical piston (80) housed in said receiving bore on the side facing said disc rotor (50) a screw member (110) screwed into an inner wall of said receiving bore on the side away from said disc rotor (50) ; and an output shaft (140) disposed between said screw member (110) and said piston (80) , wherein said output shaft and said screw member are integrally moved in the direction of said disc rotor (50) by the rotation of an input lever here by a friction pad (60) is pressed against one side of said disc rotor with the pressing motion of said piston abutting said output shaft, and of the abutment surfaces (83) of said output shaft (140) and said piston (80) , one abutment surface having the shape of a convex with a spherical surface, while the other is having in the shape of a concave or convex with a spherical surface. 2. A mechanical disc brake for vehicles as claimed in claim 1, wherein : the said output shaft (140) is provided with a large-diameter portion at a position on the distal side of the bottom wall (81) of the piston (80) with respect to said disc rotor (50) having a protruding portion formed on it; said large-diameter portion and the piston bottom wall (81) have opposing surfaces which are formed with said abutment surfaces (83) ; a through hole formed in said piston bottom wall along (81) the disc axis; wherein said protruding portion passing through said through hole and protruding beyond said piston (80) toward said disc rotor (50), is provided with a resilient stopper (170), thereby said piston (80) bottom wall is resiliently held by said stopper (170) and said large-diameter portion of said output shaft (140). 3. A mechanical disc brake for vehicles, substantially as hereinbefore described with reference to the accompanying drawings.

Documents:

1292-del-2001-abstract.pdf

1292-del-2001-claims.pdf

1292-del-2001-correspondence-others.pdf

1292-del-2001-correspondence-po.pdf

1292-del-2001-description (complete).pdf

1292-del-2001-drawings.pdf

1292-del-2001-form-19.pdf

1292-del-2001-form-2.pdf

1292-del-2001-form-3.pdf

1292-del-2001-form-5.pdf

1292-del-2001-form1.pdf

1292-del-2001-gpa.pdf

1292-del-2001-petition-137.pdf