Abstract:
A brake cylinder device with a built-in automatic shoe clearance adjustment device which prevents a chance of misassembly, loosing, or omitting the spacer. The brake cylinder device includes an adjustment bolt screwed into a pair of pistons symmetrically slidably positioned inside a cylinder body. A locator spring is positioned between both adjustment bolts. A locator is positioned at the end of the locator spring, and a spacer engages the top end of the locator and has a supporting portion to support the top end on the axis of the adjustment bolt. The supporting portion of the spacer has the front and back surfaces of the same shape.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a brake cylinder device with a built-in automatic shoe clearance adjustment mechanism. 
     2. Summary of the Related Art 
     FIG. 12 shows a conventional brake cylinder device with a built-in automatic shoe clearance adjustment mechanism. This conventional hydraulically actuating cylinder, positioned between adjacent facing ends of brake shoes, functions to automatically adjust clearances between a brake drum and the brake shoes in addition to its function to separate the brake shoes apart and to restrict the returning positions of the brake shoes. 
     This brake cylinder device is designed to be bilaterally symmetrical except for some parts such as a locator  380  in the central portion; therefore, an arrangement of the device at the right half is mainly explained here. A cylinder body  100  has a large diameter bore  110  with a bottom, a partition  130  having a small diameter bore  120  which is coaxial to the large diameter bore  110 , formed to be a fluid flow passage between opposed large diameter bores  110 ,  110  of the brake cylinder device via the small diameter bore  120 . An adjustment gear  210  is formed at the periphery on the right end of a piston  200  stroking out from the large diameter bore  110 , on which a piston head  220  is concentrically fit with a capacity to make a relative rotation. A notched groove  221  is formed at the right part of the piston head  220  to receive a shoe web of the brake shoe, not shown in FIG.  12 . 
     An adjustment bolt  300  is engaged in non-reversible screw threaded connection with an internal thread of a coaxial blind-end hole of the piston  200 . Here, “non-reversible screw threaded connection” means a screw threaded connection that does not cause relative rotation between the two members if a thrust force in the axial direction is transmitted on either one of the piston  200  or the adjustment bolt  300 . A first clutch face  310  in a conical shape formed at the left end of the adjustment bolt  300  makes a clutch engagement with a corresponding clutch face formed at the halfway of the small diameter bore  120  in the partition  130 . 
     A drive ring  320 , the outer peripheral surface of which is beveled to provide a clutch face into engagement with a corresponding internal clutch face formed on a projection of the partition  130  at the entrance of the small diameter bore  120 . Clutch engagements among the adjustment bolt  300 , the drive ring  320 , and the corresponding clutch faces of the cylinder body  100  are to be in conical shape in order to obtain a more stable rotational resistance than that of the clutch engagements with flat surfaces. The internal circumference of the drive ring  320  is provided with a fast thread, which is in mesh with a corresponding external thread  330  at the left side of the adjustment bolt  300  in a manner of reversible screw threaded connection with a slight gap (backlash hereinafter). Here, “reversible screw threaded connection” means a screw threaded connection that does cause relative rotation between the two members when a thrust force in the axial direction is applied on either one of the piston  200  or the adjustment bolt  300 . An adjustment spring  340  provided between the adjustment bolt  300  and the drive ring  320  constantly urges the drive ring  320  in the direction to be into clutch engagement with the corresponding internal clutch face of the cylinder body  100  by its spring force. 
     A through hole  350  with a shaped large diameter bore  360  is formed inside the adjustment bolt  300  extending in its axial direction. The large diameter bore  360  is formed at the left part of the through hole  350  via a stepped surface  351 , and there is a locator spring  370  positioned between facing two large diameter bores  360 ,  360  of the adjustment bolts  300 ,  300 . This locator spring  370  is to prevent free movement due to vibration caused while in braking operation by acting an urging force to the adjustment bolts  300 ,  300 . Moreover, the locator  380  and a spacer  390  are positioned between the right end of the locator spring  370  and the stepped surface  351 , so that a torsion force of the locator spring  370  does not affect on both adjustment bolts  300 ,  300 . Further, only the spacer  390  is positioned between the left end of the locator spring  370  and the stepped surface  351 . The reference number  400  is a piston cup defining a hydraulic chamber  140 ,  410  is a backup ring,  420  is a dust boot sealing the large diameter bore  110 , and  430  is an O-ring supporting the end of the adjustment bolt  300  in the side of the clutch face. 
     While in braking operation, upon pressurizing the hydraulic chamber  140  located at the bottom of the small diameter bore  120 ; the piston  200  moves the brake shoe outwardly into lining contact with the brake drum ultimately causing a braking effect. (It is noted that the shoe, lining, and drum are not shown in FIG.  12 . These components are known to those of ordinary skill in the art and no further explanation is warranted.) 
     The operation of the automatic shoe clearance adjustment mechanism is explained hereunder. While in braking operation, the adjustment bolt  300  moves together with the piston  200  outwardly. Now, if the lining wears out and an amount of outward movement of the adjustment bolt  300  takes up and exceeds the backlash between the drive ring  320  and the adjustment bolt  300 , the drive ring  320  is urged out of engagement with the corresponding clutch face and smoothly rotates. 
     When the brake is released and the adjacent brake shoe is retracted by the shoe return spring, (not shown in FIG.  12 ), the piston  200  and the adjustment bolt  300  return to the amount of the backlush, the drive ring  320  is urged once again strongly into clutching engagement disabling the rotation thereof, and the adjustment bolt  300  is thereafter caused to be rotated until the clutch face  310  at the left end of the adjustment bolt  300  comes into the clutch engagement and screwed out from the piston  200 . Accordingly, the retracted position of the piston  200  may be set in response to the amount of the lining wear. 
     As is evident from the above-described operation of the automatic shoe clearance adjustment, the locator spring  370  positioned between the facing large diameter bores  360 ,  360  of the pair of adjustment bolts  300 ,  300  is constantly urging the adjustment bolts  300 ,  300  in the axial direction in order to prevent the free movement due to vibration caused while in braking operation. However, because the torsion force of the locator spring  370  acting on the adjustment bolt  300  may result in unstable automatic shoe clearance adjustment operation, a conventional device provides the locator  380  and the spacer  390  between one end of the locator spring  370  and the stepped surface  351 . Here, the conventional device has the following points to be improved. 
     In order to act the force of the locator spring  370  to the axis center of the adjustment bolt  300 , the spacer  390  with a concave portion guiding the top of the locator  380  into the axis of the adjustment bolt  300  is used. However, this concave portion is provided only at one surface of the spacer  390 , there is a possibility of misassembling the spacer  390  into the large diameter bore  360  of the adjustment bolt  300 . 
     The piston cup  400 , the dust boot  420 , and the O-ring  430  used in the cylinder device are rubber or elastomeric members and need to be replaced periodically. Accordingly, there is a possibility of loosing the members or omitting a particular member during assembly and reassembly in addition to the above-described misassembly of the spacer  390  during reassembly. 
     This invention is made to improve the above-described points and is to provide a brake cylinder device with a built-in automatic shoe clearance adjustment mechanism enable to eliminate the possibility of loosing the members, omitting the particular member, and misassembling. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to a brake cylinder device with a built-in automatic shoe clearance adjustment mechanism. The device includes a pair of opposing pistons slidably fit in a cylinder bore of a cylinder body and a pair of adjustment bolts having a coaxial through hole. One end of each adjustment bolt is screwed into the piston with a non-reversible screw thread connection. The other end of each adjustment bolt is urged into clutching engagement with the cylinder body. A pair of drive rings, internally threadingly engage the other side of the adjustment bolt in a reversible screw thread connection with a backlash in the axial direction. The peripheral surface of the drive ring is urged by an adjustment spring into clutching engagement with a partition of the cylinder body. The pistons, adjustment bolts, adjustment springs, and drive rings are provided oppositely and symmetrically in the cylinder bore. A locator spring is positioned between two facing adjustment bolts. A locator is placed in the vicinity of the end of the locator spring. A spacer is placed between the top end of the locator and one of the adjustment bolts, having a supporting portion which engages with and supports the top end of the locator along the axis of the adjustment bolt. A fluid flow passage penetrates through the spacer, wherein the supporting portions formed on the axial center of the spacer are identically shaped both on the front and back surfaces thereof. 
     The top end of the locator has a conical shaped portion (convex shape) and the supporting portion of the spacer has a tapered concave portion. The spacer supports the top end of the locator and the conical shaped portion is disposed within and engages the tapered concave portion of the space. An angle of the tapered concave portion is designed to be larger than an angle of the conical shape top end of the locator to define a point contact between the conical shaped top end and the tapered concave portion. 
     The locators are preferably positioned one each adjacent side of the locator spring and the spacers are disposed between the top end of both locators and an associated adjustment bolt. The spacer is preferably symmetrically formed to have front and back surfaces of the same shape. The spacer is integrally pressed in the through hole of the adjustment bolt and is substantially integrated therewith. The outer circumferential diameter on the back and front surfaces of the spacer is preferably designed to be smaller than an inner diameter of the through hole of adjustment bolt. The locator is urged by the locator spring such that the top end of the locator and the supporting portion of the spacer are aligned with the axis of the adjustment bolt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1 is a sectional view of the brake cylinder device according to the present invention; 
     FIG. 2 is a sectional view of the adjustment bolt assembly; 
     FIG. 3 is a partial sectional view of the locator spring integrated with the locator at one end of the locator spring; 
     FIG. 4 is a partial sectional view of the locator spring integrated with the locator at both ends of locator spring; 
     FIG. 5 is a plan view of the spacer; 
     FIG. 6 is a longitudinal sectional view of the spacer in FIG. 5 with a curved peripheral surface; 
     FIG. 7 is a longitudinal sectional view of the spacer in FIG. 5 with a chamfered circumference; 
     FIG. 8 is a partial sectional view of another locator and spacer according to an alternate embodiment of the present invention; 
     FIG. 9 is a plan view of the clip of the piston head; 
     FIG. 10 is a left side view of the clip of FIG. 9; 
     FIG. 11 is a top view of the clip of FIG. 9; and 
     FIG. 12 is a sectional view of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of the invention is explained with reference to the figures. The brake cylinder device of the present invention includes many corresponding components as shown in the conventional art of FIG.  12  and are identified with the same reference numerals for the sake of brevity and avoiding redundant explanation of the common components previously described. 
     As shown in FIG. 1, a locator spring  500  is positioned between the facing large diameter bores  360 ,  360  on the axis of both adjustment bolts  300 ,  300 , which gives an urging force on the axis of the adjustment bolts  300 ,  300  in order to prevent the free movement of the adjustment bolts  300 ,  300  due to vibration caused during the braking operation. The locator spring  500  is of a taper-like compression coil spring. The locator spring  500  has two turns parallel the right end and the outside diameter of one turn adjacent the left end is slightly smaller than the large diameter bore  360 . Here, a substantial part of the locator spring  500  is disposed in the large diameter bores  360 ,  360  of both adjustment bolts  300 ,  300 , which minimize the entire length of the cylinder device. 
     As shown in FIGS. 1 and 3, the locator spring  500  has a locator  600  at one end. The parallel turns at one end of the locator spring  500  are pressed to be installed between a large diameter flange  610  and a small diameter flange  620 , both projecting from the locator  600 . In addition, the locator spring  500  and the locator  600  are desirably integrated for convenient handling. Further, the top end of the locator  600  has a projected conical shaped abutment (convex portion)  630 . 
     Referring to FIGS. 1 and 2, the spacer  700  positioned between the stepped surface  351  of the adjustment bolt  300  and the locator  600  may be provided only in one large diameter bore  360  considering the automatic shoe clearance function. However, the spacer  700  should be provided in both large diameter bores  360 ,  360  of the facing adjustment bolts  300 ,  300  in terms of avoiding the possibility of misassembly. 
     As shown in FIGS. 5-7, the spacer  700  has conical supporting portions (tapered concave portions)  710 ,  710  at its center of the front and back surfaces thereof, where the top end of the abutment (convex portion)  630  of the locator  600  is supported on the axis of the adjustment bolt  300 , and has a plurality of fluid flow passages  720  around an outer periphery thereof to permit the fluid passing through. Accordingly, if the supporting portions, i.e., the concave portions  710 ,  710 , are provided at the center on the front and back surfaces of the spacer  700 , there is no need to be concerned about the side of the spacer  700  during assembly. In addition, the passage  720  is at least, but not limited to, a shape capable of fluid flow between the hydraulic chamber  140  and the through hole  350  passing through the adjustment bolt  300  for the improvement of air bleeding. 
     Providing the locator  600  and the spacer  700  in the above described manner, the spring force of the locator spring  500  acts on the axial center of the adjustment bolt  300 . Thus, no biased load is generated on the adjustment bolt  300 , and the torsion force by the locator spring  500  affecting the adjustment bolt  300  is prevented, thereby enabling a stable automatic shoe clearance adjustment operation. 
     Furthermore, during assembly, the spring force of the locator spring  500  causes the top end of the abutment (convex portion)  630  to slide along the supporting portion (concave portion)  710  of the spacer  700  to automatically adjust its position on the axis of the adjustment bolt  300  so that the top end of the abutment (convex portion)  630  of the locator  600  does not deviate from the axis of the adjustment bolt  300 . To that end, the outside diameter of the locator spring  500  relative to the inside diameter of the large diameter bore  360  of the adjustment bolt  300 , the outside diameter of the large diameter flange  610  of the locator  600 , or the size and shape, of the supporting portion (concave portion)  710  of the spacer  700  may be appropriately selected. 
     In addition, FIG. 1 shows a case when the spacers  700 ,  700  are positioned on the right and left side of the device while the locator  600  is positioned only at one end of the locator spring  500 . However, the positions of the locator  600  and the locator spring  500  as appear in FIG. 1 may be reversed without detracting from their respective functions. Here, these members are bilaterally non-symmetrical, which increases a possibility for the operator to misassemble the members. However, if the spacers  700 ,  700  are provided at both sides, the locators  600 ,  600  may also be provided at both sides of the locator spring  500  to maintain bilateral symmetry as shown in FIG.  4 . Such an arrangement completely eliminates a possibility for misassembly. In such case, the locator spring  500  is in the form of a barrel shape. 
     The top end of the abutment (convex portion)  630  of the locator  600  is angled to be smaller than the angle of the concave portion  710  of the spacer  700  so that a convex-concave engagement between the two members creates a point contact. This eliminates the necessity of using a low friction material or coating the locator  600  and the spacer  700 , which reduces the manufacturing cost. 
     In addition, as is evident from the above explanation, the spacer  700  functions to act the force by the locator spring  500  on the axis of the adjustment bolt  300  and to permit the fluid flow between the hydraulic chamber  140  and the through hole  350 . Therefore, although it is not necessary for the front and back surfaces of the spacer  700  to have the same size and shape as shown in FIGS. 5-7, having the same size and shape enables a common design thus facilitating manufacture and reducing the cost. The spacer  700  may be integrally processed by sintered alloy steel, aluminum die-cast, or heat resistant thermoplastic resin, thereby further facilitating the manufacture and reducing costs. 
     Also, as a means to position the spacer  700 , the peripheral surface of the spacer  700  may be pressed in the inner circumferential surface of the large diameter bore  360  in the adjustment bolt  300  so as to facilitate the handling of the members and eliminate a problem of omitting the particular member. In this case, however, the diameter of circumference of the spacer  700  is designed (specified) to be smaller than the inside diameter of the large diameter bore  360  of the adjustment bolt  300  to avoid causing a scratch at the circumference of the front and back surfaces thereof when the spacer  700  is pressed in. For example as shown in FIG. 6, the intermediate portion of the peripheral surface of the spacer  700  may be projected to form a curved portion  730  which is pressed to engage the inner circumferential surface of the large diameter bore  360 , where the circumferences of the front and back surfaces do not contact the large diameter bore  360 . In addition, as shown in FIG. 7, chamfers  740  may be employed instead of the above described curved structure. 
     Here, the above-described embodiment of this invention explains about an example where the locator  600  has the conical shaped abutment (convex portion)  630  and the spacer  700  has the concave portion  710 . However, as shown in FIG. 8, the concave portion  630 A may be formed at the top end of the locator  600 , and the conical shaped abutment (convex portion)  710 A may be formed at the supporting portion of the spacer  700  to obtain the same effective result. 
     A piston clip  800 , as shown in FIG.  1  and FIGS. 9-11, comprises an attachment section  810  clamping the peripheral surface of a piston head  220  for its installment and an engagement section  820  engaging with the adjustment gear  210  at the front end of the piston  200 . The attachment section  810 , has a notched end to give an elastic force, and the engagement section  820  is folded from one side surface to form a reverse-U shape having a protuberance inside an adjacent end end. 
     The piston clip  800  increases the rotational resistance of the piston  200  in order to securely prevent the rotation of the piston  200  due to vibration and make the piston  200  substantially integrated with the piston head  220 . Further, when the adjustment gear  210  of the piston  200  is rotated to be adjusted by a tool from outside of the brake. The piston clip  800  has a function to allow for manual adjustment by considering if the U-shaped piston clip  800  is twisted to give a feeling of rotating over the pitch or to give a hammering (impact) noise due to the springing force. 
     The above-structure of this invention provides the following advantages. 
     Designing the front and back surfaces of the spacer to have the same shape enables to give common members, thereby facilitating the manufacture and preventing the misassembly. 
     The spacer may be integrally processed which also facilitates the manufacture. 
     The spacer may be pressed in the bore of the adjustment bolt to be substantially integrated with the adjustment bolt, which facilitates the handling of the members and eliminates a possibility of omitting the particular member when performing maintenance work. 
     The outside diameter of the circumferences at the front and back surfaces of the spacer is designed (specified) to be smaller than the inside diameter of the large diameter bore at the part of the through hole of the adjustment bolt to avoid causing a scratch at the circumference of the front and back surfaces when the spacer  700  is pressed in. This arrangement eliminates a chance of contamination by dust due to scratches and prevents biting in the piston cup or the O-ring. 
     Providing a spacer in a large diameter bore of both adjustment bolts eliminates a chance of misassembling the members. In addition, the spacer and the locator may be positioned at both sides of the locator spring, which also eliminates a chance of misassembly and gives a more stable automatic shoe clearance adjustment operation compared to the case when the locator is positioned only in one of the large diameter holes. 
     The angle of the concave portion is designed to be larger than that of the conical shaped abutment (convex portion) so that a convex-concave engagement of the locator and the spacer becomes a point contact. This reduces the manufacturing cost and facilitates a stable automatic shoe clearance adjustment operation without having an effect of torsion force by the locator spring on the adjustment bolt. 
     Integrating the locator spring with the locator positioned in the bore of the adjustment bolt facilitates handling and eliminates the chance of omitting the members when conducting maintenance. 
     While in assembling, the spring force of the locator spring causes the top end of the locator to slides along the supporting portion of the spacer to automatically align its position on the axial center of the adjustment bolt so that the top end of the locator does not deviate from the axis of the adjustment bolt. Therefore, even an unskilled person may give a urging force of the locator spring on the axis of the adjustment bolt, thereby giving a stable automatic shoe clearance adjustment operation. 
     While the foregoing invention has been shown and described with reference to a preferred embodiment, it will be understood by those possessing skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.