Abstract:
A spring brake actuator comprises a housing including a first housing portion and a second housing portion. A spring disposed in the housing exerts a biasing force tending to separate the first housing portion from the second housing portion. A band clamp connects the first housing portion with the second housing portion. The band clamp comprises at least one band segment engaging the first and second housing portions, at least one fastener securing the band segment in a tamper-resistant manner, and a cover at least partially enclosing the fastener in a tamper-resistant manner.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a spring brake actuator for use in a compressed air braking system of a vehicle. In particular, this invention relates to a mechanism for holding together the parts of the actuator housing, which encloses a powerful spring, in a tamper-resistant manner.  
         BACKGROUND OF THE INVENTION  
         [0002]    Many commercial vehicles use braking systems operated by compressed air. These systems commonly include a spring brake actuator, which is a mechanism that sets the vehicle brakes when compressed air is no longer provided to the system, such as when parking. A common type of spring brake actuator has a housing defining two chambers. Compressed air is selectively introduced into a first chamber to move a piston, push an actuator rod, and thereby operate the brake in a service brake manner. In a second chamber, compressed air constantly holds a second piston, connected with the actuator rod, in a disengaged position, whenever the vehicle is in operation. The compressed air in the second chamber acts against the bias of a powerful spring, compressing the spring. Should the air pressure in the second chamber decrease, for example when the vehicle is turned off to park, the spring expands and pushes the actuator rod to set and hold the brake in a parking brake manner.  
           [0003]    The spring must be powerful enough to set the vehicle brake by itself. The spring is held in a multi-part housing that forms part of the spring brake actuator. The spring is enclosed inside the housing at the factory. It is important that the housing be maintained in a closed condition when the actuator is in use in the field. Disassembling the housing could lead to a rapid release of the large amount of energy stored in the spring.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention relates to a spring brake actuator comprising a housing including a first housing portion and a second housing portion. A spring disposed in the housing exerts a biasing force tending to separate the first housing portion from the second housing portion. In one embodiment, a band clamp connects the first housing portion with the second housing portion. The band clamp comprises at least one band segment engaging the first and second housing portions, at least one fastener securing the band segment in a tamper-resistant manner, and a cover at least partially enclosing the fastener in a tamper-resistant manner. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, in which:  
         [0006]    [0006]FIG. 1 is an elevational view, partially in section, of a spring brake actuator including a band clamp in accordance with a first embodiment of the present invention;  
         [0007]    [0007]FIG. 2 is an enlarged sectional view of a portion of the actuator of FIG. 1, taken through a portion of the band clamp not including a fastener;  
         [0008]    [0008]FIG. 3 is a plan view of a portion of the actuator of FIG. 1 including a tamper-resistant fastener;  
         [0009]    [0009]FIG. 4 is a plan view of the band clamp shown in a disassembled condition;  
         [0010]    [0010]FIG. 5 is a plan view of the band clamp shown in a partially assembled condition;  
         [0011]    [0011]FIG. 6 is a plan view of the band clamp shown in a fully assembled condition;  
         [0012]    [0012]FIG. 7 is an elevational view of the band clamp shown in a partially assembled condition;  
         [0013]    [0013]FIG. 8 is an elevational view of the band clamp shown in a fully assembled condition; and  
         [0014]    [0014]FIG. 9 is a sectional view taken generally along line  9 - 9  of FIG. 8. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    This invention relates to a spring brake actuator for use in a compressed air braking system of a vehicle. In particular, this invention relates to a mechanism for holding together the parts of the actuator housing, which encloses a powerful spring, in a tamper-resistant manner. The invention is applicable to various spring brake actuator constructions. As representative of the present invention, FIG. 1 illustrates a spring brake actuator  10  constructed in accordance with a first embodiment of the invention.  
         [0016]    The actuator  10  includes a housing  12 . The housing  12  includes a first portion  20  centered on an axis  22  of the actuator  10 . In the illustrated embodiment, the first housing portion  20  (an upper portion as viewed in FIG. 1) is formed of sheet metal, although in other embodiments it could be formed differently, for example, as a casting. The first housing portion  20  has an annular, radially projecting flange  26  (FIG. 2).  
         [0017]    The housing  12  also includes a second housing portion  30  (FIG. 1) centered on the axis  22 . In the illustrated embodiment, the second housing portion  30  (an intermediate portion as viewed in FIG. 1) is a metal casting, although in other embodiments it could be formed differently, for example, as a stamping. The second housing portion  30  has an annular, radially projecting flange  32  (FIG. 2) that is adjacent the flange  26  of the first housing portion  20 .  
         [0018]    The actuator  10  includes a band clamp  80  that secures the first housing portion  20  to the second housing portion  30  by clamping together the flanges  26  and  32 . The band clamp  80  is described below in detail.  
         [0019]    The housing  12  further includes a third housing portion  34  centered on the axis  22 . In the illustrated embodiment, the third housing portion  34  (a lower portion as viewed in FIG. 1) is also a metal casting, although in other embodiments it could be formed differently, for example, as a stamping. The actuator  10  includes a known clamp assembly  36  that secures the third housing portion  34  to the second housing portion.  
         [0020]    The three housing portions  20 ,  30  and  34  define two chambers in the actuator  10 . A first chamber  40  is defined between the first housing portion  20  and the second housing portion  30 . A second chamber  42  is defined between the second housing portion  30  and the third housing portion  34 .  
         [0021]    The actuator  10  includes a first diaphragm  44 . The first diaphragm  44  has an outer edge portion  46  (FIG. 2) clamped between the flange  26  of the first housing portion  20  and the flange  32  of the second housing portion  30 . The first diaphragm  44  is movable in the first chamber  40  in a direction along the axis  22 .  
         [0022]    The actuator  10  also includes a second diaphragm  48 . The second diaphragm  48  has an outer edge portion  49  (FIG. 1) clamped between the second housing portion  30  and the third housing portion  34 . The second diaphragm  48  is movable in the second chamber  42  in a direction along the axis  22 .  
         [0023]    A power spring  50  and a first piston  52  are located in the first chamber  40  of the actuator  10 . A first actuator rod portion  53  is connected with the first piston  52 . The first piston  52  is in abutting engagement with an upper (as viewed in FIG. 1) side surface  54  of the first diaphragm  44 . The power spring  50  acts between the first housing portion  20  and the first piston  52  to bias the first piston and thereby the first diaphragm  44  in a direction toward the second chamber  42 , that is, in a downward direction as viewed in FIG. 1.  
         [0024]    A second piston  56  and a return spring  58  are also located in the first chamber  40  of the actuator  10 . The second piston  56  is in abutting engagement with a lower (as viewed in FIG. 1) side surface  60  of the first diaphragm  44 , opposite the first piston  52 . The return spring  58  acts between the second housing portion  30  and the second piston  56  to bias the second piston and thereby the first diaphragm  44  in a direction toward the power spring  50 , that is, in an upward direction as viewed in FIG. 1.  
         [0025]    A second actuator rod portion  62  connects the second piston  56  for movement with a third piston  64 . The third piston  64  is located in the second chamber  42  and is in abutting engagement with an upper (as viewed in FIG. 1) side surface  66  of the second diaphragm  48 .  
         [0026]    A fourth piston  68  and a return spring  70  are also located in the second chamber  42  of the actuator  10 . The fourth piston  68  is in abutting engagement with a lower (as viewed in FIG. 1) side surface  72  of the second diaphragm  48 , opposite the third piston  64 . The return spring  70  acts between the third housing portion  34  and the fourth piston  68  to bias the fourth piston and thereby the second diaphragm  48  in a direction toward the first chamber  40 , that is, in an upward direction as viewed in FIG. 1. A third actuator rod portion  74  is connected for movement with the fourth piston  68  and terminates in a mounting ear  76 .  
         [0027]    The spring brake actuator  10  is operable in a known manner to move the third actuator rod portion  74  in a reciprocal manner to actuate a vehicle brake (not shown) connected with the mounting ear  76 . Specifically, the first chamber  40  is normally pressurized with air under high pressure that keeps the second piston  56  and the first diaphragm  44  in the position shown in FIG. 1, in which the power spring  50  is substantially fully compressed.  
         [0028]    When the vehicle brake is to be actuated, air under pressure is introduced into an upper portion of the second chamber  42 , through a port not shown. The second diaphragm  48  moves downward, along with the fourth piston  68 , against the bias of the return spring  70 . This movement causes the third portion  74  of the actuator rod to move the mounting ear  76 , in turn causing the vehicle brake to be actuated (set).  
         [0029]    When the vehicle is turned off, or in an emergency situation, the air pressure in the first chamber  40  is decreased significantly. The force of the power spring  50  then acts to push the pistons  52 ,  56 ,  64  and  68 , and the actuator rod portions  53 ,  62  and  74 , in a direction (downward as viewed in FIG. 1) to actuate the vehicle brake. The power spring  50  is strong enough to actuate the vehicle brake, and to maintain it in an actuated condition to prevent the associated vehicle wheel from turning, without air pressure in the vehicle braking system. The power spring  50  is in a partially compressed condition when the brake is thus set.  
         [0030]    Because the power spring  50  stores so much energy when even partially compressed, it is important that the first and second housing portions  20  and  30  be securely held together when the actuator  10  is in use in the field. Tampering with or disassembling the housing  12  when the power spring  50  is even partially compressed could lead to a rapid release of a large amount of energy stored in the power spring.  
         [0031]    In the spring brake actuator  10 , the band clamp  80  secures together the first and second housing portions  20  and  30  in a tamper-resistant manner. The band clamp  80  includes one or more band clamp segments. In the illustrated embodiment, the band clamp  80  includes two band clamp segments  82 . In other embodiments, a different number of segments can be used; for example, a clamp having only one segment that extends completely around the housing  12  is possible.  
         [0032]    The two band clamp segments  82  in the illustrated embodiment are mirror images of each other. Each one of the band clamp segments  82  (FIGS.  4 - 6 ) includes first and second opposite end portions  84  and  86  and an intermediate portion  88 . The intermediate portion  88  extends for approximately 180 degrees around the axis  22  and has an arcuate configuration centered on the axis. Each one of the first and second end portions  84  and  86  of the band segment  82  is formed as an ear that projects radially outward from the intermediate portion  88  and that has a fastener opening  98 .  
         [0033]    The intermediate portion  88  has a generally U-shaped cross-sectional configuration (FIGS.  7 - 9 ) including opposite side walls  90  and  92  defining a channel  94 . The side walls  90  and  92  have facing angled internal surfaces  96  and  98 , respectively.  
         [0034]    In addition to the clamp segments  82 , the band clamp  80  also includes one or more fasteners for securing the band clamp to the housing  12 . In the illustrated embodiment, two fasteners  100  are provided which are identical to each other. Each fastener  100  includes a bolt  102  and a nut  104 . In other embodiments, a different number of fasteners can be provided; for example, a band clamp  80  having a single band segment would need only one fastener.  
         [0035]    The band clamp  80  also includes one or more covers for covering the fasteners of the band clamp. In the illustrated embodiment, two covers  110  are provided which are identical to each other. In other embodiments, a different number of covers can be provided; for example, a band clamp  80  having a single band segment would need only one cover.  
         [0036]    Each cover  110 , as illustrated, is preferably stamped from sheet metal and is shaped like a cap adapted to fit over end portions of the clamp segments  82  when the fasteners  100  are in position. Each cover  110  includes opposite side walls  112  and  114  in which are formed two fastener openings  116  and  118  aligned with each other. The side walls  112  and  114  are joined by an arcuate end wall  120 .  
         [0037]    When the band clamp  80  is applied to the housing  12  during assembly of the actuator  10 , the two band segments  82  are placed on the flanges  26  and  32  of the first and second housing portions  20  and  30  respectively. The band segments  82  extend around and engage both flanges  26  and  32 .  
         [0038]    A first one of the bolts  102  (FIG. 3) is inserted through the fastener openings  98  in the first end portions  84  of the band segments  82 . The head of the first bolt  102  engages the first end portion  84  of one band segment  82 . A nut  104  is screwed on the bolt  102  and engages the first end portion  84  of the other band segment  82 , as shown in FIG. 3.  
         [0039]    A second bolt  102  (FIG. 4- 6 ) is inserted through the fastener opening  98  in the second end portion  86  of one band segment  82 . The head of the second bolt  102  engages the second end portion  86  of the one band segment  82 . The second nut  104  is screwed on the second bolt  102  and engages the second end portion  86  of the other band segment  82 .  
         [0040]    The first and second fasteners  100  are tightened to a predetermined torque level. As this occurs, the angled inner surfaces  96  and  98  of the side walls  90  and  92  of the intermediate portions  88  of the band segments  82  draw the two housing flanges  26  and  32  together axially, with the first diaphragm  44  between them. The dimensions of the fasteners  100 , and the dimensions and materials of the band segments  82 , are selected so that the intermediate portions  88  of the band segments do not deform when the fasteners  100  are tightened. The band segment end portions  84  and  86  may deform slightly when the fasteners  100  are tightened. Deformation of the band segments  82  is not needed to clamp the flanges  26  and  32  together securely.  
         [0041]    The nuts  104  are then welded to the bolts  102  as shown at  106  in FIGS. 3 and 5- 6 . The welding of the nuts  104  to the bolts  102  resists tampering with the band clamp  80 , specifically, resists removal of the first and second fasteners  100  from the band clamp. The welding could be done in another manner, for example, the bolts  102  or the nuts  104  could be welded to the band segments.  
         [0042]    The covers  110  are then assembled with the other parts of the band clamp  80  as shown in FIGS.  4 - 9 . One cover  110  is placed in a position enclosing the first end portions  84  of the band segments  82  and also enclosing the associated fastener  100 . When the cover  110  is thus in position, the fastener openings  116  and  118  in the side walls  112  and  114  of the cover are located behind (radially inward of) the shank of the bolt  102 .  
         [0043]    The cover  110  is then secured in position on the band clamp  80 , in a tamper-resistant manner. In the illustrated embodiment, the cover  110  is riveted in position; in other embodiments, the cover could be secured in other tamper-resistant manners.  
         [0044]    Specifically, a rivet  130  is inserted through the fastener openings  116  and  118  in the side walls  112  and  114  of the cover  110 . The rivet  130  extends behind (radially inward of) the bolt  102 . The rivet  130  is headed to secure the rivet to the cover  110 . When the rivet  130  is thus secured to the cover  110 , the rivet, which is located behind the bolt  102 , resists removal of the cover from the band clamp  80 .  
         [0045]    The length of the rivet  130  is selected so that when the rivet is headed, the two walls  112  and  114  of the cover  110  are deformed inward into engagement with the first end portions  84  of the band segments  82 . This engagement helps to prevent rattling of the cover  110  and also helps to secure the cover in position on the band clamp  80 .  
         [0046]    In a similar tamper-resistant manner, the other cover  110  is secured in a position enclosing the second end portions  86  of the band segments  82  and also enclosing the other fastener  100 .  
         [0047]    From the above description of the invention, those skilled in the art will perceive improvements, changes, and modifications in the invention. Such improvements, changes, and modifications within the skill of the art are intended to be included within the scope of the appended claims.