Abstract:
A parking brake system including at least one braking unit actuated by at least one cable, a cylinder having a piston chamber and a rod chamber, a piston slidably received within the cylinder and having a rod connected thereto, the rod extending through the rod chamber and operably connected to the cable, a pressurized fluid source connected to the piston chamber, and a valve for controlling the flow of the fluid to the piston chamber, wherein the piston and rod move through the cylinder when the fluid pressurizes the piston chamber, thereby actuating the braking unit.

Description:
[0001]     This invention was made in the performance of a Cooperative Research and Development Agreement with the Department of the Air Force (Contract No. F33615-01-2-5804/CRADA 01-156-PR-01). Thus, the Government of the United States may have certain rights to the invention. 
     
    
     BACKGROUND  
       [0002]     The present invention is directed to a parking brake and, more particularly, to a hydraulically actuated parking brake.  
         [0003]     Parking brakes are typically used on various vehicles such as passenger cars, trucks, vans, utility vehicles, buses, freight vehicles, military vehicles, trolleys, locomotives and the like for securing the vehicle in a fixed location when the vehicle is not in use. A typical parking brake is a redundant means for securing the vehicle in a fixed location and therefore may be used in combination with a primary means for securing the vehicle in a fixed location (e.g., placing the vehicle in gear).  
         [0004]     Parking brakes typically include a braking unit mounted in the rear wheel brakes of the vehicle. A pedal or lever located in the passenger compartment of the vehicle is mechanically connected to the braking units by cables. When the pedal or lever is actuated, the cables exert a sufficient force on the braking units, thereby applying the rear wheel brakes and locking the vehicle in place.  
         [0005]     The mechanical connection between the pedal (or lever) in the passenger compartment and the braking units at the rear of the vehicle has several disadvantages. For example, the cable routings extending from the passenger compartment to the rear wheel brakes are expensive, occupy a significant amount of space and are cumbersome and difficult to install. Furthermore, the pedal (or lever) is typically positioned in an inconvenient location within the passenger compartment and requires a significant amount of components and labor to install.  
         [0006]     Accordingly, there is a need for a parking brake that may be hydraulically actuated and released with the push of a button.  
       SUMMARY  
       [0007]     One embodiment of the present invention is a parking brake system including at least one braking unit actuated by at least one cable, a cylinder having a piston chamber and a rod chamber, a piston slidably received within the cylinder and having a rod connected thereto, the rod extending through the rod chamber and operably connected to the cable, a pressurized fluid source connected to the piston chamber, and a valve for controlling the flow of the fluid to the piston chamber, wherein the piston and rod move through the cylinder when the fluid pressurizes the piston chamber, thereby actuating the braking unit.  
         [0008]     A second embodiment of the present invention provides a parking brake system including at least one braking unit actuated by at least one cable, a cylinder having a piston chamber and a rod chamber, a piston slidably received within the cylinder and having a rod connected thereto, the rod extending through the rod chamber and operably connected to the cable, a mandrel rotatably connected to the rod, a locking device operably associated with the mandrel, the locking device permitting rotation of the mandrel in a first direction and preventing rotation of the mandrel in a second direction, and a pressurized fluid source for selectively pressurizing the piston chamber such that the piston and rod extent through the cylinder and exert a force on the cable, thereby actuating the braking unit, wherein the locking device locks the piston and rod in the extended position.  
         [0009]     A third embodiment of the present invention provides a method for hydraulically actuating a parking brake including the steps of providing at least one braking unit having at least one actuating cable attached thereto, connecting the cable to a rod attached to a piston, the piston being slidably received within a cylinder having a piston chamber and a rod chamber, and supplying a pressurized fluid to the piston chamber, thereby extending the piston and rod out of the chamber such that the rod exerts a force on the cables, the force being sufficient to actuate the braking unit.  
         [0010]     Other embodiments, objects and advantages of the present invention will be apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a somewhat schematic front elevational view of a parking brake system of the present invention; and  
         [0012]      FIG. 2  is a top plan view of a detail of the parking brake system of  FIG. 1  showing a mechanical locking mechanism. 
     
    
     DETAILED DESCRIPTION  
       [0013]     As shown in  FIG. 1 , the parking brake system of the present invention, generally designated  10 , includes a housing  8 , a cylinder  12 , a piston  14 , a rod  16 , a mandrel  18 , a wrap spring  20 , a normally open solenoid valve  22 , a motor  24 , a power screw  26 , a shaft  28 , a valve  30 , a crossbar  32 , cables  34 ,  35  and a pressurized hydraulic fluid source  38 .  
         [0014]     The rod  16  includes a first end  44  and a second end  46  and may be generally rectangular in cross section. The rod  16  may include a rack  40  extending along an upper surface  42  of the rod  16 . The first end  44  of the rod  16  is connected to the piston  14  and the second end  46  is connected to the crossbar  32 .  
         [0015]     The crossbar  32  extends substantially perpendicular to the rod  16  and includes a first end  48  and a second end  50 . The first cable  34  is connected to the first end  48  of crossbar  32  and the second cable  35  is connected to the second end  50  of crossbar  32 . Each cable  34 ,  35  is also connected, at an opposite end, to a braking unit or device (not shown). The braking unit is actuated when a sufficient force, indicated by arrows F, is applied to the cables  34 ,  35  by crossbar  32 .  
         [0016]     The piston  14  is slidably received within the cylinder  12 , which is formed in the housing  8 , and forms a piston chamber  52  and a rod chamber  54  within the cylinder  12 . A gasket or seal  56  ensures a snug fit between the cylinder  12  and the piston  14 .  
         [0017]     The piston chamber  52  is in fluid communication with the fluid source  38  via fluid supply line  60  and valve  30  (that includes gaskets  31 ) and fluid exit line  70  via solenoid  22 . Fluid lines  60 ,  70  are defined within the housing  8 . The fluid source  38  may be any source or pressurized fluid (e.g., hydraulic oil). For example, the fluid source  38  may be a connection to the vehicle&#39;s anti-lock braking system or traction control system, thereby eliminating the need for additional pumps and/or compressors.  
         [0018]     The valve  30 , having a valve stem  90  and a valve seat  91 , is controlled by shaft  28 , motor  24  and power screw  26 . The shaft  28  includes a valve relief  62 , a release relief  64  and a threaded recess  66 . The threaded recess  66  receives the power screw  26  such that, when the motor  24  rotates the power screw  26  in a first direction, the shaft  28  moves in the direction shown by arrow A. Alternatively, when the motor  24  rotates the power screw  26  in the opposite direction, the shaft  28  moves in the direction shown by arrow B. Accordingly, the valve  30  may be opened and closed by operation of the motor  24 . The valve relief  62  allows the shaft  28  to move a predetermined distance prior to opening the valve  30 .  
         [0019]     Thus, the piston chamber  52  may be pressurized by closing solenoid  22  and opening valve  30  (as discussed above) such that fluid flows from the fluid source  38 , through the supply line  60 , and into the piston chamber  52 , thereby extending the piston  14 , rod  16  and crossbar  32  in the direction indicated by arrow C to apply force F on the cables  34 ,  35 , which is transmitted to a braking device (not shown).  
         [0020]     The mandrel  18  and wrap spring  20  mechanically secure the piston  14  and rod  16  in the extended (i.e., actuated) position. As shown in  FIG. 2 , a geared cylinder  74  and a central rod  72  are attached to the mandrel  18 . The central rod  72  is received in a circular recess (not shown) to allow the mandrel  18  and geared cylinder  74  to rotate about the axis of the central rod  72 . The geared cylinder  74  includes a plurality of gear teeth for engaging the rack  40 , thereby coupling the mandrel  18  to the rod  16 .  
         [0021]     The U-shaped wrap spring  20  is generally wound in a similar fashion as a torsion spring and includes a first end  76  and a second end  78 . The first end  76  is fixed and the second end  78  is free and extends into the release relief  64 . The radius of curvature of the wrap-spring  20  is slightly smaller than the radius of the mandrel  18  such that the mandrel  18  snugly fits into the wrap spring  20 . The snug fit of the wrap spring  20  permits rotation of the mandrel  18  in a first direction, shown by arrow D, but not is a second direction, shown by arrow E. Thus, the wrap spring  20  permits extension of the piston  14  and rod  16  (i.e., movement in the direction of arrow C) and prevents retraction of the piston  14  and rod  16  (i.e., movement in the direction of arrow G).  
         [0022]     The wrap spring  20  may be released by urging the second end  78  of the wrap spring  20  in the direction shown by arrow H, thereby increasing the radius of curvature of the wrap spring  20  and allowing the mandrel  18  to freely rotated in the direction of either arrow D or E. According to a first embodiment of the present invention, a release cable  80  is connected to the second end  78  of the wrap spring to provide a manual release. According to a second embodiment of the present invention, movement of the shaft  28  may release the wrap spring  20 . For example, when the shaft  28  is urged in the direction shown by arrow A, surface  65  of relief  64  engages the second end  78  of the wrap spring  20  and urges the second end  78  in the direction of arrow H, thereby releasing the mandrel  18  and rod  16 .  
         [0023]     According to an alternative embodiment of the present invention, the wrap spring  20  may be replaced with a ratcheting pall or other locking device or assembly for mechanically locking the piston and rod in the extended position. The ratcheting pall or other device or assembly should allow extension of the rod in the direction shown by arrow C, while preventing retraction of the rod in the direction shown by arrow G.  
         [0024]     Accordingly, the present invention provides a system  10  for hydraulically actuating a parking brake. The system  10  is initiated by an electrical switching device (not shown) such as a switch, a push button or the like located in the passenger compartment of the vehicle. When the switch is turned on, a signal is sent (via wire  25 , radio frequency or the like) to the solenoid  22  instructing the solenoid  22  to close, and to the motor  24 , instructing the motor  24  to rotate the power screw  26  such that the shaft  28  begins to move in the direction shown by arrow A. As the shaft  28  moves in the direction of arrow A, the relief  64  engages the second end  78  of the wrap spring  20  thereby releasing the wrap spring  20 . As the shaft  28  continues to extend beyond the length of the valve relief  62 , the valve  30  begins to open and hydraulic fluid pressure fills the piston chamber  52 .  
         [0025]     As the hydraulic fluid pressure fills the piston chamber  52 , the piston  14 , rod  16  and crossbar  32  begin to extend in the direction shown by arrow C. The extension applies a force F on the cables  34 ,  35 , thereby actuating the parking brake.  
         [0026]     Once the parking brake is fully actuated, the motor  24  rotates the power screw  26  in the opposite direction, thereby urging the shaft  28  in the direction shown by arrow B. As the shaft  28  moves in the direction of arrow B, the release relief  64  disengages the wrap spring  20 , thereby mechanically locking the piston  14 , rod  16  and crossbar  32  in the extended position. As the shaft  28  continues, the valve  30  is closed and hydraulic fluid is sealed in the supply line  60 , thereby pressurizing the line and holding piston  14  in chamber  52  to exert force F to lock the parking brake. Solenoid valve  22  may then be opened to release the pressure from the piston chamber  52 . However, due to the mechanical locking of the wrap spring  20  about the mandrel  18 , the piston  14 , rod  16  and crossbar  32  remain in the extended (i.e., actuated) position and continue to apply the force F to the cables  34 ,  35  until the wrap spring  20  is released by movement of shaft  28  in direction A (as discussed above).  
         [0027]     Although the invention is shown and described with respect to certain embodiments, equivalents and modifications will occur to those skilled in the art upon reading and understanding the specification. The present invention includes all such equivalents and modifications and is limited only by the scope of the claims.