Abstract:
A brake actuator includes an actuator body, a piston held in the actuator body, and an actuator rod coupled to the piston and coupleable to a brake to actuate the brake. A method of operating the brake actuator includes maintaining a first fluid pressure of a first fluid against a first side of the piston to urge the piston in a brake-actuating direction, and controlling a second fluid pressure of a second fluid against a second side of the piston opposite the first side of the piston to move the piston controllably in a brake-releasing direction. A brake system including the brake actuator is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The invention relates generally to braking, and more particularly to a brake actuator, a method of operating the brake actuator, and a system including the brake actuator. 
         [0003]    2. Description of Related Art 
         [0004]    A conventional fail-safe brake system includes a brake actuator having a piston coupleable to a brake to actuate the brake. Such a conventional brake actuator includes one or more springs that urge the piston in a brake-actuating direction. Pressurized air, for example, controllably moves the piston in a brake-releasing direction opposite the brake-actuating direction and against the resilient force of the one or more springs to release the brake or to vary a degree of actuation of the brake. Such brake systems may be referred to as fail-safe brake systems because if a source of the pressurized air fails, the one or more springs urge the piston in the brake-actuating direction to actuate the brake. 
         [0005]    However, the one or more springs in such a conventional fail-safe brake actuator wear over time, and exert less force as they extend from more-compressed positions to less-compressed positions. As the one or more springs wear over time, the fail-safe function of these brake systems diminishes, and therefore, disadvantageously, the one or more springs must be periodically replaced. Also, the one or more springs in these brake systems generally extend over significant lengths, thereby increasing the overall length, size, and weight of the brake actuator. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with one aspect of the invention, there is provided a method of operating a brake actuator having a piston coupleable to a brake to actuate the brake. The method involves maintaining a first fluid pressure of a first fluid against a first side of the piston to urge the piston in a brake-actuating direction, and controlling a second fluid pressure of a second fluid against a second side of the piston opposite the first side of the piston to move the piston controllably in a brake-releasing direction opposite the brake-actuating direction. 
         [0007]    Maintaining the first fluid pressure of the first fluid against the first side of the piston may involve supplying the first fluid through a check valve to a pressurized fluid reservoir in fluid communication with the first side of the piston, and preventing the first fluid from escaping the pressurized fluid reservoir through the check valve. 
         [0008]    Supplying the first fluid through the check valve to the pressurized fluid reservoir may involve supplying the first fluid through the check valve to the pressurized fluid reservoir through a pressure regulator until the first fluid in the pressurized fluid reservoir reaches the first fluid pressure. 
         [0009]    The first fluid may include gas. 
         [0010]    Controlling the second fluid pressure of the second fluid against the second side of the piston may involve supplying the second fluid at a third fluid pressure greater than the first fluid pressure to a control valve in fluid communication with the second side of the piston. 
         [0011]    The second fluid may include gas. 
         [0012]    The second fluid may include hydraulic fluid. 
         [0013]    In accordance with another aspect of the invention, there is provided a brake actuator. The brake actuator includes a piston having first and second opposite sides. The brake actuator also includes an actuator body having an inner surface defining a cavity holding the piston in sealed and slidable engagement with the inner surface such that the piston defines first and second chambers in the cavity on the first and second sides of the piston respectively, the actuator body having a first opening in fluid communication with the first chamber for receiving a first pressurized fluid, a second opening in fluid communication with the second chamber for receiving a second pressurized fluid, and a third opening in communication with the second chamber. The brake actuator also includes an actuator rod coupled to the piston on the second side of the piston, extending in sealed and slidable engagement with the actuator body through the third opening, and coupleable to a brake to actuate the brake. 
         [0014]    In accordance with another aspect of the invention, there is provided a brake system. The brake system includes a brake actuator. The brake actuator includes a piston having first and second opposite sides. The brake actuator also includes an actuator body having an inner surface defining a cavity holding the piston in sealed and slidable engagement with the inner surface such that the piston defines first and second chambers in the cavity on the first and second sides of the piston respectively, the actuator body having a first opening in fluid communication with the first chamber for receiving a first pressurized fluid, a second opening in fluid communication with the second chamber for receiving a second pressurized fluid, and a third opening in communication with the second chamber. The brake actuator also includes an actuator rod coupled to the piston on the second side of the piston, extending in sealed and slidable engagement with the actuator body through the third opening, and coupleable to a brake to actuate the brake. The brake system also includes means, in fluid communication with the first opening of the actuator body, for maintaining a first fluid pressure of the first fluid against the first side of the piston to urge the piston and the actuator rod in a brake-actuating direction. The brake system also includes means, in fluid communication with the second opening of the actuator body, for controlling a second fluid pressure of the second fluid against the second side of the piston to move the piston and the actuator rod controllably in a brake-releasing direction opposite the brake-actuating direction. 
         [0015]    The means for maintaining the first fluid pressure of the first fluid against the first side of the piston may include a pressurized fluid reservoir in fluid communication with the first opening of the actuator body, and a check valve in fluid communication with the pressurized fluid reservoir, the check valve configured to permit the first fluid to be supplied therethrough to the pressurized fluid reservoir and configured to prevent the first fluid from escaping the pressurized fluid reservoir therethrough. 
         [0016]    The means for maintaining the first fluid pressure of the first fluid against the first side of the piston further may include a pressure regulator in fluid communication with the check valve and configured to permit the first fluid to be supplied to the pressurized fluid reservoir through the check valve until the first fluid in the fluid reservoir reaches the first fluid pressure. 
         [0017]    The system may further include means for supplying the first fluid to the pressure regulator. 
         [0018]    The first fluid may include gas. 
         [0019]    The means for controlling the second fluid pressure of the second fluid against the second side of the piston may include a control valve in fluid communication with the second opening of the actuator body, and means for supplying the second fluid to the control valve at a third fluid pressure greater than the first fluid pressure. 
         [0020]    The second fluid may include gas. 
         [0021]    The second fluid may include hydraulic fluid. 
         [0022]    In accordance with another aspect of the invention, there is provided a brake system. The brake system includes a brake actuator. The brake actuator includes a piston having first and second opposite sides. The brake actuator also includes an actuator body having an inner surface defining a cavity holding the piston in sealed and slidable engagement with the inner surface such that the piston defines first and second chambers in the cavity on the first and second sides of the piston respectively, the actuator body having a first opening in fluid communication with the first chamber for receiving a first pressurized fluid, a second opening in fluid communication with the second chamber for receiving a second pressurized fluid, and a third opening in communication with the second chamber. The brake actuator also includes an actuator rod coupled to the piston on the second side of the piston, extending in sealed and slidable engagement with the actuator body through the third opening, and coupleable to a brake to actuate the brake. The brake system also includes a first pressurized fluid source in fluid communication with the first opening of the actuator body and configured to maintain a first fluid pressure of the first fluid against the first side of the piston to urge the piston and the actuator rod in a brake-actuating direction. The brake system also includes a second pressurized fluid source in fluid communication with the second opening of the actuator body and configured to control a second fluid pressure of the second fluid against the second side of the piston to move the piston and the actuator rod controllably in a brake-releasing direction opposite the brake-actuating direction. 
         [0023]    The first pressurized fluid source may include a pressurized fluid reservoir in fluid communication with the first opening of the actuator body, and a check valve in fluid communication with the pressurized fluid reservoir, the check valve configured to permit the first fluid to be supplied therethrough to the pressurized fluid reservoir and configured to prevent the first fluid from escaping the pressurized fluid reservoir therethrough. 
         [0024]    The first pressurized fluid source may further include a pressure regulator in fluid communication with the check valve and configured to permit the first fluid to be supplied to the pressurized fluid reservoir through the check valve until the first fluid in the fluid reservoir reaches the first fluid pressure. 
         [0025]    The system may further include a first fluid pump for supplying the first fluid to the pressure regulator. 
         [0026]    The first fluid may include gas. 
         [0027]    The second fluid source may include a control valve in fluid communication with the second opening of the actuator body, and a second fluid pump for supplying the second fluid to the control valve at a third fluid pressure greater than the first fluid pressure. 
         [0028]    The second fluid may include gas. 
         [0029]    The second fluid may include hydraulic fluid. 
         [0030]    Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    In drawings that illustrate embodiments of the invention: 
           [0032]      FIG. 1  is a schematic view of a brake system in accordance with a first embodiment of the invention; 
           [0033]      FIG. 2  is a cross-sectional view of a brake actuator of the brake system of  FIG. 1 ; and 
           [0034]      FIG. 3  is a schematic view of a brake system in accordance with another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Referring to  FIG. 1 , a brake system in accordance with a first embodiment of the invention is shown generally at  10 . The brake system  10  includes a brake  12  and a brake actuator  14  having an actuator rod  16  coupled to the brake  12  to actuate the brake  12 . The brake system  10  also includes a compressor  18 , a pressure regulator  20 , a check valve  22 , a pressurized fluid reservoir  24 , and a control valve  26 . 
         [0036]    In the embodiment shown, the brake  12  is a conventional disc brake. The brake  12  is actuated when the actuator rod  16  is moved in a brake-actuating direction indicated by the arrow  28 , and is released when the actuator rod  16  is moved in a brake-releasing direction indicated by the arrow  30  and opposite the brake-actuating direction. 
         [0037]    Referring to  FIG. 2 , the brake actuator  14  includes a piston  32  having a first side  34  and a second side  36  opposite the first side  34 . The brake actuator  14  also includes an actuator body  38  having an inner surface  40  defining a cavity  42 . The cavity  42  holds the piston  32  in sealed and slidable engagement with the inner surface  40  such that the piston defines first and second chambers  44  and  46  in the cavity  42  on the first and second sides  34  and  36  of the piston  32  respectively. 
         [0038]    The actuator body  38  has a first opening shown generally at  48  in fluid communication with the first chamber  44 , a second opening shown generally at  50  in fluid communication with the second chamber  46 , and a third opening shown generally at  52  in communication with the second chamber  46 . The actuator rod  16  is coupled to the piston  32  on the second side  36  of the piston  32 , and extends in sealed and slidable engagement with the actuator body  38  through the third opening  52 . 
         [0039]    Referring back to  FIG. 1 , the compressor  18  in the embodiment shown supplies pressurized gas (such as ambient atmospheric air, for example) to the pressure regulator  20 . Alternatively, the compressor  18  may be replaced with a fluid pump to supply any pressurized fluid to the pressure regulator  20 , and the compressor  18  may more generally be referred to as a “fluid pump”. 
         [0040]    The pressure regulator  20  in the embodiment shown receives pressurized gas from the compressor  18 , and is configured to supply the pressurized gas from the compressor  18  through the check valve  22  to the pressurized fluid reservoir  24  until the gas in the pressurized fluid reservoir  24  reaches a first fluid pressure. 
         [0041]    The check valve  22  in the embodiment shown permits pressurized gas received from the pressure regulator  20  to be supplied therethrough to the pressurized fluid reservoir  24 , and prevents pressurized gas from escaping from the pressurized fluid reservoir  24  therethrough. 
         [0042]    Therefore, the compressor  18 , the pressure regulator  20 , and the check valve  22  maintain pressurized gas in the pressurized fluid reservoir  24  at the first fluid pressure. However, in alternative embodiments, these components may be configured to maintain any fluid in the pressurized fluid reservoir  24  at such a first fluid pressure. 
         [0043]    In the embodiment shown, the pressurized fluid reservoir  24  has a drain cock  54  openable to release pressurized gas from the pressurized fluid reservoir  24 , although the drain cock  54  is closed during normal operation. Referring to  FIGS. 1 and 2 , the pressurized fluid reservoir  24  is in fluid communication with the first chamber  44  of the brake actuator  14  through the first opening  48  of the actuator body  38 . Therefore, the first chamber  44  of the brake actuator  14  receives a first fluid (which, in the embodiment shown, is gas) from the pressurized fluid reservoir  24  at the first fluid pressure, and the compressor  18 , the pressure regulator  20 , the check valve  22 , and the pressurized fluid reservoir  24  function as a first pressurized fluid source in fluid communication with the first opening  48  of the actuator body  38  to maintain the first fluid pressure of the first fluid against the first side  34  of the piston  32  to urge the piston  32  and the actuator rod  16  in the brake-actuating direction shown by the arrow  28 . In alternative embodiments, the brake actuator  14  may further include one or more springs (not shown) in the first chamber  44 , for example, to supplement the force from the first fluid pressure of the first fluid on the piston  32  in the brake-actuating direction shown by the arrow  28 . 
         [0044]    Referring back to  FIG. 1 , in the embodiment shown, the compressor  18  also supplies pressurized gas (such as ambient atmospheric air, for example) to the control valve  26  at a fluid pressure greater than the first fluid pressure. The control valve  26  is in communication with a brake pedal (not shown) to control a degree of brake actuation of the brake actuator  14  on the brake  12 . The control valve  26  is also in fluid communication with the second side  36  of the piston  32  and the second chamber  46  of the brake actuator  14  through the second opening  50  of the actuator body  38 , and the second chamber  46  therefore receives a second fluid (which, in the embodiment shown, is also gas) from the control valve  26 . The control valve  26  controls a second pressure of the second fluid against the second side  36  of the piston  32  by controllably regulating the pressure of the pressurized gas received from the compressor  18  in response to actuation of the brake pedal (not shown). 
         [0045]    In operation, in the embodiment shown, the compressor  18 , the pressure regulator  20 , the check valve  22 , and the pressurized fluid reservoir  24  maintain the generally constant first fluid pressure of the first fluid in the first chamber  44  and against the first side  34  of the piston  32 . In order to actuate the brake  12  or increase a degree of actuation of the brake  12 , the control valve  26  reduces a second fluid pressure of the second fluid in the second chamber  46  and against the second side  36  of the piston  32  such that the first fluid pressure of the first fluid in the first chamber  44  against the first side  34  of the piston  32  exceeds the second fluid pressure, thereby causing the piston  32  and the actuator rod  16  move in the brake-actuating direction shown by the arrow  28  to actuate the brake  12 . Alternatively, in order to release the brake  12  or reduce a degree of actuation of the brake  12 , the control valve  26  increases the second fluid pressure of the second fluid in the second chamber  46  and against the second side  36  of the piston  32  to such that the second fluid pressure exceeds the first fluid pressure of the first fluid in the first chamber  44  and against the first side  34  of the piston  32 , thereby causing the piston  32  and the actuator rod  16  to move in the brake-releasing direction shown by the arrow  30 . 
         [0046]    Therefore, actuation of the brake pedal (not shown) regulates the second pressure of the second fluid against the second side  36  of the piston  32  to move the piston  32  controllably in either the brake-actuating direction shown by the arrow  28  or in the brake-releasing direction shown by the arrow  30 , and therefore the compressor  18  and the control valve  26  function as a second pressurized fluid source in fluid communication with the second chamber  46  and the second side  36  of the piston  32  through the second opening  50  of the actuator body  38  to control the second fluid pressure of the second fluid against the second side  36  of the piston  32  and move the piston  32  and the actuator rod  16  controllably in, for example, the brake-releasing direction shown by the arrow  30 . 
         [0047]    Advantageously, in the event of failure of one or both of the compressor  18  and the control valve  26 , the pressurized fluid reservoir  24  maintains the first pressure of air in the first chamber  44  of the brake actuator  14  and against the first side  34  of the piston  32 , thereby urging the piston  32  and the actuator rod  16  in the brake-actuating direction shown by the arrow  28 . Because the brake  12  is actuated in response to failure of one or both of the compressor  18  and the control valve  26 , the brake system  10  may be referred to as a fail-safe brake system. 
         [0048]    Referring to  FIG. 3 , a brake system in accordance with another embodiment of the invention is shown generally at  60 . The brake system  60  includes a brake  62  and a brake actuator  64  having an actuator rod  66  coupled to the brake  62  to actuate the brake  62 . The brake  62 , the brake actuator  64 , and the actuator rod  66  in the embodiment shown are substantially the same as the brake  12 , the brake actuator  14 , and the actuator rod  16  respectively discussed above and shown in  FIGS. 1 and 2 . 
         [0049]    The brake system  60  also includes a compressor  68 , a pressure regulator  70 , a check valve  72 , and a pressurized fluid reservoir  74 . The compressor  68 , the pressure regulator  70 , the check valve  72 , and the pressurized fluid reservoir  74  in the embodiment shown are substantially the same as the compressor  18 , the pressure regulator  20 , the check valve  22 , and the pressurized fluid reservoir  24  respectively discussed above and shown in  FIG. 1 . Therefore, the compressor  68 , the pressure regulator  70 , and the check valve  72  maintain a first fluid (which, in the embodiment shown, is gas) in the pressurized fluid reservoir  74  at a first fluid pressure. 
         [0050]    The pressurized fluid reservoir  74  is in fluid communication with a first chamber of the brake actuator  64  (corresponding to the first chamber  44  of the brake actuator  14  shown in  FIG. 2 ) through a first opening of an actuator body of the brake actuator  64  (corresponding to the first opening  48  of the actuator body  38  of the brake actuator  14  shown in  FIG. 2 ), and therefore in the embodiment shown, the first chamber of the brake actuator  64  receives the first fluid from the pressurized fluid reservoir  74  at the first fluid pressure, and the compressor  68 , the pressure regulator  70 , the check valve  72 , and the pressurized fluid reservoir  74  function as a first pressurized fluid source in fluid communication with the first opening of the actuator body of the brake actuator  64  to maintain the first fluid pressure of the first fluid against a first side of the piston of the brake actuator  64  (corresponding to the first side  34  of the piston  32  of the brake actuator  14  shown in  FIG. 2 ) to urge the piston of the brake actuator  64  and the actuator rod  66  in a brake-actuating direction shown by the arrow  76  to actuate the brake  62 . 
         [0051]    The brake system  10  also includes a hydraulic fluid tank  78  for storing hydraulic fluid, a hydraulic fluid pump  80  in fluid communication with the hydraulic fluid tank  78 , and a control valve  82 . In the embodiment shown, the hydraulic fluid pump  80  supplies pressurized hydraulic fluid from the hydraulic fluid tank  78  to the control valve  82  at a pressure greater than the first fluid pressure. The control valve  82  is in communication with a brake pedal (not shown) to control a degree of brake actuation of the brake actuator  64  on the brake  62 . The control valve  82  is also in fluid communication with a second side of the piston of the brake actuator  64  (corresponding to the second side  36  of the piston  32  of the brake actuator  14  shown in  FIG. 2 ) through a second opening of the actuator body of the brake actuator  64  (corresponding to the second opening  50  of the actuator body  38  of the brake actuator  14  shown in  FIG. 2 ), and the second chamber of the brake actuator  64  therefore receives a second fluid (which, in the embodiment shown, is hydraulic fluid) from the control valve  82 . The control valve  82  controls a second pressure of the second fluid against the second side of the piston of the brake actuator  64  by controllably regulating the pressure of the pressurized hydraulic fluid received from the hydraulic fluid pump  80  in response to actuation of the brake pedal (not shown). 
         [0052]    The hydraulic fluid tank  78 , the hydraulic fluid pump  80 , and the control valve  82  therefore function as a second pressurized fluid source in fluid communication with the second chamber of the brake actuator  64  and the second side of the piston of the brake actuator  64  through the second opening of the actuator body of the brake actuator  64  to control the second fluid pressure of the second fluid against the second side of the piston of the brake actuator  64  and move the piston of the brake actuator  64  and the actuator rod  66  controllably in a brake-releasing direction shown by the arrow  84  opposite the brake-actuating direction shown by the arrow  76 . The control valve  82  is also in fluid communication directly with the hydraulic fluid tank  78 , to facilitate restoring hydraulic fluid to the hydraulic fluid tank  78  when the second chamber of the brake actuator  64  contracts in response to movement of the piston of the brake actuator  64  in the brake-actuating direction shown by the arrow  76 . In summary, the brake system  60  functions in substantially the same way as the brake system  10 , although in the brake system  60 , the second fluid is hydraulic fluid, whereas in the brake system  10 , the second fluid is gas. 
         [0053]    While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.