Abstract:
An electric fail-safe is operable to move a first ramp between distinct positions. The first ramp is associated with the second ramp. There are balls intermediate the first and second ramps. When the electric fail-safe brake is in an actuated condition, the second ramp forces stationary brake disks to engage rotating brake disks which rotate with a shaft to cause braking of the shaft. There is a keeper associated with the second ramp which abuts a stop surface to limit the amount of torque applied to the rotary and stationary disks after a predetermined amount of braking force has occurred. A brake with a test switch is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates to a brake that operates to prevent rotation of a shaft, when relative rotation is detected between two points that should be driven together. 
         [0002]    Modern systems are requiring increasingly precise and complex controls. One such system is a system for driving flaps or slats on an aircraft wing. A drive actuator typically drives shafts extending in each of two lateral directions, which in turn, drive actuators for pivoting the flaps and slats as needed. It is desirable that these actuators are all driven as one. 
         [0003]    Thus, it is known to put location sensors at each end of the two drive shafts. If relative rotation is detected, then an assumption is made that there has been a disconnect or break somewhere between the drive actuator and the two shaft ends. 
         [0004]    In such an instance a brake is provided to stop further rotation of the shaft. In one known brake, an electric fail-safe unit is deactivated. When the fail-safe brake is provided with current, it acts to release a primary brake. However, when current is stopped then the brake is actuated. The brake may consist of a plurality of disks. 
       SUMMARY OF THE INVENTION 
       [0005]    A brake for incorporation into a mechanical movement system has an electric fail-safe brake that may be provided with power, or disconnected from power, and is operable to move a first ramp between distinct positions when provided with power in a first condition and when not provided with power in a second condition. The first ramp is associated with the second ramp. There are balls intermediate the first and second ramps. When the electric fail-safe brake is in an actuated one of said first and second conditions, the second ramp forces stationary brake disks to engage rotating brake disks which rotate with a shaft to cause braking of the shaft. There is a keeper associated with the second ramp which abuts a stop surface. The stop surface is abutted by the keeper of the second ramp to limit the amount of torque applied to the rotary and stationary disks after a predetermined amount of braking force has occurred. A mechanical system incorporating such a brake is also disclosed. A brake being provided with a test switch is also disclosed. 
         [0006]    These and other features may be best understood from the following drawings and specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows an actuation system for flaps in an aircraft. 
           [0008]      FIG. 2  shows a brake. 
           [0009]      FIG. 3A  shows a portion of the brake in a non-engaged position. 
           [0010]      FIG. 3B  shows the engaged position. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    A mechanical drive system  20  is illustrated in  FIG. 1  having a power drive unit  22 , which may be a rotary motor. The drive unit  22  drives a shaft  40  extending in each of two lateral directions, such as through the wings of an associated aircraft. There are a plurality of flaps  24 ,  26 ,  28  and  30  each driven by actuators  36  which are ultimately driven by the drive unit  22 . Position sensors  32  and  34  sense relative rotation at ends of shaft  40 . If a position signal between the sensors  32  and  34  differ, then a determination is made that there has been a disconnect or break somewhere along one of the shafts  40 . The sensors  32  and  34  communicate with a control  300 . Brakes  38  are illustrated associated with ends of the shafts  40  and are actuated should the control  300  determine that there has been a disconnect or break due to the position sensor information from sensors  32  and  34 . 
         [0012]    The brakes  38  are shown in more detail in  FIG. 2 . 
         [0013]    Brake  38  includes an electric fail-safe brake portion  42 , an electric switch pack  44 , and a braking section  46 . The brake is capable of holding system torque by engaging a ball ramp between ramps  104  and  108 , as will be explained below. The brake is engaged by applying torque to an output ball ramp  104  by de-energizing the electric brake  42 . The electric brake engages a self-contained friction plate  105  that is connected to the output ball ramp  104 . By applying torque to the output ball ramp  104  through the electric brake  42 , the ball ramp  104  is held stationary as an input shaft  40  continues to rotate. 
         [0014]    This drives balls  107  between the output ball ramp  104  and a ball ramp  108  to separate, or increase a distance between the two ramps  104  and  108  (see  FIGS. 3A  and  FIG. 3B ). As shown in  FIG. 3A , the ramps  104  and  108  are in a non-engaged position, and the ball  107  sits at a most distant portion between surfaces  301 . In this position there is clearance. However, when the balls are driven by de-energizing the electric brake  42 , the ball  107  moves to a position such as shown in  FIG. 3B  where it is no longer at the most distant position, and there is no clearance. With this movement, the ramp  108  is forced to the right and engages a plurality of brake disks. 
         [0015]    A set of springs  111  preload the ball  107  and ball ramps  104  and  108  together upon the disengagement of the electric fail-safe brake portion  42 . Input torque translates the ball ramps  104 / 108  axially against the preload spring  111 , upon the movement of the balls  107  explained above. 
         [0016]    The pilot brake or electric fail-safe brake portion  42  will be described. When electric power is removed, such as from control  300 , springs  113  force brake plates together, as explained below to apply the brake. A brake solenoid consists of an electric coil  114  inside an iron cavity  115 . A magnetic force is created by providing power to the electric coil  114  from control  300 . This pulls a clapper plate  116  toward the iron cavity  115 , overcoming the preload in the springs  113 . This releases the brake as will be described below. 
         [0017]    When power is removed from the coil  114 , the springs  113  then apply a force to the clapper plate  116 , pushing it into contact with a friction plate  105 , which then contacts a grounding plate  117 . The grounding plate  117  is held in place by end bolts  118 . End bolts  118  clamp across sleeves  119  to the iron cavity  115 . The sleeves  119  react torque from the clapper plate  116  through grooves in the clapper plate  116 . 
         [0018]    The primary brake portion  46  is a multi-plate ball ramp brake. As mentioned, when the pilot brake  42  is disconnected from power, it grounds the output ball ramp  104 . A spline  120  allows shaft misalignment between a friction plate  105  and the output ball ramp  104 . The primary brake portion  46  is then engaged by rotating input shaft  40  and compressing spring  111 , due to the balls  107  rolling up the ball ramps  104  and  108 , and along the facing surfaces  301 , as explained above. 
         [0019]    When the ball ramp  108  is forced to the right, it removes clearance  110  between rotating frictional plates  122  and stationary plates  121  in the brake section  46 . This applies the primary brake  46  and prevents further rotation of the shaft  40 . 
         [0020]    Friction plate  122  is connected to a hub  125  by a spline  123 . The stationary plates  121  are connected to a ground by a pin  124 . Hub  125  is secured to shaft  40  by a retaining ring  126  and a spline  127 . 
         [0021]    When the balls  107  roll up ramps  104  and  108 , the ramp motion is limited by a keeper  128 , having an end  200 , contacting the hub  125 . 
         [0022]    At this point the clearance  110  is removed from the brake section  46 , and springs  129  have been compressed farther than in an initial preload condition. The initial preload is provided by keeper  128  and retaining ring  141  assembled onto ball ramp  108  compressing springs  129 . Any further ball  107  load increase resulting from torque is then transferred to the hub  125  through the keeper  128 , without passing through the brake section  46 . Thus, the amount of brake torque is limited in this embodiment. 
         [0023]    The operation of the brake  38  other than the torque limit as mentioned above may be generally as disclosed in co-pending U.S. patent application Ser. No. 12/228,595, titled “High Gain Asymmetry Brake” and owned by the assignee of this application. Aspects of the operation of the brake disclosed in that application are incorporated herein by reference. 
         [0024]    However, the present application provides the limit on the brake torque function as mentioned above. 
         [0025]    In addition, the electric switch pack  44  is included in this application, and is not in the above-mentioned application. 
         [0026]    The brake torque capacity for the brake  38  may be checked while an associated aircraft is on the ground by applying torque to the brake  38  from the system power drive unit  22  with the fail safe brake portion  42  engaged. As torque is applied to the brake  38 , system controller  300  monitors the trip point of an electrical switch pack provided by electric switches  133 . This is sent to the control  300  along with the position of the system through the position sensors. 
         [0027]    As the ball  107  roll up the ramps  104  and  108 , the ramp  104  compresses springs  130  beyond their initial preload, and moves axially to contact plate  132 , which is grounded proportionally through a spline  135 . The initial preload of springs  130  is accomplished by securing ball ramp  104  and springs  130  onto shaft  151  by retaining ring  152  and spline  153 . After sufficient movement, a plate  132  will contact and trip the switch  133 . Plate  132  is preloaded by a number of springs  134  against a retaining ring  131  in the housing  600 . The springs  134  are equally spaced around the circumference of Plate  132 . When the switch  133  is tripped, the controller  300  will be able to evaluate how much movement of the system was required to ensure that this asymmetry brake  38  is properly functioning. 
         [0028]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.