Abstract:
A valve for controlling an emergency brake system on an aircraft. The valve has separate poppets for controlling the flow of fluid from a supply line to the brake cylinders and from the brake cylinders to a tank return line. The poppets act on each other. A dampening orifice restricts fluid flow around one of the poppets thereby limiting the rate at which that poppet opens and closes. An actuator applies an externally generated control force to the poppets to activate and de-active the emergency brake system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not Applicable 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to hydraulic valves for operating an emergency brake system on a vehicle, and more particularly to such hydraulic valves for use on aircraft. 
   2. Description of the Related Art 
   Aircraft, much like other vehicles, incorporate an emergency braking system which activates the brakes for long term parking and for emergency stopping when the principal brake system fails. A lever or other activating mechanism in the cockpit is mechanically connected to a hydraulic valve which controls the flow of fluid in the aircraft&#39;s hydraulic system to and from the brake cylinders at the wheels. For long term parking, the valve is moved to a fully on position and locked there. Since the aircraft is shut down, the pumps that supply pressurized fluid in the hydraulic systems are deactivated. However, the brake system is kept energized by pressurized fluid stored in an accumulator. 
   Leakage through the valve is a critical parameter to maintaining the brakes activated for a prolonged period of time. In order to minimize that leakage, a low-cost solution is to employ a poppet valve and a series of check valves as the brake valve assembly. A general characteristic of a poppet valve is a relatively a high flow gain because the entire circumference of the seat is opened at once. In addition, for the proper feel of the brakes under dynamic conditions, the friction of the system must be relatively low. However, the combination of a high gain coupled with a low friction (low dampening) can lead to instability in particular systems that have inherent resonance problems. 
   As a consequence, it is desirable to provide a hydraulic valve for an aircraft emergency brake system that provides a higher degree of dampening for more stable operation. 
   SUMMARY OF THE INVENTION 
   A hydraulic valve is provided to control an emergency brake on a vehicle. The hydraulic valve includes a body that has a main bore into which a first passage, a second passage, and a third passage open. For example, the first passage receives pressurized fluid from a pump, the second passage communicates with brake cylinders on the vehicle, and the third passage communicates with a fluid reservoir. A first chamber and a second chamber are defined on opposites sides of a first poppet that is slidably received in the main bore. The first passage opens into the first chamber. A passageway with a dampening orifice provides a fluid path between the first and second chambers. In order for the first poppet to move, fluid has to flow through the dampening orifice. The flow is restricted by that orifice thereby limiting the rate of poppet movement. 
   A first valve seat has a seat aperture there through that extends between the first chamber and a third chamber in the bore. The second passage opens into the third chamber. A first spring biases the first poppet against the first valve seat. A second poppet is slidably received in the main bore on an opposite side of the first valve seat from the first poppet and has a portion projecting into the seat aperture and engaging the first poppet. A sensing piston is slidable within the main bore and has a piston aperture. A first end of the piston aperture communicates with the third chamber and a second end communicates with the third passage. A second valve seat is formed at the first end of the piston aperture and is selectively engaged by the second poppet. An actuator is operably coupled to transfer force to the sensing piston and thereby operate the hydraulic valve. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal cross-sectional view through a novel emergency brake valve in the off state; 
       FIG. 2  is an enlarged area of  FIG. 1  showing details of components associated with a first valve seat; and 
       FIG. 3  is a cross sectional view along line  3 — 3  in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , an emergency brake valve  10  has a body  12  with a main bore  14  having sections of different diameters. A pump supply passage  16  conveys pressurized fluid into one section of the main bore  14  and a tank return passage  20  leads from a different bore section to a tank, or reservoir, of the hydraulic system. A cylinder passage  18  extends from yet another section of the main bore  14  to the brake cylinders at the wheels of the aircraft or other vehicle. 
   A valve cartridge  22  is secured within the main bore  14 . A valve stem  24  of that cartridge has an outer surface which engages the main bore and has a closed aperture  26  which opens into a mid-section of the main bore  14 . A valve casing  28  is located within the closed aperture  26  and has a closed inner bore  30  which also opens into the mid-section of the main bore  14 . The valve stem  24  and casing  28  have aligned transverse passages  32  and  34 , respectively, which connect the pump supply passage  16  with a first chamber  36  created in the inner bore  30 , as will be described. 
   A first, or supply, poppet  38  is slidably received within the inner bore  30  of the casing  28 . A first spring  40  biases the supply poppet away from the closed end of the inner bore and creating a second chamber  42  at that end. The supply poppet  38  has a first section  44  with a relatively large diameter surface that abuts the inner diameter of the inner bore  30 , in a manner which restricts the fluid flow there between while still allowing the supply poppet to slide within the bore. A smaller diameter section  46  of the supply poppet  38  is adjacent the first chamber  36  and fluid from that first chamber is able to enter a groove  45  in the supply poppet along the casing  28  (see also  FIG. 3 ). A passageway  47  with a dampening orifice  48  in the supply poppet  38  provides a path for fluid to flow between the first chamber  36  and the second chamber  42 . Alternatively, the passageway  47  and the dampening orifice  48  can be formed in the valve casing  28 . The supply poppet  38  has a first tip  50  extending from the smaller diameter section  46  farther into the main bore  14 . 
   A tubular member  52  has a larger diameter portion engages the interior surface of the main bore  14 . A reduced diameter section of the tubular member  52  projects into the inner bore  30  of the casing  28 , thereby defining the first chamber  36  with the supply poppet  38 . A central aperture  56  opens through a first end of the tubular member  52  into the first chamber  36  forming a valve seat  54  at that opening. In certain states of the emergency brake valve  10 , as will be described, the first tip of the supply poppet engages and closes the first valve seat  54 . 
   A second, or return, poppet  58  is slidably received within the central aperture  56  of the tubular member  52  and has one end from which a pin  60  extends into the first valve seat  54  abutting the first tip  50  of the supply poppet  38 . The return poppet  58  has a second tip  62  which projects through an aperture in a first annular retainer  64  that abuts a second end of the tubular member  52 . The first retainer  64  also has a plurality of angled apertures  66  that provide fluid paths between the central aperture  56  of the tubular member  52  and a third chamber  68  of the main bore  14  into which the cylinder passage  18  opens. 
   The third chamber  68  also is defined by a sensing piston  70  that is slidably received within the main bore  14  and biased away from the first retainer  64  by a second spring  72 . The sensing piston  70  has a generally tubular shape with a central piston aperture  74  extending there through. A first end of the piston aperture  74  opens through a second valve seat  76  into the third chamber  68 . The opposite second end of the piston aperture  74  opens into a fourth chamber  78  of the main bore  14  into which the tank return passage  20  also opens. This end of the sensing piston  70  engages an annular second retainer  80  which is biased away from a third retainer  84  by a third spring  82  within the fourth chamber  78 . 
   The exterior mechanical linkage for operating the emergency brake valve  10  acts on the third retainer  84 . Specifically, an actuator  86 , such as a rod, extends through an aperture in the valve body  12  which has a seal to prevent fluid leakage around the actuator. The exterior end of the actuator  86  engages a wheel  88  on one end of a input lever  90  which is pivotally connected to the valve body  12 . As will be described, pivoting the input lever  90  exerts an axially force on the components of the emergency brake valve. 
     FIG. 1  illustrates the off state of emergency brake valve  10  in which the brakes of the aircraft are not energized and allow the wheels to move freely. In this state, the input lever  90  is unloaded and the net axially forces on the valve components place the sensing piston  70  to an extreme rightward position in the illustrated orientation of the valve. In this state, the second valve seat  76  on the sensing piston is spaced from the second poppet tip  62  opening a fluid path between the third chamber  68  and the fourth chamber  78 , which allows fluid to flow from the brake cylinder passage  18  to the tank return passage  20 . In this off state, the first spring  40  biases the supply poppet  38  rightward against the first valve seat  54  thereby closing communication between the pump supply passage  16  and the cylinder passage  18 . As a consequence, the brake cylinders are at the low tank pressure and are deactivated. 
   Reference herein to directional relationships and movement, such as top and bottom or left and right, refer to the relationship and movement of the components in the orientation illustrated in the drawing, which may not be the orientation of the valve as attached to an aircraft or other vehicle. 
   A common requirement for an aircraft braking system is to ensure that under single failure conditions, the brakes are not partially engaged during takeoff. This is achieved configuring the pin  60  of the return poppet  58  so that even if the supply poppet tip  50  fails the engage the first valve seat  54 , the flow through that valve seat is relatively low in comparison to the exhausting flow through the second valve seat  76 . This flow relationship maintains the pressure in the cylinder passage  18  below a critical level at which the brakes activate. With reference to  FIG. 2 , the return poppet pin  60  has a shaft  63  extending from the poppet body  65  and having an enlarged head  61  at its remote end. In the illustrated off position of the emergency brake valve  10 , the head  61  is in the valve seat aperture  55  which significantly reduces the size of the path through the first valve seat  54  should the supply poppet  38  fail to engage the first valve seat  54 . However in another position of the emergency brake valve  10  in which fluid flows from the pump supply passage  16  to the cylinder passage  18 , the pin head  61  is located leftward with respect to the tubular member  52  thereby not significantly affecting the flow through the valve seat. In this latter position, the smaller diameter shaft  63  is in the valve seat aperture  55 , thereby creating a larger flow area. 
   In order to activate the brakes of the aircraft, pressure within the cylinder passage  18  must increase by applying pressurized fluid from the pump supply passage  16 . This is achieved by manipulating the mechanical linkage so that the input lever  90  pushes the actuator  86  farther into the valve body  12 . This motion is transferred to the sensing piston  70  which moves to the left and into engagement with the return poppet  58  closing the path through the second valve seat  76 . Continued movement of these components causes the return poppet  58  to move leftward so that the pin  60  forces the tip  50  of the supply poppet  38  away from engagement with the first valve seat  54 . This latter motion opens a path for fluid in the pump supply passage  16  to flow through the first chamber  36 , the tubular member  52  and the first retainer passages  66  into the third chamber  68  and out through the cylinder passage  18 . As a consequence, increased fluid pressure is applied to the brake cylinders causing them to at least partially activate, depending upon the amount of motion and force supplied by the input lever  90 . 
   This opening motion of the supply poppet  38  deceases the size of the second chamber  42 . Therefore, the fluid within that second chamber must flow to the opposite side of the supply poppet  38  and into the first chamber  36  before the poppet can move. However, the path for this fluid flow is restricted by the small size of the dampening orifice  48  thereby creating a differential pressure across the supply poppet and thus a dampening force. As a consequence, the rate at which the supply poppet  38  is able to open is dampened by this restricted flow. This dampening action slows the motion of the entire series of components within the main bore  14 . 
   In the opened state, the bulk modulus of this fluid allows the pressure within the third valve chamber  68  to rise until that pressure exerts a force on the sensing piston  70  which balances the opposing force of the third spring  82 . At that point, the second tip  62  of the return poppet  58  continues to be held against the second valve seat  76 , and the pin head  61  of that poppet returns into the first valve seat aperture  55 , thereby allowing the first tip  50  of the supply poppet  38  to engage the first valve seat  54  ( FIG. 2 ). Now, the path between the pump supply passage  16  and the cylinder passage  18  is closed, which stabilizes the active brake pressure to a steady state level. 
   From the increased pressure state during activation of the aircraft brakes, movement of the input lever  90  in the opposite direction deceases the pressure within the cylinder passage  18  until the net axial force allows the sensing piston  70  to move to the right in  FIG. 1 . In other words, movement of the input lever deceases the force exerted on the third spring  82  and the force applied to the adjacent end of the sensing piston  70 . Thus, the force provided by the second spring  72  and pressure within the third chamber  68  force the sensing piston  70  away from the second tip  62  on the return poppet  54 , opening a path through the second valve seat  76  between the third chamber  68  and the tank return passage  20 . This motion of the sensing piston  70  also removes the leftward acting force previously applied to the return poppet  58 . As a consequence, the force of the first spring  40  acting the supply poppet  38  and the differential pressure across the return poppet  54  cause those poppets to move to the right until the first tip  50  of the supply poppet engages the first valve seat  54 . This closes the path between the pump supply passage  16  and the cylinder passage  18 . Thus, the previous relatively high pressure within the brake cylinder passage  18  now is relieved through the second valve seat  78  to the tank return passage  20 . 
   However, the rate of rightward motion of the supply poppet  38  is limited because fluid must flow from the first chamber  36  through the dampening orifice  48  into the second chamber  42 . The relatively small size of the dampening orifice  48  restricts that flow, thereby limiting the rate at which the supply poppet  38  is able to move into the closed position. However, this dampening action slows only the closure of the supply poppet  38  and does not affect motion of the other components of the emergency brake valve  10  at this time. 
   If the input lever  70  is not placed into the off state position, it continues to exert some force via the third spring  82 . Therefore, as pressure within the emergency brake valve  10  decreases, the force of the third spring  82  produces a counteracting movement of the sensing piston  70  toward the return poppet  58 . That motion continues until the second poppet tip  62  engages the second valve seat  76  thereby closing the path between the cylinder passage  18  and the tank return passage  20 . At this point, the brake pressure stabilizes at a new, lower level. 
   However, moving the input lever  90  from a brake active state to the off state shown in  FIG. 1 , allows the valve components to stabilize in the illustrated position at which the supply poppet  38  engages the first valve seat  52  closing the path between the pump supply passage  16  and the cylinder passage  18 . In this off state, the sensing piston  70  is biased by the second spring  72 , slightly away from the tip  62  of the return poppet  58 . This position creates a passage to relieve any pressure within the brake cylinder passage  18  to the tank return passage  20 , thereby entirely deactivating the wheel brakes. 
   The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.