Dampened vehicle emergency brake valve

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.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

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'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.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIG. 1, an emergency brake valve10has a body12with a main bore14having sections of different diameters. A pump supply passage16conveys pressurized fluid into one section of the main bore14and a tank return passage20leads from a different bore section to a tank, or reservoir, of the hydraulic system. A cylinder passage18extends from yet another section of the main bore14to the brake cylinders at the wheels of the aircraft or other vehicle.

A valve cartridge22is secured within the main bore14. A valve stem24of that cartridge has an outer surface which engages the main bore and has a closed aperture26which opens into a mid-section of the main bore14. A valve casing28is located within the closed aperture26and has a closed inner bore30which also opens into the mid-section of the main bore14. The valve stem24and casing28have aligned transverse passages32and34, respectively, which connect the pump supply passage16with a first chamber36created in the inner bore30, as will be described.

A first, or supply, poppet38is slidably received within the inner bore30of the casing28. A first spring40biases the supply poppet away from the closed end of the inner bore and creating a second chamber42at that end. The supply poppet38has a first section44with a relatively large diameter surface that abuts the inner diameter of the inner bore30, in a manner which restricts the fluid flow there between while still allowing the supply poppet to slide within the bore. A smaller diameter section46of the supply poppet38is adjacent the first chamber36and fluid from that first chamber is able to enter a groove45in the supply poppet along the casing28(see alsoFIG. 3). A passageway47with a dampening orifice48in the supply poppet38provides a path for fluid to flow between the first chamber36and the second chamber42. Alternatively, the passageway47and the dampening orifice48can be formed in the valve casing28. The supply poppet38has a first tip50extending from the smaller diameter section46farther into the main bore14.

A tubular member52has a larger diameter portion engages the interior surface of the main bore14. A reduced diameter section of the tubular member52projects into the inner bore30of the casing28, thereby defining the first chamber36with the supply poppet38. A central aperture56opens through a first end of the tubular member52into the first chamber36forming a valve seat54at that opening. In certain states of the emergency brake valve10, as will be described, the first tip of the supply poppet engages and closes the first valve seat54.

A second, or return, poppet58is slidably received within the central aperture56of the tubular member52and has one end from which a pin60extends into the first valve seat54abutting the first tip50of the supply poppet38. The return poppet58has a second tip62which projects through an aperture in a first annular retainer64that abuts a second end of the tubular member52. The first retainer64also has a plurality of angled apertures66that provide fluid paths between the central aperture56of the tubular member52and a third chamber68of the main bore14into which the cylinder passage18opens.

The third chamber68also is defined by a sensing piston70that is slidably received within the main bore14and biased away from the first retainer64by a second spring72. The sensing piston70has a generally tubular shape with a central piston aperture74extending there through. A first end of the piston aperture74opens through a second valve seat76into the third chamber68. The opposite second end of the piston aperture74opens into a fourth chamber78of the main bore14into which the tank return passage20also opens. This end of the sensing piston70engages an annular second retainer80which is biased away from a third retainer84by a third spring82within the fourth chamber78.

The exterior mechanical linkage for operating the emergency brake valve10acts on the third retainer84. Specifically, an actuator86, such as a rod, extends through an aperture in the valve body12which has a seal to prevent fluid leakage around the actuator. The exterior end of the actuator86engages a wheel88on one end of a input lever90which is pivotally connected to the valve body12. As will be described, pivoting the input lever90exerts an axially force on the components of the emergency brake valve.

FIG. 1illustrates the off state of emergency brake valve10in which the brakes of the aircraft are not energized and allow the wheels to move freely. In this state, the input lever90is unloaded and the net axially forces on the valve components place the sensing piston70to an extreme rightward position in the illustrated orientation of the valve. In this state, the second valve seat76on the sensing piston is spaced from the second poppet tip62opening a fluid path between the third chamber68and the fourth chamber78, which allows fluid to flow from the brake cylinder passage18to the tank return passage20. In this off state, the first spring40biases the supply poppet38rightward against the first valve seat54thereby closing communication between the pump supply passage16and the cylinder passage18. 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 pin60of the return poppet58so that even if the supply poppet tip50fails the engage the first valve seat54, the flow through that valve seat is relatively low in comparison to the exhausting flow through the second valve seat76. This flow relationship maintains the pressure in the cylinder passage18below a critical level at which the brakes activate. With reference toFIG. 2, the return poppet pin60has a shaft63extending from the poppet body65and having an enlarged head61at its remote end. In the illustrated off position of the emergency brake valve10, the head61is in the valve seat aperture55which significantly reduces the size of the path through the first valve seat54should the supply poppet38fail to engage the first valve seat54. However in another position of the emergency brake valve10in which fluid flows from the pump supply passage16to the cylinder passage18, the pin head61is located leftward with respect to the tubular member52thereby not significantly affecting the flow through the valve seat. In this latter position, the smaller diameter shaft63is in the valve seat aperture55, thereby creating a larger flow area.

In order to activate the brakes of the aircraft, pressure within the cylinder passage18must increase by applying pressurized fluid from the pump supply passage16. This is achieved by manipulating the mechanical linkage so that the input lever90pushes the actuator86farther into the valve body12. This motion is transferred to the sensing piston70which moves to the left and into engagement with the return poppet58closing the path through the second valve seat76. Continued movement of these components causes the return poppet58to move leftward so that the pin60forces the tip50of the supply poppet38away from engagement with the first valve seat54. This latter motion opens a path for fluid in the pump supply passage16to flow through the first chamber36, the tubular member52and the first retainer passages66into the third chamber68and out through the cylinder passage18. 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 lever90.

This opening motion of the supply poppet38deceases the size of the second chamber42. Therefore, the fluid within that second chamber must flow to the opposite side of the supply poppet38and into the first chamber36before the poppet can move. However, the path for this fluid flow is restricted by the small size of the dampening orifice48thereby creating a differential pressure across the supply poppet and thus a dampening force. As a consequence, the rate at which the supply poppet38is able to open is dampened by this restricted flow. This dampening action slows the motion of the entire series of components within the main bore14.

In the opened state, the bulk modulus of this fluid allows the pressure within the third valve chamber68to rise until that pressure exerts a force on the sensing piston70which balances the opposing force of the third spring82. At that point, the second tip62of the return poppet58continues to be held against the second valve seat76, and the pin head61of that poppet returns into the first valve seat aperture55, thereby allowing the first tip50of the supply poppet38to engage the first valve seat54(FIG. 2). Now, the path between the pump supply passage16and the cylinder passage18is 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 lever90in the opposite direction deceases the pressure within the cylinder passage18until the net axial force allows the sensing piston70to move to the right inFIG. 1. In other words, movement of the input lever deceases the force exerted on the third spring82and the force applied to the adjacent end of the sensing piston70. Thus, the force provided by the second spring72and pressure within the third chamber68force the sensing piston70away from the second tip62on the return poppet54, opening a path through the second valve seat76between the third chamber68and the tank return passage20. This motion of the sensing piston70also removes the leftward acting force previously applied to the return poppet58. As a consequence, the force of the first spring40acting the supply poppet38and the differential pressure across the return poppet54cause those poppets to move to the right until the first tip50of the supply poppet engages the first valve seat54. This closes the path between the pump supply passage16and the cylinder passage18. Thus, the previous relatively high pressure within the brake cylinder passage18now is relieved through the second valve seat78to the tank return passage20.

However, the rate of rightward motion of the supply poppet38is limited because fluid must flow from the first chamber36through the dampening orifice48into the second chamber42. The relatively small size of the dampening orifice48restricts that flow, thereby limiting the rate at which the supply poppet38is able to move into the closed position. However, this dampening action slows only the closure of the supply poppet38and does not affect motion of the other components of the emergency brake valve10at this time.

If the input lever70is not placed into the off state position, it continues to exert some force via the third spring82. Therefore, as pressure within the emergency brake valve10decreases, the force of the third spring82produces a counteracting movement of the sensing piston70toward the return poppet58. That motion continues until the second poppet tip62engages the second valve seat76thereby closing the path between the cylinder passage18and the tank return passage20. At this point, the brake pressure stabilizes at a new, lower level.

However, moving the input lever90from a brake active state to the off state shown inFIG. 1, allows the valve components to stabilize in the illustrated position at which the supply poppet38engages the first valve seat52closing the path between the pump supply passage16and the cylinder passage18. In this off state, the sensing piston70is biased by the second spring72, slightly away from the tip62of the return poppet58. This position creates a passage to relieve any pressure within the brake cylinder passage18to the tank return passage20, 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.