Patent Application
20240247524
The invention relates to the field of blowout or pressure release latches for holding closed a moveable access panel on any structure. More specifically, the invention relates to an aircraft, pressure-release latch having a calibration mechanism that adjusts the level of pressure needed to automatically open the latch.
A pressure release latch is a type of latch that is used to secure access panels on land vehicles, aircraft, or other structures that may experience an excessive buildup of pressure within the compartment enclosed by the door panel. Pressure release latches have many applications but are commonly used to secure the access panels of an aircraft's engine housing. When a predetermined, excessive level of pressure (“blowout force”) builds up inside the engine housing, the latches are designed to automatically unlock/open, which enables the door panel to pop open to avoid damaging the door panel, surrounding aircraft housing or frame, or components within the compartment. Prior art pressure-release latches typically also include a manual actuator that can be used to open the door panel from the outside in order to service components within the compartment.
Prior art pressure-release latches are typically complicated and heavy, which is especially undesirable for aerospace application. Therefore, there is a need for a lighter and more compact pressure-release latch than provided in the prior art.
Additionally, prior art pressure-release latches typically use torsion springs to create their latch locking force, and do not have the ability to adjust the torsion force created by those springs when the latch is assembled. Because torsion springs have a large variability in bias properties even within the same lot or successive lots, the manufacturer must swap out torsion springs when the completed assembly does not perform as required, i.e., open at a required blowout force. Therefore, there is also a need for a pressure-release latch that has opening force calibration means to accommodate the variability of torsion force tolerances of the springs used in their manufacture.
The invention comprises a pressure release latch that is more compact, efficient, and lightweight than prior art pressure release latches. The novel pressure release latch also includes means for adjusting the opening force required to unlock the latch and open the door panel. The novel pressure release latch can be manually opened from outside the door panel by pulling an actuator arm, which has high visibility when positioned in the unlocked/open position even if the door panel appears to be closed.
In preferred embodiments, the pressure release latch mounts to the inside of a door panel near the free-swinging edge of the door panel that can only rotate outwardly. The latch includes a latch bolt that is movable between open and closed positions by an actuator. In the closed position, the actuator locks the latch bolt in place with a latch bolt head abutting the inside surface of the frame surrounding the door panel so that the door panel cannot rotate outwardly. When excessive pressure on the inside of the door panel creates an opening force on the latch bolt that exceeds a predetermined opening force, the actuator automatically unlocks and moves the latch bolt to the open position, which retracts the latch head from contact with the door frame so that the door panel can open and relieve the internal pressure.
In one preferred embodiment, the latch bolt is pivotally mounted to a latch base and is restrained at one end by a spring-biased, toggle-linkage tensioner. In accordance with the mechanical advantage/leverage of the toggle-linkage tensioner in various configurations, the latch bolt releases soon after the rotational force exerted on the latch head created by the blowout force exceeds an opposed, pre-designed, rotational restraining force exerted on the shank end of the latch bolt by the toggle-linkage tensioner. This “latch opening force” on the toggle linkage is selected during assembly by adjusting the degree of deflection (preloaded bias) of the toggle-linkage spring. When that condition occurs, the toggle-linkage tensioner will have deflected its bias spring and rotated to a configuration where the angular orientation of its links relative to one another and the latch bolt itself no longer exert enough mechanical leverage on the latch bolt shank to keep the latch bolt from rotating to the open position. Thereafter the bolt is free to continue rotation to a more fully open position.
In preferred embodiments, the bias force exerted by the spring on the toggle linkage can be calibrated/adjusted to modify the latch opening force. In one preferred embodiment, the spring comprises a torsion spring and the bias force is adjusted by changing the amount of pre-tension (angle of deflection from its free position) in the torsion spring. Preferably, the pre-tension can be adjusted in a range of plus or minus fifteen percent. Because of this adjustment feature, the latch opening force can be calibrated to meet specific latch opening force specifications without disassembling the latch and replacing the torsion spring as is typical with prior art pressure-release latches.
In one preferred embodiment, the pressure release latch releasably locks closed a door panel on the frame to which the door panel is hingedly connected. The latch housing has a proximal end, distal end, top side, bottom side, a central aperture, and means for mounting the bottom side of the housing to the door panel. Preferably, the mounting means comprises a plurality of opposed, mounting tabs. Each tab has an aperture through which a fastener is inserted to mount the latch on the inner surface of the door panel.
The latch includes a latch bolt having an elongate shank with a distal end, proximal end, and a head formed on the proximal end. The shank of the latch bolt is mounted by a first pivot pin to the top side of the base near the proximal end of the housing. The latch bolt is rotatable between a closed position that locks the door panel closed and an open position that allows the door to swing open. The head of the latch bolt abuts the frame when the latch bolt is oriented in the closed position.
A latch bolt actuator is mounted by a second pivot pin to the top side of the base near the distal end of the housing and is connected to the shank of the latch bolt. The actuator preferably includes means for manually rotating the latch bolt between the closed and open positions from outside the door panel. In a preferred embodiment, the manual rotating means comprises an actuator arm connected to the shank of the latch bolt between the distal end of the shank and the first pivot pin. The actuator arm extends from the shank through the central aperture in the base. The actuator arm has a head formed at its free end that seats flush within the outer surface of the door panel when the latch is in the closed position, and extends outwardly from the door panel when the latch is in the open position so that a technician can more readily recognize that the latch is open even when the door appears to be shut.
The latch bolt actuator also includes means for locking the latch bolt in the closed position, and means for means for automatically unlocking and moving the latch bolt to the open position when a predetermined opening force is applied to the latch bolt. In one preferred embodiment, the latch bolt actuator comprises a spring-biased, toggle-linkage tensioner pivotally mounted at one end by a second pivot pin to the distal end of the housing and pivotally connected at the other end to the bolt shank. The linkage locks the latch bolt in the closed position, and automatically unlocks and moves the latch bolt to the open position when a predetermined opening force is applied to the latch bolt.
In one preferred embodiment, the spring-biased, toggle-linkage tensioner comprises a restraining arm, a lever arm, and a spring. The restraining arm has a distal end, and a proximal end pivotally connected to the latch bolt shank by a first linkage pin. The lever arm has a proximal end pivotally connected to the distal end of the restraining arm by a second linkage pin, and a distal end pivotally mounted to the second pivot pin. The spring biases the lever arm and restraining arm towards the head of the latch bolt. Preferably, the spring comprises at least one coil spring wound around the second pivot pin and has first and second protruding legs. The first leg sits in contact with at least one of the linkage pins when the latch is oriented in at least the closed position. In preferred embodiments, the tensioner includes a pair of restraining arms mounted on opposed sides of the lever arm and the latch bolt. The latch may also include a second torsion spring wrapped around the first pivot pin that biases the latch bolt toward the open position.
The latch has means for calibrating the magnitude of the predetermined opening force required to automatically release the locking means. Preferably, the calibrating means comprises a screw mechanism that changes the degree of deflection of the coil spring of the tensioner when the latch is oriented in the closed position. In one preferred embodiment, the screw mechanism comprises a calibration screw and a capture slot formed in a hinge bracket that houses the second pivot pin. The calibration screw can be extended into and retracted from the capture slot. The second leg of the coil spring sits in the capture slot in contact with the adjustment screw so that movement of the calibration screw within the capture slot changes the degree of deflection of the coil spring and the force it exerts on the toggle linkage.
The first pivot pin and the second linkage pin define an over-center axis. The toggle linkage is arranged so that the first linkage pin is out of alignment with the over-center axis when the latch is in the closed position. In operation, the latch bolt moves to the open position when the force on the latch bolt rotates the latch bolt and urges the toggle linkage from an angular configuration to a linear configuration aligned with the over-center axis, and then to an opposed angular configuration. The first linkage pin rotates past the over-center axis to move the latch from the closed position to the open position when the predetermined opening force is exceeded. The toggle linkage is constructed so that rotation of the first linkage pin past the over-center axis releases all restraining force of the toggle linkage on the latch bolt.
For the purpose of illustrating the invention, several embodiments of the invention are described with respect to the accompanying drawings. However, it should be understood by those of ordinary skill in the art that the invention is not limited to the precise arrangements and instrumentalities shown therein and described below. Throughout the specification, like reference numerals are used to designate like elements.
A latch in accordance with preferred embodiments of the invention is shown in
The latch 10 is operable between a closed position such as shown in
The latch 10 generally includes a base 12, a pivotable latch bolt 14, and a bias-adjustable bolt actuator, generally designated by reference numeral 16. In preferred embodiments, the lock bolt 14 is pivotally connected to the proximal end 12a of the base 12, while the bolt actuator 16 is mounted on the distal end 12b of the base 12. As described in greater detail below, the bolt actuator 16 performs multiple functions. First, it moves the latch bolt 14 between open and closed positions by application of a manual force to the manual actuator arm 37 described below. Second, it locks the latch bolt 14 in the closed position with sufficient force so that the door panel DP does not open during normal flight conditions. Third, it unlocks and moves the latch bolt 14 from the closed position to the open position when a predetermined opening force is applied to the interior of door panel DP usually caused by an excessive build-up of pressure inside the aircraft housing.
In the embodiment shown in
The door panel DP is pivotally connected to the aircraft frame AF by one or more hinges (not shown) at a hinged end so that the opposed latch end of the door panel can swing between open and closed positions. In preferred embodiments, the latch 10 is mounted close enough to the latch end of the door panel DP so that the head 14b of the latch bolt 14 can engage and abut the inner surface of the aircraft frame AF surrounding the door panel and prevent the door panel DP from opening until a predetermined internal air pressure is exceeded or the latch is intentionally opened by an operator. In the embodiment shown in
Referring to
In the embodiment shown in
Referring to
The distal end of the bolt shank 14a is connected to the bolt actuator 16. In one preferred embodiment, the bolt actuator 16 comprises a toggle linkage, designated generally by reference numeral 53, a linkage tensioner designated generally 55, and the manual actuator arm 37. In one preferred embodiment, the toggle linkage 53 comprises a first link pivotally connected to the distal end of the bolt shank 14a and a second link pivotally connected to the distal end of the base 12. The links are pivotally connected to one another.
As best seen in
In a preferred embodiment, the manual actuator arm 37 is integrally formed with the bolt shank 14a. In this embodiment, the manual actuator arm 37 comprises a pair of plate extensions 71 of the parallel bolt plates 45, which are co-planar with the bolt plates 45 but extend transversely to the length of the bolt shank 14a as best seen in
Referring to
Those of ordinary skill in the art should appreciate that the manual actuator arm 37 need not be integrally formed with the bolt shank so long as its construction can exert a rotational force on the latch bolt 14 sufficient to overcome the locking force of the toggle linkage 53. For example, the plate extensions 71 could comprise separate structural elements pivotally connected to the proximal pivot pin 29, or separate structural elements pivotally connected to the bolt shank 14a at a location different than the pivot pin 29.
In this preferred embodiment, the manual actuator arm 37 is long enough so that the head 39 extends through the central aperture 22 in the base 12 and sits higher than the base 12 as best seen in
In a preferred embodiment shown in
The linkage tensioner 55 includes a mechanism for calibrating the tension exerted by the coil springs 67. In one preferred embodiment, the calibration mechanism adjusts the tension by changing the degree of rotation of the springs when they are preloaded. In this embodiment, the calibration mechanism comprises the spring capture slot 33 and the calibration screw 34. The capture slot 33 is longer than the diameter of the first leg 67a to allow movement/position adjustment along the length of the slot 33. In the closed position, each spring 67 is deflected in the clockwise direction (relative to the image shown in
Preferably, a second torsion spring 69 is mounted on and surrounds the proximal base hinge pin 29. One leg of the spring 69 abuts the bolt shank 14a while the other abuts the base 12. The second torsion spring 69 is oriented so that it normally urges the latch bolt toward the open position as shown in
Operation of the latch 10 is illustrated in
As illustrated in
When the first linkage pin 61 swings past the over-center axis C, the locking force LF of the bolt actuator 16 transitions from a counterclockwise moment to a clockwise moment until the first leg 67a disengages from the second linkage pin 63. After that point, the rotational force of the second torsion spring 69 continues to move the latch bolt to a more fully-open position shown in
Referring to
It will be readily understood by those in the mechanical arts that the dimensions of the various components of the invention can be selected to operate as described above without limitation to the particular configuration, proportions and dimensions shown in the preferred embodiment. As such, the invention is to be defined only by the following claims and their legal equivalents.
