The assignee for this patent application is
Reporters obtained the following quote from the background information supplied by the inventors: "Switches and switch assemblies are known and are generally used to indicate the difference in, or move between, two states. Switches may be used to indicate positional changes, such as the change in a position of an object being monitored.
"There are several situations in which switches may be used in aircraft, and in particular in aircraft landing gear. The landing gear in aircraft, and in particular any changes in state of the landing gear, are monitored very careful to ensure the safety of the aircraft when in operation. Indicating means may be used to show a change in position of two components of the aircraft landing gear relative to each other. Indicating means may also be used to show a change in state of a specific component relative to its normal operational state.
"Aircraft are often towed or pushed to position the aircraft when at or near the gate, and also to move aircraft around the airport. An important consideration when towing or pushing an aircraft involves preventing the aircraft steering angle from moving beyond its mechanical limits. This is referred to as over-steer. Damage may occur when a tow vehicle attempts to steer an aircraft nose landing gear beyond its mechanical limits of travel and possibly impart a high load over the strength and of the landing gear and air frame. This loading can result in deformation, fatigue, and ultimately, failure of the parts under stress. It is useful to have an indication of whether an over-steer event has occurred as the landing gear may have become damaged.
"Tow vehicles can include warning systems to alert ground operators of potential over-steer, and ground support tow bars can have built-in fuses. In addition, the nose landing gear can have a fuseable tow fitting or disconnecting torque links to prevent towing torque transferring to the landing gear and airframe. These systems have problems because they rely on proper operation by the ground operations personnel and communicating faults or warnings to the aircraft operator (e.g. the pilot).
"In order to ascertain when an over-steer event has occurred, a monitoring system or switch may be used that can indicate when such an event has occurred. Proximity sensors coupled to an electronic control box have been used in the past to indicate the occurrence of an over-steer event. Proximity sensors are generally more expensive than mechanical switches and also require a continuous power source, such as a battery, to operate the sensors when the aircraft is not powered. These proximity sensor can also be expensive to install, causes increased weight, due to sensors, targets and associated electronics, and creates additional points of failure that affect costs associated with maintenance and reliability. Proximity sensor systems typically require 2 or more proximity sensors, thus adding to the weight and complexity of the system.
"Some large commercial aircraft use a proximity sensor based over-steer detection system. The system uses multiple proximity sensors that are mounted at the limits and detect targets that travel near the proximity sensor to indicate over-steer. Disadvantages of these systems include the inability to detect over-steer events if the system is not powered on and the requirement of a black box for conditioning and processing the proximity sensors signals that adds additional costs and must be integrated with the aircraft.
"Another problem with switches that monitor for over-steer events is that tow operators may be able to reset the switch manually. If a tow operator has caused an over-steer event, the tow operator may be inclined to reset the switch so that the over-steer will not be detected to avoid being reprimanded or punished. Also, existing mechanical switches may not be practical in a high vibration landing gear environment."
In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventor's summary information for this patent application: "Accordingly, in one aspect a switch assembly is disclosed having an actuator that is biased against a mechanical cam that triggers the switch assembly from the armed state to the disarmed state. Using a mechanical cam and switch actuator to determine if the triggering event has occurred does not required the switch assembly to be powered to record the occurrence of the triggering event, and can be indicated to the cockpit or operations personnel once the switch is powered.
"In another aspect, a switch assembly is disclosed having an actuator that is biased against a mechanical cam in the disarmed state to prevent manually resetting the switch to an armed position after the occurrence of the triggering event by moving the cam back towards the armed state.
"In yet another aspect, an over-steer detection system for detecting over-steer event of an aircraft landing gear is described using a switch assembly as described herein for monitoring the occurrence of an over-steer event and providing an indication to the cockpit and operations personnel.
"In one embodiment, an over-steer detection system for detecting an over-steer event of an aircraft landing gear is provided. The system comprises a switch having an actuator movable between an armed and disarmed position, the actuator biased towards the disarmed position; a housing coupled to the switch; a cam rotatable within the housing, the cam having an actuator-engaging portion and a trigger-engaging portion, the cam having an active position and a triggered position, in the active position the actuator-engaging portion of the cam maintains the actuator in the armed position; a trigger that engages the trigger-engaging portion of the cam to move the cam towards the triggered position in the over-steer event, in the triggered position the actuator moves to the disarmed position; and an indicator coupled to the switch to signify occurrence of the over-steer event.
"It is contemplated that the housing can be mounted to the aircraft landing gear and the trigger is a protrusion on the aircraft landing gear that engages the cam during the over-steer event. It is further contemplated that the actuator biased in the disarmed position maintains the cam in the triggered position after an over-steer event. The actuator-engaging portion of the cam can be shaped engage the actuator in the triggered position to prevent manual rotation of the cam. For example, it is contemplated that a side surface of the actuator-engaging portion defines a depression to prevent manual rotation of the cam. It is further considered that the actuator can be a plunger with a rounded end and the actuator-engaging portion of the cam has concave end portion to prevent accidental switch actuation. In some embodiments, the trigger-engaging portion of the cam can protrude from the housing in the active position, and that in the triggered position, the trigger-engaging portion of the cam is recessed within the housing. It is further considered that the an axis of rotation of the cam within the housing can be positioned to result in a large movement of the actuator-engaging portion from a small movement of the trigger-engaging portion.
"In another embodiment, a switch device is disclosed comprising a switch having an actuator moveable between a retracted and extended position, the actuator biased to the extended position; a cam housing coupled to switch; and a cam rotatable within the cam housing, the cam engaging the actuator and rotatable from an active position to a latched position, in the active position the cam maintains the actuator in the retracted position. It is contemplated that the cam can have an actuator-engaging surface that is shaped to engage the actuator in the active position to prevent unintended switch actuation. For example, the actuator can be a cylindrical plunger with a rounded end and the actuator-engaging surface can be concave shaped. It is considered that in the latched position the actuator is in the extended position and engages the cam to limit movement of the cam towards the active position. The latching surface can be shaped to limit movement of the cam when engaged with the actuator in the latched position. In alternative embodiments, the latching surface can define a depression to limit movement of the cam when engaged with the actuator in the latched position. In other alternative embodiments, the latching surface can be angled to prevent movement of the cam when engaged with the actuator in the latched position.
BRIEF DESCRIPTION OF THE DRAWINGS
"The present invention will now be described in further detail with reference to the following figures:
"FIG. 1 is an exploded view of an embodiment of a switch assembly;
"FIG. 2A is a perspective view of an embodiment of a switch assembly;
"FIG. 2B is a bottom end perspective view of the switch assembly shown in FIG. 2;
"FIG. 3 is a top view of a diagram of an embodiment of an over-steer detection system for detecting an over-steer event of an aircraft landing gear;
"FIGS. 4A-D illustrates an embodiment of a switch assembly, described herein, in use moving between an armed position to a disarmed position;
"FIGS. 5A-C illustrates an embodiment of a cam of the switch assembly, described herein, interacting with the actuator of the switch;
"FIG. 6 illustrates an embodiment of a cam and actuator geometry that may not be suitable to prevent rotation of the cam back to the armed position; and
"FIG. 7 illustrates an embodiment of a cam and actuator geometry that is preferable to prevent rotation of the cam back to the armed position."
For more information, see this patent application: Ataman, Gary.
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