Abstract:
A method and system for braking aircraft landing gear wheels after initialization of landing gear retraction. The system includes monitors, controlling components, measurement components, a fault recording memory, fault annunciation components, wheel braking system and brakes. The monitors monitor speed of the landing gear wheels and landing gear position. The control component generates braking instructions based on the monitored speed of the wheels and position of the landing gear.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to aircraft systems and, more specifically, to aircraft braking systems. 
     BACKGROUND OF THE INVENTION 
     After takeoff, the landing gear of an aircraft is retracted as soon as possible. In order to safely stow the landing gear in the fuselage, the wheel speed must be zero (not spinning). Otherwise, damage can occur to components, such as hydraulic lines, within the landing gear bay. This is of special concern when a spinning wheel has shredded. For example, tread rotating with a failed tire can potentially damage flight equipment when the rotating, failed tire enters the wheel well. 
     Presently wheel braking during landing gear retraction is a passive non-monitored function. That is, the flight crew has no way of knowing if the wheels are spinning while being retracted. Thus, the flight crew does not have the ability to stop gear retraction if the wheels are spinning. Therefore, there exists a need to ensure that wheels are not spinning before the landing gear is fully retracted. 
     SUMMARY OF THE INVENTION 
     The present invention is a method and system for braking aircraft landing gear wheels after initialization of landing gear retraction. The system takes advantage of existing physical components of a brake control system. Thus very little new hardware needs to be added to accomplish the functionality of the present invention. The present invention is an active control system. The Brake Metering Valves in an airplane can be made “less costly”, “less complex” and “lighter” by elimination of the existing gear retract function. Gear retraction is made “more safe” because the threat from a flailing tire tread is greatly reduced. The braking system formed in accordance with the present invention reliably stops tire rotation before a failed tire can enter the wheel well where a tread rotating with the tire can potentially damage combinations of flight critical equipment. 
     An embodiment of the system includes monitors, controlling components, measurement components, a fault recording memory, fault annunciation components, wheel braking system and brakes. The monitors monitor speed of the landing gear wheels and landing gear position. The control component generates braking instructions based on the monitored speed of the wheels and position of the landing gear. The measurement components provide indications proportional to wheel speed and landing gear position. The fault recording memory records incidents of wheels spinning above a threshold when the landing gear position is at a given threshold. The braking system component applies brake pressure according to the generated braking instructions. 
     The generated braking instructions suitably include instructions to implement wheel braking with onset of gear retraction, increase braking if the landing gear position is at least to a threshold position and wheel speed is greater than a speed threshold value. 
     The system also includes a component for alerting the flight crew, if the landing gear position is at least to a threshold position and wheel speed is greater than a speed threshold value. 
     The system includes a component for inhibiting landing gear retraction, if the landing gear position is at least to a threshold position and wheel speed is greater than a speed threshold value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings. 
     FIG. 1 illustrates an example system block diagram formed in accordance with the present invention; 
     FIG. 2 illustrates a flow diagram performed by the example system shown in FIG. 1; and 
     FIGS. 3-7 illustrate example embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an exemplary system  20  for monitoring and braking landing gear of an aircraft during retraction based on the monitored condition of the landing gear. The system  20  includes a braking system control unit  22 , which is electrically coupled to Flight Deck Brake and Landing Gear Controls  24 , and a wheel braking system  26 . The wheel braking system  26  suitably includes wheel brakes (not shown), electrical or hydraulic components (not shown), wheel speed monitoring devices (not shown), and landing gear position monitoring devices (not shown). The braking system control unit  22  is suitably a software and/or hardware computer-based system that analyzes signals received from the wheel braking system  26  and the Flight Deck Brake and Landing Gear Controls  24  to generate instructions (signals) for the wheel braking system  26  and provide any necessary feedback to the flight crew through the Flight Deck Brake and Landing Gear Controls  24 . The Flight Deck Brake and Landing Gear Controls  24  include a landing gear control (e.g. lever) (not shown), and alerting components (not shown), such as visual or audible warning units. 
     When the braking system control unit  22  receives a landing gear up command from the Flight Deck Brake and Landing Gear Controls  24  (i.e., landing gear control), the landing gear actuation system begins gear retraction and the braking system control unit  22  receives landing gear position monitored information and wheel speed information from the wheel braking system  26 . Based on the received monitored position, the braking system control unit  22  determines whether landing gear retraction is progressing successfully or there exists a problem—such as the wheels not slowing down adequately with respect to the monitored landing gear position information. If the landing gear retraction and braking are not progressing satisfactorily, the braking system control unit  22  instructs the wheel braking system  26  to increase wheel braking and/or alerts the flight crew of the situation and/or inhibits landing gear retraction until wheel speed is at zero for safe retraction. Also incidents of problems noted above will be recorded in memory for later retrieval within the brake control unit  22  BITE (built in test equipment). 
     FIG. 2 illustrates an exemplary process  100  that is performed by the braking system control unit  22  shown in FIG.  1 . First, at a block  102 , the process  100  begins when the landing gear lever is moved to the up position after take-off. Next, at a block  103 , the wheel brake system  26  inhibits antiskid function and at a block  104  begins auto-braking of the wheels of the landing gear based on a predefined braking ramp rate. 
     At approximately the same time, landing gear retraction begins. The predefined braking ramp rate is a schedule of increased brake pressure applied in order to stop wheel rotation by a certain time from the beginning of the braking. The time relates to gear retraction speed. At a block  106 , the wheel speed for each wheel is detected by the wheel brake system  26  (wheel speed monitoring devices) and sent to the braking system control unit  22 . At a block  108 , the wheel brake system  26  determines landing gear position based on time since the start of gear retraction or a signal from a landing gear position monitoring device, such as a linear or rotary variable differential transformer. The determined landing gear position is sent to or generated in (when time is used) the braking system control unit  22 . Next, at a decision block  110 , the braking system control unit  22  determines if the landing gear position is at a threshold value. The threshold value is a retract position of the landing gear where wheel speed should be zero before further retraction occurs. If, at the decision block  110 , the landing gear position is not at the threshold value, at a decision block  112  the braking system control unit  22  determines if the speed of all the wheels is zero. If the speed of all the wheels is not zero, the process returns to the block  106 . If the speed of all the wheels is zero, as determined at the decision block  112 , at a block  120  the braking system control unit  22  terminates gear braking. 
     If the landing gear is determined to be at the threshold value, as determined at the decision block  110 , at a decision block  116  the braking system control unit  22  again checks the speed of all the wheels. If the speed of all the wheels is zero, at the block  120  the braking system control unit  22  terminates gear braking. After gear braking is terminated, at the block  120 , at a block  122 , gear retraction continues until the gear is fully up. If, at the decision block  116  not all the wheels are at zero speed, at a block  130  the braking system control unit  22  instructs the wheel braking system  26  to increase braking for a predetermined period of time. After the predetermined period of time, the braking system control unit  22  checks the speed of the wheels at a decision block  132 . If at the decision block  132  the wheel speed is at zero, the process continues to the block  120  where gear braking is terminated and gear retraction continues at the block  122 . If at the decision block  132 , some speed still remains on one or more of the wheels, a fault is generated and recorded in BITE (built in test equipment memory) block  141  within the braking system control unit  22  and the braking system control unit  22  alerts the flight crew at a block  140  and inhibits gear retraction at a block  142 . At a block  144 , after a predetermined period of time has expired in order to allow for the wheels to reach zero speed, gear retraction inhibit is ended at block  143  and the process continues to the block  122  for full gear retraction. 
     In an alternate embodiment, increased braking that is shown at the block  130  does not occur. Instead, the process  100  goes directly from the decision block  116  to generating and recording a fault to BITE at block  141  and alerting the flight crew at the block  140 . This embodiment does not include block  142 ,  144  . . . etc. 
     Because the present invention performs active monitoring and control of wheel braking during retraction, the valve and hydraulic structure for the braking system can be designed in various ways, such as shown in FIGS. 3-7 below. In all of the following examples, the Brake System Control Unit is electrically coupled to wheel speed monitors, landing gear position monitors and flight deck brake and landing gear controls. 
     FIG. 3 illustrates a first exemplary braking system  200 . A Brake System Control Unit  202  is electrically coupled to an Autobrake Valve  204  and Antiskid Valves  210 . The braking system  200  includes a hydraulic pressure source  212  that is coupled to a Brake Metering Valve  214  and the Autobrake Valve  204 . The Autobrake Valve  204  is hydraulically coupled to a Autobrake Shuttle Valve  216 . The Autobrake Shuttle Valve  216  is hydraulically coupled to the Antiskid Valves  210 . The Antiskid Valves  210  are hydraulically coupled to the brakes of the wheels. 
     FIG. 4 illustrates a second exemplary braking system  300 . A Brake System Control Unit  302  is electrically coupled to an Autobrake/Brake Metering Valve  304 , wherein an associated control signal is the mathematically summed resultant of the autobrake and brake metering functions and Antiskid Valves  310 . The braking system  300  includes a hydraulic pressure source  312  that is coupled to the Autobrake/Brake Metering Valve  304 . The Autobrake/Brake Metering Valve  304  is hydraulically coupled to Antiskid Valves  310 . The Antiskid Valves  310  are hydraulically coupled to the brakes of the wheels. 
     FIG. 5 illustrates a third exemplary braking system  400 . A Brake System Control Unit  402  is electrically coupled to an Autobrake Selector Valve  404  and Autobrake/Antiskid Valves  410 , wherein an associated control signal is the mathematically summed resultant of the autobrake and antiskid functions. The braking system  400  includes a hydraulic pressure source  412  that is coupled to a Brake Metering Valve  406  and the Autobrake Selector Valve  404 . The Brake Metering Valve  406  is hydraulically coupled to the Autobrake Selector Valve  404 . The Autobrake Selector Valve  404  is hydraulically coupled to the Autobrake/Antiskid Valves  410 . The Autobrake/Antiskid Valves  410  are hydraulically coupled to the brakes of the wheels. 
     FIG. 6 illustrates a fourth exemplary braking system  500 . A Brake System Control Unit  502  is electrically coupled to a Brake Metering/Autobrake/Antiskid Valves  504 . The braking system  500  includes a hydraulic pressure source  512  that is coupled to the Brake Metering/Autobrake/Antiskid Valves  504 , wherein an associated control signal is the mathematically summed resultant of the Brake Metering/Autobrake/Antiskid functions. The Brake Metering/Autobrake/Antiskid Valves  504  are hydraulically coupled to the brakes of the wheels. 
     FIG. 7 illustrates a fifth exemplary braking system  600 . A Brake System Control Unit  502  is electrically coupled to current drivers  604 . The current drivers  604  are electrically coupled to electric wheel brakes. 
     While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.