Patent Application
20100076623
This application claims priority to French Application No. 08 51889, filed on 25 Mar. 2008, the disclosure of which is incorporated by reference herein in its entirety.
1. Field
The subject of the disclosed embodiments is an improved aircraft braking process.
The field of the disclosed embodiments is aviation and, more specifically, aircraft. More specifically, the field of the disclosed embodiments is aircraft braking systems.
One goal of the aspects of the disclosed embodiments is to improve aircraft braking quality. Here, quality is understood to mean both the effectiveness of the braking and the comfort of the people onboard the aircraft during the braking phase.
Another goal of the aspects of the disclosed embodiments is to protect the front landing gear of the aircraft.
2. Brief Description of Related Developments
In the state of the art, during landing, the wheels of the main landing gear of an aircraft with so-called “tricycle” landing gear, i.e., rear landing gear, located behind the center of gravity of the aircraft, touch the ground before the wheel or wheels of the front landing gear, and do so with more or less of a time shift, depending on the trim of the aircraft and the speed of the stall. If the pilot gives the braking command before the main landing gear touches down, or very quickly thereafter, the pressure can be controlled in the brakes, while the front landing gear is not yet in contact with the ground.
If this braking is sustained, i.e., done at the aircraft's maximum braking capacity, the rapid rise in pressure in the brakes can cause major torque that will result in rapid derotation of the airplane, with a risk of overloading, and hence damaging the front landing gear. This damage can go as far as breakage in the worst cases.
The aspects of the disclosed embodiments solve this problem by adapting the aircraft braking based on its trim. The disclosed embodiments introduce weighting dependent at least on the aircraft trim into the braking control loop. This guarantees that maximum braking can be obtained only if the trim is such that all of the aircraft landing gear are in contact with the ground.
The purpose of the disclosed embodiments is, therefore, an aircraft braking process controlled by a command logic in the aircraft:
In one variation, the process in the disclosed embodiments is also characterized by the fact that the braking command is modified only if the difference between the trim A and a minimum trim Amin is greater than a predetermined threshold difference ΔS, so the maximum braking possibilities can be found again when the front wheel is close to the ground.
In one variation, the process in the disclosed embodiments is also characterized by the fact that the modification of the braking command is eliminated if the braking exceeds a predetermined period of time, so as not to reduce the braking possibilities when the aircraft is supposed to have reached a trim close to Amin, independently of the measured value of A.
In one variation, the process in the disclosed embodiments is also characterized by the fact that this elimination is degressive over a predetermined period of time.
In one variation, the process in the disclosed embodiments is also characterized by the fact that the elimination is linear in time.
In one variation, the process in the disclosed embodiments is also characterized by the fact that the adaptation of the braking command continuously combines, at each possible value A of the trim, a weighted coefficient P(A) of an initial braking command with the modified command K' then being the product of the initial command K times the weighted coefficient.
In one variation, the process in the disclosed embodiments is also characterized by the fact that P(A) has a value of one if the difference between the trim A and the minimum trim Amin is less than or equal to a strictly positive threshold difference ΔS, and P(A) takes a constant value strictly less than one in the other cases.
In another variation, the process in the disclosed embodiments is also characterized by the fact that P(A) has a value of one if the difference between the trim A and the minimum trim is less than or equal to a threshold difference ΔS, which can be positive or zero, and P(A) is a decreasing function of A starting with 1.
In one variation, the process in the disclosed embodiments is also characterized by the fact that the decrease is linear.
In another variation, the process in the disclosed embodiments is also characterized by the fact that the decrease is hyperbolic.
The braking process according to the aspects of the disclosed embodiments is advantageously used by an aircraft braking device with means of braking, and said means of braking include:
The aspects of the disclosed embodiments will be better understood by reading the following description and examining the figures accompanying it. They are presented for purposes of indication and are in no way limiting:
The figures show:
The device 102 is designated, in practice, by the term “calculator.”
The memory 103 has at least some instruction codes for implementing the process in the invention. These instruction codes are recorded in a zone 103.1 of the memory 103.
The circuits 105 allow the device 102 to be connected to the other communicating devices of the aircraft 101. For the invention, these communicating devices are at least:
In this description, when an action is sent to a device, that action is in fact carried out by a microprocessor of said device controlled by instruction codes recorded in a program memory of said device.
Device 107 is connected to device 102 via an input of circuits 105 and the bus 110. If the signal produced by device 107 is analog, it is converted into a digital signal by the circuits 105 and placed at the disposal of the processor 104. This is then called the instruction signal Kc. Signal Kc varies as a function of the stress on the device 107 by the pilot of the aircraft.
In step 201, the device 102 produces an initial command signal K of the braking device 109. In the state of the art, this signal K is sent, via the bus 110, to the braking device 109. Device 109 then converts this command into a pressure in the braking system. The aircraft then slows down.
In the invention, the device 102 passes from step 201 to step 202 for aircraft trim acquisition. The trim is measured by device 102, which queries device 108 via the bus 110. In one variation of the invention, the device 108 constantly issues a measurement of the trim that is received and stored by device 102 in a memory, not shown. The trim measurement is therefore either requested from device 108 or read in a memory, which is itself regularly updated by data from device 108.
Device 102 passes from step 202 to step 203 to modify the initial command K with a view to producing a command K', called the modified command.
This modification is the type:
K′=p(A)·K
where A is a trim measurement and p is a function of A.
The result of p(A) is an interval number [0, 1]. Generally, the closer A is to the value Amin, the closer p(A) is to one.
There are several possible variations for the function p(A).
p(A) has a value of “one” when the difference between A and Amin is less than a threshold difference ΔS. For example, ΔS is 2°. Then when the different A-Amin is greater than ΔS, p(A) decreases linearly from the value 1 to the value 0, which is reached for A being a value Amax, for example a value Amax between 16° and 20° representative of the maximum trim of an aircraft on the ground. In another variation, the decrease is hyperbolic. In still another variation, the decrease starts when A is worth Amin.
From step 203, the device 102 passes to a step 204 in which it sends the modified command K' to device 109, as it would have sent the initial command K before the invention.
In one variation of the invention, the device 102 has a clock 111 and a date memory 112. In this variation, the device 102 records in the memory 112 the starting date of the braking. Braking starts as soon as device 102 receives instructions from device 107. Device 102 thinks that braking is finished if there is a predetermined time interval within which it receives no instructions from device 107. This predetermined time interval is one second, for example. An absence of instructions is equivalent to no instructions.
In this variation, in step 203, the device 102 determines the amount of time since the braking started. This determination is done by calculating the difference between the date issued by the clock 111 and the date recorded in the memory 112. If this difference is greater than a predetermined threshold ΔSt, then step 203 is not implemented and then
K′=K
In one example, ΔSt is two seconds. In practice, ΔSt is in the interval of seconds.
In this variation, in order not to risk a sudden change in braking pressure, one variation provides for the initial command K to be re-established gradually. This means that p(A) is no longer modified according to the trim, but according to the time following a law like:
p(A,t)=p(A,t−1)+(1−p(A,t−1))/2
In other words, p(A) on the date t is a function of p(A) at the time of its preceding evaluation on date t−1. It is also a function of the difference between its value at its preceding evaluation and 1. This makes it possible to guarantee fast, but non-violent re-establishment of the maximum braking.
In one variation, the law of return to the initial command K is such that one passes from p(A, ΔSt) to 1 in a predetermined time. p(A, ΔSt) is the value of p(A) ΔSt seconds after the start of braking. This rise in p(A) is linear, parabolic, logarithmic or other.
The invention thus guarantees that there will be no fast derotation of the aircraft. It also guarantees that maximum braking is available at the end of a predetermined time.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08 51889 | Mar 2008 | FR | national |
