An optimized brake pressure control method and system

Abstract

The application relates to an optimized brake pressure control method, comprising the following steps: constructing a database storing a slip rate and a combination coefficient curve, including: (1) drawing a slip rate and a corresponding combination coefficient curve under the condition that the wheel axle advancing speed and the load on the wheel remain unchanged, (2) adjusting the wheel axle advancing speed under the condition that the load on the wheel remains unchanged, and drawing a corresponding slip rate and combination coefficient curve under different wheel axle advancing speeds, and generating a three-dimensional surface graph containing speed, slip rate and combination coefficient, (3) adjusting the load on the wheel, and drawing a corresponding three-dimensional surface graph under different loads, and generating a four-dimensional surface graph containing load, speed, slip rate and combination coefficient, (4) storing the four-dimensional surface graph into the database; calculating the maximum brake pressure based on the slip rate and the combination coefficient curve; and controlling the brake pressure of the wheel based on the maximum brake pressure.

Description

Technical Field

[0001] This application relates to aircraft braking systems, and more particularly to an optimized brake pressure control method and system. Background Technology

[0002] The primary function of an aircraft braking system is to shorten the landing roll distance after landing, bringing the aircraft to a stop as quickly as possible while preventing tire blowouts. Testing, research, and usage have shown that under certain conditions, automatic braking can effectively shorten the landing roll distance. Currently, many commercial passenger aircraft are equipped with automatic braking systems that brake automatically at different deceleration rates. During landing, the automatic braking system automatically adjusts the braking pressure to ensure the aircraft decelerates at a constant rate, significantly improving passenger comfort and reducing pilot workload, while also preventing potential dangers caused by pilot error in braking.

[0003] However, when an aircraft is taxiing on the runway after landing, it is affected by many uncertain factors. These include runway conditions, the coefficient of friction between the wheels and tires and the runway, and the effects of headwinds and crosswinds, making the braking system a typical nonlinear system with nonlinearity, time-varying characteristics, and uncertainties.

[0004] In typical existing braking control laws, when the pilot depresses the accelerator pedal or the automatic braking command outputs braking pressure, the magnitude of this braking pressure is not related to the pressure of the wheels on the ground. It mainly relies on pilot skill braking or pre-selected deceleration rate braking. The typical automatic braking process is as follows: After the aircraft touches down for a period of time (touchdown protection), braking pressure is applied. If the aircraft's deceleration rate does not reach the set target, the braking pressure is increased; if the deceleration rate exceeds the set target, the braking pressure is decreased. If wheel lockup is detected based on wheel speed, the braking pressure is reduced.

[0005] Existing braking control laws cannot reflect the impact of airflow changes on aircraft lift (the same taxiing speed results in different lift distributions depending on wind speed and direction). Because wheel load data is not used, the braking system can only initially output the same braking pressure value A to both the left and right sides simultaneously. Then, it uses changes in wheel speed and aircraft trajectory deviation as feedback. If yaw is detected, the braking pressure on one side is reduced; if one tire locks up, the braking pressure is further reduced. This feedback-based adjustment is reactive and easily leads to left-right braking imbalance, causing repeated twisting and shaking. Therefore, it is necessary to change the passive control approach and adopt technical measures to improve the aircraft braking system.

[0006] Moreover, when an aircraft is landing smoothly, even if the wheels have touched the ground, the lift is still relatively large. The existing technology of traditional automatic brakes cannot sense the wheel load. In order to achieve the predetermined aircraft deceleration rate, the brake pressure is output according to the program, which can easily lock the wheels. Even if the anti-skid brake system is very reliable, frequent pressure relief adjustments will reduce braking efficiency and increase the takeoff distance.

[0007] Specifically, during high-speed taxiing, airflow (especially crosswinds) can cause different lift levels on the left and right wings, leading to an imbalance in wheel load. The aircraft's cargo load or fuel consumption from the left and right fuel tanks also contributes to this imbalance. The side with greater lift has a lower runway contact coefficient, a difference that existing braking control laws cannot detect. The heavier load side's wheels have stronger braking effect, while the other side's braking effect is weaker. Applying the same braking pressure can cause the aircraft to veer, posing a risk of runway derailment. The lighter load side is also prone to locking up. Prior to this application, even with automatic braking deceleration set during strong crosswinds, the lighter load side's wheels could frequently trigger lock-up and anti-skid mechanisms, reducing braking efficiency and increasing taxiing distance.

[0008] Furthermore, large aircraft not only exhibit asymmetrical loads on both sides, but the loads on the front and rear landing gear wheels on the same side are also not entirely the same. Therefore, during landing, the vertical load differences between the different main braking wheels are very large, and the relative relationships of the asymmetrical loads are extremely complex. Asynchronous landing of the left and right wheels, as well as front and rear wheels, crosswinds at the airport, and differences in runway conditions are all significant influencing factors. Asymmetrical braking effects can cause the wheels to yaw the aircraft.

[0009] Furthermore, besides automatic braking control laws that specify a deceleration rate, there are situations requiring maximum braking efficiency, such as during takeoff abort. Studies show that braking efficiency is highest when the applied braking pressure brings the tires to the peak friction point corresponding to the slip ratio. The performance of braking control strategies largely depends on the application of friction, i.e., the peak ground contact coefficient. This coefficient varies depending on runway conditions and is influenced by many factors such as runway condition, wheel type, and frontal pressure. Inaccurate judgment of the peak contact coefficient can lead to the braking device generating insufficient or excessive braking force, resulting in reduced braking performance. Existing automatic braking mechanisms, because they do not consider some of these important factors, consistently fail to achieve maximum braking efficiency, shortening tire life and wasting resources.

[0010] Therefore, there is a need to provide an optimized brake pressure control method and apparatus to overcome the aforementioned deficiencies in existing brake systems. Summary of the Invention

[0011] In order to maximize braking efficiency without causing the aircraft to yaw, this application proposes an optimized braking pressure control method and device, which adjusts the braking force of the wheel on the heavier side based on the braking force that the wheel on the lighter side can provide.

[0012] According to a first aspect of this application, an optimized brake pressure control method is provided, comprising:

[0013] Constructing a database storing slip ratio and bonding coefficient curves includes the following steps:

[0014] (1) Plot the curve of slip ratio versus corresponding coupling coefficient under the condition that the forward speed of the wheel axle and the vertical load on the wheel remain constant;

[0015] (2) Under the condition that the vertical load on the wheel remains unchanged, the forward speed of the wheel axle is adjusted, and at different forward speeds of the wheel axle, the curves of the corresponding slip ratio and the engagement coefficient drawn in step (1) are executed; the curves of the corresponding slip ratio and the engagement coefficient obtained at different forward speeds of the wheel axle are merged to generate a three-dimensional surface diagram containing speed, slip ratio and engagement coefficient.

[0016] (3) Adjust the vertical load on the wheel and perform step (2) under different vertical loads to draw the corresponding three-dimensional surface diagrams of speed, slip ratio and coupling coefficient; merge the corresponding three-dimensional surface diagrams of speed, slip ratio and coupling coefficient obtained under different vertical loads to generate a four-dimensional surface diagram containing load, speed, slip ratio and coupling coefficient;

[0017] (4) Store the four-dimensional surface diagram containing load, velocity, slip ratio and bonding coefficient into the database;

[0018] The maximum braking pressure is calculated based on the slip ratio and engagement coefficient curve.

[0019] The braking pressure of the wheels is controlled based on the maximum braking pressure.

[0020] According to a second aspect of this application, an optimized brake pressure control system is provided, comprising: means for performing the method as described in the first aspect.

[0021] This overview is provided to introduce, in a simplified form, some of the concepts further described in the detailed description below. This overview is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. Attached Figure Description

[0022] To describe how the above and other advantages and features of this application are obtained, a more specific description of the application briefly described above will be presented with reference to specific embodiments of the application shown in the accompanying drawings. It will be understood that these drawings depict only typical embodiments of the application and are therefore not intended to limit its scope. The application will be described and explained using the drawings and with the aid of additional features and details, in which:

[0023] Figure 1 An example flowchart of an optimized brake pressure control method according to an embodiment of this application is shown.

[0024] Figure 2 An example curve showing slip ratio versus bonding coefficient is shown.

[0025] Figure 3 An example three-dimensional surface plot of slip ratio and engagement coefficient at different wheel axle forward speeds V is shown.

[0026] Figure 4 A schematic diagram showing the change in braking efficiency over time after the anti-lock braking system intervenes is shown. Detailed Implementation

[0027] In their research, the applicant found that incorporating landing gear wheel load parameters into brake control is beneficial. Based on different wheel loads, the maximum braking pressure a wheel can withstand (i.e., the upper limit of braking pressure) can be limited to prevent wheel lock-up. This upper limit increases as the wheel load rises. Specifically, by introducing the actual load borne by the left and right main landing gear wheels during aircraft takeoff (i.e., the contact pressure between the left and right main landing gear wheels and the ground), the existing brake control law is improved. This allows the upper limit of braking pressure applied to the left and right main landing gear wheels to be actively adjusted based on real-time load, rather than the current brake control law passively correcting the braking pressure only after aircraft veers or wheels lock up. This active adjustment, occurring in real-time, ensures that the left and right braking of the aircraft remains dynamically balanced, thus overcoming flight path deviation caused by braking.

[0028] To achieve the above objectives, this application adds a wheel-load dynamic calculation device to the typical braking control device. By inputting aircraft ground speed, wheel speed, wheel load, wheel type and wear, pavement conditions, etc., this device performs maximum braking pressure calculation and slip ratio curve calculation functions, and outputs the calculated maximum braking pressure (upper limit of braking pressure) to the typical braking control device. This new device can exist as a standalone LRU (Line Replaceable Unit) or be integrated into existing aircraft system equipment. In the event of failure of this new device, the braking control law maintains its existing technical state to ensure aircraft safety.

[0029] Specifically, the tire-runway ground contact factor (hereinafter referred to as "contact factor") is related to the wheel rolling speed, tire inflation pressure, tire material, tire tread condition, and runway condition.

[0030] Through repeated research and analysis of a large amount of statistical data, the following statistical patterns were derived, and combined with... Figure 2 From the example curves of slip ratio versus binding coefficient, the binding coefficient μ max Appears in the slip ratio range of 10%-30%; μ max Varying between 0.2 and 0.8; dry cement track μ max =0.6-0.8, μ of wet cement track max =0.4-0.6.

[0031] When the braking pressure increases to the point where the slip ratio generated by the aircraft wheels reaches the slip ratio corresponding to the maximum engagement coefficient at its peak, the braking efficiency of the system rises to 100%. However, if the braking pressure is further increased, causing the slip ratio to exceed the slip ratio corresponding to the peak engagement coefficient, the coefficient of friction will rapidly decrease. If the brakes are not released in time, the aircraft wheels will quickly lock up. In this situation, the slip ratio of the aircraft wheels reaches its maximum value l, resulting in not only very low braking efficiency but also severe tire wear. Therefore, during runway taxiing after aircraft landing, the braking pressure should be increased as much as possible to achieve the slip ratio generated by the aircraft wheels reaching the slip ratio corresponding to the maximum engagement coefficient at its peak. However, it is crucial to avoid increasing the braking pressure excessively, causing the slip ratio to exceed the slip ratio corresponding to the peak engagement coefficient and resulting in wheel lockup. This application addresses this problem through relevant research.

[0032] One innovation of this application lies in calculating the maximum braking pressure (i.e., the upper limit of braking pressure) that each wheel can withstand while avoiding wheel lock-up. Whether it's manual braking or automatic braking with a set deceleration rate, once the braking pressure reaches this maximum, further increases will be prohibited. In other words, after reaching the maximum braking pressure, even if the pilot fully depresses the accelerator pedal or the aircraft has not yet reached the predetermined deceleration rate, the braking pressure will be limited to that maximum and will not continue to increase.

[0033] Therefore, this application adds a wheel load dynamic calculation device to the typical braking control device to perform the maximum braking pressure calculation function and the slip ratio-coupling coefficient curve calculation function. The maximum braking pressure calculation function can give the maximum braking pressure that each wheel can withstand under the current load pressure, thereby achieving the highest braking efficiency while actively preventing tire lock-up.

[0034] exist Figure 1An example flowchart of an optimized brake pressure control method according to an embodiment of this application is shown. The method includes:

[0035] Step 110: In order to accurately calculate the maximum braking pressure (upper limit of braking pressure), it is necessary to first obtain the relationship curve between the slip ratio and the engagement coefficient, that is, to construct a database that stores the slip ratio and engagement coefficient curves.

[0036] The slip ratio curve is related to the tire-runway contact coefficient, which in turn is related to runway wetness / dryness, tire-runway pressure, and aircraft speed, making it a dynamically changing curve. Therefore, the slip ratio and contact coefficient curve cannot be obtained through quantitative theoretical analysis and generally requires a fitting method. For example, a neural network approach can be used, employing a large number of samples for training, to obtain the slip ratio and contact coefficient curve. In traditional brake pressure control systems, the construction of the slip ratio and contact coefficient curve at most considers only a three-dimensional surface composed of speed, slip ratio, and contact coefficient. However, in the scheme of this application, an additional load dimension is added when constructing the slip ratio and contact coefficient curve, thereby forming a four-dimensional surface database of load, speed, slip ratio, and contact coefficient.

[0037] For illustrative purposes, an example process for constructing a slip ratio versus bonding coefficient curve according to this application is described below.

[0038] (1) Plot the curve of slip ratio versus corresponding combination coefficient under the condition that the forward speed V of the wheel axle (hereinafter referred to as "speed") and the vertical load N on the wheel remain unchanged.

[0039] Specifically, first, the wheel axle forward speed V and vertical load N are set on the inertial test bench and kept constant. Then, the wheel speed = ωR (ω is the angular velocity of the tire rotation, R is the outer radius of the tire), axial traction force F, and vertical load N on the wheel are measured, and the engagement coefficient μ = F / N is calculated, along with the corresponding slip ratio σ = (V - ωR) / V. Next, by changing the braking pressure (i.e., changing the axial traction force F), curves showing different slip ratios versus the corresponding engagement coefficient can be plotted. Figure 2 An example slip ratio versus binding coefficient curve has been shown in the figure.

[0040] (2) Under the condition that the vertical load N on the wheel remains constant, the forward speed V of the wheel axle is adjusted, and the corresponding slip ratio and engagement coefficient curves are plotted according to step (1) at different speeds V. Then, the corresponding slip ratio and engagement coefficient curves obtained at different speeds are merged to generate a three-dimensional surface plot containing speed, slip ratio, and engagement coefficient. Figure 3 The figure shows an example of a three-dimensional surface plot of slip ratio versus engagement coefficient at different wheel axle forward speeds V.

[0041] (3) Adjust the vertical load N on the wheel, and draw the corresponding three-dimensional surface plots of speed, slip ratio and engagement coefficient under different vertical loads N according to step (2). Then, merge the corresponding three-dimensional surface plots of speed, slip ratio and engagement coefficient obtained under different vertical loads N to generate a four-dimensional surface plot containing load, speed, slip ratio and engagement coefficient.

[0042] (4) Store the four-dimensional surface plots of the load, speed, slip ratio and bonding coefficient into the database of the test platform.

[0043] The above testing process is continuously performed for different speeds and loads. Furthermore, the four-dimensional surface diagrams of slip ratios and binding coefficients constructed from different speeds and loads can be stored in the database of the test platform, for example, in the form of an array, for future retrieval.

[0044] Below are examples of measured data for slip ratio and bonding coefficient under some example loads and speeds.

[0045] Table 1: Load 10 tons, speed 60 m / s

[0046]

[0047] Table 2: Load 10 tons, speed 50 m / s

[0048]

[0049] Table 3: Load 5 tons, speed 60 m / s

[0050]

[0051] Table 4: Load 5 tons, speed 50 m / s

[0052]

[0053] Given a two-dimensional slip-coefficient curve with load and speed, it can be expressed as an array: A[slip] = coefficient.

[0054] Given a load, the three-dimensional slip-coefficient surface can be expressed as an array A[velocity, slip ratio] = coherence coefficient.

[0055] For a four-dimensional slip-coefficient surface where load, velocity, and slip ratio all vary, it can be represented by an array as A[load, velocity, slip ratio] = slip coefficient.

[0056] It should be understood that the number of tests cannot be infinite when plotting the aforementioned curves and surfaces. Therefore, it is impossible to test every single traction force F, speed V, or load N to plot the corresponding curve. Thus, for those values ​​that were not tested, their curves can be obtained, for example, by reading relevant data from a database derived from tests on a test bench and interpolating it.

[0057] In this way, the above process can be used to construct the slip ratio and engagement coefficient curves of the aircraft wheels under different loads and speeds, thus laying the foundation for the subsequent calculation of the maximum braking pressure (i.e., the upper limit of braking pressure).

[0058] Step 120: After constructing the four-dimensional slip ratio and engagement coefficient curves, calculate the maximum braking pressure based on the slip ratio and engagement coefficient curves.

[0059] Based on experimental results and theoretical analysis, braking pressure has little effect on the friction coefficient of the brake disc, while braking torque increases linearly with increasing braking pressure. During braking, the pressure of the cold air causes the moving and stationary brake discs to press together, generating braking torque through mutual friction. This friction hinders the rolling of the wheels, causing them to tend to slide relative to the ground. The ground, in turn, exerts a static frictional force on the wheels in the opposite direction of the aircraft's motion, creating a rolling torque that maintains the wheels' rolling motion. When the ground friction reaches its maximum value (the rolling torque at this point is called the maximum rolling torque, and the braking pressure is called the critical braking pressure), if the braking pressure and braking torque continue to increase, the ground friction and rolling torque will no longer increase. The braking torque will then exceed the rolling torque, causing the wheels to decelerate until they stop rolling, resulting in relative sliding with the ground and wheel lockup.

[0060] Maximum ground friction force f max =N*μ max (N is the vertical load on the wheel, μ) max (where N is the maximum contact coefficient between the tire and the ground), where N increases as the aircraft lift decreases, and μ max It is related to factors such as aircraft speed, ground conditions, and runway conditions. Generally, it increases as speed decreases.

[0061] As mentioned above, μ max Influenced by many factors, its variation is complex and cannot be expressed by a rigorous mathematical formula. However, based on the four-dimensional slip ratio and bonding coefficient curve constructed in step 110, the slip ratio is adjusted to the maximum (peak) bonding coefficient when given a load and speed, which is μ. max Therefore, the μ can be determined based on the slip ratio and binding coefficient curves constructed above. max .

[0062] μ was determined from the slip ratio and binding coefficient curves. max Then, the maximum braking pressure can be calculated using the following formula:

[0063]

[0064] Among them, P max This indicates the maximum braking pressure, where S is the brake disc area and R is the maximum braking pressure. 刹车 For braking torque, R 轮 Let be the outer radius of the tire, ΔP be the brake dead zone pressure, N be the vertical load on the wheel, and μ be the value of μ. max This is the maximum contact coefficient between the tire and the ground.

[0065] Among these parameters, S and R 刹车 and R 轮 N can be obtained directly from, for example, the product manual or through measurement; μ can be directly detected by the corresponding sensor. max The slip ratio and engagement coefficient curves constructed above can be used to determine that ΔP is the brake dead zone pressure, which is related to the performance of the brake valve. It is a well-known parameter in the field of aircraft braking performance research, so it will not be described in detail here.

[0066] Based on the above formula, the maximum braking pressure (upper limit of braking pressure) corresponding to different speeds and different wheel loads can be calculated.

[0067] It should be understood that the slip ratio and bonding coefficient curves in this application are four-dimensional surface plots of load, velocity, slip ratio, and bonding coefficient. Furthermore, the positions of the maximum peaks in the slip ratio and bonding coefficient curves under different loads and velocities are not entirely the same. Therefore, by introducing the dimensions of load and velocity, the μ determined in this application is... max It can accurately reflect the impact of speed and load on the wheels on the maximum braking pressure, so that the calculated maximum braking pressure P max It can maximize braking efficiency while avoiding wheel lock-up.

[0068] It should also be understood that the load on the wheels changes constantly during taxiing. While theoretically the maximum braking pressure corresponding to each load value could be calculated for perfectly precise control of braking force, in practice, this approach would obviously consume significant system computing resources and lead to frequent adjustments to aircraft components, thus reducing their reliability. Furthermore, such constant adjustments are unnecessary in practical applications. Therefore, a segmented adjustment approach, such as load zoning, can be used, as further explained in the following embodiments.

[0069] Step 130: After calculating the maximum braking pressure, control the braking pressure of the wheel based on the maximum braking pressure.

[0070] As is well known, braking efficiency decreases significantly after the anti-lock braking system (ABS) intervenes. Figure 4 This diagram illustrates the change in braking efficiency over time after the anti-lock braking system (ABS) intervenes. In the diagram, braking efficiency is defined as the ratio of the area under the engagement coefficient curve between point A (the point of first brake lock-up) and point B (the point of final brake release) to the area under the dashed line between points A and B during the aircraft's braking process. It can be observed that in this diagram, two brake lock-up events occur, leading to a decrease in the engagement coefficient curve and thus reducing braking efficiency.

[0071] If the grounding protection function fails after the aircraft lands, and the solution proposed in this application is used, then even if the pilot depresses the brake pedal to the floor, the braking system must determine whether the wheel load supports the maximum braking pressure output. If the braking pressure represented by the pedal travel is greater than P... max The output braking pressure is P. max This avoids triggering the anti-lock braking system and ensures that braking efficiency is always maximized.

[0072] Since the landing and taxiing of an aircraft involves multiple stages and various conditions, it is necessary to discuss how to flexibly control the actual braking pressure applied to the wheel brakes based on the maximum braking pressure, in the context of multiple scenarios.

[0073] During normal taxiing, when manual braking is applied according to the scheme of this application, if the travel applied by the pilot through the brake pedal is less than the pressure limit (maximum braking pressure or upper limit of braking pressure) output by the wheel load dynamic calculation device according to both the left and right brake pressure calculation devices, the brake control device outputs sufficient pressure to brake. If the travel applied by the pilot through the brake pedal is greater than the pressure limit output by the wheel load dynamic calculation device according to both the left and right brake pressure calculation devices, the brake pressure is output according to the pressure limit (excess pressure is deducted to prevent tire lock-up, which would significantly reduce braking efficiency). During taxiing, the aircraft lift gradually decreases while the wheel load gradually increases, and the calculated maximum braking pressure gradually reaches a relatively high value.

[0074] In emergency situations, pilots will fully depress the accelerator pedals (e.g., to abort takeoff), aiming for maximum braking efficiency without causing tire lock-up. The slip ratio-engagement coefficient curve is related to runway conditions, wheel load, and tire slip ratio. Therefore, based on the current aircraft ground speed, wheel speed, and wheel load, the maximum braking pressure corresponding to the maximum engagement coefficient for each wheel can be calculated. Dynamic adjustment is achieved by controlling the braking pressure output of each wheel to reach this maximum braking pressure.

[0075] In automatic braking scenarios (more commonly used in operation): the pilot selects the target deceleration rate on the automatic braking selection panel. In prior technical solutions, when the aircraft's lift during drift was high, the wheel load was not significant; braking according to the target deceleration rate would increase braking pressure, potentially causing wheel lockup. Using the maximum braking pressure calculation in this application limits the upper limit of braking pressure each wheel can accept, preventing wheel lockup. If objective conditions do not allow achieving the target deceleration rate, the aircraft's lift must decrease and the wheel load must increase accordingly before the upper limit of braking pressure for each wheel can be applied according to the target deceleration rate.

[0076] Furthermore, based on different wheel loads and slip ratio-coupling coefficient curves, different braking pressures can be applied to the left and right wheels to achieve equal braking force on both sides of the aircraft, actively preventing deviation. For example, during a crosswind landing, the pilot may choose to land with the nose tilted towards the windward side. The wheel on the windward side will touch down first, exhibiting higher ground pressure, while the other wheel will touch down later. In previous technical solutions, braking the wheel that landed first would exacerbate the aircraft's nose deflection towards the windward side, making it difficult for the aircraft to straighten and align with the runway centerline, increasing the difficulty of crosswind landings. During the full landing roll, the wheel load on the windward side is lower than that on the leeward side. The same braking pressure might cause the windward wheel to lock up, frequently triggering the anti-skid mechanism and reducing braking efficiency. This application can limit the braking pressure of the wheel that landed first by calculating the maximum braking pressure based on the difference in wheel loads on both sides, and then balance the braking force on both sides by calculating the slip ratio-coupling coefficient curve.

[0077] Based on the above application content, four preferred embodiments are further provided to illustrate the actual braking control methods of the present application solution at different stages of the aircraft landing taxiing phase, so as to facilitate the understanding of those skilled in the art.

[0078] Example 1 (Normal taxiing phase):

[0079] Assuming the wheel load N is divided into three intervals, [0-N1], [N1-N2], and [N2-N3], the braking scheme during the coasting process can be simplified as follows:

[0080] For manual foot braking, three P values ​​are set, P1 max P2 max P3 max , respectively, correspond to the three intervals of N mentioned above.

[0081] When the wheel load is between [0-N1],

[0082]

[0083] When the braking pressure represented by the pedal travel is less than or equal to P1 max Output pedal travel braking pressure; when the braking pressure represented by the pedal travel is greater than P1 max Output P1 max .

[0084] When the wheel load is between [N1-N2],

[0085]

[0086] When the braking pressure represented by the pedal travel is less than or equal to P2 max Output pedal travel braking pressure; when the braking pressure represented by the pedal travel is greater than P2 max Output P2 max .

[0087] When the wheel load is between N2 and N3,

[0088]

[0089] When the braking pressure represented by the pedal travel is less than or equal to P3 max Output pedal travel braking pressure; when the braking pressure represented by the pedal travel is greater than P3 max Output P3 max .

[0090] Of course, the three load intervals are given for illustrative purposes only. In reality, the finer the load intervals are divided, the closer it is to continuous processing, and the greater the braking efficiency can be achieved. However, this also consumes more system computing resources and increases equipment wear and tear. Technicians can set an appropriate number of intervals based on the specific aircraft model and the performance of the relevant onboard equipment.

[0091] In a preferred embodiment, the depth to which the foot pedal is pressed can also reach the corresponding P. nmax At this time, an additional reaction force is applied to the pedal to press it down further, so that the driver can feel the resistance and understand that the maximum braking protection has been activated and that continuing to press down further is ineffective.

[0092] Example 2 (Aircraft just after landing and touching down):

[0093] Traditional aircraft grounding protection means that the in-flight foot brake system does not output braking pressure before the aircraft touches down or before the main landing gear has fully rotated. However, it only uses two states, 0 and 1, to determine whether the aircraft has touched down, without reflecting the changes in the aircraft's landing gear load. This results in a lag in the speed control based on the starting of the landing gear rotation.

[0094] When an aircraft changes attitude and its wheels touch down for ground protection, but other wheels do not fully touch down, the ground protection function may fail prematurely due to insufficient delay. In this situation, if the brake pedal is fully depressed in mid-air, there is a safety hazard that the braking system applies braking pressure prematurely, potentially causing deep skidding or tire blowouts during landing, resulting in a potential safety risk.

[0095] In traditional landing processes, if the brake pedal is fully depressed while the aircraft is still in the air, the ground contact protection system activates, resulting in zero braking pressure. After landing, the ground contact protection system fails. Sometimes, it might be desirable to depress the brake pedal fully to allow the braking system to output maximum braking pressure and stop the aircraft. However, this can lead to tire lock-up, triggering the anti-lock braking system (ABS) and increasing braking distance. Therefore, this situation limits aircraft takeoff and landing on short runways and in challenging terrain. However, with the solution proposed in this application, even after landing, depressing the brake pedal fully will depend on whether the wheel load supports the maximum braking pressure output, avoiding triggering the ABS and ensuring maximum braking efficiency at all times.

[0096] Example 3 (Crosswind skidding phase):

[0097] When an aircraft is taxiing in a crosswind, or when spoilers are asymmetrical, if the pilot engages automatic braking, under conventional conditions, the output pressure of the left and right brake discs is the same, resulting in equal brake disc torque. However, due to the different pressures, the contact coefficient between the wheels and the ground differs; the side with the lighter load has a smaller contact coefficient, causing the less loaded side to experience less force than the other, leading to aircraft veer. This invention aims to avoid this situation by ensuring that the ground friction force on both wheels is equal. The load on the left wheel is N. A When the coefficient of friction is μ A The load on the right wheel is N. B When the coefficient of friction is μ B The friction force on the left side of the ground is F. 左 =N A *μ A The friction force on the right side of the ground is F. 右 =N B *μ B N A N B For a known quantity that can be measured by a sensor, pre-set F 左 =F 右 Then it is necessary to control μ A With μ B Assume N A >N B Then control μ A Conversely, N A <N B Control μ B If NA =N B The solution proposed in this application requires no work.

[0098] Specifically, based on the aircraft's base speed V, the speed of the left landing gear V 左 The slip ratio σ of the left wheel was obtained. 左 Then, based on the rotational speed V of the right-side turbine wheel... 右 The slip ratio σ of the right wheel was obtained. 右 If N A >N B μ is obtained (or interpolated) by looking up (or interpolating) a table in a database storing slip-bonding coefficient curves on the measurement platform. B Subsequently, with μ B For target control μ A That is, μ A =N B *μ B / N A Calculate the corresponding target slip ratio σ 左 ', then based on the current left wheel speed of V 左 The actual slip ratio is calculated to be σ. 左 When σ 左 '>σ 左 At that time, increase the braking pressure of the left wheel. 左 '<σ 左 At that time, reduce the braking pressure on the left wheel.

[0099] By using the above-described solution, this application enables the left and right wheels to maintain a symmetrical braking effect during taxiing, thus avoiding the problem of aircraft yaw.

[0100] Example 4 (Emergency Braking Situation)

[0101] In certain special circumstances, aircraft may need to perform emergency braking during taxiing, aiming for maximum braking pressure efficiency. However, as mentioned earlier, even if the pilot depresses the brake pedal fully, it does not necessarily mean that braking efficiency is at its highest. This is because it may cause the wheels to lock up, actually reducing braking efficiency.

[0102] Because we know that during emergency braking, the wheel load N, aircraft speed V, wheel speed ωR, and slip ratio σ = (V - ωR) / V, we can find the corresponding engagement coefficient μ by consulting the four-dimensional slip ratio and engagement coefficient database. The frictional torque that the ground can provide is μ * N * R. If the current tire slip ratio is greater than the optimal slip ratio (i.e., the slip ratio at the peak position of the slip ratio-engagement coefficient curve under the wheel load N and aircraft speed V found in the database), then if a larger braking torque is applied, the tire will decelerate, the tire slip ratio will continue to increase, and the ground friction will decrease, gradually leading to wheel lock-up. Therefore, we need to reduce the braking torque. If the current slip ratio is less than the optimal slip ratio, then we can increase the braking torque, and the tire will decelerate, moving towards the optimal slip ratio. When the slip ratio equals the optimal slip ratio, the braking efficiency is the highest. In this process, the maximum braking pressure (upper limit of braking pressure) is the torque generated at the point where the engagement coefficient is the largest corresponding to the optimal slip ratio.

[0103]

[0104] The maximum braking pressure can be calculated using this formula, and the system can automatically or prompt the pilot to manually maintain the braking force at this maximum braking pressure. This ensures that emergency braking is always at its highest braking efficiency to stop the aircraft as quickly as possible.

[0105] In addition, to further improve the solution of this application, a "correction coefficient K" can be introduced into the solution. The coefficient K can represent, for example, wheel type and material, wear degree, runway pollution status and other additional factors that affect braking.

[0106] For example, when tire tread wears out excessively, the actual μ max The value will be lower than the theoretically calculated value, which means that before the maximum braking pressure limit is reached, the ground contact force is already insufficient, and the tires have already locked up.

[0107] Therefore, the maximum braking pressure of the wheel calculated according to the above scheme of this application may require additional degradation processing. In this case, a correction factor K can be introduced:

[0108] K = P 实际抱死 / P max ; or μ max实际 =K*μ max理论 ;

[0109] Among them, P 实际抱死 P refers to the maximum braking pressure when wheel lockup occurs. max This refers to the theoretical maximum braking pressure calculated using the above-described scheme of this application. μ max实际 It is the actual maximum binding coefficient, while μmax理论 The theoretical maximum binding coefficient is obtained through the above scheme (four-dimensional surface diagram) of this application.

[0110] The maximum braking pressure P when wheel lockup occurs under different wheel types, materials, wear levels, and runway contamination conditions can be tested using an inertial testing platform. 实际抱死 Subsequently, it is compared with the corresponding P calculated according to the above scheme of this application. max Dividing by this allows us to calculate P under different wheel models, materials, wear levels, and runway contamination conditions. max The corresponding correction factor K. This correction factor K can also be stored in the database for later retrieval.

[0111] Thus, after constructing a database of correction coefficients K, in the practical application of the scheme in this application, the maximum braking pressure P is calculated. max Then, a corresponding K value can be selected from the K value database based on the current wheel model, material aging, wear level, and / or runway contamination status. This is achieved by using P... max Multiply by K to obtain the final modified maximum braking pressure to be applied.

[0112] Generally, the K value defaults to 1 and is updated after each landing based on the detection results, indicating a degradation in braking performance due to wheel material aging, tire wear, or runway contamination. When the K value drops to a certain level, such as 0.7, it can trigger an avionics warning to indicate low braking efficiency and the need to check the tires.

[0113] In addition to the K-values ​​based on tire wear, corresponding K-value libraries can also be constructed based on wheel type, material aging, or runway contamination status. Furthermore, these three factors can be combined to create a more complex K-value library.

[0114] Because a long runway may have a contaminated area where other sections are clean, the K value can be set with an effective time. This effective time can be designed as, for example, x milliseconds, meaning the wheel slip ratio is checked every x milliseconds. As long as the slip ratio is not greater than σ0 (e.g., 0.3), the K value is gradually increased, for example, by multiplying it by (1+y), where y can be set according to actual needs, for example, (1+0.1) = 1.1 times or (1+0.2) = 1.2 times. This check cycle is repeated until the K value returns to 1 or the runway locks up again.

[0115] It should be understood that the examples of the correction factors described above are merely illustrative and are not intended to limit the scope of protection of this application. Other factors that have an additional impact on braking performance can also be included in the consideration of the correction factor K.

[0116] Technical effects:

[0117] 1) When applying braking pressure, the upper limit of the pressure is dynamically planned according to the wheel load in advance to actively prevent the tires from locking up, rather than adjusting the anti-skid mechanism afterward, which can reduce the braking distance.

[0118] 2) Based on the braking force provided by the lighter-loaded side wheel, adjust the braking force of the heavier-loaded side wheel to actively achieve braking balance, rather than adjusting afterward, to avoid the aircraft veering off course.

[0119] 3) During emergency braking, the optimal slip ratio is adjusted according to the wheel load, and the optimal braking pressure can be applied for different wheel conditions, which can reduce the braking distance.

[0120] While different embodiments have been described above, it should be understood that they are merely examples and not limitations. Those skilled in the art will appreciate that various modifications in form and detail may be made without departing from the spirit and scope of this application as defined in the appended claims. Therefore, the breadth and scope of this application disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

Claims

1. An optimized brake pressure control method, comprising: Constructing a database storing slip ratio and bonding coefficient curves includes the following steps: (1) Plot the curve of slip ratio versus corresponding coupling coefficient under the condition that the forward speed of the wheel axle and the vertical load on the wheel remain constant; (2) Under the condition that the vertical load on the wheel remains unchanged, the forward speed of the wheel axle is adjusted, and the curves of slip ratio and engagement coefficient plotted in step (1) are executed at different forward speeds of the wheel axle. The corresponding slip ratio and engagement coefficient curves obtained at different wheel axle forward speeds are merged to generate a three-dimensional surface plot containing speed, slip ratio and engagement coefficient; (3) Adjust the vertical load on the wheel and perform step (2) under different vertical loads to draw the corresponding three-dimensional surface diagrams of speed, slip ratio and coupling coefficient; merge the corresponding three-dimensional surface diagrams of speed, slip ratio and coupling coefficient obtained under different vertical loads to generate a four-dimensional surface diagram containing load, speed, slip ratio and coupling coefficient; (4) Store the four-dimensional surface diagram containing load, velocity, slip ratio and bonding coefficient into the database; The maximum braking pressure is calculated based on the slip ratio and engagement coefficient curve. The braking pressure of the wheels is controlled based on the maximum braking pressure.

2. The brake pressure control method as described in claim 1, characterized in that, The calculation of the maximum braking pressure based on the slip ratio and engagement coefficient curve includes: The maximum braking pressure is calculated using the following formula: Among them, P max This indicates the maximum braking pressure, where S is the brake disc area and R is the maximum braking pressure. 刹车 For braking torque, R 轮 Let be the outer radius of the tire, ΔP be the brake dead zone pressure, N be the vertical load on the wheel, and μ be the value of μ. max This is the maximum coefficient of contact between the tire and the ground; Wherein μ max It refers to the peak bonding coefficient corresponding to the slip ratio being adjusted in the four-dimensional surface plot under a given load and wheel axle forward speed.

3. The brake pressure control method as described in claim 1, characterized in that, The method of controlling the braking pressure of the wheels based on the maximum braking pressure includes: During manual braking or automatic braking with a set deceleration rate, when the braking pressure increases to the maximum braking pressure, the braking pressure is prohibited from continuing to rise.

4. The brake pressure control method as described in claim 1, characterized in that, Storing the four-dimensional surface plot, including load, velocity, slip ratio, and bonding coefficient, into the database includes: The four-dimensional surface diagram is stored in the database in array form.

5. The brake pressure control method as described in claim 1, characterized in that, The brake pressure control method is applied to the left and right wheels of the aircraft respectively, so that the braking force of the two wheels is balanced.

6. The brake pressure control method as described in claim 1, characterized in that, The brake pressure control method further includes: A database is constructed to store correction factors, which take into account wheel type and material, wear level, runway contamination status, and other additional factors affecting braking; and After calculating the maximum braking pressure based on the slip ratio and engagement coefficient curve, the maximum braking pressure is multiplied by the corresponding correction coefficient to obtain the corrected maximum braking pressure.

7. The brake pressure control method as described in claim 6, characterized in that, The correction factor is calculated using the following formula: K = P 实际抱死 / P max or μ max实际 =K*μ max理论 ; Where K represents the correction factor, P 实际抱死 P refers to the maximum braking pressure when wheel lockup occurs. max The maximum braking pressure, μ, is calculated by the step of calculating the maximum braking pressure based on the slip ratio and engagement coefficient curve. max实际 It is the actual maximum contact coefficient between the tire and the ground, while μ max理论 It is the maximum bonding coefficient obtained through the aforementioned four-dimensional surface plot.

8. The brake pressure control method as described in claim 6, characterized in that, The correction coefficient is set with an effective time, and the slip ratio of the wheel is checked cyclically with the effective time as the period and the value of the correction coefficient is gradually increased until the value of the correction coefficient returns to 1 or the wheel locks up again.

9. The brake pressure control method as described in claim 1, characterized in that, The brake pressure control method is executed in segments using a load partitioning approach.

10. An optimized brake pressure control system, comprising: Apparatus for performing the method as described in any one of claims 1-9.

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