Travel of a vehicle brake lever based on the available braking force between the brake wheel and the ground

Abstract

An aircraft, comprising: a brake lever for receiving a pilot braking input as a lever stroke of the brake lever; a brake wheel operatively coupled to the brake lever to brake the aircraft based on the lever stroke; a brake actuator operatively coupled to the brake wheel to apply a braking force in response to a braking pressure supplied to the brake actuator; and a brake pressure circuit. The brake pressure circuit is configured to: estimate a maximum braking pressure above which the brake wheel will slip relative to the ground surface; scale a lever gain of the brake lever to command the maximum braking pressure at a full stroke of the brake lever such that a remaining brake lever stroke indicates an amount of remaining braking capacity of the aircraft; and brake the brake wheel based on the lever gain and the lever stroke.

Description

Technical Field

[0001] The present disclosure generally relates to aircraft braking systems, and more particularly to an aircraft braking system that scales a brake pressure gain to command a maximum braking force at the full stroke of a brake lever such that the remaining brake lever stroke indicates the amount of remaining braking ability of the aircraft. Background Art

[0002] Aircraft are equipped with wheel brakes to decelerate the aircraft when it is traveling on the ground. Wheel brakes are typically designed to provide more braking force than can be transferred between the landing gear tires and the runway surface. For example, an anti-lock braking function is typically implemented to reduce the amount of braking applied when the wheel is in danger of becoming locked and skidding across the ground surface.

[0003] The force that can be transferred between the wheel and the ground surface depends on environmental conditions, tire properties, ground conditions, the normal force on the tire, and other factors. In wet conditions, in snowy conditions, or when there is loose gravel or other debris on the runway, the braking ability of the aircraft can be significantly reduced. Reduced braking ability can make it difficult to land the aircraft on a short runway or at high speed.

[0004] Typical aircraft braking systems command the brake pressure of the braking system based on the brake lever travel distance according to how far the pilot presses the brake lever. In an aircraft with an anti-skid system, the anti-skid limit prevents the application of a brake pressure greater than the amount the aircraft can withstand without causing the tires to skid. This maximum brake pressure amount can vary significantly when considering external factors such as runway conditions and aircraft weight. A heavy aircraft on a dry runway will withstand a high brake pressure that requires a large pilot command.

[0005] When the aircraft is lighter (due to lower fuel conditions or lighter passenger / cargo loading) and on a wet or slippery runway, the braking system will only withstand a low brake pressure before the anti-skid system limits performance. When landing the aircraft at a low weight, the pilot may only command a moderate amount of braking and, due to the large amount of remaining brake lever travel, believe that there is still significant additional braking available. In reality, the pilot may be using almost all of the braking ability. The pilot may then infer from the low lever travel that the aircraft brakes are stronger than their actual ability for future stops under similar conditions.

[0006] Accordingly, it is desirable to provide methods, systems, and aircraft that allow for increased awareness of braking ability under various conditions such that the pilot can have a better understanding of the remaining braking ability. Additionally, other desirable features and characteristics of the present disclosure will become apparent from the following detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background art. Summary of the Invention

[0007] Generally speaking, the embodiments provided herein provide a braking control system that can consider additional information such as aircraft weight and the estimated runway conditions, and adjust the relationship between the brake lever and the brake pressure such that the full travel of the brake lever is only slightly above the anti-skid limit, enabling the pilot to have a tactile estimate of how much available braking is being commanded.

[0008] In a first non-limiting example, an aircraft includes: a brake lever configured to receive a pilot braking input as a lever travel of the brake lever; a brake wheel operably coupled to the brake lever to brake the aircraft based on the lever travel; a brake actuator operably coupled to the brake wheel to apply a braking force in response to a brake pressure provided to the brake actuator; and a brake pressure circuit. The brake pressure circuit is configured to: estimate a maximum brake pressure above which the brake wheel will slip relative to the ground surface; scale a lever gain of the brake lever to command the maximum brake pressure at the full travel of the brake lever such that a remaining brake lever travel indicates an amount of remaining braking capacity of the aircraft; and brake the brake wheel based on the lever gain and the lever travel.

[0009] In a second non-limiting example, a vehicle includes a brake lever, a brake wheel, and a brake pressure circuit. The brake lever is configured to receive a pilot braking input as a lever travel of the brake lever. The brake wheel is operably coupled to the brake lever to brake the vehicle based on the lever travel. The brake pressure circuit is configured to: estimate a maximum braking force above which the brake wheel will slip relative to the ground surface; scale a lever gain of the brake lever to command the maximum braking force at the full travel of the brake lever such that a remaining brake lever travel indicates an amount of remaining braking capacity of the vehicle; and brake the brake wheel based on the lever gain and the lever travel.

[0010] In a third non-limiting example, a method of braking a vehicle on a ground surface includes: obtaining ground conditions of the ground surface on which the vehicle is operating; determining a normal force on the ground surface at a brake wheel of the vehicle; estimating a ground slip pressure of the braking system of the vehicle at which the brake wheel begins to slide relative to the ground surface; scaling a lever gain of the brake lever to command the ground slip pressure at the full travel of the brake lever; and commanding the braking system based on the lever gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The advantages of the present disclosure will be readily understood as the present disclosure will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0012] Figure 1 is a simplified top view of an aircraft during a braking event according to various embodiments;

[0013] Figure 2 According to various embodiments Figure 1 A simplified diagram of the brake lever of an aircraft;

[0014] Figure 3A and Figure 3B is a graph showing the relationship between vehicle loading and brake pressure and between ground conditions and brake pressure;

[0015] Figure 4 is a diagram showing a method for performing Figure 1 Flowchart of a method for braking an aircraft. DETAILED DESCRIPTION

[0016] The following detailed description is merely exemplary in nature and is not intended to limit the application and uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, summary or the following detailed description.

[0017] In general, the embodiments described herein increase the awareness of the vehicle operator of how much vehicle braking capacity remains. Specifically, the remaining brake lever travel indicates to the vehicle operator how much braking capacity remains in terms of ground traction. In contrast, the remaining brake lever travel in conventional systems indicates how much hydraulic pressure is available to apply to the braking system, regardless of how close the braking is to the traction limit between the wheels and the ground surface. For vehicles with large weight differences between fully loaded and unloaded conditions (e.g., aircraft, freight trucks), the embodiments provide a significant and noticeable difference to the vehicle operator.

[0018] In addition to recognizing the remaining braking capacity, the embodiments described herein also help the pilot provide comfortable braking for the passengers. For example, a lightly loaded aircraft in dry conditions will decelerate very quickly at low commanded brake pressures. By scaling the pressure according to the braking capacity, the lightly loaded aircraft will decelerate more slowly for a given lever travel because the lightly loaded aircraft will reach the anti-skid limit at lower brake pressures, as will become apparent from the following discussion.

[0019] Reference now Figure 1 , shows an example of an aircraft 100 during a braking segment of a landing phase of flight on a ground surface 102 according to some embodiments. Various forces 104 acting on the aircraft 100 under different conditions are shown to help illustrate the benefits and operation of the systems and methods described herein. In some embodiments, the embodiments described herein are applied to other vehicles. It is worth noting that freight trucks and trains may have large weight differences between loaded and unloaded conditions.

[0020] The force 104 includes an ideal maximum braking force 110 and a worst-case maximum braking force 112. The ideal maximum braking force 110 indicates the amount of braking force that the ground surface 102 and the braking wheels of the aircraft 100 would be able to provide for braking the aircraft 100 under dry conditions and with the aircraft 100 fully loaded with fuel and passengers. The worst-case maximum braking force 112 indicates the amount of braking force that the ground surface 102 and the braking wheels of the aircraft 100 would be able to provide for braking the aircraft 100 under wet / slippery conditions and with the aircraft 100 lightly loaded with fuel and passengers.

[0021] In the example provided, the ideal maximum braking force 110 is approximately four times the worst-case braking force 112. The maximum braking force Fmax is calculated according to Equation 1:

[0022] Fmax = μtires * N (Equation 1)

[0023] Mu tires (μtires) is the coefficient of friction between the tire and the ground surface. N is the normal force acting between the aircraft 100 and the ground surface 102 perpendicular to the ground surface 102. For a horizontal runway, the normal force is typically dominated by the weight of the aircraft, but at high speeds of the aircraft, it may increase or decrease due to aerodynamic forces. Therefore, the maximum braking force decreases as the coefficient of friction decreases (e.g., wet / slippery conditions), and decreases as the aircraft weight is lighter (e.g., lightly loaded with fuel and / or passengers).

[0024] According to Equation 2, the maximum force (Fbrake) applied from the brake pads of the aircraft braking system to the braking wheels is similarly given:

[0025] Fbrake = μbrakes * Nbrakes (Equation 2)

[0026] Mu brakes (μbrakes) is the coefficient of friction between the brake pad and the rotor of the braking system of the aircraft 100. Nbrakes is the force applied by the brake pad on the rotor of the braking system and is proportional to the braking pressure commanded by the braking system. In the example provided, as will be understood by those of ordinary skill in the art, the anti-skid system effectively limits Fbrake to be less than Fmax.

[0027] In a system with sufficient braking pressure capacity to command Fmax as the anti-skid limit at a given weight under dry conditions, the deceleration (amax) of the aircraft is given by Equation 3:

[0028] amax = Fmax / weight = μ (Equation 3)

[0029] Now refer to Figure 2 、 Figure 3A andFigure 3B and continue to refer to Figure 1 which shows the lever travel 200 of the brake lever 202 and the traction limit diagrams 300 and 350. In the provided example, the brake lever 202 is a foot-actuated brake pedal. In some embodiments, multiple pedals provide braking for multiple sets of brake wheels or different parts of the vehicle. For example, in a large truck, a first brake pedal can control the braking of the tractor / cab, while a second brake pedal can control the brakes on the trailer. In some embodiments, the brake lever is a manual handle in the cockpit of an aircraft. The brake lever 202 includes a foot support portion 212 and a link arm portion 214. The driver of the aircraft 100 presses on the foot support portion 212 to move the brake lever through a lever travel 206 between the shown rest position and the full lever travel position 204.

[0030] Conventional braking systems utilize a fixed braking pressure relationship where the maximum possible braking pressure is commanded at the full travel position 204. The occurrence of wheel lock-up depends largely on the ground conditions 352 and vehicle loading 312, as Figure 3A and Figure 3B shown. As the vehicle loading 312 increases, the traction limit 314 for wheel lock-up occurs at a higher braking pressure 310. Similarly, as the ground conditions 352 improve, the traction limit 354 for wheel lock-up occurs at a higher braking pressure 310. Thus, in a heavily loaded vehicle with good ground conditions, wheel lock-up occurs at the highest pressure. Conversely, the lowest braking pressure at which wheel lock-up occurs is for a lightly loaded vehicle with poor ground conditions.

[0031] The lever travel 220 shows how wheel lock-up 221 occurs at the full travel position 204 under heavy loading in dry conditions in a conventional system and in the embodiments described herein. The lever travel 222 shows how, using a conventional system, wheel lock-up 221 occurs at approximately half of the full pedal position 204 of the lever travel 206 under light loading and dry conditions. The lever travel 224 shows how, using a conventional system, wheel lock-up 221 occurs at approximately one-quarter of the full pedal position 204 of the lever travel 206 under light loading and wet conditions. Conversely, due to the lever gain adjusted according to the method described below, the embodiments described herein reach wheel lock-up 221 at a lever travel 230 for all loading and ground surface conditions. In the provided example, the lever travel 230 is at the full travel position 204 of the brake lever 212. As used herein, the term "full travel" refers to the longest travel value that, before being adjusted according to task 424 below, would result in an increase in the braking pressure applied to the braking system.

[0032] The brake pressure circuit 250 adjusts the lever gain associated with the lever travel 206. The term "lever gain" refers to the relationship between the lever travel and the hydraulic pressure commanded in the brake system 260. In the provided example, the brake pressure circuit 250 is an electronic circuit that commands the brake system 260 based on an input from the lever travel sensor 252. For example, the brake pressure circuit 250 can command a pressure control solenoid to deliver hydraulic fluid to the brake system at a pressure based on the lever travel and the lever gain. In some embodiments, the brake pressure circuit 250 is a mechanically linked system that utilizes mechanical advantage to command higher or lower pressures based on the weight of the aircraft 100 and / or other factors.

[0033] The brake system 260 includes an actuator 262 and a brake wheel 264. For example, the actuator 262 and the brake wheel 264 can be conventional brake actuators and brake wheels. In the provided example, the actuator 262 is a solenoid that selectively allows hydraulic engagement of the brake rotor. In some embodiments, the actuator 262 is an electronic circuit that manipulates an electronic circuit to provide a back EMF to the brake wheel 264. In some embodiments, other types of actuators are utilized.

[0034] Now referring Figure 4 , a method 400 for applying brakes to a vehicle is shown according to some embodiments.

[0035] Task 410 obtains the ground conditions of the ground on which the vehicle is operating. The ground conditions indicate the coefficient of friction between the aircraft tires and the runway. In the provided example, the ground conditions are estimated based on the presence of rain, snow, or other ground condition indicators.

[0036] Task 412 determines the normal force on the ground at the brake tires of the vehicle. The weight of the aircraft 100 can double when fully fueled compared to the same aircraft with a light fuel load. In the provided example, the aircraft 100 takes into account the weight of the fuel and cargo entered by the pilot before takeoff. In some embodiments, weight sensors on the wheels can be utilized to directly measure the normal force on the ground.

[0037] Task 414 estimates the ground slip pressure of the brake system above which the brake tires slide relative to the ground. For example, task 414 can utilize Equation 1 to estimate the ground slip pressure based on the normal force and the ground conditions.

[0038] Task 416 scales the lever gain of the brake lever to command the ground slip pressure at the full travel position of the brake lever. For example, a computer in the aircraft 100 can scale the brake command such that a full lever travel gives the pilot the full braking capacity estimated in task 414.

[0039] Task 418 commands the braking system based on the lever gain. For example, the hydraulic pressure in the braking system can press the brake shoes into the brake rotor. The friction between the brake shoes and the rotor generates the friction that decelerates the aircraft. In other embodiments, the torque in the braking system can come from, for example, the inductance used in regenerative braking.

[0040] Task 420 determines whether the brake lever is in the full stroke position. When the brake lever is in the full stroke position, method 400 proceeds to task 422. When the brake lever is not in the full stroke position, method 400 returns to task 418.

[0041] Task 422 determines whether the anti-skid system is activated. When the anti-skid system is not activated, method 400 proceeds to task 424. When the anti-skid system is activated, method 400 returns to task 418.

[0042] Task 424 increases the lever gain. For example, in task 424, for a given lever stroke, the brake pressure circuit 250 can increase the pressure commanded to the braking system 260. Thus, if the pilot reaches full lever stroke and the anti-skid system has not intervened, the brake pressure will rise until the anti-skid limit is reached. In the example provided, if the anti-skid limit is not reached, the brake pressure circuit 250 increases the brake pressure when the lever stroke exceeds 90% of the full lever stroke.

[0043] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that there are a large number of variations. It should also be understood that the exemplary embodiment or exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of the present invention in any way. On the contrary, the foregoing detailed description will provide a convenient roadmap for those skilled in the art to implement the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of the elements without departing from the scope of the present invention as set forth in the appended claims and their legal equivalents.

Claims

1. An aircraft, comprising: A brake lever for receiving a pilot braking input as a lever stroke of the brake lever, wherein the brake lever is movable between a rest position and a full - stroke position; A brake wheel operatively coupled to the brake lever to brake the aircraft based on the lever stroke; A brake actuator operatively coupled to the brake wheel to apply a braking force in response to a braking pressure supplied to the brake actuator; And A brake pressure circuit configured to: Estimate a maximum braking pressure above which the brake wheel will slip relative to the ground surface; Scale a lever gain of the brake lever to command the estimated maximum braking pressure at the full - stroke position of the brake lever such that when the brake lever is between the rest position and the full - stroke position, the remaining amount of brake - lever stroke to reach the full - stroke position indicates the remaining braking capacity of the aircraft, wherein the lever gain defines a relationship between the lever stroke of the brake lever and the braking pressure supplied to the brake actuator; And Brake the brake wheel based on the lever gain and the lever stroke.

2. The aircraft according to claim 1, wherein, The brake pressure circuit is further configured to obtain a ground condition of the ground surface, and wherein the estimated maximum braking pressure is based in part on the ground condition.

3. The aircraft according to claim 1, wherein The brake pressure circuit is further configured to obtain a normal force applied by the ground surface on the brake wheel, and wherein the estimated maximum braking pressure is based in part on the normal force.

4. The aircraft according to claim 3, wherein, The brake pressure circuit is further configured to obtain the weight of the aircraft and to use the weight of the aircraft as an approximation of the normal force.

5. The aircraft according to claim 1, wherein, The brake pressure circuit is further configured to increase the lever gain in response to determining that the brake lever is at or near the full - stroke position and an anti - skid braking system has not been activated.

6. The aircraft according to claim 5, wherein, The brake pressure circuit is configured to increase the lever gain when the brake lever is at or near the full - stroke position until the anti - skid braking system is activated.

7. The aircraft according to claim 1, wherein, The brake pressure circuit is further configured to: in response to detecting activation of the anti - skid system when the brake lever is in a position less than the full - stroke position, use the currently scaled lever gain throughout the braking event to maintain a consistent braking feel throughout the braking event.

8. The aircraft according to claim 1, wherein, The brake pressure circuit is further configured to scale the lever gain using linear scaling.

9. A vehicle, comprising: A brake lever for receiving a driver braking input as a lever stroke of the brake lever, wherein the brake lever is movable between a rest position and a full - stroke position; A brake wheel operatively coupled to the brake lever to brake the vehicle based on the lever stroke; and A brake pressure circuit configured to: Estimate a maximum braking force above which the brake wheel will slip relative to the ground surface; Scale the lever gain of the brake lever to command the estimated maximum braking force at the full - stroke position of the brake lever, such that when the brake lever is between the rest position and the full - stroke position, the remaining brake lever travel to the full - stroke position indicates the amount of braking capacity remaining for the vehicle, where the lever gain defines the relationship between the lever travel of the brake lever and the braking pressure supplied to a brake actuator associated with the brake wheel; And Brake the brake wheel based on the lever gain and the lever travel.

10. The vehicle according to claim 9, wherein, The brake pressure circuit is further configured to acquire the ground condition of the ground surface, and wherein the estimated maximum braking force is based in part on the ground condition.

11. The vehicle according to claim 9, wherein, The brake pressure circuit is further configured to acquire the normal force applied by the ground surface on the brake wheel, and wherein the estimated maximum braking force is based in part on the normal force.

12. The vehicle according to claim 11, wherein, The brake pressure circuit is further configured to acquire the weight of the vehicle and to use the weight of the vehicle as an approximation of the normal force.

13. The vehicle according to claim 9, wherein, The brake pressure circuit is further configured to increase the lever gain in response to determining that the brake lever is at or near the full - stroke position and the anti - lock braking system has not been activated.

14. The vehicle according to claim 13, wherein, The brake pressure circuit is configured to increase the lever gain when the brake lever is at or near the full - stroke position until the anti - lock braking system is activated.

15. The vehicle according to claim 9, wherein, The brake pressure circuit is further configured to: in response to detecting activation of the anti - lock system when the brake lever is in a position less than the full - stroke position, use the currently scaled lever gain throughout the braking event to maintain a consistent braking feel throughout the braking event.

16. The vehicle according to claim 9, wherein, The brake pressure circuit is further configured to scale the lever gain using linear scaling.

17. A method of braking a vehicle on a ground surface, the vehicle including a brake lever movable between a rest position and a full - stroke position, the method comprising: Acquire the ground condition of the ground surface on which the vehicle is operating; Determine the normal force on the ground surface at the brake wheel of the vehicle; Estimate the ground - slip pressure of the vehicle's braking system at which the brake wheel begins to slide relative to the ground surface; Scale the lever gain of the brake lever to command the estimated ground - slip pressure at the full - stroke position of the brake lever, such that when the brake lever is between the rest position and the full - stroke position, the remaining brake lever travel to the full - stroke position indicates the amount of braking capacity remaining for the vehicle, where the lever gain defines the relationship between the lever travel of the brake lever and the braking pressure supplied to a brake actuator associated with the brake wheel; And Command the braking system based on the lever gain.

18. The method according to claim 17, wherein, Determining the normal force on the ground surface is based on the weight of the vehicle.

19. The method according to claim 17, further comprising increasing the lever gain in response to determining that the brake lever is at the full - stroke position and the anti - lock braking system has not been activated.

20. The method according to claim 19, wherein Increasing the lever gain includes: increasing the lever gain when the brake lever is in the full stroke position until the anti-skid braking system is activated.

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