Braking system providing limited anti-skid control during backup operating mode

Abstract

A braking system providing limited anti-skid control during a backup operating mode. A braking system for a vehicle is disclosed, comprising: an energy storage device configured to store and release energy; a plurality of wheels; one or more processors coupled to the energy storage device when in operation; and a memory coupled to the one or more processors. The memory stores data including a database and program code, which, when executed by the one or more processors, causes the braking system to determine that the braking system is operating in a backup operating mode. In response to determining that the braking system is operating in the backup operating mode, the braking system calculates a dynamic slip of the plurality of wheels. The braking system is caused to determine a slip error by comparing the dynamic slip with a target slip value for the plurality of wheels. The braking system is also caused to calculate an anti-skid command based on the slip error.

Description

Technical Field

[0001] The present disclosure relates to a braking system for a vehicle and more particularly to a braking system that employs a limited anti-slip control strategy during a backup operating mode to conserve energy stored in an energy storage device. Background Art

[0002] Aircraft brakes are used in various situations. For example, aircraft brakes are used to slow down an aircraft during landing along a runway. Aircraft brakes may also be used during ground handling operations such as taxiing, turning, and parking.

[0003] Hydraulic aircraft braking systems include accumulators that store hydraulic brake fluid under pressure. The accumulators serve as a redundant pressure source as well as a backup fluid energy source. Specifically, brake accumulators are primarily used to provide continuous hydraulic pressure after the active hydraulic system is depressurized, and are also used as a backup energy source in the event of a loss of hydraulic pressure within the braking system or when the hydraulic power system of the aircraft becomes inoperable. However, accumulators are only capable of storing a limited amount of hydraulic brake fluid. Therefore, each time the brake pressure is applied and released, the hydraulic fluid level and pressure of the accumulator are depleted. For example, some accumulators are sized to provide only enough hydraulic fluid for approximately six to eight applications of the brakes. In addition, each time the brakes are applied, the accumulator pressure, the accumulator fluid volume, and the maximum brake pressure are all reduced. Once the accumulator becomes empty, the brakes can no longer be applied to reduce the speed of the aircraft.

[0004] In order to conserve hydraulic fluid stored in the accumulator, some functions of the braking system may be unavailable when the accumulator is being used as a backup fluid energy source. For example, at times, the braking system may use only pedal brake control (i.e., the pilot's brake input) without anti-skid control. Anti-skid control provides skid protection by briefly reducing the hydraulic pressure supplied to the wheels, which enables the wheels to rotate and avoid skidding. Omitting anti-skid control may cause problems if the aircraft is traveling along a slippery surface (e.g., an icy runway). Alternatively, in another approach, the braking system may still provide anti-skid control when the accumulator is being used as a backup fluid energy source. However, if the brakes are over-released due to skid protection, this may cause the accumulator to empty relatively quickly. Summary of the invention

[0005] According to several aspects, a braking system for a vehicle is disclosed. The braking system includes: an energy storage device configured to store and release energy; a plurality of wheels; one or more processors, which are connected to the energy storage device and electrically communicate with the plurality of wheels when in operation; and a memory, which is connected to the one or more processors. The memory stores data including a database and program code, which, when executed by the one or more processors, causes the braking system to determine that the braking system is operating in a backup operating mode. In response to determining that the braking system is operating in the backup operating mode, the braking system calculates the dynamic slip of the plurality of wheels. The braking system is also caused to determine a slip error by comparing the dynamic slip with a target slip value for the plurality of wheels, wherein the target slip value is offset relative to an ideal slip value for the plurality of wheels and causes a reduction in the braking efficiency of the braking system. The braking system is also caused to calculate an anti-skid command based on the slip error, wherein the anti-skid command reduces the amount of braking pressure applied to the plurality of wheels.

[0006] According to another aspect, an aircraft is disclosed. The aircraft includes a braking system including a plurality of wheels and an accumulator, wherein the accumulator is configured to store and release fluid energy as a pressurized hydraulic brake fluid. The aircraft also includes one or more processors coupled to the accumulator and in electrical communication with the plurality of wheels when in operation, and a memory coupled to the one or more processors. The memory stores data including a database and program code, which, when executed by the one or more processors, causes the braking system to determine that the braking system is operating in a backup operating mode, wherein the backup operating mode conserves fluid energy stored in the accumulator. In response to determining that the braking system is operating in the backup operating mode, the braking system is caused to calculate a dynamic slip of the plurality of wheels. The braking system is also caused to determine a slip error by comparing the dynamic slip with a target slip value of the plurality of wheels, wherein the target slip value is offset relative to an ideal slip value of the plurality of wheels and causes a reduction in the braking efficiency of the braking system. The braking system is also caused to calculate an anti-skid command based on the slip error, wherein the anti-skid command reduces the amount of braking pressure applied to the plurality of wheels.

[0007] In another aspect, a method for determining an anti-skid command during a backup operating mode of a braking system of a vehicle is disclosed. The braking system includes a plurality of wheels and an energy storage device configured to store and release energy. The method includes: determining, by a computer, that the braking system is operating in the backup operating mode. In response to determining that the braking system is operating in the backup operating mode, the method includes: calculating, by a computer, a dynamic slip of the plurality of wheels. The method also includes: determining a slip error by comparing the dynamic slip to a target slip value, wherein the target slip value is less than the ideal slip value and results in reduced braking efficiency compared to an ideal slip value. Finally, the method includes: calculating an anti-skid command based on the slip error, wherein the anti-skid command reduces the amount of braking pressure applied to the plurality of wheels.

[0008] The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0010] Figure 1 is a schematic diagram of a braking system including an energy storage device in the form of an accumulator according to an exemplary embodiment;

[0011] Figure 2 is a block diagram of a method of determining an anti-skid command when a brake system is operating in a backup operating mode according to an exemplary embodiment;

[0012] Figure 3 is an exemplary mu-slip curve illustrating an ideal slip point and a target slip point according to an exemplary embodiment;

[0013] Figure 4 is a diagram showing a method based on an exemplary embodiment Figure 2 A process flow chart of a method in which the system shown determines an anti-skid command;

[0014] Figure 5 is a block diagram illustrating an alternative method of determining an anti-skid command when the braking system is operating in a backup mode according to an exemplary embodiment;

[0015] Fig. 6A is a diagram showing a slipping condition according to an exemplary embodiment. Figure 5 A graph showing the brake pressure of the observation wheel shown;

[0016] Figure 6B is a graph showing a braking torque of an observation wheel according to an exemplary embodiment;

[0017] Figure 6C is a graph showing wheel speed of an observation wheel compared to actual vehicle speed according to an exemplary embodiment;

[0018] Fig.6D is a mu-slip curve of an observation wheel experiencing slip according to an exemplary embodiment;

[0019] Figure 7 is a process flow chart illustrating another method of determining brake pressure according to an exemplary embodiment;

[0020] Figure 8 According to an exemplary embodiment Figure 1An illustration of a computer system used by a braking system. DETAILED DESCRIPTION

[0021] The present disclosure relates to a braking system for a vehicle, wherein the braking system includes an energy storage device. During a standby operating mode, the energy storage device is used to supply energy to the braking system. The braking system saves the amount of energy stored in the energy storage device during the standby operating mode. Specifically, a control module of the braking system determines an anti-skid command representing a reduction in the braking pressure applied to the wheels of the vehicle. The anti-skid command is calculated based on an error between a dynamic slip of the wheel and a target slip value for the wheel. The target slip value is offset relative to an ideal slip value for the wheel and results in a reduction in the stopping efficiency of the braking system. However, since the target slip results in a reduction in the amount of braking pressure applied to the wheel, the braking system consumes less energy from the energy storage device each time the brakes are applied to reduce the speed of the vehicle.

[0022] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0023] Reference Figure 1 , a schematic diagram of a vehicle 10 having a braking system 18 is shown. The braking system 18 includes a brake pedal command 20, a control module 22, a plurality of wheels 24 ( Figure 1 Only one wheel 24 is shown in the figure), valve 26, one-way or check valve 28, energy storage device 30, piston-cylinder assembly 32 and brake stack 34. The control module 22 is in electrical communication with the brake pedal command 20 and the valve 26. When the braking system 18 is operating in a backup operating mode (described in more detail below), the valve 26 fluidly connects the piston-cylinder assembly 32 to the energy storage device 30. The energy storage device 30 is any type of device configured to store and release energy when required by the braking system 18. For example, in the embodiment shown, the energy storage device 30 is an accumulator 30A configured to store and release energy as pressurized hydraulic brake fluid. When the braking system 18 loses effective hydraulic power, the energy storage device 30 provides a backup energy source. As explained below, when the energy storage device 30 is used as a backup energy source, the braking system 18 limits the anti-skid control adopted by the braking system 18 to save energy stored in the energy storage device 30.

[0024] In such Figure 1 In the non-limiting embodiment shown, the brake system 18 employs hydraulic brake fluid and the energy storage device 30 is an accumulator 30A. The accumulator 30A is configured to store and release fluid energy as pressurized hydraulic brake fluid. Some examples of the accumulator 30A include (but are not limited to) a compressed gas accumulator (also known as a bladder accumulator) or a spring accumulator. Although Figure 1The brake system 18 is shown as employing hydraulic brake fluid, but it will be understood that the brake system 18 is not limited to a hydraulic system. For example, in another embodiment, the brake system 18 is an electronic brake system. In addition, the energy storage device 30 is not limited to the accumulator 30A. Instead, the energy storage device 30 includes any type of device configured to store and release energy, such as (but not limited to) a battery, a capacitor, or a flywheel.

[0025] In one embodiment, the vehicle 10 is an aircraft 182 (see FIG. Figure 5 However, it will be appreciated that the braking system 18 may also be used in other types of vehicles operating with a limited power source (ie, the energy storage device 30). Figure 1 Only a single brake system 18 is shown, but the aircraft may actually include multiple brake systems 18. For example, the aircraft may include separate brake systems corresponding to the left and right wheels of the aircraft.

[0026] The brake system 18 also includes a supply pressure conduit 40, a return pressure conduit 42, and a brake line conduit 44. The supply pressure conduit 40 is fluidly connected to the check valve 28 and the energy storage device 30, and the brake line conduit 44 is fluidly connected to the piston cylinder assembly 32. The valve 26 is configured to fluidly connect the brake line conduit 44 with the supply pressure conduit 40 or the return pressure conduit 42. When the valve 26 fluidly connects the supply pressure conduit 40 with the brake line conduit 44, pressurized brake fluid is supplied to the piston cylinder assembly 32. The check valve 28 prevents the brake fluid from flowing in the opposite direction of the valve 26.

[0027] The brake stack 34 includes one or more rotors 50 and one or more stators 52, wherein the rotors 50 rotate in coordination with the wheel 24. The piston cylinder assembly 32 includes a piston 54, a cylinder 56, and a biasing element 66, wherein the piston 54 is configured to translate back and forth in a linear motion in the cylinder 56. In the illustrated embodiment, the biasing element 66 is a coil spring. When the valve 26 connects the supply pressure conduit 40 to the brake line conduit 44 fluid, the pressurized brake fluid is supplied to the piston cylinder assembly 32 and causes the piston 54 to overcome the biasing force applied by the biasing element 66. Once the piston 54 overcomes the biasing force, the piston 54 translates in the cylinder 56 in the direction toward the brake stack 34. The piston 54 continues to advance toward the brake stack 34 until the end 60 of the piston 54 abuts against the brake stack 34 and applies a compressive force on the brake stack 34. When the brake stack 34 is compressed, a friction force is generated between the rotor 50 and the stator 52 to resist the rotation of the wheel 24.

[0028] The brake system 18 also includes a wheel speed sensor 70, a brake pressure transducer 72, and an accumulator pressure transducer 74, each of which is in electrical communication with the control module 22. The wheel speed sensor 70 measures the rotational speed of the wheel 24 (referred to as wheel speed 80). The brake pressure transducer 72 measures the fluid pressure within the brake line conduit 44 and generates a proportional electrical signal (referred to as brake pressure signal 82). The accumulator pressure transducer 74 measures the fluid pressure of the energy storage device 30 (i.e., accumulator 30A) and generates an accumulator pressure signal (referred to as stored energy level 84). This is because a decrease in accumulator pressure indicates a decrease in the amount of energy stored in the accumulator 30A.

[0029] The control module 22 receives wheel speed 80, brake pressure signal 82, and energy storage level 84 as inputs. The control module 22 also receives an input command 86 from the brake pedal command 20. The input command 86 represents the amount of braking requested by the braking system 18. For example, if the brake pedal command 20 is a brake pedal, the operator manually depresses the brake pedal to create the input command 86 received by the control module 22. The control module 22 determines a brake pressure command 88 that is sent to the valve 26. The brake pressure command 88 instructs the valve 26 to increase or decrease the fluid pressure supplied to the braking system 18. Specifically, the valve 26 fluidly connects the supply pressure conduit 40 and the energy storage device 30 to the brake line conduit 44 to increase the fluid pressure supplied to the braking system. The valve 26 fluidly connects the return pressure conduit 42 to the brake line conduit 44 to reduce the fluid pressure supplied to the braking system 18. For example, in one non-limiting embodiment, the valve 26 is a servo valve and the brake pressure command 88 is a milliamp signal.

[0030] The backup operating mode of the brake system 18 is now described. Specifically, when the brake system 18 experiences a loss of active power, then the control module 22 executes the backup operating mode. Specifically, the control module 22 is operatively connected to the energy storage device 30. During the backup operating mode, the control module 22 instructs the valve 26 to fluidly connect the energy storage device 30 to the brake line conduit 44. For example, if the brake system 18 employs hydraulic brake fluid, then in the event of a loss of active supply hydraulic pressure within the brake system 18, the accumulator 30A serves as a backup fluid energy source.

[0031] It will be appreciated that the energy storage device 30 contains only a fixed or limited amount of energy (e.g., hydraulic brake fluid). Similarly, if the brake system 18 is an electric brake system, the battery may contain only a limited amount of chemical energy that is easily converted to electrical energy. The disclosed backup operating mode conserves the amount of energy stored in the energy storage device 30 by instructing the brake system 18 to execute a limited anti-skid control strategy. Specifically, the backup operating mode limits the dynamic changes in the fluid pressure supplied to the brake system 18, which in turn conserves the amount of energy stored in the energy storage device 30 (i.e., hydraulic brake fluid, chemical energy, etc.).

[0032] Figure 2 1 is a block diagram 100 illustrating one method by which the control module 22 calculates the anti-skid command 90. The anti-skid command 90 is derived from the wheel speed 80. The anti-skid command 90 reduces the amount of brake pressure applied to the plurality of wheels 24 and provides anti-skid control when the vehicle 10 is stopped. However, it will be appreciated that the anti-skid command 90 provides a reduced amount of anti-skid control compared to conventional anti-skid systems. Return to Figure 2 The block diagram 100 includes a slip calculation block 103, a target slip block 104, an integrator gain k i , proportional gain k p and integrator 108 .

[0033] Reference Figure 1 and Figure 2 , the control module 22 dynamically calculates the brake pressure command 88 once the wheels 24 of the vehicle 10 rotate along the surface. For example, if the vehicle 10 is an aircraft, the control module 22 dynamically calculates the brake pressure command 88 once the wheels 24 rotate along the surface of a runway. As the wheels 24 rotate along the ground, the control module 22 receives as input or determines the wheel frequency ω based on the wheel speed 80. The control module 22 also receives as input the actual speed 102. For example, if the vehicle 10 is an aircraft, the actual speed 102 is a ground speed signal.

[0034] Continue to refer to Figure 1 and Figure 2 , the slip calculation block 103 calculates the dynamic slip 112 of the plurality of wheels 24 based on the wheel frequency ω and the actual speed 102. Specifically, in an embodiment, the slip calculation block 103 calculates the dynamic slip 112 based on the following formula 1:

[0035]

[0036] Where R represents the tire rolling radius of the tires 94 of the plurality of wheels 24 of the vehicle 10. The dynamic slip 112 is then sent to a summing node 114. The summing node 114 receives as input the dynamic slip 112 of the plurality of wheels 24 and a target slip value 116. Since the target slip value 116 is offset relative to the ideal slip value of the plurality of wheels 24, the target slip value 116 may also be referred to as a slip offset. Compared to the ideal slip value, the target slip value 116 results in a reduction in the braking efficiency of the braking system 18, which is explained below and shown in Figure 3 It will be appreciated that the target slip value 116 is a fixed value that is based on the type of tire 94 mounted on the plurality of wheels 24. The type of tire 94 depends on characteristics such as, for example, belt configuration and sidewall configuration, where belt configuration refers to either a radial or orthogonal ply configuration. Thus, if the particular type of tire 94 mounted on the wheel 24 changes, the target slip value 116 is updated.

[0037] Figure 3 An exemplary mu-slip curve 130 is shown. It will be appreciated that the mu-slip curve 130 is shown for illustration purposes and the control module 22 may not be aware of the mu-slip curve 130. The specific mu-slip curve profile 132 is based on the specific type of tire 94 ( Figure 1 ). The mu-slip curve 130 includes an x-axis representing tire slip and a y-axis representing braking efficiency. Figure 3 In the non-limiting example shown, the ideal slip point 134 represents the point along the mu-slip curve 130 that results in a maximum percentage of braking efficiency. In an embodiment, the ideal slip point 134 results in approximately 12% braking efficiency. The target slip point 136 is offset relative to the ideal slip point 134. For example, in the embodiment shown, the target slip point 136 is associated with approximately 8-10% braking efficiency. The difference between the ideal slip point 134 and the target slip point 136 is referred to as the braking efficiency reduction 140.

[0038] Reference Figure 1 and Figure 3 , it will be appreciated that the reduced braking efficiency 140 results in a reduced stopping efficiency of the braking system 18. In other words, the target slip point 136 results in a reduced performance parameter when the braking system 18 stops the vehicle 10. Some examples of braking performance parameters include, but are not limited to, stopping distance and time. If the vehicle 10 takes too long or requires too long a distance to stop, this may create an adverse condition. Therefore, the control module 22 selects a target slip point 136 that causes the braking system 18 to stop the vehicle 10 within a threshold time and a threshold distance. For example, if the vehicle 10 is an aircraft, the threshold time and the threshold distance ensure that the aircraft stays on the runway during landing. Therefore, in Figure 2 The target slip value 116 seen in 1 represents an increase in stopping distance and stopping time of the braking system 18 compared to the ideal slip value. However, the target slip value 116 also results in the braking system 18 consuming less energy from the energy storage device 30 each time the braking system 18 is applied.

[0039] Reference Figure 1 and Figure 2 The summing node 114 determines a slip error 148 by comparing the dynamic slip 112 to the target slip value 116, wherein the slip error 148 is the difference between the dynamic slip 112 and the target slip. The slip error 148 is then applied to a proportional integral (PI) controller 150 to determine the anti-slip command 90. The PI controller 150 includes a proportional gain k p , integral gain k i and integrator 108 .

[0040] The proportional gain k pCombining with the slip error 148 results in the value of the anti-slip command 90 increasing proportionally when the slip error 148 remains constant. p Higher values ​​of k result in a faster rate at which the slip error 148 is removed from the anti-slip command 90. The proportional gain k p Based on the structural dynamics and brake system dynamics (ie, valves, tires, and hydraulic systems) of the vehicle 10. If the vehicle 10 is an aircraft, the proportional gain k p It is also based on aerodynamics and ground reaction forces. Ground reaction forces refer to the friction and vertical forces applied to the aircraft. The control module 22 combines the slip error 148 with the proportional gain k p Combined, this results in a ratio value 160 which is sent to a summing node 162 .

[0041] Integral gain k i is stored in the memory 1034 ( Figure 8 ) is a fixed value in . Alternatively, the proportional gain k p is a function or is determined based on a lookup table. The integral gain k i This results in a steady-state rate reduction in the slip error 148 for a given response of the braking system 18. The integral gain k i Higher values ​​of result in a faster rate of removal of the slip error 148 from the anti-slip command 90. It will be appreciated that increasing the integral gain k i This allows the brake system 18 to quickly adjust to slip without constantly commanding the proportional gain k p The control module 22 combines the slip error 148 with the integral gain k i Combined, this results in a first integrated value 164. The first integrated value 164 is integrated by the integrator 108 and the resulting second integrated value 168 is sent to the summing junction 162.

[0042] The summing junction 162 combines the proportional value 160 and the second integral value 168, which results in the anti-skid command 90. Figure 3 , a brake pressure command 88 is determined based on the input command 86 and the anti-skid command 90. Specifically, the control module 22 determines the brake pressure command 88 based on the difference between the anti-skid command 90 and the input command 86, wherein the brake pressure command 88 indicates the amount of compressive force applied by the brake stack 34 on the plurality of wheels 24 of the vehicle 10.

[0043] Now refer to Figure 4 , an exemplary process flow diagram is shown, which illustrates a method 200 of determining the anti-skid command 90 during the backup operating mode. Figure 1 , Figure 2 and Figure 4, the method 200 begins at decision box 202. In decision box 202, the control module 22 determines whether the brake system 18 is operating in the backup operating mode. As described above, the backup operating mode conserves energy stored in the energy storage device. If the brake system 18 is operating in the backup operating mode, the method 200 may proceed to box 204.

[0044] In block 204, in response to determining that the brake system 18 is operating in the backup operating mode, the control module 22 calculates the dynamic slip 112 (see FIG. Figure 2 ). The method 200 may then proceed to block 206 .

[0045] In block 206 , the control module 22 determines the slip error 148 by comparing the dynamic slip 112 to a target slip value 116 , wherein the target slip value 116 is less than a desired slip value for the plurality of wheels 24 and results in reduced braking efficiency compared to the desired slip value.

[0046] In an embodiment, in box 206A, the control module 22 determines the slip error 148. Specifically, in box 206A, the control module 22 determines the slip error 148 based on the wheel frequency ω of the plurality of wheels 24 and the actual speed 102 of the vehicle 10. In an embodiment, the control module determines the slip error 148 based on equation 1 shown above. Then, the method 200 may proceed to box 208.

[0047] specifically refer to Figure 2 and Figure 4 In block 208A, the control module 22 combines the slip error 148 with the proportional gain k p Combined, this results in a proportional value of 160. As described above, the proportional gain k p Combining with the slip error 148 results in the value of the anti-slip command 90 increasing proportionally as the slip error 148 remains constant.

[0048] In block 208B, the control module 22 combines the slip error 148 with the integral gain k i Combined, this results in a first integrated value 164. The control module 22 also integrates the first integrated value 164, which results in a second integrated value 168. The method 200 may then proceed to block 210.

[0049] In block 210, the control module 22 calculates the anti-slip command 90 based on the slip error 148, wherein the anti-slip command 90 reduces the amount of brake pressure applied to the plurality of wheels 24. As seen in block 210A, the control module 22 determines the anti-slip command 90 by combining the proportional value 160 with the second integrated value 168. The method 200 may then proceed to block 212.

[0050] In block 212, the control module 22 determines the brake pressure command 88 based on the difference between the anti-skid command 90 and the input command 86, where the input command 86 represents the amount of braking requested by the braking system 18. The method 200 may then return to block 204, or alternatively, the method 200 may terminate.

[0051] Now turn to Figure 5 Another method of determining the brake pressure command 88 is now described. Figure 5 In the exemplary embodiment shown, the plurality of wheels 24 are part of a set of wheels 180. For example, in an embodiment, the set of wheels 24 is a set of landing gear for an aircraft 182. It will be appreciated that some large aircraft may include multiple sets of landing gear. For example, some large aircraft may include five sets of landing gear. In the non-limiting embodiment shown, the landing gear set includes four wheels 24. Each wheel 24 is monitored by a corresponding wheel speed sensor 70.

[0052] Continue to refer to Figure 5 , a single wheel 24 that is part of a set of wheels 24 is designated as an observation wheel 24A. The observation wheel 24A is monitored to determine the mu-slip coefficient μ. Although the upper left wheel 24 is designated as the observation wheel 24A, it will be understood that this illustration is merely exemplary in nature and any wheel 24 may be designated as the observation wheel 24A. It will be understood that each set of wheels 180 includes a corresponding designated observation wheel 24A. For example, an aircraft with five sets of landing gear will include five designated observation wheels 24A.

[0053] In response to determining that the wheel 24 is rotating along the surface, the control module 22 determines a first brake pressure command 188 that is applied only to the designed observation wheel 24A. It will be appreciated that the first brake pressure command 188 is determined based on the ideal slip value. Specifically, referring to Figure 3 , the first brake pressure command 188 is determined based on the ideal slip point 134 along the mu-slip curve 130, rather than the target slip point 136. Therefore, the first brake pressure command 188 does not result in a reduction in braking efficiency 140 (see Figure 3 ).

[0054] The control module 22 receives the wheel speed 80 as input from the wheel speed sensor 70A of the observation wheel 24A. The control module 22 also receives the actual speed 102 (e.g., ground speed signal) of the aircraft 182. The control module 22 determines the difference between the wheel speed 80 of the observation wheel 24A and the actual speed 102. As described in more detail below, the control module 22 determines when the observation wheel 24A begins to experience a slip condition 190 (shown in FIG. 1 ) based on the difference between the wheel speed 80 of the observation wheel 24A and the actual speed 102. Figure 6CIn response to detecting the onset of the slip condition 190, the control module 22 reduces the first brake pressure command 188, which causes the observation wheel 24A to recover from the slip condition 190. Once the observation wheel 24A has experienced at least one slip condition, the control module 22 calculates a second brake pressure command 189 applied to the remaining wheels 24 that are part of the group of wheels 180.

[0055] Fig. 6A The brake pressure 196 (ie, Figure 1 82). Figure 6B and Figure 6C The brake torque 198 of the observation wheel 24A and the wheel speed 80 of the observation wheel 24A during the slip condition 190 are respectively shown. Fig.6D An exemplary mu-slip curve 230 is shown when the designed observation wheel 24A experiences a slip condition 190 . FIG. 6A to FIG. 6D The graphs shown each include four operating points, labeled as operating point 1, operating point 2, operating point 3, and operating point 4. Fig. 6A As can be seen in FIG. 1 , the brake pressure 196 of the observation wheel 24A increases between operating point 1, operating point 2, and operating point 3. Figure 6C As seen in FIG. 1 , the observation wheel 24A begins to experience a slipping condition 190 between operating point 3 and operating point 4. However, the observation wheel 24A recovers from the slipping condition 190 after operating point 4.

[0056] Reference Figure 1 , Figure 5 , Fig. 6A and Figure 6C , the control module 22 increases the value of the first brake pressure command 188, which causes the brake pressure 196 of the observation wheel 24A to increase ( Fig. 6A The control module 22 continues to increase the value of the first brake pressure command 188 until a slip condition 190 is detected (between operating point 3 and operating point 4). The increase in the first brake pressure command 188 results in an increase in the amount of braking torque (see Figure 6B ) and the wheel speed 80 of the observation wheel 24A decreases (see Figure 6C ).

[0057] Reference Figure 1 , Figure 5 , Fig. 6A and Figure 6C, the control module 22 determines the onset of the slip condition 190 based on the difference between the wheel speed 80 of the observation wheel 24A and the actual speed 102 of the vehicle 10 (i.e., the ground speed of the aircraft). Specifically, the control module 22 determines the speed difference between the wheel speed 80 of the observation wheel 24A and the actual speed 102 of the vehicle 10 (i.e., the ground speed of the aircraft). In response to determining that the speed difference between the wheel speed 80 of the observation wheel 24A and the actual speed 102 of the vehicle 10 exceeds a threshold difference, the control module 22 determines that the designed observation wheel 24A has begun to experience the slip condition 190. The threshold speed difference represents a condition in which the observation wheel 24A slips relative to the ground and experiences a sudden decrease in speed. Figure 6C The wheel speed 80 of the observation wheel 24A is shown to suddenly decrease during the slip condition 190. Specifically, Figure 6C A line 300 is shown connecting operating point 3 and operating point 4 together, and represents the sudden decrease in wheel speed 80 during the slip condition 190. Line 304 connects operating points 1, 2, and 3 together, and represents the wheel speed 80 at which the vehicle 10 stopped prior to the slip condition 190. The gradient of line 300 when wheel 24A is observed to slip during the slip condition 190 is at least twice the gradient of line 304.

[0058] In response to detecting the onset of the slip condition 190, the control module 22 decreases the value of the first brake pressure command 188. Figure 5 and Figure 6C , the control module 22 continues to reduce the first brake pressure command 188 until the observation wheel 24A recovers from the slipping condition 190. Figure 6C As seen in FIG. 1 , when the observation wheel 24A recovers from the slip condition 190, the wheel speed 80 of the observation wheel 24A is approximately equal to the actual speed 102 and is referred to as the slip recovery condition 240. It will be appreciated that although Figure 6C Only one slip condition 190 is shown in FIG. 1 , but the observation wheel 24A experiences multiple slip conditions when the aircraft 182 is stopped. However, for simplicity, the observation wheel 24A is not shown in FIG. FIG. 6A to FIG. 6C Only a single slip condition 190 is shown in the graph shown.

[0059] Reference Fig.6D , operating points 1, 2, 3, and 4 on the mu-slip curve 230 correspond to FIG. 6A to FIG. 6C As described above, the specific mu-slip curve 230 is based on empirical data and depends on the designed observation wheel 24A ( Figure 5 ) The particular type of tire 94 used. It will be appreciated that the observation wheel 24A generates an ideal slip value when the observation wheel 24A experiences a slip condition. Specifically, with reference to Figure 3 , Figure 5 , Figure 6C and Fig.6D, in the mu-slip curve 230 (shown in Fig.6D ), the effective value of the mu-slip coefficient μ is at its ideal slip point 134. In other words, the mu-slip coefficient μ is at the ideal slip point 134 when the observation wheel 24A experiences the slip condition 190. Figure 3 , Figure 6C and 6D When the wheel speed 80 of the observation wheel 24A is at the minimum value (at the operating point 4 ), the effective value of the mu-slip coefficient μ is the ideal slip point 134 .

[0060] Reference Figure 5 and FIG. 6A to FIG. 6D In response to determining that the observed wheel 24A begins to slip 190, the control module 22 determines a second brake pressure command 189 to be applied to the remaining wheels 24. Figure 5 In the illustrated embodiment, the second brake pressure command 189 will be applied to the remaining three wheels 24. The control module 22 determines the second brake pressure command 189 based on the target slip value 116, wherein the target slip value 116 is offset from the ideal slip value and results in a reduced braking efficiency of the braking system 18. Specifically, as described above and shown in Figure 3 In FIG. 1 , the target slip point 136 is offset from the ideal slip point 134 and results in a reduction in braking efficiency 140 . A second brake pressure command 189 is then applied to the remaining plurality of wheels 24 .

[0061] Reference Figure 5 In one embodiment, the control module 22 determines the reduced second brake pressure command 270 by reducing the second brake pressure command 189 by a parameter confidence value. The parameter confidence value represents one or more varying operating conditions between the individual wheels 24 in the set of wheels 180. In an embodiment, the varying operating conditions include a coefficient of friction along the ground, an amount of brake wear, an amount of tire wear, a vehicle speed during operation of the braking system 18, and a braking torque gain. For example, one of the wheels 24 may experience a different coefficient of friction than the remaining wheels 24. Specifically, one of the wheels 24 may be rolling along a slippery or icy patch located along the runway while the other remaining wheels 24 are rolling along a dry portion of the runway. In one non-limiting embodiment, the parameter confidence value reduces the second brake pressure command 189 by approximately 10%, however, this value is exemplary in nature.

[0062] Figure 7 is shown for determining the applied Figure 5 An exemplary process flow diagram of a method 400 for providing a second brake pressure command 189 for the remaining wheels 24 of the aircraft 182 is shown. Figure 1 , Figure 5 , FIG. 6A to FIG. 6D and Figure 7 , the method 400 begins at decision block 402 . In decision block 402 , the control module 22 determines whether the brake system 18 is operating in the backup operating mode. If the brake system 18 is operating in the backup operating mode, the method 400 may proceed to block 404 .

[0063] In block 204, in response to determining that the brake system 18 is operating in the backup operating mode, the first brake pressure command 188 is applied to the observation wheel 24A (see FIG. Figure 5 ). The method 400 may then proceed to block 406 .

[0064] In block 406, the control module 22 monitors the wheel speed 80 of the observation wheel and the actual speed 102 of the vehicle 182 when the first brake pressure command 188 is applied to the observation wheel 24A. Figure 5 For an aircraft 182 in FIG. 1 , the actual speed 102 is the ground speed. Figure 5 and Fig. 6A , the control module 22 continues to increase the value of the first brake pressure command 188 while monitoring the wheel speed 80 of the observation wheel 24A and the actual speed 102 of the vehicle 10 . The method 400 may then proceed to decision block 408 .

[0065] In decision block 408, the control module 22 determines whether the observation wheel 24A has begun to slip 190 (see FIG. 1 ) based on the wheel speed 80 of the observation wheel 24A and the actual speed 102 of the vehicle 10. Figure 6C ).like Figure 6C and Fig.6D , the observation wheel 24A generates an ideal slip value (i.e., the ideal slip point 134) during the slip condition 190. For example, as explained above, in response to determining that the difference between the wheel speed 80 and the actual speed 102 of the observation wheel 24A exceeds the threshold difference, the control module 22 determines that the designed observation wheel 24A has begun to experience the slip condition 190.

[0066] If the observation wheel 24A has not initiated a slip condition 190, the method 400 returns to block 406. However, if the control module 22 determines that the observation wheel 24A has initiated a slip condition based on the wheel speed 80 of the observation wheel 24A and the actual speed 102 of the vehicle 10, the method 400 may proceed to blocks 410 and 414 simultaneously.

[0067] In block 410, in response to determining that the observed wheel 24A begins to slip 190, the control module 22 determines a second brake pressure command 189 based on a target slip value that is offset from the ideal slip value and results in a reduced braking efficiency of the braking system 18. The method 400 may then proceed to block 412.

[0068] In block 412, the control module 22 applies the second brake pressure command 189 to the remaining portion of the plurality of wheels 24. For example, Figure 5 As seen in , the second brake pressure command 189 is applied to the remaining three wheels 24 .

[0069] Blocks 414 and 416 are now described. In block 414, in response to determining that the observed wheel 24A begins to slip 190, the control module 22 decreases the value of the first brake pressure command 188. The method 400 may then proceed to decision block 416.

[0070] In decision box 416, the control module 22 determines whether the wheel speed 80 of the observed wheel 24A is approximately equal to the actual speed 102 of the vehicle 10. If the wheel speed 80 is not approximately equal to the actual speed 102, the method returns to box 414 and the first brake pressure command 188 continues to decrease. However, if the wheel speed 80 of the observed wheel 24A is approximately the same as the actual speed 102 of the vehicle 10, the slip recovery condition 240 (see Figure 6C ). The method may then return to block 404 to regenerate another slip condition 190. Alternatively, if the vehicle 10 has stopped, the method 400 may terminate.

[0071] Roughly refer to Figures 1 to 7 The present disclosure provides various technical effects and benefits for an energy storage device for a braking system. Specifically, compared to a conventional braking system, the disclosed braking system uses less energy each time the brakes are applied during a standby operating mode, which saves energy stored in the energy storage device. Therefore, in some methods, the disclosed energy storage device can be smaller and lighter than conventional devices, which in turn reduces the mass of a vehicle such as an aircraft.

[0072] Now refer to Figure 8 , the control module 22 is implemented on one or more computer devices or systems such as an exemplary computer system 1030. The computer system 1030 includes a processor 1032, a memory 1034, a mass storage memory device 1036, an input / output (I / O) interface 1038, and a human-machine interface (HMI) 1040. The computer system 1030 is operatively coupled to one or more external resources 1042 via the network 1026 or the I / O interface 1038. The external resources may include, but are not limited to, servers, databases, mass storage devices, peripheral devices, cloud-based network services, or any other suitable computer resources that may be used by the computer system 1030.

[0073] The processor 1032 includes one or more devices selected from a microprocessor, a microcontroller, a digital signal processor, a microcomputer, a central processing unit, a field programmable gate array, a programmable logic device, a state machine, a logic circuit, an analog circuit, a digital circuit, or any other device that manipulates signals (analog or digital) based on operating instructions stored in the memory 1034. The memory 1034 includes a single memory device or multiple memory devices, including (but not limited to) read-only memory (ROM), random access memory (RAM), volatile memory, non-volatile memory, static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, cache memory, or any other device capable of storing information. The mass storage memory device 1036 includes a data storage device such as a hard drive, an optical drive, a tape drive, a volatile or non-volatile solid-state device, or any other device capable of storing information.

[0074] The processor 1032 operates under the control of an operating system 1046 residing in the memory 1034. The operating system 1046 manages computer resources so that computer program code embodied as one or more computer software applications (e.g., applications 1048 residing in the memory 1034) may have instructions executed by the processor 1032. In an alternative example, the processor 1032 may directly execute the application 1048, in which case the operating system 1046 may be omitted. One or more data structures 1049 also reside in the memory 1034 and may be used by the processor 1032, the operating system 1046, or the application 1048 to store or manipulate data.

[0075] The I / O interface 1038 provides a machine interface that connects the processor 1032 to other devices and systems (e.g., the network 1026 or external resources 1042) when in operation. The application 1048 thus works in cooperation with the network 1026 or external resources 1042 by communicating via the I / O interface 1038 to provide various features, functions, applications, processes, or modules that include examples of the present disclosure. The application 1048 also includes program code executed by one or more external resources 1042, or relies on functions or signals provided by other systems or network components external to the computer system 1030. In fact, given that an almost endless number of hardware and software configurations are possible, one of ordinary skill in the art will understand that examples of the present disclosure may include applications that are located external to the computer system 1030, distributed among multiple computers or other external resources 1042, or provided by computing resources (hardware and software) provided as a service (e.g., cloud computing services) via the network 1026.

[0076] The HMI 1040 is operatively coupled to the processor 1032 of the computer system 1030 in a known manner to allow a user to interact directly with the computer system 1030. The HMI 1040 may include a video or alphanumeric display, a touch screen, speakers, and any other suitable audio and visual indicators capable of providing data to the user. The HMI 1040 also includes input devices and controls (e.g., alphanumeric keyboards, pointing devices, keypads, buttons, control knobs, microphones, etc.) capable of accepting commands or input from a user and sending the input to the processor 1032.

[0077] The database 1044 may reside on the mass storage memory device 1036 and may be used to collect and organize data used by the various systems and modules described herein. The database 1044 may include data and supporting data structures for storing and organizing the data. Specifically, the database 1044 may be arranged with any database organization or structure, including (but not limited to) a relational database, a hierarchical database, a network database, or a combination thereof. A database management system in the form of a computer software application executed as instructions on the processor 1032 may be used to access information or data stored in records of the database 1044 in response to a query, where the query may be dynamically determined and executed by the operating system 1046, other applications 1048, or one or more modules.

[0078] The description of the present disclosure is merely exemplary in nature, and variations that do not depart from the gist of the present disclosure are intended to fall within the scope of the present disclosure. These variations should not be regarded as departing from the spirit and scope of the present disclosure.

Claims

1. A braking system (18) for a vehicle (10), wherein: The braking system (18) includes a plurality of wheels (24) and an energy storage device (30), the energy storage device (30) being configured to store and release energy and supply energy to the braking system (18) during a standby operating mode, the braking system (18) comprising: one or more processors (1032) operatively coupled to the energy storage device (30) and in electrical communication with the plurality of wheels (24); and A memory (1034) coupled to the one or more processors (1032), the memory (1034) storing data including a database (1044) and program code that, when executed by the one or more processors (1032), causes the brake system (18) to: determining that the brake system (18) is operating in the backup operating mode; In response to determining that the brake system (18) is operating in the backup operating mode, calculating a dynamic slip (112) of the plurality of wheels (24); determining a slip error (148) by comparing the dynamic slip (112) to a target slip value (116) for the plurality of wheels (24), wherein the target slip value (116) is offset from an ideal slip value for the plurality of wheels (24) and results in a reduction in braking efficiency of the braking system (18); and calculating an anti-slip command (90) based on the slip error (148), wherein the anti-skid command (90) reduces the amount of braking pressure applied to the plurality of wheels (24).

2. The brake system (18) according to claim 1, wherein: The one or more processors (1032) execute instructions to: The slip error (148) is determined based on a wheel frequency (ω) of the plurality of wheels (24) and an actual speed (102) of the vehicle (10).

3. The braking system (18) according to claim 2, wherein: The one or more processors (1032) execute instructions to determine the slip error based on the following equation: Wherein, R represents the tire rolling radius of the plurality of wheels (24) of the vehicle (10), and ω represents the wheel frequency of the plurality of wheels (24).

4. The brake system (18) according to claim 1, wherein: The one or more processors (1032) execute instructions to: A proportional value is determined by combining the slip error (148) with a proportional gain (kp), wherein combining the proportional gain (kp) with the slip error (148) causes the value of the anti-slip command (90) to increase proportionally when the slip error (148) remains constant.

5. The brake system (18) according to claim 4, wherein: The one or more processors (1032) execute instructions to: determining a first integrated value (164) by combining the slip error (148) with an integrated gain value; and The first integrated value (164) is integrated to obtain a second integrated value (168).

6. The brake system (18) according to claim 5, wherein: The one or more processors (1032) execute instructions to: The anti-slip command (90) is determined by combining the proportional value with the second integrated value (168).

7. The brake system (18) according to claim 1, wherein: The one or more processors (1032) execute instructions to: A brake pressure command (88) is determined based on a difference between the anti-skid command (90) and an input command (86), wherein the input command (86) represents an amount of braking requested by the brake system (18).

8. The brake system (18) of claim 1, wherein: The target slip value (116) is a fixed value, wherein the fixed value is based on the type of tires mounted on the plurality of wheels (24).

9. The brake system (18) of claim 1, wherein: The energy storage device (30) is an accumulator (30A), a battery, a capacitor or a flywheel.

10. The brake system (18) according to claim 9, wherein: The energy storage device (30) is an accumulator (30A) configured to store and release fluid energy as pressurized hydraulic brake fluid, and wherein the standby operating mode conserves the fluid energy stored in the accumulator (30A).

11. An aircraft (182) comprising a braking system according to any one of claims 1 to 10.

12. A method of determining an anti-skid command (90) during a backup operating mode of a braking system (18) of a vehicle (10), wherein: The braking system (18) comprises a plurality of wheels (24) and an energy storage device (30) configured to store and release energy and to supply energy to the braking system (18) during the backup operating mode, the method comprising the following steps: determining, by a computer, that the brake system (18) is operating in the backup operating mode; In response to determining that the brake system (18) is operating in the backup operating mode, calculating, by the computer, a dynamic slip (112) of the plurality of wheels (24); determining a slip error (148) by comparing the dynamic slip (112) to a target slip value (116), wherein the target slip value (116) is less than a desired slip value and results in reduced braking efficiency compared to the desired slip value; and An anti-slip command (90) is calculated based on the slip error (148), wherein the anti-slip command (90) reduces an amount of braking pressure applied to the plurality of wheels (24).

13. The method according to claim 12, further comprising the steps of: The slip error (148) is determined based on a wheel frequency (ω) of the plurality of wheels (24) and an actual speed (102) of the vehicle (10).

14. The method of claim 13, further comprising determining the dynamic slip (112) based on the following equation: in, R represents the tire rolling radius of the plurality of wheels (24) of the vehicle, and ω represents the wheel frequency of the plurality of wheels (24).

15. The method according to claim 12, further comprising the steps of: A brake pressure command (88) is determined based on a difference between the anti-skid command (90) and an input command (86), wherein the input command (86) represents an amount of braking requested by the brake system (18).

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