HYDRAULIC SYSTEM FOR A VEHICLE, SUCH AS AN AIRCRAFT

Abstract

A hydraulic system for reducing mechanical loads or noise development is disclosed having at least two hydraulic pumps including a pump element, such as a piston or rotary gear. The hydraulic pumps can be speed-controlled by a pump controller to achieve a nominal pressure P0. The pump controller further includes an offset (Δx) between the pump elements and controls one of the hydraulic pumps such that the pump elements move in an anti-cyclic manner, that is, a phase shift of about 180°.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to European Application Number EP23196996.5, filed Sep. 12, 2023, the entire contents of which is hereby incorporated by reference.

BACKGROUND

The invention relates to a hydraulic system for a vehicle. The invention further relates to an aircraft equipped with such as system and a method for operating a hydraulic system.

Currently used hydraulic piston pumps or gear pumps typically generate pressure ripples. The ripples represent a pressure oscillation that is put on top of the nominal delivery pressure. For piston pumps the pressure ripples have characteristic features depending on the number of pistons and the speed of the rotating group. For other pump types, such as internal gear pumps the amount of teeth and the rotation speed typically characterizes the pressure ripples.

The conventional approach in hydraulics is to put dedicated damper or resonators downstream of the pump discharge to either reduce the energy of hydraulic (pressure) waves or to reflect (pressure) waves back.

SUMMARY

The claimed invention encompasses an apparatus and a method to reduce pressure oscillations in hydraulic systems.

The invention provides a hydraulic system for a vehicle, for example, for an aircraft, the system comprising:

• • a plurality of hydraulic pump apparatus configured for generating hydraulic pressure, each hydraulic pump apparatus comprising a hydraulic pump, wherein the hydraulic pump has a pump discharge and at least one pump element that is configured to displace hydraulic fluid through the pump discharge to generate the hydraulic pressure, wherein the pump discharges are fluidly connected to form a common discharge; and
  • a pump controller that is configured to determine an offset between a pair of pump elements, wherein the pump controller is configured to adjust the offset such that the pair of pump elements moves in an anticyclic manner.

The pump controller may be configured to adjust the offset such that one of the pair of pump elements discharges hydraulic fluid, when the other of the pair of pump elements draws in hydraulic fluid.

Some types of vehicle, such as aircraft, have a hydraulic system to actuate different elements that would otherwise be difficult to operate. Hydraulic pumps draw in hydraulic fluid from a tank and pressurized and discharge the hydraulic fluid (typically some kind of oil) into a pipe circuit. The pipes are connected to the actuators which are driven by the hydraulic fluid. Hydraulic pumps come in different types, two of which are piston pumps and rotary gear pumps. These pump elements displace the hydraulic fluid in a periodic manner, e.g., the piston due to oscillation (the rotating group transforms rotational speed into linear movement/oscillation of one or more individual pistons) and the rotary gear by rotating. This can cause pressure fluctuations which propagate through the hydraulic fluid and cause a certain periodic load on the pipe circuit or actuators.

Typically the pressure decreases during the draw in phase of the pump piston stroke or corresponding rotational angle and increases during the displacement phase, in which the fluid is pressurized and discharged. The pump controller is based on the idea that pressure fluctuations can be superposed such that their amplitudes add together. The pump controller determines the offset of the pump elements, i.e., in which phase of the pump stroke or rotational angle the respective pump element is currently in relative to the other pump element. The pump controller then adjusts the offset such that the phases are opposite, i.e., that when the pressure increases due to discharge of one pump piston the pressure decreases due to draw in of the other pump piston. The pressure fluctuations can therefore be generated with a phase shift of ideally 180° relative to each other such that the fluctuations can be reduced or ideally extinguished.

At least one pump discharge and/or the common discharge may comprise a pressure sensor that is configured for measuring the pressure of the hydraulic fluid, and the pump controller is configured to control each hydraulic pump apparatus, for example, by controlling a speed of the hydraulic pump, such that a nominal pressure is kept at the respective pump discharge and/or common discharge. A pressure sensor allows a controlled feedback to the hydraulic pumps such that a well-defined nominal pressure can be maintained. In general the pressure fluctuations generated by the hydraulic pumps will oscillate around the nominal pressure.

The hydraulic pump apparatus may include an electric pump motor that is operatively coupled to the pump controller to be controlled and that drives the hydraulic pump. Electric pump motors can be controlled easier than other types of drive. The electric pump motor is speed controllable.

The hydraulic system may include a position determining unit that is configured to determine a pump element position of each pump element, and the pump controller is configured to determine the offset based on the pump element positions of the pair of pump elements. A determination of position allows a feedback control and continuous adjustment of the offset between different pump elements. The position determination allows a measurement of the amount one pump element is rushing or dragging relative to another pump element.

The position determining unit may include a position sensor that is configured to measure a quantity that is indicative of the pump element position. The position sensor may directly or indirectly help in determining the position of the pump element.

The position sensor may be chosen from a group consisting of an optical position sensor, a magnetic position sensor, a resolver, an electrical power sensor, and an electrical current sensor. The position sensor may be disposed on the hydraulic pump, for example, the pump element/rotating group, or the electric pump motor. Most sensors can be directly connected to an element of the pump or the pump motor in order to directly read the position of the pump element. The sensors can be easily retrofitted or integrated into existing systems.

The pump controller may be configured to adjust the offset by controlling the speed of the hydraulic pump. The speed adjustments in order to control the offset are typically small compared to the overall speed of the hydraulic pump. As a result, a negative impact on the nominal pressure can be avoided while simultaneously not needing another adjustment mechanism.

The hydraulic system may comprise a hydraulic actuator that is supplied with hydraulic fluid from the common discharge. The hydraulic actuator can be used to operate various components of the vehicle.

The invention provides an aircraft comprising a hydraulic system, wherein the hydraulic system is configured to drive any of a high-lift device, a door or freight door, a landing gear, and a control surface by means of hydraulic actuators. The components can be extended or retracted using hydraulic power that is converted to linear or rotational motion by hydraulic actuators. Also it is possible to have the steering implemented via hydraulic power, specifically the landing gear or control surfaces.

The invention provides a method for operating a hydraulic system or an aircraft, the method comprising:

• • a plurality of hydraulic pump apparatus generating hydraulic pressure, each hydraulic pump apparatus comprising a hydraulic pump, wherein the hydraulic pump has least one pump element that displaces hydraulic fluid through a pump discharge to generate the hydraulic pressure, and the pump discharges are combined into a common discharge; and
  • a pump controller determining an offset between a pair of pump elements, wherein the pump controller adjusts the offset such that the pair of pump elements moves in an anticyclic manner.

The pump controller may adjust the offset such that one of the pair of pump elements discharges hydraulic fluid, when the other of the pair of pump elements draws in hydraulic fluid.

Each pump discharge may comprise a pressure sensor that measures the pressure of the hydraulic fluid, and the pump controller controls each hydraulic pump apparatus, for example, by controlling a speed of the hydraulic pump, such that a nominal pressure is kept at each pump discharge.

The hydraulic pump apparatus may comprise an electric pump motor that is controlled by the pump controller and that drives the hydraulic pump.

The method comprises:

• • a position determining unit determining a pump element position of each pump element, and the pump controller determining the offset based on the pump element positions of the pair of pump elements.

The position determining unit comprises a position sensor measuring a quantity that is indicative of the pump element position.

The pump controller adjusts the offset by controlling the speed of the hydraulic pump.

The method comprises a hydraulic actuator being supplied with hydraulic fluid from the common discharge.

The disclosed solution is based on the principle of a relative phase shift between two waves, wherein the waves have about the same amplitude and frequency. A reduction of the amplitude is possible and under ideal circumstances the waves can extinguish each other. By reducing the pressure oscillations this way, no additional heavy hardware, such as dampers or resonators, is required. As a result, a simpler installation of the system or an increased flexibility in the system is possible.

The ideas presented herein are generally applicable in hydraulic systems for vehicles, particularly in aircraft. The hydraulic systems may be powered by hydraulic powerpacks (HPPs) or electro motor pumps (EMPs).

Due to the reduced pressure oscillations, it is possible to decrease the stress loads on hydraulic components, e.g., hydraulic pipes and hydraulic actuators. Another benefit is that hydraulic noise that is generated by the pump ripples can be reduced which in turn can decrease structure borne noise and cabin noise.

The system can reduce the pump pressure ripples without additional components, e.g., dampers and resonators so that the installation effort can be decreased.

In addition, the whole system can be designed more flexible, as the dampers or resonators typically require a predefined distance to the pump discharge. Consequently, the system can be designed more efficiently compared to systems that require the damper or resonator components.

The solution is better adaptable to the current operating conditions, as the phase shift can be adjusted as needed by the circumstances.

Furthermore, the weight of the aircraft can be maintained or even reduced, e.g., by removing the dampers or resonators, as the case may be.

In an exemplary embodiment, a minimum of two electrical motor pumps is used. The electrical motor pumps should be speed controlled. The pumps may be of fixed displacement type.

The electrical motor pump may be sufficiently similar in design and size, e.g., the pulsation frequency should be similar or the same.

In some embodiments, the position of the pump piston or the angular position of the gear is monitored.

The idea is that the two electric motor pumps run in a defined phase shift such that the pressure ripple amplitudes of one pump may be in a 180° phase shift compared to the other pump. By this the pressure ripple amplitude can at least be decreased, if not reduced to zero.

The controller of one electro motor pump can use the position signal of the rotating group/gear teeth and compare it to the associated signal of the other electro motor pump. The controller then can follow the control algorithm with regards to rotating speed of the other controller by offsetting it by the amount needed for the phase shift.

The phase shift can either be calculated in each individual controller or in a centralized monitoring computer that transfers the data to the individual motor pump controllers.

A pressure transducer, which may be at each pump outlet, can be used to monitor the pressure ripples.

A position sensor for the pump can be an optical sensor or a magnetic sensor. Some motors can use an internal resolver. It is also possible to detect the position by measurement and analysis of the electric current/waveforms.

The motor controller typically sets the motor speed to keep the nominal pressure. This is typically done by monitoring the system pressure and increasing the motor speed if the pressure is dropping or decreasing the motor speed if the pressure is increasing. These control algorithms are commonly known in the art.

The motor position monitoring may feed back the position of the motor and thereby the position of the pistons/rotating group. This is typically done for both motors in parallel.

The signals can be sent to a controller that determines the time difference between the two position signals. At the same time the controller is informed about the speed setting of the motor. The controller can determine if the time difference in the position signals is corresponding to the speed, assuring the pistons are in a 180° phase shift.

If not, the controller can command one of the motors to increase speed or slow down according to the determined offset.

The control loop should have a fast enough response (quick resolvers and calculation times) of the signal to allow for the compensation.

BRIEF DESCRIPTION OF THE DRAWINGS

For an understanding of embodiments of the disclosure, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an embodiment of an aircraft;

FIG. 2 illustrates an embodiment of a hydraulic system;

FIG. 3 illustrates a function of the hydraulic system of FIG. 2;

FIG. 4 illustrates a time-pressure diagram of a single hydraulic pump; and,

FIG. 5 illustrates a time-pressure diagram of the hydraulic system of FIG. 2.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Some embodiments will now be described with reference to the Figures.

Referring to FIG. 1, an aircraft 10 comprises a fuselage 12. A pair of wings 14 is attached to the fuselage. Each wing 14 comprises an engine 16 for propulsion. The aircraft 10 comprises a tail plane section 18.

The aircraft 10 typically comprises a plurality of high-lift devices 20, which are attached to each wing 14. The high-lift device 20 on the leading edge of the wing 14 is typically called a slat 22, whereas the high-lift device 20 on the trailing edge of the wing is typically called a flap 24.

Each wing 14 and the tail plane section 18 typically comprise control surfaces 26. The control surfaces 26 which are attached to the wings 14 are called ailerons 28. The control surface 26 on the tail plane section 18 which controls the pitch of the aircraft 10 is called an elevator 30. The control surface 26 that is attached to the tail plane section 18 and controls the yaw angle is called a rudder 32.

Furthermore, the aircraft 10 may comprise a plurality of doors 34, in particular freight doors or loading doors, to access the freight space of the aircraft 10. Furthermore, the aircraft 10 comprises a plurality of landing gears (not shown) which are typically arranged near the cockpit section 36 and below the wings 14. The front landing gear near the cockpit section 36 is typically configured such that the aircraft 10 can be steered on the ground.

The aircraft 10 comprises a hydraulic system 40. The hydraulic system 40 can be operatively coupled to any of the previously mentioned components of the aircraft 10 in order to provide a means to move and steer the respective components. As depicted in FIG. 1, for example, the hydraulic system 40 can be operatively connected to the doors 34 in order to open and close them.

Referring to FIG. 2, the hydraulic system 40 is explained in more detail. The hydraulic system 40 comprises a fluid tank 42 for storing hydraulic fluid.

The hydraulic system 40 comprises a plurality of hydraulic pump apparatus 44. The hydraulic pump apparatus 44 may be configured identically. Each hydraulic pump apparatus 44 comprises a pump discharge 46 through which hydraulic fluid that was drawn in from the fluid tank 42 is discharged from the hydraulic pump apparatus 44.

Each pump discharge 46 may comprise a pressure sensor 48. The pressure sensor 48 is arranged to measure the pressure generated by the respective hydraulic pump apparatus 44. Downstream of the pressure sensors 48, the pump discharges 46 are combined into a single common discharge 50. The common discharge 50 is coupled to hydraulic actuators which drive one of the doors 34, for example. In a variant that is not shown explicitly, it is possible to have one pressure sensor 48 that is arranged to measure the pressure generated by all hydraulic pump apparatus 44. The pressure sensor 48 may be disposed on the common discharge 50.

The hydraulic system 40 comprises a pump controller 52 that is operatively coupled to each hydraulic pump apparatus 44 and each pressure sensor 48.

The hydraulic pump apparatus 44 comprises a hydraulic pump 54 which is fluidly connected to the fluid tank 42 and the pump discharge 46.

The hydraulic pump apparatus 44 may further comprise an electric pump motor 56 that is mechanically connected to the hydraulic pump 54 in order to drive it. The electric pump motor 56 is operatively connected to the pump controller 52 in order to be controlled. The electric pump motor 56 may be capable of being speed controlled.

The hydraulic pump 54 may be configured as a piston pump or a rotary gear pump. The piston and the rotary gear are examples of a pump element that is used to displace the hydraulic fluid in order to generate hydraulic pressure.

The hydraulic pump apparatus 44 comprises a position sensor 58 that is suitable to measure a quantity that is indicative of the position of the pump element. The position sensor 58 can be arranged on the hydraulic pump 54 or the electric pump motor 56. The position sensor 58 may be an optical sensor or a magnetic type sensor, such as a Hall sensor. Other sensor types are also possible. In particular, the position sensor 58 may be a power sensor or a current sensor that is connected to the electrical pump motor 56 and capable of inferring the position of the pump element based on the consumed power and or current. These methods are generally known for electric motors so they are not described here in more detail.

Referring to FIG. 3, the functioning of the pump controller 52 is described in more detail. The pump controller 52 takes in the pump element position X₁, X₂ of each pump element. Furthermore, the pump controller 52 takes in the hydraulic pressure P₁, P₂ generated by each hydraulic pump apparatus 44 and measured by the respective pressure sensor 48.

The pump element positions X₁ and X₂ are fed to a comparator unit 60, which determines an offset AX between the pump elements.

The pump controller 52 further comprises a first motor controller 62 and a second motor controller 63. Each motor controller 62, 63 is coupled to one hydraulic pump apparatus 44 in order to control its operation. Each motor controller 62, 63 in particular controls the speed of the respective electric pump motor 56.

The first and second motor controllers 62, 63 receive the respective measured pressure P₁ and P₂. In a manner known per se, the first and second motor controllers 62, 63 generate an initial control signal Ci₁ and Ci₂ that defines the speed at which the respective electric pump motor 56 should run. The initial control signals Ci₁, Ci₂ are determined such that a nominal pressure P₀ can be maintained at each pump discharge 46.

The initial control signals Ci₁, Ci₂ are fed to an adjustment unit 64. The adjustment unit 64 also receives the offset Ax determined by the comparator unit 60. From these inputs, the adjustment unit 64 generates an adjusted control signal Ca for the second motor controller 63, for example. The adjusted control signal Ca is generated such that the offset Ax between the pair of pump elements is changed. The adjusted control signal Ca is fed to the second motor controller 63 which controls the respective electric pump motor 56 accordingly.

As a result, the offset Ax between the pump elements of the hydraulic pump apparatus 44 can be adjusted in a manner that allows for the pump elements to move anti-cyclically. For example, when one of the pump elements performs a discharge stroke the other pump element does exactly the opposite and performs a drawing in stroke.

Referring to FIGS. 4 and 5, the consequences of this type of operation is illustrated. In particular it is possible to adjust the offset Ax to allow reduction of pressure fluctuations in the hydraulic system 40.

FIG. 4 depicts a time-pressure diagram and illustrates the pressure fluctuations that are typically caused by the operation of a hydraulic pump apparatus 44. The currently measured pressure P₁ oscillates around the nominal pressure P₀. As may be gathered from FIG. 4, the measured pressure P₁ typically increases when the pump element displaces the hydraulic fluid and decreases when the pump element draws in new hydraulic fluid from the fluid tank 42. Each of the hydraulic pump apparatus 44 has a similar build and therefore, the pressure fluctuations are also similar.

FIG. 5 depicts the optimal result of an optimal adjustment of the offset Ax between the pump elements of both hydraulic pump apparatus 44. As may be gathered from the diagram, the offset Δx is not zero but has a certain value that is typically given by the configuration of the hydraulic pumps 54 which causes the pressure fluctuations to align in a destructive interference pattern. The pressure peaks and pressure valleys of the hydraulic pump apparatus 44 meet at the same time but with opposite amplitude, which allows at least a reduction of the pressure fluctuations, or ideally as illustrated in FIG. 5, a complete elimination.

In order to reduce mechanical loads or noise development, a hydraulic system 40 is proposed that comprises at least two hydraulic pumps 54 having pump element, e.g., a piston or rotary gear. The hydraulic pumps 54 can be speed controlled by a pump controller 52 to achieve a nominal pressure P₀. The pump controller 52 further determines an offset (Δx) between the pump elements and controls one of the hydraulic pumps 54 such that the pump elements move in an anticyclic manner, i.e. with a phase shift of about 180°.

While at least one exemplary embodiment is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

Claims

1. A hydraulic system for a vehicle, comprising:

a plurality of hydraulic pump apparatus configured for generating hydraulic pressure, each hydraulic pump apparatus comprising a hydraulic pump, wherein the hydraulic pump has a pump discharge and at least one pump element that is configured to displace hydraulic fluid through the pump discharge to generate the hydraulic pressure, wherein the pump discharges are fluidly connected to form a common discharge; and

a pump controller configured to determine an offset between a pair of pump elements, wherein the pump controller is configured to adjust the offset such that the pair of pump elements moves in an anti-cyclic manner.

2. The hydraulic system according to claim 1, wherein the pump controller is configured to adjust the offset such that one of the pair of pump elements discharges hydraulic fluid, when the other of the pair of pump elements draws in hydraulic fluid.

3. The hydraulic system according to claim 1, wherein at least one pump discharge and/or the common discharge comprises a pressure sensor that is configured for measuring the pressure of the hydraulic fluid, and the pump controller is configured to control each hydraulic pump apparatus by controlling a speed of the hydraulic pump, such that a nominal pressure is kept at the respective pump discharge and/or common discharge.

4. The hydraulic system according to claim 1, wherein the hydraulic pump apparatus comprises an electric pump motor that is operatively coupled to the pump controller to be controlled and that drives the hydraulic pump.

5. The hydraulic system according to claim 1, further comprising a position determining unit that is configured to determine a pump element position of each pump element, and the pump controller is configured to determine the offset based on the pump element positions of the pair of pump elements.

6. The hydraulic system according to claim 5, wherein the position determining unit comprises a position sensor that is configured to measure a quantity that is indicative of the pump element position.

7. The hydraulic system according to claim 6, wherein the position sensor is chosen from a group consisting of an optical position sensor, a magnetic position sensor, a resolver, an electrical power sensor, and an electrical current sensor.

8. The hydraulic system according to claim 6, wherein the position sensor is disposed on the hydraulic pump, the pump element, or the electric pump motor.

9. The hydraulic system according to claim 1, wherein the pump controller is configured to adjust the offset by controlling the speed of the hydraulic pump.

10. The hydraulic system according to claim 1, further comprising at least one hydraulic actuator that is supplied with hydraulic fluid from the common discharge.

11. An aircraft comprising a hydraulic system according to claim 1, wherein the hydraulic system is configured to drive any of a high-lift device, a door or freight door, a landing gear, and a control surface.

12. A method for operating a hydraulic system according to claim 1, the method comprising:

a plurality of hydraulic pump apparatus generating hydraulic pressure, each hydraulic pump apparatus comprising a hydraulic pump, wherein the hydraulic pump has least one pump element that displaces hydraulic fluid through a pump discharge to generate the hydraulic pressure, and the pump discharges are combined into a common discharge; and

a pump controller determining an offset between a pair of pump elements, wherein the pump controller adjusts the offset such that the pair of pump elements moves in an anticyclic manner.

13. The method according to claim 12, further comprising:

a position determining unit determining a pump element position of each pump element, and the pump controller determining the offset based on the pump element positions of the pair of pump elements.

14. The method according to claim 13, wherein the pump controller adjusts the offset by controlling the speed of the hydraulic pump.

15. The method according to claim 12, further comprising at least one hydraulic actuator being supplied with hydraulic fluid from the common discharge.