Method of monitoring an electrohydrostatic actuator

Abstract

The disclosure relates to a method of monitoring an electrohydrostatic actuator, wherein the electrohydrostatic actuator comprises a hydraulic pump drivable by an electric motor and a hydraulic activator drivable by means of the hydraulic pump to move a component, in particular an aircraft part. The method include detecting the instantaneous speed of the electric motor; detecting an instantaneous position of the activator; detecting a parameter that relates to an instantaneous operating point of the electrohydrostatic actuator; determining a state variable relating to an efficiency of the electrohydrostatic actuator on the basis of at least the detected speed and the detected position in dependence on the detected parameter; and determining a state of the electrohydrostatic actuator on the basis of the currently determined value.

Claims

1. A method of monitoring an electrohydrostatic actuator that comprises a hydraulic pump drivable by an electric motor and a hydraulic activator drivable by means of the hydraulic pump to move a component, the method comprising the steps: detecting an instantaneous speed of the electric motor; detecting an instantaneous position of the hydraulic activator; detecting a parameter that relates to an instantaneous operating point of the electrohydrostatic actuator; determining a state variable relating to an efficiency of the electrohydrostatic actuator on the basis of at least the detected speed and the detected position in dependence on the detected parameter; and determining a state of the electrohydrostatic actuator on the basis of a currently determined value of the state variable.

2. The method in accordance with claim 1, wherein an instantaneous speed of the activator is calculated from the detected instantaneous position and is used as the basis for determining the state variable.

3. The method in accordance with claim 1, wherein the state variable is an efficiency of the electrohydrostatic actuator.

4. The method in accordance with claim 1, wherein the parameter is or relates to an instantaneous power implemented in the electrohydrostatic actuator.

5. The method in accordance with claim 1, wherein the determination of the state variable only takes place when the parameter exceeds or falls below an activation limit value.

6. The method in accordance with claim 5, wherein the activation limit value is or relates to a minimal power implemented in the electrohydrostatic actuator; and/or in that the determination of the state variable takes place at a stationary operating point of the electrohydrostatic actuator.

7. The method in accordance with claim 5, wherein the determination of the state variable takes place multiple times during an operating period of the electrohydrostatic actuator.

8. The method in accordance with claim 7, wherein the values of the determined state variable are stored, with a trend being determined on the basis of an analysis of the stored values and with a forecast being prepared therefrom relating to the state variable and/or the state of the electrohydrostatic actuator.

9. The method in accordance with claim 8, wherein a time for a replacement, a repair, and/or a service of the electrohydrostatic actuator or of one of its components is determined.

10. The method in accordance with claim 7, wherein an error state is recognized when a certain number of determined values of the state variable falls below or exceeds a threshold value.

11. The method in accordance with claim 1, wherein a certain state of the electrohydrostatic actuator relates to a wear state of the electrohydrostatic actuator.

12. The method in accordance with claim 1, wherein the hydraulic pump is an axial piston machine and/or in that the hydraulic activator is a piston-in-cylinder unit.

13. A vehicle having at least one electrohydrostatic actuator by means of which an component is movable and that is controllable by means of a control unit, with the control unit being configured to carry out the method in accordance with claim 1.

14. The vehicle in accordance with claim 13, wherein the vehicle component is an aircraft component of the primary or secondary flight control.

15. A computer program product for monitoring the electrohydrostatic actuator that comprises the hydraulic pump drivable by the electric motor and the hydraulic activator drivable by means of the hydraulic pump to move the component, wherein the computer program product is adapted to carry out the method in accordance with one of the claim 1, on an execution by a computer.

16. The method in accordance with claim 1, wherein the component is an aircraft part.

17. The method in accordance with claim 3, wherein the state variable is a volumetric efficiency of the hydraulic pump.

18. The method in accordance with claim 4, wherein the instantaneous power being determined based on a detected pressure difference, wherein the power parameters are determined based on a pressure difference between the input side and the output side of the hydraulic pump.

19. The method in accordance with claim 9, wherein the component is an electrohydrostatic actuator component that is the hydraulic pump and/or the activator.

20. The method in accordance with claim 12, wherein the axial piston machine has a constant displacement volume (V.sub.0).

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further features and details of the disclosure result from the embodiments explained in the following with reference to the Figures. There are shown

(2) FIG. 1: a schematic representation of the electrohydrostatic actuator in accordance with the disclosure in accordance with an embodiment;

(3) FIG. 2: a schematic representation of the relationship between the setting speed and the load of the activator with respect to the implemented power; and

(4) FIG. 3: a schematic representation of the steps of the method in accordance with the disclosure in accordance with an embodiment.

DETAILED DESCRIPTION

(5) As a result of their function, electrohydrostatic actuators (EHAs) provide a number of sensors and its control electronics with the possibility over actuators having an analog interface with the flight control computer of also taking over the functions of the state monitoring in addition to the position regulation. Safety-critical error cases are thus already recognized and intercepted by the actuator itself today.

(6) FIG. 1 schematically shows the design and the functional principle of an embodiment of the EHA 10 in accordance with the disclosure. The latter comprises a hydraulic pump 14 that is designed as an axial piston machine having an unchangeable displacement volume V.sub.0 and is driven via a drive shaft by an electric motor 12 at a speed n. The electric motor 12 is electrically controlled by a control unit 18 (control signal U). The volume flow Q.sub.theoretical=n.Math.V.sub.0, where V.sub.0 is the nominal displacement volume of the axial piston machine 14, theoretically conveyed by the pump 14 can be set by the setting of a certain value for the speed n.

(7) The values (A, V.sub.0) relevant to the balancing of the volume flow Q are also given in FIG. 1. A leak volume flow Q.sub.L (shown as a connection to a hydraulic oil reservoir Res) is adopted in dependence on the wear state of the pump 14. All the values required for determining the efficiency η.sub.vol, that is in particular the speed n (detected via an angle transmitter 22) and the setting speed {dot over (x)} (detected via a position encoder 20 and a subsequent differentiation) are evaluated and further processed in the control electronics or control unit 18.

(8) The hydraulic pump 14 hydraulically drives an activator 16 that is designed as a piston-in-cylinder unit and that moves a component, for example an elevator, rudder, or aileron, of an aircraft. The piston of the activator 16 has a diameter A so that the stroke of the piston results with the setting speed {dot over (x)}=dx/dt to A.Math.{dot over (x)}. This approximately corresponds to the volume flow Q.sub.effective conveyed by the hydraulic pump 14.

(9) The control electronics of the EHA 10 provides the possibility of monitoring the wear state of the axial piston pump 14. The volumetric efficiency η.sub.vol, that falls as the wear progresses (in particular due to the clearances increasing in size due to abrasion) as the running time increases serves as a significant feature here. The volumetric efficiency η.sub.vol can be approximately calculated as follows:

(10) ${\eta }_{vol}=\frac{Q_{\mathrm{effective}}}{Q_{theoret\mathrm{ical}}}=\frac{A\stackrel{.}{x}}{V_{0}n}.$

(11) It must, however, be noted here that an EHA in the primary flight control is typically operated far away from its design values and in oscillating cycles. The volumetric efficiency η.sub.vol should, however, ideally be determined at a stationary operating point at which a finite power is implemented since otherwise a singularity is present.

(12) $\underset{n.fwdarw.0}{\lim }{\eta }_{\mathrm{vol}}\left(n\right).fwdarw.\infty .$

(13) The applied external load is also decisive, in addition to the speed range, in the efficiency determination since the leak of the pump 14 is decisively defined by the pressure potential via the gaps.

(14) It becomes clear that a certain power has to be implemented at the activator 16 to determine a significant value. The efficiency calculation is therefore dependent on the operating state. Dynamic effects (compression, pulsation) are furthermore neglected in this approach.

(15) This relationship is shown in FIG. 2, where the setting speed {dot over (x)} of the actuator 16 is applied (y axis) against the applied load (x axis). Generator operation lof the activator 16, in which an external force drives the electric motor 12 and thereby generates power, is present in the second and fourth quadrants 30, that are of no further interest here. The first and third quadrans relevant to the function of the EHA 10 as a drive are divided into regions of lower power 40 (close to the origin) and regions of higher power 50. In other words, those operating points of the EHA 10 that are in the range 50 correspond to an operation in which the axial piston machine 14 implements a power sufficient for the evaluation of the volumetric efficiency η.sub.vol.

(16) In addition to the dependence on the respective operating point, the volumetric efficiency η.sub.vol also varies on the basis of production tolerances. The efficiency η.sub.vol furthermore typically initially briefly increases in operation or during the running-in procedure and thereupon reaches an optimum. Starting from this reference value that is specific to the actuator, a progressing wear can then be recognized in further operation after the running-in process.

(17) FIG. 3 schematically describes the routine in the determination of an error state on the basis of a degradation of the volumetric efficiency η.sub.vol: As described above, the calculation of the efficiency η.sub.vol also requires, beside the speed of the electric motor 12, a differentiation and filtering of the position encoder signal representing the instantaneous piston position x to obtain the linear setting speed {dot over (x)} of the activator 16. In parallel with this, the motor speed n and the differential pressure Δp present at the pump flow into an activation logic that checks in accordance with FIG. 2 whether sufficient power is implemented in the activator 16 that is required for an unambiguous determination of the efficiency η.sub.vol (that is whether the instantaneous operating point is in the range 50).

(18) If this is the case, the calculated efficiency value is used for the further trend analysis. A filter here in turn provides that outliers are neglected and a long-term trend is instead recognized. The robustness of the monitor or of the evaluation/monitoring is hereby ensured. If the calculated efficiency η.sub.vol permanently falls below a defined threshold value, the installed hydraulic pump 14 is deemed to be defective and an error state is output. This can in turn be taken as a reason for the planning of a servicing intervention, whereby an unheralded failure of the EHA 10 at a later time is avoided.

(19) The above-described steps are carried out by the control unit 18 that receives the signals required for the calculation of the efficiency η.sub.vol. The control unit 18 can be a central control (e.g. an aircraft control) or a control locally assigned to the respective EHA 10. The control unit may include memory having instructions stored therein for receiving input from one or more sensors coupled in an aircraft such as the various parameters described herein. Further, the control unit may also include instructions stored in memory for adjusting one or more actuators coupled in the aircraft, such as the various actuators described herein.

REFERENCE NUMERAL LIST

(20) 10 electrohydrostatic actuator (EHA)

(21) 12 electric motor

(22) 14 hydraulic pump (axial piston machine)

(23) 16 hydraulic activator (piston-in-cylinder unit)

(24) 18 control unit

(25) 20 position decoder

(26) 22 angle transmitter

(27) 30 range, generator operation

(28) 40 range, lower power

(29) 50 range, higher/sufficient power

(30) Δp pressure difference

(31) A piston surface

(32) n speed

(33) Res reservoir

(34) U control signal

(35) x position

(36) {dot over (x)} speed