ELECTRO HYDROSTATIC ACTUATORS

Abstract

Method for controlling and damping the motion of a hydraulic actuator in an electro hydrostatic actuator (EHA) system comprising an electric motor, a hydraulic pump and a hydraulic fluid circuit connecting the hydraulic pump and the hydraulic actuator includes comprising: energising the electric motor to drive the hydraulic pump to supply hydraulic fluid to the hydraulic actuator through the hydraulic fluid circuit in an active mode of operation; providing a flow path between the hydraulic actuator and the hydraulic pump in a damping mode of operation such that hydraulic fluid can flow via the flow path through the hydraulic pump when the hydraulic actuator is driven by an external force; and determining a desired amount of damping to be applied to the hydraulic actuator in the damping mode of operation and providing the electric motor with one or more energy consuming means configured to provide the desired amount of damping.

Claims

1. A method for controlling and damping the motion of a hydraulic actuator in an electro hydrostatic actuator (EHA) system comprising an electric motor, a hydraulic pump and a hydraulic fluid circuit connecting the hydraulic pump and the hydraulic actuator, the method comprising: energising the electric motor to drive the hydraulic pump to supply hydraulic fluid to the hydraulic actuator through the hydraulic fluid circuit in an active mode of operation; providing a flow path between the hydraulic actuator and the hydraulic pump in a damping mode of operation such that hydraulic fluid can flow through the hydraulic pump when the hydraulic actuator is driven by an external force; and determining a desired amount of damping to be applied to the hydraulic actuator in the damping mode of operation and providing the electric motor with one or more energy consuming means configured to provide the desired amount of damping, such that in the damping mode of operation when the hydraulic actuator is driven by an external force, the hydraulic fluid flowing via the flow path through the hydraulic pump causes the hydraulic pump to drive the electrical motor so as to generate energy

2. A method according to claim 1, wherein providing the one or more energy consuming means comprises choosing one or more electrical resistance elements.

3. A method according to claim 2, wherein choosing the one or more electrical resistance elements comprises choosing one or more electrical resistance elements with a fixed resistance.

4. A method according to claim 2, wherein choosing the one or more resistance elements comprises choosing one or more electrical resistance elements with a variable resistance.

5. A method according to claim 4, comprising changing the resistance of the one or more electrical resistance elements depending on the desired degree of damping.

6. A method according to claim 1, wherein providing the one or more energy consuming means comprises connecting an external electrical circuit to the motor.

7. A method according to claim 1, wherein providing the one or more energy consuming means comprises designing electromagnetic losses within one or more components of the electric motor to provide the desired amount of damping.

8. A method according to claim 1, wherein providing the one or more energy consuming elements comprises choosing standard components of the electric motor which provide the desired amount of damping.

9. A method according to claim 1, wherein providing the one or more energy consuming means comprises choosing one or more components capable of storing electrical energy.

10. A method according to claim 9, further comprising using electrical energy stored in the components to energise the electric motor in the active mode of operation.

11. A method according to claim 1, wherein determining the desired amount of damping and providing one or more energy consuming means is carried out during manufacture of the system or prior to use of the hydraulic actuator in a specific application or during use of the hydraulic actuator.

12. A method according to claim 1, wherein determining the desired amount of damping comprises determining the force which is applied to the hydraulic actuator by measuring the electrical energy generated by the electric motor.

13. A method according to claim 12, wherein measuring the energy generated by the electric motor comprises using electronic control circuitry arranged to measure the electrical energy generated and subsequently provide the one or more energy consuming means to provide the desired amount of damping

14. A method according to claim 1, wherein controlling and damping the hydraulic actuator comprises operating the system only in the active mode of operation or the damping mode of operation.

15. An electro hydrostatic actuator (EHA) comprising: a reversible hydraulic pump and an electric motor driving the hydraulic pump to supply hydraulic fluid to a hydraulic actuator; the hydraulic pump comprising an inlet and an outlet for hydraulic fluid and an active flow path arranged therebetween such that, in an active mode of operation when the pump is driven by the electric motor, hydraulic fluid is actively drawn in through the inlet and exhausted out through the outlet; the hydraulic pump further arranged such that, in a damping mode of operation, when the hydraulic actuator is driven by an external force, hydraulic fluid is forced through an inlet of the hydraulic pump and is exhausted through an outlet of the hydraulic pump which causes relative motion of the hydraulic pump which drives the electric motor; the electric motor further comprising an external electrical circuit, arranged such that any electrical energy generated by the electric motor, when the electric motor is driven by the hydraulic pump in the damping mode of operation, is consumed by the external electrical circuit to provide a desired amount of damping to be applied to the hydraulic actuator.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0049] One or more non-limiting examples will now be described, with reference to the accompanying drawings, in which:

[0050] FIG. 1 shows a fluid flow diagram for an EHA in an active mode according to the prior art;

[0051] FIG. 2 shows a fluid flow diagram for an EHA in a damping mode according to the prior art;

[0052] FIG. 3 shows a fluid flow diagram for an EHA in an active mode according to the present disclosure; and

[0053] FIG. 4 shows a fluid flow diagram for an EHA in a damping mode according to the present disclosure.

DETAILED DESCRIPTION

[0054] FIGS. 1 and 2 show a fluid flow diagram for an electro hydrostatic actuator (EHA) 2 according to the prior art. FIG. 1 shows an electric motor 4, a hydraulic pump 6, a mode valve 8, an accumulator 10 and a hydraulic actuator 12. The hydraulic actuator 12 shown in FIG. 1 consists of two separate chambers 14, 16 and an actuator ram 18. The mode valve 8 can be operated by a solenoid 20 and has two modes of operation which is typically on or off. The ram 18 is typically attached to a component on the aircraft such as an aerodynamic surface. A linear transducer 22 which is connected to the ram 18 signals when the ram 18 is in use. The EHA typically has two modes of operation: an Electric Active Mode (EAM) and a damping mode. FIG. 1 shows the EHA in EAM. During EAM the motor 4 is energised by the power supply 24 and acts to drive the pump 6. As the pump 6 is driven it causes hydraulic fluid to flow around a circuit as shown by the bold lines and the arrows in FIG. 1. This results in fluid being directed into one of the chambers 14, 16 of the hydraulic actuator 12. As fluid enters one of the chambers 14, 16 and leaves the other chamber 14, 16 this causes the ram 18 to move within the chambers 14, 16 which acts to move the aerodynamic surface it is attached to.

[0055] FIG. 2 shows a fluid flow diagram for the EHA 2 in damping mode. The damping mode can be initiated in circumstances where there is an electrical power generation failure, i.e. the electric motor 4 is not energised by the power supply 24, or electronic control path failure. The solenoid 20 is capable of activating the mode valve 8 which alters the fluid flow within the system. The damping mode introduces a damping effect to the ram 18. This may be critical for certain applications of an EHA for example when in use on an aircraft. The damping mode is also the default mode when the ram 18 is not required to be engaged i.e. the pump 6 is not driven by the motor 4. The purpose of the damping mode is to provide a damping force to the ram 18 which may be connected to an aerodynamic surface, this prevents uncontrolled motion when external aerodynamic forces are applied to the surface. In the damping mode, fluid is free to flow between one chamber 14, 16 through the mode valve 8 and to the other chamber 14, 16 of the hydraulic actuator 12. The free flow of fluid between the two chambers 14, 16 acts to damp the motion of the ram 18. During the damping mode the fluid completely bypasses the pump 6 and only travels through the mode valve 8. The damping effect on the ram 18 is fixed by the mode valve 8.

[0056] FIGS. 3 and 4 show exemplary fluid flow diagrams of an EHA 102 according to the present disclosure. Instead of the damping mode being achieved by having a mode valve separate to the pump, the damping mode is now provided by allowing the fluid within the system to drive a reversible and bi-directional pump 106 connected to a motor 104 which provides a desired damping effect. A reversible electric motor 104 is operatively connected to the pump 106. An energy consuming circuit is connected external to the motor 104. In this example, the energy consuming circuit comprises an electrical resistor 126 connected in parallel with the motor power supply 124. Similarly to the embodiment seen in FIGS. 1 and 2 the EHA 102 also comprises an accumulator 110.

[0057] In FIG. 3 the system is shown in an Electric Active Mode (EAM). During the EAM the motor 104 is energised with electrical power from the power supply 124. This may be an A.C. power supply as depicted in FIGS. 3 and 4 or alternative it may be a D.C. power supply. When energised with electrical power, the motor 104 drives the pump 106 so as to drive fluid around between the chambers 114, 116 of the hydraulic actuator 112 via the fluid path shown in bold and with corresponding arrows. Movement of fluid between the chambers 114, 116 causes movement of the ram 118. A linear transducer 122 which is connected to the ram 118 signals when the ram 118 is in use. During the EAM, electrical power from the power supply 124 bypasses an electrical resistance element 126, connected to the motor 104 and energises the motor 104 directly.

[0058] FIG. 4 shows the EHA 102 operating in a damping mode. In the damping mode, for example when there is a power supply failure, the motor 104 is no longer energised by the power supply 124. This is depicted in this Figure as the power source 124 is not supplying electrical power (circuit lines are no longer in bold). In this instance, the pump 106 is no longer driven by the motor 104 and ceases to actively move hydraulic fluid around the system. In this damping mode, fluid in each of the actuator's chamber 114, 116 is free to pass through the hydraulic circuit and drive the pump 106. The fluid may for instance enter the pump 106 via an inlet, cause the pump to rotate and exit via its outlet. It is unlikely that fluid will freely flow through the EHA 102 unless a sufficient external force is applied to the ram 118 so as to displace fluid within the chambers 114, 116. This may happen, for example, when the ram 118 operates a surface on an aircraft wing, wherein the passing airflow over the surface may be sufficient to drive the ram 118 so as to move hydraulic fluid from one of its chambers 114, 116 to the other chamber 114, 116. In doing so, fluid will flow through the pump 106 subsequently causing it to rotate. Driving the pump 106 causes the motor 104 to be driven as a result of the operative connection between them. When the motor 104 is driven by the pump the motor 104 effectively acts as a generator and produces energy. If the fluid is moved through the EHA 102 at a sufficient rate then the movement of the motor 104 may be sufficient to generate electricity. As seen in FIG. 4, any electrical energy generated by the motor 104 in this damping mode, may be dissipated via the electrical resistance element 126.

[0059] Whilst the resistor 126 is depicted as an example of a single electrical energy consuming element, it will be appreciated that the resistor 126 may be replaced by a variety of different circuit components. For example a non-exhaustive list of possible elements may include a plurality of resistors in series, a plurality of resistors in parallel and one or more variable resistors. Furthermore, in other examples such external electrical energy consuming element(s) may be replaced by alternative energy consuming means, such as energy dissipation components in the motor itself and/or electrical energy storage elements. Of course any suitable combination of one or more different energy consuming elements may be designed to provide the desired amount of damping to be applied to the hydraulic actuator in any given application.

[0060] Whilst in this description the pump 106 is described as rotating as a result of the hydraulic fluid passing through it, it will be appreciated that this may not always be the case and this may depend on the type of pump which is used. For example, the pump 106 may be caused to reciprocate as a result of hydraulic fluid driving its motion. Irrespective of the motion of the pump after it is driven by the hydraulic fluid it will be appreciated that this motion can be converted appropriately so as to drive the electric motor 104.