GB2469016A

GB2469016A - Electrically driven hydraulic actuator

Info

Publication number: GB2469016A
Application number: GB0903371A
Authority: GB
Inventors: Christopher Richard Whitley; James Roper; David Curd
Original assignee: Moog Wolverhampton Ltd; GE Aviation Systems Ltd
Current assignee: Moog Wolverhampton Ltd
Priority date: 2009-02-26
Filing date: 2009-02-26
Publication date: 2010-10-06
Also published as: GB0903371D0; WO2010097596A1

Abstract

An electrically driven hydraulic actuator comprises a variable speed motor, a variable capacity displacement pump 20 arranged to be driven by the variable speed motor 10 and a hydraulic actuator 30 driven by the variable displacement pump. A controller 40 varies the speed of motor 10 by a control signal on line 11 and varies the capacity of the pump by means of a control signal long line 21. Operational input requirements for the actuator are fed along line 41. Being able to vary the speed of the motor and the displacement of the pump enables the actuator to be able to be operated very flexibly, and the motor does not have to be driven at an excessively high or low speed, reducing wear and over-heating of the motor.

Description

HYDRAULIC ACTUATOR

The present invention relates to a hydraulic actuator, in particular an electrically driven hydraulic actuator. An advantage of electrically driven actuators is that they do not require a separate hydraulic supply circuit to be operated.

Electra-Hydrostatic Actuators (EHAs) incorporate a variable speed electrically driven motor which drives a displacement pump which delivers hydrostatic fluid to move an actuator. In order to control the actuator speed or rate of movement, the drive motor is operated at the appropriate variable speed to drive the fixed volume displacement pump to pump the fluid at the appropriate rate to the actuator. The drive motor can be driven in a clockwise or anti-clockwise direction, which in turn either extends or retracts a linear actuator or rotates a rotary actuator in one direction or the other. However, in many applications the hydraulic actuator is required to spend the majority of the time holding a load in a static position, for example holding a flap of an aircraft in a particular position during a flight. In order to maintain this static load holding, the drive motor operates at low speed which accelerates wear of the pump because of the reduced lubrication, reducing the pump working life. Thus periods between maintenance and replacement are shorter, increasing down-time and costs. This condition also leads to high heat rejection from the motor and control electronics from the motor.

An Integrated Actuator Package (lAP) incorporates a drive motor which is operated at a fixed speed in one direction only and a variable displacement pump. An example of a variable displacement pump has a swash plate which can be adjusted to different angles, either positive or negative relative to a perpendicular zero swash position, to vary the rate of fluid being pumped and thereby the speed of actuator movement. However, the drive motor in an lAP must constantly turn at speed, which generates a considerable amount of heat.

It is an aim of the present invention to provide an electrically driven hydraulic actuator which alleviates or overcomes at least some of the problems discussed above.

According to the present invention there is provided an electrically driven hydraulic actuator comprising a variable speed motor; a variable capacity displacement pump arranged to be driven by the variable speed motor; and a hydraulic actuator driven by the variable displacement pump.

By being able to vary the speed of the motor and the displacement of the pump, the actuator is able to operate very flexibly and the motor does not have to be constantly driven at an excessively high or low speed reducing wear and over-heating.

A controller may be provided which is arranged to instruct the motor to operate at a particular speed and the pump to operate at a particular capacity dependent upon the requirements of the actuator. The motor may be a unidirectional variable speed motor.

A method of controlling the flow of hydraulic fluid to an electrically driven hydraulic actuator having a variable speed motor and a variable displacement pump driven by the variable speed motor comprises: providing a control signal to the variable displacement pump to control its capacity and providing a control signal to the motor to control its speed.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows an overview of an embodiment of the present invention; Figure 2 shows a more detailed example of an embodiment of the present invention; Figure 3 illustrates an example of the internal arrangement of a controller for an embodiment of the invention; Figure 4 is a flow diagram illustrating an example of a way of operating an example of the invention; and Figure 5 is a flow diagram illustrating another example of a way of operating an example of the invention.

As shown in Figure 1, an electrically driven hydraulic actuator of an embodiment of the present invention comprises a variable speed motor 10, a variable displacement pump 20 driven by the variable speed motor 10 and a hydraulic actuator 30 driven by the variable displacement pump 20. A controller 40 is also shown which is arranged to vary the speed of the motor 10 with an appropriate control signal on line 11 and to vary the capacity of the pump 20 by providing an appropriate control signal along line 21 dependent upon operational requirements of the actuator 30 input to the controller 40 along line 41.

For example, the actuator 30 may be arranged to extend a flap on an aircraft which would involve an input signal being sent along control line 41 to the controller 40 which then selects an appropriate motor speed and pump displacement in order to produce the required action by the actuator 30. The controller 40 instructs the motor 10 to operate at the desired speed with a corresponding signal along line 11 and instructs the pump 20 to operate at the desired capacity with a control signal along line 21. The actuator 30 which may for example be a linear actuator or a rotary actuator would then extend the flap on the aircraft to the appropriate extent, If it is then desired to retract the aircraft flap, the appropriate instruction is sent to the controller 40 along control line 41.

The controller 40 then instructs motor 10 and pump 20 to operate at the appropriate speed and capacity as instructed along lines 11 and 21 respectively to control the actuator 30 to retract the flap. Once retracted, the flap may be required to be modulated in small displacements about a constant position. In order to effect this modulation about a position appropriate instructions would be provided to the controller 40 along control line 41 which would, in turn, instruct the motor 10 and pump 20 via lines 11 and 21 respectively to adopt an appropriate speed and capacity to maintain the actuator 30 in the appropriate condition.

Figure 2 shows a more detailed example of one form of a variable displacement pump 20 and a hydraulic circuit 50 between the pump 20 and actuator 30. In this example the variable displacement pump 20 comprises a barrel 22 in which a number of chambers 23 are provided. In this example two chambers 23 are shown, but any appropriate number of chambers may be used as is desired for a particular application. Each of the chambers is provided with a piston 24 which slides within and seals against the internal walls of the chamber 23. Each chamber 23 is connected to a hydraulic fluid line 51, 52 and movement of the piston 24 within each chamber 23 forces hydraulic fluid out of or into each chamber 23. The movement of the fluid in the pump 20 produces corresponding movement of the actuator 30. The pump 20 includes a swash plate 25, the angle of which is adjustable to control the extent of displacement of the pistons 24 within the chambers 23 and thus the capacity of the pump 20 at each stroke of the pistons 24. In this example the position or angle of the swash plate is controlled by a swash motor drive 26 controlled by a signal from controller 40 along control line 21.

During use the barrel 22 of the pump 22 is rotated by shaft 12 driven by the variable speed motor 10. In this example a feedback line 13 is provided to indicate to controller 40 the capacity of the pump 20 and the speed of the motor 10, which in this example is measured by a suitable sensor 14. The controller 40 is thus able to confirm that the motor 10 and pump 20 are operating as required or indicate accordingly if there is a problem.

The example shown in Figure 2 includes a rotary actuator 30 which is arranged to rotate in response to hydraulic fluid pumped along fluid line 51 by the pump 20. However, any suitable actuator may be used as is suitable for the application to which the hydraulic actuator is applied and may for example be a linear actuator. One hydraulic fluid line 52 is also shown incorporating a reservoir 53 which can accommodate expansion of the hydraulic fluid due to temperature and pressure variations or to allow for possible external leakage of hydraulic fluid over time.

Although Figure 2 shows the use of a variable swash plate pump 20, any suitable variable displacement pump may be used. For example instead of a variable swash plate pump, a radial piston pump may be used.

Figure 3 illustrates an example of the internal arrangement of the controller 40.

As can be seen, in this example there is provided a position controller 70, a pump controller 71 and a motor controller 72. The position controller 70 receives an indication of the hydrostatic fluid demand on input line 41 and determines the corresponding speed of the motor 10 and capacity of the pump 20 in order to satisfy the demand. The motor speed and pump capacity may be determined in any suitable way as known by the person skilled in the art, such as for example using control logic, an algorithm or a look up table. The desired pump capacity is provided to pump controller 71 along input line 73 and the pump controller 71 instructs the pump 20 accordingly via line 21 shown in Figure 1. The pump controller 71 may also receive a signal confirming that the pump 20 is operating at the desired capacity and may confirm this to the position controller 70 via line 74. In a similar manner, the position controller 70 instructs the motor controller 72 to drive the motor 10 at the desired speed via line 75. If desired a confirmation that the motor is operating at the desired speed may be provided to the position controller 70 via line 76.

Figure 4 is a flow diagram illustrating an example of a control process for the controller 40. Starting at step 80, the controller 40 determines at step 81 whether there is a demand for increased flow of hydrostatic fluid. If there is no demand for increased flow then the controller will return to step 80. If there is in fact a demand for increased flow of hydrostatic fluid, the controller proceeds to step 82.

At step 82 it is determined whether the pump capacity to satisfy the demand for increased flow is greater than the maximum capacity of the variable displacement pump at the speed at which the motor is currently operating. If the maximum capacity of the pump 20 is not exceeded, the controller proceeds to step 83 and adjusts the pump capacity accordingly and then returns to step 80 to await any further increased fluid flow demands. However, if the desired pump capacity exceeds the maximum of the pump 20, the controller proceeds to step 84 and increases the speed of the motor 10. At step 85 the capacity of the variable displacement pump 20 is reduced or adjusted accordingly, if required, to account for the increase in speed of the motor 10 to produce the desired hydraulic fluid flow. The controller then returns to step 80 to await any further increased fluid flow demands.

The motor 10 may be arranged to operate at one of two speeds Ni, N2 and to be increased to the higher speed, N2 when required at step 84. Enabling the motor to operate at one of a number of set speeds provides a reliable system.

However, depending upon the particular application, the motor 10 could be operated at any number of two or more set speeds or could be operated at any desired variable speed.

When it is desired to reduce the amount of fluid provided to the actuator 30, the flow diagram of Figure 4 may be operated in reverse as shown in Figure 5. As can be seen, if there is a reduced demand for hydraulic flow at step 91 the controller 40 proceeds to step 92. At step 92 it is determined whether the desired reduction in fluid flow would bring the pump below its minimum capacity at the speed at which the motor is currently operating. If not, the controller proceeds to step 93 and adjusts the capacity of the pump accordingly. However, if the desired reduction in fluid flow to the actuator 30 would bring the capacity of the variable displacement pump below its minimum capacity as determined at step 92, then the motor speed is reduced at step 94 and the capacity of the pump is increased or adjusted accordingly, if required, at step 95 before returning to step 90 to await further instructions regarding adjustments in the demand for hydraulic fluid flow.

As can be seen from the examples described above, the present invention provides for the independent control of the speed of the motor 10 and the capacity or displacement of the pump 20. Consequently, they can each be adjusted to accommodate the demands for supply of hydraulic fluid to the actuator 30 without either of the motor 10 or pump 20 being operated continuously at excessively low speeds which increase wear or excessively high speeds resulting in them heating up excessively. Although the examples illustrate an electrical motor 10, any suitable motor may be used. Furthermore, any suitable variable displacement pump 20 may be used and any desired actuator 30 may be used as is appropriate for the desired application. Although the examples have been described with reference to the operation of a flap of an aircraft, the hydraulic actuator may of course be used in any desired application as will be appreciated by a person skilled in the art.

Claims

CLAIMS: 1. An electrically driven hydraulic actuator comprising a variable speed motor; a variable displacement pump arranged to be driven by the variable speed motor; and a hydraulic actuator driven by the variable displacement pump.
2. An actuator according to claim 1, further comprising a controller arranged to instruct the motor to operate at a particular speed and the pump to operate at a particular capacity dependent upon the requirements of the hydraulic actuator.
3. An actuator according to claim 2, wherein the controller is arranged to instruct the motor to operate at one of a number of set speeds.
4. An actuator according to claim 2 or claim 3, wherein when more fluid is required to be provided to the hydraulic actuator, the controller is arranged to increase the capacity of the displacement pump until the displacement pump is operating at a maximum predetermined capacity and then to increase the speed of the motor.
5. An actuator according to claim 4, wherein when the speed of the motor is increased, the capacity of the displacement pump is reduced accordingly.
6. An actuator according to any one of the preceding claims, wherein the motor is a unidirectional variable speed motor.
7. An aircraft including an actuator according to any one of the preceding claims.
8. A method of controlling an electrically driven hydraulic actuator having a variable speed motor and a variable displacement pump driven by the variable speed motor, the method comprising: providing a control signal to the variable displacement pump to control its capacity and providing a control signal to the motor to control its speed.
9. A method according to claim 8, wherein a control signal is provided to the motor to operate it at one of a number of set speeds.
10. A method according to claim 8 or claim 9, wherein when increasing the flow of hydraulic fluid to the actuator, a control signal is provided to increase the capacity of the pump until it reaches its maximum capacity then a control signal is provided to increase the speed of the motor.
11. A method according to any one of claims 8 to 10, wherein upon decreasing the flow of hydraulic fluid to the actuator, the capacity of the pump is reduced until a predetermined minimum pump capacity is reached and the speed of the motor is then reduced.
12. An electrically driven hydraulic actuator substantially as hereinbefore described with reference to the accompanying drawings.
13. A method of controlling the flow of hydraulic fluid to an electrically driven hydraulic actuator substantially as hereinbefore described with reference to the accompanying drawings.