EP1097500A2

EP1097500A2 - Control system with integrated actuation package

Info

Publication number: EP1097500A2
Application number: EP99965714A
Authority: EP
Inventors: Steven B. Croke
Original assignee: Lucas Aerospace Power Transmission Corp
Current assignee: Lucas Aerospace Power Transmission Corp
Priority date: 1998-07-15
Filing date: 1999-07-13
Publication date: 2001-05-09
Also published as: WO2000016464A9; EP1097500A4; WO2000016464A2; WO2000016464A3; JP2002525515A

Abstract

A control system for controlling position of an object includes an integrated actuation package utilizing an electric motor driven servopump (3) to control actuator (4) position. The electric motor (2) operates at a constant direction and speed and has augmented system rotational inertia. Additionally, position of a swashplate (7) on the variable displacement servopump (4) is adjusted directly by an electrically powered rotary actuator (30).

Description

CONTROL SYSTEMWITHINTEGRATED ACTUATION PACKAGE

Field of the Invention This invention relates to a control system for controlling position of an object. The control system includes an integrated actuation package utilizing an electric motor driven servopump to control actuator position, and is useful for applications such as primary flight control. Background of the Invention

In some applications where position of an object is controlled by a distribution system, it may be desirable to employ an electric- based power distribution system in place of a hydraulic-based system. For example, in aeronautical applications, replacement of the conventional aircraft hydraulic power distribution system with an electric power distribution system offers the potential for increased aircraft reliability, maintainability, efficiency and reduced aircraft weight and manufacturing cost.

A first type of actuation system that uses direct electric power for actuation is often referred to as an electrohydrostatic actuator (EH A). A second type is often referred to as an electromechanical actuator (EMA). Generally, both of these systems employ servomotor systems that control motor rotation, i.e., motor speed and direction, to position a linear actuator. The main difference between the EHA and EMA systems is the specific manner in which energy is converted. The EHA transforms rotary energy produced by an electric motor, for example a DC motor, to linear actuator energy via a hydraulic medium charged by a fixed displacement pump. The EMA employs mechanical means, such as gears and ball screw actuator, to accomplish the energy conversion. It will be appreciated that both of these systems rely on changes of motor speed and direction, and it is thus often desirable to reduce rotational inertia that contributes to wear and more frequent maintenance of the system and its components.

Another type of actuation system for controlling position of an object employs an integrated actuation package (IAP). Although the term "integrated actuation package" and like terms have been used to describe various systems, for purposes of this application, the term "integrated actuation package" or "IAP" denotes a servopump system where control of hydraulic pump displacement, i.e., control of hydraulic flow rate and flow direction, is used to position a linear actuator. Generally, an IAP system is comprised of four primary elements: an electric motor; a hydraulic servopump; a linear hydraulic actuator; and a control system capable of translating actuator command and actuator position signals to a position error signal. Specifically, such a servopump actuation system employs a fixed speed, unidirectional motor powered by an electrical source, such as a conventional aircraft electric power source. Actuator position control is accomplished by varying the hydraulic pump output flow rate and flow direction. This action is performed by changing the displacement of the servopump, as opposed to changing the rotational speed and direction of the servopump/electric motor system as in the EHA type systems.

An existing type of IAP system employs a swashplate powered by a fixed displacement boost pump. A relief valve maintains a constant discharge pressure. Fluid from the pump flows to an electrohydrauhc servovalve (EHSV), which positions a torque motor in response to an electric signal, moving a spool and sleeve to provide control flow to stroke control systems. These stroke control pistons provide the necessary force to move the swashplate to the desired position. A feedback wire may also be incorporated into the servovalve to provide swashplate position feedback information directly to the EHSN. An example of this system is shown in Figures la and lb, and an example is also described in Acee et al., Society of Aerospace Engineers (SAE) Technical Paper No. 920968, 1992, the disclosure of which is incorporated herein by reference.

It would be desirable to provide an IAP-based control system that provides increased reliability, maintainability, efficiency and reduced weight and manufacturing cost. Summary of the Invention

It is an object of this invention to provide an IAP control system incorporating an electric motor that operates at a constant direction and speed and has augmented system rotational inertia. This permits employing a smaller electric motor with an electric output that approximates the lower steady state load requirements, but still is able to provide intermittent, higher peak loads. By decreasing the rating of the electrical motor, the system size is reduced, and the system can be accommodated in more restrictive spaces and have a lower weight. Additionally, the reduced power motor, running at constant speed, requires less supply current and produces less heat generation.

It is a further object of the invention to provide an IAP control system where the swashplate position of the variable displacement pump is driven directly by an electrically powered rotary actuator. System elements such as the boost pump, relief valve, EHSV and stroke control pistons, that are employed in existing IAP control system configurations, can be eliminated, thereby reducing the system weight. Additionally, this permits a lower steady state power draw, thereby resulting in reduced heat generation. A first embodiment of this invention relates to a control system for controlling position of an object, that comprises: an object actuator for connection to the object to adjust its position, said actuator being activated by a variable displacement pump; a source for generating a position command signal; and a controller that receives the position command signal and an object actuator position signal, and translates the position command signal and the actuator position signal to generate a pump control signal. The controller is in electrical connection with the variable displacement pump, such that the control signal effects change in displacement of the pump. The pump is driven by an electric motor that operates at a constant direction to drive the variable displacement pump, and the electric motor includes a flywheel to increase rotational inertia thereof, thereby moderating peak power loads.

Additionally, this invention relates to a control system for controlling position of an object, that comprises: an object actuator for connection to the object to adjust its position, said object actuator activated by a variable displacement pump; a source for generating a position command signal; and a controller that receives the position command signal and an actuator position signal, and translates the position command signal and the actuator position to generate a control signal. The pump includes a variable angle swashplate that controls flow direction and flow rate of hydraulic fluid therein, and a rotary electrical actuator that adjusts the swashplate to a desired angular position in response to the control signal. The rotary electrical actuator for the swashplate may include a rotational measurement device for measurement of rotational position of this actuator, and generates a rotary actuator position signal. This rotary actuator position feedback signal is received at the controller, wherein the controller includes a closed loop that sums the object actuator position and position command signals, and compares the summed signals with the rotary actuator position signal, to generate the control signal for the rotary actuator.

Brief Description of the Drawings

Figure la and lb illustrate a prior IAP control system. Figure 2 is a block diagram of an embodiment of a control system of this invention. Figure 3 is a schematic perspective view of a control system according to various embodiments of this invention. Figure 4 is a schematic view of a cooling fan for the system of Figure 3.

Figure 5 is a perspective view of a IAP control system of this invention. Detailed Description of the Preferred Embodiment

Figures la and lb illustrate a prior IAP system. Referring to the schematic illustration in Figure la, the system includes an electrical motor 2, a hydraulic servopump 3 which, in this example, is a constant discharge variable displacement piston pump including pistons 6, a linear hydraulic actuator 4, and a controller 5 capable of translating actuator command and actuator position signals, to a position error signal. Actuator 4 includes a hydraulic cylinder 22 and a linear variable displacement transducer (LVDT) 21; second actuator 4' is designed for incorporation in a second identical channel (not shown in Figure la). Pump 3 is shown in more detail in Figure lb. A swashplate 7 is powered by a fixed displacement boost pump 8. More specifically, in Figure la, a boost relief valve 9 maintains a constant discharge pressure, and fluid from the boost pump flows to an electrohydraulic servovalve (EHSV) 10, which positions a torque motor in response to an electric signal, providing control flow to stroke control systems. Specifically, stroke control pistons 12 provide force to move the swashplate 7 to the desired position. A feedback wire 13 provides swashplate position information to the EHSV 10. The system further includes: a bootstrap accumulator 15 which uses boost pump pressure to maintain pump inlet pressure; a pressure switch 16 which monitors boost output pressure to alert the controller of pump or motor failure; a shuttle valve 17 which provides make-up flow for any piston pump leakage; relief valves 18 which limits maximum system pressure; a solenoid by-pass valve 19 which is commanded and powered by the controller 5 to allow the system to have free-flow between actuator chambers during a system failure; and a filter 20. Such IAP control systems employ the parameter of actuator position as the controlled parameter. For flight control applications, for example, this parameter may correspond to airfoil position where the source 11 of the position command signal is the flight controls operated by a pilot. The position command signal is summed with the object actuator position feedback signal to produce a position error signal (or pump control signal) received at servo valve 10. For systems of the type illustrated in Figures la, the position error signal may be compared with a swashplate position signal (from feedback wire 13).

Figure 2 is a schematic illustration of a control system according to various embodiments of this invention. Similar to the IAP control system of Figure la, this system employs the parameter of object actuator position as the controlled parameter, where the system includes a servopump 3 used to power the actuator 4 for connection to the objection whose position is controlled. In the described embodiment, pump 3 is a variable displacement piston pump that provides servo control of the actuator 4 by varying the displacement and direction of the piston pump flow. This is accomplished by rotating the swashplate 7 in either of two directions from a plane perpendicular to the rotation of the pump.

The system of Figure 2 includes an electrically driven actuator 30 in connection with the swashplate 7 of pump 3. In response to the control signal received from controller 5, the rotary electrical actuator 30 adjusts the swashplate to a desired angular position. Specifically, controller 5 sums the position command signal from position command source 11 and the actuator position feed back signal from the LVDT 21 in connection with linear actuator 4, to general the control signal to actuator 30. In the described embodiment, actuator 30 includes a rotary variable displacement transducer (RVDT) position transducer 31 , that serves as a rotational measurement device to detect the rotational position of actuator 30 and provide enhanced system control. Transducer 31 is in electrical connection with controller 5, such that controller 5 receives a tilt block position feedback signal indicative of the rotary actuator position. Controller 5 sums the position command 5 signal from position command source 11 and the object actuator position signal from the LVDT 21, and compares the summed signals with the rotary actuator position feedback signal to general the control signal to actuator 30. Actuator 30 may have the form of a bidirectional electric motor, reduced speed gearbox with the RVDT 0 position transducer 31 embedded therein.

It will be appreciated that this configuration avoids the hydraulic loop including the boost pump 8, boost relief valve 9, EHSV 10 and stroke control pistons 12 present in the configuration shown in Figure la, resulting in a system with a reduced size and weight. 5 Additionally, actuator 30 only draws power from controller 5 when required, thereby reducing the steady state power draw of the overall system.

In the described embodiment, motor 2 may be an AC induction motor, such as a 115 VAC constant speed electric motor as commonly 0 employed in aircraft systems. For aircraft applications, this avoids the need to modify existing electric power generating systems. For applications that lack AC electrical power, the servopump system can be driven by a fixed speed DC motor. As in the system illustrated in Figure la, a solenoid by-pass valve 19 may be provided in electrical 5 connection with controller 5, to allow the system to have free-flow between actuator chambers during a system failure. The system of Figure 2 may further include the shuttle valve 17 to provide make-up flow for any piston pump leakage, and relief valves 18 to limit maximum system pressure. A bootstrap accumulator 15 may be 0 employed in the system of Figure 2 to maintain pump inlet pressure; since this system does not employ a boost pump, accumulator 15 may be gas-charged. Also, the system of Figure 2 may include a second actuator 4', as in the system of Figure la, designed for incorporation in a second identical channel (not shown in Figure 2).

Figure 3 illustrates schematically a single channel of an IAP control system according to an additional embodiment of this invention. In this embodiment, motor 2 is provided with increased rotational inertia. As mentioned previously, IAP-type control systems include a constant speed and direction electric motor 2 that drives the variable displacement servopump 3. Control of actuator 4 is accomplished through varying the displacement of the servopump 3 and without changing direction or speed of the rotation of the motor and pump. Systems of this type differ from various prior alternate EHA or EMA configurations in that the rotating motor and pump do not need to be accelerated and decelerated in opposite directions during actuation control. Accordingly, whereas a design goal of such prior configurations is to minimize rotating inertia, so as to minimize wear and maintenance of the system and its components, this embodiment of the present advantage takes advantage of increased inertia.

More specifically, additional mass is incorporated in the rotating pump and motor assembly. This is preferably accomplished by adding mass near the outer radius of the rotating assembly, thereby increasing inertia with minimal overall weight increases to the system. In practice, this increased mass can be incorporated in a cooling fan, as the motor will typically include such a cooling fan mounted to the outboard side of the system. In effect, the cooling fan acts as a flywheel to increase rotational inertia. This is illustrated schematically in Figure 4 where cooling fan 32 has increased mass 33 about its periphery to augment rotational inertia.

As an example, an application may require a constant load of about 4 to 5 horsepower with peak loads of short duration of about 15- 20 hp (i.e., peak loads occur when changing the position of the actuator). Typically, an electrical motor with a maximum output of 20 hp would be employed to meet the system demands. However, by incorporating the increased rotating inertia mass, a lower rated motor, for example, a motor with a maximum output of 5 hp, may be employed, that is still able to meet system demands for the short, intermittent peak loads. This embodiment of the invention may be incorporated in the system of Figure la, or preferably in the system of Figure 2.

A preferred configuration of an overall control system is illustrated in Figure 5. This system is a dual-channel actuation system, including a first channel 40 including actuator 4, electrical motor 2 and pump 3, and a second channel 40' including actuator 4', motor 2' and pump 3', mounted to manifold blocks 42, 42'. Each channel includes an electrical connector 44, 44' for connecting the electrical motor to a power source (for example, an aircraft power source), and an electrical connector 45, 45' for connecting the system to the controller 5 (Figure 2). Each motor 2 includes a flywheel 33, 33' on its cooling fan for providing increased inertia mass. Each channel includes a rotary actuator 30, 30' to drive the swashplates of the pump 3,3', respectively , including RVDT position transducers 31, 31 ' and electrical connectors for connection to the controller.

While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation of material to the teachings of the invention without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope and spirit of the appended claims.

Claims

What is claimed:

1. A control system for controlling position of an object, comprising: an object actuator for connection to the object to adjust its position, said object actuator activated by a variable displacement pump; a controller that receives a position command signal and an object actuator position signal, and translates the position command signal and the object actuator position to generate a pump control signal, wherein displacement of the variable displacement pump is effected in response to the pump control signal; and wherein an electric motor operates at a constant direction to drive said variable displacement pump, and said electric motor includes a flywheel to increase rotational inertia thereof.

2. The control system of claim 1, wherein the flywheel is incorporated with a rotating cooling fan for cooling the motor.

3. The control system of claim 1, wherein the system operates at a relatively constant power load with intermittent peak power loads, and the electrical motor has a power rating adapted for the relatively constant load, and the flywheel provides increased rotational inertia for moderation of fluctuations of power load to the motor.

4. The control system of claim 1, wherein the variable displacement pump includes a variable angle swashplate, and a position of the swashplate is adjusted in response to the pump control signal.

5. The control system of claim 4, wherein the pump control signal is received by a servovalve which adjusts the position of the swashplate in response to the pump control signal.

6. The control system of claim 5, wherein the controller sums the object actuator position and position command signals, to generate the pump control signal received at the servovalve.

7. The control system of claim 4, wherein the pump control signal is received by a rotary electrical actuator which adjusts the position of the swashplate in response to the pump control signal.

8. The control system of claim 7, wherein the controller includes a closed loop control system that sums the object actuator position and position command signals, and compares the summed signals with a rotary electrical actuator position signal to generate the pump control signal.

9. The control system of claim 1, wherein the motor operates at a relatively constant speed.

10. The control system of claim 9, wherein the motor is an AC induction motor.

11. The control system of claim 1 , wherein the variable displacement pump rotates in conjunction with the motor.

12. A control system for controlling position of an object, comprising: an object actuator for connection to the object to adjust its position, said object actuator activated by a variable displacement pump including a variable angle swashplate that controls flow direction and flow rate of hydraulic fluid therein; and a controller that receives a position command signal and an object actuator position signal, and translates the position command signal and the actuator position to generate a control signal received by a rotary electrical actuator assembly in connection with the variable angle swashplate, wherein the rotary electrical actuator adjusts the swashplate to a desired angular position in response to the control signal.

13. The control system of claim 12, wherein the electric motor operates at a constant direction and speed.

14. The control system of claim 12, wherein the motor is an AC induction motor.

15. The control system of claim 12, wherein the variable displacement pump rotates in conjunction with the motor.

16. The control system of claim 12, wherein the controller includes a closed loop control system that sums the object actuator position and position command signals, and compares the summed signals with a rotary actuator position signal to generate the control signal.

17. The control system of claim 16, wherein the rotary electrical actuator includes a rotational measurement device for measurement of rotational position thereof.