GB2082799A - Hydraulic actuator systems - Google Patents

Abstract

A parallel redundant electro hydraulic actuator system comprising an output member 1 coupled to a piston 3 or 5 associated with a pair of hydraulic valves 15 which respectively control the hydraulic pressure on opposite sides of the piston 3 or 5 under the control of respective driving means 17, the valves being controlled by input signals supplied on at least three lanes 33 each of which supplies an input signal to both said driving means in series. Preferably there are two or more such pistons 3 and 5 each having a respective associated pair of hydraulic valves and driving means, each signal lane supplying an input signal to all the driving means in series. <IMAGE>

Description

Hydraulic actuator systems This invention relates to hydraulic actuator systems.

More particularly the invention relates to socalled parallel redundant hydraulic actuator systems, that is to say systems wherein at least one function is carried out by a plurality of components in parallel so that on failure of one of the components, the function continues to be effected by the other parallel components and the system continues to operate. Such systems find application, for example, in aeronautical control systems.

In the design of such systems, a large number of possibilities presents itself in respect of which functions should be carried out by how many parallel components and the interdependence of the various functions and components.

It is an object of the present invention to provide an electro hydraulic actuator system wherein a high degree of immunity to component failure is obtained with a minimum number of components.

According to the present invention there is provided a hydraulic actuator system comprising: an output member; a piston coupled to said output member; a pair of hydraulic valves respectively arranged to control the supply of hydraulic pressurised fluid to opposite sides of said piston; a respective driving means associated with each valve; and-at least three input signal lanes each of which is arranged to supply a respective electrical input signal to both said driving means in series, the driving means being arranged to operate the valves in response to corresponding input signals on a majority of the lanes so that a force is applied to the output member by said piston in one sense or the other.

Preferably the system includes at least two said pistons, each having a respective associated said pair of hydraulic valves and driving means, each input signal lane being arranged to supply a respective input signal to all the driving means in series, and the driving means being arranged to operate the valves in response to corresponding input signals on a majority of the lanes so that the forces applied to the output member by the pistons are in unison in one sense or the other.

In such a system each said piston and its associated pair of hydraulic valves is preferably supplied from a separate source of said hydraulic pressurised fluid.

If desired the system may further include a plurality of detector means, each associated with a respective one of said input signal lanes for providing an output indicative of the position of said output member, and means for controlling the input signal applied to each said input signal lane in dependence on the output of the associated detector means.

One hydraulic actuator system in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing which is a schematic diagram of the system.

Referring to the drawing, the system includes an output member in the form of a rod 1. At spaced positions along the rod 1 there are two pistons 3 and 5. On opposite sides of the piston 3 there are chambers 7 and 9 to which pressurised hydraulic fluid may be supplied and discharged to cause movement of the piston 3 and hence the rod 1 in operation. Similar chambers 11 and 13 are provided on opposite sides of the piston 5.

Each of the chambers 7 and 9 is associated with a respective adjustable hydraulic lap valve 1 5 of conventional form operated by a respective driving means in the form of a torque motor 1 7 whereby pressurised hydraulic fluid may be admitted via an inlet port 19 to the chamber 7 or 9 from a source 21, or discharged from the chamber via an outlet port 23 to an exhaust channel 25. Similarly each of the chambers 11 and 13 is associated with a respective hydraulic valve 1 5 and a respective torque motor 1 7 for admission of pressurised fluid via an inlet port 1 9 to the chamber 11 or 13 from a source 27 or discharge of fluid via an outlet port 23 to an exhaust channel 29.

The valves 1 5 are of the three-position type having low leakage flow in the mull position.

Each of the valves 15 includes a spring loaded, non-return, pressure release valve 31 to prevent seizure due to hydraulic lock, e.g. in the event that a valve 1 5 should fail with both of the ports 19 and 23 closed.

Input signals for control of the torque motors 17 and hence the valves 1 5 are supplied in parallel on three input signal lanes 33 via respective amplifiers 35, each lane passing in series through a separate control winding 37 of each motor 17. The windings 37 of each motor 17 are preferably located on separate pole pieces of the motor to reduce the likelihood of common failures between lanes.

The system further includes four pressure detectors 39 which respectively monitor the pressures on the outlet sides of the inlet ports 1 9 of the four valves 1 5.

In addition three position detectors 41 are provided which detect the position of the rod 1 and are feed a corresponding electrical signal to the amplifier 35 of a respective of the input signal lanes 33, thereby to modify the corresponding input signal.

In normal operation of the system, with corresponding input signals on all three signal lanes 33, the valves 1 5 are operated either to admit pressurised fluid from sources 21 and 27 to chambers 7 and 11, and connect chambers 9 and 13 to the exhaust channels 25 and 29 thereby moving the rod 1 to the right in the drawing, or to admit pressurised fluid to chambers 9 and 13 from sources 21 and 27 and connect chambers 7 and 11 to the exhaust channels 25 and 29, thereby moving the rod 1 to the left in the drawing.

In the event of failure of any one electrical component such as to cause failure of one of the input signal lanes 33, the system will continue to operate in response to the signals on the other two input lanes, without impairment of the operation of any hydraulic component of the system. Preferably the system is provided with lane logic and associated circuitry to disconnect a failed lane, thus allowing the remaining lanes to control the actuator more efficiently.

Similarly, in the event of failure of a hydraulic component of the system e.g. failure of either one of the sources 21 and 27 of hydraulic fluid or a hydraulic valve 15, the system will continue to operate from the other hydraulic source without impairment of the operation of any electrical component of the system.

Thus, the system will continue to operate in response to lane commands even in the event of failure of both one electrical component and one hydraulic component.

The modification of the input signals by the signals derived from the position detectors 41 serves to improve dynamic response of the system in accordance with established servo practice.

Feedback in dependence on the currents applied to the torque motor control windings 37 may be used in the input signal lanes 33 to improve dynamic response of the system in accordance with established servo practice.

Furthermore, the use of such feedback has the advantage that amplifier outputs tend to go hardover if the current loop is broken or earthed.

Comparison of the outputs of the amplifiers can be used to detect zero signal lane failure.

The control winding arrangement of the torque motors 1 7 ensures that the torque motors receive equal total signals even if the individual lane signals differ.

The signals derived from the pressure detectors 39 may be used in conventional manner for monitoring purposes.

It will be appreciated that in alternative systems in accordance with the invention, a single piston only may be used, or more than two pistons. In the former case survival of a hydraulic failure is of course forfeited but survival of an electrical failure without impairment of the operation of any hydraulic component still occurs. With more than two pistons, each piston is preferably assocaited with a separate source of pressurised hydraulic fluid.

It will similarly be appreciated that in alternative systems in accordance with the invention more than three signal lanes may be provided. For example, with four signal lanes, a first lane failure can be absorbed more easily than with three lanes, and moreover, if the first failed lane is disconnected, a second lane failure can then be absorbed.

Claims (8)

Claims

1. A hydraulic actuator system comprising: an output member; a piston coupled to said output member; a pair of hydraulic valves respectively arranged to control the supply of hydraulic pressurised fluid to opposite sides of said piston; a respective driving means associated with each valve; and at least three input signal lanes each of which is arranged to supply a respective electrical input signal to both said driving means in series, the driving means being arranged to operate the valve means in response to corresponding input signals on a majority of the lanes so that a force is applied to the output member by said piston in one sense or the other.

2. A system according to Claim 1 including at least two said pistons, each having a respective associated said pair of hydraulic valves and driving means, each input signal lane being arranged to supply a respective input signal to all the driving means in series, and the driving means being arranged to operate the valves in response to corresponding input signals on a majority of the lanes so that the forces applied to the output member by the pistons are in unison in one sense or the other.

3. A system according to Claim 2 wherein each said piston and its associated hydraulic valves is associated with a separate source of said pressurised fluid.

4. A system according to any preceding Claim further including a plurality of detector means, each assocated with a respective one of said input signal lanes for providing an output indicative of the position of said output member, and means for controlling the input signal applied to each said input signal lane in dependence on the output of the associated detector means.

5. A system according to any preceding claim wherein each said lane employs current feedback.

6. A system according to any preceding claim wherein the driving means comprise torque motors, each said torque motor including a separate control winding connected in each said signal lane.

7. A system according to any preceding claim wherein each said hydraulic valve includes a pressure release valve to prevent seizure due to hydraulic leak.

8. A hydraulic actuator system substantially as hereinbefore described with reference to the accompanying drawing.