Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
1999-05-12
2001-05-29
Herrmann, Allan D. (Department: 3682)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
C074S424830, C188S067000, C244S075100, C403S104000
Reexamination Certificate
active
06237433
ABSTRACT:
The present invention relates to electromechanical actuators of the type having a screw-and-nut system.
BACKGROUND OF THE INVENTION
There is a desire, particularly in the field of aviation, to be able to replace hydraulic controls by electromechanical controls.
In particular, proposals have already been made to use electromechanical actuators of the type having a screw-and-nut system for the purpose of controlling the movements of aircraft control surfaces or indeed for extending and retracting landing gear.
Naturally, such actuators must be particularly reliable.
That is why electromechanical actuators are generally mounted in pairs, with one of the actuators in a pair being a passive actuator capable of taking over from the other actuator in the event of it failing.
Nevertheless, the passive actuator is subjected to the same mechanical stresses as the active actuator and it can happen, particularly for primary flight controls whose surfaces are continually loaded, that both actuators fail simultaneously.
The probability of such an accident is low. Nevertheless, to limit the consequences that could arise therefrom, it is desirable to be able to declutch from control any members that might become jammed by actuator failure. In particular, for all types of accident that can happen on an actuator, it is desirable to be able to release flight control surfaces and to prevent them becoming jammed in an end-of-stroke position.
Electromechanical actuator structures of the type having a screw-and-nut system are already known in which it is possible to decouple the screw from the motor and gear box unit which drives it so that if the unit jams, then the screw can still rotate and the controlled member is not locked in position.
In this respect, reference can be made to European patent application EP 0 555 122.
Nevertheless, the structure described in that patent application does not enable the controlled member to be released in the event of the accident being due to the nut jamming relative to the screw.
OBJECTS AND SUMMARY OF THE INVENTION
The invention proposes an actuator structure which enables the nut to be declutched from the structure which drives it in axial translation.
To this end, the invention provides an electromechanical actuator comprising a screw that is driven in rotation, a nut that is driven in translation by rotation of the screw, and a guide rod which is driven in translation by the nut, the actuator having a plurality of rollers interposed between the guide rod and the nut, said rollers having a succession of annular grooves and ridges, while the outside surface of the nut and the inside surface of the guide rod have respective pluralities of complementary grooves and ridges, the grooves and ridges of the rollers co-operating with the grooves and ridges of the nut and of the guide rod to transmit axial force on the guide rod to the nut when said rollers are in an engaged position, the nut and/or the guide rod having release channels in angular positions that are designed to coincide with the positions of the rollers when they are declutched, said channels being such that they enable at least some of the grooves and ridges to be disengaged so as to release the guide rod to move in translation relative to the nut, the actuator including means enabling said rollers to be moved from their clutched position to their declutched position.
Advantageously, the actuator can also have the various characteristics below taken singly or in any technically feasible combination:
the actuator has an intermediate piece defining a plurality of cages in which the rollers are received;
it has three rollers per cage, with the rollers in the clutched position comprising two rollers pressing against the inside surface of the guide rod while the third roller presses against the outside surface of the nut, the grooves and ridges of the third roller co-operating with the grooves and ridges of the other two rollers;
the intermediate piece has a sector which extends outside the guide rod and which co-operates with gearwheel-forming means enabling said intermediate piece to be tilted and enabling the rollers to be moved from the declutched position to the clutched position;
it includes one or more pegs extending radially through the guide rod and having one end received in a respective housing in the nut, said peg(s) preventing the guide rod form rotating relative to the nut;
the intermediate part has spring-forming means applying a radial force on the rollers to urge them into the declutching channels presented in the guide rod or in the nut;
the channels are formed in the inside surface of the guide rod;
it includes a pin extending through the guide rod and having an end received in the housing presented in the nut, said pin preventing the guide rod from rotating relative to the nut, and means enabling said pin to be moved so as to disengage it from the nut;
said means enabling said pin to be moved comprise a follower gearwheel suitable for sliding along a control rod designed to drive it in rotation; and in a variant
the pin terminates in a lever-forming arm on which a prestressed spring exerts a tilting torque, motor-driven means enabling said arm to be released for tilting.
The actuator of the invention is advantageously used in systems that require onboard actuators on vehicles, and particularly but not exclusively on board aircraft.
REFERENCES:
patent: 4179944 (1979-12-01), Conner
patent: 4375770 (1983-03-01), Druet
patent: 4530271 (1985-07-01), Cronin
patent: 4574654 (1986-03-01), Griffiths
patent: 4858491 (1989-08-01), Shube
patent: 4876906 (1989-10-01), Jones
patent: 5360185 (1994-11-01), Derrien
patent: 0025750 (1981-03-01), None
patent: 0325027 (1989-07-01), None
patent: 0555122 (1993-01-01), None
patent: 0569775 (1993-11-01), None
Blakely & Sokoloff, Taylor & Zafman
Herrmann Allan D.
TRW Systemes Aeronauliques Civils
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