Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16H—GEARING
  • F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
  • F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
  • F16H25/20—Screw mechanisms
  • F16H25/22—Screw mechanisms with balls, rollers, or similar members between the co-operating parts; Elements essential to the use of such members
  • F16H25/2204—Screw mechanisms with balls, rollers, or similar members between the co-operating parts; Elements essential to the use of such members with balls
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16H—GEARING
  • F16H25/00—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms
  • F16H25/18—Gearings comprising primarily only cams, cam-followers and screw-and-nut mechanisms for conveying or interconverting oscillating or reciprocating motions
  • F16H25/20—Screw mechanisms
  • F16H25/2021—Screw mechanisms with means for avoiding overloading

Definitions

• the present invention relates to a linear ballscrew actuator with a ballscrew mechanism and a safety unlocking device for uncoupling the ballscrew mechanism from a mechanical member controlled by the mechanism in the event of a failure .
• Ballscrew actuators are often used for accomplishing movements and positioning of mechanical members in many different applications, for example in the aeronautical field.
• An inconvenience that may occur with a ballscrew is the jamming of the balls along their path within the ballscrew.
• the translational movements of an input control member are detected by a sensor which drives an electric motor associated with a ballscrew.
• the rotational movement of the rotor of the electric motor is converted into translational movement by the ballscrew mechanism for controlling the translation of a controlled mechanical member with an axial force of multiplied strength with respect to the force imparted to the control member.
• a primary object of the present invention is to provide a reliable actuator, capable of ensuring control of the driven member also in the event of a mechanical failure (for example jamming) of the ballscrew mechanism and/or an electrical or mechanical failure of the drives controlling it (typically an electric motor) .
• Another object of the invention is to provide a linear actuator having compact dimensions, consisting of a reduced number of components, economical to manufacture.
• Figure 1 is a schematic sectional view of an actuator according to the invention
• Figure 2 is an enlarged view of a detail indicated II in figure 1
• Figure 3 is a further enlarged view of another detail of Figure 1.
• the translating control member 1 is a lever connected to a brake pedal (not shown) .
• a brake pedal not shown
• the electromechanical actuator 2 comprises an electric motor 4, preferably of the brushless type, with an outer stator 5 and an inner rotor 6 keyed onto the nut 7 of a ballscrew mechanism 8 comprised of an inner screw 9 axially translatable along the longitudinal axis x.
• the rotation of the nut 7 which is supported at opposite ends by bearings 10 and 11, causes the screw 9 to translate linearly so as to transmit this linear motion to the output member 3, which is in form of a piston.
• the spherical end la of the control member 1 is engaged in a block 12 axially slidably accommodated within a bushing 13 which, in turn, is slidably accommodated in the actuator housing 14.
• the screw 9 forms a cylindrical axial central passage 15 in which there is guided a tubular stem 16 - herein termed "intermediate" - which is coupled with the bushing 13 at the input end (to the right in the drawing) , whilst it cooperates at the output end (to the left) in a thrust relationship with the piston 3, which is also guided and partially accommodated in the cylindrical passage 15.
• a ball locking and unlocking device which allows to axially releasably connect the screw 9 to the output piston 3, as described herein after.
• the axially innermost length of the output piston 3 is tubular and has a cylindrical cavity 3a crossed by a number of radial passages 17 containing respective locking balls 18 radially interposed between a circumferential groove 19 (figure 2) formed on the axial cylindrical passage 15 of the screw 9 and a radial circumferential protrusion 21 of an unlocking rod 20.
• the rod 20 is coaxially accommodated and axially slidingly guided within the axial cavity 22 of the tubular stem 16 and is fixed at the input end to the block 12.
• a helical compression spring 26 is axially interposed between the block 12 and the bushing 13. It should be noted that in the normal operation position illustrated in figure 1 the block 12 is axially spaced apart from the right end of the tubular stem 16.
• the rod 20 is in an axial position such that the radial circumferential protrusion 21 is radially aligned with the groove 19 of the screw 9, and the locking balls 18 are held in a radially outer locking position engaged in the groove 19.
• the locking balls 18 determine a path along which the axial forces and movements of the screw 9 are transmitted to the output piston 3.
• An axial force applied (by the brake pedal) to the input control member 1 causes the block 12 to shift axially.
• a sensor 24 detects the relative axial movement between the block 12 and the bushing 13 and, through a cable 25, activates the electric motor 4.
• the driving torque outputted by the electric motor is converted by the screw mechanism 8 in a linear translation of the screw 9, which pulls the piston 3 with it owing to the locking action exerted by the balls 18.
• a rotation sensor (not shown) operatively connected to an electronic processing unit (not shown) for providing data of the angular position of the nut 7 indicative of the instantaneous axial position of the screw 9 and the piston 3.
• the screw 9 can not translate axially, the block 12 can be urged into abutment against the input end of the intermediate tubular stem 16 , compressing the spring 26.
• the rod 20 slides with respect to the tubular stem 16 and the piston 3, and reaches, with respect to these members, a more advanced relative axial position in which the locking balls 18 are forced to retract into a radially inner position in a length 27 of smaller diameter of the rod (figure 2) , to such an extent that the ballscrew mechanism is axially uncoupled from the output piston 3.
• the movements imparted by the control member 1 are so transmitted directly to the output piston 3 through the alternative path defined by the intermediate tubular stem 16. In other words, the electric motor 4 and the screw mechanism 8 are bypassed and control of the output member 3 is ensured.
• a circlip 23 is mounted in a groove 28 formed in the inner cylindrical surface of the bushing 13 for the purpose of preventing the block 12 from slipping off the bushing 13 when the block 12 approaches its end position to the right.
• the circlip 23, on the other hand, does not hinder relative axial movement between the block 12 and the bushing 13 when the control member 1 translates towards the right .
• the control that provokes relative sliding of the rod 20 with respect to the tubular stem 16, and therefore the uncoupling of the balls 18, may either be of mechanical kind, as in the illustrated example, or of other kind, for example of electrical kind, through an electromagnet or other means.
• unlocking is determined by the fact that the control force overcomes the resistance offered by the opposing spring.
• the invention is not limited to the embodiment described and illustrated herein, which is to be considered as an example of the actuator; in fact, the invention can be modified in respect of the form and arrangements of parts and details of construction, and in respect of its operation.
• the translatable member of the screw mechanism may be the nut instead of the screw, as will be apparent to those skilled in the art.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Transmission Devices (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

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ID=34611264

Family Applications (1)

Country Status (3)

Cited By (10)

Citations (4)

• 2003
  • 2003-10-31 IT ITTO20030856 patent/ITTO20030856A1/it unknown
• 2004
  • 2004-10-28 DE DE112004002095T patent/DE112004002095T5/de not_active Withdrawn
  • 2004-10-28 WO PCT/EP2004/012202 patent/WO2005050062A1/en active Application Filing

Patent Citations (4)

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