WO2001071217A1

WO2001071217A1 - Dual load path ball screw with thrust bearing

Info

Publication number: WO2001071217A1
Application number: PCT/US2000/013472
Authority: WO
Inventors: Paul Wingett
Original assignee: Alliedsignal Inc.
Priority date: 2000-03-22
Filing date: 2000-05-17
Publication date: 2001-09-27

Abstract

A dual drive ball screw (40) actuator has a ball screw shaft coupled at one end to a gear train (20) and coupled at the other end to a ball screw nut (60). The ball screw shaft (42) and ball screw nut are connected through complementary helical grooves filled with ball bearing balls (64). The outer surface of the ball screw nut is splined and can be driven by a second gear train. An output tube (70) is coupled at one end to the ball screw nut and at its opposite end has a connector portion (72) with a groove on its inner surface. A rod end (80) has a coupling member (82) for coupling to a surface to be actuated and a shaft portion (84) with a groove on its outer surface. This shaft portion is received with in the output tube portion and the corresponding grooves are coupled through the use of a plurality of ball bearing balls. The ball screw shaft (42) is journaled to a casing by a thrust bearing (100) having inner and outer races with complementary annular grooves that are coupled by ball bearings.

Description

DUAL LOAD PATH BALL SCREW WITH THRUST BEARING GOVERNMENT RIGHTS

The invention described herein was made in the performance of

work under NASA Contract No. NCC8-115 and is subject to the provisions

of Section 305 of the National Aeronautics and Space Act of 1958

(42 U.S.C. 2457).

REFERENCE TO COPENDING APPLICATION

This application is a continuation-in-part of U.S. Patent Application

Serial No. 09/312, 455, filed May 17, 1999.

TECHNICAL FIELD

This invention relates to actuator systems having dual drive path

ball screws and more particularly to a thrust bearing for use in such

systems.

BACKGROUND OF THE INVENTION

There are many components of an aircraft that are positioned by

operation of a ball screw actuator. In such an actuator, there is relative

rotation between a ball screw and a ball screw nut to achieve linear

translation of the ball screw nut. One of the actuator elements is fixed and

the other actuator element is connected to a flight control surface. Because of use of a dual drive ball screw actuator in controlling critical

surfaces for aircraft flight, it is common to construct the ball screw of inner

and outer tubular members which are interconnected at their ends. The

inner tubular member provides a primary drive path for the ball screw and

the outer tubular member provides a secondary drive path to be used in

the event of a failure in the primary drive path. This structure is known as

a dual drive actuator.

In the primary drive path, the inner tubular member is rotated. The

inner tubular member has a helical ball groove which is associated with

the ball screw nut by means of balls positioned in a portion of the helical

groove so that rotation of the inner tubular member will cause the linear

translation of the ball screw nut. The ball screw nut, in turn, is connected

to an output tube which is connected to a rod end by a rod end swivel.

The rod end is connected to the flight control surface to be actuated. So

as ball screw translates linearly so does the output tube, rod end swivel

and the rod end which then moves the flight control surface. In the

secondary drive path, the ball screw nut is rotated while locking the

primary screw, which in turn rotates and linearly translates the output tube.

Because the inner tubular member is either rotating or stationary

depending on the mode of operation, a thrust bearing must to journal the tubular member that can transfer axial thrust loads in both modes of

operation.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a thrust bearing for

journaling a shaft that alternates between rotating and stationary

operation.

Another object of the present invention is to provide a dual drive

path ball screw actuator and system that uses the thrust bearing.

The present invention achieves this object providing a dual drive

path ball screw actuator and system having a ball screw shaft coupled at

one end to a gear train and coupled at the other end to a ball screw nut.

The ball screw shaft and ball screw nut are coupled through

complementary helical grooves filled with ball bearing balls. The outer

surface of the ball screw nut is splined and can be driven by a second

gear train. An output tube is coupled at one end to the ball screw nut and

at its opposite end has a connector portion with a groove on its inner

surface. A rod end has a coupling member for coupling to a surface to be

actuated and a shaft portion with a groove on its outer surface. This shaft

portion is received with in the connector portion and the corresponding

grooves are coupled through the use of a plurality of ball bearings. The

PHX DOCS.1 181₅8₅.₂ ball screw shaft is journaled to a casing by a thrust bearing having inner

and outer races with complementary annular grooves that are coupled by

ball bearings.

These and other objects, features and advantages of the present

invention are specifically set forth in or will become apparent from the

following detailed description of a preferred embodiment of the invention

when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an actuator system employing a dual drive

ball screw having a thrust bearing contemplated by the present invention.

FIG. 2 is a cross-section taken of the dual drive ball screw of

FIG. 1.

FIG. 3 is a perspective view of the thrust bearing of FIG. 1.

FIG. 4 is a front view of the thrust bearing of FIG. 3.

FIG. 5 is a cross-section taken along line A-A of FIG. 4.

FIG. 6 is a cross-section taken along line B-B of FIG. 4. DESCRIPTION OF THE INVENTION

FIG. 1 shows an actuator system 10 that has a dual drive ball

screw 40 contemplated by the present invention. The operation of the

system 10 is controlled by an electronic control unit 12 which has a

primary controller 14 and a secondary controller 16. When movement of a

control surface to which the ball screw 40 is attached is required, the

primary controller 14 sends a signal to a primary motor 18 which in turn

drives the primary gear train 20. The primary gear train 20 is secured to a

support structure, (not shown) and is also coupled to an inner tubular

member 42 of the dual drive ball screw 40. A linear variable displacement

transducer 22 measures the linear position of the output tube 70 of the

ball screw 40 and sends a signal indicative of such position to the primary

controller 14, thereby closing the control loop. When the required position

of the control surface is reached, the primary controller 14 stops the

movement of the ball screw 40. The combination of primary controller 14,

primary motor 18, primary gear train 20 and ball screw 40 define the

primary drive path.

In the event of a failure in the primary drive a secondary drive is

provided. The secondary drive includes the secondary controller 16 which

controls a secondary motor 24 which in turn drives a secondary gear train 26. The secondary gear train 26, like its counterpart, is secured to a

support structure, (not shown). The gear train 26 is also coupled to a ball

screw nut 60 of the dual drive ball screw actuator 40. A linear variable

displacement transducer 28 measures the linear position of the output

tube 70 of the ball screw 40 and sends a signal indicative of such position

to the secondary controller 16, thereby closing the control loop. The

secondary drive path operates in the same control manner as the primary

drive path described above. When the primary drive path is operating the

secondary drive path is locked.

Referring to FIG. 2, the inner tubular member 42, which is also

referred to as a bail screw shaft, has at one end a threaded portion 44

which is coupled to and driven by the primary gear train 20. Adjacent the

threaded portion 44 is a smooth portion 46 which extends from the

threaded portion 44 to a first stop member 48. A second stop member 50

is located at the end of the ball screw shaft 42 opposite the end having the

threaded portion. Between stop member 48 and stop member 50, the

surface of the ball screw shaft 42 has a helical ball groove, (not shown in

FIG. 2 for purposes of clarity). The ball screw shaft 42 may be solid or to

reduce weight it may be hollowed out. If hollowed, then a plug 54 is

needed to prevent grease from entering the hollowed portion. The ball screw nut 60 is also a tubular shaft having on its outer

surface splines for coupling to and being driven by secondary drive train

26. On its inner surface, the ball screw nut has a helical groove, (not

shown). The portion of the ball screw shaft 42 between the stops 48 and

50 is disposed within the ball screw nut 60 so that the helical groove on

the inside surface of the screw nut 60 is connected to the helical groove

on the outside of the ball screw shaft 42 by a plurality of balls 64. Thus the

rotational movement of the ball screw shaft 42 is translated into linear

motion of the ball screw nut 60.

The ball screw nut 60 is coupled by preferably a thread and pin to

one end of the output tube 70. At the opposite end the output tube 70 has

a connector portion 72 having on its inner surface a plurality of annular

grooves 74. A rod end 80 has a coupling member 82 which is attached to

the flight control surface, (not shown), requiring actuation, and a shaft

portion 84. The shaft portion 84 may be hollow, in which case a plug 86 is

used to prevent grease from entering the hollowed portion. The outer

surface of the shaft portion 84 has a plurality of annular grooves 88, which

is the same type as the grooves 74 on the inner surface of the connector

portion 72. The shaft portion 84 is disposed within the connector

portion 72 so that the each of the grooves 74 is connected to one of the

grooves 88 by a plurality of balls 90. The connector portion 72 has three holes or slots 92, only one of which is shown, that are axially and

circumferentially staggered. Once the shaft portion 82 is inserted in the

connector portion 72, the balls 90 are inserted through these holes 92 until

the grooves 74,88 are filled with ball bearing balls 90 balls. The slots 92

are then plugged. A retaining sleeve 98 covers the connector portion 72

and a seal 96 prevents contaminants from entering these grooves 74,88.

The combination of the rod end 80 and the connector portion 72 is

referred to as a rod end swivel.

The ball screw shaft 42, the ball screw nut 60 and a portion of the

output tube 70 are mounted within a casing. The casing includes a cover

90 bolted to an aft gearbox casing 92 which is bolted to a center gearbox

casing 94. The center gearbox casing, in turn, is also bolted to a forward

gearbox casing 96. Coupled to the forward gearbox casing 96 on a side

opposite from the center gearbox casing 94 is a fixed rod end 98. The

fixed rod end 98 has a coupling member 97 which is coupled or bolted to a

structure, not shown, on the aircraft.

The ball screw shaft 42 is journaled to the fixed rod end 98 and

forward gearbox casing 96 by a thrust bearing 100. Referring to FIGs. 3-

6, the thrust bearing 100 has an annular inner race 102 that defines a

bore 104 through which is mounted the smooth portion 46 of the ball screw shaft 42 and an annular outer race 1 10 which is mounted within the

a portion of the forward gearbox casing 96 and hollow casing portion 99.

The outer surface of the inner race 102 has a plurality of annular

grooves 106 and the inner surface of the outer race 1 10 also has a

plurality of grooves 1 12. The two sets of grooves 106, 1 12 align so that

the each of the grooves 106 is connected to one of the grooves 1 12 by a

plurality of ball bearing balls 1 14. The outer race 1 10 has three holes or

slots 120, only two of which are shown in FIG. 3. The slots 120 are axially

and circumferentially staggered. The balls 1 14 are inserted through these

slots or holes 1 14 until all the grooves 106, 1 12 are filled with the balls.

The slots 120 are then plugged by plug 1 18. In the preferred embodiment,

each set of grooves 106, 1 12 has nine grooves and there are three slots

120. Each of slots 120 used to fill three of the grooves. The outer race 110

also has a slot 122 for receiving pin, not shown. The pin prevents the

outer race from spinning under a load reverser condition.

During operation of the primary drive, the inner tubular member or

ball screw shaft 42 is rotated causing the ball screw nut 60, output tube

70, and the rod end 80 to translate linearly. The thrust bearing 100 allows

the shaft 42 to rotate while transmitting the axial thrust generated to the

fixed rod end 98. When the secondary drive is in operation, the ball screw nut 60 is both rotating and translating linearly as the ball screw shaft 42 is

neither rotating nor moving linearly The output tube 70 is also rotating and

translating linearly Again, the thrust bearing 100 transmits the axial thrust

to the fixed rod end 98

Various modifications and alterations to the above-described

preferred embodiment will be apparent to those skilled in the art.

Accordingly, these descriptions of the invention should be considered

exemplary and not as limiting the scope and spirit of the invention as set

forth in the following claims

Claims

What is claimed is

1 A dual drive ball screw actuator (40) comprising

a casing having a fixed rod end (98) for mounting to a fixed

structure,

a ball screw shaft (42) having a first portion with an outer surface

adapted for engaging a first rotatable structure and a second portion

having a first groove on its outer surface, said ball screw shaft (42)

journaled to said casing by a thrust bearing (100), said thrust

bearing (100) comprising an inner race (102) defining a bore (104) for

receiving a portion of said ball screw shaft (42), said inner race having an

outer surface with a first plurality of annular grooves (106), an outer

race (1 10) disposed within said casing and having an inner surface with a

second plurality of grooves (1 12), wherein each of said grooves of said

first plurality is coupled to one of said grooves of said second plurality by a

plurality of ball bearings (1 14),

a ball screw nut (60) having an outer surface adapted for engaging

a second rotatable structure and having a second groove on its inner

surface, said ball screw nut (60) receiving said second portion of said ball

screw shaft (42) so that said first and second grooves connect through a

first plurality of balls (64), a rod end (80) having a coupling member (82) for attaching to a

surface to be actuated and a shaft portion (84) having a fourth groove (88)

on its outer surface; and

an output tube (70) coupled at one end to said ball screw nut (60)

and at its opposite end having a connector portion (72) having an inner

surface with a third groove (74), said connector portion receiving said

shaft portion (84) of said rod end (80) so that said third and fourth grooves

connect through a second plurality of balls (90).

2. The dual drive ball screw actuator (40) of claim 1 wherein

said connector portion (72) has at least one slot (92) for inserting said

second plurality of balls (90) between said third and fourth

grooves (74, 88).

3. The dual drive ball screw actuator (40) of claim 1 wherein

said connector portion (72) has three slots (92) axially and

circumferentially staggered for inserting said second plurality of

balls (90)between said third and fourth grooves (74, 88).

4. The dual drive ball screw actuator (40) of claim 1 wherein

said third and fourth grooves (74, 88) are annular grooves.

5. The dual drive ball screw actuator (40) of claim 4 wherein

said first and second grooves (106, 112) are helical grooves.

6. The dual drive ball screw actuator (40) of claim 1 wherein

said outer race (110) of said thrust bearing (100) has at least one

slot (120) for inserting said plurality of ball bearings (114).

7. The dual drive ball screw actuator (40) of claim 1 wherein

said outer race (110) of said thrust bearing (100) has three slots (120)

axially and circumferentially staggered for inserting said plurality of ball

bearings (114).

8. A thrust bearing (100) comprising:

an inner race defining a bore for receiving a rotatable shaft, said

inner race (102) having an outer surface with a first plurality of annular

grooves (106); and

an outer race (110) having an inner surface with a second plurality

of grooves (112), wherein each of said grooves 106 of said first plurality is

coupled to one of said grooves (112) of said second plurality by a plurality

of ball bearings (114).

9. The thrust bearing (100) of claim 8 wherein said outer race

has at least one slot for inserting said plurality of balls.

10. The thrust bearing of claim 8 wherein said outer race has

three slots axially and circumferentially staggered for inserting said

plurality of balls.