Description

Technical Field

This invention relates to an overtravel stop, and more particularly to a bi-directional overtravel stop for use in limiting the rotation of an actuator. The actuator can be used for movement and positioning of air¬ craft components such as a flight control surface.

Background Art

Rotational overtravel stops are often crucial components of actuators used in environments where not only cost but also reliability, weight, size and simpli¬ city are important. For example, where rotating actua¬ tors are used to adjust the flaps of an airplane wing, the reliability of the overtravel stops are crucial in order to prevent possible structural damage and also to prevent the flaps from being adjusted to an aerodynami- cally unstable position should there be a failure in the primary control for the actuator. Simplicity is also important as it helps to ensure the reliability of the stops. Of course, weight, size and power requirements are also obviously important factors with such actuators.

A number of overtravel stops have been devel¬ oped in the prior art in an attempt to meet these crucial needs. For example. Pollock U.S. Patent No. 2,902,876 and Rowley et at U.S. Patent No. 2,837,925 disclose over¬ travel stops using two gear pairs with different gear ratios, one gear being over a threaded shaft and trans¬ lating over that shaft, such that stops at either end of the translation are engaged to stop the main shaft. Lee

U.S. Patent No. 2,502,573 similarly uses two gear pairs having different gear ratios, where translation of one of the gears operates a device disconnecting the drive mo¬ tor.

Krell U.S. Patent No. 2,620,911 and House et al U.S. Patent No. 4,064,981 illustrate another type of overtravel stop which uses friction brake members which are biased together at either limit of travel. These stops often require more space and weight than is desir¬ able in those applications wherein the travel limits are separated by several thousand revolutions.

Disclosure of the Invention

In one aspect of the present invention, an ov¬ ertravel stop for a rotating shaft is provided including a fixed stop and a stop member about the shaft and adapt¬ ed for axial motion thereon to engage the fixed stop. A cam structure is provided to axially move the stop member into engagement with the fixed stop when either travel limit of the shaft is reached.

The cam structure is actuated to axially move the stop member in response to the rotational shifting of a member relative to the shaft. In one aspect of the present invention, the rotational shifting is accom¬ plished by the use of tv/o gear pairs having different gear ratios where one set of corresponding gears in the different pairs rotate together within the shaft travel limits, causing different relative rotation of the other two gears until the travel limits are reached.

In yet another aspect of the present invention, the cam structure comprises a pin and slot connection between the stop member and the shaft. In another as¬ pect, the cam structure is between the stop member and one of the gears.

The present invention provides an overtravel stop which is not only low in cost but also is reliable, simple, low in weight and small in size.

Brief Description of the Drawings

Fig. 1 is a cross-sectional view of the present invention;

Fig. 2 is a view taken along line 2-2 of Fig. 1 showing one barrel cam structure of the present inven¬ tion;

Fig. 3 is a view taken along line 3-3 of Fig.

1;

Fig. 4 is a cross-sectional view taken along line 4-4 of Fig. 3;

Fig. 5 is a view of a limiting stop of the pre¬ sent invention, taken along line 5-5 of Fig. 1;

Fig. 6 is a view of one limiting gear of the present invention, taken along line 6-6 of Fig. 1;

Fig. 7 is a cross-sectional view similar to Fig. 1 but showing the overtravel stop in its limiting positions; and

Fig. 8 is a view of an alternative embodiment of the barrel cam structure.

Best Modes for Carrying Out the Invention

The preferred embodiment of the bi-directional overtravel stop 10 for a rotary shaft 12 of the present invention is shown generally in Fig. 1. The overtravel stop 10 may be used in virtually any application where it is important to limit the rotation of a shaft 12, includ¬ ing, for example, shafts which are used to move the flaps of an aircraft wing. The shaft 12 is suitably supported for rotation with respect to a housing 14, such support

in the embodiment shown being provided by a ball bearing 16 and cap 18 structure.

A drive gear 20 is fixed to the shaft 12 for rotation therewith. The drive gear 20 extends axially along the shaft 12 (for a reason which will become appar¬ ent) and is suitably secured against axial motion, as by the lock nut 22 securing the drive gear 20 against the shaft shoulder 24 as shown. Though the drive gear 20 could, of course, be formed unitarily with the shaft 12, the above-described structure is preferable in that it allows the drive gear 20 to be changed to change the tra¬ vel limits imposed by the overtravel stop 10 (as will become apparent) .

Adjacent the drive gear 20 is an annular member 28 which includes a shift gear 30 therearound. The annu¬ lar member 28 also includes an annular flange 32 support¬ ing axially extending stop members 34. Corresponding fixed stops 36 are suitably secured to the housing 14. The stop members 34 and fixed stops 36 shown are of a type which, when axially aligned, engage each other along axially extending faces to prevent further rotation.

A barrel cam structure 40 secures the annular member 28 to the shaft 12. Specifically, an inwardly projecting cam pin 42 is fixed to the annular member 28 and received in a slot 44 in the shaft 12. As best shown in Fig. 2, the slot 44 is symmetrically curved about an axis 46 parallel to the shaft 12. The slot 44 includes an intermediate seat 48 and two ends 50,52 disposed such that the slot curvature is concave relative to the fixed stops 36 at the end of the shaft 12.

As will become apparent, the barrel cam struc¬ ture could be similarly manufactured with the above com-

ponents reversed, i.e. the pin fixed to the shaft 12 and the slot reversed and in the annular member 28.

A compression spring 56 over the shaft 12 is disposed between the inner race 58 of the ball bearing structure 16 and the annular member 28 to bias the annu¬ lar member 28 to the left in Fig. 1. The compression spring 56 is strong enough so that, during normal rota¬ tion of the shaft 12, the cam pin 42 is retained in the slot seat 48 so that the annular member 28 rotates with the shaft 12.

Limiting the rotational shifting of the annular member 28 around the shaft 12 and providing the reaction torque therebetween is a partial spline connection. Spe¬ cifically, as illustrated in Figs. 3 and 4, an inwardly projecting axial flange 60 on the annular member 28 is received in an axial slot 62 in the shaft 12. The axial slot 62 extends through less of an arc than the cam slot 44 so that this connection prevents the cam pin 42 from being shifted all the way to either slot end 50,52, thereby preventing the barrel cam structure 40 from being excessively stressed.

A pair of limiting gears 66,68 are suitably supported by the housing 14 for rotation about an axis 70 parallel to the shaft 12. Specifically, a limiting shaft 72 having a spline portion 74 and a threaded portion 76 is suitably supported for rotation, as by the ball bear¬ ing structures 78,80 shown.

The first limiting gear 66 is fixed for rota¬ tion with the limiting shaft 72 by a collar 84 having an inner spline and extending over the spline portion 74. A pin 86 is also provided which extends through the collar 84 and limiting shaft 72 to axially fix the two such that the first limiting gear 66 is axially fixed relative to

the limiting shaft 72. The first limiting gear 66 en¬ gages the shift gear 30.

The second limiting gear 68 engages the drive gear 20 and has a central threaded opening 88 located over the shaft threaded portion 76.

The first limiting gear 66 and shift gear 30 have a different gear ratio than the second limiting gear 68 and the drive gear 20.

A limiting stop member 90 is suitably secured (as by the pin 92 shown) for rotation with the limiting shaft 72 at one end of the threaded portion 76. The lim¬ iting stop member 90, which is shown in Fig. 5, includes a pair of axially projecting stops 94. The first limit¬ ing gear 66 also includes a similar pair of axially pro¬ jecting stops 96 on its side facing the threaded portion 76.

As shown in Fig. 6, the second limiting gear 68 also includes axially projecting stops 98,100 on both sides, the stops 98,100 on each side being adapted to engage the facing stops 94,96 on the limiting stop member 90 and the first limiting gear 66 respectively.

The second limiting gear 68 as shown in Fig. 6 includes a number of cutout portions 102 to minimize the weight and cost of the overtravel stop 10. Similar de¬ sirable cutouts and reductions in material, though not shown, would be apparent to a skilled manufacturer of the present invention.

An alternative embodiment to the barrel cam 40 discussed above is shown in Fig. 8. In this embodiment, the drive gear 20' is fixed to the shaft 12* as with the first described embodiment, but the shift gear 30' and annular stop flange 32' are separated. Specifically, the annular stop flange 32' is suitably secured to the shaft

12' by a spline connection 110 such that it will rotate with the shaft 12' and may move axially over the shaft 12'.

The shift gear 30' is located between the drive gear 20' and the stop flange 32'. The shift gear 30' is freely rotatable over the shaft 12', though a partial spline connection such as shown in Figs. 3 and 4 could also be provided.

The drive gear 20' and shift gear 30' have par¬ allel annular faces 112,114 between which is located a suitable bearing structure 116 allowing free rotation of the shift gear 30' relative to the drive gear 20'.

A compression spring 56' biases the stop flange 32' against the shift gear 30* and thus secures the shift gear 30' against the bearing structure 116.

The stop flange 32' includes a collar portion 118 having a concave recess 120 therein. A curved ear 122 is fixed to the shift gear 30' and received in the concave recess 120.

Still other cam structures adapted to axially shift a stop flange 32 may also be used with the present invention. For example, the concave recess in the Fig. 8 embodiment can be associated with the shift gear and the ear associated with the stop flange. Alternatively, the stop flange and shift gear could be fixed together (as in the Fig. 1 embodiment) and a concave recess and ear structure such as shown in Fig. 8 provided between the drive gear and the shift gear. Still other cam struc¬ tures will become apparent to those skilled in the art once they have had an understanding of the above-dis¬ closed embodiments of the present invention.

Industrial Applicability

Operation of the overtravel stop 10 will be presently described. Broadly, the shift gear 32 is caused to rotate with the shaft 12 until either of the selected shaft travel limits are reached. At either travel limit, the shift gear 30 is rotationally shifted around the shaft 12, which shifting through a cam struc¬ ture 40 causes the stop flange 32 to move axially to en¬ gage a fixed stop 34 and thereby stop rotation of the shaft 12.

Specifically, operation of the first described embodiment is as follows. As the shaft 12 rotates within its travel limits, it is followed by both the drive gear 20 and the shift gear 30 (the cam pin 42 being maintained in the slot seat 48 by the spring 56) .

Due to the different gear ratios involved, ro¬ tation of the drive gear 20 and shift gear 30 at the same rate causes the first and second limiting gears 66,68 to rotate at slightly different rates relative to one anoth¬ er. Since the first limiting gear 66 rotates with the limiting shaft 72, the second limiting gear 68 rotates at a slightly different rate than the shaft threaded portion 76 and thereby is caused to translate axially over the limiting shaft 72.

When the stops 94 and 98 (Fig. 7) or 96 and 100 (in phantom in Fig. 7) engage, the second limiting gear 68 is held against further rotation relative to the lim¬ iting shaft 72, and thus also rotates at the same rate as the first limiting gear 66. As a result, the drive gear 20 and shift gear 30 rotate at different rates and, since the drive gear 20 is fixed to the shaft 12, the shift gear 30 is rotationally shifted about the shaft 12.

Shifting of the shift gear 30 moves the cam pin 42 toward one end 50 or 52 of the cam slot 44. The curved configuration of the cam slot 44 thus biases the annular member 28 axially over the shaft 12, overcoming the biasing of the compression spring 56, so that the stop members 34 become aligned with and engage the fixed stops 36.

With the stop members 34 and fixed stops 36 engaged, the annular member 28 is held against further rotation. The shaft 12 is thus also held against further rotation by the action of the flange 60 and axial slot 62.

Reverse rotation of the shaft 12 away from the travel limit is, of course, easily accomplished without requiring any greater torque than used during normal ro¬ tation of the shaft 12. Reverse rotation can continue until the second limiting gear 68 translates across the shaft threaded portion 76 and engages the opposite stops 100 or 98.

It is apparent from the above that proper se¬ lection of gear ratios and thread pitch will set the ov¬ ertravel stop 10 so that one set of stops 98 or 100 of the second limiting gear 68 will engage the stops 94,96 respectively at selected limits of shaft rotation in either direction. The limits can also be modified by axially shifting the first limiting gear 66 over the lim¬ iting shaft 72 and suitable access (not shown) can be provided through the housing 14 to permit such shifting to be easily accomplished. Further, through the use of highly similar gear ratios and a small thread pitch, ro¬ tational limits spaced apart many thousands of revolu¬ tions can be easily provided with a relatively small ov¬ ertravel stop 10.

Operation of the embodiment shown in Fig. 8 is similar to that described above except that, when the shift gear 30' is caused to shift relative to the shaft 12' and drive gear 20' at either limit, the ear 122 on the shift gear 30' engages the concave recess 122 (which does not shift, being secured to the shaft 12 by the spline connection 110) to move the stop members 34 (not shown in Fig. 8) of the stop flange 32' axially into alignment and engagement with the fixed stops 36 (also not shown in Fig. 8) . This prevents further rotation of both the stop flange 32' and (through the spline connec¬ tion 110) the shaft 12'.

Other aspects, objects and advantages of the invention can be obtained from a study of the drawings, the specification and the appended claims.