US3291006A

US3291006A - Vane type oscillating hydraulic motor

Info

Publication number: US3291006A
Application number: US335777A
Authority: US
Inventors: Brundage Robert Wesley
Original assignee: Emerson Electric Co
Current assignee: Emerson Electric Co
Priority date: 1963-08-22
Filing date: 1964-01-06
Publication date: 1966-12-13
Anticipated expiration: 1983-12-13

Description

3,29LUU6 Dec. 13, 1966 R. w. BRUNDAGE VANE TYPE OSCILLATING HYDRAULIC MOTOR Original Filed Aug. 22, 1963 INVENTOR. ROBERT W. BRUNDAGE ATTORNEYS United States Patent 3,291,006 VANE TYPE OSQILLATING RAULHC MGTQR Robert Wesley Brundage, St. Louis, Mo., assignor to The Emerson Electric Company, St. Louis, Mo., a corporation of Missouri Original application Aug. 22, 1963, Ser. No. 303,905, now Patent No. 3,242,703, dated Mar. 29, 1966. Divided and this application Jan. 6, 1964, Ser. No. 335,777 7 Claims. (Cl. 92-121) This invention pertains to the art of hydraulic motors and more particularly to a positive displacement oscillating vane type hydraulic motor.

The invention is particularly applicable to powering the agitator of a laundry machine and will be described with particular reference thereto although it will be appreciated that the invention has other and broader applications.

This application is a division of my copending application Ser. No. 303,905, filed Aug. 22, 1963 now Patent No. 3,242,703, issued Mar. 29, 1966 and entitled, Hydraulic Laundry Machine Transmission which application describes the combination of a hydraulic pump selectivity energizing either a rotating hydraulic motor or an oscillating type hydraulic motor. This application describes in greater detail and claims the inventive features of the oscillating motor shown in that application.

In the art of laundry machines, it is conventional to rotate an agitator back and forth through a limited arc to agitate the clothes through the wash water. Then the clothes are spun to centrifuge the water therefrom at wash time. The agitator member must be free to rotate with the clothes.

An oscillating vane hydraulic motor is normally made up of a vane type piston rotatable in either direction in a cavity on a predetermined arc of movement somewhat less than 360 in length. A stator vane engages a hub on the piston as it rotates to divide the housing cavity into two chambers. Valve means selectively shift the high pressure from one chamber to the other to cause the piston to rotate in either direction.

Such a motor is particularly adapted to driving the agitator of a laundry machine but has been considered unsuitable for this purpose because the piston has a maximum arc of rotation somewhat less than 360, it interferes with the rotation of the agitator during the spin cycle.

The present invention contemplates an improved arrangement for disengaging the agitator from the vane piston when externally applied forces on the agitator rotate the piston beyond its normally predetermined arc of rotation.

A further problem in laundry machines is to obtain the maximum efliciency of laundering with the minimum wear and tear on the clothes. The washing efficiency is a function of the average speed of rotation of the agitator while the tendency to knot and wear the clothes is a function of the maximum speed of the agitator. To obtain high rotational speed with a given maximum speed, it is necessary to tie-accelerate the agitator from rotation in one direction and then accelerate it for rotation in the opposite direction in the minimum time. This requires a valve for the motor which is both quick acting and positive. Heretofore, it has been customary to shift the valve on oscillating motors in response to the armate position of the vane and in order to obtain quick acting valves, it has been necessary to employ over-center, energy-storing, mechanical devices such as springs or linkages which are expensive, complicated and liable to wear and breakage. Also, the valves heretofore have been built into the housing or exterior thereto, which type of construction with its valve chambers, porting,

329L005 Patented Dec. 13, 1966 seals and the like is not only expensive and bulky but the various ports and passages cause undue pressure losses.

The present invention contemplates a valve construction where the hydraulic pressures themselves cause the valve member to shift from one position to the other and the valve member itself is located in the piston cavity and also serves as the stator vane.

With such a quick acting, hydraulically actuated valve member, ditiiculty is sometimes experienced with premature actuation of the valve caused by over-speeding of the piston due to inertia and other external forces. The present invention contemplates an arrangement whereby this problem is effectively overcome.

Still another problem with vane type oscillating motors is the sealing of the stator vane to the piston hub and the end of the piston vane to the wall of the chamber. Such seals heretofore have had a tendency to wear, resulting in early maintenance and undue amount of leakage. The present invention contemplates a selfadjusting seal for these two points which compensates for wear and does not leak.

In accordance with the present invention, an oscillating vane type motor of the type described is provided wherein there are means for positively engaging the output shaft to the piston in combination with other means for disengaging such means when external torque on the shaft tends to rotate the piston beyond a predetermined point in its arc of movement.

Further in accordance with the invention, the valve member also forms the stator vane and is of an axial thickness the same as the piston and is movable to shift the supply of high pressure, hydraulic fluid from one side of the piston vane to the other.

Still further in accordance with the invention, the valve member is a unitary member and is so arranged as to be shifted from one position to the other by the hydraulic pressures in the piston cavity eliminating the need for springs and mechanical linkages.

Still further in accordance with the invention, the valve member is held in either position by the high pressure fluid being supplied to the chamber selected by the valve member and the piston moves the valve member enough to allow such high pressure fluid onto its back side such that the pressure shifts the valve member to its other position.

Still further in accordance with the invention, the motor has a pair of discharge ports of limited fluid carrying capacity so as to create a back pressure on the discharge side of the piston vane at the normal speed of operation which back pressure also acts on the valve member to prevent its premature operation in the event the pressure on the inlet side of the piston vane should drop to a value insufiicient to keep the valve member closed.

Further in accordance with the invention, the piston vane and the ends of the stator vane which engage the piston hub have grooves therein, in each of which is loosely positioned a sealing roller and a length equal to the axial thickness of the piston cavity which rollers are hydraulically urged against the side of the groove and the opposing surface to be sealed.

The principal object of the invention is the provision of a new and improved oscillating vane type hydraulic motor which is simple in construction, economical to manufacture, and which is capable of operating at high volumetric and mechanical efficiency.

Still another object of the invention is the provision of a new and improved oscillating hydraulic motor which will operate at low noise level and have a long life.

Still another object of the invention is the provision of an oscillating vane type of hydraulic motor having a O reversing valve with a small arc of travel and very little or no pressure drop through it.

Still another object of the invention is the provision of an oscillating vane type of hydraulic motor wherein the stator vane is movable to form the reversing valve for the motor.

Another object of the invention is the provision of an oscillating vane type of hydraulic motor wherein a stator vane is movable to form the reversing valve and is selfsealing under hydraulic load.

Still another object of the invention is the provision of a reversing valve for an oscillating vane type of hydraulic motor which has a positive reversing action and which does not have over-center, energy-storing mechanical devices such as springs, linkages and the like.

Another object of the invention is the provision of an oscillating vane type hydraulic motor having a hydraulically actuated valve so arranged that external forces on the output shaft will not affect the pressures on the inside of the motor to cause the valve to be reversed before the motor has completed its predetermined stroke.

Still another object of the invention is the provision of an oscillating vane type of hydraulic motor in combination with means for disengaging the shaft from the vane if the shaft is forced to travel beyond the normal predetermined ends of the stroke of the piston.

Another object is the provision of a new and improved hydraulic seal for relatively moving parts.

The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which are a part hereof and wherein:

FIGURE 1 is a side cross-sectional view of an oscillating vane type of hydraulic motor illustrating a preferred embodiment of the invention taken approximately on line 1-1 of FIG. 2;

FIGURE 2 is a cross-sectional view of FIGURE 1 taken approximately in the line 22 thereof and showing in solid lines the valve member in a position to energize the vane piston for rotation in a clockwise direction and in broken lines for rotation in a counterclockwise direction;

FIGURE 3 is a cross-sectional view somewhat similar to FIGURE 2 but showing the vane piston rotated in a clockwise direction beyond its predetermined point of travel and with the shaft disengaged from the piston;

FIGURE 4 is a view taken approximately on the line 44 of FIGURE 1 and showing the arrangement for disengaging the shaft from the vane piston when the vane piston is rotated to the position shown in FIGURE 3.

Referring now to the drawings wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only and not for the purposes of limiting same, the figures show an oscillating-vane type hydraulic motor comprised generally of a housing A, a vane type piston B, a combined stat-or vane and valve member C, and a driven output shaft D which is operatively associated with the piston B and extends upwardly through the housing to drive suitable mechanisms such as an agitator (not shown) of a laundry machine.

HOUSING The housing A shown is comprised generally of a main housing member having a downwardly facing recess defined by an upper fiat surface 11 and a cylindrical surface 12. A cover plate 13 forms the other part of the housing and extends partway into this recess and has an upwardly facing surface 14 parallel to the surface 11. A steel sleeve 16 is positioned in the recess around the outer surfaces thereof extending between the two

surfaces

11, 14 and has an inwardly facing cylindrical surface 17 which, with the

surfaces

11, 14, define the cavity in which the vane piston B and valve member C operate. Both of these members have an axial length substantially equal to the spacing between the

surfaces

11, 14 such that the upper and lower surfaces of the piston B and valve member C are in sliding sealing relationship with the

surfaces

11, 14.

PISTON The piston B is comprised generally of a hub 20 and a radially extending vane 21 having an outer end spaced slightly from the surface 17 which end has an axially extending groove 22 in which is loosely positioned a sealing roller 23 the sides of which extend beyond the end of the vane 20 to slidingly and sealingly engage the surface 17. The roller 23 has a length substantially equal to spacing of

surfaces

11, 14 such that its ends slidingly and sealingly engage these

surfaces

11, 14 and a diameter slightly less than the width of the groove 22 but greater than the depth.

The hub 20 has a generally cylindrical surface 30 coaxial with the axis of the shaft D, the arcuate ends of which surface 30 terminate in

camming surfaces

31, 32 for the purpose of engaging the valve member C and actuating the valve member C to effect reversal of the direction of rotation of the piston B, all as will appear hereinafter.

VALVE MEMBER The piston and valve member C both have a thickness substantially equal to the spacing between

surfaces

11, 14 and divide the cavity into a pair of

chambers

34, 35 which increase and decrease in volume as the piston rotates. The valve member C has the dual function of serving as the stator vane and as the valve member for shifting the high pressure hydraulic fluid from one of the motor chambers, e.g., 34, defined by one side of the vane 20 to the other motor chamber, e.g., 35, defined by the other side of the vane 21. Thus, the valve member C is comprised of a pair of

arms

40, 41 integrally joined by a base 45 and pivoted for oscillation about an axis 42 located adjacent to the surface 17. The surface 17 has a semicircular groove 44 coaxial with the axis 42 which coacts with an outer cylindrical surface on the base 45 to provide a seal.

The

arms

40, 41 of the valve member C are generally symmetrical and each is so arranged as to alternately sealingly engage either the cavity wall 17 or the piston hub surface 30 depending on the position of the valve member C.

The arm has its end defined by an arcuate surface 46 which engages the surface 17 when the valve member C is in the maximum clockwise position.

In a like manner, the end of the arm 41 has an arcuate surface 50 which sealingly engages the surface 17, when the valve member C is in the counterclockwise position.

The area of each

surface

46, 50 is so limited that considering the hydraulic forces on the valve member C and the moment arms of such forces all to be hereinafter described, the unit pressure between these

surfaces

46, 50 when in contact with the surface 17, will be at least greater than the hydraulic pressure in the high pressure chamber so as to prevent leakage of fluid therepast. On the other hand, the area of the surface should be as large as is possible so that injury to the

surfaces

46, 50 or 17 does not occur as a result of impact when the valve member C is snapped from one position to the other.

The surface of the arm 40 facing the piston hub has an axially extending groove 48 in which is loosely positioned a sealing roller 49. In the same manner, the surface of the arm 41 facing the surface 30 has an axially extending groove 52 in which is positioned a like sealing roller 53. Both

rollers

49, 53 have an axial length substantially equal to the spacing of the

surfaces

11, 14 so that their ends slidingly and sealingly engage such surfaces and their diameter is at least greater than the depth of the grooves and less than the width so that their sides extend beyond the groove and, as the valve members shift, alternately slidingly sealingly engage the surface 30. The rollers have a free inward and outward movement in the grooves greater than 0.005 inch.

The walls of the

grooves

48, 52 converge outwardly to a width just slightly less than the diameter of the sealing

rollers

49, 53 so that when either arm is rotated away from the piston surface 30, its roller will be withdrawn from contact with the surface '30 and still be retained in its groove.

The sealing

rollers

49, 53, as well as the sealing roller 23 on the end of the piston vane, provide an effective sliding seal between the members on which mounted and the opposite surface which they engage. Thus, referring only to the sealing roller 53 and assuming that the motor has not been operating, such roller 53 might assume a position in the groove 52 so as to be against the base of the groove and spaced from the surface 30. When hydraulic pressure is introduced to one side of the roller 53, fluids commence to flow between the roller 53 and the surface 30 to the opposite side. This flow of fluid first forces the roller to the far side wall of the groove 52. The roller at all times projects beyond the end of the groove .and creates a restriction to the flow of the fluid resulting in an increased velocity of fluid past the roller and a decreased pressure. Theroller thus moves outwardly of the groove toward the surface 30. This outward movement exposes the inner surface of the roller 53 to the high pressure and this pressure forces the roller both out of the groove into sealing engagement with the surface 30 and into sealing engagement with the side of the groove remote from the pressures. This engagement of the roller with the groove side wall or with the surface 30 is a tangential type of engagement such that a high unit pressure of engagement results suflicient to provide an excellent seal at these two points.

The location of the sealing

rollers

49, 53 in relation to the sealing surfaces 46, S0 and the axis 42 are important to the proper operation of the valve as will appear.

Thus, the main housing has a passage 60 opening through the surface 11 generally on the radial line between the axis of the shaft D and the axis 42, which passage forms the high pressure inlet port for the motor. This port is located just outwardly of the surface 30 and the surface of the valve member C facing the surface 30' is recessed adjacent this passage 60 so as not to interfere with the free flow of fluid therethrough.

In the counterclockwise position of the valve member C, the incoming high pressure fluid flows to the right hand chamber 35. This pressure exerts hydraulic forces on the exposed surfaces of the valve member C, which forces may be integrated as a single force F perpendicular to the mid-point of the line a extending from the place of engagement of the sealing roller 49 to the place of engagement of the surface 50 with the surface 17. The location of these two places must be such that the line of force F passes between the axis 42 and the place of engagement of the surface 50 with the surface 17. The hydraulic pressure in the chamber 35 will thus exert a counterclockwise force on the valve member C holding the surface 50 in engagement with the surface 17 The sealing roller 53 must be likewise positioned so that the high pressures in the left hand chamber 34 exert a clockwise turning moment on the valve member C.

In a like manner, the position and spacing of the axis 42 relative to the line between the sealing

rollers

49, 53 is important as will appear.

Thus, the main housing 10 also has a pair of discharge passages 61, '62 opening through the surface 11 adjacent the surface 17 and each located respectively between the axis 42 and the point where the

surfaces

46, 50 engage the surface 17. These

passages

61, 62 form the discharge ports for the motor. In accordance with the invention, a restriction is provided to the discharge of fluid from either chamber of the motor so as to create a back pressure in such chamber. This may be done by making the area of the

discharge ports

61, 62 less than that of the inlet 6 port 60 or by providing a restricting orifice in the passage leading from each port or by both.

In the counter-clockwise position of the valve member C, this back pressure exerts hydraulic forces on the exposed surfaces of the valve member C remote from the surface 30, which forces may be integrated as a single force G perpendicular to the mid-point of the line b extending from the surface on the base 45 engaging the groove 4-4 to the roller 49 and the location of the axis 4-2 must be such that this line of force G passes between the axis 42 and the point of engagement of the roller 49 with the surface 30. The back pressures in chamber 34 exert a moment on the valve member C tending to rotate it in the same counterclockwise direction as the high pressures in the other chamber 35. They also help to cause the valve member C to shift from one position to the other. The valve member C is thus 100% hydraulically actuated and held in position.

The same is true when the valve member C is in the opposite position and the back pressures in the chamber 35 tend to rotate the valve member C in a clockwise direction, the same as the high pressures in chamber 34.

This back pressure can also become important when for instance an external force such as inertia or torsion on the shaft 11 tends to rotate the piston clockwise at a rate faster than fluid is being supplied through the inlet port 60. If this were to happen, a vacuum would occur in the chamber 35 which would tend to cause the valve member C to move in a clockwise direction to break the seal between the surface 50 and the surface 17 such that when the pressure was restored, it would enter behind the valve member C and cause it to move prematurely in a clockwise direction to shift the flow of fluid from the inlet port 60 to the left hand chamber 34. The turning moment of the back pressure on the valve member C holds the surface 50 in engagement with surface 17 and prevents this from happening.

KEYING OF SHAFT TO PISTON The shaft D extends vertically downwardly through a suitable opening in the main housing 10 and through the piston B into an opening in the cover plate 13 where it is journaled by means of a bearing sleeve 72.

In accordance with the invention, the piston hub 20 is releasably keyed to the shaft D by means of a key radially slidable in a slot in the hub 20 and biased towards the shaft D by means of a spring 83, to engage one of preferably three equiangularly spaced keyways 84 in the shaft D. More than three keyways can be provided if desired. The key 80 has a pair of identical lugs 86 on its upper and lower surfaces which extend into identical arcuate grooves 88, one formed in each of the

surfaces

11, 14. The radially inner surfaces 89 of each groove are so shaped as to form a camrning surface 90 on the clockwise end as viewed in FIGURE 4 so that when the shaft 11 is rotated by means of exterior forces thereon through a sufficient clock-wise arc, the lugs 86 engage the respective camming surfaces 90 and the key 80 is then retracted from the keyway 84. The shaft is then free to rotate free of the piston B.

It is to be noted that on the embodiment shown only one cam surface, 90, is shown. If external torques on the shaft B are expected in both directions, then a similar camming surface could be provided on the opposite end of the grooves 88.

The keyways 84 and the inner end of the key 80 are tapered as at 84a, 80a respectively so that the spring 83 pushes the key 80 into wedging engagement with the keyways 84 to prevent backlash when the piston B is continuously reversed in its direction of rotation.

OPERATION In operation in the position of the valve member C in FIGURE 2, high pressure fluid enters through port 60 and flows to chamber 35 forcing piston B to move in a clockwise direction. Fluid is discharged from chamber 34 through restricting port 61, which creates a back pressure in the chambers. The high pressure and back pressure exert hydraulic forces F, G on the valve member C to hold it in this counterclockwise position. Piston B continues to move in a clockwise direction until cam surface 31 engages roller 49. This forces the valve member C to rotate slightly in a clockwise direction thus breaking the seal between the

surfaces

50 and 17. High pressure fluid then flows into the space behind the valve member C and out through the restricting discharge port 62. Pressure immediately builds up on the back side of the valve member C and this pressure causes the valve member C to move in a clockwise direction. When this occurs the roller 53 comes into contact with the surface 30, stopping further flow of fluid to the right hand chamber and the roller 49 pulled free from. the surface 30, high pressure is then communicated into the left hand chamber 34. This pressure forces the valve member C to continue its rotation in a clockwise direction and the surface 46 comes into sealing engagement with the surface 17. The high pressure on the counterclockwise side of the vane 21 then causes the piston B to rotate in a counterclockwise direction until the cam surface 32 engages the roller 53 at which time the same action occurs but in the opposite direction.

In order to cause the shifting of the flow of fluid from the inlet port 60 from one chamber of the motor to the other in a most rapid fashion, it is preferred that the valve member C have a total swing of less than While the degree of back pressure may be as desired, it has been found that the back pressures of between 1 and pounds per square inch are adequate to effect the operation in the environment of the pump shown.

When the mot-or is not energized, it is preferred that both the inlet passage 60 and the

discharge passages

61, 62 either be interconnected or connected to sump. In such event, the piston B will rotate freely under the influence of external torques applied to the shaft D. When the shaft is rotated in a clockwise direction beyond the point where cam surface 90 engages the valve member C (and would reverse direction of rotation of the piston if high pressure was being supplied), the lugs 86 engage the cam surface 90 withdrawing the key 80 from the keyway 84 and the shaft is then free to rotate independently of the piston B. The piston B remains in this position until the motor is again supplied with hydraulic fluid under pressure. At this time a hydraulic fluid flows counterclockwise through a groove 91 in the surface of the piston hub past the sealing roller 49 and the pressure then causes the vane to move in a counterclockwise direction and at the same time holds the valve member in the clockwise position shown in FIGURE 3. The key 80 then re-engages in the keyway and the motor is again engaged with the shaft D.

The surface 17 is shown as cylindrical. If desired, that portion of the surface 17 over which the vane 21 travels, can be made other than circular and the vane 21 can be formed with a sliding vane to engage thi surface such that for a constant volume supply of fluid through the port 60 the angular velocity of the piston B may vary.

The invention has been described with reference to a preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding of this specification and it is my intention to include all such modifications and alterations insofar as they come into scope of the appended claims.

Having thus described my invention, I claim:

1. In an oscillating type hydraulic motor, comprised of a housing, a vane piston member oscillatable about an axis on a limited arc of movement having a predetermined end, a shaft member oscillatable about said axis, means for positively engaging said members for simultaneous oscillation, the improvement which comprises 8 other means for disengaging said means when said members are rotated beyond an end of said arc.

2. In an oscillating type hydraulic motor, comprised of a housing, a piston member oscillatable in said housing about an axis on a limited arc of movement, a shaft member oscillatable with said piston member on said axis, a keyway on one of said members, the improvement which comprises a key radially movable on the other of said members into and out of engagement with aid keyway, and means on said housing coacting with said key for moving said key into and out of said keyway.

3. In an oscillating type hydraulic motor, comprised of a housing, a piston member oscillatable in said housing about an axis on a limited arc of movement, a shaft member extending through and oscillatable with said piston member, a keyway on one of said members, the improvement which comprises a key radially movable on the other of said members into and out of engagement with said keyway, cam means on said housing and follower means on said key for moving said key out of said keyway when said piston member is rotated through a predetermined point in its arc of movement.

4. In an oscillating type hydraulic motor, a housing, a piston member oscillatable in said housing about an axis on a limited arc of movement, a shaft member extending through and oscillatable with said piston member, a keyway on said shaft member, said piston reversing the direction of its rotation at predetermined points in its arc of movement, the improvement which comprises a key radially movable in said piston member into and out of engagement with said keyway, means for withdrawing said key from said keyway when said piston is rotated beyond said points of reversal by external torques on said shaft member.

5. In an oscillating type hydraulic motor, a housing having a cylindrical cavity defined by upper and lower parallel surfaces and a cylindrical side wall, a piston member oscillatable in said cavity on the axis of said side wall and having a maximum arc of movement less than 360, said piston reversing a direction of oscillation at predetermined points in said are of movement, a shaft member journaled for rotation in said housing and extending through said piston member, said shaft having at least one keyway where it extends through said piston member, the improvement which comprises a key radially movable in said piston member into and out of engagement with said keyway, at least one of said reversal points being short of the maximum arc of movement of said piston member, and cam means coacting with follower means on said key located beyond said point of reversal for withdrawing said key from said keyway when external torques rotate said piston member beyond the predetermined points of reversal.

6. An oscillating type hydraulic motor comprised of a housing having a cavity defined by parallel end walls and a generally cylindrical side wall, a vane piston oscillatable in said cavity on the axis of said side wall and being comprised of a cylindrical hub and a vane extending radially toward said side wall, said piston having a thickness substantially equal to the spacing of said end walls whereby the axially facing surfaces of said hub and vane are in sliding sealing engagement with said end walls, the end of said vane having an axially extending groove therein of a depth slightly less than the width, a metal sealing roller positioned in said groove in the shape of a cylinder and having a length substantially equal to the spacing of said end walls whereby its axial ends are in sliding sealing engagement with said end walls, the diameter of said roller being at least greater than the depth of said groove and less than the width of said groove, said sealing roller being radially movable in said groove and being moved radially from said groove into sealing engagement with both said cylindrical side wall and one groove side wall by hydraulic pressure used to actuate said motor.

UNITED References Cited by the Examiner STATES PATENTS Connell 91339 Kelso 91339 Damizi 91339 Zanon 6429 MARTIN P.

Dow 6429 Langford 6429 Ulrich 91339 Davis 92124 Moushey et al 92125 Riddell 92124 Rumsey et al. 92 125 SCHWADRON, Primary Examiner.

SAMUEL LEVINE, Examiner.

P. E. MASLOUSKY, Assistant Examiner.

Claims

1. IN AN OSCILLATING TYPE HYDRAULIC MOTOR, COMPRISED OF A HOUSING, A VANE PISTON MEMBER OSCILLATABLE ABOUT AN AXIS ON A LIMITED ARC OF MOVEMENT HAVING A PREDETERMINED END, A SHAFT MEMBER OSCILLATABLE ABOUT SAID AXIS, MEANS FOR POSITIVELY ENGAGING SAID MEMBERS FOR SIMULTANEOUS OSCILLATION, THE IMPROVEMENT WHICH COMPRISES OTHER MEANS FOR DISENGAGNG SAID MEANS WHEN SAID MEMBERS ARE ROTATED BEYOND AN END OF SIAD ARC.