Variable Stroke Cylinder

Abstract

In a variable stroke cylinder having a pair of pistons in which the distance between the pistons is selectively variable for selectively varying the stroke of the cylinder, a vent communicates with the space between the pistons for venting the space when the distance between the pistons is being varied.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a variable stroke cylinder and, more particularly, to a double piston cylinder in which the distance between the pistons may be easily and readily varied to vary the stroke of the cylinder.

It is frequently desirable that a given pneumatic or hydraulic motor or pumping cylinder be capable of varied input and/or output depending upon conditions encountered during use in a given system. One manner which has been employed in the past to so vary the input and/or output of such cylinders, has been to selectively increase or decrease the stroke of the power member or piston of the cylinder.

Various methods have been employed in the past to vary or adjust the stroke for this purpose. One manner of effecting such variation, has been by the use of electrical switching devices. Mechanical methods have also been employed. In the mechanical method, rather than a single working piston, a pair of working pistons are provided in the cylinder and the distance between the pistons may be selectively varied to vary the stroke of the cylinder. When the pistons are moved toward each other, the stroke will be increased and when the pistons are moved away from each other the stroke will decrease. By way of example, a double piston variable stroke cylinder is shown in United States Letters Patent No. 1,325,006.

As shown in said patent, the pistons are fitted within the cylinder with a close tolerance between the outer perimeter of each of the pistons and the cylinder wall so as to effect a sealing engagement between the pistons and the cylinder wall. As a result of this sealing engagement, variable adjustment either of one of the pistons relative to the other or of both pistons simultaneously is rendered difficult, if not impossible under some circumstances, due to the compression or expansion of the fluid sealed between the pistons. For example, when the pistons are adjusted apart so as to decrease the cylinder stroke, a progressively increasing vacuum condition occurs in the space between the pistons as adjustment proceeds. This vacuum condition renders adjustment progressively more difficult and adjustment may even become impossible where the stroke is to be widely varied. Conversely, when the pistons are moved closer together so as to increase the stroke, a pressure condition arises between the pistons which also progressively increases as adjustment proceeds. Particularly in the latter situation and where the cylinder is for hydraulic use, any leakage which may occur between the pistons and the cylinder wall into the space between the pistons during prolonged minimum stroke operation, may render adjustment to the maximum stroke condition impossible due to the non-compressible nature of the hydraulic liquid.

The variable stroke cylinder of my invention overcomes these disadvantages. In the variable stroke cylinder incorporating the principles of my invention, a double piston cylinder is provided in which the stroke is capable of being readily and easily mechanically varied over a wide range. In the cylinder of my invention, the effort necessary to adjust the stroke is both minimal and uniform over the entire range of adjustment since the likelihood of vacuum or pressure conditions occurring in the space between the pistons is obviated. Moreover, in the cylinder incorporating the principles of my invention, the stroke may be readily adjusted from the exterior of the cylinder, without necessitating disassembly of same and, once adjustment has been made, the pistons may be locked relative to each other to insure reliable operation over continued periods at the adjusted stroke in one of the embodiments of my invention.

In a principal aspect, the variable stroke cylinder incorporating the principles of my invention includes a pair of piston members positioned in a cylinder and at least one of said piston members is selectively moveable relative to the other for adjustably varying the stroke of the piston members. In my invention, vent means is provided which communicates with the space between the piston members so as to vent the space when the distance between the piston members is varied to vary the stroke of the cylinder.

In another aspect, locking means is provided whereby once the stroke has been adjusted, the piston members may be locked relative to each other.

In another aspect, each of the pistons, as well as the cylinder, are of non-curvilinear cross section, whereby when one of the piston rods is rotated relative to its piston, stroke variation is effected.

These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWING

In the course of this description, reference will frequently be made to the attached drawing in which:

FIG. 1 is an elevation cross sectioned view of one preferred embodiment of variable stroke cylinder constructed in accordance with the principles of my invention;

FIG. 2 is a partially cut away elevation cross sectioned view of a second preferred embodiment of variable stroke cylinder constructed in accordance with the principles of my invention; and

FIG. 3 is a partially cut away perspective view of a third preferred embodiment of variable stroke cylinder constructed in accordance with the principles of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, one preferred embodiment of variable stroke cylinder of my invention is shown. The cylinder comprises an elongated cylinder sleeve 10 closed at each end by cylinder heads 11 and 12 which may be threadedly secured to each end of the cylinder sleeve by way of threads 14. A suitable sealing gasket, such as an O-ring 16, may be carried in a groove 18 adjacent the inner end of each of the heads 11 and 12 so as to sealingly contact the inner wall 20 of the sleeve.

A duplex cylinder is shown in FIG. 1 in which intake and/or discharge passages 21 and 22 extend through each of the heads 11 and 12, respectively. Connecting passages 23, threaded to receive suitable fluid conduits, are provided to communicate passages 21 and 22 with the cylinder exterior. Passage 21 in head 11 is somewhat enlarged relative to passage 22 so as to receive a piston rod 24 therethrough. Passage 21 is preferably of a diameter such that when the rod 24 is journalled through the passage, an annular space obtains between the head 21 and exterior of the rod which has a cross section substantially equal to the cross sectional area of passage 22 to provide for a uniform suction and discharge rate through each of the passages. A suitable sealing gland 25 is fitted in the top of passage 21 and engages the piston rod 24 to seal the passage, but provide for sliding movement of the rod.

A pair of pistons 26 and 27 are positioned within the cylinder sleeve 10 and divide the interior of the sleeve into a pair of working chambers 28 and 29. Piston 26 is firmly threaded at 30 onto one end of piston rod 24 and the other piston 27 is also threaded at 32 on one end of another piston rod 34 and stationarily locked thereto by nut 36 which is received in a recess 38 in piston 27. Rod 24 is annular in cross section and rod 34 extends upward therethrough in journalled relationship. The end of rod 34 opposite its piston is externally threaded at 40 and rod 24 is internally threaded so that rods 24 and 34 may be axially threadedly adjusted relative to each other between the position shown in solid in FIG. 1 and the dot and dash line position also shown therein. A drive fitting may be carried on the end of either of the rods similar to the fitting D shown in FIG. 3.

A seal ring 42, formed of suitable sealing material, is carried in a groove 44 about the inner periphery of rod 24 adjacent its piston and sealingly engages the external surface of rod 34 to seal off the space 46 between the pistons 26 and 27 from the small annular area between rod 34 and the interior wall of rod 24. Suitable piston sealing rings 47 and 48 are also carried in annular grooves 49 and 50 about each of the pistons 26 and 27, respectively, and are arranged to slidingly and sealingly engage the internal wall 20 of the cylinder sleeve to prevent leakage between the pistons and wall.

An important feature of my invention is the provision of means to equalize the pressure between space 28 and the space 46 between the pistons during adjustment of the piston stroke. As shown in FIG. 1, this means comprises a bleed orifice 52 which extends between the faces of and through the thickness of piston 26 and communicates space 46 with the working space 28 above the piston. Bleed orifice 52 is of a size such that little fluid transfer will occur between space 28 and space 46 during normal operation of the cylinder either as a pump or as a motor. However, when it is desired to either increase or decrease the stroke of the cylinder, the bleed orifice operates to vent the space 46 and enable easy and uniform adjustment of the cylinder stroke.

For example, when it is desired to decrease the stroke of the cylinder, a suitable tool, such as a wrench, is applied to a suitable tool receiving surface 54 at the end of rod 24 and the rod is rotated while rod 34 is held stationary. If the rod 24 is rotated so as to move from the solid position to the dot and dash position shown in FIG. 1, piston 26 will move relatively away from the piston 27. Since the volume of the space 46 between the piston will increase, vacuum conditions would normally occur therein due to the tight seal provided by sealing rings 47 and 48 and continued adjustment would become progressively more difficult. However, due to the orifice 52, a relatively constant pressure will be maintained at all times in space 46 due to the venting of fluid from space 28 to space 46. If the storke is to be decreased, rod 24 is rotated in the opposite direction moving piston 26 closer to piston 27. Again relatively constant pressure conditions will obtain in space 46 during such adjustment, since any pressure buildup will be vented from space 46 to space 28 by way to the bleed orifice.

Referring to FIG. 2, another embodiment of variable stroke cylinder of my invention is shown in which locking means is provided to lock the piston heads relative to each other once stroke adjustment has been completed. Like the embodiment shown in FIG. 1, a pair of pistons 56 and 57 are positioned within cylinder sleeve 10. A tubular piston rod 58, somewhat similar to rod 24 in FIG. 1, is fixed by way of threaded end 60 and nut 61 to piston 56 and extends through one head of the cylinder (not shown) in a manner similar to that shown in head 11 in FIG. 1. A second rod 62 extends through the other head (not shown) of the cylinder. The distal end of piston rod 62 is of reduced diameter and externally threaded at 64 over its reduced diameter length. Piston rod 62 is threaded through piston 57 and locked thereto by a locknut 66 and the remaining threaded portion is threadedly received in the tubular rod 58 which is also internally threaded at 68 over its length. A threaded plug 70 is threaded into the rod 58 from the other end and into contact with the distal end of the piston rod 62 so as to lock the rod 62 at whatever depth it has been threaded. The plug 70, includes a suitable tool receiving surface 72 at its outer end to allow for tightening and loosening of the plug.

In order to adjust the stroke of the cylinder shown in FIG. 2, plug 70 is rotated so as to move upward and out of contacting relationship with the distal end of piston rod 62. Piston rod 62 is now held stationary and tubular rod 58 is rotated as previously described. Rotation of rod 58 causes the rod and its associated piston 56 to move axially toward or away from piston 57 and threadedly along the piston rod 62. Once piston 56 has been positioned in its desired spaced relationship from piston 57, plug 70 is again threadedly tightened into contact with the distal end of the piston rod 62, locking the pistons in their adjusted spaced relationship.

The venting arrangement shown in FIG. 2 is somewhat different than that previously described. Instead of providing a bleed orifice through piston 56, the seal rings 47 have been eliminated and the diameter of piston 56 is reduced slightly so as to provide for a small annular clearance space 74 between the perimeter of piston 56 and the inner wall 20 of the cylinder sleeve. Thus, during adjustment fluid will vent to or from spaces 46 and 28 through the annular clearance space.

Another embodiment of variable stroke cylinder of my invention is shown in FIG. 3. In this embodiment, a rod 76 threaded over its length, is threaded through piston 56' and lock nuts 77 and 78 are threaded onto one end of rod 76 into firm contact with the opposite faces of the piston so as to fix rod 76 to the piston. Rod 76 extends downward through piston 57' and is threaded into a tubular rod 80 which carries a drive fitting D at its other end. The tubular rod 80 is mounted to piston 57' for rotation relative thereto by way of a shoulder 82 at one side of the piston and a washer and nut 84 which is spaced slightly above the upper face of the piston 57' and in contact with a slightly raised shoulder 85 adjacent the end of rod 80. A slot 86 extends over a portion of the length of the rod 76 and a key-like insert 88, threaded to match the threads on rod 76, is received therein. The threads of the insert 88 are substantially flush with the threads on rod 76. The insert 88 is formed of nylon or other non-metallic material and provides a tight fit and a pre-load effect between rods 76 and 80.

To adjust the stroke of the cylinder shown in FIG. 3, tubular rod 80 is rotated. Since rod 76 is fixed to piston 56' and also since the pistons 56' and 57' are prevented from rotating due to their rectangular cross section, rod 76 will move axially into or out of rod 80 driving piston 56' toward or away from piston 57' to effect stroke adjustment.

Since tubular rod 80 is also rotatable relative to its piston 57', one or more seal rings 90 are preferably positioned in the piston for sealingly bearing against the external surface of the rod to prevent leakage between chambers 20 and 46 during operation of the cylinder. Again to insure venting of the space 46 between the pistons during adjustment, annular space 74 may be provided about piston 56' or a venting arrangement similar to that shown in FIG. 1 may be provided.

It will be appreciated that although my invention has been described as employed in a duplex cylinder, it may also be employed in a cylinder of simplex design by merely positioning both passages 21 and 22 at one end of the cylinder and providing a sealed pneumatic cushion space at the other end thereof. Moreover, it will also be understood that the embodiments of the present invention which have been described are merely illustrative of some of the applications of the principles of the invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention.

Claims

What is claimed is:

1. In a variable stroke cylinder, a cylinder member, a pair of piston members spaced a predetermined distance from each other so as to define a space therebetween, said piston members being mounted for simultaneous axial movement in said cylinder member during normal operation thereof, means for selectively moving at least one of said piston members relative to the other said piston member for adjustably varying the stroke of said piston members by moving said piston members relative to each other to vary said predetermined distance between said members, the improvement which enables rapid and extensive stroke adjustment therein and which comprises in combination therewith:

vent means communicating with said space between said piston members for venting said space when said predetermined distance between the piston members is varied to vary the stroke of the cylinder to maintain the pressure in said space substantially constant during said stroke adjustment, wherein said vent means comprises a bleed orifice in one of said piston members communicating between the face of said piston member adjacent said space and the opposite face of said piston member.

2. The cylinder of claim 1 wherein said bleed orifice is in said selectively moveable piston member.

3. The cylinder of claim 1 wherein said piston members include an elongated rod, the rod of one of said piston members being threadedly journaled through the other of said rods, whereby rotation of one of said rod effects said selective relative movement of said piston members.

4. The cylinder of claim 3 further including locking means, comprising threaded plug means positioned in the second mentioned rod and movable into contact with the first mentioned rod.

5. The cylinder of claim 3 wherein said piston members and said cylinder member are non-circular in cross section for preventing rotation of said piston members, and at least one of said rods is rotatable relative to its piston member to effect said selective relative movement of said piston members.