US2786452A - Fluid actuated cylinder having fluid cushion means - Google Patents

Description

March 26, 1957 w. R. TUCKER FLUID ACTUATED CYLINDER HAVING FLUID CUSHION MEANS Filed NOV. 29, 1954 2 Shee ts-Sheet 1 INVENTOR.

WA/?REN R. TUCKER A7 TORNEYS March 26, 1957 w. R. TUCKER FLUID ACTUATED CYLINDER HAVING FLUID CUSHION MEANS Filed Nov. 29, 1954 2 Sheets-Sheet 2 mm W; MW fiw v m R N H N 5 1. G 6 M w 7 /F W MMW h 2 W 8 y m 5/ a m H I. 1 .1]. 4 w .m H w. m m M w J 7 United States Patentl) 2,786,452 FLUID ACTUATED CYLINDER HAVING FLUID CUSHION MEANS Warren R. Tucker, Barrington, 11]., assignor to Hannifin Corporation, Des Plaines, 111., a corporation of Illinois Application November 29, 1954, Serial No. 471,783 3 Claims. (Cl. 121-68) This invention relates to fluid actuated cylinders or the like.

One principal object of the invention is to provide a fluid actuated cylinder having improved means adapted to form a fluid cushion in either end of the cylinder When the opposite end is supplied with working fluid under pressure. In this way, fluid is trapped in the cushion end of the cylinder so as to bring the piston to a smooth stop as it approaches the end of the cylinder, the fluid being allowed to escape gradually from the cushion end ofthe cylinder.

A further object is to provide a fluid actuated cylinder of the foregoing character having improved cushion valve means adapted to close the fluid supply port in the cushion end of the cylinder at any desired point in the stroke of the piston, whereby cushioning action may be provided throughout any portion of the piston stroke or even for substantially the entire stroke.

Another object of the invention is to provide an im proved cushion valve arrangement in which the cushion valve is automatically opened when working fluid is supplied to the fluid port to reverse the piston, all need for a bypass valve around the cushion valve thereby being eliminated.

It is another object of the invention to provide an improved fluid actuated cylinder of the foregoing character in which the cushion valve is closed by initial movement or the piston in its stroke and is conditioned by completion of the piston stroke for operation on the return stroke.

A further object of the invention is to provide an improved fluid actuated cylinder having means for limiting the pressure in the fluid cushion without imposing any limitation upon the Working pressure.

Further objects and advantages of the invention will appear from the following description, taken with the accompanying drawings, in which:

Figure 1 is a central longitudinal sectional view taken through an exemplary fluid actuated cylinder constituting an illustrative embodiment of the invention;

Fig. 2 is a fragmentary view similar to Fig. 1 but showing changed positions of the piston and cushion valve embodied in the cylinder;

Figs. 3 and 4 are cross-sectional views taken through the head and rod ends of the cylinder, generally along lines 3-3 and 4-d in Fig. 1;

Figs. 5 and '6 are fragmentary cross-sectional views taken through the head and rod ends, generally along lines 55 and 66 in Fig. l; and

Figs. 7 and 8 are fragmentary longitudinal sectional views taken generally along lines 7-7 and in Fig. 3.

If considered in greater detail, the drawings will be seen to illustrate an exemplary cylinder i1 which may be actuated by any suitable Working fluid, such as air or hydraulic fluid, for example. The exemplary cylinder comprises a casing 12 having a cylindrical bore 213 which defines a piston chamber in the casing. A piston 14 is slidable longitudinally along the bore 13. Sealing rings 15 are mounted in grooves 16 formed in the piston 14 to provide a seal between the piston and the-cylinder bore 13.

The opposite ends of the casing 12 are closed by head and rod end members or walls 18 and 19. An axial aperture 20 i-sformed in the rod end 19 to admit a-piston rod 21 which 'is secured to the piston 14. The piston rod 21 Patented Mar. 26,1957

is slidably guided by a bushing or gland 22 mounted in the aperture 20. A sealing ring 23 is disposed in a groove 24 formed in the gland 22 to provide a seal between the piston rod 21 and the gland 22.

In order to admit Working fluid to the opposite ends of the casing 12, the head and rod end walls 18 and 19 are formed with fluid ports 26 and 27 which extend from the ends of the casing into lateral bores or passages 28 and 29. Internal pipe threads 30 and 31 are formed in the outer ends of the bores 28 and 29 to receive fluid supply pipes (not shown). In the exemplary cylinder, the ports 26 and 27 extend axially into the opposite ends of the casing 12. It willbe seen that the port 27 in the rod end wall 19 is in the form of an annular opening around the piston rod 21.

Provision is made for closing the fluid supply ports at either end of the cylinder when the piston is moved toward that end of the cylinder by the application of working fluid to the opposite end of the cylinder. In this way, fluid is trapped in the end of the cylinder to provide a fluid cushion adapted to bring the piston to a smooth stop at the end of its stroke with a minimum of shock. For this purpose the exemplary cylinder 11 is provided with a cushion valve unit 34 which in this instance comprises a pair of poppet valves 35 and 36 adapted to close the fluid supply ports 26 and 27 at the head and rod ends of the cylinder. The valves 35 and 36 may be in the form of disks fitted with soft resilient rubber or rubber- like sealing rings 37 and 38 for sealing off the ports 26 and 27. The poppet valve 36 at the rod end of the cylinder is annular in form and is provided with a bore 39 slidably received on the piston rod 21. The sealing ring 38 fits snugly around the piston rod 21 so that it will form a seal between the rod and the poppet valve 36, as well as closing the port 27.

In order to connect the poppet valves 35 and 36 and to provide for operation of the valves by the piston 1 one or more rods 42 or other guide members are connected at their opposite ends to the poppet valves and are arranged to extend slidably through the piston 14. in this instance, there are two of the rods 42. Bores 43 are formed in the piston to receive the rods. It will be seen that sealing rings 44 are seated in grooves 45 formed along the bores 43, to provide seals between the rods 42 and the piston 14.

When the piston 14 is moved toward either end of the cylinder 11, the piston carries the rods 42 and the poppet valves 35 and 36 until one of the poppet valves seats over the corresponding port 26 or 27. The closure of the port traps fluid in the casing 12 and forms a fluid cushion. During the remainder of the stroke of the piston, the piston slides .over the rods 42 while the poppet valve 35 or 36 remains seated over the port 26 or 27. On the return stroke of the piston, the opposite poppet valve closes oil the opposite fluid port and forms a cushion at the opposite end of the cylinder. it will be appreciated that the movement of the piston initially closes the cushion valve and then conditions the cushion valve for operation on the return stroke.

In order to bleed off fluid from the fluid cushion and thereby permit completion of the piston stroke without undue resistance, the head and rod ends 18 and 19 of the exemplary cylinder 11 are equipped with bleed valves 48 and 49 which provide limited communication between the opposite ends of the casing 13 and the fluid ports 26 and 27. Thus, the bleed valves 48 and 49 serve as bypasses around the cushion valves 35 and 36 when the latter are closed over the inner ends of the fluid ports 26 and 27. It will be seen that the bleed valves 48 and '49 are in the form ofscrew threaded adjustable needle valve members 50 and 51 movable in bores 52 and 53. Ports 54 and 55 extend axially from the bores 52 and 53 to receive the neetle members and 51 in valving relation. It will be seen that the ports 54 and 55 communicate with the fluid supply ports 26 and 27. Passages 56 and 57 extend laterally from the valve bores 52 and 53 into the opposite ends of the casing 12 outside the areas sealed by the rings 37 and 38 when the poppet valves 35 and 36 are closed.

At one end of the cylinder 11, in this instance the rod end, an end surface 60 is formed on the end wall member 19 to serve as a seat around the fluid supply port 27. When the piston 14 is moved toward the rod end 19, the poppet valve 36 seats against the surface 60 to form a cushion in the rod end of the casing 12. Fluid trapped in the casing escapes through the bleed valve 49 as the piston continues its stroke toward the rod end. At the completion of its stroke, the piston 14 is arrested by engagement with the rear face of the poppet valve 36. Thus, the piston must be moved away from the poppet valve 36 before the latter can be unseated from the port 27. To bypass the poppet valve 36 and thereby apply working pressure to the entire area of the piston 14, rather than to the limited area of the ring 38 seated over the port 27,. when working fluid is supplied under pressure to the port 27 to reverse the cylinder, a bypass valve 62 is provided at the rod end of the cylinder. In the illustrated construction, the bypass valve 62 includes a check valve ball 63 movable in a bore 64 and adapted to close a port 65 leading axially from the bore 64 into the fluid port 27. A spring 66 biases the ball 63 toward the port 65. It will be seen that a lateral passage 67 extends from the bore 64 into the rod end of the casing 12 outside the area adapted to be covered by the sealing ring 38. Thus, the check valve 62 provides free communication between the port 27 and the casing 12, while preventing reverse flow of fluid through the port 65.

When working fluid under pressure is applied to the fluid port 27 to reverse the piston 14, the fluid flows into the casing 12 through the check valve 62 and thus moves the piston sutficiently to permit the poppet valve 36 to be unseated from the port 27. The working fluid unseats the poppet valve 36 and thereafter flows through the port 27 into the casing 12. The pressure of the working fluid moves and holds the poppet valve 36 against the piston 14 until the opposite poppet valve 35 engages the opposite end wall member 18.

In order to provide for opening the poppet valve 35 after the piston 14 has reached the head end of the cylinder 11, the head end member 18 is formed with a recess 70 defining a seating surface '71 around the fluid port 26. An annular surface 72 is formed on the end of the head member 13 around the recess 70 to arrest the piston 14. As the piston moves toward the head end member 18, the poppet valve 35 enters the recess 70 and seats against the surface 71 so as to close off the port 26 and form a fluid cushion between the piston and the head end member. The piston 14 continues its stroke until it is arrested by the surface 72.

In order to provide for unseating of the poppet valve 35 when working fluid is supplied to the port 26, the depth of the recess 70 is made sufficient to provide a clearance space 73 between the poppet valve 35 and the piston 14 when these components are seated against the surfaces 71 and 72, respectively. In other words, the piston 14 seats against the stop surface 72 but does not abut against the poppet valve 35 when the piston reaches the head end of the cylinder. When working fluid is applied under pressure to the port 26, the fluid unseats the poppet valve 35 from the port and thus is admitted to the casing 12 so as to be effective against the entire area of the piston 14. The pressure moves and holds the poppet valve 35 against the piston until the opposite poppet valve 36 seats against the rod end member 19 as the piston moves toward the rod end.

Since the recess 70 provides lost motion between the poppet valve 35 and the piston 14 and thus permits the poppet valve to be unseated by working fluid, it is not necessary to provide a bypass valve at the head end of the cylinder. It will be understood that a similar recess may be provided at the rod end so as to permit elimination of the bypass valve 62. Conversely, a bypass valve may be provided at the head end of the cylinder instead of the lost motion recess 70.

When either of the cushion valves closes and the piston continues to move at a rapid rate toward the cushion end of the cylinder, there is a tendency for the fluid pressure in the cushion chamber to rise to rather high values, particularly when the cylinder is being employed to move a load having considerable inertia. It has been found that the fluid pressure in the cushion end of the cylinder tends to rise to a value considerably exceeding the working pressure. When the working fluid is air or some other gas and hence is compressible, there is a tendency for the piston to rebound due to the pressure built up in the cushion end of the cylinder. While such rebounding can often be prevented by adjusting the bleed valves, this is not always the case, particularly when a massive load is being moved at high speed by the cylinder. Moreover, changes in the working conditions may require frequent readjustment of the bleed valves.

To limit the cushion pressure, and thereby control rebounding and other effects of excessive cushion pressure, the exemplary cylinder 11 is provided with relief valves 74 and 75 mounted on the head and rod end members 18 and 19. It will be seen that the respective valves 74 and 75 comprise conically pointed valve members 76 and '77 movable in bores 78 and 79 and adapted to close ports 80 and 81 leading axially from the bores 78 and 79 into the fluid ports 26 and 27. Fairly heavy springs 82 and 83 are provided to bias the valve members 76 and 77 into seating relation to the ports 80 and 81. In order to provide for adjustment of the effective strength of the springs 82 and 83, the springs are arranged between the valve members 78 and 79 and adjustable screw threaded abutments 84 and 35. Passages 36 and 87 extend between the bores 78 and 79 and the opposite ends of the casing 12. The passages 36 and 87 enter the easing outside the areas adapted to be covered by the sealing rings 37 and 38 on the poppet valves 35 and 36. Seals are formed between the valve members 76 and 77 and the bores 78 and 79 by sealing rings 88 and 89.

When the cushion pressure builds up in the head end of the casing 12 after the poppet valve 25 has closed the fluid port 26, the pressure tends to unseat the valve member 76. At a predetermined pressure, depending upon the strength of the spring 82 and the area of the valve member 76 exposed to the pressure, the valve member 76 is unseated and thus permits fluid to pass out of the casing 12 through the port 80. This tends to relieve the cushion pressure in the head end of the casing 12. When the pressure has been relieved, the valve member 76 closes the port 80. Thus, the relief valve 74 regulates the maximum cushion pressure in the head end of the casing 12. Likewise, the relief valve 75 regulates the cushion pressure in the rod end of the casing 12.

Since the relief valves 74 and 75 are connected between the casing 12 and the fluid supply ports 26 and 27, the relief valves do not impose any limitation upon the working pressure which may be applied to the cylinder. There is no possibility of working fluid being bled off through the relief valves. Accordingly, the relief valves may be set at a pressure less than the working pressure, if such and adjustment of the valves is desirable to prevent rebounding of the piston. Of course, the adjustment of the relief valves is subject to wide variation depending upon load conditions.

If the relief valve 75 at the rod end of the cylinder 11 is set at less than the working pressure, the bypass valve 62 may be dispensed with since the relief valve will open when working pressure is applied to the fluid port 27 and thus will bypass working fluid around the seated poppet valve 36 so as to apply the working fluid to the entire area of the piston 14.

In summarizing the operation of the exemplary cylinder 11, it will be assumed that the cylinder is initially in the position shown in Fig. l, with the poppet valve 36 closing the port 27 and the piston at the rod end of its stroke. Admission of working fluid under pressure to the port 27 through the passages 29 opens the check valve 62 so that the fluid will act against the entire area of the piston 14. Initial movement of the piston away from the rod end member 19 permits the working pressure to unseat the poppet valve 36 from the port 27. Due to the provision of the rods 42, there is a difference in the opposite end areas of the poppet valve 36, with the result that the pressure of the working fluid moves the poppet valve against the piston 14.

Part way along the stroke of the piston 14 toward the head end of the cylinder 11, the sealing ring 37 of the poppet valve 35 seats around the port 26. Further movement of the poppet valves 35 and 36 and the rods 42 is thereby arrested. Since the fluid between the piston 14 and the head end member 18 is no longer free to escape through the main fluid port 26, fluid pressure builds up in the head end of the casing. This cushion pressure is bled oif through the needle valve 48. If the cushion pressure rises to a predetermined value, it opens the relief valve 74 and permits fluid to escape from the cylinder to the tank through the passage 28. Thus the relief valve 74 regulates the cushion pressure, while the needle valve 48 continuously bleeds off fluid from the cushion chamber. Movement of the piston 14 toward the head end of the cylinder is arrested when the piston engages the stop surface 72, as shown in Fig. 2.

To reverse the piston 14, working fluid is applied under pressure to the head end fluid port 26. Due to the clearance space 73 between the rear end of the poppet valve 35 and the front end of the piston 14, the poppet valve 35 is free to move away from the port 26 so as to admit the working fluid to the casing 12. The working fluid moves the piston 14 and the poppet valve 35 toward the rod end of the cylinder until the poppet valve 36 closes the rod end fluid port 27 and thereby forms a fluid cushion in the rod end of the casing 12. Thereafter, the piston 14 slides along the rods 42 to condition the cushion valve unit 34 for operation of the opposite stroke of the piston. The action of the needle and relief valves 49 and 75 at the rod end is the same as at the head end of the cylinder. The movement of the piston 14 toward the rod end is arrested when the piston engages the rear surface of the poppet valve 36.

Since the relief valves are connected between the casing and the main fluid ports at opposite ends of the cylinder, there is no possibility of losing working fluid to the tank through the relief valves. Accordingly, the relief valves may be set at any desired pressure, according to the requirements for cushioning action. By setting the relief valves at a sufficiently low pressure, it is possible to prevent rebounding of the piston under all load conditions. At the same time, effective cushioning action is provided at all working speeds.

It will be evident that virtually the entire stroke of the piston may be utilized for cushioning action simply by adjusting the length of the cushion valve rods so that the cushion valves will be seated shortly after the piston begins to move. In fact, any desired portion of the effective stroke of the piston 14 may be utilized for cushioning action. This adjustment may be effected simply by varying the extent of lost motion between the crushion valve unit and the piston. Except for the thickness of the poppet valves, the cushion valve mechanism does not add to the length of the cylinder.

The cushion valve mechanism embodied in the exemplary cylinder is entirely dependable and extremely rugged. Moreover, it adds very little to the cost of the cylinder.

Various modifications, alternative constructions and equivalents may be employed without departing from the true spirit and scope of the invention as exemplified in the foregoing description and defined in the following claims.

I claim:

1. in a pressure fluid motor, a cylinder, a piston therein, passage means having one portion connected to an end of the cylinder another portion connected to fluid conducting means, said passage means conducting working fluid to and from the interior of the cylinder, cushion valve means for controlling the flow of fluid through the one portion, means actuated by the piston upon a predetermined movement of the piston towards the cylinder end to move said cushion valve means to a position to close the one portion to the outflow of fluid from the cylinder, and a loaded relief valve for relieving excess cushioning fluid when the pressure of the fluid rises above a predetermined value, said relief valve having an inlet connected to the end of the cylinder and an outlet connected to the other portion of the passage means.

2. In a pressure fluid motor, a cylinder, a piston therein, passage means having one portion connected to an end of the cylinder and another portion connected to fluid conducting means, said passage means conducting working fluid to and from the interior of the cylinder, cushion valve means for controlling the flow of fluid through the one portion, means actuated by the piston upon a predetermined movement of the piston towards the cylinder end to move said cushion valve means to a posi tion to close the one portion to the outflow of fluid from the cylinder, orifice means having an inlet connected to the end of the cylinder and an outlet connected to the other portion of the passage means for bleeding oif cushion pressure in the cylinder, and a loaded relief valve for relieving excess cushioning fluid when the pressure of the fluid rises above a predetermined valve, said relief valve having an inlet connected to the end of the cylinder and an outlet connected to the other portion of the passage means.

3. In a pressure fluid motor, a cylinder, a piston therein, each end of said cylinder being provided with passage means having one portion connected to said end of the cylinder and another portion connected to fluid conducting means, said passage means conducting Working fluid to and from the interior of said end of the cylinder, cushion valve means for controlling the flow of fluid through the one portion, means actuated by the piston upon a predetermined movement of the piston towards said end of the cylinder to move said cushion valve means to a position to close the one portion to the outflow of fluid from said end of the cylinder, and a loaded relief valve for relieving excess cushioning fluid when the pressure of the fluid rises above a predetermined value, said relief valve having an inlet connected to said end of the cylinder and an outlet connected to the other portion of the passage means.

References Cited in the file of this patent UNITED STATES PATENTS 840,877 Steedman Ian. 8, 1907 845,827 Steedman Mar. 5, 1907 1,604,548 Dapron Oct. 26, 1926 1,744,069 Dapron Jan. 21, 1930 1,807,231 Weeks May 26, 1931 2,396,052 Light Mar. 5, 1946 2,556,698 Loewe June 12, 1951 FOREIGN PATENTS 420,843 Great Britain Dec. 10, 1934

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