US2783743A

US2783743A - Hydraulic piston check for use with a pneumatically operated piston motor

Info

Publication number: US2783743A
Application number: US388878A
Authority: US
Inventors: Pappas Constantine Anthony
Original assignee: National Pneumatic Co Inc
Current assignee: National Pneumatic Co Inc
Priority date: 1953-10-28
Filing date: 1953-10-28
Publication date: 1957-03-05
Anticipated expiration: 1974-03-05

Description

March 5, 1957 c. A. PAPPAS HYDRAULIC PISTON cascx FOR USE WITH A PNEUMATICALLY OPERATED PISTON MOTOR Filed Oct. 28. 1955 W I NMINH N 3 A m I M 3 h L m Z Mm R 3 m 0 V J LEE. 00 9. 6w o a 0N \I .L o- 3 MW L N 3 A Z um MN 0 y l I l ll u n @N z IIHMYVE .4 3 m on .2 v N 2. Hw wl am i E Q Q Mm. N4 M I I 7 1|. Q6 mm 6 on 2.. "M. x 06 um m 5 do 2 ..fs. ON \IN O- Q- us i rvxwa I V W CONSTA NTINE ANTHONY PAPPAS ATTORNEY HYDRAULIC PISTON CHECK FOR USE WITH A PNEUMATICALLY OPERATED PISTON MOTOR Constantine Anthony Pappas, Dedham, Mass, assignor to National Pneumatic Co., Inc., Boston, Mass, a corporation of Delaware Application October 28, 1953, Serial No. 388,878

6 Claims. (Cl. 121-44) The present invention relates to a device and system for checking the motion of a piston or the like at one or both of its extreme limits of travel within a cylinder, and in particular to an arrangement in which an auxiliary piston, adapted to be engaged and moved by the main piston when the latter approaches its limit of motion, produces a checking action by forcing a fluid through a throttling aperture. The invention specifically relates to the means by which the auxiliary piston is restored to its normal projected position when the main piston has been moved out of engagement therewith.

In the past it has been customary to have the auxiliary checking piston mechanically spring-urged to its normal projected position, that is to say, the position in which it will be engaged by the main piston as the latter moves toward it. Mechanical springs not only add to the expense of the unit, both because of their own intrinsic cost and because of the added complexity of the unit which is required in order to permit spring repair, replacement and adjustment, but they represent a substantial source of trouble insofar as maintenance is concerned. In piston motors where many reciprocations of the pistons are involved, the frequent and numerous compressions and expansions of the restoring springs ultimately causes a weakening, and often a complete breakdown, of those springs, thus requiring replacement. It will be appreciated that spring replacement is not only troublesome and expensive, but also requires that the entire unit be taken out of service until that replacement can be made. Where the unit is a part of a more elaborate piece of equipment, as where, for example, it is employed to open and close the door of a railroad car or the like, it may be necessary to place the entire car out of service until the spring in the door operating motor has been replaced. The economic loss involved is clearly far out of proportion to the value of the individual spring being replaced. Yet replacement must be made if the entire door operating motor is not to be ruined.

Another disadvantage involved in the use of mechanical spring returns for auxiliary checking pistons is that the force of the spring acting on the auxiliary piston is inherently variable with movement of the auxiliary piston and is ordinarily not adjustable. It can be made ad justable, but only through the use of rather complicated and expensive mechanical arrangements. Yet in the life of the piston motor it will be called upon to operate under varying conditions, particularly insofar as temperature is concerned, and for optimum operation of the piston checking arrangement different return spring forces will be indicated as ambient conditions change.

The present invention'avoids these disadvantages. It completely eliminates the need for employing mechanical springs, or mechanical elements of any type, for providing return of the auxiliary checking pistons to their normal position when the main piston has been moved away therefrom. The life of thechecking system of nited States Patent 2,783,743 Patented Mar. 5, 1957 the present invention, since it has no mechanical parts to fail or become fatigued, is substantially infinite. The need for replacement or repair of parts is virtually eliminated. The restoring force exerted on the auxiliary checking piston can be readily controlled and adjusted. Moreover, said restoring force is substantially constant throughout the range of travel of the auxiliary checking piston. The instant invention has the particular advantage that the same pressure source which supplies motive power for the main piston can also supply the restoring force for the piston check, thus appreciably reducing the expense and complexity of a given installation.

To accomplish these ends, the checking piston, when it is engaged and moved by the main piston as the latter approaches its limit of travel in a given direction, is caused to move within a chamber having an exit passage of restricted size which acts as a throttling medium for a substance forced out of the chamber by the auxiliary piston as it is thus moved, this throttling effect providing the checking action for the main piston. This, in and of itself, is not novel. However, the exit passage is operatively connected to a source of pressure, either hydraulic or pneumatic, and this pressure source will, when the main piston moves away from the auxiliary piston, force said substance back into the chamber within which the auxiliary piston travels, thus restoring the auxiliary piston to its normal position. This pressure source may be the very source which is active on the main piston, or, if desired, it may be an auxiliary source.

Since the throttling effect of relatively incompressible hydraulic fluid is greater than the throttling effect of a compressible gas, it is preferred that the chamber within which the auxiliary piston moves be substantially filled with hydraulic fluid. However, it is entirely feasible to utilize a pneumatic pressure source in conjunction therewith to provide the restoring force for the auxiliary piston, and the invention is here specifically disclosed as thus employed. When a pneumatic pressure source is caused to be active upon hydraulic checking fluid, it is preferred that the exit passage from the chamber within which the checking piston moves should empty into a second chamber normally partially filled with hydraulic fluid, the pneumatic pressure source being active upon the surface of the hydraulic fluid in the second chamber so as to constantly tend to force it through the throttling passage which connects the two chambers. A comparatively unrestricted passage may also be provided between the second chamber and the first chamber on the side of the auxiliary piston opposite from that which is directed toward the throttling passage, so as to prevent the formation of a vaccuum within the first chamber when the auxiliary piston is moved away from its normal position and so as to maintain the hydraulic fluid within the second chamber at a more uniform level.

When the auxiliary checking piston is moved from its normal position by the main piston, that motion is quite rapid and hydraulic fluid is forced through the exit passage with considerable speed. This causes considerable turbulence within the second chamber, with consequent splashing or atomization of the hydraulic fluid. When a pneumatic pressure source is active onthe hydraulic fluid, it has been found desirable in many instances to employ some means for preventing the splashed or atomtravel, as defined in the appended claims and as described in this specification, taken together with the accompanying drawings, in which:

Fig. 1 is a cross sectional view of a typical piston motor in which the present invention has been incorporated, together with a schematic representation of an operating system therefor;

Fig. 2 is a detailed view of the upper portion of the end structure of the cylinder, showing a modification of the present invention;

Fig. 3 is a view similar to Fig. 2 but showing yet another modification thereof; and

Fig. 4 is a detail view on an enlarged scale showing the throttling passages through which the checking fluid passes.

The motor in conjunction with which the present invention is illustrated comprises a cylinder 2 within which pistons 4a and 4b are reciprocable, the pistons being spaced from one another and connected by red 6 having a toothed rack 8 on one surface thereof. The housing 10 interrupts the cylinder 2 substantially at the center thereof and sector gear 12 meshes with the rack 8 and is made fast to shaft 14 which is rotatably journaled in the housing 19 and which extends out therefrom. Oper ating arm 16 is mounted on the extending portion of the shaft 14 and is rotated thereby in the direction of the arrows 13 as the rod 6 is moved back and forth, the arm 16 being operatively connected to the element which is to be moved by the motor, e. g., a door or the like.

The ends of the cylinder 2 are closed by end structures generally designated 20, each of which is substantially identical with the other, and consequently a description of one will suffice for both. The structure 20 is provided with a passage 22 which opens to the interior of the cylinder 2 at the outer side of the piston 4a or 4b and which communicates with

passages

24 and 26. A screw 28 threadedly mounted in the structure 20 has a tip 30 which is adjustably projectable into the mouth of the passage 26 so as to vary the eifective area thereof. A ball 32 is seated at the upwardly facing mouth of the passage 24, and constitutes a check valve. The

passages

24 and 26 both open to passage 34 which communicates with port 36.

The end structure 29 is provided with a chamber 38 in the form of a cylinder within which auxiliary checking piston iii is slidable, the piston having an extension 49' which is slidable through end cap 4 2 which closes the end of the chamber 38 directed toward the cylinder 2. The portion of the end cap 42 which projects into the chamber 38 is of a reduced diameter so as to define the annular space 44 therearound. The end of the chamber 3% remote from the piston 49 is provided with passage 46 which communicates with angularly related passage 68, the latter emptying into a second chamber 50. An adjusting screw 52 is axially aligned with the passage and is threadedly mounted in a wall of the end structure 26 so that the eiiective area of the passages 46, 48 can be adjusted. Another passage 54 is provided between the chamber 5d and the annular piece 44. T he chamber 56 is closed by top cap 56 provided with passage 58 leading to port in the system here specifically disclosed and schematically illustrated in Fig. l, reciprocation of the main pistons 41: and il), along with rod 6, is achieved by connecting a source 62 of pneumatic pressure to a valve 6d by means of line 66. The valve 6a is provided with exhaust port and with additional ports 7t. and 72 connected respcctiveiy by lines 74 and 76 to the ports 36 in the left and right hand end structures 2% For the position of the main pistons 4a, db shown in Fig. l, the valve 64 will be so actuated as to connect the line 66 with the line 74 and so as to connect the line 76 to the exhaust port 78. Pneumatic pressure applied through the line 74 will pass through the passage 26' in the left hand end struc ture 2t and will be exerted against the piston 4a, forcing it to the right, as shown, the piston 4b also being moved 4 to the right and forcing air out of the right hand end structure 20 to the line 76 and the exhaust port 78, the ball 32 lifting to permit free flow in this direction. When it is desired to cause the pistons 4a, 4b to assume the position all the way to the left, the valve 64 is actuated to reverse the connections, pressure will flow through the line 76 into the right hand end structure 20 and will be exerted against the piston 4b, forcing it to the left, this pressure passing around the tip 30 of the adjusting screw 28, the adjustment of that screw determining, therefore, the speed with which the piston 41) will be moved, air exhausting readily from the left hand side of the cylinder 2 via the line 74, the valve 64 and the exhaust port 68.

The operation of the motor as thus far described provides no check whatsoever for movement of the pistons 41:, 4b, and if no check provisions were made the pistons would slam into the end structures 20 with great force.

in order to provide for checking action, the ports 60 in the end structures 20 are connected by lines 78 and St to the source 62 of pneumatic pressure. In addition, the chambers 38 and the passages 46 and 48 are filled with hydraulic fluid, and the chambers 50 are partially filled therewith. The air under pressure will pass into the chambers 50 and will act against the upper surface of the hydraulic fluid, thus urging that fluid out of the chambers 50 and into the chambers 38. This necessarily has the eifect of causing the pistons 49 to move inwardly, their extensions projecting into the cylinder 2 and into the path of movement of the appropriate piston 4a or 412 as that piston reaches its extreme limit of movement. When the pistons 4a, 4b assume their position shown in Fig. l, the left hand auxiliary piston 40 will assume its normal position, with its extension 40' projecting into the cylinder 2, because the main piston 44: is remote therefrom. The right hand auxiliary piston 40 cannot assume its normal position, being prevented from moving thereto by engagement with the main piston 41).

If new the valve 64 should be actuated to cause the pistons 4a, 4b to move to the left, when the piston to engages the extension 40' of the left hand auxiliary piston 49, it will force the left hand auxiliary piston 40 to move to the left. The hydraulic fluid in the chamber 38 to the left of the piston 40 will be forced through the passages 46 and 48 into the chamber 50. The setting of the screw 52 will determine the resistance which those passages will exert to the fiow of fluid therethrough, thus providing for adjustment of the degree of checking action provided. As the piston 40 moves to the left, the space to the right thereof will be filled by hydraulic fluid moving from the chamber into the chamber 38 through the passage 54 and the annular space 44. In this way the movement of the main piston assembly to the left will be checked.

As soon as the piston 4b starts to move to the left, it will withdraw from the extension 40' of the right hand auxiliary piston 40. The pneumatic pressure exerted on the hydraulic fluid in the right hand chamber 50 will then be free to force that fluid through the

passages

48 and 56 into the right hand end of the right hand chamber 38, and this will restore the right hand piston 40 to its normal position, where it will be ready to check the action of the main piston assembly the next time it is moved to the right so as to cause the main piston 4b to engage the right hand auxiliary piston extension 40'.

The checking action is of extremely short duration, and hence a substantial volume of hydraulic fluid is forced through the passages 46 and 48 at an extremely rapid rate. As a result there is considerable turbulence in the hydraulic fluid contained within the chamber 50, with much splashing and atomization. Some of the atomized hydraulic fluid may tend to enter the pipes leading to the pneumatic pressure source. This is undesirable not only because it reduces the amount of hydraulic fluid available for checking purposes but also because an accumulation of hydraulic fluid in the pneumatic system may well cause malfunctioning thereof.

Accordingly, it has been found desirable to take precautions against this, Fig. 2 illustrates one way in which loss of hydraulic fluid may be minimized. The top cap 56 is provided with a baflie 82 which covers the open mouth of the passage 58 and which has a small aperture 84 disposed at a point laterally displaced from the passage 58. This defines a tortuous path between the interior of the chamber 50 and the passage 58, through which path it is very difficult for drops or atomized particles of hydraulic fluid to pass. However, no real impediment to the application of pneumatic pressure within the chamber 50 is exerted thereby. The illustrated structure is, of course, merely typical of a variety of similar structures which might be employed for the same purpose. In Fig. 3, a check valve 86 is interposed in the line 78 and permits flow only toward the chamber 50. Hence any hydraulic fluid which might reach the check valve 86 would go no farther, and a slight inclination of the line 78 from the horizontal would cause any hydraulic fluid which might accumulate within the pipe 78 to flow back into the chamber 50.

The pistons 40 and 40' may, as is conventional, be provided with by-pass passages 41 closed on the ends of the

pistons

40 and 40 by check valve arrangements 43 schematically shown as narrow vertical rectangles. As is well known, the check valves 43 function to permit passage of fluid from. the piston rod ends of the piston to the other ends thereof and to prevent fluid flow in the opposite direction, thus facilitating return of the

pistons

40 and 40 to their operative positions.

In the system as here illustrated and described the source 62 of pneumatic pressure which is employed to power the main pistons 4a and 4b is also employed to provide the force to return the auxiliary checking pistons 40 to their normal positions. This makes for an extremely compact system. Of course, a separate source of pneumatic power could be employed for the pistonchecking system if desired, or that separate source could be a hydraulic source with a substantially continuous hydraulic connection between the source and the checking pistons 40. It would even be possible to dispense with the use of hydraulic fluid altogether, and apply pneumatic pressure directly to the pistons 40 within the chambers 38, but this would be feasible only where checking actions of minimal force are indicated, since the throttling of compressible gases is not eflective to produce an appreciable force in opposition to movement of the pistons 40.

In the system of the present invention the degree of checking action is readily controllable by the setting of the screws 52. The restoring force on the auxiliary pistons 40 is substantially constant in all positions of the pistons 40, and may readily be adjusted by varying the pneumatic pressure applied to the interior of the chambers 50. There are no moving parts involved in producing the restoring force, nor are any elements employed which are subject to fatigue. Consequently, the life of the restoring system is virtually infinite. Maintenance and down time problems are practically non-existent.

While but one major embodiment of the present invention has been here disclosed, it will be apparent that many variations may be made therein, all within the spirit of the invention defined in the following claims.

I claim:

1. In piston cushioning mechanism for use with a pneumatically operated piston motor comprising a source of pneumatic pressure, a cylinder having an end structure, a main piston slidable in said cylinder between pistons near to and remote from said end structure in response to the appropriate application of pneumatic pressure Within said cylinder, and means including a valve for conveying and controlling the application of said pneumatic pressure from said pressure source to the interior of said cylinder; the improvement which comprises said end structure comprising a first chamber in line with said cylinder, an auxiliary piston sealingly slidable therein, a piston rod connected to said auxiliary piston and extending out through a wall of said end structure into said cylinder, said auxiliary piston and piston rod being slidable between a first operative position in which said piston rod extends out into said main cylinder and into the path of movement of said main piston so as to be operatively engaged thereby when said main piston approaches said end structure, and a second operative position in which said auxiliary piston and piston rod are moved into said chamber, as by being pushed thereinto by said main piston as the latter reaches its extreme limit of movement toward said end structure, said first chamber being filled with hydraulic fluid, a second chamber in said end structure, hydraulic fluid in said second chamber only partially filling the latter up to a given level, a passage between said second chamber and that side of said first chamber on the side of said auxiliary piston opposite to said piston rod, said passage including an orifice of throttling size, said passage opening into said second chamber below said given level of hydraulic fluid, a second passage extending between the exterior of said end structure and said second chamber above said given level of hydraulic fluid, and a connection independent of said valve between said second passage and said source of pneumatic pressure.

2. In the cushioning mechanism of claim L'means operatively associated with said connection for preventing the entry of hydraulic fluid thereinto.

3. The cushioning mechanism of claim 2, in which said means comprises a bafiie operatively between said second chamber and said pneumatic source, said bafile defining a tortuous fiow path therethrough whereby atomized or splashed hydraulic fluid is substantially prevented from entering said connection.

4. The cushioning mechanism of claim 2, in which said means comprises a check valve in said connection and efiective to permit flow therethrough only from said pressure source to said second passage, whereby atomized or splashed hydraulic fluid is substantially prevented from reaching the pressure source side of said valve.

5. In the cushioning mechanism of claim 1, a third passage between said second passage below said level of hydraulic fluid and said first chamber 011 the piston rod side of said auxiliary piston, hydraulic fluid being comparatively freely passable through said third passage.

6. The cushioning mechanism of claim 1, in which said second chamber is above said first chamber, and a third passage between the bottom of said second chamber and said first chamber on the piston rod side of said auxiliary piston, hydraulic fluid being comparatively freely passable through said third passage.

References Cited in the file of this patent UNITED STATES PATENTS 899,795 Osmer Sept. 29, 1908 1,120,833 McElroy Dec. 15, 1914 1,205,818 Thomas Nov. 21, 1916 1,745,357 Crowell Feb. 4, 1930 1,942,414 Dumser Jan. 9, 1934 2,243,405 Wine May 27, 1941 2,664,860 Levetus Jan. 5, 1954 FOREIGN PATENTS 598,343 Great Britain Feb. 16, 1948