US3682042A

US3682042A - Reciprocatory fluid motor

Info

Publication number: US3682042A
Application number: US34100A
Authority: US
Inventors: Thomas William Bain
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1969-05-07
Filing date: 1970-05-04
Publication date: 1972-08-08
Anticipated expiration: 1989-08-08
Also published as: GB1272275A; DE2022061A1

Abstract

A reciprocatory motor, suitable for driving reciprocatory stirrers, for example, those used in laboratory melting-point apparatus, and driven by a working gas is controlled using a socalled bistable fluidic amplifier.

Description

Umted States Patent [151 3,682,042 Bain' [451 Aug. 8, 1972 [54] RECIPROCATORY FLUID MOTOR [56] References Cited [72] Inventor: gggnaEsnvf'allxllzm Ba in, Stockton-on- I UNITED STATES PATENTS g 3,124,999 3/1964] Woodward ..91/290 1 Asslgnw qmg Chem! Industries 3,340,896 9/1967 Mon at al. ..91/3o7 l LOndOn, England 3,396,631 8/1968 'Woodward ..9l/290 22 Filed: May 4 1970 3,516,763 6/1970 Manton ..9l/3l8 [21] Appl. No.: 34,100 Primary Examiner-Paul E. Maslousky Q Attorney-Cushman, Darby & Cushman [30] Foreign Appllcauon Prlorlty Data ['57] I ABSTRACT,

May 1969 Great "'ff""' A reciprocatory motor, suitable for driving reciproca- Y Y tory stirrers, for example, those used in laboratory [2%] 15.81. ..,.....91/3, 91/3???l meltingpoim apparatus, and driven by a working gas E z' 304 is controlled using a so-called bistable fluidic amplifi- 6 Chins, 3 Drawing figures RECIPROCATORY FLUID MOTOR The present invention relates to motors used for driving stirrers.

Motor-driven stirrers are widely used, for example in chemical processes and in methods of chemical analysis. Many such stirrers are rotary in their action but it is also known, particularly in chemical analysis, to use reciprocating stirrers. Such rotary and reciprocatory stirrers are usually driven electrically and as such have certain disadvantages. For example, they are a potential hazard in flammable atmospheres, they need frequent regular maintenance, and it is often difficult, especially at low speeds, to control their rotary or reciprocatory speeds which may in the case of reciprocatory motors lead to excessive thrust being developed and consequent breakage of equipment. We

have now devised a motor which is particularly suitable for driving a reciprocating stirrer and which, since it derives its power from a source of inert gas under pressure, avoids the particular hazards associated with electrical motors.

The present invention is based on the discovery that so-called bistable fluidic amplifiers may 7 be used directly to control the flow of working gas from a source of gas under pressure alternately to opposite sides of double-acting piston and cylinder arrangements coupled to an output shaft or member of a reciprocatory motor thereby to effect requisite reciprocation of the shaft or member.

Bistable fluidic amplifiers are familiar in the fluidics art as elements of fluidics circuitry by means of which effects are achieved with flowing gas streams analogous to effects achievable in electrical circuitry with flowing electric current. It is a feature of fluidic devices that they rely little, or not at all, on moving mechanical parts to make and break connections between different elements of the circuitry. A useful exposition of the essential principles of the fluidics art is to be found in the Fluidics Systems Design Guide, first edition (1966 published by the Fluidonics Division of the Imperial- Eastman Corporation of Chicago, but it will assist here if the working of a bistable fluidic amplifier is described in some detail with reference to a typical construction, shown in FIG. 1 of the accompanying drawings, which shows the amplifier in a diagrammatic manner.

The principle of operation of a bistable fluidic amplifier is that a fluid enters an inlet channel 1 in the amplifier through an entry port 2 and is then switched along one of two exit channels 3 and 4 to a corresponding exit port 5 or 6.

The bistable fluidic amplifier makes use'of an effect known as the Coanda effect. This effect is caused by the pressure gradient across a fluid jet which is issuing from a noule. If there is a boundary plate adjacent to this nozzle, vorticity caused by the boundary layer leads to a pressure gradient across the jet which causes the jet to bend toward the boundary plate. In the region close to the nozzle, fluid pressure is at its lowest at or near the boundary plate. The internal inlet Channel 1 of the bistable fluidic amplifier ends in a nozzle 7. Downstream from the nozzle 7 are the two exit channels 3 and 4 from the amplifier down one or other of which the Coanda effect causes the fluid jet issuing from the inlet channel to pass and be stabilized.

Switching of the fluid flow from one exit channel 3 of the amplifier to the other 4 may, for example, be carried out by directing a small side stream of fluid from a channel 8 across the path of the main stream issuing from the inlet channel. This causes a reversal of the pressure gradient across the fluid issuing from the jet which is thereby switched to the other exit channel 4. Thereafter, the fluid may be switched back along the first exit channel 3 by a second reverse acting side stream-from a channel 9 on the opposite side of the path of the main stream of fluid to the channel 8. If there is no difference in fluid pressure between the side streams, the main fluid stream will, in a .practical embodiment, choose one or other exit channel and then, because of the Coanda effect, flow along that exit channel becomes stabilized. When the fluid pressure rises sufficiently in the side stream controlling switching of motor suitable for use as a drive for reciprocatory stirrers which comprises an output shaft or member coupled to piston and cylinder means arranged to effect positive lengthwise reciprocatory movement of the shaft or member in response to the supply of working gas under pressure alternately to oppositely acting portions of the piston and cylinder means, first and second supply conduits respectively providing flow paths to the portions of the piston and cylinder means for gas received from a single source conduit connectable to a source of working gas, fluidic control means controlling the flow of gas from the source conduit to the individual supply conduits and capable of stabilizing the flow of a stream of gas from the source conduit to either one of the supply conduits but not to both jointly, so that whenever gas streaming through the fluid control means is constrained to alter its course and switch from exit along a given supply conduit to exit along the other supply conduit the flow along that other conduit becomes stabilized and continues until a new switching constraint is imposed, and means responsive to movements of the output shaft or member and arranged to cause switching constraints to be applied to gas streaming through the fluidic control means when the output shaft or member reaches positions at or proximate to the limits of its reciprocatory motion whereby to cause the gas supply to switch from one portion of the piston and cylinder means to the other portion and in consequence reverse movement of the output shaft or member.

A so-called bistable fluidic amplifier may provide the fluidic control means, each of the exit channels of which is connected to an inlet in the respective portions of the piston and cylinder means. It is convenient to provide the fluidic control means or the supply conduits leading off therefrom with ports, open to the atmosphere, one port for each exit channel and so positioned as to be readily accessible only to gas passing in the reverse direction to the normal direction of flow, the ports providing outlets for gas being exhausted from respective portions of the piston and cylinder means when temporarily idle.

The means responsive to movements of the output shaft or member and which is arranged to cause switching constraints to be applied may comprise valve means imposing a substantial impediment to (or preventing) fluid flow through branch conduits leading off from conduits supplying side streams as aforedescribed at or towards the ends of the working halfcycles of alternate portions of the piston and cylinder means. The valve means suitably may include a pair of valve members directly coupled to the output shaft or member which execute a reciprocatory movement therewith and which close or adequately obstruct respective vents to atmosphere at or towards the end of each working half cycle of respective portions of the piston and cylinder means. In the open position, each vent is open to atmosphere and the valve member may be a plate which is coupled to the piston shaft externally of the cylinder and which covers the vent when the output shaft or member reaches a position at or approximate to one limit of its reciprocatory motion. In the preferred form of the invention, the vents are located in the cylinder heads of the piston and cylinder means and are closed by resiliently padded plates attached to the piston shaft externally of the cylinder and which abut against the exterior face of the cylinder heads. v v

One form of motor constructed in accordance with the invention will now be described in greater detail by way of example with reference to FIGS. 2'and 3 of the accompanying drawings in which:

FIG. 1 shows a fluidic control device;

FIG. 2 shows the motor schematically, and with special emphasis on the gas flow circuitry; and

FIG. 3 shows in axial cross-section part of the piston and cylinder means and associated valve means of the motor shown in FIG. 2.

The motor includes 'a double action piston and cylinder arrangement indicated generally by the reference letter A which constitutes piston and cylinder means as aforedescribed, a fluidic control device indicated generally by the reference letter B, a gas inlet conduit C, and gas supply conduits indicated generally by the reference letters D and E feeding opposite portions of the piston and cylinder arrangement A. v

The piston and cylinder arrangement A includes a cylinder (see especially FIG. 3) suitable made of aluminum alloy along the axis of which extends a piston shaft 11 that protudes beyond the ends of the cylinder 10 through central openings in cylinder heads 12. Bushes 13 of filled polytetrafluoroethylene (PTFE) ensure smooth sliding fit for shaft 11 at these openings. A symmetrical composite comprising

inner discs

14 and 15 of filled PTFE having outwardly turned peripheral portions and outer

stiff nylon discs

14 and 15 of smaller diameter constitutes a double acting piston which moves with shaft 11 within the cylinder 10. The

disc

14, 15, 14' and 15 are mounted on a screwed boss 16 which is itself tightly fitted onto shaft 1 1.

Coupled to one end of shaft 11 is an extension shaft 17 which drives a stirrer (not shown). Also carried by shaft 11 at each of its ends is a plate 18 provided with resilient pads 19 which serve to reduce impact noise and shock when the plate 18 moves against the exterior face of the cylinder head 12. Covers 20 attached at each end of the cylinder 10 provide shielding for the end portions of shaft 11, the coupling at one end between shaftll and shaft 17, bushes l3 and plates 18. Each cover 20 has a vent 21 leading to atmosphere.

The cylinder 10 has orifices 22 formed in its side walls close to the cylinder heads 12 and beyond the limit of travel of the double acting piston. These orifices 22 are connected by the conduits D and E (see FIG. 2) comprising

channels

23 and 32 and

variable pressure restrictors

33 and 34 to respective exit ports 5 and 6 of the fluidic control device B which, in the form shown in FIG. 2, has the same construction as a known type of bistable fluidic amplifier. The fluidic control device B has an entry port 2 shown connected to a source of gas 25 by conduit C. The entry port 2 leads to an inlet channel 1 and thence to two divergent exit channels 3 and 4 terminating at ports 5 and 6. Leading off from the exit channels 3 and 4 are

exhaust loops

26 and 27 which discharge to atmosphere at

ports

28 and 29 respectively. The

exhaust loops

26 and 27 are so arranged that only gas flowing back along the channels 3 and 4 can readily escape through the

ports

28 and 29.

The fluidic control device B has two

transverse conduits

8 and 9 which are in communication with conduit C through

pressure restrictors

30 and 31. The

conduits

8 and 9 deliver when required cross-flowing streams of gas effective to switch the main flow of working gas from one of channels 3 and 4 to the other.

Conduits

8 and 9 are not the only conduits which receive gas from conduit C through the

restrictors

30 and 31;

other branch conduits

38 and 39 including

restrictors

40 and 41 receive such gas and in fact provide, when in communication with the atmosphere, much'preferred paths for gas flowing from

restrictors

30 and 31. The

conduits

38 and 39 normally lead to atmosphere through (see FIG. 3) ports 35, conduits 36, vents 37 and vents 21 at the ends of the piston and cylinder arrangement A. The ports 35, conduits 36, vents 37 and vents 21 together form valve means responsive to movements of the output shaft or member. Only when either of the vents 37 is blocked by a pad 19 carried by the corresponding plate 18 does the conduit 8 or the conduit 9 deliver a substantial stream of gas.

The cycle of operations of the motor shown in FIGS. 2 and 3 will now be described. Suppose that the shaft 11 is moving downwardly as seen in FIG. 3 and as indicated by the arrow in FIG. 2 but has not yet reached the lower limit of its movement. A stream of working gas, which may be air, oxygen, nitrogen, or a non-aggressive gas of similar density and viscosity to these, is being channelled from the supply 25 to the exit channel 3 of the fluidic control device B. Because of the Coanda effect there is no substantial flow down channel 4. From channel 3 the stream of working gas passes through channel 23 and restrictor 33 to the orifice 22 actually shown in FIG. 3 so forcing the piston composite with shaft 11 further downwards as seen in FIG. 3. There is no net cross-flow of gas in

conduits

8 and 9 but streams of gas are flowing through

restrictors

30 and 31,

channels

38 and 39,

restrictors

40 and 41, conduits 36 and vents 21 to atmosphere as already described. Gas being simultaneously expelled from the lower portion of the piston and cylinder arrangement A as seen in FIG. 3 escapes back through channel E and is vented to atmosphere through loop 27.

The downward movement of the shaft 11 eventually brings the top plate 18 against the cylinder head 12 and a pad 19 on the plate 18 closes vent 37. Thereupon flow of gas through conduits 38 ceases and a switching stream of gas flows through conduits 8. The main stream of working gas is thereby forced to switch to exit channel 4 and thence to conduit E so bringing about a reverse movement of the shaft 11. Although the top vent 37 then opens once again, the Coanda efiect ensures that the stream of working gas flowing through the fluidic control device B continues to pass to conduit E.

When the shaft 11 reaches the top of its stroke as seen in FIG. 3, the lower vent 37 becomes blocked by a pad 19 on the lower plate 18 and thereupon an identical sequence of events takes place involving now a switching stream of gas back to channel 3 and conduit D. A cycle of operation is then complete. The motor is in practice found to be self-starting, working gas supplied to the fluidic control device B seeking but one or other of the exit channels 3 and 4; while in theory it might initially merely divide between both channels, in practical embodiments it is found not to do so, probably because no practical embodiment can be precisely symmetrical. Once one exit channel is chosen, the Coanda effect operates to fix flow down that channel.

We have found that reciprocating motors of various sizes can be constructed according to the invention. The speed of these motors is most conveniently adjusted by varying the air supply pressure or by adjustment of the variable pressure restrictors 33 and 34 (see FIG. 2). A wide range of speed is possible.

Motors according to the invention are suitable for use in chemical plant and in chemical analysis. They are useful as a source of low thrust in liquid stirring applications, for example in melting point apparatus where the excessive thrust of conventional electrically driven stirrers often result in breakages. Having no electrical parts, the motor of the present invention is safe in potentially flammable atmospheres. We have found motors according to the invention can be smaller and are quieter and more reliable than other reciprocating air motors.

lclaim:

l. A reciprocatory motor which comprises a. an output shaft or member;

b. piston and cylinder means coupled thereto and arranged to effect positive lengthwise reciprocatory movement of the shaft or member in response to the supply of working gas under pressure alternately to oppositely acting portions of the piston and cylinder means,

c. first and second supply conduits respectively providing flow paths to the portions of the piston and cylinder means for gas received from a single source conduit connectable to a source of working d. fluid control means controlling the flow of gasfrom the source conduit through exit channels in the fluidic control means to the individual supply conduits and capable of stabilizing the flow of a stream of gas from the source conduit to either one of the supply conduits but not to both jointly, and e. means responsive to movements of the output shaft or member and arranged to cause switching constraints to be applied to gas streaming through the fluidic control means when the output shaft or member reaches positions at or proximate to the limits of its reciprocatory motion, said means comprising valve means imposing at least a substantial impediment to fluid flow through branch conduits leading from conduits supplying side streams, said valve means including a pair of valve members separate from the piston and directly coupled to the output shaft or member which execute a reciprocatory movement therewith and which at least adequately obstruct respective vents to atmosphere located at least near the end of each working half cycle of respective portions of the piston and cylinder means.

2. A reciprocatory motor as claimed in claim 1 in which the fluidic control means is a bistable fluidic amplifier having exit channels, each exit channel being connected to a supply conduit in the respective portions of the piston and cylinder means.

3. A reciprocatory motor as claimed in claim 1 in which the fluidic control means ports which are open to the atmosphere, one port for each exit channel and so positioned as to be readily accessible only to gas passing in the reverse direction to the normal direction of flow.

4. A reciprocatory motor which comprises a. an output shaft or member,

c. first and second supply conduits respectively providing flow paths to the portions of the piston and cylinder means for gas received from a single source conduit connectable to a source of working 8 d. fluidic control means controlling the flow of gas from the source conduit to the individual supply conduits and capable of stabilizing the flow of a stream of gas from the source conduit to either one of the supply conduits but not to both jointly, and

e. means responsive to movement of the output shaft or member and arranged to cause switching constraints to be applied to gas streaming through the fluidic control means when the output shaft or member reaches positions at least proximate to the limits of its reciprocatory motion, said means comprising valve means imposing at least a substantial impediment to fluid flow through branch conduits leading from conduits supplying side streams, said valve means including a pair of valve members directly coupled to the output shaft or member which execute a reciprocatory movement therewith and which at least adequately obstruct respective vents to atmosphere located at least near the end of each working half cycle of respective portions of the piston and cylinder means, each valve member being a plate coupled to said output shaft or member externally of the cylinder.

5. A reciprocatory motor which comprises a. an output shaft or member,

c. first and second supply conduits respectively providing flow paths to the portions of the piston and cylinder means for gas received from a single source conduit connectable to a source of working means responsive to movements of the output shaft or member and arranged to cause switching constraints to be applied to gas streaming through valve means including a pair of valve members directly coupled to the output shaft or member which execute a reciprocatory movement therewithand which at least adequately obstruct gas, respective vents to atmosphere located at least d. fluidic control'means controlling the flow of gas near the end of each working half cycle of respecfrom the source conduit to the individual supply' i e p fli 0f the pi and cylinder means. the conduits and capable of stabilizing the flow of a vents bing ted n e cylinder heads of the stream of gas from the source conduit to either one Piston and Cylinder means and being alternately of the supply conduits b t not to b h j i l d 10 closed and opened by resiliently padded plates attached to said output shaft or member externally of the cylinder. v 6. A reciprocatory motor, as claimed in claim 1, in

which the supply conduits leading from the fluidic control means have ports which are open to the atmosphere, one port for each conduit and so positioned as to be readily accessible only to gas passing in the reverse direction to the normal direction of flow.

the fluidic control means when the output shaft or member reaches positions at least proximate to the limits of its reciprocatory motion, said means comprising valve means imposing at least a substantial impediment to fluid flow through branch conduits leading from conduits supplying side streams, said

Claims

1. A reciprocatory motor which comprises a. an output shaft or member; b. piston and cylinder means coupled thereto and arranged to effect positive lengthwise reciprocatory movement of the shaft or member in response to the supply of working gas under pressure alternately to oppositely acting portions of the piston and cylinder means, c. first and second supply conduits respectively providing flow paths to the portions of the piston and cylinder means for gas received from a single source conduit connectable to a source of working gas, d. fluid control means controlling the flow of gas from the source conduit through exit channels in the fluidic control means to the individual supply conduits and capable of stabilizing the flow of a stream of gas from the source conduit to either one of the supply conduits but not to both jointly, and e. means responsive to movements of the output shaft or member and arranged to cause switching constraints to be applied to gas streaming through the fluidic control means when the output shaft or member reaches positions at or proximate to the limits of its reciprocatory motion, said means comprising valve means imposing at least a substantial impediment to fluid flow through branch conduits leading from conduits supplying side streams, said valve means including a pair of valve members separate from the piston and directly coupled to the output shaft or member which execute a reciprocatory movement therewith and which at least adequately obstruct respective vents to atmosphere located at least near the end of each working half cycle of respective portions of the piston and cylinder means.

4. A reciprocatory motor which comprises a. an output shaft or member, b. piston and cylinder means coupled thereto and arranged to effect positive lengthwise reciprocatory movement of the shaft or member in response to the supply of working gas under pressure alternately to oppositely acting portions of the piston and cylinder means, c. first and second supply conduits respectively providing flow paths to the portions of the piston and cylinder means for gas received from a single source conduit connectable to a source of working gas, d. fluidic control means controlling the flow of gas from the source conduit to the individual supply conduits and capable of stabilizing the flow of a stream of gas from the source conduit to either one of the supply conduits but not to both jointly, and e. means responsive to movement of the output shaft or member and arranged to cause switching constraints to be applied to gas streaming through the fluidic control means when the output shaft or member reaches positions at least proximate to the limits of its reciprocatory motion, said means comprising valve means imposing at least a substantial impediment to fluid flow through branch conduits leading from conduits supplying side streams, said valve means including a pair of valve members directly coupled to the output shaft or member which execute a reciprocatory movement thErewith and which at least adequately obstruct respective vents to atmosphere located at least near the end of each working half cycle of respective portions of the piston and cylinder means, each valve member being a plate coupled to said output shaft or member externally of the cylinder.

5. A reciprocatory motor which comprises a. an output shaft or member, b. piston and cylinder means coupled thereto and arranged to effect positive lengthwise reciprocatory movement of the shaft or member in response to the supply of working gas under pressure alternately to oppositely acting portions of the piston and cylinder means, c. first and second supply conduits respectively providing flow paths to the portions of the piston and cylinder means for gas received from a single source conduit connectable to a source of working gas, d. fluidic control means controlling the flow of gas from the source conduit to the individual supply conduits and capable of stabilizing the flow of a stream of gas from the source conduit to either one of the supply conduits but not to both jointly, and e. means responsive to movements of the output shaft or member and arranged to cause switching constraints to be applied to gas streaming through the fluidic control means when the output shaft or member reaches positions at least proximate to the limits of its reciprocatory motion, said means comprising valve means imposing at least a substantial impediment to fluid flow through branch conduits leading from conduits supplying side streams, said valve means including a pair of valve members directly coupled to the output shaft or member which execute a reciprocatory movement therewith and which at least adequately obstruct respective vents to atmosphere located at least near the end of each working half cycle of respective portions of the piston and cylinder means, the vents being located in the cylinder heads of the piston and cylinder means and being alternately closed and opened by resiliently padded plates attached to said output shaft or member externally of the cylinder.

6. A reciprocatory motor, as claimed in claim 1, in which the supply conduits leading from the fluidic control means have ports which are open to the atmosphere, one port for each conduit and so positioned as to be readily accessible only to gas passing in the reverse direction to the normal direction of flow.