Modulated Pure Fluid Oscillator

Abstract

A modulated pure fluid oscillator wherein the amplitude of a cyclically deflected power stream is periodically modulated at a frequency which is substantially lower than the cyclical deflection frequency. Amplitude modulation is achieved by issuing a periodic modulation stream in interacting relation with the power stream at sufficient pressure to limit but not override the primary cyclical power stream deflections. The modulation stream is generated by feeding back portions of the power stream which are scooped into a cylindrical vent passage disposed adjacent an output passage of the oscillator, the vent passage pressure varying as a function of the power stream deflection amplitude. Fluid is exhausted from the vent passage which acts as a vortex valve in throttling exhaust fluid as a function of vent passage pressure. Flow not exhausted from the vent passage is recirculated to interact with and limit the deflection amplitude of the power stream. Limiting the deflection amplitude reduces flow into the vent passage to cause reduced pressure therein, thereby reducing the vortex valve throttling action and reducing the flow of recirculated fluid interacting with the power stream. Consequently, the amplitude of power stream deflections increases and the modulation cycle starts over again. The modulation frequency, being dependent on vent passage pressure can be varied either by varying the power stream pressure of controlling the fluid exhaust from the vortex valve.

Description

BACKGROUND OF THE INVENTION

The present invention relates to pure fluid oscillators and more particularly to modulation techniques for producing very low frequency oscillatory fluid signals.

Prior art techniques for generating low frequency fluid signals, for example on the order of 1--10Hz., generally require pure fluid oscillators of relatively large size. for example, in negative feedback fluidic oscillators, between negative feedback loops extend between the output passages of the amplifier and its control nozzles. The oscillator output frequency is determined by the transit time required for the power stream fluid to travel from the point of contact with a control stream, through an output passage, around the feedback loops, and back through the control nozzle to the point of contact. If very low frequencies are desired, concomitant long transit times must be provided. Long transit times may be achieved by operating the oscillator at low power stream pressure, in the case of pressure controlled oscillators, or providing relatively long feedback paths for the feedback fluid to travel. Neither alternative is desirable for low frequency operation. Specifically, operation at low power stream pressures results in low pressure output signals and also has the disadvantage or providing a sporadically operative device since the feedback fluid, having a low pressure to begin with, when subjected to the losses inherent in the system produces a control signal having a pressure which is often insufficient to cause switching of the power stream. Where the power stream pressure is maintained sufficient to produce power stream switching, but the length of the feedback passage is increased sufficiently to obtain the desired low frequency signal, limitations an important consideration and often preclude practical utilization of the device.

It is therefore an object of the present invention to provide a reliable pure fluid oscillator for generating low frequency fluid signals wherein the oscillator can be kept relatively small regardless of the output frequency.

It is another object of the present invention to utilize modulation techniques in order to provide a low frequency fluidic oscillator which is smaller than prior art oscillators having corresponding output frequencies.

This invention is also concerned with techniques for effecting modulation. More specifically, there has been a relatively recent recognition by those working in fluidics of the fact that alternating-flow systems are more advantageous for many applications than direct-flow systems. The terms " alternating" and "direct" as applied to flow herein are analogous to the terms alternating-current (AC) and direct-current (DC) employed in electronic systems. For example, direct-flow fluidic systems are susceptible to drift, and more particularly to self-generated noise within the fluidic components. If, instead of using the direct-flow output level of an amplifier as an information signal, the amplitude of an alternating flow level is so employed, the amplifier may provide gain without being sensitive to drift. In addition, employing tuning techniques to modify the frequency responses of an amplifier results in higher gain in a limited frequency band than is generally achievable in direct-flow amplifiers. Increased utilization of alternating-flow systems has resulted in a requirement for simple and efficient modulation techniques for fluid systems. Specifically, since it is the modulating signal which carries the information of interest, techniques for accurately and efficiently modulating an alternating flow carrier become quite important.

It is therefore another object of the present invention to provide a simple technique for modulating the amplitude of an alternating flow carrier signal in a pure fluid amplifier.

SUMMARY OF THE INVENTION

In one aspect of the present invention a pure fluid oscillator having a cyclically deflected power stream is amplitude modulated by means of a modulation control stream which periodically varies the deflection amplitude of the power stream at a frequency which is substantially lower than the power stream cyclical deflection frequency. The modulation control stream is derived from power stream fluid received by a vent passage disposed adjacent an output passage of the oscillator so as to scoop a portion of the power stream into the vent passage. Fluid exhaust from the vent passage is controlled by a vortex valve disposed at the downstream end of the vent passage. Exhaust of fluid via the vent passage is throttled by the valve, the exhaust being increasingly throttled as the fluid flow received by the vent passage increases. A recirculation path is provided from the valve to a location adjacent the upstream portion of the cyclically deflected power stream. For large amplitudes of deflection of the oscillating power stream relatively large portions of the power streams are received by the vent passage. This in turn heavily throttles the valve and relatively large proportions of the fluid received by the vent passage are recirculated to interact with the power stream. Consequently, the amplitude of deflection of the power stream is limited, thereby limiting the amplitude of the output signal and also reducing the amount of fluid received by the vent passage. The reduction in fluid received by the vent passage reduces throttling at the vortex valve, thereby reducing recirculated modulation flow. The limiting effect on the amplitude of deflection of the power stream is thereby removed, whereupon the power stream deflection amplitude increases fluid directed to the vent passage. Increased fluid flow to the vent passage begins the modulation cycle once again. It will be seen therefore that the amplitude of deflection of the power stream is cyclically limited by cyclically increasing recirculation flow. The resulting output signal takes the form of an amplitude modulated wave which may be detected and filtered as to provide an oscillatory fluid signal having a frequency determined by the throttling action of the vortex valve, the length of the recirculation path, and the power stream pressure.

Since exhaust flow is proportional to the pressure in the vent passage, it follows that increasing power stream pressure serves to increase throttling at the vortex valve so as to increase the buildup of recirculated modulation and control flow and thereby increase the frequency of the modulation signal. If the modulated output signal from the oscillator is filtered by a low pass filter so as to block the carrier or deflection frequency of the oscillator, only the modulation frequency will be recovered, and this frequency can be controlled as a function of the power stream pressure. Thus a low frequency oscillator can be provided without requiring excessively large fluidic devices. Further, control of the modulation frequency may be achieved other than by varying the power stream pressure. Specifically, the throttling action of the vortex valve may be varied as a function of variation in size of the output port in the vortex valve. Similarly, introduction of additional fluid flow into the exhaust port of the vortex valve can effect valve throttling as desired and thereby vary the frequency of the modulating signal.

It is important to bear in mind that the length of the path traveled by the recirculating control fluid, namely the vent passage length added to path length within the vortex valve and the recirculation path communicating with the power stream, determines in part the modulation frequency. Naturally, changes in power stream pressure and externally controlled valve throttling will produce variations of this frequency as determined by the circulation path; however, it is the transmission time of the vented flow around this recirculation path which is the primary determining factor. Since the recirculation path receives only the boundary portions from the power stream, which are at substantially lower pressures than the power stream core, the recirculation time for the modulation signal is substantially longer than the recirculation time for the main portion of the power stream around a path of a similar length In addition, the recirculation time for the modulation signal is extended relative to the recirculation time for the main portion of the power stream due to the frequency response of the vortex valve action in the vent passages.

In a second embodiment of the invention a fluidic beat frequency oscillator is obtained by mixing two oscillating fluid signals of slightly different frequencies. The mixed signals are then detected and passed through a low pass filter to provide the desired beat frequency output. If one of the mixed signals is generated by a fixed frequency oscillator, and the other signal is generated by a pressure control oscillator, the beat signal frequency is variable as a function of the input pressure to the pressure controlled oscillator.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a plan view of a self-modulating pure fluid oscillator constructed in accordance with the principles of the present invention;

FIG. 1a is an illustrative waveform representing a typical signal at the output passages of the device of FIG. 1; and

FIG. 2 is a schematic representation of another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now specifically to FIG. 1 of the accompanying drawings, there is illustrated a negative feedback pressure controlled oscillator employing the principles of the present invention. It is to be understood that applicability of the principles of the present invention is not limited to negative feedback type oscillators, but rather are appropriate in any pure fluid device having an oscillatory power stream. The oscillator of FIG. 1 is substantially similar to the oscillator described in copending U.S. Pat. application Ser. No. 430,696 by F. Manion, filed Feb. 5, 1965, now abandoned and assigned to the same assignee as the present invention, and comprises a pure fluid proportional amplifier generally designated by the reference numeral 1. The cavities, passages, and nozzles needed to provide the pure fluid amplifier 1 are formed in a flat plate 11 and plate 11 is covered by a flat plate 12, the two plates being sealed in fluid tight relationship, one to the other, by means of machine screws, clamps, adhesives, or the like. For the purposes of clarity, the plates 11 and 12 are shown to be composed of a clear plastic material, however, it should be understood that any material compatible with the working fluid may be used in the construction of the amplifier. Amplifier 1 has a power nozzle 2, control nozzles 3 and 4, and a pair of output passages 6 and 7 located downstream of the nozzles. The sidewalls of the amplifier are removed by providing recesses 8 and 9 which are vented to ambient pressure via exhaust port 16 and 17 respectively to prevent boundary layer effects from affecting the position of the power stream. Output passages 6 and 7 are separated from respective recesses 8 and 9 by means of flow dividers 13 and 14, respectively. Exhaust ports or apertures 16 and 17 are defined through cover plate 12 so as to communicate between the downstream ends of respective recesses 8 and 9 and ambient pressure via respective exhaust tubes 3- and 32.

In the embodiment of FIG. 1, a pair of RLC feedback loops are provided, extending respectively from output passage 6 to control nozzle 3 and output passage 7 to control nozzle 4. More particularly, the feedback loop extending from output passage 6 comprises inductance (inertance) 19 which constitutes a relatively long narrow passage, a capacitor 21 comprising an enlarged volume in series with inductance 19, and a further inductance 22 having a restriction 23 in series therewith to represent the resistance of the feedback path. Restrictor 23 need not exist as such a in a high system, the necessary resistance being present in the amplifier per se. In a highly damped system, on the other hand, a restrictor such as 23 or a porous plug or other type of fluid resistance may be employed. A similar feedback path comprising similar components exists between output passage 7 and control nozzle 4. This feedback path is substantially identical with the feedback path previously described in order to provide symmetrical oscillatory operation and therefore will not be described in further detail. It is to be understood however that if asymmetrical oscillation is desired, the two feedback paths may include either different components or similar components having different parameter values.

Upon issuance of a power stream from the nozzle 2, a larger proportion of the stream flows to one or the other of the output passages 6 or 7 due to some initial perturbation of the stream. Assuming for the moment that a greater proportion of the flow is to the passage 6, fluid is fed back through the feedback loop extending therefrom and issues from control nozzle 3 so as to divert the power stream to output passage 7. Fluid supplied to output passage 7 then proceeds around the feedback loop extending therefrom and upon issuing from nozzle 4 diverts the power stream back to output passage 6. Thus the power stream oscillates back and forth between passages 6 and 7 at some frequency which is equal to the total transport time of the fluid about the system. The transport time is determined by the lengths of the output passages, and the feedback paths as well as the values of the RLC components in the feedback paths. It is readily apparent that the frequency of oscillation is also a function of the pressure of the power stream, since the total transport time of the fluid about the feedback loops reduces as the pressure increases, thus tending to increase the frequency of oscillation with increase in pressure.

The system as thus far described is substantially identical with the pressure control oscillator described in the above-referenced copending patent application Ser. No. 430,696 except that the pressure-controlled oscillator of said patent application provides conventional relatively large vent ports at the downstream ends of recesses 8 and 9 so as to maintain these recesses at ambient pressure throughout the entire operating range of the oscillator. In the present invention, however, relatively small exhaust ports 16 and 17 are provided and serve as a sink for exhausting fluid from the recesses 8 and 9, respectively. The downstream ends of passages 8 and 9 are curved to induce rotational or vortical flow in fluid received by the recesses 8 and 9 by virtue of deflection of the power stream at least partially beyond the apices of flow dividers 13 and 14. Fluid received by recess 8, for example, is directed around the periphery of the recess into a vortical path and is exhausted through aperture 16. The relatively small diameter of exhaust aperture 16 gives rise to a high velocity circulation at the core of the vortex which in turn gives rise to a throttling effect on the exhausting flow. The throttling action increases with increasing vortical flow, and vortical flow increases with increased power stream flow into recess 8. It is apparent that the greater the amplitude of oscillations of the power streams, the greater the flow into the recess 8. As the throttling action increases more of the power stream spillage received by the recess is spun around the periphery of the recess by the centrifugal force created at the periphery of the vortex. This portion of the spillage cannot be exhausted due to the increased throttling and is therefore fed back along the recess wall into interacting relationship with the power stream at a location slightly downstream the control nozzle 3. The greater the spillage received by recess 8 the greater the flow returned to interact with the power stream. The recirculated spillage serves two separate functions: first, it increases the pressure in the power stream; second, it provides a secondary control stream. This secondary control stream acts to limit deflection of the power stream towards recess 8 and thereby reduce the amplitude of oscillation of the power stream. The resulting smaller swing or amplitude of the power stream results in less spillage into recess 8 and consequently in less secondary control stream flow interacting with the power stream. Consequently the amplitude of the power stream begins increasing and spillage flow into recess 8 increases, thereby increasing the vorticity of the exhaust flow in the recess which in turn produces an increased throttling action of the exhaust flow. As discussed above, increased throttling causes a return of more of the spillage fluid into interacting relationship with the power stream as part of the secondary control stream.

It is seen that the effects of the secondary control stream on the amplitude of the oscillating power stream are cyclical, occurring at a frequency determined by the pressure of the fluid received by recess 8, the strength of the vortex created about exhaust port 16, and the length of the peripheral path defining the boundary walls of the recess for any given size of port 16. The secondary control stream thus serves to amplitude-modulate the oscillator output signal provided at output passage 6 of the oscillator. In a similar manner, a secondary control stream is provided about the periphery of recess 9 by means of the vortical flow induced about exhaust aperture 17. In a unit which is entirely symmetrical about the longitudinal axis of power nozzle 2, the two secondary control streams are in phase so that a cyclical compressive force is applied at both sides of the power stream to limit the amplitude or swing of the power stream in both directions simultaneously. This factor has been borne out by data resulting from tests of the device illustrated in FIG. 1. This in-phase "beating" by the secondary control streams is contrary to the 180.degree. out-of-phase relationship existing between the control signals employed at control nozzles 3 and 4 to cyclically deflect the power stream at the oscillation or carrier frequency. As a result, the output signals appearing across output passages 6 and 7 is an amplitude modulated signal in which the carrier frequency is determined by the transmit time for fluid traversing the output passages, feedback paths, and the control nozzles, whereas the modulation frequency is determined by the fluid transit time about the periphery of recesses 8 and 9. The output waveform, appearing as a differential pressure across passages 6 and 7, is illustrated in FIG. 1a.

Even though the actual path length about the recesses 8 and 9 is substantially shorter than the feedback path length from output to control passages, the modulation frequency is substantially lower than the basic oscillator carrier frequency. The reason for this is two fold: first of all the power stream has a bell-shaped transverse pressure gradient so that the spillage portion of the power stream received by the vent passages is at a substantially lower pressure and velocity than the core of the power stream which is received by output passages 6 and 7. A secondary factor accounting for the substantially lower frequency of the secondary control signal as compared with the feedback signal is the time required to increase and decrease the vorticity of flow in the vent passages.

The throttling action of the vortexes created in the vent passages may be likened to the action of a vortex valve such as the type disclosed in U.S. Pat. No. 3,324,891 to Rhoades. Specifically, in a vortex, the rotating fluid creates a centrifugal force so that there is a relatively large pressure at the outside of the vortex and a pressure gradient across the vortex. The centrifugal force is a function of the vortical velocity of the fluid which in turn is a function of the fluid flow in recesses 8 and 9 in the unit of FIG. 1. Thus as the flow into a recess increases the centrifugal force created by the vortex increases, thereby increasingly throttling exhaust from the recess and increasing the flow returned to interact with the power stream.

Since the modulation frequency is dependent to an extent on the pressure of the fluid received by the recesses 8 and 9, it is not surprising that the modulation frequency can be varied (along with the carrier frequency) as the power stream pressure is varied. Tests have shown that for a unit configured substantially like that illustrated in FIG. 1, a linear modulation frequency versus power stream pressure characteristic is achievable by varying the power stream pressure over a predetermined range. This provides a self-controlled feature whereby the modulation frequency can be adjustably set to a desired value. This is particularly advantageous where it is desired to utilize the modulation frequency as a low frequency oscillatory signal. Specifically, output passages 6 and 7 may be connected to a rectifier 26 such as the full wave rectifier disclosed in U.S. Pat. No. 3,292,648 To J. R. Colston. The full wave rectified signal may then be passed to a low pass filter 27 which blocks all carrier signal components and passes a signal at twice the modulation frequency, the modulation frequency being doubled by virtue of full wave rectification. The output of the low pass filter 27 thereby constitutes a low frequency oscillatory signal, the frequency of which may be readily controlled, such as by controlling the pressure of the power stream issued from nozzle 2. Low pass filter 27 may, for example, be of the type described in the above-referenced Colston patent. Instead of using rectifier 26 and filter 27 to obtain the low frequency oscillatory signal, I have found that a turbulence amplifier, such as the type disclosed in copending U.S. Pat. No. 3,234,955, may serve the same purpose. Specifically, if each of output passages 6 and 7 is connected to a power stream tube of respective turbulence amplifiers, the output passages of the turbulence amplifiers receive the low frequency modulation fluid signal without any carrier signal component. The reason for this is the relatively high inductance of the power stream tubes of the turbulence amplifiers, such inductance rendering the turbulence amplifier incapable of responding to the relatively high carrier frequency signal. It is important, of course, that a turbulence amplifier having a sufficiently high inductance be chosen for this purpose.

As discussed previously, the large components required to produce low frequency oscillations in prior art pure fluid devices are extremely disadvantageous and uneconomical. The modulation technique employed herein to produce low frequency oscillations with the use of rectifier 26 and low pass filter 27 avoids the disadvantages inherent in the prior art. In addition, both the carrier and modulation frequencies are generated with a single fluid amplifier element, thereby avoiding the uneconomical and inefficient prior art fluidic modulation techniques requiring separate fluid amplifier elements to generate the carrier and modulation signals.

It is to be noted that the frequency versus pressure characteristics of both the carrier and modulation signals are such to enable frequency modulation of both signals by varying the power stream pressure. Thus, where a sinusoidal pressure is applied at power nozzle 2 both the modulation signal and the carrier signal are frequency modulated at the sinusoidal signal frequency and can be appropriately employed for separate or concurrent utilization. Thus, the device of the present invention is suitable for both amplitude and frequency modulation techniques.

The amplitude modulation feature of the present invention can be used to even further advantage than previously described. Specifically, the throttling action of the vortex valve in vent passages 8 and 9 may be enhanced or retarded in various ways to effect variations in amplitude and frequency of the recirculated secondary control stream. Thus, control signals may be tangentially applied at the periphery of the vent recesses 8 and 9 in either aiding or impeding relation to the peripheral spillage flow received by the recess. Moreover, the effective size of exhaust apertures 16 and 17 may be adjusted as desired in accordance with input information, or the apertures 16 and 17 may be blocked by some external member such as a piston moving axially of the aperture or a plate moving perpendicularly thereof so as to vary the throttling action of the vortex in these recesses as a function of some desired input information signal. Valves connected in series with pipes 31 and 32 may accomplish this function. The input information signal may then be recovered by demodulating the output signal appearing at output passages 6 and 7 by utilizing a nonlinear element such as a rectifier 26 connected thereacross.

In tests performed on an oscillator configured substantially as illustrated in FIG. 1, it was found that the modulation frequency varied linearly from 5 to 10 Hz. in response to input pressure variation between 0.053 to 0.060 p.s.i.g. For the same input pressure variation, the carrier frequency was found to vary linearly between approximately 140 and 160 Hz. In the units tested, the limits of the modulation frequency range were approximately 2 Hz. and 11 Hz. For input pressures outside the range for producing these modulating frequencies, the units operated as simple sine wave oscillators, producing only the carrier frequency signal.

An interesting phenomenon was observed during testing, namely the sensitivity of the above-described unit to externally generated noise. For example, a unit operating at or near an end of its modulation range was found to switch to pure carrier mode of operation (without modulation) in response to the snap of one's fingers in the vicinity of the unit. This phenomenon would appear to render the unit of FIG. 1 suitable for operation as an acoustic detector, providing a low frequency signal from filter 27 unless disturbed by an acoustic signal above a predetermined amplitude and within a specified frequency range.

In addition to the acoustic sensitivity of the modulation signal in the device of FIG. 1, it has been found that the carrier frequency is also sensitive to externally provided acoustic signals. Specifically, operating the PCO outside the modulation range, it was found that the PCO frequency changed when subjected to acoustic signals at certain frequencies, but remained constant when subjected to signals throughout the remainder of the audio frequency range. Depending upon the operating frequency of the PCO, the number of audio frequencies to which the PCO was sensitive changed. For example, only one audio frequency was found to change the frequency of the PCO originally set to operate at 102 Hz.; however, when the PCO was originally set to operate at 104 Hz., two distinct audio frequencies produced PCO frequency changes. Further, when subjected to an audio frequency to which it is frequency-sensitive, the PCO frequency variation was found to vary as a function of the audio signal level at that "sensitive frequency."

In view of the above, it would appear that the PCO illustrated in FIG. 1, apart from its self-modulating capability, is capable of being modulated by acoustic signals at predetermined frequencies and by an amount determined by the acoustic signal level at these predetermined frequencies. The PCO could therefore serve as sonic detector; or where an acoustic signal generator is provided in proximity to the PCO, the PCO may be selectively modulated in accordance with input information controlling the actuation of the acoustic signal generator.

Referring now to FIG. 2 of the accompanying drawings, there is illustrated in schematic form another embodiment of the present invention wherein modulation techniques are employed to provide low frequency oscillatory fluid signals. More specifically, a pair of pressure controlled oscillators 40 and 60 are provided and by way of example may be of the type described in the above-referenced copending Pat. application Ser. No. 430,696 by F. M. Manion. Oscillator 40 receives an input pressure signal P.sub.1 at its power nozzle 41 and oscillator 60 receives an input pressure signal P.sub.2 at its power nozzle 61. Oscillatory differential pressures are provided across output passages 43 and 45 of oscillator 40 and 63 and 65 of oscillator 60 as functions of respective input pressure signals P.sub.1 and P.sub.2. Output passages 43 and 45 are connected to opposing control nozzles 51 and 53 respectively of a proportional fluidic amplifier 50. Output passages 63 and 65 are connected to opposing control nozzles 71 and 73 respectively of a proportional fluidic amplifier 70. Amplifiers 50 and 70, by way of example, may be of the type described and illustrated in U.S. Pat. No. 3,275,013. Amplifiers 50 and 70 are provided with respective pairs of output passages 55, 57 and 75, 77. Output passages 55 and 75 are connected together at a common point by means of a T-fitting 81; similarly output passages 57 and 77 are connected to a common point by means of T-fitting 83. T-fittings 81 and 83 are not to be construed as limiting but rather as illustrative of one of the numerous conventional techniques by which two fluidic signals may be connected to a common point. The output signals from the T-fitting 81 is applied as an input signal to a rectifier 85, the output signal from which is applied to a low pass filter 87. Similarly, the signal from fitting 83 is applied to rectifier 86 and low pass filter 88. Rectifiers 85, 86 and filters 87, 88 may, for example, be identical to rectifier 26 and filter 27 of FIG. 1.

In operation, assume that the frequencies of the output signals from oscillators 40 and 60 are slightly different. This may be achieved by employing identical oscillators and providing input signals P.sub.1 and P.sub.2 at slightly different pressures; or the oscillators themselves may be constructed to operate at different frequencies for equal input pressures. The slightly different frequency signals are fed to respective buffer amplifiers 50 and 70 which serve to isolate the two oscillators from one another and thereby prevent mutual feedback between oscillators to produce frequency distortion. The beat frequency (or difference frequency) between the two amplifier output signal frequencies is generated at fittings 81 and 83 with a 180.degree.-phase difference, and recovered by respective rectifiers 85, 86 and filters 87, 88, the latter passing only low frequency signals and blocking frequencies on the order of the PCO output frequencies. A low frequency signal may thus be obtained by spacing the frequencies of PCO's 40 and 60 as desired.

It is to be understood that the differential or push-pull configuration illustrated and described above is by way of example only. If desired, the individual output signals from fittings 81 and 83 may be used alone, rectified and filtered to provide a single-ended device wherein a low frequency output signal is provided.

If input signal P.sub.1 is held at constant pressure and input signal P.sub.2 is made variable in response to a predetermined parameter, the modulation signal appearing at the output passage of low pass filter 87 is a prescribed function of the predetermined parameter. If PCO 60 has a linear frequency versus pressure characteristic, said prescribed function is linear and represents a gain (in cycles per second versus p.s.i.) which is almost twice the gain of PCO 60 alone. Similarly, where P.sub.1 and P.sub.2 are made to vary differentially in response to the predetermined parameter, even higher gains, on the order of four times that of a single PCO, are achievable.

In a circuit configured substantially as that of FIG. 2, it was found that a frequency range from substantially 0 to 25 Hz. was obtainable, and that the frequency was linear with respect to input pressure variations over the range from 0.5 to 20 Hz.

The utilization of pressure controlled oscillators 40 and 60 in the embodiment of FIG. 2 should not be considered as limiting the scope of the present invention. Specifically, any two fluidic oscillators having their frequencies separated as desired would suffice to provide the requisite low frequency signal at filters 87 or 88. The advantage of pressure controlled oscillators resides primarily where P.sub.1 and P.sub.2 are variable relative to one another and the low frequency output signal is a function of the input pressure variation.

While I have described and illustrated several specific embodiments of my invention, it will be clear that variation of the details of construction which are specifically illustrated and described may be resorted to without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

I claim:

1. A fluidic element comprising:

nozzle means responsive to application of pressurized fluid thereto for issuing a power stream of fluid;

oscillatory control means for cyclically transversly deflecting said power stream at a carrier frequency;

output means for selectively receiving the deflected power stream; and

modulating means for cyclically limiting the deflection amplitude of said power stream at a modulation frequency which is substantially lower than said carrier frequency; said modulating means comprising: a vent passage in said element disposed for receiving varying power stream flow in proportion to the deflection amplitude of said power stream; exhaust port means disposed near the downstream end of said vent passage and communicating with an ambient pressure environment, said exhaust port means being configured wherein its maximum fluid exhaust flow rate is smaller than the power stream flow rate into said vent passage for maximum deflection amplitude of said power stream; and recirculation means responsive to power stream flow rates into said vent passage in excess of said maximum fluid exhaust flow rate for directing a fluid modulating stream into interacting relation with said power stream, said modulating stream having a maximum momentum which is sufficient to limit the deflection amplitude of said power stream and insufficient to entirely override said oscillatory control means.

2. The combination according to claim 1 wherein the downstream end of said vent passage is curved sufficiently to induce vortical flow about said exhaust port means in response to fluid flow in said vent passage, said vortical flow throttling fluid exhaust from said exhaust port as a function of the power stream flow into said vent passage, and wherein said recirculation means includes a sidewall of said vent passage disposed for receiving peripheral fluid from said vortical flow as a function of vortical flow rate and for directing said peripheral fluid into interacting relation with said power stream.

3. The combination according to claim 1 further comprising demodulation and low pass filter means connected to said output passage for providing a fluid output signal at said modulation frequency and for blocking said carrier frequency.

4. A fluidic element comprising: nozzle means responsive to application of pressurized fluid thereto for issuing a power stream of fluid, oscillatory control means for cyclically transversely deflecting said power stream at a carrier frequency; output means for selectively receiving the deflected power stream; said output means comprising a pair of output passages disposed for selectively receiving said power stream; modulating means for cyclically limiting the deflection amplitude of said power stream at a modulation frequency which is substantially lower than said carrier frequency; said modulating means comprising: a pair of vent passages, each disposed adjacent a respective output passage and separated therefrom by respective flow dividers, said vent passages being disposed to receive power stream fluid only in response to transverse deflections of said power stream beyond said respective output passages, each said vent passages having an exhaust port communicating between its downstream end and ambient pressure, the walls of each vent passage being curved to produce vortical flow about said exhaust port in response to power stream flow into said vent passage, said vortical flow throttling fluid exhaust via said exhaust port as a function of the flow rate into said vent passage, said exhaust port being sufficiently small and said vent passage wall being so configured that for large power stream deflections by said oscillatory control means a substantial portion of the fluid received by said vent passage is circulated about the periphery of the vortical flow and back into interacting relation with said power stream, the maximum momentum of the flow so circulated being sufficient to reduce but not override the deflection amplitude of said power stream produced by said oscillatory control means.

5. The combination according to claim 4 further comprising demodulation and low pass filter means connected to said output passages for providing a fluid output signal at said modulation frequency and for blocking said carrier frequency.

6. The combination according to claim 4 where said element is a pressure controlled oscillator in which said modulation frequency and said carrier frequency vary as functions of the pressure of the fluid applied to said nozzle means.

7. The combination according to claim 6 where said oscillatory control means includes negative feedback passages extending from each of said output passages for applying a portion of the flow received by each output passage in interacting relation with said power stream.

8. The combination according to claim 7 further comprising demodulation and low pass filter means connected to said output passages for providing a fluid output signal at said modulation frequency and for blocking said carrier frequency.

9. The method of monitoring an acoustic disturbance utilizing a pressure controlled fluidic oscillator in which a power stream of fluid is cyclically transversely deflected and which has a variable power stream deflection frequency versus input pressure characteristic, said method comprising the steps of:

adjusting the frequency of said pressure controlled oscillator to a value from which a predetermined power stream deflection frequency deviation ensues in response to said acoustic disturbance;

subjecting said pressure controlled oscillator to said acoustic disturbance; and

monitoring the power stream deflection frequency of said pressure controlled oscillator to provide an indication in response to said predetermined power stream deflection frequency deviation.

10. The method of generating a low frequency fluid signal comprising the steps of:

issuing a power stream of fluid at a specified pressure;

cyclically deflecting said power stream transversely of its flow direction and at a predetermined amplitude and frequency of deflection;

cyclically limiting the amplitude of deflection of said power stream at a lower frequency than said predetermined frequency by recirculating at least one low velocity portion of said power stream into deflecting relationship with said power stream, the portion of said power stream so recirculated being dependent upon the amplitude of deflection of said power stream such that more fluid is recirculated for high deflection amplitudes than low deflection amplitudes.

11. The method according to claim 10 wherein said step of cyclically limiting includes the step of recirculating fringe portions of said power stream into deflecting relationship with said power stream, the amount of fluid so recirculated being relatively large when the deflection amplitude of said power stream is maximum and relatively small when the deflection amplitude of said power stream is minimum.

12. The method according to claim 11, wherein said predetermined frequency is a function of said specified pressure and wherein said specified pressure is selectively variable.

13. The method according to claim 11 further comprising the step of selectively impeding and augmenting the recirculating fluid to vary said low frequency.