US3116382A - Pneumatic control systems incorporating pneumatically actuated switches - Google Patents

Description

1953 R. c. LOOMIS ETAL 3,

PNEUMATIC CONTROL SYSTEMS INCORPORATING PNEUMATICALLY ACTUATED SWITCHES Filed July 27, 1960 IN VEN TOR5 055,427 6 Z pom/5 W fl/voes 05 pa ae s p/ uitzwvzys United States Patent PNEUMATIC CGNTROL SYSTEMS INCGRPORAT- ING PNEUMATICALLY ACTUATED SWITCHES Robert C. Looinis, Anaheim, and Andre de Poor, West Hollywood, Calif., assignors to Econo'lite Corporation,

Los Angeles, Calif., a corporation of California Filed July 27, 1960, Ser. No. 45,651 4Claims. (Cl. 2tlti83) This invention relates generally to pneumatic control systems and more particularly to such systems incorporating pneumatically actuated switches which operate accurately throughout a wide range of actuation pressures.

The most widespread use of the present invention is in the recording of vehicle traffic. In such use, a collapsible rubber pneumatic tube is extended across the roadway with a recorder or counter, located adjacent the road, connected to one end of the tube. Each set of wheels of vehicles crossing the tube, generates pressure waves which are communicated to a deformable diaphragm of a pneumatically actuated electric switch on the counter.

It is commonplace to extend the pneumatic tube across three or more lanes and, therefore, the tubes used are often 50 to 100 ft. long. In the past, difficulties have arisen chiefly because, among other things, the pressures impressed upon or sensed by the counter switch, vary with the weights of the vehicles and the distances from the switch at which the wheels roll over the tube. For example, it may be seen that the pressure waves sensed by the counter switch varies from one extreme where a light car, eg. a Volkswagen, passes over the end of the tube which is remote from the counter to the other extreme where a heavy truck passes over the tube in the lane adjacent the counter, i.e. the counter end of the tube. When prior pneumatically actuated switches were set to be sensitive enough to record the light car of the above example, they had a tendency to record two or more counts when the heavy vehicle of the above example rolled over the tube, thus giving a false count. This was because the excessively high .pressure waves generated by such heavy vehicle oscillate or reverberate through the tube before falling below the pressure necessary to actuate the sensitively set switch.

More particularly, when a vehicle passes over the tube, each wheel generates in the tube two pressure waves, one travelling directly toward the counter and the other toward the tube end which is remote from the counter. Accordingly, each set of two wheels generates four waves. The wave of primary importance is that travelling directly from the wheel nearest the switch to the switch. This wave must be strong enough to actuate the switch, but yet must be damped quickly enough so that it will not bounce from the diaphragm, reflect from the opposite end of the tube and then actuate the switch again.

The wave travelling directly from the wheel nearest the remote end of the tube to that end also must be considered, since this wave is reflected from the tube end toward the switch. Although this reflected Wave must travel farther than said primary wave, the reflected wave may be strong enough to actuate the switch and thus give a false count unless certain remedial measures are taken.

These reflected waves and the waves emanating from the mutually facing sides of the wheels of a two-wheel set are all part of what, for ease of reference, are hereafter called secondary oscillations or reverberations.

Because of the above secondary oscillations, the in- 'staller was required to spend considerable time, after the system was set up on the road, adjusting the sensitivity of the counter switch to local trafiic conditions. At best, the technician often had to be satisfied with setting the "ice counter so that it missed about as many cars as it double recorded.

The unique control system of the present invention overcomes the above difficulties. It includes a switch which has means thereon to vent impulse pressures above a predetermined amount, which amount is only slightly greater than that needed to close the switch contacts when a light car passes over the remote endof the tube. Therefore, when a heavy truck passes over the tube near the counter, much of the excess of the resulting large impulse of air is vented before it reaches the diaphragm and is thus reduced to a value which is near to that generated by the illustrative light car. As one result of this, the doubie counts are either totally eliminated or, at least, greatly reduced.

In addition to the above venting, applicants have found it desirable to add further means to damp more quickly the secondary oscillations of all pressure waves. To this end, systems of the present invention include a control orifice communicating with the interior of the tube at a point spaced from the diaphragm. We have found that because of the mode of operation described below, such an orifice accomplishes its purpose most eifectively when located in the tube end which is remote from the switch.

With the combination of the large impulse vent and the control orifice cooperating, the control system is accurate over a wide range of actuation pressures and may be easily set to respond properly to such pressures. The light pressure waves are damped quickly and the heavy impulses are effectively reduced initially and then damped quickly.

With the foregoing in mind, it is a major object of this invention to provide a pneumatically actuated switch which will operate accurately over a wide range of actuation pressures.

It is a further object of this invention to provide a pneumatic control system which will automatically reduce actuation pressure impulses which are above a predetermined level.

Another object of this invention is to provide a quickly and easily adjusted traffic counter system.

A still further object of this invention is to provide a rugged, low cost traflic counter system.

Still another object of this invention is to provide a pneumatic control system which will vent high pressure impulses and then damp the remainder of such impulses rapidly.

An additional object of this invention is, for reasons to be set forth, to provide a control orifice at the remote end of adetecting tube which is to be placed across a road.

Other and further objects of this invention will become apparent in the detailed description below in conjunction with the attached drawings wherein:

FIGURE 1 is an overall view of a system incorporating the present invention.

FIGURE 2 is a pictorial view of a pneumatically actuated switch embodying the present invention.

FIGURE 3 is across sectional view of the switch taken along line 33 in FIGURE 2.

FIGURE 4 is a fragmentary cross sectional view of the switch taken along line 44 in FIGURE 3.

FIGURE 5 is a cross sectional view of a pressure wave damper at the end of the pneumatic tube taken along line 5-5 in FIGURE 1.

Referring now t 0 FIGURE 1, the wheels of car A are shown driving rolling over a pneumatic tube B which is extended across roadway G and anchored in a conventional manner. The right end of the pneumatic tube B is connected to a pneumatically actuated electric switch 'S of a trafiic counter C (enclosed by phantom lines) which is normally located adjacent the road. At the end of the tube B remote from the counter C, i.e. the left end,

is an orifice plug assembly P which functions in a manner described below, to damp secondary oscillations of the pressure waves caused by the wheels of the car A.

With the exception of the switch S, the counter C is conventional. It includes a disk chart D which is ro tated by a clock (not shown) at a predetermined speed, e.g. one revolution per 24 hours. Just above chart D is drive mechanism M which swings recording arm R, the latter having a pen at its lower end adapted to mark the chart D. The mechanism M may be one of several conventional types. For instance, it may be such that every time an electrical impulse is received, the arm R is swung to move the pen a predetermined small distance further from the center of the chart D. Then, the pen is returned to the center of the chart D at a predetermined interval, e.g. five minutes, 30 -minutes, or 60 minutes. Such apparatus gives an accurate indication of the number of vehicles passing that point during the predetermined period.

In order to supply the electrical impulses, the pressure waves in tube B close electrical contacts of the switch S, completing a circuit from battery V to mechanism M. Therefore, the system will record each set of wheels which passes over the tube B. Referring now to FIGURES 2, 3, and 4 the presently preferred embodiment of the switch S will be described in detail. The main portion of the switch S includes a body member or block which is centrally drilled from one side face 15a thereof, bore 16 bottoming at Ma, while its entrance end 1612 is threaded to threadably receive the hollow stem 18 of a diaphragm housing 17. The unoccupied portion 16c of bore 16 represents a central chamber within body member 15.

At the left end of stem 18, the housing 17 has an annular flange 20. The left side of flange 29 is recessed at 20a to receive a circular, flexible diaphragm 21. It will be noted that the recess 20a is of slightly greater diameter than diaphragm 21 and is slightly deeper than the thickness of said diaphragm. Therefore, the diaphragm is loosely held in place by a ring 22 so that air may leak around the diaphragm as necessary.

At the top of the ring 22, as viewed in the aspect of FIGURE 3, is a cantilever arm 24 which has a threaded hole 25 therein, through which adjustment screw 26 extends. At the left hand of the screw 26 is a knob 27 which is continuously urged to the left by spring 28 to take up any slack which may develop between the threads of the support 26 and the hole 25. With this arrangement, by turning knob 27, a contact 29, affixed to the right end of the screw 26, may be accurately adjusted to a position which is spaced (a distance proper to a given trafiic situation) from movable contact 30 secured to the free end of a cantilever spring arm 31.

Plates 33 and 34 cooperate with nut and bolt assemblies 35 to rigidly fasten the lower end of the spring arm 31 to the flange 20. The spring arm 31 is connected to one side of the battery V by way of wire 36. Spring arm 31 is insulated from the flange 20 by insulator washers 37 and 38 and an insulator sleeve 39 provided around each of the bolts 35. Therefore, the contacts 29 and 30 must be closed in order to complete the circuit from wire 36 to wire 41, attached to the block 15, in order to actuate the mechanism M (see FIGURE 1, also).

The particular configuration of spring arm 31 and the manner in which it cooperates with the diaphragm 21 is another significant aspect of this preferred embodiment. As can be seen, the arm 31 is curved so that the left face of diaphragm 21 abuts the arm only at its enlarged, central portion 31a. Therefore, the contact 30 is moved approximately twice as far as the diaphragm 21 moves portion 31. This movement advantage allows the contacts 29 and 30 to be set further apart Without requiring excessive deformation of the diaphragm 21 to close the contacts.

Another advantage of the configuration and mode of operation of the spring arm 31 is that the contacts 29 and 3%) clean each other each time they are closed. More particularly, after the diaphragm 21 moves the arm 31 sufi'iciently to close the contacts 29 and 30, further movement tends to straighten arm 31. This causes the contact 30 to move upwardly (as seen in FIGURE 3) relative to contact 29, and thereby residue from corrosion or other foreign matter which may gather on the contacts is wiped off or dislodged.

To receive pressure impulses from tube B, block 15 has a vertical inlet passage 42 extending downwardly from bore 16. The passage 42 is counterbored and threaded in order to receive hose connector 43 which holds filter screen 44 in position through pressure on washer 45. As is conventional, the exterior of the lower end of connector 43 is formed with a plurality of annular serrations 46 to hold the pneumatic tube B after it has been telescoped over the connector. Therefore, air may pass from tube B through connector passage 47, passage 42, chamber 16c, and stem bore 48, to the right face of diaphragm 21. In order to spread the impulse pressure over a wider surface area of the diaphragm 21 before the diaphragm is moved away from the flange 20, a plurality of radial grooves 4-9 are provided in the flange 20 adjacent the recess 200. By spreading the impulse pressure over a greater portion of the surface area of the diaphragm 21, movement of the diaphragm to close the contacts 29 and 3th is more positive in its action.

As previously mentioned, a significant aspect of the present invention is that it includes means to vent extra high actuation pressures and thereby reduce such impulses from the outset. In the preferred form, this means comprises a vent port 5t} which extends vertically upward from the chamber 160. The upper end of port 5% is counterbored at 51 to form an upwardly facing valve seat 51a at the circle of intersection between the port 50 and the counterbore 51. A ball 52 is adapted normally to rest on the seat 51a, the ball and seat forming a one way valve which will pass lair only after the ball is unseated. The upper end of the counterbore 51 is threaded to receive cap 53 which has cavity 54- formed therein with outlet opening 55 communicating the cavity 54 with the atmosphere. The cavity 54 is of larger diameter than the ball 52 so the passageway from the chamber to atmosphere is open throughout movement of the ball 52.

As compared to the size of the port 59, the size (and therefore the weight) of the ball 52 is such that it will not be unseated unless the pressure in the port 50 is at least slightly greater than that needed on the diaphragm 21 to move the arm 31 sufficiently to close the con-tacts 29 and .30. By way of example, it has been found that a diameter steel ball has the proper Weight and works very well with a A3" diameter vent port. With such an arrangement, the valve, formed by the ball 52 and seat 510, remains substantially closed when lightweight cars roll over the left or remote end of the tube B, whereas the high impulses of air, caused by heavy trucks on the tube near the counter, unseat the ball and, by rapid venting, are greatly diminished. Because of the above, even the first wave of pressure never exceeds the required level to any appreciable extent.

Although the structure just described functions only when high impulses are generated in tube B, damping means operates at all times on both the reduced high impulses or the non-reduced lower pressure waves. As will be now detailed, in the present invention this latter aspect is accomplished by allowing the air to flow through an orifice in and out of the system in a controlled manner.

As mentioned above and explained below, the system damps most effectively if a somewhat restricted orifice is located in the end of the tube remote from the counter. However, the following provisions are made in order that the switch 3 may be used with conventional tubes which are closed at their remote ends; and in order that, under '5. certain conditions, the efiective responses due to remotely located orifice (when they are provided) may be modified.

As illustrated in FIGURE 3, a damper port 58 is provided in block 15 opening to the chamber 160 at a point spaced from the diaphragm 21. The block is counterbored at 57, and air from the co unterbore may pass to the atmosphere through passage 63 which extends through the block 115 into the counterbore from either side. Counterbore 57 is threaded to receive an adjustment screw 59. The screw 59 has a needle-shaped valve member 60 at its inward end which cooperates with the valve seat 60a. At the outer end of the screw 59 is a hand knob 61 against which coil spring 62 urges to take up slack in the threads. With this arrangement, the needle valve formed by port 58 and member 63 may be very accurately adjusted to establish the rate at which the air may flow through the port 53 between the chamber 160 and the atmosphere. The rate of flow which is individually proper to a given installation depends on local traffic conditions, the relative stiffness of the pneumatic tube, etc. It is also determinative of the setting of contacts 29 and 39 in selecting the lower limit of operative response as will appear.

As mentioned above, the most effective place for the port or orifice is at the tube end which is remote from the counter. When the orifice is so located, it is not always essential that port 58 be provided. If port 58 be provided, it may usually be completely closed by adjustment of valve plug 60. 'On the other hand, it is sometimes advantageous to utilize port 58 in a manner to be described, even though the remotely located orifice be primarily depended upon.

An orifice plug assembly P, as shown in detail in FIG- URE 5, represents a preferred, though not limitative, arrangement whereby a proper, remotely located damping orifice may be provided.

The plug assembly P comprises fitting 64 having a series of annular serrations 65 by which it is held securely to the tube B. The fitting 64 has an axial passage 66 extending therethrough and is provided with a threaded counterbore at its left end to receive threaded cap 67. Similarly to the cap 53, the cap 67 has a cavity 68 produced therein which is communicated to the atmosphere via damper port or orifice 69. In order to prevent any small particles of dirt from entering the tube B and reaching the interior of block 15, a filter screen 72 is held in position across the passageway 66 by the cap 67 and washers 70.

With given conditions prevailing, it is often possible to establish a proper rate of damping flow through orifice 69 by selecting a plug P having an orifice diameter which is of given extent with relation to the inside diameter of the selected tube B. For instance, under given conditions it has been found that if the inside diameter of tube B be from 0.167 to 0.25", the orifice 69 may have a diameter of 0.052"i-.005.

If it be found that the dampening flow is insufficient to give proper response, orifice 58 may be opened to varying extents to compensate the insuificiency provided, of course, that the particular involved instrument has such an orifice '58. However, in the immediately following discussion it will be assumed that orifice 58 is either absent or is fully closed when plug assembly P, with its orifice 69, is used.

The orifice 69 functions to rapidly damp certain pressure waves generated by vehicle wheels better than the port 58, for a significant reason. As mentioned previously, when a set of vehicle wheels crosses over tube B, a pressure wave emanates from the outer side of each of the wheels. One of the waves travels toward the counter end of the tube B and the second wave travels toward the tubes opposite end. If the orifice 69 is at that opposite end, a major portion of the second pressure Wave effectively passes from the tube B to the atmosphere. Although the residue of that wave is reflected back toward the switch end of the tube, the reflected portion will be of very low value in the first instance. Thereafter, the

quite satisfactory results in this case, also.

reflected wave is reduced further each time it reaches and is partially vented by the orifice 69. The portion of the one wave reflected from the diaphragm is likewise reduced.

On the other hand, if that opposite (or remote) tubeend is closed and orifice 58, only, is provided, then the second Wave is reflected with full force back toward the switch S to diaphragm 21. Although the reflected wave reaches the port 58 and, with valve 60 open, is damped by partial venting before passing to the diaphragm 21, there is no gain of benefit of venting near the source of the wave, as when orifice 69 is employed.

In operation, the tube B is laid across the desired lanes of traffic and anchored in a conventional manner. Then, the knob 27 is turned until the contact is, for instance, spaced about 0.010 from the contact 30 when the diaphragm is in the position of FIGURE 4. At that time, if the orifice plug P is not used, the adjustment screw 59 is turned to regulate the amount of bleed past the needle member 6t) so that a light car passing over the remote end of the tube B will just cause diaphragm 21 to close the contacts 29 and 30.

When the plug P is used, this latter adjustment is not made, but rather the needle 6%) is, at least originally, moved to the closed position, as mentioned above. At that time, the knob 27 is turned to move contact 29 sufficiently close to contact 30 so that the pressure of a light car passing over the remote end of the tube B will close the contacts. Except for situations where the tube is extremely long, a contact spacing of about 0.010 gives As noted above, there may be occasions when, if the instrument is provided with orifice 58, orifice 58 will be opened to varying extents to modify the response from orifice 69.

It is to be understood that, while the damper orifice formed by the port 53 or the orifice 69 rapidly damps the pressure waves within the tube B, also reduces the initial pressure wave, because the air is not compressed to as high a degree as would be the case if it were not provided.

This lessening of diaphragm-operating pressure may be taken into account by reducing the pre-set gap between contacts 29 and 30 when the device is in the condition of FIGURE 4. Since, due to the movement advantage spoken of above, the extent of movement of contact 30 is about twice as great as the corresponding extent of diaphragm movement, it is possible to adjust the gap with ease and nicety to agree with the prevailing diaphragm operating pressure.

With the system set up as described above, the wheels of a light car passing over the remote end of tube B will close the contacts 29 and 30 and the secondary oscillations of the generated pressure Waves will be quickly damped out. On the other hand, if a heavy truck should pass over the tube B at a point near the counter, the system will not doube count because a major portion of the excess of the initial high impulse will be vented around the ball 52, whereby the pressure impressed upon the diaphragm 21 will not be excessively greater than the pressure generated by the wheels of the light car at the remote end of the tube B. Further, the secondary oscillations of any pressure waves will be rapidly damped because of the orifice 69 or the port 58. This additionally insures against false counts.)

While a preferred system incorporating the present invention has been shown and described in detail, it will be apparent to those skilled in the art that such is by way of illustration, only, and numerous changes and modifications may be made thereto without departing from the spirit and scope of the present invention. Therefore, it is our intention that the present invention be defined solely by the appended claims.

We claim:

1. In a pneumatic control system: a body formed with an interior air chamber; a pair of cantilevered electrical contacts normally spaced apart; diaphragm means for moving said contacts together in response to pressure of a predetermined level in said chamber; vent port means selectively communicating said chamber with the atmosphere, said vent port means being normally closed and being responsive to pressure in said chamber to open and vent when said pressure exceeds said predetermined level of pressure; damper port means communicating said chamber with the atmosphere to allow a restricted flow of air between said chamber and the atmosphere, said damper port means opening to said chamber at a position spaced from said diaphragm; valve means for adjustably controlling the rate of flow of air through said damper port means; and connector means for attaching the open end of an air tube to said body and communicating air pressure in said tube to said chamber.

2. A pneumatic control system comprising: a collapsible tube adapted to be extended across a road and anchored, said tube having two ends and being filled with air; a pneumatically actuated switch connected to one end of said tube, said switch including a fixed contact secured thereto and a movable arm to which is attached a movable contact, said contacts being adjacent to one another, said switch having a flexible diaphragm having two opposed faces, one face of said diaphragm being in com munication with the pressure in the interior of said tube, the other face of said diaphragm abutting said movable arm whereby a predetermined pressure on said one face moves said movable contact against said fixed contact; a vent port communicating with the interior of said tube, vent valve means in said port for venting air from said port to the atmosphere only when the pressure in said port exceeds the pressure on said diaphragm necessary to close said contacts; damper port means communicating the interior of said tube with the atmosphere; valve means for adjustably controlling the rate of flow of air through said damper port means; and means forming a damping orifice at the unconnected end of said tube, said orifice allowing restricted air flow therethrough.

3. A pneumatically actuated switch comprising: a body having an interior chamber formed therein; a first electrical contact connected to said body; a flexible cantilever arm attached to said body; a second electrical contact secured to the free end of said arm, said second contact being juxtaposed with respect to said first contact; diaphragm means for moving said arm to actuate said switch, said diaphragm means abutting said arm only at an intermediate portion of the arm such that said first electrical contact moves approximately twice the distance said arm is moved by said diaphragm, said diaphragm means communicating with said chamber and moving said arm in response to an actuation pressure in said chamber; a counterbore formed in the top of said body; a vent port communicating said chamber with said counterbore, said vent port and counterbore cooperating to form an upwardly facing valve seat; a valve member in said counterbore engaging said valve seat and normally shutting off said vent port, said valve member being displaceable by pressure in said vent port; a cap extending across said counterbore, said cap having a passageway therethrough through which air may freely move from said counterbore to the atmosphere; a damper port formed in said body communicating said chamber with the atmosphere, said damper port having valve means therein for adjustably controlling the flow through said port; and means adapted to be connected to a tube and communicate actuation pressure in said tube with said chamber.

4. A pneumatic pulse pressure control system comprising: a collapsible tube adapted to be extended across a road and anchored, said tube having two ends and being filled with air; switch means which may be closed by a predetermined pressure on a diaphragm in said switch means, said switch means being connected to one end of said tube with said diaphragm communicating with said air within said tube; vent valve means in said switch means selectively communicating said air to atmosphere, said vent valve means being normally closed and being opened to vent by pressure of said air in excess of a pressure slightly greater than said predetermined pressure; damper port means communicating the interior of said tube with the atmosphere to allow a restricted flow of air therebetween; valve means for adjustably controlling the flow of air through said damper port means; a fitting connected to said other tube end, said fitting having a passageway formed therein and communicating the interior of said tube with the interior of said fitting; a restrictive orifice formed in said fitting extending between said passageway and the atmosphere; and a fine mesh screen located across said passageway between said orifice and said tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,231,561 Briggs July 3, 1917 2,104,632 Agnew Jan. 4, 1938 2,153,277 Sharp Apr. 4, 1939 2,251,180 Wesley et al. July 29, 1941 2,611,045 Wayman Sept. 16, 1952 2,702,840 Jackson et al Feb. 22, 1955 FOREIGN PATENTS 18,376/34 Australia Sept. 11, 1935 929,491 Germany June 27, 1955

Claims (1)

1. IN A PNEUMATIC CONTROL SYSTEM: A BODY FORMED WITH AN INTERIOR AIR CHAMBER; A PAIR OF CANTILEVERED ELECTRICAL CONTACTS NORMALLY SPACED APART; DIAPHRAGM MEANS FOR MOVING SAID CONTACT TOGETHER IN RESPONSE TO PRESSURE OF A PREDETERMINED LEVEL IN SAID CHAMBER; VENT PORT MEANS SELECTIVELY COMMUNICATING SAID CHAMBER WITH THE ATMOSPHERE, SAID VENT PORT MEANS BEING NORMALLY CLOSED AND BEING RESPONSIVE TO PRESSURE IN SAID CHAMBER TO OPEN AND VENT WHEN SAID PRESSURE EXCEEDS SAID PREDETERMINED LEVEL OF PRESSURE; DAMPER PORT MEANS COMMUNICATING SAID CHAMBER WITH THE ATMOSPHERE TO ALLOW A RESTRICTED FLOW OF

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