US2557902A - Pneumatically operated electrical switching device - Google Patents

Description

June 19, 1951 c. R. WOODLAND 2,557,902

PNEUMATICALLY-OPERATED ELECTRICAL SWITCHING DEVICE Filed Nov. 22, 1948 2 Sheets-Sheet 1 IN [/5 N TOR CECIL ROBERT WOODLAND.

A TTOR/VE Y.

June 19, 1951 c. R. WOODLAND 2,557,902

PNEUMATICALLY-QPERATED ELECTRICAL SWITCHING DEVICE Filed Nov. 22, 1948 2 Sheets-Sheet 2 IN l/E N TOR.

CECIL ROBERT WOODLAND.

A T TORNE).

Patented June 19, 1951 cmreo STATES PATENT omcr.

Pm'immmr .OPERATEDELECTRICATJ SWITCHING DEVICE Cecil Robert Woodland, Liverpool, England, assignor to Automatic Telephone & Electric Company Limited, Liverpool, England, a British company Application Noi e'iiilir 22, 1948, serial No. 61,428 In Great Britain December 12, 1 947 6 Claims. (01. 200-86) The present inventiofi relates to electric switchmg" devices suitable for operation by changes in fluid pressure andfinds particularly advantagousapplication to switching devices operated pneumatically by vehicles passing over a tread memberlocated in the road surface, Arrangemerits of this type are already known and are widely'employed as vehicle detectors for use in vehicle-actuated traii c controlsystems. s

Usually in such arrangements the tread mernher which is composed of rubber or similar re-' silient material-- includes a cavity the volume of which is varied as the vehicle passes over the detector so as to produce a momentary increase of pressure which: operates theswitching device. Such vehicle detectors are called uponto meet very stringent operating conditions since they must be sufliciently robust'to' withstand damageby heavy vehicles passing; at high speed while still being sufli'ciently sensitive to produce correct operation whentraver'sed by a light vehicle such as a bicycle: Moreover they require careful protection to ensure that; their eflicien'cy shall not be impaired by extremes of temperature and the effects-of moisture and accumulations of foreign matter on the road-. The general object of; the invention is-to produce a switching device which will meet these requirements more satisfactorily than thosehitherto employed and which will be cheap to manufacture; easy to'maintain' and reliable in o eration. 7

Aoeording' to the invention, in an electric switching device'suitable for operation-by changes i'n'iitiid pressure, a flanged diaphragm supported onand covering theend' of a circular pipe commuh icatin'g with a control chamber is arranged tobe' moved bodily by increase in the pressure of the'fiuid w'ithinthe chamber to cause it to" e'iiect a switching operation.

The invention'will be better understood from" thefo'llowing description'of one method of carry ing itinto eifect,"r'eferencebeing had to the accompanying drawings comprising Figs. 1 to 4. Fig; 1 shows aplan view of one form of fluid operated switch according to the invention, Fig. 2 sho'wsa cross sectional view on the line AA in Fi'gi 1 in the direction ofthe arrows, while Fig. 3 is'an'elevation viewed from the right of Fig. 1. Fig. iris apla'nv'iew of a pair of switches of the type'show'n'inFigs; 1-3' mounted within a cont'ainer to provide a unit which is particularly suitable for giving unidirectional working in a vehicle ac'tuated'traific control system.

Considering'now'FigsI 1, 2and 3, the cylindrical body I of the switching device which is prefer- 2 ably of brass has secured to it the inlet pipe II, which is assumed to be-coupled to a flexible tube extending to a cavity in the pneumatic tread member set in the road surface so that the tread cavity is connected with the chamber I2. A filter comprising a fine wire mesh disc I3 fitted in a circular frame accommodated in a recess of re chamber serves to prevent the passage into the upper chamber of unwanted particles which might interfere with the proper functioning of the switch. A ring I4 of electrically insulating material such as phenol fibre board separates the diaphragm support member I5 from the body I0. Sealing compound may be applied to the upper and lower surfaces of the insulating ring I4' to secure an air-tight joint. The member I5 is provided with a circular projecting portion or pipe l6 which is undercut on its outside circumferential surface and loosely supports the diaphragm H which is flanged so as to form a circular inverted shallow dish. The diaphragm which is lightly constructed is preferably or nickel silver but may be of other material having the requisite properties. It has a thin ring or disk I8 of platinum or other suitable contact material secured to its upper face and so positioned as to'co-operate with four dome-like contacts such as 21 when the" diaphragm is lifted bodily off its seating. The inside diameter of the diaphragm is a' few thousa-ndths of an inch greater than the greatest outside diameter of the undercut portion I6 so as to permit free movement and provide a-slight' air leak as will be described later.

The bridge member I9 of phenol fibre board or like insulating material is mounted on two pillars 2i! and packing sh-im's 23 and is secured by screws 2! which are threaded into the body It and carry washers'22.

the body II] by the inclusion of insulating sleeves (not shown) over a'portion of each screw in known manner.

The bridge I9 serves to support four similar afbolt 2s.

The contacts 27 are arranged to be equidistant from the ring I8'and according to a preferred adjustment the air'gap of the order of .005" whefri'the'di'aphragm' is'at rest. It will be apparent that the "open construction of the'swltch' enables the contacts to be viewed easily during The member I5 and the pillars 20 remain electrically insulated from the assembly and adjustment stages, and the airgap, which is determined by inserting shims 23 of suitable thickness, can be measured by inserting a feeler gauge.

When the switch is included in a vehicleactuated trafiic control system, it is sealed against atmosphere by enclosing it in a suitably dimensioned and hermetically sealed metal container. The pipe II, which protrudes through a wall of the container, is coupled to a flexible tube which extends to the cavity formed within a tread of resilient material which is inserted in the surface of the road and over which vehicles pass. In this manner the air within the container, the tread cavity and the connecting tubing is isolated from the external atmosphere to prevent the ingress of moisture and other foreign matter into those parts of the system.

The cavity within the tread member is compressed upon the passage of a vehicle and the pressure of air within it and the tube is increased relative to that within the switch container. Thereupon the diaphragm IT is lifted bodily off its seating after the manner of a piston and the ring I8 is caused to engage with the contacts 21 so that an electrical path is extended from one pair of linked contacts to the other pair to transmit a signal to the controller equipment. The diaphragm aided by gravity will subsequently fall back on to its seating when the vehicle passes clear and the air pressures on both sides of the diaphragm are again substantially equal. Due to the loose fit of the diaphragm on the member I air is enabled to flow from the cavity beneath the diaphragm into the switch container. Thus if a vehicle were to come to rest on the tread member the diaphragm would be lifted initially but would not remain in the operated position. Even if this should happen other vehicles passing over the pad will produce pulses of increased pressure which will cause normal operation of the diaphragm. This will not apply of course if the stationary vehicle closes the tread cavity completely and the further vehicles pass over the detector on the side remote from the equipment of Figs. 1-3.

The volume of the switch container is preferably appreciably greater than the volume of the tread cavity, the connecting pipe and the cavity I3 and the leakage round the edge of the diaphragm is such that the back pressure within the container does not equalise the forward pressure in the tread cavity until the aforesaid electrical path has been closed for a useful period. The leakage effect may be increased if found necessary by slotting the portion I6 of the diaphragm support member I5. The slight air leak just mentioned will tend to accentuate the efiect that when a vehicle passes clear of the detector there will be a sucking action which positively.

restores the diaphragm to its seating.

The mounting of the diaphragm I1 freely on the member I6 provides an electrical advantage in that it has been found that as the diaphragm is lifted and restored it tends to rotate slightly and in consequence differing positions of the contact ring I8 are continually being presented to the contacts 21. This arrangement together with the use of two pairs of contacts, appreciably reduces the electrical fault liability of the switch. 7 It will be apparent to those skilled in the art that alternative constructions of the switch might be employed, for example a single contact member could be mounted centrally upon the bridge I9 and a co-operating contact welded to the dia- 4 phragm to which a light flexible conductor could be connected. In this case a single make contact combination is provided and one conductor terminating on the controller equipment would be connected to the contact member on the bridge and the other conductor connected to the flexible lead.

Reference will now be made to Fig. 4 which is a plan view of two pneumatic switches 30 and 3I mounted within a container 32 which is finally hermetically sealed from atmosphere to provide a unit suitable for uni-directional working in a vehicle-actuated trafiic control system. The switches are secured to the container 32 by screws (not shown) passing through the base and the end plates 33 and 34 to fit snugly and are retained by airtight soldered joints. The inlet pipes I I, shown temporarily sealed by rubber caps 46, protrude through holes in plate 33. End plate 34 to which the terminal block housing is secured has four holes fitted with insulating bushes 35 which provide paths for the bare conductors connecting appropriate switch soldering tags and terminals. It may be mentioned that all possible air leakage paths in the container created by the jointing of metal members are sealed by a liberal application of solder. I

The terminal block housing 31, shown with the cover removed, is secured to the end plate 34 by the nuts and bolts 38 and 39 and is divided into two compartments 40 and 4| by the terminal strip 42 which is of insulating material such. as phenol fibre board. The said strip interlocks with the housing and carries four terminals 43 which are secured by the hollow screws 44 threaded into the terminals. The conductors 36 are each passed through a hollow screw and connect with a terminal at a soldered joint. Each terminal is provided with two screws 45 for clamping conductors extending to the controller equipment. Compartment 40 is filled with bitumen before the unit is installed to seal the bushed holes and to act as an electrical insulator and thus the container is completely sealed from atmosphere. The unit may be expected to have to work under arduous conditions, for example below the surface of the road or pavement, and is therefore liberally coated with bitumen on the outside surfaces.

When the unit is being installed, the rubber caps 46 are removed and the appropriate flexible tubes extending from the cavities in the pneu matic treads are securely coupled and sealed to the inlet pipes. The appropriate insulated conductors terminating at the controller equipment are stripped of insulation at the ends, passed through holes in the right-hand wall of housing 37 and secured to the relevant terminals 43 by screws 45. The whole of the stripped portion of the conductors is arranged to be within the compartment 4| which is then filled with bitumen for electrical insulation purposes before the cover is attached to the terminal block housing.

I claim:

1. A. pneumatically operated electric switching device comprising, in combination, a vertical tubular element, a diaphragm of a diameter slightly in excess of that of the tubularelement positioned normally to rest upon the tubular element, said diaphragm being provided with a downwardly extending flange arranged to sur-,

round the upper portion of the vertical tubular element, a pair of contact points supported in fixed position relative to the tubular element, a

contact member carried by said diaphragm, ter-v 2. The switching device claimed in claim 1,

wherein the contact member comprises a ring of contact material supported upon the upper surface of said diaphragm and wherein the pair of contact points fixed in position relative to the tubular member is located to be engaged by said ring when the diaphragm is moved upwardly so that a circuit is completed between the said pair of contact points.

3. The switching device claimed in claim 2 comprising, in addition, a bridge of insulating material fixed relative to said tubular member and spanning the said diaphragm, said contact points being secured to said bridge so that the clearance between said contact points and said diaphragm in its normal position is readily observable and accessible for tests.

4. A pneumatically operated electrical switching device comprising in combination a chamber member having an upwardly extending tubular section, a substantially circular diaphragm of slightly larger diameter than that of the tubular section positioned to rest in normal state upon the upper edge of the tubular section, said diaphragm having a downwardly extending flange surrounding a portion of the tubular section, a contact member carried upon the upper surface of said diaphragm, a pair of contact points supported from the said chamber member in fixed location relative thereto and positioned to be contacted by the contact member carried upon the diaphragm, a filter disk supported within the said chamber member to prevent the passage therein of unwanted particles, said chamber member having an entrance port beneath the filter for connection to a conduit in which fluid pressure is subject to change for influencing the instantaneous pressure within the chamber so that at periods of pressure increase within the control chamber the diaphragm supported upon the tubular member is lifted bodily upward to provide contact between the said contact member and the two said contact points and whereby pressure equalization above and below the diaphragm member is established coincidentally with the unseating of the diaphragm from the tubular section and terminal points for connecting an external circuit to the contact points so that during periods of actual contact thereof an electrical circuit may be brought into operation.

5. A detector for road vehicles including a re silient tread member mounted to be engaged by vehicles passing thereover, a longitudinal airfilled cavity forming a part of said tread member, the volume of said cavity being variable with passage of vehicles thereover, an electrical switching device connected with said tread member for operation in accordance with the changes in pressure in said tread member, said switching device comprising a circular pipe, a circular diaphragm of a diameter slightly larger than that of said pipe arranged to be positioned at the upper edge of said pipe, said diaphragm having a downwardly extending flange arranged to surround the upper section of said pipe, a pair of contact points fixedly positioned relative to said pipe, a contact closing member supported by said diaphragm in location relative to the pair of contact points such that upon movement of the diaphragm the contact points are brought electrically together, terminal points for connecting an electrical circuit to said contact points, and means provided by said diaphragm movement under changes in the volume of fluid within the container for causing the said contact points to meet and for returning the contact points to their normally open state by pressure equalization within and without the chamber due to leakage beneath the diaphragm at time periods of initiation of the contact.

6. A pneumatically-operated electric switching device comprising, in combination, a vertical tubular element, an electrically-conducting diaphragm of a diameter slightly in excess of that of the tubular element positioned normally to rest upon the said tubular element, said diaphragm being provided with a downwardlyextending flange arranged to surround the upper portion of the vertical tubular element, a pair of contact points supported in fixed position relative to the tubular element, terminal points for connecting an external electric circuit to the pair of contact points, and a conduit connecting said tubular element with a control chamber element so that at periods of increases in fluid pressure within the control chamber the diaphragm is caused to move bodily upward to engage the pair of contact points to effect an electrical switching operation.

CECIL ROBERT WOODLAND.

REFERENCES CITED UNITED STATES PATENTS Name Date Wiley Nov. 14, 1944 Number 2,362,874

Images