US2302982A - Magnetic switch for traffic detectors - Google Patents

Description

1942- s. EJSTRI CKLAND MAGNETIC SWITCH FOR TRAFFIC DETECTORS Filed June '7, 1941 IIIIIIIIIIIIIIIII IIIIIIIIIII II I IN V EN TOR. Genoa/v E. Ste/cm ND nil;

A TTOENEYS.

Patented Nov. 24, 1942 UNITED STATES PATENT OFFICE MAGNETIC SWITCH FOR TRAFFIC DETECTORS 9 Claims.

The present invention relates to a magnetic switch for trailic detectors, or more specifically for devices used in detecting the approach or passing of motor vehicles, and is designed particularly for use in service stations or the like to apprise an attendant of the presence of a patron desiring service.

Many different types of devices have been used for producing an audible or Visible signal upon the approach of an automobile to a service station, and the most commonly used types comprise fluid filled hoses or other mechanical means over which the automobile passes to create the desired signal. These types are undesirable in that they are exposed and usually produce a hazard to pedestrians, who may stumble over them, and they are subject to mechanical wear, and interfere with proper cleaning of the pavement or driveways in which they are situated. Various electrical signaling devices have also been proposed employing the principles of induction and magnetism, but are impractical because they are It is the object of the present invention to provide a magnetic switch for a traflic detector which overcomes all of the disadvantages set forth above, and which is relatively simple in construction. and inexpensive to manufacture, install and maintain. It is a further object of the invention to provide a device of this character, in which the friction of all moving parts is reduced to an absolute minimum, and which will be sensitive to the movement of a motor vehicle within a reasonable distance of the point where it is installed, and regardless of fixed magnetic bodies in its vicinity, or even of motor vehicles which have been brought to a stop in its immediate vicinity. A still further object is the provision in a sensitive device of this kind of means to prevent its operation by the movement in its vicinity of small magnetic bodies, or movement at a great distance from it of large magnetic bodies, and to provide a device which will effect positive closing of a circuit upon passing of a motor vehicle without oscillating in a manner to make and break the circuit repeatedly.

The manner in which these objects are at-- tained, as well as further objects and advantages of the invention, are made apparent in the fol- Fig. 1 is a vertical transverse sectional View of a magnetic switch embodying the present invention;

Fig. 2 is an enlarged view in perspective portion of the mechanism illustrated in Fig. 1;

Fig. 3 is a perspective View of a modified form of the contact mechanism illustrated in Figs. 1 and 2; and

Fig. 4 is a sectional view illustrating the manner of use of the contact members shown in Fig. 3.

The magnetic switch of the present invention is shown as contained in a housing l0, preferably cylindrical in shape, and closed by a cover member H, which may be sealed in place by any suitable means and which, if desired, may be constructed to admit to the interior of the housing an inert gas for example nitrogen under pressure to decrease arcing between electric contacts carried within the housing. A bar magnet I2 is disposed within the housing and supported for oscillatory movement about a central vertical axis therein. In order to maintain the axis of the magnet l2 vertical, regardless of any slight irregularity in the position of the housing l0, and also to reduce to a minimum any frictional resistance to the turning of the magnet, it is supported within a rectangular frame 13, which is suspended from the center of the cover H by a universal connection 54, as shown. The rectangular frame l3 may, to facilitate perfect balance, be formed of two members similar to that shown, disposed at right angles to each other and crossing at their centers at the point of intersection of the axis about which the magnet oscillates. The magnet is secured, as by a screw I5, to the upper end of an elongated cylindrical vertically disposed fioat It, made preferably of very light non-magnetic material, and the magnet and float are suspended for oscillation within the frame I3 between pivot bearings, one of which is shown at I! at the lower end of the float, and the other of which is shown at IS. The upper bearing 18 which receives the pivot pin I9 is in the form of a metal block threaded into a di-electric block 28, wh ch is retained centrally of the magnet by the same screw l5, which screws the magnet to the float It. The pin [9 is insulated from the frame l3 by a di-electric bushing 2!. The housing it] contains a liquid, as shown, which is preferably carbon tetra-chloride or other liquid having a relatively high boiling point for liquids of this general character to prevent condensation, of high specific gravity, and a good di-electric in case it wets the contact points within'the housing,

due to condensation or other causes. The housing is filled with this liquid to a level at which its buoyant effect on the float IS, the magnet I2, and other parts carried thereby is sufficient to reduce to a minimum any pressure on the pivot bearings, about which the magnet oscillates. The elongated cylindrical float I 5, in this construction, presents the advantages that a great portion of its area may be immersed in the liquid without bringing the magnet or other parts too close to the liquid, and also its outer cylindrical wall is, due to its shape, so close to its axis of rotation that very little resistance is set up by friction of liquid on its outer surface to oppose its turning movement. A vane 22, formed of light non-magnetic material, is immersed in the liquid and supported by an arm in the form of a light wire 23, which is formed at an angle, so that one end of it overlies the top of the magnet where it is supported by an eye 24, in a balanced position, while its free end extends into a small recess 25 in one side of the di-electric block 20. An offset 26 is formed in the arm 23 to prevent its endwise movement through the eye 24, and the eye is set in a di-electric block, shown in dotted lines at 21, so as to insulate it from the magnet. Adjacent its upper end the arm 23 carries a small metal plate 28, normally disposed in a vertical plane, and spaced between parallel metal plates 29, which project outwardly from the side of the di-electric block 20, as best illustrated in Fig. 2. The guide wire 30 is supported by the float l6 and looped at its end, as shown at Si in Fig. 2, within the downwardly extending portion of arm 23 to limit the magnitude of its oscillatory movement. One of the plates 29 is connected by a wire, or other conductor 32, with the pivot bearing it, which preferably contains sufiicient mercury to complete a circuit to the pivot pin 19, and thence through a wire 34 to a binding post 35, which extends through and is insulated from the cover member H. The other of the plates 29 is connected as by a wire 36 (see Figs. 1 and 2) with the float [6, which through its lower pivot bearing, the frame I3, and universal connection i4, completes a circuit to a binding post 3'1, which is not insulated from the cover I I.

In practice the device described above is buried just below the surface of the pavement in a service station at whatever point in the driveway that it is desired to have the passing of an outomobile actuate a signal. As the effective range of the device is limited, it may be necessary in wide driveways to employ more than one device, and where there is more than one driveway the device may be employed in whatever number is necessary and desirable. The binding posts 35 and 3'1 are connected as by conductors 49 and 4! in the switch circuit of a relay which controls an electric signal, such for example, as a bell or electrically actuated gong (not shown) As these conductors 4E] and M form the only connection with the signal, and as the electric current necessarily carried by them is small, they may be inexpensively concealed by being embedded a slight distance in the pavement where it is necessary that they cross any part of the drive.

An automobile is, of course, a magnetic body, and possesses magnetic polarity. Hence when it passes the switch of the present invention embedded slightly below the surface of the driveway, it oscillates the bar magnet 12, it being understood that this magnet normally assumes alignment with the terrestrial magnetic flux subnormal to again break the switch circuit.

ject to what deviation may be caused by proximate magnetic bodies. The efiect on the magnetic bar l2 by a passing automobile is to cause it to oscillate about the vertical axis upon which it is suspended, and during this oscillation the vane 22 is carried with the bar, but its movement is resisted by the fluid in which it is immersed, with the consequence that it effects swinging of its support 23 with a resultant turning of the small plate 28 about a longitudinal axis causing this plate to engage and close a circuit between the two contact plates 29. This effects closing of the switch circuit, which includes the binding posts 35 and 31 in the manner set forth above, and therefore actuates the electric signal, which apprises the attendant of the service station of the presence of the automobile.

The present invention overcomes the undesirable repetition of switch closing, which ordinarily results from oscillation of the magnet in a device of this kind, because of the fact that the oscillations which precede return of the magnet to its normal position after passing of the automobile are less forceful, and therefore permit the vane 22, which also acts as a damper to these movements, to remain substantially in its vertical position, so that the plate 28 is not turned to a contact making position. Another advantage of o the structure shown herein is that an automobile brought to a stop in the immediate vicinity of the switch does not cause continued closing of the switch circuit even though it may hold the magnet bar 12 away from its normal position. This results from the fact that after initial closing of the switch by swinging movement of the magnet bar, and retarded movement of the vane 22, the vane which has been swung slightly away from its normal vertical position gravitates to If a car remains parked adjacent the switch it acts as any other fixed magnetic body, and the position to which it deflects the magnet part l2 then becomes normal, and any other automobile passing the switch will deflect the magnet bar from its new, or temporarily normal position, suillciently to actuate the switch through the medium of the vane 22 in the same manner as described above.

In Figs. 3 and 4 a modified form of the invention is illustrated, showing a structure in which the contact points of the switch are selfcleaning. In these figures the upper end of the member 23, which supports the vane 22 is guided in a pivot bar 45, which is formed Divotally with the head of a screw 46, and in this case serves to secure the magnet bar l2 to the float IS. The upper pivot pin 41, which is received by this bar, is embraced by a metallic sleeve 48, which is spaced from the pivot pin by a dielectric bushing 49. An arm 50, carried by the upper horizontal portion of the member 23, which carries the vane 22, supports a U-shaped contact member 5| in a position spaced slightly from the sleeve 48. The sleeve 48 is connected by a wire 52 with one binding post, which is included in the switch circuit (one binding post, not shown, which is included in the switch circuit) and a wire 53 connects the pivot pin 41 with the other binding post, consequently, when the vane switches from its normal vertical position the U-shaped member contacts the sleeve 48, and closes the switch circuit through the medium of the arm 50, the upper portion of the member 23, and the pivot pin 41. A positive electric connection between the pivot pin 41 and the arm 23 is preferably insured by a drop of mercury in the pivot bar 4-5. In this modified switch structure the contact is made by the contact members 48 and 5! during oscillatory movement of the magnet bar 12, with the result that the consequent wiping action between contact points automatically keeps them clean and bright.

In the normal operation of either of the two modifications disclosed herein the passage of an automobile will effect suiiiciently forceful oscillation' of the magnet to close the switch twice; once on the movement of the magnet away from the normal and once again on its return movement. The oscillation will seldom, if ever, be sufficient to efiect three or more closings of the switch.

Another advantage of the structures disclosed is that no foreign magnetic body, such as an automobile jack or other garagemans tool left in a position adjacent the switch will effect its operation because of the fact that the magnet will orient itself to the influence of the foreign body, and the vane will, under the force of gravity, assume its normal vertical position with the switch open, and a passing automobile will produce the desired result upon the magnet in any position which it may have been caused to assume.

The arm 23, which supports the vane while shown as supported pivotally from above the magnet part 12, may as well be suspended from beneath the bar by changing the relative positions of the bar it, and the di-electric block 20, as shown in Fig. 1, and various other modifications in the construction and the arrangement of the several parts herein shown and described may be made within the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. A magnetic switch closing device comprising, a magnet adapted to be oscillated by a magnetic force in its vicinity, a vane carried by the magnet and supported for pivotal movement relative thereto and immersed in a liquid, and a switch actuated by pivotal movement of the vane relative to the magnet, whereby resistance of the liquid to movement of the vane will actuate the switch upon movement of the magnet.

2. A magnetic switch closing device comprising, a magnet pivoted for swinging movement in a horizontal plane, and adapted to be oscillated by a magnetic force in its vicinity, a body of liquid underlying the magnet, 21. vane supported by the magnet for swinging movement and depending into the liquid whereby pivotal movement of the magnet will cause swinging of the vane, and a switch closed by swinging of the vane relative to the magnet.

3. In a magnetic switch closing device, a housing adapted to contain liquid, a magnet disposed above the liquid level in the housing and adapted to be oscillated by the magnetic force in its vicinity, an elongated cylindrical vertically disposed float partially immersed in the liquid and supporting the magnet at its upper end, and pivot bearings mounting the magnet and float and aligned with the vertical axis of the float.

4. In a magnetic switch closing device, a housing adapted to contain liquid, a magnet disposed above the liquid level in the housing and adapted to be oscillated by the magnetic force in its vicinity, an elongated cylindrical vertically disposed float partiall immersed in the liquid, and supporting the magnet at its upper end, and pivot bearings mounting the magnet and float and aligned with the vertical axis of the float, and a support for said pivot bearings depending for free swinging movement from the top of the housing.

5. In a magnetic switch closing device, a housing adapted to contain liquid, a magnet disposed above the liquid level in the housing and adapted to be oscillated by the magnetic force in its vicinity, an elongated cylindrical vertically disposed float partially immersed in the liquid and supporting the magnet at its upper end, and pivot bearings mounting the magnet and float and aligned with the vertical axis of the float, a vane disposed in the liquid and pivotally sup ported relative to the magnet whereby it will swing upon oscillation of the magnet, and a switch adapted to be closed by swinging movement of the vane.

6. In a magnetic switch closing device, a magnet mounted for oscillation in a horizontal plane over a body of liquid and adapted to be oscillated by a magnetic force in its vicinity, a vane depending from said magnet normally vertically into said liquid and mounted for limited swinging movement, and a switch adapted to be closed upon swinging of the vane away from vertical and opened upon return of the vane to its vertical position.

'7. In a magnetic switch closing device, a bar magnet mounted for oscillation in a horizontal plane over a body of liquid and adapted to be oscillated by a magnetic force in its vicinity, an arm pivotally mounted over and substantially parallel to the bar and having an end depending into the liquid, a vane carried by said end whereby oscillation of the magnet will swing the arm in its pivotal support, and a switch closed by such swinging of the arm.

8. In a magnetic switch closing device, a pivoted magnet adapted to be oscillated by a magnetic force in its vicinity, a pair of spaced contact plates fixed relative to the magnet, a pivoted plate disposed between said spaced plates, a vane carried by the magnet and depending into a liquid whereby pivotal movement of the magnet will effect swinging of the vane, and means whereby such swinging of the vane will swing said pivoted plate into bridging contact with said spaced contact plate.

9. A magnetic switch closing device comprising a pivoted magnet adapted to be oscillated by a magnetic force in its vicinity, a vane supported for pivotal movement relative to the magnet, a switch, means whereby said relative movement of the vane and magnet will effect closing of the switch, said vane being immersed in a body of liquid to damp its movement whereby upon movement of the magnet the vane will be retarded to produce the said relative movement of the vane and magnet and effect closing of the switch.

GORDON E. STRICKLAND.

Images