US3758733A

US3758733A - Ric material and conductive particles therein pressure sensitive stepping switches with multi layer spring contact assembly with interposed layers of lubricated non-conductive elastome

Info

Publication number: US3758733A
Application number: US00185957A
Authority: US
Inventors: G Durocher; D Durocher
Original assignee: Essex International Inc
Current assignee: Lear Corp EEDS and Interiors; ExxonMobil Oil Corp
Priority date: 1971-10-04
Filing date: 1971-10-04
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11
Also published as: FR2156039A1; FR2156039B1; JPS5112822B2; DE2248635B2; DE2248635A1; IT974649B; JPS4872669A; GB1375939A; DE2248635C3; CA968836A

Abstract

A pressure sensitive stepping switch comprises a stack of resiliently compressible, normally non-conductive elastomeric pads throughout each of which a quantity of electrically conductive particles are dispersed. Straddling each pad is a pair of conductors for connection to a source of electrical potential and to an electrical device to be operated. The pads are rendered electrically conductive in response to compression of the stack, the compressive force required to render each pad conductive being different so as to enable the pads to be rendered conductive in a predetermined sequence. Oil applied to the surface of the pad greatly increases its life.

Description

ite

v States Patent [1 1 Durocher et al.

[ Sept. ll, 1973 3,290,472 12/1966 Savage 200/166 C 3,125,739 3/1964 Deibel et al. ZOO/86.5 X 2,430,829 1 1/1947 Sepavich 200/166 C X 2,752,558 6/1956 Kane 200/166 C UX 736,048 8/1903 Wirt 200/166 G UX 12/1970 Loughran, Jr. 200/153 LB X Primary ExaminerJ. R. Scott [75 Inventors: GIIIBOH A. J. Atlorney-Learman and McCulloch DuRocher, both of Mt. Clemens, Mich.

[73] Assignee: Essex International, Inc., Fort {57] ABSTRACT Wayne, 1nd. A pressure sensitive stepping switch comprises a stack F'lcd: 1971 of resiliently compressible, normally non-conductive [2] APPL 1 5 957 elastomeric pads throughout each of which a quantity of electrically conductive particles are dispersed.

4 Straddling each pad is a pair of conductors for connec- |52l zoo/82 zoo/82 ZOO/83 tion to a source of electrical potential and to an electri- ZOO/159 ZOO/166 200,166 G cal device to be operated. The pads are rendered elec- IIIL CI. ny conductive in response to compression of the [58] Field of Search 200/86.5, 166 C, Stack the compressive force required to render each 200,166 153 L3, 83 159 81 82 pad conductive being different so as to enable the pads 82 83 J to be rendered conductive in a predetermined sei quence. Oil applied to the surface of the pad greatly in- [56] References Cited creases its life j UNITED STATES PATENTS 3,509,296 4/1970 Horshman et al'.. 200/159 R 19 Claims, 7 Drawing Figures 5 108 I 15 U l0 0 9O |0|||8- lZl "6 50 WARNING [62 MOTOR 48; 49 |4 l8 Z I, 5/ l3 7 2 2 m NW1? 7 0 2 w 4 w. 2 4 3 5 v r. 9 2 6 4 w. 3 7

a a TV 0 3 O 8 VPATENTEDSEPI 1 ms LEFT FRONT RIGHT REAR RIGHT FRONT FIG! INVENTORS GIDEON A. DUROCHER BY DANIEL J. DUROCHER ATTORNEYS LEFT REAR PATENTEDSEH 1197a 3-758733

sum

2 or 2 INVENTORS GIDEON A. DUROCHER DANIEL J- DUROCHER ATTORNEYS PRESSURE SENSITIVE STEPFING SWITCHES WI'III MULTI LAYER SPRING CONTACT ASSEMBLY WITH INTERPOSED LAYERS F LUBRICATEI) NON-CONDUCTIVE ELASTOMERIC MATERIAL AND CONDUCTIVE PARTICLES TIIEREIN This invention relates to pressure sensitive stepping switches of the kind adapted to effect sequential operation of a plurality of electrical devices in response to the application of a progressively increasing force. The switches may be converted from conductive condition to non-conductive condition, eithersimultaneously or sequentially.

There are many instances in which it is desirable to effect operation of a plurality of electrical devices in a predetermined sequence or order. For example, a vehicle may have a plurality of direction signaling lamps which are flashed sequentially to signal the vehicle driver's intention to make a turn. The switching mechanisms heretofore provided for such sequential direction signal devices have required a considerable number of movable switching parts, relays, flashers, and associated electrical components, thereby resulting in a complex and expensive assembly.

Another example of the applicability of a stepping switch of the kind with which the invention is concerned is a pressure sender device for an automotive vehicles oil pressure gauge. Such a gauge conventionally utilizes an electrically operable indicator which is responsive to changes in oil pressure to indicate whether the oil pressure is high, low, or in a safe operating range. A pressure sender device conventionally has a wire wound resistor to vary the current in the circuit of the gauges indicator so as to affect the position of the gauge indicator. Pressure gauges of this kind in use heretofore have utilized fairly expensive and somewhat fragile mechanisms such as wire wound rheostats, pivots, torsion return springs, and the like, which, although enabling the gauge to be operative within rather wide tolerances, have presented objectionable assembly and maintenance problems.

An object of this invention is to provide a stepping switch for operating in predetermined sequence a plurality of electrical devices and which overcomes the disadvantages of previously known switches for similar purposes.

Another object of the invention is to provide a stepping switch construction having a plurality of on-off switching members composed of resiliently compressible pads convertible from conductive to nonconductive condition, andvice versa, solely in response to the applying and relieving of compressive force.

A further object of the invention is to provide resiliently compressible stepping switches of the character referred to and wherein the sensitivity of the switches may be varied within wide limits and in a number of different ways. 3

Another object of the invention is to provide a resiliently compressible on-off switch provided with a lubricant which greatly increases the electrical life of I the switch. A further object of the invention is to provide a stepping switch of the character described and which itself is capable of handling large current loads, thereby avoiding the necessity of using relays and the like.

Another object of the invention is to provide a stepping switch for a vehicles signaling system and which avoids the necessity for the use of flashers.

Other objects and advantages of the invention will be pointed out specifically or will become apparent from the following description when it is considered in conjunction with the appended claims and the accompanying drawings, in which: FIG. 1 is a schematic diagram of a sequential direction signaling circuit for an automotive vehicle and in which stepping switches constructed according to the invention are included;

FIG. 2 is a side elevational view of an oil pressure sender assembly incorporating a stepping switch constructed in accordance with the invention;

FIG. 3 is a vertical sectional view of the sender and taken on the line 3-3 of FIG. 4;

FIG. 4 is a transverse sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is a side elevational view of a part of the sender;

FIG. 6 is an enlarged, plan view of a three-element .resistor incorporated in the sender assembly; and

FIG, 7 is a schematic wiring diagram of a typical oil pressure gauge and sender circuit.

The circuit illustrated in FIG. 1 constitutes a combined sequential direction signaling circuit, a hazard warning circuit, and a stop warning circuit adapted for use on a motor vehicle having three right-rear lamps l, 2, and 3, a right-front lamp 4, three left-rear lamps 5, 6, and 7, and a left-front lamp 8'. A direction signal operating switch 9 of conventional construction includes a movable right turn bridging contact 10 which in the inactive position of the operator 9 bridges a pair of fixed contacts 11 and 12 and which, when moved left to the dotted line position, bridges three fixed contacts 11, 13, and M. The switch operator 9 also includes a movable left turn bridging contact 15 which, in the inactive position of the operator, bridges fixed

contacts

16 and 17 and which, when moved to the dotted line position, bridges fixed contacts 13, I7, and 18.

The contact 13 is connected by a wire 19 to the positive terminal of a battery (not shown) or other source of electrical potential; The contacts 11 and 17 are connected by

wires

20 and 21 to the positive terminal of the source through a normally open brake pedal operated switch 22. l

The contact 12 is connected'by a wire 23 to the filament lead 240i the lamp 1.

Wires

25 and 26 connected to the wire 23 also connect the terminal 12 to filament wires 27a and 28, respectively, of the lamps 2 and 3. A diode 27 is interposed between the contact 12 and each of the lamp filament wires to prevent current flow in a direction from the lamps toward the contact 12.

The contact I6 is connected by a wire 28 to the filament wire 29 of the lamp 5. Wires 3t) and 31 also connect the wire 28 to the filament wires 32 and 33, respectively, of the lamps 6 and 7. Diodes 34 are interposed between the contact I6 and the filament wires of the lamps 5, 6 and 7 to prevent the flow of current in a direction from the lamps toward the contact 16.

, The construction of the apparatus thus far described is such that, when the direction switch operator 9 is in its normal or inactive position as shown in full lines in FIG. ll, none of the lamps 1-3 and 5-7 is illuminated. When the switch 22 is closed, however, by the vehicle driver's depressing the brake pedal, a circuit will be completed to the filaments of lamps 1, 2, and 3 from the power source via the switch 22, the wire 20, the

contacts

10, 11, and 12, and the

wires

23, 25, and 26 to the filament wires of the lamps. A circuit also will be completed from the power source to the filaments of the lamps 5, 6, and 7 via the switch 22, the

wires

20 and 21, the

contacts

15, 16, and 17, the

wires

28, 30, and 31, and the filament wires 29, 32 and 33. Closing of the switch 22, therefore, will illuminate all of the vehicle's rear lamps simultaneously to give warning that the vehicles brakes have been applied.

The fixed contact 14 is connected by a wire 35 to a terminal 36 to which four

additional wires

37, 38, 39, and 40 also are connected. The fixed contact 18 is connected by a wire 41 to a terminal 42 to which four

additional wires

43, 44, 45 and 46 also are connected. The

contacts

14 and 18 are connected to a common terminal 47 by means of

wires

48 and 49, respectively, in each of which is a diode 50, the diodes permitting current flow from the

contacts

14 and 18 in a direction only toward the terminal 47. To the terminal 47 is connected one end of a conductor 51, the other end of which is connected to the winding of an electric motor 52 having a rotatable shaft 53 indicated by the dash line.

A hazard warning switch 54 has two

terminals

55 and 56 connected by

wires

57 and 58, respectively, to the

contacts

14 and 18. The switch 54 has a first movable contact 59 that is adapted to bridge the terminals 55 and- 56, and a second movable contact 60 that is adapted to engage a fixed terminal 61 which is connected by a wire 62 to the line 19. The contacts 59 and 60 are joined by a conductor 63.

The construction and arrangement of the hazard warning switch 54 and its associated parts are such that, when the switch 54 is moved from its normally open position, as shown in FIG. 1, to its closed position, the motor 52 is energized from the power source via the line 62, either of the

wires

57 and 58, and the conductor 51 so as to effect rotation of the motor shaft 53, for a purpose presently to be explained.

The construction and arrangement of the direction signal operating switch 9 and its associated parts are such that, when either of the movable contacts or is moved from its normally inactive position, as shown in full lines in FIG. 1, to an operative position, as shown in dotted lines, the motor 53 will be energized via the line 19, the contact 13, the associated

contact

10 or 15, the

appropriate wire

48 or 49, and theconductor 51. The motor shaft 53 thus will be rotated for a purpose hereinafter to be explained.

In circuit with the right-rear lamps 1, 2 and 3 and with the right-front lamp 4 is a stepping switch 64 constructed in accordance with the invention, and comprising four independent, resiliently

compressible pads

65, 66, 67,v and 68 arranged in a stack. On opposite sides of the pad 65 is a pair of

conductive plates

69 and 70, on opposite sides of the pad 66 is a pair of conductive plates 71 and 72, on opposite sides of the pad 67 is a pair of

conductive plates

73 and 74, and on opposite sides of the pad 68 is a pair of

conductive plates

75 and 76. Between the plates 70 and 71 is an insulator 78, between the plates 72 and 73 is an insulator 79, and between the

plates

74 and 75 is an insulator 80. The component parts of the switch are supported in a suitable tubular container (not shown) which is secured in a convenient manner to a fixed support 77.

The plate 69 is connected to the filament wire 24 of the lamp 1, the plate 70 is connected to the wire 37, the plate 71 is connected to the filament wire 27a of the lamp 2, the plate 72 is connected to the wire 38, the plate 73 is connected to the filament wire 28 of the lamp 3, the plate 74 is connected to the wire 39, the plate 75 is connected to the wire 40, and the plate 76 is connected to the filament wire 81 of the lamp 4.

in circuit with the vehicles left hand lamps 5-8 is a switch 64a which is identical in all respects to the switch 64, and corresponding parts are identified by the same reference characters, followed by the suffix a.

The motor shaft 53 mounts a cam 82 having a pair of similar lobes or risers 83 spaced apart from one another by a pair of dwell areas 84. The cam 82 is mounted between the two switches 64 and 64a and in such manner that rotation of the cam causes the lobes 83 to bear against the

plates

69 and 69a so as simultaneously to subject the pads of each stack to progressively increasing compressive forces. The lobes and dwells of the cam are so shaped that the compressive force exerted by the cam on the switches 64 and 64a is relieved substantially instantaneously following maximum compression of the pads.

The pads constituting part of each switch preferably are formed of an electrically non-conductive, resiliently compressible, elastomeric material such as silicone rubber'and throughout which a plurality of electrically conductive particles are dispersed. The particles preferably are spherical and are composed of a base metal such as copper or the like, coated with a noble metal such as silver which, upon oxidation, forms an electrically conductive oxide. The size and quantity of the particles contained in each pad may vary, as sub sequently will be explained, but the size and quantity of the particles contained in each pad should be such that, when the pad is in an uncompressed state, the particles do not form a conductive path through the pad. When the pad is compressed, however, the size and quantity of particles contained therein should be such that a sufficient number thereof move into engagement so as to establish a conductive path through the pad and permit current to flow from one conductive plate through the pad to the other. The size of the particles will vary according to the current load which must be carried. Generally, particle sizes ranging from 0.005 to 0.045 inch in diameter will accommodate automotive vehicle current values.

The sensitivity of any one of the pads in a stack may be varied in any one of a number of ways. For example, the compressibility and hence the sensitivity of a pad is inversely proportional to the density and the area of the elastomeric material. The sensitivity of a pad also depends on its thickness and the quantity of conductive particles it contains. Thus, if two pads of different thickness contain the same number of particles, the thicker pad will be less sensitive than the thinner pad because the thicker pad must be compressed. to a greater degree before it can be rendered conductive. In addition, a pad containing a larger number of particles, or particles of a smaller size than the number and size of particles of an otherwise identical pad, will be rendered conductive under less compressive force than the other pad.

Any one of the foregoing factors, or a combination thereof, may be utilized to obtain pads having the desired electrical sensitivity. For purposes of illustration,

all of the pads in the switches 64 and 64a are shown as being of the same thickness, but having different size and a different quantity of conductive particles therein. Thus, the most sensitive pad may have particles of approximately 0.005 inch in diameter and constituting about 85 90 weight percent of the pad. The least sensitive pad may have particles of about 0.045 inch in diameter and constituting about 75 weight percent of the pad. The size and quantity of particles in the other pads should be so selected that the sensitivities of such other pads are between those of the most and least sensitive pads.

in the embodiment shown in FIG. 1, the right-rear lamp 1 is located at the inboard side of the vehicle, the right-rear lamp 3 is located at the outboard side of the vehicle, and the rear lamp 2 is located between the lamps l and 3. The lamp 4 is located at the right front of the vehicle. If the lamps 1, 2, and 3 are to signal a right-hand turn, therefore, the lamp 1 should be illuminated first, the lamp 2 illuminated second, and the lamp 3 illuminated third. The right front lamp 4 may be illuminated to indicate a right hand turn without regard to the sequence of the illumination of the lamps ll, 2 and 3.

To obtain the proper sequence of illumination of the lamps 1, 2, and 3, the pad 65 should be rendered conductive first, the pad 66 should be rendered conductive second, the pad 67 should be rendered conductive third, and the pads 65 and 66 should remain conductive at least until the pad 67 is rendered conductive. The pad 65 thus should be the most pressure sensitive, the pad 67 should be the least pressure sensitive and the sensitivity of the pad 66 should be between those of the

pads

65 and 67. The sensitivity of the pad 68 may correspond to the sensitivity of any of the other pads.

The sensitivity of the pads 65a, 66a, 67a and 68a should correspond to the sensitivities of the

pads

65, 66, 67, and 68, respectively.

To signal a right-hand turn, for example, the direction switch operator 9 is adjusted so as to shift the movable contact 10 from the full line position shown in FIG. 1 to the dotted line position. The motor 52 thus will be energized so as to impart rotation to the cam 82. As the cam rotates, one of the lobes 83 will engage the plate 69 and subject the entire stack of pads to compression. The compressive force exerted on the stack of pads increases progressively as the cam rotates so as to render the

pads

65, 66, and 67 conductive in succession and effect sequential illumination of the lamps l,

- 2, and 3. The lamp 4 also will be illuminated via the pad 68. Inasmuch as the compressive force applied by the cam to the stack of pads in the switch 64 increases progressively, any pad rendered conductive will remain conductive until the compressive force is relieved.

When the cam 82 rotates to a position in which the lobe 83 begins to move away from the plate 69 the compressive force on the pads of the switch 64 is relieved virtually instantaneously, thereby enabling the inherently resilient pads to expand and cause the current path-forming particles to disengage one another and break the conductive path through each path. The substantially instantaneous relieving of the compressive force on the pads thus enables all of the lamps to be extinguished simultaneously. Continued rotation of the cam thus will cause the signaling lamps to flash on and off without the need for a flasher.

The cam 82 is so located that it engages both of the switches 64, 64a simultaneously. Since movement of the movable contact 10 to the right turn indicating position has no effect on the position of the movable contact 15, however, compression of the stack of pads in the switch 64a by the cam 82 has no effect on the lamps 5-8. it will be understood, however, that movement of the switch operator 9 to the left turn indicating position will effect movement of the contact 15 to the dotted line position shown in FIG. 1 so as to enable the signaling lamps 5-8 to be flashed.

If the hazard warning switch 54 is moved from the inactive position shown in FIG. 1 to its operative position, the motor 52 will be started so as to drive the cam 82. Under these conditions compression of the pads in the switches 64 and 64a will cause both the left-hand and the right-hand sets of signaling lamps to be flashed simultaneously, thereby providing a warning signal which is different from the turn indicating signal.

The examination of switches constructed in accordance with the invention and following many thousands of cycles of operation has shown a tendency for a thin layer of oxidation to form at the interface between a conductive pad and one or both of its associated conductive plates. It is believed that the oxide film is the result of arcing between conductive particles or between the particles and the conductive plate when the pad transitions from conductive state to nonconductive state. In time the oxide film will impair the conductivity of a pad. Impairment of the, conductivity has been prevented, however, by introducing a thin film of liquid lubricant, such as machine oil, between the conductive pad and the conductive plates. The lubricant itself thus forms the interface between the pad and the conductive plates and quenches the arc.- Any residue from arcing is suspended in the oil film.

, The embodiment of the invention illustrated in FlGS. 2 7 comprises an oil pressure sender or transmitter T for internal combustion engines and comprises a hollow, metallic housing having a top wall 91 and a depending ski'rt 92. The housing accommodates a base 93 formed of insulating material and which is maintained in'assembled relation with the housing by crimping the skirt beneath the base.

Secured in any convenient manner atop the base 93 is an annular insulating and sealing gasket 89 and an electrical resistor 94 having three

resistance segments

95, 96 and 97 connected in series. Between the confronting ends of the resistance segments and 96 is a flexible arm 98 terminating at its free end in a disc-like terminal 99. Between confronting ends of the

resistances

96 and 97 is a tap arm 100 like the arm 98, and a similar arm 1101 is interposed between the confronting ends of the

resistances

95 and 97. The arm 106 terminates in a disc-like terminal 102 and the arm 101 has a similar terminal 103. At the center of the resistor 94 is a disc-like terminal 104 connected at 105 to a terminal 106 that extends through the base 93. The resistive element 97 is connected to a grounded bushing 107 which extends through the base 93 and engages the metallic skirt 92 of the housing. The arrangment is such that a current path extends from the terminal 106 to the terminal 104 and thence successively through each of the

resistive elements

95, 96 and 97 to the grounded bushing 1107.

If none of the taps 96, and 161 are bridged, the total resistance of the three

resistive segments

95, 96

and 97 is inserted in the circuit between the

terminals

104 and 107. Any one, or all, of the resistive segments may be by-passed, however, by bridging selected ones of the taps.

Fixed to the top wall 91 of the housing 90, and extending through an opening 108 in the wall is a nipple 109 that is adapted to be fitted into an opening formed in a pressurized fluid system such as the oil distribution system of an internal combustion engine. The nipple has a passageway 110 extending inwardly from the outer end thereof and which communicates with an internal bore 1 11 within which is mounted a resilient piston 112. The piston is fitted on and carried by a stem 113 projecting from one end of a ram or plunger 114 which extends into the housing 90 and terminates at its other end in a presser disc 115. The disc is slidably accommodated in and guided by a cylindrical socket 116 carried by the base 93, the socket having three axially extending slots 117 spaced uniformly from one another.

A pressure sensitive switch 118 constructed according to the invention is fitted into the socket 116 and comprises three independent, resiliently

compressible pads

119, 120, and 121, similar to the pads of the switches 64, 64a previously described.

To condition the apparatus for operation, the resistor 94 is so arranged on the base 93 that the terminal 104 lies at the bottom of the guide socket 116 and in faceto-face engagement with the lowermost pad 119. The

tap arms

98, 100 and 102 extend through the adjacent slots 117 in the guide. The tap arm 98 is reversely turned so as to locate its terminal 99 between the

pads

119 and 120. The arm 101 is reversely turned so as to locate its terminal 103 between the

pads

120 and 121. The arm 100 is reversely turned so as to locate its terminal 102 between the pad 121 and the presser disc 115 of the plunger.

Each of the pads 119 121 normally is nonconductive and each pad has a different pressure sensitivity so that a greater compressive force must be applied to one pad than to any other so as to render it conductive. Of the other two pads, one requires the application of less pressure than the other to render it conductive. For purposes of illustration, the pad 119 may be rendered conductive when subjected to a pressure of 6 psi, the pad 120 may be rendered conductive when subjected to a pressure of 30 psi, and the pad 121 may be rendered conductive when subjected to a pressure of 60 psi. The sensitivities of the respective pads may be adjusted, however, in any one of the several ways previously discussed.

The pressure transmitter T is adapted to be incorporated in the circuit of a conventional oil pressure gauge 125 having an oscillatable needle 126 operable to indicate a low, normal, or high pressure. The position of the needle is determined by a bimetallic member the temperature of which is controlled, by a resistance heater 127. The circuit includes a source of electrical potential such as a battery 13 which is connected to the heater 127 via a contact of a vehicle's ignition switch 128, a current limiting resistor 129, a choke coil 130, and a constant voltage regulator 131. The heater 127 is connected to the terminal 106 and thence to the terminal 107 via the resistor 94. The

switches

119, 120, and 121 are connected in parallel with the resistor 94 so that selected ones of the

resistive elements

95, 96,

and 97 may be inserted in or removed from the gauge circuit.

When the apparatus is assembled and in place in a pressure fluid system, fluid under pressure may enter the passageway and act on the piston 112 so as to displace the ram 114, thereby subjecting the stacked pads of the switch 1 18 to progressively increasing pressure proportional to that in the system. If the pressure of the fluid is relatively low, such as would be the case if the engine is not operating, none of the switch pads will be compressed an amount sufflcient to render it conductive. Thus, the total resistance of the resistor 94 will be in the gauge circuit so as to cause the indicator needle to show no pressure. When the engine operates, however, the pressure of the oil should be sufficiently high to cause displacement of the ram 114 an amount sufficient to render the

switch pads

119 and 120 conductive, thereby effecting bridging of all three of the

conductive heads

99, 100 and 103 so as to remove the

resistance segments

95 and 96 from the gauge circuit and permit the indicator to reflect normal oil pressure.

Should the oil pressure rise to an abnormal or unsafe level, the ram 114 will compress the stacked switch pads an amount sufficient to render the third pad 121 conductive, thereby removing the third resistance 97 from the indicator circuit and enabling the indicator to reflect a high oil pressure.

Should the oil pressure fall from the normal operating pressure, the ram 114 will exert progressively less compressive force on the stacked switch pads so as to enable only the pad 119 to be conductive. In this instance, the two

resistances

96 and 97 will be in the gauge circuit, thereby causing the indicator to reflect a lowpressure.

The longevity of the switch 118 may be improved by providing a small quantity of a lubricant, such as machine oil, at the interface between each pad and its conductive head.

The disclosed embodiments are representative of presently preferred forms of the invention, but are intended to be illustrative rather than definitive thereof. The invention is defined in the claims.

We claim:

1. A switch construction comprising a stack of individual pads each of which is formed of an electrically non-conductive, resilient elastomer having electrically conductive particles dispersed therethrough, each of said pads being responsive to compression thereof to establish an electrically conductive path therethrough; an electrical conductor on opposite sides of each of said pads; and means for applying on and longitudinally through said stack of pads a compressive force of such magnitude as to render a selected number of said pads electrically conductive.

2. The construction set forth in claim 1 wherein the compressive force required to render each of said pads conductive is different.

3. The construction set forth in claim 1 wherein the resiliency of each of said pads differs.

4. The construction set forth in claim 1 wherein the quantity of conductive particles contained in each of said pads is different.

5. The construction set forth in claim 1 wherein the size of the particles contained in each of said pads is different.

6. The construction set forth in claim 1 wherein the thickness of each of said pads differs.

7. The construction set forth in claim 1 including a liquid lubricant between each of said bodies and the conductors in engagement therewith.

8. The construction set forth in claim 7 wherein said lubricant is oil.

9. The construction set forth in claim 1 wherein said force applying means applies a progressively increasing force on said stack.

10. The construction set forth in claim 1 wherein said force applying means releases the force applied to said stack substantially instantaneously.

1 1. The construction set forth in claim 1 wherein said force applying means progressively releases the force applied on said stack.

12. The construction set forth in claim 1 wherein said force applying means comprises a rotary cam.

13. The construction set forth in claim 12 including means for rotating said cam.

14. The construction set forth in claim 1 wherein said force applying means comprises a reciprocable member bearing against said stack.

15. The construction set forth in claim 14 including means for reciprocating said member.

116. Current control apparatus comprising a body formed of electrically non-conductive elastomeric material throughout which electrically conductive particles are dispersed in such quantity as to establish an electrically conductive path through said body, and a lubricant other than said material and said particles at least on the outer surface of said body.

17. Apparatus for operating in sequence a plurality of electrical devices, said apparatus comprising a stack of resilient, electrically non-conductive pads each of which has a sufficient quantity of electrically conductive particles therein to render it electrically conductive in response to the application of a predetermined compressive force on said pad; means for connecting each of said pads in circuit with a different electrical device and with a source of electrical energy; and operating means for subjecting opposite ends of said stack of pads to a compressive force of such magnitude as to render one after another of said pads electrically conductive and to maintain conductive each pad rendered conductive until all of said pads are rendered conductive.

18. The apparatus set forth in claim 17 wherein said operating means is operable to relieve the compressive force on all pads in said stack substantially simultaneously.

19. The apparatus set forth in claim 17 wherein said operating means is operable to relieve the compressive force on said pads in sequence.

I =l= l=

Claims

8. The construction set forth in claim 7 wherein said lubricant is oil.

11. The construction set forth in claim 1 wherein said force applying means progressively releases the force applied on said stack.

16. Current control apparatus comprising a body formed of electrically non-conductive elastomeric material throughout which electrically conductive particles are dispersed in such quantity as to establish an electrically conductive path through said body, and a lubricant other than said material and said particles at least on the outer surface of said body.