US3087980A

US3087980A - Method and apparatus for preheating spark plugs

Info

Publication number: US3087980A
Application number: US105604A
Authority: US
Inventors: George O Monnig
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-04-26
Filing date: 1961-04-26
Publication date: 1963-04-30
Anticipated expiration: 1980-04-30

Description

April 30, 1963 G. o. MONNIG 3,087,980

METHOD AND APPARATUS FOR FREE-{EATING SPARK PLUGS Filed April 26, 1961 2 Sheets-Sheet 1 METHOD AND APPARATUS FOR PREHEATING SPARK PLUGS Filed April 26, 1961 April 30, 1963 e. o. MONNlG 2 Sheets-Sheet 2 FIG.7

FIGS

FIGJO United States Patent EJ937986 METH BD AND APPARATUS F911 PBEHEATHNG SPARK PLUGS George (1. Mormig, s Carrsvvoid, Clayton, Mo. Filed Apr. 26, 61, Ser. No. 165,6iid 7 Claims. (ill. 123--146.5)

The present invention relates to a method and apparatus for preheating spark plugs, and particularly relates to a device which can be controlled from a remote convenient location, such as inside a vehicle, to heat the center electrode of the spark plugs in a conventional internal combustion engine prior to starting the engine.

It is well known that conventional gasolene engines of the internal combustion type are diilicult to start if they are allowed to become very cold. This is due to a combination of factors such as increased viscosity of oil and lower battery output which reduce the cranking speed, lower volatility of fuel and the tendency of vaporized fuel to recondense on cold internal surfaces in the engine. All of these factors lead to difiiculty in obtaining a sufficient concentration of fuel vapor in the immediate vicinity of the spark so that ignition may take place.

It has been known for some time that starting is facilitated if the spark plugs are removed and heated immediately prior to the starting attempt. This promotes vaporization of fuel near the spark. Numerous prior devices have attempted to accomplish this heating in a convenient manner by adding an electrical resistance heating element to the spark plug structure in order to heat the nearby gases in the combustion chamber.

In the prior devices, the heating element is exposed directly to the gases within the combustion chamber and is electrically grounded to the main engine structure. This arrangement is characterized by important disadvantages which cause the devices to be impractical under normal operating conditions and the devices have not been extensively used.

The present invention includes a spark plug structure in which the heating element is mounted immediately above or Within the tip of the center, or high voltage, electrode of the spark plug and is not exposed directly to gases in the combustion chamber. With the present structure, the disadvantages of the prior devices are avoided and a method of heating the spark plug which is useful and practical under normal operating conditions results.

Among the advantages of the present invention over prior devices are the following:

(1) The present invention avoids preignition. The heating elements in prior devices would, under normal operating conditions, reach suficiently high temperatures, even with no heating current flowing, that p-reignitioin would occur. This is serious difiiculty which outweighs in importance ease in cold weather starting. The high temperatures would result from the direct exposure of a large portion of the surface area of the heating elements to the burning mixture, so that heat is conducted to the heating element during the power stroke and the lack of sufiicient provision for conducting this heat away during the remainder of the engine cycle of operation. In the present invention, the heating element is not exposed dircctly to burning gases and the difficulty does not arise.

(2) The present invention avoids interference with insulation. In all spark plugs, a length of porcelain insulating surface separates the high voltage electrode from the grounded shell. If this length is reduced by the presence of a grounded heating element, or the electrical leads to it, the probability that the spark will be short circuited by combustion products deposited on the insulating surface during normal engine operation is increased. The length of insulating surface is decreased in prior devices but not in the present invention.

(3) The present invention provides more efiiciency of heating. In prior devices, the heating element is subject to coating by combustion products deposited during normal engine operation. This coating interferes with the passage of heat from the element to the gas in the combustion chamber and thus diminishes its eifectiveness as a starting aid. In the present invention this does not occur since, under normal operations, the tip of the center electrode, through which heat is transferred from the heating element to the gas in the combustion chamber, remains free of deposits.

(4) The present invention efficiently uses the electrical energy available for heating the element. The prior devices employ heating elements With one lead grounded. Thus, in a multicylinder engine, all the elements must be connected in parallel across the source of electrical energy. Assuming conventional material in the heating element and reasonable practical dimensions of it, calculation shows that the electrical energy would have to be furnished at lower voltages and higher currents than conventional storage batteries can efficiently supply. In the present invention, it will be seen, the heating elements in the spark plugs of a multicylinder engine may be connected in series or in a series-parallel combination as well as in parallel and calculation shows that a current within the normal operating capabilities of conventional storage batteries and convenient sizes of wire would be drawn.

These examples serve to indicate that important practical advantages results from the use of the new and novel heated spark plug structure in the present invention. In addition, the present invention includes a switching device diiferent from the prior devices, and this switching device is an essential part of the present invention.

In the present invention, the heating elements are connected electrically to the center electrode, or high voltage electrode, of the spark plug; therefore it is necessary to provide means for connecting the heating elements in the spark plugs of a multicylinder engine to a low voltage source of electrical energy, such as a storage battery, prior to starting and then to disconnect them from the low voltage source and from each other before the engine is started and run. The present invention cannot supply heat while the engine is running, whereas the prior devices can, if it is desired.

The second element of the present invention, the switching device, is located in the distributor head of the gasoline engine, and the switching is accomplished by making or breaking electrical connection between contacts in the distributor head. This may conveniently be done by mounting the distributor head by means of screw threads on a base in a manner to be described and raising or lowering it by rotating it. However, it is Within the scope and spirit of the present invention to secure the relative motion of the members carrying the contacts by some other simple means such as movement of a member inside the distributor head. In the majority of engine designs, it is feasible to rotate the distributor head about of a turn, having it undergo linear displacement of about one inch at the same time. However, if in a particular installation, this proves undesirable, an alternative method of securing the relative motion of the electrical contacts could easily be employed and is within the scope and spirit of this invention. For simplicity only a method in which the distributor head is rotated will be described.

It is one of the principal objects of the present invention to provide a method of preheating spark plugs in an internal combustion engine. It is another object of the present invention to provide an apparatus which is simple, sturdy, reliable, easy to construct and serves to preheat the spark plug prior to starting the engine.

' connected in series.

Another object is to provide a spark plug having a resistance heater embedded in or immediately above the tip thereof integral therewith, said heating element being protected from shock, exposure, etc., and which can be connected to a low voltage power source before starting the engine.

Still another object of the present invention is to provide a novel spark plug having a resistance heating element in or immediately above the tip of .the center electrode which is connected to the normal electrical system of the vehicle to warm the gases in the immediate vicinity of the spark gap prior to starting the engine.

Another object is to provide a system for preheating the tip of the high voltage electrode of a spark plug including a movable distributor cap to connect a voltage source .to a resistance heater so that a current is developed therein to warm the tip prior to starting the engine.

Still another object is to provide a device in which heating elements in a set of spark plugs can be connected to a convenient source of electrical energy, normal, a storage battery, and can be disconnected from the voltage source and from each other immediately prior to starting. A set of conductors can be arranged so that the heaters are Alternatively, the set of conductors can be arranged so that a parmlel or a combination series-parallel connection of the spark plug heating elements results.

A further object is to provided a spark plug preheating arrangement which utilizes the center electrode of the high potential spark system in the low potential heating system.

These and other objects and advantages will become apparent hereinafter.

The present invention comprises a method of preheating spark plugs prior to starting the engine. The present invention further comprises a spark plug having a heating element within the body of the tip portion thereof, said heating element being electrically connectable through movable distributor elements with a low voltage source to establish or interrupt electrical contact between said heating elements and said voltage source.

The present invention further includes the method and apparatus hereinafter described and claimed.

In the following drawings wherein like figures refer to like parts wherever they occur:

FIG. 1 is a view of the distributor of a gasolene engine showing the method of rotating the distributor cap from the dashboard of a vehicle,

FIG. 2 is a fragmentary sectional view of the present switching device located in the distributor head and an r enlarged partially broken side elevational view of a spark plug electrically connected thereto,

FIG. 3 is an enlarged fragmentary sectional view of the spark plug tip and heating element shown in FIG. 2,

FIG. 4 is a sectional view taken along 44 of FIG. 3,

FIG. 5 is an enlarged fragmentary sectional view of one modified form of spark plug tip and heating element,

FIG. 6 is an enlarged fragmentary sectional view of an additional form of spark plug tip and heating element,

FIG. 7 is an enlarged fragmentary sectional view of a further modification of the spark slug tip and heating element.

FIG. 8 is a diagrammatic representation of an electrical circuit with the spark plug resistance heaters connected in parallel,

FIG. 9 is a diagrammatic representation of an electrical circuit with the spark plug resistances connected in series, and

FIGS. 10 and 11 are diagrammatic representations of an electrical circuit with the spark plug resistances connected in various series-parallel combinations.

FIG. 1 shows a distributor 16 including a distributor cap 11 and a base 12 mounted on a gasoline engine 13. The cap 11 includes a conventional center port 14- adapted to receive a connection from a conventional spark coil (not shown) which supplies high voltage from a low voltage source, normally a 6, 12 or 24 volt storage battery, or a magneto armature.

The distributor 10 also includes a conventional rotor 15 (FIG. 2) having a spring connection 16 to the center port 14 and an arm 17 which supplies high voltage from the coil to spaced conductors 18. Each of the conductors 18 is connected to a spark plug 19 by a conductor 20 engaged with a contact 21 on the upper end of a center electrode 22.

The spark plug 19 includes a high voltage insulator 23 around an electrically conducting bar 22 and a conducting shell 24 threaded at one end 25 to engage the engine 13. A conventional second electrode 25a is fastened to the shell lower end 25 and resides in the combustion chamber and is outwardly spaced from the lower end of the conducting bar 22. The second electrode 25a is grounded through the shell 24 to the engine 13.

The lower end of the insulating body 23 is tapered toward the conducting bar 22 and is provided with an inwardly extending spiraling slot 26 (FIG. 3) which houses a resistance heating element 27. The slot 26 is slightly larger than the heating element 27 to allow for expansion thereof without cracking the insulator 23. A second set of slots 28 cuts across the coil slot 26 and are constructed and arranged to receive insulating bars 29 which retain the heating element 27 in the slot 26, and prevent it from coming into contact with a metal cap 31 attached to the lower end of the conducting bar 22. The cap 31 acts as the tip of the conducting bar 22 and, with the second or low potential electrode 25a, defines a spark gap therebetween.

The heating element 27 is in electrical contact at 32 with the cap 31 and at 33 with a second conducting bar 34 embedded in the insulator 23.

The conducting bar 34 continues through the insulator 23 and connects to a terminal post 35 embedded in the outer top portion of the insulator 23, and electrically insulated from the center conducting bar. A conductor 37 connects the post 35 to a, port 38 on the distributor cap 11.

Pairs of electrical contacts 39 and 40 (FIG. 2) positioned in the distributor cap 11 and extending into the interior thereof are connected by pairs of

conductors

41 and 42 to two conductor

cables containing conductors

20 and 37, respectively, leading to spark plugs 19. For simplicity, only two pairs of

contacts

39 and 40 are shown in FIG. 2. In the present device there is one pair of

contacts

39 and 40 for each spark plug in a multicylinder engine which it is desired to heat. Normally, all of the plugs are heated. The pairs are spaced uniformly around the inner wall of the distributor cap 11, each pair being under one of the contacts 18 associated with a cylinder and found in a conventional distributor cap.

A member 43 fitted to the insulating base 12 has an outer rim 44 around the periphery of the top edge thereof and a second rim 4-5 spaced inwardly and downwardly from the outer rim 44.

A set of spaced disconnected conductors 46 and spaced disconnected conductors 47 are positioned around the rims 44 and respectively. The number of these conductors and their length and position along the periphery of the rims 44 and 45 determines, in a manner which is indicated in FIGS. 8-1l, and which will be apparent later, whether the heating elements in the spark plugs of a multicylinder engine are connected in series across a source of electrical energy 48 or in parallel across it or in a series-parallel combination. Two of the conductors 47 are connected to the terminals of the voltage source 48, if the engine has an even number of spark plugs 19 and the heaters 27 are connected in series. This is shown in FIGS. 2 and 9. If the engine has an odd number of spark plugs 19 and the heaters 27 are connected in series, one of the conductors '47 is con nected to one terminal of the voltage source 43 and one of the conductors 46 is connected to its other terminal. If the heaters 27 are connected in parallel, the spaced disconnected conductors 46 are replaced by a continuous ring and the spaced disconnected conductors 47 are replaced by continuous ring and these two rings are connected to the terminals of the voltage source 48 (FIG. 8). If one of the terminals of the voltage source 43 is grounded, as is commonly the practice in vehicles, the ground connection 49 is the electrical equivalent of a connection to the grounded terminal and is more convenient.

The distributor cap 11 is movably mounted to an insulating base 12 by means of a multi-lead thread 50. The pitch of the thread 58 is such that a rotation of the cap 11 corresponding to about a two inch displacement of a dog 52 attached to the periphery of the cap 1 corresponds to a one inch vertical displacement of the cap ill. The control cable 51 rotates cap 11 thus raising or lowering it. The control cable 51 (FIG. 1) is mounted in alignment with the ridges of the threads 5d so that the center wire does not bind against the easing as the cap 11 rotates and rises. A vertical displacement or" the cap 11 of at least one inch is required for insulation since, when the engine is running, the high voltage pulse from the spark coil which is applied to the conducting bar 22 in the spark plugs also reaches the

contacts

39 and 48. For this reason they must be suitably insulated from all grounded metal parts.

in operation, using the arrangement of

conductors

46 and 47 indicated in FIGS. 2 and 9 when the control knob 53 is pulled out, all of the heaters in the spark plugs, of a multicylinder engine are connected in series across the voltage source 423. The circuit for one heater would be, proceeding from the hot terminal of the voltage source 48 around the circuit to ground, as follows: conductor 47, contact 39, conductor 41, cable connector contact 41a, conductor 37 in a high voltage insulated cable, band condoctor 35 on spark plug, conducting bar 34 in high voltage insulator of spark plug, heating element 27, spark plug tip: 31, conducting bar 22 in high voltage insulator of spark plug, terminal 21 of spark plug, conductor 20 in high voltage insulated cable, cable connector contact 42a in distributor head, conductor 42, contact 46, conductor 45, and thence to the contact 40 associated with another spark plug and around a similar circuit to the next contact 47 and so on through all spark plugs to the contact 47 connected to the other terminal (or ground if it is grounded) of the voltage source. The contacts 47 connected to the two terminals are adjacent contacts, but, for convenience in illustration, this is not indicated in FIG. 2, and, in FIG. 9, the locus of the contacts has been unwrapped to form a straight line.

Alternatively, the length and positioning of the

conductors

46 and 47 along the rims 44 and 45 could be arranged so that a parallel connection (FIG. 2) or variou series-parallel combinations (FIGS. and 11) would result. In this way, regarding all of the heating elements as one electrical load, the resistance of the load" can be varied to suit the electrical characteristics of the source 48. If the source 48 is a conventional lead storage battery, and the heating elements 27 are made of Nichrome wire, and the number of cylinders in the engine is six or eight a series connection would be preferable. However, it is possible that under certain other circumstances a combination series-parallel connection would be preferable.

Having heated the spark plugs for a period of about to seconds, the knob 53 is pushed in, rotating and lowering the distributor cap 11 and isolating all the heating elements 27 from each other and from the voltage source 48. The engine is then ready to be started and run.

A modified form of spark plug heating element is shown in FIG. 5. This structure, '55, includes a conducting bar 22 having a threaded lower end 30* engaged with a conducting cap 31 as in the construction shown in FIG. 3. However, the heating element 56 is a resistance disc made of a material, such as a carbon-clay mixture, having higher resistivity than Nichrome. The resistance disc 56 has an opening 57 in the center thereof through which the conducting bar 22 is fitted. The conducting bar 22 is in circular electrical contact with the resistance disc 56 at the edge defined by the opening 57. A second conducting bar 34 is in electrical contact with the outer periphery of the resistance disc 56 through a ring conductor 58 fitted in close fitting contact with the upper surface of the resistance disc 56. A circular electrical insulator 59 having an L-shaped cross section spaces the resistance disc 56 from the cap 31. The insulator 59 defines an electrically insulating air gap 60 between the resistance disc 56 and the cap 31.

The heating current fiows radially from the conducting bar 22 through the resistance 56 to the circular conductor 53, and heat passes through the air gap 6% to the cap 31.

A further modification of the present invention is shown in FIG. 6. A coiled heating element 61, such as a coil of Nichrome wire, is located in a cavity 62 within the lower end of the conducting bar 22. The heating element 61 also may be a cylinder of some material having higher resistivity than Nichrome, such as a mixture of clay and carbon. The lower end of the heating element 61 is connected electrically to and supported by a cap 63 which forms the lower boundary of the cavity 62. The upper end of the heating element 61 is electrically connected to and supported by a projection 64 extending from the conducting bar 34 through a hole 65 in conducting bar 22 into the cavity 62. The heating element or is supported so that it does not touch the walls of the cavity 62 and a voltage impressed between conducting bars 2.2 and 34 causes a current to flow through the heating element 61. The cavity 62 containing the heating element may contain air or it may be sealed and contain an inert gas to prevent oxidation of the heating element 61.

A further modification of the present invention is shown in FIG. 7. A spark plug 66 includes an insulator 23, provided with an enlarged opening 67 around the high potential electrode 22 and immediately above the lowermost end thereof, and a resistance heater 68 in the opening 67 adjacent to and connected at one end to the high potential electrode 22 and at the other end to a second conducting bar 34 also positioned in the insulator 23.

This invention is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of the disclosure which do not constitute departures fromthe spirit and scope of the invention.

What is claimed is:

1. A vehicle distributor for a gasoline engine comprising a fixed base, a rotatable vertically movable cap, a threaded connection between said cap and base, means for moving said cap relative to said base, said means being operable from within the vehicle, a series of contacts fixed on said cap and adapted to be connected to the vehicle spark plugs and normally electrically well insulated from ground, a member fixed to said distributor base, a series of conductors fixed to said member, means connecting two of said conductors to the two terminals of a low voltage source, said contacts and conductors constructed and arranged to establish and interrupt an electrical connection between said low voltage source and the vehicle spark plugs when said cap is rotatively and vertically moved relative to said base.

2. A system for preheating a spark plug comprising a distributor having relatively movable elements, a low voltage source, a spark plug, an electrical resistance heater at the end of the high potential electrode of said plug, means for relatively moving said distributor elements, conductor means connecting said heater to said distributor,

7 conductor means connecting said low voltage source to the distributor, said distributor elements being constructed and arranged to establish an electrical connection including said conductor means, said low'voltage source, and said resistance heater when said elements are moved relative to each other.

3. A system for preheating a gasoline engine spark plug having a portion adapted to extend into a combustion chamber comprising a distributor having relatively movable elements, spaced contacts on one of said elements, a spark plug having a lower portion adapted to extend into a combustion chamber including high and ground potential electrodes defining a spark gap, an electrical resist ance heater positioned within said lower portion adjacent to said spark gap, conductors electrically connecting the first named spaced distributor contacts with ends of said resistance heater, a set of spaced conductors on the other of said distributor elements, one conductor in the set being connected to one terminal of a source of electrical energy and another conductor of the set being connected to the other terminal of the source of electrical energy, and means for moving said distributor elements relatively, thereby efiecting electrical connection between said contacts and establishing a current through said resistance heater.

4. A system for preheating vehicle spark plugs comprising a distributor having a fixed base and a rotatable longitudinally movable cap, means for moving said cap, said means being operable from within the vehicle, spaced electrical contacts movable with said cap, spaced electrical contacts fixed on said base, a low voltage source, conductor means connecting one of said base contacts to a first terminal of a low voltage source, means for connecting another of said base contacts to the other terminal of the low voltage source, a spark plug comprising an insulator body provided with a coil slot in the lowermost end thereof, a high potential electrode in said body having an exposed tip end, a conductor cap fastended to said tip end and covering the slot in said insulator body, a ground potential electrode defining a spark gap with said cap, a heating element positioned in said insulator slot, said heating element positioned in said insulator slot, said heating element being electrically connected at one end to said high potential electrode cap, the remainder of said heating element including the second end thereof being electrically insulated from said high potential electrode and cap, and a second conductor extending through said insulator and electrically connected to the second end of the heating element, and means electrically connecting said high potential electrode and said second conductor to the distributor cap contacts, said distributor being constructed and arranged to engage said cap contacts with said base contacts when said cap is moved in one direction, thereby establishing an electrical circuit including said low voltage source and said resistance element and causing a voltage drop across said resistance element, said circuit being interrupted when said distributor cap is returned to its normal engine operating position.

5. A system for preheating vehicle spark plugs comprising a distributor having a fixed base and a rtotatable longitudinally movable cap, means for moving said cap, said means being operable from within the vehicle, spaced electrical contacts movable with said cap, spaced electrical contacts fixed on said base, a low voltage source, conductor means connecting one of said base contacts to the terminal of the low voltage source, means for connecting another of said base contacts to the other terminal of said low voltage source, a spark plug comprising an in .sulating body, a ring conductor at the outer periphery of the lowermost end of said body, a high potential electrode in said body having an exposed tip end, a disc shaped electrical resistance material heating element having an opening therethrough, said high potential electrode being positioned in said opening and in circular electrical contact with said heating element at said opening, said heating element also being in circular electrical contact with said ring conductor to establish a voltage drop across said heating element, a conductor cap fastened to the exposed end of said high potential electrode, an insulator spacing said cap from said heating element, a ground potential electrode defining a spark gap with said high potential electrode cap, and a second conductor extending through said insulator and in electrical contact with said ring conductor, and :means electrically connecting said high potential electrode and said second conductor to the distributor cap contacts, said distributor being constructed and arranged to engage said cap contacts with said base contacts when said cap is moved in one direction, thereby establishing an electrical circuit including said low voltage source and said resistance element and causing a voltage drop across said resistance element, said circuit being interrupted when said distributor cap is returned to its normal engine operating position.

6. A system for preheating vehicle spark plugs comprising a distributor having a fixed base and a rotatable longitudinally movable cap, means for moving said cap,

said means being operable from within the vehicle, spaced electrical contacts movable with said cap, spaced electrical contacts fixed on said base, a low voltage source, conductor means connecting one of said base contacts to a first terminal of a low voltage source, means for connecting another of said base contacts to the other terminal of said low voltage source, a spark plug structure including a metal shell, a high voltage electrical insulator mounted within the shell, a pair of electrically conducting bars positioned in the insulator, said bars being electrically insulated from each other along their length and insulated from the shell, one of said bars being the high potential electrode of said plug and having a tip end extending beyond the lowermost end of the insulator, said high potential electrode being provided with an opening in the lower end thereof communicating with the insulator, a resistance heating element positioned in said opening, one end of said heating element being electrically connected with said high potential electrode and the other end being ele trically connected to the second conductor, said element being insulated from said high potential electrode except at the point of electrical connection thereto, and conductor means positioned in the mouth of the high potential electrode opening to protect the heating element therein and to define a spark gap with a projection on said shell, and means electrically connecting said high potential electrode and said second conductor to the distributor cap contacts, said distributor being constructed and arranged to engage said cap contacts with said base contacts when said cap is moved in one direction, thereby establishing an electrical circuit including said low voltage source and said resistance element and causing a voltage drop across said resistance element, said circuit being interrupted when said distributor cap is returned to its normal engine operating position.

7. A system for preheating vehicle spark plugs comprising a distributor having a fixed base and a rotatable longitudinally movable cap, means for moving said cap, said means being operable from within the vehicle, spaced electrical contacts movable with said cap, spaced electrical contacts fixed on said base, a low voltage source, conductor means connecting one of said base contacts to a first terminal of the loW voltage source, means for connecting another of said base contacts to the other terminal of said low voltage source, a spark plug structure including a metal shell, 21 high voltage electrical insulator mounted within the shell, a pair of electrically conducting bars positioned in the insulator, said bars being electrically insulated from each other along their length, and insulated from the shell, one of said bars being the high potential electrode of said plug and having a tip end extending beyond the lowermost end of the insulator, said insulator being provided with an enlarged opening around the high potential electrode and immediately above the lowermost 9 end of the insulator, a resistance heating element electrically connected at one end to the high potential electrode and at the other end to the second conductor, said heating element being positioned Within the opening. in the insulator and electrically insulated from the high potential electrode except for the point of connection thereto, and means electrically connecting said high potential electrode and said second conductor to the distributor cap contacts, said distributor being constructed and arranged to engage said cap contacts with said base contacts when 10 said cap is moved in one direction, thereby establishing an electrical circuit including said low voltage source and said resistance element and causing a voltage drop across said resistance element, said circuit being interrupted when said distributor cap is returned to its normal engine operating position.

References Cited in the file of this patent UNITED STATES PATENTS 915,891 Schaake et a1 Mar. 23, 1909 1,458,375 Aiken June 12, 1923 1,667,960 Theis May 1, 1928 1,784,541 Rouillard Dec. 9, 1930 2,214,276 Hughes Sept. 10; 1940