US3059835A

US3059835A - Rotary blower

Info

Publication number: US3059835A
Application number: US2027A
Authority: US
Inventors: George P Hanley; Kenneth L Hulsing
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1960-01-12
Filing date: 1960-01-12
Publication date: 1962-10-23
Anticipated expiration: 1979-10-23

Description

Oct. 23, 1962 G. P.v HANLEY E'I'AL ROTARY BLOWER 2 Sheets-Sheet 1 Filed Jan. 12, 1960 INVENTORS @af Oct. 23, 1962 G. P. HANLEY ETAL 3,059,835

ROTARY BLOWER Filed Jan. 12, 1960 2 Sheets-Sheet 2 INVENTORS" ATTOE/V'y United States Patent O 3,059,335 RGTARY BLWER George P. Hanley, Northville, and Kenneth L. Huising,

Plymouth, Mich., assignors to General Motors Corporation, Detroit, lt/lich., a corporation of Delaware Filed lan. 12, 1960, @ein No. 2{927 14 Claims. (Cl. 23u-itil) This invention relates to rotary blowers of pumps of the positive displacement type, and more particularly to a blower of the type having two synchronously driven multi-lobed impellers or rotors, such blowers being particularly adapted among other uses for supplying scavenging and charging air to a two-cycle internal combustion engine.

In such rotary blowers, the maintenance of minimum clearances between the rotors and between the rotors and their housings is essential to maximum volumetric efficiency. On the other hand, the provided clearances must normally be suliciently large to prevent actual contact between these parts. Otherwise, the high relative rubbing velocity of the metal-to-metal surfaces will develop high temperatures and excessive wear rapid-ly followed by seizure, welding or galling of the surfaces. Moreover, it is diiiicult to maintain such clearances at their desired design minimum in service. Operational deviations occur as a result of differential thermal expansion of the various blower parts, elastic deformations from various causes, wear of the driving gear and bearings and cumulative tolerances resulting from manufacturing and assembly errors. To insure sutiicient clearances under all operating conditions, expensive machining operations have been required to obtain the necessary accuracy of the various blower components. In the past, rather expensive close tolerance bearing arrangements have also been used in order to maintain the necessary clearances between the rotors and between the rotors and their housings.

The invention contemplates an improved blower of the type described having a lrotor configuration permitting wider latitude in manufacturing tolerances and variation in the displacement characteristic of the blower by simple changes in the addendum and dedendum dimensions of the rotors with corresponding changes in the root contour of the impeller and in the mating surfaces of the rotor housing having a blower housing structure permitting maximum mounting versatility and suiiicient rigidity to minimize elastic ldeformations due to assembly or operating conditions; and having relatively simple, inexpensive bearing means for supporting and maintaining the clearances of the lrotor assemblies with respect to each other and to the blower housing members. These factors all contribute to providing a blower which is Irelatively simple and inexpensive to manu-facture, and has a high volumetric efficiency.

The foregoing and other objects, advantages and features of the invention will be more thoroughly understood and apparent vfrom the following description of a preferred embodiment thereof, reference being made therein to the accompanying drawings, in which:

FIGURE 1 is a transverse sectional view showing the blower of the invention mounted on a two-cycle internal combustion engine of the uniflow scavenged type;

FIGURE 2 is an elevational end view of the blower as viewed in FIGURE l with portions thereof broken ICC away to show certain details of the bearing construction of the invention in elevation and in section; and

FIGURE 3 is an elevational side View of the blower taken in the plane of the line 3 3 of FIGURE l with portions thereof broken away and in section.

Referring more particularly to FIGURE 1 of the draw ings, an engine yframe or block member for a two-cycle internal combustion engine is indicated generally at lll. The block lll delines an air box 1l which extends longitudinally of the engine between a lower crankcase defining portion 12 and an upper cylinder supporting portion i3. An engine driven blower 30 is mounted on one side of the upper portion of the engine frame and is adapted to supply pressurizexi scavenging and charging air -to the block defined air box. The engine frame is preferably symmetrical about its longitudinal vertical plane to provide alternative :blower mounting locations on either side of the engine in accordance with the teaching of copending United States patent application Serial No. 34,728, tiled, lune 8, 1960 in the names of George W. Conover, Kenneth L. Hulsing and Joseph Koehler and entitled Internal Combustion Engine.

rl`he air box li embraces several inline cylinder liners la which are slidably mounted and supported by the upper and lower block portions in aligned ports 15, l5 and lo. Each cylinder liner 14 has a circumferential belt of inlet ports 17 intermediate its ends. These ports are connected directly to the air box proper. A cylinder head lill is secured to the upper face of the cylinder vblock and closes the upper end of the several cylinders. A piston 19 is reciprocahly mounted in each of the cylinder liners and cooperates with the closed end thereof to deine `an expansible c-ombustion chamber 20. The lpiston is connected in a conventional manner by a wrist pin 21 and a connecting rod 22 to the engine crankshaft, not shown. Reciprocation of Jthe several pistons 30 within their respective cylinders serves to control the admission of scavenging and charging air through the inlet ports 17 into such cylinders. This provides uniflow scavenging of the combustion gases through exhaust valves, not show-n, which are reciprocably mounted in the cylinder head and control the opening of ports leading to suitable exhaust passages and manifolds, also not shown. Such exhaust valves are operated in a conventional manner by a camshaft 38 through conventional valve actuating mechanisms of the overhead .rocker type which are not shown except for one cam follower tappet 40.

Referring now to the several FIGURES 1-3, the blower Sil includes a housing 31 comprising an intermediate liousing member 32 and two identical and interchangeable end plates 33 and 34. These end plates are secured to opposite ends of the intermediate housing member 32 and cooperate `therewith to denne a pumping chamber 35. The side of the intermediate housing member 32 opposite the engine frame has inlet ports 36 extending therethrough and supports an air in- .let housing member 37. The air inlet housing 37 pivotally supports an engine shutdown valve 38 which is biased by a spring 39 toward a closed shutdown position and is normally latched in its open position shown in broken line `for normal engine operation. The engine adjacent side of the intermediate housing member is provided with a mounting flange 40 which mates with the blower mounting pads 41 of the engine frame and is supported vertically by a laterally extending shoulder defining boss 42. The engine mounting side of the intermediate housing member is provided with a pressurized air outlet at 43 which mates with and is connected to the engine air box through a port 44 defined by and extending through Ithe side Wall of the engine block.

A pair of cooperating two-lobed impellers i5 are rotatably supported within each lblower compartment $5 and are driven to provide pumping displacement of air from the compressor inlet to its outlet d3. The impellers 45 have mating involute profiles which may be formed with conventional gear tooth cutting machinery. This in in contrast to the very expensive and diflicu-lt machining operations which must be done in manufacturing impellers having either straight or helical lobes of conventional Roots type cross-section. To meet the scavenging air requirements of the different engine applications, the displacement characteristics of the impellers may be changed as needed by varying the mating addendum and dedendum diameters of the impellers, that is, by varying the outer diameters of the rotors and making corresponding changes in the mating surfaces i7 of the housing and making corresponding changes in root contour 1;8. This may be accomplished without changing the precision mating involute profiles. Thus the same elements may be machined by proper Setting to provide the different scavenging and accessory air requirements for a wide range of installations. This is in contrast to conventional Roots blowers wherein different drive gears are required to provide different pumping ratios for a given shaft spacing. To provide some latitude in machining tolerances and to insure proper sealing with minimum running clearances between the impellers and the mating housing surfaces under running conditions, each peripheral portion of the impellers is provided with two longitudinally extending grooves it? which provide wear accommodating ribs Sti and S'. During the initial breaking-in periods, these ribs rapidly wear in to provide the proper clearances if any metalto-metal scung occurs between the several members. Proper sealing clearance ymay also be provided between the several impeller and housing surfaces by coating these members with a `suitable high temperature resistant grease in assembly.

The end plates and the intermediate housing member are preferably cast of aluminum. With precision permanent type molds, such castings require a minimum of dimensional iinishings. A plurality of reinforcing compression heat-transferring ri-bs 32 extend between the inlet and outlet sides of the intermediate housing member 3?. and prevent excessive elastic distortion of the member due to the generated air pressure on the discharge side of the housing. The identical end plates 33 and 34 each comprise a web 69 defining the end wall of the blower chamber 35 and a peripheral flange 70 extending therefrom opposite the adjacent end of the intermediate Ahousing member. These peripheral flanges of the end plates 33 and 34 are pilot dowelled at 5l and secured to the mating end faces of the intermediate housing member 32 by a plurality of bolts 52. Each end plate has two spaced parallel bores 53 extending therethrough adjacent their upper and lower ends, as viewed in FIGURES l and 2. Bolts S4 inserted in these bores threadably engage tapped holes provided in the blower mounting pad of the cylinder block. iIn conjunction with the block-defined boss 42j, these bolts thus serve to support the assembled blower unit in its mounted position on the side of the block.

Stub shafts 5'5 and 56 are rigidly secured to, carried by and project from opposite ends of each impeller 45. These stub shafts are rotatably journaled in parallel aligned bores 58 which extend through journal defining bosses or projections 71 and '72 upstanding from the webs of each end plate 33 and 34. The journal bores 58 of each end plate are intersected by and pressure lubricated through parallel passages 62j to maintain the stud shafts and their respective impellers in proper position radially of the journals. These passages are interconnected by a third passage `63 which extends therebetween closely adjacent the journals 58. The ends of the passages 62` opposite their respective journals open on the engine mounting faces 66 of the end plate. The lower of these two passages in each end plate is connected to a drilled passage 64 which extends transversely of and intersects the main longitudinally extending oil supply gallery 65 of the engine block.

Suitable face-type oil and compression seal rings 59 seal the shafts and end plate journals with respect to the blower chamber. These seal rings embrace the shafts and are interposed between the shaft mounting hubs of the impellers and the adjacent end plates. These rings are biased into sealing engagement with the adjacent end plates by springs 6% which are housed within counterbored recesses 61 formed in the impeller shaft mounting hub. Counterbores 67 formed in the end plates adjacent the seals 59 are drained through passages 68 extending radially therefrom through the journal bosses. This draining of the counterbores 67 prevents the seal 59 from being subjected to oil pressure and equalizes oil flow in both directions along the journals from the oil inlet passages 62.

A third projection 73 extends outwardly of each end plate web 69 intermediate the journal bosses 7l and 72. These several projections are preferably finished flush with the peripheral flanges 37 of their respective end plates. The third projection 73 is coextensive with a reinforcing rib '74- which extends transversely of the end plate web in parallel relation to the bosses defining the passages 62 and those defining the holes 53 for the blower mounting bolts. The rib '74- also intersects the boss defining the oil passage 63. It will be noted that the several projections, the mounting bolts, the hole dening bosses and the rib '7d serve to reinforce the web of each end plate against elastic distortion, and particularly on the discharge side of the blower due to the location of the oil passage bosses.

ln accordance with certain aspects of the invention, a thrust washer is secured by a self-locking bolt '76 to the end of each stub shaft 55. These washers are preferably of ground and hardened steel. in assembly, the outer washer mounting end faces of the stub shafts S'S are precision located with respect to the adjacent axial end faces of their respective impellers to provide proper sealing clearance between the end plate chamber wall 69 and the axial end faces of the impellers and to provide necessary bearing clearance for the thrust washers with respect to the mating aluminum end faces of their adjacent journal bosses 7i and 72. A cast iron thrust plate 78 is spacedly bolted by self-locking bolts 79 to the end plate projections 7l, 72, and 73 with spacer washers Si) interposed therebetween. The several bolts 79 are disposed in flanking relation to the thrust washers. ln addition to the several holes from the bolts 79, the thrust plate '78 is perforated to spacedly embrace the heads of the washer securing bolts 76. The thickness of the spacer washers il@ is selected to provide the necessary bearing clearances between the shaft carried thrust washers, the thrust plate and the end faces of the adjacent journal bosses. These thrust bearing surfaces are pressure lubricated by ports 8l in the journal boss end faces. The ports 81 intersect the oil supply passages 62 and thus continuously supply lubrication to the mating steel-to-aluminum surfaces of the thrust washer and journal boss end face. Direct lubrication of the mating steel-to-cast-iron surfaces of the thrust washers and thrust plate is accomplished through a plurality of ports 82 in the rotating washer, the ports ft2 being intermittently aligned with the supply port S1.

With this thrust plate bearing construction, the axial position of the impellers and the related impeller-housing clearances are relatively easy to maintain in assembly being dependent on a very limited number of pieces. By

providing such thrust control at a single location, such impeller-housing clearances are also maintainable within a proper range under operational conditions since the provided single location thrust control is not as susceptible to differential expansions between the rotors and the housing assemblies. The impellers 45 are synchronously driven 'with respect to each other by two timing gears 83 and S3' preferably having helical teeth. The gears 83 and `835 are suitably keyed or splined on the ends of the stub shafts 56 and secured thereto by self-locking stud bolts 34 and 85 and washers 86 and 87. One of the gears S3 or 83 may be directly driven olf the main gear train. However, in the illustrative embodiment, a spring support member 88 of a resilient coupling 89 is secured to the timing gear 83 by a plurality of bolts 9i). The member S8 supports two sets of leaf springs 9i in parallel spaced relation. These spring sets resiliently engage the narrower surface dimensions of an elliptical drive cam 92. The cam 92 is drivingly splined at 93 to one end of a quill shaft 94 and the opposite end of the quill shaft is drivingly connectible to the accessory gear drive train of the engine. The several bolts 90' also secure a retainer ring 95 to the spring support member S8, This ring retains both the spring packs 911 and the driving cam 92 in assembled driving positions within the coupling 39. This resilient coupling serves to isolate the blower unit from torque fluctuations in the accessory gear drive and engine output.

A cover member 96 is secured in sealing relation to the end plate 34 by the bolts 52. This cover member embraces the blower driving elements and is perforated to provide a flanged opening 97. This ange is normally sealed with respect to the accessory and timing gear housing of the engine to define an oil receiving compartment 98. ln addition to the oil from the shaft journals S8, this compartment also collects the oil supplied to the gears through the ports 81 in the end plate 34. The upper port 8l also supplies oil to the spring packs 9d through intermittently aligned ports 99 in the gear 8f3. A second cover member lili? is also secured to the end plate 33 by the end plate securing bolts V5'2. This cover is imperforate and defines a second oil receiving compartment 101. The oil receiving compartments 97 and lill are both drained and vented through ports lil-Z extending through their respective end plate iianges 70. The ports v102` are located to maintain a gear tooth immersing oil level and mate with crankcase connected ports 103 in the side wall of the engine block.

From the foregoing description of a preferred embodiment of the invention, it will be apparent to those skilled in the art that various changes might be made therein without departing from the scope and spirit thereof as dened in the following claims.

We claim:

1. A positive displacement rotary blower comprising a pair of lobed impellers, a housing defining a pumping chamber and rotatably mounting said impellers, said housing including an intermediate housing member having an inlet port and an outlet port therein opening on opposite sides of said chamber with respect to a plane passing through a rotative axes of said impellers and two end plates secured to opposite ends of said intermediate housing member and dening the end walls of said pumping chamber, said end plates each having two spaced parallel bearing delining portions, said bearing portions having co-planar end faces opposite said chamber and bearing bores extending therethrough, shaft journal portions extending from, rigidly secured to and rotatably journaling said impellers in said end plate bearing bores, said journal portions at one end of said impeller projecting slightly beyond the adjacent end plate, timing gears drivingly connected to said projecting journal ends in spaced relation to the adjacent co-planar end faces and engaged to drive said lobed impellers in cooperatively phased intermeshed pumping relation to each other, drive means associated with one of said gears for driving said impellers to effect pumping displacement from said inlet port to said outlet port, the shaft journals at the opposite end of said impellers each having a hardened thrust washer secured thereto, said washers each being in bearing relation with the adjacent co-planar end face of one of the journal bearing defining portions, and a stationary thrust member secured in spaced parallel relation to said journal end faces and in bearing relation to said washers, whereby said thrust washers and members restrain axial thrust movement of said impellers thereby maintaining said impellers in proper rotative sealing clearance with said end walls.

2. A positive displacement rotary blower comprising a housing defining a pumping chamber, said housing inciuding an intermediate housing member having an inlet port and an outlet port therein opening on opposite sides of said chamber, and two end plates secured to opposite ends of said intermediate housing member and defining the end walls of said pumping chamber, said end plates each having two spaced parallel bearing dening portions, said bearing portions having co-planar end faces opposite said chamber end walls and bearing bores extending therethrough, a pair of lobed impellers including shaft journal portions extending therefrom, rigidly secured to and rotatably journaling said impellers in said end plate bearing bores, drive means associated with one end of said impellers and operable to drive said lobed impellers in cooperatively phased intermeshed pumping relation to each other to effect pumping displacement from said inlet port to said outlet port, the shaft journals at the opposite end of said impellers each having a hardened thrust washer secured thereto in bearing relation with the end face of the journal bearing defining portions in the end plate, and a stationary thrust member secured in spaced parallel relation to said journal end faces and in bearing relation to said washers, said thrust washers and members thereby restraining axial thrust movement of said impellers and maintaining said impellers in proper rotative sealing clearance with said end walls.

3. In a rotary blower, a housing deiining a pumping chamber and having an inlet port and an outlet port therein opening on said chamber, an impeller rotatably mounted in said pumping chamber, said housing defining two spaced end walls of said pumping chamber having endwise sealing clearance with said impeller, said end walls having aligned bearing defining portions, said bearing portions having bearing bores extending therethrough and at least one of said portions having a bearing end face opposite said chamber, shaft journal portions extending from, rigidly secured to and rotatably journaling said impeller in said bearing bores, drive means associated with said impeller and operable to drive said impeller to effect pumping displacement from said inlet port to said outlet port, one of said shaft journals having a hardened thrust washer secured to the end thereof in bearing relation with the adjacent end face of said one bearing delining portion, and a stationary thrust member secured in spaced parallel relation to said one journal end face and in bearing relation to said washer whereby said thrust washer and member restrain axial thrust movement of said impeller and maintain said impeller in proper endwise rotative sealing clearance with said end walls.

4. In a rotary blower, an aluminum housing dening a pumping chamber and having an inlet port and an outlet port therein opening on said chamber, an impeller rotatably mounted in and having normal sealing clearance with said pumping chamber, said housing defining two spaced end walls of said pumping chamber, said end walls having aligned bearing defining portions and said bearing portions having bearing bores extending therethrough and at least one of said portions having a bearing end face opposite said chamber, shaft journal portions extending from, rigidly secured to and rotatably journaling said impeller in said bearing bores to maintain said impeller in proper radial sealing clearance with said housing chamber, drive means associated with said impeller and operable to drive said impeller to effect pumping displacement from said inlet port to said outlet port, a hardened steel thrust washer secured to the end of one of said shaft journals in bearing relation with the adjacent end face of said one bearing defining portion, and a stationary cast iron thrust member secured in spaced parallel relation to said one journal end face and in bearing relation to said washer whereby said thrust washer and member restrain axial thrust movement of said impeller and maintain said impeller in proper endwise rotative sealing clearance with said chamber defining end walls.

5. ln a rotary blower as defined in claim 4, passage means in said end walls for supplying lubricant to and intersecting said bearing bores.

6. ln a rotary blower as defined in claim 5, a lubricant supply port intersecting said passage means and opening on said one end face, said port directing lubricant between said end face and said washer, and said washer having at least one port extending therethrough and intermittently connectable with said end face port to direct oil between said Washer and stationary member.

7. A positive displacement rotary blower comprising a housing defining a pumping chamber and including an intermediate housing member having an inlet port and an outlet port opening on opposite sides of said chamber and two end plates secured to opposite ends of said intermediate housing member and defining the end walls of said pumping chamber, said end plates each having two spaced parallel bearing defining portions, said bearing portions having bearing bores extending therethrough and the bearing portions of at least one of said end plates having finished co-planar bearing end faces opposite said chamber, a pair of lobed impellers cooperatively intermeshed 'to effect pumping displacement between the inlet and outlet ports, journal portions extending from, rigidly secured to and rotatably journaling said impellers in said end plate bearing bores to maintain said impellers in rotative sealing clearance with respect to each other and radially with. respect to said intermediate housing member, means for driving said impellers in phased relation to each other to effect pumping displacement from said inlet port to said outlet port, a hardened thrust washer secured to the end of the shaft journals mounted in said one end plate, said washer being in bearing relation with the bearing end faces of said one end plate, and a stationary thrust member secured in spaced parallel relation to said journal end faces and in bearing relation to said washers, said thrust washers and members restraining axial thrust movement of said impellers thereby maintaining said impellers in proper rotative sealing clearance with said end walls.

8. A positive displacement rotary blower as set forth in claim 7 wherein said end plates are of aluminum, said thrust washers are of hardened steel, and said thrust member is of cast iron.

9. A positive displacement rotary blower as set forth in claim 7, passage means in said end plates for supplying lubricant to and intersecting said bearing bores.

10. A positive displacement rotary blower as set forth in claim 9, a lubricant supply port intersecting said passage means and opening on the end faces of said one plate, said ports directing lubricant between said end faces and said washers, and said washers each having at least one port extending therethrough and intermittently connectable `with said end face ports to direct oil between said washers and stationary member.

11. A positive displacement rotary blower comprising a housing defining a pumping chamber and having an inlet port and an outlet port opening thereon, said housing including an intermediate housing member and two interchangeable end plates each having a peripheral flange secured to opposite ends of said intermediate housing member and a web portion defining opposite end walls of said pumping chamber, said end plates each having two spaced parallel bearing defining portions extending outwardly from its web portion, said bearing portions having bearing end faces opposite said chamber co-planar with the end faces of the end plate flange and bearing bores extending therethrough, two impellers rotatably mounted in said chamber and having rotative sealing clearances with respect to each other and cooperating to effect pumping displacement between said inlet and outlet ports, said impellers each having a plurality of intermeshing lobes extending longitudinally thereof, said lobes having side faces of involute form interconnected outwardly by an outer peripheral portion of constant radius spaced radially from said chamber defining surfaces of said intermediate member, said peripheral portion having a plurality of ribs extending longitudinally thereof, said ribs having rotative sealing clearance with the chamber defining surfaces of said intermediate member, the involute side faces of each impeller being interconnected inwardly by root surfaces of constant radius defining sealing clearances with the peripheral ribs of the other impelier, journal portions extending from, rigidly secured to and rotatably journaling said impellers in said end plate bearing bores to maintain proper sealing clearances between said impellers and said intermediate housing, said journal portions at one end of said impeller projecting beyond the adjacent end plate, helical timing gears driviugly connected to said projecting journal ends in spaced relation to the adjacent bearing end faces and engaged to drive said impellers in phased relation to each other, the shaft journals at the opposite end of said impellers each have a thrust washer secured thereto, said washer being in bearing relation with the bearing end faces of the journal bearing defining portions of the adjacent end plate, a stationary thrust member secured in spaced parallel relation to said bearing end faces and in bearing relation to said washers, said thrust washers and member restraining axial thrust movement of said impellers thereby maintaining said impellers in proper rotative sealing clearance with said end walls, and drive means associated with one of said gears for driving said impellers to effect pumping displacement from said inlet port to said outlet port.

12. A positive displacement rotary blower as set forth in claim l1 wherein said end plates are of aluminum, said thrust washers are of hardened steel, and said thrust member is of cast iron.

13. A positive displacement rotary blower as set forth in claim 1l, said end plates each having two parallel lubricant supply passages therein intersecting said bearing bores and a third passage extending between said two passages, the passage-defining portions of said end plates reinforcing the outlet sides thereof, and means for supplying pressurized oil to one of said passages.

14. A positive displacement rotary blower as set forth in claim 13, a lubricant supply port intersecting said passage means and opening on the end faces of said plates, said ports adjacent said gears directing lubricant thereon and said ports adjacent said washers directing lubricant between said end faces and said washers, and said washers each having at least one port extending therethrough and intermittently connectable with said end face ports to direct oil between said washers and stationary member.

References Cited in the file of this patent UNITED STATES PATENTS Re. 24,932 Davey Jan. 3l, 1961 12,350 Holly Feb. 6, 1855 1,645,967 Patterson Oct. 18, 1927 1,795,579 Storey Mar. 10, 1931 2,014,932 Hallett Sept. 17, 1935 2,096,870 Vollenbroich Oct. 26, 1937 (ther references on following page) 9 UNITED STATES PATENTS Manseld Feb. 3, 1942 Simons Mar. 10, 1942 Collier Apr. 13, 1943 Irons July 27, 1943 Shaeffer Dec. 24, 1946 Guibert et al. Apr. 13, 1948 Houghton Nov. 29, 1949 McCulloch Dec. 20, 1949 Flanagan Aug. 22, 1950 Muller Oct. 24, 1950 10 Rawlins Dec. 26, 1950 Wachter Apr. 15, 1952 Pauget Sept. 1, 1953 Bayles Feb. 23, 1954 Thomas et al. Feb. 12, 1957 Smith Oct. 14, 1958 Aumick Jan. 19, 1960 FOREIGN PATENTS Great Britain Jan. 16, 1939 Great Britain Oct. 26, 1943