US2644389A

US2644389A - Diffuser for air conditioning systems

Info

Publication number: US2644389A
Application number: US123927A
Authority: US
Inventors: George S Dauphinee
Original assignee: W B CONNOR ENGINEERING CORP
Current assignee: W B CONNOR ENGINEERING CORP
Priority date: 1949-10-27
Filing date: 1949-10-27
Publication date: 1953-07-07
Anticipated expiration: 1970-07-07

Description

I w s p i July 7, 1953 G. s. DAUPHINEE I 2 6 DIFFUSER FOR AIR CONDITIONING SYSTEMS Filed Oct. 27, 1949 2 Sheets-Sheet 1 GEORGE .S. DAUPLHNEE I INVENTOR.

July 7, 1953 s. s. pAUPHINEE DIFFUSER FOR AIR CONDITIONING SYSTEMS 2 Sheets-Sheet 2 Filed Oct. 27, 1949 IN VEN TOR. GEORGE s DAUPHINEE AT TOCIN 53f.

FIGS.

:entire floor area.

Patented July 7, 1953 UNITED STATES PATENT i OFFICE DIFFUSER FOR AIR CONDITIONING SYSTEMS George S. Dauphinee, Brooklyn, N. Y., assignor to W. B. Connor Engineering Corp., New York, N. Y., a corporation of New York Application October 27, 1949, Serial No. 123,927

12 Claims.

ed in exposed position, thereby requiring the ducts to be disposed compactly and inconspicuously and as harmoniously as possible with the "architectural features of the conditioned enclosure. closure is considerable and the cooling requirements for different sections of the floor area vary Frequently the floor area of the endepending upon the activity and conditions of use of these sections.

Under the conditions indicated the operation of the air outlet devices of the air conditioning system must be extremely flexible to meet vary- 'ing demands and requirements. A large number of relatively low volume outlets must be provided and arranged initially to uniformly cover the some of the outlets may furnish more than the average air volume, some may furnish less than the average air volume, and others may be shut off entirely. The air discharge velocity from the outlets must be relatively high in order to pro- 5- ,vide sufficient throw for uniform coverage and to equalize the air supply and room temperature in "enclosures having initial temperature differentials up to 25 degrees F. Under these high velocity and high duct static conditions noise prevention becomes a serious problem in the design of the air outlet especially when the outlets are throttled, resulting in excessive impact and vortex noises.

Accordingly it is a primary object of the present invention to provide an improved air outlet device of the character indicated which is constructed and arranged in such a manner as to minimize the generation of objectionable noises upon the discharge of air therethrough,

A further object of the invention is the provision of an outlet device of the character indicated provided with a simple and inexpensive mation of high velocity jets of large mass within However,v in actual operation 5 throttling means operating to prevent the for- 'F. P. M. and 4" W. G.

the device and consequently minimizing vo-rte and impingement noises.

The apparatus shown in the drawings discloses an air outlet device capable of operating with air velocities in the duct of about 3000 F. P. M. and duct static pressure of about 1 W. G. pressure when 0.7" W. G. only is necessary to produce the specified flow volume and the device must further permit suffucient throttling to obtain a 50% volume reduction or more or even to be shut ofi entirely against 1 W. G. pressure or more without producing objectionable noises or apprecia bly increasing the normal room noise level. However, the invention also contemplates outlet devices capable of operating satisfactorily at much higher duct velocities and pressure, 8000 The foregoing objects, as well as additional objects and advantages of the invention will be readily apparent in the course of the following detailed description taken in connection with the accompanying drawings which illustrate preferred embodiments of the invention,

and wherein: V

Fig. 1 is a vertical sectional view of an air outlet device embodying the features of the invention, the device bein shown attachedto an air supply duct.

Fig. 2 is a' sectional view taken along the line 2--2 of Fig. 1.

Fig. 3 is an air flow diagram illustrating the advantages of the improved air outlet device over an outlet device of conventional design.

Fig. 4 is a vertical sectional view of a modified form of air outlet device.

Fig. 5 is a sectional view taken along line 55 of- Fig. 4

Conventional air outlets and ceiling diffusers are generally provided with a neck which is attached directly at an opening in the air supply duct with the result that the impingement of the air stream in the duct against the sharp edge of the duct opening will generate objectionable whistling noises. The air outlet device of the present invention is provided with a mounting ring which is dished upwardly so that its upper surface will be disposed on alevel slightly higher than the duct opening which receives the device,

thereby deflecting the air stream away from whistling contact with the relatively sharp, thin metal edge of the duct opening.

In general air flowing from the supply duct into:

an outlet device enters the device obliquely impinging-On the side of the neck which in turn deflects the air downwardly or outwardly parallel to the wall of the neck. The stream velocity through the neck is not uniform. On the impinging side it may be 1 times the average velocity or more, and on the opposite side the velocity may be substantially zero. The direction of the obliquely entering air stream is determined by the air velocity of approach within the duct and the higher the velocity, the greater will be the impact and the noise generated thereby. A sharp edge entry, as in most conventional outlets, further contributes to the generation of objectionable noises. In the present outlet device the entry to the device is provided with a rolled or generously rounded edge which ispreferably backed with sound absorbing material in order to lessen undesirable noise and vibration due to impact of air at the entry.

The final stream discharged from the outlet device to the conditioned enclosure must have a definite direction and a substantially uniform velocity. The discharge direction, except in special cases, is substantially horizontal or slightly downward. Uniform discharge velocity is. especially important when the outlet discharge orifice is a continuous peripheral slot or a number of individual peripheral slots. In order toprovide for such flow control, it has been conventional practice to provide the air entry with various typesof deflecting. members which frequently take the form of vertical vanes positioned crosswise at right angles to the flow direction in the distributing duct. Such deflecting vanes convert the single air stream entering the outlet device into a plurality of streams distributed over the entry neck area and. greatly contribute toward the promotion of uniform flow from the discharge orifice of the outlet device. However, the

flow characteristics of the separate streams are the same as those of the single original stream. For example, if the inlet is provided with three deflecting vanes, four separate streams or channels are produced. For each of the individual streams, as for the original stream, the air velocity on the impingement side of the channel will be approximately 1 times average and on the opposite side will be approximately zero, the total result being. an increase in impact noise. The design and construction of the present outlet avoids this latter disadvantage by not requiring the use of deflecting vanes.

As have been previously stated, an eflicient air outlet device should be provided with means for throttling or volume control. When throttling is accomplished in th conventional devices in the customary manner by a damper or valve, high velocities will beproduced throughthe restricted passage of the device. When the differential pressure across the restricted passage is high, a high velocity jet of large mass will be produced resulting in excessive impact and vortex noises. The present invention operates to prevent the formation of high velocity jets of large mass within the outlet device by having the air flow from the inlet opening into a plenum defined by a perforated cylinder fitted with a closure disc or diaphragm. axially slidable therewithin for variable throttling effect. The perforated wall provides uniformity of flow, breaks the air stream down into a multiplicity of streams having relatively small mass, and, before merger of the streams, causes a rapid reduction in velocity after passage through the restricted or throttled perforated passage.

Referring first to Figs. 1 and 2 of the drawings, the air outlet device includes a casing com.-

prising a base member or mounting ring In and cover piece H. The device may be secured to an air distributing duct i2 by means of bolts l3 and a gasket [4 is preferably interposed between mounting ring 10 and duct l2. Mounting ring i0 is dished upwardly todefine the attachment flange l5 and a raised portion 16 which extends into the duct 12 on a level slightly above the duct opening. By reason of the latter arrangement and the presence of gasket l4, whistling contact of the air stream in the duct against the sharp metal edge of the duct opening is avoided, as may be readily seen in the flow diagram of Fig. 3' which illustrates a conventional outlet device on the left and the improved outlet device on. the. right side thereof. Line it represents the magnitude and direction of the duct velocity head, line b the duct static pressure and line 0 the resultant direction of the air stream and its magnitude on entering the outlet.

The air entry into the outlet deviceis defined by a. central opening I! formed in mounting. ring II] and having a rolled or generously roundededge Ila. A layer of sound absorbing material It is applied to the entire inner surface, of mounting ring l0 and backs up the rounded edge Ila of inlet opening H in order to minimize noise and vibration due to air impact thereat. Cover. piece ll is also lined with a layer of sound. absorbing material IS. The sound absorbing layers are preferably from to /2" thick and may be sprayed. on. or may be prepared sheet cemented in place.

A perforated cylinder 20, having a plurality of perforations 20a, surrounds and depends from inlet opening l'l. Cylinder 20 isprovidedwith a closure disc or diaphragm 2| axially slidable therewithin to produce the desired throttling effect without generating objectionable high velocity solid streams and resultant erratic flow within the device. Diaphragm 2! is provided with. a sealing member or ring 22, and sound. absorbing material 23 is mounted on diaphragm. 2.! within the ring 22. An adjusting screw 25 passes through the bottom of cover. piece I IV into thread ed engagement with nut 24. A washer 26 is secured to screw 25 on the inside of cover piece I l. The thrust of the adjusting screw 25-is taken up by the nut 24 in one direction and by the bottom of cover piece I l in the opposite direction. Diaphragm 2! may be raised by means of adjusting screw 25 to progressively cut off. portions of the perforated wall area of cylinder 20 and produce a throttling effect and. complete throttling is accomplished when seal member 22 contacts the bottom of rounded inlet edge Ha.

After passage through the perforated cylinder 20, air will pass into the annular space between said cylinder andthe casing l l and then toward the discharge orifice 211 formed in the casing. While a single discharge orifice is illustrated in Figs. 1 and 2, two or more discharge orifices may be provided when it is desired to discharge the air from the outlet in various directions.

The free open area of perforated cylinder 20 is preferably such as to provide for a differential pressure of about 0.25" W. G. or approximately three tenths of the full pressure loss through the device at maximum volume and when diaphragm 2| is at fully open position. This provision insures reasonably uniform flow through the perforated cylinder and allows reduction of the height of the cylinder in the interest of compactness of design. The throttling sensitivity is also favorably affected since the higher the ratio of the differential pressure of the perforated cylinder to the total pressure loss, the more sensitive will be the throttling effect resulting from movement of the diaphragm 2|. For compactness-in design, the size of the perforations in cylinder 26 should be not more than approximately diameter and for other practical considerations not less than diameter. The open area of the wall of cylinder 26 should preferably be between 40 to 60%. The stated values are given for purposes of illustration only since they may be varied to meet different requirements.

' The following example will illustrate the advantages of the construction of the present invention with particular attention to perforated cylinder 20:

Diameter of perforation 0.10" Open area 50% Coefficient of contraction 80% The perforation has a slightly rounded edge on one side due to punch effect, and when this edge is upstream or on the air entry side, the coefficient of contraction is greater than that for the sharp edge orifice. The proximity of the jets emerging from the perforated cylinder further efiects an increase in area of the vena contracta or contracted emergent jet. The flow area at the vena contracta would be 50 0.80 or 40% of the gross sheet area. The emergent small streams or jets produced are close together and will merge quickly to form a solid stream of relatively low velocity. The distance between the perforated cylinder and the point of merger will be in the order of 4 to 5 times the diameter of the perforation and for a perforation diameter of 0.1" will be approximately If the differential pressure across the perforated wall were 0.1"v W. G., the velocity at the vena contracta would be practically 4000 F. P. M. and at the 'point of merger 1 would be 4000x040 or 1600 F. P. M. The'noise resulting from impact at such velocities is negligible. From the foregoing it is evident that the perforated cylinder 20 provides (1) uniformity of flow, (2) breaks the air stream down into a multiplicity of streams having relatively small mass and (3) before merger, causes a rapid reduction in velocity of the contracted jets after passage through the restricted perforated passages in the cylinder wall.

The device constructed as has been described P will provide satisfactory quiet operation in the majority of cases under the conditions indicated. When quieter operation is desired under more severe conditions or when it is necessary to provide for the absorption of noises originating in the air supply duct in addition to those originating in the outlet device a baflie member or cylinder 3!) may be provided. Cylinder 30 is preferably perforated and is provided on its inner surface with a thin fibrous sheet 3| of felt or the like and on its outer surface with a layer of sound absorbing material 32 similar to the sound absorbing layers l8 and I9 previously described. The sound absorbing qualities of baflie cylinder 30 are enhanced by perforating and the thin sheet 3| prevents the passage of dust and protects the porous sound absorbing layer 32 from dust collection. Cylinder 311 may be provided with an attachment flange 33 secured to mounting ring It by means of screws 34 with sound absorbing layer l8 compressed between said attachment flange and mounting ring. Perforated cylinder 26 may be secured in position in a similar manner, as shown in Fig. 1; or in any other 6 suitable manner. In order to facilitate the flow of air to the discharge orifice 21, baffle cylinder may be shorter in length on the side opposite the discharge orifice.

Figs. 4 and 5 illustrate a modified form of the invention. The air outlet device includes a casing comprising a mounting ring and a cover piece 4|. The device may be secured to the air distributing duct 42 by means of bolts 43 and a gasket 44 is preferably interposed between mounting ring 46 and duct 42. Mounting ring 46 is dished upwardly to define the attachment flange 45 and a raised portion 46 which extends into the duct 42 on a level slightly above the duct opening. The air entry into the outlet device is defined by a central opening 41 formed in mounting ring 40 and having a rolled or generously rounded edge 41a. A layer of sound absorbing material 48 is applied to the entire inner surface of mounting ring 46 and backs up the rounded edge 41a of inlet opening 41. Cover piece 4| is also lined with a layer of sound absorbing material 49. Cover piece 4| is provided with a plurality of annular steps 56 in order to retain various bafiiing and damping elements, said elements being spot welded in place or secured in any other suitable manner.

An inner cylinder 5| is secured at its lower end to an annular step 50 of cover piece 4| and is of sufficient length to project slightly into sound absorbing layer 48 of mounting ring 4|], said cylinder encompassing inlet opening 41 and defining a separate plenum or compartment 52 for the air stream entering the device. Cylinder 5| is provided with a plurality of perforations 5|a throughout its area. A damper element 53 is axially slidable within cylinder 5| for throttling purposes. Said damper element includes a lower drum or skirt portion 54 and an upper compartment 55 separated by an intermediate perforated plate 56. Upper compartment 55 is packed with sound damping material 51 such as glass wool. Skirt portion 54 is provided with a recess for retaining a sealing member 58. Damper element 53 carries a nut 59 which is secured to plate 56. An adjusting screw 66 passes through the bottom of cover piece 4| into threaded engagement with nut '59. A washer 6| is secured to screw 66 on the inside of cover piece 4|. The thrust of the adjusting screw is taken up by the nut 59 in one direction and by the bottom of cover piece 4| in the opposite direction. Damper element 53 'may be raised by means of adjusting screw 60 to progressively cut off portions of the perforated wall area of cylinder 5| to produce a throttling effect.

A pair of baflie members or cylinders 62 and 63 are supported concentrically with respect to inner cylinder 5| on annular steps 56 of cover pieF 4|. Alternate segments, 62a and 63a, of the intermediate cylinders 62 and 53 are perforated for air passage therethrough and alternate segments are unperforated and lined on the inside with sound damping material 621) and 631). In order to achieve maximum sound damping effect combined with uniform flow, cylinders 52 and 63 are so arranged with respect to each other that the perforated and sound-damped areas of one of the cylinders are in alignment with the sounddarnped and perforated areas respectively of the other of said cylinders, as clearly shown in Figs. 4 and 5. Cover piece 4| is provided with a pair of oppositely disposed discharge orifices 64 for distributing the air stream emerging from the outlet device. The flow of air proceeds from' air inlet 47 into compartment 52, through perforated cylinder 5!, through. the perforated areas 62a of baffle cylinder through the perforated areas 63a. of bafile cylinder 63 and finally through the discharge orifices 64, as indicated by the arrows in Figs. 4 and 5. I

It is emphasized that this specification is given by way of example and that special requirements may occasion higher velocities than those referred to herein which might require more extensive sound absorbing material or surface. Again, there may be occasions when the air velocities and duct static pressure are moderate and where full lining of the outlet with sound absorber material may not be necessary. Parts 13 and .32 may be omitted. It may also be found advisable to increase the perforation diameter or to increase the open area or both beyond the preferred limits previously stated. Thus, certain additional modifications may be made within the scope of the following claims without departing from. the invention. It is intended that all matter contained in the foregoing specification and shown in the accompanying drawings be interpreted merely as illustrative and not in a limiting sence.

' What is claimed is:

l. A diffuser for use in an aii conditioning or ventilating device and adapted. for connection to the. opening of an air supply duct, comprising a casing for connection to said supply duct, an air inlet orifice in said casing, ana-ir outlet orifice in said casing, a periorated'cylinder communicating with said inlet orifice and defining a separate compartment occupying a portion or the space within said casing between said inlet and outle orifices, a damper member axially slidable within said cylinder, actuating means for said damper member operable externally of said and at least one baflle member disposed between said cylinder and said casing, said baffle member having a layer of sound absorbing material applied thereto.

2. A diffuser for use in an air-conditioning or ventilating device and adapted for connection to the opening of an air supply duct, comprising a g casing for connection to said supply 'duct, an air inlet orifice in said casing, an air outlet orifice in said casing, a perforated cylinder communicating with said inlet orifice and defining a separate compartment occupying a portion of the space within said casing between said inlet and outlet orifices, a damper member axially slidable within. said cylinder, actuating means for said damper member operable externally of said casing, and at least one cylindrical bafiie member disposed between said cylinder and said casing, said bafile member having its wall uniformly spaced from the outer surface of the cylinder, said ballie member being perforated throughout its area and having a layer of sound absorbing material applied thereto.

3. An air outlet device for connection to the opening of an air supply duct, comprising a casing for connection to said supply duct and defined by a base member and a cover piece depending therefrom, said base member being dished upwardly to define a peripheral. attachment flange and an inner elevated portion adapted to be disposed on a level slightly above said duct opening, said base member having a centrally disposed air inlet orifice provided with a rolled, rounded airimpact edge, said cover piece having an air outlet orifice, a perforated cylinder communicating with said inlet orifice and defining a separate compartment occupying a portion of the space within said casing between said inlet and outlet orl fices, a damper member slidable within said cylinder, and actuating means for said damper member operable externally of said cover piece.

4. An air outlet device for connection to the opening of an air supply duct, comprising a casing for connection to said supply duct and defined by a base member and a cover piece dependingtherefrom, said base member being dished upwardly to define a peripheral attachment flange and an inner elevated portion adapted to be dis posed on a level slightly above said duct opening, said base member having a centrally disposed air inlet orifice provided with a rolled, rounded airimpact edge, the inner surfaces of said cover piece and said base member including said air-impact edge being lined with sound absorbing material, said cover piece having an air outlet orifice, a perforated cylinder communicating with said in.- let orifice and defining a separate compartment occupying a portion of the space within said casing between said inlet and outlet orifices, a damper member slidable within said cylinder, and actuating means for said damper member operable externally of said cover piece.

5. An air outlet device for connection to the opening of an air supply duct, comprising a casing for connection to said supply duct and defined by a base member and a cover piece depending therefrom, said base member being dish-ed upwardly to define a peripheral attachment flange and an innor elevated portion adapted to be disposed on a level slightly above said duct opening, said base member having a centrally disposed air inlet orifice provided with a rolled, rounded air-impact edge, the inner surfaces of said. cover piece and said base member including said air-impact edge being lined with sound absorbing material, said cover piece having an air outlet orifice, a perforated cylinder communicating with said inlet orifice and defining a separate compartment occupying a portion of the space within said casing between said inlet and outlet orifices, a damper member slidable within said cylinder, actuating means for said damper member operable externally of said cover piece, and at least one bafile member disposed between said cylinder and said cover piece, said baflle member having a layer of sound absorbing material applied thereto.

6. An air outlet device for connection to the opening of an air supply duct, comprising a casmg for connection to said supply duct and defined by a base member and a cover piece de-- pending therefrom, said base member being dished upwardly to define a peripheral attachment flange and an inner elevated portion adapted to be disposed on a level slightly above said duct opening, said base member having a centrally disposed air inlet orifice provided with a rolled, rounded air-impact edge, the inner surfaces of said cover piece and said base member including said air-impact edge being lined with sound absorbing material, said cover piece having an air outlet orifice, a perforated cylinder communicating with said inlet orifice and defining a separate compartment occupying a portion of the space within said casing between said inlet and outlet orifices, a damper member slidable within said cylinder, actuating means for said damper member operable externally of said cover piece, and at least one cylindrical baffle member disposed between said cylinder and said cover piece, said bafile member being perforated and having a layer of sound absorbing material applied thereto.

7. An air outlet device for connection to the opening of an air supply duct, comprising a casing for connection to said supply duct and defined by a base member and a cover piece depending therefrom, said base member being dished upwardly to define a peripheral attachment flange and an inner elevated portion adapted to be disposed. on a level slightly above said duct opening, said base member having a centrally disposed air inlet orifice provided with a rolled, rounded air impact edge, the inner surfaces of said cover piece and said base member including said airimpact edge being lined with sound absorbing material, said cover piece having an air outlet orifice, said base member supporting a perforated cylinder communicating with said inlet orifice to define a separate compartment occupying a portion of the space within said casing between said inlet and outlet orifices, at least one baffle member supported by said base member and disposed between said cylinder and said cover piece, a damper member slidable within said cylinder, and actuating nieansfor said damper member oper able externally of said cover piece.

8. An air outlet device for connection to the opening of an air supply duct, comprising a casing for connection to said supply duct and de= fined by a base member and a cover piece depend ing therefrom, said base member being dished up" wardly to define a peripheral attachment fiange and an inner elevated portion adapted to be dis= posed on a level slightly above said duct opening, said base member having a centrally disposed air inlet orifice provided with a rolled, rounded air= impact edge, the inner surfaces of said said cover piece and said base member including said airimpact edge being lined with sound absorbing material, said cover piece having an air outlet orifice, said cover piece supporting a perforated cylinder communicating at its upper end with said inlet orifice to define a separate compart ment occupying a portion of the space within said casing between said inlet and outlet orifices, at least one baffle member supported by said cover piece concentrically with said cylinder, a damper member slidable within said cylinder, and actuating means for said damper member operable externally of said cover piece.

9. An air outlet device for connection to the opening of an air supply duct, comprising a casing for connection to said supply duct and defined by a base member and a cover piece depending therefrom, said base member being dished upwardly to define a peripheral attachment flange and an inner elevated portion adapted to be disposed on a level slightly above said duct opening, said base member having a centrally disposed air inlet orifice provided with a rolled, rounded air-impact edge, the inner surfaces of said cover piece and said base member including said air-impact edge being lined with sound absorbing material, said cover piece having an air outlet orifice, said cover piece supporting a perforated cylinder communicating at its upper end with said inlet orifice to define a separate compartment occupying a portion of the space within said casing between said inlet and outlet orifices, concentric cylindrical baffle members supported by said cover piece and disposed externally of said perforated cylinder, alternate sectors of said bafile members being perforated and lined with sound damping material, the perforated sectors of a given baffle member being in alignment with the sound-damped sectors of an adjacent baflie member, a damper member slidable within said perforated cylinder, and actuating means for said damper member operable externally of said cover piece.

10. A diffuser for use in an air conditioning or ventilating system and adapted for connection to the opening of an air supply duct, comprising a casing for connection to said supply duct, an air inlet orifice and an air outlet orifice in said casing, a perforated cylinder having a perforated wall communicating at one end with said air inlet orifice and defining a separate compartment within said casing, the other end of said perforated cylinder being closed and means to vary the perforated area of said hollow member to regulate the air volume.

11. A diffuser for use in an air conditioning or ventilating system and adapted for connection t the opening of an air supply duct, comprising a casing for connection to said supply duct, an air inlet orifice and an air outlet orifice in said casing, a hollow member having a perforated wall communicating at one end with said air inlet orifice and defining a separate compartment within said casing, a damper member closing the other end of said hollow member, said damper member being axially slidable within said hollow member to vary the degree of perforated area of said hollow member.

12. A diffuser for use in an air conditioning or ventilating system and adapted. for connection to the opening of an air supply duct, comprising a casing for connection to said supply duct, an air inlet orifice and an air outlet orifice in said casing, a hollow member having a perforated wall communicating at one end with said air inlet orifice and defining a separate compartment within said casing, a damper member closing the other end of said hollow member, said damper member being axially slidable within said hollow member to vary the degree of perforated area of said hollow member, said damper being lined with sound absorbing material.

GEORGE S. DAUPHINEE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 312,177 Ayer Feb. 10, 1885 493,295 Robinson Mar. 14, 1893 857,098 McNees June 18, 1907 1,115,873 Spencer Nov. 3, 1914-. 1,319,526 Hauser Oct. 21, 1919 1,659,880 Kauffman Feb. 21, 1928 1,705,778 Munroe et al Mar. 19, 1929 1,921,457 Dickinson Aug. 8, 1933 2,197,614 Hall et a1 Apr. 16, 1940 2,299,299 Bills Oct. 20, 1942 2,332,969 Higley Oct. 26, 1943 2,392,393 Kennedy Jan. 8, 1946 FOREIGN PATENTS Number Country Date 618 Germany 1877