US2885202A

US2885202A - Resilient cushioning arrangement

Info

Publication number: US2885202A
Application number: US429057A
Authority: US
Inventors: Trumper Konrad
Original assignee: SIEGENER EISENBAHNBEDARF AG FA
Current assignee: SIEGENER EISENBAHNBEDARF AG FA; SIEGENER EISENBAHNBEDARF AG Firma
Priority date: 1952-12-08
Filing date: 1954-05-11
Publication date: 1959-05-05
Anticipated expiration: 1976-05-05
Also published as: GB769560A; FR1089112A

Description

May 5, l959 K. TRUMPER RESILIENT cusHIoNING ARRANGEMENT Filed may 11, 1954 4 Sheets-Sheet 1 Inventor-1' Holy/Ab WUMPER May 5, 1959 K. TRUMPER RESILIENT cusHroNING ARRANGEMENT 4 Sheets-Sheet 2 Filed May l1, 1954 m wm .mm m, mw mmh; wmv. um um.. mm.. wm. F. n@ A m00 mzvk May 5, 1959 K TRUMPER 2,885,202

RESILIENT CUSHIONING ARRANGEMENT Filed May l1, 1954 4 Sheets-Sheet 5 ,Inl/anton' KONRAD Wm PER #Maf May 5, 1959 K. TRUMPER `2,885,202

RESILIENT CUSHIONING ARRANGEMENT Filed May 11, 1954 4 4 sheets-sheet 4 Inventor? KONRAD mmfffz RESILIENT 'CUSHIDNING ARRANGEMENT Konrad 'Triimper, Grotzingen, `near Karlsruhe, Germany,

,assigner to Firma Siegener Eisenbahnbedarf Aktiengesellschaft, Krs. Siegen, Germany Application May 11, 1954, Serial No. 429,057

lClaims priority, vapplication Germany May 1,6, 1953 23 Claims. (Cl. 267-15) The present invention relates 'to ,a resilient cushioning arrangement for resiliently connecting two elements, and more particularly to a cushioning arrangement for :resiliently supporting a vehicle frame on wheel axles.

Progressively acting resilient suspensions are known which serve the purpose of producing a resilient support which is substantially uniform and independent of the weight of the load. Since it is very difcult to obtain this result with mechanical means, air is generally used ascu'shioning element for this purpose.

'It 'has been found that an air cushion has a very hard .resilient characteristic under full load, and therefore two consecutively acting air cushions having diierent pressure .have been provided in the prior art. However, the characteristic of resiliency of suspensions of this type is unstable at the point in which the second air cushion is subjecteldto the load whereby unfavorable operational conditions are caused when a medium load acts on the cushioning arrangement.

vIt 'is one object of the present invention to overcome the disadvantages of the known air cushioning arrangements, and to provide a cushio-ning arrangement which .',hasasubstantially constant natural oscillation frequency.

Itis another object of the present invention to provide a cushioning arrangement in which resilient air cushion- .ing .means having a hyperbolic characteristic, and solid .resilient means having a linear characteristic of resiliency 'are simultaneously effective.

`Itfis consequently `an object of the invention to providearesilient cushioning arrangement whose character- .istic of yresiliency is a combination of a linear character- `istic .and Ya hyperbolic characteristic of resiliency.

lIt is a further object of the present invention to connect the mechanical resilient cushioning means, and the ,air cushioning means to the resiliently connected elements by means of an operating liquid.

.It is astill vfurther object of thepresent invention to .providemeansfor keeping the resiliently connected ele- .,ments, such as a vehicle frame and the wheel axles at a Jsubstantially constant distance so that the height of the :frame .and of the body of the vehicle remains substantially constant.

,It is also an object of vthe present invention to provide vcontrol means for automatically supplying operating lliquid to the system, and vfor .automatically supply air `to the air cushioning means wheneverthe relative position between 'the resiliently connected elements changes yso as to hold such elements in a substantially constant relativev position.

With these objects in view the present invention mainly consists "in a cushioning arrangement for resiliently connecting `two elements, such as a'gframegand the wheel :aXle of a vehicle,.and comprises, in combination, cylin- 'der'means adapted -to be mounted on kone ofthe ele- ;ments piston means arrangedin the cylinder meansgslid- :ably 'therein and adapted'to beA mounted on the other of the elements, operating liquid in the cylinder means withinthespace kenclosed bythe piston means, air cushioning 2,885,202 ylatertted ,May 5 1959 means operatively connected to the operating liquid for cushioning relative movement of the piston means and of the cylinder means, the air cushioning means having `a hyperbolic characteristic of resiliency, and mechanical cushioning means including a resilient member consisting of a solid resilient material and being operatively connected to the operating liquid for cushioning relative movement of the piston means and of the cylinder means, the mechanical cushioning means having a linear characteristic of resiliency whereby the cylinder means and the piston means, and thereby the two elements, are resiliently connected according to the combined characteristics of resiliency of the cushioning means.

Preferably a liquid moving means, such as a pump, is provided for adding and removing operating liquid. A The pump is controlled by control means which are actuated by the relative movement between the resiliently connected elements.

Preferably an air moving means, such as an air compressor, is provided which is connected to the closed air cushioning vessel. In this embodiment other operating means are provided for controlling the operation of the compressor in accordance with the relative position of the two resiliently connected elements for holding the same in a substantialyy constant relative position.

Preferably dampening means are provided for dampening the movement of the piston and cylinder control means.

The novel .features which are considered as characteristie for the invention are set forth in particular inthe appended claims. The invention itself, however, both `as to its construction and its method of operation, to-

gether with additional objects and advantages thereof, will be best understood from the following description of specic embodiments when Vread in connection with the accompanying drawings, in which:

Fig. l is a schematic view showing a preferred ernv`bodiment of the present invention;

Fig. 2 is a schematic view showing the embodiment of Fig. l provided with automatic control means for holding the two resiliently connected elements in a substantially constant relative position;

Fig. 3 is a schematic view showing an embodiment of the present inventionin which a control cylinder and piston is provided as operating means;

Fig. 4 is a fragmentary schematic View showing an arrangement kaccording to the present invention app-lied to a set of wheel axles; and

Fig. 5 is a `schematic View showing an embodiment of the present invention including dampening means for the control means.

Referring now to the drawings, and more particularly toFig. l, the frame `ll of a vehicle is arranged above the wheel axle and the wheels 2 of which only one is shown in Fig. 1. The frame l is resiliently supported on the wheels 2 through thecylinder 4 and the piston 3 slidably mounted in the same. A liquid conduit means 5 connects the cylinder 4 with a closed air cushioning vessel 6, and with a cylinder member 7. A piston 8 is movable in the closed vessel 6 and denes in lone end portion of the same an air space in which an air cushion 9 of compressed air is contained. The other .end of the vessel' is lled 4with operating liquid. A piston member l0 is slidably arranged inthe cylinder member 7 and moves in accordance `with the `movement of the operating liquid in the same. Aresilient memberv l1 consisting. of a solid material urgesthe piston member lil toward the end `of the cylinder member 7 which communicates with the liquid conduit means '5. The arrangement is .preferably such that-both'cushioning-means,namely thefcorn- -pressed air cushion-9 andthe resilient kmember 11,.-act vsimultaneously, hutvit-y vis -.also contemplated to y.delay `the d. by `pittori 3 and cylinder 4,.and thereby the relative position cylindermember 101 is open at the end in which the metal maar` uqind conduit man s. A. liquid mi 15 including a valve cylinder and `rnvalveipiso 15'1is arranged :in the supplynnd discharge conduits `llie `valve piston has 18, 19whichcooperatewith the conduits 1.3.` `14. lever systeml'lcon :piston withthe piston 3 with the 1aothatrelativemovementbetween 1 2 and between piston 3`andcylinder 4 dental #shifting of the valve 15 betvireen` three .1, la one position,liquid` is supplied `to the liquid 5. in the second i position a liquid-indiscontrol piston 38 as described previously with reference to only one cylinder and piston 4, 3. The arrangement of Fig. 4 is used for care having relatively turnable wheel axles.

Referring now to Fig.` 5 it will be appreciatedthat the arrangement correspondsltothe embodiment shown in Fig. 3. i The` modied embodiment of Fig. 3 includes dampening `meauafor dampening the movement of the valve piston and of the valve cylinder 39 of the liquid control valve 15.l The valve cylinder `39 is` movably mounted and rigidly connected to a dampening cylinder 40. Consequently, the supply'and discharge conduits 13.

-\ 14 have to be connected to the valve cylinder by means position i the` .conduits 13, i

of exible hoses 13 and 14'. The valve piston? `15' is rigidly connected to the dampening piston 42 which has passages 43 passingitherethrough, so that movement of the valve piston 15'and of thedampening piston 42 is dampened due to the actionof a liquidqcontained in thedampeningcylinder40.` On thcllfhand,

`the dampening cylinder 48 is rigidly 41 which passes throughs spring housing `44twhich"is secured to a fixed support. The spring 47

urgesthe discs

48 and 49 apartso that the `movement of "the roda 41 is frame` `litera `desired height, or for loweringtheisame. i i

Fig. 2 further` showsair control meansfor `adding i ,i airto the air cushion 9in thevessel, and for air from the same. A compressor 28 is connectedby `sir supplyand discharge conduits `30,1131 and 25 to the` closed vessel 6. An air control valve 27 is: located in the supply dischargeconduit and includea a :valve piston iormedwith two passages 32 and 33.` The valve piston is` connected to the` operating means, shown to be a lever system 29 which is connected on one hand to theframe l and to the cylinder 4 and on `thle other hand tothe wheel axle; and to the piston 3 that relative movement between piston 3 and cylin- `4 shiftsthe air control valve between three positions. one position air issupplied `bythe compressor 28 to air cushion 9. and in the second position the supply and discharconduits 30, 31are closed, and in the third airis dischargedkfromthe iair cushionthrough conduitt ln additionthereto conduits 35 `und 36 are providedwhichcan beclosed and opened; by manually operated ugs air cushion 9 at will. By the compressor 28 and aircontrol means 27 and 29 the position of the frame: 1 andthe wheels 2 can be held sub- `lhlll.: t u u i mthemodiedembodimentshowninlig. 3 theliquid operatingmeansis not a lever system, but a `control cylpiston 37,`38,"17'\arranged in the liquidconduitmcenl i5. Relative movement between thepiston`3 and :the `cylinder 4` movement of :the

ai riad. so met 'nsliquidis Implied 4or `therefromtoholdthecylin- 4. `The cylinders 4 are connected air valve means, 34 for varying the volume i.

resiliently dampened when the llanges and 46 engage thedisumana.19.1` y i M j Thearrangement operates in the `following manner: When the frame andthe wheel axles of` a" `vehicle tend `to move relative to` each other, operating `liquid is moved through the conduit means 5 or 5a`so that the air cushioning means 6, 8, 9, andthe mechanicalresilient cushioning means 10, 11 in thecylinderfmcans 6, 7 become operative. The mechanical resilient member 11 `consists ofmetal or rubber andihas a linear characteristic of resiliency, while the aircushioning means 8, 9 have `a hyperbolic characteristic ofl resiliency` so that the resilient action of the arrangement takes place accordance with the characteristic of resiliency obtained by superimposing the characteristics of the two cushioning of the air cushion 9 for moving the piston 3 and cylinder 4 apart when the samewere moved towards each other due `to operational conditions. On the other` hand,` air will be discharged from` the air cushion 9 when the piston 3 and cylinder 4 move apart. i

The dampening means acting on the liquid control valve 15 will dampen theautomatic operation inthe event that the `cushioning, arrangement is subject to "sudden jolts. In theevent that the wheel 2 moves over an obstacle so that the piston 3 exerts a sudden pressure on the operating liquid, such pressure impulse is conveyed by the` liquidand moves the `postori 38 in a rapid motion whereby the dampening piston is also operated through the piston rod 17'. `Since such movement is a rapid jolt, the` liquid in `cylinder `4t) Icannot pass through the passages 43 in theldampening piston 42 since `the same moves too rapidly so that the sudden pressurelintpulsc is transferred through theliquidmto the resriwall gol. the eylinderf40 `which intnrn abuts against the 48 throughthe rodi41 andthe tlange 45, the spring disc 48being spring-loaded by the pretensioned spring` 47. Consequently,` a movementof the piston 38 is possible due to the resilient mounting of the cylinder lon the spring 47, while no signilicant relative movementl takes place betweenthe dampening piston 42 and the cylinder controlcylinder 37a Afor moving the 75 40 if the transmitted impulse is "a sudden `and rapid jolt.

'assenso l*The liquid controlvalve is vnot actuated'lby Va short `and .rapid impulse.

When the load is gradually increased, rvwhich corresponds to a slow change of the pressure in the cy1inders'4 and in the adjacent conduit portion 5a, `the'piston 38 and the dampening piston 42 are slowly displaced 'so that the liquid can ilow through Vthe passages 43 resulting in a .relative motion between vthe piston 42 andthe cylinder 40. During such operation 'the control valve l15 is actuated, and permits passage of liquid.

It will be understood that each ofthe elements described above, or two or more together, may also find a useful application in other types of cushioning diering vfrom the .types described above.

While the invention has been illustrated and described as embodied in air cushioning arrangement including solid and gaseous cushioning means, and control means for keeping constant the relative position between the frame and the axles of a vehicle, it is not intended to be "limited to the details shown, since various `modifications and structural changes may be made without ydeparting inany way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention 'that others can by applying current knowledge readily adapt it `for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended 'to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. Cushioning arrangement for resiliently connecting the frame element of a vehicle with the-wheel axle element of the same, and comprising, in combination, 'a set of cylinders adapted to `contain van operating liquid, and adapted to be connected to one of said elements; a set of pistons slidably arranged in said cylinders, respectively, and adapted to be connected tothe other of vsaid elements; a closed air cushioning vessel adapted to contain a compressible gaseous medium in one end portion thereof; liquid conduit means connecting the other end portion of said air cushioning vessel wtih `said cylinders so that said air cushioning vessel is adapted to contain operating liquid at the other end thereof; a cylinder member having one end communicating with said liquid conduit means for receiving operating liquid; a piston member movable in said cylinder member and adapted to be moved by said operating liquid when said pistons and cyl- Vinders move relative to each other; a resilient member consisting of a solid resilient material and having a linear rcharacteristic of resiliency and urging said piston member toward said one end of said cylinder member whereby said frame element and said wheel element are resiliently connected for movement according to the linear characteristic of resiliency of said resilient member superimposed :from said liquid conduit means; a control cylinder located in said liquid conduit means so that operating liquid ows into and out of said control cylinder in accordance with the relative movement between said sets of cylinders and pistons; and a control piston slidably mounted in said control cylinder and being connected to said liquid valve means and moving the same between said positions in A:such manner that operating liquidissuppliedto, or discharged from, said liquid conduit means to`ho1d the rerspectively associated .pistons and cylinders of said cylin- -ders Land pistons, and thereby said two elements in a substantially constant vrelative position.

`2. VA cushioning arrangement as claimed .in claim ,11 and comprising dampening vmeans connected to asaid liquid control valve means 'for `dampening movements of the same.

3.A `cushioning arrangement las claimed in claim 1 wherein said liquid ycontrol valve means includes a movably mounted valve-cylinder and a valve piston movable in said valve cylinder, said `valve piston being connected to said controlrpiston `for movement therewith; amovable vdampening cylinder rigidly connected to said valve cylinder; a dampening piston formed with passages vtherethrough and being movable in said dampening cylinder, said dampening piston being rigidly connected to said valve piston for ymovement therewith; a fixed support;.and spring means Vabutting `at one vend against said xed support and at the other end against said darnpening cylinder for holding 4said dampening cylinder in spaced relationship to said lixed support.

4. A Acushioning Aarrangement yas 4claimed in claim l whereinsaid resilient member is a 'metal spring.

5. Cushioning arrangement for resiliently connecting two elements comprising, in combination, cylinder means adapted to be mounted on one of said elements; piston means arranged in said cylinder means slidable therein and adapted to be mounted on the other of said elements; air cushioning means having a hyperbolic characteristic of resiliency and including a rst expansible and contractible working chamber means; mechanical cushioning means including a resilient member consisting of a solid resilient material and a second expansible and contractible working chamber means adjacent and resilient member, `said mechanical cushioning means having Va linear characteristic of resiliency; conduit means connecting said first and-second working chamber means-inparallel with each Aother and in series with said cylinder means; Aand an operating liquid in vsaid conduit means, said 'first and second working chamber means, and said cylinder means so that said 'iirst and second working chamber lmeans expand and contract simultaneously but independently of each other during movement of said piston means whereby said cylinder means and said-piston means and thereby said two elements are resiliently connected according to the superimposed characteristics of resiliency of said cushioning means.

6. Cushioning arrangement ffor resiliently connecting two elements comprising, in combination, cylinder means adapted to be mounted on one `of said elements; piston means arranged in said cylinder means slidably therein and adapted to be mounted on the other of said elements;'air

Acushioning means having -a hyperbolic characteristic Vof yresiliency and including airst expansible and contractible working chamber means; lmechanical cushioning means including a resilient member'consiting vof a=solidfresilient material and a second expansible and contractible working chamber means adjacent said resilient member, said mechanical cushioning means having a linear characteristic of resiliency; conduit means connecting said rst and second working chamber means and said cylinder means and including a least one operating cylinder; an oper-atliquidin said conduit means, said rst and second'working chamber means, and said cylinder means whereby said cylinder means and said piston means and thereby said two elements yare resiliently connected according to the superimposed characteristics of resiliency ofsaid cushioning means; liquidmoving means lconnected 4to said conduit means for adding additional operative liquidto said operative liquid and for removing part-of said operative liquid; and control means including control valve means for controlling said moving means, Yandanoperating piston slidable in 'said operating 'cylinder and actuated in accordancewith relative movement'between said cylinder means r`and said piston -means,-said-operat `acusaron 7;; Ousltioning arrangement `for resiliently o comprising, in combination cylinder means adapted ltowhemounted on one of said elements; piston meallvamwdfin said cylinder means slidahly therein andadaptedvztohe mountedon the other of saidelements;

. and 1mm un mammoet manqua moving air cusllounglmcans having `a hyperbolic characteristic nfl including a first expansible and conchamber` means; mechanical cushiony moana including a resilient member of a solidresilientlmsterial a secoadexpansihle andconi tractble working .chamber means adjacent :said r resilient. i mechanical` `cushioning means having a linaahchnacteristic of resiliency; conduit` means connesting saidlirstand second workingchambermeans and v saklcylindeemeans and including at least one operating cylinderranoperating liquid insaid conduit means, `said rstmndraeennd working chamber means, `and said `cylinmeansmhereby said cylindcrmeansand said piston thereby said two elements are resiliently to the superimposed characteristics of `ttdsaidcushioning means; liquid moving means ing partiel operative liquid; control means includina valve meansrfor controlling said moving conduit means `for adding additional l operative liquidto said operative liquid and torremovmearmrand; an operating piston slidable in said operating l Wunderland; actuated in t accordance with `relative movemeut said cylinder means and said piston means,

aaidopentiM-piston being connected-to saidcontrol valve means the same to control said liquid moving `rllsuausin suchmanner; `that operative liquid is `sunplied to or fromg said `working chamber" means toholdfsaidpiston means relative to` said cylinder means and` therehysaid two elements in a substantially constant relativo and dampening means connected tosaid for dampening movcmentof, the same. 38. arrangement as set forth in claim 5 and including means for adding compressed` air to said air cushioning means and for removing air from the same for holding said means and said cylinder means andethereby said two elements `in a substantially constantgrelative positions y l 9. .An arrangement as set forth in claim `andlinclud-` il!! mm. controlled by said piston means `and connected tosaiduconduit means for adding additional `operative liquid would operative `liquid andfor `removing part of said liquid so` as to hold said" piston `means andsaidocylindermeans and thereby said :two elements in substantially constant relative position. l

`l0. Anarrangementas set forth in claim 8 wherein l said `rneanslftn' `adding `compressednir is controlled by said piston t r d s "11. An arrangement as set forth in claimS and including means connected to saidconduit means foradding additional: operative liquid to said `operative liquid and forlremoving part of said operative liquid; and control means actuated by relative movement between said cylindermeans and said piston means saidliquid moving means in such a manner that operative liquid is supplied to or discharged from said conduit means to holdsadpiston means and said cylinderzmeans two elements in asubstantiallyconstant piston means and controlling said air moving means in such `a manner that air is suppliedto or discharged from said `air cushioningnieans to hold said piston means and said cylinder means nndtherebysaid two elements in a substantially constant relative` position.

`meansand thereby said two elements in a substantially constant relative position.

14. An arrangement as set forth in claim 5 and comprising liquid moving means `including control valve means and being connected to said conduit means for adding additional operative liquid to said operative liquid and for removing part of said operative liquid; and control lever-means connected to said cylinder means and to` said piston means and being actuated by relative movement between the same, said control lever means being connected to said control valve means for controlling said liquid moving means in such` a manner as to maintainsaid two elements in a substantially` constant relative position.

l5. An arrangement as set forth in claim 14 and including means controlled by said piston means for adding compressed air to said air `cushioning means and for removing air from the same for holding said piston means and said cylinder means and thereby said two elements in substantially constantrelative position.

16. An arrangement asset forth in claim 5 `wherein said cylindermeansincludes a set of cylinders; wherein said piston means includes a set of pistons slidable in said cylinders; wherein said air cushioning `mcansfincludc a closed vessel, a cornpressiblc` gaseous medium in one end portion of said vessel, and a first piston member movable in said vessel; wherein said mechanical cushioning means includ: a spring cylinder member and a resilient member 1 consisting of a solid resilient material and located in one end portion of said spring cylinder member, and a second piston member movable in said spring cylinder member and engaging said resilient member; and wherein said conduit means connect the other end portion of said vessel, and the other end portion of said spring `cylinder member with said cylinders; and wherein said operating liquid is located in said `conduit means, in said other end portions of said vessel and `of said spring cylinder member, and in said cylinders.

17. An arrangement as set forth in claiml and including pump means for saidoperating liquid; supply and discharge conduit means connecting said pump means with said conduit means and containing part of said operating liquid;.control valve means in said supply and discharge `conduit means and being movable `between a trst position in which said pump means supplies said operating `liquid to said conduit means, a second closing position, and a third position in` which operating liquid is'discharged from `said conduit means into said pump to hold said two elements in a substantially constant relal2.` An arrangementas set forth in clsimtS inair'` moving means for adding compressed air to said air` cushioning means and for removing air from the same; and air supply control means actuated by relativa-isttovetnrcntV between said cylinder means and said tive position.

18.. An arrangement as set forth in claim 17 and including manually operatedvalves in said supply and discharge "conduit means, respectively, for supplying and discharging said operating liquid by a manual operation.

19. An arrangement as set forth in claim 17 wherein said operatingmeans include lever means connected to aasaaoa said control valve means and to said sets of cylinders and pistons.

20. An arrangement as set forth in claim 16 and including air compressor means; air supply and discharge conduit means connecting said air compressor means with said one end portion of said vessel, air control valve means located in said air supply and discharge conduit means and being movable between a first position in which said compressor means supplies air to said vessel, a second closing position, and a third position in which air is discharged from said vessel; and operating means for said air control valve connected to and removed by said cylinders and pistons during relative movement of the same, said operating means being connected to said valve means and moving the same between said positions in such a manner that air is supplied to or discharged from said vessel to hold said two elements in a substantially constant relative position.

21. An arrangement as set forth in claim 20 and including manually operated air valve means in said air supply and discharge conduit means.

22. An arrangement as set forth in claim 16 and including control means for controlling the positions of said first and second piston members; and hydraulic operating means connected to said sets of cylinders and pistons and being moved during relative movement of the same, said operating means being connected to said control means and operating the same to hold the respectively associated pistons and cylinders and thereby said two elements in a substantially constant relative position.

23. An arrangement as set forth in claim 6 wherein said control valve means includes a Valve casing containing part of said operating liquid and a valve member movable in said valve casing, said valve member being rigidly connected to said operating piston for movement therewith; a dampening cylinder iXedly connected to said valve casing; operating liquid in said dampening cylinder; a dampening piston in said dampening cylinder and rigidly connected to said valve member for movement therewith; means for supporting said dampening cylinder and said valve casing for movement with each other in axial direction; and resilient means for urging said dampening cylinder and said valve casing into a normal position.

References Cited in the le of this patent UNITED STATES PATENTS 886,617 Lovejoy May 5, 1908 1,013,487 Gruss Ian. 2, 1912 1,291,016 Kellogg Jan. 14, 1919 1,301,474 Martens Apr. 22, 1919 1,378,281 Ross May 17, 1921 1,664,510 Hughes Apr. 3, 1928 1,956,669 Charles May 1, 1934 1,990,517 Bedford et al. Feb. 12, 1935 2,021,043 Bedford et al. Nov. 12, 1935 2,106,289 Wallace Jan. 25, 1938 FOREIGN PATENTS 728,207 Germany Nov. 23, 1942 173,017 Austria Nov. 10, 1952