US3554155A

US3554155A - Drive mechanism for a steerable propeller

Info

Publication number: US3554155A
Application number: US774028A
Authority: US
Inventors: Hans Eichinger
Original assignee: Carl Hurth Maschinen und Zahnradfabrik GmbH and Co
Current assignee: Gleason Hurth Tooling GmbH
Priority date: 1967-11-11
Filing date: 1968-11-07
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12

Abstract

A steerable propeller for watercraft wherein the propeller is driven through a planetary system, the same being loosely mounted but self-centering in operation. A further feature limits the radial play of the planetary parts to minimize tooth contact when same is not operating.

Description

United States Patent [72] Inventor Hans Eichinger [50] Field ofSearch 115/17, 34, Munich, Germany 3 5; 74/797 [21] Appl. No. 774,028 [22] Filed Nov. 7, 1968 [56] References Clted Patented 1971 UNITED STATES PATENTS [731 Assign Maschinen'md zahmdfabr'k 1,389,622 9/1921 Buehler 74/797 ff zf' 3,358,668 12/1967 Post et a1. 115/17X 1 a corpora ion 0 ermany I 32 Priority Nov. 11, 1967, Feb. 21, 1968 FOREIGN PATENTS 1 [33] Germany 1,234,308 5/1960 France 115/34 f -[31] 1,531,749 and 1,650,729 983,462 2/ 1965 Great Britain.

Primary Examiner-Trygve M. Blix Attorney-Woodhams, Blanchard and Flynn [54] DRIVE MECHANISM FOR A STEERABLE M PROPIPLLER ABSTRACT: A steerable propeller for watercraft wherein the 10 Clams 7 Drawmg propeller is driven through a planetary system, the same being [52] US. Cl 115/35 loosely mounted but self-centering in operation. A further fea- [51] Int. Cl B63h1/14, ture limits the radial play of the planetary parts to minimize B63h 5/06 tooth contact when same is not operating.

II 111 j s presently known nianri Steerable propellers'arefas'iisfcornnionly ltnown, used to drive and steer watercraft. According to one proposal which is not as yet a part of theknown artithe torque driving the I vehicle (as when a boat supplied with'such gearing is being driven bysome other means and the steerable propeller is idle and is raised out of the water) is much greater if the gear train stands still during such moving. 1 i

To overcome this disadvantage, theinvention further provides that the gearing member which is to be guided, for example the planetary carrier supportingthe planet gears, is suppropeller is transmittedfrom 'a gear train positioned above the water to a gear trainpositioried below the waterlinethrough a shaft whiohis arranged substantially vertically 'and erating at a relatively highrotational speed andafsmalltorque. Thus,

the moment of fr *ez i t: t'io ri wliic must be resistediliy the control unit and, if desired, by a stabilizirigbla'deis-minimized. According' to the same not yet publishedproposal, the rotational speed forthe'propeller in the underwater housing'isreduced 1 to a' value which is suitablelforfithe"propeller,- namely, by I vantagelthat ala'rgjefreductionfgearing can; be accommodated in a smallareaflhus th underwaterhousing which'interferes with the propellers effectiveness canbe maintained small.

Since" the planetary 1 gearing must be' accornmodatedin a small zone for-the above-described'reasons,'- yet same can be subjected to a relatively high. load, for example by a suddentorque on the-propeller as whe'nithe propellerhitsganobstaele', it is necessary both tha'tfthe reaetive'effecton the gear train; is

maintained *as small as possible and-"that ca re'is" taken that all possible't'eeth of the gear train load; i l I To attain thisthe present invention provides'that in i t'leas 't' one off'the elements-pr the planetary 'gearingirii g, ge'ans rl'pla 'et gears,- is radi- 7 any resiliently-supported (also referred -to floatingl'y mountedland is guided'iri the teethjofl at least one other ele- 'r'nentwhichisjradially'rigidlysupportem A Planet y s arinsi t' m a d r s P t c ar in drive mechanisnisiin which the torque gl'iid'e'd'to the unmeans of aplanetary-gearin' "'Thisconstrnctionhas the ad: a

bearing :ofvibrationdampe'r. v 1 r A further advantageous construction of the invention is that "the propeller shaft is supported radially and axially rigidly.

ported radially resiliently and .that said member, for example the propeller shaft, is' surrounded 'by -a' sleeve or the like,

whereby the play between the sleeve and the surrounded part, .thus for example the propeller shaft, is smaller thanthe radial component of the. tooth play between the teeth of the guiding partand the teeth of the guided part so that the unloaded adjustable gearing member is supported on'the sleeve but not on .the teeth.

A particularly.advantageousconstructionof the invention is that the'adjustable and'supportable member, for example the planetjcarrier, is supported at least at one point with a radially "adjustablebearing which centers under an axialpressure. for

example a conical roller bearing. This advantageous construction is described in detail. in eonnectionwith one embodiment.

I It'isadvantageous for theabove-described embodiment to minimize the nonnalnoise'of running if the radially resilient that fthe element driving the propeller shaft, for example the planet gears'or the planet carrier, is guided substantially by the teethof at least one of-theother elements, for example the sun gear, and that the element driving the propeller shaft is connected to the propeller shaft through an atleast radially flexiwhich no. specialsteps'aretaken for receiving themoment of gearingEis done without. deflections iniorder-"to fprevent jammingor-the'lilge. from occurring-dueto the'steering movement in'the planetarylg'earin'g' 'l'he invention, therefore, pro- 7 vides thattthe planetaryfgearing is;. positioned bel ind the reversing gearing and-that th reversing gearing is connected 7 to the planetary gearing" through a flexible coupling, for example a splined. or' toothed, coupling.

A furtherernbodime'nt oftheinyention is that two elements,

for example thering gear] and thejplane't gears are resiliently the third elementlfor example the sun gear.' v

. According to theinvention an advantageous construction is chosen 'so that the propeller shaft supporting the propeller is rigidly connected tonne of the elements of the planetary gearradial play,.l he propeller in this embodiment is unefiected by I the flexibility of the invention and this can be of importance for apparatus of large output capacity. A further embodiment, in which the'propeller shaft is also rigidly supported, is that the propeller shaft is supported'radially and axially rigidly and is essentially rigidly connected to .theelement of the-planetary derwater' gear train through;aflvertical-lenmr shaft about the a .S m r mple .theplanet carr er, said element dl'llllng axis of which the steering movement-- is 'Prforrned'and in P w ni n at least one f the elementsfor'example either the ring'gear or the sun gear isradially resiliently supported 'andis guided in the teeth of the planet gears. For all described' structures in particular for the lastde cribed structure,the-coupling-of the resiliently supported elements with the connecting"parts. is obtained through resilient members, for example rubbcrlinings or rubber sleeves. Thus the resiliency is combined with a restoring force.

'. Furthermoremost elastic materials, .for'example rubber, have v adamping capacity whereby the rubber elements further quiet supported and are guided directly or'indirectly in theteeth of 'ing and that the propeller shaftis radially resiliently supported on the side facing the planetary gearing-'throughwhich the propeller shaft supports itself, ,for examplethro ugh the planetary' set on the central internally toothed-ring. The internally toothed ring can thereby be rigidly suppo'rtedwhich-can be advantageous to the sturdiness of the planetary gearing.

If a planetary gearing is not in 'operation, the gearing ele-' ments, if they are supported radially resiliently as in the invention,'move downwardly due to the gravity so far that the teeth I of the planetary gears (at leastone of the planetary gears) lies ofresting load is undesirable becausein" having nomovement means of vibrations applied thereto. The danger in a movin'g without play in the tooth spaceor the tooth spaces. This type the running.

Further characteristics and advantages of the invention will be understood by reading the followingdescription.

a The invention is illustrated by one embodiment in the drawings, in which:

FIG. 1 is a side elevational-iiiew of a se-Nc alled steerable propeller for a watercraft, the embodiment referring to the steerable propeller. I

FIG. Zisa longitudinal view ofia' gear train of the invention.

- FIG. 3 is a cross-sectional view of a planetary gearing of the I invention in an enlarged, scale.

4-4 of FIG. 2 whereby the bodybf the planet carrier is not illustrated and" only the planet gears and'the corresponding {shaft of the gear member are illustrated.

FIG. 5 is a'detailed illustration of a tooth and a tooth space to further-explain the invention. i

FIG. 6 illustrates a modified embodiment for the connection of the propeller shaft to theplanetary gearing. FIG. 7 illustrates a further embodiment of the invention.

' The steerable'propeller is, for. the purpose of driving and steeringa watercraft 10 or the like, mounted to a suitable place on the outside of the watercraft, for example to the the propeller shaft is connected with a friction- FIG. 4 is a schematical cross-sectional view along the line stern. The fastening means are known and are therefore not illustrated. The drive is provided by a drive motor (which is provided in the watercraft but which is not illustrated) through conventional drive transfer mechanisms, for example through a transfer shaft 11, onto the coupling flange 12 of a drive shaft 13, said drive shaft being supported in an abovewater housing 14 of the steerable propeller. A bevel gear 15 is fixedly connected to the free end of the drive shaft 13. The bevel gear is in a meshing engagement with a bevel gear 16 which is secured rotationally fixed on a center shaft 17. The center shaft 17 is arranged vertically and extends through the above-water housing 14, a control housing 18, a shaft housing 19 and terminates in an underwater housing 20. The center shaft 17 can be made of several pieces 17a, 17b for reasons of a favorable installation. The single parts are connected by one or, if desired, several couplings 21. The propeller is pivoted about the axis of the center shaft 17 for the purpose of steer ing. The center shaft 17 drives a direction changing gearing, here a gear train comprising a planetary gearing, which is supported in a gear housing 22. The propeller shaft 23 which carries the propeller P is also supported in the gear housing 22.

The underwater housing is fastened, here screwed, together with a control sleeve 24. A platelike bevel gear is secure to the upper end of the control sleeve 24, said end extending into the control housing 18. The control sleeve 24 and the platelike bevel gear 25 are concentrically arranged to the center shaft 17 at the bottom end of which is fixed a bevel gear 31. The shaft housing 19 and the control sleeve 24 are sealed by a suitable sealing. A bevel gear 27 is in meshing engagement with a platelike bevel gear 25. The bevel gear 27 is fixed to one end of a control shaft 28 which is supported in the control housing 18. A worm gear 29 is secured to the other end of the control shaft 28, a worm 30 engaging said worm gear. The worm 30 has a stub shaft 30a projecting out of the control housing. A connecting shaft 30b being securable to said stub shaft in order to rotate the underwater housing from a steering wheel (not illustrated) through the mentioned elements and to thus pivot the propeller P about the axis of the center shaft 17 and to control the watercraft.

FIG? 3 illustrates in detail the gear train positioned under the water level. The above-mentioned gear 31 is in a meshing engagement with a bevel gear 32 which is secured to a hollow shaft 33. The hollow shaft 33 or the bevel gear 32 is supported by two bearings 34, 34a. The propeller shaft 23 penetrates through the hollow shaft 33. The "propeller shaft 23 is supported at its right end in the gear housing by means of a double conical roller bearing 35. The double conical roller bearing 35 comprises two conical roller bearings 36, 37, the

inner races

38, 39 of which are positioned on a stub shaft 40 of the propeller shaft 23. They are spaced-apart by a sleeve 41. The two inner races are secured to the stub shaft 40 by means ofa washer 53 and screws 5 4 The outer races 42 43 axially abut a flange 44 arranged between said outer rings, said flange forming a unit with the housing 22 .or being connected to said housing. Shrunk rings 45, 46 are shrtink onto the outer rings 42, 43, which shrunk rings are slotted. Saidslots are engaged by one or several pins 47 which thus prevent the outer rings 42,

43 from rotating. Clearance 48, 49 is provided between the neck 22a of the gear housing receiving the bearings and the outer shrunk rings and 46. The outer rings or the shrunk rings are axially secured with snap rings 50, 51. Strong springs 52 which axially press onto the outer rings 42, 43 are provided in the flange 44, said springs urging the lifting of the conical roller bearing off the flange which, however, is prevented by the washer 53 and the screw 54. However, the axial springs cause a reduction of the abutment pressure between the outer rings and the flange when the double conical roller bearing 35 is not under stress so that the conical roller bearings, when there is no axial stress, using the clearance 48, 49 radially, can move radially.

Washers

55, 56 can be inserted between bearing and flange.

An internally toothed, annularly shaped ring gear 60 is centered and screwed (or bolted) in the gear housing 22. A

number of planet gears 61, 62 63 are in meshing engagement with the internal teeth, said planet gears being rotatably but not longitudinally supported in a planet carrier 66 bymeans of stub shafts 64 and, if desired, bearings 65.;The planet carrier 66 is secured on the propeller shaft 23 with a toothed coupling 67 against rotation and with suitable means against axial movement. The third member of thepl anetary gearing is an externally toothed sun gear 68 whiqhisin meshing engagement with the planetary gears. The sun gear 68 has a neck portion 69 which at its free end is provided/with a toothed coupling 70. Said coupling engages the internal teeth with which the above-described bevel gear 32 isprovided. The sun gear 68 is suspended without other support within such lastnamed teeth and is guided radially only through same. The sun gear 68 is axially maintained by suitable means for example by a snap ring 71. 4

Since the double conical roller bearing 35 is of a radially resilient construction, the planet gears or their planet carrier and indirectly also the sun gear 68 are guided by the meshing teeth on the ring gear 60.

lfa peripheral force acts on the teeth, the teeth are inclined to adjust to the operating pitch circles. However, ifa centering peripheral force is not provided, the toothed parts will fall downwardly through gravity inasmuch as the tooth clearance permits such fall. This is,schematically illustrated in FIG. 5. Only a space 72 of the annularly shaped ring gear 60 is illustrated. If the invention is not applied, the planet carrier with the planet gears will slide downwardly until, for example, one tooth 73 lies without play in the'respective space 72 (dashdotted line 74). During operationthe planet carrier would rise again due to the-peripheral forces acting on the teeth and the teeth of the planet gears would adjust to the operating pitch circles so that, aside from radially deflecting larger forces, the gearing would run smoothly. However, if the gearing remains in the described rest condition for a long period of time, the tooth flank will hammer itself into the space flank, particularly, if the gearing is in a moving vehicle but itself out of operation as is frequently the case with steerable propellers.

To overcome the above deficiency, the hollow shaft 33 is provided with a sleeve 75 which surrounds the planetary carrier shaft with little play, indicated by the space 76. Thus, the tooth no longer rests on the space but the propeller shaft rests on the sleeve 75 so that the tooth 73 takes approximately the position as illustrated in full lines in FIG. 5, so that a

space

77, 78 is provided between the tooth flanks. The planet carrier with the planet gears, and thus also the propeller shaft with the double bearing 35, are thereby positioned slightly underneath the axis of tliering gear.

When the propeller starts to operate at first it does not have its full torque and more important yet it does not have the full pushing force which is to be received by the conical roller bearing 36. Thus, the teeth of the planet gears can adjust centrally due to the peripheral forces to the operating pitch circles and also to the planet carrier shaft (propeller shaft 23), the teeth 73 being slightly above the illustrated place and abutting a space flank. The bearing 35 follows said central movement because'a relatively small axial force is at first still present. In the meantime the full pushing force of the propeller has built up. The pushing force maintains the bearing 35 in the central position.

The relatively small sun gear 68 is of a light weight and, in the example, does not require any special measures. If desired, it is of course also possible to apply the invention to the sun gear or to the ring gear.

If the propeller is stopped, the planetary carrier shaft (propeller shaft 23) returns to lie on the sleeve 75 so that the planetary gears are supported free from the ring gear teeth.

A further embodiment of the planetary gearing for a steerable propeller according to the invention is illustrated in H0. 6. The parts illustrated'in FIG. 6 are substantially the same as those illustrated in FIG. 3. The difference is that the propeller shaft itself is supported substantially radially, and also axially and also that the internal tooth ring 60' and the resiliency of l the planet gears 61, (i2, 63

is provided in the connection between the propeller shaft 23' andthe planet carrier 66. A toothedcoupling 79 is provided for 'this' purpose on the propeller shaft and'fin the planetary carrier which coupling manner. Thus, the-propellershaft 23." with the planet carrier least due of the sun gears lt is advantageousto support both surr gears 60' and 687' resiliently. The sun gear 68" and the bevel gear 32 are, as,above-described or in any other suitable manner resiliently coupled for this pirrpose The internal tooth ringso' -is freely movably 'received'bys'crews s2- throughrubber sleeves 81 or through equivalent elements. Thescrews 82 are positioned in the housingResilient members which have a damping capacity arefvery advantageous in a propeller drive. Therefore all other resilient coupling of the planetary gearing can also be 'provided'with rubber intermediate layers or thelike. lt is also possible. to provide between gear hub and tooth ringoffthe adjustable gears in a known manner-a rubber packing by 'means of vulcanizing or any equivalent'means. v I v The hearings in the gear train of FIG. Zare illustratedas ball conical roller bearings. lnasmuch as the bearings arenot a part of the invention, nothing is prescribed in this respect (it would also be possible to provide sliding bearings). Lubricating bearings and in the other FIGS. are illustrated as rollers or maintenance andsealing elements are not illustrated and" described because theyare not apartof the invention. 1

A steerable propeller which, in the underwater portion,is provided with a reductioir gearing in form of a planetary gearing has considerable advantages. The .torque at the vertical center shaft can hesma ll and thus the reaction moment which I acts on the control and/or blade is also correspondingly small which is advantageous as ,tothe construction of the control (steering mechanism) and/or the degree of flow effectiveness. By choosing a planetary gear a large reduction gearing can be placed in a small underwater gearing which also improves the degree of the propeller effectiveness. l v

This, with respect to-the loading capacity, the structure of the planetary gearing is particularly advantageous because jammings or cants due to the control movement cannot occur in the planetary gearing and because the load is distributed to a large number of teeth. Thus, the relationship of the propeller diameter andto the diameter of the underwater gear housing is made more favorable yet. The invention also increases the sturdiness and the operating safety of the steerable propeller.

lclaim: f

l. A drive mechanism for a propeller positioned below the water lineon-watercraft and the. like,:said propeller being driven by an engine inboard of the watercraft, comprising:

. frame means; v v a drive'shaft supported by .said frame means for rotation 7 about a generally vertical axis and having a first gear secured to the lower end thereof and rotatable therewith;

enclosure meansbelow said water line of said watercraft secured to saidframe means, said lower end of said drive shaft extending into said enclosure means; 5

said driven shaft, said planetary gear means comprising a.

pair of concentric, radially spacedgear members and a planetary carrier member carrying planetary gears, said planetary gears being mounted for simultaneous meshing I engagement with said pair of radially spaced, concentric gear members; andv v, 1 means floatingly mounting any two of the aforementioned members for a larger radial displacement-than woul result from nonnal manufacturing tolerances in sai planetary gear means so that saidtwo members are capa- -ble of a radial displacement relative to the remaining radially fixed member, the teeth of the radially fixed member guiding the radial displacement of the two floatingly mounted members. I 2. The drive rneclianisrrr defined in claim. 1, wherein said c drive mechanism for said propeller includes means for controlling said propeller about a generally vertical axis of a steering shaft, said steering shaft being substantially parallel to said driveshaft. V

3. The drive mechanism defined in claim 1, wherein said planetary carrier member is fixedly secured to said driven shaftyand wherein said driven shaft issupported for rotation by bearings located adjacent opposite ends thereof, the bearings adjacent one end permitting a radial displacement of bothsaidone end of said driven shaft and said planet carrier 'member fixed thereto for providing said floating mounting.

4. The drive mechanism defined in claim 3, including sleeve means surrounding said driven shaft, the spacing between said driven shaft and said sleeve means being less than the radial displacement of said driven shaft whereby said driven shaft will be supported by. said sleeve means when said drive mechanismis at rest. i

, 5. The drive mechanism defined in claim 3, including means forsupporting said bearings located adjacent said one end of said driven shaft for movement radially of said enclosure means, said bearing supporting means further being responsive to the axial thrust of saidpropeller to reduce the radial displacement of said oneend of said driven shaft to zero.

shaft, said driven shaft being mounted solely for rotation; and

wherein said pair of'c'oncentric gearmembers are mounted for radial displacement relative to said driven shaft.

'end thereof externally. of said enclosure means and rotatable therewith; V I planetary gear means in said enclosure means coupling said first gear on said drive shaft to saiddriven shafi for effecting a high-ratio reduction of speed from said drive shaft to 7. The drive mechanism defined in claim 1, wherein said driven shaft is mounted solely for rotation; wherein said planetary carrier memberand said driven shaft include means for floatingly mounting said planetary carrier to said driven shaft for radialdisplacement relative to said driven shaft; and wherein one of said concentric gear members includes means for floatingly mounting same for radial displacement relative 'to said driven shaft.

8. The drive mechanism defined in claim I, wherein said planetary gear means includes a second gear in meshing engagement with said first gear, said second gear having first coupling means thereon' one of said concentric gear members having an elongated neck extending axially therefrom, the free end of said neck having second coupling means thereon drivingly engageable with said first coupling means, said driving engagement providing a pivotal mounting for said one of said concentric gear members to-permit a radial displacement thereof relative to said driven shaft.

9. The drive mechanism defined in claim 1. including resilient mounting meansfor floatingly mounting said one of said concentric gear members to said enclosure means to per mit a radial displacement; of saidoneof said concentric gear members relative to said driven shaft. 7 7

l0. Thedrive mechanism defined in claim 5, wherein said bearing support means includes means capable of frictionally resisting radial movement of said bearings; and wherein the magnitude of said frictional resistance is a function of said axial thrust of said propellerto controlsaid radial displacement of said driven shaft.

Claims

1. A drive mechanism for a propeller positioned below the water line on watercraft and the like, said propeller being driven by an engine inboard of the watercraft, comprising: frame means; a drive shaft supported by said frame means for rotation about a generally vertical axis and having a first gear secured to the lower end thereof and rotatable therewith; enclosure means below said water line of said watercraft secured to said frame means, said lower end of said drive shaft extending into said enclosure means; a generally horizontal drive shaft rotatably supported in said enclosure means and having said propeller secured to one end thereof externally of said enclosure means and rotatable therewith; planetary gear means in said enclosure means coupling said first gear on said drive shaft to said driven shaft for effecting a high-ratio reduction of speed from said drive shaft to said driven shaft, said planetary gear means comprising a pair of concentric, radially spaced gear members and a planetary carrier member carrying planetary gears, said planetary gears being mounted for simultaneous meshing engagement with said pair of radially spaced, concentric gear members; and means floatingly mounting any two of the aforementioned members for a larger radial displacement than would result from normal manufacturing tolerances in said planetary gear means so that said two members are capable of a radial displacement relative to the remaining radially fixed member, the teeth of the radially fixed member guiding the radial displacement of the two floatingly mounted members.

2. The drive mechanism defined in claim 1, wherein said drive mechanism for said propeller includes means for controlling said propeller about a generally vertical axis of a steering shaft, said steering shaft being substantially parallel to said drive shaft.

3. The drive mechanism defined in claim 1, wherein said planetary carrier member is fixedly secured to said driven shaft; and wherein said driven shaft is supported for rotation by bearings located adjacent opposite ends thereof, the bearings adjacent one end permitting a radial displacement of both said one end of said driven shaft and said planet carrier member fixed thereto for providing said floating mounting.

4. The drive mechanism defined in claim 3, including sleeve means surrounding said driven shaft, the spacing between said driven Shaft and said sleeve means being less than the radial displacement of said driven shaft whereby said driven shaft will be supported by said sleeve means when said drive mechanism is at rest.

5. The drive mechanism defined in claim 3, including means for supporting said bearings located adjacent said one end of said driven shaft for movement radially of said enclosure means, said bearing supporting means further being responsive to the axial thrust of said propeller to reduce the radial displacement of said one end of said driven shaft to zero.

6. The drive mechanism defined in claim 1, wherein said planetary carrier member is fixedly secured to said driven shaft, said driven shaft being mounted solely for rotation; and wherein said pair of concentric gear members are mounted for radial displacement relative to said driven shaft.

7. The drive mechanism defined in claim 1, wherein said driven shaft is mounted solely for rotation; wherein said planetary carrier member and said driven shaft include means for floatingly mounting said planetary carrier to said driven shaft for radial displacement relative to said driven shaft; and wherein one of said concentric gear members includes means for floatingly mounting same for radial displacement relative to said driven shaft.

8. The drive mechanism defined in claim 1, wherein said planetary gear means includes a second gear in meshing engagement with said first gear, said second gear having first coupling means thereon; one of said concentric gear members having an elongated neck extending axially therefrom, the free end of said neck having second coupling means thereon drivingly engageable with said first coupling means, said driving engagement providing a pivotal mounting for said one of said concentric gear members to permit a radial displacement thereof relative to said driven shaft.

9. The drive mechanism defined in claim 1, including resilient mounting means for floatingly mounting said one of said concentric gear members to said enclosure means to permit a radial displacement of said one of said concentric gear members relative to said driven shaft.

10. The drive mechanism defined in claim 5, wherein said bearing support means includes means capable of frictionally resisting radial movement of said bearings; and wherein the magnitude of said frictional resistance is a function of said axial thrust of said propeller to control said radial displacement of said driven shaft.