US2701951A

US2701951A - Hydrodynamic coupling

Info

Publication number: US2701951A
Application number: US157568A
Authority: US
Inventors: Vladimir J Jandasek
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1950-04-22
Filing date: 1950-04-22
Publication date: 1955-02-15
Anticipated expiration: 1972-02-15

Description

Feb. l5, 1955 Filed April 22, 195o V. J. JANDASEK HYDRODYNAMIC COUPLING 2 Sheets-Sheet l Feb. l5, 1955 v, J, JANDASEK 2,701,951

HYDRODYNAMIC COUPLING Filed April 22. 1950 2 Sheets-Sheet 2 Vladimir-J andasef,

UnitedStates Patent O 2,701,951 Y HYDRoDYNAMlc coUrLlNG Vladimir J. Jandasek, North Riverside, Ill., assigner to BilgI- Wamer Corporation, Chicago, lll., a corporation o mois Application April 22, 195m Serial No. 157,568

Cial.. (Cl. 60-50 This invention relates tohydrodynamic coupling devices and, more particularly, to such devices adapted to transmit power between driving and driven structures by the kinetic energy of a liquid.

Hydrodynamic coupling devices comprise a rotating varied pump or impeller forcibly transmitting liquid to a varied turbine or runner to effect rotation thereof, the impeller being connected to a source of power,such as an engine, and the runner being connected to a workperforming member. In the event torque conversion is desired, a third vaned member in the form of a stator or reaction member is interposed between the impeller and runner to effect a controlled flow of the liquid from the runner to the impeller for this purpose. Moreparticularly, the impeller and runner each include spaced semitoroidal annular members consisting of a casing and core ring or shroud connected by vanes extending therebetween and forming passages therewith for the liquid, the impeller and runner being closely adjacent to each other but separated by a small gap so that their passages provide a substantially continuous path for the uid circulated therethrough by the action of the vanes.

During the operation of such hydrodynamic coupling device, considerable fluid pressure is had in the liquid circuit of the impeller and runner, and this pressure will tend to expand the coupling device in such manner that the gap between the inlet and outlet of the passages of the impeller and runner will be increased. It is important that the inlet and outlet of the passages of the impeller and runner should be maintained as close as practicable to prevent the escape of the ud circulating in the runner and impeller, or by-passing or short-circuiting of the uid, due to the tendency of the circulating liquid attempting to follow the path of least resistance, such by-passing or short-circuiting of the liquid being detrimental in that there is a loss of the maximum ow of the liquid per r second through the passages of the runner and impeller which results in shock losses and low torque eiciency of the fluid coupling device.

The centrifugal force of the rotating liquid will produce an axial thrust tending to separate the impeller and runner, with consequent widening of the gap between the inlet and outlet passages of the same. For example, when-the impeller and runner are surrounded by a casing providing a fluid chamber in which the impeller and runner are disposed, it has been found that pressures exist in the space between the impeller and the surrounding casing, the space between the runner and the surrounding casing, and also between the impeller and runner shrouds or core rings. Axial thrusts will be produced if the unit pressures on opposite sides of the impeller are not equal, and if these pressures do not act on equal areas of the impeller, and this is also applicable to the runner. These thrusts are caused by the pressure differences in the spaces between the impeller, runner and the surrounding casing, and by the action of the centrifugal forces of the liquid in these spaces. Also, when the runner rotates with considerable slippage, the pressure in the space between the impeller and the casing will be smaller than v,the pressure in the space between the runner and the-,casing Various means have been attempted to prevent axial ,thrust for the purposes of equalizing pressures in the aforesaid spaces; for. example, providing small openings in the impeller and runner casings connecting the space between the impeller and runner'vl and surrounding casing with the liquid in the working circuit and by making the gaps between the casings or of the device.

2,701,951 yatenter Feb. 15, 1955 lt is an object of the present invention to vprovide n an improved hydrodynamic coupling device having the provision for maintaining the vaned elements thereof in such close proximity to each other as to obtain maximum efficiency of the kinetic energy of the fluid circulating in the device.

1t is another object of the invention to provide an iinproved hydrodynamic coupling device having mechanical means for effectively maintaining the varied elements in close proximity to each other to confine the circulating liquid in the passages defined by the vanes of the elements thereof.

lt is a further objfect of the invention to provide an improved hydrodynamic coupling device having expandible and contractible means for maintaining equal unit pressures on opposite sides of the various vaned elements thereof to prevent axial thrust tending to separate the vaned elements and thereby disturb the effect of fluid y circulation in the device.

Still another object of the invention is to provide a hydrodynamic coupling device designed to provide equal unit pressures on opposite sides of a vaned impeller element to prevent separation thereof from a v aned runner element by action of unequal fluid pressures on the impeller element and to thereby effect maximum flow of the uid for any given period of time within the passages defined by the varies of the elements and consequent absence of shock losses and low torque efficiency Other objects and advantages of the invention will become apparent from the following description when it is with reference to the drawings i'ri which:

Fig. 1- illustrates a transverse cross-section of my improved hydrodynamic coupling device;

Fig. 2 is a face view of the impeller and one of the stators of my improved coupling device, the view being taken on line 2-2 of Fig. l;

Fig. 3 lis a face view of the turbine and the other of the stators of my improved coupling device, the view being taken on line 3-3 of Fig. 1; and

Fig. 4 is a rear view of the coupling Idevice.

The hydrodynamic coupling device, illustrating the preferred embodiment of the invention, is of the torque,- converting type and comprises the 'pump or impeller generally indicated at 10, a turbine or runner 11, and two stator elements respectively indicated at 12 and 13. These elements of the torque converter are preferably formed of sheet metal.

The pump impeller comprises an annular semi-torcidal hollow casing indicated at 14, an inner semi-toroidal annular ring 15, hereinafter referred to as the core ring, the casing 14 and the core ring 15 beingconnected by a plurality of vanes 16 which are of arcuate shape as viewed in Fig. l and curved as in Fig. 2, with the outer arcuate edge of each vane connected by any suitable means, such as by welding, to the casing 14 and the inner arcuate edge of each vane being welded to the core ring 15 to provide a plurality of fluid passages `in the varied element or impeller 10. The runner 11 comprises an outer casing 17 connected to an inner core ring 18 by a plurality of curved vanes 19 welded to the casing and core ring and defining therewith a plurality of fluid passages in the runner 11 as shown in Fig. 3. Disposed between the radially inner ends of the passages lin the runner 11 and impeller 10 are a pair of reaction members or

stators

12 and 13, the reaction member 12 comprising an annular element 20 and a radially outer ring 2l connected by means 'of vanes 22 to define fluid passages. The reaction member 13 is similarly constructed having anannular element 23, a radially outer ring 24 connected by means of curved varies 25 to define a plurality of tiuid passages.

The impeller 10 is adapted to be rotated by a drive shaft. 26 connected to any suitable source of power, such' as an engine, the drivewshafty '26 being bolted as at Z7 to a drive plate 28 connected by means of bolts 29 to an annular sheet metal shell 30 of semi-toroidal shape.

The casing 14 of the impeller 10 is welded at its radially outer periphery to the shell 30 as indicated at 31, so

, that rotation of the drive shaft 26 by the engine will rotate the impeller 10. The shell 30 and the drive plate 28 define a tluid chamber 32 entirely lled with lluxd, and in which is disposed and enclosed the various described

vaned elements

10, 11, 12 and 13, whereby, upon rotation lof the impeller 10, the vanes 16 thereof will forcibly urge the uid in the impeller radially outward and into the passages of the runner 11 and against the curved vanes 19 of the runner 11, the uid llowing radi- Ially inward through the passages of the runner 11 and into and through the passages of the reaction members 12 v and 13, and thence into the passages of the impeller,

as indicated 'by the arrows in Fig. l. y

It may be noted that the space 33 between the casing 1'7 of the runner 11 and the drive plate 28 is lled with the lluid and also that the space 34 between the casing 14 of the impeller 10 and the shell 30 is also filled wit-h tluid. The space 3S between the core rings 1S and 18 of the impeller and runner and 1l, respectively, define a uid chamber as shown in Fig. l.

The runner 11 is drivingly connected to a sleeve shaft 3&5 surrounding a solid shaft 37 which has its front end rotatably mounted in t-'he plate 2S. This driving con nection is provided by a conical ring 3S surrounding these latter shafts and welded as at 39, to the casing 17 of the runner lli, the inner periphery of the ring 3b being mounted upon and secured to a hub 40 splned as at 41 to the sleeve shaft 35. The shell 30 and the casing 14 of the impeller l@ have their radially inner edges rotatably mounted upon a stationary sleeve 42, bolted as at 43 to a housing 44. The

annular members

20 and 23 of the

reaction elements

12 and 13 are secured as by welding to respective hubs 45 and 46 surrounding the stationary sleeve 42, the hub 4S being disposed upon a sleeve bearing 47 between the hub 45 and the station-ary sleeve 42, with the hub 46 and sleeve 42 having a sleeve bearing 48 disposed therebetween. A plurality of thrust washers are respectively disposed between the hub 40 of the runner 11 and the hub 4S of the stator 12, between the hubs 45 and 46 of the

stators

12 and 13, and between the hub 46 and the impeller casing 14, as shown in Fig. l. A one-way brake 49 is provided between the hub 45 of the stator 12 and the stationary sleeve 42 and a similar one-way brake Sti is provided between the hu-b 46 of the stator 13 and the stationary sleeve 42. The one-

way brakes

49 and 50 may be of any suitable construction, as, for example, that construction shown in the copending application of Youngren, English and Het-l tinger, Serial No. 25,064, filed May 4, 1948, and hence the one-way brakes 49 and 5t) will not be further detailed.

The described hydrodynamic coupling device is of the torque-converter type and operates in accordance with well-known principles of such devices. The impeller 10, which is driven by the drive shaft 26, causes fluid to circulate within the path as indicated by the arrows in Fig. 1. The impeller causes the lluid therein to be directed and impinge on the curved vanes of the runner 11 and causes it to rotate in the same direction as the impeller 10. The torque on the runner is greater than the torque applied to the impeller due to the action of the

stators

12 and 13 which are held against rotation lby the

brakes

49 and 50 at this time, the stators functioning to change the direction of lluid flow between the runner and impeller which serves to change the direction of the stream of fluid in such a way as to alter the torque ratio between the drive shaft 26 and the sleeve shaft 36. After the speed of the runner has reached a predetermined value, depending upon the load on the runner, the

stator members

12 and 13 will begin rotating in a direction releasing the over-running brakes 49 yand 50, and the torque converter will then function as a simple iluid coupling or clutch and in which stage of the converter, the runner is driven at substantially the same speed as the impeller.

In hydrodynamic coupling devices of the torque-convexting type described, as well as those devices consisting of only an impeller and runner and acting as a lluid clutch, it is of paramount importance in order to obtain maximum eficiency that the vaned elements be maintained as closely as possible to each other during operation of the device. This is due to the fact that any substantial spacing of the elements from each other will distu-rb maximum tluid ilow through the vaned passages of vice.

the elementsV b the circulating tluid by-passing or shortcireuting the uid circuit of the device and llowing into the spaces between the core rings, and the casings4 and the surrounding structure through the gaps between the casings and core rings of the vaned elements' of the de- This short-circuiting or by-passing materially impairs the efficiency of the device. For example, escape of the fluid into the space between the core rings results in eddy losses and consequent low torque ellciency of the device. In other words, by by-passing or shortcircuiting, it is meant that the circulating fluid will a1- ways tend to escape from the working circuit into the space between the core rings, or the spaces between the impeller and running casings and the surrounding structure, through the gaps between the casings and core rings .of the impeller and runner, as these gaps alord paths of least resistance, with consequent loss of the maximum llow of the uid per second within the vaned passages of the coupling elements resulting in -shock losses and low torque elllciency of the device. Accordingly, it is necessary that the various vaned elements of the coupling be positioned as closely as possible to each other to minimize by-passing or short-circuiting of the circulating uid to obtain maximum efliciency of the fluid coupling.

'In hydrodynamic coupling devices, such as s-hown in the drawings, it has been found that definite pressures may exist in the space 33 between the drive plate 28 and the runner 11, in the space 34 between the impeller casing and shell 30, and also in the space 3S between the

core rings

15 and 18 of the impeller and runner elements. If the unit pressures of the uid on opposite sides of the impeller, i. e. the pressure of the lluid in space 35 is greater than the pressure of the lluid in space 34, and if these pressures do not act on equal areas of the impeller, an axial thrust will be produced tending to separate the impeller and runner and to widen the gap, such as at 52 in Fig. l, between the entrance and exit passages of the impeller and runner. These thrusts tend to be caused by any lluid pressure differences in the space 3S between the impeller and runner core rings and in the space 34 between the impeller and the shell 30, and

by the action of the centrifugal forces of the fluid in these spaces. It wil-l be apparent that, if no means are provided to prevent such unequal pressures, considerable axial thrust may be thus imposed upon the impeller inasmuch as the tluid pressure in the impeller is considerably greater than that of the fluid pressure exterior of the impeller. Further, when the r-unner rotates with considerable slippage, the pressure of the fluid in the space 34 between the outer shell and the casing of the impeller wil-l be smaller than that in the space 33 between the casing 17 of the runner 11 and the drive plate 28. Also, when the runner rotates with little slippage, the pressure of the fluid in the space 33 between the plate 28 and the turbine will be less than that in the space 34 between the outer shell and the casing 14 of the impeller 10. Furthermore, the pressure in the space 33 will be less than that in the space`35 between the impeller and the turbine. These differences in the pressures will produce axial thrusts tending to separate the impeller and the runner during the operation thereof, causing disturbance of the energizing fluid flow through these two elements. This condition is particularly aggravated in the case of a torque converter in which the curved blades of the impeller and runner cooperate with the curved blades of the stator or stators to increase torque, creating substantially greater pressures in the converter than in coupling devices consisting only of an impeller and runner.

The present invention has for its principal object the considerable advantage of controlling, by partially equalizing, the pressures of the fluid in fluid coupling devices to substantially minimize axial thrust heretofore had in the unequal balance of unit pressures in such devices, and particularly in fluid coupling devices of the torqueconverting type, during the operation of the devices. Refem'ng to Fig. l, it may be noted that the shell 30 is welded as at 31 to the casing 14 of the impeller 10, and this is the only connection between the shell 30 and the casing 14. When the runner has not attained the same speed as the impeller and rotates with considerable slippage, the pressure between the outer shell, such as 30, and the casing, such as 14, of the impeller will be smaller than that between the casing, such as 11, of the runner and the driving structure, such as the driving plate 28, so that axial thrusts will also be produced. The present embodiment of the invention is directed to means capable of insuring control of, by partlally equallzmg, pressures in the space 34 so that by the pressure on opposite sides thereof and will not be moved axially. 'Ihis is due to the outer shell 30 being connected to the impeller casing 31 so that the radially extending portions of the shell, adjacent to the impeller casing and defining therewith the fluid-filled space 34, is free to expand and contract under fluctuating increasing and decreasing pressures of vthe fluid in the space 34. By providing a space 34 into which fluid under pressure can seep from the space 35 and thereby counteract the ',pressure in space 35, axial movement of the impeller is pre vented. The casing 30 can expand and contract because the fluid pressure in space 34 will be much larger than the air pressure outside of the casing 30. As the pressures of the fluid in the space 35 and in the space 34 are thus substantially equalized, the impeller will not be axially moved away from the runner and stators but will be maintained in close proximity thereto. To permit expansion and contraction of the shell 30 for the purpose described, the shell 30 is formed of sheet metal of sufficiently light gauge to permit movement of the axially extending portions thereof rearwardly of the vaned elements', and more particularly the casing 14 of the impeller 10.

For the purpose of preventing leakage between the inner peripheral edge of the shell 30 and the stationary sleeve 42, an annular sleeve bearing 54 is fixed to one side of said edge and an annular seal ring 55 is received within a grooveA 56 within the stationary sleeve 42 abutting the sleeve 54 and, in addition, a seal ring 57 is disposed between the sleeve 54 and an annular boss 58, integral with the stationary casing 44. It may be noted that this arrangement, as shown in Fig. l, permits axial movement of the radially extending portions of the shell 30 in either direction while effectively preventing the escape of fluid from the fluid chamber 34, either by leakage or pressure of the fluid.

lt may be noted from an inspection of Fig. l that the core ring of the impeller 10 and the core ring 18 of the runner 11 have their radially inner ends 59 and 60 extending beyond the vanes thereof and overlapping the radially outer annular rings 2l and 24 of the stators lf2 and f3, respectively, to prevent the undue escape of the circulating fluid into the space 35 between the core rings during the transmission of the fluid from the runner 11 to the stator 12 and from the stator 13 to the impeller 10 during operation of the torque converter. This arrangement is of value in confining the maximum flow of fluid within the stators and the runner and impeller.

It will be apparent from the foregoing description, taken in connection with the drawings, that I have provided an improved hydrodynamic coupling device, with one of its distinctive features being the utilization of means for preventing separation of the vaned elements thereof from their close proximity to each other by axial thrust imposed by the circulation of the fluid in the coupling device, the resultant maintenance of the vaned elements in close proximity insuring maximum efficiency of the device and that, while the invention has been particularly described and shown with respect to a fluid coupling device of the torque-converting type comprising an impeller, a runner and stators, the invention is equally applicable to fluid couplings forming a fluid clutch and consisting only of vaned impeller and runner elements. It will be further obvious that the invention is applicable also to fluid torque converters or to hydrodynamic coupling devices of the torque-converting type utilizing one or more impellers, turbines or reaction members. Accordingly, the invention is not to be limited to the particular embodiments illustrated. as it will be readily apparent that various modifications may be made by those skilled in the art without departure from the invention as defined in the following claims.

l claim:

l. ln a hydrodynamic coupling device, impeller and turbine elements in iuxtaposed relation and rotatable about Va common axis, saidelements having vanes defining fluid passages communicating with each other and effecting circulation of fluid in said passages during rotation of said impeller element; an enclosure defining a fluid chamber receiving said elements and spaced therefrom to the impeller casing will be balanced 6 providefluid-filled spaces between said enclosure and each of said elements, the fluid in said passages having access to said fluid-filled spaces, said enclosure having at least a portion thereof, defining the fluid-filled space between the same and the exterior of one of said elements, formed of flexible material contractible and expansible by the presence of the fluid pressure in said fluid-filled spaces of said chamber and which presence of the fluid pressure in said fluid-filled spaces of said chamber also counteracts the fluid pressure between said elements to prevent relativke axial movement of said elements away from each ot er.

2. In a hydrodynamic coupling device', impeller and turbine elements in juxtaposed relation and rotatable about a common axis, said elements having vanes defining fluid passages communicating with each other and effecting circulation of fluid said impeller; an enclosure defining a fluid chamber receiving said elements and spaced from said runner element to provide a, fluid-filled pocket between said enclosure and said runner element, said enclosure including a shell connected to said impeller element and defining with the exterior thereof a fluid-filled pocket between the same and said impeller element, the fluid in said passages having access to said fluid-filled pockets, said shell being of flexible material contractible and expansible by the presence of the fluid in said fluid pockets and which presence of the fluid pressure in said fluid pockets also counteracts the fluid pressure between said elements to prevent relative axial movement of said elements away from each other during operation of said device.

3. In a hydrodynamic coupling device, impeller and turbine elements in juxtaposed relation and rotatable about a common axis, said elements having vanes defining a plurality of fluid passages communicating with each other and effecting circulation of fluid in said'passages during rotation of said impeller element; an enclosure defining a fluid chamber receiving said elements and spaced from said turbine element to provide a fluid-filled pocket between said enclosure and said turbine element, said enclosure including a shell in the form of a dished-like stampingof annular form defining with the exterior of said impeller element a fluid pocket, the fluid in said passages vhaving access fo said fluid-filled pockets, said stamping having its radially outer periphery secured to the radially outer periphery of said impeller element and having a flexible radially extending portion contractible and expansible by the presence of the fluid pressure in said fluid pockets and which presence of the fluid pressure in said fluid pockets also counteracts the fluid pressure between said elements to prevent relative axial movement of said elements away from each other during operation of said device.

4. In a transmission, driving and driven shafts rotatable about a common axis and in axial spaced relation to each other; a hydrodynamic coupling device including an impeller element connectedl to rotate with said driving shaft, and a runner element connected to rotate with said driven shaft, each of said elements comprising a hollow, annular, substantially semi-toroidal casing, a plurality of vanes within and connected to said casing, and a substantially semi-torcidal core ring within said casing and connected to said vanes, said vanes defining a plurality of fluid passages in said casing with the fluid passages in one of said elements communicating with the fluid passages' in the other element, said vanes being effective to provide circulation of fluid in said passages during rotation of said impeller; and means enclosing said impeller and runner and defining a fluid chamber having fluidI therein filling the space between said core rings, the fluid passages in said elements, and further defining fluid pockets between the exterior of each of the casings of each element and the enclosing means, said enclosing means including an annular hollow sheet metal shell connected at its radially outer periphery to said impeller casing and having a radially extending flexible .portion movable axially of said driven shaftfor contraction and expansion of said shell by the presence of the fluid pressure in said pockets and which presence of fluid pressure in said fluid pockets also .counteracts the uid pressure between said core rings to prevent relative axial movement of said elements avvay from each other during operation of said device.

5. In a transmission, driving and driven shafts rom said passages during rotation of 7 tatable about a. common axis and being disposed in axially spaced relation; a hydrodynamic coupling device including: an impeller connected to said driving shaft, a runner connected to said driven shaft, said impeller and runner each comprising a hollow annular substantially semi-foroidal casing, a plurality of' curved arcuate vanes within and connected to said casing, and a substantially semi-toroidal core ring within said casing and connected to said vanes, said vanes connecting said casing and core ring and defining a plurality of fluid passages in said casing; a stator comprising spaced annular members and a plurality of .curved vancs connecting said annular members and defining iluidpassages therewith, said impeller and runner being disposed in proximity to each other and said stator being disposed between radially inner portions of said impeller and runner, one of the annular members of said stator defining with said core rings of said impeller and runner a fluid space between said impeller and runner; and means enclosing said impeller, runner and stator and defining a closed uid chamber defining fluid-filled `pockets exterior of said impeller and runner, said fluid passages having ac cess to said fluid-filled pockets, said enclosing means .including an annular hollowsheet metal shell connected at its radially outer portion to said impeller casing and defining the fluid-filled pocket between said enclosing means and exterior of the impeller, said shell having a flexible radially inner peripheral portion spaced from said impeller casing for movement axially of said driven shaft by the presence of the fluid pressure in said fluid-filled pockets and which presence of the fluid pressure in said fluid-filled pockets also counteracts the fluid pressure in said fluid space between said impeller and runner to prevent relative axial movement of said impeller and runner during operation of said device. l

6. In a transmission, driving and driven shafts rotatable about a common axis; a drive plate rotatable with said driving shaft; a hydrodynamic coupling device comprising an impeller element, a turbine element, and a stator element, said impeller and runner elements each comprising a substantially semi-toroidal casing and core ring, and a plurality of curved vanes connecting said casing and core ring and defining therewith arcuate fluid passages, the outlet of the passages in said impeller element and the inlet of the passages in vsaid runner element being disposed adjacent each other, said stator element comprising a pair of radially spaced annular i members and vanes connecting the members and defining therewith a plurality of fluid passages between the inlet of the passages in said impeller and the outlet of the passages in said runner element, the vanes of said elements being effective to circulate flid through the passages therein, said core rings of said impeller and runner elements and one of said annular members of said stator element defining a fluid space between said elements; an annular, hollow, semi-toroidal sheet metal shell surrounding said driving shaft and connected at its radially outer periphery to said drive plate and connected to the radially outer periphery of said impeller casing, said shell and said drive plate defining a fluid chamber in which said elements are disposed, said drive plate being spaced from said turbine casing and defining therewi-th a fluid pocket, said shell being spaced from said impeller casing radially inward of its connection to said impeller casing and defining with said impeller casing a fluid pocket and being capable of flexing to contractl and expand by the presence of the fluid pressure in said pockets and which presence of fluid pressure in said pockets also counteracts the fluid pressure in said fluid space between said impeller and runner to prevent relative axial movement of said impeller and' runner during operation of said device.

7. In a hydrodynamic coupling device, an impeller element, a runner element, and a stator element, each element having a casing, core ring and varies effective to circulate fluid from one to the other of said elements during rotation of said impeller, said core rings defining a fluid-filled space between said elements, and means enclosing said impeller and Arunner elements and defining 'g clement located adjacent to v a fluid chamber in which said elements are relatively rotatable, the enclosing means and the casings of the impeller and runner elements defining fluid pockets between the latter casings and enclosing means, said means having at least a portion thereof movable relative to said elements by the presence of the uid pressure in said fluidfilled pockets between said enclosing means and the casing of the impeller element and between said enclosing means and the .casing of the runner element, and which presence ofhfluid pressure in said pockets also counteracts the fluid pressure in the fluid-filled space between said core rings to prevent relative axial movement of said elements during operation of said device.

8. hydrodynamic coupling device including driving and driven shafts rotatable about a common axis; vaned impeller and runner elements respectively connected to said shafts and arranged side by side for rotation with the vanes of said elements being effective to circulate fluid within said elements upon rotation of the impeller element; and a shell forming a closed fluid chamber around said vaned elements and having a flexible axial end wall to permit lexpansion and contraction of the fluid chamber by variations in the pressure of the fluid in the chamber externally of thevaned elements, the vaned e flexible end wall being fixed at its outer circumference to a peripheral portion of the shell but being freely movable at its radially inner portion in an axial direction, and the other vaned element being supported by the opposite axial end wall of the shell against movement away from the first mentioned element, whereby any tendency of the elements to be moved axially away from each other by internal fluid pressures is largely counteracted by the pressure of the surrounding fluid in the chamber and any resultant unbalance in axial fluid pressures is taken up by equal, oppositely directed forces in the shell walls.

9. A device according to claim 8, wherein each of said elements comprises a hollow, annular, substantially semitoroidal casing in which the vanes are within and connected -to said casing, and a substantially semi-torcidal core ring within said casing and connected to said vanes, said vanes defining a plurality of fluid passages in each element with the fluid passages in one of said elements communicating with those in the other elements to provide circulation oflfiuid between the elements during rotation of said impeller; said core rings defining a fluidfilled chamber therebetween, said shell being connected at -its radially outer periphery to said impeller element casing and having its radially extending flexible end wall movable axially by variations in fluid pressure in said shell, said fluid pressure in the shell counteracting the fluid pressure in the space between said core rings and thereby opposing relative axial movement of said impeller element away from said runner element during operation of said device.

10. A device according to claim 8, wherein said shell comprises an annular, hollow, semi-toroidal sheet metal member surrounding the driven shaft of the device, and a drive plate connected to the radially outer periphery of the sheet metal member, said shell being connected to the radially outer periphery of said impeller element, said sheet metal member and said drive plate together defining the fluid chamber in which said elements are disposed, said member being spaced axially from said impeller element radially inward of its connection to said impeller element and being capable of flexing to contract and expand as a result of said pressure variations.

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