GB2118643A - Hydrodynamic transmission device - Google Patents

Abstract

A hydraulic coupling or torque converter (10) includes a double- acting clutch piston (3c) selectively engageable with a loose turbine (25), for transmitting drive from the turbine via damper (46) to output shaft (33), or with casing (31) for providing direct drive. With manual selector valve (75) in the neutral position shown, working fluid is directed to both sides of the piston to centralise it, and with valve (75) in its alternative setting fluid is directed to chamber (61) to engage the piston with the turbine. Direct drive is obtained under the control of a second valve (89). This arrangement facilitates gear changes in a semi-automatic transmission driven by the output shaft. <IMAGE>

Description

SPECIFICATION Transmission device The present invention is generally concerned with transmission devices incorporating a hydraulic coupling unit and locking clutch, in other words with transmission devices of the kind comprising a fluid-tight housing; a hydraulic coupling unit (such as a hydraulic coupling or torque converter) in said housing and comprising: an impeller wheel, an input element with which said impeller wheel is constrained to rotate, a first shaft, generally a driving shaft, with which said input element is constrained to rotate, and a turbine wheel; and a locking clutch in said housing comprising: a coupling element which is free to move in an axial direction, an output element which said coupling element is adapted to rotate, and a second shaft, generally a driven shaft, with which said output element is constrained to rotate, said coupling element being adapted to be frictionally constrained to rotate with the input element.

The invention is more particularly concerned with transmission devices of this kind designed to be fitted to automotive vehicles, especially, but not exclusively, where the transmission device is of the semi-automatic kind.

The driving shaft with which the input element of a transmission device of this kind is constrained to rotate is then the output shaft of the motor of the vehicle, whereas the driven shaft with which its output element is constrained to rotate is usually the input shaft of a gearbox, the output element possibly itself constituting this shaft.

On starting, and more generally on each change of gear ratio, the locking clutch is ineffective during a first stage and it is the hydraulic coupling unit which is operative between the input element and the output element, with all the necessary progressive action, due to the corresponding hydraulic fluid, but at the cost of slip which is inherent in this arrangement and which results in a loss of efficiency.

During a second stage, the locking (or "lock up") clutch coupling element provides direct mechanical coupling between the input element and the output element so as to bypass the hydraulic coupling unit and thus improve the overall efficiency by eliminating the slip due to the latter.

For the hydraulic coupling unit to be able to intervene between the input element and the output element in the aforementioned first stage, it is currently common practice to constrain the turbine wheel to rotate with the output element, the impeller wheel being constrained to rotate with the input element.

This arrangement, which has given and can continue to give satisfaction, in practice gives rise to a number of disadvantages.

In effect, the output element is continuously driven in rotation, either by the turbine wheel of the hydraulic coupling unit or by the coupling element of the locking clutch, and the same therefore applies to the input shaft of the associated gearbox.

As a result, the latter must necessarily comprise a clutch-type mechanism adapted to permit change from one gear ratio to another.

A gearbox of this kind is incompatible with the use, known per se, of synchromesh devices or direct-drive dog clutches, with which a change of ratio or reversing of the direction of rotation requires interruption of the input torque.

A general object of the present invention is to provide an arrangement whereby these disadvantages may be overcome and also offering further advantages.

The invention consists in a transmission device comprising a fluid-tight housing; a hydraulic coupling unit in said housing and comprising: an impeller wheel, an input element with which said impeller wheel is constrained to rotate, a first shaft with which said input element is constrained to rotate, and a turbine wheel which is freely rotatable; a locking clutch in said housing and comprising: a coupling element which is free to move in an axial direction, an output element which said coupling element is adapted to rotate, and a second shaft with which said output element is constrained to rotate; first friction means adapted to constrain selectively said coupling element to rotate with said input element; and second friction means adapted to constrain selectively said turbine wheel of said hydraulic coupling unit to rotate with said coupling element of said locking clutch.

By virtue of this arrangement, between the operative phase of the hydraulic coupling unit and that of the locking clutch on changing gear ratio, there systematically occurs an interruption in the drive to the output element, during which this output element, and thus the input shaft of the gearbox, is no longer constrained to rotate with the input element, and which may where required be exploited to bring about the necessary change of ratio.

As the coupling element of the locking clutch itself constitutes a cut-off device in this respect, no special clutch-type cut-off device is required in the associated gearbox, which may with advantage and economically consist of a simple gearbox using parallel trains.

Alternatively, a variator may be substituted therefor if desired.

In the arrangement in accordance with the invention, the turbine wheel of the hydraulic coupling unit is with advantage mounted so as to rotate freely.

This offers the advantage of protecting it when the locking clutch is operative.

Finally, whereas is usual - the locking clutch comprises, between its coupling element and the output element and in order to filter out vibration inherent in the kinematic system in which it is inserted, a torsional damper device, the torsional damper device advantageously operates continuously, whether it is the hydraulic coupling unit or the locking clutch which is operative.

In effect, in either case the rotation of the output element by the input element is effected through the intermediary of the coupling element of the locking clutch, and thus through the intermediary of the torsional damper device placed between the latter and said output element.

In practice, the supply of fluid to the housing of the transmission device in accordance with the invention is, as known per se, controlled by distribution means and the inlet element of the transmission device is constituted by its housing, more precisely by a transverse wall thereof.

Therefore, and in accordance with the invention, these distribution means may comprise a fluid inlet, a fluid outlet, a transverse wall in said housing, a first axial chamber in said housing delimited between said coupling element of said locking clutch and said transverse wall of said housing, a second axial chamber in said housing delimited between said coupling element and said turbine wheel, and changeover means adapted to alternately couple said fluid inlet and said fluid outlet to one or the other of said chambers.

In this way, the coupling element of the locking clutch may be rotationally linked to the turbine wheel of the hydraulic coupling unit or to the input element in a very simple manner.

For preference, in the "dead" configuration of the device, the pressure in the axial chambers delimited in the housing by the coupling element of the locking clutch is the same for both chambers, so that, self-centered between the turbine wheel of the hydraulic coupling unit and the corresponding transverse wall of the housing forming the input element, the coupling element of the locking clutch is with advantage-subjected to only minimal rotational drag, since it is in contact neither with said turbine wheel nor with said wall of the housing.

This offers the advantage of facilitating any change of ratio in the associated gearbox, for the reasons explained hereinabove.

Other objects and advantages will appear from the following description of an example of the invention, when considered in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claims.

Figure 1 shows one half of a transmission device in accordance with the invention in axial cross-section in the "dead" configuration of the device. together with a block schematic of the associated distribution means.

Figure 2 is a partial view in circumferential cross-section of the transmission device on the line Il-Il in Figure 1, shown in flat projection.

Figures 3 and 4 are similar to Figure 1 but on a smaller scale and iilustrate the operation of the transmission device in accordance with the invention.

Figure 5 relates to part of Figure 1 and shows an alternative embodiment.

Figure 1 shows a transmission device 10 with hydraulic coupling unit 11 and locking clutch 1 2 of the kind fitted to certain automotive vehicles.

In practice, in the embodiment shown, the transmission device is of the semi-automatic kind, that is to say controlled by a lever (not shown) accessible to the user for engaging forward or reverse drive or a neutral "dead" or parking position.

Since a transmission device of this kind does not of itself constitute the object of the present invention, it will not be described in complete detail here. Only those of its component parts necessary to an understanding of the invention will be described.

In a manner known per se hydraulic coupling unit 11 and locking clutch 12 are conjointly disposed within a common rotating housing 1 3 which is fluid-tight and therefore adapted for the circulation of any fluid appropriate to the implementation of hydraulic coupling unit 11 and locking clutch 12.

In the embodiment shown, housing 13 is fastened to a tubular hub 14 by means of which it is centered on an internal bearing surface 1 5 of a fixed bearing 16, with a bearing shell 17 placed between them.

Be this as it may, rotary housing 13 in practice forms the input element of the transmission device, having a transverse wall 31 on the side axially opposite tubular hub 14 adapted to be constrained by a driving diaphragm 1 9 to rotate with a first shaft 20, in practice a driving shaft and the vehicle motor output shaft in the case of an application to an automotive vehicle.

To center it on driving shaft 20, rotary housing 13 has an axially projecting boss 21 by means of which it is engaged in a complementary recess 22 in said shaft; in practice, in the embodiment shown, this is a hollow boss mounted on transverse wall 31 by virtue of a central opening therein.

In the embodiment shown, hydraulic coupling unit 11 is a hydraulic coupling which comprises, in a manner known per se, an impeller wheel 24 and a turbine wheel 25 adapted to conjointly define a hydraulic circuit for the corresponding fluid within rotary housing 1 3.

Alternatively, a torque converter might be used in which case a stator wheel would be inserted in the hydraulic circuit between turbine wheel 25 and impeller wheel 24, in line with those parts of these wheels nearest the axis of the device in the radial direction.

In a manner known per se, annular wall 26 of impeller wheel 24 is formed directly by part of the corresponding transverse wall of rotary housing 13, so that impeller wheel 24 is constrained to rotate with the input element which rotary housing 13 constitutes.

Conjointly, annular wall 27 of turbine wheel 25 is supported by a tubular hub 28.

In a manner also known per se, locking clutch 12 comprises, within rotary housing 13, a coupling element 30 in the form of a plate extending generally transversely relative to the axis of the device, between annular wall 27 of turbine wheel 25 and transverse wall 31 of rotary housing 1 3 opposite the transverse wall of the latter forming annular wall 26 of impeller wheel 24, its configuration, as shown, being adapted to that of said transverse wall 31 of rotary housing 13.

As will be described in more detail hereinafter, coupling element 30 is adapted to rotate an output element 32 which is itself constrained to rotate with a second shaft 33, in general a driven shaft.

In practice, in the embodiment shown, output element 32 consists of a tubular hub which by virtue of a splined arrangement is constrained to rotate with driven shaft 33 which is tubular and directly constitutes the output shaft of the transmission device, intended to be constrained to rotate with the input shaft of the associated gearbox, for example, or to constitute an input shaft itself.

Shaft 33 is in practice centered on a third shaft 35 by virtue of its internal bearing surface. Shaft 35 is tubular and directly constrained by a splined coupling to rotate with rotary housing 13, more precisely with transverse wall 31 thereof, through the intermediary of the corresponding boss 21. It is adapted to drive any accessory (not shown), such as an oil pump, for example.

For the purpose of centering shaft 33, shaft 35 has a locally projecting bearing surface-36 such that an annular space 37 is left free between shafts 33 and 35, rendered fluid-tight by a rotary seal 38 disposed to this end in a groove in said bearing surface 36.

Likewise, an annular space 108 is left free between shaft 33 and hub 14 of rotary housing 13. It is rendered fluid-tight by a rotary seal 39 placed to this end between shaft 33 and the corresponding bearing 1 6.

The tubular hub constituting output element 32 also serves-to center turbine wheel 25 of hydraulic coupling unit 11, comprising to this end an axial extension 40 on which is engaged hub 28 of said turbine wheel 25.

Axial stops 41 are disposed between hub 28 of turbine wheel 25 and the corresponding transverse wall 26 of rotary housing 13, between hub 28 and the tubular hub constituting output element 32, and between this tubular hub and the corresponding transverse wall 31 of said rotary housing 13.

In the embodiment shown, it is through the intermediary of the torsional damper device 43 that coupling element 30 of locking clutch 12 is adapted to rotate output element 32.

In a manner known per se, torsional damper device 43 comprises two coaxial parts mounted to rotate relative to one another within predetermined limits of relative angular movement and against the action of springs 44 disposed circumferentially between them.

One of these parts is constituted by a disk 45 fastened to the tubular hub constituting output element 32, by crimping to the median part of this tubular hub, for example, and as shown.

The other of said parts consists of two guide rings 46 extending one on each side of disk 45 and, beyond the periphery of the latter, axially fastened to one another by spaced rivets 48.

At least one lug 49 is cut out from one of guide rings 46. It extends axially and is engaged with clearance in a notch 50 formed for this purpose at the periphery of disk 45, to limit relative angular movement between the coaxial parts thus constituted.

Conjointly, each of spring 44 is disposed in a housing formed partially by a window 51 formed to this end in disk 45 and partially by windows 52 also formed to this end in guide rings 46.

By the same rivets 48 which attach them to one another, guide rings 46 are attached to spaced tangs 53 which are elastically deformable in the axial direction. These tangs may be in pairs, as shown in Figures 1 and 2, and extend substantially tangentjally to a circumference of the device. At its opposite end each is attached by a rivet 54 to coupling element 30 of locking clutch 12; in practice, in the embodiment shown, these rivets are inserted in bores 58 in one of guide rings 46 so as to limit any buckling of tangs 53 on rotation of the device in the direction opposite to its normal direction of rotation.

Also, coupling element 30 of locking clutch 12 is mounted to move axially, piston fashion, and in the embodiment shown has to this end on its internal periphery an axial return 55 by means of which it is engaged upon the tubular hub constituting output element 32.

It is also adapted to be constrained by friction clutch means to rotate with the input element which rotary housing 13 constitutes.

To this end, in the embodiment shown, it has an annular clutch surface 57 in the vicinity of its external periphery and facing a clutch surface 56 formed for this purpose on the internal surface of transverse wall 31 of rotary housing 13. In the embodiment shown, clutch surface 57 carries a friction lining 66 adapted to cooperate frictionally with clutch surface 56.

Alternatively, clutch lining 66 may be carried by clutch surface 56 of rotary housing 13, the corresponding clutch surface 57 of coupling element 30 not carrying any friction lining in this case.

These arrangements are well known per se and as they do not constitute part of the present invention will not be described in more detail here.

In accordance with the invention, turbine wheel 25 is mounted so as to rotate freely and to this end its hub 28 is in practice engaged with little friction on axial extension 40 of the tubular hub constituting output element 32. Like the input element constituted by rotary housing 13, it is also adapted to be constrained by friction clutch means to rotate with coupling element 30 of locking clutch 12, alternately with said input element.

In the embodiment shown in Figures 1 to 4, turbine wheel 25 to this end comprises an annular clutch surface 60 extending around its axis and behind its annular wall 27, opposite a clutch surface 59 provided for this purpose on coupling element 30. cltuch surface 60 being adapted to cooperate frictionally with coupling element 30.

In the embodiment shown, clutch surface 60 has a friction lining 65.

In practice, coupling element 30 delimits two axial chambers within rotary housing 13. One chamber 61 is formed between it and the corresponding transverse wall 31 of rotary housing 1 3. The other chamber 62 is formed between it and annular wall 27 of turbine wheel 25.

These chambers are rendered fluid-tight by seals 63 and 64 provided for this purpose on the tubular hub constituting output element 32 and axial extension 40 thereof.

At the end of tubular shaft 35 a passage 71 formed in transverse wall 31 of rotary housing 13, and more specifically in the corresponding part of axial boss 21 of the latter, enables an axial bore 67 of shaft 35 to communicate with chamber 61 through axial stop 41 disposed between the tubular hub constituting output element 32 and said transverse wall 31.

Similarly, passages 68, 69 and 70 provide communication between chamber 62 and annular space 37 between shaft 33 and shaft 35.

Passages 68, 69, and 70 are formed in correspondence with one another (and partially in the form of annular grooves in the case of passages 69 and 70) in shaft 33, axial extension 40 of the tubular hub constituting output element 32 and hub 28 of turbine wheel 25, respectively.

The supply of fluid to rotary housing 13 of the transmission device thus constituted is controlled by distribution means comprising, in the usual manner, a pump 72 whose inlet pipe extends into a return sump 73 with discharge controlled by a valve 74.

As the transmission device is semi-automatic, the fluid distribution means comprise operating means controlled by a lever accessible to the user.

In the figures these operating means are schematically represented by a slide valve the slide 76 of which is operated by the associated lever and urged by a spring 77 towards a fixed stop 78 defining its unoperated position.

The slide 76 has two bearing surfaces.

In addition to discharge openings 80 at its ends, the cylinder in which it moves comprises an opening 81 connected to the outlet of pump 72, a discharge opening 82 incorporating a throttling device 83, and two openings 84 and 85 associated with rotary housing 13; in practice, in the embodiment shown and where they open into said cylinder, openings 81 and 84 open out to constitute annular grooves 81' and 84'.

In the unoperated position shown in Figure 1, which corresponds to a "dead" neutral or parking configuration of the transmission device, opening 81 communicates with both of openings 84 and 85. whereas opening 82 is shut off.

On the other hand, in the operated position shown in Figures 3 and 4, which correspond to forward and reverse drive configurations of the transmission device, only opening 84 communicates with opening 81 whereas opening 85 communicates with discharge opening 82.

In accordance with the invention, the distribution means adapted to control the transmission device further comprises changeover means 89 adapted to alternately couple to the fluid inlet from pump 72 or to the associated sump 73 one or other of axial chambers 61 and 62 delimited in rotary housing 13 by coupling element 30 of locking clutch 12.

In the figures, changeover means 89 are schematically represented by a slide valve, the slide 86 of which is controlled by a device which is adapted to actuate locking clutch 30 and, since it does not constitute part of the present invention, will not be described here.

Slide 86 comprises a number of bearing surfaces and is constantly urged by a spring 87 in the direction towards a stop 88 which defines its unoperated position.

In addition to discharge openings 90 at its ends, the cylinder in which it moves comprises two openings 92 and 93 respectively connected to openings 84 and 85 of the cylinder of operating means 75, and two openings 94 and 95 respectively connected by pipes 96 and 97 to axial bore 67 of shaft 35 and annular space 37 between shaft 35 and shaft 33.

In the unoperated position shown in Figures 1 and 3, openings 92 and 93 are respectively connected to openings 94 and 95.

For the operated position shown in Figure 4 and which, as will be explained hereinafter, corresponds to actuation of locking clutch 12, opening 92 is connected to opening 95 whereas opening 93 is shut off. By virtue of a throttling passage 98 provided for this purpose in the corresponding bearing surface of slide 86 (Figure 1), opening 94 is connected to discharge opening 90.

It results from the foregoing that, in the "dead" neutral position shown in Figure 1, the fluid source constituted by pump 72 feeds chamber 61 of rotary housing 13 through, in succession, openings 81 and 84 of operating means 75, openings 92 and 94 of changeover means 89, pipe 96, internal bore 67 of shaft 35, passage 71 in transverse wall 31 of rotary housing 13 and the corresponding axial stop 41. It also feeds chamber 62 of rotary housing 1 3 through, in succession, passages 81 and 85 of operating means 75, passages 93 and 95 of changeover means 89, pipe 97, annular space 37 between shafts 33 and 35, passage 68 in shaft 33, passage 69 in axial extension 40 of the tubular hub constituting outlet element 32 and passage 70 in hub 28 of turbine wheel 25.

Having equal pressures on both sides, the piston which constitutes coupling element 30 of locking clutch 12 therefore centers itself in a median position in which, as shown, it is equaily spaced from clutch surface 56 of transverse wall 31 of rotary housing 13 and friction lining 60 on turbine wheel 25.

Conjointly, the fluid entering the smaller diameter part of chambers 61 and 62 flows into the larger diameter part and thence into the hydraulic circuit defined between impeller wheel 24 and turbine wheel 25 of hydraulic coupling unit 11, leaving this hydraulic circuit in the smaller diameter part thereof.

It then enters the annular space 108 between shaft 33 and hub 14 of rotary housing 13. Then, via a passage 29 provided for this purpose in bearing 1 6 and controlled by a valve 100, it returns to the sump 73.

Since turbine wheel 25 is freely rotatable and since coupling element 30 of locking clutch 12 is spaced from turbine wheel 25 and also from transverse wall 31 of rotary housing 13, output element 32 is not acted on by any driving force apart from possible drag due, for example, to its previous rotation or to the proximity of rotating walls or members, as is well known in such configurations.

The same applies, advantageously, to output shaft 33.

In other words, no torque is transmitted under these conditions.

If, on the other hand, when commanded by the corresponding lever slide 76 of operating means 75 moves to the operated position (Figure 3), only chamber 61 of rotary housing 13 is supplied with fluid by pump 72, along the same path as previously.

Chamber 62 of rotary housing 1 3 is connected to the discharge outlet, however, since the corresponding opening 85 of operating means 75 is then connected to the discharge outlet through opening 82 of said means.

Because of the different pressures on its opposite sides, the piston which constitutes coupling element 30 of locking clutch 12 is applied against friction lining 65 of turbine wheel 25 so that, by friction, turbine wheel 25 of hydraulic coupling unit 11 is constrained to rotate with coupling element 30 of locking clutch 12 and, by virtue of the latter and torsional damper device 43, with output element 32 and thus with output shaft 33.

In other words, hydraulic coupling unit 11 is then operative, its turbine wheel 25 being itself driven hydraulically in rotation by the input element constituted by rotary housing 13, and torque may thus be transmitted.

Note that by virtue of the throttling facility 83 associated with opening 82 of operating means 75, the entry into service of hydraulic coupling unit 11 has the advantage of being modulated.

When the conditions beneficial to entry into service of locking clutch 12 are fulfilled, slide 86 of changeover means 89 also moves to the operated position (Figure 4).

The foregoing arrangements are then reversed: chamber 62 of rotary housing 13 is then connected to pump 72, openings 95 and 92 of changeover means 89 being then in communication with opening 84 of operating means 75, whereas chamber 61 of rotary housing 13 is connected to the discharge outlet, through opening 94 of changeover means 89, opening 98 of the corresponding slide 86 and opening 90 of said changeover means 89.

Moving away from friction lining 65 on turbine wheel 25, the piston constituted by coupling element 30 of locking clutch 12 applies its friction lining 66 to clutch surface 56 of transverse wall 31 of rotary housing 1 3 constituting the input element of the transmission device.

Hydraulic coupling unit 11 is then bypassed, except that, by virtue of coupling element 30 of locking clutch 12 and torsional damper device 43, the driving in rotation of output element 32 and thus of output shaft 33 is mechanically implemented by the input element which rotary housing 1 3 constitutes, for transmission of the corresponding torque.

Annular wall 27 of turbine wheel 25 is preferably fluid-tight so as to avoid, with hydraulic coupling unit 11 operative (Figure 3), unwanted entry of pressurized fluid through annular wall 27 from chamber 62 of rotary housing 13 then connected to the discharge outlet.

Thus it is with advantage possible to use only one value of fluid pressure, as described hereinabove.

In the embodiment shown in Figures 1 to 4, turbine wheel 25 is a casting, of metal, for example, so that to provide a support for friction lining 65 or taform a clutch surface it has an annular boss 102 projecting from the back of its annular wall 27 and integral therewith.

In an alternative arrangement (Figure 5), turbine wheel 25 has an annular wall 27 of stamped metal, for example, and bears, on the back of the latter, a ring 103 which may, for example, be attached by soidering to said annular wall 27. It has a simple clutch surface 60 facing a friction lining 65 carried by clutch surface 59 of coupling element 30 of locking clutch 12, as shown, or itself carries a friction lining of this kind.

In the embodiment shown in Figures 1 to 4, annular wall 27 of turbine wheel 25 is of itself fluid-tight.

In the embodiment shown in Figure 5, which usually involves the use of clipped on vanes, it may be rendered fluid-tight by the application of any appropriate coating material.

It will be understood that various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

Claims (7)

1. A transmission device comprising a fluidtight housing; a hydraulic coupling unit in said housing and comprising: an impeller wheel, an input element with which said impeller wheel is constrained to rotate, a first shaft with which said input element is constrained to rotate, and a turbine wheel which is freely rotatable; a locking clutch in said housing and comprising: a coupling element which is free to move in an axial direction, an output element which said coupling element is adapted to rotate, and a second shaft with which said output element is constrained to rotate; first friction means adapted to constrain selectively said coupling element to rotate with said input element; and second friction means adapted to constrain selectively said turbine wheel of said hydraulic coupling unit to rotate with said coupling element of said locking clutch.

2. A device according to claim 1, wherein said turbine wheel comprises an annular wall and an annular surface behind said annular wall adapted to cooperate frictionally with said coupling element of said locking clutch.

3. A device according to claim 1 or claim 2, comprising means adapted to control the supply of fluid to said housing and distribution means adapted to control said fluid supply control means, comprising a fluid inlet, a fluid outlet, a transverse wall in said housing, a first axial chamber in said housing delimited between said coupling element of said locking clutch and said transverse wall of said housing, a second axial chamber in said housing delimited between said coupling element and said turbine wheel, and changeover means adapted to alternately couple said fluid inlet and said fluid outlet to one or the other of said chambers.

4. A device according to claim 3, wherein, in a "dead" neutral configuration of the device, said chambers are both coupled to said fluid inlet, whereby no torque is transmitted.

5. A device according to claim 3 or claim 4, wherein said annular wall of said turbine wheel is fluid-tight.

6. A transmission device substantially as herein described and illustrated with reference to Figures 1 to 4 of the accompanying drawings.

7. A transmission device substantially as herein described and illustrated with reference to Figures 1 to 4 of the accompanying drawings, modified substantially as herein described and illustrated with reference to Figure 5 of the accompanying drawings.