GB2323141A

GB2323141A - A viscous fluid operated friction coupling with short circuiting means

Info

Publication number: GB2323141A
Application number: GB9809544A
Authority: GB
Inventors: Adrian Chludek
Original assignee: GKN Viscodrive GmbH
Current assignee: GKN Viscodrive GmbH
Priority date: 1996-05-17
Filing date: 1997-05-16
Publication date: 1998-09-16
Anticipated expiration: 2017-05-16
Also published as: GB2323140B; GB2323141B; GB9809542D0; GB2323140A; GB9809544D0

Abstract

A coupling comprises a friction coupling 12 loaded by a piston 19 which is mounted in a pressure chamber 21 of a speed-sensing control assembly 13. The pressure chamber 21 contains a disc-shaped rotational member 22 and a disc-shaped pumping and control member 23 having a shear channel 37 with a rotational stop 41 mounted therein. The stop 41, depending on its position, seals connecting channels 30, 32, 43 and is rotatably moved by resilient end stops 201, 202 so that, as the frictional forces increase, the stop 41 is moved from one position to another. This results in aperture 31 causing short circuiting between the channel 32 leading to reservoir 26 and the connecting channel 43 leading to the pressure chamber 21. In this way, the pressure build-up by means of the shear channel 37 collapses so that, at different speeds, the pressure build-up and thus the transferable torque is reduced until end stops 201, 202 spring back into position. Pressure chamber 21 contains a viscous fluid that is pressurized by the rotational member 22 when housing 14 rotates relative to hub 16.

Description

2323141 1 PATENTS ACT 1977 GMD/A9475GB Title: CONTROLLABLE COUPLING DEVICE

Description of Invention

This invention relates to a coupling device with two parts which are coaxially rotatable relative to one another, and comprising, a friction coupling having fiction plates of which altemate plates are connected respectively to one and to the other of said rotatable pails; and fitillier comprising, ail actuating device for the friction coupling, which actuatIng device comprises all annular chamber in one of said rotatable pails which annular chamber contains a viscous fluid, a rotaflonal member which is arranged ill the annular chamber and which is drivingly connected to the other one of said rotatable pails, and which acts on the viscous fluid; the actuating device, when the rotatable pails rotate relative to one another, causing an increase ill fluid pressure for the purpose of loading the fliction t> coupling for transmitting torque between the rotatable pails. Such a coupling device will hereafter be referred to as a coupling device of the kind specified.

C) When the rotatable pails of the coupling rotate relative to one another, the 0 shearing action ill the Iiighly viscous fluid causes a pressure to be built up in the annular chamber, which pressure axially loads the fi'lction plates of the ffiction coupling into ffictional engagement xvith one another thereby causing the coupling C) 0 to transmit torque between the rotatable pails.

Devices of said type are used ill motor vehicles and agricultural machinery to generate a locking moment between the tw pails rotating relative to one another which is dependent oil the speed differential therebetween.

The two pails rotating relative to one another may be pails of a differential drive or they inay be connected to such pails of a differential drive, and by usim) such ail assembly in a differential drive, a limited slip differential is produced which "locks" (has its differential action itillibited) as a function of the differential speed between the pails.

2 A coupling device of said type is known fi.om JP-7-17162 Y2 for example, wherein the rotational member is connected so as to be rotationally fast with one of the parts rotating relative to one another, whereas the other one of the parts forms an annular chamber which is delimited by a displaceable piston for loading the ffiction coupling. With an increasing differential speed the pressure build-up generated in the annular chamber increases, and causes the displacement of the piston.

A device of this type is also known fi.oni DE-19505800.3 wherein, for the purpose of linilting the pressure generated in the annular chamber, there is provided C 1 1 a shortcircult line between the anniflar chainber and a reservoir, which line opens as a function of the pressure. However, the pressure-dependent control system can pass on the speed differential only indirectly, as a result of which there may be ffiterference for example due to the temperature of the viscous fluid. The channels required for the shortcircult line render the device more expensive.

It is therefore the object of the present invention to provide a differential speed sensing coupling of the type herein first set forth which comprises torque limiting means which are siniplified and whicli, in 1)aiilciilai., do not require any additional housing bores.

0 In accordance witli the invention, in a coupling device of the kind specified, in the annular chamber there is provided rotationally movable means for providing a short circuit connection between a repon of high pressure in the 0 c) 0 annular chamber and a region of low pressure in the annular clialliber.

The actuating device for the ffiction coiiplliig itself may be characterised in a preferred embodiment in that inside the annular chamber there is disposed a pressure build-up and control member which is rotatable relative to said annular chamber to a limited extent and which is provided with a cl rc urn ferenti ally extending annular groove which is dellmited by two ends, which is closed by the t) contacting rotational member and which forins a shear channel with said rotational 0 member; that the annular chamber is delimited by a movable piston; that in the one of the pails rotatable relative to one another, there is formed a reservoir with a variable volume coninitinicatin- with the anniflar chainber. and that upon relative 0 5 j rotation of the parts rotatable relative to one another, one end of the shear channel with a lower fluid pressure is connected to the i-esei-voli. , and the other end of the shear channel with a higher fluid pressure is connected to the pall of the annular chamber which is delimited by the movable piston.

The pressure build-tip and control member which is rotatable to a limited extent may have its rotation limited by resilient stop means, e.g. be held between two elastically resilient end stops which, when a given differential speed between the parts rotatable relative to one another is exceeded, as a result of being elastically resilient, pennit fitillier rotation of the pressure build-up and control member and thus provides for said shoilcircult connection between the end of the shear channel with the higher pressure and the end of the shear channel with the lower pressure.

Depending on the desired curve of the locking moment generated by the fliction coupling as a function of the differential speed, it is possible to correct the forces generated in the annular chamber. For this purpose it is possible to provide spring means which are supported on the housing and which load the plates on the rov de spring rneans which are supported on the side facing the piston or to p 1 0 housing and load the piston ori the side facing the plates or to provide spring rneans which are arranged in a pretensioned condition between the piston and the ffiction coupling while continuously loading the latter with a inininium force.

The reservoir may be formed by the rotational housing and an axially movable spring-loaded piston rotating with the rotational housing or by a springloaded membrane or it may comprise a resilient compensatnig element in a chamber forming the reservoir. The highly viscous fluid contained therein inay be a dilataiit fluid for example, i.e. a inedmin whose viscosity increases as a function of the shear rate.

To explain the invention, reference is made to the accompanying drawings, wherein:- Figure 1 is a pailially cut-away view which shows two plates which are movable relative to one another with a groove constituting a shear channel being 0 C forined in one of the plates; 4 Figure 2 is a longitudinal section of a coupling of the kind specified; Figure 3 is a detailed view of a first embodiment of a pumping and control disc with a rotational member, in a plan view (a) and in a longitudinal section (b), in a first position; Figure 4 shows the pumping and control disc and the rotational member according to Figure 3 in a plan view (a) and in two longitudinal sections (b, c) in a third position; Figure 5 shows a pumping and control disc, in the form of a detail, in section (a), in a fi-ont view (b) and a rear view (c); Figure 6 shows a conveyor disc of a coupling in accordance with the invention with an associated 1)uiiiplii,(:,, and conti.ol disc in a fli- st conveying position (a) and in a second shoil circulted position (b).

Figure 7 shows a conveyor disc witli an associated pumping and control disc in a first conveying position (a) and in a second shortcirculted position (b).

Fi-ure 1 is a cut-away illustration of a first plate or disc 1 and a second plate or disc 2 whose end faces 4 contact one another. The first plate 1 is assumed to be fixed, with the second plate 2 moving relative to the first plate 1 at the speed Viz. In the end face 33 of the first plate 1 there is formed a groove 5 whose cross-section is rectangular and which, at its sides, compiises two delimiting walls 6, 7. The groove 5 and end face 3) form a shear cliannel 8 which contains a viscous medium. Said shear channel comprises a length 1,,, and a height or thickness s.

When the plate 2 moves, the medium in the shear channel behaves in accordance with the given linear speed profile which refers to the fixed plate 1. The surfaces are each subject to adhesion conditions, both as regards the plate 1 and the plate 2, i.e. with reference to the plate 2, the speed pi-ofile would be reciprocal. With reference to the plate 1, the shearing action In the shear channel results in a pressure p and a quantIty flow Q.

As the applications shown liere do not i-efer to relative linear movements but to relative rotational movements, the gn.oove forming the shear channel preferably extends circumferentially, as shown in Figures 2 to 7.

Figure 2 shows a coupling assembly 11 which comprises a controllable ffiction coupling 12 in the form of a mulfi-plate coupling, and a speedsensing control assembly 13. The friction coupling comprises a housing 14 in which outer C plates 15 are held so as to be rotationally fast, as well as a hub 16 on which there are arranged interposed inner plates 17 so as to be rotationally fast. The fi-iction 0 coupling is loadable by means of a piston 19 which forms pail of said control assembly 13 which is arranged in the housing 14 and comprises the axially 0 C) movable piston 19 and a rotational housing 20, which two pails rotate with the 0 housing 14. Both together fonll a pressure chamber 21 which contains a discshaped rotational inember 22 and a disc-shaped pumping and control member 233. The rotational rnernber 22 is connected to said hub 16 so as to be rotationally fast therewith, with said hub 16 being driven. By. ineans of a rotational stop (not C illustrated) which engages a circumferential groove (not illustrated) in the rotational housing 20, the puniping and control member 2,33 is rotatable relative to the rotational housing 20 to a limited extent. Ail 0-ring 335 arranged in the piston 19 serves as spring means, thus ensuring close contact between the rotational member 22 and the pumping and control inember 2.3 3.

When the rotational ineinber dilven by, the hub 16 via toothing means changes its direction of rotation, it inoves the puinping and control inember 23 3 0 0 fi-om its one end position deterniinecl by a rotational stop and circumferential groove into the other end position detennined by the rotational stop and circumferential groove. Furtherniore, the rotational housing 20 contains a reservoir 26 which is delimited by ail axially movable annular piston 27. The latter is supported by plate springs 28 oil the housing, 20, so that tile reservoir 26 always compensates for changes in volume ill the pressure chamber 2 1. Tile rotational housina 'M is shown to have ail axial connectino channel W which, ill the circumferential position illustrated, ovedaps with a conti-ol apeilure 331 in the pumping and control member 23). The control aperture 1 is positioned at one end of the shear channel 338 which is forined by a circumferentially delimited groove in the pumping and control inember 23 and by the surface of the rotational member 22. The pails rotating relative to one another are sealed relative to one another by 6 seals. The gap between the rotational member 22 and the piston 19 radially outside the 0-ring 35 is to be regarded as part of the pressure chamber 2 1. Screws 39, 40 provide for filling and ventilating the pressure chamber and the reservoir. Plate springs 25 are supported on the housing 14 and act on the piston 19 so that they t> form a counter force relative to the effect of the pressure chamber.

Figure 33, m the form of a detail iiii a plan view and axial section, shows a rotational housing 20 and a pumping and control member 23). The plan view shows the circumferentially extending groove 337 which is delimited by side walls 54, 55 and at whose ends there are provided control apertures 3) 1 and 3-35. The control aperture 33 shown in section is located above a further connecting channel 332 in the rotational housing. The control apeiltire 3 1 located at the other end overlaps with a radial connecting channel 43) (not shown in the section) in the rotational g housing. The position of a further through-aperture 30 Ill the rotational housing 20 0 is shown in dashed lines. Dashed lines in the section and plan view indicate the rotational stop 41 arranged on the reverse side of the pumping and control member 0 23 and the circumferentially delimited groove 42 which limit the rotation of the pumping and control member 23) relative to the rotational housin, (1 20.

0 Figure 4 shows the sailie details as Figure _33 in a plan view and two sections, with the same reference numbers being used. Howevel., ill tills Figure the rotational stop 41 has assumed the opposed end position Ill the circumferentially delimited groove 42. Now the control aperture 3l overlaps with the connecting channel 330 leading to the reservoir, whereas the second control apeiture 33 is connected to the connecting channel 43) leading to the pressure chamber. The pressure build-up now takes place at the end of the groove 37 at the control aperture 3) 3). Dashed lines in the plan view indicate the position of the first connecting channel 32 leading to the reservoir, which in this case has no function.

C Figures 5a, 5b and 5c, ill the forin of a detail, show a pumping and control member 233 of the type already described above on several occasions, with the control apertures 31, 333 and the groove 37 as well as the rotational stop also being identifiable as details.

7 Oil the reverse side of the inember (Figure 5c) it is possible to identify a surface region 51 which comprises the control apertures 31, 33 and which is designed ill such a way that, depending oil its position, it is able to rest sealingly on the connecting channels 30, 32, 43). The suiface region 51 is circumferentially delimited ill such a way that, depending on its position, it is able either to open or close a throttle bore. The reinaming surface, oil its reverse side, comprises a plurality of annular ribs 53) ill order to reduce ffiction and adhesion relative to the housing. A suiface 52 positioned opposite the surface 51 carries the rotational stop 41 projecting beyond said surface.

In Figures 6a and 6b, ally details corresponding to Figure 3 have been given the same reference numbers. Ill Figure 6a, the rotational stop 41 is in its end position ill the circumferentially dellnilted groove 42 betweeii two end positions which are fornied by resillew ciid stops 201, 202. As a restilt. the conn-ol aperture 31 at the one end of the groove 37 is connected to the coiinecting channel 43 leading to the pressure chambei., x%liei-eas the second control aperture 333 is connected to the reservoir by the coiiiiectiii,, channel 39 Up to a desired speed differential between said pails which are rotatable relative to one another, the resilient end stops 201, 202 call be assumed to be substantially rigid, i.e. the fi-iction forces applied to the gn-oove are not suitable for overcoming the spring forces, so that tlici.e exists all exact con- elation between the ends of the groove and the apeniii-es 3) 1, 33), as shown, or, ill the opposite direction of rotation, between the ends of the grooves wid the apertui.es 30 alld 331 1.

In Figure 6b, the rotatioiial stop is ill a changed position which is achieved by the resilience of the rotational stop 201. As a result, the aperture 31 in the pumping and control member now causes shortcirculting between the channel 32 leading to the reservoir and the coiiiiectlii,, chaimel 43) leading to the pressure 0 0 chamber. At the sanie tline, by ineans of the cliaimel 32 to tile reservoir, the aperture 1 at the one end of the,,,i-oo.e is slioilcii. cititeel witli the aperture 3 32 at the C other end of the groove, Ill tlils way, the pressure build-up by ineans of the groove collapses so that, at the different differential speed, the pressure build-up and thus 8 die torque transferable by the fliction coupling is reduced until the end stop 201 again springs back into the position according to Figure 6a.

Any details in Figures 7a and 7b which correspond to those in Figure 6 have been given the same reference numbers. Again, in Figure 7a, the rotational stop ill the circumferentially delli-nited groove 242 is in its end position between two fi.ecly reachable end positions formed by the resilient end stops 201, 202, whereas Figure 7b shows a position which is rotated beyond the end position, with the end stop 201 being resilient. Ill additioti to the details shown ill Figure 6, the housing is provided with two further axial bores 203), 204 which also establish a connection with the reservoir, and two further bores 205, 206 are provided in the pumping and control member inside the annular groove 37. Ill the freely reachable end positions according to Figure 7a, which call be reached without compressing the end stops 201, 202 by fi.eely rotating the pumping and control nieniber, said apertures do riot have ally flinction. Ill the positlon as illustrated ill Fig,-ure 7b, the resilient end stop 201 is compressed by a sniall amount relative to the position shown in Figure 6b. The sliortcirculting function ill the region of the two ends of die groove, as explained with reference to Figure 6b, does riot yet take place.

However, the apertures 203), 205 overlap one another, which has a double effect in that the region between the aperture and the apeilure 203) is connected to the reservoir at both ends, so that all effective pressure btilid-up cannot take place here. However, between the apeiltire 203) which now sci-\,es as a suction aperture out of the reservoir and the channel 43 leading to the pressure chamber, there occurs an 0 effective pressure build-up oil a substantially reduced channel leng-th, so that the pressure build-up does not collapse completely, but is reduced to pail of the channel length. In consequence, the pressure and thus the torque transferable by the fliction coupling is limited to a predetennined value. Ill the opposite direction of rotation and upon rotation of the pumping and control disc relative to the housing, the apertures 204, 206 overlap ill the sanic way,. Ill both directions of C1 relative rotation, a further conipi.esslon of the end stop 201, 202 causes a situation as described above with reference to Figin.e 6b.

9 In the above described embodinients, the means for limiting the pressure established in the annular chamber operates automatically in response to the speed difference creating the pressure or to the pressure itself. It would further be possible to provide for external control of the pressurelimiting means.

c

Claims

1. A coupling device with two pails whicli are coaxially rotatable relative to one another, and comprising a friction coupling having ffiction plates of which alternate plates are connected respectively to one and to the other of said rotatable pails; and further comprising an actuating device for the fliction coupling, which actuating device comprises an annular chainber in one of said rotatable parts which annular chamber contains a viscous fluid, a rotafional ineniber wbich is arranged in the annular chamber and which is drivingly connected to the other one of said rotatable pails, and which acts on the viscous fluid, the actuating device, when the C rotatable pails rotate relative to one another, causing an increase in fluid pressure for the purpose of loading the friction coupling for transmitting torque between the C 11-5 0 rotatable pails, wherein, in the annular clian-iber, there is provided rotationally movable means for providing, a short circult connection between a region of high pressure in the annulai. chamber and a region of low pressure in the annular chamber.

2. A coupling device according to Clann 1, wherein the rotationally movable means for providing the short circuit connection is autornatically controlled as a function of the relative speed between the rotational ineinber and the annulai. chamber, or as a function of the pressure in the annular charnber, or as a function of the rotational speed of the rotational ineiriber.

A coupling device according to Galin 2 yllei.eiii the rotationally movable means for providing the short circuit connection is controllable directly by fluid C shearing as a function of the differential rotational speed between the rotational meniber and the annular clianiber.

4. A coupling device according to Claiin 1 wherein the rotationally movable 0 0 means for providing the sliort circuit connection is extenially controllable.

C 11

5. A coupling device according to any one of Claims 1 to -3, wherein inside the annular chamber there is disposed a pressure build-up and control member which is rotatable relative to said annular chamber to a limited extent and which is provided with a circumferenti ally extending annular groove delimited by two ends, 0 0 said groove being closed by the contacting rotational member and which forms a shear channel with said rotational member; the annular chamber being delimited by a movable piston, and in one of said rotatable pails there is provided a reservoir of variable volume communicating with the annular chamber; the arrangement being such that upon relatIve rotation of said rotatable pails one end of the shear channel having a lower fluid pressure is connected to the reservoir and the other end of the shear channel liaviii,,:,, a higher fluid pressure is connected to a pail of the annular chamber delimited by said movable piston; the pressure build- up and control merriber having its rotation limited by resilient stop means which, when a given differential rotational speed betweeii said rotatable pails is exceeded, perri-de further rotational movement of the pressure build-up and control member and thus provides for said short ciretilt coiiiiectioil bet\veeii the end of the shear channel having the higher pressure and the end of the shear cliannel having the lower 0 pressure.

6. A coupling device according to Claim 4 wherem said end stops comprise C compression spring elements.

7. A coupling, device substantially, as hereMbefore described witil reference to Figures 1 to 5 modified in accordance with Figure 6 or Figure 7 of the 0 0 accompanying drawings.

0