FRICTION DEVICES

Abstract: A liquid cooled clutch (48) for a multi-layshaft constant mesh change speed gear train comprises multiple interleaved annular clutch elements (74, 78) axially slidably coupled by drive dogs at their inner and outer peripheries in the usual way. Sandwiched between the clutch elements are a series of floating elements (82) not drivably coupled to either the inner or outer clutch elements but located axially between them and freely rotatable. The elements (82) are of similar construction to that of the clutch elements. Their presence serves to avoid the well known problem of stick-slip. Actuation of the clutch elements is by non-rotatable pistons (84) acting through ball races (86) whereby the pistons need not rotate with the clutch elements.

Description: FRICTION DEVICES This invention relates to friction devices. An example of the application of the invention is to mult i- inter leaved plate-type clutch mechanisms for multi-layshaft (two or more layshafts) constant mesh change speed gear trains. Certain aspects of the matter disclosed herein may be applicable to friction mechanisms for use in other applications including both clutch and brake mechanisms. In the case of multi-plate interleaved clutch mechanisms for use in multi-layshaft constant mesh change speed gear trains, several problems arise. Firstly, there is the problem of the requirement for smooth operation, particularly with regard to take up of drive from rest. Depending on the variables of the transmission concerned, including its geometry and layout, vibrations and judder are found to arise which are not readily controlled by conventional means, and there is need for an improved means for reducing the tendency for judder and/ or vibration and/or general lack of smooth clutch operation to be provided. According to the invention there is provided a friction device. The friction device may be a multi-plate interleaved clutch assembly. The clutch assembly may comprise an assembly of interleaved plates, one set having drive means at its outer periphery and the other set having drive means at its inner periphery. The plates or clutch elements are provided with means for frictio al engagement. Such means may comprise the provision of friction means to transmit drive by frictional engagement between successive clutch elements. Conventionally, such friction means has been provided in the form of a friction facing on one of the sets of clutch elements. According to the invention there is provided in an assembly of interleaved clutch elements of which one set of clutch elements is drivably coupled at its outer periphery and another set at its inner periphery, at least one floating clutch element which is not drivably coupled to either of the sets of clutch elements. The floating clutch element may comprise a metallic clutch plate or element faced with friction material, the clutch elements of the two drivably connected sets being plain metal plates. Alternatively, the floating clutch element may be a plain metal plate and the driven clutch elements may be friction -surfaced. The main difference between the floating clutch element and the other clutch elements between which it is sandwiched is that it lacks drive elements and transmits drive between its neighbours by frictional engagement therewith. In an embodiment described below, a clutch assembly incorporating the floating friction element is the take-off-from-rest clutch of a six ratio gear train and the assembly has particularly smooth operating characteristics. Other design requirements for multi-layshaft constant mesh gear trains include not only the need for particularly compact format where the transmission is for use in an automobile, but also the need to integrate the gear train to the total transmission assembly so that, for example, the fluid pressure required to operate the gear train (for example to effect ratio changes) is comparable to the requirements of other parts of the transmission, such as the differential lock-up mechanisms acting between left and right side wheels of the vehicle and front and rear axles thereof, where a four wheel drive is provided. Previously proposed clutch arrangements for multi-layshaft gear trains have been based upon the concept of providing rotating clutch actuating systems for transmission of thrust to the rotating clutch elements. The provision of such rotating pistons has necessitated elaborate and costly sealing arrangements for the pistons, together with associated axial drillings in the clutch layshafts. The piston seals in such assemblies inevitably have a high leakage rate and until now this has been accepted as an inevitable feature of such systems. However, for integration into a total transmission package, such an arrangement is unacceptable and improvements in this respect are required. _ According to this aspect of the invention there is provided a multi-plate clutch assembly for a multi-layshaft gear train wherein a clutch- actuating piston and cylinder assembly is arranged to transmit clutch actuating thrust to the clutch elements through rotary bearing means. Prefer ably, , the rotary bearing means comprises a race of rotary elements such as balls or rollers. The race may be mounted directly on the piston. The piston may be slidable within a cylinder formed in the housing of the gear train. The cylinder may be a bore formed in an end wall of the gear train housing. Alternatively, the cylinder may be formed in a cylinder member supported by the gear train housing intermediate the ends thereof. The latter arrangement is appropriate where the clutch means is itself located otherwise than at the end of the housing. The invention also provides a drive transmission comprising a gear train as defined above. The gear train may be provided in combination with drive output means to a front wheel drive automobile transmission. The φear train may be connected to automatic control means effecting clutch control and ratio changing in accordance with sensed vehicle motion variables.. Clutch engagement may be provided by means of fluid pressure control apparatus providing for progressive clutch engagement, particularly for take-off from rest, whereby an automatic vehicle tranmission can be provided without the need for a torque converter or fluid coupling. The invention also provides a friction device and a gear train incorporating same having any novel feature or any novel combination of features disclosed herein. An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig 1 shows a section through a gear train; Fig 2 shows, somewhat diagrammatic ally , a modification of the gear train of Fig 1; and Fig 3 is a diagram of the gear train of Fig 1. As shown in Fig 1, a gear train 10 comprises a first layshaft 12, an input or main shaft 14 and a second layshaft 16 , all mounted within a gear train housing 18. Gears 20 and 22 on layshaft 12 are in ddlrect constant mesh with main shaft gears 24, 26 respectively. Likewise, gears 26 and 28 on layshaft 16 are in direct constant mesh with main shaft gears 24 and 26 also. In addition, a main shaft gear 30 is in direct constant mesh with a gear 32 on layshaft 16. Layshaft 12 carries an output gear 34. The latter directly drives a differential mechanism 36 from which propel lor shafts 38 transmit drive in opposite directions to the front wheels of an aut omobi le . ' Drive input to main shaft 14 is through a torsionally damped mechanical input coupling 40. Drive is transmitted at all times via the housing 42 of a clutch 44 to main shaft input gear 30 and hence to layshaft input gear 32, and hence at all times to layshaft 16 άtself . Input clutch 44 provides for direct transmission of drive to the main shaft output gears 24, 26. Clutch assemblies 46 , 48 on layshaft 16 provide for selective transmission of drive from the layshaft.16 to its output gears 26 and 28 - respectively. Thus, drive input from coupling 40 can be transmitted direct on engagement of clutch 44 , or at two higher torque ratios on selective engagement of clutches 46 and 48. Thus, input shaft 14 and layshaft 16 provide effectively three transmission ratios between the input coupling and the input shaft gears 24 and.26. From gears 24 and 26 on the input shaft, torque can be transmitted at two selectable additional ratios to final output gear 34 by selective operation of layshaft clutches 50 and 52, whereby the gear train 10 provides six torque paths in all. Input gear 22 of layshaft 12 is directly coupled to the housing 54 of clutch 50, of which the clutch inner member 56 is directly coupled to layshaft 12. Likewise, layshaft input gear 20 is directly coupled to the inner member 58 of clutch the 52, and latter* s housing 60 is directly mounted on the layshaft 12. Input shaft 14 is jour ailed on ball races 62 and 64 which are closely spaced and provide excellent support for the main shaft output gears 24 and 26. Likewise, layshaft 16 is journalled on ball races 66 and 68 which provide similar support for that shaft. Output shaft 12 is journalled on roller races 70 and 72. Gear train 10 is extremely compact and provides a six torque path automatic transmission with direct mechanical drive input and the attendant fuel efficiency characteristics. Attention is now directed to features of the construction of the clutch means of the gear train. Clutch 48 is employed for drive take-up from rest. It comprises an interleaved assembly of annular clutch elements. These elements comprise a first set of clutch elements 74 keyed at their inner peripheries to the clutch inner member 76 which is directly mounted on layshaft 16. A second set of clutch elements 78 are keyed at their outer peripheries to the clutch housing 18 which is directly drivably coupled to the layshaft output gear 28. Sandwiched between the clutch elements 74 and 78 are a series of floating clutch elements 82. These latter are not dr ivably coupled to the inner or outer clutch members 76 and 80 but are located ax i a l ly . between these members and are free ly rotatable . They serve to frictionally engage the clutch elements 74 and 78 and to transmit drive therebetween . The floating clutch elements 82 each comprise an annular steel plate having a friction surface on its opposite f aces . Their construction is similar to that of a conventional clutch element , but without the provision of torque -transmitting dr ive formations at either their inner or outer peripher ies . In use , the f loating clutch elements 82 are surprisingly found to reduce or eliminate vibration , judder and any stick/slip tendency of the clutch e lements " . 74 and 78 , whereby the drive take-up and gear change characteristics of the transmission are greatly improved . ' Similar provision may be made in the other clutches of the gear train or any one cr more of them according to need . Clutch 48 is actuated by a piston 84 slidable in a bore formed in the end wall of. housing 18 and acting through a ball race 86 on an annular pressure member 88, whereby compressive thrust is applied to the clutch elements for clutch engagement purposes. In this manner, piston 84 is non-rotatable and is directly supplied with fluid pressure, hydraulic or pneumatic through a suitable inlet coupling (not shown) formed in the housing 18. Similar provision is made for clutches 46, 50 and 52. Fig 2 shows a modification of the gear train of Fig 1. In the Fig 1 embodiment, one of the six available transmission ratios is equal to one of the others due to the equal layshaft spacing, whereby only five different ratios are available. Therefore, in Fig 2, in order to achieve six different transmission ratios, the gear 24 on input shaft 14 is provided in the form of a two-gear cluster 24 A, 24B. Corresponding changes are provided on layshafts 12 and 16, the former having an input gear 20A meshing with gear 24A, and the latter having its gears 26 A, 28A meshing with the input shaft gears 24A, 24B respectively. The operation of this embodiment is as previously described. • The above embodiments are particularly applicable to multi-layshaft constant mesh change speed gear trains such as those of our prior applications and patents , such as EP 00 12 022 and EP 00 41 320 and EP 01 07 667 and EP 02 14 972 . We hereby incorporate the disclosure of our above-mentioned prior specifications in this application by reference. The problems of stick-slip operation are of particular significance in relation to drive take- up from rest in an automatic transmission , such as those of our prior patent cases mentioned above, but also arise in other friction devices operating in liquid environments . A well known example of such is the multi-plate transmission brake of many agricultural tractors . Special oils have been developed to reduce this problem in such mechanisms. It is believed that the present invention may well provide a considerable improvement in performance of such braking systems. In an embodiment which has been tested , there have been provided three outer and three inner annular clutch elements with six floating clutch elements sandwiched between them . However , it may not be essential to provide a floating element between each pair of clutch elements . Only one such floating element may be sufficient . With regard to the clutch actuation system , the ball races disclosed above may of course be replaced by roller races . In one particularly advantageous modification , a clutch assembly has been devised which employs a needle roller race and is so compact that it can replace the synchronisation clutch assembly of a conventional single layshaft gear train , thereby permitting automatic or semi-automatic control of the gear train . The provision of clutch-actuating pistons acting through ball or roller races or like bearing means provides the very considerable advantage that the considerable fluid loss which has in the past occurred between the rotating pistons and their cylinder assemblies is avoided , whereby a much smaller hydraulic pump can be employed , such as a remote pump feeding the gear box and a limited slip differential or the like . The detailed disclosure of the embodiment described above is susceptible of considerable development and modification • The clutch elements themselves can be of any suitable form conventional or otherwise with any suitable driving arrangement , including of course the conventional axially slidable keys and key ways . References above to frictional engagement of the friction elements and the floating elements are intended to include not only actual physical contact but also drive transmission in the presence of a film of oil on the confronting surfaces.

Claims: C LA IMS : 1. A brake or clutch comprising two sets of interleaved rotatable friction elements , the sets having respective coupling means whereby relative rotation of the sets can be effected , and means for applying compression to the assembly of friction elements to change the torque transmission characteristics of the assembly , characterised by at least one floating element interleaved between the friction elements and mounted so as to be rotatable relative to both sets of friction elements . 2. A brake or clutch according to claim 1 characterised in that said floating element is surfaced with friction material and is of form similar . to that of the adjacent friction elements . 3. A brake or clutch according to claim 1 or claim 2 characterised in that said friction elements and said floating element are annular in form and are mounted so as to be axially slidable , one of said sets of friction elements having inner drive formations and the other set having outer drive formations , and the floating element having no such drive formations . 4. A brake or clutch according to any one of the preceding claims characterised in that said friction elements and said floating element operate in a liquid cooled environment. 5. A gear train comprising a clutch according to any one of the preceding claims characterised in that said clutch is arrangedfor drive take-up from rest in a vehi c le. 6. A clutch comprising rotatable c lutch elements and a piston and cylinder assembly to actuate same characterised in that rotary bearing means is provided to transmit clutch-actuating thrust from said piston and cylinder assembly to said clutch elements while permitting relative rotation therebetween. 7. A clutch according to claim 6 characterised in that said clutch comprises two sets of interleaved rotatable annular clutch elements and said bearing means comprises an annular ball or roller race arranged between an * annular piston forming the piston of said piston and cylinder assembly and an end one of said clutch elements . 8. A gear train comprising a clutch according to claim 6 or claim 7 characterised in that said gear train comprises a multi-layshaft constant mesh change speed gear train and said clutch is mounted coaxially with respect to one of said layshafts to control transmission of drive through said layshaft. 9. A gear train comprising a clutch according to claim 6 or claim 7 characterised in that said gear train comprises a single layshaft constant mesh change speed gear train and said clutch provides for selective coupling of one of the gears of said train to a shaft thereof.

Inventors: TAILBY RAYMOND ALFRED, WINDSOR-SMITH CLAUDE PETER, TAILBY, RAYMOND, ALFRED, WINDSOR-SMITH, CLAUDE, PETER
Applicants: TAILBY RAYMOND A, WINDSOR SMITH CLAUDE P, TAILBY, RAYMOND, ALFRED, WINDSOR-SMITH, CLAUDE, PETER
Application year: 1987
Main classification: F16D13
IPC codes: F16D13, F16D25, F16D48, F16D55, F16H3