IMPROVEMENTS IN AND RELATING TO VISCOUS FLUID COUPLING DEVICES

Abstract: A fluid coupling contains a working fluid and in­ cludes a rotatable driving member (11), which is mount­ ed for co-axial rotation within a working chamber (26) forming part of a rotatable driven member (12). A valve plate (42) is mounted within the driven member (12) for rotation therewith and divides the driven member (12) into the working chamber (26) and a fluid reservoir (40). A rotary valve member (46) controls the flow of work­ ing fluid between the fluid reservoir (40) and the working chamber (26) through a valve port (44) in the valve plate (42). The valve plate (42) is carried by a valve shaft (56) mounted co-axially with the driven member (12). A tem­ perature responsive bi-metal coil (64), mounted exter­ nally of and co-axially with the driven member, has its inner end (85) fixed for rotation with the valve shaft (56) and its outer end (78) resiliently fixed for rotation with the driven member (12). In order to reduce wear and fretting of the valve shaft, the outboard end of the valve shaft (56) is journalled in a bearing member (60) sup­ ported by a bracket member (72) fixed to the exterior face (70) of the external wall (55) of the driven member (12) for co-axial rotation therewith. The outer end (78) of the coil is embraced by an elastomeric sleeve (82) which is received in a recess (80) in the driven member (12) and the inner end (85) of the coil is received in a slot (88) in the valve shaft (56).

Description: DE9#cRIPTior# "IMPROVEMENTS IN AND RELATING TO VISCOUS FLUID COUPLING DEVICES" The present invention relates to torque transmitting viscous shear couplings and in particular to such couplings which utilise a valve mechanism for controlling the flow of fluid within the coupling, the valve mechanism being operated by a temperature sensitive bimetal coil mounted externally of the drive. Such couplings are well knom and their construction and operation have been described in numerous patents typical of which are British Patents 898,442 and 1,540,708. A major problem with such couplings is associated with retention of the bi-metal coil and the need to eliminate fretting and wear of the bi-metal attacliment means and of the valve shaft utilised for transmitting rotational movement from the bi-metal coil to an internally located rotary valve member. The fretting and wear of the outer end of the bi-metal coil and the valve shaft are the result of vibrations transmitted to the drive when operating in its normal environment on an internal combustion engine. The vibration can be particularly severe when the coupling is mounted on the front of a four cylinder vehicle engine. Various methods have been employed previously for attaching the outer end of the bi-metal coil to the coupling driven member including rigid fixing methods such as staking or welding, resilient methods which provide some degree of angular or angular and radial freedom to the outer end of the bi-metal coil by inserting rubber or rubber-like seaiant/adhesive compounds between he outer end of the bi-:netal coil and its locating means on the coupling driven member and by attachment means which permit the outer end of the bi metal coil to slide freely in the radial direction. The various attachment means employed previously have had various degrees of success in reducing the problems associated with the outer end of the bi-metal coil but have not been totally successful in eliminating wear of the valve shaft, It is an object of the Present invention to provide an improved means for mounting the temperature sensitive bi-metal coil and valve shaft in a coupling of the type described which substantially eliminates the wear, fretting and breakage problems associated with previous couplings. According to the present invention there is provided a fluid coupling containing a working fluid and including a rotatatable driving member, at least a part of which is mounted for co-axial rotation within a working chamber forming part of a rotatable driven member, fluid shear spaces defined by opposing faces of the driving member and the working chamber, a valve plate mounted within the driven member for rotation therewith and dividing the driven member into the said working chamber and a fluid reservoir, a valve port in the valve plate, a rotary valve member operable to control the flow of working fluid between the fluid reservoir and the working chamber through said valve port, a valve shaft mounted co-axially with the driven member and extending through a bore in an external wall of the driven member adjacent to the reservoir, the end of the valve shaft within the reservoir being fixed to the rotary valve arm for rotation therewith, a temperature responsive bi-metal coil mounted externally of and co-axially with the driven member, said bi-metal coil including an inner end fixed for rotation with tre valve shaft and an outer end resiliently fixed for rotation with the driven member, and waive shaft bearing means including a bracket member fixed to the exterior face of said external wall of the driven member for co-axial rotation ;therewith and a bearing member supported by said bracket which journals the external end of said valve shaft. Repeated radial displacement of the external end of the valve shaft, result from radial vibrations of the coils of the bi-metal coil is eliminated by the bearing means. The bearing means is preferably a sleeve bearing which may be made from any suitable material e.g. steel backed bronze, a steel backed polymer (e.g. nylon or polytetrafluoroethylene), or a sintered bronze. A convenient manner of achieving the resilient coupling between the coil and driven member, which permits angular flexibility between said outer end of the coil and the driven member, is to enclose the outer end of the coil in an elastomeric sleeve which is received in a correspondingly shaped recess in the driven member. The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a fluid coupling device according to the present invention; Figure la shows a detail of Fig. 1 to a larger scale; Figure 2 is a front elevation of the coupling of Figure 1; Figure 3 is a front elevation of the coupling of Figure 1 with the bearing bracket removed; Figure 4 is a scrap view of one face of the working chamber in the direction of arrow A in Figure 1; and Figure 5 is an end view of the housing in the direction A. Referring now to the drawings, Figure 1 illustrates a torque transmitting viscous shear fluid coupling of the temperature responsive type generally designated 10 which contains a viscous working fluid (not shown) and includes a driving member 11 and a driven member 12, the driven member being Journalled for co-axial rotation with the driving member by means of a bearing 15. The driven member 12 includes a housing member generally designated 17 and a cover member 19. The housing member 17 comprises a sintered steel spider member 21 and an annular steel disc member 23 fixed for co-axial rotation therewith. The spider member has an annular centre boss 25 having a bore 27 dimensioned to receive the bearing 15 and a plurality of radially extending arms 29 formed integrally with the centre boss 25. Each radial arm 29 includes at its outer end a boss 31 having a bore 33. Formed by means of a step in each radial arm.is a spigot location diameter 16 adapted to locate the fan or fan blades 14 or other driven device coaxially with the driving member 11. The fan or fan blades 14 is fixed by means of studs 18 and nuts 20 to the driven member 12. Preferably, the studs 18 are fixed to the annular disc member 23 at 35, for example by projection welding, each stud passing through a respective bore 33 in an arm 29 of the spider member 21. The annular disc member 23 and the spider member 21 may similarly be fixed to each other by projection welding through the arms as at 37. The bore 39 of the annular disc member 23 is preferably made smaller than the bore 27 of the spider member 21 thereby forming an abutment 41 for axial location of the driven member 12 against the bearing 15. THe outer margin 43 of the annular disc member is attached to the cover member 19 at 45. The means of attachment may be by rolling an annular flange formed on the cover member over the outer margin of the annular disc member 23 as illustrated in Figure 1 but other means such as screws may also be used. The driving member 11 includes a threaded bore 22 for connection to a source or rotational energy (not shown). A drive disc 24, which forms part of the driving member II, is enclosed within a working chamber 26 formed as part of the driven member 12 and defining shear spaces 28 and 30 between the opposing faces 32, 34 and 36, 38 of the working chamber 26 and drive disc 24. The working chamber 26 is separated from a reservoir 40 by means of a valve plate 42 containing a valve port 44. A rotary valve member 46 is provided to open or close the valve port 44. Adjacent to the periphery of the drive disc 24 there is provided an outlet port 48 in the wall 32 of the working chamber connected by ducts 54 to the reservoir 40. The outlet port 48 is provided with a scoop member 52 (Fig.4) formed by a blocked groove 50 formed in the face 32 of the working chamber 26. The wall 55 of the driven member defines the front wall of the reservoir and includes an aperture 66 (Fig0 Ia) for locating a valve shaft 56. As shown, most clearly in Fig.1a, the valve shaft is attached rigidly to the valve arm by rivetting or staking for rotation therewith at 68. A suitable seal 58 is provided to prevent leakage of fluid from the reservoir 40. A bracket member 72 (Fig.2) is fixed to the front face 70 of the driven member by means of screws or other suitable fastening means such as rivets at 74. Formed in the centre of the bracket is a cup 62 adapted to receive a bearing 60 having a bore 76 for supporting and journalling the outboard end 56a of the valve shaft 56o Angular rotation of the valve member 46 to open or close the valve port 44 is controlled by a temperature responsive bi-metal coil 64 located in a recess 86 in the front wall of the coupling driven member 12. The bi-metal coil includes a first straight tang 78 which is fixed resiliently to the driven member by means of an elastomeric sleeve 82 fitted tightly over the tang 78, the combined tang and sleeve being an interference fit in a recess or slot 80 formed in a boss 84 within the recess 86. The slot 80. may be conveniently cast in the boss 84 as any casting draft angle can be readily accommodated by the elastomeric sleeve 82. The bi-metal coil further includes a second straight tang 85 (Fig.1a and 3) which is fitted closely into a slot 88 in the valve shaft 56 to impart rotational movement thereto upon changes in temperature ambient to the bi-metal coil. In operation, the driving member 11 is driven by means of an accessory drive shaft of an internal combustion engine, usually the water pump drive shaft, shear resistance of the viscous fluid in the working chamber 26 causing the driven member 12 to rotate at an r.p.m. that is somewhat lower than the r.p.m. of the driven member. By virtue of the difference in r.p.m. between the driving disc 24 and the driven member 12 viscous fluid is gathered by the scoop 52 and passes through ducts 54 into the reservoir 40. As long as the temperature externally of the coupling is above a predetermined limit the temperature responsive bi-metal coil 64 maintains the rotary valve member 46 in a position in which the valve port 44 remains open. Fluid from the reservoir 40 therefore passes through the valve port 44 into the working clamber 26 whereby sufficient fluid is maintained within the working spaces 28 and 30 to establish a maximum r.p0m. of the driven member. When the temperature externally of the colin drops below a pre-determined limit the temperature responsive bi-metal coil 64 moves the rotary valve member 46 into a position in which the valve port 44 is closed thereby preventing fluid flowing from the reservoir 40 to the llorking chamber 26. The scoop 52 however continues to pass fluid from the working chamber 26 thereby emptying the working chamber and shear spaces 28 and 30 of viscous fluid and hence reducing the degree of drive between the driving member 12 and driven member 11. The r.p.m. of the driven member then falls until it is substantially free-wheeling around the driving member with very little drive being transmitted. When the temperature again rises the temperature responsive'bi-metal coil 64 moves the valve member 46 into a position in which the valve port 44 is open thereby allowing fluid to pass#from the reservoir 40 to Othe working chamber 26 and shear spaces 28, 30. The amount of fluid in the shear spaces 28, 30 gradually increases until the maximum drive condition is re-established and the r.p.m. of the driven member rises to a maximum.

Claims: Ci!b#iNS 1. A fluid coupling containing a working fluid and including a rotatable driving member (it), at least a part of which is mounted for co-axial rotation within a working chamber (26) forming part of a rotatable driven member (12), fluid shear spaces (28,30) defined by opposing faces of the driving member (11) and the working chamber (26), a valve plate (42) mounted within the driven member (12) for rotation therewith and dividing the driven member (12) into the said working chamber (26) and a fluid reservoir (40), a valve port (44) in the valve plate (42), a rotary valve member (46) operable to control the flow of working fluid between the fluid reservoir (40) and the working chamber (26) through said valve port (-44), a valve shaft (56) mounted co-axially with the driven member (12) and extending through a bore (66) in an external wall (55) of the driven member (12) adjacent to the reservoir (40), the end of the valve shaft (56) within the reservoir (40) being fixed to the rotary valve member (46) for rotation therewith, and a temperature responsive bi-metal coil (64) mounted externally of and co-asially with the driven member (12), said bi-metal coil (64) including an inner end (85) fixed for rotation with the valve shaft (56) and an outer end (78) resiliently fixed for rotation with the driven member (12), characterised by valve shaft bearing means including a bracket member (72) fixed to the exterior face (70) of said external wall (55) of the driven member (12) for co-axial rotation therewith and a bearing member (60j supported by said bracket (62) which jowenais the external end of said valve shaft (56). 2. A fluid coupling as claimed in claim 1 characterised in that the outer end (78) of the bimetal coil (64) is embraced by an elastomeric sleeve (82) which is received in a correspondingly shaped recess (80) in the driven member (12). 3. A fluid coupling as claimed in claim 2 characterised in that said outer end (78J comprises a straight tang over which said elastomeric sleeve (82) is fitted. 4. A fluid coupling as claimed in claim 3 characterised in that the combined tang (78) and sleeve (82) are an interference fit in the recess (80). 5. A fluid coupling as claimed in claim 2, 3 or 4 characterised in that the recess (80) is cast in a boss part (84) of the driven member (12). 6. A fluid coupling as claimed in any of claims 1 to 5 characterised in that the inner end (85) of the bimetal coil (64) comprises a straight tang which is received in a slot (88) in the valve shaft (56).

Inventors: ELLIS, NORMAN
Applicants: HOLSET ENGINEERING COMPANY LIMITED
Application year: 1981
Main classification: F16D35
IPC codes: F16D35, F01P7