Magnetically actuated viscous fluid coupling
This invention relates generally to viscous fluid clutches more particularly to viscous fluid clutches which are actuated by a magnetic field in response to temperature changes in a sensed medium. 
     Viscous fluid couplings have received wide acceptance in the automobile industry for controlling the amount of power needed to rotate the radiator cooling fan. The most common form of such viscous fluid couplings is the air temperature response type such as illustrated in U.S. Pat. No. 3,055,473. In certain applications, however, it has become desirable to sense directly the water temperature in the radiator rather than temperature of the air passing through the radiator. To date, many arrangements have been proposed to accomplish this result. These arrangements, however, have made use of wet or dry plate clutches that are generally pneumatically actuated or electromagnetic clutches that are electrically actuated. In each of these arrangements the advantages achieved through the use of viscous fluid have not been applied. 
     Accordingly, it is an object of the present invention to provide a viscous fluid coupling which may be simply and inexpensively constructed to be actuated by a mechanism that directly senses the water temperature of the radiator. 
     In accordance with a feature of the invention, a valve arm is provided in a viscous fluid coupling to be moved axially upon actuation of a magnetic field from a position in which the fluid storage chamber of the coupling is in direct fluid communication with the operating chamber via a fluid inlet opening to a position in which such communication is blocked. As is well known, the blocking of such fluid communication and the maintenance of a continuous flow of viscous fluid out of the operating chamber via a pumping opening results in the operating chamber being emptied of viscous fluid. Without fluid in the operating chamber the torque transfer between the clutch member of the coupling and the fan supporting housing is substantially eliminated. By unblocking the communication, viscous fluid is permitted to flow via the inlet opening into the operating chamber from the fluid storage chamber at a rate faster than the rate of flow of fluid via the pumping opening from the operating chamber to the fluid storage chamber. This allows for a transfer of torque from the clutch member to the fan supporting housing via the viscous fluid. The valve arm is moved in response to movement of an armature that is moved through a solenoid action upon energization of a coil. 
     The difference between a standard air actuated viscous fluid coupling such as shown in U.S. Pat. No. 3,055,473 and that of the disclosure has been kept to a minimum. Major changes within the coupling exist in the transposition of an axially movable armature for the rotationally movable thermo-responsive spring. The remaining portions of the viscous fluid coupling are basically the same. External of the coupling a coil and appropriate energization and switching means are provided. 
    
    
     FIG. 1 is a side elevational view, taken along the center-line of a viscous fluid coupling assembly according to the invention. 
    
    
     FIG. 1 illustrates a modulated viscous fluid coupling 10 and an accessory driving structure 12 comprising a pulley 14 connected to a shaft flange 16 and a companion hub plate 18 by bolts 20. A water pump housing 22 supported on the engine (not shown) has connected thereto a stub mounting shaft 24 which is mounted, by force fit, integral with hub plate 18. The unsupported end of stub shaft 24 extends into an annular opening 26 in the shaft flange 16. Bearings 28 are provided in a known manner to allow shaft 24 to rotate relative to housing 22. End 30 of shaft 24 is provided to drive a pump (not shown) for circulating water through the engine&#39;s cooling system. Pulley 14 is suitably driven by a belt from the engine to provide a driving input for both coupling 10 and the water pump. 
     Coupling 10 includes a driving shaft 32 integral with shaft flange 16. Shaft 32 is provided with a reduced intermediate portion 34 which functions as an inner race supporting means for ball bearing assembly 36. A shoulder 38 formed on shaft 32 restrains ball bearing 36 in one axial direction. A further shaft portion 40 is provided with surface serrations and is connected to a shaft portion 42. 
     A clutch member 44 is provided with a hub portion 46 and a plate portion 48 having a plurality of concentric annular coupling lands 50 formed on the back side thereof. Hub portion 46 is provided with a straight wall opening 52 which has an interference fit with shaft portion 42 so that clutch member 44 rotates with and is axially retained on shaft 32. Hub portion 46 is pressed onto the shaft until it abuts the inner race of bearing assembly 36 to axially confine the bearing assembly in the other direction of axial movement. 
     Clutch member 44 is provided with an annular recess 54 formed in a face of plate 48 on the side opposite annular lands 50. A pair of diametrically opposed axially directed holes 56 are disposed slightly radially outward of annular lands 50 and terminate in annular recess 54. Annular lands 50 terminate or alternatively are cut away in the form of a V notch to form a pair of diametrically opposed radially directed channels which are circumferentially coincident and in communication with holes 56. The structure defines a known fluid commencing with the area adjacent annular lands 50, the radial channels, axially directed holes 56 and annular recess 54. 
     A fan support housing member 58 includes a hub 60 which is supported on the lateral surface of the outer race of ball bearing assembly 36 and is disposed in an interference fit therewith. A shoulder portion 62 reacts against an end surface of the outer race and limits movement of housing member 58 in one axial direction. A plurality of fan blades 64 are secured at the shank portion of the blades by bolts 66 radially intermediate body portion 68 of housing member 58. 
     Cooling fins (not shown) are formed on the outer surface of housing member 58 adjacent fan blades 64. The cooling fins are arranged to provide additional cooling area to dissipate heat which is generated in the coupling. 
     A plurality of concentric annular lands 70 are formed integral with housing 58. Lands 70 are positioned in an axial overlapping relationship with annular lands 50 to form a fluid operating chamber therebetween. Lands 50 and 70 are disposed in a position so that when oil or other viscous fluid means is disposed therebetween torque can be transmitted from one member to the other by fluid shear as disclosed in U.S. Pat. No. 2,948,268. 
     A cover plate 74 and a valve plate 76 cooperate to define a fluid storage chamber 78. Valve plate 76 is received in an annular notched recess provided in housing member 58 to laterally confine the valve plate. Cover plate 74 abuts the periphery of valve plate 76 along an annular surface to confine the valve plate 76 in both axial directions. The peripheral portion of cover plate 74 is fixed integrally with housing member 58 by an annular spun over portion 80. An O ring 82 disposed in an annular recess functions to retain the fluid within the operating assembly and to prevent interleakage of the fluid. 
     Valve plate 76 further includes a notched portion 84 which fits within recess 54 of clutch member 44 and extends radially across the opening of holes 56. As defined in U.S. Pat. No. 3,055,473 viscous fluid in the operating chamber is directed under centrifugal force through the radial channels to the axially directed holes 56 and into the annular recess 54. From there, notched portion 84 creates a high pressure area along its leading edge during rotation of clutch member 44. A hole (not shown) is provided in valve plate 76 to direct fluid out of the leading high pressure area into fluid storage chamber 78. 
     Rotation of shaft 32 results in rotation of clutch member 44. With viscous fluid in the operating chamber a viscous drive is created between clutch member 44 and housing member 58 to rotate the housing member with the clutch member. In the illustrated embodiment the majority of this drive exists in the land portion 50-70. 
     Valve plate 76 further includes a hole 86 radially located relative to the rotational axis of shaft 32 which communicates fluid from storage chamber 78 to the operating chamber. The hole is provided to introduce viscous fluid from the fluid storage chamber back into the operating chamber under the centrifugal force of rotation of housing 58. Appropriate holes may be provided in clutch member 44 to allow the viscous fluid to flow to both axial surfaces of the clutch member. 
     A valve arm 88 is provided to be moved in an axial direction between a first position as illustrated in FIG. 1 to a second position in which an outer portion 90 covers hole 86 and prevents fluid from flowing from fluid storage chamber 78 to the operating chamber. In the second position of valve arm 88, the centrifugal force of the fluid in the fluid storage chamber acts to aid the sealing of outer portion 90 of valve arm 88 against valve plate 76. 
     Valve plate 76 includes an axially aligned hole 92. An armature 94, made of a magnetic material such as steel, projects through valve plate hole 92 and includes a shoulder portion 96. The sliding fit of armature 94 in hole 92 along with shoulder portion 96 acts to form a semi-seal between fluid storage chamber 78 and the operating chamber. It should, however, be appreciated that during operation of coupling 10 the viscous fluid is located radially outwardly away from hole 92. A coil spring 98 encircles armature 94 and is interposed between valve arm 88 and valve plate 76. The spring acts to bias the armature to the left in FIG. 1. Shaft 32 is preferably flared out around clutch member 44 in order to aid in retention of the clutch member relative to the shaft. Shaft 32 is made of a magnetic material such as steel. The distance between the outer end portion of shaft 32 and shoulder 96 of armature 94 is maintained to a minimum for reasons to be hereinafter explained. 
     An electrical coil 100 is provided in encircling relationship to housing 22. Appropriate leads 102 and 104 are provided to coil 100 and to an electrical source of energy 106 to energize the coil. A known switch 108, schematically illustrated, is located in the radiator of the vehicle and used to actuate the coil when the temperature of the water within the radiator exceeds a predetermined value. Upon actuation of coil 100 a magnetic field is created through housing 22 and shaft 32. The field is of significant magnetic force to draw armature 94 to the right in FIG. 1 toward shaft 32. This drawing force is a solenoid type action. Upon movement of armature 94 toward shaft 32, outer portion 90 of valve arm 88 moves from its first position to its second position in which it covers hole 86 in valve plate 76. 
     Preferably, shoulder 96 does not contact shaft 32. Such contact would result in rubbing which is detrimental to clutch life. The contact is prevented by the prior contact of outer portion 90 with valve plate 76 in the disclosed embodiment. 
     Valve plate 76, clutch member 44 and housing 58 are made of non-magnetic materials such as aluminum. This will result in preventing a reduction in the strength of the magnetic field created by coil 100. 
     Coil 100 may also be located in other places such as in encircling relationship to shaft 32 or directly on shaft 32 with the electrical contacts being provided through slip rings. 
     The location of armature 94 is preferably located along the axis of rotation of shaft 32 to prevent the introduction of centrifugal force into its operation. For this reason, valve arm 88 is preferably balanced around the axis of shaft 32 by portion 110.