Abstract:
An electronically-controlled fluid coupling device having a front mounted fan and electrical actuation without a tethered harness. The fluid coupling device combines an inverted viscous clutch, drive pulley and a split electromagnetic actuator package. In this arrangement, the electrical portion of the split electromagnetic actuator is not physically attached to the fan drive, but is instead mounted to a stationary member. The remaining actuator components are integral to the fan drive and are composed of only mechanical parts. The inverted clutch arrangement having remote electronic control allows three output modes: engaged, partially engaged, or disengaged.

Description:
RELATED APPLICATION 
   The present application is a continuation application of U.S. patent application Ser. No. 10,929,801, filed on Aug. 30, 2004, now U.S. Pat. No. 7,083,032 entitled “Electronically Controlled Fluid Coupling Device”, which is incorporated by reference herein. 

   TECHNICAL FIELD 
   The invention relates generally to fan drive systems and more specifically to an electronically controlled fluid coupling device. 
   BACKGROUND ART 
   The present invention relates to fluid coupling devices of the type including both fluid operating chamber and a fluid reservoir chamber, and valving which controls the quantity of fluid in the operating chamber. 
   Although the present invention may be used advantageously in fluid coupling devices having various configurations and applications, it is especially advantageous in a coupling device of the type used to drive a radiator cooling fan of an internal combustion engine, and will be described in connection therewith. 
   Fluid coupling devices (“fan drives”) of the viscous shear type have been popular for many years for driving engine cooling fans, primarily because their use results in substantial saving of engine horsepower. The typical fluid coupling device operates in the engaged, relatively higher speed condition only when cooling is needed, and operates in a disengaged, relatively lower speed condition when little or no cooling is required. Today, electrically actuated viscous fan drives are commonplace because they can be precisely controlled between an engaged, partially engaged, and disengaged mode to control output at a given fan speed as determined by the vehicles engine computer. 
   Today&#39;s electrically actuated viscous fan drives have the actuator mounted to either the front or the rear side of the fan drive. In both cases, the actuators are mounted to the drives through a ball bearing and the stationary electrical wires are then tethered to a stationary location on the engine or shroud or whatever optimum for the particular customer application. The length of tether for front mount actuators becomes a limiting factor for large fan applications and the axial length of the rear mount actuator limits the use from narrow package applications. Durability of either design is a function of bearing life and tether life. Ideally, a fan drive without a tether is desired if this improves durability and lowers cost while sustaining fan drive performance attributes. 
   The front mounted electrical actuator was result of an evolution of earlier air-actuated viscous fan drives used in heavy truck and large bus applications. The bi-metal control spring on the front of the viscous drive was simply replaced by a bearing mounted pneumatic solenoid. Durability issues with the tether and higher fuel economy requirements forced the heavy-duty industry to switch to pneumatic on-off friction clutches with no tether (air supply coming through the center of the mounting bracket-pulley subassembly). Today the heavy-duty industry is now facing even stiffer fuel economy and noise control requirements which has forced a need for variable speed or at least multi-speed fan drives. As a result, viscous drives are being considered again which has lead to the need for rear-actuated viscous fan drive. Subsequently, a rear mount electrical actuator was developed which has helped reduce potential tether durability problems associated with the front mount style actuator and in addition provides the customer an easier means to install the fan drive and associated tether. 
   Front actuated viscous fan drives continue to exist though for light to medium duty applications because the axial length and cost are better than rear actuated. However, in some light duty gas engine applications where the fan clutch is driven by the waterpump, a system resonance problem exists caused by numerous factors including mass and cg of the fan drive. 
   SUMMARY OF THE INVENTION 
   The present invention is intended to minimize the aforementioned problems with tethered actuators and system resonance while incorporating desirable features such as a high-speed reservoir and a combined “failsafe” and anti-drainback option. 
   The present invention enables a viscous fan drive with a front-mounted fan and electrical actuation without a tethered harness. The device of the present invention combines an inverted viscous clutch, a drive pulley and a split electromagnetic actuator resulting in a purely mechanical package that provides several advantages over existing engine-driven electronically managed viscous fan drives. An inverted clutch is one where the conventional clutch is essentially flipped around such that the central shaft is the output shaft while the finned members are the input. 
   In this configurations the electrical portion of the actuator is not physically attached to the fan drive but rather is mounted to a stationary member of the drive pulley. The remaining actuator components are integral to the fan drive and as a result the fan drive itself has purely mechanical parts. The arrangement allows for fast response times to engage or disengage the clutch and also allows for open loop control of the electrical actuation, 
   Other features, benefits and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the attached drawings and appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  an exploded perspective view of the major components of an electronically controlled fluid coupling device according to one embodiment of the present invention; 
       FIG. 2  is section view of an assembled electronically controlled fluid coupling device of  FIG. 1 ; and 
       FIG. 3  an exploded perspective view of the electronically controlled fluid coupling device of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings, which are not intended to limit the invention,  FIGS. 1-3  illustrates one form of a fluid coupling device  10  (“viscous fan drive”) of a type utilizing the present invention. As best shown in  FIG. 1 , the fluid coupling device consists of three major subassemblies, including a fan drive subassembly  5 , an electromagnet subassembly  7 , and a waterpump subassembly  9 . The waterpump subassembly  9 , shown here as an engine-mounted waterpump subassembly  9  driven by a crankshaft pulley system, could also be a stand-alone bracket-pulley subassembly. As shown in  FIG. 2 , the electromagnet subassembly  7  is mounted to the stationary waterpump housing and the fan drive subassembly  5  mounts to the waterpump subassembly  9 . 
   As best shown in  FIGS. 2 and 3 , the fan drive subassembly  5  includes an output shaft  20 , a body  22 , a ball bearing  24 , a rotor  26 , a reservoir plate  28  having a fill port  29 , a cover  30 , a torsion spring  31  an armature valve subassembly  32  having an attached valve arm  33 , a gasket  34 , a bushing  36 , a pulley  38 , a pole  40 , a second gasket  42 , a hub  44 , and a plurality of rivets  46 . The body  22  and cover  30  are finned along their respective outer peripheries. 
   The electromagnetic subassembly  7  includes a coil  48  and steel housing  50  that is mounted to the stationary waterpump subassembly  9 . The coil  48  has a wire harness  52  that is electrically coupled to a controller  54  and power source  55 , The controller  54  receives electrical signals from a plurality of engine sensors  57  regarding engine and vehicle operating conditions. The controller  54  interprets these signals to direct the power source  55  to send electrical current to the coil  48  via the wire harness  52  to control the output from the fluid coupling device  10  in a manner described in more detail below. Other elements of the electromagnetic circuit contained with the fan drive subassembly  5  include the pole  40 , the armature valve subassembly  32 , the hub  44  and pulley  38 . Further, the threaded steel adapter  62  on the waterpump subassembly  9  completes the electromagnetic circuit. 
   As shown in  FIGS. 1 and 2 , the waterpump subassembly  9  consists of a central rotatable waterpump shaft  56  bearing mounted within a stationary housing  58  which is mounted directly to the engine block face (not shown) near the crankshaft pulley (not shown) via mounting holes  60  using bolts (not shown). In an alternative embodiment (not shown), the waterpump subassembly could be a stand-alone bracket-pulley subassembly. The waterpump shaft  56  is coupled to a plurality of impellers (not shown) used to control engine coolant flow within an engine cooling system to cool the engine. As best shown in  FIG. 2 , the pulley is coupled to the threaded steel adapter  62  of the waterpump shaft via the hub  44  and pole piece  40 . Thus, the waterpump shaft  56  rotates at the same rotational rate as the pulley  38  to drive the impellers and therein provide coolant flow to the engine. 
   As best seen in  FIG. 2 , the steel engine-driven pulley  38  is sandwiched between the die-cast aluminum cover  30  and the non-ferrous hut)  44  by way of rivets  46  or bolts (not shown) and sealed utilizing the first gasket  34  and second gasket  42 . The pulley  38  is coupled to the engine crankshaft via a belt  70  and also provides an element of the electromagnetic control circuit. The pulley  38  thus rotates the cover  30  at a rate determined by the engine operating speed translated to the pulley  38  via the crankshaft and belt  70 . 
   The die-cast aluminum cover  30  has an overlying region  72  that is roll-formed around the outer periphery  74  of the die-cast aluminum body  22 . Thus, the body  22  rotates at the same rotational rate as the cover  30 . The output shaft  20  is rotatably mounted within the body  22  using a ball bearing  24  and Is affixed to the rotor  26 . The volume of space around rotor  26  and bounded by cover  30  and body  22  define a fluid chamber  43  having a quantity of viscous fluid (not shown), while the cover  30  and reservoir plate  28  define a fluid reservoir  41 . Further, a fluid reservoir  41  is fluidically coupled with the fluid chamber  43  through fill port  29 . The valve arm  33  covers or uncovers the fill port  29 , depending upon the actuation of the electrical coil  48 , to control the flow of fluid between the fluid reservoir  41  and fluid chamber  43 . In addition: the fluid chamber  43  is fluidically coupled to a working chamber  45 , defined between the rotor  26 , body  22 , and cover  30 . The amount of viscous fluid contained in the working chamber  45 , in conjunction with the rotational speed of the cover  30  coupled to the pulley  38 , determines the torque transmitted to the rotor  26  that rotates the output shaft  20 . In other words, the torque response is a result of viscous shear within the working chamber  45 . 
   The rotor  26  also includes a scavenge chamber  27  that returns viscous fluid from the working chamber  45  to reservoir  41 . Disposed adjacent the radially outer periphery of the operating chamber  45  is a pumping element  25 , also referred to as a “wiper” element  25 , operable to engage the relatively rotating fluid in the operating chamber  45 , and generate a localized region of relatively higher fluid pressure. As a result, the pumping element  47  continually pumps a small quantity of fluid from the operating chamber  45  back into the reservoir chamber  41  through a scavenge chamber  27 , in a manner well known in the art. 
   While not shown, the output shaft  20  may be coupled to a fan having a plurality of fan blades. Thus, the rotation of output shaft  20  may rotate the fan to cool the radiator or other engine components. 
   The pole  40  has a threaded inner portion  76  that is threaded onto the threaded steel adapter  62 . The outer periphery  78  of the pole  40  is located between an outer projection  80  of the hub  44  and the threaded inner portion  76 . The pole  40  also has a base region  82  that abuts the threaded steel adapter  62  of the waterpump shaft  56  and extends substantially perpendicularly with respect to the length of the threaded inner portion  76  and extends between the hub  44  and the reservoir plate  28  (is shown to the left of the threaded steel adapter  62  in  FIG. 2 ). The pole  40  also has an inward center projection  84  that extends substantially perpendicular from the base region  82  and opposite the outer periphery  78 . The pole  40  also has a plurality of pole pieces  86  separated by gaps  88  that extend around the outer periphery of the base region  82 . 
   The valve arm armature subassembly  32  has a series of tooth-like projections  90 , or leaf-like projections  90 , that extend outward from a central region  92 . The central region  92  has a central hole  94  containing the non-ferrous bushing  36  that is used to pilot the valve arm armature subassembly  32  around the inward center projection  84  of the pole  40 . When assembled, the leaf-like projections  90  slightly overlap the respective pole pieces  40 . A torsion spring  31  coupled to the assembly  32  maintains the projections  90  in a preset position wherein the leaf-like projections  90  are misaligned with the respective pole pieces  40 . Upon magnetization, the projections  90  will attempt to line up with the pole pieces  40 , therein rotating the subassembly  32  relative to the pole pieces  40 . 
   The valve arm  33  is coupled to the central region  92  of the valve arm assembly  32  and extends towards the reservoir plate  28 . The valve arm  33  is cantilevered at its free end. The valve arm  33  thus rotates with the subassembly  32  to cover or uncover the fill port  29 . In an unmagnetized state (wherein no electrical current is flowing through the coil  48 ), the torsion spring  31  maintains the subassembly  32  such that the valve arm  33  is positioned wherein the fill port  29  is uncovered. This position is known as the “failsafe on” position, in that fluid flows from the fluid reservoir  41  to the fluid chamber  43  through the fill port  29  is maintained in the absence of electrical current flowing to the coil  48 , which maintains the rotor and output member in an engaged position to provide cooling airflow even in the absence of electrical actuation to prevent overheating of the attached engine. 
   The amount of electrical power supplied in terms of pulse width modulation from the external controller  54  and power source  55 , and hence the amount of magnetic flux available to control the relative positioning of the valve arm  33 , is determined by the external controller  54 . The controller  54  receives a set of electrical inputs from various engine sensors  57  that monitor various engine operating conditions relating to engine temperature, fuel economy, emissions or other engine operating conditions affecting the performance of the engine. For example, one of the sensors  57  could be an engine mounted coolant sensor or a pressure sensor mounted to the air conditioner. The controller  54  has a stored look up table that determines a desired engine operating range for a given engine speed. When the controller  54  determines that one or more of these sensors  57  are sensing cooling conditions outside the desired operating range, the external controller  54  will direct the power source  55  to send electrical power to the coil  48  as a function of this electrical signal. Thus, for example, if the external controller  54  determines that the engine coolant temperature is too low, or that the engine temperature is too low, a signal may be sent from the controller  54  to the power source  55  to activate the coil  48  to a desired pulse width, therein providing a magnetic field within the fluid coupling device  10 . Upon magnetization, the projections  90  will attempt to line up with the pole piece  40 , therein rotating the subassembly  32  relative to the pole piece  40  The rotation of the subassembly  32  therein causes the coupled valve arm  33  to rotate and cover the fill hole  29 , therein preventing viscous fluid flow to the working chamber  45 . The reduction of viscous fluid within the working chamber  45  minimizes shearing of the viscous fluid within the working chamber  45  to drive the rotor  26  and output member  20 . Hence, a fan coupled to the output member  20  would rotate slower in this condition to bring cooling conditions within a desired range. 
   Similarly, if the external controller  54  determines from one or more of the sensors  57  that the engine, or engine coolant temperature, is above an undesired high range, no signal is sent from the external controller  54  to the power source  55  and coil  48 . The valve arm  33  is thus maintained in a position wherein the fill port  29  is uncovered, therein allowing maximum fluid flow from the fluid reservoir  41  to the fluid chamber  43  and to the working chamber  45 . This provides maximum torque response of the rotor  26  to rotate the output shaft  20 . This in turn rotates the fan and fan blades to provide maximum cooling to the radiator to cool the engine coolant. 
   The present invention provides numerous advantages over currently available front and rear actuated viscous fan drives. For example, the electrical portion of the actuator is not physically attached to the fan drive, but rather is mounted to a stationary member of the drive pulley. As such, there is no tethered wire harness and no actuator bearing. This leads to easier and less costly manufacturing, as there are no wires or connectors. Further, the coil is easily replaced, which lowers service and warranty costs. 
   Further, the remaining actuator components are integral with the engine side of the fan drive, This leads to lower overhanging mass on the drive components, which leads to higher system resonant frequency and possible improvements in waterpump durability. This also leads to compact packaging, which can improve vehicle costs. 
   While the invention has been described in connection with one embodiment, it will be understood that the invention is not limited to that embodiment. On the contrary, the invention covers all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims. 
   For example, an accumulator plate could also be used in conjunction with the reservoir plate to enable a failsafe valve arm feature yet allow an anti-drainback feature. An example of the use of an accumulator plate in conjunction with a fluid reservoir is described in U.S. application Ser. No. 10/287,325 to May et al., entitled “Electronically Controlled Viscous Fan Drive”, which is herein incorporated by reference. 
   Further, in another alternative embodiment, the valve arm  33  could be coupled to the valve arm subassembly  32  such that it covers the fill port  29  in the absence of electrical activation of the coil  48 . Thus, the clutching mechanism is engaged when current is applied from power source  55  (“non-failsafe mode”). 
   Finally, in another embodiment, the amount of pulse width modulation to said electrical coil could be such to generate a magnetic field in which the valve arm partially covers the fill port  29 . The magnetic field generated would be less than the magnetic field necessary to rotate the subassembly  32  completely to the second position covering the fill port  29 . This third position would allow partial engagement of said rotor  26  and output at an infinite number of midlevel outputs to more precisely control the amount of cooling available to the radiator.