Abstract:
A fan drive system is provided that is hydraulically controlled having an electrical failure mode wherein midrange operation of the fan drive system is maintained. Accordingly, in the failure mode, a fan drive system hydraulic relief valve is not closed thereby ensuring a degree of operation of the fan drive system even during periods of electrical failure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a PCT International Application of U.S. patent application No. 61/197,928 filed on 31 Oct. 2008. The disclosure of the above application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to fan drive systems that are hydraulically controlled with integral cooling. 
     BACKGROUND OF THE INVENTION 
     Friction coupling devices and fluid coupling devices that drive radiator cooling fans for over the road trucks, such as class  8  trucks, are generally of two types, dry friction clutch assemblies and viscous drives, respectively. 
     Dry friction clutch assemblies tend to have two operating conditions “ON and OFF” referring to when a friction clutch is either fully engaged or fully disengaged. When a friction clutch assembly is providing cooling the clutch is fully engaged and not slipping. When the friction clutch assembly is not providing cooling the assembly is fully disengaged and slip speed is at a maximum between a clutch plate and an engagement surface. 
     Dry friction clutch assemblies generally have low thermal capacity since they typically do not incorporate fluid flow cooling mechanisms. Therefore these clutch assemblies have minimal cooling capability and are unable to cycle repeat in short durations of time. The thermal energy that is generated during engagement at high engine speeds can cause the clutch lining to “burn up” or cause the clutch assembly to become inoperative. 
     Viscous drives, on the other hand, have become popular due to their ability to cycle repeat, engage at higher engine speeds, and operate at varying degrees of engagement. Viscous drives have an operating range of engagement and are generally less engaged at higher engine speeds and generally more engaged at lower engine speeds. Viscous drives never fully engage due to the torque transfer through viscous fluid shear. 
     Due to the size constraints, viscous drives are also thermally and torsionally limited since viscous drives are always slipping to some degree, they are incapable of turning at fully engaged peak operating speeds. Furthermore, the continuous slipping means viscous drives are continuously generating heat, unlike friction clutch assemblies. Viscous drives are further limited in that as engine cooling requirements increase, larger and more costly viscous drives are required. Thus, some high cooling requirement vehicles viscous drives can become impractical in size and cost. 
     Due to increasing engine cooling requirements, it is desirable that a fan drive system be capable of not only providing increased cooling over traditional fan drive systems, but also that it have the combined advantages of a friction clutch assembly and of a viscous drive, as stated above, without the associated disadvantages. It is also desirable that the fan drive system be practical and reasonable in size and cost and to be approximately similar to and preferably not to exceed that of traditional fan drive systems. 
     To overcome the disadvantages of the aforementioned traditional fan drive systems, a new fan drive system has been developed which can be referred to as a solenoid actuated hydraulically controlled fan drive system. A housing assembly is provided which is typically 12-16 inches in diameter. To minimize parasitic drag losses, the housing is not completely filled with hydraulic fluid, but is typically filled such that there is 1-2 inches of hydraulic fluid spaced around a circumference (assuming that the housing is being spun). The fan drive system is engine driven via a belt or chain driven pulley. A stationary bracket rotatably mounts the pulley to the chassis of the vehicle. The pulley is fixably connected to the housing assembly. A clutch assembly within the housing assembly is selectively engaged to connect the rotative fan with the housing assembly. The hydraulic aforementioned clutch is activated via hydraulic pressure. The hydraulic pressure is generated through the use of a pitot tube. The pitot tube is fixably connected to the mounting bracket. The fluid, which is rotating within the housing, is used to generate pressure through momentum exchanged at an aperture in the stationary pitot tube. The pitot tube is also fluidly connected with a piston engaging circuit through which a clutch friction pack engages a fan hub which is rotatably mounted to the housing assembly. To control the amount of fan engagement with the housing assembly via the friction pack, a hydraulic control arrangement is provided. The hydraulic control arrangement regulates the pressure within the piston housing by selectively connecting the pitot tube with a reservoir sump. The reservoir sump occurs due to the void of fluid in the center of the housing assembly. A solenoid actuated relief valve is utilized to selectively regulate the fluid connection between the pitot tube and the low pressure sump formed within the housing assembly. To ensure full engagement of the rotating fan hub with the housing (fan locked in position), the solenoid actuated relief valve completely blocks the sump, causing the full pressure developed by the pitot tube to be applied to the friction pack, which torsionally connects the fan hub with the housing assembly. The amount of torsional connection between the housing and fan hub is varied by utilizing an electronic controller system to selectively open and close the solenoid valve, thereby controlling the amount of pressure applied to the friction pack by the piston. 
     Since the pressure acting on the piston is controlled by the solenoid, operation of the fan drive system during a period of solenoid or electrical failure must be considered. In most applications, “fail safe” operation provided by a bias spring in the valve that is overcome by the solenoid. In an instance of electrical failure, the spring will close the relief valve, providing full pressure from the pitot tube to the piston. The full pressure will ensure that the fan hub will always be engaged on. However, there are major disadvantages of a failure mode operation wherein the fan is fully engaged. The fully engaged failure mode causes very heavy loads to be placed on the fan even though full cooling capacity is not required. Furthermore, a fully engaged failure mode causes unnecessary fuel consumption and can cause damage to the transmission and accessory belt drive system. Conversely, if the failure mode is such that the fan is permanently disengaged, then the vehicle will not have adequate cooling during most operating conditions. Therefore, it is desirable to provide a failure mode operation for the hydraulically controlled fan drive system which overcomes the aforementioned disadvantages. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, the present invention provides a fan drive system which is hydraulically controlled that has an electrical failure mode wherein a midrange operation of the fan drive system is maintained. Accordingly, in the failure mode, a relief valve of the fan drive system is not closed thereby ensuring a degree of operation of the fan drive system even during periods of electrical failure. The fan drive system of the present invention has an electrical failure mode which does not fully lock on the fan hub to the fan housing. Accordingly, slippage between the fan and fan hub housing is maintained and therefore shifting operations or abrupt stops of the engine during periods of electrical failure mode operation does not generate as great a concern for damage to the fan belts, fan drive system, or transmission. 
     The above noted and other features of the present invention will be more apparent to one skilled in the art as the accompanying invention is better described in the accompanying drawings and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a vehicle utilizing a hydraulically controlled fan drive system in accordance with an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of a pulley, housing and fan shaft of the fan drive system of the present invention; 
         FIG. 3  is a cross-sectional view of one of the solenoid valves utilized in the fan drive system of the present invention; 
         FIG. 4  is a cross-sectional view of a pressure relief valve of a fan drive system of the present invention. 
         FIG. 5  is an enlargement of the pressure relief valve illustrated in  FIG. 4 ; 
         FIG. 6  is a sectional view similar to that of  FIG. 2  of another preferred embodiment fan drive system of the present invention; 
         FIG. 7  is an enlargement of a portion of a relief valve in the fan drive system shown in  FIG. 6 ; 
         FIG. 8  is an electrical schematic illustrating the operation of a solenoid in the relief valve shown in  FIG. 7 ; 
         FIG. 9  is a partial sectional view of still another embodiment of the present invention in which the relief valve is external to the fan drive system; and 
         FIG. 10  is a graph comparing maximum pressure in relationship to fan speed during normal operation and during modulated operation due to an electrical failure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , a perspective view of a vehicle  10  utilizing a hydraulically controlled fan drive system  12  in accordance with an embodiment of the present invention is shown. The system  12  uses rotational energy from a liquid cooled engine  14  at an increased ratio to turn a radiator cooling fan  16  to provide airflow through a radiator  18 . The system  12  includes a housing assembly  20  fixed to a pulley  22 , which is coupled to and rotates relative to a crankshaft (not shown) of the engine  14 , via a pair of belts  24 , within an engine compartment  25 . Of course, the present invention may be relatively operative in relation to various components and via any number of belts or other coupling devices, such as a timing chain. The housing assembly  20  is mounted on the engine  14  via a mounting bracket  26 . The housing assembly  20  hydraulically engages the fan  16  during desired cooling intervals to reduce temperature of the engine  14  or to perform other tasks further discussed below. 
     The fan  16  may be attached to the housing assembly  20  by any suitable means, such as is generally well known in the art. It should be understood, however, that the use of the present invention is not limited to any particular configuration of the system  12 , or fan mounting arrangement, or any particular application for the system  12 , except as is specifically noted hereinafter. 
     Referring now to  FIG. 2 , a cross-sectional view of the system  12  in accordance with an embodiment of the present invention is shown. The system  12  includes an input circuit  30 , the housing assembly  20 , a piston  116  assembly, an engaging circuit  36  having a mechanical portion  38  and an electrical portion  40  ( FIG. 3 ), and a variable cooling and lubrication circuit  42 . The input circuit  30  provides rotational energy to the housing assembly  20 . The engaging circuit  36  engages the housing assembly  20  to a fan shaft  44 , via the piston assembly  116 , to rotate the fan  16  ( FIG. 1 ). The fan  16  may be coupled to the fan shaft  44  via bolt  46 , which is threaded into the fan shaft  44 , or by other techniques known in the art, such as being coupled to a fan hub  47 . The fan shaft  44  may be a single unit, as shown, or may be split into a fan shaft portion and a clutch shaft portion. The variable cooling circuit  42  provides distribution of hydraulic fluid  48  cooling and lubricating components within the housing assembly  20 . The hydraulic fluid may be an oil-based fluid or similar fluid known in the art. 
     The input circuit  30  includes the pulley  22  that rotates about the mounting bracket  26  on a set of pulley bearings  50 . The pulley bearings  50  are held between pulley bearing notches  52 , in a stepped inner channel  54  of the pulley  22 , and pulley bearing retaining rings (not shown). The pulley  22  may be of various type and style, as known in the art. The inner channel  54  corresponds with a first center opening  62  in the housing assembly  20 . 
     The housing assembly  20  includes a die cast body member  70 , and a die cast cover member  72 , that may be secured together by bolts (not shown) through bolt holes  73  in the outer periphery of the die cast member  70  and cover member  72 . It should be understood that the present invention is not limited to use with a cast cover member, but may also be used with other members such as a stamped cover member. The housing assembly  20  is fastened to the pulley  22 , via fasteners (not shown) extending through the cover member  20  into the pulley  22  in designated fastener holes  76 . The housing assembly  72  rotates in direct relation with the pulley  22 . Bearing  78  is positioned between the housing assembly  20  and the fan shaft  44 . The bearing  78  is held within the housing assembly  20  between a corresponding housing bearing notch in the body member  70  and a housing bearing retainer ring  84 . A seal  88  resides on a fan side of the housing assembly  20  for retaining the hydraulic fluid  48  within the housing assembly  20 . 
     The body member  70  has a fluid reservoir  92  containing the hydraulic fluid  48 . Cooling fins  94  are coupled to an exterior side  96  of the body member  70  and perform as a heat exchanger by removing heat from the hydraulic fluid  48  and releasing it within the engine compartment  25 . 
     The piston assembly  116  includes a piston housing  100  rigidly coupled to a distribution block  102 , which is rigidly coupled to the bracket  26 . The piston housing  100  has a main pitot tube channel  110  (inside a pitot tube  152 ), that has a piston branch  112  and a controller branch  114 , for flow of the hydraulic fluid  48  to a translating piston  116 . The controller branch also connects with to a hydraulic fluid controller  306  ( FIGS. 4-5 ) via line  177 , pocket  178 , axial stand line  186  and hose line  302 . The piston  116  has a pressure side  122  and a drive side  124 , with respective pressure and drive pockets. The piston translates along a center axis  130  to engage the housing assembly  20  to the fan shaft  44 , via hydraulic fluid pressure from the piston branch  112 . 
     The engaging circuit  36  includes a hydraulic fluid supply circuit which is inclusive of main pitot tube channel  110 , a clutch plate assembly which includes clutch plates  144 , a return assembly  136 , and a control circuit which include is inclusive of lines  186 ,  302  and a remotely located fluid controller  306  ( FIGS. 4 and 5 ). The hydraulic circuit applies pressure on the piston  116  to drive an end plate  140 , riding on a separation bearing  142  between the endplate  140  and the piston  116 , against clutch plates  144  within the clutch plate assembly  134  and engages the fan  16  (via clutch plates  156  and fan shaft  144 ). The control circuit controls operation of the piston  116  and engagement of the fan  16 . Of course, any number of clutch plates may be used. Also, although a series of clutch plates are utilized to engage the fan  16  other engagement techniques known in the art may be utilized. 
     The hydraulic circuit may include a baffle  146  separating a relatively hot cavity side  148  from a relatively cool cavity side  150  of the fluid reservoir  92  and the pressure pitot tube  152 . The pressure tube  152  although shown as being tubular in shape may be of various sizes and shapes. The pressure tube  152  receives hydraulic fluid  48  from within the cool side  150 , providing cooling to the engaging circuit  36 , due to flow of the fluid  48  from rotation of the housing assembly  20 , carrying the fluid  48  in a radial pattern around an inner periphery  154  of the housing assembly  20 . The pressure tube  152  is rigidly coupled within the piston housing  100  and is therefore stationary. The housing assembly  20  is only partially filled with fluid so that the drag of the fluid traveling within the housing  20  is limited. Accordingly, when the housing  20  is spun the fluid tends to by centrifugal force hug the periphery of the housing. Therefore the periphery of the housing has the greatest pressure due to fluid velocity and the center of the housing tends to be the sump region having the lowest fluid pressure. As fluid  48  is circulating about the inner periphery  154 , a portion of the fluid  48  enters the pressure tube  152  through an office  153  and applies pressure on the pressure side  122  of the piston  116 . 
     The fan shaft  44  has multiple cooling passageways  164  that extend between a fan shaft chamber  166  and an inner drum chamber  168  allowing passage of fluid  48  therein. Fluid  48 , after entering the drum chamber  168 , passes across and directly cools the plates  144 ,  156  and returns to the fluid reservoir  92  through slots  170  in a drum housing  158 . The slots  170  may be of various size and shape and have various orientations relative to the center axis  130 . The cooling passageways  164  although shown as extending perpendicular to the center axis  130  may extend parallel to the center axis  130 , similar to the slots  170 . 
     The return assembly  136  includes a return spring  172  and a spring retainer  174 . The spring  172  resides in the fan shaft chamber  166  and are coupled between the fan shaft  44  and the spring retainer  174 . The spring retainer  174  has a quarter cross-section that is “L” in shape and is coupled between the piston drive side  124  and the end plate  140 . The springs  172  are in compression and exert force on the piston  116  so as to disengage the clutch plates  144 ,  156  when fluid pressure on the piston pressure side  122  is below a predetermined level. 
     The cooling circuit  42  also includes a second pitot tube or lubrication tube  182 . Although, only a single lubrication tube is shown, any number of lubrication tubes may be used, especially in applications where increased flow is desired. The lubrication tube  182  provides high flow rates at low pressures and as with the first tube may be of various size and shape. Fluid  48 , from the cool side  150 , enters the lubrication tube  182  and is directed into the fan shaft chamber  166  where it then passes through the cooling passageways  164  and cools the clutch plates  144 ,  156 . Fluid  48  may also exit the fan shaft chamber  166  through the slots  170 . Fluid exiting from the fan shaft chamber  166  or the drum housing  158  enters the hot side  148 , where the cooling fins  94  dissipate heat from the hot side  148  into the engine compartment  25 . The cooling circuit  42  not only cools and lubricates the clutch pack  156  but also other portions of the engaging circuit  36 . 
     Referring now to  FIGS. 3 and 4 , the electrical portion  40  of the control circuit utilizes two solenoid valves  225  (forming a bi-directional actuator) electrically coupled to a main controller  176  to electrically control the fluid pressure within the pitot tube  152 . 
     The solenoid valve assembly  225  includes an armature  236  coupled to a valve spool  308 . The valve spool  308  is partially surrounded by a valve body  240 , while the armature  236  is positioned within a cavity region  242 . A coil bobbin  244  and a pole piece  246  are produced. An air gap  247  is also created between the armature  236  and the pole piece  246 . 
     A coil  250 , electrically coupled to a main controller  176 , is contained within a cavity region  252  defined between the coil bobbin  244  and a flux tube  254 . 
     The armature assembly  236  is coupled to a spring  260  that is contained within a spring retainer  262  that is contained within the pole piece  246 . The spring  260  normally biases the armature  236  toward a shoulder  249  of the valve body  240 . 
     The main controller  176  is electrically coupled to various engine operating sensors  179  and may be contained within the system  12  or may be separate from the system  12  as shown. The main controller  176  is preferably microprocessor based such as a computer having a central processing unit, memory (RAM and/or ROM), and associated input and output buses. The main controller  176  may be a portion of a central vehicle main control unit, an interactive vehicle dynamics module, a cooling system controller, or may be a stand-alone controller as shown. The main controller  176  generates a signal in the form of a pulse width modulated (PWM) current or analog current. 
     When current is passed through the coil  250  from the controller  176 , a magnetic flux is created that extends through the armature  236 , air gap  247 , pole piece  246  flux tube  254 , and valve body  240 . 
     The fluid controller has two solenoid valve assemblies  225  which are opposing one another as shown in  FIG. 4 . The solenoid assemblies are connected together via the valve spool  308  which translates in valve bore  324  ( FIG. 5 ). Valve spool  308  is biased to the right by spring  312  pushing against shoulder  314  to provide a first biasing force F 1 . The spool  308  is biased to the left by spring  316  which pushes against shoulder  315  providing a biasing force F 2 . The valve bore  324  intersects with a transverse passage  326  which is in turn connected with the hose line  302 . Balancing grooves  328  and  330  are provided to reduce spool drag. Adjacent to the transverse passage  326 , the spool valve  308  has a landing  332  with a metering edge  334 . The metering edge  334  is typically positioned to have a very small leakage by being positioned closely adjacent to a leading edge  336  of the transverse passage  326  (the position shown in  FIG. 5  is exaggerated to the right for illustrative purposes). To obtain maximum pressure (Pc Normal  FIG. 10 ) on the piston pressure side  122  (and thereby obtain maximum fan  16  engagement), the solenoids  225  position the landing  332  to cutoff transverse passage  326  from sump port  340  ( FIG. 4 ). 
     Sump port  340  is connected with a second sump line  304 . The sump line  304  is connected with a mounting base axial line  181  ( FIG. 2 ) intersecting with a mounting base radial line  184  allowing fluid therein to pass into first center opening  62 . To modulate the pressure on the pressure side  122  of piston  116 , the controller  176  controls the two solenoid valves  225  to allow an opening of line  302  by powering the solenoid valves  225  to provide for a controlled leakage by moving the spool valve  308  in a rightward direction. To release the fan  16  from the housing  20 , the right solenoid valve  225  is powered to move the spool to its furthest rightward position, fully connecting the pressure side  122  of the piston  116  with the sump line  340 . This control scheme can be accomplished through proportional control or with pulse width modulation. Upon an electrical failure, the position of the spool  308  will be determined by the opposing forces ( FIGS. 1 and 2 ) exerted upon the spool valve by the two springs  312  and  314 . Accordingly, at virtually all engine speeds, a mid-pressure force (Pc modulated—See  FIG. 10 ) will be present to partially engage the fan  16  with the housing  20 . Furthermore, this partial engagement mode will provide an appropriate minimum amount of engine cooling. Additionally, the failure mode operation will not lock the fan  16  to the housing  20 , preventing extreme loading on the belts and pulleys during transmission shifting. 
     Referring to  FIGS. 6-8 , a preferred embodiment fan drive assembly according to the present invention is provided. Fan drive assembly  407  functions in a manner similar to that of fan drive system  12  having a housing  420  driven by a pulley  422  which are rotatably mounted on a base  424 . The housing  420  can be selectively joined with a fan hub  426  by engagement of a clutch pack  428  actuatable by a piston  430 . The piston  430  is pressurized in a manner as afore described through a line  432  which insects with a line  434  provided in a pitot tube  436 . Pitot tube line  434  is connected with a line  438 . Line  438  as shown in  FIG. 7 , enters into a pressure controller  440  which is mounted within a portion of base  424  that is surrounded by the pulley  422  and housing  420 . The controller  440  has an opposing dual spring biased spool  442  which is biased by springs  444  and  446 . Springs  444  and  446  provide corresponding F 1  and F 2  forces acting upon the spool  442 . An exhaust line  448  connects with a sump line  450  provided in the base  424 . The valve spool  442  has a conical surface  452  for selective mating engagement with a conical valve seat  454 . When mated against the conical valve seat  454 , the spool  442  cuts off fluid communication from line  438  to line  448  thereby ensuring maximum pressure within the pressure side  431  of the piston  430 . During normal operation, the position of valve spool  442  is controlled by a circuit  460 . Control circuit  460  controls a dual coil solenoid actuator having coils  462  and  464 . Coil  462  can be actuated to cause valve spool  442  to be shifted to the left as shown in  FIG. 7 , line  438  is placed in fluid connection with line  448  essentially causing the pressure chamber  431  of the piston to be evacuated to sump and therefore ensuring non-engagement of the fan hub  426  with the housing  420 . Activation of coil  464  causes the valve spool  452  to be shifted to the right causing its valve surface  452  to engage with valve seat  454  thereby closing off fluid communication of line  438  with line  448  and ensuring maximum pressure available within the piston pressure chamber  431 . Upon an electrical failure, springs  446  and  444  will modulate the maximum pressure available in the pressure side  431  of the piston in a manner as previously described with springs  312  and  314 . 
     Referring to  FIG. 9 , a partial portion of a fan drive assembly  507  is provided. Fan drive assembly  507  has a line  510  which is in turn connected line  302  as previously described for the fan drive assembly shown in  FIGS. 1-4 . Fan drive assembly  507  also has a line  512  which is provided with a sump line  304  as previously described for the fan drive shown in  FIGS. 1-4 . The control of the fan drive assembly  507  will be essentially identical as that as previously described for the dual solenoid relief valve type controller  306 . 
     Fan drives  407  and  507  are essentially similar to fan drive  12 . In fan drives  407  and  507 , the base  424  directly supports the fan hub  426  via needle bearings  470 . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited, since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification and following claims.