Abstract:
Hydraulic fan drive system with oil pressure control. A microprocessor based three-way valve is utilized for modulating the oil pressures. Closed loop feedback is used for optimal control of the fan speed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to U.S. patent application Ser. No. 61/117,199 entitled Fan Drive System With Sensor Feedback (DKT 08131) and U.S. patent application Ser. No. 61/117,201, entitled Fan Drive System With Lubrication Flow System (DKT 08132), both filed on the same day as the present application. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to fan drive systems and more particularly to wet friction fan drive systems with oil pressure control. 
       BACKGROUND OF THE INVENTION 
       [0003]    The invention relates generally to fan drive systems and more particularly to hydraulic and wet friction-type clutches for fan drive systems. There are various types of friction coupling devices and fluid coupling devices used to drive various devices or systems, such as radiator cooling fans for internal combustion engines. These friction clutch devices generally include dry friction clutch assemblies, viscous drive clutch assemblies, and wet friction clutch assemblies. Dry friction clutch assemblies have only two stages of operation: fully engaged or fully disengaged. Dry friction clutch assemblies also generally have low thermal capacity since they typically do not incorporate fluid flow cooling mechanisms. Viscous drive clutch assemblies have the ability to engage at higher engine speeds and can have varying degrees of engagement. Viscous drives are never fully engaged for internal viscous sheer purposes. Viscous drives slip to some degree at all times, making them incapable of turning at frilly engaged peak operating speeds or at higher speeds than originally designed. Viscous drives are further limited in that the more engine cooling that is needed, the larger and more costly the viscous drive and cooling fan that are required. 
         [0004]    Wet friction clutches are popular particularly for their use in situations involving severe service where the fan drives are in constant service and carry a constant load. Wet friction systems have the advantage of a friction clutch assembly as well as the ability to provide increased engine cooling. 
         [0005]    Wet friction fan drive assemblies are shown, for example, in U.S. Pat. Nos. 7,047,911, 7,249,664 and 7,178,656. These systems utilize hydraulically controlled fan drives with certain methods of engagement. The hydraulic systems include a housing assembly containing a hydraulic fluid and an engaging circuit. The engaging circuit includes a pitot tube coupled within the housing assembly that receives at least a portion of the hydraulic fluid. An energizing circuit engages the housing assembly to a fan shaft in response to supplying the hydraulic fluid from the pitot tube. 
         [0006]    Although these wet friction clutch systems described above provide improved fan drive control systems and assemblies, particularly as to the engagement pressure and control, as well as the removal of internally generated heat, it is an object of the present invention to provide a further improved assembly and system. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides improved methods for controlling the pressure applied to the clutch pack of a fan drive system and consequent engagement of the wet friction clutch. In one embodiment, the wet friction clutch system is controlled when it is desirable to modulate the fan speed independent from the engine speed. This embodiment also provides closed loop feedback on fan speed for optimal control. A microprocessor based three-way valve is utilized for modulating the oil pressure. 
         [0008]    In another embodiment of the invention, a unique sensor is provided in the central shaft eliminating the need for routing sensor wires. The sensor provides speed feedback signals in the clutch system. This embodiment also simplifies the assembly of the device. 
         [0009]    Another embodiment of the present invention has particular applicability for cooling a wet friction clutch system when it is operating continuously in a high slip region. Applications in which the wet friction clutches operate under continuous high slip conditions are known as “severe service” applications. In order to remove the substantial heat which is generated internally in these wet friction clutches, the clutch lubrication oil is circulated from the clutch through a heat exchanger and then brought back in a cooled condition. A modular valve mechanism is provided with coaxial oil passages for transporting lubrication oil to and from the wet friction clutch. A coaxial lubrication oil path is utilized for both the outgoing and incoming oil lines around the control valve. 
         [0010]    These objects, purposes, benefits and details of embodiments of the present invention, as well as other aspects and features of the invention, will become apparent from the following description of the invention when taken in view of the attached drawings and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a prospective view of a wet friction clutch assembly in accordance with an embodiment of the present invention. 
           [0012]      FIG. 2  is a cross-section of the wet friction clutch assembly as shown in  FIG. 1 . 
           [0013]      FIG. 3  is a prospective view of a modular coaxial valve design in accordance with an embodiment of the present invention. 
           [0014]      FIG. 4  illustrates the lubrication flow communication paths in accordance with an embodiment of the present invention. 
           [0015]      FIG. 5  illustrates the lubrication oil passageways in accordance with an embodiment of the present invention. 
           [0016]      FIG. 6  illustrates a control valve subassembly in accordance with the present invention. 
           [0017]      FIG. 7  illustrates a fan speed sensor module in accordance with the present invention. 
           [0018]      FIG. 8  is a cross-section of the fan speed sensor module as shown in  FIG. 7 . 
           [0019]      FIG. 9  illustrates an overmolded lead frame assembly in accordance with an embodiment of the present invention. 
           [0020]      FIG. 10  illustrates a three-way valve circuit in accordance with an embodiment of the present invention. 
           [0021]      FIG. 11  illustrates an alternate fan speed sensor embodiment. 
           [0022]      FIG. 12  is an enlarged view of circled portion  12  in  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    In the following Figures, the same reference numerals will be used to refer to the same components. While the present invention is described with respect to a method and system for a hydraulically controlled fan drive system, the present invention may be adapted and applied to various systems including vehicle systems, cooling systems, fan drive systems, friction drive systems, or other systems that would be obvious to persons of ordinary skill in the art. 
         [0024]    In the following description, various operating parameters and components are described for one constructed embodiment of the invention. The specific parameters and components are included only as examples and are not meant to be limiting. The invention has application in both vehicle and non-vehicle environments. Non-vehicle applications include generator sets, pumping stations, and the like. Also, in the following description, various fan drive components and assemblies are described only as an illustrative example. The fan drive components and assemblies may be modified depending upon the application in accordance with the abilities and knowledge of persons of ordinary skill in the art. 
         [0025]      FIG. 1  illustrates a wet friction fan clutch assembly  10  in accordance with a preferred embodiment of the present invention. The assembly includes the housing member  12  which has a fan mounting plate  14  on one side and a drive pulley  16  on the other side. Openings  15  are provided for fastening a fan  18  to the mounting plate  14 . The pulley  16  is an input pulley and is a part of a fan drive system which is driven by a belt that is in operable connection with the engine, preferably of a vehicle. Torque from the input pulley  16  is translated through the clutch assembly  10  to the fan mounted on the mounting plate  14 . The speed of the fan  18  is controlled by the clutch assembly  10 , and the fan is used to provide cooling as needed. 
         [0026]    The wet friction clutch assembly  10  is mounted on a stationary base member  20 . The base member  20  is adapted to be mounted on a vehicle or engine block of a vehicle as known in the art. For this purpose, mounting holes  22  are provided. 
         [0027]    As described in more detail below, lubrication oil is circulated through the mounting shaft on which the wet friction clutch assembly is mounted in order to cool the assembly. For this purpose, an outflow oil fitting  24  and an inflow oil fitting  26  are provided. Hot lubrication oil is passed through the oil fitting  24  to an external heat exchanger (not shown) which cools the lubrication oil. The cooled oil is then circulated back into the clutch assembly through the input oil fitting  26 . 
         [0028]    As shown in  FIG. 1  and as known in the art, the housing is preferably made from a metal material, such as aluminum or magnesium, and contains a plurality of fin members  17  which are used to dissipate heat to the atmosphere and thus help cool the clutch assembly  10 . The housing member  12  is fixedly connected to the input pulley  16  and thus rotates at the same speed as the pulley, namely the input speed to the fan drive assembly. 
         [0029]    As indicated, the fan mounting plate  14  and thus the bladed fan member attached to the plate are operated by the wet friction clutch assembly in order to rotate and provide cooling as needed. In severe service applications, the fan member is typically continuously spinning or operating in some manner. This provides constant slippage of the clutch mechanism and thus the constant generation of heat that needs to be dissipated. Without dissipating the heat, the life and durability of the clutch mechanism would be significantly reduced. 
         [0030]      FIG. 2  is a cross-sectional view of the wet friction fan drive assembly  10  as shown in  FIG. 1 . The cross-sectional view illustrates the details of the fan drive assembly itself, as well as a preferred embodiment of the integrated three-way control valve mechanism  25  in accordance with the present invention. 
         [0031]    The wet friction fan drive assembly is a hydraulically controlled fan drive system which uses rotational energy from the vehicle engine, which is preferably a liquid cooled engine, at an increased ratio to turn the cooling fan, which is attached to the fan plate  14 , to provide air flow through a radiator. The housing member or assembly  12  is fixed to the pulley which is coupled to and rotates relative to a crankshaft (not shown) of the engine with a fan belt used typically within an engine compartment of a vehicle. Of course, as mentioned above, 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. 
         [0032]    Key features of the present invention include a wet friction fan drive system with a unique fan speed sensor, a unique hydraulic valve design that enables electrical signals from the fan speed sensor to pass through the center of the valve body, and a unique lubrication system used to cool the fan drive assembly. The lubrication system passes lubrication oil concentrically around the housing of the valve body. In accordance with a preferred embodiment of the invention, the valve design is independent of the clutch shaft subassembly and can be used in an infinite number of permutations of the base shaft design. 
         [0033]    The basic operation of the wet friction clutch is described in U.S. Pat. Nos. 7,047,911, 7,249,664 and 7,178,656 the disclosure of which are hereby incorporated herein by reference. In general (as shown in  FIG. 2 ), the housing member  12  includes a body member  30  and a cover member  32  which are securely affixed together, such as by bolts  33  or other fasteners. The body member  30  is also securely affixed to the input pulley  16 , such as by fasteners  34 , and both rotate at the same speed. The input pulley  16  is attached by bearing members  40  to the base member  20  as shown. The base member  20  includes a central shaft member  50  which includes the integrated controller for a valve mechanism as described below. The fan plate member  14  is mounted in the housing member  12  by bearing member  52  and is only activated and rotated when the clutch mechanism is activated. In this regard, the clutch mechanism  60  includes a plurality of clutch plates as shown in  FIG. 2  and is activated by a clutch piston member  62 . When the piston member  62  is activated, the friction clutch mechanism  60  translates the rotational energy of the housing member  12  to the fan plate member  14  and thus rotates the fan. 
         [0034]    The housing  12  includes a fluid reservoir for storing and retaining the hydraulic fluid. A piston mechanism has a pitot tube  70  that is coupled to the piston housing assembly and receives a portion of the hydraulic fluid. 
         [0035]    The clutch mechanism  60  includes a clutch pack  61  and a drum housing  63  as known in the art. The clutch pack  61  includes multiple clutch plates which are coupled to the drum housing  63  and a second series of clutch plates that are coupled to the shaft and to the fan plate  14 . Any number of clutch plates may be used and may vary from one to several clutch plates depending on the desired engagement effect and depending upon space limitations. A control circuit controls operation of the piston and its engagements to the piston mechanism. 
         [0036]    The hydraulic fluid after entering the drum housing passes across and cools the friction plates and then returns to the fluid reservoir. A more detailed view of the modular co-axial valve mechanism  25  of the preferred embodiment in accordance with the present invention is shown in  FIG. 3 . The valve mechanism  25  performs several functions, it controls the hydraulic pressure supplied to the clutch piston  62 , provides passages for the flow of lubrication oil, and houses the clutch control circuit board and sensor interconnection mechanism. 
         [0037]    The hydraulic pressure applied to the clutch piston  62  is controlled by modulating the position of the valve plunger  76  through the solenoid motor  77 . The hydraulic pressure is developed in the pitot tube  70  and then routed into the valve area  79  through shaft entry ports  80 . When the solenoid motor  77  is deenergized, the valve return spring  81  pushes the valve plunger  76  back against the forward valve seat  82 . In this position, the valve closes off the pressure supplied from the pitot tube  70  and allows any pressure in the pressure chamber  83  to vent back through the piston housing supply passage  84 , the shaft pressure port  85  and the valve head valve ports  86 . 
         [0038]    The pressure vents back through these passages and ports to the oil sump inside the clutch housing. 
         [0039]    When the solenoid motor  77  is energized, it pulls the valve plunger  76  against the valve return spring  81  and throttles the oil flow through the conical flow regulation passage  87  between the valve plunger  76  and the valve head  88 . Since the flow area through the flow regulation passage  87  is a function of the position of the valve plunger  76 , the pressure drop through the flow regulation passage  87  and subsequent pressure developed at the shaft pressure port  85  can be regulated by controlling the position of the valve plunger  76 . 
         [0040]    The valve plunger  76  is supported on one end by a radial bearing surface between the valve plunger  76  and a pilot bore  89  in the mounting shaft  50 . The opposite end of the valve plunger  76  is pressed into a solenoid armature  91  which is radially supported by the pilot bore  92  and the valve head  88  via a non-magnetic bushing  93 . The solenoid armature  91  further incorporates a stepped conical reluctance gap  94  that helps to linearize the force versus displacement curve of the solenoid motor  77 . Magnetic stiction is prevented between the solenoid armature  91  and the rear solenoid pole  95  by a non-magnetic washer  96 . 
         [0041]    The solenoid motor  77  consists of a coil  97  that is wound around a bobbin  98  that develops a magnetic field in the stepped conical reluctance gap  94  in order to generate a force. A magnetic circuit for the solenoid motor is completed with a flux can  99  that is mechanically connected to the valve head  88  and the rear solenoid pole  95 . 
         [0042]    In one embodiment of the invention, the speed of the fan is detected by fan speed sensor module  100 . The module  100  is also shown in  FIGS. 7 and 8 . Module  100  houses a back—biased Hall-effect gear tooth sensor  101  that senses the passing of the teeth on the fan speed target ring  102 . The sensor module  100  is a modular sub-assembly that is connected to the side of the mounting shaft  110  and is retained with retaining ear members  103  (as shown in  FIGS. 7 and 8 ). 
         [0043]    The sensor module  100  makes electrical contact with the co-axial electrical lead frame assembly  114  through a set of spring contact members  116 . This is also shown in  FIG. 9 . The electrical lead frame assembly  114  further connects the fan speed sensor electrically to the valve control printed circuit board  120  ( FIG. 3 ). The sensor module can also be positioned at the end of the frame assembly as shown in  FIGS. 11 and 12 . The lead frame assembly  114  also incorporates a thermistor  118  for directly measuring the temperature of the fluid within the clutch mechanism, such as hydraulic oil or automatic transmission fluid (ATF). The thermistor  118  is connected across the fan speed sensor ground and output in a way to superimpose the fan speed sensor output and the thermistor temperature on the same signal line. 
         [0044]    The valve control printed circuit board  120  is hermetically sealed from the environment through an O-ring sealed electrical end cap member  122 . This is shown in  FIG. 3 . The end cap member  122  further meets with a sealed electrical connector  124  which connects the clutch to the vehicle wiring harness. This configuration allows for a PCB mounted connector header which minimizes the complexity of the vehicle wiring harness electrical connection and provides a robust electrical interconnection. 
         [0045]    An alternate embodiment of a fan speed sensor system is shown in  FIGS. 11 and 12 . An electrical contact  170  at the end of the electrical lead frame member  110 ′ is positioned in receptacle  172  which is mounted in the printed circuit board  190 . The receptacle  172  holds the electrical contact  170  with a plurality of spring finger members which allows compensation for thermal expansion and contraction of the lead frame member and other components. A cap member  176  is positioned over the end of the central shaft member  50 ′. The cap member  176  is secured in place by a plurality of screws  180  or other fastener members. Projecting members  182  and  184  extend from the end of the electrical lead frame member  110 ′ and are positioned in corresponding openings  183  and  185 , respectively, in the printed circuit board member  190 . 
         [0046]    A printed circuit board  190  is preferably molded into the cap member  176 . The circuit board  190  is connected to the electrical contact  170 . A surface mount Hall Effect Device  192  is positioned on the circuit board  190 , along with a flux concentrator  194 . 
         [0047]    A magnetic ring  196  with alternating N and S members is molded or bonded into member  198  which in turn is connected or fastened to the fan mounting plate  141 . In this manner, when the fan is caused to rotate by the valve mechanism, the speed of the fan is sensed and determined by the Hall Effect Device  192 . 
         [0048]    In accordance with a preferred embodiment of the present invention, the clutch lubrication oil supply is routed out of the fan drive, through a heat exchanger, and then back into the fan drive. In the present embodiment, lubrication oil flow is developed through the stationary pitot tube  70 . As better shown in  FIG. 4 , the lubrication oil path is routed through the piston housing hot oil path  131  through the piston housing spacer member  132 , through a hole in the mounting shaft  50  and into the hot oil passage  133 . The hot oil passage  133  is created between the inner diameter of the mounting shaft  50  and the outer lube tube  134 . From hot oil passage  133 , the hot ATF flows out of the clutch assembly through the hot oil exit port  24  in the mounting shaft  20 . After the hot oil has been removed from the fan drive assembly, it is plumbed externally through a heat exchanger (not shown) where it is cooled before it is recirculated to the inlet oil return port  26 . 
         [0049]    After the cooled oil enters the inlet port  26 , it flows concentrically between the outer lube tube  134  and the flux can  99 . Once the cooled oil reaches the valve head  88 , it flows through the valve head via valve head passages  137  ( FIG. 3 ). The cooled oil then flows through a cold oil port  138  in the mounting shaft  50 , back through the piston housing spacer member  132  and through the piston housing cold oil passage  139  back into the friction plates in the clutch mechanism  60 . 
         [0050]    The control valve subassembly  150  also includes an orientation notch  151  ( FIGS. 3 and 6 ) that mates with a spring pin member  152  to insure proper angular orientation of the control valve subassembly  150  within the mounting shaft  50 . The subassembly  150  is retained within the mounting shaft  50  by two spring pin members  153  that press into the valve head ports  86 . 
         [0051]    Some known hydraulic valve assemblies used to control pressure in wet friction fan clutches are two-way poppet designs. These regulate the flow restriction between the clutch pack actuation piston and the hydraulic sump. Since the pressure applied to the piston varies with the square of input speed, larger flow passages are required through the valve to prevent the clutch from self-energizing at high input speeds due to flow restriction through the vent path. In contrast, the present invention utilizes a three-way valve design  200  ( FIG. 10 ) in which the valve modulates flow between the piston and the vent and enables the use of smaller oil passages and allows the fan clutch to achieve lower disengaged speeds for energy conversion. This also allows for substantially infinite control of said fan speed between its minimum and maximum rotational speed conditions—i.e. fully disengaged, fully engaged, and infinitely in between. 
         [0052]    The hydraulic valve mechanism is a normally closed valve design. This means that when the electrical power is lost, the clutch will completely disengage. This feature accommodates many future fan clutch applications that will use high pulley ratios to drive the clutch, the clutch ratios being greater than 1.4:1. With high pulley ratios at this level, the fan torque at high engine speeds if the valve were to fully engage when electrical power was lost, would exceed the rating of the engine accessory drive. Furthermore, if the valve were to fully engage the clutch when electrical power is lost, the fan torque at high engine speeds would exceed the rating of the engine accessory drive. With the clutch mechanism disengaging when electrical power is removed, there is no need to engage the cooling fan at all during much of the vehicle drive cycle. Under these conditions, the present invention will conserve electrical energy. 
         [0053]    Another advantage of the embodiment shown herein of the present invention relates to the routing of the wires to the speed sensor. Since the control valve utilizes most of the interior space of the shaft member, it is difficult to route the speed sensor wires around the valve. With the embodiment of the present invention as shown in the drawings, the sensor wires are routed through the center of the valve, rather than around it, which eliminates complex wire routing paths. In addition, the spring contact system for making electrical contact between the fan speed sensor subassembly and the valve assembly simplifies the final assembly. 
         [0054]    With the present invention, an onboard microcontroller performs all of the necessary control functions. With this method, only four control wires are required (CAN+, CAN−, +Vbattery, −Vbattery). None of these control wires need to be connected directly to the Engine Control Unit (“ECU”), which frees connector pins for the original equipment manufacturers (“OEMs”) to use for other functions. 
         [0055]    With other known systems, typically five pins are available for the fan drive control. However, when fan speed feedback is added to the system, five pins are not sufficient to provide all of the control functionality desired. For example, to achieve the desired control, seven wires would be required (Coil+, Coil−, Thermal Switch+, Thermal Switch−, Fan Speed Output, +5VDC, and Gnd). The use of a thermistor  118  in the present invention also reduces noise and energy consumption. Known heavy duty multi-speed control systems (“HDMS”) use a thermal switch to measure the ATF temperature in the clutch and send back signals to the vehicle ECU when a temperature limit is reached. The ECU then typically will fully engage the clutch in order to eliminate the slip heat generation and allow the ATF to cool. This strategy, however, represents a significant amount of wasted energy required to turn the fan at high speeds when it is not required for engine cooling. It also could develop a high level of undesirable noise. In contrast, with the present invention, the use of a thermistor to measure the ATF temperature in conjunction with the microcontroller, implements a more sophisticated slip heat protection strategy. 
         [0056]    In addition, the onboard microcontroller also makes it easier for the HDMS fan clutch to be applied on applications where the ECUs do not have pulse width modulation (“PWM”) drivers capable of driving the control valve solenoid coil, or where the OEMs do not have the engineering resources available to implement new control logic for operating the fan clutch. 
         [0057]    The embodiment of the present invention described herein also seals the electronics from moisture entry under the extreme thermal cycling and environmental conditions which are typical of motor vehicle applications. An electrical connector is molded and integrated into the rear cap of the valve subassembly. An O-ring is then used to seal the cap on the outer valve sleeve. The wires are sealed when the mating connector is inserted into the molded connector cap. In addition, the connector cap embodies the connector pin members which are soldered directly to the printed circuit board (PCB) and then protrude through an open hole in the connector cap. Upon final assembly, the electronics cavity is filled with potting compound through the connector cap hole to provide vibration robustness and rigidity for the connector pins. 
         [0058]    The present invention also addresses the non-linear force verses displacement curve typical of solenoids. This is accomplished through the stepped armature to the rear flux cap interface in a structure that intentionally increases the magnetic reluctance when the armature nears its fully retracted or naturally highest force position. The present invention is thus able to realize a nearly fiat force versus displacement curve over the valve stroke, which typically is four millimeters in length. This significantly improves the open looped controllability of the valve. 
         [0059]    While preferred embodiments of the present invention have been shown and described herein, numerous variations and alternative embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention is not limited to the preferred embodiments described herein but instead limited to the terms of the appended claims.