Abstract:
Pneumatic fan drive assembly with improved capacity, longevity and heat control. The output member is positioned radially internally of the output member. The friction mechanism has longer movement (moment) arms and torque. The friction engagement has an increased friction surface arm. A portion of the heat generated by the friction mechanism is evacuated to the atmosphere rather than being completely internalized in the assembly. The friction material for the friction lining alternatively can be formed of a plasma spray.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/669,673, filed Jul. 10, 2012, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to a pneumatic fan clutch and more particularly to a fan clutch which has improved capacity and longevity. 
       BACKGROUND OF THE INVENTION 
       [0003]    Vehicle engines commonly utilize cooling assemblies to remove excess heat from the engine and maintain an optimal operating temperature. The cooling assembly pumps a coolant through the engine and other components in order to control engine temperature. Heat generated within the engine and other components is absorbed by the coolant and dispersed into the surrounding atmosphere through the use of a radiator. In order to improve dispersal by the radiator, it is common to utilize fan assemblies to draw or force air past the radiator to assist in temperature transmission. 
         [0004]    It is not always desirable for such fan assemblies to be run continuously. At times, it is desirable for the temperature within the coolant to increase rather than decrease. Additionally, continuous operation when unnecessary places a non-required draw on the engine and thereby reduces efficiency. To compensate for this, present fan assemblies utilize fan clutch assemblies that allow for the selective engagement of the fan to the engine such that the fans are engaged only when necessary. The fan clutch assemblies may be operated in a host of configurations including hydraulic and air-pressure actuated. It is common for these systems to be biased towards fan operation such that when failure occurs in the clutch assembly, the fan continuously operates to keep the engine cool. 
         [0005]    An issue with these fan assemblies and associated clutch assemblies relates to their capacity and longevity. Since space is often limited in vehicle engine compartments, it is important to supply a fan clutch which has as much capacity as possible for the size and space allowed in the component in the vehicle. Also due to warranty requirements and the expense required to replace components in a vehicle, it is important to provide a fan clutch which has increased durability and longevity—perhaps to last to the life of the engine or vehicle. 
         [0006]    Another issue with current fan clutch assemblies relates to the amount of heat generated during use which also affects durability and longevity. In many known clutch assemblies, the heat generated from the friction clutch mechanism is internalized in the assembly. This can reduce the life of the friction member and the entire clutch assembly. 
         [0007]    It would therefore be highly desirable to have an improved pneumatic clutch fan assembly with increased capacity and durability and without significantly changing its external size or shape. Another object would be to provide a fan assembly which operates in a cooler manner. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object to the present invention to provide a clutch assembly with increased capacity and durability and without significantly increasing its size or shape. It is further an object of the present invention to provide a clutch assembly which internalizes a smaller amount of the heat generated during use, and which is less expensive and easier to manufacture and assemble. 
         [0009]    In accordance with the objects of the present invention, clutch assemblies are provided with improved structures and improved friction members, and with increased capacity and durability. A central piston chamber is positioned therein and feeds a pressure chamber. A translatable clutch piston is in communication with the pressure chamber and is movable between piston neutral and activated positions in response to air pressure fed into the pressure chamber. A rotating input drive member is provided along with a clutch housing. A cone clutch element translates between a clutch engaged position against a friction member to a clutch disengaged position in response to the clutch piston moving between the neutral and activated positions. The cone clutch element engages the rotating drive shaft when in the clutch engaged position. A clutch spring biases the cone clutch element towards the clutch engaged position with a clutch engagement force. 
         [0010]    In one preferred embodiment of the invention, input and output members are provided with increased leverage ratios (from extended radial length) and increased surface area for the friction member, and without significantly changing the external size and shape of the clutch assembly. The housing and friction member (clutch output) are part of the smaller radial component, while the input drive member comprises the larger radial component. This provides a larger moment arm, as well as a new path for the frictional heat generated during use. The configuration allows heat generated from the friction clutch mechanism to pass to the ambient air. The ambient air provides for a second path of heat evacuation. Some heat will still be internalized in the clutch, but the path is longer and some of the heat will also be exhausted to the atmosphere. These features provide a fan clutch assembly with greater torque and capacity, as well as increased durability—and without necessarily changing the exterior size or shape of the clutch assembly. 
         [0011]    A plasma spray friction material can also be provided as part of the friction engagement mechanism. A metal-based material in powder form is applied by a plasma spray or similar high velocity/high temperature deposition. 
         [0012]    Since the inventive clutch assembly has more torque and durability, it can be used in more applications and with larger cooling fans. 
         [0013]    Other objects and features of the present invention will become apparent when viewed in light of the detailed description and preferred embodiments when taken in conjunction with the attached drawings and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  depicts a prior art cone clutch fan drive assembly. 
           [0015]      FIG. 2  illustrates a cone clutch fan drive in accordance with a first embodiment of the present invention, the clutch assembly illustrated in the clutch engaged position; 
           [0016]      FIG. 3  illustrates the cone clutch fan drive of  FIG. 2  with the clutch assembly illustrated in the clutch disengaged position; and. 
           [0017]      FIG. 4  illustrates an alternate friction member which can be utilized with an embodiment of the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]      FIG. 1  depicts a cone clutch fan drive assembly  10  of a type known in the industry. The fan drive assembly  10  includes a clutch assembly  12  having a clutch housing  14 . The present invention provides novel and valuable improvements to such clutch assemblies that provides increased torque, capacity, and durability, as well as less heat buildup, without significantly changing the exterior size and configuration of the assembly. 
         [0019]    The components and operation of the clutch assembly  12  are similar to the clutch assemblies shown and described in U.S. patent application Ser. No. 10/905,505 entitled “Reduced Axial Length Air Actuated Cone Clutch Fan Drive,” now abandoned, and U.S. Pat. No. 7,731,006. Thus, many of the components contained in the clutch assembly utilized herewith, as well as the basic operation thereof, do not need to be discussed and reference is made to these two references for a further discussion and description of them. 
         [0020]    The clutch actuating assembly  12  includes a central piston chamber  18  positioned within the chamber cap  22 . Preferably positioned along the centerline of the drive assembly  10 , the central piston chamber  18  provides a pathway through the clutch actuating assembly  12  through which pressurized air may be selectively passed. The pressurized air passes through the central piston chamber  18  and into a pressure chamber  20  formed between a chamber cap  22  and a translatable clutch piston  24 . When air pressure is supplied, the pressure chamber  20  becomes pressurized and the translatable clutch piston  24  is moved into a clutch disengaged position. In this position, the translatable clutch piston  24 , is in operable communication with a cone-shaped clutch friction member  28 . The friction member typically has an annular wedge shape and is securely affixed to the housing member  14 . As piston member  24  is forced in the direction of arrow  30 , the clutch is in its disengaged position. When in its disengaged position, the cone clutch friction member  28  disengages from the rotating input member  16  such that the input member  16  rotates independently from the cone clutch friction member  28 . 
         [0021]    The cone clutch friction member  28  travels axially only a small distance between the engaged and disengaged positions. In operation, the travel of the cone clutch friction member can be on the order of 0.05-0.15 inches. 
         [0022]    A clutch spring  34  positioned within the clutch housing  14  biases the cone clutch friction member  28  towards a clutch engaged position (see arrow  32  in  FIG. 1 ). When pressure within the pressure chamber  20  is released, the clutch spring  34  moves the cone clutch friction member  28  into the clutch engaged position and the translatable clutch piston  24  moves into the piston neutral position. The clutch spring  34  also provides a maximum spring force which in turn translates into a clutch engagement force between the cone clutch friction member  28  and the rotating input member  16 . This force prevents slippage between the member  28  and the input member  16 . 
         [0023]    A needle bearing member  50  is positioned in between the rotating input member  16  and the cone clutch friction member  28 . The needle bearing member  50  preferably is a dual needle bearing member as shown in  FIG. 1 . 
         [0024]    In conventional air actuated cone clutches, such as the one shown in  FIG. 1 , the friction member  28  is a solid ring of friction material having a tapered or frustoconical annular shape. The friction member is held in place against the inner surface of the outer drum housing member  14 . The friction material can be made of any conventional friction liner material and be allowed to float against retainer plates  29 , or be secured in any conventional manner, such as by bonding. The friction member can also have a continuous 360° piece of friction material, or segmented into numerous pieces or sections, which is/are attached to a wedge shaped member. 
         [0025]    As an alternate embodiment, it is also possible to mount or attach the friction member or friction liner to the radially outer surface of the input drive member  16 . 
         [0026]    The housing  14  is the output member of the fan assembly  10  and has a fan member or the like (not shown) attached to its front axial end (the left end in  FIG. 1 ). The fan is attached to the housing by a series of bolts  15 . The input drive member  16  is directly connected to the input pulley member  40 . A plurality of bolts  42  attach the pulley member  40  to the input member  16 . The pulley member is attached to an engine belt (not shown) which is driven by the engine essentially at or close to the engine RPM speed. 
         [0027]    In known clutch assemblies, the input member  16  is positioned radially inside the housing  14 . This structure is shown in  FIG. 1 . The frustoconical cone friction member  28  has its larger diameter end positioned facing the fan member end of the fan assembly and facing axially away from the pulley member  40 . 
         [0028]    An actual known fan assembly of the type shown in  FIG. 1  is a Model K-30 clutch made and sold by BorgWarner Inc., Auburn Hills, Mich. The dimensions of a popular K-30 model are as follows: a radially outer housing diameter A of 200.8 mm (7.9 inches), a radially outer friction member diameter B of 164.25 mm (6.47 inches), a radially inner friction member diameter C of 151.2 mm (5.95 inches), and an axial length D of the cone-shaped friction member  28  of 24.4 mm (0.96 inches). If the average diameter of the friction member (about 157.7 mm-6.21 inches) is multiplied by pi (3.1416) and also multiplied by its axial length of D, the result is about 18.7 sq. inches of friction member surface. Also, the ratio of the outer diameter B of the friction member (164.25 mm-6.47 inches) to the outer diameter A of the fan assembly (200.8 mm-7.9 inches) is about 82%. 
         [0029]      FIGS. 2 and 3  illustrate an embodiment of the present invention. The structure of fan assembly  100  is the same in  FIGS. 2 and 3 , with the difference being that the fan assembly in  FIG. 2  is shown in the engaged position, while the fan assembly in  FIG. 3  is shown in the disengaged position. (The gap between the friction member and drive member is exaggerated in the drawings for clarity.) 
         [0030]    Also, where the components of the fan assembly shown in  FIGS. 2 and 3  are the same as those shown in  FIG. 1 , the components are referred to by the same reference number. In all the Figures, the fan assemblies and pulley are attached to a mounting member  55  which is securely mounted to a vehicle in a conventional manner. Pneumatic pressure used to operate the fan assembly is also supplied to the assemblies  10  and  100  through passageways  56  in the mounting member  55 . 
         [0031]    An improvement of the invention over the prior art relates to the radially outer portions of the housing member  114  (which is the output member) and radially outer portion of the input drive member  116 . With preferred embodiments of the present invention, the housing member  114  and friction member  128 , which are part of the output of the fan clutch assembly, are part of the smaller radial component. As shown, the input member  116  is preferably wrapped around and over the output member becoming the larger radial component. This results in a larger moment arm, as well as a new path for frictional heat losses directly to the ambient air. 
         [0032]    In the prior art fan assemblies, as shown in  FIG. 1 , the heat created by the frictional clutch engagement is directed radially inwardly into the internal portions of the fan assembly. See arrow  70  in  FIG. 1 . This creates additional heat for the fan assembly which is undesirable. 
         [0033]    The improvement in heat dispersement from a pneumatic fan drive mechanism in accordance with the present invention is shown by a comparison of arrows  70  and  170 - 171  in  FIGS. 1 and 2 , respectively. In the prior art fan drive mechanism, most of the heat generated by the friction clutch mechanism is contained internally through the input member  16 , as shown by arrow  70 . This increases the heat of the entire assembly  10 . In contrast, with the embodiment of the present invention as shown in  FIGS. 2  and  FIG. 3 , a large portion of the heat generated by the friction clutch mechanism is dissipated into the atmosphere or ambient air, as shown by arrow  170 . This maintains the friction clutch mechanism and entire fan drive assembly at a lower temperature. 
         [0034]    The input drive member  116  can be made of a single piece, but preferably, as shown in  FIGS. 2 and 3 , the input drive member  116  is comprised of two parts, a radially oriented inner component  117  and an outer axial oriented component  118 . The two components can be held together in any manner, such as by bolts or fasteners  120 . 
         [0035]    The friction member  128  is shown being attached to the radial outer surface of the output drive member  114 . It is also possible, however, for the friction member to be attached to the radially inner surface of the input member  116 . 
         [0036]    In  FIGS. 2 and 3 , the frustoconical cone frictional member is situated in a position reverse to the friction cone member in  FIG. 1 . In  FIGS. 2 and 3 , the larger diameter end of the cone is axially positioned facing the pulley member  40  of the fan assembly and facing away from the fan member. 
         [0037]    The present invention provides a friction member which is positioned at a radial distance from the centerline of the fan assembly greater than the radial distance of the friction member in the prior art. This creates a larger moment arm which in turn results in greater torque for engaging the frictional engagement. In addition, the surface area of the friction member  128  is greater in surface area than the surface area of the friction member  28  in the prior art which creates greater frictional engagement. 
         [0038]    To illustrate this feature and its advantages, as an example, assume that the fan drive assembly  100  has essentially the same diameter AA as the radially outer diameter A of the fan drive assembly  10  in  FIG. 1 . Thus, the embodiment of the invention as shown in  FIGS. 2 and 3  substantially corresponds to the size and shape of the prior art fan drive assembly. As indicated above, the outer diameter A of the fan assembly in  FIG. 1  is 200.8 mm (7.9 inches). In the embodiment shown in  FIGS. 2 and 3 , the outer diameter AA is 201 mm (7.9 inches). 
         [0039]    Even though the outer dimensions of the two fan assemblies are substantially the same, the friction member is spaced radially further away from the centerline of the assembly. Also, the friction member surface area is significantly greater. In  FIGS. 2 and 3  with the outer assembly diameter of 201 mm (7.9 inches), the radially outer friction member diameter BB is 176.6 mm (6.94 inches), the radially inner friction member diameter CC is 158 mm (6.23 inches), and the axial length DD of the friction member is 33.7 mm (1.33 inches). 
         [0040]    In comparison with the prior art assembly in  FIG. 1  of comparable size and shape, the present invention provides a friction member which has about 38% more frictional surface area and about an 8% larger torque (moment) arm (87% vs. 82%). With more frictional engagement area, the working area for the friction member  118  is significantly larger than the prior art which spreads out the energy. This reduces the amount of heat per unit area generated by the friction member and also increases its durability and life. The longer moment arm creates more torque to frictionally engage the output member to the input member. 
         [0041]    In the  FIG. 1  assembly, the ratio of the surface area of the friction member (18.7 square inches) to the maximum outer diameter A (7.9 inches) is about 2.4, while in the  FIG. 2  assembly the ratio of the friction member (27.6 square inches) to the maximum outer diameter AA (7.9 inches) is 3.3. A ratio of about 3.0 or greater is preferred. 
         [0042]    The increase in the length of the moment arm for the frictional engagement of the clutch creates more torque. This means that less force is necessary to engage the friction member for the same amount of desired fan speed. 
         [0043]    As indicated, due to the structure and construction of the friction member  128 , it is greater in functional diameter and radial distance than friction members used in similarly sized and shaped prior art pneumatic clutches, such as friction member  28  in  FIG. 1 . This in turn allows the diameter of the mating faces of the input and output members to be increased resulting in a clutch assembly with increased strength and torque in the same size and shape package. 
         [0044]    The increase in torque is shown by the following formula: 
         [0000]    
       
         
           
             Torque 
             = 
             
               
                 
                   ( 
                   
                     μ 
                     · 
                     F 
                   
                   ) 
                 
                 
                   2 
                    
                   
                     ( 
                     
                       sin 
                        
                       
                           
                       
                        
                       α 
                     
                     ) 
                   
                 
               
               × 
               
                 
                   ( 
                   
                     D 
                     + 
                     d 
                   
                   ) 
                 
                 2 
               
             
           
         
       
     
         [0000]    where μ is the coefficient of friction, F is the normal force, α is the friction angle, D is the major contact diameter, and d is the minor contact diameter. 
         [0045]    Any increase in the length of the moment arm can be significant. However, for optimum torque for engagement of the friction member, an increase in length of at least 2-5% is preferred. As indicated above, with the embodiment shown in  FIGS. 2 and 3 , the increase in the length of the moment arm is 8%. 
         [0046]    With increased torque, the present invention can be used in more fan and cooling applications. The inventive fan assembly can be utilized with larger cooling fans and larger cooling systems, but with a fan assembly having the same size and configuration as the prior art. 
         [0047]    Also, any increase in the frictional surface area of the friction member can be significant. For purposes of the present invention, an increase of at least 10-15% is preferred. As indicated above, with the embodiment shown in  FIGS. 2 and 3 , the increase in the surface area of the cone shaped friction member relative to the  FIG. 1  prior art is about 47%. This feature also allows fan assemblies which utilize the present invention to be used in more applications and with cooling fans of larger size and diameter. 
         [0048]    Another embodiment of the invention is shown in  FIG. 4 . In this embodiment, the friction material  218  positioned on the friction member  228 , is a substrate formed by a plasma spray or similar high voltage/high temperature deposition. The substrate is preferably formed from a metal based friction material in powder form. The high temperature application processes resulted in melted particles which the high velocity achieves a good densification and packing of the particles to the friction member surface. A wide variety of thermal spray technologies can be used, although higher velocity versions, such as HVOF (high velocity oxygen fuel), are believed to have very good densifications. 
         [0049]    The standard method of getting high performance metal based friction material from powder form to a pad of material that&#39;s bonded to a substrate is a) deposit powder into a molding die, b) apply high pressure to pack powder together, c) bake the packed powder shape at very high temperature so particles melt together, and d) bond the baked shape to s substrate via adhesives or other mechanical techniques such as rivets. All four steps can be combined into one by using a thermal/mechanical spray process such as plasma spray. 
         [0050]    Typically, plasma spray is used to prevent wear by depositing very hard materials to a substrate. In this invention, the deposited material is being used to create friction rather than avoid wear. 
         [0051]    With this embodiment of the invention, the spraying medium can be a composite of many ingredients rather than a typical spray of homogeneous mixture. Due to being a composite mix, some of the particles may not melt as easily as other components in the mix, yielding a final substrate layer that&#39;s not only different in chemistries, but also different in phase structures. Adjoining lower melt particles will act as binders to the higher melt particles that may not have adhered as well in the melted matrix. 
         [0052]    Particle size of the various powder components as well as temperatures and velocities can be optimized for each application and powder mix. 
         [0053]    For the fan drive application shown, the substrate is a cone clutch. Attaching metal based material, such as sintered copper brake pad, is very difficult and costly when using known technologies as outlined above. The new process alleviates the need to use adhesives, rivers or other specialized fixturing to bond the sintered copper material to an aluminum or steel substrate. 
         [0054]    Any material exhibiting a tendency to melt and bond together when physically launched onto a substrate can be used. One example comprises steel and copper based, however, certain lower melt organic materials may work depending on the friction material mix. 
         [0055]    While the invention has been described in connection with one or more embodiments, it is to be understood that the specific mechanisms and techniques which have been described are merely illustrative of the principles of the invention, numerous modifications may be made to the methods and apparatus described without departing from the spirit and scope of the invention as defined by the appended claims.