Abstract:
An on/off clutch assembly is disclosed having a two component spring end cap. The spring end cap includes a steel cap portion and a non-metallic portion. The non-metallic portion extends along the entire length of the steel cap portion and is located between the steel cap portion and the piston rod. The new design insulates the steel piston rod from the steel spring end cap. This results in reduced corrosion of seals within the clutch assembly and contributes to improved conditions for bearings within the clutch assembly.

Description:
TECHNICAL FIELD 
   The present invention relates generally to a cone clutch fan drive and more particularly to a pneumatic cone clutch fan drive having a two-component spring end cap including a steel cap portion and a non-metallic portion. 
   BACKGROUND OF THE INVENTION 
   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. 
   It is not always desirable for such fan assemblies to 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 present invention relates to friction coupling devices that drive radiator-cooling fans. A common friction-coupling device is that of the dry friction drive style, otherwise referred to interchangeably hereinafter with a friction clutch assembly. Dry friction drives are used for their simplicity, cool operating temperature, and ability to turn at fully engaged peak operating speeds. 
   Although the present invention may be used advantageously in 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 for an over the road truck, such as a class 8 truck, and will be described in connection therewith. 
   Dry friction drives tend to have two operating conditions “ON and OFF”, which refer to when an associated friction clutch is either fully engaged or fully disengaged. When a friction clutch assembly is fully engaged, the assembly provides cooling to an associated engine and is not slipping. When a friction clutch assembly is fully disengaged slippage between the clutch plate and an engagement surface is at a maximum, thus providing little rotational output to drive an associated fan. 
   There are several disadvantages of known dry friction drives. One disadvantage is damage done to O-rings or seals within the friction clutch assembly. It has been determined that one source of damage done to the O-rings is due to contamination introduced into the environment. Another disadvantage is failure of the bearings within the friction clutch assembly. Bearing failure has been linked with excessive vibrations to the assembly. 
   These problems stem from the interaction between components in known friction clutch assemblies. There is a spring assembly that resides between the rotating drive shaft and the clutch housing. The spring assembly includes a spring and two end caps, each positioned at one end of the spring. The first end cap is translatable along the piston rod in response to a fluidic control circuit demanding disengagement of the clutch assembly. The first end cap is made from steel and the piston rod is made from steel. Therefore, the steel end cap moves back and forth over the steel piston rod. Internal metal-to-metal contact between the piston rod and spring end cap, sets up the perfect environment for fretting corrosion when coupled with engine vibrations, thus producing significant amounts of oxide particles which contaminate and degrade a nearby seal. 
   Another problematic issue with known dry friction drives is the costly step of machining radii in the inner diameter of the steel spring end cap. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a clutch assembly in which the steel end cap is insulated from the steel piston rod. The present invention provides for a non-metallic insulation that will prevent corrosion and act to reduce vibrations delivered to the front and rear ball bearings. Further, the non-metallic insulation will be molded, thus allowing for radii to be directly molded into the component. 
   The proposed invention, consisting of a multi-piece spring end cap eliminates the contamination, providing for a clean and debris free environment for extended seal and bearing life, while at the same time, dampening vibrations within the clutch assembly. 
   In accordance with the objects of the present invention, the translatable steel end cap is made from two components. There is a steel cap portion and a non-metallic portion. The non-metallic portion extends along the steel cap portion and is located between the steel cap portion and the piston rod. 
   Other objects and features of the present invention will become apparent when viewed in light of the detailed description and preferred embodiment when taken in conjunction with the attached drawings and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a vehicle utilizing a friction clutch assembly in accordance with an embodiment of the present invention; 
       FIG. 2  is a quarter side cross-sectional view of a friction clutch assembly in accordance with an embodiment of the prior art; 
       FIG. 3  is an illustration of a cone clutch fan drive in accordance with the present invention in a clutch engaged position; 
       FIG. 4  is an illustration of a cone clutch fan drive in accordance with the present invention in the clutch-disengaged position; 
       FIG. 5  is an illustration of an alternative embodiment of the fan drive in accordance with the present invention; and 
       FIG. 6  is an illustration of another alternative embodiment of the fan drive in accordance with the present invention. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the following figures the same reference numerals will be used to refer to the same components. While the present invention is described primarily with respect to a cone clutch fan drive system, the present invention may be adapted and applied to various systems including: hydraulic systems, electrical systems, pneudraulic systems, mechanical systems, pneumatic systems, vehicle systems, cooling systems, fan drive systems, friction drive systems, or other systems. 
   In the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting. 
   Also, in the following description various fan drive components and assemblies are described as an illustrative example. The fan drive components and assemblies may be modified depending upon the application. Although the following description addresses a specific type of control system that drives a clutch assembly, it should be noted that those of ordinary skill in the art will recognize other types of control systems to which the present invention may be incorporated. 
   Referring now to  FIG. 1 , a perspective view of a vehicle  10  utilizing a fluidically 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 friction clutch assembly  20  that is fixed to one or more pulleys, such as pulley  22 , which is coupled to and rotates relative to a crankshaft (not shown) of the engine  14 . The pulleys rotate 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 friction clutch assembly  20  is mounted on the engine  14  via a mounting bracket  26 . The friction clutch assembly  20  pneumatically engages the fan  16  during desired cooling intervals to reduce the temperature of the engine  14 . 
   The fan  16  may be attached to the friction clutch 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. 
   In summary,  FIGS. 2–6  illustrate a quarter side cross-sectional view of the friction clutch assembly  20  having a rotating shaft  27  with a thermal energy transfer portion  28  in an engaged position in accordance with an embodiment of the prior art ( FIG. 2 ) and according to a preferred embodiment of the present invention in both the engaged ( FIG. 3 ) and disengaged position ( FIG. 4 ). As will be described further below, a new two-component spring end cap is disclosed in the present invention as presented in  FIGS. 3 ,  4 ,  5  and  6 . 
   Referring specifically to  FIG. 2 , a known assembly  20  includes a translatable clutch housing  30  and a drive shaft  27  which is coupled to and rotates with the drive pulley  32 . The clutch housing  30  is attached to an engine-cooling fan, such as fan  16 . A friction liner, also referred to as a clutch element  34 , is coupled to the clutch housing  30  using a series of stamped plates  41  and screws  43  (the cross section shows one plate  41  and a pair of screws  43 ) and resides between the clutch housing  30  and the rotating drive shaft  27 . 
   A clutch spring  36  engages the clutch housing  30  with the drive shaft  27  in a friction clutch engagement area  38 . In operation, the drive pulley  32  rotates in turn rotating the drive shaft  27 , which when engaged rotates the translatable clutch housing  30 . The rotation of the housing  30  is translated to the radiator-cooling fan  16  to provide airflow through a radiator  18 . 
   The drive shaft  27  has the transfer portion  28 , as well as a friction contact portion  40  and a spring/bearing portion  42 . The transfer portion  28  is generally vertical in orientation, whereas the friction contact portion  40  and the spring/bearing portion  42  are generally horizontal in orientation. A bearing  48  couples the spring/bearing portion  42  to a non-rotating shaft  79 . The transfer portion  28  has a pulley contact surface  44  that corresponds with a shaft contact surface  46  on the drive pulley  32 . 
   The clutch spring  36  is held in position by a first spring end cap  37  and a second spring end cap  39 , one situated at each end of the spring  36 . The first and second spring end caps  37 ,  39  are positioned around the piston rod  74  and all three components are made from steel. Further, the first spring end cap  37  moves back and forth along the piston rod  74  in response to motion of the piston head  82 . The second spring end cap  39  preferably does not move along the piston rod  74 . 
   Known clutch assemblies are problematic due to the motion of the metal first spring end cap  37  moving over the metal piston rod  74 . This contact between the piston rod  74  and the end cap  37  provides the ideal environment for fretting corrosion when coupled with engine vibrations, thus producing significant amounts of oxide particles that contaminate and degrade a nearby seal  45  and contribute to shortened lives of bearings  48  within the clutch system. 
   The proposed invention, as illustrated in  FIGS. 3–5 , is a clutch spring mechanism, shown generally at  47 , including a multiple piece spring end cap  49  that eliminates the contamination, provides for a clean and debris free environment for extended seal and bearing lives, while at the same time, dampening vibrations within the clutch assembly. The present invention provides for a two-component spring end cap  49  having a steel cap portion  51  and a non-metallic portion  53 . The non-metallic portion  53  is located between the steel cap portion  51  and the piston rod  74 . 
   Further, the non-metallic portion  53  is molded. It could be molded from many different types of materials including, but not limited to, nylon. An advantage of molding the non-metallic portion is that the required inner diameter  55  can be molded directly into the part, as opposed to machining it into the completely steel component. 
   There are a number of different configurations for the non-metallic component  53 . In one embodiment, the non-metallic portion  53  is attached to the steel cap portion  51 . In a second embodiment, the non-metallic portion  53  is attached to the exterior surface of the piston rod  74 . In a third embodiment, illustrated in  FIG. 5 , there is a non-metallic portion  53  positioned between the steel end cap portion  51  and the piston rod  74  and a second non-metallic portion  253  positioned between the second spring end cap  39  and the piston rod  74 . In a fourth embodiment, illustrated in  FIG. 6 , the non-metallic portion  153  is positioned along the piston rod  74  between the steel cap portion  51  and the second spring end cap  39  and extends the length of the steel cap portion  51  and the second spring end cap  39 . 
   The drive pulley  32  includes a center protruding portion  60  and a pulley portion  62 . The center portion  60  extends forward away from the pulley portion  62  and is in contact with the shaft  27 . The center portion  60  includes the shaft contact surface  46  and is coupled to the drive shaft  27 . 
   The friction clutch assembly  20  also includes a fluidic control circuit  70  that is operated via a main controller  72 . The fluidic control circuit  70  includes a piston rod or pneumatic transfer conduit  74  with a fluid channel  76  residing therein for the transfer of fluid, such as air, into a piston reservoir  78  of a fluid cylinder  80 . The fluid cylinder  80  resides over a piston head  82 . The piston reservoir is also referred to as a pressure chamber  78  that is defined by the clutch housing and piston head. A fluid pump  84  and a corresponding valve  85  are fluidically coupled to the fluid channel  76 . The main controller  72  is coupled to the pump  84  and to the valve  85  and adjusts the flow of the fluid into and out of the pressure chamber  78 . The valve  85  may, for example, be in the form of a solenoid. 
   The main controller  72  may be contained within the system  12  or may be separate from the system  12  as shown. The main controller  72  may be 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  72  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  72  may be coupled to a plurality of sensors  77  located throughout the engine that give inputs regarding particular engine operating conditions. The main controller  72  interprets these signals to adjust the flow of fluid into and out of the fluid reservoir  78 , therein precisely controlling the engagement or disengagement of the friction clutch assembly and therein precisely controlling the engine operating temperature to achieve a desired balance of engine performance characteristics such as fuel economy and emission. 
   The friction clutch assembly  20  is frequently engaged, as shown in  FIGS. 2 and 3 . When engaged no fluid is pumped into the chamber or reservoir  78 . The piston head  82  and thus the housing  30  are in a fully engaged position. In the engaged position the spring  36  is decompressed or in an expanded state. 
   When cooling is no longer desired the main controller  72  pumps fluid into the reservoir  78 , which causes the piston head  82  to shift rearward (rightward in  FIG. 4 ), towards the shaft  27 . As the piston head  82  shifts rearward, the housing  30  also shifts rearward, thereby, compressing the spring  36  and causing the clutch element  34  and thus the housing  30  to disengage with the drive shaft  27 . This is the so-called disengaged position as shown in  FIG. 4 . 
   Of course, in other preferred embodiments, the engagement and disengagement mechanism of a preferred embodiment of the present invention may be reversed, wherein the clutch mechanism is maintained in a disengaged state in the absence of activation from the main controller and still fall within the spirit of the present invention. 
   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.