Abstract:
An air-actuated fan clutch having a translatable piston in communication with a pressure chamber and moveable between a piston neutral position and a piston activated position in response to air pressure. A clutch spring biases a clutch housing into engagement with a clutch element that is coupled for rotation with a drive shaft when the piston is in the piston neutral position. Movement of the piston to the piston activated position moves the clutch housing away from the clutch element to inhibit transmission of rotary power through the fan clutch. A valve and an actuator are provided to prevent movement of the piston from the piston neutral position when air pressure acting on the piston would be below a predetermined threshold.

Description:
TECHNICAL FIELD 
     The present invention relates generally to fan clutch assemblies and more particularly to methods and systems for improving the operation of airactuated cone clutch fan assemblies. 
     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 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 an 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 plurality 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. 
     Airactuated friction clutch assemblies of this type which work well for their intended purpose are found in U.S. Pat. Nos. 7,731,006, 7,055,668, and 7,430,956. 
     An issue with airactuated fan clutch assemblies relates to situations where the air pressure is too low to adequately cause actuation of the fan drive. This could result, for example, from a leak in the air supply, or a drain of pressure due to constant repeated usage. Without sufficient pneumatic pressure, the friction clutch might not engage solidly causing possible overheating and damage to the friction assembly and clutch. 
     It would therefore be desirable to have pneumatic clutch fan assembly with a system for protecting the fan assembly by preventing engagement of the friction clutch when a low pressure situation exists. 
     It would also be desirable to provide a clutch assembly with a pneumatic control mechanism that would prevent slip damage due to low, external operating air pressure. 
     It would further be desirable for such a clutch assembly to provide optimal performance and operation at all times during operation. 
     SUMMARY OF THE INVENTION 
     In one form, the present teachings provide an air-actuated fan clutch that includes a drive shaft, a clutch element, a friction liner, a clutch housing, a clutch spring, a piston, a first directional valve and an actuator. The drive shaft is rotatable about an axis. The clutch element is coupled to the drive shaft for rotation therewith. The friction liner is disposed about the clutch element. The clutch housing is rotatable relative to the drive shaft about the axis and is movable relative to the clutch element along the axis between a first position, in which the clutch element, the friction liner and the clutch housing cooperate to permit transmission of rotary power between the clutch element and the clutch housing, and a second position in which transmission of rotary power between the clutch element and the clutch housing is inhibited. The clutch spring biases the clutch housing toward the first position. The piston is movable along the axis between a piston neutral position and a piston activated position. Movement of the piston from the piston neutral position to the piston activated position causes corresponding movement of the clutch housing into the second position. Movement of the piston from the piston activated position to the piston neutral position causes corresponding movement of the clutch housing into the first position. The first directional valve has a first port, a second port and a first valve element. The first port is configured to be coupled to a source of fluid pressure. The second port is coupled in fluid communication with the piston. The first valve element is movable between a first element position, in which the first and second ports are not in fluid communication with one another, and a second element position in which the first and second ports are in communication with one another. The actuator is coupled to the first directional valve and configured to be coupled to the source of fluid pressure. The actuator provides at least one output that is configured to move the valve element of the first directional valve. The at least one output is at least partly based on a magnitude of a fluid pressure acting on the actuator and is produced when the magnitude is greater than or equal to a predetermined fluid pressure. 
     In another form, the present teachings provide a method of operating an air-actuated fan clutch. The fan clutch includes a piston, a clutch housing, a clutch element and a clutch spring. The piston is movable under fluid pressure to cause corresponding relative movement between the clutch housing and the clutch element such that rotary power is transmit-able between the clutch element and the clutch housing. The clutch spring biases the clutch housing away from the clutch element. The method includes: providing a first directional valve having a first valve element that is movable between a closed position and an open position, the first valve element being biased into the closed position; providing fluid pressure to a first directional valve while the first valve element is in the closed position; and moving the first valve element from the closed position to the open position to transmit fluid pressure to the piston to disengage the fan clutch in response to determining that a magnitude of the fluid pressure is greater than or equal to a predetermined value. 
     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 representative vehicle utilizing a fluidically controlled fan drive system. 
         FIG. 2  depicts a quarter side cross-sectional view of a friction cone clutch assembly. 
         FIG. 3  depicts a preferred embodiment of an electro-pneumatic 3-way control system in accordance with the present invention. 
         FIG. 4  depicts an alternate electronic pneumatic control system. 
         FIG. 5  depicts another alternate embodiment of the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     While the present invention is described primarily with respect to a system for a pneumatically controlled fan drive system, the present invention may be adapted and applied to various systems including: hydraulic 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 preferred embodiments. These specific parameters and components are included only by way of example and are not meant to be limiting the invention to the described embodiment or systems having its particular structure or operational parameters. 
     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 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. 
     Referring now to  FIG. 1 , a perspective view of a representative vehicle  10  utilizing a representative fluidically controlled fan drive system  12  which can incorporate an embodiment of the present invention. 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 . 
     Referring now to  FIG. 2 , a quarter side cross-sectional view of the friction clutch assembly  20  is shown. The assembly  20  includes a translatable clutch housing  30  and a rotating shaft  32 . The clutch housing  30  is attached to an engine cooling fan, such as fan  16 . The rotating shaft  32  is coupled to a drive pulley, such as pulley  22 . A friction liner  34  is coupled to the clutch housing  30  and resides between the clutch housing  30  and the rotating shaft  32 . A clutch spring  35  engages the clutch housing  30  with the rotating shaft  32 . The clutch spring  35  resides on spring carriers or retainers  36 , within a clutch spring area  38 , and within the shaft  32 . 
     In operation, air, as represented by arrows  39 , is forced in and out of the spring area  38 , through the passages  46  through a piston rod bearing groove  47 , through a rear cavity  49 , through a shaft channel  51 , and into the housing cavity  53 . 
     The friction clutch assembly  20  also includes a fluidic control circuit that is operated via a main controller  50 . The fluidic control circuit includes a piston rod or pneumatic transfer conduit  54  with a fluid channel  56  residing therein for the transfer of fluid, such as air, into a piston reservoir  58  of an air cylinder  59 . The air cylinder  59  resides over a piston  61 . A fluid pump  60  and corresponding solenoid  57  are fluidically coupled to the fluid channel  56 . The main controller  50  is coupled to the pump  60  and to the solenoid  57  and adjusts the flow of the fluid into and out of the reservoir  58 . The solenoid may be replaced with other types of valves known in the art. 
     When air pressure is supplied, the reservoir  58  becomes pressurized and the clutch piston member  61  is moved into a piston activated position. In this position, the translatable clutch piston member  61  moves the clutch housing  30  relative to the cone clutch element  28  into a clutch disengaged position. (This position is shown in  FIG. 2 .) When in the clutch disengaged position, the clutch housing  30  is disengaged from the cone clutch element  28  and the rotating drive shaft  32  such that the clutch housing  30  is independently rotatable relative to the clutch element  28  and the rotating drive shaft  32 . 
     The clutch spring member  35  is positioned within the clutch housing  30  and biases the clutch housing  30  relative to the cone clutch element  28  into a clutch engaged position. When pressure within the pressure chamber is released, the clutch spring  35  moves the clutch housing  30  relative to the cone clutch element  28  into the clutch engaged position and the translatable clutch piston  61  moves into the piston neutral position. The clutch spring  35  also provides a maximum spring force which in turn translates into a clutch engagement force between the clutch housing  30  and the cone clutch element  28 . This force prevents slippage between the clutch housing  30  and the cone clutch element  28 . 
     The main controller  50  may be contained within the system  12  or may be separate from the system  12  as shown. The main controller  50  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  50  may also 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. 
     In operation, the friction clutch assembly  20  is frequently engaged. When engaged, no fluid is pumped into the reservoir  58 . In such situations, the piston  61  is in the piston neutral position, the clutch housing  30  is in the clutch engaged position (relative to the clutch element  28 ) and the spring  35  is in an expanded state. When cooling is no longer desired, the main controller  50  pumps fluid into the reservoir  58 , which causes the piston  61  to shift rearward, towards the shaft  32 . As the piston  61  shifts rearward, the housing  30  also shifts rearward, thereby compressing the spring  35  and causing the friction liner  34  and thus the clutch housing  30  to disengage from the clutch element  28 . As the spring  35  compresses, the volume of the spring retainer area  38  decreases, which forces air within the spring retainer area  38  to pass through the passages  46 . 
     The present invention creates new airactuated controls that add the feature of preventing exposure to low air pressure that could allow slipping damage to the clutch during disengaged operation. For this purpose, an anti-slip valve mechanism  75  is provided. 
     A first embodiment of a system for preventing the friction clutch from slipping and from possibly becoming damaged if the pneumatic pressure in the vehicle is too low, is shown in  FIG. 3 . This system  100  is an electro-pneumatic system which is solenoid based with additive electrical and pneumatic pilot signals operating on a three-way valve biased by a spring. The valve is essentially an on-off valve and is calibrated such that it will not allow air to flow to the friction clutch mechanism until it exceeds a certain value. 
     In order to prevent burn out of the valve, i.e. overheating and damage, particularly at high differential speeds, the system  100  is calibrated to not allow the passage of air until the air pressure is at least 60 psi and preferably at least 80 psi. 
     From the compressor or air pump  60 , the pressurized air flows to pilot valve  57 . The main controller  50  is programmed with the logic for operating all of the various systems in the vehicle. In this instance, the electric solenoid pilot valve  125  is an on-off valve which only is actuated when the main controller  50  determines that cooling is not needed. When opened, air can pass through it to valve  130 . 
     When the valve  57  is opened, the air flows to the second valve  130  which is operated by a pneumatic pilot  135 . Valve  130  is only opened when the air pressure exceeds a certain critical value, such as, for example, 60 psi. The biasing force from spring member  140  prevents the valve  130  from operating until the pilot vehicle air pressure reaches the preset value. 
     Once the minimum air pressure is reached, the valve  130  is opened allowing the pneumatic pressure to flow to the friction clutch mechanism  20  and operate it as set forth above. As evident from  FIG. 3 , both valves  57  and  130  need to be energized in order to provide air pressure to flow to the clutch mechanism  20 . 
     The main controller or “Electronic Control Unit” (“ECU”) for the vehicle is coupled both to the solenoid valve  57  and the pump  60 . 
       FIG. 4  depicts an alternate embodiment  150  of the invention. In this embodiment, air supplied from the compressor pump  60  flows to a pneumatic valve  155  which operates a pilot for the on-off valve  160 . The ECU  50  controls the solenoid valve  165  which is an electric pilot. The valve  160  is biased by spring member  140 . Both the electric pilot and pneumatic pilot signals are required to provide air pressure to flow to the clutch mechanism  20 . 
     When the air pressure through pneumatic pilot valve  155  exceeds the minimum value, such as, for example, 60 psi, and the solenoid valve  165  is energized, the air pressure is allowed to flow to and operate the friction clutch assembly  20 . 
     In  FIG. 4 , the electrical-pneumatic pilot solenoid valve in the vehicle is modified to add the air pilot feature. The connection of the air line to the valve pilot is internal to the valve. This addition insures that the friction clutch would not be subjected to air pressure at such a low pressure that it would result in slippage of the friction liner. In order for the valve to allow air pressure to the clutch, both the signal from the ECU and sufficient air pressure is needed. 
     The operation of the system to prevent damage to the friction liner can be carried out by types of valves other than electro-pneumatic valves. As shown in system  200  depicted in  FIG. 5 , a pressure switch  210  is utilized to prevent low pressure slippage in the friction clutch assembly. 
     The pressure switch  210  closes at the critical pressure level, such as 60 psi or 80 psi, and allows the electrical signal from the controller to pass through to valve  220  (or solenoid vale  230 ). The valve  220  is an on-off valve and opens to allow or pressure to flow to, and operate, friction clutch assembly  10 . The valve  220  has a biasing spring  225  and an electrical solenoid valve  230 . 
     In  FIG. 5 , the pressure control switch is in series with the air control solenoid valve. The pressure switch  210  monitors the air pressure in the vehicle. This system  200  assures that the friction clutch  20  would not be subjected to a low air pressure that would result in liner slippage. In order for the valve  200  to allow any air pressure to the clutch, both the signal from the ECU and sufficient air pressure would be needed. 
     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.