Abstract:
A master clutch includes a pressure plate adjacent to a friction disc. A centrifugal weight forces the pressure plate and friction disc into engagement when in a desired install position. A locking device retains the centrifugal weight in the desired installed position. A controller sends an electronic command to a system component, such as an engine, to disengage the locking device. In one example, the electronic command may be an engine speed command that is above an engine speed limit in a normal vehicle operating mode. Commanding the engine to run at a speed greater than the typical engine speed limit moves the centrifugal weight out of the desired installed position making the master clutch operational.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a method and apparatus for installing a centrifugal master clutch into a vehicle.  
         [0002]     Typically, a normally open clutch assembly includes a rotating input member such as a flywheel, that selectively engages one or more friction discs. The friction discs transmit rotation from the flywheel by one or more pressure plates. A transmission input shaft is driven by rotation of the friction discs. A plurality of centrifugal weights are pivotally mounted to move radially outward in response to rotation of the clutch assembly. As the rotational speed of the clutch assembly increases, rollers on the centrifugal weights are forced up a ramped surface to force engagement of the pressure plates with the friction discs and transmit rotational drive to the input shaft.  
         [0003]     Installation of a clutch assembly requires proper alignment between the friction discs and the flywheel. Normally closed clutch assemblies use a biasing force that normally clamps the pressure plates against the friction discs to maintain proper alignment during assembly. Disadvantageously, a normally open clutch assembly does not clamp the friction discs until the centrifugal weights are driven outward by rotation of the clutch assembly. Therefore, the friction discs are not held in a desired aligned position during assembly. Some other alignment method is thus necessary for a normally open clutch assembly.  
         [0004]     One example alignment device for normally open clutch assemblies include cammed sleeves that are inserted within the clutch assembly to hold the centrifugal weights in a position where the pressure plates hold the friction plates in proper alignment with the flywheel.  
         [0005]     The cammed sleeves are costly and time consuming to install and produce. Another known-alignment device utilizes shear pins to retain the centrifugal weights in a desired position. Once the clutch is installed in a powertrain it may be necessary to run the engine at high speeds to make the clutch operational. The high speeds cause the shear pins to break such that the clutch becomes operational. Typically, the end customer of the vehicle receiving the clutch may prefer that the engine be limited to less than full operating speed while at stand still during a normal vehicle operating mode. Limiting engine speed is a common feature for powertrains incorporating progressive shift and vehicle speed sensor anti-tampering. Unfortunately, the limited engine speed may be below what is required to make the clutch operational, for example, below the speed at which the shear pins will break.  
         [0006]     Customers typically have the preference of performing powertrain configuration in a different area than where the powertrain is installed onto the chassis. What is needed is a method and apparatus for overriding the normal vehicle operating mode once the powertrain is installed onto the chassis.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention includes a master clutch having a pressure plate adjacent to a friction disc. A centrifugal weight forces the pressure plate and friction disc into engagement when in a desired install position. A locking device such as a shear pin retains the centrifugal weight in the desired installed position. A controller sends an electronic command to a system component, such as an engine, to disengage the locking device. In one example, the electronic command may be an engine speed command that is above an engine speed limit in a normal vehicle operating mode. Commanding the engine to run at a speed greater than the typical engine speed limit moves the centrifugal weight out of the desired installed position and shears the pin making the master clutch operational.  
         [0008]     The inventive steps of installing a normally open clutch may include positioning clutch components of the master clutch in a desired position. The clutch components are locked in the desired position and the clutch is installed onto the engine. The normal vehicle operating mode is temporarily disabled, and a clutch install mode is activated. The clutch install mode may include an engine speed command that is above the engine speed limit of the normal vehicle operating mode. The clutch components are driven with the engine in the clutch install mode to unlock the clutch components. In one example, a shear pin is broken to free the centrifugal weight from the desired install position. Once the master clutch becomes operational, the normal vehicle operating mode is restored.  
         [0009]     According the present invention provides a simple and cost effective device for maintaining alignment of friction discs of a normally open clutch assembly during assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0011]      FIG. 1  is a schematic view of master clutch of a vehicle powertrain.  
         [0012]      FIG. 2  is a cross-sectional view of an example clutch assembly including a positioning pin;  
         [0013]      FIG. 3  is an enlarged cross-sectional view of the positioning pin shown in  FIG. 2 ;  
         [0014]      FIG. 4  is an enlarged cross-sectional view of the positioning pin shown in  FIG. 3  after being sheared.  
         [0015]      FIG. 5  is a flow chart depicting one example clutch installation method. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     A powertrain is schematically shown in  FIG. 1  and includes an engine  2  and a transmission  4 . The engine  2  includes an output shaft for driving the transmission  4 , which drives vehicle wheels  8 , as known.  
         [0017]     A controller  9  communicates with the engine  2  and transmission  4 . The controller  9  commands the engine  2  and transmission  4  in response to parameters stored within the controller  9  and the operating conditions of the engine  2  and transmission  4 . The powertrain typically operates in a normal vehicle operating mode. The normal vehicle operating mode may include, for example, engine speed limits to prevent full operating speed while at a stand still. As explained upon, such speed limits can make clutch installation difficult.  
         [0018]     Referring to  FIGS. 1 and 2 , a clutch assembly  10  includes a clutch cover  12  attached to a flywheel  14 . A plurality of centrifugal weights  16  are pivotally mounted within the clutch cover  12  and move radially outward in response to rotation of the clutch cover  12 . Each centrifugal weight  16  is biased toward a central axis  18  by a biasing spring  20 . Rollers  21  are mounted to each centrifugal weight  16  and ride along surfaces of a ramp plate  22  and an inner surface of the clutch cover  12 . The ramp plate  22  includes a ramped surface  24  on which the roller  21  moves to cause axial movement of the ramp plate  22 . Axial movement of the ramp plate  22  is transmitted through a clamp spring  26  to pressure plates  28 . Friction discs  30  are disposed between the pressure plates  28  such that axial movement of the pressure plates  28  clamps the friction discs  30  therebetween.  
         [0019]     The biasing member  20  biases the centrifugal weight  16  toward the axis  18  such that the pressure plates  28  are not engaged to the friction discs  30 . An alignment tool (not shown) such as a splined shaft is used to align the position of the friction discs  30  relative to the clutch cover  12  and flywheel  14 . However, once the alignment tool is removed and prior to an input shaft  32  of the transmission  4  being installed into the clutch assembly  10 , the friction plates  30  are not restrained and are free to move out of the set alignment.  
         [0020]     One example clutch assembly  10  includes a plurality of pins  34  holding a corresponding plurality of centrifugal weights  16  in a position causing axial movement and thereby engagement between the pressure plates  28  and the friction discs  30 . Each of the pins  34  hold a corresponding centrifugal weight  16  in a position causing application of a clamping force on the friction discs  30  that holds the friction discs  30  in the desired aligned position.  
         [0021]     Referring to  FIG. 3 , each pin  34  extends through an opening  36  in the clutch cover  12  and into a cavity  38  defined within the centrifugal weight  16 . The biasing spring  20  exerts a force holding the pin  34  against one side of the opening  36 . The opening  36  for the clutch cover  12  may extend through the entire thickness of the clutch cover  12  or may be configured as a blind hole not extending entirely through the clutch cover  12 . In one example, all the centrifugal weights  16  are held, however, it may only be required to hold selected centrifugal weights  16  to retain the friction discs  30  in a desired aligned position.  
         [0022]     The pins  34  are intended for temporarily holding the centrifugal weights  16  during assembly, and prior to installation of the input shaft  32 . The pin  34  is fabricated from a frangible material that shears in response to centrifugal force driving the centrifugal weights  16  radially outward.  
         [0023]     Referring to  FIG. 4 , assembly of the input shaft  32  to the clutch assembly  10  fixes the friction discs  30  in the desired aligned position. Accordingly, the pins  34  are no longer required to maintain friction disc  30  alignment. The pin  34  maintains position of the centrifugal weights  16  until the clutch assembly  10  is rotated to a speed that creates sufficient centrifugal force to shear the pin  34 . The pin  34  shears along a shear plane  40  in response to the centrifugal force from the centrifugal weights  16 . Once the pin  34  has sheared, the centrifugal weights  16  rotate freely responsive to rotation of the clutch assembly  10 .  
         [0024]     Residue from the pin  34  is simply dropped into the clutch assembly  10 . As appreciated, the environment within the clutch assembly  10  includes residue from the friction discs  28 . Additional residue and material from the pin  34  is substantially insignificant in comparison to the residue and debris found within the clutch assembly  10  and does not affect operation of the clutch assembly  10 . The sheared remains of the pin  34  may contact one another sporadically during clutch operation. Such sporadic contact will shear and wear additional material from the sheared ends until such contact no longer occurs.  
         [0025]     As described above, the clutch assembly  10  is rotated to a speed to create sufficient centrifugal force to shear the pin  34 . However, for example, an engine speed limit in the normal vehicle operating mode may prevent the engine from being driven to a speed needed to shear the pin  34 . To this end, the present invention provides a method to temporarily disable the normal vehicle operating mode.  
         [0026]     In operation, clutch components of the clutch assembly  10  are aligned, as described above. In particular, the pin  34  is arranged to lock the centrifugal weight  16  to force the pressure plates  28  and friction discs  30  against one another.  
         [0027]     The controller  9  temporarily disables the normal vehicle operating mode by activating a clutch install mode. The clutch install mode may be initiated in response to an input, such as performing an initiation sequence on a vehicle system. An operator can manipulate, for example, an ignition switch, shift lever, service brake, accelerator pedal, and/or cruise control switch in a particular sequence to request the controller  9  to enter the clutch install mode. In another example, the initiation sequence may be performed by installing a service tool into a communications port broadcasting a message to the engine  2  or transmission  4 . In yet another example, diagnostic switches may be manipulated to send the message to the controller  9 .  
         [0028]     The controller  9  may also refer to different systems as part of the process of transitioning from the normal vehicle to clutch install mode as a check. The controller  9  could enter the clutch install mode in response to the initiation sequence, for example, by also referencing an engine mode, ABS mode, hours of operation, transmission mileage, and/or number of ignition cycles. If for example, the hours of operation, transmission mileage, and ignition cycles are zero, then the controller  9  will recognize that the clutch has not yet become operational and will enter the clutch install mode.  
         [0029]     Once the clutch install mode is entered, the engine may be driven to the speed needed to unlock the locking device, such as by shearing the pin, so that the clutch becomes operational. The engine may be commanded to a desired speed by the controller  9  sending an engine speed, engine torque, engine speed limit, or engine torque limit command to the engine  2 . Once the clutch become operational, the controller  9  will be restored to the normal vehicle operating mode.  
         [0030]     The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.