Abstract:
A two speed belt drive system comprising a crankshaft module ( 200 ) comprising a first pulley ( 213 ) engaging a first belt ( 10 ) and a second pulley ( 206 ) engaging a second belt ( 20 ), a clutch module ( 100 ) engaging the first belt and the second belt, the second belt ( 20 ) engaged to an engine accessory, the crankshaft module having a clutch spring ( 205 ) for frictional driving of the second pulley, and the clutch module having a clutch ( 57 ) for selectively driving the second belt.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a two speed belt drive system comprising a crankshaft module comprising a first pulley engaging a first belt and a second pulley engaging a second belt, a clutch module engaging the first belt and the second belt, the second belt engaged to an engine accessory, the crankshaft module having a clutch spring for frictional driving of the second pulley, and the clutch module having a clutch for selectively driving the second belt. 
       BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to automotive accessory belt drive systems (ABDS drives). 
         [0003]    Representative of the art is U.S. Pat. No. 7,798,928 which discloses a dual ratio belt drive system comprising a clutch unit mounted directly to a driver rotating shaft, a one-way clutch mounted directly to the driver rotating shaft, a plurality of rotating accessories rotatably connected to the clutch unit and rotatably connected to the driver rotating shaft through the one-way clutch such that the accessories are driven by the clutch unit at a first speed ratio and driven directly by the driver rotating shaft through said one-way clutch at a second speed ratio, with the clutch unit operating at a predetermined value of an engine operating condition thereby defining the transition between the first and second speed ratios, and the clutch unit being engaged at engine start. 
         [0004]    What is needed is a two speed belt drive system comprising a crankshaft module comprising a first pulley engaging a first belt and a second pulley engaging a second belt, a clutch module engaging the first belt and the second belt, the second belt engaged to an engine accessory, the crankshaft module having a clutch spring for frictional driving of the second pulley, and the clutch module having a clutch for selectively driving the second belt. The present invention meets this need. 
       SUMMARY OF THE INVENTION 
       [0005]    The primary aspect of the invention is a two speed belt drive system comprising a crankshaft module comprising a first pulley engaging a first belt and a second pulley engaging a second belt, a clutch module engaging the first belt and the second belt, the second belt engaged to an engine accessory, the crankshaft module having a clutch spring for frictional driving of the second pulley, and the clutch module having a clutch for selectively driving the second belt. 
         [0006]    Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
         [0007]    The invention comprises a two speed belt drive system comprising a crankshaft module comprising a first pulley engaging a first belt and a second pulley engaging a second belt, a clutch module engaging the first belt and the second belt, the second belt engaged to an engine accessory, the crankshaft module having a clutch spring for frictional driving of the second pulley, and the clutch module having a clutch for selectively driving the second belt. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
           [0009]      FIG. 1  is a front view of a belt drive system. 
           [0010]      FIG. 2A  is a front view of the crankshaft module. 
           [0011]      FIG. 2B  is a rear view of the crankshaft module. 
           [0012]      FIG. 3  is a cross-sectional view of the crankshaft module. 
           [0013]      FIG. 4  is an exploded view of the crankshaft module. 
           [0014]      FIG. 5  is a rear view of the crankshaft damper assembly. 
           [0015]      FIG. 6  is a side view of the isolating spring. 
           [0016]      FIG. 7A  is a front view of the spring carrier. 
           [0017]      FIG. 7B  is a rear view of the spring carrier. 
           [0018]      FIG. 8  is a front view of the clutch spring. 
           [0019]      FIG. 9  is a front view of the pulley. 
           [0020]      FIG. 10  is a cross-sectional view of the secondary clutch module. 
           [0021]      FIG. 11  is a chart of system operation. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]      FIG. 1  is a front view of a belt drive system. System  1000  comprises a front-end accessory drive for an internal combustion engine (E). In  FIG. 1  the front of the engine is shown and the rest is omitted for clarity. 
         [0023]    The inventive system  1000  comprises a belt  10  and a second belt  20 . Various engine and vehicle accessory components are driven by belt  20 . Belt  10  and belt  20  are each a multi-ribbed belt. This means the ribs extend in parallel along the endless direction of the belt. 
         [0024]    Belt  10  is only entrained about clutch module  100 , crankshaft module  200  and tensioner  30 . Belt  10  transmits power from crankshaft module  200  to clutch module  100 . Belt  20  is entrained about crankshaft module  200 , clutch module  100  and the accessories including the alternator  40 , power steering pump  50  and water pump  60 . Belt  20  also engages tensioner  70 , idler  80  and idler  90 . Tensioner  70  maintains proper load in belt  20 . 
         [0025]    Tensioner  30  maintains proper belt load in belt  10 . Tensioner  70  and tensioner  30  are each known in the art. Proper belt load prevents belt slip and noise. 
         [0026]      FIG. 2A  is a front view of the crankshaft module.  FIG. 2B  is a rear view of the crankshaft module. FIG.  3  is a cross-sectional view of the crankshaft module. Referring to  FIG. 3 , crankshaft module  200  comprises damper assembly  201 , hub  300 , isolating spring  202 , spring carrier  203 , bushing  204 A, bushing  204 B, clutch spring  205 , pulley  206 , bearing  207 , bearing  208 , retainer  209 , shield  210 , retainer  211 . Damper assembly  201  comprises inertia member  2010  and elastomeric member  212 . Elastomeric member  212  comprises a resilient material which allows slight incremental oscillatory movement of inertia member  2010  relative to hub  300 , which in turn damps crankshaft oscillations caused by cylinder firing events. Isolating spring  202  is loaded in the unwinding direction. Shield  210  prevents debris from entering the device. 
         [0027]    Inertia member  2010  further comprises pulley  213 . Pulley  213  and pulley  206  engage belt  10  and belt  20  respectively. Hub  300  comprises spring receiving portion  301  and spring stop  302 . An end  2020  of isolating spring  202  engages stop  302 . Isolating spring  202  is nested within spring receiving portion  301 . Hub  300  is rigidly connected to an engine crankshaft. 
         [0028]      FIG. 6  is a side view of the isolating spring. Isolating spring  202  engages spring carrier  203 . End  2021  of spring  202  engages stop  2030 , see  FIG. 7B . Spring carrier  203  further comprises outer cylindrical surface  2031 . Clutch spring  205  frictionally engages surface  2031 . 
         [0029]    End  2050  of spring  205  engages receiving portion  2032 , see  FIG. 7A . Pulley  206  comprises inner surface  2061  and outer surface  2060 , see  FIG. 9 . Clutch spring  205  frictionally engages inner surface  2061 .  FIG. 4  is an exploded view of the crankshaft module. 
         [0030]    In operation hub  300  drives isolating spring  202  in an unwinding direction. End  2020  of spring  202  engages stop  302 . Spring  202  in turn drives spring carrier  203 . Spring carrier  203  drives clutch spring  205  in an unwinding direction. This causes clutch spring  205  to radially expand against surface  2061 , which causes spring  205  to frictionally engage and drive pulley  206 . When clutched in this manner, pulley  206  rotates at the same speed as hub  300 . Pulley  213  also rotates at the same speed as pulley  206  in this mode. 
         [0031]    When clutch spring  205  is not driving pulley  206 , spring  205  radially contracts thereby disengaging from surface  2061 . Pulley  206  can then overrun and rotate faster than hub  300 . This condition occurs during engine deceleration for example, when the belt drive system inertia prevents deceleration of the belt drive system at the same rate as the engine. Each of the accessories, such as the alternator, has an inertia. The inertia may prevent the accessory from decelerating as quickly as the engine, at which point it is said to overrun the engine. 
         [0032]    Clutch module  100  is described in U.S. Pat. No. 7,798,928, for example see  FIG. 9 . U.S. Pat. No. 7,798,928 is incorporated herein in its entirety by reference.  FIG. 10  is a cross-sectional view of the clutch module  100 .  FIG. 10  depicts the upper half of a cross-sectional view, the lower half being a mirror image and symmetric with the upper half. Clutch module  100  comprises an electromagnetic clutch with coil  57 . Coil  57  is attached to a stationary housing  77  thru back plate  75 . Housing  77  does not rotate and is used to mount the clutch to a surface, for example, an engine surface. Rotor  73  with pulley  71  is rotatably installed on ball bearing  55  on housing  77 . Bearing  55  comprises a ball bearing but may also comprise any suitable bearing known in the art. Clutch plate  61  is moveably attached to second pulley  69  with shafts  67 , for example, three shafts  67  symmetrically spaced about pulley  69 . Rubber pads  65  bias plate  61  away from rotor  73  when coil  57  is not energized. This method of attachment allows plate  61  to move axially from pulley  69  towards rotor  73  when the coil  57  is energized and the clutch is thereby engaged. Pulley  69  also comprises hub  53  by which pulley  69  is directly connected to an accessory, such as a power steering pump shaft. Coil  57  is contained within a width of pulley  71  and plate  61  is contained within a width of pulley  69 . Coil  57  is connected to an engine ECU system  400 , known in the art, whereby engine speed signals can be used to control and thereby activate or deactivate coil  57  according to the switching speed. Coil  57  is connected to the vehicle electrical system, known in the art. 
         [0033]    The inventive system comprises two operating modes. In operating Mode  1 , secondary clutch module  100  is open or released, namely, electromagnetic clutch coil  57  is de-energized. As a result pulley  206  acts as the driver for the belt drive system through belt  20 . The speed of the belt drive is a function of the diameter of pulley  206 . Pulley  206  rotates at the same RPM speed as the engine crankshaft. This is typical during off-idle conditions. 
         [0034]    Power from the engine crankshaft flows from hub  300  through stop  302  to isolating spring  202 , then to spring carrier  203 , then to cutch spring  207  and then to pulley  206  and on to belt  20 . Pulley  213  drives belt  10 , which engages secondary clutch module  100 . 
         [0035]    Crankshaft torsional vibrations are isolated from pulley  206  through operation of isolating spring  202 . 
         [0036]    Spring  202  has a torsional spring rate, which allows torsional load vibrations to be absorbed by the spring  202 . Since the crankshaft torsional vibrations are thereby isolated from pulley  206 , the vibrations are also isolated from the belt drive system. 
         [0037]    In operating Mode  2 , secondary clutch module  100  is closed or locked, that is, the electromagnetic clutch coil is activated which locks pulley  69  to pulley  71 . In this mode pulley  213  is the driver for the belt drive system. The speed of the drive is a function of the diameter of pulley  213 . Pulley  213  has a greater diameter than pulley  206 . Pulley  213  drives belt  10 . Belt  10  drives the secondary clutch module  100 . Secondary clutch module then drives belt  20 . Due to the difference in diameter between pulley  213 , pulley  206  and the secondary clutch module  100 , the speed of belt  20  is increased and pulley  206  rotates faster than the engine crankshaft. Pulley  206  is said to “overrun” the hub  300  (crankshaft). Clutch spring  205  is disengaged from surface  2061  in the overrun condition and is considered “open”. Mode  2  is used when the engine speed is low, such as at idle. An increase in belt speed allows engine idle speed to be decreased allowing the belt to maintain proper speed for the alternator and air conditioning compressor, for example. A lower engine idle speed reduces fuel consumption. 
         [0038]      FIG. 11  is a chart which provides an example of how the system operates. The clutch module drive ratio versus engine speed is illustrated. The drive ratio is the ratio between pulley  206  and pulley  71 . 
         [0039]    The desired switching speed centers a speed zone where the system may operate in either mode. The speed zone range serves to limit repeated switching between modes as the engine speed varies around the switching speed, for example, in a range of approximately 200 RPM. At idle the accessory drive is in mode  2  and clutch  57  is engaged, thereby driving belt  20  with pulley  71 . Pulley  206  is in an overrun condition in mode  2 , with spring  205  disengaged. 
         [0040]    As engine speed increases and approaches the desired switching speed, clutch module  100  switches from mode  2  to mode  1  when clutch  57  de-energizes and disengages. The accessories are driven by pulley  206  in mode  1 . Use of pulley  206  reduces the overall accessory speed because it has a smaller diameter than pulley  71 . As engine speed decreases below the switching speed, clutch module clutch  57  engages, thereby switching from mode  1  to mode  2 , which in turn increases overall accessory speed in mode  2  and during idle. 
         [0041]    For example if the switching speed is 1200 rpm, when the system is in mode  2 , the switch from mode  2  to mode  1  occurs approximately 100 rpm above the switching speed as engine speed increases. Conversely, when the system is in mode  1 , the switch from mode  1  to mode  2  occurs approximately 100 rpm below the switching speed as engine speed decreases. 
         [0042]    In a typical situation, engine idle speed can be reduced by 50 to 100 RPM by use of the inventive system. For example, a typical engine idle speed can be approximately 600 RPM. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Size 
                 Speed Mode 
                 Speed Mode 
               
               
                   
                 Pulley 
                 (mm) 
                 1 (RPM) 
                 2 (RPM) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 213 Crankshaft 
                 147.8 
                 1200 
                 1200 
               
               
                   
                 206 Crankshaft 
                 88.0 
                 1200 
                 1831 
               
               
                   
                 69 Clutch module 
                 127.1 
                 1395 
                 1395 
               
               
                   
                 71 Clutch module 
                 115.5 
                 914.3 
                 1395 
               
               
                   
                 Belt 20 speed (m/s) 
                   
                 5.52 
                 8.44 
               
               
                   
                   
               
             
          
         
       
     
         [0043]    By way of example and not of limitation, Table 1 illustrates a set of example design parameters for the system. 
         [0044]    Mode  2  allows accessories to operate at a speed that enables them to function properly and efficiently at lower engines speeds, for example, 50 RPM to 100 RPM below a typical idle speed, for example, 600 RPM. Mode  1  slows the accessories but still allows accessories to operate at a speed that enables them to function properly and efficiently for off-idle engine speeds above the switching speed. Slowing the accessories reduces overall fuel consumption and vehicle emissions, improves the efficiency of the accessories, and improves vehicle acceleration performance. Speeding up the accessories at idle allows for overall reduction of engine idle speed which reduces fuel consumption and vehicle emissions. 
         [0045]    Although forms of the invention have been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.