Abstract:
An improved belt clutch engages to couple one shaft to at least one other shaft and disengaged to decouple the shafts. Known belt clutches fail to smoothly and completely disengage the belt from traction pulleys on the shafts and drag results. The improved belt clutch includes rollers outlining the engaged belt and constrain the disengaged belt to smoothly and completely disengage the belt from the traction pulleys. The new improved belt clutch provides, among other things, higher efficiency when driven in either direction and smoother operation when engaged or disengaged at high speed than prior art belt clutches.

Description:
The present application claims the priority of U.S. Provisional Patent Application Ser. No. 61/099,908 filed Sep. 25, 2008, which application is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Present invention relates in general to belt clutches and in particular to apparatus for reducing drag when a belt clutch is disengaged. 
     Belt clutches engage traction pulleys to transmit torque from one shaft to at least one other shaft and disengages to stop the torque from being transmitted. Some known belt clutches that are engaged by either moving an idler pulley against a belt to tighten it around the traction pulleys and disengaged by moving it away to loosen the belt. Other belt clutches are engaged by moving one of the traction pulleys away from the other traction pulley and disengaged by moving the traction pulleys together. Both types of belt clutches share a common problem. When the clutch is disengaged, the belt is normally still in contact with belt surfaces of the traction pulleys which are moving at different speeds. This creates a significant amount of undesirable drag and belt wear. 
     If an enclosure is correctly positioned around the perimeter of the belt of an engaged belt clutch, when the belt clutch is disengaged, the inside surface of the enclosure will constrain the belt in a position which causing the belt to separate from the traction pulleys. This allows the traction pulleys to rotate freely without dragging on the belt and provides a very simple and efficient combination clutch and speed reducing or speed increasing, power transmission device. 
     However, the mere presence of an enclosure around the belt still has disadvantages. When the belt is disengaged at high speed and moves out against the enclosure, the belt hits some parts of the stationary enclosure, causing the belt to rapidly bounce around between the pulleys and the enclosure, causing vibration, noise, added wear, heat, and loss of efficiency. Accordingly, a need remains for a simple belt clutch mechanism which biases the belt away from the traction pulleys and eliminates the belt drag and vibration when disengaged or being disengaged during operation up to its rated speed. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing an improved belt clutch which engages to couple one shaft to at least one other shaft and disengages to decouple the shafts. Known belt clutches fail to smoothly and completely disengage the belt from traction pulleys on the shafts and drag results. The improved belt clutch includes rollers which outline the engaged belt and constrain the disengaged belt to smoothly and completely disengage the belt from the traction pulleys. The new improved belt clutch provides, among other things, higher efficiency when driven in either direction and smoother operation when engaged or disengaged at high speed than prior art belt clutches. 
     In accordance with one aspect of the invention, there is provided a belt clutch comprising a first traction pulley, a second traction pulley, and a belt coupling the traction pulleys. The belt is disengaged by moving at least one of the traction pulleys toward the other traction pulley. Constraints reside outside the belt, spaced at least about one belt thickness outside the belt when the belt clutch is engaged (i.e., under tension due to separation of the traction pulleys). The constraints preferably comprise a first constraint partially circling the first traction pulley and reaching toward the second traction pulley and a second constraint partially circling the second traction pulley and reaching toward the first traction pulley. The inside surfaces of both halves of the partial enclosure provide a low friction inside surface for contact with the outside surface of the belt so that the belt slides gently to a stop when it is disengaged from the traction pulleys and moves out against the enclosures. Wherever the enclosure exists, it should be at least about the thickness of the belt away from the traction pulleys and there should be at least a partial rim around each side of the enclosure extending toward the inside (the traction pulley side) of the enclosure at least about the thickness of the belt. The distance between the inside of the rim on one side of the enclosure and the inside of the rim on the other side should be slightly larger than the width of the belt to keep the belt in line with the traction pulleys but not prevent it from moving back and forth in the enclosure on its own power when the clutch is engaged and disengaged. In the disengaged position, the parts of the enclosure around the belt must be positioned so that the belt stays tight against them preventing the belt from dragging against the traction pulleys. 
     In accordance with yet another aspect of the present invention, there is provided a belt clutch including bearings (or rollers) for constraining the disengaged belt. The rollers may be mounted to a housing or other element of the belt clutch assembly and located in the correct positions to cause the belt to separate from the traction pulleys and to allow the belt to glide to a stop more slowly when released at high speed. This embodiment, like the previous one, allows the belt clutch to be driven in either direction under full rated load with comparable efficiency. But it can also be quickly disengaged during no load conditions up to its rated speed and it will smoothly come to rest against the rollers completely away from the rotating traction pulleys. 
     In accordance with yet another aspect of the present invention, there is provided a belt clutch employing one idler pulley and translationally fixed traction pulleys. The idler pulley is moved towards the belt to tighten the belt and engage the belt clutch. This embodiment is preferred for applications where the input and output shafts cannot move with respect to each other and the torque is not transmitted through the side of the belt that rolls over the idler pulley. 
     In accordance with another embodiment of the present invention, there is provided an automatic, bi-directional belt clutch employing a single actuator to move two idler pulleys together against the outside surfaces of the belt to engage the clutch, and away from each other to disengage the clutch. The two idler pulleys and the actuator form a shuttle which is free to float in a grove which is approximately perpendicular to a line between the centers of the two traction pulleys. With no torque applied to the clutch the actuator moves the two idler pulleys to a fixed position that partly tightens the belt around the two traction pulleys and causes the pulleys to rest in a position about equidistant from the line between the centers of the two traction pulleys. Therefore, when torque is applied to the drive pulley, the part of the belt placed in tension by the traction pulleys tries to straighten out and pushes the shuttle in its direction which increases the tension on the other side of the belt. This action is highly desirable because it automatically increases the belt tension on the lower tension side of the drive as the torque increases and lowers the tension as the torque decreases which lowers belt wear and increases efficiency. It can be seen from the description of the prior art and the above summary of the present invention, how this new concept of a belt drive clutch with a low friction, belt capturing enclosure and an automatic, bi-directional belt tensioning devise can overcome the disadvantages of the frictional drag and other limitations associated with the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1A  is an engaged prior art belt clutch. 
         FIG. 1B  is a disengaged prior art belt clutch. 
         FIG. 2A  is an example of a first embodiment of the present invention having a low friction inner surface to constrain the belt during disengagement, in the disengaged position. 
         FIG. 2B  is an example of the first embodiment of the present invention having low friction pads on the inner surface to constrain the belt causing the belt to separate from the traction pulleys in the disengaged position. 
         FIG. 2C  is a cross-sectional view of a belt enclosure, low friction pad, and belt taken along line  2 C- 2 C of  FIG. 2B . 
         FIG. 3A  is an example of the first embodiment of the present invention having rollers, in the engaged position. 
         FIG. 3B  is an example of the first embodiment of the present invention having rollers, in the disengaged position. 
         FIG. 4A  is a second embodiment of the present invention, with one idler pulley, in the engaged position. 
         FIG. 4B  is the second embodiment of the present invention, with one idler pulley, in the disengaged position. 
         FIG. 5A  is a third embodiment of the present invention, with two cooperating idler pulleys, in the disengaged position. 
         FIG. 5B  is the third embodiment of the present invention, with two cooperating idler pulleys, in the engaged position with no torque applied. 
         FIG. 5C  is the third embodiment of the present invention, with two cooperating idler pulleys, in the engaged position with torque applied. 
         FIG. 6  shows a three speed hybrid transmission according to the present invention with direct drive capability for an internal combustion engine or a large electric motor, the hybrid transmission comprising three belt clutches each with different reduction ratios. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     A prior art belt clutch  10  is shown engaged in  FIG. 1A , and disengaged in  FIG. 1B . The belt clutch  10  includes traction pulleys  14  and  16  on shafts  18  and  20  respectively, and a belt  12  coupling the traction pulleys  14  and  16 . When the traction pulleys  14  and  16  are moved closer together to disengage, the belt  12  attempts to assume a round shape. Unfortunately, the belt generally remains in contact with the traction pulleys at locations  22   a  and  22   b , and drag results causing wear on the belt and lost efficiency. 
     A belt clutch assembly  24   a  of a first embodiment of the present invention with enclosures  26   a  and  26   b  having a low friction inner surface  25  to constrain the belt  12  when disengaged from the traction pulleys  14  and  16  is shown in  FIG. 2A  and an improved belt clutch  24   b  with the enclosures  26   a  and  26   b  having low friction pads  27  on the inner surface to constrain the belt  12  causing the disengaged belt  12  to separate from the traction pulleys  14  and  16  is shown in  FIG. 2B . The enclosures  26   a  and  26   b  restrict the outward movement of the belt  12  around the traction pulleys  14  and  16  when they move closer together and the belt  12  is disengaged. After belt  12  is disengaged, the belt  12  resides tightly against the inner surface  25  of enclosures  26   a  and  26   b  to keep the belt  12  completely separated the traction pulleys  14  and  16  to eliminate any belt drag. The low friction inner surface  25  preferably has a coating to reduce friction and the low friction pads  27  are preferably a low friction material to reduce drag or are coated with a low friction material to reduce drag. The enclosures  26   a  and  26   b  are preferably translationally fixed to the traction pulley  14  and the traction pulley  16  respectively. One or both of the traction pulley  14  and the traction pulley  16  are moveable to disengage the belt clutch  24   a  and  24   b  and the corresponding enclosure  26   a  and/or  26   b  preferably moves with the traction pulley  14  and/or the traction pulley  16  to maintain the position of the low friction inner surface  25  or the low friction pads  27  to the traction pulley  14  and/or  16 . 
     A cross-sectional view of the belt enclosure  26   b , the low friction pad  27 , and the belt  12  taken along line  2 C- 2 C of  FIG. 2B  is shown in  FIG. 2C . The belt enclosure  26   b  includes rims  26 ′ extending toward the belt  12  on each side of the enclosure  26   b  which center the belt  12  in the enclosure  26   b.    
     A belt clutch assembly  30  having rollers, of the first embodiment of the present invention, is shown in the engaged position in  FIG. 3A  and in the disengaged position in  FIG. 3B . The traction pulley  14  is fixedly mounted to shaft  18  which is rotatably mounted to a member  34  of the belt clutch assembly  30 , and the traction pulley  16  is fixedly mounted to shaft  20  which is rotatably mounted to a member  36  of the belt clutch assembly  30 . One or both of the members  34  and  36  are moving members and are kept in alignment with each other by a guide bar  38  attached to the moving member  36  sliding in a guide slot  39  in moving member  34 . In the engaged position, the belt clutch assembly  30  transmits power in either direction, from the shaft  18  to the shaft  20  or from the shaft  20  to the shaft  18 , through traction pulleys  14  and  16  and belt  12 . When engaged, the traction pulley  14  separates from the traction pulley  16  far enough to tighten the belt  12  on the traction pulleys  14  and  16  to the correct tension to transmit the required torque between traction pulleys  14  and  16 . Preferably, the member  34  separates from the member  36  as the traction pulley  12  separates from the traction pulley  16  to maintain the spacing between the members  34  and  36  and the traction pulleys  14  and  16  respectively. 
     Constraints comprising rollers  32   a  and  32   b  are positioned around the belt  12  and may be attached to the member  34  and  36  respectively. The rollers  32   a  and  32   b  are preferably separated from the belt  12  by about one belt thickness when the belt  12  is in tension (i.e., when the clutch is engaged). Adjacent rollers  32   a  and  32   b  on each members  34  and  36  are spaced d 1  apart, and adjacent roller  32   a  and  32   b  across the members  34  and  36  are spaced d 2  apart, and are close enough together to prevent the belt  12  from bulging outward between adjacent rollers  32   a  and  32   b . In the disengaged position, the traction pulleys  14  and  16 , and the moving members  34  and  36 , are moved together to remove tension from the belt  12 , and the belt  12  moves outward and against the rollers  32   a  and  32   b . Because the belt  12  is constrained by the rollers  32   a  and  32   b , resulting in very little resistance to tangential motion of the belt  12  when the belt  12  contacts the rollers  32   a  and  32   b , at high speed the belt  12  moves away from the traction pulleys  14  and  16  and the belt  12  assumes it&#39;s position against the rollers  32   a  and  32   b  and smoothly comes to rest. 
     While the first embodiment is described herein as including one or two moving traction pulleys, any belt clutch assembly having two or more traction pulleys where one or more of the traction pulleys are moveable to remove tension from a belt, is intended to come within the scope of the present invention. 
     A second embodiment of a belt clutch assembly  40  according to the present invention, with only one idler pulley  44 , is shown in  FIG. 4A  in the engaged position and in  FIG. 4B  in the disengaged position. The single idler pulley  44  is mounted to a translating shaft  42  to engage and disengage the belt clutch assembly  40 . Rollers  32  are positioned around the belt  12  and may be attached to a clutch housing  41  or otherwise mounted. The rollers  32  are separated from the belt  12  by about one belt thickness when the belt  12  is in tension (i.e., when the clutch is engaged). In the disengaged position, the idler pulley  44  is moved away from the belt  12  to remove tension from the belt  12 , and the belt  12  moves outward and against the rollers  32 , but may remain in contact with the idler pulley  44 . Because the portion of the belt  12  between the traction pulleys  14  and  16  and opposite the idler pulley  44  is constrained by the rollers  32 , the belt  12  moves away from the traction pulleys  14  and  16 . Because the belt  12  is constrained by the rollers  32  resulting in very little resistance to tangential motion of the belt when the belt contacts the rollers  32 , the belt  12  smoothly assumes its disengaged position against the rollers  32 . 
     In  FIG. 4A  the pulley  44  has been moved into belt  12  with enough force to provide adequate belt tension to transmit the required torque from traction pulley  14  to traction pulley  16  in the counter clockwise direction, or from traction pulley  16  to traction pulley  14  in the clockwise direction, which produces the maximum belt tension in the straight (or opposite the idler pulley  44 ) side of the belt  12 . However, when torque is applied to traction pulley  14  or  16  in the opposite direction, which produces maximum tension in the idler pulley  44  side of the belt  12 , the force on the idler pulley  44  must be greatly increased to allow transmission of the same amount of torque. This increased force on idler pulley  44  decreases the overall efficiency of the drive. Therefore, belt clutch assembly  40  is only recommended for applications where the idler pulley  44  is on the low tension side of the belt  12 . 
     A third embodiment of the belt clutch assembly  50  according to the present invention, with two cooperating idler pulleys  52   a  and  52   b  rotatably mounted on shafts  54   a  and  54   b , is shown in  FIG. 5A  in the disengaged position, and in  FIG. 5B  and  FIG. 5C  in the engaged position. Rollers  32  are positioned around the belt  12  and may be attached to a clutch housing  51  or otherwise mounted. The rollers  32  are separated from the belt  12  at the closest point by about one belt thickness when the belt  12  is in tension (i.e., when the clutch is engaged). The belt clutch assembly  50  is similar to the belt clutch assembly  40  above, except that the single idler pulley  44  is replaced by the two cooperating idler pulleys  52   a  and  52   b  on opposite ends of an actuator  56 . When the clutch is engaged and no torque is applied the actuator  56  and the pulleys  52   a  and  52   b  are biased to a centered position by the belt  12 , but will move back and forth in a direction that is about perpendicular to the center line between the two shafts  18  and  20  when torque is applied in different directions. The actuator  56  and the pulleys  52   a  and  52   b  are about laterally centered on an actuator centerline  57  approximately centered between adjacent edges of the two traction pulleys  14  and  16 , but generally a little closer to the smaller of the two pulleys. 
     In  FIG. 5A , the actuator  56  has separated the idler pulleys  52   a  and  52   b  to disengage the belt clutch assembly  50 . Because the portions of the belt  12  between and around the traction pulleys  14  and  16  are constrained by the rollers  32 , the belt  12  is held away from the traction pulleys  14  and  16 . Because the belt  12  is constrained by the rollers  32  during disengagement, the belt  12  smoothly assumes its disengaged position against the rollers  32 . The rollers  32  are positioned (both location and spacing) around the belt  12  so that when the belt  12  is disengaged it makes contact with all of the rollers  32  and is completely out of contact with the traction pulleys  14  and  16 . 
     In  FIG. 5B  the actuator  56  pulls the idler pulleys  52   a  and  52   b  together until the belt  12  is pulled against the traction pulleys  14  and  16  and there is no slack but there is still very little tension in the belt  12 . 
       FIG. 5C  shows the belt drive assembly  50  in operation in the clockwise direction with traction pulley  14  driving traction pulley  16  under a heavy load. The increased tension in the lower side of the belt  12  which is pressed against idler pulley  52   b  is pushing the actuator  56  and the two idler pulleys  52   a  and  52   b  toward pulley  52   b  with the two idler pulleys  52   a  and  52   b  maintaining the same separation with respect to each other as in  FIG. 5B . The geometry of the upper and lower paths of the belt  12  is such that motion of the idler pulleys  52   a  and  52   b  away from center increases the total path of the belt  12 , and thus increases tension in the belt  12 . This is seen in comparing  FIGS. 5B and 5C  where the lower path is at shallow angles and approaches a minimum length straight flat path, and the upper path assumes larger angles and the path length continues to grow as the idler pulley  52   a  moves downward. This increases the tension in the belt  12  as the torque on the traction pulley  14  increases, which keeps the belt  12  from slipping under heavy load, and also increases efficiency by decreasing the tension in the belt  12  under light load. If the direction of the torque reverses, the actuator  56  slides in the opposite direction and performs the same tension limiting function providing automatic and completely bi-directional and torque compensating when engaged but drag free when disengaged. 
     A three speed hybrid transmission  60  with direct drive capability for an internal combustion engine  80  or a large electric motor (not shown), comprising three belt clutches  62 ,  64 , and  66  each with different reduction ratios, is shown in  FIG. 6 . Each of the belt clutches  62 ,  64 , and  66  are preferably of the type described above as belt clutch assembly  50 , the third embodiment of the belt clutch according to the present invention, with actuator  56  operating two idler pulleys  52   a  and  52   b  (see  FIG. 5 ). The belt clutches  62 ,  64 , and  66  are fixedly connected together with spacers  72  between them to create space for actuators  56 , they and share a common input shaft  68  and an output (or drive) shaft  76 . The output shaft  76  is operatively connected to at least one wheel to drive a vehicle. The case of an electric motor  70  is fixedly mounted to the housing of belt clutch  66  so that with the proper coupling, the electric motor  70  can drive shaft  68  efficiently. A bell housing  82  of the engine  80  is also fixedly mounted between the engine  80  and the housing of belt clutch  66  so that with the proper coupling, the engine  80  can also the output shaft  76  efficiently. The engine  80  must be coupled to the output shaft  76  through a uni-directional clutch (not shown), such as a clutch bearing or the like, so that when the electric motor  70  alone is driving shaft  76  through one of the belt clutches  62 ,  64 , or  66 , the engine  80  does not need to turn. If the engine  80  is replaced by a second electric motor, the clutch bearing may not be necessary. 
     The combination of elements shown in  FIG. 6  represents a very efficient, plug-in, parallel hybrid drive system, because the electric motor  70  can very efficiently drive a vehicle up to speed, engaging each of the different ratio belt clutches  62 ,  64 , and  66 , one at a time, and when the high gear belt is engaged, engine  80  can be started and/or engaged and both the electric motor  70  and the engine  80  can drive the vehicle. When the engine  80  is engaged the high gear clutch can be disengaged and the engine  80  can drive the vehicle at high speed without any drag from the transmission  60 . This hybrid drive system  60  needs no torque converter or any other slipping clutch type of energy wasting device because the engine  80  is never used to accelerate the vehicle from a standing start or at low speed. With an adequate battery pack this vehicle could be driven efficiently in the city for a long distance without ever turning on the engine  80 . 
     While the hybrid transmission  60  is described above in the context of a hybrid electric/internal combustion vehicle, a transmission comprising at least two belt clutches as described herein may have other applications, such as an electric only vehicle, and an transmission comprising at least two belt clutches as described herein is intended to come within the scope of the present invention. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.