Abstract:
A hybrid power train for farm tractors, wherein the elements defining at least one of the electric machines are housed in a structural casing formed in one piece. The structural casing forms an integral part of the supporting structure of the tractor in the form of a half-shell open on one side, so as to permit assembly of an insulating element, a stator, and a shaft fitted with a respective rotor to form the electric machine part of the hybrid power train. The diesel engine of the agricultural tractor is mechanically connected to the Power take-off mechanism by routing the PTO shaft through a number of hollow shafts for transmitting power from the diesel engine to and from the two electric machines by means of a conventional epicyclic gear train.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a hybrid power train coupling mechanical and electrical power and, more particularly, to forming the hybrid power train in a configuration that can be utilized in agricultural tractors.  
         [0002]     Hybrid power trains, in which part of the energy produced by an internal combustion engine is converted into electric energy to improve control of the power train, are known in the art. A hybrid power train of this type is described and claimed in European Patent No. EP-01203947.5, the contents of which are hereby incorporated herein by reference. One of the problems posed by this type of power train is the bulk of the system, which generally renders the hybrid power train system unsuitable for use on farm tractors.  
         [0003]     Moreover, known hybrid power trains are difficult to produce and involve a large number of component parts, thus increasing the cost and complexity as compared with conventional power trains for agricultural tractors. Known hybrid engines, in fact, comprise a housing containing the two electric motors, each of which in turn comprises a respective casing.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the present invention to provide a hybrid power train capable of practical utilization in an agricultural tractor.  
         [0005]     It is an advantage of this invention to provide a hybrid power train that is more compact and easier to manufacture than heretofore known in the art.  
         [0006]     It is a feature of this invention to provide a hybrid power train system in which the known electric motor casings are replaced with structural casings.  
         [0007]     It is another advantage of this invention that the structural casings replacing the known electric motor casings are made of cast iron.  
         [0008]     It is still another advantage of this invention that the formation of the structural casings from cast iron enables the power of the electric motors to be increased for a given size of the power train.  
         [0009]     It is another feature of this invention that the combining an increased electric power and compactness of the structural casings permit the utilization of the hybrid power trains on farm tractors.  
         [0010]     It is another object of this invention to provide a solution to the problem of connecting the diesel engine mechanically to the power take-off mechanism on an agricultural tractor.  
         [0011]     It is yet another advantage of this invention that by using a small number of easy-to-assemble component parts that manufacture of the electric machines for the hybrid power train is greatly simplified.  
         [0012]     It is still another feature of this invention that the disposal of heat generated by the electric machines can be accomplished either directly to the outside or by means of coolant circulated in channels formed in the structural casings.  
         [0013]     It is yet another feature of this invention to connect the diesel engine of an agricultural tractor to the PTO by routing the PTO shaft through a number of hollow shafts for transmitting power from the diesel engine and to and from the two electric machines by means of a conventional epicyclic gear train.  
         [0014]     These and other objects, features and advantages are accomplished according to the instant invention by providing a hybrid power train for farm tractors, wherein the elements defining at least one of the electric machines are housed in a structural casing formed in one piece. The structural casing forms an integral part of the supporting structure of the tractor in the form of a half-shell open on one side, so as to permit assembly of an insulating element, a stator, and a shaft fitted with a respective rotor to form the electric machine part of the hybrid power train. The diesel engine of the agricultural tractor is mechanically connected to the Power take-off mechanism by routing the PTO shaft through a number of hollow shafts for transmitting power from the diesel engine to and from the two electric machines by means of a conventional epicyclic gear train. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawing, wherein:  
         [0016]     The Figure is schematic cross-sectional view of a hybrid power train for an agricultural tractor incorporating the principles of the instant invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     A power train  10 , which is a hybrid type, is formed of a diesel engine  11  (not shown) for rotating a shaft  17 ; and a number of units  12 ,  13 ,  14 ,  15 ,  16 , the functions of which are explained in detail below. Working from left to right on the drawing, a connecting/disconnecting unit  12  is depicted. Unit  12  is known in the art and is formed of a first stage  12   a  for connecting and disconnecting the diesel engine  11  to or from the shaft  17 . The first stage  12   a  is engaged or released by the operator by means of a sleeve  18  and a lever  19  operated by conventional actuating means (not shown). To engage and release the first stage  12   a , the sleeve  18  is moved in a direction defined by an axis  20 , which is also the longitudinal axis of symmetry of the shaft  17 .  
         [0018]     Downstream from first stage  12   a , unit  12  further includes a second stage  12   b , also known in the art and formed of a clutch device  21  for connecting and disconnecting the shaft  17  to or from a hollow shaft  22 . By activating a portion  21   b  of clutch device  21  (by known means not shown), shaft  22 , being integral with shaft  17 , is rotated in the same direction as the diesel engine  11 . Conversely, by activating a portion  21   a  of clutch device  21 , the power generated by diesel engine  11  is transmitted to shaft  22  in the opposite direction to before by a set of three intermeshing gears  23 ,  24 ,  25 , of which gear  24  is an idler gear, a shaft  25   a , and gears  25   b  and  25   c . Both stages  12   a ,  12   b  are supported in known manner by a support  27  preferably, though not necessarily, made of cast iron. Hollow shaft  22  houses, coaxially, a shaft  28  for powering a PTO; and shafts  17 ,  22 ,  28  all have the same longitudinal axis of symmetry  20 .  
         [0019]     Unit  13  includes a first electric machine  29  housed in a structural casing  30 , which also houses an electric insulating element  31  on which rests a conventional stator  32 . A known rotor  33  completes electric machine  29 , and is defined by a pack of laminations  33   a  fitted to a shaft  34  supported on two ball bearings  35 ,  36   a . Bearing  35  is housed in a seat  30   a  formed in a wall  30   b  of the structural casing, and bearing  36   a  is housed in a seat  37   a  formed in a plate  37  at an opening  37   c.    
         [0020]     A structural casing  30 , also advantageously, though not necessarily, made of cast iron, is bolted by known means on one side to support  27 , and on the other side thereof to both plate  37  and a structural casing  38  forming part of the next unit  14 . Being open on the side facing unit  14 , the structural casing  30  permits easy assembly of the component parts of electric machine  29 . Two chambers  38   a ,  38   b  are defined inside structural casing  38  of unit  14 , and are separated by a wall  39  having an opening  39   a . The first chamber  38   a  houses an epicyclic gear train  40 , the component parts of which and the way in which they are connected to the other parts of power train  10  are explained in detail below.  
         [0021]     Structural casing  38 , and in particular the second chamber  38   b , houses elements forming part of a second electric machine  41 , which is generally formed of the same component parts as first electric machine  29 . Accordingly, the second electric machine  41  includes an electric insulating element  42 , on which rests a conventional stator  43 , and is completed by a rotor  44  fitted to a shaft  45  supported on two ball bearings  46 ,  47 . Shaft  45  is also hollow and coaxial with axis  20 , and rotor  44  comprises a pack of laminations  44   a . Since the second chamber  38   b  is also open, at least on one side, outwardly towards the next unit  15 , the component parts of second electric machine  41  are assembled easily inside second chamber  38   b.    
         [0022]     As stated above, an actuating means (not shown) operates lever  19  to engage or release the sleeve  18 , which can be released automatically when power train  10  is running, or manually by the user operating a lever (not shown) or a pedal (not shown) to start directly in fully electric mode when the power train  10  is off. When the power train  10  is running, in fact, the tractor hydraulic circuit (not shown) is already pressurized so that enough hydraulic power is available to automatically release sleeve  18  to switch to the fully electric mode. Conversely, when the power train  10  is off, no hydraulic power is available to start directly in fully electric mode, so a manual control must be provided to release sleeve  18 . Otherwise, operation of electric machines  29 ,  41  would rotate shaft  17 , thus resulting in undesired start-up of the diesel engine  11 .  
         [0023]     The epicyclic gear train  40  is formed of a planet carrier  40   a  integral with hollow shaft  22 ; and a number of planet wheels  40   b , each connected to planet carrier  40   a  by a respective spindle  40   c . The epicyclic gear train  40  also includes a sun gear  40   d  integral with hollow shaft  34  of electric machine  29 ; and a ring gear  40   e  integral with hollow shaft  45  of second electric machine  41 . By means of known mechanisms also described in EP-01203947.5, the description of which is incorporated herein by reference, the epicyclic gear train  40  divides and recombines the mechanical power supplied by diesel engine  11 , and the electric power produced by electric machines  29 ,  41 .  
         [0024]     The hollow shaft  45  of the second electric machine  41  provides for actually adding the mechanical energy transmitted to the shaft  45  by the ring gear  40   e  of the epicyclic gear train  40  to the rotational energy supplied by rotor  44 . As stated, structural casing  30 , plate  37 , and structural casing  38  are preferably made of cast iron and connected to one another by known fastening means, such as a number of bolts and respective nuts, so that the structural whole housing the two electric machines  29 ,  41  is extremely compact and solid. The bearing  46  is housed in a seat  46   a  formed in wall  39 , close to opening  39   a ; bearing  47  is housed in a seat  47   a  formed in a wall  48  of the next unit  15 ; and wall  28  has an opening  47   b.    
         [0025]     Unit  15  includes a structural casing  49  in turn forming the wall  48  and housing a conventional HI/LO transmission  50 . The HI/LO transmission  50  rotates a pinion  51  of the rear wheel differential (not shown). More specifically, HI/LO transmission  50  includes two clutch devices  50   a ,  50   b , both for rotating a shaft  52  to which the pinion  51  is fitted. The clutch device  50   a  substantially is formed of a clutch and two gears  53 ,  54 , gear  54  being fitted to shaft  52 . Similarly, device  50   b  is formed of a clutch and two gears  55 ,  56 . Gear  56  is also fitted to shaft  52 , whereas gears  53  and  55  are fitted to a hollow shaft  53   a.    
         [0026]     The angular speed of pinion  51 , therefore, depends on which of the two clutches is engaged, and, therefore, on which of the two pairs of gears  53 ,  54  or  55 ,  56  rotates shaft  52 . In other words, when clutch device  50   a  is engaged, HI mode is engaged and pinion  51  rotates at a high angular speed; and, to rotate pinion  51  at low speed, clutch device  50   a  is simply released and device  50   b  engaged to engage LO mode. Gear  56  always transmits motion to a known device  57  for transmitting motion to the front wheels (not shown). As shown in the accompanying drawing, PTO shaft  28  rotates a gear  58  meshing with a gear  59  for transmitting motion to a shaft controlling auxiliary facilities  60  (shown only partly).  
         [0027]     At unit  16 , shaft  28  is fitted with a PTO clutch  61 ; and unit  16  is also housed in a structural casing  16   a . Structural casings  49  and  16   a  are also advantageously made of cast iron.  
         [0028]     It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. Accordingly, the following claims are intended to protect the invention broadly as well as in the specific form shown.