Abstract:
An agricultural vehicle includes an internal combustion engine, an electric machine for driving one powertrain and a number of devices selectively drivable by the powertrain. The powertrain has a first section associated to the internal combustion engine, a second section and a first clutch for coupling the first and second sections. The electric machine and at least one of the devices are associated to the second section.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The invention described and claimed hereinbelow is also described in European Patent Application EP 11006154.6, filed on Jul. 27, 2011. This European Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an agricultural vehicle and a method of operation thereof. 
         [0003]    Agricultural vehicles such as tractors, combine harvesters, forage harvesters and like have powerful internal combustion engines that are not operating continuously at their maximum rated power or at a fuel-efficient power level. It has been found that in only about 80% of the time such a vehicle and its driver spend working on a field a substantial amount of the engine power is indeed used. The remaining 20% of the time are spent waiting for other vehicles to finish their jobs, or in auxiliary activities such as maneuvering, coupling and uncoupling implements or trailers. All these activities require only a minute fraction of the power the internal combustion engine is capable of delivering. 
         [0004]    Being optimized for high power operation, most internal combustion engines have mediocre efficiencies when running at low power, and considerable economies in fuel might be achieved if efficiency at low power could be improved. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention overcomes the shortcomings of conventional operation of agricultural vehicles, such as those mentioned above. 
         [0006]    To that end, the invention provides an agricultural machine which operates efficiently both at high and low power levels, and a method of operation therefore. 
         [0007]    In an embodiment, the invention provides an agricultural vehicle comprising an internal combustion engine, an electric machine for driving one powertrain and a plurality of devices selectively drivable by the one powertrain. The powertrain comprises a first section associated to the internal combustion engine, a second section associated to the electric machine and to at least one of the plurality of devices and a first clutch for coupling the first and second section. 
         [0008]    Preferably, the at least one device is a low power device which is likely to be used in a waiting state of the vehicle or in auxiliary operations, so that it can be operated driven by the electric machine operating as a motor while the internal combustion engine is off. By switching off the internal combustion engine when power demand is low, operation of the combustion engine at an inefficient power level can be avoided. 
         [0009]    According to an embodiment of the invention, the at least one device is an air conditioning unit. The invention thus allows maintaining the air condition unit working while the vehicle is waiting, so that a comfortable temperature may be maintained in a driver cabin of the vehicle, although its internal combustion engine may not be working. 
         [0010]    According to another embodiment of the invention, the at least one device is a hydraulic pump. Such a pump may be used advantageously for driving a lifting unit, in particular for lifting an implement or a trailer, in order to couple it to the vehicle. 
         [0011]    According to another embodiment, the at least one device is a power take-off shaft. In field operation, such a shaft is conventionally used for driving an implement carried by the agricultural vehicle, and the power transmitted by it is a substantial fraction of the total power delivered by the internal combustion engine. However, in auxiliary operations such as coupling and uncoupling the implement, it may be necessary to rotate the power take-off shaft by a small angle in order to bring a terminal connector of the power take-off shaft into an orientation in which it can be coupled to a drive shaft of the tool. Obviously, this rotation requires only a minute fraction of the power the internal combustion engine could deliver, and energy is saved by leaving the internal combustion engine switched off in such a situation and using the electric machine as a motor to drive the power take-off shaft. 
         [0012]    Evidently, the above-identified embodiments are combinable by associating two or more devices selected among an air conditioning unit, a hydraulic pump and a power take-off shaft to a second section of the powertrain. 
         [0013]    Preferably, the powertrain further comprises a second clutch which delimits first and second subsections of said second section, where the first clutch and the electric machine are associated to the first subsection and the at least one device is associated to the second subsection. In this way, the electric machine is connected to the internal combustion engine, in particular for operation as a motor that assists the internal combustion engine in driving the powertrain, while the second subsection and the device associated to it are idle. 
         [0014]    One of the devices drivable by the powertrain should be a wheel shaft. Since vehicle locomotion usually requires a substantial portion of the power of the internal combustion engine, the wheel shaft is preferably associated to the first section. In this way, the wheel shaft is driveable by the internal combustion engine regardless of whether the first clutch is open or closed. 
         [0015]    Preferably, the electric machine is also operable as a generator driven by the powertrain, so that at a given time the electric machine generates the electric energy that will be needed for its operation later on. 
         [0016]    In order to minimize the impact of electric power generation on the load of the internal combustion engine, a controller is provided for operating the electric machine as a generator, whenever the vehicle is in a brake mode. The brake mode may involve operation of friction brakes or an engine brake mode. In either case, the electric machine will have a decelerating effect that contributes to the braking action and converts into electric energy part of the kinetic energy of the vehicle that would otherwise be lost. 
         [0017]    Further, an electric power outlet is provided that is powered by the electric machine. The electric power outlet can be used for operating electric appliances of various types. 
         [0018]    The invention also provides a method of operating an agricultural vehicle as described above. The method includes driving an electric generator (which, preferably but not necessarily in the above-described electric machine) by means of the internal combustion engine, storing electrical energy from said generator in a battery and driving said at least one device using the electric machine while the internal combustion engine is off. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Further features and advantages of the invention will become apparent from the description of embodiments that follows, with reference to the attached figures, wherein: 
           [0020]      FIG. 1  is a block diagram of a tractor according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The following is a detailed description of example embodiments of the invention depicted in the accompanying drawings. The example embodiments are presented in such detail as to clearly communicate the invention and are designed to make such embodiments obvious to a person of ordinary skill in the art. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention, as defined by the appended claims. 
         [0022]    The tractor of  FIG. 1  comprises an internal combustion engine  1 , a gearbox  2  connected to the internal combustion engine by a drive shaft  3 , and wheel shafts  4  with wheels  5 , at least one of which wheel shafts  4  is driven via gearbox  2  and a differential gear  6 . 
         [0023]    The drive shaft  3  extends straight through gearbox  2  to a primary member of a first friction clutch  7 . A secondary member of clutch  7  is mounted at the end of a secondary shaft  8  which carries a gearwheel  9  and extends through a second gearbox  10 . The second gearbox  10  is depicted in an idle state. By displacing a dog clutch  11  of the second gearbox  10  to the left or right along shaft  8 , one of gearwheels  12 ,  13  is locked to the secondary shaft  8 , so as to drive a power take-off shaft  14  at a first or second transmission ratio. 
         [0024]    The gearwheel  9  is engaged with two other gearwheels  15 ,  16 . Gearwheel  15  drives a hydraulic lubricant pump  17  through a shaft  18 . There is no clutch between the secondary shaft  8  and the shaft  18 , so that whenever the secondary shaft  8  rotates, the pump  17  is driven. By means of a hydraulic valve, not shown, at the output of pump  17 , the output pressure of pump  17  can be switched between a low level, appropriate for feeding lubricant to bearings of the tractor, and a high level, appropriate for driving hydraulic pistons of a lifting device. Such a lifting device, for example, may comprise a three point hitch or three point linkage, which is conventionally used for attaching a plough, a harrow, a counterweight or other implements to rear and/or front ends of a tractor. 
         [0025]    The gearwheel  16  drives a gearwheel  19  mounted on a layshaft  20 , along with an electric machine  21 . A belt drive  28  and a second friction clutch  22  connect layshaft  20  to a compressor  23  of an air conditioning unit which controls the temperature in a driver cabin of the tractor. 
         [0026]    An electric converter  24  is connected between the electric machine  21  and a battery  25 . The electric machine  21  is operable as a motor, powered by electric energy from the battery  25 , or as a generator charging the battery  25 , depending on the mode of operation of the converter  24 . 
         [0027]    When the electric machine  21  is in generator mode, the electric energy provided by it can be made available to electric appliances of various types by an electric power outlet, not shown, e.g., of the type conventionally used in buildings for two- or three-phase AC electric power. Such a power outlet may be provided in particular inside or close to the driver cabin, so as to enable, e.g., operation of a vacuum cleaner within the driver cabin. Further, a power outlet can advantageously be provided at a rear or the side of the tractor body, in order to provide electric power to an implement coupled to the tractor. 
         [0028]    If the power outlet is directly connected to the electric machine  21 , in parallel to converter  24 , it may be useful to provide a generator operating mode for internal combustion engine  1 , in which its speed is controlled so that 50 Hz or 60 Hz AC power is directly output by electric machine  21 . Else, a second converter may be needed, so that electric power from electric machine  21  is first converted into DC by converter  24 , and then into 50 Hz or 60 Hz AC by the second converter. Of course, alternatively, DC power from converter  24  might be supplied to the power outlet. 
         [0029]    While the tractor is not moving, the internal combustion engine  1  may be switched off, and clutch  7  is open. Electric machine  21  then functions as a motor which drives the compressor  23 , keeping the driver cabin cool while the driver has to wait for some other machine to finish its job on the field he is going to work on. 
         [0030]    While the electric machine  21  is working as a motor, the input shaft  18  of the hydraulic pump  17  is rotating, too. But as long as the output pressure of pump  17  is at the low level, the load imposed on electric machine  21  by pump  18  is small. On the other hand, if the output pressure is set at the high level, the electric machine  21  can be used for powering the three-point hitch. 
         [0031]    Further, by momentarily displacing dog clutch  11  from its idle position, power take-off shaft  13  can be rotated, so that a drive shaft of some implement coupled to the hitch can be brought into locking fit with a terminal connector  26  at the distal end of PTO shaft  13 . In this way, any preparations for field operation of the tractor that do not require the driving power of combustion engine  1  can be carried out efficiently while combustion engine  1  is off. 
         [0032]    In field operation, when combustion engine  1  is working, electric machine  21  works as a motor or as a generator, depending on the circumstances. Whenever the power demand of the wheel shaft  4  or of an implement connected to power take-off shaft  13  rises strongly, electric machine  21  can be temporarily operated as a motor, in order to avoid fast and energy-inefficient load transitions of combustion engine  1 . 
         [0033]    The electric machine  21  is operated as a generator whenever controller  27  detects a deficient charging state of battery  25 . Further, regardless of the charging state of the battery, electric machine  21  should work as generator whenever controller  27  detects that the driver is pressing a brake pedal or combustion engine  1  is running in brake mode. 
         [0034]    The following list of reference signs of various elements mentioned above is included (as follows), for ease of explanation: 
       REFERENCE NUMERALS 
       [0000]    
       
           1  internal combustion engine 
           2  gearbox 
           3  drive shaft 
           4  wheel shaft 
           5  wheel 
           6  differential gear 
           7  clutch 
           8  second shaft 
           9  gearwheel 
           10  second gearbox 
           11  dog clutch 
           12  gearwheel 
           13  gearwheel 
           14  PTO shaft 
           15  gearwheel 
           16  gearwheel 
           17  hydraulic pump 
           18  shaft
         19  gearwheel   
     
           20  layshaft 
           21  electric machine 
           22  clutch 
           23  compressor 
           24  converter 
           25  battery 
           26  terminal connector 
           27  controller 
           28  belt 
       
     
         [0063]    As will be evident to persons skilled in the art, the foregoing detailed description and figures are presented as examples of the invention, and that variations are contemplated that do not depart from the fair scope of the teachings and descriptions set forth in this disclosure. The foregoing is not intended to limit what has been invented, except to the extent that the following claims so limit that.