Abstract:
A hybrid utility vehicle includes a tool-supporting frame and an electrical power source driven by an engine. Right and left rear wheels independently driven by permanent magnet electric motors and front wheels electrically steerable over a range of approximately 180 degrees operate under the control of a vehicle controller responsive to steering and speed input controls to provide zero turn radius operation with minimum slippage and tire scuffing. Space efficiency provided by the electric steering and an electrically driven tool deck facilitate a variety of tool mounting configurations including a rear discharge deck with a chute passing under the vehicle frame between the driven wheels. An inverter connected to the electrical power source provides 110/220 volt output. The power source also functions as a high powered, high rpm, low noise starter motor.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to utility vehicles and more specifically to off-road hybrid electric vehicles such as lawn and garden tractors. 
       BACKGROUND OF THE INVENTION 
       [0002]    Off-road utility vehicles such as garden tractors typically include a basic carrier unit with an internal combustion engine and electrical power source. The carrier unit is powered by the engine, either through a direct mechanical drive or a hydraulic drive, or indirectly through the electrical power supply and one or more electric traction motors. 
         [0003]    The carrier unit accepts various selectively replaceable attachments which are powered by the engine and/or electrical source. For example, a riding lawn mower includes a deck supported under a vehicle frame. Usually the cut material discharge chute is located on the side of the deck, and therefore the ability to trim on either side of the machine is limited. Some rear discharge machines have chutes which pass over a rear frame portion and transmission for directing cut material into a hopper. For example, U.S. Pat. No. 6,631,607 shows a rear discharge chute which directs cut material over a pair of hydrostatic transmissions. Avoiding interference with drive transmission structure prevents optimization of rear discharge chute size and configuration, and most rear chutes have a smaller capacity than that necessary for optimum machine productivity. 
         [0004]    Conventional transmissions for riding mowers and similar utility vehicles often require a differential lock for maximum traction. However, when making tight turns, such as when mowing around a tree, wheel slip will cause tire scuffing and will tear up turf. 
         [0005]    Vehicles having front caster wheels and independently drivable rear wheels provide zero turn radius maneuverability and eliminate most wheel slip. By driving one drive wheel forwardly while driving the other in reverse, a spin turn maneuver may be accomplished. Zero turn radius vehicles are sometimes uncomfortable for some first time users to operate, and operation on slopes can be difficult with the front caster wheel construction. Many people prefer a positive front wheel steer arrangement with a conventional steering wheel. Commonly assigned U.S. Pat. No. 6,454,032 shows a drive and steer type of arrangement providing automotive type of controls which are more comfortable to most consumers, but positive front wheel steer for better control on slopes is lacking. It is desirable to provide a front wheel steer option for utility vehicles with control that can be easily incorporated into the vehicle electronic controller. The rear wheels should be capable of steering the vehicle by driving when the front wheel steer option is disabled or not selected. On start-up of the vehicle, the position of the steered front wheels should be ascertainable. 
         [0006]    For compact, high power drive arrangement in hostile environments such as encountered by lawn and garden tractors and other utility vehicles, brushless permanent magnet direct current (PMDC) motors and permanent magnet electrical power generators are available. With permanent magnet generators, the option to vary field current and thus the magnetic flux to vary output voltage is unavailable. Driving the generator at different speeds causes considerable variation in the output voltage. To provide sufficient operating voltage, the generator must either be wound for sufficient voltage at low engine speed which results in high over-voltage at full engine speed, or be wound for high speeds which requires constant full engine speed operation even if power requirements are low. Components have to be sized or a protective circuit such as an intermediate bus and capacitors or the like provided to accommodate over-voltages and prevent damage to the system. 
         [0007]    Typical ring gear starter configurations for hybrid vehicles are noisy, and cranking speed is relatively slow. The starter motor adds cost and weight to the vehicle. 
         [0008]    More consumers are desiring 110 or 240 volt output from the utility vehicle so electrical tools can be operated and back-up house power can be provided as necessary. Engine overload and engine stoppage, particularly upon initial loading of the electrical system, can be a problem. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore an object of the present invention to provide an improved hybrid utility vehicle. It is a further object to provide such a vehicle which overcomes one or more of the aforementioned problems. 
         [0010]    It is another object to provide a utility vehicle having an improved steering arrangement. It is a further object to provide such a vehicle which has improved drive arrangement. 
         [0011]    It is yet another object of the present invention to provide an improved hybrid utility vehicle. It is a further object to provide such a vehicle which facilitates better placement of vehicle components and attachments. 
         [0012]    It is another object to provide an improved hybrid utility vehicle having improved power distribution structure. 
         [0013]    In one embodiment of the invention, a hybrid utility vehicle includes a tool-supporting frame and an electrical power source driven by an engine. Right and left rear wheels independently driven by permanent magnet electric motors and front wheels electrically steerable over a range of approximately 180 degrees operate under the control of a vehicle controller responsive to steering and speed input controls to provide zero turn radius operation with minimum slippage and tire scuffing at varying vehicle speeds. Space efficiency provided by the electric steering and an electrically driven tool deck facilitate a variety of tool mounting configurations including a rear discharge deck with a chute passing under the vehicle frame between the driven wheels. The electric wheel motor drives are on the external side of the frame rails, and the cut material conveying chute may be mounted much lower than is possible in a traditional lawn tractor layout which requires chute routing over a transmission. The hybrid construction eliminates need for a traditional transmission so the space can be used for moving grass and other cut material to a rear hopper. Also, the material chute located in the middle rather than at a side of the machine facilitates trimming unhindered by discharge structure on either side of the machine. 
         [0014]    An inverter connected to the electrical power source provides 110 and/or 220 volt output for utility power use so hand tools and lawn tools can be operated and back-up house power can be provided from the vehicle. The power source also functions as a high powered, high rpm, low noise starter motor. The controller filters operator speed requests utilizing a torque control map. A control algorithm avoids engine overload and engine stoppage by causing electrical load to be taken from the battery pack and gradually applying generator load to allow governor to match engine droop. 
         [0015]    The hybrid vehicle can be operated from a battery pack when quiet operation is required. The vehicle  10  does not require hydraulic systems and is particularly suited for operation in environments where oil leaks pose a particular problem, such as on golf course. 
         [0016]    These and other objects, features and advantages of the present invention will become apparent from a reading of the description which follows when taken with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a side perspective view of a hybrid utility vehicle with portions broken away to better show the component layout on the vehicle. 
           [0018]      FIG. 2  is an enlarged top view of steerable front wheel structure on utility vehicle of  FIG. 1 . 
           [0019]      FIG. 3  is a control system block diagram including an electronic vehicle controller for the vehicle of  FIG. 1 . 
           [0020]      FIGS. 4A-4D  show a logic flow chart for operation of the controller of  FIG. 3 . 
           [0021]      FIG. 5  is a logic flow chart showing shut-down procedure for the vehicle of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    Referring now to  FIG. 1 , therein is shown a utility vehicle  10  such as a riding mower or other grounds care machine having a tool-carrying frame  12  supported by right and left rear driven wheels  14  and  16  and front steerable wheels  18  and  20 . A driven tool  24 , shown in  FIG. 1  as a mower deck, is supported from the underside of the frame  12  and includes a plurality of driven blade members  26  ( FIG. 3 ) powered by electric motor structure  26 ′. The electric motor structure  26 ′ may include a permanent magnet dc motors  26 ′ individually driving each of the blade members  26  or other suitable drive arrangement including but not limited to a single motor driving the blade members  26  through a belt drive. The motors  26 ′ can be “pancake” type motors to for more clearance on the top of the deck  24 . 
         [0023]    The frame  12  includes a rear frame portion  12   r  on each side of the vehicle  10  supporting right and left integrated wheel motor assemblies  34  and  36 , each having a brushless permanent magnet dc motor  34 ′ and  36 ′ and a planetary reduction gear structure  34   g  and  36   g  located substantially entirely outwardly of the rear frame portion  12   r  and generally within rims  38  of the wheels  14  and  16 . The construction of the rear frame portion  12   r  and the compact wheel motor assemblies  34  and  36  leaves a rearwardly opening accommodation space  40  between the assemblies and below the top of the rear frame portion  12   r  unencumbered with transmission or other wheel drive structure. A seat  42  is supported from the top of the rear frame portion  12  behind an operator control area  46  and a hood area  48  which extends forwardly from the control area. A steering control  50  is located in the area  46 . 
         [0024]    An internal combustion engine  60  centered behind the front wheels  18  and  20  is supported in the hood area  48 . A combination starter/alternator  66  is supported at the forward end of the engine  60  between the front wheels  18  and  20  to generate electrical power using the engine  60  and to provide high rpm, high torque engine starting at a low noise level. In the embodiment shown for a conventional lawn and garden tractor, the engine provides about fifteen horsepower and the alternator puts out about thirteen kilowatts of power at full engine power from a three phase permanent magnet brushless generator. As a starter, the depicted starter/alternator provides combustion engine cranking torque of greater than 40 Nm. It is to be understood that other engine/generator combinations and power outputs could be used. 
         [0025]    A rectifier/inverter  68  ( FIG. 3 ) is connected to the alternator which operates to boost generator voltage above the back emf of the generator. Current is injected into an inductance to provide the voltage increase. An output  70  is connected to a battery pack  74  and to bus  76  having a bus voltage above 36 volts and typically about 42 volts. By operating the generator at an output level below the voltage on the bus  76  good efficiency over a wide range of engine speeds is achieved without need for a complicated voltage management scheme. With a back emf lower than the bus voltage, the electronics are designed to boost the generator output up to the bus voltage. When generating, controller transistors in the rectifier/inverter  68  are commutated 180 degrees out of phase from motoring. The inductance of the machine thus adds the supply voltage to the back emf voltage which raises the output over the bus voltage for charging the batteries. The necessary bus voltage can be generated efficiently over a wide range of engine speeds which allows running the engine at low speed for quiet operation when full power is not needed. The bus  76  is connected to an inverter  80  with an 110 volt or 240 volt outlet  82  which can be conveniently located adjacent the accommodation space  40  near the rear of the vehicle  10  for powering hand tools, providing emergency power to a building, and the like. The battery pack  74  can be of thin film absorbed glass mat or other compact construction which can be located adjacent the seat  42  near the inverter  80 . 
         [0026]    The front wheels  18  and  20  as shown in  FIGS. 1 and 2  are steerable wheels movable over a range of about 180 degrees from a zero radius right turn position to a zero radius turn left position. In  FIG. 2 , the wheel  18  is shown approaching the left-most turn position. The wheels  18  and  20  are connected to a transverse axle member  90  for pivoting about upright axes (see  18   a  in  FIG. 2 ), and a steering linkage  92  generally of the type shown and described in commonly assigned U.S. Pat. No. 6,456,925 provides positive steering of the wheels through a rack and pinion structure  96 . In one embodiment ( FIG. 1 ), an electric motor  100  powers the rack and pinion structure  96  and provides a drive by wire function which is independent of a mechanical linkage connecting a steering wheel directly to the steering linkage  92 . Alternatively, a conventional mechanical steering linkage (not shown) can be provided between a steering wheel and the steering linkage  92  as described in the aforementioned U.S. Pat. No. 6,456,925 with the motor  100  acting as a power steering assist if desired. Another type of drive by wire steering control is shown in  FIG. 3  wherein, rather than using a single motor, separate electrically operated steering motors  108  and  110  independently pivot the wheels about the wheel axes  18   a.  For added traction and maneuverability, the steered wheels  18  and  20  can be driven by compact motors (location  18   h ) or the like. In situations wherein steered front wheels are deemed not to be necessary, the steering structure can be removed completely so the wheels  18  and  20  simply caster and steering control is achieved as described below using full time independent drive of the wheel motor assemblies  34  and  36 . 
         [0027]    The compact arrangement of the wheel motor assemblies  34  and  36  providing the relatively large accommodation space  40  facilitates mounting of a rear material discharge chute  140  under the area of the seat  42  and generally under the frame  12 . The chute  140  is connected to the rear central portion of the mower deck  24 . Since the drive structure for the wheels  14  and  16  extends outwardly and away from the accommodation space  40 , the chute can have a more direct route rearwardly and chute size can be greater than with convention transmission systems. A cut material hopper  144  is shown connected to the rear frame portion  12   r,  and the chute  140  opens into the upper front portion of the hopper  144 . The rear discharge deck  24  facilitates close trimming on both sides of the vehicle  10 . In addition, the construction permits transverse movement of the deck  24  for further trimming enhancement and more top deck clearance for improved tool lift. Electric actuators indicated generally at  150  in  FIG. 1  provide implement and tool lift and tool offset functions. 
         [0028]    Referring now to  FIG. 3 , therein is shown an electronic vehicle controller  160  having a steering input  162  from the steering control  50 , a speed command and direction input  164  from a foot pedal, and a brake command input  166  from a brake pedal. The pedals and steering control  50  are located at the control area  46  and are shown to include variable resistors providing an analog voltage signal to the controller  160  dependent on the selected position of each operator control. The controller  160  also receives start and run signals from a key switch assembly  168  and engine speed and operating condition information via lines  170 . 
         [0029]    The vehicle controller  160  calculates the differential speeds of the right and left wheels  14  and  16  such that the vehicle can be steered and controlled with only differential traction drives and caster wheels without need to steer the wheels  14  and  16 . The controller  160  then outputs a steering signal via lines  174  and  176  to the steering motors  108  and  110 , when the vehicle  10  is so equipped (or to a single steering motor if the steered wheels are mechanically linked for steering), to control the positions of the steered wheels  18  and  20 . Feedback lines  178  and  180  (or a single line if a single steering motor is used) provide feedback signals to the controller  160  utilized primarily to verify that the steered wheels  14  and  18  are correctly positioned at vehicle start up. When the steerable wheels  18  and  20  are powered, the controller  160  provides speed control to the wheel drives depending on the steering input at  162  and the foot pedal speed input at  164 . The right and left wheel motors  34 ′ and  36 ′ are connected to motor controllers  184  and  186  which received right and left wheel speed commands from the controller  160  dependent also on the steering input at  162  and the foot pedal speed input at  164 . Speed and current feedback signals from the right and left wheel motors  34 ′ and  36 ′ are also inputted to the motor controllers at  194  and  196 . The current feedback is added to the basic control at  184  and  186  and enables vector control if desired to enhance the control functions. 
         [0030]    The steering and drive arrangement provides full time steerable differential drive wherein both rear wheels provide drive at all times for good traction characteristics. The vehicle turns well since the wheels are rotated at speeds matched to the requested turn angle. This control of the individual wheel speed is accomplished without need for a complicated and bulky spin steer transmission. When utilized with a 180 degree or other short radius steering linkage, a high degree of vehicle maneuverability is achieved. The controller  160  utilizes the steering input signal at  162  and the desired ground speed input at  164  from the foot pedals to compute the correct wheel speed for the rear drive motors  34 ′ and  36 ′. Further, details of a control system for controlling the driven wheels may be had by reference to the aforementioned U.S. Pat. No. 6,456,925. 
         [0031]    The deck motors  26 ′ ( FIG. 3 ) are controlled with a deck control switch  206  connected to the controller  160 . The controller  160  directs power from the bus  76  to the motors  26 ′ when the switch  206  is closed. An inverter switch  208  connected to the controller  160 , when closed, turns on the inverter  80  so that power can be supplied through the outlet  82 . The controller  160  filters operator speed requests at  164  utilizing a torque control map stored in controller memory. A control algorithm executed by the controller avoids engine overload and engine stoppage by causing electrical load to be taken from the battery pack  74  as necessary and gradually applying generator load to allow a governor on the engine to match engine droop. If the engine  60  stops for any reason, the controller  160  initiates a shut-down routine ( 300  of  FIG. 5 ). Upon indication at  301  of stoppage, right and left drive speed and torque are set to zero ( 302  and  303 , respectively), and 120 ms delay is initiated at  304 . Thereafter, the ignition relay is set to off and the control state is returned to initialization. 
         [0032]    Referring to  FIGS. 4A-4D , a logic flow chart is shown for the operation of the controller  160 . On turn-on of the vehicle  10 , inputs are sampled at  400  to determine if there are any problems in the system or if a previous error state has not been corrected, and if so ( 401 ), the state is returned to Error at  402 , an error message is provided at  403 , and shutdown procedure is begun at  404 . 
         [0033]    Upon indication at  401  that no problems are detected, the state of the system is checked at  410 . If the vehicle is in the initiation state, such as occurs at with normal start-up procedures, drive speeds are set to zero at  411  and interlock conditions such as brake on, speed control in neutral and mower deck off are checked at  412 . If all the pre-established conditions are met, the ignition relay is turned on at  413  and the state of the key switch  168  is polled at  414 . If the switch is in the start position, engine cranking is begun ( 415 ). If the switch is not in the start position, the alternator is disengaged at  416 . If cranking is indicated at  410 , key position is checked at  420 , and if starting is indicated, the interlock conditions are checked at  421 . If conditions are as prescribed, the starter is turned on at  422 , a generator speed is entered at  423 . If the generator speed is sufficient for providing proper voltage to the bus  76 , the generator is activated at  425  and the run timer is begun at  426 . State is set to running at  427 . 
         [0034]    If the key is not in the start position at  420 , the starter is turned off at  430 , and a two-second time out is established at  431 . Generator speed is checked after two second at  432 , and, if sufficient, power generation is begun at  433  and the state is set to running at  434  prior to the next pass through the routine. If at  421  it is determined that not all of the interlock conditions are met, the starter is turned off at  440 , a short time-out delay is established at  441  after which the shutdown procedure is begun at  442 . If generator speed has not reached an acceptable level at  432  and generator speed is indicated to be below a minimum speed at  451 , the shutdown procedure is begun at  452 . 
         [0035]    Once the state at  410  is determined to be run, the drive to the wheel motor assemblies  34  and  36  at full torque is commanded at  460  and vehicle conditions are checked ( FIG. 4D ). If the operator is properly positioned relative to the vehicle at  461 , the seat error flag is cleared at  462  and the deck switch  206  is polled at  463 . If the deck is on and the deck flag is clear at  464 , and if the foot pedal is in the neutral condition at  465 , the deck is engaged at  466 . If an override condition exists, such as mow in reverse switch has been activated ( 467 ), the deck override flag is set to true at  468 . Otherwise, the deck override flag is cleared at  469 . If the foot pedal is not in neutral at  465  and if the foot pedal is in reverse at  470 , the deck override flag is checked ( 471 ). If the deck override flag has previously been set to true at  468  indicating a proper override condition exists, the deck engagement is enabled at  472 . Otherwise, the deck is disengaged at  474  and the deck error flag is set at  475 . If the foot pedal is not in reverse ( 470 ), the deck override flag is set to false at  480  and the deck is engaged at  481 . 
         [0036]    If at  461  it is determined that seat switch is off and at  483  ( FIG. 4C ) the vehicle brake is not engaged, shutdown is initiated at  484 . If the seat switch is off ( 461 ) and the brake is on ( 483 ) the deck switch is polled at  485  and, if off, the deck is disengaged ( 486 ) and the deck error flag is set at  487 . If the seat switch is on at  461  and the deck off indication is received at  463 , the error deck flag is checked at  488  and deck override flag is checked at  489  before disengaging the deck at  490 . The steering algorithm  494  continues after condition checks. 
         [0037]    Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.