Abstract:
An electric implement power management system includes an electronic controller that monitors total electric implement load and commands a transmission to reduce the speed of the traction drive wheels below the desired traction drive speed if the total electric implement load reaches a maximum allowable load.

Description:
FIELD OF THE INVENTION 
     This invention relates to an electric implement power management system for multiple electric implements such as electric grass cutting reels or electric planters that are carried or pulled by work vehicles. 
     BACKGROUND OF THE INVENTION 
     Electric implements may be carried or pulled by work vehicles. For example, three or more electrically powered cutting reels may be carried by fairway mowers, greens mowers, trim mowers and other turf care products. Electric seeding equipment pulled by tractors may include multiple seeding row units having electric motors. 
     Electric power for these implements may be supplied by an alternator or generator driven directly by an internal combustion engine, or by an energy storage device or fuel cell charged by the alternator. Electric motors for the implements may include brush-less permanent magnet motors, commutated electric motors, or other electric motors. 
     With a typical alternator, particularly a Lundell-type alternator having an output rectifier, if more current is demanded than the alternator can supply, the alternator&#39;s output voltage may collapse, yet the current may not correspondingly increase. The alternator&#39;s electrical power output does not stay at the maximum available, but drops precipitously. 
     As a result, if current demand by multiple electrically powered implement motors is very high, approaching or exceeding the capacity of the power generating component, the electrical power may be significantly lower due to a sharp voltage drop. Once the voltage drops too far, it can be insufficient to power other electrical functions on the work vehicle, resulting in a condition commonly referred to as “brownout.” Other power generating devices such as permanent magnet alternators, electrochemical batteries, DC machines and others suffer from overload problems of a type similar to the above. For example, electrochemical cells will undergo voltage collapse under high load conditions, particularly when the battery is highly discharged. 
     If the total electrical implement load reaches or exceeds the maximum allowable load, the implements may stall or fault and stop functioning. For the above reasons, it is desired to provide an electric implement power management system that reduces the peak power demands on an alternator. It is desired to provide an electric implement power management system that reduces peak power demands before total electric implement load reaches an overload condition. 
     SUMMARY OF THE INVENTION 
     An electric implement power management system includes an electronic controller that receives input regarding the electric load on the alternator and sets the transmission to a desired traction drive speed if the total electric load does not exceed a maximum allowable load, or to a reduced traction drive speed if the total electric load exceeds the maximum allowable value. The power management system reduces peak power demands on the alternator, and reduces the traction drive speed before reaching an overload condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a fairway mower having an electric implement power management system according to a first embodiment of the invention. 
         FIG. 2  is a block diagram of an electric implement power management system according to a first embodiment of the invention. 
         FIG. 3  is a logic diagram of an electric implement power management system according to the first embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     One embodiment of the electric implement power management system is shown in  FIGS. 1 and 2  on fairway mower  100 . The fairway mower may include traction vehicle  101  that carries a plurality of electrically powered reel-type cutting units  102 ,  103 . The electric implement power management system is not limited to grass mowing machines such as fairway mowers, but also may be provided on other electrically powered implements such as electric planters having multiple row units that are carried or pulled by work vehicles such as tractors. 
     Now referring to  FIG. 2 , in one embodiment of the electric implement power management system, internal combustion engine  200  may mechanically drive generator or alternator  201  directly through a belt and pulley arrangement. Alternatively, the internal combustion engine may indirectly drive a generator or alternator through a hydraulic motor. Or the alternator may charge a battery or other storage device that powers electrically powered implements. The alternator may provide electric power to a plurality of electric implements such as electric implement motors  204  through motor controllers  203  electrically coupled to the alternator, or such as electric motors on multiple row units of a planter. 
     In one embodiment of the power management system, electronic controller  202  may be electrically coupled to a plurality of motor controllers  203 . The electronic controller may be a vehicle controller that is provided on-board a work vehicle such as a grass mowing machine or tractor. The electronic controller may control the presence, absence or any other aspect of electrical energy to motor controllers  203  and electric implement motors  204 . The electric implement load may be provided as an input to the electronic controller. 
     In one embodiment, the power management system may include an electronically controlled transmission  205  that transmits rotational power from internal combustion engine  200  to traction drive wheels  206  of the work vehicle. Alternatively, the power management system may include an electric power source and electric traction drive system connected to the drive wheels. 
     In one embodiment, the power management system may have a variable traction speed control  207  that an operator may use to set a desired traction drive speed of the work vehicle. For example, the variable traction speed control may be a pedal that is operatively engaged to a potentiometer or position sensor to produce a signal to controller  202  indicating a desired traction drive speed. If transmission  205  is a hydrostatic transmission, controller  202  may be signal-connected to a solenoid of a proportional pressure control valve. The output current that energizes the solenoid may be substantially proportional to the corresponding pedal position signal. For a given engine speed, controller  202  may command transmission  205  to rotate the wheels  206  at a desired traction speed based on position of the foot pedal. Similarly, in the case of an electric traction drive system, the controller may command the wheels to rotate at a desired traction speed based on position of the foot pedal. However, if the controller detects the total electric implement load on the alternator exceeds a maximum allowable load, the controller may command the transmission or electric traction drive system to rotate the wheels at a lower desired traction speed for the same foot pedal position. 
     In one embodiment, as shown in the flow diagram of  FIG. 3 , the electronic controller may receive input from the traction drive speed control (e.g., pedal position) in block  301 . The electronic controller may monitor the alternator and receive input regarding the total electric implement load on the alternator in block  302 . The electronic controller may determine the total electric implement load on the alternator by monitoring bus voltage, bus current, and/or the regulator output from the alternator field voltage line. 
     In one embodiment, the electronic controller may determine if the total electric implement load is at or over a maximum allowable load in block  303 . For example, the electronic controller may determine the total electric implement load is at or over the maximum allowable load if bus voltage is below a specified preset voltage. In the case of a 48V or 56V alternator, the controller may determine the total electric implement load is at or over the maximum if bus voltage is below a lower specified preset voltage such as 43 volts or 50 volts respectively. Similarly, the electronic controller may determine the total electric implement load is at or over the maximum if bus current is above a specified preset current limit such as 270 amps. Alternatively, the electronic controller may monitor the regulator output from the alternator field voltage line. The regulator may switch the alternator field voltage line on and off depending on the bus voltage. The electronic controller may determine that the total electric implement load is at or over the maximum allowable load if the regulator turns on the alternator field voltage line at close to or approaching 100%. 
     If the electronic controller determines the total electric implement load does not exceed the maximum allowable load, the electronic controller may set the transmission to the desired traction speed as a function of pedal position in block  304 . If the electronic controller determines the total electric implement load exceeds the maximum allowable load, the electronic controller may set the transmission to a reduced traction drive speed in block  305 . The reduced traction drive speed may be a function of pedal position, or may be a function of the difference between the total electric implement load and the maximum allowable load. The electronic controller may continue to command the transmission at the reduced traction drive speed as long as the total electric implement load continues to exceed the maximum allowable load. For example, the reduced traction drive speed may be only 50% or 75% of the speed input based on the position of traction speed control  207 , depending on operation conditions. 
     Having described a 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.