Abstract:
An electric working vehicle, including a motor, to supply a driving force to at least one wheel of plural wheels; a rotary-type blade attached on part of the vehicle body; a blade motor; a battery to supply electric power to the running and blade motor; a first power converter to convert the electric power from the battery for the running motor; a second power converter to convert the electric power from the battery for the blade motor; and a controller portion to control at least power conversion operations of the first and second converter, wherein as least, the first power converter is able to operate regeneration, and the controller portion controls the second power converter in such a manner that regeneration electric power when the first power converter operates under condition of the regeneration is supplied to the blade motor, depending on a charging condition of the battery.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an electric working vehicle, such as, a lawn mower, a snowplow or a harvester, etc., for example, i.e., for conducting a predetermined work and also being able to move by itself, with electromotive forces. 
         [0002]    For example, in the following Patent Documents 1 and 2 is already known a working machine or a power plant, rotationally driving a blade cutter, and thereby conducting a job, e.g., grass cutting, for example, as an actuator (i.e., the lawn mower). 
         [0003]    However, such the lawn mower is equipped with, in accordance with the conventional technology as was mentioned above, not only an electric motor for use of driving, but also an internal combustion engine for use of rotational driving of an onboard dynamo, in addition to rotation of the blade cutter; i.e., achieving so-called a hybrid-method working vehicle. 
         [0004]    Further, in the following Patent Document 3 is already known a technology for driving by an electric motor, with applying a battery as an electric power source, wherein an electric lawn mower achieving high accuracy in the grass cutting is also already known. 
       PRIOR ART DOCUMENTS 
       [0005]    &lt;Patent Documents&gt;
   [Patent Document 1] Japanese Patent Laying-Open No. 2004-275026 (2004);   [Patent Document 2] Japanese Patent Laying-Open No. 2006-507789 (2006); and   [Patent Document 3] Japanese Patent Laying-Open No. Hei 5-30832 (1993).   
 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    However, within such the working vehicle as was disclosed in the conventional technology mentioned above, in particular, the electric lawn mower disclosed in the Patent Document 3, no consideration is paid upon regeneration of the electric motor, i.e., the electric power source. 
         [0010]    This enables to use the motor as a dynamo while utilizing that motor to be braking power or force (i.e., a regenerative brake), when the lawn mower moves down on a downhill, etc., for example. And, with charging the electric power generated in that occasion to the battery, as well as, elongating an operating hour of that lawn mower, it is possible to increase an efficiency of energy utilization by reducing a useless waste of energy (i.e., electric power). 
         [0011]    However, when lawn mower moves down on the downhill, if the battery is under the condition of being fully charged up, it is impossible to return the electric power generated back to the battery (i.e., charge), and in general, this is consumed to be a current flow through a load resistor for use of discharging. Or, in particular, a lead storage battery, since it has a relatively large internal resistance, has a possibility of being in the condition of overvoltage, even if it is not the full-charge condition, depending on an amount of electric power regenerated; however, if trying to escape from the overvoltage by reducing the electric power regenerated, then also the braking force of the vehicle is reduced, and sometimes, this brings about a danger to an operator or driver. Then, for the purpose of avoiding the overvoltage, and also protecting the battery and also electric equipment connected with the battery from a breakdown due to the overvoltage, without reducing the braking force of the vehicle, it is conducted to consume the electric power regenerated through a regeneration resistor for use of discharging, even under the condition that the battery is overvoltage. 
         [0012]    For that reason, conventionally, there is a necessity of a resistor having a relatively large size or configuration, being tolerable with large heat-generation, and this increases a number of parts; therefore, there are drawbacks, i.e., increasing a manufacturing cost and a product const, as well, and therefore being disadvantageous from an economical viewpoint. 
         [0013]    Furthermore, there can be also considered consumption of the unnecessary electric power regenerated, by turning electric current through other motor (s), which is/are provided on the working vehicle, without utilizing such load resistor for use of discharging as mentioned above; however, it is acknowledged by the inventors of the present invention that, in such a case, there is a possibility that the working vehicle may causes an injury to a person who is conducting a work with using it, in particular, when that other motor rotates an actuator, such as, the blade cutter, i.e., being not preferable. 
         [0014]    Then, according to the present invention, being accomplished by taking the drawback (s) of the conventional technology mentioned above into the consideration thereof, an object thereof is to provide a safe electric working vehicle, applying an electric motor therein, not only for use of running, but also for driving an actuator for conducting a work, being able to consume regeneration electric power without using the load resistor for use of discharging, and further not causing an injury to the person who is conducting the work with using thereof, in that instance, even under the condition where the battery is fully charged. 
         [0015]    For achieving the object mentioned above, according to the present invention, first of all, there is provided an electric working vehicle, comprising: a body of vehicle; plural numbers of wheels, which are attached to said body; a running motor, which is configured to supply a driving force for running to at least one wheel of said plural numbers of wheels; a means, which is configured to be attached on part of said body of vehicle, and thereby conducting a predetermined work therewith; a work motor, which is configured to execute the predetermined work with using said working means; a battery, which is configured to be attached on part of said body of vehicle, and to supply electric power to said running motor and said work motor; a first power converter, which is configured to convert the electric power from said battery into required electric power to supply it to said running motor; a second power converter, which is configured to convert the electric power from said battery into required electric power to supply it to said work motor; and a controller portion, which is configured to control at least power conversion operations of said first power converter and said second converter, wherein as least, said first power converter is able to operate regeneration, and said controller portion controls said second power converter in such a manner that regeneration electric power when said first power converter operates under condition of the regeneration is supplied to said work motor, depending on a charging condition of said battery. 
         [0016]    And, also, according to the present invention, there is further provided the electric working vehicle, as described in the above, wherein, preferably, further said controller portion controls said second power converter in such a manner that a torque component of the electric power to be supplied from said second power converter to said work motor is suppressed to a degree so that said work motor does not work said working means. Or, preferably, said means for conducting the predetermined work is a blade for cutting grasses, and in that case, preferably, said controller portion controls said second power converter, so as to supply and consume electricity to said work motor, depending on an operating condition of said blade for cutting grasses, as well as, the charging condition of said battery, and further, said controller portion controls said second power converter, so that the torque component of the electric power to be supplied comes down to be almost zero (0), when said blade for cutting grasses is stopped. 
         [0017]    According to the present invention mentioned above, there can be provided a safe electric working vehicle, in particular, a lawn mower, applying an electric motor therein, not only for use of running, but also for driving an actuator for conducting a work, for enabling to maintain a stable braking force, chiefly, as the vehicle, and further not causing an injury to the person who is conducting the work with using thereof, in that instance, since being able to consume the regenerated electric power without using the load resistor for use of discharging, even under the condition where the battery is fully charged. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0018]    Those and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings wherein: 
           [0019]      FIG. 1  is a view for showing an outlook configuration of an electric lawnmower, as an example of an electric working vehicle, according to an embodiment of the present invention; 
           [0020]      FIG. 2  is a circuit block diagram for showing the electric lawnmower mentioned above, in particular, mainly, electromotive parts thereof; 
           [0021]      FIG. 3  is a circuit block diagram for showing details of a motor for running and a motor for driving a blade, and also a controller of the motor for running and a controller of the motor for driving the blade; 
           [0022]      FIG. 4  is a circuit block diagram for showing further details of the controller of the motor for driving the blade mentioned above; and 
           [0023]      FIG. 5  is a flowchart for showing an example of a processing method of control for use of consumption of a regenerated electric power within a drive circuit of the controller of the motor for driving the blade mentioned above. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Hereinafter, detailed explanation will be given on an electric lawn mower, applying an electric motor therein, not only for use of running, but also for driving an actuator for conducting a work, as an example of the electric working vehicle, according to an embodiment of the present invention, by referring to drawings attached herewith. 
         [0025]    First of all,  FIG. 1  attached herewith shows the configuration of the electric lawn mower, as the example of the electric working vehicle, according to the present invention, briefly, wherein said lawn mower comprises a pair of front wheels  10  and  11 , as well as, a pair of rear wheels  20  and  21 , and the front wheels  10  and  11  are attached to a lower surface of a car body shown by a broken line  100  in the figure, in a freely rotatable and movable manner, through casters  12  and  13 , respectively, while the rear wheels  20  and  21  are attached to the lower surface of the car body, fixedly. Furthermore, no driving means is provided for the front wheels  10  and  11 , and on the other hand, a motor  30  for running (hereinafter, being called a “running motor”) is attached to the rear wheels  20  and  21 , through a reduction gear  40  and respective driving shafts thereof. 
         [0026]    However, in the present embodiment is applied a brushless DC motor to be the running motor  30 , as an example thereof, and to that motor is supplied a DC power from a battery  50  on the vehicle, after being converted into three-phases AC current having a desired frequency thereof by means of a controller (i.e., a converter)  60  for the running motor, including a CPU and an inverter of PWM method therein. 
         [0027]    Also, with the battery  50  on the vehicle is connected a motor  70  for use of working (not for running), i.e., for driving a blade (hereinafter, being called a “blade motor”), through a controller  65  (i.e., the converter) for the blade motor, including a CPU and an inverter of PWM method therein, and therefore the DC current is converted into three-phases AC current having a desired frequency thereof by the blade motor controller  65  and is supplied to the blade motor  70 . Further, at a lower end of a rotating output shaft of this blade motor  70  for use of working is attached a rotary-type blade  80 , as a cutter for conducting the work, i.e., cutting grasses. 
         [0028]    Thus, according to the lawn mower having such configuration as was mentioned above, a rotating torque generated by the running motor  30  is transmitted to both the left and the right wheels  20  and  21 , via the reduction gear  40  mentioned above. In that instance, due to the function of the reduction gear  40 , the rotating torque of the motor is transmitted to driving shafts  22  and  23 , while being differentially decelerated, respectively, and thereby it is possible to rotate/drive the left and the right wheels  20  and  21 , at a desired ratio between them in the rotating torques (i.e., rotating speeds), and therefore a running direction of the vehicle can be controlled, freely. However, at this instance, the front wheels  10  and  11  come to move, following a moving direction that is determined by the rear wheels  20  and  21 , due to the function of the casters  12  and  13 . On the other hand, the rotating torque generated by the blade motor  70 , not for running, i.e., for driving the blade, rotates/drives the cutter blade  80 , and thereby cutting the grasses. 
         [0029]    Next,  FIG. 2  attached herewith is a circuit block diagram for showing electromotive parts thereof, in particular, within the lawn mower according to the present invention, the outlook configuration thereof being shown in the above, wherein the constituent elements, which are shown in  FIG. 1  mentioned above, are shown with attaching the same reference numerals thereof. 
         [0030]    Thus, to the battery  50  are electrically connected the controller  60  for the running motor and the controller  65  for driving the blade motor, in parallel with, and the electric power of the three-phases AC for driving is supplied to the running motor  30  and the blade motor  70 , respectively. And, into the controller  60  for the running motor is inputted, for example, braking information indicative of pushing-down of a braking pedal, acceleration information indicative of pushing-down of an acceleration pedal, which are provided on the lawn mower, and further information of a car speed, etc., from sensors, which are not shown herein, and the controller  60  of that running motor executes a predetermined calculation(s), upon basis of those information, with using software, which is stored in advance within an internal memory of the CPU, etc., thereby controlling the rotating torque and the speed, which are outputted from the running motor  30 . On the other hand, the controller  65  for the blade motor also execute a predetermined calculation, upon basis of ON/OFF information of the blade motor, i.e., the information indicative of if the blade  80  should be rotated or not by the blade motor  70 , thereby controlling the rotating torque and the speed of the blade motor  70 . Further, in part of those running motor  30  and the blade motor  70  are attached sensors  31  and  71 , for example, to detect the rotation speeds thereof, respectively, and a sensor  72  to detect driving current for the blade motor, wherein the outputs thereof, i.e., motor information, are fed back to the controllers  60  and  65 , respectively. 
         [0031]    Following to the above,  FIG. 3  attached herewith shows the running motor  30  and the blade motor  70  mentioned above, as well as, the details of the controller  60  for that running motor and the controller  65  for the blade motor, wherein as is apparent from the figure, each motor controller  60  or  65  comprises an inverter circuit  601  or  651 , each having six (6) pieces of electric power elements, such as, power transistors, FETs, or IGBTs, including commutating diodes therein, etc., for example. Also, each motor controller  60  or  65  comprises a drive circuit  602  or  652  for producing control signals for controlling conduction/interruption of each power element of that inverter circuit, and a CPU  603  or  653  for controlling that drive circuit, respectively. Also, other than those, the constituent elements attached with such the same reference numerals as was mentioned above are same to those mentioned above and therefore the explanation thereof will be omitted herein. 
         [0032]    In this figure are shown a charging circuit (i.e., a DC converter)  90  for charging up that battery with using a commercial electric power source, as well as, the battery  50  mounted on the car mentioned above. Thus, that charging circuit (i.e., the DC converter)  90  may be mounted in part of the electric lawn mower, i.e., being the working vehicle, or may be prepared or formed in a separate body therefrom, and with this, it is possible to charge up the battery  50 , for example, by inserting a plug  91  into a household power source (e.g., a socket). 
         [0033]    In addition thereto, within the electric lawn mower, i.e., the working vehicle, according to the present invention, in particular, the running motor  30  thereof, normally, conducts the followings, selectively, between so-called a “powering” operation for achieving a required rotating operation with supply of electric power from the battery  50 , and, for example, a “regeneration” operation for generating electric power with using the braking force when the vehicle goes down a hill. The current from the battery  50  mentioned above at this time is shown by a arrow “powering” or “regeneration” in the figure. Thus, when operating in this “regeneration” operation, the regeneration current flows into the battery  50 , through the inverter circuit  601 , which builds up the controller  60  for the running motor. However, in that instance, if the battery  50  is in the condition of being charged up to the prescribed capacity thereof, already (hereinafter, being called “full-charge condition”), supply of the regeneration electric power mentioned above brings the battery to be overcharged, and this is not preferable from a viewpoint of protection of the battery. 
         [0034]    Then, according to the present invention, in the “regeneration” operation, in particular, when the battery  50  is in the “full-charge condition”, the regeneration current from the inverter circuit  601  is supplied, not to the battery  50  mentioned above, but to the blade motor  70 , so as to rotate/drive the blade  80  for conducting the grass cutting. With this fact, with utilizing the “regeneration” electric power, not to be used for charging the battery, for the operation of the blade motor  70 , it is possible to reduce a waste of the electric power of the battery  50  on the vehicle, and to keep a stable braking force of the vehicle, as well. 
         [0035]    However, in that instance, when the blade motor  70  in an operating condition (i.e., rotating/driving), it is preferable to utilize the “regeneration” electric power for operation of the blade motor  70 . However, in particular, when the blade  80  is stopped the rotation/driving thereof (for example, when the lawn mower only moves to a destination, but not conducting the work of grass cutting), the supply of the “regeneration” electric power to the blade motor  70  results into rotation of the blade for conducting the grass cutting work, and unprepared or careless rotation of the blade accompanying this may cause a possibility of injuring a worker who is operating the lawn mower, and so on, and therefore this is undesirable. 
         [0036]    Then, according to the present invention, in such case, although the “regeneration” electric power maintained above is supplied to the blade motor  70 ; however, that “regeneration” electric power is consumed within the blade motor  70 , with safe and certainty, without rotating that blade  80 , unpreparedly or carelessly, by controlling the drive circuit  652  of the controller  65  for the blade motor, the details of which will be mentioned later. 
         [0037]    Hereinafter, detailed explanation will be given on an example of the detailed circuit configuration of the drive circuit  652  mentioned above, for consuming the “regeneration” electric power mentioned above by means or within the blade motor  70 , and also an example of a method for processing control for that, by referring to  FIGS. 4 and 5  attached herewith. 
         [0038]    First of all, in  FIG. 4  is shown the detailed circuit configuration of the drive circuit  652  mentioned above; however even in this figure, the constituent elements attached with the reference numerals, being same to those mentioned above, are similar to those mentioned above. 
         [0039]    In the figure, a rotation speed signal from the rotation speed sensor  71 , which is attached on part of the motor  70  is detected by a speed detector portion  6526 , and thereby a motor rotation speed can be obtained. 
         [0040]    On the other hand, the rotation speed obtained in the above is compared with a target speed (for example, being inputted from the CPU shown in  FIG. 3 ) in a subtracter  6524 , and as a result thereof, being combined with a zero (0) torque instruction and battery voltage, a torque current instruction “Iq*” and an excitation current instruction “Id*” are produced in a current instruction calculator portion  6527 . Also, detection of the currents of U-phase and V-phase from the sensor  72  (in the present embodiment, two (2) sets of current detectors for detecting the currents of U-phase and V-phase, for example) is made by means of a current detector portion  6521 , and the current components, i.e., torque current “Iq” and excitation current “Id” are produced by a 3-phase/2-phase coordinate converter portion  6522 , to be inputted into a current controller portion  2628 . In this current controller portion  2628  are obtained q-axis voltage (Vq) and d-axis voltage (Vd), upon basis of the current instructions and feedback currents, which are inputted, and upon basis of those voltages, in a 2-phase/3-phase coordinate converter portion  6529  are produced control signals Vu, Vv and Vw, for controlling elements of the inverter circuit  651  of supplying 3-phase rotating stator currents to be supplied to the blade motor  70 , as is similar to that in the conventional art. 
         [0041]    Further, in the present embodiment, the rotating torque generated by the blade motor  70  is suppressed by brining the torque current instruction “Iq*” corresponding to a “zero torque” instruction from an outside to zero (0), and for that reason, the blade  80  will not rotates, unpreparedly or carelessly. Thus, the “regeneration” electric power mentioned above is used within the blade motor  70 , not in the form of the rotating torque, but in the form of the excitation current, and consumed in the form of heat generation of windings. 
         [0042]    Next, the processing of control for consuming the “regeneration” electric power by the glade motor  70  will be shown by referring to a flowchart shown in  FIG. 5 . In the figure, when the processing is started, first of all, determination is made on whether the running motor  30  is in the condition of the “powering” operation, or in the condition of the “regeneration” operation (step S 51 ). As a result thereof, if being determined in the “powering” operation, that process is stopped. However, the determination on whether the motor  30  is in the “regeneration” operation or not, for example, as is shown in  FIG. 3 , may be made by determining that the said motor  30  is in the regeneration operation condition within the drive circuit  602  for controlling the inverter circuit  601  of supplying electric power to the running motor  30 , and outputting the result thereof to an outside as a “regeneration signal”, as shown in the figure, or in the place of this, for example, while detecting the current flowing between the inverter circuit  601  and the battery  50  it is also possible to determined the “regeneration” condition, depending on the direction of flowing thereof (the inverter circuit→the battery). 
         [0043]    On the other hand, when the motor  30  is determined to be in the “regeneration” operation condition, further determination is made on the charging condition of the battery  50  mentioned above. Thus, determination is made on whether the battery  50  is in the full-charge condition or not (for example, SOC-80% to 100%) (step S 52 ). As a result thereof, in case where the battery  50  is in the full-charge condition (see “YES” in the figure), further determination is made on whether the blade motor  70  is in a driving (or ON) condition or not (step S 53 ). This may be determined, for example, with utilizing a switch or an instruction for instructing start/end of the grass cutting operation (for example, ON/OFF information shown in  FIG. 4 ). And, as a result of the determination in the step S 53  mentioned above, if the blade motor  70  is in the operating (ON) condition (see “YES” in the figure), all the regeneration electric power is supplied to the blade motor  70  (step S 55 ), and then the process is ended. In this instance, all the regeneration electric power is consumed while keeping the blade motor rotating. On the other hand, if the blade motor  70  is not in the operating (ON) condition (see “NO” in the figure), after generating the zero (0) torque instruction (step S 54 ), the process shifts into the step S 55 , similar to the case where it is in the driving (ON) condition, i.e., all the regeneration electric power is supplied to the blade motor  70 , and then the process is ended. However, since the zero (0) torque instruction is generated, all the regeneration electric power is consumed while stopping the blade driving. 
         [0044]    However, in the step S 52  mentioned above, when the battery  50  is determined not in the full-charge condition (see “NO” in the figure), further determination is made on whether the battery voltage is overcharge or not (step S 56 ). 
         [0045]    As a result thereof, when the battery voltage is overvoltage (see “YES” in the figure), in the similar manner to that mentioned above, further determination is made on whether the blade motor  70  is in the operating (ON) condition or not (step S 57 ). When the blade motor  70  is in the operating (ON) condition (see “YES” in the figure), the electric power to be supplied to the blade motor is increased (step S 59 ). Next, determination is made on whether the battery is overvoltage or not (step S 60 ), and when it is determined to be overcharge, then the process movers into a step S 59 , in which the electric power supplied to the blade motor is further increased. Increase of the electric power supplied to the blade motor is continued until when the overcharge condition of the battery is dissolved. When the battery is not in the condition of the overcharge, the process is ended. On the other hand, when the blade motor  70  is not in the operating (ON) condition (see “NO” in the figure), the zero (0) torque instruction is generated (step S 58 ). Thereafter, also the electric power supplied to the blade motor is kept to increase, until when the overcharge condition of the battery is dissolved. When the battery is not in the condition of the overvoltage, the process is stepped. 
         [0046]    On the other hand, in the step S 56  mentioned above, if it is determined that the battery voltage is not the overvoltage (see “NO” in the figure), further determination is made on whether the regeneration electric power was already absorbed or not by the blade motor (step S 61 ). As a result thereof, when the determination is made that the regeneration electric power was already absorbed (see “YES” in the figure), in addition thereto, determination is made if the battery is acceptable or not the regeneration electric power much more than the present condition (step S 62 ). The determination on whether the battery is acceptable or not the regeneration electric power much more than the present condition can be made, for example, by providing a threshold value to be a little bit lower than a threshold value of the overvoltage of the battery voltage. 
         [0047]    As a result thereof, when the determination is made that the battery is acceptable the regeneration electric power more than the present condition (see “YES” in the figure), the electric power supplied to the blade motor is decreased (step S 63 ). Next, determination is made whether the electric power supplied to the blade motor is zero (0) or not (step S 64 ), and if it is zero (0), then the process is ended. If it is not zero (0), the process turns back to the step S 62 , and then determination is made on whether the battery is acceptable or not the regeneration electric power more than the present condition, and if it is acceptable, further the electric power supplied to the blade motor is decreased (step S 63 ). If it is determined that the battery is unacceptable more than the present condition in the step S 62 , or if it is determined that the regeneration electric power was not already absorbed in the step S 64 , then the process is ended. On the other hand, if it is determined that the regeneration electric power was not already absorbed in the step S 61 , also the process is ended. 
         [0048]    Furthermore, in the explanation mentioned above, the battery  50  is made up with four (4) pieces of batteries, which are connected in series, and the voltage thereof, 58˜64V (=(14.5˜16V)/1 piece×4), is set to be a reference for determining the overvoltage (=V 1 , see the step S 56 ), while as a reference of the voltage unacceptable for the battery (see the step S 61 ) is set to 56˜62V=V 2 . Further, with this, the voltage being acceptable for the battery comes to 56˜62V, being equal to or less than the V 2 . 
         [0049]    With such charging control of the regeneration electric power as was mentioned above, driving of the blade motor  70  is conducted while returning the regeneration electric power to the battery. Thus, with this, it is possible to protect the battery  50  from consuming the electric power unnecessarily. On the other hand, in case where the blade motor  70  is not under the operation (e.g., “ON”) condition, i.e., under the stopping condition, as the result of determination, as was shown in  FIG. 4  mentioned above, the “regeneration” electric power is used, not in the form of the rotating torque, but in the form of the excitation current, within the blade motor  70 ; in other words, it is consumed in the form of heat of the windings (see steps S 55  and S 58 ). In more details, in the present embodiment, the “zero (0) torque” instruction is outputted to the current instruction calculator portion  6527  building up the drive circuit  652  for the blade motor  70  mentioned above. Thus, the torque current “Iq” is set to zero (0), and thereby the rotating torque generated by the blade motor  70  is made small. For that reason, the blade will not rotate, unpreparedly or carelessly, while the “regeneration” electric power is consumed in the form of heat generation of the windings, e.g., the excitation current. 
         [0050]    Also, in particular, in case of a lead storage battery, since it has a large internal resistance even when not being in the “full-charge condition”, it shows a phenomenon of rising up a terminal voltage thereof (seems to be not preferable for the battery), and then, it is impossible to return the regeneration electric power to the battery, more than that, if the terminal voltage rises up to be a certain value or higher than that, even if not being in the “full-charge condition”, for the purpose of protecting equipment thereof, such as, (at least) the controller, etc. In that case, it is preferable to send a part of the regeneration electric power (i.e., only that, which cannot be absorbed by the battery) towards the non-running motor, so as to be absorbed therein, as is similar when being in the “full-charge condition”. In more details, this can be deal with, by observing the battery voltage during when the regeneration is conducted, even if the battery is not in the “full-charge condition”, and increasing the current to be supplied to the blade (non-running) motor when that voltage looks to be equal to or greater than a certain threshold value, until when that voltage goes down to be equal to or less than that threshold value. In other words, the regeneration energy is absorbed by the blade motor, when being in the condition of the overvoltage, even if not being in the “full-charge condition”. 
         [0051]    However, the controlling process mentioned above is accomplished, for example, by the CPU  653 , which builds up the motor controller  65  for the blade motor  70  shown in  FIG. 4  mentioned above, through execution of the software being stored in an internal memory thereof. However, the present invention should not be restricted only to such configuration as was mentioned above, and also, for example, the CPU  653  may be shared with the CPU  603 , which builds up the motor controller  60  for the running motor  30  mentioned above. Further, in the embodiment mentioned above, although the explanation was given that the “regeneration” electric power is consumed, not in the form of the rotating torque, but in the form of the exciting current, within the blade motor  70 ; however, the present invention should not be limited to only to this, other method (s) than that may be applicable, if it does not accompany the unprepared or careless rotation of the blade motor  70 . 
         [0052]    Although it is preferable to apply a position sensor having high resolution power and to execute (current) feedback control, because they increase an accuracy of the zero (0) torque, and also from a viewpoint of safety; however, in the place thereof, may be a position sensor having a low resolution power and a feed-forward control.