Abstract:
Several embodiments of electric vehicle control and control apparatus wherein the amount of regenerative braking of the vehicle and the type of braking is determined by current conditions to provide simpler and more effective control regardless of condition of the power source for the vehicle.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to an electric motor driven vehicle and more particularly to one having an improved regenerative braking system for a DC shunt powered driving motor therefore.  
         [0002]     As shown in Japanese Published Patent Application Hei 10-309005 (A) it has been proposed to employ a DC shunt motor for the driving of electric powered vehicles such as golf carts and the like. There the armature coil and the field coil are connected in parallel to a common electric power source. As is known, it is possible to energize the armature coil and the field coil independently from each other. The amount of current supplied to the armature coil is controlled based on the position of a operator controlled vehicle speed control such as, for example, an accelerator pedal. Then a specific current is supplied to the field coil depending on the armature current value. This is generally done by reference to a field map that is constant or pre-designed for each motor. This produces a specific torque from the electric motor to control the operation required by the various operating conditions of the electric vehicle.  
         [0003]     In these types of electric vehicles there are also provided regenerative braking functions according to certain driving conditions. For example it is common to decelerate the vehicle to a specified speed without freewheeling when the accelerator control is released. In addition an arbitrary speed may be limited on a downhill run with the accelerator control remaining on. Also it is common to detect motion of unattended vehicle and apply braking of the vehicle and/or switch traveling direction between forward and reverse with the accelerator control remaining on during traveling. These controls are conventionally performed usually by controlling the voltages applied to the armature and field coils.  
         [0004]     However, the voltage and capacity of the battery change according to conditions of use. Thus the torque of regenerative braking changes with the voltage and capacity of the battery and stabilized regenerative operation cannot be obtained. That is, as the characteristic among revolution speed (N), torque (T), and current (I) of the motor changes along with the battery voltage, it would be necessary to make a map of N-T-I characteristic for each battery voltage. This makes a control program complicated, requiring a large memory capacity and a large-sized circuit.  
         [0005]     As an alternative in U.S. Pat. No. 6,686,712 it has been proposed to use various regenerative controls are performed according to vehicle speeds and independently of the position of the accelerator control. This, however, can give rise to a situation that control performed could be different from the intention of the operator. For example, if the vehicle decelerates on an uphill run, the armature current could become excessive even if the position of the accelerator control does not call for it.  
         [0006]     It is, therefore, one principal object of the invention to compensate for the regenerative braking operations depending on the status of the battery depending on its voltage and capacity.  
         [0007]     It is another principal object of the invention to provide vehicle speed control in response to the operator&#39;s intentions.  
         [0008]     It is a still further object of the invention to provide a shunt motor control capable of maintaining constantly stabilized motor torque regardless of changes in voltage and capacity of the battery.  
       SUMMARY OF THE INVENTION  
       [0009]     A first feature of this invention is adapted to be embodied in a regenerative braked shunt motor operated vehicle powered from a battery and having an armature coil and a field coil. In accordance with the invention the current values in the coils is monitored during vehicle operation and the regenerative braking is varied in response to the measured values.  
         [0010]     Another feature of the invention is adapted to be embodied in a method of applying regenerative braking to shunt motor operated vehicle comprising the steps of monitoring the current values in the coils during vehicle operation and varying the regenerative braking response to the measured values. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a partially schematic, top plan view of an electric powered vehicle constructed and operated in accordance with the invention.  
         [0012]      FIG. 2  is a schematic electrical diagram showing the motor control on accordance with the invention.  
         [0013]      FIG. 3  is a block diagram of a part of the control shown in  FIG. 2 .  
         [0014]      FIG. 4  is a graph of circuit control in accordance with the invention.  
         [0015]      FIG. 5  is a graph showing the armature circuit control employed in  FIG. 4 .  
         [0016]      FIG. 6  is a graph showing the field current control employed in  FIG. 4 .  
         [0017]      FIG. 7  is a graph, in part similar to  FIG. 4 , of circuit control in accordance with another feature of the invention.  
         [0018]      FIG. 8  is a graph showing the field current control employed in  FIG. 7 .  
         [0019]      FIG. 9  is a graph showing how the driving direction is determined from the current applied.  
         [0020]      FIG. 10  is a graph, in part similar to  FIGS. 4 and 7 , of current control of another feature of the invention.  
         [0021]      FIG. 11  is a graph, in part similar to  FIGS. 4, 7  and  10 , of current control of still another feature of the invention.  
         [0022]      FIG. 12  is a graph used for field current control of the embodiment of  FIG. 11 . 
     
    
     DETAILED DESCRIPTION  
       [0023]     Referring now in detail to the drawings and initially to  FIG. 1 , an electrically powered vehicle such as a golf cart, as an example of vehicle with which the invention may be practiced is identified generally by the reference numeral  21 . This golf cart  21  is provided with a body, frame  22  that rotatably supports in any desired manner paired front wheels  23  and rear wheels  24 . In the illustrated embodiment, the rear wheels  24  are driven by a shunt type electric motor  25  through a transmission  26 . Associated with some or all of the wheels  23  and  24  (only the front wheels  23  in the illustrated embodiment) are brakes  27  of any desired type.  
         [0024]     An operator may be seated on a suitable seat (neither of which are shown) behind an accelerator pedal  28 , for controlling the speed of the electric motor  25 , a brake pedal  29 , for operating the wheel brakes  27 , and a steering wheel  31 , for steering the front wheels  23  in any desired manner.  
         [0025]     Also juxtaposed to the operator&#39;s position is a main switch  32 , and a direction control switch  33 , for controlling the direction of travel of the golf cart  21  by controlling the direction of rotation of the motor  25 . The main switch  32  and the direction control switch  33  are connected to a controller  34 . Operation of the accelerator pedal  28  is transmitted to an on off pedal switch  35  and an accelerator opening degree sensor  36  connected to the controller  34 , to send on or off state of the accelerator  28  and its degree of opening to the controller  34 .  
         [0026]     A plurality of batteries  37  as power sources are mounted suitably on the body frame  22  and are connected through a relay  38  to the controller  34 .  
         [0027]     Referring now to  FIG. 2  this is a circuit block diagram of the electric vehicle  21  using the shunt motor  25  and embodying the invention. Electric power sent from the batteries  37  is supplied through the relay  38  to an MPU  39  having a memory and a control circuit to supply the necessary power to various driving circuits as will be described.  
         [0028]     Signals from the main switch  32 , the pedal switch  35 , the direction control switch  33  and the accelerator opening sensor  36  are inputted to the MPU  39 , from which a command signal for drive-controlling the motor  25  is outputted. Further it is possible to interconnect a personal computer  41  or an external terminal device  42  and the MPU  39  through wire or wireless means such as infrared rays either to input a control program into the MPU  39  or read contents stored in the MPU  39 .  
         [0029]     Continuing to refer to  FIG. 2 , the motor  25  is of the shunt coil type with an armature coil  43  and a field coil  44  connected to an armature driving circuit  45  and a field driving circuit  46 , respectively.  
         [0030]     The armature driving circuit  45  is a bipolar circuit formed as shown in  FIG. 2  with upper and lower rows of FETs, eight in each row. Driving current is supplied to the armature coil  43  by alternately switching on or off the upper and lower rows of FETs.  
         [0031]     The field driving circuit  46  is an H-bridge circuit formed with four FETs and capable of changing the direction of current by simultaneously turning on or off the diagonally opposing FETs. It should be noted that the number of the FETs used in the armature driving circuit  45  and the field driving circuit  46  is not limited to that mentioned above but may be appropriately determined according to the amount of current required for the motor  25 .  
         [0032]     A current sensor  47  is interposed between the armature driving circuit  45  and the armature coil  43  of the motor  25 . In a like manner, current sensor  48  is interposed between the field driving circuit  46  and the field coil  44  of the motor  25 . The current sensors  47  and  48  detect currents actually flowing through the coils  43  and  44  respectively. The detected currents of the motor driving command signals coming from the MPU  39  are feedback-controlled. In this way, the currents flowing in the armature and field sides are accurately controlled to produce torque in the motor  25  corresponding to the depression amount of the accelerator pedal. The motor  25  is provided with a speed sensor  49  made up of an encoder and other components.  
         [0033]     A method of control by the controller  34 , as shown in  FIG. 2  will now be described by reference to the block diagram of  FIG. 3   
         [0034]     The input signal from the accelerator pedal  28  operated by the driver is amplified by an amplifier  51  and sent together with the vehicle speed signal from the speed sensor  49  to a vehicle speed determination circuit  52 . The vehicle speed determination circuit  52  determines the speed of the vehicle  21  and determines whether or not the vehicle speed has exceeded a specified reference value (for example a limit speed of 22 km/h in a golf course). A determination result of the vehicle speed determination circuit  52  or a binary signal of determination on whether or not the vehicle speed has exceeded the specified limit speed, together with the signal from the accelerator pedal  28 , is inputted to an armature command current operation circuit  53 . In addition, the on/off signal of the pedal  28  from the pedal switch  35  and the accelerator opening (depression amount) signal from the accelerator opening sensor  36  are sent to the armature command current operation circuit  53  directly or through the vehicle speed determination circuit  52 .  
         [0035]     The armature command current operation circuit  53  is a circuit built within the MPU  39  shown in  FIG. 2  to calculate a command current value for driving the motor  25  according to the accelerator pedal depression amount. This calculation is carried out for example with a map predetermined according to the accelerator pedal depression amount. The power source voltage from the batteries  37  is converted based on the calculated command current value into a coil driving voltage. The command current (la) of a calculated pulse width is applied to the armature coil  43  by a PWM control method.  
         [0036]     The MPU  39  is provided with a map (la-lf map)  54  for the field coil current (lf) for driving the motor  25  at a maximum efficiency according to the armature coil current (la). A field coil current lf is determined from the la-lf map  54  according to the command current la of the armature coil  43  and inputted to a field command current operation circuit  55 . The field command current operation circuit  55  converts the power source voltage from the batteries  37  into a coil driving voltage based on the lf obtained with the map  54  and applies a command current (lf) of a calculated pulse width to the field coil  44  by a PWM control method. Since the motor  25  is driven with the la and lf calculated as described, a torque commensurate with the accelerator pedal depression amount is obtained.  
         [0037]     In addition, regenerative braking is performed as shown in the following embodiment with the regenerative current corresponding to operating conditions based on the armature current la detected with the current sensor  47 . This applies regenerative breaking when the operator releases the accelerator pedal  28 . This will now be described by reference to  FIGS. 4-6 .  
         [0038]      FIG. 4  is a chart showing how a regenerative braking process is applied at the time when the driver of the electric vehicle releases the accelerator pedal  28 . The release of the accelerator pedal at the time t 1  is detected by the pedal switch  35  ( FIG. 2 ).The horizontal axis represents elapsed time. At the same time as the driver releases the accelerator pedal  28  at a time t 1  when driving, the armature current la which has been flowing in the positive direction is set to zero. From the time t 1 , the vehicle  21  coasts. After that, with a dwell interval of about several milliseconds interposed for electric stability, an armature current la is applied beginning at the time t 2  in a negative direction. This is in the regenerative direction opposite to the driving direction.  
         [0039]     The armature current la is controlled by changing its pulse width by the PWM of the armature command current operation circuit  53 . Up to the time t 1 , a command current of a pulse width calculated according to the accelerator pedal opening up to that time is applied. From the time t 1  on, a command current with no substantial pulse signal with zero pulse width is applied. Next, from the time t 2  on, command current is applied while its pulse width being gradually increased by the PWM control of the armature command current operation circuit  53 . Due to the change in the pulse width, regenerative current increases gradually. The rate of increase in the regenerative current (gradient toward the negative side of the graph) is predetermined with a fixed gain constant. In this way, regenerative current is obtained within the pulse width and the freewheeling speed decreases gradually.  
         [0040]     The amount of regenerative armature current la is determined with the v-la map of  FIG. 5  representing the relationship between the vehicle speed v and the armature current la. For example, it is programmed as follows. In cases where the vehicle speed when the driver releases the accelerator pedal is not lower than the limit speed of 22 km/h in the golf course, the armature current la takes a maximum value of 250 amperes. When the vehicle speed slows down to 22 km/h or below by braking, the current value becomes a value commensurate with the vehicle speed. When the vehicle speed slows down below  10  km/h, the armature current la is made to zero so that regenerative braking is over. These values for the vehicle speeds may be set as desired by the program.  
         [0041]     The field current amount corresponding to the armature current la is determined according to the la-lf map shown in  FIG. 6  (counterpart of the la-lf map  54  of  FIG. 3 ) representing the relationship between the armature current la and the field current lf.  
         [0042]     Regenerative braking is performed with the armature current la and the field current lf determined as described above. The regenerative braking starts from a time t 3  slightly after the time t 2  by applying the current lf to the field coil  44 .  
         [0043]     The field current lf is of a value corresponding to the armature current la of up to the time t 1 , up to the time t 2  and decreases from the time t 2  on. This rate of decrease (gradient of the graph) is predetermined with a fixed gain constant. From the time t 3  on, field current lf is applied according to the la-lf map to obtain regenerative current corresponding to the la. The time t 3  (point A) is the time point when the value of lf according to the la-lf map becomes greater than the value of lf up to that time. After the point A, lf is applied according to the la-lf map.  
         [0044]     The time t 4  (point B) is the time point when the value of armature current la obtained with the v-la map of  FIG. 5  becomes greater. From a time t 4  on, the armature current la is calculated according to the v-la map while the field current lf is calculated according to the la-lf map.  
         [0045]     When the vehicle decelerates down to 10 km/h as set from the v-la map of  FIG. 5  at a time t 5 , the armature current la becomes zero. The field current lf starts decreasing at a time t 6  with a little delay and takes a minimum value at a time t 7  when the regenerative braking process comes to an end.  
         [0046]     After that, when the driver intends to stop the vehicle, the driver operates the brake pedal. In order to speed up, the driver operates the accelerator pedal. Incidentally, it is also possible to design a v-la map to perform regenerative braking until the vehicle speed comes to zero.  
         [0047]     Another embodiment of regenerative braking is shown in  FIGS. 7 and 8 . This embodiment applies regenerative braking to limit maximum vehicle speed. Referring first to  FIG. 7  this is a time chart showing a regenerative braking process for controlling that the vehicle does not exceed a limit speed even when the driver continues depressing the accelerator pedal  28 . The dotted curve denotes the vehicle speed during this operation.  
         [0048]     In case the vehicle speed exceeds the limit speed v 1  at a time t 1 , caused by, for example the vehicle going down an incline, the armature current la of positive direction is lowered to zero toward a time t 2  by decreasing pulse width by PWM control  53 . After a lapse of several milliseconds, predetermined by a timer, from a time t 3  on, armature current la is applied in negative direction to start regenerative braking.  
         [0049]     In this case, whether or not the vehicle speed has exceeded the limit speed v 1  is determined with the vehicle speed determination circuit  52  shown in  FIG. 3 . If it has, control is made to start regenerative braking. The field current lf is controlled according to the la-lf map of  FIG. 8 . The armature current la during regenerative braking increases in proportion to the amount the vehicle speed exceeds the limit value.  
         [0050]     After the armature current la in negative direction flows to start regenerative braking, the vehicle speed may still increases due to inertia for some period of time, and then decreases. When the vehicle speed lowers down to the limit speed at a time t 4 , la is decreased according to a predetermined gain constant down to zero at a time t 5  then the regenerative braking is stopped.  
         [0051]     If the driver continues depressing the accelerator pedal  28 , after the time t 5  at which regenerative braking is stopped, the armature current la increases in positive direction to continue driving state of the vehicle. If the vehicle speed again exceeds the limit speed v 1 , the regenerative braking as aforenoted is repeated.  
         [0052]      FIGS. 9 and 10  illustrate another embodiment of regenerative braking in a case where an unattended vehicle starts descending on a slope or the like. When no accelerator input is detected and a vehicle speed greater than a specified speed, for example 1 km/h, is detected, the MPU  39  determines the vehicle to be in an unattended driving state. In that case, first it is detected in which direction, forward or reverse, the vehicle is moving.  
         [0053]      FIG. 9  is a graph showing a search current process for detecting the direction the vehicle  21  is moving. This is done by applying a search current in either a positive or negative direction of the field coil  44  and finding which direction of applying the search current, positive or negative, results in the detection of current on the armature coil  43  indicated with the dotted curve. The current flowing in the armature coil  43  is the regenerative current. In the event current is detected in the armature coil  43  when a search current in positive direction is applied to the field coil  44 , the electric vehicle  21  is determined to be moving forward. In this case, a current (regenerative current) will not be detected if a search current in the negative direction is applied. In contrast, if a current is detected on the armature coil  43  when a search current in negative direction is applied, the vehicle  21  is determined to be moving in reverse direction.  
         [0054]     After the driving direction is detected by the search current process of  FIG. 9 , regenerative braking is started as shown in  FIG. 10 . The period from time t 1  to time t 2  of  FIG. 10  represents the search current process time shown in  FIG. 9 . For example, if the vehicle  21  is determined to be moving forward, an armature current la is applied so as to produce torque in reverse direction, against the moving direction of the vehicle  21 . When the vehicle speed becomes zero at a time t 4 , the armature current la is also brought back to zero.  
         [0055]     If the search current applied to the field coil is different in direction, positive or negative, from the field current lf for regenerative braking, a time interval of about several milliseconds is required between the time t 2  and t 3  to securing electric stability. Also, before and after the period of time (between t 5  and t 6 ) in which the field current lf is lowered with a fixed gain constant, the field current is kept constant for a period of several milliseconds by a timer.  
         [0056]     After the vehicle stops the regenerative braking process is concluded and current flow becomes zero both in the armature and field coils  43  and  44 .  
         [0057]     Referring now to  FIGS. 11 and 12 , these show are a regenerative braking process in the so-called plugging operation, in which the driving direction, forward or reverse, is switched by operating the direction control switch  33  when driving the vehicle with the accelerator pedal  28  depressed without operating the brake pedal  29  or changing the position of the accelerator pedal  28 .  
         [0058]     Simultaneously with operating the direction control switch  33  at a time t 1  while driving forward, the armature current la becomes zero. At the time t 2  the armature current la flows in the negative direction. In this case, in order that the vehicle  21  moving forward is quickly braked and switched to move in reverse, the field current lf is made to be the maximum, 25 amperes, regardless of the vehicle speed as shown in  FIG. 12 .  
         [0059]     When the vehicle speed lowers to a speed of for example 1 km/h just before a stop (at a time t 3 ), the armature current la is set to zero, and after a time interval of several milliseconds set by a timer, the field current lf is set to zero. Then, again after a time interval of several milliseconds set by the timer, the driving direction is switched at a time t 6  to drive in reverse. Incidentally, as the driver continues depressing the accelerator during that time, the field current after the time t 6  flows in the reverse driving direction.  
         [0060]     It should be apparent that the maps for the current control used in the regenerative braking operations described are only examples and may be appropriately modified according to driving conditions and motor performance, etc. It is possible to perform regenerative braking while monitoring the vehicle speed according to preset limit speed, corresponding to various conditions of use of the electric vehicle, as a golf cart for driving on cart paths with varying grades or for other uses. This invention may be applied to various types of vehicles using a DC shunt motor as a driving source. Of course those skilled in the art will readily understand that the described embodiments are only exemplary of forms that the invention may take and that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.