Abstract:
A control system for controlling a vehicle which has an engine for driving at least one of wheels thereof and a motor for driving at least one of the rest of the wheels thereof. The control system includes: a motor generator configured to be driven by the engine for generating first alternating-current power at a first voltage; an inverter which converts the first alternating-current power to second power at a second voltage lower than the first voltage or to third direct-current power at a third voltage; and a battery to be charged with the second power supplied from the inverter. The motor is supplied with the third direct-current power at the third voltage obtained from the first alternating-current power.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The present invention relates to a control system and a control method for controlling a four wheel drive (4WD) vehicle, in which either one of a pair of front wheels or a pair of rear wheels are driven by an engine and the other pair of wheels are driven by a motor.  
         [0003]     2. Description of Related Art  
         [0004]     Japanese Patent Application Laid-open Publications No. 2002-152911 and 2002-200932 disclose a 4WD vehicle in which front wheels thereof are driven by an engine and rear wheels thereof are driven by a motor. Electric power to be supplied to the motor is generated by a power generator driven by the engine.  
       SUMMARY OF THE INVENTION  
       [0005]     In the above-described vehicle, the power generator for the motor is provided separately from a power generator for electric equipments of the vehicle. Accordingly, the number of parts/equipments is increased and spaces are wasted. Further, the weight and costs of the vehicle are increased.  
         [0006]     An object of the present invention is to provide a control system and a control method for controlling a motor powered 4WD vehicle, which provide a simplified system configuration.  
         [0007]     An aspect of the present invention is a control system for controlling a vehicle which has an engine for driving at least one of wheels thereof and a motor for driving at least one of the rest of the wheels thereof, the control system comprising: a motor generator configured to be driven by the engine for generating first alternating-current power at a first voltage; an inverter which converts the first alternating-current power to second power at a second voltage lower than the first voltage or to third direct-current power at a third voltage; and a battery to be charged with the second power supplied from the inverter, wherein the motor is supplied with the third direct-current power at the third voltage obtained from the first alternating-current power. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The invention will now be described with reference to the accompanying drawings wherein:  
         [0009]      FIG. 1  is a block diagram showing a configuration of a control system for a motor powered 4WD vehicle according to a first embodiment of the present invention.  
         [0010]      FIG. 2  is a flowchart showing an operation of the control system for a motor powered 4WD vehicle according to the first embodiment when starting an engine.  
         [0011]      FIG. 3  is a flowchart showing an operation of the control system for a motor powered 4WD vehicle according to the first embodiment when charging a battery.  
         [0012]      FIG. 4  is a flowchart showing an operation of the control system for a motor powered 4WD vehicle according to the first embodiment when driving a motor.  
         [0013]      FIG. 5  is a table for describing operation states of respective devices in the control system for a motor powered 4WD vehicle according to the first embodiment.  
         [0014]      FIG. 6  is a block diagram showing a configuration of a control system for a motor powered 4WD vehicle according to a second embodiment of the present invention.  
         [0015]      FIG. 7  is a table for describing operation states of respective devices in the control system for a motor powered 4WD vehicle according to the second embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Embodiments of the present invention will be explained below with reference to the drawings, wherein like members are designated by like reference characters.  
         [0017]     A control system CS 1  according to a first embodiment of the present invention controls a vehicle, in which either one of a pair of front wheels or a pair of rear wheels are driven by an engine and the other pair of wheels are driven by a motor. As shown in  FIG. 1 , this system CS 1  includes an engine  1 , a 42-V alternator (a motor generator)  2  which is connected to the engine  1  through a belt and generates a three-phase alternating-current power at 42 V (a first rated voltage) by use of torque of the engine  1 , and a 14-V battery E 1  for supplying electric power to various electric devices mounted on the vehicle.  
         [0018]     The system CS 1  further includes a step-up and step-down inverter  3 , and a motor M 1  which is driven by direct-current power outputted from the step-up and step-down inverter  3 . The step-up and step-down inverter  3  converts the three-phase alternating-current power outputted from the 42-V alternator  2  into direct-current power. Meanwhile, the step-up and step-down inverter  3  lowers the voltage of the three-phase alternating power from 42 V to 14 V (a second rated voltage), rectifies the current thereof, and supplies the rectified power to the 14-V battery E 1  for charging the battery E 1 . Further, the step-up and step-down inverter  3  converts the direct-current power outputted from the 14-V battery E 1  into three-phase alternating-current power and increase the voltage thereof, and supplies the three-phase alternating-current power to the 42-V alternator  2 .  
         [0019]     In addition, the system CS 1  includes an engine controller  12 , a motor controller  9  for controlling the drive of the motor M 1 , and a drive circuit  6  for controlling the drive of the step-up and step-down inverter  3  and of the 42-V alternator  2 . The engine controller  12  outputs an ignition signal to the engine  1  and controls an injector based on a detection signal of a revolution sensor  10  provided on the engine  1  and a detection signal of an accelerator sensor (not shown).  
         [0020]     A detection signal of a wheel speed sensor (not shown), the detection signal of the accelerator sensor, and a detection signal of a rotational position sensor  11  for detecting a rotation angle of the 42-V alternator  2  are inputted to the motor controller  9 . Based on the respective detection signals, the motor controller  9  opens and closes a switch SW 2  (a second switch) provided between the step-up and step-down inverter  3  and the motor M 1 , and also outputs a control signal to a field controller  13  for controlling a field current of the motor M 1  (a current flowing in a field coil).  
         [0021]     An output shaft of the motor M 1  is connected to rear wheels  5  through a differential  4 . Here, an example of driving the rear wheels  5  with the motor M 1  will be explained. However, when driving the rear wheels  5  with the engine power, the motor M 1  drives front wheels instead.  
         [0022]     The 42-V alternator  2  is provided with a field controller  8  for controlling a field current of the 42-V alternator  2 . This field controller  8  is operated under control of the drive circuit  6  and the motor controller  9 .  
         [0023]     The step-up and step-down inverter  3  includes six switching elements Tr 1  to Tr 6  of insulated gate bipolar transistors (IGBTs), metal oxide semiconductor field effect transistors (MOS-FETs), or the like. A ground terminal of the step-up and step-down inverter  3  is connected to a negative terminal of the 14-V battery E 1  through a switch SW 1  (a first switch) and is then connected to ground.  
         [0024]     A positive terminal of the 14-V battery E 1  is connected to a neutral point of three-phase field coils of the 42-V alternator  2 . A voltage sensor  7  is provided for measuring the charging voltage of the 14-V battery E 1 .  
         [0025]     An operation signal of an accelerator switch SW 3  and a detection signal of the voltage sensor  7  are inputted to the drive circuit  6 . Upon receipt of these signals, the drive circuit  6  outputs driving signals to control input terminals of the six switching elements Tr 1  to Tr 6  included in the step-up and step-down inverter  3 . Further, the drive circuit  6  outputs a control signal for opening and closing the switch SW 1 .  
         [0026]     In the system CS 1 , by allowing the step-up and step-down inverter  3  to perform a powering operation while the switch SW 1  is turned on (closed) and the switch SW 2  is turned off (open) under control of the drive circuit  6  and the motor controller  9 , it is possible to convert the direct-current power discharged from the 14-V battery E 1  into the three-phase alternating-current power, to use the 42-V alternator  2  as an electric motor, feeding this three-phase alternating-current power, and thereby to start the engine  1 . Meanwhile, by allowing the step-up and step-down inverter  3  to perform a regenerative operation, using the 42-V alternator  2  as a power generator, it is possible to rectify the three-phase alternating-current power generated by the 42-V alternator  2  and lower the voltage thereof, thereby to charge the 14-V battery E 1 . In addition, by allowing the step-up and step-down inverter  3  to perform a regenerative operation while turning the switch SW 1  off and turning the switch SW 2  on, it is possible to power the motor M 1  and allow the vehicle to perform 4WD drive.  
         [0027]     Next, operations of the control system CS 1  will be described in terms of (A) starting the engine, (B) charging the 14-V battery, and (C) driving in 4WD mode, respectively. Here, actions of the 42-V alternator  2 , the step-up and step-down inverter  3 , the 14-V battery E 1 , the switches SW 1  and SW 2 , and the motor M 1  in the respective operations are as shown in  FIG. 5 .  
         [0000]     (A) Operation When Starting the Engine  
         [0028]      FIG. 2  is a flowchart showing a process operation when starting the engine. Firstly, when the accelerator switch is turned on in Step S 1 , an instruction signal is outputted to the field controller  8  under control of the drive circuit  6  to apply a field current thereto. In this way, the field current of the 42-V alternator  2  becomes controllable in Step S 2 .  
         [0029]     Thereafter, the switch SW 1  is turned on in Step S 3 . In this way, an output voltage (14 V at the maximum) from the 14-V battery E 1  is applied to the neutral point of the 42-V alternator  2 . Further, in Step S 4 , the drive circuit  6  controls output signals to the control input terminals of the switching elements Tr 1  to Tr 6  in the step-up and step-down inverter  3 , and thereby controls on and off states of these switching elements Tr 1  to Tr 6 . In Step S 5 , the drive circuit  6  causes the step-up and step-down inverter  3  to generate the three-phase alternating-current power (approximately 1 kW (kilowatts) at the maximum) from the power supplied from the battery E 1  (approximately 1 kW at the maximum) while increasing the voltage thereof to approximately 20 Vrms (root mean squared voltage).  
         [0030]     The generated three-phase alternating-current power is applied to the 42-V alternator  2 . Accordingly, a shaft of the 42-V alternator  2  rotates as the electric motor and cranks the engine  1 . Simultaneously, the engine controller  12  outputs the ignition signal to the engine  1  and outputs a fuel injection signal to the injector. Accordingly, the engine  1  is started in Step S 6 .  
         [0000]     (B) Operation When Charging the Battery  
         [0031]     Next, an operation when charging the 14-V battery E 1  will be described with reference to a flowchart shown in  FIG. 3 ,  
         [0032]     In Step S 11 , the drive circuit  6  determines whether or not the engine  1  is started. When the engine  1  is started, in Step S 12 , the motor controller  9  determines whether or not the vehicle is in 4WD mode, or in other words, whether the motor M 1  is in operation and the switch SW 2  is turned on.  
         [0033]     Meanwhile, when the vehicle is in 4WD mode, in Step S 13 , the motor controller  9  outputs the control signal to the field controller  8  and thereby controls the field current of the 42-V alternator  2 .  
         [0034]     Thereafter, the switch SW 1  is turned on in Step S 14 . In this way, the 42-V alternator  2  functions as a power generator and the step-up and step-down inverter  3  performs the regenerative operation. Accordingly, the alternating-current power (approximately 4 kW at the maximum) generated by the 42-V alternator  2  is rectified, and the voltage thereof (11 to 42 Vrms) is lowered by controlling the on and off states of the respective switching elements Tr 1  to Tr 6 . In Step S 15 , the 14-V battery E 1  is charged with the direct-current power (approximately 1 kW at the maximum) at an appropriate charging voltage (14 V) adjusted based on the detection signal of the voltage sensor  7 .  
         [0035]     In this embodiment, the 14-V battery E 1  is connected between a negative bus of the step-up and step-down inverter  3  and the neutral point of the 42-V alternator  2 . In this way, a zero-phase voltage is applied to the inverter output voltage, which increases the voltage of the direct-current power formed by the inverter.  
         [0000]     (C) Operation in 4WD Mode  
         [0036]     Next, an operation in the 4WD mode will be described with reference to a flowchart shown in  FIG. 4 . Firstly, in Step S 21 , the motor controller  9  determines whether or not the 4WD drive is to be performed based on the detection signal of the wheel speed sensor and on the detection signal of the accelerator sensor, When performing the 4WD drive, in Step S 22 , the drive circuit  6  outputs an instruction signal to the field controller  8  to apply a field current thereto. In this way, the field current of the 42-V alternator  2  becomes controllable.  
         [0037]     Further, in Step S 23 , the motor controller  9  outputs another instruction signal to the field controller  13  to apply a field current thereto. In this way, the field current of the motor M 1  becomes controllable. Then, in Step S 24 , the 42-V alternator  2 &#39;s shaft is rotated by use of the torque of the engine  1  and is thereby operated as the power generator. In Step S 25 , the three-phase alternating-current power (approximately 4 kW at the maximum) generated by the 42-V alternator  2  is rectified by the step-up and step-down inverter  3 .  
         [0038]     At this time, in Step S 26 , the switch SW 2  is turned on under control of the motor controller  9 . Accordingly, the direct-current power (approximately 4 kW at the maximum) at a voltage of 16 to 60 V obtained by the rectification of the step-up and step-down inverter  3  is applied to the motor M 1  and a shaft of the motor M 1  is thereby rotated. The 4WD drive is thus achieved in which the front wheels are driven by the engine  1  and the rear wheels are driven by the motor M 1 .  
         [0039]     As described above, in the control system CS 1 , when the engine  1  is running, it is possible to rectify the electric power generated by the 42-V alternator  2 , lowering the voltage thereof, and thereby to charge the 14-V battery E 1 . Moreover, in the 4WD mode, it is possible to rectify the three-phase alternating-current power generated by the 42-V alternator  2  and to supply the power to the motor M 1 . Therefore, the single inverter can serve as the inverter for charging the 14-V battery E 1  and as the inverter for feeding power to the motor M 1 . Accordingly, it is possible to simplify a system configuration.  
         [0040]     In other words, the single motor generator (the 42-V alternator  2 ) can supply the electric power to the motor and the battery having mutually different rated voltages respectively. Accordingly, it is possible to provide flexibility in layout, and to reduce weight and cost.  
         [0041]     Meanwhile, when starting the engine  1 , it is possible to drive the 42-V alternator  2  by converting the power discharged from the 14-V battery E 1  into three-phase alternating power by use of the step-up and step-down inverter  3 , and feeding the three-phase alternating power to the 42-V alternator  2  for starting the engine  1 . Accordingly, no other power source is required to start the engine  1 . In this way, it is possible to simplify the system configuration.  
         [0042]     In other words, when starting the engine, it is possible to convert the power discharged from the battery into the three-phase alternating-current power at the first rated voltage by use of the step-up and step-down inverter, to rotate a shaft of the motor generator feeding the three-phase current power thereto, and thereby to start the engine. Accordingly, no other power source is required to start the engine. In this way, it is possible to simplify the system configuration.  
         [0043]     Moreover, the 42-V alternator  2 &#39;s shaft is rotated and the engine  1  is started when the accelerator switch SW 3  is turned on. Accordingly, it is possible to realize an idle stop operation in which the engine is temporarily stopped only while the vehicle is not in motion, thereby improving gas mileage,  
         [0044]     In other words, the engine is started when the accelerator switch for detecting an accelerating operation is turned on. Accordingly, it is possible to realize the idle stop operation, thereby improving gas mileage.  
         [0045]     Meanwhile, the start of the engine  1  and the charge of the 14-V battery E 1 , and the drive of the motor M 1  are switched by changing the on (closed) and off (open) states of the switch SW 1  and the switch SW 2 . Accordingly, when starting the engine  1  or charging the 14-V battery E 1 , it is possible to ensure disconnection between the motor M 1  and the step-up and step-down inverter  3  by turning the switch SW 2  off. When driving the motor M 1 , it is possible to ensure disconnection between the 14-V battery E 1  and the step-up and step-down inverter  3 . Therefore, it is possible to prevent malfunction and improve operability.  
         [0046]     In other words, by changing the open state and the closed state of the first and second switches, it is possible to ensure disconnection between the motor and the step-up and step-down inverter when starting the engine or charging the battery. Meanwhile, it is possible to ensure disconnection between the battery and the step-up and step-down inverter when driving the motor. Therefore, it is possible to prevent malfunction and to improve operability.  
         [0047]      FIG. 6  is a block diagram showing a control system CS 2  for a motor powered 4WD vehicle according to a second embodiment of the present invention. As shown in the drawing, the control system CS 2  includes the engine  1 , the 42-V alternator (the motor generator)  2 , the 14-V battery E 1 , the motor controller  9 , the field controller  8 , the engine controller  12 , the revolution sensor  10 , the rotational position sensor  11 , and the voltage sensor  7  as similar to the above-described first embodiment. The control system CS 2  further includes an inverter  3 ′.  
         [0048]     In the system CS 2 , a DC-DC converter  21  having two switching elements Tr 11  and Tr 12  is provided at a subsequent stage to the inverter  3 ′. An output terminal of the DC-DC converter  21  is connected to the 14-V battery E 1 . The system CS 2  includes a first drive circuit  6   a  for controlling the inverter  3 ′ and the DC-DC converter  21  based on the detection signal of the voltage sensor  7  and on the detection signal of the accelerator switch SW 3 .  
         [0049]     The inverter  3 ′ does not have a function to lower or increase the voltage. Instead, the DC-DC converter  21  lowers the voltage of the direct-current power outputted from the inverter  3 ′, and supplies the power to the 14-V battery E 1 . That is, the inverter  3 ′ and the DC-DC converter  21  collectively constitute a step-up and step-down inverter. Moreover, the DC-DC converter  21  increases the voltage of the power discharged from the 14-V battery E 1 , and applies the power to the inverter  3 ′.  
         [0050]     Further, an H-bridge circuit  22  and a second drive circuit  6   b  for controlling the drive of this H-bridge circuit  22  are provided at a subsequent stage to the inverter  3 ′. The H-bridge circuit  22  includes four switching elements Tr 21  to Tr 24 . By turning these switching elements Tr 21  to Tr 24  on and off, it is possible to control driving or stopping, and a direction of rotation of a permanent magnet direct-current motor M 2 , which is provided at a subsequent stage to the H-bridge circuit  22 .  
         [0051]     Here, the motor M 2  is connected to the rear wheels  5  through the differential  4  as similar to the above-described first embodiment.  
         [0052]     Next, operations of the control system CS 2  will be described. Here, actions of the 42-V alternator  2 , the inverter  3 ′, the 14-V battery E 1 , the H-bridge circuit  22 , and the motor M 2  when starting the engine, charging the battery, and in the 4WD mode, are shown as indicated in  FIG. 7 .  
         [0053]     Firstly, the first drive circuit  6   a  operates to start the engine  1  when detecting that the accelerator switch SW 3  is turned on. When starting the engine  1 , the electric power of the 14-V battery E 1  is applied to the inverter  3 ′. Then, the electric power is converted into the three-phase alternating-current power by the inverter  3 ′, and the power is applied to the 42-V alternator  2 . In this way, the 42-V alternator  2 &#39;s shaft is rotated and the engine  1  is started.  
         [0054]     Meanwhile, when the engine  1  is running, the electric power generated by the 42-V alternator  2  is rectified by the inverter  3 ′, converted into a power at a predetermined voltage by the DC-DC converter  21 , and then supplied to the 14-V battery E 1  for charging the 14-V battery E 1 .  
         [0055]     Moreover, when driving the motor M 2 , the three-phase alternating-current power generated by the 42-V alternator  2  is supplied to the inverter  3 ′. The inverter  3 ′ performs the regenerative operation, whereby the power is supplied to the. H-bridge circuit  22 . Then, the respective switching elements Tr 21  to Tr 24  in the H-bridge circuit  22  are turned on and off under the control of the second drive circuit  6   b.  Accordingly, driving power is applied to the motor M 2  and the motor M 2  is thereby driven.  
         [0056]     As described above, in the control system CS 2  for a motor powered 4WD vehicle according to the second embodiment, as similar to the first embodiment, when the engine  1  is running, it is possible to rectify the electric power generated by the 42-V alternator  2  and lower the voltage thereof, and thereby to charge the 14-V battery E 1 . Moreover, in the 4WD mode, it is possible to rectify the three-phase alternating-current power generated by the 42-V alternator  2  and to supply the power to the motor M 2 . Therefore, the single inverter can serve as the inverter for charging the 14-V battery E 1  and as the inverter for driving the motor M 2 . Accordingly, it is possible to simplify a system configuration.  
         [0057]     Meanwhile, when starting the engine  1 , it is possible to drive the 42-V alternator  2  by converting the power discharged from the 14-V battery E 1  into the three-phase alternating-current power by use of the DC-DC converter  21  and the inverter  3 ′, feeding the three-phase alternating-current power to the 42-V alternator  2 , and thereby to start the engine  1 . Accordingly, no other power source is required to start the engine  1 . In this way, it is possible to simplify the system configuration.  
         [0058]     Moreover, the 42-V alternator  2 &#39;s shaft is rotated and the engine  1  is started when the accelerator switch SW 3  is turned on. Accordingly, it is possible to realize the idle stop operation, thereby improving gas mileage.  
         [0059]     Furthermore, the voltage of the direct-current power outputted from the inverter  3 ′ is lowered by the DC-DC converter  21  to the voltage (the second rated voltage) suitable for charging the 14-V battery E 1 ; meanwhile, the voltage of the power discharged from the 14-V battery E 1  is increased by the DC-DC converter  21  and the electric power for starting the engine  1  is thereby outputted to the inverter  3 ′. Accordingly, a conventional inverter can be used as the inverter  3 ′. As a result, it is possible to lower the number of different parts/devices. Such limitation is extremely advantageous when constructing circuits.  
         [0060]     The preferred embodiments described herein are illustrative and not restrictive, and the invention may be practiced or embodied in other ways without departing from the spirit or essential character thereof. The scope of the invention being indicated by the claims, and all variations which come within the meaning according to claims are intended to be embraced herein.  
         [0061]     The present disclosure relates to subject matters contained in Japanese Patent Application No. 2003-363191, filed on Oct. 23, 2003, the disclosure of which is expressly incorporated herein by reference in its entirety.