Patent Publication Number: US-2016229293-A1

Title: Electrically driven vehicle

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention invention relates to an electrically driven vehicle. “The electrically driven vehicle” in the present specification includes a hybrid vehicle that is equipped with both a motor and an engine, and a fuel cell vehicle. 
     2. Description of Related Art 
     Four-wheel-drive electrically driven vehicles that are equipped with motors in front and rear regions thereof have been studied. For example, Japanese Patent Application Publication No. 2005-323455 (JP-2005-323455 A) discloses an electrically driven vehicle that is mounted with a hybrid system, which is equipped with an engine and a motor as drive sources for front wheels, in a vehicle front region. And the electrically driven vehicle is mounted with another motor as a drive source for rear wheels in a vehicle rear region. “The vehicle front region” means a front side with respect to the position of a center of gravity of the vehicle in a longitudinal direction of the vehicle, or a front side with respect to a center in the longitudinal direction of the vehicle. By the same token, “the vehicle rear region” means a rear side with respect to the position of the center of gravity of the vehicle in the longitudinal direction of the vehicle, or a rear side with respect to the center in the longitudinal direction of the vehicle. 
     As one mode of a four-wheel-drive electrically driven vehicle, there may be a mode in which one of the drive sources for the front and rear wheels is used for normal running, and the other is supplementarily used in specific cases. Typically, there is a mode in which the vehicle usually runs with two wheels driven, and a switchover to four-wheel drive is made when running on a snowy road. Alternatively, there may be a mode in which four-wheel drive is adopted only when a large acceleration is required. In other words, such a four-wheel-drive electrically driven vehicle has a vehicle concept in which one of the drive sources for the front and rear wheels is regarded as a main drive source, and the other is regarded as an auxiliary drive source. If such a concept is assumed, it is preferable that the auxiliary drive source be able to be fitted at relatively low cost as an option for the two-wheel-drive vehicle. Then, vehicle manufacturers can increase the number of vehicle variations at low cost. For example, for the same type of vehicle, a two-wheel-drive vehicle and a four-wheel-drive vehicle modified as a specification for cold places or a specification for high output can be realized at low cost. The present specification provides an art capable of turning a two-wheel-drive system into a four-wheel-drive system through minimum required alterations. That is, the present specification provides an art capable of changing a two-wheel-drive electrically driven vehicle into a four-wheel-drive electrically driven vehicle at low cost. 
     Incidentally, the aforementioned “auxiliary” drive source is meant to be a drive source that is not used during normal running, but is used in specific cases (e.g., when running on a snowy road, when running on a slope, or when a large acceleration is required). In the present specification, the word “auxiliary” includes the meaning of the word “temporarily”. 
     SUMMARY OF THE INVENTION 
     An electrically driven vehicle according to a first aspect of the invention is equipped with a battery, a front motor, a front inverter, a rear motor, a rear inverter, and a distributor. The front motor is arranged in a front region of the vehicle. The front motor is configured to drive front wheels. The front inverter is arranged in the front region of the vehicle. The front inverter is configured to convert an electric power of the battery into an alternating-current electric power and supply the alternating-current electric power to the front motor. The rear motor is arranged in a rear region of the vehicle. The rear motor is configured to drive rear wheels. The rear inverter is arranged in the rear region of the vehicle. The rear inverter is configured to convert an electric power of the battery into an alternating-current electric power and supply the alternating-current electric power to the rear motor. The distributor is configured to distribute the electric power of the battery to the front inverter and the rear inverter. One of the rear inverter and another device that is attached to and removed from the vehicle together with the rear inverter is provided with the distributor. 
     An electrically driven vehicle according to a second aspect of the invention is equipped with a battery, a front motor, a front inverter, a rear motor, a rear inverter, and a distributor. The front motor is arranged in a front region of the vehicle. The front motor is configured to drive front wheels. The front inverter is arranged in the front region of the vehicle. The front inverter is configured to convert an electric power of the battery into an alternating-current electric power and supply the alternating-current electric power to the front motor. The rear motor is arranged in a rear region of the vehicle. The rear motor is configured to drive rear wheels. The rear inverter is arranged in the rear region of the vehicle. The rear inverter is configured to convert an electric power of the battery into an alternating-current electric power and supply the alternating-current electric power to the rear motor. The distributor distributes the electric power of the battery to the front inverter and the rear inverter. One of the front inverter and another device that is attached to and removed from the vehicle together with the front inverter is provided with the distributor. 
     According to the aforementioned configurations, a two-wheel-drive electrically driven vehicle can be changed into a four-wheel-drive electrically driven vehicle at low cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1A  is a schematic layout diagram of an inverter and a battery at the time when a front-wheel-drive electrically driven vehicle is viewed laterally; 
         FIG. 1B  is a schematic layout diagram of the inverter and the battery at the time when the front-wheel-drive electrically driven vehicle is viewed from above; 
         FIG. 2A  is a schematic layout diagram of an inverter and a battery at the time when an electrically driven vehicle according to the first embodiment of the invention is viewed laterally; 
         FIG. 2B  is a schematic layout diagram of the inverter and the battery at the time when the electrically driven vehicle according to the first embodiment of the invention is viewed from above; 
         FIG. 3  is a schematic block diagram of a drive system of the electrically driven vehicle according to the first embodiment of the invention; 
         FIG. 4A  is a schematic layout diagram of an inverter and a battery at the time when an electrically driven vehicle according to the second embodiment of the invention is viewed laterally; 
         FIG. 4B  is a schematic layout diagram of the inverter and the battery at the time when the electrically driven vehicle according to the second embodiment of the invention is viewed from above; 
         FIG. 5A  is a schematic layout diagram of an inverter and a battery at the time when an electrically driven vehicle according to the third embodiment of the invention is viewed laterally; 
         FIG. 5B  is a schematic layout diagram of the inverter and the battery at the time when the electrically driven vehicle according to the third embodiment of the invention is viewed from above; 
         FIG. 6A  is a schematic layout diagram of an inverter and a battery at the time when an electrically driven vehicle according to the fourth embodiment of the invention is viewed laterally; 
         FIG. 6B  is a schematic layout diagram of the inverter and the battery at the time when the electrically driven vehicle according to the fourth embodiment of the invention is viewed from above; 
         FIG. 7  is a plan view showing an example of the structure of a distributor (with no cover); and 
         FIG. 8  is a plan view showing another example of the structure of a distributor (with no cover). 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In many cases, an inverter is arranged close to a motor. This is because the loss in an electric power transmission path should be reduced by shortening the length of a power cable between the inverter and the motor. For example, in a front-wheel-drive electrically driven vehicle, the motor and the inverter are mounted in a front region of the vehicle, and a battery and the inverter are connected to each other by a power cable. In the case where such a two-wheel-drive electrically driven vehicle is changed into a four-wheel-drive electrically driven vehicle, another motor and another inverter are needed to be mounted in a rear region of the vehicle. In this case, an electric power supply path from the battery to the inverter needs to be changed from an existing path. The change is considered to have the following three modes. In the first mode, the electric power supply path from the battery to the inverter in the front region of the vehicle (a front inverter) is left untouched, and an electric power supply path from the battery to the inverter in the rear region of the vehicle (a rear inverter) is newly added. In the second mode, the front inverter is newly provided with an electric power distributor (hereinafter referred to as distributor), and an electric power supply path from the distributor to the rear inverter needs to be newly added. In the third mode, the newly mounted rear inverter is provided with an electric power distributor (hereinafter referred to as distributor), and an electric power supply path from the battery to the respective front and rear inverters through the distributor is newly provided. 
     In the aforementioned first and second modes, the electric power supply path of a drive source with which the vehicle is originally equipped is utilized. Therefore, one of the first and second modes seems to be the lowest in cost. However, in the first mode, a connection terminal of the front inverter to which a power cable leading to the battery is attached needs to be changed. Furthermore, in the second mode, a power cable connection terminal of the battery needs to be changed. That is, in both the first and second modes, an existing device needs to be changed. In contrast, in the third mode, from the standpoint of the battery, it is necessary only to switch over a connection destination of the power cable extending from the terminal of the battery to the distributor with which the rear inverter is equipped. From the standpoint of the front inverter, it is necessary only to switch over a connection destination of the power cable extending from the front inverter to the aforementioned distributor. That is, there is no need to change the existing battery and the front inverter at all. Besides, the distributor can also be mounted together with the rear inverter. Therefore, the operation of mounting the distributor itself is not required. In this manner, the two-wheel-drive vehicle can be changed into the four-wheel-drive vehicle at low cost by mounting the rear inverter or another device that is attached/removed to/from the rear inverter at the same time, with the distributor. 
     In the following, the motor and the inverter for driving front wheels will be referred to as a front motor and a front inverter respectively, and the motor and the inverter for driving rear wheels will be referred to as a rear motor and a rear inverter respectively. Besides, the battery is typically arranged between the front inverter and the rear inverter. More specifically, the battery is often arranged below a rear seat, in a rear region (in front of a rear compartment), or below a front seat. Besides, the battery may also be arranged between right and left front seats. 
     One feature of the electrically driven vehicle disclosed by the present specification consists in that the rear inverter or another device that is attached/removed to/from the vehicle together with the rear inverter is provided with a distributor that distributes the electric power of the battery to the respective inverters. The distributor may be provided inside a housing of the rear inverter, or may be attached to an outside of the housing. Alternatively, the distributor may be attached to the rear motor that is combined with the rear inverter. In this case, the rear motor is equivalent to an example of “another device that is attached/removed simultaneously with the rear inverter” as mentioned above. In any case, the distributor can also be attached to the vehicle at the same time by performing an operation of attaching the rear inverter. Therefore, the efficiency of the operation of making a shift to the four-wheel-drive vehicle is high. The rear motor is a typical example of “another device” as mentioned above. However, “another device” may not necessarily be this rear motor. For example, in the same manner as the rear motor and the rear inverter are optional, “another device” may be another voltage converter that is optionally mounted adjacently to the rear inverter. 
     In the case where the rear motor is an optional drive source, the rear motor is an auxiliary drive source that supplements the driving force of the front motor that is used for normal running, as described above. In this case, a motor whose maximum output is smaller than that of the front motor is adopted as the rear motor. In other words, the rear motor is an auxiliary drive source, and is a drive source that is less frequently used than the front motor. It should be noted herein that it is determined whether “the frequency of use” is high or low depending not only on whether the frequency with which the drive source is used is high or low but also on whether the sum of the electric power output from the inverter is large or small or the like, for example, in the case where the vehicle is caused to run at a constant speed. That is, the front inverter may be an inverter that is mainly used when the vehicle runs, and the rear inverter may be an inverter that is supplementarily used. 
     Incidentally, in the aforementioned aspect of the invention, there is assumed a case where the front motor is a main drive source and the rear motor is an auxiliary drive source (an optional drive source). However, the roles of the front motor and the rear motor may be reversed. That is, in the case where the front motor is an auxiliary drive source, the front inverter or another device that is attached/removed to/from the vehicle together with the front inverter may be provided with the distributor that distributes the electric power of the battery to the respective inverters. 
     The features other than those mentioned above will be described. Incidentally, the technical elements mentioned below are technical elements that are independent of one another, and are technically useful alone or in various combinations. These technical elements should not be limited to the combination set forth in the claims at the time of the filing of the application. 
     In the case where the rear motor is an auxiliary drive source, a fuse may be provided in an electric power supply path between the distributor and the rear inverter. Even if an inconvenience is caused in the rear motor or the rear inverter for some reason, the fuse is cut off, so the rear inverter can be detached from the electric power supply path between the battery and the front inverter. In that case, the vehicle can continue to run only by the front drive source regardless of the state of the rear drive source. 
     In the case where the front motor is a main drive source, the front inverter is equipped with a step-up circuit that steps up the voltage of the battery, and an inverter circuit that converts the output of the step-up circuit into an alternating current. On the other hand, the rear inverter may adopt a configuration in which the rear motor is auxiliary and therefore has only an inverter circuit without having a step-up circuit. In other words, the input/output voltage of the rear inverter is equal to the voltage of the battery. In such a case, the front inverter has a step-up circuit, so the influence of high-frequency noise of the inverter circuit on the battery is small. In the rear inverter, however, the battery and the inverter circuit are directly coupled to each other, so the influence of high-frequency noise on the battery may be great. In order to suppress the influence of high-frequency noise of the rear inverter, a choke coil may be provided in the electric power supply path between the distributor and the rear inverter. 
     The battery may be arranged between the front inverter and the rear inverter in the longitudinal direction of the vehicle. 
     The length of the power cable that is connected to the terminal of the battery and the terminal of the distributor may be shorter than the length of the power cable that is connected to the terminal of the distributor and the terminal of the front inverter. 
     The distance between the battery and the rear inverter in the longitudinal direction of the vehicle may be shorter than the distance between the battery and the front inverter in the longitudinal direction of the vehicle. 
     The layout of a motor, an inverter, and a battery of an electrically driven vehicle (a hybrid vehicle  200 ) whose two front wheels are driven will be described.  FIG. 1A  is a schematic layout diagram of a front motor, a front inverter, and a battery at the time when the hybrid vehicle  200  is viewed laterally.  FIG. 1B  is a schematic layout diagram (a planar layout diagram) at the time when the hybrid vehicle  200  is viewed from above. In the drawings, front seats and a rear seat are depicted by virtual lines. 
     In the hybrid vehicle  200 , two front wheels are driven, and an engine  4 , a front motor  5 , and a front inverter  3  are arranged in a front compartment in a front region of the vehicle. Outputs of the engine  4  and the front motor  5  are transmitted to front wheels  41 . The transmission path will be described later with reference to  FIG. 3 . The front inverter  3  is fixed to a housing of the front motor  5 . This is because the loss in electric power transmission should be suppressed by shortening the distance between the inverter and the motor as described above. 
     A battery  6  that stores an electric power for driving the front motor  5  is arranged below the rear seat. The battery  6  and the front inverter  3  are connected to each other by a power cable  209 . The power cable  209  is equivalent to an electric power supply path (an electric power transmission path) that transmits the electric power of the battery  6  to the front inverter  3 . The power cable  209  electrically connects a terminal  6   a  of the battery  6  and a terminal  3   a  of the front inverter  3  to each other. In each of  FIG. 1  and the following drawings, power cables that supply an electric power from the battery to the inverter are depicted by thick lines. Rear wheels are denoted by a reference numeral  42 . In the hybrid vehicle  200 , the rear wheels  42  are driven wheels that do not have a driving force. 
     In  FIGS. 1A and 1B , the position of a center of gravity of the vehicle is denoted by a reference symbol G. A region in front of the position G of the center of gravity is equivalent to a front region of the vehicle (a vehicle front region), and a region behind the position G of the center of gravity is equivalent to a rear region of the vehicle (a vehicle rear region). The same holds true for the following drawings. 
     Next, the layout of a battery, motors and inverters in the electrically driven vehicle (a hybrid vehicle  2 ) according to the first embodiment of the invention will be described with reference to  FIGS. 2A and 2B . The hybrid vehicle  2  is obtained by adding a rear motor  7  and a rear inverter  8  for driving rear wheels to the two-wheel-drive hybrid vehicle  200  of  FIGS. 1A and 1B . Accordingly, the engine  4 , the front motor  5  and the front inverter  3  are arranged in the same manner as in  FIGS. 1A and 1B . However, the wiring of power cables is different from that of  FIGS. 1A and 1B . 
     The rear motor  7  and the rear inverter  8  are installed in the vehicle rear region. “The vehicle rear region” includes, for example, a region behind the vehicle with respect to the position G of the center of gravity of the vehicle in the longitudinal direction of the vehicle. The rear motor  7  is an auxiliary drive source, and has a smaller output than the front motor  5  as a main drive source. For example, the maximum output of the front motor  5  is 50 kW, and the maximum output of the rear motor  7  is 5 kW. The hybrid vehicle  2  usually runs by the engine  4  and the front motor  5 , and supplementarily drives the rear motor  7  according to need. For example, when the vehicle tends to slip on a snowy road, the rear motor  7  is driven to cause the vehicle to run with its four wheels driven. Alternatively, the rear motor  7  is driven to provide torque assistance at the time of hill start. The rear motor  7  and the rear inverter  8  are attached, as optional equipment of the two-wheel-drive hybrid vehicle  200 , in accordance with the request made by a user. 
     As is the case with the front inverter  3 , the rear inverter  8  is also fixed to a housing of the rear motor  7 . This is because the loss in electric power transmission between the rear inverter  8  and the rear motor  7  can be suppressed by shortening the distance between the rear inverter  8  and the rear motor  7 . The rear inverter  8  may be fixed onto a floor panel instead of being attached to the rear motor  7 . 
     Referring to  FIGS. 1A and 1B  and  FIGS. 2A and 2B , the two-wheel-drive hybrid vehicle  200  and the four-wheel-drive hybrid vehicle  2  are different from each other in the wiring of the electric power supply paths from the battery  6  to the inverter, namely, the power cables. In the hybrid vehicle  2 , a power cable  9   a  that extends from the battery  6  is connected to a distributor  10 . To be more precise, the power cable  9   a  connects the terminal  6   a  of the battery  6  and a terminal  52  of the distributor  10  to each other. The distributor  10  distributes an output electric power of the battery  6  to the rear inverter  8  and the front inverter  3 . The distributor  10  is attached to a housing of the rear inverter  8 . Since the distributor  10  is fixed to the housing of the rear inverter  8 , the power cable from the distributor  10  to the rear inverter  8  passes the interiors of the distributor  10  and the rear inverter  8 , and is not visible in  FIGS. 2A and 2B . 
     The distributor  10  and the front inverter  3  are connected to each other by a power cable  9   b.  To be more precise, the power cable  9   b  connects the terminal  3   a  of the front inverter  3  and the terminal  52  of the distributor  10  to each other. In  FIGS. 2A and 2B , two terminals of the distributor are depicted in a simplified manner as a single terminal. The connection of the power cables will be described later in detail with reference to  FIGS. 7 and 8 . The electric power from the battery  6  is first transmitted to the distributor  10  in the rear region of the vehicle. In the case where the rear motor  7  is driven, the electric power of the battery  6  bifurcates in the distributor  10 , and is supplied to the rear inverter  8  and the front inverter  3 . As is apparent from  FIGS. 1A and 1B  and  FIGS. 2A and 2B , the electric power supply path of the two-wheel-drive hybrid vehicle  200  with its front wheels driven and the electric power supply path of the four-wheel-drive hybrid vehicle  2  are different from each other only in the range indicated by a reference symbol A in  FIGS. 2A and 2B , and are identical to each other in other respects. This means, namely, that there is no need to change the terminal  6   a  of the battery  6  and the terminal  3   a  of the front inverter  3  at all in making a shift to the four-wheel-drive vehicle by attaching the rear motor  7  and the rear inverter  8  to the two-wheel-drive hybrid vehicle  200 . Furthermore, it is sufficient to change the wiring of the power cables only in the range denoted by the reference symbol A, and the required change in the wiring of the power cables in the two-wheel-drive hybrid vehicle  200  is also minimized. 
     Besides, the distributor  10  is attached to the housing of the rear inverter  8 . As is apparent from the foregoing structure, the operation of making a shift from the two-wheel-drive hybrid vehicle  200  with its front wheels driven to the four-wheel-drive vehicle is performed simply by mounting the vehicle with an assembly of the rear motor  7 , the rear inverter  8  and the distributor  10  and replacing the power cables. Moreover, the hybrid vehicle  200  and the hybrid vehicle  2  are identical to each other in most of the wiring paths of the power cables. The hybrid vehicle  2  according to the first embodiment of the invention can be changed from a two-wheel-drive configuration to a four-wheel-drive configuration at low cost. 
     The drive system of the hybrid vehicle  2  will be described with reference to  FIG. 3 . The battery  6  is connected to the distributor  10  by the power cable  9   a.  The power cable  9   a  that extends from the battery  6  is connected to a first terminal  52   a  of the distributor  10 . The electric power supply path is divided into two electric power supply paths inside the distributor  10 . One of the electric power supply paths is the power cable  9   b  through which an electric power is supplied to the front inverter  3 , and the other is a power cable  9   c  through which an electric power is supplied to the rear inverter  8 . The power cable  9   b  is connected to a second terminal  52   b  of the distributor  10  and the terminal  3   a  of the front inverter  3 . Incidentally, since the distributor  10  is attached to the housing of the rear inverter  8 , the power cable  9   c  is invisible in  FIGS. 2A and 2B . 
     A fuse  12  and a choke coil  13  are connected to an electric power supply path between an electric power bifurcation point B in the distributor  10  and the rear inverter  8 . The choke coil  13  is inserted to reduce the influence exerted on the battery  6  by switching noise of the inverter  8 . Besides, in the case where an overcurrent has flowed through the rear inverter  8 , the fuse  12  is cut off. Due to the cutoff of the fuse  12 , the rear inverter  8  is detached from the electric power supply path from the battery  6  to the front inverter  3 . By detaching the rear inverter  8 , the vehicle can continue to run by the battery  6  and the front inverter  3  even when an inconvenience is caused in the rear inverter  8 . 
     The drive voltage of the front motor  5  is higher than the output voltage of the battery  6 . Therefore, the front inverter  3  has a step-up circuit  31  and an inverter circuit  32 . In other words, the front inverter  3  is equipped with the step-up circuit  31  between the inverter circuit  32  and the battery  6 . The step-up circuit  31  includes a reactor, and can reduce the influence exerted on the battery  6  by switching noise of the inverter circuit  32 , through the use of the reactor. On the other hand, the rear inverter  8  is not equipped with a step-up circuit, so the choke coil  13  is inserted in the electric power supply path between the rear inverter  8  and the battery  6 . The choke coil  13  reduces the influence exerted on the battery  6  by switching noise of the rear inverter  8 . 
     The front inverter  3  is supplied with an electric power from the battery  6  via the distributor  10 , and converts the electric power of the battery  6  into an alternating-current electric power, and supplies the alternating-current electric power to the front motor  5 . The front motor  5  operates upon being supplied with an electric power from the front inverter  3 . An output torque of the front motor  5  and an output torque of the engine  4  are synthesized with each other by a motive power distribution mechanism  91 , and are transmitted to the front wheels  41  via a differential  92 . Incidentally, the motive power distribution mechanism  91  also distributes the output torque of the engine  4  to the front wheels  41  and the front motor  5  in some cases. In such cases, the hybrid vehicle  2  generates an electric power by the front motor  5  while running by the motive power of the engine  4 . The battery  6  is charged with the generated electric power. 
     The rear inverter  8  is mounted on the rear motor  7 . In a rear drive system, the rear inverter  8  is supplied with an electric power from the battery  6  via the distributor  10 , converts the electric power of the battery  6  into an alternating-current electric power, and supplies the alternating-current electric power to the rear motor  7 . As described above, the output of the rear motor  7  is smaller than the output of the front motor  5 , and the rated voltage of the rear motor  7  is equal to the output voltage of the battery  6 . Therefore, the rear inverter  8  does not have a step-up circuit. The rear motor  7  operates upon receiving an alternating current of the same voltage as of the battery  6 , from the rear inverter  8 . A driving force of the rear motor  7  is directly transmitted to the rear wheels  42 . The rear inverter  8 , the rear motor  7 , and the distributor  10  are coupled to one another to constitute a single unit. The rear inverter  8  and the distributor  10  may be connected to each other and mounted separately from the rear motor  7 . In this case as well, the operation of change can be facilitated. 
     As described above, the hybrid vehicle  2  can be additionally equipped later with the rear motor  7 , the rear inverter  8 , and the distributor  10  as optional equipment. Those devices also facilitate the operation of changing the power cables that connect the battery and the inverters to one another. The hybrid vehicle  2  according to the first embodiment of the invention can be changed from a two-wheel-drive configuration to a four-wheel-drive configuration at low cost. In particular, if the battery is provided with the distributor that distributes an electric power to the respective inverters when changing a two-wheel-drive vehicle into a four-wheel-drive vehicle, a battery for two-wheel drive and a battery for four-wheel-drive need to be prepared, so the manufacturing cost rises substantially. Thus, in the present embodiment of the invention, the rear inverter that is mounted on the two-wheel-drive vehicle is provided with the distributor that distributes an electric power, so a shift to the four-wheel-drive vehicle can be made at low cost while diverting an existing system of the two-wheel-drive vehicle. 
     Other features of the hybrid vehicle  2  will be described. The battery  6  is mounted below the rear seat. In other words, the battery  6  is arranged between the front inverter  3  and the rear inverter  8  in the longitudinal direction of the vehicle. The longitudinal direction of the vehicle is shown in the drawings. It should be noted herein that a space “between the front inverter  3  and the rear inverter  8 ” may be a space between a front-wheel axle and a rear-wheel axle, or a space onto which a passenger compartment is projected in a vehicle plan view of  FIG. 2B . Besides, as is apparent from  FIGS. 2A and 2B , the battery  6  is close to the rear inverter  8 . Then, the distance between the battery  6  and the rear inverter  8  in the longitudinal direction of the vehicle is shorter than the distance between the battery  6  and the front inverter  3  in the longitudinal direction of the vehicle. This is advantageous in that the power cable  9   a  between the battery  6  and the distributor  10  can be shortened. Besides, the distance between the battery  6  and the rear inverter  8  in the longitudinal direction of the vehicle includes the length of the power cable  9   a  between the output terminal  6   a  (an output connector portion) of the battery  6  to the rear inverter  8  and an input terminal (an input connector portion) of the rear inverter  8 . Besides, the battery  6  is arranged behind the front inverter  3  in the longitudinal direction of the vehicle in a vehicle lateral view of  FIG. 2A , so the power cable  9   a  from the battery  6  to the distributor  10  attached to the rear inverter  8  can be made shorter than the power cable  9   b  from the distributor  10  attached to the rear inverter  8  to the front inverter  3 . A total of electric power consumption of the two inverters flows from the battery  6  to the distributor  10 . Therefore, the loss in electric power transmission can be reduced as the wiring distance of the power cable (the length of the cable) from the battery  6  to the distributor  10  decreases. Besides, the battery  6  and the rear inverter  8  are arranged close to each other. The word “close” also includes a case where the battery  6  and the rear inverter  8  are arranged behind the position G of the center of gravity of the vehicle with respect to the vehicle. For example, the battery  6  may be arranged below the rear seat, and the rear inverter may be arranged in a luggage space. 
     Next, an electrically driven vehicle (a hybrid vehicle  2   a ) according to the second embodiment of the invention will be described.  FIG. 4A  is a schematic diagram showing the layout of a battery, inverters, and motors at the time when the hybrid vehicle  2   a  is viewed laterally, and  FIG. 4B  is a schematic layout diagram (a planar layout diagram) at the time when the hybrid vehicle  2   a  is viewed from above. The hybrid vehicle  2   a  is different from the hybrid vehicle  2  according to the first embodiment of the invention in the mounting position of the battery  6 . The hybrid vehicle  2   a  is identical to the hybrid vehicle  2  according to the first embodiment of the invention in the layout of other devices, namely, the front motor  5 , the front inverter  3 , the engine  4 , the rear motor  7 , the rear inverter  8 , and the distributor  10 . The rear motor  7 , the rear inverter  8 , and the distributor  10  are coupled to one another to constitute a single unit. The unit can be mounted on the vehicle by a single operation. Besides, a drive system of the hybrid vehicle  2   a  is also expressed in a block diagram of  FIG. 3 . 
     The battery  6  is arranged between the two front seats. In this place, an axle is arranged in a conventional FR vehicle. Therefore, the shape of a passenger space can be made close to the shape of a passenger space of the conventional FR vehicle by arranging the battery in this place. As a result, the user does not feel very uncomfortable. 
     In the hybrid vehicle  2   a  according to the second embodiment of the invention as well, the rear inverter  8  is provided with the distributor  10  that distributes the electric power of the battery  6  to the respective inverters. As a result, the hybrid vehicle  2   a  according to the second embodiment of the invention has the same advantage as the hybrid vehicle  2  according to the first embodiment of the invention. 
     In the hybrid vehicle  2   a  according to the second embodiment of the invention, the battery  6  is arranged substantially at the center in the longitudinal direction of the vehicle. The terminal  6   a  of the battery  6  that is connected to the power cable  9   a  is located at a rear end of the battery. Thus, the distance between the terminal  6   a  of the battery  6  and the rear inverter  8  (the distance in the longitudinal direction of the vehicle) is shorter than the distance between the terminal  6   a  of the battery  6  and the front inverter  3  (the distance in the longitudinal direction of the vehicle). That is, the power cable  9   a  between the battery  6  and the distributor  10  can be made short. 
     Next, an electrically driven vehicle according to the third embodiment of the invention (a hybrid vehicle  2   b ) will be described.  FIG. 5A  is a schematic view showing the layout of a battery, inverters, and motors at the time when the hybrid vehicle  2   b  is viewed laterally.  FIG. 5B  is a schematic layout diagram (a planar layout diagram) at the time when the hybrid vehicle  2   b  is viewed from above. In the hybrid vehicle  2   b,  the distributor  10  is mounted in a housing of a voltage converter  21  as an optional component instead of being mounted on the rear inverter  8 . The hybrid vehicle  2   b  is identical to the hybrid vehicle  2   a  according to the second embodiment of the invention in other structural details. The voltage converter  21  is a device that steps down the voltage of the battery  6  to the same voltage as the rated voltage of a household electric appliance (e.g., 100 V). Although not shown in the drawings, an electric power output cable extends from the voltage converter  21 , and an outlet of the household electric appliance is connected to a tip of the electric power output cable. The outlet is installed in the vehicle. The household electric appliance can be used in the hybrid vehicle  2   b.  The voltage converter  21  is mounted on the vehicle together with the rear motor  7  and the rear inverter  8 . The voltage converter  21  is equivalent to an example of another device that is attached/removed to/from the vehicle together with the rear inverter  8 . The voltage converter  21  is mounted with the distributor  10 . The voltage converter  21  is arranged close to the rear inverter  8 , and the distributor  10  and the rear inverter  8  are connected to each other by the short power cable  9   c.  To be more precise, a third terminal  52   b  of the distributor  10  and a terminal  8   a  of the rear inverter  8  are connected to each other by the short power cable  9   c.    
     Unlike the hybrid vehicle according to the first or second embodiment of the invention, in the hybrid vehicle  2   b  according to the third embodiment of the invention, the rear inverter  8  is not mounted with the distributor  10 , but a device that is attached/removed to/from the vehicle together with the rear inverter  8  is mounted with the distributor  10 . For example, the device is the voltage converter  21 . Since the voltage converter  21  is arranged close to the rear inverter  8 , the distributor  10  is arranged close to the rear inverter  8 . This hybrid vehicle  2   b  has also the same advantage as the hybrid vehicle according to the first or second embodiment of the invention. It should be noted herein that “the arrangement of the voltage converter  21  close to the rear inverter  8 ” includes a case where the rear inverter  8  and the voltage converter  21  are arranged behind the position G of the center of gravity of the vehicle with respect to the vehicle in the longitudinal direction of the vehicle. 
     Next, an electrically driven vehicle  2   c  according to the fourth embodiment of the invention will be described.  FIG. 6A  is a schematic diagram showing the layout of a battery, inverters, and motors at the time when the electrically driven vehicle  2   c  is viewed laterally, and  FIG. 6B  is a schematic layout diagram (a planar layout diagram) at the time when the electrically driven vehicle  2   c  is viewed from above. The electrically driven vehicle  2   c  is a so-called pure EV that does not have an engine. Besides, in the electrically driven vehicle  2   c,  a main motor that outputs a driving force for normal running is mounted in a vehicle rear region, and an auxiliary motor is mounted in a vehicle front region. A front motor  25  is a piece of removable optional equipment that can be mounted later on a two-wheel-drive vehicle whose rear wheels are driven. 
     In the electrically driven vehicle  2   c,  a rear motor  27  as a main driving force and a rear inverter  28  that supplies an alternating-current electric power to the rear motor  27  are mounted in the rear region of the vehicle, and the front motor  25  as an auxiliary driving force and a front inverter  23  that supplies an alternating-current electric power to the front motor  25  are mounted in the front region of the vehicle. The rear inverter  28  is fixed to the rear motor  27 , and the front inverter  23  is fixed to the front motor  25 . As described in the first embodiment of the invention, an attempt to shorten the distance between a motor and an inverter by coupling them to each other contributes toward reducing the loss in electric power transmission. The front inverter  23  may be provided separately from the front motor  25 . 
     In the electrically driven vehicle  2   c,  the distributor  10  that bifurcates the output electric power of the battery  6  is fixed to a housing of the front inverter  23 . The terminal  6   a  of the battery  6  and the terminal  52  of the distributor  10  are connected to each other by the power cable  9   a.  This terminal  52  is the first terminal  52   a  of  FIG. 3 . The terminal  52  of the distributor  10  and a terminal  28   a  of the rear inverter  28  are connected to each other by the power cable  9   b.  This terminal  52  is the second terminal  52   b  of  FIG. 3 . The distributor  10  and the front inverter  23  are also connected to each other by a power cable, but the power cable passes through the interiors of the distributor  10  and the front inverter  23  and hence is invisible in  FIGS. 6A and 6B . 
     The electrically driven vehicle  2   c  is obtained by mounting an electrically driven vehicle originally as a two-wheel-drive vehicle whose rear wheels are driven later with a drive system for front wheels, and thus changing the two-wheel-drive vehicle into a four-wheel-drive vehicle. Specifically, the drive system for front wheels is constituted of the front motor  25  and the front inverter  23 . When the drive system for front wheels is mounted, the distributor  10  can also be mounted together with the front inverter  23 , so the single operation of mounting the distributor  10  is not required. Besides, with the two-wheel-drive vehicle whose rear wheels are driven, the battery  6  and the rear inverter  28  are connected to each other by a power cable. However, when the two-wheel-drive vehicle is changed into a four-wheel-drive vehicle, there is no need to change the output terminal of the battery  6  and the input terminal of the rear inverter  28 . Therefore, the electrically driven vehicle  2   c  according to the fourth embodiment of the invention also has the same advantage as the hybrid vehicle according to the first, second or third embodiment of the invention. 
     The battery  6  is mounted between two front seats. The hybrid vehicle according to the fourth embodiment of the invention is identical to the hybrid vehicles according to the second and third embodiments of the invention in the mounting position of the battery  6 . However, the battery  6  is installed such that the output terminal  6   a  thereof is located in a vehicle front region (in front of the position G of the center of gravity). Therefore, the distance from the output terminal  6   a  of the battery  6  to the distributor  10  (the distance in the longitudinal direction of the vehicle) is shorter than the distance from the output terminal  6   a  of the battery  6  to the rear inverter  28  (the distance in the longitudinal direction of the vehicle). A total of electric power consumption of the two inverters, namely, the rear inverter and the front inverter flows through the power cable  9   a  between the battery  6  and the distributor  10 , so the loss in electric power transmission can be reduced as the distance therebetween decreases. This also holds true for the first to third embodiments of the invention. 
     Next, the structure of the distributor  10  will be described with reference to  FIGS. 7 and 8 .  FIG. 7  is a plan view deprived of a cover of the distributor  10 , and shows an internal structure of a case  51 . The case  51  is made of resin. Metal plates whose internal resistance is smaller than that of a wire cable are used as conductive members inside the case. These metal plates are generally referred to as bus bars. P-bus bars that connect a positive electrode of the battery  6  and positive electrodes of the respective inverters to one another are denoted by reference symbols  53   a  and  53   b  respectively. N-bus bars that connect a negative electrode of the battery  6  and negative electrodes of the respective inverters to one another are denoted by reference symbols  54   a  and  54   b  respectively. The choke coil  13  is connected between the first P-bus bar  53   a  and the second P-bus bar  53   b.  The fuse  12  is connected between the first N-bus bar  54   a  and the second N-bus bar  54   b.    
     One end of the first P-bus bar  53   a  and one end of the first N-bus bar  54   a  are directed toward one lateral face of the case  51 . One end of the first P-bus bar  53   a  and one end of the first N-bus bar  54   a  are equivalent to the first terminal  52   a  of the distributor  10 . The power cable  9   a  that extends from the battery  6  is connected to the first terminal  52   a.  A connector that is provided at a tip of the power cable  9   a  is denoted by a reference symbol  56   a.    
     The other end of the first P-bus bar  53   a  and the other end of the first N-bus bar  54   a  are also directed toward one lateral face of the case  51 . The other end of the first p P-bus bar  53   a  and the other end of the first N-bus bar  54   a  are equivalent to the second terminal  52   b  of the distributor  10 . The power cable  9   b  that extends from the front inverter  3  is connected to the second terminal  52   b.  A connector that is provided at a tip of the power cable  9   b  is denoted by a reference symbol  56   b.    
     One end of the second P-bus bar  53   b  and one end of the second N-bus bar  54   b  are directed toward another lateral face of the case  51 . One end of the second P-bus bar  53   b  and one end of the second N-bus bar  54   b  are equivalent to a third terminal  52   c  of the distributor  10 . A connector  55  of the power cable  9   c  that is connected to the rear inverter  8  is combined with the third terminal  52   c.    
     The first terminal  52   a  and the second terminal  52   b  of the distributor  10  are provided on the same lateral face of the case  51 . The power cables  9   a  and  9   b  can be connected to this distributor  10  from the same direction. 
       FIG. 8  is a view of a distributor according to another example (a distributor  10   a ).  FIG. 8  is a plan view of the distributor  10   a  deprived of its cover. In  FIGS. 7 and 8 , like components are denoted by like reference symbols respectively. The distributor  10   a  is different from the distributor  10  of  FIG. 7  in the shape and layout of the first P-bus bar  53   a,  the second P-bus bar  53   b,  the first N-bus bar  54   a,  and the second N-bus bar  54   b,  but is identical to the distributor  10  of  FIG. 7  in function. In the distributor  10   a , the first terminal  52   a  and the second terminal  52   b  are provided on two parallel lateral faces of the case  51  respectively. 
     The points to remember about the art described in the embodiments of the invention will be described. In any one of the embodiments of the invention, the distributor  10  has the housing separate from the inverter. The distributor may be built in the inverter. In that case, the distributor may not have any individual housing. 
     In the fourth embodiment of the invention, the distributor  10  is attached to the housing of the front inverter  23 . In an electrically driven vehicle that has a main drive source on rear wheels and an auxiliary drive source (a front motor) on front wheels, a distributor may be attached to another device that is attached/removed together with the front inverter  23  that supplies an electric power to the front motor as an auxiliary drive source. 
     The distributor  10  is not absolutely required to be attached to the inverter for the auxiliary drive source, but may be attached to a device that is attached/removed to/from the vehicle together with the auxiliary drive source. This example is described in the third embodiment of the invention. Furthermore, it is preferable that the distributor  10  be installed in the vicinity of the inverter for the auxiliary drive source. Thus, during the operation of mounting the auxiliary drive source on the vehicle, the distributor can also be efficiently mounted. 
     The front motor and the front inverter may be accommodated in a single housing, or may be accommodated in separate housings. By the same token, the rear motor and the rear inverter may be accommodated in a single housing, or may be accommodated in separate housings. Besides, the art disclosed by the present specification is also applicable to an electrically driven vehicle that has three or more motors. The art disclosed by the present specification is also applicable to, for example, an electrically driven vehicle that is equipped with one front motor and two rear motors. In the present specification, for the sake of convenience, “the vehicle front region” and “the vehicle rear region” have been described with respect to the position G of the center of gravity of the vehicle, but the invention is not limited thereto. For example, “the vehicle front region” and “the vehicle rear region” may be defined with respect to the center in the longitudinal direction of the vehicle. “The center in the longitudinal direction of the vehicle” includes the substantial center of a line that links a front end portion of the vehicle and a rear end portion of the vehicle with each other. 
     Specifically, the battery may be a lithium-ion battery, a fuel battery, a large-capacity capacitor, or other types of batteries. 
     While the concrete examples of the invention have been described above in detail, these are nothing more than exemplifications, and do not limit the claims. The art set forth in the claims includes various modifications and alterations of the concrete examples exemplified above. The technical elements described in the present specification or the drawings are technically useful alone or in various combinations, and are not limited to the combinations set forth in the claims at the time of the filing of the application. Besides, the art exemplified in the present specification or the drawings can achieve a plurality of objects at the same time, and is technically useful by achieving one of the objects in itself.