19lf. Instead, the oil 10f may also be supplied to the right front motor Mrf and the left front motor Mlf by a common oil pump.

In order to supply the oil 10f to lubrication sites such as gears and bearings, a mechanical oil pump OPm is arranged in the front drive unit Pf. As illustrated in FIG. 3, the mechanical oil pump OPm is connected to the left counter shaft 14l. Therefore, the mechanical oil pump OPm is driven during propulsion of the vehicle Ve to pump up the oil 10f from the oil pan 9f, and the oil 10f is delivered to the above-mentioned lubrication sites including gears and bearings.

As illustrated in FIG. 1, an electric storage device (referred to as Bat in FIG. 1) 20 is electrically connected with the front drive unit Pf and the rear drive unit Pr through a power controller PC comprising an inverter. For example, a secondary battery such as a lithium-ion battery, an all-solid battery or the like may be adopted as the electric storage device 20. Whereas, a permanent magnet synchronous motor is adopted as each of the motors Mrf, Mlf, Mrr, and Mlr. That is, motor-generators are adopted as the motors Mrf, Mlf, Mrr, and Mlr. Specifically, the right front motor Mrf is connected with the electric storage device 20 through a right front power controller PCrf, the left front motor Mlf is connected with the electric storage device 20 through a left front power controller PClf, the right rear motor Mrr is connected with the electric storage device 20 through a right rear power controller PCrr, and the left rear motor Mlr is connected with the electric storage device 20 through a left rear power controller PCIr. Therefore, output torques and regenerative braking torques of the motors Mrf, Mlf, Mrr, and Mlr may be controlled independently or separately. Here, the output torques and the regenerative braking torques of the motors Mrf, Mlf, Mrr, and Mlr may also be controlled by a common power controller as long as the output torques and the regenerative braking torques of those motors can be controlled independently.

Thus, in the vehicle Ve, the output torques of the motors Mrf, Mlf, Mrr, and Mir may be controlled independently. Therefore, an operating mode of the vehicle Ve may be selected from a two-wheel drive mode and a four-wheel drive mode. For example, the vehicle Ve may be propelled in the two-wheel drive mode by operating the right rear motor Mrr and the left rear motor Mir as prime movers while interrupting power supply to the right front motor Mrf and the left front motor Mlf. Whereas, in the four-wheel drive mode, the vehicle Ve is propelled by all of the motors Mrf, Mlf, Mrr, and Mlr. In this case, a ratio between: the output torques of the front motors Mrf and Mlf; and the output torques of the rear motors Mrr and Mir, may be altered arbitrarily in line with the driver's preference.

The operating mode is selected to control mainly a driving torque in a desired manner. In order to select the operating mode, the vehicle Ve is further provided with a mode selector switch 21 that is operated by a driver. For example, the four-wheel drive mode may be selected from a truck mode, a drift mode, a manual range mode, and a manual sports mode. Specifically, in the truck mode, driving torques and regenerative braking torques of the motors Mrf, Mlf, Mrr, and Mir are controlled in such a manner as to enhance a turning performance of the vehicle Ve. In the drift mode, torques of the wheels 1rf, 1lf, 2rr, and 2lr are controlled separately in such a manner as to reduce an under steering and to optimize tractions of the wheels 1rf, 1lf, 2rr, and 2lr thereby enhancing a turning performance and a driving accuracy of the vehicle Ve.

In order to manually change a driving characteristic (i.e., a shift range) as a relation between an operating amount of the accelerator pedal and a required drive torque in the manual range mode or the manual sports mode, the vehicle Ve is provided with a shifting device S such as a shift lever or a paddle shifter. Specifically, in the manual range mode, a position of the shifting device S or an operation of the shifting device S is detected by a shift position sensor 22, and the shift range is changed in accordance with the detection signal of the shift position sensor 22. Whereas, in the manual sports mode, the shift range is changed in response to the operation of the shifting device S so that a large driving torque is ensured to a high-speed range to enhance the acceleration performance or the power performance.

Thus, the operating mode of the vehicle Ve is selected from the above-described operating modes by operating the mode selector switch 21 and the shifting device S. Instead, the normal mode in which an acceleration and an energy efficiency (i.e., an electric milage) of the vehicle Ve are moderated may be selected by operating the mode selector switch 21 and the shifting device S to cancel the selection of the above-described operating modes. For example, the mode selector switch 21 may be adapted to shift the operating mode stepwise each time it is operated. Instead, a plurality of dedicated mode selector switches 21 corresponding to the respective operating modes may also be arranged.

In order to control the motors Mrf, Mlf, Mrr, and Mlr and the electric oil pumps OPrf, OPlf, OPrr, and OPlr in accordance with the selected operating mode and shift range, the vehicle Ve is provided with a controller 23. The controller 23 is composed mainly of a microcomputer, and performs a calculation using incident data and program stored in advance, with reference to maps stored in advance. Results of the calculations are transmitted from the controller 23 to the motors Mrf, Mlf, Mrr, and Mir and the electric oil pumps OPrf, OPlf, OPrr, and OPlr in the form of command signal.

Turning to FIG. 4, there is shown an example of incident signals to the controller (referred to as ECU in FIG. 4) 23 and output signals from the controller 23. As shown in FIG. 4, for example, a vehicle speed signal, an accelerator position signal (referred to as PAP signal in FIG. 4), a shift position signal, a mode selector switch signal, an upshifting signal, a downshifting signal, a track mode signal, a drift mode signal etc. are transmitted to the controller 23. The controller 23 transmits a control signal of the torque of the left rear motor Mir driving the left rear wheel 2lr, a control signal of the torque of the right rear motor Mrr driving the right rear wheel 2rr, a control signal of the left rear oil pump OPlr for the left rear wheel 2lr, a control signal of the right rear oil pump OPrr for the right rear wheel 2rr, a control signal of the torque of the left front motor Mlf driving the left front wheel 1lf, a control signal of the torque of the right front motor Mrf driving the right front wheel 1rf, a control signal of the left front oil pump OPlf for the left front wheel 1lf, a control signal of the right front oil pump OPrf for the right front wheel 1rf, and so on.

FIG. 5 shows an example of a driving torque map for determining a driving torque required to propel the vehicle Ve (hereinafter referred to as the required driving torque). The map shown in FIG. 5 is stored in the controller 23, and is configured to determine the required driving torque based on a speed of the vehicle Ve and a position of the accelerator pedal. Specifically, in FIG. 5, the horizontal axis represents the speed of the vehicle Ve, the vertical axis represents the required driving torque, and each curve represents the position of the accelerator pedal. The driving torque map may be configured to differentiate the required driving torque with respect to a predetermined position of the accelerator pedal in accordance with the selected operating mode and shift range. For example, the map shown in FIG. 5 may be configured to increase the magnitude of the required driving torque with respect to a predetermined position of the accelerator pedal in the lower shift ranges during operation in the manual range mode.

In addition, a temperature region map shown in FIG. 6 is stored in the controller 23. The map shown in FIG. 6 is configured to determine a ratio between the torques of the front motors Mrf and Mlf and the torques of the rear motors Mrr and Mlr based on temperatures of the motors Mrf, Mlf, Mrr, and Mir when the vehicle Ve is operated in the four-wheel drive mode. As described above, the four-wheel drive mode includes the track mode, the drift mode, the manual sports mode, and the manual range mode. In FIG. 6, the horizontal axis represents the temperature of the front motor Mrf or Mlf, and the vertical axis represents the temperature of the rear motor Mrr or Mlr. For example, in a case that the temperature of the right front motor Mrf and the temperature of the left front motor Mlf are different, the higher temperature may be employed to determine the ratio between the torques of the front motors Mrf and Mlf and the torques of the rear motors Mrr and Mlr. Likewise, in a case that the temperature of the right rear motor Mrr and the temperature of the left rear motor Mir are different, the higher temperature may be employed to determine the ratio between the torques of the front motors Mrf and Mlf and the torques of the rear motors Mrr and Mlr. In the following explanation, the right front motor Mrf and the left front motor Mlf will be commonly referred to as the front motor Mf, and the right rear motor Mrr and left rear motor Mlr will be commonly referred to as the rear motor Mr.

In the map shown in FIG. 6, a region in which the temperature of the front motor Mf is lower than a first predetermined temperature T1 and the temperature of the rear motor Mr is lower than a second predetermined temperature T2 is a region A. In a case that both of the temperatures of the front motor Mf and the rear motor Mr fall within the region A, in order to generate the required driving torque for propelling the vehicle Ve, the ratio between the output torque of the front motor Mf delivered to the front wheels 1rf and 1lf and the output torque of the rear motor Mr delivered to the rear wheels 2rr and 2lr is set to a ratio determined based on e.g., the selected operating mode.

In the map shown in FIG. 6, a region in which the temperature of the front motor Mf is equal to or higher than the first predetermined temperature T1 but lower than a first restrictive temperature T3 and the temperature of the rear motor Mr is lower than the second predetermined temperature T2 is a region B. In a case that both of the temperatures of the front motor Mf and the rear motor Mr fall within the region B, the torque of the front motor Mf at a point when the temperature of the front motor Mf and the temperature of the rear motor Mr enter the region B is set as an upper limit torque of the front motor Mf, and the output torque of the rear motor Mr is adjusted to satisfy the required driving torque. Specifically, the first restrictive temperature T3 is set to a level possible to protect the front motor Mf, for example, to a rated temperature.

In the case that the torque of the front motor Mf is thus limited based on the temperature thereof, the front motor Mf serves as the “first motor” of the embodiment of the present disclosure, the front wheels 1rf and 1lf serve as the “first drive wheel” of the embodiment of the present disclosure, the rear motor Mr serves as the “other prime mover” or the “second motor” of the embodiment of the present disclosure, and the rear wheels 2rr and 2lf serve as the “second drive wheel” of the embodiment of the present disclosure.

Therefore, even if the required driving torque to propel the vehicle Ve is increased in the situation where a point representing the temperature conditions of the front motor Mf and the rear motor Mr which is governed by the temperatures of the front motor Mf and the rear motor Mr (hereinafter, the point representing temperature conditions of the motors Mf and Mr) falls within the region B, the torque of the front motor Mf is fixed to the torque at the time point when the temperature of the front motor Mf enters the region B. In other words, the torque of the front motor Mf is not increased to be greater than the upper limit torque. In this situation, the rear motor Mr is controlled so as to satisfy the required driving torque to propel the vehicle Ve. For this purpose, a torque for driving the front wheels 1rf and 1lf in this situation is calculated by multiplying the torque of the front motor Mf being fixed by a gear ratio of the front drive unit Pf, and a shortage of the torque with respect to the required driving torque to be generated by the rear motor Mr is calculated by subtracting calculated torque for driving the front wheels 1rf and 1lf from the required driving torque. In other words, the required driving torque is satisfied by increasing only the output torque of the rear motor Mr to generate the calculated shortage of the torque.

Given that both of the torques of the front motor Mf and the rear motor Mr are maintained constant after the point representing temperature conditions of the motors Mf and Mr enters the region B, the torque of the front motor Mf and the torque of the rear motor Mr are maintained to the torque at the point when the point representing temperature conditions of the motors Mf and Mr enters the region B. If the required driving torque is reduced in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region B, the torque of at least one of the front motor Mf and the rear motor Mr is reduced so as to reduce a difference between a target value of the ratio between the torques of the front motor Mf and the rear motor Mr to achieve the required driving torque determined in accordance with e.g., the operating mode (hereinafter, referred to as the target torque ratio) and the actual ratio between the torques of the front motor Mf and the rear motor Mr.

In the map shown in FIG. 6, a region in which the temperature of the rear motor Mr is equal to or higher than the second predetermined temperature T2 but lower than a second restrictive temperature T4 and the temperature of the front motor Mf is lower than the first predetermined temperature T1 is a region C. In a case that both of the temperatures of the front motor Mf and the rear motor Mr fall within the region C, the torque of the rear motor Mr at the point when the temperature of the front motor Mf and the temperature of the rear motor Mr enter the region C is set as the upper limit torque of the rear motor Mr, and the output torque of the front motor Mf is adjusted to achieve the required driving torque. Specifically, the second restrictive temperature T4 is set to a level possible to protect the rear motor Mr, for example, to a rated temperature.

In the case that the torque of the rear motor Mr is thus limited to the upper limit torque, the rear motor Mr serves as the “first motor” of the embodiment of the present disclosure, the rear wheels 2rr and 2lr serve as the “first drive wheel” of the embodiment of the present disclosure, the front motor Mf serves as the “other prime mover” or the “second motor” of the embodiment of the present disclosure, and the front wheels 1rf and 1lf serve as the “second drive wheel” of the embodiment of the present disclosure.

Therefore, even if the required driving torque to propel the vehicle Ve is increased in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region C, the torque of the rear motor Mr is fixed to the torque at the point when the temperature of the rear motor Mr enters the region C. In other words, the torque of the rear motor Mr is not increased to be greater than the upper limit torque. In this situation, the front motor Mf is controlled to satisfy the required driving torque to propel the vehicle Ve. For this purpose, a torque for driving the rear wheels 2rr and 2lr in this situation is calculated by multiplying the torque of the rear motor Mr being fixed by the gear ratio of the rear drive unit Pr, and a shortage of the torque with respect to the required driving torque to be generated by the front motor Mf is calculated by subtracting calculated torque for driving the rear wheels 2rr and 2lr from the required driving torque. Thus, only the output torque of the front motor Mf is increased in this case to satisfy the required driving torque.

Given that both of the torques of the front motor Mf and the rear motor Mr are maintained constant after the point representing temperature conditions of the motors Mf and Mr enter the region C, the torque of the front motor Mf and the torque of the rear motor Mr are maintained to the torques at the point when the temperature conditions enter the region C. Further, if the required driving torque is reduced in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region C, the torque of at least one of the front motor Mf and the rear motor Mr is reduced so as to reduce the difference between the target torque ratio determined in accordance with the operating mode and the actual ratio between the torques of the front motor Mf and the rear motor Mr.

In the case that the torque of the front motor Mf is thus limited to less than the first limit torque, the front motor Mf serves as the “first motor” of the embodiment of the present disclosure, the front wheels 1rf and 1lf serve as the “first drive wheel” of the embodiment of the present disclosure, the rear motor Mr serves as the “other prime mover” or the “second motor” of the embodiment of the present disclosure, and the rear wheels 2rr and 2lf serve as the “second drive wheel” of the embodiment of the present disclosure.

Thus, if the torque of the front motor Mf is equal to or greater than the first limit torque when the point representing temperature conditions of the front motor Mf and the rear motor Mr enter the region D, the torque of the front motor Mf is reduced less than the first limit torque. For this purpose, a torque for driving the front wheels 1rf and 1lf in this situation is calculated by multiplying the torque of the front motor Mf reduced to be less than the first limit torque by the gear ratio of the front drive unit Pf, and a shortage of the torque with respect to the required driving torque to be generated by the rear motor Mr is obtained by subtracting the calculated torque for driving the front wheels 1rf and 1lf from the required driving torque.

Likewise, if the required driving torque to propel the vehicle Ve is increased in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region D, the torque of the front motor Mf is limited to be less than the first limit torque. For this purpose, a torque for driving the front wheels 1rf and 1lf in this situation is calculated by multiplying the torque of the front motor Mf limited to be less than the first limit torque by the gear ratio of the front drive unit Pf, and a shortage of the torque with respect to the required driving torque to be generated by the rear motor Mr is obtained by subtracting the calculated torque for driving the front wheels 1rf and 1lf from the required driving torque.

If the torque of the front motor Mf is less than the first limit torque when the point representing temperature conditions of the motors Mf and Mr enter the region D, or if the required driving torque is maintained or reduced in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region D, the torques of the front motor Mf and the rear motor Mr are maintained. Instead, the torque of at least one of the front motor Mf and the rear motor Mr is reduced thereby reducing a difference between the target torque ratio and the actual ratio between the torque of the front motor Mf and the torque of the rear motor Mr.

In the map shown in FIG. 6, a region in which the temperature of the rear motor Mr is equal to or higher than the second restrictive temperature T4 and the temperature of the front motor Mf is lower than the first restrictive temperature T3 is a region E. In a case that both of the temperatures of the front motor Mf and the rear motor Mr fall within the region E, the output torque of the rear motor Mr is limited to be less than a second limit torque and the output torque of the front motor Mf is adjusted to achieve the required driving torque. The second limit torque is determined based on the temperature of the rear motor Mr. For example, the second limit torque may be set to a magnitude by which a heat generation of by the rear motor Mr is reduced less than the cooling capacities of the rear oil pumps OPrr and OPrl. Instead, the second limit torque may also be set to the magnitude achieved by shutting down the rear power controllers PCrr and PCrl, i.e., to zero. Accordingly, the second limit torque is less than the upper limit torque set at the time when the temperature of the rear motor Mr reaches the second predetermined temperature T2.

In the case that the torque of the rear motor Mr is thus limited to be less than the second limit torque, the rear motor Mr serves as the “first motor” of the embodiment of the present disclosure, the rear wheels 2rr and 2lr serve as the “first drive wheel” of the embodiment of the present disclosure, the front motor Mf serves as the “other prime mover” or the “second motor” of the embodiment of the present disclosure, and the front wheels 1rf and 1lf serve as the “second drive wheel” of the embodiment of the present disclosure.

Thus, if the torque of the rear motor Mr is equal to or greater than the second limit torque when the point representing temperature conditions of the motors Mf and Mr enters the region E, the torque of the rear motor Mr is reduced to be less than the second limit torque. For this purpose, a torque for driving the rear wheels 2rr and 2lr in this situation is calculated by multiplying the torque of the rear motor Mr thus reduced to be less than the second limit torque by the gear ratio of the rear drive unit Pr, and a shortage of the torque with respect to the required driving torque to be generated by the front motor Mf is obtained by subtracting the calculated torque for driving the rear wheels 2rr and 2lr from the required driving torque.

Likewise, if the required driving torque to propel the vehicle Ve is increased in the situation where the point representing temperature conditions of the front motor Mf and the rear motor Mr falls within the region E, the torque of the rear motor Mr is also set to be less than the second limit torque. For this purpose, a torque for driving the rear wheels 2rr and 2lr in this situation is calculated by multiplying the torque of the rear motor Mr reduced to be less than the second limit torque by the gear ratio of the rear drive unit Pr, and the shortage of the torque with respect to the required driving torque to be generated by the front motor Mf is obtained by subtracting the calculated torque for driving the rear wheels 2rr and 2lr from the required driving torque.

If the torque of the rear motor Mr is less than the second limit torque when the point representing temperature conditions of the motors Mf and Mr enters the region E, or if the required driving torque is maintained or lowered in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region E, the torques of the front motor Mf and the rear motor Mr are maintained to the current torques. Instead, the torque of at least one of the front motor Mf and the rear motor Mr is reduced thereby reducing a difference between the target torque ratio and the actual ratio between the torque of the front motor Mf and the torque of the rear motor Mr.

In the map shown in FIG. 6, a region in which the temperature of the front motor Mf is equal to or higher than the first predetermined temperature T1 but lower than the first restrictive temperature T3, and the temperature of the rear motor Mr is equal to or higher than the second predetermined temperature T2 but lower than the second restrictive temperature T4 is a region F. In a case that both of the temperatures of the front motor Mf and the rear motor Mr fall within the region F, the torque of the front motor Mf at the point when the temperature of the front motor Mf enters the region F is set as the upper limit torque of the front motor Mf, and the torque of the rear motor Mr at the point when the temperature of the rear motor Mr enters the region F is set as the upper limit torque of the rear motor Mr. Therefore, even if the driving torque required to propel the vehicle Ve is increased in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region F, the torque of the front motor Mf and the torque of the rear motor Mr are fixed when the point representing temperature conditions of the motors Mf and Mr enters the region F. In other words, the torque of the front motor Mf and the torque of the rear motor Mr will not be increased. In this situation, therefore, the vehicle Ve is propelled by the torque equal to or less than the required driving torque. If the required driving torque is maintained constant in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region F, the torques of the front motor Mf and the rear motor Mr are maintained constant. By contrast, if the required driving torque is reduced in the situation where the point representing temperature conditions of the motors Mf and Mr falls within the region F, the torque of at least one of the front motor Mf and the rear motor Mr is reduced thereby reducing the difference between the target torque ratio and the actual ratio between the torque of the front motor Mf and the torque of the rear motor Mr.

In the case that the point representing temperature conditions of the motors Mf and Mr falls within the region F, the front motor Mf and the rear motor Mr serve as the “first motor” and the “other prime mover” or the “second motor” of the embodiment of the present disclosure, and the front wheels 1rf and 1lf and the rear wheels 2rr and 2lr serve as the “first drive wheel” and the “second drive wheel” of the embodiment of the present disclosure.

In the map shown in FIG. 6, a region in which the temperature of the front motor Mf is equal to or higher than the first restrictive temperature T3 and the temperature of the rear motor Mr is equal to or higher than the second restrictive temperature T4 is a region G. In a case that both of the temperatures of the front motor Mf and the rear motor Mr fall within the region G, it is necessary to cool the front motor Mf and the rear motor so as to protect these motors. To this end, in a case that the point representing temperature conditions of the front motor Mf and the rear motor Mr falls within the region G, the output torque of the front motor Mf is restricted to the first limit torque or less, and the output torque of the rear motor Mr is restricted to the second limit torque or less. That is, in this case, the driving torque for propelling the vehicle Ve is limited by the first limit torque of the front motor Mf and the second limit torque of the rear motor Mr, even if the driving torque greater than the total of the torque of front motor Mf limited by the first limit torque and the torque of the rear motor Mr limited by the second limit torque is required. In other words, the front motor Mf generates the first limit torque, and the rear motor Mr generates the second limit torque. Whereas, when the required driving torque is reduced to or less than the total of the torque of front motor Mf limited by the first limit torque and the torque of the rear motor Mr limited by the second limit torque, the torque of at least one of the front motor Mf and the rear motor Mr is reduced thereby reducing the difference between the target torque ratio and the actual ratio between the torque of the front motor Mf and the torque of the rear motor Mr.

In the case that the point representing temperature conditions of the front motor Mf and the rear motor Mr falls within the region G, the front motor Mf and the rear motor Mr serve as the “first motor” and the “other prime mover” or the “second motor” of the embodiment of the present disclosure, and the front wheels 1rf and 1lf