Vehicle driving force control apparatus

A vehicle driving force control apparatus is provided to prohibit a change in a shift schedule that will cause insufficient power generation of a generator that supplies power to an electric motor to drive a first drive wheel. The vehicle driving force control apparatus has a shift schedule change section, a power sufficiency determining section and a shift schedule change prohibit section. The shift schedule change section is configured to change a shift schedule of a transmission of the main drive source. The power sufficiency determining section is configured to determine whether generated power of the generator will be insufficient by a change in the shift schedule by the shift schedule change section, when an electromotive force of the generator is driving the electric motor that supplies torque to the first drive wheel. The shift schedule change prohibit section is configured to prohibit a change of the shift schedule by the shift schedule change section, upon the power sufficiency determining section determining that the generated power of the generator will be insufficient.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle driving force control apparatus configured so as to drive an electric motor that transmits drive torque to subordinate wheels by means of electromotive force generated by a generator.

2. Background Information

This type of vehicle driving force control apparatus has been proposed for both front and rear wheel drive vehicles (refer to Japanese Patent Utility Model No. 55-138129 (1stpage, FIG. 2)) in which one pair of wheels from among the front wheels and rear wheels are driven by the power of an internal combustion engine through a transmission as the main drive wheels, and the other pair of wheels, from among the front wheels and rear wheels, is driven by an electric motor. The driving force of the internal combustion engine drives a generator and the electromotive force generated by this generator is supplied to an electric motor. Thereafter, when the accelerator pedal is stepped down on and the vehicle speed is less than a present value, the electric motor operates to drive the front wheels and rear wheels.

SUMMARY OF THE INVENTION

It has been discovered that in the above mentioned driving force control apparatus that since the electric motor is driven by the electromotive force generated by the generator that is driven by the internal combustion engine, if the generator cannot overcome the counterelectromotive force of the electric motor, it cannot generator power. In other words, when the engine rotational speed is increased, the rate of increase will be small with a low engine rotational speed and then the rate grows larger as the vehicle speed increases. In contrast, the counterelectromotive force of the electric motor is “0” when the engine rotational speed is “0” and then increases at a fixed rate of increase following increases in the engine rotational speed. Because of this, the power generation capacity line of the generator is less then the counterelectromotive force of the electric motor during the period between when the engine rotational speed is “0” until a designated engine rotational speed is reached. Consequently, power generation current generated by the generator cannot flow and the electric motor cannot generate drive torque. If, however, the engine rotational speed increases and exceeds the designated engine rotational speed, the power generation current generated by the generator will increase in response to this thereby allowing the electric motor to generate drive torque.

In the above mentioned driving force control apparatus, a transmission is equipped on the output side of the internal combustion engine. When the vehicle speed is fixed, the internal combustion engine rotational speed varies according to the variable speed ratio of the transmission and the amount of power generated by the generator driven by this internal combustion engine varies in response to the internal combustion engine rotational speed.

In contrast, vehicles equipped with a traction control apparatus to prevent acceleration slippage of the drive wheels are controlled to prevent acceleration slippage when acceleration slippage in the drive wheels occurs such as when travelling on road surfaces with a low frictional coefficient by changing the upshift schedule. The upshift schedule changes the upshift variable speed line that upshifts from the 1 st speed gear position to the 2nd speed gear position of the automatic transmission to a high vehicle speed compared with a normal variable speed line and then reducing the engine rotational speed or providing a braking force to the drive wheels using the throttle opening degree or cutting fuel while controlling the upshift of the automatic transmission.

In this manner, if the shift schedule is changed by the traction control apparatus so as to control upshifts while acceleration slippage occurs and the acceleration slippage cancelled, the shift schedule will return to a shift schedule that uses the original normal variable speed line. Because of this, the engine rotational speed changes to a comparatively high state and the amount of power generated by the generator can overcome the counterelectromotive force of the electric motor allowing the generated current to be supplied to the electric motor by means of controlling the upshifting of the automatic transmission from the 1 st speed gear position to the 2nd speed gear position even if the vehicle speed exceeds the normal variable speed line while acceleration slippage occurs when driving the electric motor using the amount of power generated by the generator in vehicles equipped with a traction control apparatus. Because the shift schedule returns to a shift schedule that uses the original normal variable speed line when the acceleration slippage is cancelled in a state in which the electric motor is being driven, there is an unsolved problem of the danger of the automatic transmission shifting up to the 2nd speed gear position and the engine rotational speed decreasing thereby resulting in insufficient power generation or the impossibility of power generation.

Thereupon, an object of the present invention is to solve of the above-mentioned problems and provide a vehicle driving force control apparatus that can prevent the occurrence of insufficient power generation or the impossibility of power generation by the generator.

In order to achieve the above-mentioned object, a vehicle driving force control apparatus of a vehicle is provided that has generator driven by a main drive source and an electric motor driven by electric power from the generator to supply torque to a first drive wheel. The vehicle driving force control apparatus has a shift schedule change section, a power sufficiency determining section and a shift schedule change prohibit section. The shift schedule change section is configured to change a shift schedule of a transmission of the main drive source. The power sufficiency determining section is configured to determine whether generated power of the generator will be insufficient by a change in the shift schedule by the shift schedule change section, when an electromotive force of the generator is driving the electric motor that supplies torque to the first drive wheel. The shift schedule change prohibit section is configured to prohibit a change of the shift schedule by the shift schedule change section, upon the power sufficiency determining section determining that the generated power of the generator will be insufficient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially toFIGS. 1 and 2, a vehicle driving force control apparatus will now be explained in accordance with a first embodiment of the present invention. As seen inFIG. 1, a four wheel drive vehicle is diagrammatically illustrated that is equipped with the vehicle driving force control apparatus in accordance with the present invention. As shown inFIG. 1, the vehicle in accordance with this embodiment has left and right front wheels1L and1R that are driven by an internal combustion engine or main drive source2, and left and right rear wheels3L and3R that are driven by an electric motor or subordinate drive source4, which is preferably a direct current (DC) electric motor. Thus, the front wheels1L and1R serve as the main drive wheels, while the rear wheels3L and3R serve as the subordinate drive wheels.

A portion of the engine output torque Te of the internal combustion engine2is transmitted to the left and right front wheels1L and1R through an automatic transmission5, equipped with a torque converter, and a differential gear5ain a conventional manner. An endless drive belt6transfers power from the internal combustion engine2to a generator7, which supplies electrical energy to the electric motor4. Thus, a portion of the engine output torque Te of the internal combustion engine2is transmitted to the generator7through the endless belt drive6to supply electrical energy to the electric motor4.

The generator7rotates at a rotational speed Ng that is equal to the product of the rotational speed Ne of the internal combustion engine2and the pulley ratio of the endless drive belt6. The load placed on the internal combustion engine2by the generator7due to the field current Ifg of the generator7is adjusted by the 4WD controller8to generate a voltage corresponding to the load torque. The generator7then generates an electromotive force in proportion to this load torque. The voltage generated by the generator7can be supplied to the electric motor4through the electrical line9. A junction box10is provided at an intermediate point in the electrical line9between the electric motor4and the generator7. The drive shaft of the electric motor4can be connected to the rear wheels3L and3R via a reduction gear11, a clutch12and a differential gear13in a conventional manner. Each of the left and right output sides of the differential gear13are linked to the left and right rear wheels3L and3R through the drive shafts13L and13R, respectively.

The clutch12is preferably an electromagnetic clutch that connects and disconnects in response to a clutch control command issued from the 4WD controller8. Of course, a hydraulic clutch can be used for clutch12is certain situations to carry out the present invention. Thus, the clutch12transmits torque from the electric motor4to the rear wheels3L and3R at a torque transfer rate corresponding to the clutch control command from the 4WD controller8. The clutch12has an input shaft12acoupled to the electric motor4via the reduction gear11, and an output shaft12bcoupled to the rear wheels3L and3R via the differential gear13. Preferably, the clutch12is turned on to perform an engagement operation in which the input and output shafts12aand12bare connected such that the drive torque from the electric motor4is transmitted to the rear wheels3L and3R. When the clutch12is turned off, a disengagement or release operation occurs in which the input and output shafts12aand12bare disengaged such that the drive torque from the electric motor4is no longer transmitted to the rear wheels3L and3R. Thus, when the clutch12is engaged, the vehicle is in a four-wheel (multi-wheel) drive state in which all of the wheels1L,1R,3L and3R are driven. When the clutch12is released, the vehicle is in a two-wheel (non-all wheel) drive state in which only the front wheels1L and1R are driven by the internal combustion engine2.

According to the present invention, as explained below in more detail, a shift schedule change prohibit method is used to prohibit changes in a shift schedule which will result in the generator7generating insufficient power in a drive state of, for example, four-wheel drive, in which the electric motor4drives the subordinate drive wheels3L and3R. Because of this, an effect is obtained that makes it possible to maintain a shift schedule when that shift schedule is changed from a normal variable speed line to a high vehicle speed thereby reliably preventing reductions in the rotational speed of the main drive source due to the transmission upshifting and to appropriately control the drive torque of the electric motor4.

A main throttle valve15and a sub throttle valve16are disposed inside the intake passage14(e.g., an intake manifold) of the internal combustion engine2. The throttle opening of the main throttle valve15is adjusted and controlled in accordance with the amount of depression of the accelerator pedal17, which also constitutes or functions as an accelerator position detecting device or sensor, or a throttle opening instructing device or sensor. In order to adjust the throttle opening degree of the main throttle valve15, the main throttle valve15is either mechanically linked to the depression amount of the accelerator pedal17, or adjusted/controlled electrically by an engine controller18in accordance with the depression amount detection value from an accelerator sensor17athat detects the depression amount of the accelerator pedal17or the degree of opening of the main throttle valve15. The depression amount detection value from the accelerator sensor17ais outputted as a control signal to the 4WD controller8. The accelerator sensor17aconstitutes an acceleration or throttle instruction sensor. Thus, the phrase “accelerator position opening degree” as used herein refers to either a throttle opening amount of the main throttle valve15or a depression amount of the accelerator pedal17or similar accelerator device.

The sub throttle valve16uses a stepper motor19as an actuator for adjusting its throttle opening degree in response to drive signals from a motor controller20. Specifically, the throttle opening degree of the sub throttle valve16is adjusted and controlled by the rotational angle of the stepper motor19, which corresponds to the step count. The rotational angle of the stepper motor19is adjusted and controlled by a drive signal from the motor controller20. The sub throttle valve16is provided with a throttle sensor19ashown inFIG. 2. The step count of the stepper motor19is feedback-controlled based on the throttle opening detection value detected by this throttle sensor19a. The output torque of the internal combustion engine2can be controlled (reduced) independently of the driver's operation of the accelerator pedal17by adjusting the throttle opening of the sub throttle valve16so as to be smaller than the throttle opening of the main throttle valve15.

The apparatus is also equipped with an engine rotational speed sensor21that detects the rotational speed Ne of the internal combustion engine2. The engine rotational speed sensor21outputs a control signal that is indicative of the engine rotational speed Ne to both the engine controller18and the 4WD controller8.

In addition, a shift position sensor25is installed that functions as a gear ratio detection device or section detects the shift position of the aautomatic transmission5. The shift position detected by the shift position sensor25is input to the 4WD controller8. Even further, the 4WD switch26is installed close to the driver's seat that selects a drive state or mode. The switch signal of this 4WD switch26is input to the 4WD controller8. The 4WD switch26forms part of a drive mode selection section of the present invention.

The wheels1L,1R,3L and3R are provided with wheel speed sensors24FL,24FR,24RL, and24RR, respectively. Each speed sensor24FL,24FR,24RL, and24RR outputs a pulse signal corresponding to the rotational speed of the respective wheel1L,1R,3L and3R to the 4WD controller8. Thus, the wheel speeds VWFL˜VWRRdetected by these wheel speed sensors24FL,24FR,24RL, and24RR are also output to the 4WD controller8. Each of the pulse signals serves as a wheel speed detection value indicative of the rotational speed of the respective wheel1L,1R,3L and3R, respectively. The wheel speed sensors24RL and24RR constitute an output shaft rotational speed detector or sensor of the clutch12.

As shown inFIG. 2, the generator7has a three-phase stator coil SC connected in a delta formation and a field coil FC. Each of the connection nodes of the stator coil SC is connected to a rectifying circuit30made up of diodes and the rectifying circuit30delivers a maximum DC voltage Vg of, for example, 42 V.

One end of the field coil FC is connected to the output side of the rectifying circuit30through a diode D1and to a battery32of a prescribed voltage (e.g., 12 volts) through a diode D2in the reverse direction and a 4WD or 12-volt relay31. The other end of the field coil FC is connected to the cathode sides of the diodes D1and D2through a flywheel diode DF in the forward direction, and is grounded through a bipolar transistor33comprising a voltage regulator.

The 12-volt battery32supplies operating electric power to the 4WD controller8with the 12-volt relay31that is installed in the 12-volt electric power supply line in order to connect and disconnect the power to the clutch12, which is preferably an electromagnetic clutch.

The circuitry that supplies the field current Ifg through the rectifying circuit30and the diode D1forms a self excited circuit and the circuitry that supplies the field current Ifg through the battery32and the diode D2forms a separately excited circuit. The diodes D1and D2function as a select-high mechanism that selects the higher voltage between the voltage of the self excited circuit and the voltage of the separately excited circuit.

The 4WD or 12-volt relay31is configured such that one end of its relay coil is connected to the output side of an ignition coil or relay35that is connected to the battery32through an ignition switch34and the other end of the relay coil connected to the 4WD controller8.

The generator load torque Tg that the generator7imposes on the engine2and the generated voltage Vg are controlled by the 4WD controller8by adjusting the field current Ifg going through the field coil FC. The bipolar transistor33receives a pulse width modulated (PWM) generator control command (duty ratio or field current value) C1from the 4WD controller8and adjusts the value of the field current Ifg of the generator7in accordance with the generator control command C1.

The motor relay36and the current sensor37are connected in series inside the junction box10. The motor relay36connects and disconnects the electric power supplied to the electric motor4in accordance with a command from the 4WD controller8. The current sensor37detects the armature current Ia supplied to the electric motor4from the generator7and outputs the detected armature current Ia to the 4WD controller8. The motor voltage Vm of the electric motor4is detected at the 4WD controller8.

As mentioned above, the field current Ifm of the electric motor4is controlled by a pulse width modulated field current control command, i.e., motor output torque command, from the 4WD controller8and the drive torque Tm is adjusted by adjusting the field current Ifm. The temperature of the electric motor4is detected by the thermistor38and the temperature detection value is fed to the 4WD controller8. The rotational speed Nm of the output shaft of the electric motor4is detected by the motor rotational speed sensor39and the rotational speed Nm is also fed to the 4WD controller8.

The electric clutch12has an excitation coil12chaving one end connected to the output side of the 4WD relay31and the other end connected to the 4WD controller8. Inside of the 4WD controller8, the other end of the excitation coil12cis connected to ground via a switching transistor40that serves as a switching element. The current in the excitation coil12cis controlled by a pulse width modulated clutch control command CL supplied to the base of the transistor40. As a result, the torque transmitted to the rear wheels3L and3R (subordinate drive wheels) from the electric motor4is controlled.

The 4WD controller8is a control unit that preferably includes a microcomputer with a 4WD control program that is operatively coupled to the internal combustion engine2and the electric motor4to control the torque applied to the left and right front wheels1L and1R by the internal combustion engine2and the torque applied to the left and right rear wheels3L and3R by an electric motor4as discussed below. The 4WD controller8can also include other conventional components such as an input interface circuit, an output interface circuit, and storage devices such as a ROM (Read Only Memory) device and a RAM (Random Access Memory) device. The memory circuit stores processing results and control programs. The RAM of the 4WD controller8stores statuses of operational flags and various control data for the control program. The ROM of the 4WD controller8stores various operations for the control program. The 4WD controller8is capable of selectively controlling any of the components of the driving force control apparatus in accordance with the control program. It will be apparent to those skilled in the art from this disclosure that the precise structure and algorithms for 4WD controller8can be any combination of hardware and software that will carry out the functions of the present invention. In other words, “means plus function” clauses as utilized in the claims should include any structure including, but not limited to, hardware and/or algorithm or software that can be utilized to carry out the function of the “means plus function” clause. Moreover, the terms “device” and “section” as utilized in the claims should include any structure, i.e., hardware alone, software alone, or combination of hardware and software.

As shown inFIG. 3, the 4WD controller8includes a generator control section8A, a relay control section8B, a motor control section8C, a clutch control section8D, a surplus torque computing section8E, a target torque limiting section8F, a surplus torque converting section8G and a traction control section8T.

As shown inFIG. 4, at a prescribed sampling time cycle, the 4WD controller8executes the processing of the surplus torque computing section8E, the target torque limiting section8F, and the surplus torque converting section8G in sequence based on the input signals. Together, the surplus torque computing section8E, the target torque limiting section8F, and the surplus torque converting section8G constitute an output torque control section of the 4WD controller8.

Through the bipolar transistor45of the voltage adjuster22, the generator control section8A monitors the generated voltage V of the generator7and adjusts the generated voltage Vg of the generator7to the required voltage by adjusting the field current Ifg of the generator7. Thus, the generator control section8A functions as a generation load torque adjusting section.

The relay control section8B controls shutting off and connecting the electrical power supply from the generator7to the electric motor4.

The motor control section8C calculates a corresponding motor torque target value Tm based on the generator load torque target value Tgt computed by the surplus torque converting section8G (discussed below). Thus, the clutch control section8D controls the state of the clutch12by outputting a clutch control command to the clutch12. The clutch control section8D constitutes the clutch engagement control section of the present invention. Then the clutch control section8D calculates the clutch transmission torque TCLof the electric clutch12by executing the calculation of the Equation (1) shown below based on the motor torque target value Tm. Next, the clutch control section8D converts the clutch transmission torque TCLinto a clutch current command value ICL. The clutch control section8D then pulse-width modulates (PMW) the clutch current command value ICL, and calculates a clutch current control output CL having a duty ratio that corresponds to the clutch current command value ICL. The clutch current control output CL is delivered to the switching transistor40.
TCL=Tmt×KDEF×KTM+TCL0(1)
In this Equation (1), KDEFis the reduction ratio of the differential gear13, KTMis the clutch torque margin and TCL0is the clutch initial torque.

Next, the surplus torque computing section8E will be discussed which executes the processing shown inFIG. 5. First, in step S1, the wheel speeds computed based on the signals from the wheel speed sensors24FL,24FR,24RL and24RR are used to subtract the wheel speed of the rear wheels3L and3R (subordinate drive wheels) from the wheel speed of the front wheels1L and1R (main drive wheels) and find the slippage speed ΔVF, which is the magnitude of the acceleration slippage of the front wheels1L and1R. Then, the 4WD controller8proceeds to step S2.

The slippage speed ΔVFcan be calculated as follows. The average front wheel speed VWf(which is the average of the left and right wheel speeds for the front wheels1L and1R) and the average rear wheel speed VWr(which is the average of the left and right wheel speeds for the rear wheels3L and3R) are calculated using the following two Equations (2) and (3):
VWf=(VWfl+VWfr)/2  (2)
VWr=(VWrl+VWrr)/2  (3)

Now, the slippage speed (acceleration slippage magnitude) ΔVFof the front or main drive wheels1L and1R is calculated by the differential between the average front wheel speed VWfand the average rear wheel speed VWr, as set forth in the following Equation (4):
ΔVF=VWf−VWr(4)

In step S2, the 4WD controller8determines whether or not the calculated slippage speed ΔVFexceeds a prescribed value, such as zero. Thus, steps S1and S2constitute an acceleration slippage detection section that estimates if acceleration slippage is occurring in the front wheels1L and1R that is driven by the internal combustion engine2. If slippage speed ΔVFis determined to be zero or below, it is estimated that the front wheels1L and1R are not experiencing acceleration slippage and the 4WD controller8proceeds to step S3, where a target generator load torque Tgt is set to zero. The 4WD controller8then proceeds to the target torque limiting section8F process.

Conversely, if in step S2slippage speed ΔVFis determined to be larger than zero, it is estimated that the front wheels1L and1R are experiencing acceleration slippage, and thus, control proceeds to step S4.

In step S4, the absorption torque TΔVFrequired for suppressing the acceleration slippage of the front wheels1L and1R is calculated using the Equation (5) below and the 4WD controller8proceeds to step S5. The absorption torque TΔVFis an amount that is proportional to the acceleration slippage magnitude, as set forth in the following Equation (5):
TΔVF=K1×ΔVF(5)where: K1 is a gain that is found through experimentation or the like.

In step S5, a current load torque TG of the generator7is calculated based on the Equation (6) below, and then the 4WD controller8proceeds to step S6.

TG=K2⁢Vg×IaK3×Ng(6)
where: Vg: voltage of the generator7,Ia: armature current of the generator7,Ng: rotational speed of the generator7,K3: efficiency, andK2: coefficient.

In step S6, the surplus torque, i.e., the target generator load torque Tgt that the generator7should impose, is found based on the Equation (7) stated below, and the 4WD controller8returns to the beginning of the control loop.
Tgt=TG+TΔVF(7)

Next, the processing executed by the target torque (control) limiting section8F will be explained based onFIG. 6. The processing of the target generator load torque Tgt in the flow chart ofFIG. 6constitutes a generator control section configured to control a generation load torque of the generator7to substantially correspond to an acceleration slippage magnitude of the drive wheel, when the acceleration slippage detection section estimates acceleration slippage occurring in the drive wheel.

First, in step S11, the target torque limiting section8F of the 4WD controller8determines whether or not the target generator load torque Tgt is larger than the maximum load capacity HQ of the generator7. The 4WD controller8proceeds to the beginning of the control program to repeat the processing if the 4WD controller8determines that target generator load torque Tgt is less than or equal to the maximum load capacity HQ of the generator7. Conversely, the 4WD controller8proceeds to step S12if the 4WD controller8determines that the target generator load torque Tgt is larger than the maximum load capacity HQ of the generator7.

In step S12, the excess torque ΔTb, which is a portion of target generation load torque Tgt that exceeds the maximum load capacity HQ, is found according to the following Equation (8):
ΔTb=Tgt−HQ.(8)
Then, the 4WD controller8proceeds to step S130.

In step S13, the current engine torque Te is computed based on the signals from the throttle sensor19aand the engine rotational speed sensor21using an engine torque calculation map. Then, the 4WD controller8proceeds to step S14.

In step S14, the engine torque upper limit value TeM is calculated by subtracting the excess torque ΔTb from the engine torque Te, as set forth in the following Equation (9):
TeM=Te−ΔTb.(9)
After the engine torque upper limit value TeM is outputted to the engine controller18, the 4WD controller8proceeds to step S115.

In this equation, the engine controller18is not related to the operation of the accelerator pedal17by the operator but limits this engine torque Te such that the input engine torque upper limit value TeM becomes the upper limit value of the engine torque Te.

In step S15, the maximum load capacity HQ is assigned as the target generation load torque Tgt, and then the 4WD controller8process ends and proceeds to the surplus torque converting section8G process.

Next, the processing executed by the surplus torque converting section8G will be explained based onFIG. 8.

First, in step S20, the 4WD controller8determines if the vehicle is experiencing acceleration slippage by determining if the slippage speed ΔVFis larger than zero. If the slippage speed αVFis determined to be larger than zero, the 4WD controller8proceeds to step S22because the front wheels1L and1R are experiencing acceleration slippage. If the 4WD controller8determines that the slippage speed ΔVFis less than or equal to zero, then the 4WD controller8does not proceed to step S21because the front wheels1L and1R are not experiencing acceleration slippage.

In step S21, a determination is made as to whether or not the vehicle is in a four wheel drive state by checking if the operating flag F4WDis set to “0”. When the operating flag F4WDis set to “0”, this represents that the electric motor4is not driven and the vehicle is in a two-wheel drive state. If this operating flag F4WDis set to “0”, then the process ends without the surplus torque conversion process executing and returns to the surplus torque computing section8E process. If the operating flag F4WDis set to “1”, the process proceeds to step S23.

In contrast, when the result of the determination of step S20is the slippage speed ΔVFis determined to be larger than zero, the determination is that the front wheels1L and1R are experiencing acceleration slippage and the process proceeds to step S22. In step S22, the operating flag F4WDis set to “1”, and the process proceeds to step S23.

In step S23, the rotational speed Nm of the motor4detected by the motor rotational speed sensor39is input and then based on that rotational speed Nm of the motor4, the motor field current target value Ifmt is computed referencing the motor field current target value computation map shown in step S23ofFIG. 8.

The target motor field current calculation map was created based on the first gear of the drive range (D) of the automatic transmission5, which is the gear with the highest gear ratio in that range. For example, the 1stspeed that is the largest gear ratio in the drive range (D) of the automatic transmission5. The motor field current target value Ifmt follows a characteristic curve that is plotted with the motor rotational speed Nm on the horizontal axis and the motor field current target value Ifmt on the vertical axis as shown inFIG. 8. In the range of motor rotational speeds Nm from zero to the first predetermined value N1, the motor field current target value Ifmt holds at a preset maximum current value IMAX. If the motor rotational speed increases beyond the predetermined value N1, the motor field current target value Ifmt decreases accordingly at a comparatively large slope. Then, at rotational speeds between a second predetermined value N2that is larger than the first predetermined value N1and a third predetermined value N3that is larger than the second predetermined value N2, the motor field current target value Ifmt holds at a low current value ILthat is smaller than the initial current value IIN. If the motor rotational speed Nm increases further and exceeds the first predetermined value N3, the motor field current target value Ifmt decreases at a still larger slope until it reaches 0.

Thus, the field current of the electric motor4is held at a fixed prescribed current value IMAXin the range of rotational speeds Nm from 0 to the predetermined value N1and reduced using a known using a known weak magnetic field control method when the electric motor4is rotating at a speed above the predetermined value N1(seeFIG. 8). In short, when the electric motor4rotates at a high speed the motor torque decreases due to the rise in the induced voltage E in the electric motor4. Therefore, as discussed earlier, when the rotational speed Nm of the electric motor4reaches or exceeds the prescribed value N1, the current flowing to the electric motor4is increased and the required motor torque Tm is obtained by reducing the field current Ifm of the electric motor4and lowering the induced voltage E. As a result, even if the electric motor4rotates at a high speed, the required motor torque Tm can be obtained because the motor induced voltage E is kept from rising and the motor torque is prevented from decreasing. Also, the price of the electronic control circuit can be reduced in comparison with continuous field current control because the motor field current Ifm is controlled in two stages: a stage for when the rotational speed is below a prescribed value and another stage for when the rotational speed is at or above a prescribed value.

Next, the process proceeds to step S24. In this step, the motor field current target value Ifmt computed in step S23is output to the motor control section8C and the process proceeds to step S25.

Next, the process proceeds to step S25. In step S25, the 4WD controller8calculates the motor induced voltage E based on the motor rotational speed Nm and the motor field current target value Ifmt calculated in step S23using the motor induced voltage calculation map shown inFIG. 8. The motor induced voltage calculation map is configured such that curves for different motor field current target values Ifmt are plotted on a graph having the motor rotational speed Nm on the horizontal axis and the motor induced voltage E on the vertical axis. The motor induced voltage E increases substantially linearly as the motor rotational speed Nm increases, and the motor induced voltage E also increases as the motor field current target value Ifmt increases.

Next, the process proceeds to step S26. In this step a determination is made as to whether or not a four-wheel drive state is established. As an example, this determination determines whether or not the last motor torque target value Tmt(n−1) is equal to or less than the previously set motor torque threshold value TmTH. When the last motor torque target value Tmt(n−1) greater than less than the previously set motor torque threshold value TmTH, the determination is that a four-wheel drive state is not established and the process proceeds to step S27. When the last motor torque target value Tmt(n−1) less than the previously set motor torque threshold value TmTH, the determination is that a four-wheel drive state is established and the process proceeds to step S30.

In step S27, the corresponding motor torque target value Tmt is computed based on the generated power load torque target value Tgt computed by the surplus torque computing section8E and the process proceeds to step S28.

In step S28, the 4WD controller8calculates the armature current value Iat based on the motor torque target value Tmt and the motor field current target value Ifmt using the armature current target value calculation map shown inFIG. 9. The armature current target value calculation map is configured such that curves for different motor field current target values Ifmt are plotted on a graph having the motor torque target value Tmt on the horizontal axis and the armature current target value Iat on the vertical axis. When the motor output torque Tmt is zero, the armature current target value Iat is zero regardless of the value of the motor field current target value Ifmt. As the motor output torque Tm increases the armature current target value Iat increases, but as the motor field current target value Ifmt increases the armature current target value Iat decreases. When the motor output torque Tmt becomes larger, the armature current target values Iat go to zero sequentially in order from the smallest motor field current target value Ifmt.

Next, the process proceeds to step S29. In this step, after computing the armature current target value Iat, the resistance of the electrical line9and the combined resistance R of the coil resistance of the motor4, as well as the voltage target value VG of the generators from the induced voltage E based on the following equation (9), the process ends and then returns to the surplus torque computing section8E.
VG=Iat×R+E(9)

In contrast, in step S30, after executing the motor torque reduction process in which the value obtained by subtracting the prescribed reduction amount ΔTmt from the last motor torque target value Tmt(n−1) is computed as the current motor torque target value Tmt(n) (=Tmt(n−1−ΔTmt), the process proceeds to steps S31. In this step, a determination is made as to whether or not the motor torque target value Tmt(n) is equal to or less than “0”. When the motor torque target value Tmt(n) greater than zero, the process proceeds to step S28. When Tmt(n) less than or equal to 0, the process proceeds to step S32.

In step S30, the operating flag F4WDis reset to “0” indicating a transition to a two-wheel drive state. After the operating flag F4WDis reset to “0”, the process ends.

The traction control section8T also executes the traction control process shown inFIG. 10. The traction control section8T uses the shift schedule such as the one shown inFIG. 11to change the shift point of the automatic transmission5. The shift schedule shown inFIG. 11has three shift schedules. Each shift schedule includes one or more upshift variable speed lines for upshifting from a low (first) speed gear position to a high (second) speed gear position of the transmission5. For example, the 1stTCS shift schedule uses the 1sttraction control variable speed line LTC1ofFIG. 11for upshifting from a first (low) speed gear position to a second (high) speed gear position of the transmission5, while the 2ndTCS shift schedule uses the 2ndtraction control variable speed line LTC2ofFIG. 11for upshifting from a first (low) speed gear position to a second (high) speed gear position of the transmission5.

This traction control process is executed as a timer interrupt process at each of a prescribed time (for example, 10 msec). At first, in step S41, a determination is made as to whether or not the slippage speed ΔVFis larger then a preset slippage speed threshold value ΔVFTH. When the slippage speed ΔVFgreater than preset slippage speed threshold value ΔVFTH, the result of the determination is that acceleration slippage is occurring at the front wheels1L and1R and the process proceeds to step S42.

Then, in step S42, a determination is made as to whether or not the front wheel drive torque TF, read from the torque sensor27, is smaller than the preset drive torque threshold value TTH. When the front wheel drive torque TFless than the preset drive torque threshold value TTH, the process proceeds to step S43.

In step S43, the traction control section8T sets the 2ndTCS shift schedule for the automatic transmission5. The 2ndTCS shift schedule uses the 2ndtraction control variable speed line LTC2ofFIG. 11that sets the upshift variable speed line to a vehicle speed higher than the normal variable speed line LUindicated by the solid lines of the dot and dashed lines. This upshift variable speed line uses the variable speed map, shown inFIG. 11for the transmission controller41that controls the variable speed of the automatic transmission5, to upshift from the 1 st speed gear position to the 2nd speed gear position. Thereafter, the process proceeds to step S44.

In this process of step S44, the traction control section8T executes the traction control process to control the wheel torque. In particular, the throttle opening degree of the sub throttle valve16that controls the slippage speed ΔVFis set and this value is outputted to the motor controller20. Also, during the traction control process, a fuel control process is carried out to cut fuel to the internal combustion engine2and/or a braking process that provides a braking force to the front drive wheels1L and1R. After this the timer interrupt process ends.

Meanwhile, when the determination of step S42results in the front wheel drive torque TFbeing determined to be greater than or equal to the preset drive torque threshold value TTH, then the process proceeds to step S45.

In step S45, a determination is made by the 4WD controller8as to whether or not the operating flag F4WDis set to “1” by the surplus torque converting section8G discussed earlier. If this operating flag F4WDis set to “0”, then the process proceeds to step S46.

In step S46, the 4WD controller8sets the 1stTCS shift schedule that uses the 1sttraction control variable speed line LTC1which is located at the vehicle speed position midway between the normal variable speed line LUfor the transmission controller41indicated by the dot and dashed lines inFIG. 11and the 2nd traction control variable speed line LTC2. After this, the process proceeds to step S44, where the traction control section8T executes the traction control process as discussed earlier.

Meanwhile, when the determination of step S45results in a determination that the operating flag F4WDis set to “0”, then the process proceeds to step S47. In this step, a determination is made as to whether or not the 2ndTCS schedule is set. When the 2ndTCS schedule is set, the process proceeds to step S44, where the traction control section8T executes the traction control process, as discussed earlier, using the 2ndTCS schedule as is without any changes. When the 2ndTCS schedule is not set, the process proceeds to step S46, where the 1stTCS shift schedule is set as the current shift schedule as discussed earlier.

When the determination of step S41results in ΔVFless than or equal to 0, the determination is that acceleration slippage has not occurred and the process proceeds to step S48. Then, a determination is made as to whether or not the operating flag F4WDof the surplus torque converting section8G is set to “1”. When this operating flag F4WDis set to “1”, the timer interrupt process ends as is without any changes. When the operating flag F4WDis set to “0”, the process proceeds to step S49and sets a normal schedule that selects the normal variable speed line LUfor the transmission controller41indicated by the solid lines inFIG. 11and then ends the timer interrupt process.

The process of steps S45, S47and S48inFIG. 10corresponds to the shift schedule change prohibit section since the shift schedule remains unchanged (i.e., shift schedule change is prohibited) when the determinations in steps S45and S47are “Yes”, or the determination in step S48is “Yes”. The process of steps S42, S45and S48also constitute the power sufficiency determining section. Also, the process of steps S43, S46and S49corresponds to the shift schedule change section.

Next, the operation of the first embodiment will be discussed referring to the timing charts ofFIG. 12.

Now, by placing the selector lever of the automatic transmission to the parking range (P) and turning the ignition switch ON, the internal combustion engine2will start with the vehicle in a stopped state.

As shown in the graph (a) ofFIG. 12, the operator sets the 4WD switch26to ON in this stopped state at a time t1. At this time t1, because the selector lever is set to the parking range as shown in the graph (c) ofFIG. 12, the relay control section8B governs the 4WD relay31to an OFF state and the input of the power system power supply is stopped to the 4WD controller8. This occurs along with the supply of electrical power from the battery32to the field coil FC of the generator7, the motor relay36of the junction box10, and the clutch coil12aof the electromagnetic clutch12being stopped.

From this stopped state, the operator then shifts the selector lever from the parking position (P) to the drive range (D) through the reverse position (R) and the neutral position (N) at time t2and selects the drive range (D) at time t3. Thereafter, as shown in the graph (b) ofFIG. 12, the 4WD relay31is governed to an ON state by the relay control section8B at time t4at which a prescribed time of for example, about 0.05 seconds has passed.

Because the vehicle is stopped in this state, the average front wheel speed VWfof the front wheels1L and1R and the average rear wheel speed VWrof the rear wheels3L and3R are both “0” and the slippage speed ΔVFis also “0”. Because of this, an initialization process executed when the ignition switch is set to ON resets the operating flag F4WDto “0” in the processing ofFIG. 8executed by the surplus torque converting section8G. This ends the process and returns to the surplus torque computing section8E from step S20to step S21without executing the processes of steps S22˜S32.

Because of this, the generator control output C1and the motor field output MF are both set to OFF by the generator control section8A based on the generated voltage target value VG. The clutch control output CL is also set to OFF by the clutch control section8D. Therefore, the power generated by the generator7and the drive of the electric motor4are stopped along with the clutch12being set to a clutch disengaged state.

Because of this state, at a time t5, if acceleration slippage occurs in the front wheels1L and1R (main drive wheels) due to the vehicle travelling in the forward direction on road surfaces with a low frictional coefficient, such as roads wet with rain, snow or frost, wheel speed differences of the front and rear wheels will make the slippage speed ΔVFa positive value even if the accelerator pedal17is stepped down on strongly and vehicle quickly accelerates or the accelerator pedal17is not stepped down on strongly.

At this time, the clutch control output CL is controlled to a prescribed duty rate by the clutch control section8D setting the clutch12to a clutch engaged state. Because the slippage speed ΔVFchanges to a positive value in the processing ofFIG. 5in the surplus torque computing section8E simultaneous with this, the process proceeds from step S2to step S4. Then, the required absorption torque TΔVFis computed in order to multiply the gain K1 by the slippage speed ΔVFand restrain the acceleration slippage. Next, the equation (5) discussed earlier is used to compute the current generated load torque TG (step S5) based on the current generated voltage Vg, armature current Ia and generator rotational speed Ng. Since this current generated load torque TG has a comparatively small generator rotational speed Ng while the vehicle is traveling, it will increases in proportion to increases in the generated voltage Vg and the armature current Ia. Also, since the absorption torque TΔVFand the current generated load torque TG are multiplied to compute the generated load torque target value Tgt, this generated load torque target value Tgt increases as well.

The generated voltage Vg produced by the generator7is controlled by the processing ofFIG. 8of the surplus torque converting section8G. Since the slippage speed ΔVFis a positive value, the process proceeds to step S22and the operating flag F4WDis set to “1”. Next, the process proceeds to step S23. In this process, the voltage value obtained by multiplying the running resistance R by the armature current target value Iat computed by referencing the armature current target value computing map ofFIG. 9based on the motor torque target value Tmt and the motor field current target value Ifmt is added to the induced voltage E in the motor4and this sum obtained.

Hereupon, the motor field current target value Ifmt is computed referencing the motor field current target value computation map in step S23in the processing ofFIG. 8based on the motor rotational speed Nm. Because the motor rotational speed Nm is still slow while the vehicle is travelling, the motor field current target value Ifmt at this time is set to the maximum current value IMAX.

The computed motor field current target value Ifmt is output to the motor control section8C as is without any changes which in turn starts driving of the motor4(step S24).

Because the motor induced voltage E, computed in step S25, also increases at this time, the armature current target value Iat, computed in step S27, rises with the passage of time and, as shown in the graph (f) ofFIG. 12, the motor torque Tm increases as well. The rear wheels3L and3R start driving by means of transferring this increase to the rear wheels. While this occurs, the electromagnetic clutch12is also set to a linked state by the clutch control section8D.

As a result, when acceleration slippage occurs in the front wheels1L and1R (main drive wheels) when quickly accelerating or travelling on road surfaces with a low frictional coefficient, the rear wheels3L and3R (subordinate drive wheels) are driven by the motor4so as to cancel the acceleration slippage in the front wheels1L and1R thereby making it possible to travel in the vehicle smoothly.

During this time, in the traction control section8T, the shift schedule for the transmission controller41is set to a normal shift schedule by the initialization process executing at the time when the ignition switch is set to ON and the slippage speed ΔVFdoes not exceed the slippage speed threshold value ΔVFTH. For that reason, the process proceeds from step S41to step S48and even if the operating flag F4WDis set to “1”, the normal shift schedule will continue to be set as is without any changes.

Thereafter, if the slippage speed ΔVFexceeds the slippage speed threshold value ΔVFTH, at a time t6 the process will proceed from step S41to step S42in the processing ofFIG. 10in the traction control section8T. As shown in the graph (i) ofFIG. 12, the front wheel drive torque TFwill exceed the drive torque threshold value TTHat time t3 when the drive range (D) was selected. Because of this the process proceeds to step S45. Hereupon, because the operating flag F4WDis set to “1”, the process proceeds to step S47and a normal shift schedule is set. Since the 2ndTCS shift schedule is not set, the process proceeds to step S46and the1stTCS shift schedule is set for the transmission controller41. Thereafter, the process proceeds to step S44and the throttle opening degree of the sub throttle valve16is reduced. This occurs along with the process to cut fuel to the internal combustion engine2as necessary and the application of a braking force to the front wheels1L and1R (drive wheels). Then, the acceleration slippage of the front wheels indicated by the dashed lines in the graph (d) ofFIG. 12is restrained, and the acceleration is faster than the rear wheel vehicle speed indicated by the solid lines by the amount of the slippage speed threshold value ΔVFTHonly.

After this, the motor torque Tm is controlled to an almost uniform value after rising quickly as shown in the graph (f) ofFIG. 12. Then, if the front wheel drive torque TFdecreases gradually and, at time t7, drops to a value less than the drive torque threshold value TTHdue to the vehicle traveling on road surfaces with a low frictional coefficient, such as roads slick with snow or frost, then the process proceeds from step S42to step S43in the processing ofFIG. 10. In step S42to step S43in the processing ofFIG. 10, the 2ndTCS shift schedule for the transmission controller41is set, and the upshift variable speed line from the 1st speed gear position to the 2nd speed gear position of the automatic transmission5is changed to a higher vehicle speed.

Thereafter, at a time8t, when the acceleration slippage in the front wheels subsides and the slippage speed ΔVFis equal to or less than the slippage speed threshold value ΔVF, the process proceeds from step S41to step S48. The fact that the operating flag F4WDcontinues to set to “1”, however, maintains the shift schedule at the 2ndTCS shift schedule as shown in the graph (g) ofFIG. 12.

Then, if the front wheels1L and1R speeds and the rear wheels3L and3R speeds almost coincide at a time t9, the slippage speed ΔVFwill become “0” and the process proceeds from step S20to step S21in the processing ofFIG. 8. Because the operating flag F4WDcontinues to set to “1”, the process proceeds to step S23and the control state of the electric motor4is maintained.

Thereafter, if the motor torque target value Tmt is equal to or less than the motor torque threshold value Th, then the process proceeds from step S26to step S30in the processing ofFIG. 8by establishing a four-wheel drive state and then by executing the motor torque reduction process, the motor torque target value Tmt is sequentially reduced by a prescribed reduction value ΔT. The motor torque Tm also reduces following a fixed slope in proportion to the reduction of the motor torque target value Tmt. If the motor torque target value Tmt is equal to or less than “0” at a time t11, then the process proceeds to step S32where the operating flag F4WDis reset to “0”. The processing will then complete as is from step S21.

If the operating flag F4WDis reset to “0” in this manner, the process proceeds from step S48to step S49in the traction control process ofFIG. 10and the shift schedule is restored to a normal shift schedule.

According to the embodiment discussed above, as a result of starting the traction control, the shift schedule of the transmission controller41is changed to the 1sttraction control variable speed line LTC1set by the 1stTCS shift schedule with a vehicle speed higher than the normal variable speed line LUthat upshifts from the 1stspeed gear position to the 2nd speed gear position in a normal shift schedule. In addition, when the road surface has a small frictional resistance, the upshift to the 2nd speed gear position is restrained thereby allowing favorable traction control by means of changing to the 2ndtraction control variable speed line LTC2set by the 2ndTCS shift schedule with a vehicle speed higher than the 1sttraction control variable speed line LTC1.

Although traction control will end when the slippage speed ΔVFreduces to a value equal to or lower than the slippage speed threshold value ΔVFTHand the shift schedule of the transmission controller41returns to a normal shift schedule, the torque conversion process ofFIG. 8, that drives the electric motor4, will not end the four-wheel drive state until the motor torque target value Tmt is equal to or less than the motor torque threshold value Th even if the slippage speed ΔVFis “0”. Even after the traction control ends, the control will continue. Because the torque conversion process, after this traction control ends, prohibits the shift schedule from being restored to the normal shift schedule and maintains the 2ndTSC shift schedule, there will be not upshift to the 2nd speed gear position and the 1stgear position will be maintained even if the accelerator position opening degree is low and there is an interval between the normal variable speed line LUand the 2ndtraction control variable speed line LTC2. This makes it possible to maintain the power generation capacity of the generator7and execute accurate torque control of the electric motor4without any reductions in the engine rotational speed Ne.

In contrast to this, when the shift schedule is restored to the normal shift schedule at the time when the traction control ends as indicated by the dashed lines in the graph (d) ofFIG. 12, the action of the automatic transmission5upshifting from the 1st speed gear position to the 2nd speed gear position when the accelerator position opening degree is low and the vehicle speed is between the normal variable speed line LUand the 2ndtraction control variable speed line LTC2will reduce the engine rotational speed Ne. Then, the quantity of power generated by the generator7will reduce in proportion to the reductions in the engine rotational speed Ne leading to the following problems.

A problem of insufficient power generation that makes it impossible to ensure the quantity of power generation required to ensure the armature current Ia that the generator7requires for the electric motor4or a problem of not being able to generate power in which the quantity of power generated by the generator7, in its worst state, is less than the induced electrical power of the electric motor. A problem of poor control that does not allow motor torque required by the electric motor4to be generated.

Because the embodiment discussed above prohibits changes to shift schedules that return shift schedules set to variable speed lines with vehicle speeds higher than the normal variable speed line LUto the normal variable speed line LU, this embodiment reliably prevents the automatic transmission from upshifting to the 2ndspeed gear position and maintains the 1stspeed gear position thereby making it possible to reliably prevent the occurrence of insufficient power generation by the generator7.

The embodiment discussed above described when changing the shift schedule up to the 2ndTCS shift schedule while the vehicle is travelling on road surfaces with a low frictional coefficient, such as roads slick with snow or frost. When travelling on road surfaces with a small mid level frictional coefficient, such as roads wet with falling rain however, the 1stTCS shift schedule will be maintained without the amount of reduction of the front wheel drive torque TFbecoming smaller and dropping to a value less than the drive torque threshold value TTH. For this case as well, the shift schedule returning to a normal shift schedule at the time when traction control ends is also prohibited. In the processing ofFIG. 10, although the process proceeds from step S42to step S45when the front wheel drive torque TFonce again exceeds than the drive torque threshold value TTHwhile travelling on road surfaces with a small mid level frictional coefficient after the front wheel drive torque TFdrops to a value less than the drive torque threshold value TTH, the operating flag F4WDis set to “1” and the shift schedules are set to the 2ndTCS shift schedule up until the last. Because of this, the process proceeds to step S44directly without proceeding from step S47to step S46and the 2ndTCS variable speed line LTC2is prohibited from returning to the 1stTCS variable speed line LTC1thereby making it possible to reliably prohibit the automatic transmission5from upshifting from the 1 st speed gear position to the 2nd speed gear position.

The embodiment discussed above described a case when the automatic transmission5was used but the invention is not limited to such a method. A belt drive non-stage transmission or a toroidal type non-stage transmission can also be used. For this case, the gear ratio can be detected by detecting the rotational speed on the input side and the rotational speed on the output side of the non-stage transmission to prohibit the transmission from shifting towards the direction of a smaller gear ratio.

Furthermore, the embodiment discussed above described a case in which the generated voltage Vg of the generator7is computed based on the armature current target value Iat and the motor induced voltage E to control the field control output MF of the generator7based on this generated voltage Vg but the invention is not limited to such a method. It is also possible to either multiply a proportional control gain by the value of deviations ΔIa between the armature current target value Iat and the actual armature current Ia supplied to the electric motor4detected by the current sensor37or to multiply a integrated control gain by an integral value of the deviations ΔIa to compute the generator field current Ifg, compute the duty rate in proportion to this generator field current Ifg and supply a controlled power generation control output, with this duty rate, to the bipolar transistor33.

Even further, the embodiment discussed above described a case in which the electromagnetic clutch12was used as a clutch but the invention is not limited to such a method. A fluid-pressure clutch can also be used. For this case, the clutch linkage force can be controlled by means of electrically controlling a pressure control valve that controls the fluid pressure supplied to the fluid-pressure clutch. Any type of other clutches that can electrically control the clutch linkage force can also be used.

Even further, the embodiment discussed above described a case in which the input shaft of the generator7was linked to the internal combustion engine2through a belt6but the invention is not limited to such a method. The input shaft of the generator7can be linked to a rotating part from the output side of the transfer case up until the front wheels1L and1R. For this case, the engine load when idling is also reduced.

Even further, the embodiment discussed above described a case in which the motor rotational speed sensor39was used as a motor rotational speed detection method and directly detect the motor rotational speed Nm using this motor rotational speed sensor39but the invention is not limited to such a method. The motor rotational speed can be estimated based on the wheel speeds VWRLand VWRRdetected by the wheel speed sensors24RL and24RR and the reduction ratio of the differential gear13.

Even further, the embodiment discussed above described a case in which the change to a four-wheel drive state is in proportion to the acceleration slippage of the front wheels but the invention is not limited to such a method. Changing to a four-wheel drive state can also be in proportion to the accelerator position opening degree.

In addition, the embodiment discussed above described a case in which the present invention was used in a four-wheel vehicle wherein the front wheels1L and1R are the main drive wheels and the rear wheels1RL and1RR are the subordinate drive wheels but the invention is not limited to such a method. The rear wheels1RL and1RR can be the main drive wheels and the front wheels1L and1R the subordinate drive wheels.

Even further, the embodiment discussed above described a case in which the present invention was used in a four-wheel drive vehicle but the invention is not limited to such a method. The present invention can be used in vehicles comprising two or more wheels wherein a portion of the main drive wheel(s) are driven by an internal combustion engine and the remaining subordinate drive wheel(s) are driven by an electric motor. The present invention can also be used in electrically driven apparatuses which drive electric motors which drive wheels utilizing a generator that is rotated by another rotational drive source such as an internal combustion engine.

As used herein, the following directional terms “forward, rearward, above, downward, vertical, horizontal, below and transverse” as well as any other similar directional terms refer to those directions of a vehicle equipped with the present invention. Accordingly, these terms, as utilized to describe the present invention should be interpreted relative to a vehicle equipped with the present invention.

This application claims priority to Japanese Patent Application No. 2002-259160. The entire disclosure of Japanese Patent Application No. 2002-259160 is hereby incorporated herein by reference.