Power control device for electric vehicles

Abstract

To provide a driving force control device of an electric vehicle suppressing a temperature of a motor as a driving force source from reaching a restrictive temperature and suppressing travelling stability from being reduced when reaching the restrictive temperature.SOLUTION: A driving force control device of an electric vehicle is constituted of: an upper limit torque setting part 26 setting a torque at a time of reaching a first prescribed temperature as an upper limit torque of a first motor when a temperature of the first motor is a first prescribed temperature or higher and also lower than a first restrictive temperature; a limit torque setting part 27 setting a first limit torque smaller than the torque set by the upper limit torque setting part 26 as the upper limit torque of the first motor, when the temperature of the first motor is the first restrictive temperature or higher; a target torque setting part 28 setting a torque of a second motor on the basis of the upper limit torque of the first motor, a target torque distribution ratio as a target value of a ratio of the torque transmitted to front wheels and rear wheels, or a driving torque required by the electric vehicle.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a driving force control device for an electric vehicle including a motor as a driving force source for either the front wheel or the rear wheel and another driving force source such as an engine or a motor as a driving force source for the other wheel.

Background Art

[0002] Patent Document 1 describes a control device for a four-wheel drive vehicle including a front motor as a driving force source for a pair of front wheels and a rear motor as a driving force source for a pair of rear wheels. When the operation of the rear motor is restricted according to the temperature of the rear motor or the temperature of the power storage device, this control device sets the output torque of the rear motor to a restricted torque determined based on the temperature of the rear motor, subtracts a torque corresponding to the restricted torque of the rear motor from the driving torque required for the vehicle, and sets the subtracted torque as the output torque of the front motor. That is, when the torque of the rear motor is restricted, the torque of the rear motor is reduced to the restricted torque and the torque of the front motor is increased so as to satisfy the driving torque required for the vehicle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The control device described in Patent Document 1 outputs a limiting torque from the rear motor according to the temperature of the rear motor. Therefore, for example, when driving by outputting torque from the rear motor and front motor based on a target torque distribution ratio between the front and rear wheels, when the temperature of the rear motor reaches a predetermined temperature, the torque of the rear motor is reduced, while the torque of the front motor is increased by an amount equivalent to the reduction in the torque of the rear motor. As a result, the torque distribution ratio between the front and rear wheels deviates sharply and significantly from the target torque distribution ratio, which may reduce driving stability.

[0005] This invention has been made in view of the above technical problems, and aims to provide a drive force control device for an electric vehicle that can suppress the motor temperature, which serves as a drive force source, from reaching a limit temperature, and also suppress the decrease in driving stability when the limit temperature is reached. [Means for solving the problem]

[0006] To achieve the above objective, the present invention provides a drive force control device for an electric vehicle capable of setting a four-wheel drive driving mode in which the vehicle is driven by the first motor and the other drive force source, comprising: a first motor that drives a first drive wheel, which is one of the front wheels and the rear wheels; and another drive force source different from the first motor that drives a second drive wheel, which is the other of the front wheels and the rear wheels, the device further comprising a controller that controls the first motor, the controller when the temperature of the first motor reaches a predetermined first temperature, and when the temperature of the first motor is above a predetermined first predetermined temperature and below a predetermined first limit temperature to protect the first motor The device is characterized by comprising: an upper limit torque setting unit that sets the torque at a point as the upper limit torque of the first motor; a limit torque setting unit that, when the temperature of the first motor is equal to or greater than the first limit temperature, sets a first limit torque, which is smaller than the torque set by the upper limit torque setting unit and determined according to the temperature of the first motor, as the upper limit torque of the first motor; and a target torque setting unit that sets the torque of the other driving force source based on the upper limit torque of the first motor and a target torque distribution ratio, which is a target value of the ratio of the torque transmitted to the front wheel and the rear wheel, or the driving torque required for the electric vehicle.

[0007] In the present invention, the other driving force source includes a second motor, the controller is configured to control the second motor, the upper limit torque setting unit sets the torque at the time the second motor reaches a predetermined second temperature as the upper limit torque of the second motor when the temperature of the second motor is above a predetermined second temperature and below a predetermined second limit temperature to protect the second motor, and the target torque setting unit may set the torque at the time the first motor reaches a predetermined first temperature as the upper limit torque of the first motor and the torque at the time the second motor reaches a predetermined second temperature as the upper limit torque of the second motor when the temperature of the first motor is above a predetermined first temperature and below a predetermined first limit temperature, and the temperature of the second motor is above a predetermined second temperature and below a predetermined second limit temperature.

[0008] In the present invention, the other driving force source includes a second motor, the controller is configured to control the second motor, the limiting torque setting unit sets a second limiting torque determined according to the temperature of the second motor as the upper limit torque of the second motor when the temperature of the second motor is above a second limiting temperature predetermined to protect the second motor, and the target torque setting unit may set the first limiting torque as the upper limit torque of the first motor and the second limiting torque as the upper limit torque of the second motor when the temperature of the first motor is above the first limiting temperature and the temperature of the second motor is above the second limiting temperature.

[0009] In the present invention, the other power source includes a second motor, the controller is configured to control the second motor and is configured to set a manual range mode that determines the required drive torque of the electric vehicle based on a plurality of drive characteristics, and includes a shift device that changes the drive characteristics in the manual range mode by the driver's shift operation, and the controller may prohibit the change in the drive characteristics that increases the required drive torque in the manual range mode when the temperature of the first motor is above a first predetermined temperature and the temperature of the second motor is above a second predetermined temperature that is lower than a second limit temperature predetermined to protect the second motor. [Effects of the Invention]

[0010] According to the present invention, when the temperature of the first motor that drives the first drive wheel, which is one of the front or rear wheels, is above a first predetermined temperature but below a first limit temperature, the torque at the time the first predetermined temperature is reached is set as the upper limit torque of the first motor. Therefore, it is possible to suppress the temperature of the first motor from rising above the first predetermined temperature, or to reduce the rate of temperature rise. As a result, it is possible to suppress the temperature of the first motor from reaching the first limit temperature.

[0011] Furthermore, if the required drive torque continues to increase while the temperature of the first motor is below the first predetermined temperature, the torque at the point when the temperature of the first motor exceeds the first predetermined temperature is set as the upper limit torque of the first motor, and the torque of the first motor is fixed at the upper limit torque, while the torque of the other drive sources gradually increases. Subsequently, when the temperature of the first motor rises above the first limit temperature, the torque of the first motor is reduced to the limit torque, and the torque of the other drive sources continues to increase. In other words, the torque distribution ratio gradually deviates from the target torque distribution ratio from the point when the first predetermined temperature is reached, and after the first limit temperature is reached, the rate of change of that deviation increases. Therefore, it is possible to suppress abrupt changes in the torque distribution ratio and suppress a decrease in driving stability. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic block diagram showing the drive system of a four-wheel independent drive vehicle in an embodiment of the present invention. [Figure 2] This is a skeleton diagram showing an example of a rear-wheel drive unit. [Figure 3] This is a skeleton diagram showing an example of a drive unit on the front wheel side. [Figure 4] This is a block diagram illustrating the input and output signals of a controller. [Figure 5] This diagram schematically shows the required drive torque map used in the D range. [Figure 6] This diagram schematically shows a temperature range map for determining the torque relationship between the front motor and the rear motor. [Figure 7] This is a block diagram showing the functional configuration of the controller. [Figure 8] This is a flowchart illustrating an example of control performed in an embodiment of the present invention. [Modes for carrying out the invention]

[0013] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the embodiments described below are merely examples of how the present invention may be implemented and do not limit the invention.

[0014] The electric vehicle targeted by this invention is a vehicle with a total of four wheels, two at the front and two at the rear, wherein a motor is provided as a driving force source for at least one of the two front wheels and the two rear wheels, and an engine or motor is provided as a driving force source for the other wheel, so that the two front wheels and the two rear wheels can be driven independently of each other. The two front wheels may be connected to the driving force source for the front wheels via an appropriate differential mechanism, and the two rear wheels may be connected to the driving force source for the rear wheels via an appropriate other differential mechanism. Furthermore, the electric vehicle targeted by this invention may be an electric vehicle configured so that a motor is provided as a driving force source corresponding to each of the four front and rear wheels, and the driving torque and regenerative braking torque (regenerative torque) of each of the four wheels can be controlled independently of each other.

[0015] Figure 1 schematically shows an example of a four-wheel independent drive vehicle, which is configured to allow independent control of the driving torque or regenerative braking torque of the front and rear wheels, as well as to allow all four wheels to be driven independently. The electric vehicle shown here (hereinafter simply referred to as "vehicle") Ve has left and right front wheels 1r, 1l and left and right rear wheels 2r, 2l, and drive units Pf, Pr are provided as driving force sources corresponding to the front wheels 1r, 1l and the rear wheels 2r, 2l, respectively. These drive units Pf, Pr are mainly composed of a motor and a gear reduction mechanism (transmission mechanism), respectively.

[0016] Fig. 2 shows an example of the drive unit Pr on the rear wheel 2r, 2l side in a skeleton diagram. This drive unit Pr is composed of a pair of drive systems that control the left and right rear wheels 2r, 2l independently of each other. Since these drive systems have a symmetric configuration, they will be described together without specifically distinguishing between "right" and "left". In the following description, when the suffix of a reference sign is one character, "f" indicates the front wheel, "l" indicates the left wheel, "r" indicates the right wheel or the rear wheel. When the suffix is two characters, the first character "f" indicates the front wheel, "r" indicates the rear wheel, the second character "r" indicates the right wheel, and "l" indicates the left wheel.

[0017] In the drive unit Pr for the rear wheels 2r, 2l, motors Mrr and Mrl are mounted with their rotation central axes oriented in the longitudinal direction of the vehicle Ve. Drive gears 3rr and 3rl are attached to the rotor shafts of these motors, and these drive gears 3rr and 3rl mesh with counter-driven gears 4rr and 4rl. The counter-driven gears 4rr and 4rl have a larger diameter than the drive gears 3rr and 3rl. Therefore, these gear pairs constitute a speed reduction mechanism. Counter-drive gears 5rr and 5rl, which are bevel gears, are provided so as to rotate integrally on the same axis as the counter-driven gears 4rr and 4rl. These counter-drive gears 5rr and 5rl mesh with driven gears 7rr and 7rl, which are bevel gears integral with drive shafts 6rr and 6rl connected to the rear wheels 2r, 2l. By making the driven gears 7rr and 7rl have a larger diameter than the counter-drive gears 5rr and 5rl, these gear pairs can also be used as a speed reduction mechanism.

[0018] These motors Mrr, Mrl, the reduction gear mechanism, and each bevel gear are housed in a liquid-tight manner inside the casing 8. Electric oil pumps OPrr, OPrl for supplying oil for cooling and lubrication are provided for the motors Mrr, Mrl inside this casing 8. These oil pumps OPrr, OPrl are configured to rotate at a rotational speed based on the output torque, rotational speed, or temperature of the motors Mrr, Mrl and discharge oil. Note that the oil pumps OPrr, OPrl on the rear wheel 2r, 2l side may be a single oil pump that supplies oil 10r to the left and right motors Mrr, Mrl together. These oil pumps OPrr, OPrl are provided at appropriate locations on the outside of the casing 8 of the vehicle Ve, configured to suck up the oil 10r from the oil reservoir 9r and supply the oil 10r to the motors Mrr, Mrl via the cooling oil passages 11rr, 11rl provided penetrating the casing 8.

[0019] Although not particularly shown in the drawings, the oil 10r is configured to reflux from the inside of the casing 8 to the oil reservoir 9r. Also, an oil cooler may be provided in the middle of the cooling oil passages 11rr, 11rl.

[0020] FIG. 3 shows an example of the drive unit Pf on the front wheel 1r, 1l side in a skeleton diagram. Since this drive unit Pf has a bilaterally symmetric configuration, it will be described together without particularly specifying "right" or "left". Motors Mfr, Mfl are mounted with their rotation central axes facing in the width direction (lateral direction) of the vehicle Ve, and drive gears 12fr, 12fl are attached to their rotor shafts, and these drive gears 12fr, 12fl are meshed with idler gears 13r, 13l. Counter shafts 14r, 14l are provided parallel to the rotation central axes of these idler gears 13r, 13l, and the idler gears 13r, 13l are meshed with counter driven gears 15fr, 15fl attached to these counter shafts 14r, 14l.

[0021] The counter-driven gears 15fr and 15fl are larger in diameter than the drive gears 12fr and 12fl attached to the motors Mfr and Mrl, and these gear pairs constitute a reduction mechanism. The counter-drive gears 16fr and 16fl are attached to the counter shafts 14r and 14l, and these counter-drive gears 16fr and 16fl mesh with the driven gears 18fr and 18fl, which are integrated with the drive shafts 17fr and 17fl connected to the front wheels 1r and 1l. The driven gears 18fr and 18fl are larger in diameter than the counter-drive gears 16fr and 16fl, and these gear pairs constitute a reduction mechanism.

[0022] The motors Mfr and Mfl on the front wheels 1r and 1l are configured to be cooled by oil 10f, similar to the motors Mrr and Mrl on the rear wheels 2r and 2l. Specifically, electric oil pumps OPfr and OPfl are provided corresponding to the motors Mfr and Mfl on the front wheels 1r and 1l. These oil pumps OPfr and OPfl are configured to draw oil 10f from the oil reservoir 9f and supply it to the motors Mfr and Mfl via the cooling oil passages 19fr and 19fl. These oil pumps OPfr and OPfl are configured to rotate at a rotational speed based on the output torque and rotational speed of the motors Mfr and Mfl, or the temperature of the motors Mfr and Mfl, and to discharge oil.

[0023] Although not specifically shown in the diagram, the oil used to cool the motors Mfr and Mfl is configured to recirculate into the oil reservoir 9f. An oil cooler may also be installed in the middle of the cooling oil passages 19fr and 19fl. The oil pumps on the front wheels 1r and 1l may be a single oil pump that supplies oil 10f to both the left and right motors Mfr and Mfl simultaneously, similar to the oil pumps on the rear wheels 2r and 2l described above.

[0024] An oil pump OPm is provided to pump up oil for lubrication. This oil pump OPm is a mechanical pump and, in the example shown in Figure 3, is connected to the countershaft 14l on the left front wheel 1l side. Therefore, this oil pump OPm is driven when the vehicle Ve is running, and is configured to pump oil 10f from the oil reservoir 9f and to supply oil 10f to predetermined lubrication points such as gears and bearings provided in the drive unit Pf on the front wheel 1r,1l side.

[0025] A power storage device (Bat) 20 is provided to exchange power with each of the motors Mfr, Mfl, Mrr, Mrl and the oil pumps OPfr, OPfl, OPrr, OPrl. This power storage device 20 is mainly composed of secondary batteries such as lithium-ion batteries and solid-state batteries. Each of the motors Mfr, Mfl, Mrr, Mrl is, for example, a permanent magnet type synchronous motor, and these motors Mfr, Mfl, Mrr, Mrl are connected to the power storage device 20 via power controllers PCfr, PCfl, PCrr, PCrl, which are mainly inverters. Therefore, the output torque and braking torque of each motor Mfr, Mfl, Mrr, Mrl during energy regeneration are controlled independently of each other. Note that the power controllers PCfr, PCfl, PCrr, PCrl only need to have independent functions and may be configured as a single unit.

[0026] As described above, the vehicle Ve can independently control the output torque of each motor Mfr, Mfl, Mrr, and Mrl. Therefore, for example, it can switch between a two-wheel drive mode in which motors Mrr and Mrl are controlled as the driving force source and power to motors Mfr and Mfl is turned off, and a four-wheel drive mode in which each motor Mfr, Mfl, Mrr, and Mrl are controlled as the driving force source. Furthermore, when driving in four-wheel drive mode, the ratio of the output torque of the front and rear motors can be appropriately changed based on the driving characteristics required by the driver.

[0027] A mode selection switch (mode selection unit) 21 is provided on the vehicle Ve for the driver to select a driving characteristic (driving mode). Specifically, the driving modes are control modes that control the drive torque based on predetermined criteria, and include a track mode that improves cornering performance by controlling the drive torque and regenerative torque (braking torque) of each motor Mfr, Mfl, Mrr, Mrl, a drift mode that improves agility and driving precision during cornering by individually controlling the torque of each of the four wheels to eliminate understeer or control to optimal traction, and a manual sport mode that improves acceleration performance or power performance by securing a large drive torque up to high vehicle speeds.

[0028] Furthermore, the vehicle Ve is equipped with a shift device such as a shift lever or paddle shifters (not shown), and the operation of the shift device is detected by a shift position sensor 22. In response to the signal from the shift position sensor 22, it is configured to set a manual range mode that changes the drive characteristics (shift range), which is the relationship between the accelerator operation amount and the required drive torque. These driving modes (including the manual range mode) control the torque balance of the front and rear wheels or output a large drive torque, and therefore correspond to a four-wheel drive driving mode in which all motors Mfr, Mfl, Mrr, and Mrl are driven.

[0029] The system is configured to select one of these driving modes using the mode selection switch 21 or the shift device, or to deselect a mode and select the normal mode. The mode selection switch 21 may be provided in multiple locations corresponding to different driving modes, or a single mode selection switch may be provided, with the selected driving mode being cycled through based on the number of times it is operated.

[0030] A controller 23 is provided for controlling each motor Mfr, Mfl, Mrr, Mrl and each electric oil pump OPfl, OPfr, OPrl, OPrr based on the aforementioned driving mode and shift range. The controller 23 is mainly composed of a microcomputer and is configured to perform calculations using input data and pre-stored data according to a predetermined program or by referring to a predetermined map, and to output the results of the calculations as control command signals to each of the aforementioned motors Mfr, Mfl, Mrr, Mrl and electric oil pumps OPfl, OPfr, OPrl, OPrr.

[0031] Figure 4 shows examples of input and output signals for performing this type of control. Examples of input signals include vehicle speed signal, accelerator opening signal, shift position signal, mode selection switch signal, shift up (+) signal, shift down (-) signal, track mode signal, and drift mode signal. Examples of output command signals include the torque of motor Mrl for the left rear wheel 2l, the torque of motor Mrr for the right rear wheel 2r, the control signal for oil pump OPrl for the left rear wheel 2l, the control signal for oil pump OPrr for the right rear wheel 2r, the torque of motor Mfl for the left front wheel 1l, the torque of motor Mfr for the right front wheel 1r, the control signal for oil pump OPfl for the left front wheel 1l, and the control signal for oil pump OPfr for the right front wheel 1r.

[0032] Figure 5 shows an example of a drive torque map stored in the controller 23 for determining the drive torque required for the vehicle Ve. This drive torque map determines the drive torque required for the vehicle Ve based on the vehicle speed and accelerator opening, with vehicle speed on the horizontal axis and the required drive torque on the vertical axis, and each accelerator opening shown as a curve. In addition, if manual range mode is set, the required drive torque for each accelerator opening may be changed and determined according to the driving mode and selected shift range, for example, by setting the required drive torque to increase as the selected range becomes lower.

[0033] Furthermore, when the vehicle is driven in four-wheel drive mode with the Track Mode, Drift Mode, Manual Sport Mode, Manual Range Mode, etc. set or selected, the controller 23 stores a temperature range map that determines the torque relationship between motors Mfr, Mfl and motors Mrr, Mrl, according to the temperature conditions of each motor Mfr, Mfl, Mrr, Mrl. Figure 6 shows an example of this temperature range map, with the temperature of motors Mfr, Mfl on the horizontal axis and the temperature of motors Mrr, Mrl on the vertical axis. If the temperatures of motors Mfr and Mfl are different, the temperature of the higher-temperature motor Mfr (Mfl) may be used and the temperature range map in Figure 6 may be referred to. Similarly, if the temperatures of motors Mrr, Mrl are different, the temperature of the higher-temperature motor Mrr (Mrl) may be used and the map in Figure 6 may be referred to. In the following explanation, motors Mfr and Mfl will be collectively referred to as the front motor Mf, and motors Mrr, Mrl will be collectively referred to as the rear motor Mr.

[0034] In the temperature range map shown in Figure 6, the region (Area A) where the temperature of the front motor Mf is below the first predetermined temperature T1 and the temperature of the rear motor Mr is below the second predetermined temperature T2 is a region where the distribution ratio between the output torque of the front motor Mf (i.e., the torque transmitted to the front wheels 1r, 1l) and the output torque of the rear motor Mr (i.e., the torque transmitted to the rear wheels 2r, 2l) is set to a distribution ratio based on the set or selected driving mode.

[0035] In the region (region B) where the temperature of the front motor Mf is above the first predetermined temperature T1 and below the first limiting temperature T3, and the temperature of the rear motor Mr is below the second predetermined temperature T2, the upper limit torque of the front motor Mf is set to the torque at the time region B is reached, and the output torque of the rear motor Mr is set to satisfy the torque required for the vehicle Ve. Here, the first limiting temperature T3 may be a temperature determined to protect the front motor Mf (for example, the rated temperature).

[0036] In this case, the front motor Mf corresponds to the "first motor" in the embodiment of the present invention, the front wheels 1r and 1l correspond to the "first drive wheels" in the embodiment of the present invention, the rear motor Mr corresponds to the "other driving force source" or "second motor" in the embodiment of the present invention, and the rear wheels 2r and 2l correspond to the "second drive wheels" in the embodiment of the present invention.

[0037] Therefore, for example, if the temperature conditions of the front motor Mf and rear motor Mr are in the B region, and the required drive torque for the vehicle Ve increases, the torque of the front motor Mf is fixed to the torque at the time the temperature of the front motor Mf reached the B region, and the torque of the rear motor Mr is set to the torque obtained by subtracting the torque transmitted to the front wheels 1r and 1l, which is obtained by multiplying the torque of the front motor Mf by the gear ratio of the drive unit Pf, from the required drive torque. In other words, the required drive torque is satisfied by increasing only the output torque of the rear motor Mr.

[0038] Furthermore, if the torque of the front motor Mf and the rear motor Mr is continuously maintained at a constant level from the point when the temperature conditions of the front motor Mf and the rear motor Mr reach region B, the torque of the front motor Mf and the rear motor Mr will be maintained at the torque level at the point when region B was reached. In addition, if the temperature conditions of the front motor Mf and the rear motor Mr are in region B, and the driving torque required for the vehicle Ve decreases, the torque of at least one of the motors Mr(Mf) of the front motor Mf and the rear motor Mr will be reduced so as to decrease the difference between the target value of the torque distribution ratio (target torque distribution ratio) determined according to the driving mode, etc., and the actual torque distribution ratio.

[0039] In the region where the temperature of the rear motor Mr is above the second predetermined temperature T2 and below the second limiting temperature T4, and the temperature of the front motor Mf is below the first predetermined temperature T1 (region C), the upper limit torque of the rear motor Mr is set to the torque at the time region C is reached, and the output torque of the front motor Mf is set to satisfy the torque required for the vehicle Ve. Here, the second limiting temperature T4 may be a temperature determined to protect the rear motor Mr (for example, the rated temperature).

[0040] In this case, the rear motor Mr corresponds to the "first motor" in the embodiment of the present invention, the rear wheels 2r and 2l correspond to the "first drive wheels" in the embodiment of the present invention, the front motor Mf corresponds to the "other driving force source" or "second motor" in the embodiment of the present invention, and the front wheels 1r and 1l correspond to the "second drive wheels" in the embodiment of the present invention.

[0041] Therefore, for example, if the temperature conditions of the front motor Mf and rear motor Mr are in the C region, and the required drive torque for the vehicle Ve increases, the torque of the rear motor Mr is fixed to the torque at the time the rear motor Mr's temperature reached the C region, and the torque of the front motor Mf is set to the torque obtained by subtracting the torque transmitted to the rear wheels 2r and 2l, which is obtained by multiplying the torque of the rear motor Mr by the gear ratio of the drive unit Pr, from the required drive torque. In other words, the required drive torque is satisfied by increasing only the output torque of the front motor Mf.

[0042] Furthermore, if the torque of the front motor Mf and the rear motor Mr is continuously maintained at a constant level from the point when the temperature conditions of the front motor Mf and the rear motor Mr reach the C region, the torque of the front motor Mf and the rear motor Mr will be maintained at the torque level at the point when the temperature conditions of the front motor Mf and the rear motor Mr are in the C region. In addition, if the driving torque required for the vehicle Ve decreases when the temperature conditions of the front motor Mf and the rear motor Mr decrease, the torque of at least one of the motors Mf (Mr) of the front motor Mf and the rear motor Mr will be reduced so as to reduce the difference between the target torque distribution ratio according to the driving mode, etc. and the actual torque distribution ratio.

[0043] Furthermore, in the region where the temperature of the front motor Mf is above the first limit temperature T3 and the temperature of the rear motor Mr is below the second limit temperature T4 (region D), the output torque of the front motor Mf is set to less than a predetermined first limit torque, and the output torque of the rear motor Mr is set to satisfy the torque required for the vehicle Ve. This first limit torque is a torque determined according to the temperature of the front motor Mf, and may be, for example, a torque determined so that the amount of heat generated by the front motor Mf is less than the amount of cooling by the oil pumps OPfr and OPfl, or it may be the torque when the power controllers PCfr and PCfl are shut down (zero). In other words, the first limit torque is smaller than the upper limit torque set when the temperature of the front motor Mf reaches the first predetermined temperature T1.

[0044] In this case, the front motor Mf corresponds to the "first motor" in the embodiment of the present invention, the front wheels 1r and 1l correspond to the "first drive wheels" in the embodiment of the present invention, the rear motor Mr corresponds to the "other driving force source" or "second motor" in the embodiment of the present invention, and the rear wheels 2r and 2l correspond to the "second drive wheels" in the embodiment of the present invention.

[0045] Therefore, for example, if the torque of the front motor Mf is greater than or equal to the first limiting torque when the temperature conditions of the front motor Mf and the rear motor Mr are in the D region, the torque of the front motor Mf is reduced to less than the first limiting torque, and the torque of the rear motor Mr is set based on the torque obtained by subtracting the torque transmitted to the front wheels 1r and 1l, which is obtained by multiplying the torque of the front motor Mf by the gear ratio of the drive unit Pf, from the required drive torque.

[0046] Furthermore, when the temperature conditions for the front motor Mf and rear motor Mr are in the D region, if the required drive torque for the vehicle Ve increases, the torque of the front motor Mf is set to less than the first limiting torque, and the torque of the rear motor Mr is set based on the torque obtained by subtracting the torque transmitted to the front wheels 1r and 1l, which is obtained by multiplying the torque of the front motor Mf by the gear ratio of the drive unit Pf, from the required drive torque.

[0047] Furthermore, if the torque of the front motor Mf is less than the first limiting torque when the temperature conditions of the front motor Mf and the rear motor Mr are in the D region, or if the required drive torque is maintained or reduced while the temperature conditions of the front motor Mf and the rear motor Mr are in the D region, the torque of the front motor Mf and the rear motor Mr will be maintained, or the torque of at least one of the motors Mr(Mf) of the front motor Mf and the rear motor Mr will be reduced so that the difference between the target torque distribution ratio and the actual torque distribution ratio becomes smaller.

[0048] The region where the temperature of the rear motor Mr is above the second limiting temperature T4 and the temperature of the front motor Mf is below the first limiting temperature T3 (region E) is a region in which the output torque of the rear motor Mr is set to less than a predetermined second limiting torque, and the output torque of the front motor Mf is set to satisfy the torque required for the vehicle Ve. This second limiting torque is a torque determined according to the temperature of the rear motor Mr, and may be, for example, a torque determined so that the amount of heat generated by the rear motor Mr is less than the amount of cooling by the oil pumps OPrr, OPrl, or it may be the torque when the power controllers PCrr, PCrl are shut down (zero). In other words, the second limiting torque is smaller than the upper limit torque set when the temperature of the rear motor Mr is at the second predetermined temperature T2.

[0049] In this case, the rear motor Mr corresponds to the "first motor" in the embodiment of the present invention, the rear wheels 2r and 2l correspond to the "first drive wheels" in the embodiment of the present invention, the front motor Mf corresponds to the "other driving force source" or "second motor" in the embodiment of the present invention, and the front wheels 1r and 1l correspond to the "second drive wheels" in the embodiment of the present invention.

[0050] Therefore, for example, if the torque of the rear motor Mr is greater than or equal to the second limiting torque when the temperature conditions of the front motor Mf and the rear motor Mr are in the E region, the torque of the rear motor Mr is reduced to less than the second limiting torque, and the torque of the front motor Mf is set based on the torque obtained by subtracting the torque transmitted to the rear wheels 2r and 2l, which is obtained by multiplying the torque of the rear motor Mr by the gear ratio of the drive unit Pr, from the required drive torque.

[0051] Furthermore, when the temperature conditions for the front motor Mf and rear motor Mr are in the E region, if the required drive torque for the vehicle Ve increases, the torque of the rear motor Mr is set to less than the second limiting torque, and the torque of the front motor Mf is set based on the torque obtained by subtracting the torque transmitted to the rear wheels 2r and 2l, which is obtained by multiplying the torque of the rear motor Mr by the gear ratio of the drive unit Pr, from the required drive torque.

[0052] Furthermore, if the torque of the rear motor Mr is less than the second limiting torque when the temperature conditions of the front motor Mf and rear motor Mr are in the E region, or if the required drive torque is maintained or reduced when the temperature conditions of the front motor Mf and rear motor Mr are in the E region, the torque of the front motor Mf and rear motor Mr will be maintained, or the torque of at least one of the motors Mf(Mr) of the front motor Mf and rear motor Mr will be reduced so that the difference between the target torque distribution ratio and the actual torque distribution ratio becomes smaller.

[0053] Furthermore, the region (F region) where the temperature of the front motor Mf is above the first predetermined temperature T1 and below the first limit temperature T3, and the temperature of the rear motor Mr is above the second predetermined temperature T2 and below the second limit temperature T4, is the region in which the upper limit torque of the front motor Mf and the upper limit torque of the rear motor Mr are set to the torque at the time the F region is reached. Therefore, for example, when the temperature conditions of the front motor Mf and the rear motor Mr are in the F region, if the driving torque required for the vehicle Ve increases, the torque of the front motor Mf and the torque of the rear motor Mr are fixed to the torque at the time the temperature conditions became the F region. In other words, the vehicle runs with a torque of less than or equal to the required driving torque. Furthermore, when the temperature condition is in the F region, if the required drive torque is maintained at a constant level, the torque of the front motor Mf and the rear motor Mr will be maintained at a constant level. If the required drive torque decreases, the torque of at least one of the motors Mf(Mr) between the front motor Mf and the rear motor Mr will be reduced so that the difference between the target torque distribution ratio and the actual torque distribution ratio becomes smaller.

[0054] In this case, the front motor Mf and rear motor Mr correspond to the "first motor" and "other driving force source" or "second motor" in the embodiments of the present invention, and the front wheels 1r, 1l and rear wheels 2r, 2l correspond to the "first drive wheel" and "second drive wheel" in the embodiments of the present invention.

[0055] In the region (G region) where the temperature of the front motor Mf is above the first limiting temperature T3 and the temperature of the rear motor Mr is above the second limiting temperature T4, cooling is necessary to prevent a decrease in the durability of the front motor Mf and the rear motor Mr. Therefore, the G region is a region in which the output torque of the front motor Mf is set to below the first limiting torque and the output torque of the rear motor Mr is set to below the second limiting torque. In other words, when the temperature conditions are in the G region, the front motor Mf outputs the first limiting torque and the rear motor Mr outputs the second limiting torque until the required drive torque drops below the drive torque generated by outputting the first limiting torque from the front motor Mf and the second limiting torque from the rear motor Mr. Furthermore, if the required drive torque falls below the drive torque generated by outputting a first limiting torque from the front motor Mf and a second limiting torque from the rear motor Mr, the torque of at least one of the front motor Mf or rear motor Mr will be reduced so as to minimize the difference between the target torque distribution ratio and the actual torque distribution ratio.

[0056] In this case, the front motor Mf and rear motor Mr correspond to the "first motor" and "other driving force source" or "second motor" in the embodiments of the present invention, and the front wheels 1r, 1l and rear wheels 2r, 2l correspond to the "first drive wheel" and "second drive wheel" in the embodiments of the present invention.

[0057] Figure 7 shows an example of a functional configuration for controlling each motor Mfr, Mfl, Mrr, and Mrl in the controller 23. The controller 23 shown in Figure 7 consists of a requested drive torque calculation unit 24, a temperature range determination unit 25, an upper limit torque setting unit 26, a limit torque setting unit 27, and a target torque setting unit 28. The requested drive torque calculation unit 24 calculates the drive torque required for the electric vehicle Ve by referring to the above drive torque map. That is, it calculates the requested drive torque based on the vehicle speed signal, accelerator opening signal, and drive torque map stored in the controller 23 that are input to the controller 23.

[0058] The temperature region determination unit 25 determines which region on the temperature region map the temperature conditions of the front motor Mf and the rear motor Mr belong to. That is, it reads the temperature signals of the front motor Mf and the rear motor Mr, and determines the region based on these signals and the temperature region map.

[0059] The upper limit torque setting unit 26 sets the torque at the time the temperature conditions of the front motor Mf and the rear motor Mr transition to one of the B, C, or F regions as the upper limit torque for the front motor Mf and the rear motor Mr.

[0060] The limiting torque setting unit 27 sets the limiting torque of the front motor Mf and the rear motor Mr as the upper limit torque of the front motor Mf and the rear motor Mr when the temperature conditions of the front motor Mf and the rear motor Mr transition to one of the D, E, or G regions.

[0061] The target torque setting unit 28 sets the torque of the other motor based on the upper limit torque of at least one of the front motor Mf and the rear motor Mr set by the upper limit torque setting unit 26 and the limit torque setting unit 27, as well as the drive torque required for the vehicle Ve and the target torque distribution ratio.

[0062] An example of control by this controller 23 will be explained with reference to the flowchart shown in Figure 8. In the control example shown in Figure 8, first, input data is acquired in step S1. The input data acquired here includes accelerator opening, vehicle speed, motor temperature, oil temperature, shift range, and driving mode. Next, the required drive torque is calculated (step S2). This step S2 is performed by the required drive torque calculation unit 24, which retrieves the drive torque map and determines the required drive torque based on the accelerator opening signal and vehicle speed signal input to the controller 23.

[0063] Next, the temperature conditions of the front motor Mf and the rear motor Mr are calculated to determine which region of the temperature region map they fall into (step S3). That is, the region is determined based on the temperature signals of the front motor Mf and the rear motor Mr input to the controller 23. Specifically, the temperature region determination unit 25 determines whether the temperature of the front motor Mf is above the first predetermined temperature T1, above the first limiting temperature T3, and whether the temperature of the rear motor Mr is above the second predetermined temperature T2, above the second limiting temperature T4, and then determines the region based on the determination results.

[0064] Next, based on the region calculated in step S3, the target torque for each motor Mf, Mr is set (step S4). Specifically, if the region calculated in step S3 is region A, the target torque for each motor Mf, Mr is set based on the target torque distribution ratio as described above. If the region calculated in step S3 is region B, region C, or region F, the upper limit torque setting unit 26 sets the upper limit torque of at least one of the front motor Mf and rear motor Mr to the torque at the time that region is reached, based on the temperature conditions, and the target torque setting unit 28 sets the target torque for each motor Mf (Mr) based on the required drive torque and its upper limit torque. Furthermore, if the region calculated in step S3 is one of the D, E, or G regions, the limit torque setting unit 27 sets the upper limit torque of at least one of the front motor Mf and rear motor Mr to the limit torque based on the temperature conditions, and the target torque setting unit 28 sets the target torque for each motor Mf, Mr based on the required drive torque and its upper limit torque.

[0065] Then, based on the target torque of each motor Mf and Mr set in step S4, the power controllers PCfr, PCfl, PCrr, and PCrl are controlled to output torque from each motor Mf and Mr (step S5).

[0066] Furthermore, the aforementioned vehicle Ve can be set to a manual range mode, which is configured to set a shift range corresponding to the driver's shift operation. Since this shift range changes the required drive torque relative to the accelerator opening, when a shift operation that sets a relatively large required drive torque (downshift operation) is performed, the required drive torque changes in steps. On the other hand, when the temperature condition is in the F region, the upper limit torque of the front motor Mf and the rear motor Mr is set to the torque at the time the F region is reached, and when it is in the G region, the upper limit torque of the front motor Mf and the rear motor Mr is set to a limit torque determined according to the temperature of those motors Mf and Mr. In other words, when the temperature condition is in the F or G region, the torque of each motor Mf and Mr cannot be increased beyond the torque at the time the region is reached, and therefore the drive torque of vehicle Ve cannot be increased.

[0067] Therefore, in the control example shown in Figure 8, following step S5, it is determined whether the temperature condition is in the F region or the G region (step S6). If the determination in step S6 is positive because the temperature condition is in the F region or the G region, the change in the shift range by downshifting in manual range mode is prohibited (step S7), and this routine is terminated. Conversely, if the determination in step S6 is negative because the temperature condition is not in the F region or the G region, this routine is terminated immediately. In addition to step S7, a signal may be output to inform the driver that the change in the shift range is prohibited.

[0068] As described above, when the temperature of the front motor Mf exceeds the first predetermined temperature T1, or the temperature of the rear motor Mr exceeds the second predetermined temperature T2, the torque at that point can be set as the upper limit torque for the front motor Mf and the rear motor Mr. This can suppress the temperature of the front motor Mf and the rear motor Mr from rising above the first predetermined temperature T1 and the second predetermined temperature T2, or reduce the rate of temperature rise of the front motor Mf and the rear motor Mr. As a result, it is possible to suppress the temperature of the front motor Mf and the rear motor Mr from reaching the first limit temperature T3 and the second limit temperature T4.

[0069] Furthermore, the torque at the point when the temperature of the front motor Mf exceeds the first predetermined temperature T3, or when the temperature of the rear motor Mr exceeds the second predetermined temperature T4, is defined as the upper limit torque for the front motor Mf and the rear motor Mr. Therefore, if the temperature of either the front motor Mf or the rear motor Mr gradually increases as the required drive torque increases, the torque of the front motor Mf (Mr) is fixed when the temperature of the front motor Mf exceeds the first predetermined temperature T1, or when the temperature of the rear motor Mr exceeds the second predetermined temperature T4, while the torque of the other motor Mr (Mf) gradually increases. Subsequently, when the temperature of the front motor Mf exceeds the first limit temperature T3, or when the temperature of the rear motor Mr exceeds the second limit temperature T4, the torque of one motor Mf (Mr) is reduced to the limit torque, and the torque of the other motor Mr (Mf) continues to increase. In other words, the torque distribution ratio gradually deviates from the target torque distribution ratio after reaching the first predetermined temperature T1 or the second predetermined temperature T2, and the rate of change of this deviation increases after reaching the first limit temperature T3 or the second limit temperature T4. Therefore, it is possible to suppress abrupt changes in the torque distribution ratio and suppress a decrease in driving stability.

[0070] Furthermore, the drive force control device for the electric vehicle in the embodiment of the present invention may be configured not only when the front motor Mf or rear motor Mr heats up while driving in four-wheel drive mode, but also, for example, when driving in two-wheel drive mode with the rear motor Mr as the drive force source, and the temperature of the rear motor Mr heats up to a second predetermined temperature T2, the torque of the rear motor Mr at that time may be set as the upper limit torque, and if the rear motor Mr alone cannot output the required drive torque due to an increase in the required drive torque of the vehicle Ve, the device may be configured to switch to four-wheel drive mode and output the insufficient torque from the front motor Mf.

[0071] Furthermore, the front motor Mf and rear motor Mr heat up due to copper loss, iron loss, etc., and heat up when regenerative braking torque is output, just as it does when drive torque is output. Therefore, the drive force control device for the electric vehicle in the embodiment of the present invention may be configured to be executed during regenerative braking and to set an upper limit value for the regenerative torque of the front motor Mf and rear motor Mr according to the temperature of the front motor Mf and rear motor Mr.

[0072] Furthermore, the electric vehicle in the embodiment of the present invention is not limited to a vehicle equipped with a motor as a driving force source for the front wheels and a motor as a driving force source for the rear wheels, but may also be a so-called hybrid vehicle equipped with a motor as a driving force source for either the front or rear wheels and an engine as a driving force source for the other wheel. In this case, when the motor temperature exceeds a predetermined temperature, the torque at that time may be set as the upper limit torque of the motor, and when the required driving torque increases, the insufficient torque may be output from the engine. [Explanation of symbols]

[0073] 1r,1l front wheel 2r,2l rear wheel 21 Mode Selection Switch 22 Shift position sensor 23 Controllers 24. Requested drive torque calculation unit 25 Temperature range judgment section 26 Upper limit torque setting section 27 Torque limit setting section 28 Target Torque Setting Unit Mfr, Mfl, Mrr, Mrl motor Mf Front Motor Mr Rear Motor Ve electric vehicle

Claims

1. A drive force control device for an electric vehicle, comprising a first motor that drives a first drive wheel, which is one of the front wheels or the rear wheels, and another drive force source different from the first motor that drives a second drive wheel, which is the other of the front wheels or the rear wheels, and capable of setting a four-wheel drive driving mode in which the vehicle is driven by the first motor and the other drive force source, The system includes a controller for controlling the first motor, The aforementioned controller, A torque limit setting unit sets the torque at the time the first motor reaches the predetermined temperature as the upper limit torque of the first motor when the temperature of the first motor is above a predetermined first predetermined temperature and below a predetermined first limit temperature for protecting the first motor. A limit torque setting unit sets a first limit torque, which is less than the torque set by the upper limit torque setting unit and determined according to the temperature of the first motor, as the upper limit torque of the first motor when the temperature of the first motor is above the first limit temperature, It is configured with a target torque setting unit that sets the torque of the other drive source based on the upper limit torque of the first motor, a target torque distribution ratio which is a target value of the ratio of torque transmitted to the front wheel and the rear wheel, or the drive torque required for the electric vehicle. A drive force control device for electric vehicles, characterized by the following features.

2. A drive force control device for an electric vehicle according to claim 1, The aforementioned other power source includes a second motor, The controller is configured to control the second motor, The upper limit torque setting unit sets the torque at the time the second motor reaches the second predetermined temperature as the upper limit torque of the second motor, when the temperature of the second motor is above a predetermined second predetermined temperature and below a predetermined second limit temperature for protecting the second motor. The target torque setting unit sets the torque at the time the first predetermined temperature is reached as the upper limit torque of the first motor, and the torque at the time the second predetermined temperature is reached as the upper limit torque of the second motor, when the temperature of the first motor is above the first predetermined temperature and below the first limit temperature, and the torque at the time the second predetermined temperature is reached as the upper limit torque of the second motor. A drive force control device for electric vehicles, characterized by the following features.

3. A drive force control device for an electric vehicle according to claim 1, The aforementioned other power source includes a second motor, The controller is configured to control the second motor, The limiting torque setting unit sets the second limiting torque, determined according to the temperature of the second motor, as the upper limit torque of the second motor when the temperature of the second motor is above a predetermined second limiting temperature for protecting the second motor. The target torque setting unit sets the first limit torque as the upper limit torque of the first motor and the second limit torque as the upper limit torque of the second motor when the temperature of the first motor is equal to or greater than the first limit temperature and the temperature of the second motor is equal to or greater than the second limit temperature. A drive force control device for electric vehicles, characterized by the following features.

4. A drive force control device for an electric vehicle according to claim 1, The aforementioned other power source includes a second motor, The controller is configured to control the second motor, It is configured to allow setting a manual range mode that determines the required drive torque of the electric vehicle based on multiple drive characteristics, The system includes a shift device that changes the driving characteristics in the manual range mode by the driver's shift operation, The aforementioned controller, When the temperature of the first motor is above the first predetermined temperature, and the temperature of the second motor is above a second predetermined temperature that is lower than a second limit temperature predetermined to protect the second motor, the change in the drive characteristics that increases the required drive torque in the manual range mode is prohibited. A drive force control device for electric vehicles, characterized by the following features.

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