Driving force controller of electric vehicle

Abstract

To provide a driving force controller of an electric vehicle that can suppress abnormal noise and vibration during traveling, by properly controlling a motor as a driving force source.SOLUTION: Provided is a driving force controller of an electric vehicle which comprises a motor for driving first drive wheels, and another driving force source for driving second drive wheels, and in which a four-wheel drive traveling mode can be set for traveling using the motor and the other driving force source. In the driving force controller of the electric vehicle, if a motor operation point being defined by output torque and rotary speed of the motor is determined to enter into a predetermined avoidance area where abnormal noise or vibration becomes marked according to drive of the motor (YES in step S5), a torque distribution rate that is a ratio of the torque of the first drive wheels and the torque of the second drive wheels is changed from a predetermined reference torque distribution rate, so that the motor operation point deviates from the avoidance area (step S9).SELECTED DRAWING: Figure 8

Description

[Technical field]

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

[0002] Patent Document 1 describes an electric vehicle including a first differential mechanism in which a first motor, a right drive wheel, and a first connecting shaft are connected to enable differential rotation, a second differential mechanism in which a second motor, a left drive wheel, and a second connecting shaft are connected to enable differential rotation, pinion gears meshing with a sun gear provided on the first connecting shaft and a sun gear provided on the second connecting shaft, and an electric motor provided to be able to transmit torque to the pinion gear. This electric vehicle can transmit torque to the left and right drive wheels by outputting torque from the first motor and the second motor, and can appropriately control the differential rotation speed between the left and right drive wheels by controlling the rotation speed of the electric motor.

[0003] Patent Document 2 describes an electric vehicle including a drive unit connected to one of the left and right drive wheels and a drive unit connected to the other of the left and right drive wheels. Each of the drive units uses a motor as a drive force source, and the motor control device is configured to switch control of the motor, which is the drive force source of the drive wheel, from torque control to rotation speed control when a disturbance factor that causes a sudden change in the rotation speed of any of the drive wheels is detected. Specifically, the motor control device is configured to switch to rotation speed control with the rotation speed corresponding to the wheel speed as the target rotation speed when a disturbance factor is detected while the motor is being driven by torque control so as to follow a target torque corresponding to the required torque of the vehicle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-283836 A [Patent Document 2] JP 2011-200036 A Summary of the Invention [Problem to be solved by the invention]

[0005] The electric vehicle described in Patent Document 1 and Patent Document 2 includes motors corresponding to the left and right drive wheels, and can run by transmitting different torques to the left and right drive wheels by appropriately controlling the torques of the motors. On the other hand, the motor provided as the drive power source of the electric vehicle is usually configured by an AC motor, so the output torque pulsates according to the rotation angle of the motor. In addition, the torque transmitted to the drive wheels pulsates according to the meshing of the gears that transmit the torque from the motor to the drive wheels. There is a possibility that abnormal noise and vibrations are generated due to mechanical factors according to the configuration of such a motor and the configuration of the power transmission unit between the motor and the drive wheels. Furthermore, since the AC motor outputs a switch signal to the inverter according to its rotation speed to control the torque of the motor, there is a possibility that abnormal noise and vibrations are generated due to such electrical factors. The abnormal noise and vibrations caused by the above mechanical and electrical factors may become noticeable due to resonance with the motor and the power transmission unit, and therefore the driver may feel uncomfortable depending on the driving state such as the torque output from each motor and the rotation speed of each motor.

[0006] The present invention has been made in consideration of the above-mentioned technical problems, and aims to provide a driving force control device for an electric vehicle that can suppress abnormal noise and vibration during driving by appropriately controlling the motor as a driving force source. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present invention provides a driving force control device for an electric vehicle that includes a motor that drives a first drive wheel, which is one of the front wheels and the rear wheels, and another driving force source different from the motor that drives a second drive wheel, which is the other of the front wheels and the rear wheels, and that is capable of setting a four-wheel drive driving mode in which the vehicle runs using the motor and the other driving force source, the device including a controller that controls the motor, the controller including an avoidance area determination unit that determines whether a motor operating point, which is determined by the output torque and rotational speed of the motor, falls within a predetermined avoidance area in which abnormal noise or vibration becomes noticeable when the motor is driven, and a torque distribution ratio change unit that, when it is determined by the avoidance area determination unit that the motor operating point falls within the avoidance area, changes a torque distribution ratio, which is the ratio between the torque of the first drive wheel and the torque of the second drive wheel, from a predetermined reference torque distribution ratio so that the motor operating point falls outside the avoidance area.

[0008] In the present invention, the controller may further include a guard value setting unit that determines upper and lower limit values ​​for the amount of change in the torque distribution ratio, and the guard value setting unit may determine the upper and lower limit values ​​for the amount of change in the torque distribution ratio when a reference torque distribution ratio is set in order to maintain the behavior of the electric vehicle.

[0009] In the present invention, the torque distribution ratio change unit may start changing the torque distribution ratio earlier as the amount of change in the torque distribution ratio increases.

[0010] In the present invention, when the avoidance area determination unit determines that the motor operating point will enter the avoidance area due to a change in the output torque of the motor, the output torque of the motor may be maintained at the torque before entering the avoidance area, and the torque of the other driving power source may be changed in accordance with the required driving torque of the electric vehicle. Effect of the Invention

[0011] According to the present invention, when it is determined that a motor operating point determined by the output torque and rotation speed of the motor falls within an avoidance area where abnormal noise or vibration becomes noticeable due to the motor being driven, the torque distribution ratio, which is the ratio between the torque of the first drive wheel and the torque of the second drive wheel, is changed from a predetermined reference torque distribution ratio so that the motor operating point falls outside the avoidance area. Therefore, it is possible to suppress the motor operating point from entering the avoidance area while satisfying the required drive torque of the electric vehicle. As a result, it is possible to suppress the driver from feeling uncomfortable due to the generation of abnormal noise or vibration. [Brief description of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a schematic diagram of a drive system of a four-wheel independent drive vehicle according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a skeleton diagram showing an example of a rear wheel side drive unit. [Diagram 3] FIG. 2 is a skeleton diagram showing an example of a front wheel side drive unit. [Figure 4] FIG. 4 is a block diagram illustrating input and output signals of a controller. [Diagram 5] FIG. 4 is a diagram illustrating a required drive torque map. [Figure 6] FIG. 1 is a diagram showing an example of an avoidance region where abnormal noise and vibration become noticeable due mainly to the driving of a motor. [Figure 7] FIG. 2 is a block diagram showing a functional configuration of a controller. [Figure 8] 4 is a flowchart illustrating an example of control executed in the embodiment of the present invention. [Figure 9] 11 is a time chart illustrating an example in which the torque distribution ratio is changed so that the motor operating point does not enter the avoidance area when the vehicle speed increases while the vehicle's required driving torque is maintained constant during straight-line driving. [Figure 10] 10 is a time chart for explaining an example in which the torque distribution ratio is changed so that the motor operating point does not enter the avoidance area when the required driving torque of the vehicle increases. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Next, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiment described below is merely an example of the case where the present invention is implemented, and is not intended to limit the present invention.

[0014] The electric vehicle targeted by the present invention is an electric vehicle having a total of four wheels, two front wheels and two rear wheels, in which a motor is provided as a drive power source for at least one of the two front wheels and the two rear wheels, and an engine, a motor, or the like is provided as a drive power 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 a drive power source for the front wheels via an appropriate differential mechanism, and the two rear wheels may be connected to a drive power source for the rear wheels via another appropriate differential mechanism. Furthermore, the electric vehicle targeted by the present invention may be an electric vehicle configured to have a motor as a drive power source corresponding to each of the front and rear four wheels, so that the drive torque and regenerative braking torque (regenerative torque) of each of the four wheels can be controlled independently of each other.

[0015] FIG. 1 shows a schematic example of a four-wheel independent drive vehicle that is configured to be able to control the drive torque or regenerative braking torque of the front and rear wheels independently of each other, and to drive all four wheels independently of each other. The electric vehicle (hereinafter, simply referred to as the vehicle) Ve shown here has left and right front wheels 1r, 1l and left and right rear wheels 2r, 2l, and drive units Pf, Pr are provided as drive force sources corresponding to the front wheels 1r, 1l and the rear wheels 2r, 2l, respectively. Each of these drive units Pf, Pr is mainly composed of a motor and a gear reduction mechanism (transmission mechanism). The front wheels 1r, 1l and the left and right rear wheels 2r, 2l correspond to the "first drive wheel" and the "second drive wheel" in the embodiment of the present invention.

[0016] An example of a drive unit Pr on the side of the rear wheels 2r, 2l is shown in a skeleton diagram in Fig. 2. This drive unit Pr is composed of a pair of drive systems that independently control the left and right rear wheels 2r, 2l, and since these drive systems are symmetrical, they will be described together without being specifically designated as "right" and "left". In the following description, when the suffix of a reference symbol is one letter, "f" indicates the front wheel, "l" indicates the left wheel, and "r" indicates the right wheel or the rear wheel, and when it is two letters, the first letter "f" indicates the front wheel, "r" indicates the rear wheel, and the second letter "r" indicates the right wheel, and "l" indicates the left wheel.

[0017] The drive unit Pr of the rear wheels 2r, 2l is equipped with motors Mrr, Mrl with their central axis of rotation directed in the longitudinal direction of the vehicle Ve, and drive gears 3rr, 3rl are attached to the rotor shafts thereof, and the drive gears 3rr, 3rl are meshed with the counter driven gears 4rr, 4rl. The counter driven gears 4rr, 4rl have a larger diameter than the drive gears 3rr, 3rl, and therefore these gear pairs constitute a reduction mechanism. The counter driven gears 4rr, 4rl are provided on the same axis as the counter driven gears 4rr, 4rl so as to rotate integrally, and the counter drive gears 5rr, 5rl are meshed with the driven gears 7rr, 7rl which are bevel gears integral with the drive shafts 6rr, 6rl connected to the rear wheels 2r, 2l. By making the driven gears 7rr, 7rl larger in diameter than the counter drive gears 5rr, 5rl, these gear pairs can be used as a reduction mechanism.

[0018] FIG. 3 shows a skeleton diagram of an example of the drive unit Pf on the front wheels 1r, 1l side. Since the drive unit Pf has a bilaterally symmetrical configuration, it will be described together without specifying "right" or "left". The motors Mfr, Mfl are mounted with their rotational center axis facing the width direction (lateral direction) of the vehicle Ve, and drive gears 12fr, 12fl are attached to the rotor shafts, and the drive gears 12fr, 12fl mesh with the idle gears 13r, 13l. Countershafts 14r, 14l are provided parallel to the rotational center axis of the idle gears 13r, 13l, and the idle gears 13r, 13l mesh with counter driven gears 15fr, 15fl attached to the countershafts 14r, 14l.

[0019] The counter driven gears 15fr, 15fl have a larger diameter than the drive gears 12fr, 12fl attached to the motors Mfr, Mrl, and these gear pairs form a reduction mechanism. The counter drive gears 16fr, 16fl are attached to the counter shafts 14r, 14l, and these counter drive gears 16fr, 16fl mesh with the driven gears 18fr, 18fl that are integral with the drive shafts 17fr, 17fl that are connected to the front wheels 1r, 1l. The driven gears 18fr, 18fl have a larger diameter than the counter drive gears 16fr, 16fl, and these gear pairs form a reduction mechanism.

[0020] The vehicle Ve shown in FIG. 1 is provided with an electric storage device (Bat) 19 that exchanges electric power with each of the motors Mfr, Mfl, Mrr, Mrl. The electric storage device 19 is mainly composed of a secondary battery such as a lithium ion battery or a solid-state battery. That is, the electric storage device 19 is composed of a DC power source. Each of the motors Mfr, Mfl, Mrr, Mrl is, for example, a permanent magnet synchronous motor. These motors Mfr, Mfl, Mrr, Mrl are connected to the electric storage device 19 via power controllers PCfr, PCfl, PCrr, PCrl that mainly include inverters that convert the DC voltage of the electric storage device 19 into an AC voltage and apply it to the motors Mfr, Mfl, Mrr, Mrl, and also convert the AC voltage generated by the motors Mfr, Mfl, Mrr, Mrl into a DC voltage to charge the electric storage device 19. Therefore, the output torque and the braking torque during energy regeneration of each of the motors Mfr, Mfl, Mrr, Mrl are individually controlled independently of each other. It should be noted that the power controllers PCfr, PCfl, PCrr, and PCrl only need to have independent functions, and may be configured as an integrated unit as a whole.

[0021] The vehicle Ve configured as described above can control the output torque of each of the motors Mfr, Mfl, Mrr, Mrl independently of each other, and can therefore switch between, for example, a two-wheel drive mode in which the motors Mrr, Mrl are controlled as driving force sources and the supply of electricity to the motors Mfr, Mfl is stopped, and a four-wheel drive mode in which the motors Mfr, Mfl, Mrr, Mrl are controlled as driving force sources. When traveling in the four-wheel drive mode, the torque distribution ratio, which is the ratio of the torque transmitted to the front wheels 1r, 1l to the torque transmitted to the rear wheels 2r, 2l, in other words, the ratio of the output torque of the front and rear motors Mfr, Mfl, Mrr, Mrl, can be appropriately changed based on the driving characteristics required by the driver.

[0022] The four-wheel drive driving modes are mainly control forms that control the driving torque based on predetermined standards, and include driving modes such as a track mode that improves cornering performance by controlling the driving torque and regenerative torque (braking torque) of each motor Mfr, Mfl, Mrr, and Mrl, a drift mode that individually controls the torque of each of the four wheels to eliminate understeer or to optimize traction, thereby improving agility and driving precision during cornering, a manual sports mode that ensures large driving torque up to high vehicle speeds to improve acceleration performance or power performance, and a manual range mode that changes the driving characteristics (shift range), which is the relationship between the accelerator operation amount and the required driving torque, in response to a shift operation (not shown) by the driver, and the driver can switch between these driving modes by operating a switch (not shown) that selects the driving mode.

[0023] A controller 20 is provided for controlling each of the motors Mfr, Mfl, Mrr, Mrl based on the above-mentioned driving modes etc. The controller 20 is mainly constituted by a microcomputer, and is configured to perform calculations using input data and pre-stored data in accordance with a prescribed program or by referring to a prescribed map, and to output the results of the calculations as control command signals to each of the above-mentioned motors Mfr, Mfl, Mrr, Mrl.

[0024] Examples of input signals and output signals for performing such control are shown in Fig. 4. Examples of input signals include a vehicle speed signal from a vehicle speed sensor (not shown) that detects the vehicle speed, an accelerator opening signal from an accelerator opening sensor that detects the amount of operation of an accelerator device (not shown), a mode selection switch signal from a switch that selects the above-mentioned driving mode, and a steering angle signal from a steering angle sensor (not shown) that detects the steering angle of the vehicle Ve. Examples of output command signals include the torque of the motor Mrl for the left rear wheel 2l, the torque of the motor Mrr for the right rear wheel 2r, the torque of the motor Mfl for the left front wheel 1l, and the torque of the motor Mfr for the right front wheel 1r.

[0025] 5 shows an example of a map stored in the controller 20. This map is a drive torque map that determines the drive torque required for the vehicle Ve based on the vehicle speed and the accelerator pedal depression, with the horizontal axis representing the vehicle speed and the vertical axis representing the required drive torque, and each accelerator depression being shown by a curve. Note that the magnitude of the required drive torque relative to the accelerator pedal depression may be set differently depending on the selected driving mode, in which case a drive torque map may be provided for each selected driving mode.

[0026] The controller 20 determines the required drive torque by referring to the drive torque map based on the vehicle speed and the accelerator opening. Then, based on the selected driving mode, the required drive torque of the vehicle Ve, the gradient angle of the road on which the vehicle Ve is traveling, the steering angle signal detected by the steering angle sensor, etc., the ratio (torque distribution ratio) between the torque of the front wheels 1r, 1l and the torque of the rear wheels 2r, 2l required to satisfy the required drive torque is determined, and the required torque of the motors Mfr, Mfl and the motors Mrr, Mrl is determined. Then, based on the rotation speed and the required drive torque of each of the motors Mfr, Mfl, Mrr, Mrl, the switch signal of the inverter provided in the power controllers PCfr, PCfl, PCrr, PCrl is output, so that the torque is output from each of the motors Mfr, Mfl, Mrr, Mrl.

[0027] On the other hand, abnormal noise and vibration are generated due to electrical factors based on inverter switch signals corresponding to the rotation speeds of the motors Mfr, Mfl, Mrr, Mrl, and mechanical factors based on meshing of gears provided between the motors Mfr, Mfl and the front wheels 1r, 1l, or meshing of gears provided between the motors Mrr, Mrl and the rear wheels 2r, 2l, etc. Such abnormal noise and vibration become noticeable due to resonance with the components that constitute the motors Mfr, Mfl, Mrr, Mrl and the drive units Pf, Pr.

[0028] FIG. 6 shows an example of an area where abnormal noise and vibration become prominent mainly due to the driving of the motors Mrr and Mrl when the torque distribution ratio between the front wheels 1r and 1l and the rear wheels 2r and 2l is set to a predetermined distribution ratio (hereinafter, referred to as the avoidance area). The horizontal axis in FIG. 6 indicates the vehicle speed, and the vertical axis indicates the required drive torque of the vehicle Ve. This avoidance area is an area determined based on the structures of the motors Mrr and Mrl, the inverter, or the drive unit Pr, and can be determined by experiments or simulations. As shown in FIG. 2, the gear ratio between the motors Mrr and Mrl and the rear wheels 2r and 2l is constant, so the horizontal axis in FIG. 6 is synonymous with the rotation speed of the motors Mrr and Mrl, and since the torque distribution ratio between the front wheels 1r and 1l and the rear wheels 2r and 2l is set to a predetermined distribution ratio as described above, the required drive torque is synonymous with the output torque of the motors Mrr and Mrl. In other words, the avoidance area is determined based on the rotation speed and output torque of the motors Mrr and Mrl.

[0029] In addition, since the avoidance area is determined based on the structure of the motors Mfr, Mfl, Mrr, Mrl, the inverter, or the drive units Pf, Pr, etc., it is also possible to define an avoidance area that is primarily caused by the operation of the motors Mfr, Mfl.

[0030] The avoidance region is determined by the vehicle speed and the required drive torque as shown in Figure 6. Therefore, for example, when the vehicle is traveling at a required drive torque of a predetermined torque T1, if the vehicle speed increases or decreases in the direction A in Figure 6, the driving point of the vehicle Ve, which has the required drive torque and the vehicle speed as parameters, may shift into the avoidance region, or, when the vehicle is traveling at a predetermined vehicle speed V1, if the required drive torque increases or decreases in the direction B in Figure 6, the driving point of the vehicle Ve may shift into the avoidance region.

[0031] As described above, the present invention is configured such that when it is predicted that the operating point of the vehicle Ve, in other words the motor operating point determined by the rotational speeds and output torque of the motors Mfr, Mfl and motors Mrr, Mrl, the torque distribution ratio between the front wheels 1r, 1l and the rear wheels 2r, 2l is changed so that the vehicle runs at a motor operating point outside the avoidance area.

[0032] Fig. 7 shows an example of a functional configuration for controlling each of the motors Mfr, Mfl, Mrr, Mrl in the controller 20. The controller 20 shown in Fig. 7 is made up of a required drive torque calculation unit 21, a reference torque distribution rate determination unit 22, a motor operating point prediction unit 23, an avoidance area determination unit 24, a guard value setting unit 25, and a torque distribution rate change unit 26.

[0033] The required drive torque calculation unit 21 refers to the drive torque map to calculate the drive torque required for the vehicle Ve. That is, the required drive torque is calculated based on the vehicle speed signal and accelerator pedal position signal input to the controller 20, and the drive torque map stored in the controller 20.

[0034] The reference torque distribution ratio determination unit 22 determines a torque distribution ratio (reference torque distribution ratio) that is determined based on the selected driving mode, the required driving torque of the vehicle Ve, the gradient angle of the road on which the vehicle Ve is traveling, the steering angle, etc. In other words, regardless of whether the motor operating point is in the avoidance area or not, the torque distribution ratio is determined in the same manner as in the conventional case.

[0035] The motor operating point prediction unit 23 predicts the locus of the operating points of the motors Mfr, Mfl, Mrr, Mrl within a predetermined period. For example, the change in vehicle speed within a predetermined period when the current accelerator opening is maintained is predicted based on the gradient angle of the road detected by a navigation system or the like, or the change in the required driving torque for maintaining the current vehicle speed is predicted based on the gradient angle of the road surface detected by a navigation system or the like. Next, the predicted vehicle speed is multiplied by the gear ratio of the drive units Pf, Pr to predict the rotation speed of the motors Mfr, Mfl, Mrr, Mrl, and the predicted required driving torque is multiplied by the torque distribution rate and the gear ratio of the drive units Pf, Pr to predict the output torque of the motors Mfr, Mfl, Mrr, Mrl. The motor operating point prediction unit 23 may predict the change in vehicle speed within a predetermined period based on the rate of change of the current vehicle speed, or may predict the change in the required driving torque within a predetermined period based on the rate of change of the accelerator opening. In this case, the torque distribution ratio may be predicted assuming that the current torque distribution ratio is maintained.

[0036] The avoidance area determination unit 24 determines whether or not the operating points of the motors Mfr, Mfl, Mrr, and Mrl predicted by the motor operating point prediction unit 23 are within the avoidance area. Specifically, the avoidance area based on the operating points of the motors Mfr, Mfl and the avoidance area based on the operating points of the motors Mrr, Mrl are obtained in advance by experiments, simulations, or the like, these avoidance areas are stored in the controller 20, and it is determined whether or not the operating points of the motors Mfr, Mfl, Mrr, and Mrl predicted by the motor operating point prediction unit 23 are within the avoidance area.

[0037] The driving force control device according to the embodiment of the present invention is configured to change the torque distribution ratio from the reference torque distribution ratio when the avoidance area determination unit 24 determines that the operating points of the motors Mfr, Mfl, Mrr, and Mrl are within the avoidance area. On the other hand, when the reference torque distribution ratio is set to maintain the behavior of the vehicle Ve when the vehicle Ve is turning or traveling on a rough road such as a rocky area, if the torque distribution ratio is changed or the change amount is large, the behavior of the vehicle Ve may not be maintained. Therefore, when the reference torque distribution ratio is set to maintain the behavior of the vehicle Ve, the guard value setting unit 25 determines the upper and lower limit values ​​of the change amount of the torque distribution ratio so as to prohibit the change of the torque distribution ratio or reduce the change amount based on the traveling environment of the vehicle Ve.

[0038] The torque distribution ratio changing unit 26 changes the torque distribution ratio between the front wheels 1r, 1l and the rear wheels 2r, 2l in order to prevent the driving points of the motors Mfr, Mfl, Mrr, Mrl from entering the avoidance area. Specifically, when the avoidance area determining unit 24 determines that the driving points of the motors Mfr, Mfl, Mrr, Mrl are within the avoidance area, the torque distribution ratio is changed from the current torque distribution ratio to a torque distribution ratio that puts the driving points of the motors Mfr, Mfl, Mrr, Mrl outside the avoidance area.

[0039] In this case, the torque distribution ratio may be changed so that the torque of the front wheels 1r, 1l is increased and the torque of the rear wheels 2r, 2l is decreased, or the torque distribution ratio may be changed so that the torque of the rear wheels 2r, 2l is increased and the torque of the front wheels 1r, 1l is decreased, but since a large change in the torque distribution ratio may change the behavior of the vehicle Ve, it is preferable to increase the torque of one of the driving wheels 1r, 1l (2r, 2l) and decrease the torque of the other driving wheel 2r, 2l (1r, 1l) so that the torque distribution ratio becomes small. Note that, when the upper and lower limits of the change amount of the torque distribution ratio are set by the guard value setting unit 25, the torque distribution ratio is changed within the range.

[0040] An example of control by the controller 20 will be described with reference to the flowchart shown in Fig. 8. In the control example shown in Fig. 8, first, input data is acquired in step S1. The input data acquired here includes the accelerator opening, vehicle speed, driving mode, etc. Next, the required drive torque is calculated (step S2). This step S2 is executed by the required drive torque calculation unit 21, which calls up a drive torque map and finds the required drive torque based on the accelerator opening signal and vehicle speed signal input to the controller 20.

[0041] Next, a reference torque distribution ratio is determined (step S3). This step S3 is executed by the reference torque distribution ratio determination unit 22, and the reference torque distribution ratio is determined based on the required driving torque of the vehicle Ve calculated in step S2, and signals input to the controller 20 such as the gradient angle of the road and the steering angle.

[0042] Next, the locus of the operating points of the motors Mfr, Mfl, Mrr, and Mrl within a predetermined period is predicted (step S4). This step S4 is executed by the motor operating point prediction unit 23, and the locus of the motor operating points determined by the vehicle speed and the required drive torque is calculated based on the current vehicle speed and the required drive torque and the gradient angle of the road, or based on the rate of change of the current vehicle speed and the required drive torque.

[0043] In this control example, when the driving points of the motors Mfr, Mfl, Mrr, Mrl are predicted to enter the avoidance area, the torque distribution ratio between the front wheels 1r, 1l and the rear wheels 2r, 2l is changed at a predetermined rate to prevent the motor driving points from entering the avoidance area. Therefore, the predetermined period in step S4 is set to a period during which the driving points of the motors Mfr, Mfl (Mrr, Mrl) predicted to enter the avoidance area can be changed to driving points outside the avoidance area by changing the torque distribution ratio at a predetermined rate.

[0044] Next, it is determined whether the operating points of the motors Mfr, Mfl, Mrr, Mrl predicted in step S4 are within the avoidance area (step S5). This step S5 is executed by the avoidance area determination unit 24, and it is determined whether the locus of the operating points of the motors Mfr, Mfl, Mrr, Mrl predicted in step S4 is within the avoidance area based on the operating points of the motors Mfr, Mfl stored in advance in the controller 20 and the avoidance area based on the operating points of the motors Mrr, Mrl. Note that step S5 may determine that the operating points of the motors Mfr, Mfl, Mrr, Mrl are within the avoidance area when the output torque of the motors Mfr, Mfl, Mrr, Mrl is within the range between the minimum torque and the maximum torque of the avoidance area, or when the rotation speed of the motors Mfr, Mfl, Mrl is within the range between the minimum rotation speed and the maximum rotation speed of the avoidance area.

[0045] If the driving points of the motors Mfr, Mfl, Mrr, and Mrl are not within the avoidance area and thus the negative determination is made in step S5, the torque distribution ratio for determining the torque of the motors Mfr, Mfl, Mrr, and Mrl is set to the reference torque distribution ratio (step S6), and this routine is terminated. On the other hand, if the driving points of the motors Mfr, Mfl, Mrr, and Mrl are within the avoidance area and thus the positive determination is made in step S5, then it is determined whether or not the vehicle is turning (step S7). This step S7 is a step for determining whether or not the vehicle is in a running state in which the reference torque distribution ratio is set so as to maintain the behavior of the vehicle Ve, and therefore it is not limited to whether or not the vehicle is turning, and it may be determined whether or not the vehicle is running on a rough road such as a rocky road or a road with a relatively small friction coefficient, for example.

[0046] If the answer of step S7 is affirmative because the vehicle is turning, an upper limit value and a lower limit value of the change amount of the torque distribution ratio are set (step S8). This step S8 is executed by the guard value setting unit 25, and the upper limit value and the lower limit value of the change amount of the torque distribution ratio can be set to a range for maintaining the behavior of the vehicle Ve or for which the driver does not feel uncomfortable due to the change in the behavior. That is, the magnitudes of the upper limit value and the lower limit value may be determined according to the running state of the vehicle Ve, such as the turning radius during turning. Note that the change of the torque distribution ratio may be prohibited according to the running state of the vehicle Ve, in which case the upper limit value and the lower limit value in step S8 may be set to zero.

[0047] If the result of step S7 is negative because the vehicle is not turning, or following step S8, the torque distribution ratio is changed (step S9) and this routine ends. This step S9 is executed by the torque distribution ratio changing unit 26, and the torque distribution ratio is changed at a predetermined rate of change toward a torque distribution ratio that puts the operating points of the motors Mfr, Mfl, Mrr, Mrl outside the avoidance area, or the torque of one of the motors Mfr, Mfl (Mrr, Mrl) is changed in accordance with a change in the required drive torque while maintaining the torque of the other motor Mrr, Mrl (Mfr, Mfl).

[0048] This predetermined rate of change is a rate of change determined to suppress changes in the behavior and operability of the vehicle Ve caused by abrupt changes in the torque distribution ratio, and can be determined based on experiments, simulations, etc. Therefore, in order to change the torque distribution ratio at a constant rate of change, when the amount of change in the torque distribution ratio required for the operating points of the motors Mfr, Mfl, Mrr, and Mrl to deviate from the avoidance region is large, it is preferable to change the torque distribution ratio earlier than when the amount of change in the torque distribution ratio is small. Note that, when step S8 is executed to set upper and lower limit values ​​for the amount of change in the torque distribution ratio, the torque distribution ratio is changed within the range between the upper and lower limit values.

[0049] Fig. 9 shows a time chart for explaining an example in which the torque distribution ratio is changed so that the motor operating point does not enter the avoidance area when the vehicle speed increases while the required driving torque of the vehicle Ve is kept constant during straight-ahead driving. At time t0 in Fig. 9, the torque distribution ratio between the front wheels 1r, 1l and the rear wheels 2r, 2l is set to a reference torque distribution ratio. In the example shown here, the reference torque distribution ratio is set to 5:5. As the vehicle speed gradually increases from time t0, it is predicted that the operating points of the motors Mrr, Mrl will enter the avoidance area, and the above step S9 is executed to change the torque distribution ratio.

[0050] In FIG. 9, the broken line indicates the case where the torque distribution ratio for the operation points of the motors Mrr and Mrl is 9:1 for getting out of the avoidance area, and the solid line indicates the case where the torque distribution ratio is 7:3. As shown in FIG. 9, when the change amount of the torque distribution ratio is large (when changing to 9:1), the torque distribution ratio is changed at a predetermined change rate at time t1, and when the change amount of the torque distribution ratio is small (when changing to 7:3), the torque distribution ratio is changed at a predetermined change rate at time t2, which is later than time t1. Therefore, in either case, at time t3, which is before time t4 when the vehicle speed reaches the avoidance area, the torque distribution ratio is changed to the torque distribution ratio for getting the operation points of the motors Mrr and Mrl out of the avoidance area. Then, at time t6 when the vehicle speed increases to a speed higher than the maximum vehicle speed (time t5) of the avoidance area, the torque distribution ratio starts to be changed to the reference torque distribution ratio. Note that when changing the torque distribution ratio to the reference torque distribution ratio, it is also preferable to change it at a predetermined change rate in order to suppress changes in the behavior and operability of the vehicle Ve.

[0051] FIG. 10 shows a time chart for explaining an example in which the torque distribution ratio is changed so that the motor operating point does not enter the avoidance area when the required driving torque of the vehicle Ve increases. At time t10 in FIG. 10, the torque distribution ratio between the front wheels 1r, 1l and the rear wheels 2r, 2l is set to a reference torque distribution ratio. In the example shown here, the reference torque distribution ratio is set to 5:5. Then, at time t11, the required driving torque gradually increases due to an increase in the accelerator opening, etc. Usually, the rate of change of the required driving torque is faster than the rate of change of the vehicle speed. Therefore, at time t11 when the required driving torque starts to increase, for example, it is predicted that the operating points of the motors Mrr, Mrl will enter the avoidance area, and the above step S9 is executed to change the torque distribution ratio.

[0052] Specifically, as the required drive torque increases, the torque of the motors Mrr and Mrl increases, causing the motor operating point to enter the avoidance region. Therefore, when the required drive torque increases, before the motor operating point enters the avoidance region, the torque of the motors Mrr and Mrl is maintained and the torque of the other motors Mfr and Mfl is increased to change the torque distribution ratio. Therefore, in the example shown in Figure 10, at time t11, only the motors Mfr and Mfl are increased, so that the torque distribution ratio changes in accordance with the increase in the required drive torque.

[0053] At time t12, the required drive torque is kept constant, and at the same time, the torques of the motors Mfr and Mfl are kept constant, so that the torque distribution ratio is kept constant. In the example shown in FIG. 10, the torque distribution ratio is 7:3 at time t12.

[0054] As described above, when it is predicted that the motor operating point will enter the avoidance area where abnormal noise or vibration becomes noticeable due to the driving of the motor, the torque distribution ratio is changed from the reference torque distribution ratio, so that the motor operating point can be prevented from entering the avoidance area while satisfying the required driving torque of the vehicle Ve. As a result, it is possible to prevent the driver from feeling uncomfortable due to the generation of abnormal noise or vibration.

[0055] Furthermore, when the vehicle is turning or traveling on a rough road and the reference torque distribution ratio is set to maintain the vehicle behavior, the upper and lower limits of the torque distribution ratio change amount can be set to prevent the torque distribution ratio from changing significantly to suppress abnormal noise or vibration, or the change in the torque distribution ratio can be prohibited, thereby preventing the vehicle behavior from being unable to be maintained.

[0056] Furthermore, when the required drive torque changes and it is predicted that the motor operating point will enter the avoidance area, by changing the torque of the other motor in response to the change in the required drive torque, even if the behavior of the vehicle Ve changes slightly due to the change in the torque distribution ratio, it is possible to prevent the driver from individually feeling the change in behavior due to the change in the required drive torque and the change in behavior due to the change in the torque distribution ratio. In other words, even if the behavior of the vehicle Ve changes due to the change in the torque distribution ratio, it is possible to prevent the driver from feeling uncomfortable.

[0057] The driving force control device for an electric vehicle in the embodiment of the present invention is not limited to one that prevents the operating point of either motor from entering the avoidance zone when traveling in four-wheel drive mode, but may be configured, for example, to drive the other motor Mfr, Mfl to switch to four-wheel drive mode when the operating point of the motor Mrr, Mrl is predicted to enter the avoidance zone while traveling in two-wheel drive mode with the motors Mrr, Mrl as driving force sources, and to appropriately control the torque distribution ratio. That is, when the reference torque distribution ratio is set to 0:10, when the operating point of the motors Mrr, Mrl is predicted to enter the avoidance zone, the torque distribution ratio may be changed to, for example, 3:7.

[0058] Furthermore, the motor operating point where abnormal noise and vibration become noticeable is not limited to when the motor is outputting drive torque, but also exists when the motor is outputting regenerative torque (braking torque). Therefore, the driving force control device in the embodiment of the present invention may be configured to change the torque distribution ratio when the motor operating point is predicted to enter the avoidance zone, not only when the vehicle is running while outputting drive torque from each of the motors Mfr, Mfl, Mrr, and Mrl, but also when the vehicle is running while outputting regenerative torque (braking torque).

[0059] Furthermore, the electric vehicle in the embodiment of the present invention is not limited to a vehicle equipped with a motor as a driving power source for the front wheels and a motor as a driving power source for the rear wheels, but may be a so-called hybrid vehicle equipped with a motor as a driving power source for either the front wheels or the rear wheels and an engine as a driving power source for the other wheel. Even in such a case, when it is predicted that the motor operating point will enter the avoidance zone, the motor torque is changed so that the motor operating point is moved out of the avoidance zone, and the engine torque is changed to satisfy the required driving torque of the vehicle, thereby changing the torque distribution ratio, thereby suppressing the generation of abnormal noise and vibration caused by the motor operating point entering the avoidance zone. [Explanation of symbols]

[0060] 1r,1l front wheel 2r,2l rear wheel 20 Controller 21 Required driving torque calculation unit 22 Reference torque distribution ratio determination unit 23 Motor operating point prediction unit 24 Avoidance area judgment unit 25 Guard value setting section 26 Torque distribution ratio change unit Mfr, Mfl, Mrr, Mrl Motor Ve Electric Vehicle

Claims

1. A driving force control device for an electric vehicle includes a motor that drives a first drive wheel, which is one of front wheels and rear wheels, and a driving force source different from the motor that drives a second drive wheel, which is the other of the front wheels and the rear wheels, and is capable of setting a four-wheel drive driving mode in which the vehicle travels using the motor and the other driving force source, A controller for controlling the motor is provided. The controller: an avoidance zone determination unit that determines whether a motor operating point, which is determined by an output torque and a rotation speed of the motor, falls within a predetermined avoidance zone in which abnormal noise or vibration becomes noticeable when the motor is driven; a torque distribution ratio changing unit that changes a torque distribution ratio, which is a ratio between a torque of the first driving wheel and a torque of the second driving wheel, from a predetermined reference torque distribution ratio so that the motor operating point deviates from the avoidance area when the avoidance area determining unit determines that the motor operating point is within the avoidance area. A driving force control device for an electric vehicle.

2. The driving force control device for an electric vehicle according to claim 1, The controller: A guard value setting unit that determines an upper limit value and a lower limit value of the change amount of the torque distribution ratio, The guard value setting unit determines an upper limit value and a lower limit value of a change amount of the torque distribution ratio when a reference torque distribution ratio is set to maintain a behavior of the electric vehicle. A driving force control device for an electric vehicle.

3. The driving force control device for an electric vehicle according to claim 1, The torque distribution ratio changing unit starts changing the torque distribution ratio earlier as the change amount of the torque distribution ratio is larger. The driving force control device for an electric vehicle is characterized by the above.

4. The driving force control device for an electric vehicle according to claim 1, When the avoidance area determination unit determines that the motor operating point enters the avoidance area due to a change in the output torque of the motor, the output torque of the motor is maintained at the torque before entering the avoidance area, and the torque of the other driving power source is changed in accordance with the required driving torque of the electric vehicle. A driving force control device comprising:

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