Control device, vehicle equipped with control device, and control method

Abstract

This control device is applied to a brake system of a vehicle equipped with a drive motor including a front wheel motor and a rear wheel motor. Upon acquiring a braking request by the driver of the vehicle, one or a plurality of processors included in the control device executes first processing for switching from regenerative braking to reverse-phase braking for one of the front wheel motor and the rear wheel motor when a vehicle speed of the vehicle is equal to or lower than a first vehicle speed, and executes second processing for switching from the regenerative braking to the reverse-phase braking for the other motor different from the one of the front wheel motor and the rear wheel motor when the vehicle speed is equal to or lower than a second vehicle speed different from the first vehicle speed.

Description

Control Device, Vehicle Equipped with the Control Device, and Control Method

[0001] The present disclosure relates to a control device, a vehicle equipped with the control device, and a control method.

[0002] In a vehicle that transmits drive torque output from a drive motor to wheels, in addition to regenerative braking of the drive motor, a technique of performing reverse-phase braking by exciting the drive motor to rotate in the reverse direction is known.

[0003] For example, Patent Document 1 discloses a vehicle that travels forward when torque is generated in the forward rotation direction of a traveling motor, the vehicle including a vehicle speed detection means for detecting the vehicle speed of the vehicle, a vehicle attitude detection means for detecting the attitude of the vehicle, a traveling state detection means for detecting the traveling state of the vehicle from the vehicle speed and attitude of the vehicle, and a control means for intermittently generating torque in the reverse rotation direction of the traveling motor to generate a reverse braking force. The control means varies the amount of reverse braking force generated based on the traveling state detected by the traveling state detection means.

[0004] Further, Patent Document 2 discloses a braking device for a vehicle including a rotor having a permanent magnet and a stator capable of rotationally driving the rotor, a permanent magnet synchronous motor connecting the rotor to each of at least a pair of wheels of the vehicle, a power storage means for storing power supplied to the permanent magnet synchronous motor, and a conversion control means for converting the power of the power storage means to excite the stator and control the rotation of the rotor. The braking device includes a synchronous excitation control means for exciting the stator in the same phase as the excitation of the stator in the rotation direction of the rotor according to the control of the conversion control means and applying an excitation brake to the wheels by supplying power. The braking device for a vehicle is characterized by stopping the wheels by the excitation brake.

[0005] Furthermore, Patent Document 3 discloses a brake system for an electric vehicle having a reversible drive motor, characterized by comprising: a detection sensor for detecting a state requiring emergency braking; a determination means for determining that it is an emergency based on the detection result of the detection sensor; and a motor control means for reversing the motor when it is determined to be an emergency.

[0006] Japanese Patent Publication No. 2013-252023, Japanese Patent Publication No. 2013-135528, Japanese Patent Publication No. 2004-187445

[0007] In vehicles that transmit drive torque from a drive motor to the wheels, even if there is some abnormality in the friction brakes, the vehicle can be decelerated by utilizing the regenerative braking force from the drive motor. However, as the vehicle speed decreases, the regenerative braking force of the drive motor decreases, which may prevent the vehicle from coming to a complete stop.

[0008] As a countermeasure, it is conceivable to use reverse-phase braking force as described in Patent Documents 1 to 3. That is, when the vehicle speed falls below a predetermined value, it is conceivable to switch from regenerative braking to reverse-phase braking. However, there was a problem in that when switching from regenerative braking to reverse-phase braking, a moment of loss of braking force occurred, during which the driver of the vehicle could no longer feel the deceleration.

[0009] In light of these circumstances, the purpose of this disclosure is to provide a technology that suppresses the loss of braking force when switching from regenerative braking to reverse-phase braking while a vehicle is in motion.

[0010] A control device according to one embodiment of the present disclosure is a control device applied to a brake system of a vehicle equipped with drive motors including a front wheel motor and a rear wheel motor, comprising one or more processors and one or more memories connected to the one or more processors in a communicative manner, wherein when the one or more processors receive a braking request from the driver of the vehicle, they execute a first process for one of the front wheel motors and the rear wheel motors to switch from regenerative braking to reverse phase braking when the vehicle speed is less than or equal to a first vehicle speed, and execute a second process for the other of the front wheel motors and the rear wheel motors that is different from the one motor, to switch from regenerative braking to reverse phase braking when the vehicle speed is less than or equal to a second vehicle speed that is different from the first vehicle speed.

[0011] A vehicle according to one embodiment of the present disclosure includes a drive motor including a front wheel motor and a rear wheel motor, a brake system that applies regenerative braking force or reverse-phase braking force to the wheels in addition to friction braking force, and the control device described above.

[0012] A control method according to one embodiment of the present disclosure is a control method applied to a brake system of a vehicle equipped with drive motors including a front wheel motor and a rear wheel motor, and includes, when a computer receives a braking request from the driver of the vehicle, a first process of switching one of the front wheel motor and the rear wheel motor from regenerative braking to reverse phase braking when the vehicle speed is less than or equal to a first vehicle speed, and a second process of switching the other of the front wheel motor and the rear wheel motor, which is different from the one motor, from regenerative braking to reverse phase braking when the vehicle speed is less than or equal to a second vehicle speed which is different from the first vehicle speed.

[0013] According to one embodiment of the present disclosure, it is possible to suppress the loss of braking force when switching from regenerative braking to reverse-phase braking while the vehicle is in motion.

[0014] This is a schematic diagram showing an example of the configuration of a vehicle equipped with a control device according to one embodiment of this disclosure. This is a block diagram showing an example of the configuration of a control device according to one embodiment of this disclosure. This is a diagram illustrating the coordinated braking of friction braking and regenerative braking under normal conditions according to a comparative example. This is a diagram illustrating the coordinated braking of friction braking and regenerative braking under abnormal conditions according to a comparative example. This is a diagram illustrating the coordinated braking of friction braking, regenerative braking and reverse-phase braking under abnormal conditions according to one embodiment of this disclosure. This is a flowchart illustrating an example of the operation of a control device according to one embodiment of this disclosure.

[0015] Preferred embodiments of this disclosure will be described in detail below with reference to the attached drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant descriptions will be omitted.

[0016] (1. Overall Vehicle Configuration) Vehicle 1 is an electric vehicle that transmits the drive torque output from the drive motor 3 to the wheels 2LF, RF, LR, and RR (hereinafter, unless otherwise specified, they will be collectively referred to as "wheels 2"). Specifically, the drive motor 3 includes a front wheel motor 3F and a rear wheel motor 3R. Vehicle 1 is a four-wheel drive electric vehicle that transmits the drive torque output from the front wheel motor 3F to the front wheels 2LF and 2RF, and the drive torque output from the rear wheel motor 3R to the rear wheels 2LR and 2RR.

[0017] Vehicle 1, as a drive system, further includes, in addition to the front wheel motor 3F and rear wheel motor 3R described above, a front wheel inverter 4F, a rear wheel inverter 4R, a front wheel converter 5F, a rear wheel converter 5R, and a battery 6.

[0018] The front wheel motor 3F outputs drive torque transmitted to the front wheels 2LF and 2RF via the front wheel differential mechanism 7F and the front wheel drive shaft 8F. The front wheel motor 3F may be configured as a three-phase AC motor. In this case, the rotor (not shown) rotates due to the rotating magnetic field formed by the supply of three-phase AC power to the stator (not shown), and drive torque is output. The front wheel motor 3F also has a function of regenerative power generation by receiving rotational torque from the front wheels 2LF and 2RF transmitted via the front wheel drive shaft 8F when three-phase AC power is not supplied to the stator, causing the rotor to rotate.

[0019] The rear wheel motor 3R outputs drive torque transmitted to the rear wheels 2LR and 2RR via the rear wheel differential mechanism 7R and the rear wheel drive shaft 8R. The rear wheel motor 3R may be configured as a three-phase AC motor. In this case, the rotor (not shown) rotates due to the rotating magnetic field formed by the supply of three-phase AC power to the stator (not shown), and drive torque is output. The rear wheel motor 3R also has a function of regenerative power generation, where the rotor rotates by receiving the rotational torque of the rear wheels 2LR and 2RR transmitted via the rear wheel drive shaft 8R when three-phase AC power is not supplied to the stator.

[0020] The front wheel inverter 4F converts the DC power supplied from the battery 6 into, for example, three-phase AC power and supplies it to the front wheel motor 3F. The front wheel inverter 4F also converts the, for example, three-phase AC power regenerated by the front wheel motor 3F into DC power and supplies it to the front wheel converter 5F. The drive of the front wheel inverter 4F is controlled by the vehicle control device 20, which will be described later.

[0021] The rear wheel inverter 4R converts the DC power supplied from the battery 6 into, for example, three-phase AC power and supplies it to the rear wheel motor 3R. The rear wheel inverter 4R also converts the, for example, three-phase AC power regenerated by the rear wheel motor 3R into DC power and supplies it to the rear wheel converter 5R. The drive of the rear wheel inverter 4R is controlled by the vehicle control device 20.

[0022] The front wheel converter 5F boosts the voltage of, for example, three-phase AC power regenerated by the front wheel motor 3F to at least the required charging voltage of the battery 6 and supplies it to the battery 6. The drive of the front wheel converter 5F is controlled by the vehicle control device 20.

[0023] The rear wheel converter 5R boosts the voltage of, for example, three-phase AC power regenerated by the rear wheel motor 3R to at least the battery 6's required charging voltage and supplies it to the battery 6. The drive of the rear wheel converter 5R is controlled by the vehicle control device 20.

[0024] Battery 6 supplies power to the front wheel motor 3F and the rear wheel motor 3R, respectively. Battery 6 is a rechargeable secondary battery such as a lithium-ion battery or a solid-state battery with a rated voltage of 200V to 800V. However, the rated voltage and type of battery 6 in this disclosure are not particularly limited. Battery 6 may be provided separately for the front wheel motor 3F and the rear wheel motor 3R.

[0025] Vehicle 1 further comprises a brake system including a brake pedal 9, a stroke sensor 10, a brake booster 11, brake piping 12, and brake devices 13LF, 13RF, 13LR, and 13RR (hereinafter collectively referred to as "brake device 13" unless otherwise specified). Each brake device 13LF, 13RF, 13LR, and 13RR is provided corresponding to the wheels 2LF, 2RF, 2LR, and 2RR, and includes a rotating body such as a disc or drum (not shown) that rotates with the axle, and a brake pad (not shown). The brake booster 11 increases the hydraulic pressure of the brake fluid in the fluid chamber (not shown). In this embodiment, the braking force applied to the wheels 2 is adjusted by the vehicle control device 20 controlling the hydraulic pressure according to the amount the brake pedal 9 is pressed, as detected by the stroke sensor 10. However, the brake system in this disclosure is not limited thereto, and may also be a mechanical configuration in which hydraulic pressure is applied in direct response to the amount the brake pedal 9 is pressed. In addition to the frictional braking force described above, the brake system provided in the vehicle 1 can also apply regenerative braking force or reverse-phase braking force to the wheels 2, but details will be described later.

[0026] Vehicle 1 further includes an electric steering device 14 provided on the front wheel drive shaft 8F. The electric steering device 14 includes an electric motor (not shown) and a gear mechanism (not shown), and adjusts the steering angle of the front wheels 2LF and 2RF by being controlled by a vehicle control device 20. The vehicle control device 20 controls the electric steering device 14 based on the steering angle of the steering wheel 15 by the driver of vehicle 1. Here, if vehicle 1 is configured to perform automatic driving control, the vehicle control device 20 controls the electric steering device 14 based on the steering angle of the steering wheel 15 by the driver during manual driving. On the other hand, during automatic driving, the vehicle control device 20 controls the electric steering device 14 based on a steering angle or steering angular velocity set by a known or arbitrary method.

[0027] Vehicle 1 is further equipped with a vehicle speed sensor 16 that detects the vehicle speed of vehicle 1. Any known or arbitrary sensor can be used as the vehicle speed sensor 16, as long as it can detect the vehicle speed of vehicle 1. The vehicle speed sensor 16 transmits information indicating the detection result to the vehicle control device 20.

[0028] In addition, the vehicle 1 may be equipped with an ambient environment sensor 17, a GNSS (Global Navigation Satellite System) sensor 18, and a notification device 19.

[0029] The ambient environment sensor 17 may include a front-facing camera (not shown) and a rear-facing camera (not shown) driven by the vehicle control device 20. The front-facing camera captures the area in front of the vehicle 1 and generates image data. Here, the front-facing camera may be a stereo camera including a pair of left and right cameras, or it may be a monocular camera. The rear-facing camera captures the area behind the vehicle 1 and generates image data. The front-facing camera and the rear-facing camera may be equipped with image sensors such as CCD (Charged Coupled Devices) or CMOS (Complementary Metal Oxide Semiconductor), and transmit the generated image data to the vehicle control device 20. The ambient environment sensor 17 may also include one or more distance measuring sensors from among radar sensors such as LiDAR (Light Detection And Ranging) or millimeter-wave radar and ultrasonic sensors.

[0030] The GNSS sensor 18 is driven by the vehicle control device 20 and receives satellite signals from positioning satellites such as GPS (Global Positioning System) satellites. The GNSS sensor 18 transmits the vehicle 1's position information, which is included in the received satellite signals, to the vehicle control device 20. In addition to the GPS sensor, the GNSS sensor 18 may also be equipped with an antenna that receives satellite signals from other satellite systems that determine the vehicle 1's position.

[0031] The notification device 19 is driven by the vehicle control device 20 and notifies the driver of the vehicle 1 of various information by means such as image display or audio output. The notification device 19 includes, for example, a display device provided in the instrument panel and a speaker provided in the vehicle 1. The display device may be a display device provided in a navigation system.

[0032] The vehicle control device 20 includes one or more electronic control units (ECUs) that control various parts of the vehicle 1. The vehicle control device 20 may be divided into appropriate parts according to function, etc., as long as it is not logically contradictory, and installed in the vehicle 1. Furthermore, some or all of the components of the vehicle control device 20 may be installed in the control device 30 described later.

[0033] (2. Control device) The control device 30 according to this embodiment will be described with reference to Figure 2.

[0034] (2-1. Configuration Example) The control device 30 functions as a device applied to the brake system of a vehicle 1 equipped with drive motors 3 including a front wheel motor 3F and a rear wheel motor 3R, by having one or more CPUs (Central Processing Units) or other processors execute a computer program. The computer program is a computer program that causes the processor to execute the operations that the control device 30 should perform, which will be described later. The computer program executed by the processor may be recorded on a recording medium that functions as a memory unit 32, which will be described later, or it may be recorded on a recording medium built into the control device 30 or on any recording medium that can be attached externally to the control device 30.

[0035] The recording medium for storing computer programs may include magnetic media such as hard disks, floppy disks, and magnetic tapes; optical recording media such as CD-ROMs, DVDs, and Blu-ray®; magneto-optical media such as floppy disks; memory elements such as RAM and ROM; flash memory such as USB memory and SSDs; and other media capable of storing programs.

[0036] At least the vehicle control device 20 is connected to the control device 30 via a dedicated line or a communication means such as CAN (Controller Area Network) or LIN (Local Internet). In this embodiment, the control device 30 is provided in the vehicle 1 separately from the vehicle control device 20, but an embodiment in which some or all of the components of the control device 30 are provided integrally with the vehicle control device 20 is also possible.

[0037] The control device 30 comprises a processing unit 31 and a storage unit 32.

[0038] (Processing Unit) The processing unit 31 comprises one or more processors such as a CPU and various peripheral components. Part or all of the processing unit 31 may consist of updatable components such as firmware, or it may be a program module that is executed by instructions from the CPU, etc.

[0039] (Storage Unit) The storage unit 32 is composed of one or more storage elements such as RAM or ROM that are connected to the processing unit 31 in a communicative manner. However, the type and number of storage units 32 are not particularly limited. The storage unit 32 stores information such as computer programs executed by the processing unit 31, various parameters used in arithmetic processing, detection data, and calculation results.

[0040] (2-2. Functional Configuration of the Processing Unit) The functional configuration of the processing unit 31 of the control device 30 will be described below. The processing unit 31 includes an acquisition unit 33, a braking request determination unit 34, an abnormality determination unit 35, a switching determination unit 36, and a braking command unit 37. Each of these units is a function realized by the execution of a computer program by one or more processors such as a CPU. However, some or all of the acquisition unit 33, braking request determination unit 34, abnormality determination unit 35, switching determination unit 36, and braking command unit 37 may be configured using analog circuits.

[0041] (Acquisition Unit) The acquisition unit 33 acquires the vehicle speed of the vehicle 1 from the vehicle speed sensor 16 via the vehicle control device 20. The acquisition unit 33 also acquires the amount of depression of the brake pedal 9 from the stroke sensor 10 via the vehicle control device 20. However, the vehicle speed sensor 16 and the stroke sensor 10 may be directly connected to the control device 30 via a dedicated line or communication means such as CAN or LIN. In this case, the acquisition unit 33 directly acquires the vehicle speed of the vehicle 1 from the vehicle speed sensor 16 and directly acquires the amount of depression of the brake pedal 9 from the stroke sensor 10 without going through the vehicle control device 20.

[0042] (Braking Request Determination Unit) The braking request determination unit 34 determines whether or not a braking request has been made by the driver of the vehicle 1, based on the amount of depression of the brake pedal 9 acquired by the acquisition unit 33. Specifically, the braking request determination unit 34 may determine that a braking request has been made by the driver of the vehicle 1 if the amount of depression of the brake pedal 9 is equal to or greater than a specified value. This specified value can be set as appropriate.

[0043] (Anomaly Detection Unit) The anomaly detection unit 35 determines whether or not an anomaly has occurred in the brake system of the vehicle 1. Here, the anomaly in the brake system may be, for example, a failure of the brake booster 11, and the cause of the failure of the brake booster 11 can be isolated and detected. The anomaly in the brake system may also be, for example, a vapor lock phenomenon or a fade phenomenon. The vapor lock phenomenon refers to a phenomenon in which the brake fluid boils due to the heat generated by the brake device 13, generating bubbles and causing the hydraulic pressure to become ineffective. The fade phenomenon refers to a phenomenon in which the friction material of the brake pads decomposes due to abnormal overheating of the brake pads, generating gas and reducing the friction force. For example, the fade phenomenon can be detected based on a temperature model inside the brake that can be calculated from the cumulative value of the brake operating time. In addition to these, an anomaly in the brake system can also be detected when the vehicle 1 does not decelerate despite a change in the angle of the brake pedal 9, or when the detected value of the stroke sensor inside the brake booster 11 does not change.

[0044] (Switching Determination Unit) When the vehicle speed acquired by the acquisition unit 33 is equal to or lower than the first vehicle speed with respect to, for example, the front wheel motor 3F corresponding to one of the front wheel motor 3F and the rear wheel motor 3R, the switching determination unit 36 determines that it executes the first process of switching from regenerative braking to reverse-phase braking. Further, when the vehicle speed acquired by the acquisition unit 33 is equal to or lower than the second vehicle speed different from the first vehicle speed with respect to, for example, the rear wheel motor 3R corresponding to the other motor different from the one motor described above among the front wheel motor 3F and the rear wheel motor 3R, the switching determination unit 36 determines that it executes the second process of switching from regenerative braking to reverse-phase braking. However, the present disclosure is not limited thereto, and the rear wheel motor 3R may be selected as the execution target of the first process, and the front wheel motor 3F may be selected as the execution target of the second process.

[0045] Here, referring to FIGS. 3 to 5, taking the case where an abnormality has occurred in the brake booster 11 as an example, the technical significance of executing the above-described first process and second process will be described. FIGS. 3 and 4 are diagrams for explaining the cooperative braking of friction braking and regenerative braking according to a comparative example. FIG. 5 is a diagram for explaining the cooperative braking of friction braking, regenerative braking, and reverse-phase braking according to the present embodiment.

[0046] As shown in FIG. 3, when the brake booster 11 is functioning normally, even if the regenerative braking becomes less effective as the vehicle 1 decelerates, the required braking force by the driver of the vehicle 1 can be satisfied by the pressure boost by the brake booster 11. On the other hand, as shown in FIG. 4, when an abnormality has occurred in the brake booster 11, when the regenerative brake becomes less effective as the vehicle 1 decelerates, the pressure boost by the brake booster 11 cannot be utilized, and there arises a problem that the required braking force by the driver cannot be satisfied.

[0047] In contrast, according to the present embodiment, as shown in FIG. 5, even when an abnormality occurs in the brake booster 11, regenerative braking can be switched to reverse-phase braking before the regenerative braking becomes ineffective, so that the required braking force by the driver can be satisfied. Further, for example, when the vehicle speed of the vehicle 1 is less than or equal to the first vehicle speed, the regenerative braking of the front-wheel motor 3F is switched to reverse-phase braking, and when the vehicle speed of the vehicle 1 is less than or equal to a second vehicle speed different from the first vehicle speed, the regenerative braking of the rear-wheel motor 3R is switched to reverse-phase braking. That is, by shifting the timing of switching from regenerative braking to reverse-phase braking between the front-wheel motor 3F and the rear-wheel motor 3R, the braking force by any one of the front-wheel motor 3F and the rear-wheel motor 3R can always be ensured. Therefore, it is possible to suppress the loss of braking force associated with the switching from regenerative braking to reverse-phase braking.

[0048] The first vehicle speed and the second vehicle speed are preferably greater than or equal to the vehicle speed of the vehicle 1 at the start point of decrease in the regenerative braking force and less than or equal to the vehicle speed of the vehicle 1 at the time of obtaining the braking request by the driver of the vehicle 1. Note that the information indicating the first vehicle speed and the second vehicle speed is stored in advance in the storage unit 32 so as to be referable by the switching determination unit 36. The reason why it is preferable that the first vehicle speed and the second vehicle speed are within the above-described range is as follows.

[0049] In an electric vehicle, when the brake booster 11 fails, in addition to the backup of the brake system by VDC (Vehicle Dynamics Control) control, regenerative braking can be used. However, at low speeds of the vehicle 1, the regenerative braking force becomes small, and there is a risk that the vehicle 1 cannot come to a complete stop. In contrast, by setting the first vehicle speed and the second vehicle speed within the above-described range, the switching from regenerative braking to reverse-phase braking is executed before the regenerative braking force starts to decrease, so that the situation where the vehicle 1 cannot come to a complete stop can be avoided. In addition to the case where the brake booster 11 fails, the situation where the vehicle 1 cannot come to a complete stop can also be avoided for the same reason when the friction braking does not operate due to damage to the brake pipe 12 (more specifically, the hydraulic circuit). <An example of the first vehicle speed is 30 km / h, which is the speed at which the regenerative braking force begins to decrease. An example of the second vehicle speed is 25 km / h, which is the speed at which the switch from regenerative braking to reverse-phase braking is completed, using the first vehicle speed as the criterion. However, this disclosure is not limited to these examples, and the relative magnitudes of the first and second vehicle speeds may be reversed, and they can be set appropriately according to the type of vehicle 1, etc. The difference between the first and second vehicle speeds can be set appropriately so as to ensure the time required for switching from regenerative braking to reverse-phase braking.

[0051] Furthermore, the first and second vehicle speeds may be dynamically set while the vehicle 1 is running, based on the ambient temperature or battery temperature of the vehicle 1. This is because the effectiveness of regenerative braking depends on the ambient temperature or battery temperature of the vehicle 1. For example, the first and second vehicle speeds may be set higher because the vehicle speed at which regenerative braking force begins to decrease tends to increase as the ambient temperature or battery temperature of the vehicle 1 deviates from the appropriate temperature. The ambient temperature of the vehicle 1 can be detected by an ambient temperature sensor (not shown) provided on the outer surface of the vehicle 1, etc. The battery temperature can be detected by a temperature sensor (not shown) provided in an optional or known battery management system (BMS).

[0052] (Braking Command Unit) The braking command unit 37 generates a first command signal to apply a reverse rotation voltage to, for example, the front wheel motor 3F, which is the target of the first processing among the front wheel motor 3F and the rear wheel motor 3R, and transmits the generated first command signal to the vehicle control device 20. Based on the first command signal from the braking command unit 37, the vehicle control device 20 applies reverse-phase braking force to the front wheels 2LF and 2RF by controlling, for example, the front wheel inverter 4F. The braking command unit 37 also generates a second command signal to apply a reverse rotation voltage to, for example, the rear wheel motor 3R, which is the target of the second processing among the front wheel motor 3F and the rear wheel motor 3R, and transmits the generated second command signal to the vehicle control device 20. Based on the second command signal from the braking command unit 27, the vehicle control device 20 applies reverse-phase braking force to the rear wheels 2LR and 2RR by controlling, for example, the rear wheel inverter 4R. Specifically, when the front wheel motor 3F and the rear wheel motor 3R are configured as three-phase AC motors, the first and second command signals apply a reverse rotation voltage to the respective motors by swapping two lines of the corresponding three-phase power supply. The reverse rotation voltage is a voltage that generates a reverse rotational magnetic field in the front wheel motor 3F or the rear wheel motor 3R, thereby applying reverse torque to the rotor (not shown) of the front wheel motor 3F or the rear wheel motor 3R. The timing for applying the reverse-phase braking force will be described later.

[0053] Furthermore, the braking command unit 37 generates a third command signal to cause the front wheel motor 3F or the rear wheel motor 3R to function as a regenerative generator, and transmits the generated third command signal to the vehicle control device 20. The vehicle control device 20 applies regenerative braking force to the wheels 2 by controlling the front wheel inverter 4F and the rear wheel inverter 4R based on the third command signal from the braking command unit 37. At this time, the regenerative power obtained by the rotation of the rotors of the front wheel motor 3F and the rear wheel motor 3R in response to the rotational torque of the wheels 2 is converted into DC power by the front wheel inverter 4F and the rear wheel inverter 4R and supplied to the battery 6. The timing of applying regenerative braking force will be described later.

[0054] (2-3. Example of Control Device Operation) Referring to Figure 6, an example of the operation of the control device 30 according to this embodiment will be explained in accordance with the flowchart.

[0055] In step S10, the braking request determination unit 34 determines whether or not the driver of vehicle 1 has made a braking request. Specifically, the braking request determination unit 34 obtains the amount of depression of the brake pedal 9 via the acquisition unit 33 and determines whether or not the driver of vehicle 1 has made a braking request based on the amount of depression. If it is determined that there is a braking request, the process proceeds to step S11. On the other hand, if it is determined that there is no braking request, the process ends.

[0056] In step S11, the abnormality determination unit 35 determines whether or not an abnormality has occurred in the brake system. If it is determined that an abnormality has occurred (step S11: YES), the process proceeds to step S12. If it is not determined that an abnormality has occurred (step S11: NO), the process proceeds to step S18.

[0057] In step S12, the switching determination unit 36 ​​determines whether the vehicle speed of vehicle 1 is less than or equal to the first vehicle speed. Specifically, the switching determination unit 36 ​​obtains the vehicle speed of vehicle 1 via the acquisition unit 33 and determines whether the vehicle speed is less than or equal to the first vehicle speed. If it is determined that the vehicle speed is less than or equal to the first vehicle speed (step S12: YES), the process proceeds to step S13. On the other hand, if it is not determined that the vehicle speed is less than or equal to the first vehicle speed (step S12: NO), the process proceeds to step S18.

[0058] In step S13, the switching determination unit 36 ​​determines to execute a first process, which is to switch from regenerative braking to reverse-phase braking, for one of the motors, for example, the front wheel motor 3F, which corresponds to one of the front wheel motors 3F and the rear wheel motor 3R. In this example of operation, the front wheel motor 3F is selected as the target of the first process because when the vehicle 1 decelerates, most of the kinetic energy is concentrated in front of the vehicle 1, and it is necessary to apply a braking force to the front wheels 2LF and 2RF that is sufficient to suppress this kinetic energy. However, this disclosure is not limited to this example of operation, and the rear wheel motor 3R may be selected as the target of the first process instead of the front wheel motor 3F. The process then proceeds to step S14.

[0059] In step S14, the braking command unit 37 generates a first command signal to apply a reverse rotation voltage to, for example, the front wheel motor 3F, which is the target of the first processing among the front wheel motor 3F and the rear wheel motor 3R, and transmits the generated first command signal to the vehicle control device 20. As a result, reverse-phase braking force is applied to the front wheels 2LF and 2RF as described above. However, this disclosure is not limited to this example of operation, and if the rear wheel motor 3R is selected as the target of the first processing, reverse-phase braking force may be applied to the rear wheels 2LR and 2RR by applying a reverse voltage to the rear wheel motor 3R. The process then proceeds to step S15.

[0060] In step S15, the switching determination unit 36 ​​determines whether the vehicle speed of vehicle 1 is less than or equal to the second vehicle speed, in the same manner as in step S12. If it is determined that the vehicle speed is less than or equal to the second vehicle speed (step S15: YES), the process proceeds to step S16. On the other hand, if it is not determined that the vehicle speed is less than or equal to the second vehicle speed (step S15: NO), the process waits until the vehicle speed becomes less than or equal to the second vehicle speed.

[0061] In step S16, the switching determination unit 36 ​​determines to execute a second process, which switches from regenerative braking to reverse-phase braking, for the other motor among the front wheel motor 3F and the rear wheel motor 3R, for example, the rear wheel motor 3R. However, this disclosure is not limited to this example of operation, and if the rear wheel motor 3R is selected as the target for the first process, the front wheel motor 3F is selected as the target for the second process instead of the rear wheel motor 3R. The process then proceeds to step S17.

[0062] In step S17, the braking command unit 37 generates a second command signal to apply a reverse rotation voltage to, for example, the rear wheel motor 3R, which is the target of the second processing among the front wheel motor 3F and the rear wheel motor 3R, and transmits the generated second command signal to the vehicle control device 20. As a result, reverse-phase braking force is applied to the rear wheels 2LR and 2RR as described above. However, this disclosure is not limited to this example of operation, and if the front wheel motor 3F is selected as the target of the second processing, reverse-phase braking force may be applied to the front wheels 2LF and 2RF by applying a reverse voltage to the front wheel motor 3F. After that, the process ends.

[0063] As described above, this example of operation allows for a staggered execution timing between the first process and the second process, thereby suppressing the loss of braking force associated with the switch from regenerative braking to reverse-phase braking. More preferably, the switch from regenerative braking to reverse-phase braking related to the second process (or first process) is performed after the switch from regenerative braking to reverse-phase braking related to the first process (or second process) is completed.

[0064] Furthermore, if the process proceeds from step S12 or S13 to step S18, in step S18, the braking command unit 37 generates a third command signal that causes the front wheel motor 3F and the rear wheel motor 3R to function as regenerative generators, and transmits the generated third command signal to the vehicle control device 20. As a result, regenerative braking force is applied to the wheels 2 as described above. The process then ends.

[0065] (3. Summary) As described above, the control device 30 according to this embodiment is applied to the brake system of a vehicle 1 equipped with a drive motor 3 including a front wheel motor 3F and a rear wheel motor 3R. The processing unit 31 of the control device 30 performs a first process for one of the motors, the front wheel motor 3F and the rear wheel motor 3R, which switches from regenerative braking to reverse-phase braking when the vehicle speed of the vehicle 1 is at or below a first vehicle speed. The processing unit 31 of the control device 30 also performs a second process for the other motor, the front wheel motor 3F and the rear wheel motor 3R, which switches from regenerative braking to reverse-phase braking when the vehicle speed is at or below a second vehicle speed different from the first vehicle speed.

[0066] With this configuration, the timing of switching from regenerative braking to reverse-phase braking can be staggered between the front wheel motor 3F and the rear wheel motor 3R, so that braking force from either the front wheel motor 3F or the rear wheel motor 3R can always be secured. Therefore, it is possible to suppress the loss of braking force when switching from regenerative braking to reverse-phase braking while the vehicle 1 is in motion due to a malfunction in the brake system or the like.

[0067] Preferred embodiments of the present disclosure have been described in detail above with reference to the attached drawings, but the present disclosure is not limited to such examples. It is clear to any person with ordinary skill in the art to which the present disclosure belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these will naturally also be understood to fall within the technical scope of the present disclosure. For example, the functions etc. included in each component or each step etc. can be rearranged in a logically consistent manner, and multiple components or steps etc. can be combined into one or divided into two.

[0068] As one variation, the first and second processes in this disclosure are not limited to cases where an abnormality occurs in the brake system, as in the embodiments described above, but may also be executed when the brake system is functioning normally. For example, if the processing unit 31 of the control device 30 predicts that the State of Charge (SOC) of the battery 6 will exceed a specified value due to regenerative braking after receiving a braking request from the driver of the vehicle 1 and before the vehicle 1 comes to a stop, the switching from regenerative braking to reverse-phase braking related to the first and second processes described above may be executed. This makes it possible to avoid a situation in which the battery 6 becomes fully charged during the operation of regenerative braking, resulting in the regenerative braking becoming ineffective. The specified value is, for example, 90% to 95%, but this disclosure is not limited thereto and can be set as appropriate from the viewpoint of avoiding the full charge described above.

[0069] As another variation, the braking request from the driver is not limited to a braking request related to friction braking that can be obtained via the brake pedal 9, but may also be a braking request related to regenerative braking that can be obtained via paddle shifters (not shown) provided on the spokes (not shown) of the steering wheel 15.

[0070] Furthermore, the technology disclosed herein can also be realized as a vehicle 1 equipped with the control device 30 described in the above-described embodiment, a control method executed by the control device 30, a computer program that causes a computer to function as the control device 30 described above, and a non-temporary tangible recording medium on which the computer program is recorded.

[0071] 1: Vehicle, 3F: Front wheel motor, 3R: Rear wheel motor, 30: Control device, 31: Processing unit, 32: Memory unit, 33: Acquisition unit, 34: Brake request determination unit, 35: Abnormality determination unit, 36: Switching determination unit, 37: Brake command unit

Claims

1. A control device applied to a brake system of a vehicle equipped with drive motors including a front wheel motor and a rear wheel motor, comprising one or more processors and one or more memories connected to the one or more processors in a communicative manner, wherein the one or more processors, upon receiving a braking request from the driver of the vehicle, execute a first process for one of the front wheel motors and the rear wheel motors, which switches from regenerative braking to reverse-phase braking when the vehicle speed is less than or equal to a first vehicle speed, and execute a second process for the other of the front wheel motors and the rear wheel motors, which is different from the one motor, which switches from regenerative braking to reverse-phase braking when the vehicle speed is less than or equal to a second vehicle speed different from the first vehicle speed.

2. The control device according to claim 1, wherein the first vehicle speed and the second vehicle speed are greater than or equal to the vehicle speed of the vehicle at the time the reduction of regenerative braking force begins, and less than or equal to the vehicle speed of the vehicle at the time the braking request is acquired.

3. The control device according to claim 1 or 2, wherein one or more processors execute the first process and the second process when they detect that an abnormality has occurred in the brake system.

4. A vehicle comprising: a drive motor including a motor for the front wheels and a motor for the rear wheels; a brake system that applies regenerative braking force or reverse-phase braking force to the wheels in addition to frictional braking force; and the control device described in claim 1.

5. A control method for a brake system applied to a vehicle equipped with drive motors including a front wheel motor and a rear wheel motor, the control method comprising: when a computer receives a braking request from the driver of the vehicle, executing a first process for one of the front wheel motor and the rear wheel motor to switch from regenerative braking to reverse-phase braking when the vehicle speed is less than or equal to a first vehicle speed; and executing a second process for the other of the front wheel motor and the rear wheel motor, which is different from the one motor, to switch from regenerative braking to reverse-phase braking when the vehicle speed is less than or equal to a second vehicle speed which is different from the first vehicle speed.

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