Control device for electric vehicles

Abstract

This optimizes the torque distribution between the front and rear wheels when regenerative braking is performed on the front and rear wheels during braking based on accelerator operation. [Solution] A control device for an electric vehicle, each of which is equipped with brakes 6, 7 and electric motors 3, 5 on the front wheels 2 and rear wheels 4, is configured to determine the required regenerative torque 8a according to the amount of acceleration / deceleration operation during deceleration, determine the torque distribution ratio 8b between the front and rear wheels based on vehicle information including vehicle speed, determine the regenerative torque 8c based on the required regenerative torque, vehicle information and torque distribution ratio, determine the required regenerative value 9c based on the required brake torque and regenerative torque due to braking based on pedal operation, and determine the regenerative torque 8d between the front and rear wheels based on the required regenerative value, required regenerative torque and torque distribution ratio.

Description

Technical Field

[0001] The present invention relates to a control device for an electric vehicle that can be driven by an electric motor such as a motor or a motor-generator, and more particularly to a device for controlling the braking force of an electric vehicle that can be driven by an electric motor having front and rear wheels provided individually in the front and rear, and that can brake the front and rear wheels by a so-called mechanical brake such as a friction brake.

Background Art

[0002] One of the advantages of an electric vehicle is that it can improve energy efficiency and reduce greenhouse gas emissions by performing energy regeneration during deceleration. When performing energy regeneration, in order to make the regeneration efficiency as high as possible, the regeneration amount is controlled, such as increasing the regeneration amount by the wheel with the larger ground load. Along with this, the torque distribution ratio of the front and rear wheels becomes a ratio corresponding to the regeneration amount, which affects the stability of the vehicle behavior. Here, the torque distribution ratio of the front and rear wheels is the ratio of the torque borne by the front wheels and the ratio of the torque borne by the rear wheels among the driving torque and braking torque of the vehicle as a whole.

[0003] An example of a device for controlling the torque distribution ratio between the front and rear wheels is described in Patent Document 1. The control device described in Patent Document 1 is configured to stabilize the vehicle's behavior by reducing the amount of regenerative braking and temporarily reducing the torque distribution ratio of the rear wheels when the vehicle's behavior becomes unstable during regenerative braking on all four wheels. Furthermore, the fastening force of the electromagnetic coupling that sets the torque distribution ratio is adjusted at a timing delayed from the timing of the reduction in the amount of regenerative braking. In other words, the invention described in Patent Document 1 reduces the regenerative braking force with excellent responsiveness when a skid is predicted or detected due to the rear wheels losing grip. In that case, reducing the regenerative braking force may change the torque distribution ratio between the front and rear wheels, potentially reducing the stability of the vehicle's behavior, so it is preferable to maintain the torque distribution ratio between the front and rear wheels. In the invention described in Patent Document 1, the torque distribution ratio between the front and rear wheels is adjusted by an electromagnetic coupling, but if the torque distribution ratio is adjusted by an electromagnetic coupling when changing the regenerative braking force, for example, in a rear-wheel drive-based 4WD, the rear wheel torque may not decrease immediately, and the grip of the rear wheels may weaken, potentially causing the vehicle's behavior to become unstable. Therefore, in the invention described in Patent Document 1, when there is a possibility of skidding or when skidding occurs, the regenerative braking force is controlled first, and then the torque distribution ratio is controlled by the coupling.

[0004] Furthermore, Patent Document 2 describes an invention aimed at improving regenerative braking efficiency without disrupting the front-to-rear torque balance during regenerative braking of the four front and rear wheels. The device described in Patent Document 2 determines the ideal front-to-rear wheel distribution ratio during deceleration when the brake pedal is pressed, corrects this ratio based on power generation efficiency, and then determines the regenerative torque of the front and rear wheels based on the corrected result. More specifically, the device described in Patent Document 2, for example, detects and calculates the vehicle deceleration and calculates the ideal front-to-rear wheel distribution ratio based on this vehicle deceleration. On the other hand, the power generation efficiency of either the front or rear motor changes depending on the regenerative torque, and the regenerative torque with good power generation efficiency does not necessarily coincide with the torque determined by the ideal front-to-rear wheel distribution ratio. Therefore, the invention described in Patent Document 2 corrects the torque determined by the ideal front-to-rear wheel distribution ratio with the torque determined from power generation efficiency, and the resulting correction of the ideal front-to-rear wheel distribution ratio is kept within a predetermined range. In the invention described in Patent Document 2, even if the front-to-rear torque distribution ratio thus obtained deviates from the ideal front-to-rear torque distribution ratio, it is within a predetermined tolerance range. Therefore, the front-to-rear torque balance is not significantly disrupted, and since the torque of either the front or rear is set to improve power generation efficiency, regenerative efficiency can be improved. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-118394 [Patent Document 2] Japanese Patent Publication No. 2004-135471 [Overview of the project] [Problems that the invention aims to solve]

[0006] The device described in Patent Document 1 is a device that changes the torque distribution ratio between the front and rear wheels during so-called regenerative braking in accordance with the vehicle's behavior, such as skidding. Therefore, if skidding is not detected or predicted, the torque distribution ratio is maintained. Consequently, even if braking is performed by pressing the accelerator pedal or brake pedal, the torque distribution ratio is maintained as long as there is no change in behavior such as skidding, so the torque distribution ratio may not necessarily be suitable for the torque state, such as driving or braking.

[0007] Furthermore, the device described in Patent Document 2 corrects the ideal front-to-rear wheel distribution ratio when deceleration is requested by pressing the brake pedal, within an acceptable range, based on the power generation efficiency of either the front or rear motor, to determine the front and rear regenerative braking torque. However, braking requests are also generated when the accelerator pedal is released while the vehicle is in motion, but the invention described in Patent Document 2 is not configured to determine the front and rear regenerative braking torque based on braking requests based on accelerator operation. Therefore, there is still room for improvement in optimizing the front and rear torque distribution during deceleration or braking.

[0008] This invention has been made in view of the above technical problems, and aims to provide a control device for an electric vehicle that can optimize the torque distribution between the front and rear wheels when regenerative braking is performed on the front and rear wheels during braking based on accelerator operation. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a control device for an electric vehicle, each of which is provided with a brake operated by pedal operation and an electric motor that generates driving force and braking force in response to acceleration and deceleration operations, wherein the control device is configured to determine the required regenerative torque according to the amount of acceleration and deceleration operation during deceleration of the electric vehicle, to determine the torque distribution ratio between the front wheel and the rear wheel based on vehicle information including the vehicle speed of the electric vehicle, to determine the regenerative torque that can be regenerated based on the required regenerative torque, the vehicle information and the torque distribution ratio, to determine the required regenerative value based on the required brake torque from the brakes based on pedal operation and the regenerative torque that can be regenerated, and to determine the regenerative torque between the front wheel and the rear wheel based on the required regenerative value, the required regenerative torque and the torque distribution ratio.

[0010] In the present invention, upper and lower limit values ​​are set in advance for the torque distribution ratio, and if the torque distribution ratio between the front wheels and the rear wheels, determined based on vehicle information including the vehicle speed of the electric vehicle, exceeds either of the upper or lower limit values, the regenerative torque may be determined based on the limit value of the torque distribution ratio, the requested regenerative torque, and the vehicle information. [Effects of the Invention]

[0011] According to the present invention, the regenerative torque that can be regenerated is determined from the required regenerative torque corresponding to the amount of acceleration / deceleration operation during deceleration. Based on this regenerative torque that can be regenerated and the required brake torque based on the brake operation, the required regenerative value that should be generated by energy regeneration is determined. At the same time, based on this required regenerative value, the required regenerative torque, and the torque distribution ratio, the regenerative torque that should be performed on the front and rear wheels is determined. Therefore, it becomes possible to perform regenerative braking that reflects the amount of acceleration / deceleration operation, such as the amount of accelerator pedal operation during deceleration, and since the regenerative torque on the front and rear wheels is based on the torque distribution ratio, efficient energy regeneration can be performed while ensuring the stability of the electric vehicle's behavior. [Brief explanation of the drawing]

[0012] [Figure 1]This is a schematic block diagram showing the drive and braking control systems of an electric vehicle in an embodiment of the present invention. [Figure 2] This is a block diagram showing the functional configuration of a control device in an embodiment of the present invention. [Figure 3] This is a flowchart illustrating an example of control performed in an embodiment of the present invention. [Modes for carrying out the invention]

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

[0014] The electric vehicle targeted by this invention is a vehicle that can be driven and braked by electric motors and brakes provided corresponding to the front and rear wheels, respectively. An example of this is schematically shown in Figure 1. The electric vehicle 1 shown here is a so-called electric vehicle (BEV), and is equipped with electric motors 3 that drive the left and right front wheels 2 and also perform regenerative braking, and electric motors 5 that drive the left and right rear wheels 4 and also perform regenerative braking as driving force sources. These electric motors 3 and 5 are electric motors with power generation functions, such as permanent magnet synchronous motors, and rotate to output torque by receiving power from a power storage device via an inverter (not shown), etc., and also function as a generator when forcibly rotated by an external force. The reaction force when functioning as a generator becomes the regenerative braking force. The generated power is basically charged into a power storage device. Hereinafter, the electric motor 3 on the front wheel 2 side will be called "front MG3", and the electric motor 5 on the rear wheel 4 side will be called "rear MG5".

[0015] Furthermore, brakes 6 are provided on the left and right front wheels 2, and similarly, brakes 7 are provided on the left and right rear wheels 4. These brakes 6 and 7 are so-called mechanical brakes that generate braking torque by friction, and one example is a hydraulic brake that operates using hydraulic pressure.

[0016] A powertrain ECU8 is provided as a controller for the front MG3 and rear MG5 mentioned above. In addition, a brake ECU9 is provided as a controller for the brakes 6 and 7. These powertrain ECU8 and brake ECU9 are electronic control devices mainly composed of a computer consisting of a processing element (CPU), memory elements (RAM, ROM), and various interfaces. They are configured to perform calculations according to a predetermined program using input data and pre-stored data, and to output the results of these calculations as control command signals.

[0017] The powertrain ECU8 is configured to control the rotational speed and torque of the front MG3 and rear MG5 via a control unit consisting of the inverter and a converter (not shown) mentioned above. Examples of data input to the powertrain ECU8 for this control include the amount (angle) of depression of the accelerator pedal 10, and vehicle information such as vehicle speed, acceleration / deceleration, and tire slip ratio. Depression and release of the accelerator pedal 10 constitute the acceleration / deceleration operation in the embodiment described here, and the amount (angle) of depression is the amount of acceleration / deceleration operation. In addition, data pre-stored in the powertrain ECU8 includes, for example, a map that defines the front and rear wheel torque distribution ratio according to the vehicle information.

[0018] Furthermore, the brake ECU 9 is configured to output command signals to a brake hydraulic control circuit (not shown) to control the hydraulic pressure, i.e., braking force, of each brake 6 and 7. The data input to the brake ECU 9 for this control includes the force or angle of the brake pedal 11, and the wheel speeds of the front wheels 2 and rear wheels 4. These powertrain ECU 8 and brake ECU 9 are connected via CAN (Controller Area Network) or similar to allow them to exchange data with each other.

[0019] The control device in the embodiment of the present invention is mainly composed of the above-mentioned power train ECU 8 and brake ECU 9. The power train ECU 8 and the brake ECU 9 cooperate to control the brake torque and regenerative braking torque of the front wheels 2 and the rear wheels 4. The control is performed by using various data as described above to perform calculations and output command signals. An example of various functions thereof is shown in FIG. 2 as follows.

[0020] First, the power train ECU 8 includes a required regenerative torque calculation unit 8a which is a functional configuration for obtaining the required regenerative torque to be generated by energy regeneration. Since the regenerative torque generated by the accelerator operation affects the deceleration or braking performance and energy efficiency of the electric vehicle 1, a preferable required regenerative torque is determined in advance according to vehicle information including the operation amount of the accelerator pedal 10 and the vehicle speed, and the required regenerative torque can be obtained based on the input acceleration / deceleration operation amount and the vehicle information at that time.

[0021] When the electric vehicle 1 is decelerated, it is preferable to assign the regenerative torque for deceleration to the wheels with a large ground load or a small slip ratio, and this improves the energy regeneration efficiency. Therefore, a torque distribution ratio calculation unit 8b which is a functional configuration for obtaining the torque distribution ratio between the front and rear wheels based on vehicle information such as the load and deceleration applied to the front wheels 2 and the rear wheels 4 is provided in the power train ECU 8.

[0022] When the electric vehicle 1 is decelerated, the regenerative torque generated in the electric vehicle 1 may be limited depending on the driving state such as the vehicle speed, deceleration, or road surface condition. The power train ECU 8 includes a regenerative torque calculation unit 8c as a functional configuration for obtaining the regenerative torque. The regenerative torque is calculated based on the required regenerative torque based on the above-mentioned acceleration / deceleration operation amount, vehicle information, and torque distribution ratio. The calculation may be performed based on an arithmetic expression including the required regenerative torque, vehicle information such as the vehicle speed or deceleration, and the torque distribution ratio as coefficients, or a map prepared in advance.

[0023] Furthermore, the power train ECU 8 includes a front and rear regeneration torque calculation unit 8d as a functional configuration for obtaining regeneration torque at the front wheels 2 and the rear wheels 4. This front and rear regeneration torque calculation unit 8d mediates the above-mentioned required regeneration torque and a regeneration request value, which will be described later and is transmitted from the brake ECU 9, and distributes the regeneration torque as a result of the mediation to the front and rear wheels based on the above torque distribution ratio, thereby calculating the regeneration torque at the front wheels 2 and the rear wheels 4. The power train ECU 8 outputs the regeneration torque as a result of such mediation as a control command value to the front MG3 and the rear MG5.

[0024] On the other hand, the brake ECU 9 has a function of calculating a required brake torque based on a brake operation amount such as the depression force or the depression amount of the brake pedal 11, or in addition to this, based on the wheel speed, and further includes a regeneration cooperative control unit 9a that mediates the required brake torque and the regenerable torque transmitted from the power train ECU 8 to obtain a regeneration request value. The regeneration request value is a control amount corresponding to the torque borne by energy regeneration among the required brake torque, and thus can be obtained based on the required brake torque and the regenerable torque, and also includes the regenerative braking torque at the front wheels 2 and the regeneration torque at the rear wheels 4. The torque obtained by excluding the torque corresponding to the regeneration request value from the required brake torque becomes the brake torque to be generated by the brakes 6, 7, and the brake ECU 9 outputs a control command (for example, a hydraulic pressure command) corresponding to the brake torque.

[0025] An example of the control of the present invention will be explained using the control device described above as an example. Figure 3 is a flowchart illustrating this control example, and the control shown here is repeatedly executed at predetermined short intervals by the powertrain ECU 8 and brake ECU 9 described above when the electric vehicle 1 is running or in motion. First, in step S1, various vehicle information is read. The vehicle information to be read includes information indicating the driving status of the electric vehicle 1, such as vehicle speed, wheel speed, rotational speed of the front MG3 and rear MG5, acceleration and deceleration operation amounts such as the amount the accelerator pedal 10 is pressed down and the force or amount the brake pedal 11 is pressed down, and information indicating the overall status of the electric vehicle 1 including its power unit, such as the remaining charge (SOC) of the energy storage device (not shown), the maximum allowable torque of the front MG3 and rear MG5, and the maximum possible torque or maximum power of the system as a whole.

[0026] Based on the information read, the required regenerative torque corresponding to the acceleration / deceleration operation amount, such as the amount the accelerator pedal 10 is pressed, is calculated in step S2. This is the function of the required regenerative torque calculation unit 8a described above.

[0027] On the other hand, in step S3, the torque distribution ratio, which is the ratio of regenerative torque to be handled by the front wheels 2 and the rear wheels 4, is determined based on the information read. This is the function of the torque distribution ratio calculation unit 8b mentioned above.

[0028] Since the torque distribution ratio is known, the regenerative torque available based on acceleration and deceleration operations is calculated in step S4 based on that torque distribution ratio, vehicle information, and the requested regenerative torque. This is the function of the regenerative torque calculation unit 8c mentioned above.

[0029] In the embodiment of the present invention, the control device coordinates regenerative braking based on acceleration and deceleration operations such as the amount the accelerator pedal 10 is pressed, and braking based on deceleration operations such as pressing the brake pedal 11, and distributes the regenerative torque resulting from the mediation of these braking forces between the front wheels 2 and the rear wheels 4. That is, the regenerative torque resulting from the mediation is distributed to the front wheels 2 and the rear wheels 4 according to the torque distribution ratio, but if the torque distribution ratio is excessive or inappropriate, the vehicle's behavior may become unstable. To avoid such a situation, a predetermined range for the torque distribution ratio is set in advance. In step S5, it is determined whether the torque distribution ratio calculated in step S3 falls within the predetermined range, that is, whether it exceeds either the upper or lower limit. If the result of the determination in step S5 is "yes", the torque distribution ratio calculated in step S3 is adopted. Conversely, if the result of the determination in step S5 is "no", in step S6, the torque distribution ratio is guarded at the upper or lower limit of the predetermined range. In other words, if the value exceeds the upper limit, the torque distribution ratio determined by the upper limit is adopted; if it falls below the lower limit, the torque distribution ratio determined by the lower limit is adopted.

[0030] In step S7, the regenerative torque resulting from the aforementioned arbitration is distributed to the front 2 wheels and rear 4 wheels according to the torque distribution ratio adopted. Then, in step S8, the command value for generating the distributed regenerative torque is determined, and in step S9, that command value is output, and the routine shown in Figure 3 is temporarily terminated.

[0031] According to the control shown in Figure 3 above, regenerative braking is performed that reflects acceleration and deceleration operations, such as the amount of accelerator pedal operation during deceleration, so energy regeneration during deceleration of the electric vehicle 1 can be performed efficiently. Furthermore, when braking operations are performed, such as when the brake pedal 11 is pressed, the braking torque based on the brake operation and the braking torque based on the acceleration and deceleration operations are arbitrated to determine the respective braking torques, so that braking or deceleration can be performed without excess or deficiency. Moreover, the regenerative torque required for the electric vehicle 1 is allocated to the front wheels 2 and rear wheels 4 based on vehicle information including the driving state of the electric vehicle 1, so the behavior of the electric vehicle 1 during deceleration can be stabilized. In particular, a predetermined range is set for the distribution ratio of regenerative torque to the front wheels 2 and rear wheels 4, which is defined by upper and lower limit values, and the torque distribution ratio is limited to that range, so the distribution of regenerative torque during deceleration is optimized and the behavior of the electric vehicle 1 can be stabilized.

[0032] It should be noted that the present invention is not limited to the embodiments described above. The electric vehicle in the present invention may be one in which an electric motor and brakes are provided for both the front and rear wheels, and therefore may be an electric vehicle configured to independently drive and brake each of the four front and rear wheels. Furthermore, the brakes are not limited to hydraulic brakes, but may be any brake that generates braking force according to the amount of operation. Moreover, the control device according to the present invention may be configured as an electronic control device mainly consisting of a single computer, instead of being composed of the powertrain ECU and brake ECU described above. [Explanation of Symbols]

[0033] 1. Electric Vehicle 2 Front wheels 3. Electric motor (front MG) 4 Rear wheels 5. Electric motor (rear MG) 6,7 Brake 8 Powertrain ECU 8a Required regenerative torque calculation unit 8b Torque distribution ratio calculation unit 8c Regenerative Torque Calculation Unit 8d Front and rear regenerative torque calculation unit 9 Brake ECU 9a Regenerative Coordination Control Unit 10. Accelerator pedal 11 Brake pedal

Claims

1. A control device for an electric vehicle, in which brakes operated by pedal operation and electric motors that generate driving force and braking force in response to acceleration and deceleration operations are provided on each of the front and rear wheels, The required regenerative torque is determined according to the amount of acceleration / deceleration operation during deceleration of the electric vehicle. Based on vehicle information including the vehicle speed of the electric vehicle, the torque distribution ratio between the front wheels and the rear wheels is determined. Based on the requested regenerative torque, the vehicle information, and the torque distribution ratio, the regenerative torque is determined. Based on the brake torque required by the brake based on the operation of the pedal and the regenerative torque, the regenerative request value is determined. The system is configured to determine the regenerative torque for the front wheel and the rear wheel based on the regenerative request value, the requested regenerative torque, and the torque distribution ratio. A control device for electric vehicles characterized by the following features.

2. A control device for an electric vehicle according to claim 1, Upper and lower limit values ​​are set in advance for the torque distribution ratio. If the torque distribution ratio between the front and rear wheels, determined based on vehicle information including the vehicle speed of the electric vehicle, exceeds either of the upper or lower limit values, the regenerative torque is determined based on the limit value of the torque distribution ratio, the requested regenerative torque, and the vehicle information. A control device for electric vehicles characterized by the following features.

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