Control device for an electric vehicle

Abstract

The present invention is to optimize the front-rear torque distribution when regenerative braking is performed on the front and rear wheels at the time of braking based on accelerator operation. The present invention provides a control device for an electric vehicle in which a brake and an electric motor are provided for each of front and rear wheels, the control device being configured to perform the following processes: calculating a requested regenerative torque corresponding to an operation amount of an acceleration / deceleration operation at the time of deceleration; calculating a torque distribution ratio of the front and rear wheels based on vehicle information including a vehicle speed; calculating a regenerative torque available based on the requested regenerative torque, the vehicle information, and the torque distribution ratio; calculating a regenerative request value based on a requested brake torque generated by the brake based on pedal operation and the regenerative torque available; and calculating a regenerative torque of the front and rear wheels based on the regenerative request value, the requested regenerative torque, and the torque distribution ratio.

Description

Technical Field

[0001] This invention relates to a control device for an electric vehicle capable of operating by an electric motor or a motor / generator, and more particularly to a device for controlling the braking force of an electric vehicle that is capable of driving the front and rear wheels by separate electric motors located at the front and rear, and of braking the front and rear wheels by so-called mechanical brakes such as friction brakes. Background Technology

[0002] One of the advantages of electric vehicles is their ability to regenerate energy during deceleration, thereby improving energy efficiency and reducing greenhouse gas emissions. When regenerating energy, the amount of regeneration is controlled to maximize efficiency, for example, by increasing the amount of regeneration from wheels with high ground load. However, this control results in a torque distribution ratio between the front and rear wheels that corresponds to the amount of regeneration, which can affect the stability of the vehicle's behavior. Furthermore, the torque distribution ratio between the front and rear wheels refers to the proportion of the overall driving or braking torque of the vehicle that is borne by the front wheels and the proportion that is borne by the rear wheels.

[0003] Patent Document 1 describes an example of a device for controlling the torque distribution ratio between the front and rear wheels. The control device described in Patent Document 1 is configured such that, when the vehicle's behavior becomes unstable during regenerative braking of all four wheels, the regenerative braking amount is reduced, and the torque distribution ratio of the rear wheels is temporarily reduced to stabilize the vehicle's behavior. Furthermore, the clamping force of the electromagnetic coupler that sets the torque distribution ratio is adjusted at a time delayed from the moment the regenerative braking amount decreases. That is, the invention described in Patent Document 1 reduces the highly responsive regenerative braking force when it is predicted or detected that the rear wheels are slipping due to loss of traction. In this case, if the regenerative braking force is reduced, the torque distribution ratio between the front and rear wheels changes, and the stability of the vehicle's behavior may decrease; therefore, 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 coupler. However, if the torque distribution ratio adjustment based on the electromagnetic coupler is performed when the regenerative braking force is changed, for example, in a rear-wheel drive-based 4WD system, the rear wheel torque does not immediately decrease, the rear wheel traction weakens, and the vehicle's behavior becomes unstable. Therefore, in the invention described in Patent Document 1, when there is a possibility of lateral slippage or when lateral slippage occurs, the regenerative braking force is controlled first, and then the torque distribution rate based on the coupler is controlled.

[0004] Furthermore, Patent Document 2 describes an invention aimed at improving regenerative efficiency without disrupting the front-rear torque balance during regenerative braking of all four wheels. In the device described in Patent Document 2, the ideal front-rear wheel distribution ratio during deceleration when the brake pedal is depressed is determined, corrected based on the power generation efficiency, and the regenerative torque of the front and rear wheels is determined based on the result of this correction. More specifically, in the device described in Patent Document 2, for example, the vehicle deceleration is detected / calculated, and the ideal front-rear wheel distribution ratio is calculated based on that deceleration. On the other hand, the power generation efficiency of either the front or rear motor varies depending on the regenerative torque, and the regenerative torque with good power generation efficiency may not necessarily match the torque determined by the ideal front-rear wheel distribution ratio. Therefore, in the invention described in Patent Document 2, the torque determined by the ideal front-rear wheel distribution ratio is corrected based on the torque determined by the power generation efficiency, and the resulting correction to the ideal front-rear wheel distribution ratio is set within a predetermined range. In the invention described in Patent Document 2, the front and rear wheel distribution ratio calculated in this way is within a preset allowable range even if it deviates from the ideal front and rear wheel distribution ratio. Therefore, the front and rear torque balance will not be significantly disrupted, and the front and rear torque can be set to improve power generation efficiency, thereby improving regeneration efficiency.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-118394

[0006] Patent Document 2: Japanese Patent Application Publication No. 2004-135471 Summary of the Invention

[0007] 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 based on vehicle behavior such as skidding. Therefore, the torque distribution ratio is maintained as long as skidding is not detected or predicted. Thus, for example, even when braking is performed by the amount of pressure applied to the accelerator pedal or the brake pedal, the torque distribution ratio is maintained as long as there is no change in behavior such as skidding. Therefore, the torque distribution ratio may not necessarily be suitable for the state of driving or braking torque.

[0008] Furthermore, in the device described in Patent Document 2, the ideal front-rear wheel distribution ratio during a deceleration request when the brake pedal is depressed is corrected within an acceptable range based on the power generation efficiency of either the front or rear motor, thereby determining the front-rear regenerative braking torque. However, a braking request is 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-rear regenerative braking torque based on the braking request based on accelerator operation. Therefore, there is room for improvement in optimizing the front-rear torque distribution during deceleration or braking.

[0009] The present invention was made in view of the above-mentioned technical problems, and its purpose is to provide a control device for an electric vehicle that can optimize the front and rear torque distribution when regenerative braking is performed on the front and rear wheels during braking based on throttle operation.

[0010] To achieve the above objectives, the present invention provides a control device for an electric vehicle. The electric vehicle has brakes actuated by pedal operation on both the front and rear wheels, and motors that generate driving and braking forces according to acceleration and deceleration operations. The control device is configured to perform the following processes: determining a requested regenerative torque corresponding to the amount of the acceleration / deceleration operation during deceleration of the electric vehicle; determining a torque distribution ratio between the front and rear wheels based on vehicle information including the vehicle speed; determining a regenerative torque based on the requested regenerative torque, the vehicle information, and the torque distribution ratio; determining a regeneration request value based on the requested braking torque generated by the brakes based on pedal operation and the regenerative torque; and determining the regenerative torque between the front and rear wheels based on the regeneration request value, the requested regenerative torque, and the torque distribution ratio.

[0011] In this invention, upper and lower limits of the torque distribution ratio can be preset. If the torque distribution ratio between the front wheel and the rear wheel, calculated based on vehicle information including the speed of the electric vehicle, exceeds either of the upper or lower limits, the regenerative torque is calculated based on the limit of the torque distribution ratio, the requested regenerative torque, and the vehicle information.

[0012] Invention Effects

[0013] According to the present invention, the regenerative torque is calculated based on the requested regenerative torque corresponding to the amount of acceleration / deceleration operation during deceleration. The regenerative request value to be generated through energy regeneration is calculated based on this regenerative torque and the requested braking torque based on the braking operation. Furthermore, the regenerative torque to be executed on the front and rear wheels is calculated based on this regenerative request value, the requested regenerative torque, and the torque distribution ratio. Therefore, regenerative braking reflecting the amount of acceleration / deceleration operation such as the accelerator pedal operation during deceleration can be performed, and the front and rear regenerative torques become torques based on the torque distribution ratio. Thus, efficient energy regeneration can be achieved while ensuring the stability of the electric vehicle's behavior. Attached Figure Description

[0014] Figure 1 This is a block diagram schematically illustrating the drive and braking control system of an electric vehicle according to an embodiment of the present invention.

[0015] Figure 2 This is a block diagram illustrating the functional structure of the control device in an embodiment of the present invention.

[0016] Figure 3 This is a flowchart illustrating an example of control performed in an embodiment of the present invention. Detailed Implementation

[0017] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the embodiments described below are merely examples of implementing the present invention and do not limit the scope of the invention.

[0018] The electric vehicle targeted in this invention is a vehicle capable of driving and braking the front and rear wheels via correspondingly provided electric motors and brakes. Figure 1 An example is illustrated below. The electric vehicle 1 shown here is a so-called battery electric vehicle (BEV), and it has an electric motor 3 that drives the left and right front wheels 2 and performs regenerative braking, and an electric motor 5 that drives the left and right rear wheels 4 and performs regenerative braking as a driving force source. These electric motors 3 and 5 are permanent magnet synchronous motors or other motors with generator functions. They output torque by rotating when supplied with electricity from an energy storage device via an inverter (not shown), and they function as generators when forced to rotate by an external force. The reaction force when functioning as a generator becomes the regenerative braking force. In addition, the generated electricity is basically charged to the energy storage device. Hereinafter, the electric motor 3 on the front wheel 2 side will be referred to as "front MG3", and the electric motor 5 on the rear wheel 4 side will be referred to as "rear MG5".

[0019] 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 through friction, and as an example, hydraulic brakes that operate by hydraulic pressure.

[0020] A powertrain ECU8 is provided as the controller for controlling the aforementioned front MG3 and rear MG5. Furthermore, a brake ECU9 is provided as the controller for controlling each of the brakes 6 and 7. These powertrain ECU8 and brake ECU9 are electronic control devices primarily composed of a computer consisting of a processing unit (CPU), storage units (RAM, ROM), and various interfaces. They are configured to use input data and pre-stored data to perform calculations according to a prescribed program, and output the results of these calculations as control command signals.

[0021] The powertrain ECU8 is configured to control the speed or torque of the front MG3 and rear MG5 via a control unit consisting of the aforementioned inverter or a converter (not shown). Examples of data input to the powertrain ECU8 for this control include vehicle information such as the amount of pressure applied to the accelerator pedal 10 (aperture angle), vehicle speed, acceleration / deceleration, or tire slip ratio. The application and release of the accelerator pedal 10 constitutes acceleration / deceleration operations in the embodiment described herein, and the amount of pressure applied (aperture angle) represents the acceleration / deceleration operation. Furthermore, examples of data pre-stored in the powertrain ECU8 include a mapping table that determines the front-to-rear wheel torque distribution ratio based on vehicle information.

[0022] Furthermore, the brake ECU9 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 ECU9 for this control includes the pedal force or angle of the brake pedal 11, the wheel speed of the front wheel 2 or the rear wheel 4, etc. These power system ECUs 8 and brake ECU9 are then connected via a Controller Area Network (CAN) or similar means to enable them to send and receive data.

[0023] In embodiments of the present invention, the control device is primarily composed of the aforementioned power system ECU8 and brake ECU9. These power system ECU8 and brake ECU9 operate in coordination, thereby controlling the braking torque or regenerative braking torque of the front wheels 2 and rear wheels 4. As described above, this control is performed by calculating various data and outputting command signals. However, if one example of these various functions is shown as a configuration, then... Figure 2 As shown.

[0024] First, the powertrain ECU 8 has a functional structure, namely the requested regenerative torque calculation unit 8a, which calculates the requested regenerative torque to be generated through energy regeneration. The regenerative torque generated by throttle operation affects the deceleration or braking performance and energy efficiency of the electric vehicle 1. Therefore, the preferred requested regenerative torque is determined in advance based on vehicle information including the amount of operation of the accelerator pedal 10 or the vehicle speed, and the requested regenerative torque can be calculated based on the input acceleration / deceleration operation amount and the vehicle information at that time.

[0025] In the case of a decelerating electric vehicle 1, it is preferable to have the wheels with large ground loads or small slip ratios bear the regenerative torque used for deceleration, and by doing so, the energy regeneration efficiency is improved. Therefore, a functional structure, namely a torque distribution ratio calculation unit 8b, is provided in the powertrain ECU 8 to calculate the torque distribution ratio between the front and rear wheels based on vehicle information such as the load or deceleration applied to the front wheels 2 and the rear wheels 4.

[0026] When the electric vehicle 1 decelerates, the regenerative torque generated in the electric vehicle 1 is sometimes limited depending on the driving conditions, such as vehicle speed or deceleration and road surface conditions. The powertrain ECU 8 has a regenerative torque calculation unit 8c as a functional structure for calculating the regenerative torque. The regenerative torque is calculated based on the requested regenerative torque based on the aforementioned acceleration / deceleration operation amount, vehicle information, and torque distribution ratio. This calculation can be performed using a formula that includes the requested regenerative torque, vehicle information such as vehicle speed or deceleration, and torque distribution ratio as coefficients, or a pre-prepared mapping table.

[0027] Furthermore, the powertrain ECU8 includes a front and rear regenerative torque calculation unit 8d, which is a functional structure for calculating the regenerative torque on the front wheel 2 and the rear wheel 4. This front and rear regenerative torque calculation unit 8d coordinates the requested regenerative torque and the regenerative request value (described later) transmitted from the brake ECU9, and distributes the regenerative torque as a result of this coordination to the front and rear wheels according to the torque distribution ratio, thereby calculating the regenerative torque on the front wheel 2 and the rear wheel 4. The powertrain ECU8 outputs the regenerative torque as a result of this coordination as a control command value to the front MG3 and the rear MG5.

[0028] On the other hand, the brake ECU9 has the function of calculating the requested braking torque based on braking operation quantities such as pedal force or depress amount of brake pedal 11, or based on wheel speed in addition to these. Furthermore, it has a regeneration coordination control unit 9a that coordinates the requested braking torque with the regenerative torque transmitted from the power system ECU8 to determine the regeneration request value. The regeneration request value is a control quantity in the requested braking torque equivalent to the torque undertaken through energy regeneration, and therefore can be determined based on the requested braking torque and the regenerative torque, including the regenerative braking torque on the front wheel 2 and the regenerative torque on the rear wheel 4. The torque from the requested braking torque minus the torque equivalent to the regeneration request value becomes the braking torque to be generated by the brakes 6 and 7, and the brake ECU9 outputs a control command (e.g., a hydraulic command) equivalent to this braking torque.

[0029] An example of the control of the present invention being performed by the aforementioned control device will be described. Figure 3This is a flowchart illustrating the control example. When the electric vehicle 1 is in the starting state or in motion, the control shown here is repeatedly executed at predetermined short intervals by the aforementioned power system ECU8 and brake ECU9. First, in step S1, various vehicle information is read. The read vehicle information 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, the amount of acceleration or deceleration operation indicated by the accelerator pedal 10 or the braking pedal 11, as well as information indicating the overall status of the power units including the electric vehicle 1, such as the maximum possible torque or maximum power of the system as a whole. This information includes the remaining charge (SOC) of the energy storage device (not shown) and the maximum allowable torque of the front MG3 and rear MG5.

[0030] Based on the information read, in step S2, the requested regenerative torque corresponding to the acceleration / deceleration operation amount, such as the amount of pressure applied to the accelerator pedal 10, is calculated. This is the function of the aforementioned requested regenerative torque calculation unit 8a.

[0031] On the other hand, in step S3, based on the information read, a torque distribution ratio is calculated as the proportion of the regenerative torque that should be borne by the front wheel 2 and the rear wheel 4. This is the function of the aforementioned torque distribution ratio calculation unit 8b.

[0032] By determining the torque distribution ratio, and based on that torque distribution ratio, vehicle information, and the requested regenerated torque, the regenerated torque based on acceleration and deceleration operations is calculated in step S4. This is the function of the aforementioned regenerated torque calculation unit 8c.

[0033] In embodiments of the present invention, the control device coordinately performs regenerative braking based on acceleration and deceleration operations such as the amount of accelerator pedal 10 being depressed, and braking based on deceleration operations such as the amount of brake pedal 11 being depressed. The regenerative torque, as a result of coordinating these braking forces, is shared and borne by the front wheels 2 and the rear wheels 4. That is, the regenerative torque, as a result of coordination, is distributed to the front wheels 2 and the rear wheels 4 according to a torque distribution ratio. However, if the torque distribution ratio is too large or inappropriate, the vehicle's behavior may become unstable. To avoid this, a predetermined range for the torque distribution ratio is defined. In step S5, it is determined whether the torque distribution ratio calculated in step S3 is within the predetermined range, i.e., whether it exceeds either the upper or lower limit. If the determination result of step S5 is "yes," the torque distribution ratio calculated in step S3 is adopted. Conversely, if the determination result of step S5 is "no," the torque distribution ratio is limited to the upper or lower limits of the predetermined range in step S6. That is, if the torque distribution ratio exceeds the upper limit, the torque distribution ratio determined by the upper limit will be used; if the torque distribution ratio is below the lower limit, the torque distribution ratio determined by the lower limit will be used.

[0034] In step S7, based on the torque distribution ratio thus adopted, the regenerative torque, as a result of the aforementioned coordination, is distributed to the front wheel 2 and the rear wheel 4. Then, in step S8, the command value for generating the distributed regenerative torque is calculated, and in step S9, the command value is output, temporarily ending the process. Figure 3 The routine shown.

[0035] According to the above Figure 3 The control shown performs regenerative braking that reflects acceleration / deceleration operations such as the amount of accelerator pedal operation during deceleration, thus effectively regenerating energy during the deceleration of the electric vehicle 1. Furthermore, when braking operations such as depressing the brake pedal 11 are performed, the braking torque based on the braking operation and the braking torque based on acceleration / deceleration operations are coordinated to determine each braking torque, thus enabling braking or deceleration without over- or under-braking. Moreover, the regenerative torque requested by the electric vehicle 1 is distributed to the front wheels 2 and rear wheels 4 based on vehicle information including the driving state of the electric vehicle 1, thus stabilizing the behavior of the electric vehicle 1 during deceleration. In particular, a predetermined range defined by upper and lower limits is set in the distribution ratio of regenerative torque to the front wheels 2 and rear wheels 4, and the torque distribution ratio is limited within this range, thus appropriately distributing the regenerative torque during deceleration and stabilizing the behavior of the electric vehicle 1.

[0036] Furthermore, the present invention is not limited to the above-described embodiments. The electric vehicle of the present invention can be configured to independently drive and brake each of its front and rear wheels, as long as each wheel has an electric motor and a brake. Moreover, the brake is not limited to a hydraulic brake; any brake that generates braking force based on the amount of operation is acceptable. Furthermore, the control device involved in the present invention can be configured as an electronic control device based on a single computer, replacing the aforementioned power system ECU and brake ECU.

[0037] Symbol Explanation

[0038] 1-Electric vehicle, 2-Front wheel, 3-Electric motor (front MG), 4-Rear wheel, 5-Electric motor (rear MG), 6, 7-Brake, 8-Powertrain ECU, 8a-Request 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, wherein the electric vehicle is equipped with brakes actuated by pedal operation on both the front and rear wheels, and an electric motor that generates driving force and braking force according to acceleration and deceleration operations, the control device for the electric vehicle being characterized in that... The control device for the electric vehicle is configured to perform the following processing: Calculate the requested regenerative torque corresponding to the amount of the acceleration / deceleration operation during the deceleration of the electric vehicle; The torque distribution ratio between the front wheels and the rear wheels is determined based on vehicle information including the speed of the electric vehicle. The regenerative torque is calculated based on the requested regenerative torque, the vehicle information, and the torque distribution ratio. The regeneration request value is calculated based on the requested braking torque generated by the brake based on the operation of the pedal and the regenerable torque; and The regeneration torques of the front and rear wheels are calculated based on the regeneration request value, the requested regeneration torque, and the torque distribution ratio.

2. The control device for an electric vehicle according to claim 1, characterized in that, The upper and lower limits of the torque distribution ratio are preset. If the torque distribution ratio between the front wheel and the rear wheel, calculated 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 calculated based on the limit value of the torque distribution ratio, the requested regenerative torque, and the vehicle information.

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