Driving force control device for electric vehicle

Abstract

To provide a driving force control device for an electric vehicle that is able to control a creep driving force during traveling on an off-road.SOLUTION: If a required driving force according to an amount of operation of an accelerator device is larger than a first creep driving force continuously for a predetermined time or more when a vehicle is traveling on an off-road at a vehicle speed equal to or lower than a predetermined vehicle speed (Yes in step S4), a required driving force in a case where the accelerator device is not operated is switched to a second creep driving force smaller than the first creep driving force (step S5).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a driving force control device for an electric vehicle equipped with an electric motor as a driving force source, and more particularly to a device for controlling creep driving force when the accelerator pedal is not being operated. [Background technology]

[0002] Patent Document 1 describes a vehicle control device that generates a driving force when the depression amount of the accelerator pedal is equal to or greater than a predetermined amount, and generates a braking force when the depression amount of the accelerator pedal is less than the predetermined amount, thereby controlling the driving force and the braking force by a so-called one-pedal operation. In order to suppress the discomfort felt by a driver who is not used to a vehicle in which the driving force and the braking force are controlled by one-pedal operation, this control device is configured to increase the braking force when the accelerator is released when the number of times the brake pedal is depressed becomes equal to or greater than a predetermined number while the vehicle is decelerating by one-pedal operation, and to decrease the braking force when the accelerator is released when the number of times the accelerator pedal is depressed again becomes equal to or greater than a predetermined number. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-155157 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, so-called conventional vehicles equipped with an engine as a driving force source are configured to generate a creep driving force when the accelerator pedal operation amount is set to zero (accelerator off) when the vehicle is stopped or traveling at a very low vehicle speed. Therefore, like conventional vehicles, conventional electric vehicles equipped with an electric motor as a driving force source are also configured to generate a driving force equivalent to the creep driving force when the accelerator pedal operation amount is set to zero when the vehicle is stopped or traveling at a very low vehicle speed. However, since the creep driving force when the accelerator is off is set uniformly depending on the vehicle speed, there is room for technical improvement to generate an appropriate driving force depending on the traveling situation.

[0005] The present invention has been made in light of the above technical problems, and has an object to provide a driving force control device for an electric vehicle that is capable of controlling creep driving force during off-road driving. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides a driving force control device for an electric vehicle which includes an electric motor as a driving force source and an accelerator device operated by a driver, and which sets the required driving force when the accelerator device is not operated at a predetermined vehicle speed or below a predetermined vehicle speed to a predetermined first creep driving force, and which includes a controller for controlling the electric motor, and which is characterized in that when the required driving force corresponding to the operation amount of the accelerator device is greater than the first creep driving force for a predetermined period of time or more when traveling off-road at a vehicle speed or below the predetermined vehicle speed, the controller switches the required driving force after the accelerator device is no longer operated to a second creep driving force which is smaller than the first creep driving force. Effect of the Invention

[0007] The driving force control device for an electric vehicle in this invention switches the required driving force after the accelerator device is no longer operated to a second creep driving force smaller than the first creep driving force when a driving force larger than a first creep driving force is continuously required for a predetermined time or more while traveling off-road at a low vehicle speed. Therefore, it is possible to prevent the driving force from becoming excessive during the transitional period of switching operation when, for example, a large driving force is output and the operation amount of the accelerator device is reduced to operate the brake device in order to stop or decelerate after going over a large rock. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1A is a diagram showing a state in which an electric vehicle is traveling on a road with small unevenness, and FIG. 1B is a diagram showing a state in which the electric vehicle is running over a rock. [Diagram 2] 3 is a flowchart illustrating an example of control executed by a driving force control device according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a diagram showing an example of a map for determining a first creep driving force and a second creep driving force. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the accompanying drawings. Note that the embodiment described below is merely an example of the implementation of the present invention, and is not intended to limit the present invention.

[0010] The electric vehicle according to the embodiment of the present invention includes an electric motor as a driving force source. This electric motor can be configured in the same manner as an electric motor provided as a driving force source for a conventional electric vehicle or hybrid vehicle. That is, in addition to functioning as a motor that outputs driving torque when power is supplied from an electricity storage device, the electric motor also functions as a generator that converts at least a part of the motive power into electric power when the output shaft is rotated. As such an electric motor, a synchronous motor having a permanent magnet provided on the rotor can be used.

[0011] The electric vehicle may be a two-wheel drive vehicle in which one electric motor is connected to a pair of front wheels or a pair of rear wheels, a four-wheel drive vehicle in which one electric motor is connected to all wheels, or an in-wheel motor vehicle in which an electric motor is provided on each wheel.

[0012] An electric vehicle is provided with an accelerator pedal which the driver depresses when requesting driving, and a brake pedal which the driver depresses when requesting braking.The electric vehicle is also provided with an electronic control unit (hereinafter, referred to as ECU) which determines the torque required of the electric motor (required torque) in accordance with the pedal operation.The accelerator pedal corresponds to the "accelerator device" in the embodiment of the present invention, and the ECU corresponds to the "controller" in the embodiment of the present invention.

[0013] The ECU can be configured in the same manner as an ECU installed in a conventional vehicle, i.e., it is mainly configured with a microcomputer, and is configured to calculate the required torque of the electric motor based on signals input from various sensors installed in the electric vehicle and pre-stored maps and arithmetic expressions, and to output a signal corresponding to the required torque to a power control unit such as an inverter connected to the electric motor.

[0014] The signals input to the ECU are, for example, a signal from an accelerator opening sensor that detects the amount of depression (operation amount) of the accelerator pedal, a signal from a brake sensor that detects the amount of depression or pressure of the brake pedal, a signal from a vehicle speed sensor that detects the vehicle speed of the electric vehicle, etc. The electric vehicle of the present invention is also configured to be able to select drive characteristics (driving modes) such as the magnitude of drive torque relative to the amount of accelerator operation, the rate of change of drive force or braking force, or, in the case of a four-wheel drive vehicle, the ratio of torque transmitted to the front and rear wheels (front / rear distribution ratio).

[0015] Specifically, the vehicle is configured to be able to set at least a driving characteristic (off-road mode) suitable for off-road driving. A mode switch signal for the driver to select such a driving mode is input to the ECU. The driving mode selected by the mode switch may include an auto mode that determines the condition of the road based on the on-board camera and map information, and automatically sets the driving mode according to the condition of the road.

[0016] The ECU is configured to be able to change the required driving force (creep driving force) when the accelerator pedal is not operated according to the driving conditions. Specifically, the ECU is configured to change the creep driving force when the electric vehicle Ve runs on a road with relatively small unevenness as shown in Fig. 1(a) from the creep driving force after the electric vehicle Ve has gone over a large rock as shown in Fig. 1(b).

[0017] A flow chart for explaining an example of this control is shown in Fig. 2. In the control example shown in Fig. 2, first, it is determined whether or not the off-road mode is selected (step S1). This step S1 can be determined based on a signal input from a mode switch to the ECU. Note that step S1 is a step for determining whether or not the driving environment requires going over a relatively large step, and it may also be determined whether or not the shift position is a low range position that outputs a relatively large driving force.

[0018] If the off-road mode is not selected and therefore the answer is negative in step S1, this routine is temporarily terminated. On the other hand, if the off-road mode is selected and therefore the answer is positive in step S1, then it is determined whether the vehicle speed is equal to or lower than a predetermined vehicle speed (step S2). The predetermined vehicle speed in step S2 can be set to a predetermined upper limit vehicle speed within a range in which a creep driving force is generated.

[0019] If the vehicle speed is higher than the predetermined vehicle speed and the result of the negative determination in step S2 is negative, this routine is temporarily terminated. On the other hand, if the vehicle speed is equal to or lower than the predetermined vehicle speed and the result of the positive determination in step S2 is negative, the duration during which a driving force greater than the first creep driving force F1 is required is counted (step S3), and it is determined whether the duration is equal to or longer than a predetermined time (step S4). These steps S3 and S4 are steps for determining whether the vehicle is traveling on a road on which the creep driving force cannot be used for driving, such as when a relatively large rock is being driven over. Therefore, the predetermined time can be set to a time that allows the determination of whether the accelerator pedal is being depressed to drive over a rock or the like. The first creep driving force F1 is a required driving force that is set when the normal mode is selected and the accelerator is not operated, or when the vehicle is traveling on a flat road without the accelerator being operated, and is determined based on the map shown in FIG. 3.

[0020] The map shown in Fig. 3 is for setting the creep driving force (vertical axis) according to the vehicle speed (horizontal axis), and the first creep driving force F1 is shown by a solid line. That is, the first creep driving force F1 is set to become smaller as the vehicle speed increases. Note that Ff in Fig. 3 indicates the rolling resistance (running resistance) of the electric vehicle Ve, and the vehicle speed V1 at which the rolling resistance Ff and the first creep driving force F1 intersect corresponds to the predetermined vehicle speed in step S2.

[0021] If the duration during which a driving force greater than the first creep driving force F1 is requested is less than the predetermined time and the answer to step S4 is negative, the routine is temporarily terminated. On the other hand, if the duration during which a driving force greater than the first creep driving force F1 is requested is equal to or greater than the predetermined time and the answer to step S4 is positive, the creep driving force is switched to the second creep driving force F2 (step S5).

[0022] This second creep driving force F2 is determined based on a map shown by a dashed line in Fig. 3. That is, the second creep driving force F2 is determined based on a signal input from the vehicle speed sensor to the ECU. This second creep driving force F2 is set to be smaller than the first creep driving force F1 as shown in Fig. 3. Also, when the vehicle is stopped and at a predetermined vehicle speed V1, the first creep driving force F1 and the second creep driving force F2 are determined to be the same magnitude. Note that in Fig. 3, the creep driving force Fc generated in a conventional vehicle equipped with an engine as a driving force source is shown by a dashed line.

[0023] Next, the duration during which a braking force greater than the first creep driving force F1 is required is counted (step S6), and it is determined whether the duration is equal to or greater than a predetermined time (step S7). Steps S6 and S7 are steps for determining whether the driver is braking with the intention of stopping the vehicle, and whether the creep driving force can be returned to the first creep driving force F1. Therefore, the predetermined time can be set to a time that allows for determining whether the driver has depressed the brake pedal with the intention of stopping the vehicle. In addition, in order to determine whether the vehicle can be maintained stopped even if the creep driving force is returned to the first creep driving force F1, the time during which a braking force greater than the first creep driving force F1 is required is counted here.

[0024] If the duration during which a braking force greater than the first creep driving force F1 is required is less than the predetermined time and the result of the negative determination in step S7 is therefore negative, the process returns to step S6. That is, the creep driving force is maintained at the second creep driving force F2. On the other hand, if the duration during which a braking force greater than the first creep driving force F1 is required is equal to or greater than the predetermined time and the result of the positive determination in step S7 is negative, the creep driving force is switched to the first creep driving force F1 (step S8) and this routine is temporarily terminated.

[0025] As described above, when the duration during which a driving force greater than the first creep driving force F1 is required is less than the predetermined time, the creep driving force is set to the first creep driving force F1, which is the same as in normal driving, so that a relatively large driving force can be generated. Therefore, when traveling on a road with relatively small unevenness, the vehicle can be traveled by operating only the brake pedal.

[0026] In addition, when a driving force larger than the first creep driving force F1 is required for a duration equal to or longer than a predetermined time, the creep driving force is switched to the second creep driving force F2, thereby preventing the driving force from becoming excessive during a transitional period when, after a large driving force is output to overcome a relatively large step, the accelerator pedal depression amount is reduced and the brake pedal is depressed in order to stop the vehicle. As a result, it is possible to prevent the electric vehicle Ve from rolling down a step such as a rock due to unintentional forward movement.

[0027] Furthermore, when a braking force greater than the first creep driving force F1 is required for a duration longer than a predetermined time, the creep driving force can be switched to the first creep driving force F1, thereby generating the same creep driving force as under normal circumstances, thereby preventing the driver from feeling uncomfortable.

[0028] In addition, the electric vehicle in the embodiment of the present invention is not limited to an electric vehicle equipped with only an electric motor as a driving force source, but may be a hybrid vehicle equipped with an internal combustion engine and an electric motor as driving force sources. In that case, the electric vehicle may be configured to execute the above-mentioned control example when torque is transmitted only from the electric motor to the drive wheels. [Explanation of symbols]

[0029] Ve Electric Vehicle

Claims

[Claim 1] 1. A driving force control device for an electric vehicle including an electric motor as a driving force source and an accelerator device operated by a driver, the driving force control device setting a required driving force to a predetermined first creep driving force when the accelerator device is not operated at a vehicle speed equal to or lower than a predetermined vehicle speed, A controller for controlling the electric motor is provided, The controller: When the vehicle is traveling off-road at a vehicle speed equal to or lower than the predetermined vehicle speed, if the required driving force corresponding to the operation amount of the accelerator device continues to be greater than the first creep driving force for a predetermined period of time or more, the required driving force after the accelerator device is no longer operated is switched to a second creep driving force smaller than the first creep driving force. A driving force control device for an electric vehicle.

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