Braking / driving force control method and braking / driving force control device for electric vehicle

Abstract

Provided is a braking / driving force control method for an electric vehicle for controlling a driving force and a regenerative braking force, which are braking / driving forces of the electric vehicle, wherein: a basic braking / driving force to be generated by an electric motor is set on the basis of an accelerator operation amount of a vehicle; and a driving force is decreased with respect to the basic braking / driving force, or a regenerative braking force is increased with respect thereto, with decreasing inter-vehicle distance to a preceding vehicle which travels in front of the vehicle or with increasing speed relative to the preceding vehicle in a direction in which the preceding vehicle approaches.

Description

Braking / driving force control method and braking / driving force control device for electric vehicle

[0001] The present invention relates to a braking / driving force control method and a braking / driving force control device for an electric vehicle.

[0002] 2. Description of the Related Art There is known a device that controls the driving force of a vehicle in accordance with the distance between the vehicle and a vehicle in front (see, for example, Patent Document 1).

[0003] JP 2011-143798 A

[0004] The driving operation assistance device described in Patent Document 1 sets the driving force so that a specified distance is maintained between the vehicle and the vehicle in front within a preset time, regardless of the driving force that is set according to the driver's accelerator operation amount, so the driver's intentions cannot be reflected in the acceleration and deceleration of the vehicle.

[0005] An object of the present invention is to provide a braking / driving force control method and braking / driving force control device for an electric vehicle that can reflect the driver's intention in the acceleration / deceleration of the vehicle and adjust the distance between the vehicle and a vehicle in front.

[0006] In one aspect of the present invention, a basic braking / driving force to be generated by an electric motor is set based on the amount of accelerator operation, and the shorter the distance between the vehicle and the vehicle in front becomes, or the greater the relative speed between the vehicle and the vehicle in front becomes in the direction of approaching the vehicle in front, the more the basic braking / driving force is corrected to reduce the driving force or increase the regenerative braking force.

[0007] In another aspect of the present invention, a basic braking / driving force to be generated by an electric motor is set based on the accelerator operation amount, and a correction is made to the basic braking / driving force by increasing the driving force or decreasing the regenerative braking force as the distance between the vehicle and the vehicle in front increases or as the relative speed between the vehicle and the vehicle in front increases in the direction away from the vehicle in front.

[0008] According to the above aspect, the basic braking / driving force to be generated by the electric motor is set based on the amount of accelerator operation, and then corrections are made to the basic braking / driving force by decreasing or increasing the driving force or increasing or decreasing the regenerative braking force depending on the distance to the vehicle in front and the relative speed to the vehicle in front, so that the driver's intentions can be reflected in the acceleration / deceleration of the vehicle and the distance to the vehicle in front can be adjusted.

[0009] 6 is a schematic diagram showing a general configuration of a vehicle according to an embodiment; FIG. 7 is a control block diagram of a controller; FIG. 8 is a flowchart of braking / driving force control executed by a controller; FIG. 9 is a diagram showing the relationship between accelerator operation amount and vehicle speed and braking / driving force; FIG. 10 is a flowchart showing steps for setting a correction amount for braking / driving force; FIG. 11 is a diagram showing the relationship between vehicle speed and THW or TTC and the correction amount; FIG. 12 is a diagram showing the relationship between THW or TTC and the correction amount at an arbitrary vehicle speed in FIG. 6; FIG. 13 is a timing chart showing the correction of driving force when the inter-vehicle distance decreases; FIG. 14 is a timing chart showing the correction of driving force when the inter-vehicle distance increases; FIG. 15 is a timing chart showing the correction of driving force when a vehicle cuts in.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Hereinafter, a driver's operation to request braking / driving force using a braking / driving force requesting operation means such as an accelerator pedal will be referred to as an "accelerator operation," and the amount of operation will be referred to as an "accelerator operation amount." Braking / driving force refers to driving force and braking force. If the braking / driving force is positive, it becomes driving force, and if it is negative, it becomes braking force.

[0011] 1 is a schematic diagram showing the general configuration of an electric vehicle (hereinafter referred to as vehicle) 1. Vehicle 1 is an electric vehicle that generates its driving force and regenerative braking force (hereinafter also referred to as braking / driving force) by an electric driving source. Vehicle 1 is equipped with a braking / driving force generating device 2, a control mode selecting device 3, a braking / driving force control device 4, and sensors 5, 6, and 7.

[0012] The braking / driving force generation device 2 includes an inverter 21, a battery 22, an electric motor 23, a reducer 24, and wheels 25. Based on a command input from the braking / driving force control device 4, the inverter 21 converts direct current input from the battery 22 into alternating current and outputs the alternating current to the electric motor 23. Based on a command input from the braking / driving force control device 4, the inverter 21 also converts alternating current input from the electric motor 23 into direct current and inputs the direct current to the battery 22. The reducer 24 includes a transmission 24A and a differential gear 24B, and reduces the output of the electric motor 23 at a predetermined gear ratio based on the control of the braking / driving force control device 4 and transmits the reduced output to the wheels 25.

[0013] The control mode selection device 3 is composed of switches, dials, buttons, touch panels, etc., and allows the user to select the control mode of the braking / driving force control device 4. The control modes include, for example, a first control mode that generates a braking force similar to that of an engine brake in an engine-driven vehicle, and a second control mode that corrects the braking / driving force by, for example, making the regenerative braking force generated by the electric motor 23 stronger than in normal mode, thereby enabling the vehicle 1 to accelerate and decelerate with good response by operating the accelerator pedal alone. The second control mode is also called one-pedal mode.

[0014] The braking / driving force control device 4 includes an accelerator position sensor 5 as an accelerator operation amount sensor, a vehicle speed sensor 6 , a vehicle distance sensor 7 , and a controller 8 .

[0015] The accelerator position sensor 5 detects the amount of accelerator operation of the vehicle 1. The accelerator position sensor 5 is configured by, for example, a pedal stroke sensor, and detects the amount of operation of an accelerator pedal 51, which serves as a driving force request operation means, as the accelerator operation amount.

[0016] The vehicle speed sensor 6 is configured by, for example, a rotation speed sensor of the wheels 25, and detects the speed of the vehicle 1 (hereinafter referred to as vehicle speed).

[0017] The inter-vehicle distance sensor 7 is mounted on the vehicle 1 and detects the distance between the vehicle and a vehicle ahead. In this embodiment, the inter-vehicle distance sensor 7 includes a camera 71 and a radar 72, and the radar 72 detects the inter-vehicle distance between the vehicle ahead recognized by the camera 71. Note that the radar 72 may be a laser radar, a millimeter-wave radar, a LiDAR (Light Detection and Ranging), or the like.

[0018] The controller 8 controls the braking / driving force generated by the electric motor 23 based on the vehicle speed, the accelerator operation amount, etc. The controller 8 is realized by, for example, a microcomputer including a calculation unit such as a CPU or a GPU, a storage unit such as a ROM or a RAM, and an input / output unit such as an input / output interface. The control mode selection device 3, the accelerator position sensor 5, the vehicle speed sensor 6, the inter-vehicle distance sensor 7, and the inverter 21 are electrically or communicatively connected to the controller 8.

[0019] 2 is a control block diagram of the controller 8. As shown in FIG. 2, the controller 8 includes a memory unit 81, a correction necessity determination unit 82, a basic braking / driving force setting unit 83, a preceding vehicle detection determination unit 84, a relative vehicle speed acquisition unit 85, a correction amount setting unit 86, and a braking / driving force setting unit 87.

[0020] The memory unit 81 stores a computer program for causing the controller 8 to function, various maps used for control, various thresholds, etc. The maps stored in the memory unit 81 include, for example, a map that defines the relationship between the accelerator operation amount and the vehicle speed and the basic braking / driving force, and a map for setting a correction amount.

[0021] Correction necessity determining unit 82 determines whether or not braking / driving force correction is necessary based on the input from control mode selection device 3 .

[0022] The basic braking / driving force setting unit 83 sets basic braking / driving forces based on the accelerator operation amount and the vehicle speed. The basic braking / driving forces are braking / driving forces that are applied without correction.

[0023] The preceding vehicle detection / determination unit 84 detects the presence or absence of a preceding vehicle based on the output of the inter-vehicle distance sensor 7. The preceding vehicle detection / determination unit 84 also detects a vehicle suddenly appearing within a range of an inter-vehicle distance equal to or less than a predetermined value, i.e., a vehicle cutting in.

[0024] The relative vehicle speed acquisition unit 85 acquires the relative speed of the host vehicle with respect to the vehicle in front. The relative vehicle speed acquisition unit 85 may acquire the relative speed by calculation from the change in the inter-vehicle distance acquired from the inter-vehicle distance sensor 7, or may acquire the relative speed from the inter-vehicle distance sensor 7 if the inter-vehicle distance sensor 7 detects the relative speed.

[0025] The correction amount setting unit 86 sets a correction amount for the basic braking / driving force based on the determination result of the preceding vehicle detection determination unit 84, the accelerator operation amount, the vehicle speed, the inter-vehicle distance, and the relative vehicle speed.

[0026] Braking / driving force setting unit 87 sets the braking / driving forces to be generated by electric motor 23 based on the determination result of correction necessity determination unit 82, the basic braking / driving force, and the correction amount. Braking / driving force setting unit 87 outputs a command to inverter 21 to output the set braking / driving force, and causes electric motor 23 to drive or regenerate in accordance with the command.

[0027] 3 is a flowchart of the braking / driving force control executed by controller 8. The control routine shown in the flowchart is pre-programmed, and this program is installed in controller 8. In accordance with the program, controller 8 repeatedly executes the following control routine at an operation cycle of, for example, about 10 milliseconds.

[0028] In step S1 of FIG. 3, the controller 8 acquires the outputs of the control mode selection device 3 and the sensors 5, 6, and 7, that is, the control mode, accelerator operation amount, vehicle speed, and following distance.

[0029] In the next step S2, correction necessity determination unit 82 determines whether or not the second control mode for correcting the braking / driving force has been selected. If it is determined in step S2 that the second control mode has not been selected, the process returns to step S1, and if it is determined that the second control mode has been selected, the process proceeds to step S3.

[0030] In step S3, basic braking / driving force setting unit 83 sets basic braking / driving forces based on the accelerator operation amount and vehicle speed, for example, by referring to a map such as that shown in Figure 4. In Figure 4, the bottom line indicates the basic braking / driving forces when the accelerator operation amount is zero, and the higher the line, the greater the basic braking / driving force when the accelerator operation amount is greater.

[0031] In the following step S4, the preceding vehicle detection determination unit 84 determines whether or not a preceding vehicle has been detected based on the output of the inter-vehicle distance sensor 7. If it is determined in step S4 that a preceding vehicle has not been detected, the process proceeds to step S8, where the basic braking / driving force is set as the final braking / driving force.

[0032] On the other hand, if it is determined in step S4 that a vehicle in front has been detected, the relative vehicle speed acquisition unit 85 acquires the relative vehicle speed of the host vehicle with respect to the vehicle in front in step S5. In the following step S6, the correction amount setting unit 86 sets a correction amount for the braking / driving force. If the set correction amount is positive and greater than zero, this means that the braking / driving force is to be increased from the basic braking / driving force, and if the correction amount is negative, this means that the braking / driving force is to be decreased from the basic braking / driving force. The method for setting the correction amount will be described in detail below.

[0033] In step S7, braking / driving force setting unit 87 sets the final braking / driving force to a value obtained by adding the correction amount to the basic braking / driving force, and outputs a command to electric motor 23 to output the set braking / driving force. If the set braking / driving force is positive, positive torque is output from electric motor 23 to become driving force, and if it is negative, regeneration is performed by electric motor 23 to become braking force.

[0034] 5 is a flowchart showing steps for setting the correction amount. In step S61 in FIG. 5, the correction amount setting unit 86 calculates THW (Time Headway), which is the headway time from the host vehicle to the vehicle in front, and TTC (Time to Collision), which is the time to collision until the host vehicle reaches the vehicle in front, using the following equations (1) and (2): THW = Inter-vehicle distance / Vehicle speed of host vehicle (1) TTC = Inter-vehicle distance / Relative vehicle speed (2)

[0035] In the following step S62, the correction amount setting unit 86 refers to maps such as those shown in Figures 6 and 7, and sets a first correction amount based on the TWH and the vehicle speed, and sets a second correction amount based on the TTC and the vehicle speed.

[0036] Fig. 6 is a diagram showing the relationship between vehicle speed, THW, TTC, and the correction amount, and Fig. 7 is a diagram showing the relationship between THW, TTC, and the correction amount at any vehicle speed in Fig. 6. As shown in Fig. 6, the first correction amount and the second correction amount are set so that the driving force is increased or the regenerative braking force is decreased as the TWH or TTC exceeds a range determined according to the vehicle speed, and the driving force is decreased or the regenerative braking force is increased as the TWH or TTC falls below the range. Note that Figs. 6 and 7 correspond to both TWH and TTC for convenience, but in practice, maps with different characteristics are used for TWH and TTC.

[0037] Returning to FIG. 5 , in step S63, the correction amount setting unit 86 sets a first coefficient based on the accelerator operation amount and a second coefficient based on the vehicle speed. When the accelerator operation amount is equal to or greater than a predetermined amount, the first coefficient reduces the correction amount obtained by adding the first and second correction amounts to a value within a range from the correction amount to zero. For example, the first coefficient is a value within a range from 0 to 1, and is set smaller as the accelerator operation amount increases. When the vehicle speed is within a predetermined speed range, the second coefficient reduces the correction amount obtained by adding the first and second correction amounts to a value within a range from the correction amount to zero. For example, the second coefficient is a value within a range from 0 to 1, and is set small when the vehicle speed is low or high, and large when the vehicle speed is between low and high.

[0038] In the following step S64, correction amount setting unit 86 sets the correction amount for braking / driving force using the following equation (3): Correction amount=(first correction amount+second correction amount)×first coefficient×second coefficient (3).

[0039] In the next step S65, the preceding vehicle detection determination unit 84 detects whether or not a vehicle has cut in. If it is determined in step S65 that a vehicle has not cut in, the correction amount setting unit 86 sets an allowable upper limit and an allowable lower limit of the correction amount based on the vehicle speed in step S70. The allowable upper limit and allowable lower limit may be, for example, fixed values ​​determined for each vehicle speed.

[0040] On the other hand, if it is determined in step S65 that a vehicle has cut in, the correction amount setting unit 86 subtracts a third correction amount from the correction amount set in step S64 in order to further reduce the driving force or further increase the regenerative braking force in step S66. Note that the third correction amount is a fixed value in this embodiment.

[0041] In the next step S67, the correction amount setting unit 86 sets an upper limit and a lower limit of the correction amount based on the vehicle speed. The lower limit of the correction amount set in step S67 is set so as to allow a greater decrease in driving force or an increase in regenerative braking force than the lower limit of the correction amount set in step S70 in order to obtain the effect of subtracting the third correction amount from the correction amount.

[0042] In the following step S68, the correction amount setting unit 86 limits the correction amount to within the upper and lower allowable limits set in steps S67 and S70. Thereafter, in step S69, the correction amount setting unit 86 limits the amount of change in the correction amount over time, i.e., performs a so-called change rate limit. The amount of limit imposed on the change in the correction amount over time differs depending on whether the correction amount changes in the negative direction or the positive direction. As already explained, the correction amount set in this manner is used to correct the driving force when a leading vehicle is detected.

[0043] 8 to 10 are timing charts showing examples of braking / driving force correction when the inter-vehicle distance narrows, when the inter-vehicle distance widens, and when a vehicle cuts in. As shown in Fig. 8, when the host vehicle is traveling at a faster speed than the vehicle in front and the inter-vehicle distance narrows, the correction amount increases in the negative direction, reducing the driving force or increasing the regenerative braking force. As a result, the driving force of the host vehicle decreases or the regenerative braking force increases, causing the host vehicle's speed to decrease and eventually reach a speed close to that of the vehicle in front.

[0044] Thereafter, as shown in Figure 9, if the vehicle in front travels faster than the host vehicle and the inter-vehicle distance increases, the correction amount increases in the positive direction to increase the driving force or decrease the regenerative braking force. As a result, the driving force of the host vehicle increases or the regenerative braking force decreases, causing the host vehicle's speed to increase and eventually approach the speed of the vehicle in front.

[0045] On the other hand, if another vehicle cuts in front of the host vehicle, the correction amount increases in the negative direction, decreasing the driving force or increasing the regenerative braking force, as shown in Figure 10. As a result, the driving force of the host vehicle decreases or the regenerative braking force increases, so the host vehicle's speed decreases and the host vehicle eventually travels at a speed close to that of the vehicle in front.

[0046] 10 shows THW correction, which sets a first correction amount based on THW, and TTC correction, which sets a second correction amount based on TTC, but this is shown to illustrate the timing difference between THW correction and TTC correction, and THW correction and TTC correction may be performed even in the cases shown in Figures 8 and 9. Whether THW correction and TTC correction are performed depends on the magnitude of the inter-vehicle distance, vehicle speed, and relative vehicle speed, and both may be performed, or only one of them may be performed.

[0047] According to the above-described embodiment, the basic braking / driving force to be generated by the electric motor 23 is set based on the accelerator operation amount, and then corrections are made to the basic braking / driving force by decreasing or increasing the driving force or increasing or decreasing the regenerative braking force depending on the distance to the vehicle in front and the relative speed to the vehicle in front. This allows the driver's intentions to be reflected in the acceleration / deceleration of the vehicle 1, and the distance to the vehicle in front to be adjusted.

[0048] According to the embodiment, when the accelerator is operated, the driving force or regenerative braking force is corrected, so the driver's intention can be understood from the accelerator operation amount and reflected in the braking / driving force.

[0049] According to the embodiment, the driving force or regenerative braking force is corrected based on the inter-vehicle distance and the relative vehicle speed, so that the braking and driving force can be appropriately corrected according to the driving conditions of the vehicle in front and the vehicle itself.

[0050] According to the embodiment, the first correction amount based on the inter-vehicle distance and the second correction amount based on the relative vehicle speed are summed to obtain the correction amount for the basic braking / driving force, so even if one of the first correction amount and the second correction amount is small, the other can compensate for it. Furthermore, since the correction amount is limited after the summation, it is possible to prevent the summation from becoming too large.

[0051] According to the embodiment, the amount of change in the correction amount over time is limited, so that the braking / driving force is prevented from changing suddenly due to the correction amount, and the driver is prevented from feeling uncomfortable.

[0052] According to the embodiment, when the accelerator operation amount is equal to or greater than a predetermined amount, the correction amount is reduced to a value within the range from the correction amount to zero, thereby appropriately reflecting the driver's intention to accelerate quickly.

[0053] Furthermore, when the vehicle speed is within a predetermined speed range, the correction amount is reduced to a value within the range from the predetermined correction amount to zero, so that the correction amount can be flexibly set for each vehicle speed range.

[0054] As described above, the best configurations, methods, and the like for implementing the present invention have been disclosed in the above description, but the present invention is not limited thereto. That is, although the present invention has been particularly illustrated and described mainly with reference to specific embodiments, those skilled in the art can make various modifications to the above-described embodiments in terms of shape, material, quantity, and other detailed configurations without departing from the scope of the technical idea and purpose of the present invention. Furthermore, the above-disclosed descriptions limiting the shape, material, and the like are provided as examples to facilitate understanding of the present invention and are not intended to limit the present invention. Therefore, descriptions using names of components that are free from some or all of the limitations on shape, material, and the like are included in the present invention.

[0055] The braking / driving force generation device 2 may include an internal combustion engine, which drives a generator to supply electricity to the electric motor 23, thereby driving the wheels 25 with the electric motor 23, or the wheels 25 may be driven by the electric motor 23 and the internal combustion engine together. In other words, the vehicle 1 may be a so-called series hybrid vehicle or a parallel hybrid vehicle.

[0056] In the braking / driving force control device 4, the driving force request operation means is constituted by the accelerator pedal 51, and the accelerator operation amount sensor is constituted by the accelerator position sensor 5, but other configurations may also be used. For example, the driving force request operation means may be constituted by an operation lever, an operation dial, or the like, and the accelerator operation amount sensor may be constituted by a sensor such as a stroke sensor or potentiometer that detects the amount of operation of these.

[0057] The vehicle speed sensor 6 is not particularly limited, and may be, for example, a ground speed sensor.

[0058] The inter-vehicle distance sensor 7 may be equipped with only one of the camera 71 and the radar 72, or, for example, may be equipped with multiple cameras 71 and no radar 72, or may be equipped with multiple radars 72 and no camera 71.

[0059] Controller 8 may set the correction amount by a method other than that described in the embodiment. For example, correction amount setting unit 86 may set a first correction coefficient based on the vehicle speed and the TWH value, and a second correction coefficient based on the vehicle speed and the TTC value, and then set the correction amount for braking / driving force by the following equation (4): Correction amount = Basic braking / driving force × First correction coefficient × Second correction coefficient (4)

[0060] Controller 8 may correct the braking / driving forces by a method other than that described in the embodiment. For example, correction amount setting unit 86 may set the first correction coefficient and the second correction coefficient without setting a correction amount, and braking / driving force setting unit 87 may correct the braking / driving forces using the following equation (5): Braking / driving force = basic braking / driving force × first correction coefficient × second correction coefficient (5)

[0061] The third correction amount may be a variable value, and may be a value that varies depending on the vehicle speed, for example.

[0062] 1...vehicle, 8...controller, 23...electric motor

Claims

1. A braking / driving force control method for an electric vehicle that controls the driving force and regenerative braking force that are the braking / driving forces of the electric vehicle, the method setting a basic braking / driving force to be generated in an electric motor based on the accelerator operation amount of the electric vehicle, and correcting the basic braking / driving force by decreasing the driving force or increasing the regenerative braking force as the inter-vehicle distance to a leading vehicle traveling in front of the electric vehicle decreases, or as the relative speed to the leading vehicle increases in the direction approaching the leading vehicle.

2. A braking / driving force control method for an electric vehicle that controls the driving force and regenerative braking force, which are the braking / driving forces of the electric vehicle, comprising: setting a basic braking / driving force to be generated in an electric motor based on the accelerator operation amount of the electric vehicle; and correcting the basic braking / driving force by increasing the driving force or decreasing the regenerative braking force as the inter-vehicle distance from a leading vehicle traveling in front of the electric vehicle increases, or as the relative speed from the leading vehicle increases in the direction away from the leading vehicle.

3. A braking / driving force control method according to claim 1 or 2, wherein the driving force or the regenerative braking force is corrected when an accelerator pedal is operated.

4. A braking / driving force control method according to claim 1 or 2, wherein the driving force or the regenerative braking force is corrected based on the inter-vehicle distance and based on the relative speed.

5. A braking / driving force control method according to claim 1 or 2, wherein a first correction amount based on the inter-vehicle distance and a second correction amount based on the relative speed are summed to obtain a correction amount for the basic braking / driving force, and the correction amount for the basic braking / driving force is limited to within an allowable upper limit and an allowable lower limit.

6. A braking / driving force control method according to claim 5, wherein the amount of change over time of a correction amount for the basic braking / driving force is limited.

7. A braking / driving force control method according to claim 1 or 2, wherein, when the accelerator operation amount is equal to or greater than a predetermined amount, a correction amount for the basic braking / driving force is reduced to a value within a range from the correction amount to zero.

8. A braking / driving force control method according to claim 1 or 2, wherein, when the speed of the electric vehicle is within a predetermined speed range, a correction amount for the basic braking / driving force is reduced to a value within a range from the correction amount to zero.

9. A braking / driving force control device for an electric vehicle that controls the driving force and regenerative braking force that are the braking / driving forces of the electric vehicle, comprising a controller that sets a basic braking / driving force to be generated in an electric motor based on the accelerator operation amount of the electric vehicle, and that corrects the basic braking / driving force by reducing the driving force or increasing the regenerative braking force as the inter-vehicle distance to a leading vehicle traveling in front of the electric vehicle becomes smaller, or as the relative speed to the leading vehicle increases in the direction approaching the leading vehicle.

10. A braking / driving force control device for an electric vehicle that controls the driving force and regenerative braking force that are the braking / driving forces of the electric vehicle, comprising a controller that sets a basic braking / driving force to be generated in an electric motor based on the accelerator operation amount of the electric vehicle, and that corrects the basic braking / driving force by increasing the driving force or decreasing the regenerative braking force as the inter-vehicle distance from a leading vehicle traveling in front of the electric vehicle increases, or as the relative speed from the leading vehicle increases in the direction away from the leading vehicle.

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