JP2024155601A - Control method for electric vehicle and control system for electric vehicle - Google Patents

Abstract

An electric vehicle control method and an electric vehicle control system are provided that suppress a decrease in braking torque unintended by a driver when controlling the braking torque of a host vehicle based on the inter-vehicle distance between the host vehicle and a preceding vehicle.
[Solution] A lower limit torque is calculated, which is a braking torque that increases as the distance between the host vehicle and a preceding vehicle traveling in front of the host vehicle becomes longer, and when a basic torque command value generated based on the accelerator opening is higher than the lower limit torque, the basic torque command value is set as the motor torque command value to control the drive motor based on the motor torque command value, and the torque when the basic torque command value matches the lower limit torque is held as the previous value of the motor torque command value, and when the current value of the lower limit torque is higher than the previous value of the motor torque command value, the higher of the current value of the basic torque command value and the previous value of the motor torque command value is set as the current value of the motor torque command value.
[Selected figure] Figure 5

Description

The present invention relates to a control method for an electric vehicle and a control system for an electric vehicle.

There is a known technology for driving an electric vehicle 10 in a so-called one-pedal mode in which the vehicle is accelerated or decelerated by operating only the accelerator pedal. With this technology, even when there is no preceding vehicle ahead and the driver wishes to drive at a constant speed, releasing the accelerator pedal causes the vehicle to decelerate too much, creating an uncomfortable feeling. Similarly, when the driver releases the accelerator, the vehicle decelerates more than intended, causing the vehicle speed to drop, and the driver has to accelerate again, resulting in a deterioration in fuel efficiency. In response to this, there is a known technology for controlling the braking torque of the vehicle based on the distance between the vehicle and the preceding vehicle in an electric vehicle (see Patent Document 1). With this technology, when the distance between the vehicles is long, the braking torque is weakened, resulting in a braking torque appropriate to the traffic conditions, reducing the burden on the driver in operating the accelerator and reducing the deterioration in fuel efficiency caused by unintended acceleration and deceleration.

Patent No. 6625039

However, if the distance between the vehicle and the vehicle ahead increases while the vehicle is decelerating, or if the vehicle ahead moves away from the vehicle's lane, the braking torque decreases even though the driver is decelerating using the accelerator pedal, creating an uncomfortable feeling.

The present invention aims to provide a method and system for controlling an electric vehicle that suppresses unintended reductions in braking torque when controlling the vehicle's braking torque based on the distance between the vehicle and a preceding vehicle.

The control method for an electric vehicle according to the present invention generates a basic torque command value based on the accelerator opening, and when the accelerator opening decreases, the basic torque command value becomes the braking torque for the drive motor of the vehicle. In this control method, a lower limit torque is calculated as a braking torque, and the lower limit torque increases as the distance between the vehicle and a preceding vehicle traveling in front of the vehicle increases, or as the division value obtained by dividing the distance by the vehicle speed of the vehicle increases. When the basic torque command value is higher than the lower limit torque, the basic torque command value is set as the motor torque command value to control the drive motor based on the motor torque command value, and the torque when the basic torque command value matches the lower limit torque is held as the previous value of the motor torque command value. When the current value of the lower limit torque is equal to or lower than the previous value of the motor torque command value, the higher of the current value of the basic torque command value and the current value of the lower limit torque is set as the current value of the motor torque command value. In addition, if the current value of the lower limit torque is higher than the previous value of the motor torque command value, the current value of the base torque command value or the previous value of the motor torque command value, whichever is higher, is set as the current value of the motor torque command value.

According to the present invention, regardless of the current value of the lower limit torque, the motor torque command value, i.e., the braking torque, is equal to or less than the braking torque based on the previous value of the motor torque command value until the current value of the basic torque command value exceeds the previous value of the motor torque command value, so that a decrease in braking torque unintended by the driver can be suppressed. In addition, when the current value of the lower limit torque becomes lower than the previous value of the motor torque command value, the current value of the motor torque command value is set to the current value of the lower limit torque, so that the braking torque is increased when the vehicle-to-vehicle distance becomes shorter, and the driver's accelerator pedal operation amount can be reduced.

FIG. 1 is a block diagram illustrating the basic configuration of an electric vehicle system to which a control method for an electric vehicle according to this embodiment is applied. FIG. 2 is a flowchart illustrating a main process of drive control of an electric vehicle. FIG. 3 is a diagram showing an example of an accelerator opening-torque table in the accelerator mode. FIG. 4 is a diagram showing an example of an accelerator opening-torque table in the one-pedal mode. FIG. 5 is a flowchart illustrating the motor torque command value calculation process. FIG. 6 is a correction torque table showing the relationship between the correction torque to be added to the basic torque command value calculated based on the accelerator opening degree and the inter-vehicle distance between the host vehicle and a preceding vehicle traveling ahead of the host vehicle. FIG. 7 is a lower limit torque table showing the relationship between the vehicle distance between the host vehicle and a preceding vehicle traveling ahead of the host vehicle, with respect to the lower limit torque to be compared with the basic torque command value calculated based on the accelerator opening degree. FIG. 8 is a diagram showing the logic of the motor torque command value calculation process. FIG. 9 is a diagram for explaining a flow of calculation of a motor torque command value in a comparative example. 10A and 10B are diagrams showing the relationship between the base torque command value, the third correction torque, the motor torque command value, and the accelerator opening applied in the comparative example. FIG. 10A shows the relationship between the third correction torque and the inter-vehicle distance. FIG. 10B shows the distribution of the motor torque command value when the third correction torque of the comparative example is applied to the characteristic curve of the base torque command value when the accelerator opening is set to zero in a coordinate space whose axes are the vehicle speed and the base torque command value. FIG. 10C shows the characteristic curve of the base torque command value when the accelerator opening is changed while keeping the vehicle speed (V1) shown in FIG. 10B constant in a coordinate space whose axes are the accelerator opening and the base torque command value, and the distribution of the motor torque command value when the third correction torque of the comparative example is applied to the base torque command value. 11A shows the relationship between the correction torque and the inter-vehicle distance, FIG. 11B shows the distribution of the motor torque command value when the correction torque and lower limit torque of this embodiment are applied to the characteristic curve of the base torque command value when the accelerator opening is set to zero in a coordinate space whose axes are vehicle speed V and the base torque command value, and FIG. 11C shows the distribution of the motor torque command value when the correction torque and lower limit torque of this embodiment are applied to the characteristic curve of the base torque command value when the accelerator opening is changed while keeping the vehicle speed (V1) shown in FIG. 11B constant in the coordinate space whose axes are accelerator opening and the base torque command value. FIG. 12 is a time chart of the motor torque command value and the vehicle speed when the inter-vehicle distance changes when the accelerator opening of the electric vehicle is changed by the control method (control system) for the electric vehicle of this embodiment.

The following describes an embodiment of the present invention.

<System configuration of electric vehicle 10>
Fig. 1 is a block diagram showing a system configuration of an electric vehicle 10 equipped with a control device for the electric vehicle 10 according to the present embodiment. The electric vehicle 10 is an automobile that is equipped with a motor 18 as a part or all of the drive source of the vehicle and can run by the driving force of the motor 18, and includes electric automobiles and hybrid automobiles. Note that while the electric vehicle 10 shown in Fig. 1 is equipped with one motor 18, the present embodiment can also be applied to a configuration equipped with multiple motors 18.

Signals indicating vehicle conditions such as accelerator opening APO, vehicle speed V, rotor phase α of motor 18, and three-phase AC currents iu, iv, and iw of motor 18 are input as digital signals to motor controller 12 (control device). Information on the inter-vehicle distance D between the host vehicle and a preceding vehicle traveling ahead of the host vehicle in the same lane as the host vehicle is input to motor controller 12 from a radar or navigation device mounted on electric vehicle 10. Motor controller 12 generates PWM signals tu, tv, and tw for controlling motor 18 based on the input signals. In addition, it generates a drive signal for inverter 16 according to the generated PWM signals tu, tv, and tw.

The motor controller 12 also receives a signal from a mode switch (mode SW) that determines the driving mode of the electric vehicle 10 based on the driver's operation. The driving modes include an accelerator mode in which almost no braking torque is generated even when the accelerator operation is released, and a one-pedal mode in which a regenerative torque (regenerative current) that becomes a strong braking torque is generated when the accelerator operation is released, and the electric vehicle 10 can be stopped.

The inverter 16 converts the direct current supplied from the battery 14 to alternating current by turning on and off two switching elements (e.g., power semiconductor elements such as IGBTs and MOS-FETs) provided for each phase, and supplies the desired current to the motor 18.

The motor 18 (three-phase AC motor) generates driving force from the AC current supplied from the inverter 16, and transmits the driving force to the left and right drive wheels 24a, 24b via the reduction gear 20 and the drive shaft 22. When the motor 18 rotates along with the drive wheels 24a, 24b while the vehicle is running, it generates a regenerative driving force, thereby recovering the vehicle's kinetic energy as electrical energy. In this case, the inverter 16 converts the AC current generated during regenerative operation of the motor 18 into DC current and supplies it to the battery 14.

The current sensor 26 detects the three-phase AC currents iu, iv, and iw that flow through the motor 18. However, since the sum of the three-phase AC currents iu, iv, and iw is zero, the currents of any two phases may be detected and the current of the remaining phase may be calculated.

The rotation sensor 28 is, for example, a resolver or an encoder, and detects the rotor phase α of the motor 18.

<Overall system control flow>
2 is a flowchart showing the flow of the process performed by the motor controller 12. The process from step S201 to step S204 is constantly executed at regular intervals while the vehicle system is activated.

In step S201, a signal indicating the vehicle state (vehicle information) is input to the motor controller 12. Here, the vehicle speed V (km/h), accelerator opening APO (%), and rotor phase α (rad) of the motor 18 are input. In addition, the rotation speed N (rpm) of the motor 18, the three-phase AC currents iu, iv, and iw flowing through the motor 18, and the DC voltage value Vdc (V) of the battery 14 are input.

The vehicle speed V (km/h) is acquired by communication from a vehicle speed sensor (not shown) or another controller. Alternatively, the motor controller 12 obtains the vehicle speed V (m/s) by multiplying the motor angular velocity detection value ωm by the tire dynamic radius r and dividing by the gear ratio of the final gear, and then multiplies the value by 3600/1000 to convert the unit to obtain the vehicle speed V (km/h).

The accelerator opening APO (%) is obtained from an accelerator opening sensor (not shown) or is obtained via communication from another controller such as a vehicle controller (not shown).

The rotor phase α (rad) of the motor 18 is obtained from the rotation sensor 28. The motor angular velocity detection value ωm, which is the mechanical angular velocity of the motor 18, is obtained by dividing the rotor angular velocity ω (electrical angle) by the number of pole pairs p of the motor 18. The rotation speed N (rpm) of the motor 18 is obtained by multiplying the obtained motor angular velocity detection value ωm by 60/(2π). The rotor angular velocity ω is obtained by differentiating the rotor phase α.

The three-phase AC currents iu, iv, and iw (A) flowing through the motor 18 are obtained from the current sensor 26.

The DC voltage value Vdc (V) is detected by a voltage sensor (not shown) provided on the DC power supply line between the battery 14 and the inverter 16. The DC voltage value Vdc (V) may also be detected from a signal related to the power supply voltage value transmitted from a battery controller (not shown).

In step S202, the motor controller 12 sets the motor torque command value Tmf*.

When the driving mode is the accelerator mode, the motor controller 12 calculates the basic torque command value Tm1 requested by the driver by referring to the accelerator opening APO-torque table shown in FIG. 3 based on the accelerator opening APO and rotation speed N (or vehicle speed V) input in step S201, and sets the basic torque command value Tm1 as the motor torque command value Tmf*.

When the driving mode is the one-pedal mode, the motor controller 12 calculates the basic torque command value Tm1 requested by the driver by referring to the accelerator opening APO and rotation speed N (or vehicle speed V) input in step S201 by referring to the accelerator opening-torque table shown in FIG. 4, and sets the motor torque command value Tmf* by executing the motor torque command value calculation process described below. However, the accelerator opening-torque table is an example, and is not limited to those shown in FIGS. 3 and 4.

In step S203, the motor controller 12 calculates the d-axis current command value id* and the q-axis current command value iq* based on the motor torque command value Tmf*, the motor angular velocity detection value ωm, and the DC voltage value Vdc calculated in step S202. For example, a table is prepared in advance that defines the relationship between the motor torque command value Tmf*, the rotation speed N of the motor 18, and the DC voltage value Vdc, and the d-axis current command value and the q-axis current command value. Then, the d-axis current command value id* and the q-axis current command value iq* are calculated by referring to this table.

In step S204, the motor controller 12 performs current control to make the d-axis current id and the q-axis current iq match the d-axis current command value id* and the q-axis current command value iq* obtained in step S203. For this purpose, first, the d-axis current id and the q-axis current iq are obtained based on the three-phase AC currents iu, iv, and iw input in step S201 and the rotor phase α of the motor 18. Next, the d-axis voltage command value vd is calculated from the deviation between the d-axis current command value id* and the d-axis current id, and the q-axis voltage command value vq is calculated from the deviation between the q-axis current command value iq* and the q-axis current iq. Note that a non-interference voltage required to offset the interference voltage between the d-q orthogonal coordinate axes may be added to the calculated d-axis voltage command value vd and q-axis voltage command value vq.

Next, the three-phase AC voltage command values vu, vv, and vw are calculated from the d-axis voltage command value vd, the q-axis voltage command value vq, and the rotor phase α of the motor 18. Then, the PWM signals tu(%), tv(%), and tw(%) are calculated from the calculated three-phase AC voltage command values vu, vv, and vw and the DC voltage value Vdc. By opening and closing the switching elements of the inverter 16 using the PWM signals tu, tv, and tw calculated in this manner, the motor 18 can be driven at the desired torque indicated by the motor torque command value Tmf*.

[Motor torque command value calculation process]
Fig. 5 is a flow chart for explaining the motor torque command value calculation process. Fig. 6 is a correction torque table showing the relationship between the correction torque ΔT (offset amount) added to the basic torque command value Tm1 calculated based on the accelerator opening APO and the inter-vehicle distance D between the host vehicle and the preceding vehicle traveling ahead of the host vehicle. Fig. 7 is a lower limit torque table showing the relationship between the lower limit torque TL compared with the basic torque command value Tm1 calculated based on the accelerator opening APO and the inter-vehicle distance D between the host vehicle and the preceding vehicle traveling ahead of the host vehicle.

Here, it is assumed that the driving mode input to the motor controller 12 is one-pedal mode.

In step S501, the motor controller 12 inputs information on the accelerator opening APO, the vehicle speed V, and the vehicle distance D. Note that step S501 may be considered as part of step S201.

In step S502, the motor controller 12 inputs the accelerator opening APO and the rotation speed N (or the vehicle speed V) into the accelerator opening APO-torque table shown in FIG. 4 to calculate the basic torque command value Tm1 required by the driver.

In step S503, the motor controller 12 inputs the vehicle distance D into the torque correction table shown in FIG. 6 to calculate the correction torque ΔT (step S503a in FIG. 11), and corrects the basic torque command value Tm1 by adding the correction torque ΔT to the basic torque command value Tm1 (step S503b in FIG. 11). The correction torque ΔT shown in FIG. 6 has a characteristic that it is set to zero when the vehicle distance D with the preceding vehicle is equal to or greater than D1 (e.g., 20 [m]), becomes negative when the vehicle distance D is shorter than D1, and becomes monotonically lower as the vehicle distance D becomes shorter than D1, thereby avoiding a collision with the preceding vehicle. Note that the horizontal axis of the torque correction table shown in FIG. 6 may apply the divided value "vehicle distance D/vehicle speed V" obtained by multiplying the vehicle distance D by the vehicle speed V.

In step S504, the motor controller 12 inputs the vehicle distance D into the lower limit torque table shown in FIG. 7 to calculate the lower limit torque TL. The lower limit torque TL is a torque to be compared with the basic torque command value Tm1, and when the vehicle distance D is equal to or greater than D2 (e.g., 50 [m]), the braking torque is set to a value slightly lower than zero, for example, a value that realizes the deceleration when coasting with the accelerator opening APO set to zero in accelerator mode. In addition, the lower limit torque TL has a characteristic of monotonically decreasing as the vehicle distance D becomes shorter than D2. Note that the horizontal axis of the lower limit torque table shown in FIG. 7 may apply the divided value "vehicle distance D/vehicle speed V" obtained by multiplying the vehicle distance D by the vehicle speed V.

In step S505, the motor controller 12 performs a filter process on the lower limit torque TL to remove noise components contained in the lower limit torque TL (noise contained in the information on the inter-vehicle distance D). The filter process, for example, calculates the average value of the current value of the calculated lower limit torque TL and the previous value (one or more), and sets the average value as the current value of the lower limit torque TL.

In step S506, the motor controller 12 compares the base torque command value Tm1 (current value) with the lower limit torque TL (current value), and if the base torque command value Tm1 is higher than the lower limit torque TL, sets the base torque command value Tm1 (current value) to the motor torque command value Tmf* (step S506a in FIG. 11). In addition, the motor controller 12 holds the torque when the base torque command value Tm1 (current value) matches the lower limit torque TL (current value) as the previous value of the motor torque command value Tmf*.

In step S507, the motor controller 12 determines whether the current value of the lower limit torque TL is higher than the previous value of the motor torque command value Tmf*. If NO, the process proceeds to step S508. If YES, the process proceeds to step S509.

In step S508, if the motor controller 12 determines that the current value of the lower limit torque TL is equal to or less than the previous value of the motor torque command value Tmf*, it sets the current value of the motor torque command value Tmf* to the higher of the previous value of the base torque command value Tm1 and the current value of the lower limit torque TL.

Therefore, if the current value of the lower limit torque TL is equal to or lower than the previous value of the motor torque command value Tmf* and is higher than the current value of the base torque command value Tm1, the current value of the lower limit torque TL is set as the current value of the motor torque command value Tmf*, and the current value of the motor torque command value Tmf* may become lower than the previous value.

On the other hand, if the current value of the lower limit torque TL is equal to or less than the previous value of the motor torque command value Tmf* and is lower than the current value of the base torque command value Tm1, the current value of the base torque command value Tm1 is set as the current value of the motor torque command value Tmf*. In this case, if the current value of the base torque command value Tm1 is equal to or less than the previous value of the motor torque command value Tmf*, the current value of the motor torque command value Tmf* is equal to or less than the previous value of the motor torque command value Tmf*, and if the current value of the base torque command value Tm1 is higher than the previous value of the motor torque command value Tmf*, the current value of the motor torque command value Tmf* is higher than the previous value of the motor torque command value Tmf*.

In step S509, if the motor controller 12 determines that the current value of the lower limit torque TL is higher than the previous value of the motor torque command value Tmf*, it sets the higher of the previous value of the base torque command value Tm1 and the motor torque command value Tmf* as the current value of the motor torque command value Tmf*. In this case, for example, if the current value of the base torque command value Tm1 is higher than the previous value of the motor torque command value Tmf*, the current value of the motor torque command value Tmf* will be higher than the previous value of the motor torque command value Tmf*.

In step S508, if the current value of the lower limit torque TL becomes equal to or lower than the previous value of the lower limit torque TL, this may be reflected in the current value of the motor torque command value Tmf*, which may become equal to or lower than the previous value of the motor torque command value Tmf*.

However, in steps S508 and S509, if the current value of the lower limit torque TL becomes higher than the previous value of the lower limit torque TL, this is not reflected in the current value of the motor torque command value Tmf*.

Figure 8 is a diagram showing the logic of the motor torque command value calculation process. As shown in Figure 8, the motor controller 12 includes a comparison element 121, a switch element 122, a selection element 123, and a delay element 124 as components that execute the motor torque command value calculation process.

The comparison element 121 receives the lower limit torque TL (current value, step S505) and the output of the delay element 124 (the previous value of the motor torque command value Tmf*). The comparison element 121 outputs 1 if the output of the delay element 124 is equal to or greater than the lower limit torque TL, and outputs 0 if the output of the delay element 124 is lower than the lower limit torque TL.

The output of the delay element 124, the lower limit torque TL, and the output of the comparison element 121 are input to the switch element 122. When the output of the comparison element 121 is 1, the switch element 122 selects and outputs the output of the delay element 124, and when the output of the comparison element 121 is 0, the switch element 122 selects and outputs the lower limit torque TL.

The output of the switch element 122 and the base torque command value Tm1 (current value, step S503) are input to the selection element 123. The selection element 123 outputs the larger of the output of the switch element 122 and the base torque command value Tm1 as the motor torque command value Tmf* (current value), and if the output of the switch element 122 and the base torque command value Tm1 match, the selection element 123 outputs either value as the motor torque command value Tmf* (current value).

The motor torque command value Tmf* (present value) is input to the delay element 124. The delay element 124 performs a Z-transform on the motor torque command value Tmf* (present value), multiplies it by a function (z ⁻¹ ), and generates an output that is sample-delayed, that is, a value that becomes the motor torque command value Tmf* (previous value) for the comparison element 121 and the switch element 122, and outputs this to the comparison element 121 and the switch element 122.

[Motor torque command value Tmf* output in comparative example]
FIG. 9 is a diagram for explaining a flow of calculation of the motor torque command value Tmf* in the comparative example. FIG. 10 is a diagram showing the relationship between the base torque command value Tm1, third correction torque ΔT3, motor torque command value Tmf*, and accelerator opening APO applied in the comparative example. FIG. 10(a) shows the relationship between the third correction torque ΔT3 and the inter-vehicle distance D. FIG. 10(b) shows the distribution of the motor torque command value Tmf* when the third correction torque ΔT3 of the comparative example is applied to the characteristic curve of the base torque command value Tm1 when the accelerator opening APO is set to zero in a coordinate space whose axes are vehicle speed V and base torque command value Tm1. FIG. 10(c) shows the characteristic curve of the base torque command value Tm1 when the accelerator opening APO is changed while keeping the vehicle speed V (V1) shown in FIG. 10(b) constant, and the distribution of the motor torque command value Tmf* when the third correction torque ΔT3 of the comparative example is applied to the base torque command value Tm1 in the coordinate space whose axes are accelerator opening APO and base torque command value Tm1.

In the comparative example, steps S901 and S902 are executed in parallel with step S502 shown in FIG. 5.

In step S901, the motor controller 12 inputs the vehicle distance D (and vehicle speed V) into a first torque correction table (similar to the torque correction table shown in FIG. 6) to calculate a first correction torque ΔT1. The first correction torque ΔT1 is zero when the vehicle distance D is equal to or greater than D1, but is a value lower than zero when the vehicle distance D is shorter than D1, and decreases monotonically as the vehicle distance D becomes shorter.

In step S902, the motor controller 12 inputs the vehicle distance D (and vehicle speed V) into the second torque correction table to calculate the second correction torque ΔT2. The second correction torque ΔT2 is zero when the vehicle distance D is between zero and D2 (>D1), but becomes greater than zero when the vehicle distance D is longer than D2 and increases monotonically until the vehicle distance D reaches D3, which is longer than D2, and becomes constant when the vehicle distance D is equal to or greater than D3.

In step S903, the motor controller 12 adds the first correction torque ΔT1 and the second correction torque ΔT2 to generate the third correction torque ΔT3.

In step S904, the motor controller 12 calculates the motor torque command value Tmf* by adding the basic torque command value Tm1 calculated in step S502 and the third correction torque ΔT3.

As shown in FIG. 10(a), the third correction torque ΔT3 becomes lower than zero when the inter-vehicle distance D is lower than D1, and decreases monotonically as the inter-vehicle distance D becomes lower than D1. The third correction torque ΔT3 becomes zero when the inter-vehicle distance D is equal to or greater than D1 and equal to or less than D2. The third correction torque ΔT3 becomes higher than zero when the inter-vehicle distance D is longer than D2, and increases monotonically as the inter-vehicle distance D becomes longer than D2, and becomes a constant value when the inter-vehicle distance D reaches D3, which is longer than D2.

In the coordinate space shown in FIG. 10(b), where the horizontal axis represents vehicle speed V and the vertical axis represents torque, the relationship between vehicle speed V and base torque command value Tm1 when accelerator opening APO is set to zero can be represented by a single characteristic curve (APO: 0%).

Here, when the third correction torque ΔT3 is applied to the basic torque command value Tm1 and the vehicle distance D becomes shorter than D1, the motor torque command value Tmf* shifts in the vertical direction to region A, which is lower than the characteristic curve (APO: 0%), and the motor torque command value Tmf* can be set in region A.

On the other hand, when the vehicle distance D becomes longer than D2, the motor torque command value Tmf* shifts to region C in the vertical axis direction, which is higher than the characteristic curve (APO: 0%). More specifically, the motor torque command value Tmf* can be set in region C between the characteristic curve (APO: 0%) representing the basic torque command value Tm1 when the accelerator opening APO is zero, and the characteristic curve B representing the motor torque command value Tmf* obtained by adding the third correction torque ΔT3 (vehicle distance D ≧ D3) to the basic torque command value Tm1 when the accelerator opening APO is zero. In this case, the maximum value of the second correction torque ΔT2 (the value when the vehicle distance D is D3 or more) is appropriately set so that the motor torque command value Tmf* does not become a positive value.

Therefore, when the accelerator opening APO is zero and the vehicle distance D becomes shorter, the motor torque command value Tmf* can be decreased (the braking torque can be increased) without causing the driver to feel uncomfortable, and conversely, when the vehicle distance D becomes longer, the motor torque command value Tmf* can be increased (the braking torque can be decreased) without causing the driver to feel uncomfortable.

However, in the comparative example, the third correction torque ΔT3 (first correction torque ΔT1 + second correction torque ΔT2) is added regardless of the degree of accelerator opening APO, i.e., the magnitude of the basic torque command value Tm1.

As a result, as shown in FIG. 10(c), in the region where the accelerator opening APO is equal to or greater than "x2", the basic torque command value Tm1 is positive, but in this case too, the motor torque command value Tmf* is increased by adding the third correction torque ΔT3 (the second correction torque ΔT2 component). This results in a driving torque greater than that requested by the driver, which causes the driver to feel uncomfortable.

Furthermore, in the region where the accelerator opening APO is lower than "x2" and equal to or greater than "x1", the basic torque command value Tm1 is negative, but even in this case, the third correction torque ΔT3 (the second correction torque ΔT2 component) is added to generate a positive motor torque command value Tmf*. Therefore, even though the driver is requesting braking torque, a driving torque that accelerates the electric vehicle 10 is applied, which gives the driver a sense of discomfort.

[Motor torque command value Tmf* output in this embodiment]
FIG. 11 is a diagram showing the relationship between the base torque command value Tm1 applied in this embodiment, the correction torque ΔT, the motor torque command value Tmf*, and the accelerator opening APO. FIG. 11(a) shows the relationship between the correction torque ΔT and the inter-vehicle distance D. FIG. 11(b) shows the distribution of the motor torque command value Tmf* when the correction torque ΔT and lower limit torque TL of this embodiment are applied to the characteristic curve of the base torque command value Tm1 when the accelerator opening APO is set to zero in a coordinate space whose axes are the vehicle speed V and the base torque command value Tm1. FIG. 11(c) shows the characteristic curve of the base torque command value Tm1 when the accelerator opening APO is changed while keeping the vehicle speed V (V1) shown in FIG. 11(b) constant in a coordinate space whose axes are the accelerator opening APO and the base torque command value Tm1, and the distribution of the motor torque command value Tmf* when the correction torque ΔT and lower limit torque TL of this embodiment are applied to the base torque command value Tm1.

As shown in FIG. 11(a), in this embodiment, a correction torque ΔT is added to the base torque command value Tm1, but this correction torque ΔT is zero when the inter-vehicle distance D is equal to or greater than D1, and decreases monotonically when the inter-vehicle distance D is lower than D1, and no correction is made to increase the base torque command value Tm1. Also, in this embodiment, the corrected base torque command value Tm1 is compared with the lower limit torque TL, and the higher value is set as the motor torque command value Tmf*. Furthermore, in this embodiment, the torque when the corrected base torque command value Tm1 and the lower limit torque TL match is held as the previous value of the motor torque command value Tmf*.

Then, when the current value of the lower limit torque TL is equal to or less than the previous value of the motor torque command value Tmf*, the current value of the base torque command value Tm1 or the current value of the lower limit torque TL, whichever is greater, is set as the current value of the motor torque command value Tmf*. Alternatively, when the current value of the lower limit torque TL is higher than the previous value of the motor torque command value Tmf*, the current value of the motor torque command value Tmf*, whichever is greater, is set as the current value of the motor torque command value Tmf*.

In the coordinate space shown in FIG. 11(b) where the horizontal axis represents vehicle speed V and the vertical axis represents torque, the relationship between vehicle speed V and base torque command value Tm1 when accelerator opening APO is set to zero can be represented by a single characteristic curve (APO: 0%), as in FIG. 10.

Here, when the correction torque ΔT is applied to the basic torque command value Tm1 and the vehicle distance D becomes shorter than D1, the motor torque command value Tmf* shifts in the vertical direction to region E, which is lower than the characteristic curve (APO: 0%), and the motor torque command value Tmf* can be set within the range of region E.

On the other hand, the torque when the basic torque command value Tm1 coincides with the lower limit torque TL can be held as the previous value of the motor torque command value Tmf*, but its upper limit value is when the inter-vehicle distance D is D2 or greater. Therefore, when the inter-vehicle distance D is D1 or greater, the motor torque command value Tmf* can be set in the region G between the characteristic curve (APO: 0%) that represents the basic torque command value Tm1 when the accelerator opening APO is zero and the characteristic curve F when the motor torque command value Tmf* is set to the upper limit value of the lower limit torque TL.

In this embodiment, as described above, no correction torque is applied to the base torque command value Tm1 in a direction that increases its value, and the torque when the base torque command value Tm1 and the lower limit torque TL match is held as the previous value of the motor torque command value Tmf*.

Therefore, for example, as shown in FIG. 11(b), a horizontal line H passing through the position where the vertical line of vehicle speed V=V1 intersects with characteristic curve F is extended in FIG. 11(c). Then, as shown in FIG. 11(c), a motor torque command value Tmf* that is higher than the base torque command value Tm1 is permitted in region J surrounded by the horizontal line H, the characteristic curve of base torque command value Tm1, and a vertical line I passing through the position where the horizontal line H intersects with the characteristic curve of base torque command value Tm1. However, setting of a motor torque command value Tmf* that is higher than the base torque command value Tm1 in regions other than region J is prohibited.

Therefore, an increase in the motor torque command value Tmf* is permitted when the basic torque command value Tm1 is higher than the previous value of the motor torque command value Tmf*, thereby reducing the decrease in braking torque or acceleration that is unintended by the driver.

[Time chart]
FIG. 12 is a time chart of the motor torque command value Tmf* and the vehicle speed V when the inter-vehicle distance D changes when the accelerator opening APO of the electric vehicle 10 is changed by the control method (control system) for the electric vehicle 10 of this embodiment.

As shown in FIG. 12, it is assumed that before time t1, the driver sets the accelerator opening APO to X2 and drives the vehicle at a constant speed, starts decreasing the accelerator opening APO at time t1, reduces the accelerator opening APO to X1 at time t4, maintains the accelerator opening APO at X1 from time t4 to time t7, increases the accelerator opening APO at time t7, and returns the accelerator opening APO to the original opening of X2 at time t11 to drive the vehicle at a constant speed.

It is also assumed that the inter-vehicle distance D from the preceding vehicle is always longer than D1 and is approximately constant until time t3, decreases from time t3 to time t5, becomes approximately constant between time t5 and time t6, increases after time t6, and reaches D2 at time t9.

Before time t1, the basic torque command value Tm1 is higher than the lower limit torque TL, so the basic torque command value Tm1 is set as the motor torque command value Tmf*.

At time t1, the motor torque command value Tmf* and the basic torque command value Tm1 begin to decrease as the accelerator opening APO decreases, and at time t2, the motor torque command value Tmf* coincides with the lower limit torque TL. The value of the motor torque command value Tmf* or the lower limit torque TL at time t2 is held as the previous value of the motor torque command value Tmf*.

From time t2 onwards, the base torque command value Tm1 becomes lower than the lower limit torque TL.

At this time, if the current value of the lower limit torque TL is equal to or less than the previous value of the motor torque command value Tmf*, the higher of the current value of the base torque command value Tm1 and the current value of the lower limit torque TL is set as the current value of the motor torque command value Tmf*. Therefore, from time t2 to time t3, the lower limit torque TL is set to the motor torque command value Tmf*, and the motor torque command value Tmf* maintains the value at time t2.

At time t3, the lower limit torque TL starts to decrease. Even in this case, if the current value of the lower limit torque TL is equal to or less than the previous value of the motor torque command value Tmf*, the higher of the current value of the base torque command value Tm1 and the current value of the lower limit torque TL is set as the current value of the motor torque command value Tmf*. In other words, between time t3 and time t5, the lower limit torque TL is lower than the base torque command value Tm1 and decreases, so the motor torque command value Tmf* also decreases as the lower limit torque TL decreases.

Between time t5 and time t6, the lower limit torque TL is constant but is higher than the basic torque command value Tm1, so the lower limit torque TL is set as the motor torque command value Tmf*, and the motor torque command value Tmf* maintains the value at time t5.

At time t6, the lower limit torque TL starts to increase. In this case, the current value of the lower limit torque TL becomes higher than the previous value of the motor torque command value Tmf*. At this time, the higher of the current value of the base torque command value Tm1 and the previous value of the motor torque command value Tmf* is set as the current value of the motor torque command value Tmf*. Between time t6 and time t8, the previous value of the motor torque command value Tmf* remains higher than the current value of the base torque command value Tm1, so the motor torque command value Tmf* maintains the value at time t6.

At time t8, the base torque command value Tm1 reaches the motor torque command value Tmf*, and then becomes higher than the previous value of the motor torque command value Tmf*. At this time, the higher of the current value of the base torque command value Tm1 and the previous value of the motor torque command value Tmf* is set as the current value of the motor torque command value Tmf*, and therefore the current value of the base torque command value Tm1 is set as the current value of the motor torque command value Tmf*. After time t8, the base torque command value Tm1 is set to the motor torque command value Tmf*.

At this time, the vehicle speed V over time (V(Tmf*)) starts to decrease after time t1 and becomes constant at time t11, but the vehicle distance D to the preceding vehicle is taken into consideration and the decrease in braking torque associated with an increase in the lower limit torque TL is suppressed, reducing the discomfort felt by the driver.

When the motor torque command value Tmf* is set by the basic torque command value Tm1, the time progression of the vehicle speed V (V(Tm1)) starts to decrease after time t1 and becomes constant at time t11, which is the same as the time progression (V(Tmf*)). However, the braking torque becomes large, so there is excessive deceleration even though the inter-vehicle distance D is sufficient, which gives the driver a sense of discomfort.

Here, it is assumed that the inter-vehicle distance D reaches D2 at time t9 and becomes longer than D2 thereafter. At this time, the lower limit torque TL reaches its maximum value at time t9 and maintains that value thereafter. Also, in FIG. 12, the basic torque command value Tm1 and the lower limit torque TL coincide at time t10. Therefore, it is assumed that the lower limit torque TL is set to the motor torque command value Tmf* between time t6 and time t10, and the time progression of the vehicle speed V (V(TL)) at this time is considered.

In this case, the deceleration is kept lower in the time transition (V(TL)) than in the time transition (V(Tmf*)), and the distance D to the preceding vehicle is also shorter than in the case of the time transition (V(Tmf*)). However, after time t6, the braking torque is suppressed without the driver operating the accelerator, which gives the driver a sense of discomfort.

[Effects of this embodiment]
According to the control method for the electric vehicle 10 of this embodiment, a basic torque command value Tm1 is generated based on the accelerator opening APO, and when the accelerator opening APO decreases, the basic torque command value Tm1 becomes a braking torque for the drive motor (motor 18) of the host vehicle. In this control method for the electric vehicle 10, a lower limit torque TL is calculated as a braking torque, and the lower limit torque TL increases as the inter-vehicle distance D between the host vehicle and a preceding vehicle traveling in front of the host vehicle increases, or as the division value obtained by dividing the inter-vehicle distance D by the vehicle speed V of the host vehicle increases. When the basic torque command value Tm1 is higher than the lower limit torque TL, the basic torque command value Tm1 is set to a motor torque command value Tmf* to set the motor torque command value The drive motor (motor 18) is controlled based on Tmf*, and the torque when the basic torque command value Tm1 matches the lower limit torque TL is held as the previous value of the motor torque command value Tmf*. When the current value of the lower limit torque TL is equal to or less than the previous value of the motor torque command value Tmf*, the higher of the current value of the basic torque command value Tm1 or the current value of the lower limit torque TL is set as the current value of the motor torque command value Tmf*. When the current value of the lower limit torque TL is higher than the previous value of the motor torque command value Tmf*, the higher of the current value of the basic torque command value Tm1 or the previous value of the motor torque command value Tmf* is set as the current value of the motor torque command value Tmf*.

By using the above method, the motor torque command value Tmf*, i.e., the braking torque, will be equal to or less than the braking torque based on the previous value of the motor torque command value Tmf* regardless of the current value of the lower limit torque TL until the current value of the basic torque command value Tm1 exceeds the previous value of the motor torque command value Tmf*, so that a decrease in braking torque unintended by the driver can be suppressed. Also, when the current value of the lower limit torque TL becomes lower than the previous value of the motor torque command value Tmf*, the current value of the motor torque command value Tmf* is set to the current value of the lower limit torque TL, so that the braking torque is increased when the inter-vehicle distance D becomes shorter, and the amount of accelerator pedal operation by the driver can be reduced.

In this embodiment, a correction torque ΔT is added to the basic torque command value Tm1. The correction torque ΔT is zero when the vehicle distance D is equal to or greater than a predetermined threshold value (D1), and becomes less than zero when the vehicle distance D falls below the threshold value (D1), and the correction torque ΔT decreases monotonically as the vehicle distance D decreases.

By using the above method, the base torque command value Tm1 is corrected to be lower when the vehicle distance D becomes shorter than the threshold value (D1), so that the vehicle distance D from the preceding vehicle can be controlled so that it does not become too close.

According to the control system for the electric vehicle 10 of this embodiment, a basic torque command value Tm1 is generated based on the accelerator opening APO, and when the accelerator opening APO decreases, the basic torque command value Tm1 becomes the braking torque for the drive motor of the vehicle. In the control system for the electric vehicle 10, a lower limit torque TL calculation unit (motor controller 12) calculates a lower limit torque TL, which is a braking torque, and which increases as the inter-vehicle distance D between the host vehicle and a preceding vehicle traveling in front of the host vehicle increases or as the divided value obtained by dividing the inter-vehicle distance D by the vehicle speed V of the host vehicle increases, and a control unit (motor controller 12) sets the basic torque command value Tm1 to a motor torque command value Tmf* when the basic torque command value Tm1 is higher than the lower limit torque TL and controls the drive motor (motor 18) and holds the torque when the base torque command value Tm1 coincides with the lower limit torque TL as the previous value of the motor torque command value Tmf*. When the current value of the lower limit torque TL is equal to or less than the previous value of the motor torque command value Tmf*, the motor torque command value setting unit (motor controller 12) sets the current value of the motor torque command value Tmf* to the higher of the current value of the base torque command value Tm1 and the current value of the lower limit torque TL, and when the current value of the lower limit torque TL is higher than the previous value of the motor torque command value Tmf*, sets the current value of the motor torque command value Tmf* to the higher of the current value of the base torque command value Tm1 and the previous value of the motor torque command value Tmf*.

With the above configuration, regardless of the current value of the lower limit torque TL, the motor torque command value Tmf*, i.e., the braking torque, will be equal to or less than the braking torque due to the previous value of the motor torque command value Tmf* until the current value of the basic torque command value Tm1 exceeds the previous value of the motor torque command value Tmf*, so that a decrease in braking torque unintended by the driver can be suppressed. In addition, when the current value of the lower limit torque TL becomes lower than the previous value of the motor torque command value Tmf*, the current value of the motor torque command value Tmf* is set to the current value of the lower limit torque TL, so that the braking torque is increased when the inter-vehicle distance D becomes shorter, and the amount of accelerator pedal operation by the driver can be reduced.

Although the embodiments of the present invention have been described above, the above embodiments merely show some of the application examples of the present invention, and the technical scope of the present invention is not intended to be limited to the specific configurations of the above embodiments. Furthermore, the above embodiments can be combined as appropriate.

10 Electric vehicle, 12 Motor controller, 18 Motor

Claims (3)

1. A method for controlling an electric vehicle, comprising: generating a basic torque command value based on an accelerator opening degree, and when the accelerator opening degree is decreasing, the basic torque command value becomes a braking torque for a drive motor of the vehicle,
calculating a lower limit torque as the braking torque becomes larger as the inter-vehicle distance between the host vehicle and a preceding vehicle traveling in front of the host vehicle becomes longer or as a divided value obtained by dividing the inter-vehicle distance by a vehicle speed of the host vehicle becomes larger;
when the basic torque command value is higher than the lower limit torque, the basic torque command value is set as a motor torque command value to control the drive motor based on the motor torque command value, and a torque when the basic torque command value coincides with the lower limit torque is held as a previous value of the motor torque command value;
when the current value of the lower limit torque is equal to or less than the previous value of the motor torque command value, the current value of the base torque command value or the current value of the lower limit torque, whichever is higher, is set as the current value of the motor torque command value;
a current value of the motor torque command value being set to the higher of the current value of the base torque command value and the previous value of the motor torque command value when the current value of the lower limit torque is higher than the previous value of the motor torque command value. The method for controlling an electric vehicle according to claim 1, further comprising adding to the basic torque command value a correction torque that is zero when the vehicle distance is equal to or greater than a predetermined threshold, that is less than zero when the vehicle distance falls below the threshold, and that monotonically decreases as the vehicle distance decreases. 1. A control system for an electric vehicle, which generates a basic torque command value based on an accelerator opening degree, and when the accelerator opening degree decreases, the basic torque command value becomes a braking torque for a drive motor of the vehicle,
a lower limit torque calculation unit that calculates a lower limit torque as the braking torque becomes longer as a vehicle-to-vehicle distance between the host vehicle and a preceding vehicle traveling in front of the host vehicle becomes longer or as a divided value obtained by dividing the vehicle-to-vehicle distance by a vehicle speed of the host vehicle becomes higher;
a motor torque command value setting unit that, when the base torque command value is higher than the lower limit torque, sets the base torque command value as a motor torque command value to control the drive motor based on the motor torque command value, and holds a torque when the base torque command value coincides with the lower limit torque as a previous value of the motor torque command value,
The motor torque command value setting unit is
when the current value of the lower limit torque is equal to or less than the previous value of the motor torque command value, the current value of the base torque command value or the current value of the lower limit torque, whichever is higher, is set as the current value of the motor torque command value;
a current value of the motor torque command value that is greater than the current value of the base torque command value or the previous value of the motor torque command value when the current value of the lower limit torque is higher than the previous value of the motor torque command value;

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