JP7735664B2 - Electric vehicle control device - Google Patents

Description

This invention relates to a control device for an electric vehicle that controls the amount of regeneration of a motor connected to the drive wheels.

Patent Document 1 describes a regenerative braking control device for an electric vehicle that is configured to recover energy while achieving a good braking feel during deceleration. The control device described in Patent Document 1 is configured to brake the vehicle using braking torque from a mechanical brake device (friction braking device) and regenerative braking (regenerative torque) from a motor. Specifically, the control device estimates the maximum braking torque (ideal braking torque) within the range in which the wheels do not lock, sets the mechanical braking torque so that it is smaller than that ideal braking torque, and sets the braking torque that is the difference between that ideal braking torque and the mechanical braking torque as the regenerative braking torque. Note that the ideal braking torque is estimated based on the vehicle weight and height (or height of the center of gravity) of the electric vehicle.

Japanese Patent Application Laid-Open No. 2010-200590

In electric vehicles, it is desirable to set a large amount of regeneration from the motor. This amount of regeneration is set based on the vehicle's weight. The control device described in the aforementioned Patent Document 1 is configured to estimate the ideal braking torque based on the vehicle weight and brake the vehicle using mechanical braking torque and regenerative braking torque. However, in the case of towing vehicles such as trucks, the vehicle weight varies significantly depending on the load condition. For example, if the target regeneration amount is set based on a heavy load, when the load decreases, the regenerative torque braking amount may become excessive, causing the drive wheels to slip. On the other hand, if the target regeneration amount is set based on a light load, when the load increases, the regeneration amount decreases, reducing regenerative efficiency. Furthermore, even with the same load and vehicle weight, the limit at which the drive wheels slip will change depending on the shape of the load or the position and method of loading or towing, and ultimately the regeneration amount. In such cases, depending on the vehicle's load status or towing condition, the energy regeneration efficiency may decrease, resulting in energy regeneration loss.

The present invention has been devised with an eye on the above-mentioned technical problems , and aims to provide a control device for an electric vehicle that is capable of suppressing the occurrence of regenerative energy loss by taking into account the traction state.

In order to achieve the above object, the present invention provides a control device for an electric vehicle that includes at least a motor having a power generating function and is configured to brake the vehicle using the regenerative torque of the motor when decelerating, and that includes a controller for controlling the electric vehicle, wherein the controller is configured to determine the center of gravity position of the electric vehicle during transportation based on the towing state of an object being transported by the electric vehicle, calculate a drive wheel distance which is the distance from the center of gravity position during transportation to the drive wheels, estimate the load acting on the drive wheels based on the drive wheel distance, the wheelbase of the electric vehicle, and the weight of the electric vehicle including the weight of the object being transported, and set the amount of regeneration of the motor based on the estimated load.

According to this invention, the center of gravity position of the vehicle during transportation and the drive wheel distance, which is the distance from the center of gravity position during transportation to the drive wheels, are calculated based on the towing state of the load. Then, the load acting on the drive wheels is estimated based on the drive wheel distance, the wheelbase of the electric vehicle, and the weight of the electric vehicle, including the weight of the load, to determine the deceleration limit (slip limit) at which the drive wheels do not slip. The amount of regeneration of the motor is then set according to the load acting on the drive wheels and the deceleration limit. Therefore, as described above , even if the load acting on the drive wheels varies depending on the towing position and method, the amount of regeneration can be set according to the towing state. In other words, an appropriate amount of regeneration can be set according to the vehicle state, thereby avoiding or suppressing regeneration loss. In other words, a decrease in energy efficiency can be avoided or suppressed.

1 is a diagram schematically illustrating a vehicle to which an embodiment of the present invention is applied; 10A and 10B are diagrams for explaining the center of gravity position and the driving wheel distance; FIG. 10 is a diagram for calculating a change in driving wheel distance. 10 is a diagram for calculating the variation of the center of gravity position and the driving wheel distance. FIG.

Embodiments of the present invention will be described with reference to the drawings. Note that the embodiments shown below are merely examples of how the present invention can be realized and are not intended to limit the scope of the present invention.

The vehicle targeted by this embodiment of the present invention is an electric vehicle equipped with at least a motor with a power generating function and a battery capable of supplying and receiving electric power to the motor. Alternatively, it may be a hybrid vehicle further equipped with an engine as a power source.

Figure 1 shows a specific example of an electric vehicle according to an embodiment of the present invention. The electric vehicle (hereinafter referred to as "vehicle") Ve shown in Figure 1 generates driving force by transmitting driving torque output by a motor 1, which serves as a driving force source, to rear wheels 2. In other words, Figure 1 shows the configuration of a rear-wheel drive vehicle in which the rear wheels 2 are the driving wheels. Note that the vehicle Ve in this embodiment of the present invention may also be a front-wheel drive vehicle in which the front wheels 3 are the driving wheels. Alternatively, it may be a four-wheel (all-wheel) drive vehicle in which both the front wheels 3 and the rear wheels 2 are driving wheels. Furthermore, if an engine is installed as the driving force source, a transmission (not shown) may be provided on the output side of the engine, and the driving torque output by the driving force source may be transmitted to the driving wheels via the transmission.

Motor (MG) 1 is configured, for example, as a permanent magnet synchronous motor or an induction motor. Therefore, motor 1 generates driving torque when supplied with electric power, and generates electricity when forced to rotate by the inertial force of the vehicle Ve while it is running. The negative torque that accompanies this electricity generation becomes the braking force (braking torque) for the vehicle Ve.

The motor 1 is connected to a power supply 4. This power supply 4 supplies power to the motor 1 and also includes a storage device that stores the power generated by the motor 1, an inverter that converts voltage or frequency, and more.

The output shaft (rotor shaft) of the motor 1 is connected to a differential gear 5, which is a final reduction gear. The differential gear 5 is configured to output drive torque for running to the rear wheels (drive wheels) 2. The front wheels 3 are steerable wheels, and are connected to a steering mechanism 6.

A brake device 7 is provided on each of the front wheels 3 and rear wheels 2. This brake device 7 is similar to a conventionally known brake mechanism and may be a friction brake such as a disc brake, drum brake, or powder brake. In other words, the brake device 7 is configured to generate a friction force using hydraulic pressure or electromagnetic force, thereby generating a braking force in a direction that stops the rotation of the front wheels 3 and rear wheels 2.

The vehicle is also provided with pedals 8 for controlling driving conditions such as acceleration and deceleration. The pedals 8 may consist of two pedals: an accelerator pedal and a brake pedal, or may be a so-called one-pedal acceleration/deceleration control device.

The vehicle is also provided with an electronic control unit (ECU) 9 that controls the motor 1, power supply 4, brake device 7, and other components. The ECU 9, which corresponds to the "controller" in this embodiment of the present invention, is primarily comprised of a microcomputer and is configured to perform calculations using input data, pre-stored data, and programs, and to output the calculation results as control command signals. The input data includes, for example, vehicle speed, acceleration, accelerator opening (i.e., required drive force), brake pedal force, road surface friction coefficient μ, vehicle weight, wheel speeds of each wheel, the position (or height) of the center of gravity of the vehicle Ve, the distance from the center of gravity to the drive wheels (drive wheel distance), the on/off status of the towing switch, the rotation speed and torque of the motor 1, and various other sensor values. The pre-stored data includes a map that determines the regenerative braking torque based on the center of gravity position and drive wheel distance. The ECU 9 outputs, as control command signals, a torque (drive torque, regenerative torque) command signal for the motor 1 and a braking torque command signal for the brake device. Although the example of FIG. 1 shows an example in which one ECU is provided, a plurality of ECUs may be provided, for example, for each device to be controlled or for each control content.

In an electric vehicle Ve configured as described above, it is preferable to set the motor's regeneration amount to a large value. On the other hand, in a towing vehicle such as a truck, the regeneration amount varies depending on the load condition of the cargo. For example, when the load is heavy or light, or even when the load and vehicle weight are the same, the limit at which the drive wheels slip varies depending on the shape of the load (the transported object in this invention) and the loading or towing position and method, and as a result, the regeneration amount also varies. In such cases, the energy regeneration efficiency decreases, which may result in energy regeneration loss. Therefore, in this embodiment of the present invention, the regeneration amount is configured to be set depending on the towing condition of the vehicle.

Specifically, the ECU 9 is configured to calculate the upper limit deceleration at which regeneration is possible by the motor 1. In other words, the ECU 9 is configured to calculate the deceleration limit value (slip limit value) at which the rear wheels 2 do not slip.

Figure 2 is a diagram illustrating the center of gravity position of vehicle Ve and the distance between that center of gravity position and the drive wheels (hereinafter simply referred to as drive wheel distance). Figure 2(a) is a diagram illustrating the center of gravity position H_base and drive wheel distance Lr_base when not towing. Figure 2(b) is a diagram illustrating the center of gravity position H_add(a) and drive wheel distance Lr_add(a) when a towing object 10 such as luggage or a trailer house is towed behind the vehicle. Figure 2(c) is a diagram illustrating the center of gravity position H_add(b) and drive wheel distance Lr_add(b) when a towing object 10 such as luggage is loaded on top of the vehicle.

In this embodiment of the invention, the regeneration amount without towing shown in Figure 2(a) is set as the reference state, and the vehicle weight M_add, the height of the center of gravity when towing H_add, and the drive wheel distance Lr_add are calculated relative to this reference state. In other words, correction values for these three parameters are calculated. The load acting on the drive wheels is then calculated based on these correction values. The slip limit (deceleration that does not cause slip) is then calculated based on the load acting on the drive wheels (i.e., rear wheels 2), and the target regeneration amount is set. Note that the ellipses in Figure 2(a) to (c) indicate the friction limit (slip limit). In other words, they indicate the magnitude of the load acting between the rear wheels 2 and the road surface (friction circle range).

The above-mentioned drive wheel distance Lr_add may be calculated depending on whether the wheels (wheels of the towed object) of the towed object 10 are in contact with the road surface, or whether the towed object is a load that does not contact the road surface. Furthermore, the drive wheel distance Lr_add may be calculated based only on the increase or decrease in the distance in the fore-and-aft direction of the vehicle, and may also take into account the increase or decrease in the vehicle's height. Furthermore, if the towed object 10 moves laterally while traveling, the correction value may be set smaller than in normal cases where the towed object 10 does not move while traveling, taking into account slippage during turns, etc.

The magnitude of the friction limit ar of the rear wheels (drive wheels) 2 shown by the friction circles in Figures 2(a) to 2(c) can be expressed by the following formula. First, the load Wr and the load change dw of the rear wheels 2, which are regenerative wheels, are expressed as follows:
Wr=M×g×(L-Lr)/L...(1)
dw=(M×ar×H)/L...(2)
where M represents the vehicle weight, g represents the gravitational acceleration, L represents a predetermined wheelbase , and Lr represents the distance from the center of gravity of the vehicle to the drive wheels (drive wheel distance) . Using these equations, the friction limit ar of the rear wheels 2 can be calculated as follows:
M×ar=μ× (Wr+dW)
=μ×(M×g×(L-Lr)/L+(M×ar×H)/L)
where μ represents the friction coefficient of the road surface. Finally, the friction limit ar of the rear wheel 2 is
ar×(1-(μ×H)/L)=g×(μ×(L-Lr)/L)
And further organizing it,
ar=g×(μ×(L-Lr))/(L-μ×H)...(3)
Here, H indicates the height of the center of gravity.

Calculating the friction limit ar for the examples shown in Figures 2(b) and 2(c) using equation (3), we find that the drive wheel distance Lr_add is smaller in Figure 2(b) than in Figure 2(c), and the height H_add of the center of gravity is lower in Figure 2(b ) than in Figure 2(c). Therefore, the friction limit ar is larger in Figure 2(b) than in Figure 2(c), and therefore the friction circle (slip limit) is also larger in Figure 2(b). In other words, even when towing an object with the same load, towing it from the rear of the vehicle as in Figure 2(b) will result in a greater amount of regeneration than towing it in an upward direction as in Figure 2(c).

In this way, in this embodiment of the present invention, the regeneration amount, which varies depending on the towing position and method, is set by determining the friction limit (i.e., slip limit) from the center of gravity position, drive wheel distance, and the load acting on the drive wheels (rear wheels) 2. Therefore, an appropriate regeneration amount can be set according to the state of the vehicle Ve, and as a result, regeneration loss can be avoided or suppressed. In short, the friction limit ar changes depending on the center of gravity position H_add and drive wheel distance Lr_add described above, which in turn changes the amount of power that can be regenerated. Therefore, by setting the target regeneration amount according to the friction limit ar, it is possible to avoid or suppress a decrease in energy regeneration efficiency.

The above describes an embodiment of the present invention, but the present invention is not limited to the above example and may be modified as appropriate within the scope of achieving the object of the present invention. As described above, the friction limit ar changes depending on the vehicle weight M_add, center of gravity position H_add, and drive wheel distance L_add, which are amounts of change from reference values, and the amount of regeneration also changes accordingly. Therefore, the method of calculating the friction limit ar is not limited to the above example.

For example, the vehicle weight M_add may be calculated from the driving power required during acceleration. Furthermore, the drive wheel distance L_add may be calculated based on the change in the center of gravity position (center of gravity position during transport ) from the state without a load being transported, calculated based on the towing state, such as the change in the acceleration sensor value, the vertical lift of the vehicle, or the change in the viewing angle of the onboard camera . For example, as shown in FIG. 3 , the change in the drive wheel distance L_add is calculated based on the acceleration and sensor values a given number of times (for example, four times). Furthermore, as shown in FIG. 4 , the change in the center of gravity position H_add may be detected by an onboard camera 11 mounted in front of the vehicle, and the change may be displayed on a display (for example, a navigation system display) 12. In this case, the center of gravity position H_add and the drive wheel distance L_add are corrected according to the change indicated by the solid line relative to the reference indicated by the dashed line. Note that FIG. 4A shows the change relative to the reference during acceleration without towing, and FIG. 4B shows the change relative to the reference during acceleration with towing.

1 Motor 2 Rear wheels (drive wheels)
3 Front wheels 4 Power supply unit 5 Differential gear 6 Steering mechanism 7 Brake device 8 Pedal 9 Electronic control unit (ECU)
10 towed object 11 in-vehicle camera 12 display Ve vehicle

Claims (1)

A control device for an electric vehicle including a motor having at least a power generating function, the control device being configured to brake the vehicle by a regenerative torque of the motor during deceleration,
a controller for controlling the electric vehicle;
The controller
determining a center of gravity position of the electric vehicle during transportation based on a towing state of the transported object transported by the electric vehicle;
Calculating a drive wheel distance, which is the distance from the center of gravity position during transport to the drive wheel;
estimating a load acting on the drive wheels based on the drive wheel distance, a wheel base of the electric vehicle, and a weight of the electric vehicle including a weight of the transported object;
A control device for an electric vehicle, characterized in that the control device is configured to set a regeneration amount of the motor based on the estimated load.