JP7757670B2 - Control method for electric vehicle and electric vehicle - Google Patents

Description

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

Patent Document 1 discloses an electric vehicle equipped with a motor as a first driving force source for driving the vehicle, and a flywheel as a second driving force source for recovering and storing the vehicle's kinetic energy as mechanical energy. The document also discloses control in which the vehicle's kinetic energy is recovered and stored in the flywheel as mechanical energy when the vehicle decelerates, and then that mechanical energy is used to drive the vehicle when it accelerates.

JP 2015-116106 A

The control described in the above document requires deceleration in order to store mechanical energy in the flywheel. This creates the problem that mechanical energy cannot be stored in the flywheel in situations where high-load driving is performed continuously, such as when driving on highways in North America.

The present invention aims to enable the storage of mechanical energy in the flywheel even during continuous high-load driving.

According to one aspect of the present invention, there is provided a control method for an electric vehicle including a power storage device, a first motor as a main drive source operated by electric energy from the power storage device, a flywheel as a sub-drive source, and a controller that controls drive force. In the control method, the controller performs an energy storage operation in which the first motor rotates the flywheel to store rotational energy in the flywheel when the output of the power storage device is lower than maximum output , and after performing the energy storage operation, determines whether acceleration is necessary while traveling based on at least information related to the position and speed of the host vehicle and information related to a vehicle in front, and if acceleration is not necessary, stores the rotational energy as electric energy in the power storage device .

The above aspect makes it possible to store rotational energy (mechanical energy) in the flywheel even when driving under continuous high loads.

FIG. 1 is a schematic diagram of a powertrain of an electric vehicle according to the first embodiment. FIG. 2 is a time chart of the vehicle speed and battery output when a typical electric vehicle is running. FIG. 3 is a flowchart showing a control routine according to the first embodiment. FIG. 4 is a timing chart when the control routine according to the first embodiment is executed. FIG. 5 is a schematic diagram of a powertrain of an electric vehicle according to the second embodiment. FIG. 6 is a schematic diagram of a powertrain of an electric vehicle according to the third embodiment.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

[First embodiment]
The first embodiment will be described with reference to FIGS. 1 to 4. FIG.

Figure 1 is a schematic diagram of the powertrain of an electric vehicle 1 (hereinafter simply referred to as "vehicle 1") according to this embodiment. In the following description, the direction of travel of vehicle 1 will be referred to as "front," the direction of reversal will be referred to as "rear," the left side of vehicle 1's direction of travel will be referred to as "left," and the right side will be referred to as "right."

The vehicle 1 includes a first motor 2 as the main drive source, a battery 3 as an electricity storage device that supplies power (electrical energy) to the first motor 2, a controller 4 that controls the driving force, and a left front wheel 12FL and a right front wheel 12FR that are driven by the driving force generated by the first motor 2. Note that when there is no need to distinguish between the left front wheel 12FL and the right front wheel 12FR, they are sometimes collectively referred to as the front wheels 12F. In addition, while the electricity storage device in this embodiment is a battery 3, it is not limited to this and may be any device that has a storage function, such as a capacitor.

The first motor 2 is located in a motor room provided at the front of the vehicle body. The driving force generated by the first motor 2 is transmitted to the left front wheel 12FL and right front wheel 12FR via the power transmission mechanism 11, a gearbox 8 including a final gear, and the left front wheel drive shaft 9FL and right front wheel drive shaft 9FR. The power transmission mechanism 11 may be any mechanism capable of transmitting the power of the first motor 2, and may be, for example, a gear set consisting of multiple spur gears.

The controller 4 includes an inverter that controls the input and output power of the battery 3, and controls the input and output power of the battery 3 and the output of the first motor 2 according to the required driving force.

The vehicle 1 also includes a flywheel (hereinafter sometimes abbreviated as "FW") 5 as an auxiliary drive source. FW5's rotational axis is collinear with the rotational axes of the left rear wheel 12RL and right rear wheel 12RR, and is connected to the left rear wheel 12RL via the left rear wheel drive shaft 10RL and to the right rear wheel 12RR via the right rear wheel drive shaft 10RR. A second clutch 7 (CL2 in the figure) is installed between the left rear wheel drive shaft 10RL and the right rear wheel drive shaft 10RR, connecting and disconnecting power transmission between FW5 and the left rear wheel 12RL and right rear wheel 12RR. When there is no need to distinguish between the left rear wheel 12RL and the right rear wheel 12RR, they are sometimes collectively referred to as the rear wheel 12R.

FW5 is also connected to the first motor 2 via an auxiliary power transmission mechanism 11A branching off from the power transmission mechanism 11. A first clutch 6 (CL1 in the figure) is installed in the auxiliary power transmission mechanism 11A, which connects and disconnects the power transmission between the first motor 2 and FW5. The auxiliary power transmission mechanism 11A can be any mechanism capable of transmitting power from the first motor 2 located at the front of the vehicle to FW5 located at the rear of the vehicle, and can, for example, be a transmission mechanism combining a rotating shaft extending in the fore-and-aft direction of the vehicle with a bevel gear.

The first clutch 6 and the second clutch 7 can be a known clutch mechanism, such as a friction clutch, that has the function of connecting and disconnecting power transmission. Furthermore, the first clutch 6 and the second clutch 7 are switched between engaged and disengaged states by the controller 4.

In the vehicle 1 described above, when the first motor 2 is driven by power from the battery 3 with the first clutch 6 engaged and each second clutch 7 disengaged, FW5 rotates. Even if the first clutch 6 is subsequently disengaged, FW5 continues to rotate by inertia. In other words, the electrical energy of the battery 3 is stored in FW5 as rotational energy. Rotating FW5 with the first motor 2 in this way and storing rotational energy in FW5 is also referred to as energy storage operation.

When each second clutch 7 is engaged while rotational energy is stored in FW5, the left rear wheel 12RL and the right rear wheel 12RR are driven by the stored rotational energy.

Figure 2 is a time chart of vehicle speed and battery output when a typical electric vehicle (i.e., an electric vehicle without FW5) is traveling. This time chart is for a situation where high-speed traveling continues for an extended period of time, such as on a highway in North America.

Even when driving at high speeds, battery output is not very large and remains nearly constant as long as the vehicle speed remains constant. On the other hand, battery output increases during acceleration. In particular, when accelerating from high speeds, as in area A in the diagram, battery output increases significantly, reaching its maximum value during driving. When determining the capacity of the battery to be installed in an electric vehicle, this maximum battery output during driving must be taken into consideration. In other words, if the maximum battery output during driving can be reduced, the battery capacity can be reduced, which in turn allows the power unit to be made more compact.

In this embodiment, during high-load driving, such as when accelerating from a high vehicle speed, not only are the front wheels 12F driven by the first motor 2, but the rear wheels 12R are also driven using the rotational energy stored in FW5. In other words, the required output is not met solely by the first motor 2, but part of it is met by the rotational energy of FW5. This makes it possible to reduce the output of the battery 3, which is the power source for the first motor 2.

It is conventionally known to provide a FW5 as an auxiliary power source and utilize the rotational energy of the FW5 during acceleration at start-up, etc. However, in conventional systems, the kinetic energy of the vehicle 1 is stored as rotational energy in the FW5 during deceleration. Therefore, when high-speed driving continues for an extended period of time, it is not possible to store rotational energy in the FW5.

In contrast, in the vehicle 1 of this embodiment, FW5 is rotated by the driving force of the first motor 2, so rotational energy can be stored in FW5 even when the vehicle is not decelerating. Therefore, rotational energy can be stored in FW5 even when the vehicle continues to travel at high speed for an extended period of time, and the rotational energy of FW5 can be used when accelerating from a high vehicle speed. The control of FW5 in this embodiment is described below.

Figure 3 is a flowchart showing the FW5 control routine executed by controller 4. This control routine stores rotational energy in FW5 when the battery 3 output is lower than maximum output if future acceleration is predicted during constant speed driving, and uses that rotational energy for driving during acceleration. For example, if the required output during acceleration is 100 kW, the output of first motor 2 is set to 70 kW, and the remaining 30 kW is covered by the rotational energy of FW5. FW5 is then rotated so that it has enough rotational energy to generate 30 kW.

The following is a detailed explanation of the steps in the flowchart.

In step S100, controller 4 determines whether the vehicle is moving based on the vehicle speed. If the vehicle is moving, it executes the processing of step S101; if the vehicle is not moving, it ends the current routine. The vehicle speed used for this determination may be the value detected by a vehicle speed sensor (not shown) provided on vehicle 1, or may be a value calculated based on a signal from an artificial satellite or the like.

In step S101, the controller 4 reads vehicle 1's position information, speed information, and leading vehicle information obtained from radar, sensors, GPS (Global Positioning System), car navigation systems, etc. (none of which are shown) mounted on the vehicle 1. The leading vehicle information includes, for example, the vehicle speed of the leading vehicle and the distance between vehicle 1 and the leading vehicle. The vehicle 1's position information includes not only the current position of vehicle 1, but also the upcoming driving route.

In step S102, controller 4 determines whether or not there is a shortage of rotational energy (also referred to as FWE) for FW5. If there is a shortage, it executes the processing of step S103, and if there is no shortage, it executes the processing of step S104. An insufficient FWE means that the output allocated to FW5 during acceleration cannot be covered.

In step S103, controller 4 determines whether there is a margin in the battery output. If there is a margin, it executes the processing of step S104. If there is no margin, it ends the current routine. A margin in the battery output refers to a case where the current battery output is lower than the maximum output of battery 3, such as when driving at a constant speed. In other words, the determination in step S103 determines whether energy storage operation can be performed.

In step S104, controller 4 determines whether acceleration is necessary, and if acceleration is necessary, executes the processing of step S105, or if acceleration is not necessary, executes the processing of step S114. Whether acceleration is necessary is determined based on the information read in step S101. A determination that acceleration is necessary occurs, for example, when it is predicted from the inter-vehicle distance and relative speed between vehicle 1 and the vehicle in front that vehicle 1 will catch up with the vehicle in front and an overtaking operation will be necessary. It is also determined that acceleration is necessary when it is known from map information in the car navigation system that the speed limit will increase up ahead.

In step S105, controller 4 determines whether or not it is necessary to generate an FWE, i.e., whether or not it is necessary to perform an energy storage operation. If it is not necessary to generate an FWE, it executes the processing of step S106, and if it is necessary, it executes the processing of step S107. For example, if the current vehicle speed of vehicle 1 is high (e.g., 80 km/h or higher), the battery output will be at or near maximum output in order to accelerate from there, so it is determined that it is necessary to generate an FWE.

In step S106, the controller 4 holds the FWE. In other words, if FW5 is already rotating, it maintains the rotating state, and if FW5 is stopped, it maintains the stopped state.

In step S107, controller 4 generates FWE, i.e., performs energy storage operation.

After completing the processing of step S106 or step S107, the controller 4 determines in step S108 whether or not FWE needs to be released. If release is necessary, the controller executes the processing of step S109. If release is not necessary, the controller returns to the processing of step S101. Here, the controller determines whether or not FWE needs to be used to suppress peak battery output based on various requirements, and if FWE use is necessary, the controller determines that release is necessary. For example, the controller determines that release is necessary when starting acceleration from a high vehicle speed, when catching up with a vehicle in front and starting to overtake, when the accelerator pedal is depressed heavily, etc. Furthermore, if the vehicle is equipped with a switch that allows the driver to select whether or not to use FWE during acceleration, and the switch has selected the use of FWE, the controller also determines that release is necessary.

If it is determined that release is necessary, the controller 4 releases the FWE by engaging the second clutch 7 in step S109.

After releasing the FWE in step S109, the controller 4 reads information in step S110 in the same way as in step S101, and determines whether acceleration is necessary in step S111 in the same way as in step S104. If it is determined in step S111 that acceleration is necessary, the process returns to step S102, and if it is determined that acceleration is not necessary, the process executes step S112.

In step S112, the controller 4 determines whether or not there is any remaining amount of FWE. If there is any remaining amount, it executes the processing of step S113; if there is no remaining amount, it ends this routine.

In step S113, the controller 4 charges the battery 3 with the FWE as electrical energy. Specifically, when the first motor 2 is capable of regenerative power generation, the first clutch 6 is engaged to rotate the first motor 2 using the FWE to generate regenerative power, and the electrical energy generated thereby is charged into the battery 3. This stops the rotation of the FW5.

Steps S114 and S115, which are executed when it is determined in step S104 that acceleration is not required, are the same as steps S112 and S113 described above.

The reason why battery 3 is charged using FWE in steps S113 and S115 is as follows:

When FW5 rotates, there is a risk of vibration occurring due to the rotation. Furthermore, when FW5 rotates, a gyro moment is generated when the vehicle 1 moves up and down in response to unevenness in the road surface or when turning around a curve in the road. This gyro moment acts in a direction that tilts the vehicle body and changes the direction of the vehicle body, reducing the maneuverability and handling stability of the vehicle 1.

Therefore, when it is determined that acceleration is not necessary, FW5 is stopped to suppress the effects of vibration and gyro moment associated with rotation. However, simply stopping FW5 would waste the FWE, so the FWE is converted into electrical energy and charged into battery 3.

Figure 4 is an example timing chart when the above control routine is executed. The dashed lines in the chart of battery output and first motor output represent the case when FW5 is not installed.

A stopped vehicle 1 starts moving at timing T1, and at timing T2, it finishes acceleration and starts constant-speed driving. As it reaches constant-speed driving, the battery output and the output of the first motor also become approximately constant. The above information is also read to determine whether or not there will be further acceleration. If it detects at timing T3 that acceleration is necessary, energy storage operation begins at timing T4. The battery output increases temporarily to perform the energy storage operation, but once the FWE is generated, it returns to the magnitude before the energy storage operation began.

When acceleration begins at timing T5, the battery output is increased to increase the output of the first motor 2, and FWE is released. Without FW5, this acceleration would increase the battery output to its maximum. In contrast, in the vehicle 1 of this embodiment, the FWE stored in FW5 is used as driving force, so the same acceleration force can be obtained with a lower motor output than when FW5 is not provided. Because the output of the first motor 2 is lower, the battery output is also lower than when FW5 is not provided.

Then, at timing T6, acceleration ends and constant speed traveling begins again. Note that Figure 4 shows the case where the FWE is used up during acceleration from timing T5 to timing T6, but if there is FWE remaining at timing T6, the remaining FWE will be used to charge battery 3 as described above.

As described above, this embodiment provides an electric vehicle equipped with a battery 3 (power storage device), a first motor 2 as a main drive source powered by the electric energy of the battery 3, a flywheel 5 as a secondary drive source, and a controller 4 that controls drive force. The controller 4 performs an energy storage operation in which the first motor 2 rotates the flywheel 5 and stores rotational energy in the flywheel 5 when the output of the battery 3 is lower than the maximum output. This allows rotational energy to be stored in the flywheel 5 even when not decelerating.

In this embodiment, the controller 4 uses the rotational energy for driving in combination with the driving force of the first motor 2, for example, during high-load driving. As a result, when accelerating from a state of continuous high-speed driving, for example, the amount of energy taken from the battery 3 can be reduced by the amount of rotational energy used by the FW 5. In other words, the required acceleration can be achieved while suppressing the peak of battery output during acceleration.

In this embodiment, the controller 4 performs energy storage operation when the output of the battery 3 is lower than the maximum output and the vehicle is traveling at a constant speed. In this way, when there is a margin of battery output, the energy storage operation can be performed appropriately.

In this embodiment, the controller 4 may store the rotational energy in the battery 3 as electrical energy. For example, this may occur when an energy storage operation has been performed but the rotational energy no longer needs to be used for driving. This prevents the rotational energy from going to waste even when rotational energy has been generated but there is no longer an opportunity to use it.

In this embodiment, the flywheel 5 is connected to a drive shaft (left rear drive shaft 10RL and right rear drive shaft 10RR) different from the drive shaft (left front drive shaft 9FL and right front drive shaft 9FR) driven by the first motor 2. This eliminates the need to place the flywheel 5 in the motor room where the first motor 2 and other components are located, simplifying the vehicle's on-board layout. Furthermore, the vehicle enters four-wheel drive mode during acceleration, improving driving stability.

[Second embodiment]
The second embodiment will be described with reference to FIG.

Figure 5 is a schematic diagram of the powertrain of a vehicle 1 according to this embodiment. The difference from the first embodiment is that there is no auxiliary power transmission mechanism 11A that transmits the power of the first motor 2 to FW5, and instead a second motor 13 is provided to drive FW5. Regarding control, the difference is that when performing energy storage operation, FW5 is driven by the second motor 13 instead of the first motor 2.

In this embodiment, by providing a second motor 13 separate from the first motor 2 for driving FW5, controllability is improved compared to the configuration of the first embodiment. That is, in the configuration of the first embodiment, when controlling the output of the first motor 2, it is necessary to calculate a target output that combines the output for driving and the output for energy storage operation, whereas in the configuration of this embodiment, it is sufficient to calculate the target output for each motor 2, 13. Furthermore, in the vehicle 1 of the first embodiment, the processing of steps S113 and S115 of the control routine described above cannot be executed unless the first motor 2 is in a state where regeneration is possible, but in the vehicle 1 of this embodiment, these processes can be executed at any time.

Furthermore, since the battery 3 and the second motor 13 can be connected by electrical wiring, the auxiliary power transmission mechanism 11A is not required. This eliminates restrictions on the handling of the auxiliary power transmission mechanism 11A, improving the design freedom of the vehicle 1.

The second motor 13, FW 5, first clutch 6, and second clutch 7 may be integrated into a FW unit. This integration makes installation on the vehicle 1 easier than installing each element separately on the vehicle 1. Furthermore, housing the FW unit in a compact housing increases the flexibility of the vehicle layout.

As described above, this embodiment further includes a second motor 13 separate from the first motor 2. The controller 4 then performs an energy storage operation in which the second motor 13, instead of the first motor 2, rotates the flywheel 5 and stores rotational energy in the flywheel 5 when the output of the battery 3 is lower than its maximum output. By providing the second motor 13 for driving the flywheel 5 in addition to the first motor 2 as the main drive source, the controllability of output control is improved. Furthermore, by eliminating the need for the auxiliary power transmission mechanism 11A from the first motor 2 to the flywheel 5, the degree of freedom in vehicle layout is improved.

[Third embodiment]
The third embodiment will be described with reference to FIG.

Figure 6 is a schematic diagram of the powertrain of a vehicle 1 according to this embodiment. The difference from the second embodiment is that there are two FWs 5, instead of one in the second embodiment. Hereinafter, the two FWs 5 will be referred to as a first FW 5A and a second FW 5B, respectively. Note that when there is no particular need to distinguish between them, they will be referred to as FWs 5.

The first FW5A and second FW5B are capable of generating the same output, but the output they can generate is smaller than that of the FW5 in the second embodiment. However, the total output of the two FW5s is equal to or greater than that of the FW5 in the second embodiment. For example, if the output that the FW5 in the second embodiment can generate is 30 kW, then the output that the first FW5A and second FW5B can generate is 20 kW.

By dividing the FW5 into two units as described above, the degree of freedom in vehicle layout is increased.

Furthermore, the greater the output of FW5, the greater the strength required for each element, such as the bearings of FW5, the fixing members that secure FW5 to vehicle 1, and the mounting parts on the vehicle 1 side. Furthermore, the greater the strength of these elements, the higher the cost. In this regard, by dividing FW5 into two pieces, as in this embodiment, the strength required for each element can be reduced compared to when there is only one piece, resulting in reduced costs.

As described above, in this embodiment, the flywheel 5 comprises a first flywheel 5A connected to one of the left and right drive wheels 12RL, 12RR, and a second flywheel 5B connected to the other. This increases the degree of freedom in vehicle layout. It also reduces costs while ensuring acceleration force equal to or greater than that achieved with a single flywheel 5.

In the above-described embodiments, the electric vehicle 1 has been described as a so-called battery electric vehicle (BEV), in which the only drive source is the first motor and the only power source is the battery 3, but the electric vehicle 1 to which each embodiment can be applied is not limited to this. For example, it may be a so-called extended-range electric vehicle equipped with a power-generating engine, or a so-called hybrid electric vehicle equipped with a motor as one of multiple drive sources.

Furthermore, in each of the above-described embodiments, a configuration has been described in which the first motor 2 drives the front wheel 12F and the FW5 drives the rear wheel 12R, but each of the embodiments can also be applied to a configuration in which the first motor 2 and FW5 drive the same drive wheel.

It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical concept described in the claims.

1. Electric vehicle, 2. First motor, 3. Battery, 4. Controller, 5. Flywheel, 6. First clutch, 7. Second clutch, 13. Second motor

Claims (8)

an electricity storage device;
a first motor as a main drive source that is operated by the electric energy of the power storage device;
a flywheel as a secondary drive source;
a controller for controlling the driving force;
A control method for an electric vehicle comprising:
the controller performs an energy storage operation in which the first motor rotates the flywheel to store rotational energy in the flywheel when the output of the power storage device is lower than a maximum output , and after performing the energy storage operation, determines whether acceleration is necessary while the vehicle is traveling based on at least information related to a position and speed of the vehicle and information related to a vehicle in front, and if acceleration is not necessary, stores the rotational energy in the power storage device as electrical energy . 2. The method for controlling an electric vehicle according to claim 1,
The controller uses the rotational energy for driving in combination with the driving force of the first motor. 3. The method for controlling an electric vehicle according to claim 1,
The controller uses the rotational energy for driving together with the driving force of the first motor during high-load driving. The method for controlling an electric vehicle according to any one of claims 1 to 3,
The control method for an electric vehicle, wherein the controller performs the energy storage operation when the output of the power storage device is lower than a maximum output and the vehicle is traveling at a constant speed. an electricity storage device;
a first motor as a main drive source that is operated by the electric energy of the power storage device;
a flywheel as a secondary drive source;
a controller for controlling the driving force;
In an electric vehicle equipped with
the controller performs an energy storage operation in which the first motor rotates the flywheel to store rotational energy in the flywheel when the output of the power storage device is lower than a maximum output , and after performing the energy storage operation, determines whether acceleration is necessary while the vehicle is traveling based on information related to at least a position and a speed of the vehicle and information related to a vehicle in front, and if acceleration is not necessary, stores the rotational energy in the power storage device as electrical energy . The electric vehicle according to claim 5 ,
An electric vehicle, wherein the flywheel is connected to a drive shaft different from a drive shaft driven by the first motor. 7. The electric vehicle according to claim 5 or 6 ,
further comprising a second motor separate from the first motor;
the controller performs an energy storage operation of rotating the flywheel using the second motor instead of the first motor to store rotational energy in the flywheel when the output of the power storage device is lower than a maximum output. The electric vehicle according to any one of claims 5 to 7 ,
The electric vehicle includes, as the flywheels, a first flywheel connected to one of the left and right drive wheels, and a second flywheel connected to the other of the left and right drive wheels.