JP7709099B2 - Hybrid Vehicles - Google Patents

Description

This case relates to a hybrid vehicle that implements regenerative motoring control.

Conventionally, hybrid vehicles are known that are able to obtain regenerative braking force by charging a battery with regenerative power generated by a driving motor. In this type of hybrid vehicle, there is a risk that regenerative braking force will not be obtained if the charging of the battery is limited (for example, if the battery is nearly fully charged or if the battery breaks down). Therefore, a control (regenerative motoring control) has been proposed that balances the power balance by having a motor other than the driving motor consume regenerative power and idle the engine. This type of control makes it possible to ensure regenerative braking force while limiting the charging of the battery (for example, see Patent Document 1).

JP 2020-049974 A

In the above-mentioned regenerative motoring control, the rotation speed when the engine is idling is set according to the magnitude of the regenerative power. On the other hand, if the accelerator pedal is depressed during regenerative motoring control to end regenerative power generation and the engine start conditions are met, the engine is controlled to rotate independently at a rotation speed according to the accelerator opening. This causes the engine rotation speed to fluctuate suddenly, which can cause the driver to feel uncomfortable.

For example, when the engine speed during regenerative motoring control is relatively high, if the accelerator pedal is lightly depressed, the engine speed drops suddenly and the engine noise and vibration become extremely quiet. When this happens, the driver feels as if the engine has become quieter, even though he or she is trying to accelerate the vehicle. This makes it seem as if the driver's operation of the vehicle is not in harmony with the actual behavior of the vehicle, and the driver does not get a good driving feeling.

One of the objectives of this invention was devised in light of the above-mentioned problems, and is to provide a hybrid vehicle that improves the driving feeling. However, this objective is not the only objective. Another objective of this invention is to achieve effects that cannot be obtained with conventional technology, which are derived from the configurations shown in the "Description of Embodiments" described below.

The disclosed hybrid vehicle can be realized as the following disclosed aspects or application examples, and solves at least some of the above problems.
The disclosed hybrid vehicle includes an engine, a motor that drives the wheels and performs regenerative braking, a generator that generates electricity using the driving force of the engine and drives the engine, a battery connected to the motor and the generator, and a control device that performs regenerative motoring control to supply regenerative power of the motor to the generator when the accelerator is off during driving and to motor the engine at a predetermined target rotation speed. The control device calculates a required power generation amount according to the driving state, and when the regenerative motoring control is stopped by an accelerator on operation while the regenerative motoring control is being performed, if the required power generation amount is less than a threshold, performs continuous motoring control to supply power from the battery to the generator to continue motoring of the engine.

According to the disclosed hybrid vehicle, when regenerative motoring control is stopped by accelerator-on operation, if the required power generation amount is below a threshold, continuous motoring control is implemented. Continuous motoring control is a control that continues engine motoring by supplying battery power to the generator without regenerative braking to the motor. By implementing such control, it is possible to reduce the change in engine rotation speed immediately after the end of regenerative motoring control, and to suppress sudden changes in engine operating noise and vibration. This improves the driving feeling when accelerating from regenerative motoring control.

FIG. 1 is a block diagram showing a configuration of a hybrid vehicle. 4 is a graph illustrating an example of the relationship between an accelerator opening degree and a driver requested output. 4 is a graph illustrating an example of the relationship between vehicle speed and a target rotation speed of an engine. 4 is a graph illustrating an example of the relationship between the engine rotation speed and a threshold value of the required power generation amount. 3 is a graph illustrating an example of an output characteristic of an engine. 1 is a flowchart illustrating a control flow. 4 is a time chart illustrating a control action.

The disclosed hybrid vehicle can be implemented according to the following examples.

[1. Device configuration]
1 is a block diagram illustrating the configuration of a hybrid vehicle 1 according to an embodiment. The hybrid vehicle 1 (also simply referred to as vehicle 1) is a hybrid vehicle (HEV, Hybrid Electric Vehicle) or a plug-in hybrid vehicle (PHEV, Plug-in Hybrid Electric Vehicle) equipped with an engine 2 and a motor 3 as drive sources, a generator 4 as a power generation device, and a battery 5 as a power storage device. A plug-in hybrid vehicle means a hybrid vehicle capable of externally charging the battery 5 or externally supplying power from the battery 5. A plug-in hybrid vehicle is provided with a charging port (inlet) for inserting a charging cable through which power is supplied from an external charging facility, and a receptacle (outlet) for external power supply.

The engine 2 is an internal combustion engine such as a gasoline engine or a diesel engine. A generator 4 is connected to the drive shaft of the engine 2. The generator 4 is a generator (electric motor/generator) that combines the function of driving the engine 2 with the power of the battery 5 and the function of generating electricity using the driving force of the engine 2. The generated electricity of the generator 4 is used to drive the motor 3 and charge the battery 5. A speed change mechanism (not shown) may be installed on the power transmission path connecting the engine 2 and the generator 4.

The motor 3 is an electric motor (electric motor/generator) that has both the function of propelling the vehicle 1 using the power of the battery 5 and the power generated by the generator 4, and the function of charging the battery 5 with power generated by regeneration. The battery 5 is a secondary battery such as a lithium-ion secondary battery or a nickel-metal hydride battery. The drive shaft of the motor 3 is connected to the drive wheels of the vehicle 1. A speed change mechanism (not shown) may be installed on the power transmission path connecting the motor 3 and the drive wheels.

A clutch 6 is interposed on the power transmission path connecting the engine 2 and the motor 3. The engine 2 is connected to the drive wheels via the clutch 6, and the motor 3 is disposed closer to the drive wheels than the clutch 6. The generator 4 is connected to the engine 2 side than the clutch 6. When the clutch 6 is disconnected (released), the engine 2 and the generator 4 are disconnected from the drive wheels, and the motor 3 is connected to the drive wheels. Therefore, for example, by operating only the motor 3, "EV driving (motor-only driving)" is realized. In addition, by operating the engine 2 and causing the generator 4 to generate electricity, "series driving" is realized. Series driving means that the vehicle runs on the driving force of the motor 3 while the generator 4 generates electricity with the driving force of the engine 2.

On the other hand, when the clutch 6 is connected (fastened), the engine 2, motor 3, and generator 4 are all connected to the drive wheels. Therefore, for example, by operating only the engine 2, "engine running (running only with the engine)" is achieved. In addition, by driving the motor 3 and the generator 4, "parallel running" is achieved. The above series running and parallel running are both referred to as "hybrid running".

The operating states of the engine 2, motor 3, generator 4, battery 5, and clutch 6 are controlled by a control device 10. The control device 10 is a computer (electronic control device, ECU, Electronic Control Unit) that has the function of controlling the operating states of at least the engine 2 and the generator 4. The control device 10 has a built-in processor (arithmetic processing device) and memory (storage device). The contents of the control performed by the control device 10 (control program) are stored in the memory, and are executed by appropriately loading the contents into the processor.

In this embodiment, an accelerator opening sensor 7, a brake opening sensor 8, and a vehicle speed sensor 9 are connected to the control device 10. The accelerator opening sensor 7 is a sensor that detects parameters corresponding to the amount of depression of the accelerator pedal (accelerator opening, accelerator pedal stroke, throttle opening, etc.). The brake opening sensor 8 is a sensor that detects parameters corresponding to the amount of depression of the brake pedal (brake opening, brake pedal stroke, brake fluid pressure, etc.). The vehicle speed sensor 9 is a sensor that detects the traveling speed (vehicle speed) of the vehicle 1. Information detected by each of these sensors 7 to 9 is transmitted to the control device 10.

Figure 2 is a graph illustrating the characteristics that define the relationship between the accelerator opening [%] detected by the accelerator opening sensor 7 and the driver required output [kW] set by the control device 10. The accelerator opening is the amount of depression of the accelerator pedal (e.g., the accelerator pedal stroke or the rotation angle of the accelerator pedal relative to the fulcrum) expressed as a percentage. The driver required output is a parameter that corresponds to the magnitude of the output (in other words, horsepower, power, or power) that the driver is requesting to run the vehicle 1. The driver required output is generally set to a larger value as the accelerator opening is larger. The output of the drive source of the vehicle 1 is controlled so that, for example, the output becomes larger as the driver required output or vehicle speed becomes larger.

Figure 3 is a graph illustrating the relationship between the vehicle speed [km/h] detected by the vehicle speed sensor 9 and the target rotation speed [rpm] of the engine 2. The solid line graph in Figure 3 shows the characteristics of the engine 2 when motoring (when the vehicle 1 is decelerating), and the dashed line graph in Figure 3 shows the characteristics of the engine 2 when firing (when the vehicle 1 is accelerating). Motoring means that the engine 2 is idling using the generator 4 (the engine 2 is rotated and driven without burning the fuel mixture in the cylinders), and firing means that the engine 2 is rotated independently by supplying fuel and intake air to the engine 2 (the fuel mixture is burned in the cylinders). Firing can be performed at least in a driving mode in which the engine 2 is operating, and can be performed during series driving, for example.

The target rotation speed of engine 2 during motoring is set to increase as the vehicle speed increases, as shown by the solid line graph in Figure 3. However, in a high-speed region where the vehicle speed is equal to or higher than a predetermined vehicle speed, the target rotation speed of engine 2 is limited (clipped) to a predetermined upper limit rotation speed. In addition, the target rotation speed of engine 2 during firing is set to a value smaller than the target rotation speed set during motoring for the same vehicle speed, as shown by the dashed line graph in Figure 3.

If the target rotation speed setting as shown in Figure 3 is strictly adhered to, the target rotation speed will inevitably drop when the state of engine 2 transitions from a motoring state to a firing state, which may result in a worsening driving feeling. For example, when the accelerator pedal is depressed during regenerative motoring control and engine 2 enters a firing state, the rotation speed of engine 2 (engine rotation speed) drops suddenly, causing the driver to feel uncomfortable. In light of this issue, the control device 10 of this embodiment sets and controls a target rotation speed differently from the characteristics of the dashed line graph in Figure 3 when the accelerator is turned on (the accelerator opening exceeds a predetermined opening) during regenerative motoring control.

2. Control Configuration
The control device 10 performs at least a regenerative motoring control and a continuous motoring control. The continuous motoring control is performed when the regenerative motoring control is stopped by an accelerator-on operation. In addition to these controls, the control device 10 preferably also performs a first power generation control and a second power generation control.

Regenerative motoring control is a control that supplies regenerative power from the motor 3 to the generator 4 and motors (idles) the engine 2 at a predetermined target rotation speed while the vehicle is traveling and the accelerator is off (when the accelerator opening is below a predetermined opening, and the driver's required torque and driver's required output are below a predetermined threshold). The conditions for implementing regenerative motoring control include at least that the vehicle 1 is traveling and the accelerator is off. In addition, the conditions for implementing regenerative motoring control may include conditions such as the charge rate of the battery 5, the presence or absence of a battery failure, the battery temperature, the brake opening, the braking force required for the vehicle 1, the operating state of a friction brake device (not shown), and the road surface state. If the accelerator is turned on during regenerative motoring control, the regenerative motoring control stops and the motor 3 drives the wheels.

Each of the continuous motoring control, the first power generation control, and the second power generation control is a control that is implemented instead of the regenerative motoring control when the accelerator is turned on to stop the regenerative motoring control. One of these controls is selected and implemented based on the required power generation amount and the driver's required output when the accelerator is on. In this embodiment, a case where each of the continuous motoring control, the first power generation control, and the second power generation control is implemented is described, but the first power generation control and the second power generation control can be omitted.

Table 1 summarizes typical implementation conditions and control contents for each of regenerative motoring control, continuous motoring control, first power generation control, and second power generation control. Continuous motoring control is selected when the required power generation amount is relatively small. On the other hand, first power generation control and second power generation control are selected when the required power generation amount is relatively large. In addition, first power generation control is selected when the driver required output is relatively small. In contrast, second power generation control is selected when the driver required output is relatively large.

Continuous motoring control is control that continues motoring of the engine 2 by supplying power from the battery 5 to the generator 4 without regenerative braking of the motor 3. In other words, continuous motoring control is control that idles the engine 2 while the motor 3 is driving the wheels (EV driving state). In other words, continuous motoring control is control that wastes power from the battery 5 in the generator 4 regardless of the driving of the vehicle 1, and can be said to be control that has disadvantages in terms of electricity consumption. However, by continuing motoring instead of immediately starting firing of the engine 2 when the regenerative motoring control ends, it is possible to easily suppress changes in the rotation speed of the engine 2, which has the advantage of making it easier to improve the driving feeling.

The rotation speed of the engine 2 during continuous motoring control is preferably fixed to the target rotation speed at that time (e.g., the time when the accelerator pedal is depressed). This makes the rotation speed of the engine 2 constant before and after the end of regenerative motoring control, and the operating sounds (noise) and vibrations of the engine 2 do not change, so the driver does not feel uncomfortable. If the vehicle speed changes during continuous motoring control, the target rotation speed of the engine 2 may be set based on the characteristics shown by the solid line graph in Figure 3. In other words, the target rotation speed during continuous motoring control may be set in the same way as during regenerative motoring control.

In addition, if the target rotation speed of the regenerative motoring control is extremely high, if the target rotation speed is taken over as the rotation speed of the engine 2 during the continuous motoring control, there is a risk that the power of the battery 5 will be consumed excessively. Therefore, the rotation speed of the engine 2 during the continuous motoring control may be fixed to a predetermined speed (e.g., a rotation speed slightly lower than the target rotation speed) that is different from the target rotation speed so long as the driving feeling is not impaired. In this case, the predetermined speed may be set according to the vehicle speed within the range between the solid line graph and the dashed line graph in FIG. 3. The closer the predetermined speed set here is to the solid line graph in FIG. 3, the better the driving feeling will be, and the closer it is to the dashed line graph in FIG. 3, the less power consumption will be.

The conditions for starting the continuous motoring control are exemplified below. In this embodiment, the continuous motoring control is started when at least condition 1 and condition 2 are both satisfied. Thereafter, if condition 2 is satisfied and the accelerator is turned on, the continuous motoring control can be continued. Condition 3 is an additional condition for confirming that there is a reserve in the battery power.
Condition 1: The regenerative motoring control is ended by the accelerator ON operation.
Condition 2: The required power generation amount is less than the threshold value.
Condition 3: The charging rate of the battery 5 is equal to or higher than a predetermined first charging rate.

The "required power generation amount" included in the above condition 2 will be described in detail. The required power generation amount is the amount of power that the various electrical equipment (on-board electrical equipment) installed in the vehicle 1 and the driver are requesting the vehicle 1 to generate, and means the amount of power that should be generated by the generator 4. The required power generation amount is calculated according to at least the driving state of the vehicle 1, for example, based on the vehicle speed and the operating state of the on-board electrical equipment (air conditioner device, multimedia device, various electronic control devices, electrical appliances connected to an external power supply outlet, etc.). The required power generation amount increases as the vehicle speed increases and as the power consumption of the on-board electrical equipment increases. The required power generation amount may be calculated taking into account the operating state of the battery 5 (such as the charging rate and health level). For example, the required power generation amount may be increased when the charging rate or health level of the battery 5 is low.

The "threshold" included in the above condition 2 will be described in detail. The threshold is an index value for determining whether the operating state of the engine 2 that drives the generator 4 becomes a highly efficient operating state (a predetermined thermal efficiency or higher) when the generator 4 is made to generate power equivalent to the required power generation amount. In other words, the threshold is the minimum value of the required power generation amount that can operate the engine 2 with high efficiency. If the generator 4 is made to generate a required power generation amount equal to or greater than the threshold, the thermal efficiency of the engine 2 becomes equal to or greater than the predetermined efficiency, resulting in a highly efficient operating state. On the other hand, if the generator 4 is made to generate a required power generation amount less than the threshold, the thermal efficiency of the engine 2 becomes less than the predetermined efficiency, resulting in an inefficient operating state. Therefore, in this embodiment, when the required power generation amount is less than the threshold, motoring of the engine 2 is continued (i.e., "firing of the engine 2 and power generation by the generator 4" is suspended) to prevent a decrease in fuel efficiency.

Figure 4 is a graph illustrating the relationship between the rotation speed of engine 2 and the threshold value of the required power generation. The threshold value is set based on at least the rotation speed of engine 2. A graph showing the change in the threshold value versus the rotation speed of engine 2 can be expressed as a curve (high efficiency power generation line) as shown by the solid line in Figure 4. Alternatively, the shape of this curve can be simplified to represent the change in the threshold value versus the rotation speed of engine 2 as a broken line or a straight line. If such a relationship is specified in advance, the threshold value at that time can be calculated according to the rotation speed of engine 2.

The threshold curve shown in Figure 4 will be described in detail. Figure 5 is a graph illustrating the output characteristics (relationship between rotation speed and torque) of engine 2. The thick solid line in Figure 5 shows the relationship between the rotation speed and maximum torque of engine 2. The thin solid line in Figure 5 is a curve connecting operating points at which the same thermal efficiency (fuel economy) is obtained at a certain thermal efficiency interval, and is a contour line for high and low thermal efficiency. The dashed line graph in Figure 5 is a line indicating the lower torque limit of the operating point at which high efficiency (predetermined thermal efficiency) is achieved. The shape of the dashed line graph in Figure 5 is reflected in the shape of the solid line graph in Figure 4.

The output (power) of engine 2 at each operating point located on the dashed line in Figure 5 is expressed as the product of the torque and rotational speed at that operating point. The maximum power generation of generator 4 is roughly proportional to the output of engine 2. Therefore, the solid line graph in Figure 4 can be obtained by calculating the product of torque, rotational speed, and a predetermined coefficient at each operating point located on the dashed line in Figure 5 and plotting the relationship between this value and the rotational speed of engine 2 on a graph. Note that if it is desired to operate engine 2 with higher thermal efficiency, a dashed line graph corresponding to that thermal efficiency can be drawn in Figure 5 and a solid line graph (high efficiency power generation line) corresponding to the dashed line graph can be obtained.

The first power generation control is a control in which the generator 4 generates power while firing the engine 2 while maintaining the rotation speed of the engine 2. Preferably, the generator 4 generates power while firing the engine 2 while fixing the rotation speed of the engine 2 to the target rotation speed at that time. In other words, the first power generation control is a control in which, when the regenerative motoring control is stopped by the accelerator-on operation, the setting of the target rotation speed based on the dashed line graph in FIG. 3 is suspended and the target rotation speed at that time is maintained. This suppresses sudden changes in the operating noise and vibration of the engine 2 before and after the accelerator is turned on, improving the driving feeling. However, if the continuous motoring control was performed before the start of the first power generation control and the rotation speed of the engine 2 was fixed to a predetermined speed different from the target rotation speed, the rotation speed of the engine 2 may continue to be fixed to that predetermined speed in the first power generation control.

In the first power generation control, the torque of the engine 2 can be set to be greater as the accelerator opening (or the corresponding driver required output) becomes greater. Meanwhile, the rotation speed of the engine 2 is maintained stably without any sudden changes. The rotation speed of the engine 2 can be changed by adjusting the load of the generator 4 on the engine 2 (the power that the generator 4 converts into electric power). In this way, in the first power generation control, the control device 10 can function to increase the torque of the engine 2 while maintaining the rotation speed of the engine 2 as the accelerator opening becomes greater.

The conditions for starting the first power generation control are exemplified below. In this embodiment, the first power generation control is started when condition 1 or condition 4 is satisfied and condition 5 is also satisfied. Thereafter, if condition 5 is satisfied and the accelerator is turned on, the first power generation control can be continued. Condition 6 is an additional condition for implementing the first power generation control only when the driver's required output is relatively small. Condition 7 is an additional condition for confirming that the battery power has little remaining power, for example, "second charging rate≦first charging rate".
Condition 4: Continuous motoring control is in effect.
Condition 5: The required power generation amount is equal to or greater than the threshold value.
Condition 6: The driver's required output is equal to or less than a predetermined value.
Condition 7: The charging rate of the battery 5 is less than a predetermined second charging rate.

The second power generation control is a control that is implemented instead of the first power generation control when the above condition 6 is not satisfied (when the driver's required output exceeds a predetermined value), assuming that the implementation conditions for the first power generation control include the above condition 6, and is a control that increases the rotation speed of the engine 2. In the second power generation control, the fixation of the rotation speed of the engine 2 is released, and the engine 2 can operate at a rotation speed higher than the target rotation speed (or the predetermined speed). In other words, the second power generation control is a control that resumes setting the target rotation speed based on the dashed line graph in FIG. 3 when the driver deeply depresses the accelerator pedal.

The conditions for implementing the second power generation control are exemplified below. When any one of conditions 1, 4, and 8 is satisfied and condition 9 is also satisfied, the second power generation control is started. Thereafter, if condition 9 is satisfied and the accelerator is turned on, the first power generation control can be continued. Condition 10 is an additional condition for confirming that there is no remaining battery power, and is, for example, "third charging rate≦second charging rate."
Condition 8: The first power generation control is being performed.
Condition 9: The driver's required output exceeds a predetermined value.
Condition 10: The charging rate of the battery 5 is less than a predetermined third charging rate.

In the first power generation control, the rotation speed of the engine 2 is fixed at a target rotation speed (or a predetermined speed). In contrast, in the second power generation control, the operating state of the engine 2 is controlled so that the rotation speed of the engine 2 increases to a value higher than the target rotation speed (or the predetermined speed). The rotation speed of the engine 2 is controlled according to the vehicle speed, for example. As a result, as the accelerator opening increases and the vehicle speed increases, the operating noise and vibration of the engine 2 become larger, achieving a natural and intuitively understandable driving feeling.

3. Flowchart
6 is a flowchart illustrating the flow of control performed by the control device 10. The control shown in this flowchart is repeatedly executed in the control device 10 at a predetermined cycle, for example, when a power switch of the vehicle 1 (not shown) is on and the vehicle 1 is ready to run (READY state). Steps A1 to A3 mainly correspond to regenerative motoring control, and steps A4 to A7 mainly correspond to continuous motoring control. Steps A8 to A11 mainly correspond to first power generation control, and step A12 corresponds to second power generation control.

In step A1, it is determined whether or not the conditions for implementing the regenerative motoring control are satisfied. If the conditions are satisfied, the control proceeds to step A2. On the other hand, if the conditions in step A1 are not satisfied, the control in this cycle is terminated.
In step A2, the target rotation speed of the engine 2 is set according to the vehicle speed, for example, based on the characteristics shown in the solid line graph in Fig. 3. Here, the faster the vehicle speed, the higher the target rotation speed of the engine 2 is set. In other words, since the faster the vehicle speed, the greater the regenerative power generated by the motor 3, the higher the target rotation speed of the engine 2 driven by the generator 4 is set to in order to have the generator 4 consume power of an amount commensurate with the regenerative power.

In step A3, regenerative motoring control is performed based on the target rotation speed set in step A2. That is, the regenerative power of the motor 3 is supplied to the generator 4, and the generator 4 motors (runs idling) the rotation speed of the engine 2 to the target rotation speed.
In step A4, it is determined whether the accelerator is on. If it is determined that the accelerator is not on, the control for this cycle is terminated. From the next cycle onwards, the regenerative motoring control is continued as long as the conditions for implementing the regenerative motoring control are satisfied. On the other hand, if it is determined that the accelerator is on in step A4, the regenerative motoring control is terminated and the control proceeds to step A5.

In step A5, the required power generation amount and a threshold value are calculated. The required power generation amount is calculated based on, for example, the vehicle speed and the operating state of the on-board electrical equipment. For example, the faster the vehicle speed is, the greater the value of the required power generation amount is calculated to be. Alternatively, the greater the power consumption of the on-board electrical equipment is, the greater the required power generation amount is calculated to be. The threshold value is calculated as a value corresponding to the rotation speed of engine 2 at that time, based on, for example, the characteristics shown in Figure 4.

In step A6, it is determined whether the required power generation amount calculated in step A5 is less than a threshold value. If the required power generation amount is less than the threshold value, control proceeds to step A7, where continuous motoring control is implemented instead of regenerative motoring control. In continuous motoring control, the generator 4 is controlled to a powered state using power from the battery 5, and the engine 2 is driven at idle. At this time, the motor 3 is also controlled to a powered state so as to generate a driving force according to the accelerator opening, and the wheels are driven.

The rotation speed of engine 2 during continuous motoring control is set according to the vehicle speed, at least within the range between the solid line graph and the dashed line graph in Figure 3. This reduces the change in rotation speed of engine 2 when transitioning from regenerative motoring control to continuous motoring control, reducing the sense of discomfort felt by the driver. In addition, the rotation speed of engine 2 is preferably fixed to the target rotation speed during the immediately preceding regenerative motoring control. This leaves the rotation speed of engine 2 unchanged, so the driver does not feel uncomfortable.

If the required power generation amount is equal to or greater than the threshold value in step A6, it is determined that the engine 2 can be operated with high efficiency, and control proceeds to step A8. In step A8, the driver's required output is calculated based on the accelerator opening, for example, based on the characteristics shown in FIG. 2. The greater the accelerator opening, the greater the driver's required output is set to. In the following step A9, it is determined whether the driver's required output calculated in step A8 is equal to or less than a predetermined value. If this condition is met, control proceeds to step A10.

In step A10, a first power generation control is implemented in which the generator 4 generates power while firing the engine 2, with the rotation speed of the engine 2 fixed at the target rotation speed at that time. This transitions the operating state of the engine 2 from a motoring state to a firing state. The torque of the engine 2 is set according to the driver's required output. Meanwhile, the target rotation speed of the engine 2 in the firing state is maintained at the same speed as the target rotation speed of the engine 2 in the motoring state. This results in almost no change in the operating noise and vibration of the engine 2, improving the driving feeling.

In the following step A11, it is determined whether the accelerator is off. If it is determined that the accelerator is not off, control returns to step A8, and the driver request output is calculated again. Thereafter, the first power generation control continues as long as the driver request output is equal to or less than a predetermined value. Also, if it is determined in step A11 that the accelerator is off, the control for this cycle ends. From the next cycle onwards, regenerative motoring control is resumed as long as the conditions for implementing regenerative motoring control are met.

If it is determined in step A9 that the driver requested output exceeds a predetermined value, control proceeds to step A12. In step A12, second power generation control is implemented instead of first power generation control, and the rotation speed of engine 2 is changed to a rotation speed higher than the target rotation speed at that time. The torque of engine 2 is set according to the driver requested output. During second power generation control, the output of engine 2 is larger than during first power generation control, and the generated power of generator 4 also increases.

In the following step A11, it is determined whether the accelerator is off. If it is determined that the accelerator is not off, control returns to step A8, and the driver request output is calculated again. Thereafter, the second power generation control continues as long as the driver request output exceeds a predetermined value. Also, if it is determined in step A11 that the accelerator is off, the control for this cycle ends. From the next cycle onwards, regenerative motoring control is resumed as long as the conditions for implementing regenerative motoring control are met.

[4. Effect]
FIG. 7 is a time chart illustrating the action of the control performed by the control device 10. Here, it is assumed that the regenerative motoring control is performed before time _t1 and the accelerator is off. When the accelerator pedal is slightly depressed at time _t1 to turn the accelerator on, the regenerative motoring control is stopped and the continuous motoring control is started. The state of the motor 3 transitions from a regenerative power generation (regenerative braking) state to a power running state at time _t1 . On the other hand, the state of the engine 2 remains in a motoring state even after time _t1 . At this time, the rotation speed of the engine 2 is fixed to, for example, a target rotation speed during the regenerative motoring control. Since the power for the generator 4 to idle the engine 2 is taken from the battery 5, the output of the battery 5 increases slightly at time _t1 .

If the continuous motoring control is not performed, firing of the engine 2 is started at time _t1 and the target rotation speed is set relatively low, so that the actual rotation speed of the engine 2 drops as shown by the dashed line in Fig. 7. However, in this embodiment, the continuous motoring control is performed without starting firing, so that it is easy to keep the rotation speed of the engine 2 almost constant without changing it before and after time _t1 . Also, if the continuous motoring control is not performed, as shown by the two-dot chain line in Fig. 7, the engine 2 starts and the torque of the engine 2 may become a slightly large value at time _t1 . On the other hand, in this embodiment, the engine 2 does not start at time _t1 , so the torque of the engine 2 does not change before and after time _t1 and becomes a constant value (a negative value equivalent to friction torque).

When the accelerator pedal is depressed further at time _t2 , the driver's requested output increases as the accelerator opening increases. This increases the output of the motor 3, and the requested power generation amount increases as the vehicle speed increases. In addition, as shown by the dotted line in FIG. 7, a threshold value is calculated according to the rotation speed of the motored engine 2. As long as the requested power generation amount is below the threshold value, the continuous motoring control is maintained. This is because even if the engine 2 is started in a state in which the requested power generation amount is below the threshold value, the operating state of the engine 2 will not be a highly efficient operating state (a thermal efficiency equal to or higher than a predetermined preset value).

When the required power generation amount reaches or exceeds the threshold value at time _t3 , first power generation control is implemented instead of continuous motoring control. The state of the engine 2 transitions from the motoring state to the firing state at time _t3 . On the other hand, in the first power generation control, the target rotation speed of the engine 2 is maintained at the target rotation speed before time _t3 , and the actual rotation speed of the engine 2 is also constant. Therefore, there is almost no change in the operating noise and vibration of the engine 2, and the driving feeling is improved.

In the first power generation control, the torque of the engine 2 is set to be larger as the accelerator opening degree increases. On the other hand, since the target rotation speed of the engine 2 is kept constant even after time _t3 , the output of the engine 2 (the product of the rotation speed and the torque) increases as the torque increases, and the generated power of the generator 4 also increases gradually. As a result, the power taken from the battery 5 decreases, and the output of the battery 5 decreases as the torque of the engine 2 increases in a positive range.

When the driver's required output exceeds a predetermined value at time _t4 , the second power generation control is implemented instead of the first power generation control. In the second power generation control, the setting of the target rotation speed based on the dashed line graph in FIG. 3 is resumed. As a result, the rotation speed of the engine 2 increases, and the torque of the engine 2 and the generated power of the generator 4 also increase. Therefore, as the accelerator opening is increased, the operating sound and vibration of the engine 2 become louder, realizing a natural and intuitive driving feeling. In addition, the power taken from the battery 5 is further reduced, and the output of the battery 5 is further reduced. After that, when the increase in the accelerator opening stops at time _t5 , the increase in the rotation speed and torque of the engine 2 also stops, and the output of the battery 5 becomes constant.

Point _P1 in Fig. 4 is a point representing the rotation speed and required power generation amount of the engine 2 at time _t1 in Fig. 7, and is a state point representing the state of the vehicle 1 at the start of the continuous motoring control. Point _P1 is located in the motoring continuation region, which is a region below the graph of the threshold (high efficiency power generation line). In the continuous motoring control, for example, the rotation speed of the engine 2 is fixed at a target rotation speed (or a predetermined speed). As a result, the state point of the vehicle 1 moves directly upward from point _P1 as the required power generation amount increases, and reaches point _P2 when the required power generation amount becomes equal to the threshold.

Point _P2 represents the rotation speed and required power generation amount of the engine 2 at time _t3 in Fig. 7, and represents the state of the vehicle 1 at the start of the first power generation control. In the first power generation control, the rotation speed of the engine 2 is fixed to a target rotation speed (or a predetermined speed). Therefore, the state point of the vehicle 1 enters the firing power generation area, which is an area above the graph of the threshold value (high efficiency power generation line). As the required power generation amount increases, the state point of the vehicle 1 moves further straight upward from point _P2 , and reaches point _P3 when the driver's required output becomes equal to the predetermined value.

Point _P3 represents the rotation speed and required power generation amount of the engine 2 at time _t4 in Fig. 7, and represents the state of the vehicle 1 at the start of the second power generation control. In the second power generation control, the rotation speed of the engine 2 can increase higher than the target rotation speed (or a predetermined speed). Therefore, the state point of the vehicle 1 moves to the right in Fig. 7 as the rotation speed of the engine 2 increases, and moves upward in Fig. 7 as the required power generation amount increases.

5. Effects
(1) The hybrid vehicle 1 of this embodiment includes an engine 2, a motor 3 that drives the wheels and performs regenerative braking, a generator 4 that generates electricity using the driving force of the engine 2 and drives the engine 2, and a battery 5 connected to the motor 3 and the generator 4. The hybrid vehicle 1 also includes a control device 10 that performs regenerative motoring control, which supplies regenerative power from the motor 3 to the generator 4 while the vehicle is traveling and the accelerator is off, to motor the engine 2 at a predetermined target rotation speed. The control device 10 calculates a required power generation amount according to the traveling state, and performs continuous motoring control if the required power generation amount is less than a threshold value when the regenerative motoring control is to be stopped by an accelerator-on operation. The continuous motoring control is a control in which the power of the battery 5 is supplied to the generator 4 to continue motoring the engine 2.

By implementing such control, it is possible to reduce the change in rotation speed of engine 2 immediately after the end of regenerative motoring control, and to suppress sudden changes in the operating sounds (noise) and vibrations of engine 2. In other words, by continuing motoring instead of immediately starting firing of engine 2 when regenerative motoring control ends, it is possible to easily suppress changes in the rotation speed of engine 2. Therefore, it is possible to improve the driving feeling during acceleration after regenerative motoring control.

Note that continuous motoring control is only implemented when the required power generation amount is below a threshold value. In other words, motoring of the engine 2 is continued only when the remaining power of the battery 5 (the power stored in the battery 5) is not expected to decrease significantly. Therefore, there is no shortage of power for driving the vehicle 1 while continuous motoring control is being implemented, and a good driving feeling can be provided.

(2) During continuous motoring control, the control device 10 can continue motoring of the engine 2 while fixing the rotation speed of the engine 2 to the target rotation speed at that time. In this way, by fixing the rotation speed of the engine 2 to the target rotation speed, fluctuations in the rotation speed of the engine 2 after the end of regenerative motoring control can be suppressed. In other words, since the rotation speed of the engine 2 does not change when transitioning from regenerative motoring control to continuous motoring control, changes in the operating noise and vibration of the engine 2 can be suppressed. Therefore, the driving feeling during acceleration from regenerative motoring control can be improved.

(3) When the required power generation amount is equal to or greater than a threshold value, the control device 10 can implement a first power generation control in which the engine 2 is fired while maintaining the rotation speed of the engine 2 and the generator 4 generates power. By implementing such control, power can be generated by the generator 4 while suppressing changes in the operating noise and vibration of the engine 2. This makes it possible to prevent a drop in the power of the battery 5 while improving the driving feeling. In addition, because the power of the battery 5 is secured, there is no risk of a shortage of power to drive the motor 3, and a good feeling of acceleration can be achieved.

(4) During the first power generation control, the control device 10 can implement control to maintain the rotational speed of the engine 2 while increasing the torque of the engine 2 as the accelerator opening becomes larger. For example, the driver's required output is set based on the characteristics shown in FIG. 2, and the torque of the engine 2 is controlled based on this driver's required output. This control makes it possible to suppress changes in the operating noise and vibration of the engine 2 while increasing the output of the engine 2, thereby further improving the driving feeling. Furthermore, by increasing the output of the engine 2, the amount of power generated by the generator 4 can be increased. Therefore, the power for driving the motor 3 can be increased, and a good feeling of acceleration can be achieved.

(5) When the driver's requested output exceeds a predetermined value during the first power generation control, the control device 10 can execute a second power generation control to increase the rotation speed of the engine 2. For example, when the driver's requested output increases, such as after time _t4 in Fig. 7, the rotation speed of the engine 2 can be increased to realize a natural behavior of the engine 2 and improve the driving feeling. In addition, the power generated by the generator 4 can be increased to improve the acceleration performance of the vehicle 1 and improve the driving feeling.

(6) The above-mentioned required power generation amount can be calculated based on the vehicle speed or the operating state of the on-board electrical equipment. By such control, the power generation amount requested from the vehicle 1 by various electrical equipment (on-board electrical equipment) and the driver can be accurately calculated. Therefore, the timing to transition the engine 2 from a motoring state to a firing state can be appropriately determined, and a good acceleration feeling can be achieved while improving the driving feeling. In addition, the above-mentioned threshold value can be set based on the rotation speed of the engine 2. By such control, it can be accurately determined whether the engine 2 is in a state in which it can operate with high efficiency. Therefore, it is possible to improve fuel efficiency during power generation while improving the driving feeling.

[6. Other]
The above embodiment is merely illustrative, and is not intended to exclude various modifications or application of techniques not explicitly stated in the embodiment. Each configuration of the embodiment can be modified in various ways without departing from the spirit of the embodiment. Furthermore, each configuration of the embodiment can be selected as necessary, or can be combined appropriately.

For example, in the above embodiment, a control device 10 that performs regenerative motoring control, continuous motoring control, first power generation control, and second power generation control is exemplified, but the first power generation control and the second power generation control can be omitted. At least when regenerative motoring control is stopped by accelerator-on operation, the required power generation amount and a threshold value are used to determine whether or not to perform continuous motoring control, thereby achieving the same effect as the above embodiment.

The rotation speed of engine 2 during continuous motoring control may be fixed to the target rotation speed, or may be fixed to a predetermined speed other than the target rotation speed (for example, a rotation speed slightly lower than the target rotation speed). Furthermore, the rotation speed of engine 2 may not be fixed but may be treated as a variable value, as long as the driving feeling is not impaired. For example, the rotation speed of engine 2 may be set so as to fall within a predetermined speed range including the target rotation speed. The same applies to the rotation speed of engine 2 during first power generation control, and may be fixed to the target rotation speed, or may be fixed to a predetermined speed other than the target rotation speed, or may be a variable value.

This invention is applicable to the hybrid vehicle manufacturing industry and also to the hybrid vehicle control device manufacturing industry.

1. Vehicle (hybrid vehicle)
Reference Signs List 2: engine 3: motor 4: generator 5: battery 6: clutch 7: accelerator opening sensor 8: brake opening sensor 9: vehicle speed sensor 10: control device

Claims (6)

The engine,
A motor for driving the wheels and for regenerative braking;
a generator that generates electricity using a driving force of the engine and drives the engine;
a battery connected to the motor and the generator;
a control device that performs regenerative motoring control for supplying regenerative power of the motor to the generator when the vehicle is running and the accelerator is released, and motoring the engine at a predetermined target rotation speed,
the control device calculates a required amount of power generation according to a driving state, and if the required amount of power generation is less than a threshold when the regenerative motoring control is to be stopped by an accelerator-on operation, executes a continuous motoring control in which the electric power of the battery is supplied to the generator to continue motoring of the engine;
The control device calculates the required power generation amount based on a vehicle speed or an operating state of an on-board electrical device, and sets the threshold value based on a rotation speed of the engine. 2. The hybrid vehicle according to claim 1, wherein, during the continuous motoring control, the control device continues motoring of the engine while fixing the rotation speed of the engine at the target rotation speed at that time. 3. The hybrid vehicle according to claim 1, wherein the control device, if the required power generation amount is equal to or greater than the threshold value, implements a first power generation control in which the engine is fired while maintaining the engine rotation speed, and the generator is caused to generate power. 4. The hybrid vehicle according to claim 3, wherein, during the first power generation control, the control device increases the torque of the engine as an accelerator opening degree increases, while maintaining the rotation speed of the engine. 5. The hybrid vehicle according to claim 3, wherein the control device implements a second power generation control for increasing a rotation speed of the engine when a driver requested output exceeds a predetermined value during the first power generation control. (delete)