Hybrid vehicles

Abstract

Invention details;

Description

Hybrid vehicles

[0001] The present invention relates to a hybrid vehicle equipped with an engine and a motor.

[0002] In a conventional hybrid vehicle equipped with an engine and a motor, one of a plurality of driving modes is selected depending on the driving state, and the operating states of the engine and the motor are controlled according to the selected driving mode. Examples of driving modes include an EV driving mode in which the vehicle runs solely on the driving force of the motor, and a hybrid driving mode in which the vehicle runs using both the engine and the motor. Hybrid driving modes include a parallel driving mode in which the driving force of the engine and the motor is transmitted to the drive wheels, and a series driving mode in which the vehicle runs by transmitting the driving force of the motor to the drive wheels while generating electricity using the driving force of the engine (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2018-100013

[0004] In the technology described in Patent Document 1, a condition for switching the driving mode from EV driving mode to hybrid driving mode is to determine whether the battery voltage has dropped to a lower limit voltage. This control allows, for example, starting the engine when battery power is low to reduce battery power consumption or charge the battery. However, when the battery voltage drops, the upper limit battery output decreases, reducing the vehicle's drive torque. This increases torque fluctuations before and after starting the engine, potentially degrading the driving feel.

[0005] Furthermore, when the vehicle's drive torque decreases, the driver may press the accelerator pedal hard to start the engine. In this case, the driver's requested torque increases suddenly, causing the vehicle's drive torque to become excessive, further deteriorating the driving feel. In addition, the sudden increase in drive torque may cause the vehicle to accelerate strongly, so the driver must quickly release the accelerator pedal immediately after the engine starts, resulting in poor operability.

[0006] One of the objectives of the present invention was invented in light of the above-mentioned problems, and is to provide a hybrid vehicle that can improve driving feel and operability. However, in addition to this objective, another objective of the present invention is to achieve effects derived from the various configurations shown in the "Description of the Invention" below, which cannot be obtained with conventional technologies.

[0007] The disclosed hybrid vehicle can be realized as the following disclosed aspects or application examples, and solves at least part of the above-mentioned problems. The disclosed hybrid vehicle includes an engine and a motor that can operate independently of each other, a battery that stores power for operating the engine and the motor, and a control device that controls the operating states of the engine and the motor. The control device starts the engine when condition A is met while the motor is operating and the engine is not operating. Condition A is that the battery output remains at or above a predetermined value for at least a predetermined time.

[0008] According to the disclosed hybrid vehicle, if condition A is met while the motor is operating and the engine is not operating, control is performed to start the engine, thereby suppressing fluctuations in the vehicle's drive torque and improving the driving feel. In addition, because the engine can be started without the driver having to depress the accelerator pedal, excessive drive torque can be prevented when the engine is started, improving operability.

[0009] Fig. 1 is a block diagram showing the configuration of a hybrid vehicle; Fig. 2 is an example flowchart of control relating to engine start determination; Fig. 3 is an example flowchart of control relating to driving mode selection determination and engine start determination; Fig. 4 is a time chart for explaining control actions;

[0010] The disclosed hybrid vehicle may be implemented according to the following examples.

[0011] 1. Device Configuration Fig. 1 is a block diagram illustrating the configuration of a hybrid vehicle 1 according to an embodiment. This 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 is a hybrid vehicle that allows external charging of the battery 5 or external power supply from the battery 5. A plug-in hybrid vehicle is provided with a charging port (inlet) for inserting a charging cable that supplies power from an external charging facility, and a power outlet (outlet) for external power supply.

[0012] The engine 2 is an internal combustion engine such as a gasoline engine or a diesel engine. A generator 4 is coupled 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 power from a battery 5 and the function of generating electricity using the driving force of the engine 2. The power generated by 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.

[0013] The motor 3 is an electric motor (electric motor / generator) that has both the function of propelling the vehicle 1 using power from the battery 5 and 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.

[0014] A clutch 6 is interposed in 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 closer to the clutch 6. When the clutch 6 is disengaged (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, an "EV driving mode (motor-only driving mode)" is realized. In addition to this, by operating the engine 2 and causing the generator 4 to generate electricity, a "series driving mode" is realized.

[0015] On the other hand, when the clutch 6 is engaged (connected), the engine 2, motor 3, and generator 4 are all connected to the drive wheels. Therefore, for example, by operating only the engine 2, an "engine driving mode (engine-only driving mode)" is realized. In addition, by driving the motor 3 and the generator 4, a "parallel driving mode" is realized. The above-mentioned series driving mode and parallel driving mode are both sub-modes included in the "hybrid driving mode," and at least one of them can be implemented. One of the above driving modes is selected by the control device 10, which will be described later, depending on the driving state of the vehicle 1.

[0016] The vehicle 1 is provided with an EV priority mode switch 7. The EV priority mode switch 7 is a switch for changing the conditions for switching the driving mode from EV driving mode to hybrid driving mode (series driving mode or parallel driving mode), and is operated by the driver. Information on the operating position of the EV priority mode switch 7 is transmitted to the control device 10. In this embodiment, when the EV priority mode switch 7 is operated to the ON position, the driving mode control state is set to "EV priority mode," and when the EV priority mode switch 7 is operated to the OFF position, the state of the vehicle 1 is set to "normal mode."

[0017] The EV priority mode is a mode in which the EV driving mode is implemented with priority over the hybrid driving mode, compared to the normal mode. In other words, the EV priority mode is a mode in which it is more difficult to start the engine 2 than the normal mode. Therefore, when focusing on the conditions (engine start conditions) for starting the engine 2 when the motor 3 is operating and the engine 2 is not operating, the engine start conditions in the EV priority mode are stricter than the engine start conditions in the normal mode. Conversely, the normal mode is a mode in which the EV driving mode is not prioritized, compared to the EV priority mode. In other words, the normal mode is a mode in which it is easier to start the engine 2 than the EV priority mode. Therefore, the engine start conditions in the normal mode are looser (less stringent) than the engine start conditions in the EV priority mode.

[0018] [2. Control Configuration] 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 unit, ECU) that selects one of a plurality of driving modes depending on the driving state of the vehicle 1 and performs control according to that driving mode. The control device 10 incorporates a processor (arithmetic processing device) and a memory (storage device). The contents of the control (control program) performed by the control device 10 are stored in the memory, and are executed by being read into the processor as appropriate.

[0019] The control device 10 includes a battery control unit 11, a driving control unit 12, a motor control unit 13, and an engine control unit 14. These elements are shown by conveniently classifying the functions of the control device 10, and can be realized by software (programs) or hardware (electronic control circuits). These elements may be integrated into a single piece of software or hardware, or may be distributed across multiple pieces of software and hardware.

[0020] For example, the battery control unit 11 may be built into a battery ECU (Battery Management Unit, BMU) for managing the battery 5. The driving control unit 12 may be built into a vehicle ECU (driving control ECU such as an HEV-ECU or PHEV-ECU) for managing the powertrain of the vehicle 1. The motor control unit 13 may be built into a motor ECU (Motor Control Unit, MCU) for managing the motor 3. The engine control unit 14 may be built into an engine ECU for managing the engine 2.

[0021] The battery control unit 11 manages the operating state of the battery 5 and calculates various parameters representing the operating state of the battery 5. The battery control unit 11 calculates the state of charge (SOC), state of health (SOH), and state of power (SOP), etc., based on information such as the voltage, current, and battery temperature of the battery 5. Information on the voltage, current, and battery temperature of the battery 5 is detected by a voltage sensor, a current sensor, and a temperature sensor (not shown).

[0022] In this embodiment, the battery control unit 11 calculates the "battery output" of the battery 5 and its upper limit (maximum value) "upper limit output" as the output state. The battery output refers to the power [kW] actually drawn from the battery 5 to drive the motor 3 and various electrical components. The value of the battery output is calculated based on the current and voltage discharged from the battery 5. The upper limit output refers to the power [kW] equivalent to the rated output of the battery 5, and refers to the upper limit of the battery output that can be drawn and used from the battery 5 at that time. The value of the upper limit output is set according to the operating state of the battery 5 (such as the charging rate, health, voltage, current, and battery temperature) and the driving state of the vehicle 1 (such as the driving mode, vehicle speed, outside air temperature, accelerator opening, and brake opening). The value of the upper limit output in the EV priority mode is set higher than the value of the upper limit output in the normal mode. Here, if the value of the upper limit output in EV priority mode is defined as the "first upper limit value" and the value of the upper limit output in normal mode is defined as the "second upper limit value," then "first upper limit value > second upper limit value" holds true.

[0023] The driving control unit 12 manages the driving state of the vehicle 1 and calculates various parameters that represent the driving state of the vehicle 1. The driving control unit 12 calculates a driver-requested torque (torque corresponding to the driving force requested by the driver from the vehicle 1) based on information such as accelerator pedal position, brake pedal position, and vehicle speed. The driving control unit 12 also selects and sets one driving mode from among a plurality of driving modes based on the calculated driver-requested torque, the operating state of the battery 5 (such as the charging rate, health, voltage, current, and battery temperature), and the driving state of the vehicle 1 (such as the vehicle speed, outside air temperature, accelerator pedal position, and brake pedal position). Information on the accelerator pedal position and brake pedal position is detected by an accelerator pedal sensor, a brake pedal sensor, and a brake fluid pressure sensor (not shown). Information on the vehicle speed and outside air temperature is detected by a vehicle speed sensor and an outside air temperature sensor (not shown).

[0024] In this embodiment, the driving control unit 12 determines whether to change the driving mode to the hybrid driving mode by determining the conditions (engine start conditions) for starting the engine 2 in the EV driving mode (when the motor 3 is operating and the engine 2 is not operating). The engine start conditions determined here differ between the EV priority mode and the normal mode, and the engine start conditions are set stricter in the EV priority mode than in the normal mode (making it more difficult to change to the hybrid driving mode).

[0025] The engine start conditions in EV priority mode are exemplified below. Condition A is the only required condition, while conditions B to G are optional conditions that are not required. Condition A: The battery output remains at or above a predetermined value for a predetermined period of time or more. Condition B: The battery output reaches a first upper limit value. Condition C: The driver requested torque is at or above a first threshold value. Condition D: The vehicle speed is at or above a first speed. Condition E: The accelerator opening is at or above a first predetermined opening. Condition F: The charging rate of the battery 5 is at or below a first predetermined charging rate. Condition G: The battery voltage of the battery 5 is at or below a lower limit voltage.

[0026] The engine start conditions in normal mode are exemplified below. Conditions H to M are optional conditions that are not essential. Condition H: Battery output reaches a second upper limit value. Condition I: Driver requested torque is equal to or greater than a second threshold value. Condition J: Vehicle speed is equal to or greater than a second speed. Condition K: Accelerator opening is equal to or greater than a second predetermined opening. Condition L: The charge rate of battery 5 is equal to or less than a second predetermined charge rate. Condition M: Battery voltage of battery 5 is equal to or less than a lower limit voltage.

[0027] The lower limit voltages included in conditions G and M are voltages that are set in advance to allow a margin for the operation of battery 5 in terms of control, and are voltages that are slightly higher than the lowest voltage at which battery 5 can be used appropriately (the limit value that battery 5 has). Condition H is preferably set together with condition B. Similarly, condition I is preferably set together with condition C, and condition J is preferably set together with condition D. Condition K is preferably set together with condition E, condition L is preferably set together with condition F, and condition M is preferably set together with condition G. In any case, in EV priority mode, the engine start conditions are generally more difficult to meet than in normal mode.

[0028] The following are examples of preferable magnitude relationships for the values ​​included in Conditions A to M: Second upper limit value < predetermined value < first upper limit value Second threshold value ≦ first threshold value (more preferably, second threshold value < first threshold value) Second vehicle speed ≦ first vehicle speed (more preferably, second vehicle speed < first vehicle speed) Second predetermined opening ≦ first predetermined opening degree (more preferably, second predetermined opening degree < first predetermined opening degree) First predetermined charging rate ≦ second predetermined charging rate (more preferably, first predetermined charging rate < second predetermined charging rate)

[0029] The above-mentioned predetermined value may be a fixed value set in advance, or may be a variable value set according to the first upper limit value and the second upper limit value. In the latter case, the first upper limit value and the second upper limit value may be multiplied by a predetermined coefficient. Specific examples of setting the predetermined value are shown below. Predetermined value = k １ × first upper limit value (where 0 < k １ <1) Predetermined value = k ２ × second upper limit (where 1 < k ２ ) Predetermined value = k ３ × first upper limit value + (1-k ３ ) × second upper limit (where 0 < k ３ <1)

[0030] The predetermined time may be a fixed value (for example, several seconds to several tens of seconds) that is set in advance, or may be a variable value that is set according to the operating state of the battery 5. For example, an estimated time from the time when the battery output of the battery 5 reaches a predetermined value or more until the battery voltage gradually decreases and reaches a lower limit voltage may be calculated, and a predetermined time that is shorter than this estimated time may be set. Alternatively, the predetermined time may be set according to the operating state of the battery 5. For example, the lower the charging rate, health level, or battery temperature of the battery 5, the shorter the predetermined time may be set.

[0031] The accelerator pedal may have a detent (a catch structure) that temporarily increases the pedaling resistance just before the full stroke position when the driver depresses the pedal. The accelerator opening corresponding to the position of such a detent is called the "detent opening." During normal accelerator operation, a region of accelerator opening smaller than the detent opening is mainly used, and the engine start condition is met when the accelerator pedal is depressed hard enough to exceed the detent opening. For example, the first predetermined opening is set to at least a larger opening than the detent opening. Meanwhile, the second predetermined opening may be a larger opening than the detent opening (i.e., a larger opening than the detent opening but smaller than the first predetermined opening) or may be a smaller opening than the detent opening.

[0032] The motor control unit 13 manages the operating state of the motor 3. Here, the operating state of the motor 3 is controlled so as to obtain a motor output according to the driving mode set by the driving control unit 12. The operating state of the motor 3 can be controlled by adjusting the operation of an inverter (not shown) interposed in a high-voltage circuit between the battery 5 and the motor 3. For example, in the EV driving mode or the series driving mode, the inverter is controlled so as to generate a motor torque equivalent to the driver's requested torque within the allowable range of the battery output. In the parallel driving mode, the inverter is controlled so that the sum of the engine torque and the motor torque becomes equal to the driver's requested torque. The drive torque of the vehicle 1 in the EV driving mode corresponds to the output torque of the motor 3.

[0033] The engine control unit 14 manages the operating state of the engine 2. Here, the operating states of the engine 2 and auxiliary machinery (not shown) are controlled so as to obtain an engine output according to the driving mode set by the driving control unit 12. When the driving force of the engine 2 is used to generate electricity with the generator 4, the engine control unit 14 may be configured to control both the engine 2 and the generator 4.

[0034] The operating state of the engine 2 can be controlled by adjusting the operation of a fuel injection valve, a throttle valve, the generator 4, etc. (not shown). For example, in the engine running mode, the fuel injection valve, the throttle valve, etc. are controlled so that an engine torque equivalent to the torque requested by the driver is generated. The drive torque of the vehicle 1 in the engine running mode has a magnitude equivalent to the output torque of the engine 2.

[0035] Furthermore, in the parallel driving mode, the fuel injection valve, throttle valve, etc. are controlled so that the sum of the engine torque and the motor torque becomes equal to the torque required by the driver. The driving torque of the vehicle 1 in the parallel driving mode corresponds to the sum of the output torque of the engine 2 and the output torque of the motor 3. On the other hand, in the series driving mode, the fuel injection valve, throttle valve, etc. are controlled so that the engine 2 continues to operate in an efficient operating range, and the operating state of the generator 4 (an inverter, not shown, interposed in the high-voltage circuit between the battery 5 and the generator 4) is controlled. The driving torque of the vehicle 1 in the series driving mode corresponds to the output torque of the motor 3.

[0036] 2 is an example of a flowchart of control related to the start determination of the engine 2. The control shown in this flowchart can be repeatedly executed at a predetermined cycle inside the control device 10 in a situation where at least the motor 3 is operating and the engine 2 is stopped (for example, in the EV driving mode). The control shown in this flowchart can be implemented in any hybrid vehicle 1 that has at least an EV driving mode and a hybrid driving mode, regardless of whether the EV priority mode switch 7 (EV priority mode, normal mode) is present.

[0037] In step A1, the battery control unit 11 calculates the upper limit output of the battery 5 based on the operating state of the battery 5 and the running state of the vehicle 1. In step A2, a predetermined value related to the engine start condition is set based on the upper limit output of the battery 5. The predetermined value is set to a value that is at least smaller than the upper limit output calculated in step A1. In the following step A3, it is determined whether the battery output of the battery 5 is equal to or greater than a predetermined value and whether this state has continued for a predetermined time or longer. If this condition is met, control proceeds to step A4, where the engine control unit 14 starts the engine 2. On the other hand, if the condition of step A3 is not met, control for this cycle ends.

[0038] According to the above control, even if the battery output is below the upper limit output (even if condition B and condition H are not satisfied), if a long period of time has passed while the battery output is at a relatively high level, the engine 2 will start. In other words, it is possible to start the engine 2 without depending on whether conditions C and I related to the driver's required torque or conditions E and K related to the accelerator pedal position are satisfied. Therefore, fluctuations in the drive torque of the vehicle 1 immediately after starting the engine 2 are reduced, improving the driving feel.

[0039] In addition, the engine 2 can be started without depending on whether conditions D and J related to the vehicle speed are satisfied, and the engine 2 can be used at lower speeds than with existing control. Furthermore, the engine 2 can be started without depending on whether conditions F and L related to the charging rate of the battery 5 and conditions G and M related to the battery voltage are satisfied, and it is possible to avoid the battery 5's charging rate or battery voltage becoming insufficient immediately after starting the engine 2.

[0040] FIG. 3 is an example flowchart of control related to the determination of the selection of the driving mode and the determination of whether to start the engine 2. The control shown in this flowchart can be repeatedly executed within the control device 10 at a predetermined interval while at least the motor 3 is operating and the engine 2 is stopped (e.g., in the EV driving mode). In the control of this flowchart, the conditions for starting the engine 2 in the EV priority mode are relaxed. Steps B1, B4, B5, and B7 in FIG. 3 correspond to steps A1 to A4 in FIG. 2. The control shown in this flowchart can be implemented in a hybrid vehicle 1 that has an EV driving mode and a hybrid driving mode and has an EV priority mode switch 7 (EV priority mode, normal mode).

[0041] In step B1, a first upper limit value and a second upper limit value are calculated based on the operating state of the battery 5 and the driving state of the vehicle 1. The first upper limit value is the upper limit output value in EV priority mode, and the second upper limit value is the upper limit output value in normal mode. In the following step B2, it is determined whether the driving mode control state is the EV priority mode based on the operating position of the EV priority mode switch 7. If it is the EV priority mode, the process proceeds to step B3, and if it is not the EV priority mode (if it is the normal mode), the process proceeds to step B10. In the former route, the first upper limit value is used as the upper limit output of the battery 5, and in the latter route, the second upper limit value is used as the upper limit output of the battery 5.

[0042] If the process proceeds to step B3 (EV priority mode), a first threshold value for condition C related to engine start is set. The first threshold value is set, for example, according to the running state of the vehicle 1. In addition, in step B4, a predetermined value is set based on the first upper limit value and the second upper limit value calculated in step B1. The predetermined value is set, for example, within a range that is less than the first upper limit value and greater than the second upper limit value.

[0043] In step B5, it is determined whether the battery output of the battery 5 is equal to or greater than a predetermined value and whether this state has continued for a predetermined time or longer. If this condition is met, control proceeds to step B6; if not, control proceeds to step B9. In step B6, the EV priority mode is cancelled, and the operation position of the EV priority mode switch 7 is automatically changed to the OFF position. In addition, in step B7, the engine control unit 14 starts the engine 2.

[0044] Thereafter, in step B8, the driving mode is switched from the EV driving mode to the hybrid driving mode (series driving mode or parallel driving mode), and the control for this cycle ends. When the series driving mode of the hybrid driving mode is implemented, control is performed to cause the generator 4 to generate electricity using the driving force of the engine 2, and control is performed to drive the vehicle using the driving force of the motor 3. When the parallel driving mode of the hybrid driving mode is implemented, control is performed to drive the vehicle using the driving force of the engine 2 and the motor 3. The operating state of the motor 3 is controlled by the motor control unit 13. The operating states of the engine 2 and the generator 4 are controlled by the engine control unit 14.

[0045] When the process proceeds from step B5 to step B9, it is determined whether any of the engine start conditions for the EV priority mode other than the condition determined in step B5 is satisfied. For example, it is determined whether the driver-requested torque is less than the first threshold (negation of condition C). If this condition is satisfied (i.e., condition C is not satisfied), the control proceeds to step B12, where the EV driving mode is maintained, and the control for this cycle is terminated. On the other hand, if the condition of step B9 is not satisfied (i.e., condition C is satisfied), the control proceeds to step B13, where the driving mode is switched from the EV driving mode to the hybrid driving mode (series driving mode or parallel driving mode), and the control for this cycle is terminated.

[0046] When the process proceeds from step B2 to step B10, a second threshold value for condition I relating to engine start is set. The second threshold value is set, for example, to a value smaller than the first threshold value depending on the running state of the vehicle 1. In the following step B11, it is determined whether the engine start condition in normal mode is satisfied. For example, it is determined whether the driver requested torque is less than the second threshold value (negation of condition I).

[0047] If the condition of step B11 is met (i.e., if condition I is not met), control proceeds to step B12, where the EV driving mode is maintained, and control for this cycle ends. On the other hand, if the condition of step B11 is not met (i.e., if condition I is met), control proceeds to step B13, where the driving mode is switched from the EV driving mode to the hybrid driving mode (series driving mode or parallel driving mode), and control for this cycle ends.

[0048] 4(A) to 4(F) are time charts for explaining the control action when condition A is satisfied in EV priority mode, causing the engine 2 to start and the driving mode to transition from EV driving mode to series driving mode. (A) shows the change over time in the operating position of the EV priority mode switch 7, (B) shows the change over time in the accelerator opening, and (C) shows the change over time in the drive torque of the vehicle 1. In addition, (D) shows the change over time in the battery output, (E) shows the change over time in the battery voltage, and (F) shows the change over time in the engine speed.

[0049] As shown by the solid line in FIG. ０ The previous operation position of the EV priority mode switch 7 was the ON position, and the EV priority mode was set. ０ The previous engine speed was 0, and the driving mode was the EV driving mode. As shown by the solid line in FIG. 4B, when the driver ０ The accelerator opening is increased at time t １ It is assumed that an operation to maintain the accelerator opening at that time was performed.

[0050] As the accelerator opening increases, the output torque of the motor 3 increases, and the drive torque of the vehicle 1 increases as shown by the solid line in FIG. 4(C). At this time, the battery output of the battery 5 increases as shown by the solid line in FIG. 4(D). ０ From time t １ It increases until time t １Thereafter, the value is maintained according to the accelerator opening. The battery output at this time is assumed to be the predetermined value according to condition A. Meanwhile, the battery voltage decreases at time t ０ From time t １ It decreases significantly between time t １ It continues to decrease gradually thereafter.

[0051] Time t １ A predetermined time after time t ２ If the battery output is maintained at or above a predetermined value until time t, condition A is met. As a result, control to start the engine 2 is executed, and the engine speed increases as shown by the solid line in FIG. 4(F). At this time, the operation position of the EV priority mode switch 7 is automatically changed to the OFF position as shown by the solid line in FIG. 4(A). Also, at time t ３ After the engine speed reaches the predetermined speed, the predetermined speed is maintained, and the operating state of the engine 2 becomes stable. As a result, the power generation state of the generator 4 also becomes stable.

[0052] As shown by the solid line in FIG. 4(E), the battery voltage ２ From time t ３ It rises until time t ３ Thereafter, the battery output gradually decreases at a gentle gradient. ２ From time t ３ It decreases until time t ３ Thereafter, the voltage is maintained at a substantially constant value. At this time, not only the battery output drawn from the battery 5 but also the power generated by the generator 4 is supplied to the motor 3. This makes it easier to obtain a sufficiently large output torque from the motor 3, and the drive torque is not insufficient. Therefore, as shown by the solid line in FIG. 4(C), ２ From time t ３ Not only until time t ３ From then on, the drive torque remains almost constant, improving the driving feel.

[0053] 4A to 4F are graphs for comparison purposes, showing the control action when the engine start condition does not include condition A. When condition A does not exist, the time t２ The EV driving mode continues thereafter. As a result, the battery voltage decreases from time t ２ It continues to decrease after that, and at time t ４ At this time, as shown by the dashed line in FIG. 4D, the upper limit value (first upper limit value) of the battery 5 may be significantly limited. In this case, as shown by the dashed line in FIG. 4D, the battery output decreases from time t ４ and at time t ４ Therefore, as shown by the dashed line in FIG. ４ It can be seen that the driving torque decreases thereafter and a good driving feeling is not obtained.

[0054] Also, the driver of vehicle 1 notices a decrease in the driving torque, and at time t ５ Assume that the accelerator pedal is depressed at time t. At this time, when the accelerator opening becomes equal to or greater than the detent opening, the engine start condition is met, and control to start the engine 2 is executed. As shown by the dashed line in FIG. 4(F), the engine rotation speed increases from time t ５ It then rises. ６ After the engine speed reaches the predetermined speed, the predetermined speed is maintained, and the operating state of the engine 2 becomes stable. As a result, the power generation state of the generator 4 also becomes stable.

[0055] As shown by the dashed line in FIG. 4(E), the battery voltage ５ From time t ６ It rises until time t ６ Thereafter, the battery output gradually decreases at a gentle gradient. ５ From time t ６ It decreases until time t ６ After that, it is maintained at a substantially constant value. ５ From time t ６ Until time t ５ Since the accelerator opening is now larger than before, the driver's requested torque increases. ５ From time t ６It can be seen that the drive torque becomes temporarily excessive between the two points, resulting in an unsatisfactory driving feel.

[0056] [5. Effects] (1) The hybrid vehicle 1 of this embodiment includes an engine 2 and a motor 3 that can operate independently of each other, a battery 5 that stores power for operating the engine 2 and the motor 3, and a control device 10 that controls the operating states of the engine 2 and the motor 3. The control device 10 starts the engine 2 when condition A is met while the motor 3 is operating and the engine 2 is not operating (i.e., the battery output of the battery 5 remains at or above a predetermined value for a predetermined period of time or longer). In this way, by executing control to start the engine 2 when condition A is met while the motor 3 is operating and the engine 2 is not operating, fluctuations in the drive torque of the vehicle 1 can be suppressed and the driving feel can be improved. For example, in a vehicle 1 for which condition H is the engine start condition, the engine 2 can be started with sufficient time before the battery output reaches the second upper limit.

[0057] Furthermore, in a vehicle 1 in which one of the engine start conditions is "the accelerator pedal being depressed so hard that it exceeds the detent opening," the engine 2 can be started without the driver depressing the accelerator pedal hard. This prevents the driving torque from becoming excessive when starting the engine 2, improving the operability of the vehicle 1. In this way, the hybrid vehicle 1 of this embodiment can improve the driving feel and operability.

[0058] (2) The hybrid vehicle 1 described above can have an EV priority mode and a normal mode. In the EV priority mode, the conditions for starting the engine 2 when the motor 3 is operating and the engine 2 is not operating are set stricter than in the normal mode. In other words, the engine start conditions are set looser in the normal mode than in the EV priority mode. Furthermore, the predetermined value included in condition A can be set to a value that is less than a first upper limit value and greater than a second upper limit value. The first upper limit value is the upper limit value of the battery output in the EV priority mode, and the second upper limit value is the upper limit value of the battery output in the normal mode.

[0059] Furthermore, the control device 10 can execute control to start the engine 2 when condition A is met in the EV priority mode, the motor 3 is operating, and the engine 2 is not operating. By setting the engine start conditions in this manner, the engine start conditions can be made more lenient than in the general EV priority mode, but more strict than in the normal mode. Therefore, while maintaining the EV driving state as much as possible, the start timing of the engine 2 can be slightly advanced when the motor 3 is running under high load, thereby suppressing torque fluctuations in the vehicle 1 and improving the driving feel.

[0060] (3) The predetermined time period included in condition A can be set to be shorter than the time from the time when the battery output reaches a predetermined value or more until the battery voltage of the battery 5 drops to the lower limit voltage. By setting the engine start condition in this way, the engine 2 can be started before the battery voltage drops excessively, and torque fluctuations of the vehicle 1 can be suppressed to improve the driving feel.

[0061] [6. Other] The above-described embodiment is merely illustrative, and does not intend to exclude various modifications or applications of techniques not explicitly stated in the present embodiment. The components of the present embodiment can be modified in various ways without departing from the spirit of the present embodiment. Furthermore, the components of the present embodiment can be selected or combined as needed. For example, although the vehicle 1 is provided with the EV priority mode switch 7, the EV priority mode switch 7 can be omitted, and the EV priority mode and the normal mode can be automatically set according to known conditions. Furthermore, the EV priority mode and the normal mode themselves may be omitted. In other words, the conditions for switching the driving mode from the EV driving mode to the hybrid driving mode may be fixed. By executing control to start the engine 2 when condition A is satisfied at least while the motor 3 is operating and the engine is not operating, the same effects as those of the above-described embodiment can be achieved.

[0062] The present invention is applicable to the manufacturing industry of hybrid vehicles and the manufacturing industry of control devices for hybrid vehicles.

[0063] REFERENCE SIGNS LIST 1 Vehicle (hybrid vehicle) 2 Engine 3 Motor 4 Generator 5 Battery 6 Clutch 7 EV priority mode switch 10 Control device 11 Battery control unit 12 Travel control unit 13 Motor control unit 14 Engine control unit