Hybrid electric vehicles

Abstract

This invention provides a hybrid electric vehicle with control for implementing a driving mode suitable for improving off-road performance. The hybrid electric vehicle includes an engine and a drive motor that drive the drive wheels, a battery that supplies power to the drive motor for driving, a coupling mechanism located between the engine and the drive wheels that allows for torque transmission and can be switched between direct and buffered coupling, a power generation mechanism that generates electricity based on the torque transmitted from the engine via the coupling mechanism, and a vehicle control unit that can switch between a first driving mode and a second driving mode with a throttle operation pattern that further improves off-road performance than the first driving mode. In the first driving mode, when buffered coupling is used, the vehicle control unit limits the power generation of the power generation mechanism using a first condition; in the second driving mode, when buffered coupling is used, it limits the power generation of the power generation mechanism using a second condition that is less restrictive than the first condition.

Description

Technical Field

[0001] This invention relates to a hybrid electric vehicle with a driving mode that enhances off-road capability. Background Technology

[0002] Patent Document 1 illustrates a vehicle in an HEV (Hybrid Electric Vehicle) that has a driving mode that improves off-road capability on difficult roads, and which includes a drive motor and an engine. In this driving mode, the vehicle prohibits driving only the drive motor, but instead drives both the engine and the drive motor.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-66747 Summary of the Invention

[0006] Technical issues

[0007] In previous hybrid electric vehicles, there was room for improvement in the control of driving modes that enhance off-road performance, and the following problems exist as an example.

[0008] Typically, engine power is transmitted to the drive wheels via a torque converter, which amplifies and buffers torque transmission. The torque converter also features a lock-up mechanism that allows switching from a connection that amplifies and buffers torque to a direct connection. In HEVs, while a portion of the engine's power is used to generate electricity, the power transmitted from the engine via the torque converter is sent to the generator. Because energy loss occurs in the torque converter when the lock-up mechanism is open (not directly connected), conventional HEVs sometimes prevented power generation when the torque converter's lock-up mechanism was open. On the other hand, in off-road driving modes, a highly responsive drive motor capable of power output is often used. Furthermore, because the engine load changes significantly in off-road driving modes, the torque converter's lock-up mechanism is engaged.

[0009] Therefore, in previous HEVs, when driving in off-road mode to enhance performance, electricity was consumed by the drive motor on the one hand, and power generation was limited by the unlocking mechanism on the other hand, resulting in a problem of disrupted power balance.

[0010] The purpose of this invention is to provide a hybrid electric vehicle that enables vehicle control in a driving mode suitable for improving off-road performance.

[0011] Technical solution

[0012] The hybrid electric vehicle described in the first embodiment is characterized by comprising: an engine and a drive motor that drive drive wheels; a battery that supplies power for driving to the drive motor; a coupling mechanism located on the torque transmission path between the engine and the drive wheels, and capable of switching the engine and the drive wheels between a direct coupling and a buffer coupling; a power generation mechanism capable of generating electricity using the torque of the engine transmitted via the coupling mechanism; and a vehicle control unit capable of switching between a first driving mode and a second driving mode with a throttle operation diagram that improves off-road capability compared to the first driving mode. In the first driving mode, when the buffer coupling is applied, the vehicle control unit uses a first condition to limit the power generation of the power generation mechanism, and in the second driving mode, when the buffer coupling is applied, it uses a second condition with a more lenient restriction than the first condition to limit the power generation of the power generation mechanism.

[0013] The hybrid electric vehicle described in the second method is based on the hybrid electric vehicle described in the first method, characterized in that the power generation limit value of the second condition includes a value larger than the power generation limit value of the first condition, and the power generation variation limit value of the second condition is larger than the power generation variation limit value of the first condition.

[0014] The hybrid electric vehicle described in the third embodiment is based on the hybrid electric vehicle described in the first or second embodiment, characterized in that the limit value of the generated power in the second condition varies according to the cooling status of the engine.

[0015] The hybrid electric vehicle described in the fourth embodiment is characterized in that, based on the hybrid electric vehicle described in any one of the first to third embodiments, the hybrid electric vehicle includes a charge-discharge control unit for controlling the charging and discharging of the battery, wherein the charge-discharge control unit makes the range of the battery in the second driving mode from the lower limit of the charge reserve that can be discharged to the upper limit of the charge reserve that can be charged wider than the range in the first driving mode.

[0016] The hybrid electric vehicle according to the fifth embodiment is based on the hybrid electric vehicle according to any one of the first to third embodiments, characterized in that the vehicle control unit allows the engine to stop in the first driving mode, prohibits the engine from stopping in the second driving mode, and delays the timing of switching to allow the engine to stop when switching from the second driving mode to the first driving mode.

[0017] Technical effect

[0018] According to the present invention, even when a buffer connection is applied in the second driving mode that improves off-road capability, the power generation of the power generation mechanism is restricted by the second condition that is more relaxed. Therefore, it is easier to generate electricity than in the first driving mode, and the power balance between the power consumption of the driving motor and the power generation of the power generation mechanism can be suppressed.

[0019] Therefore, vehicle control with a second driving operation mode suitable for improving off-road performance was achieved. Attached Figure Description

[0020] Figure 1 This is a block diagram illustrating a hybrid electric vehicle according to an embodiment of the present invention.

[0021] Figure 2 This is an explanatory diagram showing the relationship between the SOC (state of charge) of a high-voltage battery and charge / discharge control.

[0022] Figure 3 This is a flowchart illustrating the driving mode switching process performed by the vehicle control unit.

[0023] Figure 4 This is a timing diagram showing the time variation of torque during the transition from engine driving to EV driving.

[0024] Symbol Explanation

[0025] 1. Hybrid electric vehicles

[0026] 2a Drive wheel

[0027] 11 Engine

[0028] 12. Travel motor

[0029] 15. Torque converter (connection mechanism)

[0030] 15a Locking mechanism

[0031] 22 Converter

[0032] 24 High-voltage battery

[0033] 40 Driving Operations Unit

[0034] 41 Throttle Control Unit

[0035] 44 Second Driving Mode Transfer Operation Unit

[0036] 51 Cooling device

[0037] 52 sensors

[0038] Q0a, Q0b center values

[0039] Q1a, Q1b SOC upper limit

[0040] Q2a, Q2b SOC lower limit Detailed Implementation

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0042] The hybrid electric vehicle 1 according to an embodiment of the present invention is a HEV, comprising a drive wheel 2a, an engine 11 as an internal combustion engine, a drive motor 12 as an electric motor, a torque converter 15 and a continuously variable transmission 17 located on the path for transmitting torque from the engine 11 to the drive wheel 2a, and an input clutch 16 capable of disengaging the engine 11 when driving as an EV (Electric Vehicle). EV driving refers to driving using only the power of the drive motor 12. In the above configuration, the torque converter 15 corresponds to an example of the linkage mechanism of the present invention. The drive motor 12 functions as an example of the power generation mechanism of the present invention.

[0043] The torque converter 15 includes a locking mechanism 15a, and connects the input shaft and output shaft in a manner that amplifies and buffers torque through the transmission of torque via the working oil when the locking mechanism 15a is open. Conversely, when the locking mechanism 15a is closed, the torque converter 15 directly connects the input shaft and output shaft. The connection when the locking mechanism 15a is open corresponds to an example of the buffered connection of the present invention, while the connection when the locking mechanism 15a is closed corresponds to an example of the direct connection of the present invention.

[0044] The drive motor 12 is configured to transmit torque to the drive wheel 2a without passing through the torque converter 15. The input clutch 16 is located between the continuously variable transmission 17 and the torque converter 15.

[0045] In the hybrid electric vehicle 1, when power is output from the engine 11, the power is transmitted to the drive wheel 2a via the torque converter 15 and the continuously variable transmission 17. When the locking mechanism 15a is open, the power of the engine 11 is transmitted through the torque converter 15 under torque amplification and buffering effects. At this time, energy loss occurs in the torque converter 15 due to the flow of internal working oil. When the locking mechanism 15a is closed, the power of the engine 11 is transmitted directly without the aforementioned amplification and buffering effects. Furthermore, when power is output from the drive motor 12, the power is transmitted to the drive wheel 2a via the continuously variable transmission 17. If both the engine 11 and the drive motor 12 are driven, their combined power is transmitted to the drive wheel 2a. When driving using only the power of the drive motor 12, by disengaging the input clutch 16, interference from the engine 11 can be eliminated, allowing power to be transmitted from the drive motor 12 to the drive wheel 2a. Furthermore, by outputting power exceeding the requested power value for driving from the engine 11, and by utilizing regenerative operation to allow the driving motor 12 to absorb the aforementioned power exceeding the requested power value, it is possible to generate electricity using the driving motor 12 and to charge the high-voltage battery 24.

[0046] The hybrid electric vehicle 1 further includes: an auxiliary unit 21 for driving the engine 11; a converter 22 for driving the drive motor 12; a high-voltage battery (equivalent to the battery of the present invention) 24 for supplying driving power to the drive motor 12; a hydraulic circuit 26 for driving the locking mechanism 15a of the torque converter 15; a vehicle control unit 31 for controlling the auxiliary unit 21, the converter 22, and the hydraulic circuit 26; and a driving operation unit 40 operable by the driver. The driving operation unit 40 includes a throttle operation unit 41, a brake operation unit 42, a steering operation unit 43, and a second driving mode transfer operation unit 44 for switching driving modes. The operation amount of the throttle operation unit 41 and the operation information of the second driving mode transfer operation unit 44 are sent to the vehicle control unit 31. The vehicle control unit 31 is an example of the vehicle control unit and the charging / discharging control unit of the present invention.

[0047] The hybrid electric vehicle 1 also includes: a cooling device 51, which cools the electrical system (high-voltage battery 24 and converter 22); and a sensor (e.g., a water temperature gauge for engine coolant) 52, which detects the cooling status of the engine 11. The output of the sensor 52 is sent to the vehicle control unit 31, which is capable of controlling the cooling intensity of the cooling device 51.

[0048] The vehicle control unit 31 consists of a single ECU (Electronic Control Unit) or multiple ECUs interconnected with each other. The vehicle control unit 31 may include a battery control ECU that manages the charging and discharging of the high-voltage battery 24. The vehicle control unit 31 controls the operation of the drive motor 12 and the locking mechanism 15a of the torque converter 15 based on driving operations and the state of various parts of the hybrid electric vehicle 1 by executing a control program through the CPU (Central Processing Unit) within the ECU.

[0049] The vehicle control unit 31 can switch the driving mode of the hybrid electric vehicle 1 to a first driving mode and a second driving mode that improves off-road capability compared to the first driving mode.

[0050] The first driving mode is a driving mode suitable for driving on normal paved roads without snow and / or mud. It can also be a normal driving mode, or an intelligent driving mode with more stable power output characteristics for throttle operation compared to the normal driving mode, or a sport mode with more rapid power output characteristics for throttle operation compared to the normal driving mode.

[0051] The second driving mode is suitable for off-road driving on difficult roads such as snow, mud, and gravel. It features a throttle operation diagram (also called a throttle opening diagram) that improves off-road capability compared to the first driving mode. The throttle operation diagram represents the characteristics of power output in response to throttle input. The second driving mode includes two modes: Mode A, used to suppress wheel spin on difficult roads, and Mode B, used to extricate oneself from deep snow or mud. The throttle operation diagrams for Mode A and Mode B can differ. For example, the throttle operation diagram for Mode A might be one that outputs less power even with significant throttle input compared to the first driving mode. Conversely, the throttle operation diagram for Mode B might be one that easily outputs more power at low speeds compared to the first driving mode. Furthermore, in the second driving mode, in addition to changing the throttle operation diagram, to improve off-road capability, the parameters of traction control, the control method of the braking device, and the number of drive wheels 2a and / or the method of power distribution to each drive wheel 2a can also be changed from the first driving mode. Although the first driving mode is a driving mode without speed limit, the second driving mode can be a mode that can only be selected at low speeds, such as below 40 km / h.

[0052] <Power Generation Restrictions and Controls>

[0053] In the first driving mode and the second driving mode, the vehicle control unit 31 switches the driving power (switching between the drive of the engine 11 and the driving motor 12), the state of the locking mechanism 15a, and the limitation of power generation using the power of the engine 11, as shown in the following function table 1.

[0054] Table 1

[0055] [Function List 1]

[0056]

[0057] The "Power Generation Limit Value" in the table refers to the maximum permitted power generation. The "Power Generation Variation Limit Value" refers to the limit value for the magnitude of the time variation in power generation. The "Power Generation Limit When Open" and "Power Generation Limit When Closed" refer to the power generation limits when the locking mechanism 15a is open and closed, respectively. The power generation limit when the first driving mode is open in Function Table 1 corresponds to an example of the first condition of the present invention, and the power generation limit when the second driving mode is open corresponds to an example of the second condition of the present invention.

[0058] In the second driving mode, there are instances where the driver drastically and rapidly operates the throttle control unit 41 based on the condition of difficult roads and the vehicle's movements. In such cases, the requested power output to the drive wheels 2a also changes drastically and rapidly. When the requested power is high, the vehicle control unit 31 increases the power ratio of the drive motor 12, combining the power of the drive motor 12 with the power of the engine 11 to meet the requested power. On the other hand, when the requested power is low, the vehicle control unit 31 uses the converter 22 to control the drive motor 12 to regenerate, generating negative torque in the drive motor 12. This allows the power of the engine 11 to be combined with the negative power of the drive motor 12 to meet low power requests. At this time, the regenerative operation generates electricity from the drive motor 12, and the generated electricity is used to charge the high-voltage battery 24.

[0059] In the second driving mode, as shown in Function Table 1, by setting a large limit value for the generated power, a large amount of electricity can be generated even when the requested power output to the drive wheel 2a is small, and this large amount of electricity can be used to charge the high-voltage battery 24. Furthermore, by setting a large limit value for the change in generated power, even when the requested power changes drastically, the limit value for generated power can be quickly increased from a small value to a large value, allowing for the generation of a large amount of electricity. Therefore, even when the driving motor consumes a large amount of power, the high-voltage battery 24 can be charged using this large amount of electricity, and disruption of the power balance can be prevented.

[0060] <Cooling control and power generation limitation control based on engine cooling status>

[0061] The vehicle control unit 31 also switches between the cooling control of the electrical system and the power generation limitation control based on the engine cooling status in the first driving mode and the second driving mode, as shown in the function table below 2.

[0062] Table 2

[0063] [Table 2]

[0064]

[0065] The “Electrical System” in the table mainly corresponds to the high-voltage battery 24 and the converter 22. The electrical system is cooled by air cooling, liquid cooling, or both, and the “Cooling Intensity” in the table is controlled by the driving task of the air-cooled fan, the driving task of the liquid-cooled pump, or both. Figure 1 The cooling device 51 is equivalent to an air-cooled fan and a liquid-cooled pump. The “engine cooling condition” in the table refers to the degree of cooling of the engine 11 and the degree of cooling capacity of the engine 11, and can be determined based on, for example, the temperature of the engine coolant, the external gas temperature, the intake air temperature, the exhaust air temperature, the vehicle speed, or a combination thereof. Figure 1 Sensor 52 is equivalent to the temperature sensor or vehicle speed sensor mentioned above. In Function Table 2, the content of the power generation limit control based on engine cooling status in the second driving mode is equivalent to an example of the second condition of the present invention.

[0066] In the second driving mode, the throttle is applied sharply and rapidly, resulting in frequent and extensive charging and discharging of the high-voltage battery 24. Consequently, the electrical system is more prone to overheating compared to the first driving mode. Therefore, based on the aforementioned cooling control, the cooling of the electrical system is enhanced in the second driving mode, thereby suppressing overheating.

[0067] Furthermore, in the second driving mode, since the engine 11 is driven at low speed and the output of the generator 11 is increased to generate electricity, it is conceivable that even if the cooling of the engine 11 is set to maximum, the engine 11 will become very hot. Therefore, as described above, the vehicle control unit 31 changes the limit value of the generated electricity in the second driving mode according to the cooling condition of the engine 11, thereby reducing the load on the engine 11 when it becomes very hot, and thus suppressing overheating of the engine 11. It should be noted that when the cooling intensity of the engine 11 is variable, in the second driving mode, control that increases the cooling intensity of the engine 11 more quickly than in the first driving mode can be used simultaneously.

[0068] <Charging and discharging control of high-voltage batteries>

[0069] Figure 2 This is an illustrative diagram showing the relationship between the state of charge (SOC) of a high-voltage battery and charge / discharge control. (See diagram for example.) Figure 2 As shown, the vehicle control unit 31 switches the charging and discharging control of the high-voltage battery 24 between the first driving mode and the second driving mode. For example, firstly, regarding the upper limits Q1a and Q1b of the SOC that can charge the high-voltage battery 24, the vehicle control unit 31 makes the upper limit Q1b of the second driving mode higher than the upper limit Q1a of the first driving mode. Furthermore, regarding the lower limits Q2a and Q2b of the SOC that can discharge from the high-voltage battery 24, the vehicle control unit 31 makes the lower limit Q2b of the second driving mode lower than the lower limit Q2a of the first driving mode. With this setting, the usable range of the SOC of the high-voltage battery 24 in the second driving mode is wider than that in the first driving mode.

[0070] Furthermore, regarding the SOC center values ​​Q0a and Q0b, which serve as the boundary between issuing a charging request and a discharging request when the vehicle is in a driving state where either charging or discharging can be selected, the vehicle control unit 31 sets the center value Q0b of the second driving mode to be higher than the center value Q0a of the first driving mode. With this setting, even when repeatedly performing large-scale discharging and large-scale charging in the second driving mode, it is difficult to cause the SOC of the high-voltage battery 24 to be depleted.

[0071] Furthermore, the vehicle control unit 31 controls the power generation limit based on the SOC of the high-voltage battery 24, ensuring that more power is generated when the SOC is lower. This control prevents the high-voltage battery 24 from becoming depleted, even during repeated charging and discharging in the second driving mode.

[0072] <Driving mode switching processing>

[0073] Figure 3This is a flowchart illustrating the driving mode switching process performed by the vehicle control unit. The vehicle control unit 31 performs the driving mode switching process during the startup of the hybrid electric vehicle 1. In this process, the driver operates the second driving mode transfer operation unit 44 (Yes in step S1), and if the vehicle speed is within the speed range of the second driving mode (Yes in step S2), the vehicle control unit 31 switches the driving mode to the second driving mode (Step S3). In step S3, if the engine 11 stops before switching to the second driving mode, the engine 11 is driven; if the locking mechanism 15a is closed before switching to the second driving mode, the locking mechanism 15a is switched to open. Furthermore, the throttle operation diagram is switched to the second driving mode diagram, and the control of the braking device, traction control, and power distribution to the drive wheels 2a are switched to the second driving mode mode.

[0074] Next, starting from the switch in step S3, the vehicle control unit 31 immediately switches the limit value for the change in generated power to a larger value (step S4). Furthermore, starting from the switch in step S3, the vehicle control unit 31 immediately switches the limit value for generated power to a larger value (step S5). It should be noted that the vehicle control unit 31 can execute the processing in step S5 with a time delay. Through the switch between steps S4 and S5, the vehicle control unit 31 then performs simultaneous power generation control processing, thereby performing power generation and charging of the high-voltage battery 24 according to the power generation limit conditions of the second driving mode. In the aforementioned power generation control processing, the vehicle control unit 31 determines the generated power based on the vehicle state, such as the driver's driving operation, the SOC of the high-voltage battery 24, and the cooling state of the engine 11, and performs power generation processing and charging of the high-voltage battery 24.

[0075] After switching to the second driving mode, if the driver releases the second driving mode switching operation unit 44 (yes in step S6) or the vehicle speed exceeds the range of the second driving mode (yes in step S7), the vehicle control unit 31, while keeping the engine 11 stopped, switches the control content of other driving modes to the first driving mode (step S8). Through step S8, the locking mechanism 15a can be switched to closed according to the driving state, and the throttle operation diagram can be switched to the diagram of the first driving mode. Furthermore, the control of the braking device, traction control, and power distribution control of the drive wheels 2a are switched to the first driving mode.

[0076] Next, the vehicle control unit 31 immediately switches the limit value for the change in generated power to a smaller value starting from the switch in step S8 (step S9). Furthermore, the vehicle control unit 31 immediately switches the limit value for generated power to a smaller value starting from the switch in step S8 (step S10). It should be noted that the vehicle control unit 31 can perform the switch between steps S9 and S10 with a time delay. After the switch between steps S9 and S10, the vehicle control unit 31 performs simultaneous power generation control processing, thereby executing power generation and charging of the high-voltage battery 24 according to the power generation limit conditions of the first driving mode. In the aforementioned power generation control processing, the vehicle control unit 31 determines the generated power based on the vehicle state, such as the driver's driving operation, the SOC of the high-voltage battery 24, and the cooling state of the engine 11, and performs power generation processing and charging of the high-voltage battery 24.

[0077] Next, the vehicle control unit 31 times the delay time (e.g., a few seconds) (step S11), and then switches the engine 11 to stop (step S12). This switch allows the engine 11 to stop and transition to EV driving, for example, when the SOC of the high-voltage battery 24 is high. It should be noted that after the switch in step S8, if the locking mechanism 15a is switched off before the delay time has elapsed, the vehicle control unit 31 can allow the engine 11 to stop without waiting for the delay time.

[0078] This driving mode switching process enables the switching between the first and second driving modes.

[0079] Next, the significance of the delay processing in step S11 of the driving mode switching process will be explained. Figure 4 This is a timing diagram showing the time-varying torque during the transition from engine-driven to EV-driven operation. The timing diagram shows the time-varying torque with and without power generation.

[0080] like Figure 4As shown in the timing diagram, when switching from engine driving to EV driving, the torque of the drive motor 12 increases while the torque of engine 11 decreases from a positive value to zero, keeping the total torque of both constant. This torque control allows the hybrid electric vehicle 1 to switch to EV driving without acceleration fluctuations. During torque control, the torque of engine 11 (via torque converter 15) is calculated by the vehicle control unit 31 based on the drive parameters of engine 11. The torque of engine 11 can be calculated relatively accurately when the locking mechanism 15a is closed. However, when the locking mechanism 15a is open, an estimation error occurs in the amount of torque amplified in the torque converter 15, making accurate torque calculation difficult. If the calculated torque of engine 11 is incorrect, the total torque of engine 11 and drive motor 12 is not constant, causing acceleration fluctuations in the hybrid electric vehicle 1 during the EV driving switch, resulting in driver discomfort.

[0081] like Figure 4 As shown by the dotted line, if the torque of engine 11 is low before switching to EV driving, the aforementioned error will be relatively smaller. However, as... Figure 4 As shown by the solid line, when generating electricity in the second driving mode, the driving motor 12 generates negative regenerative torque, which is added to the torque of the engine 11. Therefore, the torque output from the engine 11 increases. Consequently, in this state, if switching from engine driving to EV driving occurs, it results in a large error in the calculated torque of the engine 11, and causes a large acceleration change in the hybrid electric vehicle 1 when switching to EV driving.

[0082] On the other hand, due to the existence Figure 3 The delayed processing (step S11) means that during the delay period, the power generation decreases according to the power generation limit of the first driving mode, and consequently, the torque of engine 11 decreases. For example, in Figure 4 During engine operation, the torque state transitions from the solid line to the dashed line. Therefore, by switching to EV driving thereafter, the error in the calculated torque value of engine 11 is reduced, suppressing large acceleration fluctuations in the hybrid electric vehicle 1. This is the significance of the aforementioned delay processing.

[0083] As described above, according to this embodiment, the hybrid electric vehicle 1 experiences more relaxed power generation restrictions when the locking mechanism 15a is open in the second driving mode, which enhances off-road capability, compared to when the locking mechanism 15a is open in the first driving mode. Therefore, power generation is easier to achieve in the second driving mode, improving the power balance in that mode. Thus, vehicle control suitable for the second driving mode is realized.

[0084] Furthermore, in the hybrid electric vehicle 1 according to this embodiment, the limit value of the generated electricity in the second driving mode, as well as the limit on the amount of change of generated electricity, are set to larger values ​​than when the locking mechanism 15a is open in the first driving mode. Therefore, even in cases where the requested output power changes drastically in the second driving mode, electricity is generated quickly and in large quantities. Thus, the electricity balance in the second driving mode can be further improved.

[0085] Furthermore, in the hybrid electric vehicle 1 according to this embodiment, the limit value of the generated electricity in the second driving mode varies depending on the cooling condition of the engine 11. When sufficient power generation occurs in the second driving mode, it is conceivable that the engine 11, driven at low speed, is subjected to a large load, resulting in increased heat generation in the engine 11. Therefore, according to the above configuration, the generated electricity can be suppressed based on the cooling condition of the engine 11, thus preventing excessive heat generation in the engine 11 due to power generation in the second driving mode.

[0086] Furthermore, according to the hybrid electric vehicle 1 of this embodiment, the vehicle control unit 31 enables the use area of ​​the high-voltage battery 24 in the second driving mode (the area from the upper limit of SOC Q1a, Q1b to the lower limit of SOC Q2a, Q2b), Figure 2 The control is implemented in a manner that expands the usable area of ​​the high-voltage battery 24 compared to the first driving mode. According to this control, even in situations such as when the throttle operation unit 41 is abruptly operated in the second driving mode, which enhances off-road capability, and the driving motor 12 repeatedly generates and consumes large amounts of power, causing significant fluctuations in the SOC of the high-voltage battery 24, these fluctuations can be addressed by expanding the usable area of ​​the high-voltage battery 24.

[0087] Furthermore, according to the hybrid electric vehicle 1 of this embodiment, when switching from the second driving mode to the first driving mode, the vehicle control unit 31 delays the timing of allowing the engine 11 to stop. In this embodiment, by generating a relatively large amount of electricity in the second driving mode, the SOC of the high-voltage battery 24 becomes high when switching from the second driving mode to the first driving mode, thus generating a switching request from engine driving to EV driving. In such a case, the above-described delay processing, as referred to... Figure 4 As explained above, since the engine 11 temporarily reduces its output and then switches to EV driving, the error contained in the estimated value of the engine 11's torque can be reduced, and the acceleration variation of the hybrid electric vehicle 1 based on the error can be reduced.

[0088] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. For example, although a torque converter 15 with a locking mechanism 15a is shown as a connection mechanism in the above embodiments, any connection mechanism can be used as long as it is a mechanism that can switch between buffer connection and direct connection. In addition, although in the above embodiments, the conditions related to power generation are represented by limit values ​​such as the limit value of generated power and the limit value of the change in generated power, the ease of generating a request can be used instead of the limit values. Making the restrictions related to power generation relaxed is equivalent to making it easy to generate a request related to power generation. Therefore, the description of the principle of relaxing the restrictions in this specification can be replaced by the description of the principle of making it easy to generate a request. In addition, although the path for transmitting power from the engine to the drive motor 12 is shown in the above embodiments, Figure 1 While the above embodiment illustrates a shift to a second driving mode via driver input, a configuration could also be employed where an engine is connected to the front wheels and a drive motor to the rear wheels, with power transmitted from the engine through the front wheels, the driving surface, and the rear wheels to the drive motor. The power transmission path can be varied. Furthermore, although the above embodiment shows a shift to a second driving mode via driver input, a configuration could also be used where, for example, the control unit of a hybrid electric vehicle determines difficult roads and automatically shifts to a second driving mode. The shifting method can be varied. Moreover, the detailed aspects shown in the embodiment can be appropriately modified without departing from the spirit of the invention.

Claims

1. A hybrid electric vehicle, characterized in that, have: The engine and drive motor drive the drive wheels; A battery that supplies power to the drive motor for driving; A connecting mechanism located on the torque transmission path between the engine and the drive wheel, capable of switching the engine and the drive wheel between a direct connection and a buffer connection; A power generation mechanism that can generate electricity using the torque of the engine transmitted via the connecting mechanism; as well as The vehicle control unit is capable of switching between a first driving mode and a second driving mode that employs a throttle operation diagram that improves off-road capability compared to the first driving mode. When the buffer connection is applied in the first driving mode, the vehicle control unit uses a first condition to limit the power generation of the power generation mechanism. When the buffer connection is applied in the second driving mode, the vehicle control unit uses a second condition to limit the power generation of the power generation mechanism. The second condition is more lenient than the first condition. The first condition and the second condition include at least one of a limit value for the amount of electricity generated and a limit value for the amount of change in the amount of electricity generated.

2. The hybrid electric vehicle according to claim 1, characterized in that, The power generation limit for the second condition includes values ​​larger than the power generation limit for the first condition. The limit for the change in power generation under the second condition is greater than the limit for the change in power generation under the first condition.

3. The hybrid electric vehicle according to claim 1, characterized in that, The limit value for the generated electricity under the second condition varies depending on the cooling condition of the engine.

4. The hybrid electric vehicle according to claim 2, characterized in that, The limit value for the generated electricity under the second condition varies depending on the cooling condition of the engine.

5. The hybrid electric vehicle according to any one of claims 1 to 4, characterized in that, The hybrid electric vehicle includes a charge / discharge control unit for controlling the charging and discharging of the battery. The charging and discharging control unit makes the range of the battery in the second driving mode, from the lower limit of the charge margin that can be discharged to the upper limit of the charge margin that can be charged, wider than the range in the first driving mode.

6. The hybrid electric vehicle according to any one of claims 1 to 4, characterized in that, The vehicle control unit allows the engine to stop in the first driving mode, prohibits the engine from stopping in the second driving mode, and delays the timing of switching to allow the engine to stop when switching from the second driving mode to the first driving mode.

7. The hybrid electric vehicle according to claim 5, characterized in that, The vehicle control unit allows the engine to stop in the first driving mode, prohibits the engine from stopping in the second driving mode, and delays the timing of switching to allow the engine to stop when switching from the second driving mode to the first driving mode.

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