Hybrid vehicle

Abstract

A hybrid ECU (control device) in the present invention initiates rotation synchronization control for synchronizing the engine rotational speed Ne and the rotational speed of a drive shaft when, while traveling in a series mode, a transition request is made indicating the need to transition to a parallel mode from the series mode on the basis of a required driving force Fd that is required for traveling (time t1). The hybrid ECU initiates engagement control between an engine and the drive shaft by means of an engine clutch (engagement device) when the rotation synchronization control has been completed (time t2) and when the vehicle speed V becomes greater than a prescribed permitted vehicle speed Vps at which the transition from the series mode to the parallel mode is permitted (time t3).

Description

Hybrid vehicles

[0001] The present invention relates to a hybrid vehicle that switches between a series mode in which the vehicle runs using an electric motor as a drive source while generating electricity using the power of an internal combustion engine, and a parallel mode in which the vehicle runs using both the internal combustion engine and the electric motor as drive sources.

[0002] Conventionally, there is known a technology relating to a hybrid vehicle that switches between a series mode in which the vehicle runs using an electric motor as a drive source while generating electricity using power from an internal combustion engine, and a parallel mode in which the vehicle runs using both the internal combustion engine and the electric motor as a drive source. For example, Patent Document 1 (JP-A-2005-102226) describes a hybrid vehicle equipped with a clutch that switches between power from the motor and power from the engine. In this hybrid vehicle, when the vehicle speed reaches or exceeds a predetermined value at which the vehicle transitions from the series traveling mode to the parallel traveling mode, control is performed to synchronize the rotation speed of an engagement member on the motor side of the clutch with the rotation speed of an engagement member on the engine side.

[0003] JP 2013-123964 A

[0004] However, since it takes time to synchronize the rotation speed of the internal combustion engine with the rotation speed of the motor side, i.e., the drive shaft side, if rotation speed synchronization control is started after the vehicle speed reaches a predetermined value or higher at which the mode should transition from series mode to parallel mode, the mode cannot be transitioned to parallel mode quickly, and there is a risk that the user's acceleration request will not be fully satisfied.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a hybrid vehicle that can more quickly transition from series mode to parallel mode.

[0006] In order to achieve the above-mentioned object, the hybrid vehicle of the present invention is provided with an internal combustion engine, an electric motor connected to a drive shaft, an engagement device that switches between connecting and disconnecting the internal combustion engine and the drive shaft, and a control device that switches between a series mode in which the vehicle runs using the electric motor as a power source while generating electricity using power from the internal combustion engine, and a parallel mode in which the vehicle runs using the internal combustion engine and the electric motor as a power source.The control device is characterized in that, when a transition request is made to transition from the series mode to the parallel mode based on the required driving force required for driving while the vehicle is running in the series mode, the control device starts rotation synchronization control to synchronize the rotation speed of the internal combustion engine and the rotation speed of the drive shaft, and when the rotation synchronization control is completed and the vehicle speed becomes greater than a predetermined allowed vehicle speed that allows the transition from the series mode to the parallel mode, the control device starts engagement control of the internal combustion engine and the drive shaft using the engagement device.

[0007] In the hybrid vehicle of the present invention, since the rotation synchronization control is initiated when a transition request is made to transition from the series mode to the parallel mode, the rotation synchronization control can be continued until the vehicle speed reaches a predetermined permissible vehicle speed that permits the transition from the series mode to the parallel mode. Therefore, the hybrid vehicle of the present invention can more quickly transition from the series mode to the parallel mode.

[0008] FIG. 1 is a schematic configuration diagram of a hybrid vehicle according to a first embodiment. FIG. 2 is an explanatory diagram showing an example of a system configuration provided in the vehicle according to the first embodiment. FIG. 3 is an explanatory diagram showing a method for setting a predetermined allowed vehicle speed. FIG. 4 is a flowchart showing an example of parallel mode transition control. FIG. 5 is an explanatory diagram showing an example of time-varying changes in vehicle speed, each driving force, engine rotation speed, and driving mode when the parallel mode transition control of the first embodiment is executed. FIG. 6 is an explanatory diagram showing an example of a system configuration provided in a vehicle according to a second embodiment. FIG. 7 is an explanatory diagram showing an example of time-varying changes in vehicle speed, each driving force, engine rotation speed, and driving mode when the parallel mode transition control of the second embodiment is executed. FIG. 8 is an explanatory diagram showing an example of time-varying changes in vehicle speed, each driving force, engine rotation speed, and driving mode when the parallel mode transition control of the third embodiment is executed. FIG. 9 is an explanatory diagram showing an example of time-varying changes in vehicle speed, each driving force, engine rotation speed, and driving mode when the parallel mode transition control of the fourth embodiment is executed. FIG. 10 is an explanatory diagram showing a target engine rotation speed in rotation speed synchronization control according to a fifth embodiment. FIG. 11 is an explanatory diagram showing a schematic configuration of a hybrid ECU according to a sixth embodiment.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] [First embodiment] Fig. 1 is a schematic diagram of a hybrid vehicle according to a first embodiment. A hybrid vehicle 1 (hereinafter referred to as "vehicle 1") according to this embodiment is capable of traveling by driving front wheels 3 using the output of an engine 2, and is equipped with an electric front motor 4 (electric motor) that drives the front wheels 3. Vehicle 1 is a plug-in hybrid vehicle (PHEV) that is capable of external charging, in which an external power source supplies power to an on-board power storage device for charging, and external power feeding, in which the power storage device supplies power to electrical appliances outside the vehicle. Note that vehicle 1 is not limited to a plug-in hybrid vehicle, and may be a hybrid vehicle.

[0011] The engine 2 is capable of driving a drive shaft 8 of the front wheels 3 via a reduction gear 7, and is also capable of driving a motor generator 9 via the reduction gear 7 to generate electricity. The engine 2 is driven and controlled by an engine control unit 22 (hereinafter referred to as the "engine ECU 22"). The reduction gear 7 is configured to be able to switch the reduction ratio, and has a built-in engine clutch 16 (engine clutch) that can connect and disconnect the transmission of power between the output shaft of the engine 2 and the drive shaft 8 of the front wheels 3. The engine clutch 16 is a wet-type multi-plate hydraulic friction engagement device, but may also be, for example, an electric friction engagement device, or may be a meshing engagement device without being limited to a friction engagement device. The engine clutch 16 is driven and controlled by a hybrid control unit 20 (hereinafter referred to as the "hybrid ECU 20") described below via an engine clutch control unit 16a (hereinafter referred to as the "engine clutch ECU 16a").

[0012] The front motor 4 is powered by high-voltage power supplied from a drive battery 11 and a motor generator 9 mounted on the vehicle 1 via a front inverter 10, and drives a drive shaft 8 of the front wheels 3 via a reduction gear 7. The front inverter 10 has a front motor control unit 10a (hereinafter referred to as the "motor ECU 10a") and a generator control unit 10b (hereinafter referred to as the "generator ECU 10b"). The motor ECU 10a controls the output of the front motor 4 based on a control signal from the hybrid ECU 20. The generator ECU 10b has a function of controlling the amount of power generated by the motor generator 9 based on a control signal from the hybrid ECU 20.

[0013] The drive battery 11 is a power storage device that includes a battery module (not shown) that is composed of multiple battery cells, such as secondary batteries such as lithium-ion batteries. The drive battery 11 is equipped with a battery monitoring unit 11a (hereinafter referred to as the "battery ECU 11a") that monitors the temperature and state of charge (SOC) of the battery module. The battery ECU 11a also calculates the amount of power that can be charged to the drive battery 11 based on the temperature, state of charge, and usage status (integrated values ​​of input and output currents).

[0014] The hybrid ECU 20 is a control device for comprehensively controlling the vehicle 1 and includes input / output devices, storage devices (e.g., ROM, RAM, non-volatile RAM), a central processing unit (CPU), and a timer. The hybrid ECU 20 is connected to the reduction gear 7, the motor ECU 10a, the generator ECU 10b, the battery ECU 11a, and the engine ECU 22. The hybrid ECU 20 is also connected to various sensors, such as an APS sensor 13 (FIG. 2) that detects the accelerator operation amount and a vehicle speed sensor 14 (FIG. 2) that detects the vehicle speed. Based on the detection results and operation information input from these devices, the hybrid ECU 20 calculates the required driving force Fd (FIG. 5) required to drive the vehicle 1, and transmits control signals to each ECU and the reduction gear 7. The hybrid ECU 20 controls the driving mode switching, the output of the engine 2 and the front motor 4, the amount of power generated by the motor-generator 9, and the reduction ratio of the reduction gear 7.

[0015] The driving modes include EV mode, series mode, and parallel mode. In EV mode, the engine 2 is stopped, and the front motor 4 is driven by electric power supplied from the drive battery 11 to drive the vehicle. In series mode, the engine clutch 16 is disengaged, and the motor generator 9 is operated by the engine 2. The front motor 4 is then driven by electric power generated by the motor generator 9 and electric power supplied from the drive battery 11 to drive the vehicle. In series mode, the rotational speed of the engine 2 is maintained within a fuel-efficient range, and electric power generated by surplus output is supplied to the drive battery 11 to charge the drive battery 11. In parallel mode, the engine clutch 16 is engaged, and power is mechanically transmitted from the engine 2 via the reduction gear 7 to drive the front wheels 3. The front motor 4 is then driven by electric power generated by the engine 2 operating the motor generator 9 and electric power supplied from the drive battery 11 to drive the vehicle. The hybrid ECU 20 switches the driving mode based on the charging rate of the drive battery 11, the required driving force Fd, the vehicle speed V (FIG. 5), the amount of chargeable electric power, and the like.

[0016] When the driving mode is transitioned from the series mode to the parallel mode, the engine 2 and the drive shaft 8 are connected by engaging the engine clutch 16. At this time, in order to prevent shock from occurring during engagement, it is necessary to synchronize the rotation speed of the engine 2 (hereinafter referred to as "engine rotation speed Ne") with the rotation speed of the front motor 4 (hereinafter referred to as "motor rotation speed") while taking into account deceleration by the speed reducer 7 (i.e., to synchronize with the rotation speed of the drive shaft 8 while taking into account deceleration by the speed reducer 7). Therefore, the hybrid ECU 20, as configured below, executes rotation synchronization control for synchronizing the engine rotation speed Ne with the motor rotation speed and engagement control of the engine clutch 16 to transition from the series mode to the parallel mode.

[0017] 2 is an explanatory diagram showing an example of a system configuration of the vehicle 1 according to the first embodiment. As shown in the figure, the hybrid ECU 20 includes a vehicle body information acquisition unit 30 and a transition control unit 40 as components for performing a transition process from the series mode to the parallel mode.

[0018] The vehicle body information acquisition unit 30 has a required driving force calculation unit 31 and a vehicle speed acquisition unit 32. The required driving force calculation unit 31 calculates the required driving force Fd based on the accelerator opening degree detected by the APS sensor 13, etc. The vehicle speed acquisition unit 32 acquires the vehicle speed V detected by the vehicle speed sensor 14. The vehicle body information acquisition unit 30 outputs the calculated required driving force Fd and the acquired vehicle speed V to the transition control unit 40.

[0019] The transition control unit 40 has a driving mode determination unit 41, a transition request determination unit 42, a transition permission determination unit 43, a rotation synchronization control unit 44, and an engagement control unit 45. The driving mode determination unit 41 determines whether the current driving mode is set to EV mode, series mode, or parallel mode, and outputs the determination result to the transition request determination unit 42.

[0020] When predetermined transition conditions are met while the driving mode of the vehicle 1 is set to the series mode, the transition request determination unit 42 issues a transition request, which is a request to execute a transition to the parallel mode. The predetermined transition conditions include the required driving force Fd being greater than the SR possible driving force Fsr (FIG. 5) and the PR possible driving force Fpr being greater than the SR possible driving force Fsr (FIG. 5). The SR possible driving force Fsr is the driving force that the vehicle 1 can output in the series mode, and the PR possible driving force Fpr is the driving force that the vehicle 1 can output in the parallel mode, and both are calculated based on the current state of the vehicle 1. The transition request determination unit 42 outputs the transition request to the transition permission determination unit 43 and the rotation synchronization control unit 44.

[0021] The transition permission determination unit 43 permits a transition from the series mode to the parallel mode when predetermined permission conditions are met after the transition request determination unit 42 issues a transition request. The predetermined permission conditions include the vehicle speed V being greater than a predetermined permission vehicle speed Vps (FIG. 5) and the completion of the rotation synchronization control described below. However, the transition permission determination unit 43 does not permit the transition if the vehicle speed V does not become greater than the predetermined permission vehicle speed Vps even after a first predetermined time Δt1 (predetermined cancellation determination time) has elapsed since the transition request. The first predetermined time Δt1 is set as a threshold value for prioritizing suppression of a decrease in power generation amount due to the rotation synchronization control continuing for a long period of time over the transition from the series mode to the parallel mode. If the transition permission determination unit 43 permits the transition, it outputs a notification to the engagement control unit 45 to that effect.

[0022] FIG. 3 is an explanatory diagram illustrating a method for setting the predetermined permitted vehicle speed Vps. Assume that at time ta, the vehicle speed V exceeds the predetermined permitted vehicle speed Vps, permission to transition to the parallel mode is granted, and transition to the parallel mode is completed. Assume that the vehicle 1 decelerates from time ta at a predetermined deceleration assuming a rapid deceleration. At time td, the vehicle speed V drops to a stalled vehicle speed at which the engine 2 connected to the drive shaft 8 stalls. The lower limit vehicle speed of the vehicle 1 at which the parallel mode can be executed is set so that the time Δtbc required from time tb to the completion of engagement and disengagement of the engine clutch 16 (time tc) is shorter than the time Δtbd from time tb when the vehicle 1 reaches the lower limit vehicle speed to time td. In other words, the lower limit vehicle speed is set so that engagement and disengagement of the engine clutch 16 is completed before the vehicle 1 reaches the stalled vehicle speed, even if the vehicle 1 is decelerating at the predetermined deceleration. The predetermined permissible vehicle speed Vps is set to include a predetermined margin with respect to the lower limit vehicle speed so as to prevent frequent switching of the driving mode due to minute changes in the vehicle speed V. The predetermined margin is set so as to ensure a time Δtab required for the vehicle 1 to reach the lower limit vehicle speed from time ta when the vehicle 1 is decelerating at the predetermined deceleration.

[0023] Returning to the description of FIG. 2 , when the transition request determination unit 42 issues a transition request, the rotation synchronization control unit 44 executes rotation speed synchronization control to synchronize the engine rotation speed Ne with the motor rotation speed while taking into account deceleration by the reducer 7. The rotation speed synchronization control is executed until the absolute value ΔN of the difference between the engine rotation speed Ne and the motor rotation speed becomes less than a predetermined reference value ΔNref, which indicates completion of synchronization. The engine rotation speed Ne is detected by a rotation speed detection sensor (not shown) and input to the hybrid ECU 20 via the engine ECU 22. The motor rotation speed is detected by a rotation speed detection sensor (not shown) and input to the hybrid ECU 20 via the motor ECU 10. However, if the rotation synchronization control is not completed (ΔN<ΔNref) even after a second predetermined time Δt2 has elapsed since the transition permission was issued, the rotation synchronization control unit 44 terminates the rotation synchronization control. The second predetermined time Δt2 is set as a threshold value that prioritizes suppressing a decrease in power generation due to a long period of rotation synchronization control over transition from the series mode to the parallel mode. In this case, the execution of the transition process from the series mode to the parallel mode is terminated.

[0024] When the transition is permitted by the transition permission determination unit 43 and the rotation synchronization control by the rotation synchronization control unit 44 is completed (ΔN<ΔNref), the engagement control unit 45 executes engagement control of the engine clutch 16. That is, the engagement control unit 45 executes control to switch the engine clutch 16 from a disconnected state to an engaged state using a hydraulic actuator (not shown).

[0025] (Parallel Mode Transition Control) Next, an example of the parallel mode transition control executed by the hybrid ECU 20 will be described with reference to Fig. 4. Fig. 4 is a flowchart showing an example of the parallel mode transition control. The process shown in Fig. 4 is executed by the hybrid ECU 20 while the driving mode of the vehicle 1 is set to the series mode.

[0026] First, the hybrid ECU 20 determines whether the engine speed Ne is greater than 0 (step S1). If the hybrid ECU 20 determines that the engine speed Ne is equal to or less than 0 (No in step S1), the engine 2 is not operating, and the hybrid ECU 20 waits until the engine speed Ne becomes greater than 0.

[0027] When the hybrid ECU 20 determines that the engine speed Ne is greater than 0 (Yes in step S1), it determines whether the required driving force Fd is greater than the SR possible driving force Fsr (step S2). When the hybrid ECU 20 determines that the required driving force Fd is equal to or less than the SR possible driving force Fsr (No in step S2), it executes the processing from step S1 onwards again. In this case, the driving mode setting is maintained in the series mode. On the other hand, when the hybrid ECU 20 determines that the required driving force Fd is greater than the SR possible driving force Fsr (Yes in step S2), it determines whether the PR possible driving force Fpr is greater than the SR possible driving force Fsr (step S3).

[0028] If the hybrid ECU 20 determines that the PR possible driving force Fpr is equal to or less than the SR possible driving force Fsr (NO in step S3), it executes the processes from step S1 onward again. In this case, the driving mode remains set to the series mode. On the other hand, if the hybrid ECU 20 determines that the PR possible driving force Fpr is greater than the SR possible driving force Fsr (YES in step S3), it requests a transition from the series mode to the parallel mode (step S4). Then, the hybrid ECU 20 starts executing rotation synchronization control (step S5). That is, the transition request triggers the start of synchronization of the engine rotation speed Ne with the motor rotation speed.

[0029] Next, the hybrid ECU 20 determines whether the transition request is continuing (step S6), and if it determines that the transition request is not continuing (No in step S6), it executes the processes from step S1 onwards again. On the other hand, if it determines that the transition request is continuing (Yes in step S6), the hybrid ECU 20 determines whether the current vehicle speed V is greater than a predetermined permitted vehicle speed Vps (step S7).

[0030] If the hybrid ECU 20 determines that the current vehicle speed V is equal to or less than the predetermined permitted vehicle speed Vps (No in step S7), it determines whether or not the first predetermined time Δt1 has elapsed (step S8). If the hybrid ECU 20 determines that the first predetermined time Δt1 has not elapsed (No in step S8), it executes the processing from step S7 onwards. On the other hand, if the vehicle speed V does not become greater than the predetermined permitted vehicle speed Vps even after the first predetermined time Δt1 has elapsed (Yes in step S8), the hybrid ECU 20 executes the processing from step S1 onwards again. In this case, the driving mode is maintained in the series mode.

[0031] If the hybrid ECU 20 determines that the current vehicle speed V is greater than the predetermined permitted vehicle speed Vps (Yes in step S7), it permits a transition from the series mode to the parallel mode (step S9). Next, the hybrid ECU 20 determines whether the absolute value ΔN of the difference between the engine rotation speed Ne and the motor rotation speed is less than a predetermined reference value ΔNref, i.e., whether the rotation synchronization control is completed (step S10).

[0032] When the hybrid ECU 20 determines that the rotation synchronization control has not been completed (ΔN>ΔNref) (No in step S10), it determines whether or not the second predetermined time Δt2 has elapsed (step S11). When the hybrid ECU 20 determines that the second predetermined time Δt2 has not elapsed (No in step S11), it executes the processing from step S10 onwards. On the other hand, when the rotation synchronization control has not been completed even after the second predetermined time Δt2 has elapsed (Yes in step S11), it executes the processing from step S1 onwards again. In this case, the driving mode is maintained in the series mode.

[0033] When the hybrid ECU 20 determines that the rotation synchronization control is complete (Yes in step S10), it executes engagement control of the engine clutch 16 (step S12) and ends this routine. When the engagement control is completed, the engine 2 and the drive shaft 8 are connected by the engine clutch 16, and the transition of the driving mode to the parallel mode is completed.

[0034] Effect of First Embodiment As described above, in the vehicle 1 of the first embodiment, when a transition request to transition from the series mode to the parallel mode is made based on the required driving force Fd required for traveling while the vehicle is traveling in the series mode, the hybrid ECU 20 (control device) starts rotation synchronization control to synchronize the engine rotation speed Ne with the rotation speed of the drive shaft 8. When the rotation synchronization control is completed (time t2) and the vehicle speed V becomes greater than a predetermined permitted vehicle speed Vps that permits a transition from the series mode to the parallel mode (time t3), the hybrid ECU 20 starts engagement control of the engine 2 (internal combustion engine) and the drive shaft 8 by the engine clutch 16 (engagement device).

[0035] The effects of the first embodiment will be described with reference to FIG. 5. FIG. 5 is an explanatory diagram showing an example of time changes in vehicle speed V, each driving force, engine speed Ne, and driving mode when the parallel mode transition control of the first embodiment is executed. Now, assume that the vehicle 1 starts traveling while starting the engine 2 from time t0, and that starting of the engine 2 is completed at time t1. Also, assume that at time t1, the requested driving force Fd is greater than the SR available driving force Fsr, and the PR available driving force Fpr is also greater than the SR available driving force Fsr. Therefore, in this example, a transition request is made at time t1. Also, assume that at time t3, the vehicle speed V becomes greater than a predetermined permitted vehicle speed Vps, and transition permission is granted.

[0036] In the vehicle 1 of the first embodiment, rotation synchronization control is executed in response to a transition request at time t1. As a result, for example, if rotation synchronization control is completed at time t2, which is earlier than time t3, and transition permission is granted at time t3, the driving mode is promptly transitioned from the series mode to the parallel mode. On the other hand, as shown in the comparative example in the figure, if rotation synchronization control is initiated at the time t3 when the vehicle speed V becomes greater than a predetermined permitted vehicle speed Vps, transition from the series mode to the parallel mode is not possible until the rotation synchronization control is completed (time t4). In this way, in the vehicle 1 of the first embodiment, rotation synchronization control can be performed until the vehicle speed becomes greater than the predetermined permitted vehicle speed Vps, thereby accelerating the transition of the driving mode compared to the comparative example. Therefore, the vehicle 1 of the first embodiment can more quickly transition from the series mode to the parallel mode.

[0037] Furthermore, if the vehicle speed V does not exceed the predetermined permitted vehicle speed Vps (Yes in step S8 of FIG. 4 ) even after a first predetermined time Δt1 (predetermined cancellation determination time) has elapsed after the transition request (time t1), the hybrid ECU 20 cancels the transition from the series mode to the parallel mode and maintains the driving mode in the series mode. With this configuration, if the vehicle speed V does not increase sufficiently even after a transition request is made, such as when traveling on a road with a high gradient, the transition from the series mode to the parallel mode can be canceled and power generation in the series mode can be prioritized.

[0038] [Second embodiment] Figure 6 is an explanatory diagram showing an example of a system configuration provided in a vehicle according to a second embodiment. The configuration of the vehicle 1 according to the second embodiment is the same as that of the first embodiment except for the following description, and therefore, duplicated descriptions will be omitted and the same reference numerals will be used. As shown in the figure, the vehicle 1 according to the second embodiment includes a mode selection switch 15. Furthermore, in the hybrid ECU 20 according to the second embodiment, the vehicle body information acquisition unit 30 includes a mode selection unit 33.

[0039] The mode selection switch 15 is a switch that allows the driver to select between a normal mode and a high-response mode that provides enhanced acceleration response compared to the normal mode. The mode selection switch 15 is mounted inside the vehicle cabin (not shown). The high-response mode includes, for example, a power mode that provides powerful and highly responsive driving during straight-line acceleration by increasing the response of the front motor 4, and a tarmac mode that improves cornering performance by increasing the distribution of driving force to the rear wheels. The mode selection switch 15 outputs an instruction signal indicating the mode selected by the driver to the hybrid ECU 20. A mode selection unit 33 of the hybrid ECU 20 receives the instruction signal from the mode selection switch 15 and selects either the normal mode or the high-response mode in accordance with the instruction signal. The mode selection unit 33 outputs information about the selected mode to the transition control unit 40.

[0040] When the transition permission determination unit 43 of the second embodiment receives information indicating that the high-response mode has been selected from the mode selection unit 33, it sets the predetermined permitted vehicle speed Vps in the parallel mode transition control to a value that is lower than the value when the normal mode is selected. Figure 7 is an explanatory diagram showing an example of time changes in the vehicle speed V, each driving force, engine speed Ne, and driving mode when the parallel mode transition control of the second embodiment is executed. As in the example shown in Figure 5, it is assumed that the vehicle 1 starts traveling while starting the engine 2 from time t0, the engine 2 is started completely at time t1, a transition request is made, and the rotation synchronization control is completed at time t2.

[0041] When the normal mode is selected by the mode selection switch 15, the vehicle speed V becomes greater than a predetermined permitted vehicle speed Vps (here, "Vps1") at time t3, and transition permission is granted. On the other hand, when the high-response mode is selected by the mode selection switch 15, the hybrid ECU 20 (transition permission determination unit 43) sets the predetermined permitted vehicle speed Vps to a value (here, "Vps2") that is slower than that in the normal mode, as described above. As a result, when the high-response mode is selected, transition permission is granted at time t31, which is earlier than time t3. This allows the transition from series mode to parallel mode to be carried out more quickly when the driver desires high output responsiveness, thereby satisfying the driver's request.

[0042] However, the upper limit of the amount of sliding of the predetermined permissible vehicle speed Vps corresponds to a predetermined margin for creating the time Δtab in Fig. 3 when the vehicle 1 is decelerating at the above-mentioned predetermined deceleration. As described above, the lower limit vehicle speed at which the parallel mode can be executed is set so that the vehicle speed does not drop below the engine stall speed at which the engine 2 stalls when decelerating at the predetermined deceleration, the predetermined permissible vehicle speed Vps is set with a predetermined margin for the lower limit vehicle speed, and the amount of sliding is set within the range of the predetermined margin.

[0043] [Third Embodiment] Next, a third embodiment of the present invention will be described. The configuration of the vehicle 1 of the third embodiment is the same as that of the first embodiment, except for some differences in the content of the parallel mode transition control, and therefore, duplicated explanations will be omitted and the same reference numerals will be used. Figure 8 is an explanatory diagram showing an example of time changes in vehicle speed V, each driving force, engine rotation speed Ne, and driving mode when the parallel mode transition control of the third embodiment is executed. Unless otherwise specified, it is assumed that time changes similar to those in the example shown in Figure 5 also occur in Figure 8.

[0044] As described above, the conditions for requesting a transition from series mode to parallel mode include the required driving force Fd becoming greater than the SR available driving force Fsr. In other words, the SR available driving force Fsr is a predetermined threshold value for the required driving force Fd at which the transition from series mode to parallel mode should be made. When a transition request is made (time t1), the hybrid ECU 20 of the third embodiment calculates the deviation ΔF between the required driving force Fd and the SR available driving force Fsr.

[0045] The hybrid ECU 20 (transition permission determination unit 43) then sets the predetermined permitted vehicle speed Vps according to the deviation ΔF. Specifically, the hybrid ECU 20 sets the predetermined permitted vehicle speed Vps to a value that is lower as the deviation ΔF increases. As a result, as illustrated in FIG. 8 , the predetermined permitted vehicle speed Vps is set to a value "Vps2" that is lower than the value "Vps1" obtained when the deviation ΔF is not taken into account, and transition permission is granted at time t31, which is earlier than time t3. Therefore, when the deviation ΔF is large, that is, when the driver's acceleration request is strong, transition from the series mode to the parallel mode can be performed more quickly. However, as in the second embodiment, the upper limit of the amount of slide of the predetermined permitted vehicle speed Vps is a predetermined margin relative to the lower limit vehicle speed of the parallel mode.

[0046] Furthermore, the hybrid ECU 20 (rotation synchronization control unit) sets the rate of change of the engine speed Ne during rotation synchronization control according to the deviation ΔF. Specifically, the hybrid ECU 20 increases the rate of change of the target rotation speed (not shown) of the engine 2 during rotation synchronization control as the deviation ΔF increases. As a result, as illustrated by the change from the solid line (engine speed Ne when the deviation ΔF is not taken into account) to the two-dot chain line in the figure, the rate of change of the engine speed Ne increases as the deviation ΔF increases. As a result, the completion of rotation synchronization control can be accelerated from time t2 to time t21. Therefore, when the deviation ΔF is large, i.e., when the driver's acceleration request is strong, the transition from the series mode to the parallel mode can be performed more quickly.

[0047] In the parallel mode transition control of the third embodiment, in other words, the smaller the deviation ΔF, the smaller the rate of change of the engine speed Ne in the rotation synchronization control is set, so that the state in which the engine speed Ne is high continues for a relatively long time, and it is possible to ensure the amount of power generation in the series mode.

[0048] [Fourth Embodiment] Next, a fourth embodiment of the present invention will be described. The configuration of the vehicle 1 of the fourth embodiment is the same as that of the first embodiment, except for some differences in the content of the parallel mode transition control, and therefore, duplicated explanations will be omitted and the same reference numerals will be used. Figure 9 is an explanatory diagram showing an example of time changes in vehicle speed V, each driving force, engine rotation speed Ne, and driving mode when the parallel mode transition control of the fourth embodiment is executed. Unless otherwise specified, it is assumed that time changes similar to those in the example shown in Figure 5 also occur in Figure 9.

[0049] In the fourth embodiment, when a transition request is made (time t1), the hybrid ECU 20 calculates a predicted arrival time Δte, which is the time it takes for the vehicle speed V to exceed a predetermined permitted vehicle speed Vps, based on the vehicle speed change rate at that time. The vehicle speed change rate may be calculated based on the vehicle speed V. The hybrid ECU 20 (rotation synchronization control unit 44) then sets a change rate of the engine speed Ne during rotation synchronization control according to the predicted arrival time Δte. Specifically, the hybrid ECU 20 increases the change rate of the target rotation speed (not shown) of the engine 2 during rotation synchronization control as the predicted arrival time Δte decreases. As a result, as illustrated by the change from the solid line (the engine speed Ne without considering the predicted arrival time Δte) to the dashed-two-dot line in the figure, the shorter the predicted arrival time Δte, the greater the change rate of the engine speed Ne. As a result, the completion of the rotation synchronization control can be accelerated from time t2 to time t21. Therefore, when the predicted arrival time Δte is large, i.e., when the driver's acceleration request is large, the transition from the series mode to the parallel mode can be performed more quickly.

[0050] In the parallel mode transition control of the fourth embodiment, as in the third embodiment, the longer the predicted arrival time Δte, the larger the change rate of the engine speed Ne in the rotation synchronization control is set. Therefore, the state in which the engine speed Ne is high continues for a relatively long time, and it is possible to ensure the amount of power generation in the series mode.

[0051] Fifth Embodiment Next, a fifth embodiment of the present invention will be described. The configuration of the vehicle 1 in the fifth embodiment is the same as that in the first embodiment, except for some differences in the content of the parallel mode transition control, and therefore, duplicated explanations will be omitted and the same reference numerals will be used. Figure 10 is an explanatory diagram showing the target rotation speed of the engine 2 in rotation speed synchronization control in the fifth embodiment. The two-dot chain line in Figure 10 represents the target rotation speed Net1 of the engine 2 in rotation synchronization control when the charging rate of the drive battery 11 (power storage device) is equal to or higher than a predetermined value, and the solid line represents the target rotation speed Net2 of the engine 2 in rotation synchronization control when the charging rate is less than the predetermined value.

[0052] As shown in the figure, the hybrid ECU 20 (rotation synchronization control unit 44) of the fifth embodiment sets the target rotation speed Net2 of the engine 2 in rotation synchronization control to be higher than the target rotation speed Net1 for synchronization with the motor rotation speed when the charging rate of the drive battery 11 is below a predetermined value. The predetermined value is set as a threshold that prioritizes charging the drive battery 11 over hastening the completion of rotation synchronization control. This makes it possible to ensure the amount of charge to the drive battery 11 when the charging rate of the drive battery 11 has fallen below the predetermined value.

[0053] However, this control is only performed from the start of rotation synchronization control until the vehicle speed V becomes higher than a predetermined permitted vehicle speed Vps. After the vehicle speed V becomes higher than the predetermined permitted vehicle speed Vps (Yes in step S7 of FIG. 4), the hybrid ECU 20 sets the target rotation speed Net2 of the engine 2 to the target rotation speed Net1 for synchronization with the motor rotation speed. After the rotation synchronization control is completed (Yes in step S10), engagement control is started (step S12).

[0054] [Sixth Embodiment] Next, a sixth embodiment of the present invention will be described. The configuration of the vehicle 1 of the sixth embodiment is the same as that of the first embodiment except for the following description, and therefore, duplicated descriptions will be omitted and the same reference numerals will be used. Fig. 11 is an explanatory diagram showing a schematic configuration of a hybrid ECU 20 of the sixth embodiment. As shown in the figure, the hybrid ECU 20 of the sixth embodiment has a storage unit (storage device) 50 that stores map information and route information.

[0055] The map information includes at least road surface gradient information. The route information is a route connecting a start point and an end point on a map selected by the driver of the vehicle 1. The map information and route information may be, for example, information used by a navigation device (not shown) installed in the vehicle 1, or may be information obtained from an external route search server.

[0056] When a transition request is made (step S4 in FIG. 4 ), the hybrid ECU 20 of the sixth embodiment determines whether a route with a gradient equal to or greater than the predetermined gradient exists on the planned driving route based on the map information and route information. The planned driving route is the route the vehicle 1 plans to travel in the near future. The planned driving route may be set based on, for example, information on the distance required from the time the transition request is made until the actual transition to the parallel mode, which information is accumulated through experiments, analysis, or experience. The predetermined gradient is set as a threshold value that indicates that power generation in the series mode should be prioritized over quickly completing the rotation synchronization control.

[0057] If the hybrid ECU 20 determines that the planned driving route includes a route with a gradient equal to or greater than a predetermined gradient, it does not start the rotation-synchronization control even if a transition request is made, but starts the rotation-synchronization control after the vehicle speed V becomes greater than a predetermined permitted vehicle speed Vps (the process of step S5 in FIG. 4 is executed after the process of step S9 is executed). With this configuration, if it is known in advance that the presence of a road surface with a high gradient will make it difficult for the vehicle speed V to increase and therefore difficult to permit a transition to the parallel mode, the hybrid ECU 20 can ensure the amount of power generated in the series mode, and therefore the amount of charge to the drive battery 11, by delaying the start of the rotation-synchronization control.

[0058] Although the description of the embodiment has been completed above, the aspects of the present invention are not limited to this embodiment. For example, the configurations and controls of the first to sixth embodiments may be used in appropriate combination.

[0059] REFERENCE SIGNS LIST 1 Vehicle (hybrid vehicle) 2 Engine (internal combustion engine) 4 Front motor (electric motor) 8 Drive shaft 11 Drive battery (electricity storage device) 15 Mode selection switch 16 Engine clutch (engagement device) 20 Hybrid control unit (control device) Fd Required driving force Fpr PR possible driving force Fsr SR possible driving force (predetermined switching threshold) Ne Engine rotation speed Net1, Net2 Target rotation speed V Vehicle speed Vps, Vps1, Vps2 Predetermined permitted vehicle speed ΔF Deviation Δt1 First predetermined time (predetermined stop determination time) Δte Predicted arrival time

Claims

1. A hybrid vehicle comprising: an internal combustion engine; an electric motor connected to a drive shaft; an engagement device that switches between connection and disconnection between the internal combustion engine and the drive shaft; and a control device that switches between a series mode in which the vehicle runs using the electric motor as a drive source while generating electricity using power from the internal combustion engine, and a parallel mode in which the vehicle runs using the internal combustion engine and the electric motor as a drive source, wherein the control device, when a transition request to transition from the series mode to the parallel mode is made based on a required driving force required for running while the vehicle is running in the series mode, starts rotation synchronization control to synchronize the rotation speed of the internal combustion engine and the rotation speed of the drive shaft; and when the rotation synchronization control is completed and the vehicle speed becomes higher than a predetermined allowed vehicle speed that allows a transition from the series mode to the parallel mode, starts engagement control of the internal combustion engine and the drive shaft by the engagement device.

2. A hybrid vehicle as described in claim 1, characterized in that the vehicle mode is selectable between a normal mode and a high-response mode that has higher acceleration response than the normal mode, and when the vehicle mode is set to the high-response mode, the control device sets the predetermined permitted vehicle speed to a lower vehicle speed than the normal mode.

3. The hybrid vehicle described in claim 1, characterized in that the conditions for making the transition request include the required driving force being greater than a predetermined switching threshold, which is the driving force that can be output in the series mode, and the control device sets the predetermined permitted vehicle speed to a lower vehicle speed the greater the deviation between the required driving force when the transition request is made and the predetermined switching threshold.

4. The hybrid vehicle described in claim 1, characterized in that the conditions for making the transition request include the required driving force being greater than a predetermined switching threshold, which is the driving force that can be output in the series mode, and the control device sets a larger rate of change in the rotation speed of the internal combustion engine in the rotation synchronization control the greater the deviation between the required driving force when the transition request is made and the predetermined switching threshold.

5. The hybrid vehicle described in claim 1, characterized in that when the transition request is made, the control device calculates a predicted time until the vehicle speed becomes greater than the predetermined permitted vehicle speed based on the vehicle speed change rate, and sets a larger rate of change in the rotation speed of the internal combustion engine in the rotation synchronization control as the predicted time becomes shorter.

6. The hybrid vehicle according to claim 1, further comprising a power storage device that stores the electric power generated by the internal combustion engine, wherein the control device, when the charge rate of the power storage device is less than a predetermined value, sets the target rotation speed of the internal combustion engine in the rotation synchronization control to be higher than the rotation speed for synchronization with the rotation speed of the drive shaft until the vehicle speed becomes higher than the predetermined permitted vehicle speed.

7. The hybrid vehicle described in claim 1, characterized in that if the vehicle speed does not exceed the predetermined permitted vehicle speed even after a predetermined cancellation judgment time has elapsed after the start of the rotation synchronization control, the control device cancels the transition from the series mode to the parallel mode and maintains the driving mode in the series mode.

8. A hybrid vehicle as described in any one of claims 1 to 7, characterized in that when the transition request is made, the control device determines based on map information that there is a route on the planned driving route with a gradient of at least a predetermined value, the control device does not start the rotation synchronization control even if the transition request is made, and starts the rotation synchronization control after the vehicle speed becomes greater than the predetermined permitted vehicle speed.

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