Patent Publication Number: US-2022227352-A1

Title: Vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority of Japanese Patent Application No. 2021-006002, filed on Jan. 18, 2021, the content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a vehicle. 
     BACKGROUND ART 
     There is a vehicle including, in a power transmission path between an engine and a drive wheel, a connection-disconnection device (for example, a clutch) capable of connecting and disconnecting the power transmission path. Such a connection-disconnection device is configured to be capable of connecting the power transmission path by, for example, being supplied with hydraulic pressure by a mechanical oil pump driven by rotation (operation) of the engine. 
     However, in recent years, a vehicle may stop supply of fuel to the engine to stop rotation of the engine during deceleration or stop of the vehicle from the viewpoint of improving fuel efficiency. When the rotation of the engine is stopped, the mechanical oil pump driven by the rotation of the engine is also stopped. Therefore, the mechanical oil pump cannot supply the necessary hydraulic pressure to the connection-disconnection device capable of connecting and disconnecting the power transmission path between the engine and the drive wheel, and thus a response performance of the vehicle to an acceleration command (or a start command) or the like may decrease. 
     Therefore, Japanese Patent No. 6521019 discloses a technique in which an electric oil pump is provided in addition to the mechanical oil pump, and hydraulic pressure of the electric oil pump is used when the necessary hydraulic pressure cannot be secured by the mechanical oil pump. 
     However, in the related art described above, the hydraulic pressure of the electric oil pump is used when the necessary hydraulic pressure cannot be secured by the mechanical oil pump. Therefore, it is necessary to provide the electric oil pump in addition to the mechanical oil pump, which may complicate a configuration of a vehicle. In addition, in the related art described above, when a state where the necessary hydraulic pressure cannot be secured by the mechanical oil pump continues for a long time, it is necessary to drive the electric oil pump during that time, and thus electric power consumption of the vehicle may increase. 
     SUMMARY 
     The present invention provides a vehicle capable of preventing a decrease in response performance to an acceleration command given to the vehicle with a simple configuration. 
     According to an aspect of the present invention, there is provided a vehicle including: an internal combustion engine; a rotary electric machine configured to rotationally drive the internal combustion engine; a connection-disconnection device provided to connect and disconnect a power transmission path between the internal combustion engine and a drive wheel, the connection-disconnection device being configured to connect the power transmission path in response to supply of hydraulic pressure equal to or higher than a predetermined value; a hydraulic pressure supply device configured to supply hydraulic pressure to the connection-disconnection device; a hydraulic pressure control device configured to control the supply of the hydraulic pressure supplied by the hydraulic pressure supply device to the connection-disconnection device; and a control device configured to control the internal combustion engine and the rotary electric machine, where: the hydraulic pressure supply device includes: a mechanical hydraulic pressure supply device that is driven in accordance with rotation of the internal combustion engine to supply the hydraulic pressure to the connection-disconnection device; and a pressure accumulator configured to supply the hydraulic pressure to the connection-disconnection device by pressure accumulated in advance, the control device executes: fuel cut-off control to stop fuel supply to the internal combustion engine based on a deceleration command given to the vehicle; and rotation speed maintaining control to maintain a rotation speed of the internal combustion engine at a predetermined rotation speed larger than 0 by rotationally driving the internal combustion engine by the rotary electric machine or supplying fuel to the internal combustion engine when the rotation speed of the internal combustion engine decreases to a predetermined rotation speed along with the execution of the fuel cut-off control; and the hydraulic pressure control device supplies the hydraulic pressure to the connection-disconnection device by the pressure accumulator when the hydraulic pressure supplied to the connection-disconnection device by the mechanical hydraulic pressure supply device is less than the predetermined value when an acceleration command is given to the vehicle. 
     According to the present invention, it is possible to provide a vehicle capable of preventing a decrease in response performance to an acceleration command given to the vehicle with a simple configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example of a partial configuration of a vehicle according to an embodiment of the present invention; 
         FIG. 2  shows an example of a schematic configuration of a transmission included in the vehicle according to the embodiment of the present invention: 
         FIG. 3  is a timing chart showing a first example of an operation of the vehicle according to the embodiment of the present invention; 
         FIG. 4  is a timing chart showing a second example of the operation of the vehicle according to the embodiment of the present invention; 
         FIG. 5  is a timing chart showing a third example of the operation of the vehicle according to the embodiment of the present invention; 
         FIG. 6  is a timing chart showing a fourth example of the operation of the vehicle according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of a vehicle of the present invention will be described in detail with reference to the drawings. 
     (Configuration of Vehicle) 
     As shown in  FIG. 1 , a vehicle  1  of the present embodiment is a so-called hybrid electrical vehicle that includes an engine  11 , a motor generator  12 , a transmission TM, a hydraulic pressure supply device  15 , a hydraulic pressure control device  16 , a battery  17 , an electric power conversion device  21 , a control device  22 , and a drive wheel DW. In  FIG. 1 , a thick solid line indicates mechanical connection, a double broken line indicates electrical wiring, a solid line arrow mark indicates a control signal, and a broken line indicates an oil passage. 
     The engine  11  is rotationally driven by being supplied with fuel (for example, gasoline). Power output from the engine  11  (hereinafter, also simply referred to as the output of the engine  11 ) is transmitted to the drive wheel DW via the transmission TM that is mechanically connected to the engine  11 , and is used for traveling of the vehicle  1 . The engine  11  is also mechanically connected to the motor generator  12 . Therefore, the motor generator  12  can be rotationally driven by the output of the engine  11 , while the engine  11  can also be rotationally driven by power output from the motor generator  12  (hereinafter, also simply referred to as the output of the motor generator  12 ). 
     The engine  11  is also mechanically connected to a mechanical hydraulic pressure supply device  15 A, which will be described later, included in the hydraulic pressure supply device  15 . When the engine  11  is rotationally driven, the mechanical hydraulic pressure supply device  15 A is also driven. 
     The motor generator  12  is, for example, a three-phase AC motor, and functions as a motor that outputs power by being supplied with electric power. The motor generator  12  is electrically connected to the battery  17  via the electric power conversion device  21 . 
     Here, the battery  17  is, for example, a battery that includes a plurality of power storage cells connected in series and is configured to be capable of outputting a high voltage of 100 to 400 [V]. As each power storage cell of the battery  17 , a lithium ion battery, a nickel hydrogen battery, or the like can be used. The electric power conversion device  21  includes an inverter, a DC/DC converter, and the like, and is a device that is controlled by the control device  22  to perform electric power conversion. For example, the electric power conversion device  21  converts DC power supplied from the battery  17  into three-phase AC power and supplies the three-phase AC power to the motor generator  12 , or converts three-phase AC power supplied from the motor generator  12  into DC power and supplies the DC power to the battery  17 . 
     The motor generator  12  is supplied with electric power from the battery  17  via the electric power conversion device  21 , thereby rotationally driving the engine  11 . When the motor generator  12  rotationally drives the engine  11 , as will be described later, a rotation speed of the engine  11  can be maintained at a predetermined rotation speed (for example, a rotation speed N 1  described later) larger than 0 [rpm] even when fuel supply to the engine  11  is stopped due to execution of fuel cut-off control. The output of the motor generator  12  may be transmitted to the drive wheel DW via the transmission TM so as to be used for traveling of the vehicle  1 . 
     The motor generator  12  also functions as a generator that generates electric power by being rotationally driven. The motor generator  12  is rotationally driven by the engine  11  that is rotationally driven in accordance with fuel supply, and is also rotationally driven by power input from the drive wheel DW in accordance with braking or the like of the vehicle  1 . The electric power generated by the motor generator  12  is supplied to the battery  17  via the electric power conversion device  21 , and is used to charge the battery  17 . 
     The transmission TM is a multistage transmission having a plurality of gear stages (for example, seven stages), and is provided in a power transmission path from the engine  11  to the drive wheel DW. As an example, as shown in  FIG. 2 , the transmission TM includes a torque converter  13  and a gearbox  14 . 
     The torque converter  13  includes a pump impeller  131 , a turbine runner  132 , a stator  133 , and a lock-up clutch  134 . The pump impeller  131  is mechanically connected to the engine  11  and the motor generator  12 , and rotates integrally along with rotational driving of the engine  11  and the motor generator  12 . The turbine runner  132  includes a hydraulic oil inflow port disposed close to a hydraulic oil discharge port of the pump impeller  131 . The turbine runner  132  is mechanically connected to an input shaft  141  of the gearbox  14  and rotates integrally with the input shaft  141 . The stator  133  is interposed between the turbine runner  132  and the pump impeller  131 , and deflects a flow of hydraulic oil returning from the turbine runner  132  to the pump impeller  131 . The stator  133  is supported by a housing (not shown) or the like of the torque converter  13  via a one-way clutch  135 . The torque converter  13  can transmit power (rotational power) from the pump impeller  131  to the turbine runner  132  via the hydraulic oil by circulating the hydraulic oil in a circulation path formed between the pump impeller  131  and the turbine runner  132 . 
     The lock-up clutch  134  is a clutch capable of mechanically connecting and disconnecting the engine  11  to and from the input shaft  141  of the gearbox  14 . By bringing the lock-up clutch  134  into an engaged state, the output of the engine  11  can be directly transmitted to the input shaft  141  of the gearbox  14 . That is, when the lock-up clutch  134  is in the engaged state, the engine  11  (more precisely, an output shaft of the engine  11 ) and the input shaft  141  of the gearbox  14  rotate integrally. 
     The gearbox  14  includes the input shaft  141  to which the output of the engine  11  and the motor generator  12  is transmitted via the torque converter  13 , a plurality of transmission mechanisms capable of shifting power transmitted to the input shaft  141 , and an output member  144  including an output gear  144   a  that outputs the power shifted by any one of the plurality of transmission mechanisms toward the drive wheel DW. 
     The plurality of transmission mechanisms included in the gearbox  14  include a first transmission mechanism  142  and a second transmission mechanism  143 . The first transmission mechanism  142  includes a first transmission clutch  142   a , a first drive gear  142   b  that rotates integrally with the input shaft  141  when the first transmission clutch  142   a  is in an engaged state, and a first driven gear  142   c  that rotates integrally with the output member  144 . The second transmission mechanism  143  includes a second transmission clutch  143   a , a second drive gear  143   b  that rotates integrally with the input shaft  141  when the second transmission clutch  143   a  is in an engaged state, and a second driven gear  143   c  that rotates integrally with the output member  144 . The clutches provided in the transmission mechanisms included in the gearbox  14  (that is, the transmission TM), namely the first transmission clutch  142   a  and the second transmission clutch  143   a , are hereinafter also referred to as the transmission clutch. 
     Although only the first transmission mechanism  142  and the second transmission mechanism  143  are shown in  FIG. 2  as the transmission mechanisms included in the gearbox  14 , the gearbox  14  also includes, for example, a transmission mechanism (not shown) other than the first transmission mechanism  142  and the second transmission mechanism  143 . 
     Whether each clutch included in the transmission TM, namely the lock-up clutch  134 , the first transmission clutch  142   a , and the second transmission clutch  143   a  (hereinafter, also simply referred to as the clutch of the transmission TM), is in an engaged state or a released state is controlled by the control device  22 . The clutch of the transmission TM is operated by hydraulic pressure of hydraulic oil supplied from the hydraulic pressure supply device  15  to the transmission TM. For example, the clutch of the transmission TM can be brought into the engaged state when hydraulic pressure equal to or higher than a predetermined value (for example, hydraulic pressure P 1  to be described later) is supplied to the transmission TM by the hydraulic pressure supply device  15 , and thus the power transmission path from the engine  11  to the drive wheels DW can be connected. 
     Referring back to  FIG. 1 , the hydraulic pressure supply device  15  is controlled by the hydraulic pressure control device  16  to supply the hydraulic pressure to the transmission TM. Specifically, the hydraulic pressure supply device  15  includes the mechanical hydraulic pressure supply device  15 A, a pressure accumulator  15 B, and a check valve  31 . 
     The mechanical hydraulic pressure supply device  15 A is a so-called mechanical oil pump, and is configured to be capable of being driven in accordance with rotation of the engine  11  to supply the hydraulic pressure to the transmission TM. That is, the mechanical hydraulic pressure supply device  15 A can supply the hydraulic pressure to the transmission TM when the engine  11  rotates, and, on the other hand, cannot supply the hydraulic pressure to the transmission TM when the engine  11  does not rotate. Even when the engine  11  rotates, the mechanical hydraulic pressure supply device  15 A cannot supply the transmission TM with hydraulic pressure necessary for bringing the clutch of the transmission TM into the engaged state when the rotation speed of the engine  11  is low. In other words, when the rotation speed of the engine  11  is less than a predetermined rotation speed (for example, the rotation speed N 1  described later), the mechanical hydraulic pressure supply device  15 A cannot supply the transmission TM with hydraulic pressure necessary to connect the power transmission path from the engine  11  to the drive wheel DW. The hydraulic pressure supplied to the transmission TM by the mechanical hydraulic pressure supply device  15 A is hereinafter also referred to as the line pressure. 
     The pressure accumulator  15 B is an accumulator capable of accumulating pressure of hydraulic oil introduced into the pressure accumulator  15 B, and is configured to be capable of supplying the accumulated hydraulic pressure (hereinafter, also referred to as the accumulated pressure) to the transmission TM. For example, the pressure accumulator  15 B is connected to a branch oil passage branched from an oil passage connecting the mechanical hydraulic pressure supply device  15 A and the transmission TM (for example, the clutch of the transmission TM) via the check valve  31 . 
     When the line pressure supplied by the mechanical hydraulic pressure supply device  15 A is higher than the accumulated pressure, a part of hydraulic oil flowing through the oil passage connecting the mechanical hydraulic pressure supply device  15 A and the transmission TM is introduced into the pressure accumulator  15 B via the check valve  31 . Even when the line pressure supplied by the mechanical hydraulic pressure supply device  15 A is equal to or lower than the accumulated pressure, the check valve  31  prevents the hydraulic oil introduced into the pressure accumulator  15 B from returning to the oil passage connecting the mechanical hydraulic pressure supply device  15 A and the transmission TM, and thus the accumulated pressure is maintained. 
     The check valve  31  can also be forcibly opened by an actuator or the like controlled by the hydraulic pressure control device  16 . Therefore, for example, by opening the check valve  31  when the line pressure is not raised due to stop of the engine  11  or the like, the hydraulic oil introduced into the pressure accumulator  15 B can be discharged to the oil passage connecting the mechanical hydraulic pressure supply device  15 A and the transmission TM, and thus the accumulated pressure can be supplied to the transmission TM. It should be noted that the check valve  31  can be achieved by, for example, one or a plurality of one-way valves. 
     The hydraulic pressure control device  16  is configured to be capable of communicating with the control device  22  and the hydraulic pressure supply device  15 . The hydraulic pressure control device  16  controls supply of hydraulic pressure supplied to the transmission TM by the hydraulic pressure supply device  15  based on information from the control device  22 . The hydraulic pressure control device  16  is achieved by, for example, an electronic control unit (ECU) including a processor that performs various types of calculation, a storage device that stores various types of information, an input-output device that controls input and output of data between inside and outside of the hydraulic pressure control device  16 , and the like. 
     For example, the hydraulic pressure control device  16  opens the check valve  31  when an acceleration command is given to the vehicle  1 . As a result, the hydraulic pressure (accumulated pressure) accumulated in the pressure accumulator  15 B can be supplied to the transmission TM as described above. The acceleration command given to the vehicle  1  may include, for example, accelerator-ON of the vehicle  1  and brake-OFF of the vehicle  1 . Here, the accelerator-ON refers to a state where an amount of operation performed on an accelerator pedal of the vehicle  1  is equal to or higher than a predetermined amount (for example, a state where the accelerator pedal is depressed), and the brake-OFF refers to a state where an amount of operation performed on a brake pedal of the vehicle  1  is less than a predetermined amount (for example, a state where the brake pedal is not depressed). 
     More specifically, when an acceleration command is given to the vehicle  1 , if the hydraulic pressure (line pressure) supplied to the transmission TM by the mechanical hydraulic pressure supply device  15 A is less than a predetermined value necessary for bringing the clutch of the transmission TM into the engaged state, the hydraulic pressure control device  16  opens the check valve  31  and causes the pressure accumulator  15 B to supply the hydraulic pressure to the transmission TM. As a result, the hydraulic pressure supplied to the transmission TM can be secured, and the clutch of the transmission TM can be brought into the engaged state, that is, the power transmission path from the engine  11  to the drive wheel DW can be connected. 
     The control device  22  is a device that controls the engine  11 , the transmission TM, the electric power conversion device  21 , the hydraulic pressure control device  16 , and the like, and is achieved by, for example, an ECU including a processor that performs various types of calculation, a storage device that stores various types of information, an input-output device that controls input and output of data between inside and outside of the control device  22 , and the like. 
     Various sensors (not shown) are connected to the control device  22 . The control device  22  controls the engine  11 , the transmission TM, the electric power conversion device  21 , the hydraulic pressure control device  16 , and the like based on information input from the various sensors. Examples of the sensors connected to the control device  22  include a rotation speed sensor that detects the rotation speed of the engine  11 , a vehicle speed sensor that detects a speed of the vehicle  1  (hereinafter, also referred to as the vehicle speed), a brake pedal sensor that detects ON and OFF of the brake, an accelerator pedal sensor that detects ON and OFF of the accelerator, a gear position sensor that detects the gear stage of the transmission TM, a battery sensor that detects output of the battery  17 , and the like. Further, a hydraulic pressure sensor that detects the hydraulic pressure supplied to the transmission TM by the hydraulic pressure control device  16  may be connected to the control device  22 . The control device  22  may notify the hydraulic pressure control device  16  of the hydraulic pressure detected by the hydraulic pressure sensor. In addition, the control device  22  may instruct the hydraulic pressure control device  16  to open the pressure accumulator  15 B, for example, based on the hydraulic pressure detected by the hydraulic pressure sensor. 
     For example, when a deceleration command is given to the vehicle  1  while the vehicle  1  is traveling, the control device  22  executes fuel cut-off control to stop the fuel supply to the engine  11 . The deceleration command given to the vehicle  1  may include, for example, accelerator-OFF of the vehicle  1  and brake-ON of the vehicle  1 . Here, the accelerator-OFF refers to a state where the amount of operation performed on the accelerator pedal of the vehicle  1  is less than a predetermined amount (for example, a state where the accelerator pedal is not depressed), and the brake-ON refers to a state where the amount of operation performed on the brake pedal of the vehicle  1  is equal to or higher than a predetermined amount (for example, a state where the brake pedal is depressed). 
     The control device  22  may execute the fuel cut-off control when the deceleration command is given to the vehicle  1  and a predetermined execution condition of the fuel cut-off control is satisfied. When the vehicle  1  decelerates and the vehicle speed becomes equal to or lower than a predetermined speed (for example, 10 [km/h]), the control device  22  may stop the engine  11  at that time. 
     When the rotation speed of the engine  11  decreases to a predetermined rotation speed along with the execution of the fuel cut-off control, the control device  22  executes rotation speed maintaining control to maintain the rotation speed of the engine  11  at a predetermined rotation speed (for example, the rotation speed N 1  described later) larger than 0 [rpm]. During the rotation speed maintaining control, the control device  22  maintains the rotation speed of the engine  11  at the predetermined rotation speed, for example, by rotationally driving the engine  11  by the motor generator  12 . During the rotation speed maintaining control, the control device  22  may also maintain the rotation speed of the engine  11  at the predetermined rotation speed by supplying fuel to the engine  11 . The control device  22  maintains the rotation speed of the engine  11  at the predetermined rotation speed by performing the rotation speed maintaining control until a predetermined condition is satisfied, such as when the vehicle speed is equal to or less than a threshold value (for example, 5 [km/h]). 
     When the acceleration command is given to the vehicle  1 , the control device  22  notifies the hydraulic pressure control device  16  of the acceleration command. The hydraulic pressure control device  16  that has received the notification of the acceleration command from the control device  22  can cause the pressure accumulator  15 B to supply the hydraulic pressure to the transmission TM by opening the check valve  31  as described above. 
     (Operation Example of Vehicle) 
     Next, operation examples of the vehicle  1  will be described with reference to  FIGS. 3 to 6 . 
     First Example 
     First, a first example of an operation of the vehicle  1  will be described with reference to  FIG. 3 . As shown in  FIG. 3 , it is assumed that any one of the transmission clutches and the lock-up clutch  134  of the transmission TM is in the engaged state, and the accelerator is turned off at a time T 0  when the vehicle  1  is traveling (that is, vehicle speed&gt;0). Then, it is assumed that a predetermined execution condition of the fuel cut-off control is satisfied at a time T 1  after the time T 0 . In this case, the control device  22  starts the fuel cut-off control from the time T 1 . 
     When the lock-up clutch  134  is in the engaged state, the engine  11  is mechanically connected to the drive wheel DW via the transmission TM. Therefore, when the lock-up clutch  134  is in the engaged state and the vehicle  1  is traveling at a certain vehicle speed, even if the fuel cut-off control is executed, the engine  11  can be rotationally driven by power from the side of the drive wheel DW. It is also possible to supply predetermined hydraulic pressure P 1  to the transmission TM by the line pressure of the mechanical hydraulic pressure supply device  15 A along with the rotational driving of the engine  11 . Here, the hydraulic pressure P 1  is hydraulic pressure necessary for bringing the clutch of the transmission TM (for example, the transmission clutches) into the engaged state. 
     On the other hand, when the vehicle speed decreases while the lock-up clutch  134  is in the engaged state (that is, when the power transmitted from the side of the drive wheel DW to the engine  11  decreases), a stall of the engine (hereinafter, also referred to as the engine stall) may occur. Therefore, from the viewpoint of engine stall prevention, when the control device  22  detects that the vehicle speed reaches a predetermined speed V 1  (speed V 1 &gt;0) based on the information from the vehicle speed sensor during the fuel cut-off control, the control device  22  brings the lock-up clutch  134  into the released state. In the example shown in  FIG. 3 , at a time T 2  after the time T 1 , since the control device  22  detects that the vehicle speed has reached the speed V 1 , the control device  22  brings the lock-up clutch  134  into the released state (shown as “LCOFF”). 
     When the lock-up clutch  134  is in the released state, the power from the side of the drive wheel DW is not transmitted to the engine  11 , and thus the rotation speed of the engine  11  decreases. If nothing is performed in this state, the rotation of the engine  11  is stopped. Therefore, when the control device  22  detects that the rotation speed of the engine  11  has decreased to the rotation speed N 1  based on the information from the rotation speed sensor after the lock-up clutch  134  is brought into the released state, the control device  22  executes the rotation speed maintaining control to maintain the rotation speed of the engine  11  at the rotation speed N 1 . 
     During the rotation speed maintaining control, the control device  22  supplies, for example, electric power of the battery  17  to the motor generator  12  to rotationally drive the engine  11  by the motor generator  12 . At this time, the control device  22  controls driving of the motor generator  12  via the electric power conversion device  21  in such a manner that the rotation speed of the engine  11  is maintained at the rotation speed N 1 . 
     In the example shown in  FIG. 3 , at a time T 3  after the time T 2 , the control device  22  detects that the rotation speed of the engine  11  has reached the rotation speed N 1 , and thus starts to rotationally drive the engine  11  by the motor generator  12  and maintains the rotation speed of the engine  11  at the rotation speed N 1 . Here, the rotation speed N 1  is the rotation speed of the engine  11  at which the hydraulic pressure P 1  described above can be secured as the line pressure of the mechanical hydraulic pressure supply device  15 A. 
     In this way, the control device  22  can maintain the rotation speed of the engine  11  at the rotation speed N 1  by the rotation speed maintaining control, and thus supply the hydraulic pressure P 1  to the transmission TM by the line pressure of the mechanical hydraulic pressure supply device  15 A. 
     Thereafter, the control device  22  executes the rotation speed maintaining control until the vehicle speed reaches a predetermined speed V 2  (speed V 2 &lt;speed V 1 ). Here, the speed V 2  is a speed immediately before the vehicle  1  stops (that is, a speed at which the vehicle  1  is expected to stop soon), and may be, for example, 5 [km/h]. As a result, the rotation speed of the engine  11  is maintained at the rotation speed N 1  until the vehicle speed reaches the speed V 2  (that is, until immediately before the vehicle  1  stops). 
     Then, when the vehicle speed reaches the speed V 2 , the control device  22  ends the rotation speed maintaining control. In the example shown in  FIG. 3 , since the vehicle speed reaches the speed V 2  at a time T 4  after the time T 3 , the control device  22  ends the rotation speed maintaining control (here, the rotational driving of the engine  11  driven by the motor generator  12 ) at that time. 
     When the rotation speed maintaining control is ended in this way, the rotation speed of the engine  11  decreases toward 0 [rpm] since the fuel cut-off control is being executed. In the example shown in  FIG. 3 , at a time T 5  after the time T 4 , the rotation speed of the engine  11  becomes 0 [rpm]. 
     In addition, when the rotation speed maintaining control is ended and the rotation speed of the engine  11  becomes lower than the rotation speed N 1 , the line pressure supplied by the mechanical hydraulic pressure supply device  15 A also decreases. As a result, the hydraulic pressure that can be supplied to the clutch of the transmission TM also decreases toward 0 [Pa] from the time T 4 . 
     In the example shown in  FIG. 3 , if the rotation speed maintaining control is not performed, the rotation speed of the engine  11  falls below the rotation speed N 1  after the time T 3  and directly decreases toward 0 [rpm], as shown by a thick broken line in  FIG. 3 . Therefore, after the time T 3 , the supply of the hydraulic pressure P 1  to the transmission TM cannot be maintained by the line pressure of the mechanical hydraulic pressure supply device  15 A. As a result, the transmission clutches of the transmission TM are in the released state, and the power transmission path from the engine  11  to the drive wheel DW is disconnected. In such a state, when the acceleration command is given to the vehicle  1 , it takes time to connect the clutch of the transmission TM again, and as a result, response performance of the vehicle  1  to the acceleration command may decrease. 
     Although an example in which the fuel cut-off control is executed based on accelerator-OFF as the deceleration command given to the vehicle  1  has been described in the operation example described here, the present invention is not limited thereto. For example, the fuel cut-off control may be executed based on brake-ON instead of the accelerator-OFF or brake-ON after the accelerator-OFF. 
     Second Example 
     Next, a second example of the operation of the vehicle  1  will be described with reference to  FIG. 4 . The second example is an example of a case where the acceleration command is given to the vehicle  1  when the rotation speed of the engine  11  is maintained at the rotation speed N 1  by the rotation speed maintaining control. In the following description of  FIG. 4 , the same components as those in  FIG. 3  are denoted by the same reference numerals, and description thereof will be omitted as appropriate. 
     As shown in  FIG. 4 , it is assumed that the accelerator is ON at a time T 6  when the rotation speed of the engine  11  is maintained at the rotation speed N 1  by the rotation speed maintaining control, that is, at the time T 6  when the vehicle speed is a speed V 3  (speed V 3 &gt;speed V 2 ) before reaching the speed V 2  (see  FIG. 3 ). 
     When the control device  22  detects that the accelerator is ON based on the information from the accelerator pedal sensor, the control device  22  ends the fuel cut-off control and restarts the fuel supply to the engine  11 . In addition, the control device  22  ends the rotation speed maintaining control along with the end of the fuel cut-off control. 
     At the time T 6 , the rotation speed of the engine  11  is the rotation speed N 1 , and the mechanical hydraulic pressure supply device  15 A is in a state where the supply of the hydraulic pressure P 1 , which is necessary for bringing the clutch of the transmission TM into the engaged state, to the transmission TM can be maintained. Therefore, as the accelerator is ON, the rotation speed of the engine  11  increases without delay, and power of the engine  11  is transmitted to the drive wheel DW to increase the vehicle speed. 
     As described above, in the vehicle  1 , the rotation speed of the engine  11  is maintained at the rotation speed N 1  by the motor generator  12  due to rotation speed instruction control until the vehicle speed reaches the speed V 2 , and the mechanical hydraulic pressure supply device  15 A is in the state where the necessary hydraulic pressure can be appropriately supplied to the transmission TM. Therefore, when the acceleration command is given to the vehicle  1  until immediately before the vehicle  1  stops, smooth acceleration can be achieved with little delay in response to the acceleration command. 
     Third Example 
     Next, a third example of the operation of the vehicle  1  will be described with reference to  FIG. 5 . The third example is an example of a case where the acceleration command is given to the vehicle  1  after the vehicle  1  stops. In the following description of  FIG. 5 , the same components as those in  FIG. 3  are denoted by the same reference numerals, and description thereof will be omitted as appropriate. 
     As shown in  FIG. 5 , at the time T 4 , the vehicle speed of the vehicle  1 , which is decelerating in a state where the brake is ON and the accelerator is OFF, decreases to the speed V 2 , and thus the rotation speed maintaining control (for example, the rotational driving of the engine  11  driven by the motor generator  12 ) is ended. As a result, the rotation speed of the engine  11  decreases toward 0 [rpm] from the time T 4 , and becomes 0 [rpm] at the time T 5 . 
     When the rotation speed of the engine  11  falls below the rotation speed N 1 , the hydraulic pressure supplied to the transmission TM by the mechanical hydraulic pressure supply device  15 A also decreases. As a result, the hydraulic pressure supplied to the transmission TM also decreases toward 0 [Pa] from the time T 4 . The vehicle  1  is stopped substantially at the same time as the time T 5  (that is, the vehicle speed is 0 [km/h]). 
     It is assumed that the brake is OFF at a time T 7  after the vehicle  1  stops. When brake-OFF is detected based on the information from the brake pedal sensor, the control device  22  ends (turns off) the fuel cut-off control and restarts the fuel supply to the engine  11 . As a result, the engine  11  starts to be driven to rotate. 
     However, since the rotation of the engine  11  is stopped from the time T 5  to the time T 7 , the mechanical hydraulic pressure supply device  15 A is not driven at the time T 7 , and the hydraulic pressure cannot be supplied to the transmission TM by the mechanical hydraulic pressure supply device  15 A. Therefore, the control device  22  notifies the hydraulic pressure control device  16  of the acceleration command given to the vehicle  1 , thereby controlling the hydraulic pressure control device  16  to supply the hydraulic pressure accumulated in the pressure accumulator  15 B to the transmission TM. As a result, as indicated by reference numeral A in  FIG. 5 , the hydraulic pressure supplied to the transmission TM can be rapidly increased by using the hydraulic pressure accumulated in the pressure accumulator  15 B before the rotation speed of the engine  11  increases and before the mechanical hydraulic pressure supply device  15 A enters the state where the necessary hydraulic pressure can be supplied to the transmission TM. 
     The hydraulic pressure supplied to the transmission TM is increased by the pressure accumulator  15 B in a short period of, for example, about 0.5 [sec]. During this time, the rotation speed of the engine  11  increases, and the mechanical hydraulic pressure supply device  15 A enters the state where the necessary hydraulic pressure can be appropriately supplied to the transmission TM. Therefore, the hydraulic pressure supplied to the transmission TM can be quickly increased to the hydraulic pressure P 1 , and for example, when the accelerator is ON at a time T 8  immediately after the time T 7 , the power of the engine  11  is transmitted to the drive wheel DW without delay, and smooth acceleration (start) can be achieved with little delay in response to the acceleration command. 
     As described above, when the vehicle  1  and the engine  11  are stopped and the hydraulic pressure cannot be appropriately supplied from the mechanical hydraulic pressure supply device  15 A to the transmission TM, the hydraulic pressure supplied to the transmission TM can be rapidly increased by supplying the hydraulic pressure to the transmission TM by the pressure accumulator  15 B, so that excellent acceleration (start) can be achieved with little delay in response to the acceleration command given to the vehicle  1 . 
     Although an example in which the hydraulic pressure is supplied from the pressure accumulator  15 B to the transmission TM based on brake-OFF as the acceleration command given to the vehicle  1  has been described in the operation example described here, the present invention is not limited thereto. For example, the hydraulic pressure may be supplied from the pressure accumulator  15 B to the transmission TM based on accelerator-ON instead of brake-OFF. 
     Fourth Example 
     Next, a fourth example of the operation of the vehicle  1  will be described with reference to  FIG. 6 . In the following description of  FIG. 6 , the same components as those in  FIG. 3  are denoted by the same reference numerals, and description thereof will be omitted as appropriate. In addition, in  FIG. 6 , a solid line denoted by reference numeral NE indicates the rotation speed of the engine  11  (also refer to an arrow denoted by NE in  FIG. 2 ), and a broken line denoted by reference numeral NM indicates rotation speed of the input shaft  141  of the gearbox  14  (also refer to an arrow denoted by NM in  FIG. 2 ). 
     As shown in  FIG. 6 , it is assumed that any one of the transmission clutches and the lock-up clutch  134  of the transmission TM is in the engaged state, and the accelerator is turned off at a time T 10  when the vehicle  1  is traveling (that is, vehicle speed&gt;0). Then, it is assumed that a predetermined execution condition of the fuel cut-off control is satisfied at a time T 11  after the time T 10 . In this case, the control device  22  starts the fuel cut-off control from the time T 11 . At this time, it is assumed that the gear stage of the gearbox  14  is, for example, a fourth speed. 
     It is assumed that the brake is ON at a time T 12  after the time T 11 . By turning on the brake in addition to turning off the accelerator, the vehicle speed is further decreased from the time T 12 . In addition, at this time, since the lock-up clutch  134  is in the engaged state, the rotation speed of the engine  11  and the rotation speed of the input shaft  141  of the gearbox  14  further decrease as the vehicle speed is decreased. 
     When the vehicle speed decreases while the lock-up clutch  134  is in the engaged state, the rotation speed of the engine  11  may also decrease accordingly. However, the control device  22  can lower the gear stage of the gearbox  14  and thus increase the rotation speed of the engine  11  and the rotation speed of the input shaft  141  of the gearbox  14  to a rotation speed corresponding to the vehicle speed and the gear stage (transmission ratio) by the power from the side of the drive wheel DW. In the example shown in  FIG. 6 , the control device  22  changes the gear stage of the gearbox  14  from the fourth speed to a third speed at a time T 13 . Accordingly, the rotation speed of the engine  11  and the rotation speed of the input shaft  141  of the gearbox  14  temporarily increase from the time T 13 . 
     At a time T 14  when the vehicle speed further decreases, the control device  22  changes the gear stage of the gearbox  14  from the third speed to a first speed this time. Accordingly, the rotation speed of the engine  11  and the rotation speed of the input shaft  141  of the gearbox  14  increase again from the time T 14 . Then, when the vehicle speed further decreases after the gear stage is set to the first speed (that is, after the gear stage is lowered) in this way, the control device  22  brings the lock-up clutch  134  into the released state. As a result, occurrence of the engine stall can be prevented. 
     In the example shown in  FIG. 6 , the control device  22  brings the lock-up clutch  134  into the released state at a time T 15 . However, at this time, since the rotation speed of the engine  11  is equal to or higher than the rotation speed N 1 , the above-described hydraulic pressure P 1  is obtained as the hydraulic pressure that can be supplied to the transmission TM by the line pressure. Therefore, at this time, the hydraulic pressure P 1  can be supplied to the transmission TM by the line pressure as necessary. 
     When the lock-up clutch  134  is in the released state, the power from the side of the drive wheel DW is transmitted to the gearbox  14 , but is not transmitted to the engine  11 . Therefore, as shown in  FIG. 6 , the rotation speed of the input shaft  141  of the gearbox  14  temporarily increases even after the time T 15  along with the change to the first speed, while the rotation speed of the engine  11  decreases from the time T 15 . That is, the rotation speed of the input shaft  141  of the gearbox  14  and the rotation speed of the engine  11  deviate from each other. If nothing is performed in this state, the rotation of the engine  11  is stopped. 
     Therefore, when the control device  22  detects that the rotation speed of the engine  11  has decreased to the rotation speed N 1  based on the information from the rotation speed sensor after the lock-up clutch  134  is brought into the released state, the control device  22  executes the rotation speed maintaining control. In the example shown in  FIG. 6 , since the rotation speed of the engine  11  reaches the rotation speed N 1  at a time T 16  after the time T 15 , the control device  22  executes the rotation speed maintaining control from the time T 16 , and maintains the rotation speed of the engine  11  at the rotation speed N 1  by rotational driving provided by the motor generator  12 . As described above, the rotation speed maintaining control (that is, the rotational driving of the engine  11  driven by the motor generator  12 ) is ended when the vehicle speed reaches the speed V 2  (not shown in  FIG. 6 ), for example. Then, at a subsequent time T 17 , the vehicle  1  stops (that is, the vehicle speed=0). 
     In this way, the control device  22  continuously executes the fuel cut-off control from when the vehicle  1  reaches the predetermined speed V 1  (speed V 1 &gt;0) to when the vehicle  1  stops. Therefore, a period during which the fuel cut-off control is performed can be maximized, and thus fuel efficiency of the vehicle  1  can be improved. 
     On the other hand, as indicated by reference numeral B in  FIG. 6 , the control device  22  may temporarily stop the fuel cut-off control after the lock-up clutch  134  is brought into the released state, and supply fuel to the engine  11  to maintain the rotation speed of the engine  11 . In this case, while the fuel is supplied to the engine  11 , a decrease in the rotation speed of the engine  11  can be prevented even if the engine  11  is not rotationally driven by the motor generator  12 . As a result, a period in which the motor generator  12  rotationally drives the engine  11  can be shortened, and thus it is possible to reduce electric power consumed by the motor generator  12 . 
     As described above, according to the vehicle  1  of the present embodiment, when the acceleration command is given to the vehicle  1 , if the hydraulic pressure supplied to the transmission TM by the mechanical hydraulic pressure supply device  15 A is less than the hydraulic pressure necessary for connecting the power transmission path, the hydraulic pressure can be rapidly supplied to the transmission TM by the pressure accumulator  15 B. Therefore, even when the rotation speed maintaining control (maintenance of the rotation speed N 1  of the engine  11 ) executed along with the start of the fuel cut-off control is ended when the vehicle speed is equal to or lower than the speed V 2 , excellent response performance to the acceleration command can be maintained by the hydraulic pressure supplied by the pressure accumulator  15 B. Therefore, with a simple configuration using the pressure accumulator  15 B, electric power consumed in the vehicle  1  can be reduced while maintaining excellent response performance to the acceleration command. 
     Since the rotation speed of the engine  11  is maintained at the rotation speed N 1  by the motor generator  12  until the vehicle speed reaches the speed V 2 , that is, until immediately before the vehicle  1  stops, excellent responsiveness to the acceleration command can be maintained for a long time. 
     (Modification) 
     In the example described above, as shown in  FIG. 2 , when the rotation speed of the engine  11  decreases due to the execution of the fuel cut-off control, the control device  22  executes the rotation speed maintaining control (for example, rotationally drives the engine  11  by the motor generator  12 ) so as to maintain the rotation speed of the engine  11  at the rotation speed N 1  from when the decreased rotation speed reaches the rotation speed N 1  (for example, the time T 3 ) to when the vehicle speed becomes equal to or lower than the speed V 2  (for example, the time T 4 ). However, the present invention is not limited thereto. 
     For example, the control device  22  may maintain the rotation speed of the engine  11  at the rotation speed N 1  by executing the rotation speed maintaining control from when the decreased rotation speed of the engine  11  reaches the rotation speed N 1  (for example, the time T 3 ) to when the acceleration command is given to the vehicle  1 . The acceleration command includes, for example, operations such as accelerator-ON and brake-OFF. In this way, since the rotation speed of the engine  11  can be maintained at the rotation speed N 1  until the acceleration command is given to the vehicle  1 , the necessary hydraulic pressure (for example, the hydraulic pressure P 1 ) can be supplied from the mechanical hydraulic pressure supply device  15 A to the transmission TM regardless of the decrease in the vehicle speed (for example, even after the vehicle  1  stops), and thus excellent response performance can be maintained. 
     In addition, for example, the control device  22  may maintain the rotation speed of the engine  11  at the rotation speed N 1  by executing the rotation speed maintaining control from when the decreased rotation speed of the engine  11  reaches the rotation speed N 1  (for example, the time T 3 ) to when a predetermined period (for example, 5 [sec]) elapses. In this way, it is possible to prevent an increase in electric power consumption due to a long-term continuous operation of the motor generator  12  as an electric motor. 
     In addition, for example, the control device  22  may maintain the rotation speed of the engine  11  at the rotation speed N 1  by executing the rotation speed maintaining control from when the decreased rotation speed of the engine  11  reaches the rotation speed N 1  (for example, the time T 3 ) to when a remaining capacity of the battery  17  is equal to or less than a threshold value. When the rotation speed of the engine  11  is maintained by the motor generator  12 , the electric power of the battery  17  is used. In this case, the control device  22  recognizes the remaining capacity of the battery  17  based on information input from the battery sensor, and maintains the rotation speed of the engine  11  using the electric power of the battery  17  when the remaining capacity of the battery  17  is larger than the threshold value. In this way, since the electric power of the battery  17  is not used when the remaining capacity of the battery  17  is equal to or less than the threshold value, the battery  17  can be prevented from being overdischarged. 
     If the accumulated pressure of the pressure accumulator  15 B is supplied to the transmission TM, the clutch of the transmission TM can be brought into the engaged state. Therefore, even when the vehicle  1  is traveling (that is, when the vehicle speed&gt;0) without executing the rotation speed maintaining control described above, it is conceivable that the accumulated pressure of the pressure accumulator  15 B is appropriately supplied to the transmission TM, and thus the clutch of the transmission TM is brought into the engaged state. However, in this case, when the clutch of the transmission TM is brought into the engaged state, there is a possibility that an excessive shock occurs, which may lead to a decrease in marketability of the vehicle  1 . 
     Specifically, in a clutch that connects and disconnects between one side and the other side, a shock (torque fluctuation) does not occur even when the clutch is rapidly engaged (hereinafter, also referred to as the sudden engagement) as long as a rotation speed of the one side and a rotation speed of the other side are the same. On the other hand, the shock occurs if the sudden engagement occurs when there is a difference between the rotation speed of the one side and the rotation speed of the other side. 
     If the vehicle  1  is stopped and the engine  11  is also stopped, the rotation speed of the engine  11 , the rotation speed of the input shaft  141 , and a rotation speed of the output member  144  are all zero. Therefore, when the vehicle  1  is stopped and the engine  11  is also stopped, even if the accumulated pressure of the pressure accumulator  15 B is supplied to the transmission TM and the clutch of the transmission TM is suddenly engaged as indicated by reference numeral A in  FIG. 5 , an excessive shock that may lead to a decrease in the marketability of the vehicle  1  does not occur. 
     On the other hand, when the vehicle  1  is traveling (that is, the vehicle speed&gt;0) and the engine  11  is stopped, if the clutch of the transmission TM is in the released state, in most cases, a difference occurs between the rotation speed of the engine  11 , the rotation speed of the input shaft  141 , and the rotation speed of the output member  144 . Therefore, in such cases, if the accumulated pressure of the pressure accumulator  15 B is supplied to the transmission TM to suddenly engage the clutch of the transmission TM, an excessive shock may occur, which may lead to a decrease in the marketability of the vehicle  1 . Therefore, according to the control device  22 , as described above, only w % ben the vehicle  1  and the engine  11  are stopped, the accumulated pressure of the pressure accumulator  15 B is supplied to the transmission TM to engage the clutch of the transmission TM. Therefore, occurrence of the excessive shock that may lead to the decrease in the marketability of the vehicle  1  is avoided. 
     Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and modifications, improvements, and the like can be made as appropriate. 
     At least the following matters are described in the present specification. Although corresponding constituent elements and the like in the above-described embodiment are shown in parentheses, the present invention is not limited thereto. 
     (1) A vehicle (vehicle  1 ) includes: 
     an internal combustion engine (engine  11 ); 
     a rotary electric machine (motor generator  12 ) configured to rotationally drive the internal combustion engine: 
     a connection-disconnection device (lock-up clutch  134 , first transmission clutch  142   a , second transmission clutch  143   a ) provided to connect and disconnect a power transmission path between the internal combustion engine and a drive wheel (drive wheel DW), the connection-disconnection device being configured to connect the power transmission path in response to supply of hydraulic pressure equal to or higher than a predetermined value; 
     a hydraulic pressure supply device (hydraulic pressure supply device  15 ) configured to supply hydraulic pressure to the connection-disconnection device; 
     a hydraulic pressure control device (hydraulic pressure control device  16 ) configured to control the supply of the hydraulic pressure supplied by the hydraulic pressure supply device to the connection-disconnection device; and 
     a control device (control device  22 ) configured to control the internal combustion engine and the rotary electric machine, 
     in which the hydraulic pressure supply device includes: 
     a mechanical hydraulic pressure supply device (mechanical hydraulic pressure supply device  15 A) that is driven in accordance with rotation of the internal combustion engine to supply the hydraulic pressure to the connection-disconnection device; and 
     a pressure accumulator (pressure accumulator  15 B) configured to supply the hydraulic pressure to the connection-disconnection device by pressure accumulated in advance, 
     the control device 
     executes fuel cut-off control to stop fuel supply to the internal combustion engine based on a deceleration command given to the vehicle, and 
     executes rotation speed maintaining control to maintain a rotation speed of the internal combustion engine at a predetermined rotation speed larger than 0 by rotationally driving the internal combustion engine by the rotary electric machine or supplying fuel to the internal combustion engine when the rotation speed of the internal combustion engine decreases to a predetermined rotation speed along with the execution of the fuel cut-off control, and 
     the hydraulic pressure control device 
     supplies the hydraulic pressure to the connection-disconnection device by the pressure accumulator if the hydraulic pressure supplied to the connection-disconnection device by the mechanical hydraulic pressure supply device is less than the predetermined value when an acceleration command is given to the vehicle. 
     According to (1), the hydraulic pressure can be quickly supplied to the connection-disconnection device by the pressure accumulator if the hydraulic pressure supplied to the connection-disconnection device by the mechanical hydraulic pressure supply device is less than the predetermined value when the acceleration command is given to the vehicle, and thus it is possible to prevent a decrease in response performance to the acceleration command by a simple configuration using the pressure accumulator. 
     (2) The vehicle according to (1), in which the control device executes the rotation speed maintaining control from when the rotation speed of the internal combustion engine decreases to the predetermined rotation speed to when a speed of the vehicle becomes equal to or less than a threshold value. 
     According to (2), since the rotation speed of the internal combustion engine is maintained at the predetermined rotation speed until the speed of the vehicle becomes equal to or less than the threshold value, excellent responsiveness to the acceleration command can be maintained for a long time. 
     (3) The vehicle according to (1), 
     in which the control device executes the rotation speed maintaining control from when the rotation speed of the internal combustion engine decreases to the predetermined rotation speed to when the acceleration command is given to the vehicle. 
     According to (3), by maintaining the rotation speed of the engine at the predetermined rotation speed until the acceleration command is given to the vehicle, excellent responsiveness to the acceleration command can be maintained regardless of any decrease in the vehicle speed, for example, even when the vehicle is in a stopped state. 
     (4) The vehicle according to (1), 
     in which the control device executes the rotation speed maintaining control from when the rotation speed of the internal combustion engine decreases to the predetermined rotation speed to when a predetermined period elapses. 
     According to (4), since the rotation speed maintaining control can be ended when the predetermined period has elapsed since the rotation speed of the internal combustion engine decreases to the predetermined rotation speed, an increase in electric power consumption of the rotary electric machine and deterioration in fuel efficiency caused by long-term execution of the rotation speed maintaining control can be prevented. 
     (5) The vehicle according to (1), 
     in which the rotary electric machine rotationally drives the internal combustion engine by electric power supplied from a battery (battery  17 ) of the vehicle, and 
     the control device executes the rotation speed maintaining control from when the rotation speed of the internal combustion engine decreases to the predetermined rotation speed to when the battery is in a predetermined state. 
     According to (5), for example, when a remaining capacity of the battery is equal to or less than a threshold value, the eclectic power of the battery is not used as electric power for rotationally driving the internal combustion engine, so that the battery can be prevented from being overdischarged. 
     (6) The vehicle according to any one of (1) to (5), 
     in which the control device continuously executes the fuel cut-off control from when the vehicle reaches a predetermined speed to when the vehicle stops. 
     According to (6), a period during which the fuel cut-off control is performed can be maximized, and thus the fuel efficiency of the vehicle can be improved.