Vehicle control system

Abstract

The present invention provides a vehicle control device that can suppress the decrease in acceleration responsiveness during re-acceleration. [Solution] A control device for a vehicle equipped with an engine having a supercharger and capable of controlling its rotational speed independently of the rotational speed of the drive wheels, further comprising a controller that controls the engine based on the amount of operation of the accelerator device, wherein the controller is configured to allow motoring control (step S14) to control the rotational speed of the engine in order to maintain the supercharger pressure when the amount of operation of the accelerator device θact becomes smaller than a determination threshold θth (step S12), and the determination threshold is set to a larger value as the vehicle speed increases.

Description

Technical Field

[0004] , ,

[0001] This invention relates to a control device for a vehicle equipped with an engine having a supercharger for pressurizing air.

Background Art

[0002] Patent Document 1 describes a control device for a hybrid vehicle in which an engine, a first motor, and an output shaft are connected so as to be differentially rotatable, and a second motor is connected to the output shaft so as to be torque-transmittable. The hybrid vehicle configured in this way has an HV running mode in which the torque of the engine is transmitted to the drive wheels via the output shaft and runs, and an EV running mode in which the engine is stopped and only the torque of the second motor is transmitted to the drive wheels and runs. Therefore, the running mode can be switched from the EV running mode to the HV running mode, for example, when an acceleration request is made.

[0003] On the other hand, when a supercharger driven by the exhaust of the engine is provided, when switching from the EV running mode to the HV running mode, the acceleration responsiveness may decrease due to supercharging delay by the supercharger. Therefore, the control device described in Patent Document 1 is configured to output the shortage of drive torque accompanying the supercharging delay from the second motor.

[0004] On the other hand, there may be a case where the torque that can be output from the second motor is less than the torque that can compensate for the shortage of drive torque accompanying the supercharging delay. Therefore, the control device described in Patent Document 1 determines before switching from the EV running mode to the HV running mode that the torque that can be output from the second motor is less than the torque that can compensate for the shortage of drive torque accompanying the supercharging delay. In that case, the engine is started before switching to the HV running mode so as to increase the supercharging pressure. Note that the control device described in Patent Document 1 determines the target rotational speed of the engine before switching to the HV running mode based on the intake pipe pressure, the degree of acceleration request, or the dischargeable power of the power storage device.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-041869 [Overview of the initiative] [Problems that the invention aims to solve]

[0006] In the hybrid vehicle described in Patent Document 1, the engine, first motor, and output shaft are connected in a differential rotation manner, so that the engine speed can be set appropriately without depending on the rotational speed of the output shaft (i.e., the vehicle speed). In a vehicle in which the engine speed can be set without depending on the vehicle speed in this way, the target engine speed is usually set based on the required driving force and the vehicle speed. For example, if there is a request to decelerate while driving by transmitting engine torque to the drive wheels, the engine speed is reduced to the equivalent of the idle speed, or the engine is stopped. Consequently, the boost pressure, which depends on the engine speed, also decreases as the engine speed decreases. Therefore, if the boost pressure decreases due to temporary deceleration, for example, to avoid a collision with an obstacle or a preceding vehicle, the acceleration response when accelerating again afterward may deteriorate.

[0007] This invention was made in view of the above-mentioned technical problems, and the object of this invention is to provide a vehicle control device that can suppress the decrease in acceleration responsiveness during re-acceleration. [Means for solving the problem]

[0008] To achieve the above objective, this invention provides a vehicle control device comprising an engine having a supercharger for pressurizing supplied air and capable of controlling the rotational speed independently of the rotational speed of the drive wheels, wherein the supercharger is configured to pressurize the air according to the rotational speed of the engine and further comprises an accelerator device operated by the driver and a controller that controls the engine based on the amount of operation of the accelerator device, wherein the controller is configured to perform rotational speed control to control the rotational speed of the engine in order to maintain the supercharge pressure from the supercharger when the amount of operation of the accelerator device falls below a predetermined determination threshold, and the determination threshold is set to a larger value as the vehicle speed increases.

[0009] Furthermore, in this invention, the controller may set the target engine speed in the rotational speed control to a higher speed as the vehicle speed increases.

[0010] Furthermore, this invention further includes a throttle valve for controlling the amount of air supplied to the engine, and the controller may set the opening degree of the throttle valve in the rotational speed control to a higher degree as the vehicle speed increases.

[0011] Furthermore, in this invention, the controller may perform the rotational speed control when the boost pressure becomes less than a predetermined boost pressure.

[0012] Furthermore, the predetermined boost pressure may be set to a higher value as the vehicle speed increases.

[0013] Furthermore, in this invention, the controller may terminate when the rotation speed control continues for a predetermined period of time.

[0014] Furthermore, in this invention, the controller may set the predetermined time to be longer as the vehicle speed increases.

[0015] Furthermore, in this invention, the controller may set the predetermined time to be longer as the amount of operation of the accelerator device increases.

[0016] Furthermore, this invention further includes a braking device operated by the driver, and the controller may set the predetermined time to be shorter as the operating force of the brake increases. [Effects of the Invention]

[0017] In this invention, the engine's rotational speed can be controlled independently of the rotational speed of the drive wheels, and the supercharger installed in the engine pressurizes the air supplied to the engine in accordance with the engine's rotational speed. Therefore, by appropriately controlling the engine's rotational speed, the pressure of the air supplied to the engine (supercharger pressure) can be appropriately controlled. In other words, by increasing the supercharger pressure in advance, it is possible to suppress deterioration of the responsiveness when increasing the engine's torque, or in other words, the acceleration responsiveness during acceleration.

[0018] Furthermore, the controller that controls the engine performs rotational speed control, which controls the engine speed and throttle valve opening to maintain boost pressure when the accelerator pedal input falls below a threshold value, and sets a higher threshold value the faster the vehicle speed. Therefore, rotational speed control can be performed when temporarily decelerating at relatively high speeds, such as when slowing down to avoid a collision with an obstacle or a preceding vehicle and then accelerating afterward. In other words, rotational speed control can be performed when re-acceleration is expected or when the engine noise is loud. As a result, even if a loud engine noise is generated by performing rotational speed control, it is possible to suppress discomfort for the driver. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a skeleton diagram illustrating an example of a vehicle in an embodiment of this invention. [Figure 2] Figure 2 is a schematic diagram showing an example of an engine. [Figure 3] Figure 3 is a block diagram for explaining the functional configuration of the controller. [Figure 4] Figure 4 is a flowchart for explaining a control example executed by the controller. [Figure 5] Figure 5 is a flowchart for explaining a control example for determining permission for motor running control. [Figure 6] Figure 6 is a diagram showing an example of a first map for obtaining an opening determination threshold value. [Figure 7] Figure 7 is a flowchart for explaining an example of motor running control. [Figure 8] Figure 8 is a diagram showing an example of a second map for obtaining a target engine speed. [Figure 9] Figure 9 is a diagram showing an example of a third map for obtaining a target throttle opening. [Figure 10] Figure 10 is a diagram showing an example of a fourth map for obtaining a permission time for motor running control. [Figure 11] Figure 11 is a time chart for explaining changes in vehicle speed, accelerator opening, engine speed, throttle opening, and boost pressure when the control example shown in FIG. 4 is executed. [Figure 12] Figure 12 is a flowchart for explaining a control example in which boost pressure is added as a condition for permitting motor running control. [Figure 13] Figure 13 is a diagram showing an example of a fifth map for obtaining a boost determination threshold value. [Figure 14] Figure 14 is a diagram showing an example of a sixth map for obtaining a second permission time. Embodiments for Carrying Out the Invention

[0020] This invention will be described based on the embodiments shown in the drawings. Note that the embodiments described below are merely examples when this invention is embodied, and do not limit this invention.

[0021] Figure 1 schematically shows a skeleton diagram illustrating an example of a vehicle in an embodiment of this invention. The vehicle Ve shown in Figure 1 is a hybrid vehicle equipped with an engine (ENG) 1, a first motor (MG1) 2, and a second motor (MG2) 3 as driving forces.

[0022] Engine 1 can be configured in the same way as conventional engines that use gasoline or diesel as fuel, and is configured to generate power by burning a mixture of supplied air and fuel.

[0023] Figure 2 schematically shows an example of the engine 1. The intake system of the engine 1 shown in Figure 2 is provided with an intake pipe 4, which is connected to an intake manifold 5 attached to the engine 1 body. The exhaust system of the engine 1 is provided with an exhaust pipe 6, which is connected to an exhaust manifold 7 attached to the engine 1 body.

[0024] Furthermore, the engine 1 is equipped with a supercharger 8 for pressurizing the air supplied to the engine 1. This supercharger 8 consists of a compressor 9 located in the intake pipe 4 and a turbine 11 located in the exhaust pipe 6 and connected to the compressor 9 via a shaft 10. In other words, the supercharger 8 shown here is a conventional exhaust turbine type supercharger (turbocharger). Therefore, the turbine 11 is rotated by the exhaust, causing the compressor 9 to rotate at the same speed, and as a result, the air supplied to the engine 1 (intake) is pressurized. That is, as the rotational speed of the engine 1 increases, the amount of exhaust increases, so the boost pressure from the supercharger 8 increases in proportion to the engine speed.

[0025] In the example shown in Figure 2, an exhaust bypass 12 is provided to allow exhaust gas to flow from the upstream side to the downstream side of the turbine 11, bypassing the turbine 11. The exhaust bypass 12 is equipped with a wastegate valve 13 to control the ratio of exhaust gas passing through the turbine 11 to exhaust gas passing through the exhaust bypass 12. Therefore, by reducing the opening of the wastegate valve 13, the amount of exhaust gas passing through the turbine 11 can be increased.

[0026] An air cleaner 14 is provided upstream of the intake manifold 4, and an air flow meter 15 for measuring the amount of intake air from the engine 1 is provided downstream of the air cleaner 14 and upstream of the compressor 9 in the intake manifold 4. Furthermore, an intercooler 16, which is a heat exchanger that cools the intake air compressed by the supercharger 8 by exchanging heat between the intake air and outside air or coolant.

[0027] A throttle valve 17 is provided in the intake manifold 4, downstream of the intercooler 16 and upstream of the intake manifold 5. This throttle valve 17 is configured to be operated by a motor 18, and its rotation angle is appropriately controlled according to a command signal from a controller 19, which will be described later. In other words, the amount of air flowing through the intake manifold 4 can be controlled by controlling the rotation angle of the throttle valve 17 (i.e., the rotation angle of the motor 18). In the following description, the rotation angle of the throttle valve 17 will be referred to as the throttle opening.

[0028] A boost pressure sensor 20 is provided between the intercooler 16 and the throttle valve 17 in the intake manifold 4 to detect the pressure inside the intake manifold 4 downstream of the compressor 9, and a throttle opening sensor 21 is provided near the throttle valve 17 to detect the throttle opening.

[0029] The intake manifold 4 is provided with an air recirculation bypass 22 that recirculates air from the downstream side to the upstream side of the compressor 9, bypassing the compressor 9. An air bypass valve 23 is provided in this air recirculation bypass 22. Therefore, for example, if the throttle opening suddenly decreases, the air bypass valve 23 can be opened to suppress the generation of surges and protect the compressor 9.

[0030] The output torque of engine 1, configured as described above, is controlled by a throttle valve 17, a fuel injector (not shown), an ignition system (not shown), and a wastegate valve 13, among others.

[0031] The first motor 2 and the second motor 3 can be configured in the same way as motors provided as power sources in conventional electric vehicles and hybrid vehicles. That is, in addition to functioning as motors that output driving torque to increase the rotational speed of the output shaft when power is supplied from an energy storage device (not shown), they are configured to function as generators that convert at least a portion of the power of the output shaft into electricity as the output shaft is rotated along with them. Specifically, each of the motors 2 and 3 is composed of an AC motor such as a synchronous motor or an induction motor.

[0032] In the vehicle Ve shown in Figure 1, a power split mechanism 25 is connected to the output shaft 24 of the engine 1. This power split mechanism 25 is a differential mechanism configured to split the torque of the engine 1 between the first motor 2 and the output shaft 26 connected to a drive wheel (not shown). In the example shown in Figure 1, it is composed of a single-pinion type planetary gear mechanism. Specifically, the power split mechanism 25 is composed of a sun gear S, a ring gear R, and a carrier C that holds the sun gear S and the pinion gear P that mesh with the ring gear R so that they can rotate and revolve. The first motor 2 is connected to the sun gear S, the output shaft 26 is connected to the ring gear R, and the engine 1 is connected to the carrier C.

[0033] Therefore, by balancing the torque input from engine 1 to carrier C and the torque input from first motor 2 to sun gear S, torque is transmitted to ring gear R while maintaining the rotational speeds of engine 1 and first motor 2. In other words, by outputting a torque from first motor 2 that is greater than the torque input from engine 1 to carrier C and the torque acting on sun gear S according to the gear ratio of power split mechanism 25, the engine speed decreases due to the torque corresponding to that torque difference. Conversely, if the torque of first motor 2 is less than the torque input from engine 1 to carrier C and the torque acting on sun gear S according to the gear ratio of power split mechanism 25, the engine speed increases due to the torque corresponding to that torque difference. In other words, by appropriately controlling the torque (reaction torque) of first motor 2, the engine speed can be continuously changed. In other words, the power split mechanism 25 can function as a continuously variable transmission that sets the engine speed to a desired speed, without depending on the rotational speed of the output shaft 26 (i.e., the rotational speed of the drive wheels 27).

[0034] Furthermore, if the direction of the reaction torque of the first motor 2 increases the rotational speed of the first motor 2, the first motor 2 functions as a motor. Conversely, if the direction of the reaction torque of the first motor 2 decreases the rotational speed of the first motor 2, the first motor 2 functions as a generator.

[0035] Furthermore, the second motor 3 is connected to the ring gear R. Therefore, if the torque transmitted from the engine 1 to the ring gear R via the power split mechanism 25 is less than the torque required for the vehicle Ve, the second motor 3 is operated as a motor to add torque. Conversely, if the torque transmitted from the engine 1 to the ring gear R via the power split mechanism 25 is greater than the torque required for the vehicle Ve, the second motor 3 is operated as a generator to subtract torque.

[0036] The first motor 2 and the second motor 3 described above are electrically connected via an inverter (not shown). Therefore, the power generated by either the first motor 2 or the second motor 3 can be supplied to the other motor. In other words, power corresponding to the difference between the total power consumed by the first motor 2 and the second motor 3 and the total power generated by the first motor 2 and the second motor 3 is output from or charged into the energy storage device.

[0037] Furthermore, the output shaft 26 may be connected to other transmission mechanisms, such as a stepped transmission mechanism. Alternatively, instead of the output shaft 26, an output gear may be connected to a ring gear R, and the drive wheels may be connected via a gear train or the like that meshes with the output gear.

[0038] As described above, the vehicle Ve can be configured to run in an EV driving mode, where the engine 1 is stopped and the vehicle runs solely on the power of the second motor 3, and in an HV driving mode, where the vehicle runs using the power of the engine 1 or by rotating the engine 1. In the HV driving mode, the required driving power for the vehicle Ve is determined based on the amount of operation of the accelerator device (accelerator pedal) 28 operated by the driver (hereinafter referred to as accelerator opening) and the vehicle speed, and the required charging power for the energy storage device is also determined. The sum of this driving power and charging power is then set as the required power for the engine 1.

[0039] Then, based on the required power of engine 1 and a predetermined optimal fuel efficiency map, the required torque and target rotational speed of engine 1 are determined, and the throttle opening, fuel injection amount, ignition timing, or the opening of the wastegate valve 13 are appropriately controlled according to the determined required torque. In addition, the reaction torque of the first motor 2 is appropriately controlled to control the engine speed so that it reaches the target rotational speed.

[0040] An electronic control unit (hereinafter referred to as "controller") 19 is provided to control the engine 1 and each of the motors 2 and 3 described above. This controller 19 is mainly composed of a microcomputer and is configured to receive signals from various sensors installed on the vehicle Ve and to determine command signals to the engine 1 and each of the motors 2 and 3 based on the input signals and pre-stored maps and calculation formulas.

[0041] In the example shown in Figure 1, signals are input to the controller 19 from the vehicle speed sensor 29, the accelerator position sensor 30 which detects the accelerator opening, the pedal force sensor 32 which detects the operating force (pedal force) of the brake device (brake pedal) 31 operated by the driver, the crank angle sensor 33 which detects the engine speed, the throttle position sensor 21, and the boost pressure sensor 20.

[0042] The vehicle control device in this embodiment of the invention is configured to suppress a decrease in acceleration responsiveness when re-accelerating after temporary deceleration. In other words, when temporary deceleration occurs, the device is configured to maintain the amount of air flowing to the turbine 11 and thus maintain the boost pressure by maintaining the engine speed at a high rotational speed or maintaining the throttle opening at a high opening.

[0043] Figure 3 shows a block diagram illustrating the functional configuration of the controller 19. The controller 19 shown in Figure 3 includes a motoring permission determination unit 34, a target engine speed setting unit 35, a target throttle opening setting unit 36, and a motoring execution unit 37.

[0044] The motoring permission determination unit 34 determines whether or not to permit motoring control that raises the engine speed during deceleration to a level higher than the engine speed determined from the accelerator opening and vehicle speed. This motoring control corresponds to "speed control" in the embodiment of this invention.

[0045] The target engine speed setting unit 35 and the target throttle opening setting unit 36 ​​set the target engine speed and throttle opening in motoring control in order to improve acceleration responsiveness during re-acceleration.

[0046] When motoring control is permitted by the motoring permission determination unit 34, the motoring execution unit 37 controls the first motor 2 and the motor 18 to achieve the target engine speed and target throttle opening set by the target engine speed setting unit 35 and the target throttle opening setting unit 36.

[0047] Figure 4 shows a flowchart illustrating an example of control performed by the vehicle control device in an embodiment of this invention. The control shown in Figure 4 is performed when the vehicle is driving at a speed equal to or greater than a predetermined vehicle speed set in HV driving mode. In other words, it is performed when the accelerator opening is equal to or greater than a predetermined opening. In the example shown in Figure 4, first, it is determined whether or not to allow motoring control (step S1). Specifically, it is determined whether or not to allow motoring control by the control shown in Figure 5.

[0048] In the control example shown in Figure 5, first, a threshold (hereinafter referred to as the opening degree determination threshold) θth for determining whether or not to allow motoring control is determined (step S11). Specifically, the opening degree determination threshold θth is determined from the vehicle speed detected by the vehicle speed sensor 29 and a first map pre-stored in the controller 19. This opening degree determination threshold θth corresponds to the "determination threshold" in this embodiment of the invention.

[0049] Figure 6 shows an example of the first map, with vehicle speed on the horizontal axis and the throttle opening threshold θth on the vertical axis. The configuration is such that the throttle opening threshold θth increases as the vehicle speed increases. This is because when the vehicle decelerates by reducing the throttle opening while traveling at high speed, it is assumed that the vehicle will re-accelerate to the speed it was at before deceleration. In this case, the system is configured to improve acceleration responsiveness during re-acceleration, or in other words, to suppress the decrease in engine speed (i.e., boost pressure) that accompanies deceleration, by switching to motoring control earlier. Conversely, when the vehicle decelerates by reducing the throttle opening while traveling at low speed, the driving torque required during subsequent acceleration is small, and it is possible that the vehicle will stop without re-accelerating. In this case, the system is configured not to switch to motoring control in order to suppress the increased load on the first motor 2, which controls the engine speed, and the energy storage device that exchanges power with the first motor 2.

[0050] Furthermore, the throttle opening determination threshold θth is set to be greater than the idle-off determination threshold and less than the braking request threshold. The idle-off determination threshold is the throttle opening that determines when to stop engine 1 (reducing the rotational speed to "0"), and is set, for example, to a throttle opening of "0" or slightly greater than "0". The braking request threshold is the throttle opening that determines when braking force is required for vehicle Ve, and is a throttle opening determined based on a drive force map used in conventional vehicles. This drive force map is typically used to determine the drive force and braking force required for vehicle Ve from vehicle speed and throttle opening, and is configured to set a smaller drive force (or larger braking force) as the vehicle speed increases when the throttle opening is the same, and to set a larger drive force (or smaller braking force) as the throttle opening increases when the vehicle speed is the same. In other words, when driving at a predetermined vehicle speed, braking force is required when the throttle opening is below the predetermined opening.

[0051] Following step S11, it is determined whether the actual accelerator opening θact is less than the opening threshold θth (step S12). In other words, it is determined whether the accelerator opening θact has become smaller than the opening threshold θth. If the actual accelerator opening θact is greater than or equal to the opening threshold θth and therefore determined negatively in step S12, motoring control is deemed not permitted (step S13). Conversely, if the actual accelerator opening θact is less than the opening threshold θth and therefore determined positively in step S12, motoring control is deemed permitted (step S14), and this routine is terminated.

[0052] If step S13 described above determines that motoring control is not permitted, in other words, if a negative determination is made in step S1, this routine is terminated. That is, the operating point (torque and rotational speed) of engine 1 is determined based on the accelerator opening and vehicle speed, and engine 1 is controlled to reach that operating point, and the first motor 2 is also controlled. Conversely, if step S14 determines that motoring control is permitted, in other words, if a positive determination is made in step S1, motoring control is executed (step S2).

[0053] This motoring control controls the amount of air flowing toward the turbine 11 to maintain the boost pressure. Specifically, the first motor 2 maintains the engine speed at a predetermined speed, and the motor 18 maintains the throttle opening at a predetermined opening. Figure 7 shows a flowchart illustrating an example of the control for setting the engine speed and throttle opening, in other words, an example of motoring control.

[0054] The example shown in Figure 7 is executed when it is determined that motoring control should be performed. First, a target engine speed to maintain boost pressure is calculated (step S21). The target engine speed in step S21 is determined based on the vehicle speed. Specifically, as shown in Figure 8, a second map is pre-stored in the controller 19 that sets the target engine speed to a higher value the higher the vehicle speed. The target engine speed is calculated from the vehicle speed detected by the vehicle speed sensor 29 and the second map. The target engine speed is set so that the engine noise is below the sound pressure level of the driving noise corresponding to the vehicle speed. Next, the rotation speed of the first motor 2 is controlled to achieve the target engine speed (step S22), and this routine is terminated.

[0055] In parallel with steps S21 and S22 described above, a target throttle opening to maintain boost pressure is calculated (step S23). The target throttle opening in step S23 is determined based on the vehicle speed. Specifically, as shown in Figure 9, a third map is pre-stored in the controller 19 that sets the target throttle opening to a higher degree the higher the vehicle speed, and the target throttle opening is calculated from the vehicle speed detected by the vehicle speed sensor 29 and the third map. This is because the higher the vehicle speed, the higher the engine speed is maintained, and air flows quickly from the intake manifold 4 through the engine body 1 to the exhaust manifold 6, causing the internal pressure of the intake manifold 4 to decrease, thus allowing more air to be taken into the intake manifold 4 in order to maintain boost pressure. Next, the rotation angle of the motor 18 is controlled to achieve the target throttle opening (step S24), and this routine is terminated.

[0056] After performing motoring control as described above, it is determined whether a permit time, determined based on the accelerator opening and vehicle speed, has elapsed (step S3). The permit time in step S3 is set to suppress an increase in the load on the first motor 2 and the energy storage device due to continuing motoring control, or to suppress the driver from feeling uncomfortable due to a high engine speed when re-acceleration is not performed.

[0057] Figure 10 shows an example of a fourth map for setting the permitted time, with vehicle speed on the horizontal axis and permitted time on the vertical axis, and multiple lines corresponding to the accelerator opening. As shown in Figure 10, the faster the vehicle speed, the longer the permitted time is set. This is because at higher vehicle speeds, the time required to decelerate sufficiently is longer, and the driver is less likely to perceive the abnormal noise caused by motoring control as an abnormality. Also, as shown in Figure 10, the higher the accelerator opening, the longer the permitted time is set. This is because it is assumed that the driver intends to re-accelerate when operating the accelerator, and this is to allow the boost pressure to be maintained during the period of accelerator operation.

[0058] If step S3 is negatively determined because the permitted time has not elapsed, the process returns to step S2. Conversely, if step S3 is positively determined because the permitted time has elapsed, the motoring control is terminated (step S4), and this routine is temporarily ended. In this case, the engine speed and throttle opening are rapidly reduced towards the target engine speed and target throttle opening determined based on the accelerator opening and vehicle speed.

[0059] Figure 11 schematically shows a time chart illustrating the changes in vehicle speed, accelerator opening, engine speed, throttle opening, and boost pressure when the control example shown in Figure 4 is executed. In the example shown in Figure 11, at time t0, the accelerator opening is maintained at a predetermined opening for steady driving. Therefore, the engine speed, throttle opening, and boost pressure are kept constant. At time t1, the accelerator opening begins to decrease. As a result, the vehicle speed gradually decreases due to driving resistance, etc. Also, since engine 1 is controlled to operate at a point based on the accelerator opening and vehicle speed, the engine speed and throttle opening begin to decrease at time t1. As the amount of exhaust from engine 1 decreases due to the decrease in engine speed and throttle opening, the boost pressure begins to decrease at time t1.

[0060] At time t2, the accelerator opening becomes smaller than the opening threshold θth, allowing motoring control. Therefore, from time t2 onwards, the engine speed and throttle opening are controlled based on the vehicle speed to maintain boost pressure. In addition, since the engine 1 is not being driven, the fuel supply is stopped, causing the vehicle speed to continuously decrease, and consequently, the engine speed and throttle opening decrease at a relatively small rate of change.

[0061] Furthermore, Figure 11 shows the changes in vehicle speed, engine speed, throttle opening, and boost pressure when the above motoring control is not performed, indicated by dashed lines. When motoring control is not performed, the engine speed and throttle opening continue to decrease after time t2, and the boost pressure decreases accordingly. Note that the engine speed is continuously reduced until it reaches idle speed or stops.

[0062] At time t3, the accelerator opening is increased, and at time t4, it exceeds the accelerator opening threshold θth. As a result, motoring control is deemed not permitted, and the engine speed and throttle opening are controlled based on the accelerator opening and vehicle speed. Consequently, from time t4, the engine speed and throttle opening begin to increase in line with the increase in accelerator opening. In addition, the boost pressure begins to increase in line with the increase in engine speed and throttle opening. As a result, the torque of engine 1 increases rapidly, causing the vehicle speed to increase from time t4.

[0063] In contrast, when motoring control is not performed, the engine 1 is stopped and the throttle valve 17 is closed. Therefore, if the accelerator opening increases at time t3, it takes time for the engine 1 to be cranked, then started, and then for the boost pressure to increase as the engine speed increases. As a result, it takes time for the driving force to increase, delaying the timing at which the vehicle speed begins to increase.

[0064] As described above, since the engine 1 is connected to the drive wheels 27 via a power split mechanism 25 that can function as a continuously variable transmission, the rotational speed of the engine 1 can be controlled independently of the rotational speed of the drive wheels 27. In addition, the supercharger 8 provided on the engine 1 pressurizes the air supplied to the engine 1 according to the rotational speed of the engine 1. Therefore, by appropriately controlling the rotational speed of the engine 1, the pressure of the air supplied to the engine 1 (supercharger pressure) can be controlled. As a result, even during deceleration, by appropriately controlling the rotational speed of the engine 1 and the throttle opening, the supercharger 8 can be activated and the supercharger pressure can be increased in advance. As a result, deterioration in acceleration responsiveness when increasing the torque of the engine 1, such as during re-acceleration, can be suppressed.

[0065] Furthermore, motoring control is executed when the accelerator opening becomes smaller than the opening threshold θth, and this threshold is set to a larger value as the vehicle speed increases. Therefore, motoring control can be executed when temporarily decelerating at relatively high speeds, such as when decelerating to avoid collisions with obstacles or preceding vehicles and then accelerating afterward. In other words, motoring control can be executed when re-acceleration is expected or when the road noise is loud. Therefore, even if a loud engine noise is generated by executing motoring control, it is possible to suppress discomfort for the driver.

[0066] Furthermore, the power split mechanism 25 described above is configured to control the engine speed using the first motor 2. That is, when motoring control is performed, the first motor 2 outputs either drive torque (torque in the direction of increasing the rotational speed of the first motor 2) or regenerative torque (torque in the direction of decreasing the rotational speed of the first motor 2). Therefore, by performing motoring control in driving conditions where re-acceleration is expected, it is possible to suppress an increase in the load on the first motor 2 and the load on the energy storage device that exchanges power with the first motor 2.

[0067] Furthermore, the vehicle control device in this embodiment of the invention only needs to be able to maintain a boost pressure corresponding to the vehicle speed during re-acceleration, and may determine whether to permit motoring control based on the boost pressure in addition to the accelerator opening. Figure 12 shows a flowchart illustrating a control example in which boost pressure is added as a condition for permitting motoring control. Note that steps identical to those in the control example shown in Figure 5 are given the same step numbers and their explanations are omitted.

[0068] In the control example shown in Figure 12, if a positive result is obtained in step S12, the boost pressure determination threshold Pth is determined (step S15). Specifically, the boost pressure determination threshold Pth is determined from the vehicle speed detected by the vehicle speed sensor 29 and the fifth map pre-stored in the controller 19.

[0069] Figure 13 shows an example of the fifth map, with vehicle speed on the horizontal axis and the boost pressure threshold Pth on the vertical axis. The boost pressure threshold Pth is configured to increase as the vehicle speed increases. This is because, under steady-state driving conditions, the boost pressure is set higher at higher vehicle speeds. In other words, the boost pressure threshold Pth is set to maintain a boost pressure corresponding to the vehicle speed at the moment when acceleration is required to drive the vehicle.

[0070] Following step S15, it is determined whether the actual boost pressure Pact is less than the boost pressure threshold Pth (step S16). In other words, it is determined whether the boost pressure Pact has become smaller than the boost pressure threshold Pth. If the judgment in step S16 is negative because the actual boost pressure Pact is greater than or equal to the boost pressure threshold Pth, it is determined that motoring control is not permitted (step S13). Conversely, if the judgment in step S16 is positive because the actual boost pressure Pact is less than the boost pressure threshold Pth, it is determined that motoring control is permitted (step S14), and this routine is terminated.

[0071] By determining whether or not to allow motoring control based on the boost pressure in this way, it is possible to suppress the transition to motoring control when the throttle opening suddenly decreases, while the engine speed is still high and the boost pressure is high. As a result, it is possible to suppress the load on the first motor 2, which is used to maintain the engine speed by motoring control, from increasing prematurely.

[0072] Furthermore, the vehicle control device in this embodiment of the invention may be configured to terminate motoring control when a second permitted time, determined based on brake operation and vehicle speed, has elapsed in addition to a permitted time determined based on accelerator opening and vehicle speed.

[0073] Figure 14 shows an example of a sixth map for setting the second permission time, with vehicle speed on the horizontal axis and the second permission time on the vertical axis, and multiple lines corresponding to brake pedal force are shown. As shown in Figure 14, the faster the vehicle speed, the longer the second permission time is set. This is because at higher vehicle speeds, the time required to decelerate sufficiently increases, and the driver is less likely to perceive the abnormal noise caused by motoring control as an unpleasant sensation. Also, as shown in Figure 14, the stronger the brake pedal force, the shorter the second permission time is set. This is because strong brake pedal force is expected to result in rapid re-acceleration, and the sudden deceleration causes a rapid decrease in vehicle speed, which can suppress the driver from feeling uncomfortable with the abnormal noise associated with motoring control.

[0074] Furthermore, the vehicle in this embodiment of the invention is not limited to a hybrid vehicle equipped with the power split mechanism 25 as described above, but may also be a so-called series-type hybrid vehicle in which an engine and a generator that do not transmit torque to the drive wheels are connected, and the electricity generated by the generator is supplied to the drive motor for propulsion. Alternatively, it may be an engine vehicle that has only an engine as a driving force source and is equipped with a continuously variable transmission that can continuously control the rotational speed ratio between the engine and the drive wheels.

[0075] Furthermore, the supercharger is not limited to a turbocharger driven by the engine's exhaust, but may also be a supercharger driven by the power of the engine's output shaft. In that case, motoring control only requires appropriate control of the engine speed, and does not require control of the throttle opening. [Explanation of Symbols]

[0076] 1 Engine 2,3,18 Motors 4. Intake pipe 5. Intake Manifold 6 Exhaust pipes 7 Exhaust manifold 8. Supercharger 9 Compressor 10 shafts 11 Turbine 12 Exhaust Bypass 13 Wastegate Valve 14. Air cleaner 15. Air flow meter 16 Intercooler 17 Throttle valve 19 Controllers 20. Supercharger pressure sensor 21 Throttle position sensor 22 Air recirculation bypass 23 Air bypass valve 24,26 Output shaft 25 Power split mechanism 27 Drive wheels 28. Accelerator device (accelerator pedal) 29. Vehicle speed sensor 30. Accelerator position sensor 31. Brake system (brake pedal) 32. Pedal force sensor 33 Crank Angle Sensor 34 Motoring permission determination unit 35 Target engine speed setting unit 36 Target throttle opening setting section 37 Motoring Execution Unit C Carrier P pinion gear R Ring Gear S Sangiya Vehicle

Claims

1. A vehicle control device comprising an engine having a supercharger that pressurizes the supplied air and capable of controlling the rotational speed independently of the rotational speed of the drive wheels, wherein the supercharger is configured to pressurize the air according to the rotational speed of the engine, The accelerator device operated by the driver, The system further comprises a controller that controls the engine based on the amount of operation of the accelerator device, The aforementioned controller, The system is configured to perform rotational speed control to maintain the boost pressure from the supercharger when the amount of operation of the accelerator device falls below a predetermined threshold, The aforementioned threshold value is set to a larger value as the vehicle speed increases. A vehicle control device characterized by the following features.

2. A vehicle control device according to claim 1, The aforementioned controller, The faster the vehicle speed, the higher the target engine speed in the rotational speed control is set. A vehicle control device characterized by the following features.

3. A vehicle control device according to claim 1, The engine further includes a throttle valve that controls the amount of air supplied to the engine, The aforementioned controller, The faster the vehicle speed, the higher the opening degree of the throttle valve in the rotation speed control is set to. A vehicle control device characterized by the following features.

4. A vehicle control device according to claim 1, The aforementioned controller, The rotational speed control is executed when the boost pressure falls below a predetermined boost pressure. A vehicle control device characterized by the following features.

5. A vehicle control device according to claim 4, The predetermined boost pressure is set to a higher value as the vehicle speed increases. A vehicle control device characterized by the following features.

6. A vehicle control device according to any one of claims 1 to 4, The aforementioned controller, The rotation speed control terminates when it continues for a predetermined time. A vehicle control device characterized by the following features.

7. A vehicle control device according to claim 6, The aforementioned controller, The faster the vehicle speed, the longer the predetermined time is set. A vehicle control device characterized by the following features.

8. A vehicle control device according to claim 6, The aforementioned controller, The larger the amount of operation on the accelerator device, the longer the predetermined time is set. A vehicle control device characterized by the following features.

9. A vehicle control device according to claim 6, The vehicle further comprises a braking device operated by the aforementioned driver, The aforementioned controller, The greater the operating force of the brake, the shorter the predetermined time is set. A vehicle control device characterized by the following features.

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