Control system for hybrid vehicle

Abstract

Control system for a hybrid vehicle (Ve), which includes: an internal combustion engine (1); a first motor (2) that controls the speed of the internal combustion engine (1); a second motor (3) that exerts a braking torque on drive wheels (5) when energy is regenerated; and an electrical storage device (6) which is electrically connected to the first motor (2) and the second motor (3), wherein the control system is designed to decelerate the hybrid vehicle (Ve) by controlling the second motor (3) to generate the braking torque and controlling the first motor (2) to reduce the speed of the internal combustion engine (1), characterized by the fact that: the control system includes a control device (21) that controls the internal combustion engine (1), the control unit (21) is designed to select a control mode of the internal combustion engine (1) from: a low-power mode in which the hybrid vehicle (Ve) is decelerated in response to a deceleration operation by reducing the torque and power of the internal combustion engine (1) at a predetermined rate and simultaneously generating the braking torque by the second engine (3); and a high-performance mode in which the hybrid vehicle (Ve) is decelerated in response to a deceleration operation by reducing the torque and power of the internal combustion engine (1) at a rate lower than the predetermined rate of the low-performance mode and simultaneously generating the braking torque by the second engine (3).

Description

[0001] Embodiments of the present disclosure relate to the technique of a control system (hereinafter referred to as "control system"; accordingly in related terms) for a hybrid vehicle in which a prime mover includes an engine and a motor generator, and more particularly to a control system for controlling the engine during deceleration of the hybrid vehicle.

[0002] JP 2017-223309 A describes a control device for a vehicle designed to prevent an abrupt increase in the rotational speed of an internal combustion engine (hereinafter referred to as "engine speed") during vehicle deceleration and to reduce a shock that occurs due to the elimination of gear backlash in a power transmission path of the vehicle. Specifically, the control device taught in JP 2017-223309 A is applied to a vehicle including a lock-up clutch.According to the teaching of JP 2017 - 223 309 A, the control device selects a control mode of the lock-up clutch from the following modes: a full engagement mode in which the lock-up clutch is fully engaged; an acceleration slip mode in which differential rotation of the lock-up clutch is possible during acceleration of the vehicle; and a deceleration slip mode in which differential rotation of the lock-up clutch is permitted during deceleration of the vehicle.

[0003] For example, the control device taught in JP 2017-223309 A determines that when a change in engine torque (hereinafter, "engine torque") due to the release of an accelerator pedal is greater than a predetermined value, the engine torque is abruptly increased, generating a shock. In this case, the lock-up clutch control mode is not immediately shifted from the full engagement mode to the deceleration slip mode. Specifically, in this case, the lock-up clutch control mode is shifted from the full engagement mode to the acceleration slip mode and further shifted to the deceleration slip mode after the vehicle is put into a running state.

[0004] Thus, according to the teaching of JP 2017-223309 A, an abrupt increase in engine speed and the generation of shock during deceleration can be prevented by controlling the lock-up clutch. Furthermore, although JP 2017-223309 A does not describe a technique for directly controlling a change in engine torque, it is also possible to control the engine speed and torque using the control device taught in JP 2017-223309 A, thus preventing an abrupt change in torque and the generation of shock.

[0005] However, if the accelerator pedal is fully released, causing a throttle valve to close completely to reduce the engine torque to zero, air intake is abruptly reduced, thereby increasing exhaust gases. Furthermore, if such control is applied to a hybrid vehicle with an engine and a motor generator, the motor generator and a battery cannot be adequately protected depending on the engine condition. For example, this would cause the motor generator to overheat and the battery to overcharge.

[0006] Aspects of the present invention have been conceived in consideration of the above-mentioned technical problems, and therefore, an object of the present invention is to provide a control system for a hybrid vehicle configured to reduce exhaust gases during deceleration of the vehicle and to protect a motor and a battery.

[0007] This object is achieved by the features of the independent claim. Advantageous developments of the invention are defined in the subclaims.

[0008] The control system according to the embodiment of the present disclosure is applied to a hybrid vehicle including: an internal combustion engine; a first motor that controls a rotational speed of the internal combustion engine; a second motor that applies braking torque to drive wheels when energy is regenerated; and an electrical storage device electrically connected to the first motor and the second motor. The control system is configured to decelerate the hybrid vehicle by controlling the second motor to generate the braking torque and controlling the first motor to reduce the rotational speed of the internal combustion engine. The control system includes a control device that controls the internal combustion engine.To achieve the above-mentioned object, the control apparatus according to the exemplary embodiment of the present disclosure is configured to select a control mode of the internal combustion engine from the following modes: a low-power mode in which the hybrid vehicle is decelerated in response to a deceleration operation by reducing a torque and power of the engine (hereinafter, "engine power" for short) at a predetermined rate and simultaneously generating the braking torque by the second motor; and a high-power mode in which the hybrid vehicle is decelerated in response to a deceleration operation by reducing the torque and power of the engine at a rate lower than the predetermined rate of the low-power mode and simultaneously generating the braking torque by the second motor.

[0009] In one non-limiting embodiment, the high power mode may include: a first control mode in which the hybrid vehicle is decelerated while reducing the torque and speed of the engine such that an operating point of the engine is shifted along an optimal fuel consumption curve; and a second control mode in which the hybrid vehicle is decelerated while reducing the torque of the engine at a same rate as in the first control mode, the speed of the engine is reduced at a greater rate than in the first control mode, and the power of the engine is reduced at a lower rate than in the low power mode, so as to reduce emissions.

[0010] In one non-limiting embodiment, the controller may be further configured to select the control mode of the internal combustion engine based on a charge level of the electrical storage device or an acceptable value of input power for the electrical storage device when the vehicle is decelerating.

[0011] In one non-limiting embodiment, the controller may be further configured to: select the first control mode when the charge level of the electrical storage device is lower than a first threshold level, select the second control mode when the charge level of the electrical storage device is higher than the first threshold level but lower than a second threshold level, and select the low power mode when the charge level of the electrical storage device is higher than the second threshold level.

[0012] In one non-limiting embodiment, the control device may be further configured to: select the first control mode when the acceptable value of the input power for the electrical storage device is greater than a first acceptable value, select the second control mode when the acceptable value of the input power for the electrical storage device is less than the first acceptable value but greater than a second acceptable value, and select the low power mode when the acceptable value of the input power for the electrical storage device is less than the second acceptable value.

[0013] In a non-limiting embodiment, the control device may be further configured to: determine whether the input power (Win) for the electrical storage device is less than a currently acceptable value of the input power for the electrical storage device when the internal combustion engine (1) is controlled in the first control mode, determine whether the input power for the electrical storage device is less than a currently acceptable value of the input power for the electrical storage device when the internal combustion engine (1) is controlled in the second control mode, select the first control mode, if the input power (Win) for the electrical storage device is less than the currently acceptable value of the input power for the electrical storage device and the internal combustion engine (1) is controlled in the first control mode, select the second control mode,when the input power for the electrical storage device is greater than the currently acceptable value of the input power for the electrical storage device and the internal combustion engine (1) is controlled in the first control mode, but is less than the input power for the electrical storage device when the internal combustion engine is controlled in the second control mode, and to select the low-power mode when the input power for the electrical storage device is greater than the currently acceptable value of the input power for the electrical storage device and the internal combustion engine (1) is controlled in the second control mode.

[0014] In one non-limiting embodiment, the controller may be further configured to determine whether the vehicle can be decelerated in the high-performance mode in response to the deceleration operation using an equation of motion in which a torque of the second motor and a torque of the internal combustion engine are used as parameters.

[0015] In one non-limiting embodiment, the control device may be further configured to: select the control mode of the internal combustion engine based on a required deceleration taking into account a shift range, an operation amount of a brake pedal, an operation speed of a predetermined pedal in a one-pedal mode, and a road gradient with respect to a flat road, select the first control mode or the second control mode when a predetermined condition of the required deceleration is satisfied, and select the low power mode when the predetermined condition of the required deceleration is not satisfied.

[0016] In one non-limiting embodiment, the hybrid vehicle may further include a power split mechanism that splits an output power of the internal combustion engine between an output member and the first motor. The power split mechanism may include a planetary gear unit having an input member connected to the internal combustion engine, a reaction member connected to the first motor, and an output member connected to the output member. The second motor may be connected to a power transmission path between the drive wheels and the output member.

[0017] Thus, according to the exemplary embodiment of the present disclosure, the hybrid vehicle is decelerated by controlling the engine speed by the first motor and transmitting braking torque generated by the second motor to the drive wheels. When the hybrid vehicle is decelerated in the high-power mode, the engine torque and power are reduced at a rate lower than the predetermined rate of the low-power mode. In this situation, therefore, the air intake to the engine is reduced more slowly than in the low-power mode, in which the engine speed and torque are reduced promptly. For this reason, the air intake for controlling the air / fuel ratio to reduce gaseous pollutant emissions can be accurately estimated.

[0018] As described above, the high-power mode can be selected from the first control mode and the second control mode. Specifically, in the first control mode, the engine is controlled so that an operating point of the engine is shifted along an optimal fuel consumption curve. Conversely, in the second control mode, the torque of the engine is reduced at a substantially similar rate to the first control mode, the engine speed is reduced at a greater rate than the first control mode, and the engine power is reduced at a smaller rate than the low-power mode. Therefore, in the second control mode, the output of the engine can be reduced while reducing a regeneration amount of the second motor compared to the first control mode.This means that, for example, when the charge level of the electric storage device is high, selecting the second control mode can decelerate the hybrid vehicle while reducing emissions and charging the electric storage device within an upper limit. Therefore, overcharging of the electric storage device can be prevented.

[0019] The control mode of the internal combustion engine may be selected based on the fact that the second motor is in a state where it can generate the braking torque to decelerate the vehicle while maintaining the output torque of the internal combustion engine. For example, to decelerate the hybrid vehicle while slowly reducing the output power of the internal combustion engine to reduce emissions, the second motor may generate the braking torque greater than the output torque of the internal combustion engine to decelerate the hybrid vehicle when a temperature of the second motor itself or a power control unit falls within a predetermined range. Therefore, the first control mode or the second control mode is selected when, for example, the temperature of the second motor is lower than the predetermined value.For this reason, the control mode of the internal combustion engine can be appropriately selected to reduce the emissions of gaseous pollutants while protecting the electrical storage device, motors and power control unit.

[0020] Furthermore, the control mode of the internal combustion engine can be selected based on the required deceleration, taking into account the gear shift range, the amount of operation of a brake pedal, the operation speed of a predetermined pedal in a one-pedal mode, or the road gradient. Therefore, the required deceleration can be achieved while reducing gaseous pollutant emissions and protecting the electric storage device and motors.

[0021] Features, aspects and advantages of exemplary embodiments of the present invention will become more fully understood with reference to the following description and accompanying drawings, which should not be construed as limiting the invention in any way. Fig. 1 is a schematic diagram showing an example of a powertrain of the hybrid vehicle to which the control system according to the exemplary embodiment of the present disclosure is applied; Fig. 2 is a block diagram showing an example of a control system of the Fig. 1 shows the vehicle shown; Fig. 3 is a diagram showing changes in torque of an internal combustion engine or output of the internal combustion engine during deceleration of the vehicle in a high-power mode and a low-power mode; Fig. 4 is a map for controlling the internal combustion engine in a first control mode, a second control mode and a low power mode; Fig. 5A is a flowchart showing a routine for selecting the control mode of the internal combustion engine based on a charge level, and Fig. 5B is a diagram showing threshold levels of the charge level; Fig. 6A is a flowchart showing a routine for selecting the control mode of the internal combustion engine based on an input power to the battery, and Fig. Figure 6B is a graph showing threshold levels of input power; Fig. 7A is a flowchart showing a routine for selecting the control mode of the internal combustion engine based on an output of the internal combustion engine, Fig. 7B is a time chart showing temporal changes in the input power, the output power of the internal combustion engine, and an operation of an accelerator pedal, and Fig. 7C is a map illustrating a determination of an operating point of the internal combustion engine during the execution of the Fig. 7A shows the routine shown; Fig. 8 is a flowchart showing a routine for selecting the control mode of the internal combustion engine based on a possible output torque of the second motor; Fig. 9A is a flowchart showing a routine for selecting the control mode of the internal combustion engine based on a required deceleration, and Fig. Figure 9B is a diagram showing thresholds of required delay; Fig. 10 is a flowchart showing a routine for selecting the control mode of the internal combustion engine depending on whether a B range is selected; Fig. 11A is a flowchart showing a routine for selecting the control mode of the internal combustion engine based on an operation of a brake pedal, and Fig. 11B is a diagram showing a threshold value of operation; Fig. 12A is a flowchart showing a routine for selecting the control mode of the internal combustion engine based on a release speed of a predetermined pedal in a one-pedal mode, and Fig. Figure 12B is a graph showing threshold values ​​of the release rate; Fig. 13A is a flowchart showing a routine for selecting the control mode of the internal combustion engine based on a road gradient, and Fig. 13B is a diagram showing threshold values ​​of road gradient; Fig. 14 is a schematic diagram showing another example of a structure of the hybrid vehicle to which the control system according to the exemplary embodiment of the present disclosure is applied; Fig. 15 is a flowchart showing a routine for selecting the control mode of the internal combustion engine of the Fig. 14 based on a possible output torque of the second motor; and Fig. 16 is a graph showing changes in engine torque or engine output when the engine is controlled in the first control mode when the hybrid vehicle is accelerated.

[0022] Hereinafter, preferred embodiments of the present disclosure are explained with reference to the accompanying drawings. Fig. 1 shows an example of a powertrain of a hybrid vehicle (hereinafter referred to simply as the “vehicle”) Ve to which the control system according to the exemplary embodiment of the present disclosure is applied. A prime mover of the vehicle Ve includes an internal combustion engine (in Fig. 1 referred to as ENG) 1, a first engine (in Fig. 1 referred to as MG1) 2 and a second engine (in Fig. 1 (referred to as MG2) 3. In the vehicle Ve, an output of the internal combustion engine 1 is distributed to the first motor 2 and drive wheels 5 via a power split mechanism 4. Electric power generated by the first motor 2 can be supplied to the second motor 3 to generate torque, and driving force generated by the second motor 3 can be supplied to the drive wheels 5.

[0023] The first motor 2 and the second motor 3 are each a motor generator, which operates not only as a motor to generate torque by supplying them with electric power, but also as a generator to generate electric power by supplying them with torque. For example, an AC motor such as a permanent magnet synchronous motor or an induction motor can be used as the first motor 2 and the second motor 3, respectively. The first motor 2 and the second motor 3 are each electrically powered by a battery (in Fig. 1 (referred to as BATT) 6. The rotational speed of the internal combustion engine 1 is controlled by the first motor 2, and the second motor 3 is operated as a motor by supplying it with the electricity generated by the first motor 2, so that the second motor 3 generates a driving force for driving the vehicle Ve.

[0024] Electricity generated by the first motor 2 and the second motor 3 is stored in the battery 6 as an electrical storage device. For example, a secondary battery such as a nickel-hydride battery, a lithium-ion battery, and a capacitor can be used as the battery 6. As described above, the first motor 2 and the second motor 3 are each connected to the battery 6. Therefore, the electricity generated by the first motor 2 can be stored in the battery 6, and the first motor 2 can be driven as a motor by supplying electricity from the battery 6 to the first motor 2. Similarly, the electricity generated by the second motor 3 can be stored in the battery 6, and the second motor 3 can be driven as a motor by supplying electricity from the battery 6 to the second motor 3.

[0025] The power split mechanism 4, as a single-pinion planetary gear, is arranged between the internal combustion engine 1 and the first motor 2, on the one hand, and the drive wheels 5, on the other, to transmit torque therebetween. The power split mechanism 4 includes a sun gear 7 as a reaction element, a ring gear 8 as an output element arranged concentrically with the sun gear 7, a plurality of pinions 10 arranged between the sun gear 7 and the ring gear 8, and a carrier 9 as an input element that supports the pinion 10 for rotation about its own axis and another axis.

[0026] The power split mechanism 4 is arranged coaxially with the internal combustion engine 1 and the first motor 2. Specifically, an output shaft 1a of the internal combustion engine 1 is connected to the carrier 9 of the power split mechanism 4, so that the output shaft 1a serves as an input shaft of the power split mechanism 4. To cool and lubricate the power split mechanism 4 and reduce the temperature of the first motor 2 and the second motor 3 resulting from iron loss and copper loss, an oil pump 11 is arranged on a side opposite the side of the power split mechanism 4 where the internal combustion engine 1 is located. Specifically, the carrier 9 of the power split mechanism 4 is also connected to a rotating shaft 11a of the oil pump 11, so that the oil pump 11 is driven by the internal combustion engine 1 to generate hydraulic pressure.

[0027] The first motor 2 is arranged between the oil pump 11 and the power split mechanism 4. In the first motor 2, a hollow rotor shaft 2b, which rotates integrally with a rotor 2a, is connected to a hollow rotating shaft of the sun gear 7 of the power split mechanism 4. The rotating shaft 11a of the oil pump 11 extends through the rotor shaft 2b and the sun gear 7 to be connected to the output shaft 1a of the internal combustion engine 1.

[0028] A first drive gear 12 as an external gear is integrally formed around the ring gear 8 of the power split mechanism 4 to serve as an output member, and a countershaft 13 is arranged parallel to a common rotational axis of the power split mechanism 4 and the first motor 2. A countershaft gear 14, which is diametrically larger than the first drive gear 12, is mounted on one end of the countershaft 13 (ie, the right side in Fig. 1) is adapted to be rotated integrally therewith, being in meshing engagement with the first drive gear 12, so that a torque transmitted from the first drive gear 12 is multiplied. A countershaft gear (ie, a final drive gear) 15 is thus fitted onto the further end of the countershaft 13 (ie, the left side in Fig. 1) is ensured to be rotated integrally therewith while being in meshing engagement with a differential ring gear (i.e., a final drive gear) 17 of a differential gear unit 16 as a final stage. Thus, the ring gear 8 of the power split mechanism 4 is connected to a drive shaft 5a and the drive gear 5 via an output line 18 including the first drive gear 12, the countershaft 13, the countershaft gear 14, the countershaft gear 15, and the differential ring gear 17.

[0029] In the drive train of the vehicle Ve, an output torque of the second motor 3 can be added to the torque supplied from the power split mechanism 4 to the drive shaft 5a. For this purpose, a rotor 3a of the second motor 3 is connected to a rotor shaft 3b extending parallel to the countershaft 13 to rotate integrally therewith, and a second drive gear 19 is fitted onto a front end of the rotor shaft 3b to rotate integrally therewith while being in meshing engagement with the countershaft gear 14. Thus, the ring gear 8 of the power split mechanism 4 is connected to the second motor 3 via the differential ring gear 17 and the second drive gear 19. That is, the ring gear 8 and the second motor 3 are respectively connected to the drive gear 5 via the differential ring gear 17 and the drive shaft 5a.

[0030] Since the prime mover of the vehicle Ve includes the internal combustion engine 1 and the motors 2 and 3, an operating mode of the vehicle Ve can be selected from a plurality of modes. A control system for selecting the operating mode of the vehicle Ve is described below with reference to Fig. 2. The opening degree of a throttle valve, the ignition timing of the internal combustion engine 1, and so on can be electrically controlled. The first motor 2 and the second motor 3 are each connected to an inverter 20, so that the first motor 2 and the second motor 3 can be selectively operated as a motor or a generator. As described above, the electricity generated by the first motor 2 and the second motor 3 can be stored in the battery 6, and the electricity can be supplied from the battery 6 to the first motor 2 and the second motor 3.

[0031] The internal combustion engine 1, the first motor 2, the second motor 3, the battery 6, the inverter 20, and so on are controlled by an electronic control unit (hereinafter abbreviated as the "ECU") 21 as a control device. The ECU 21 includes a microcomputer as its main component, and detection signals from a detector 22 and information signals from on-board circuits are transmitted to the ECU 21.The ECU 21 receives the detection signals from the detector 22, which includes an air flow sensor 22a that detects an air intake amount, an accelerator pedal sensor 22b that detects an operation of an accelerator pedal and a drive request, a brake sensor 22c that detects an operation of a brake pedal, an engine speed sensor 22d that detects a rotational speed of the output shaft 1a of the engine 1, an engine speed sensor 22e that detects rotational speeds of the first motor 2 and the second motor 3, a torque sensor 22f that detects torques of the engine 1 and the torques of the first motor 2 and the second motor 3, an SOC sensor 22g that detects a state of charge (hereinafter abbreviated as “SOC”) level of the battery 6, a vehicle speed sensor 22h that detects a speed of the vehicle Ve, and so on.Furthermore, a map for determining the operating mode, a map for determining an optimal fuel-efficient operating point of the internal combustion engine 1, a map for determining a required power, and so on are integrated into the ECU 21. The ECU 21 is configured to perform a calculation based on the signals received from the detector 22 and the pre-installed data such as the above-mentioned maps, and to transmit a calculation result in the form of a command or control signal. Optionally, a plurality of the ECUs may be provided in the vehicle Ve, as needed.

[0032] As described above, the operation mode of the vehicle Ve can be selected from a plurality of modes by controlling the engine 1, the first motor 2, and the second motor 3 by the ECU 21 with reference to the map that determines the operation mode based on a required driving force and a vehicle speed. Specifically, the operation mode of the vehicle Ve can be selected from a hybrid mode (hereinafter abbreviated as the "HV mode") in which the vehicle Ve is driven by the engine 1, and an electric vehicle mode (hereinafter abbreviated as the "EV mode") in which the vehicle Ve is driven by the first motor 2 and the second motor 3 while supplying electricity from the battery 6 to the motors 2 and 3.

[0033] According to conventional engine control in hybrid vehicles, when the initially depressed accelerator pedal is released, engine torque is promptly reduced to meet such a deceleration request, while engine speed is reduced by the first motor to reduce vibration and noise. However, if the torque or engine power is linearly reduced in response to the deceleration request, pollutant emissions may increase. In a gasoline engine, fuel is injected into cylinders according to air intake. Therefore, if the throttle valve is fully closed immediately upon the initially depressed accelerator pedal being released, pollutant emissions may increase. In this situation, in particular, air intake is abruptly reduced, thereby increasing an estimated air intake error.As a result, the fuel cannot be injected in an appropriate amount, and the air-fuel ratio may be inappropriately changed. To avoid such a disadvantage, the control system according to the exemplary embodiment is configured to change an engine torque and an engine speed (i.e., an output of the internal combustion engine) so as to prevent an increase in pollutant emissions during deceleration of the vehicle Ve.

[0034] Fig. Figure 3 is a graph showing a reduction in engine torque or engine power during vehicle deceleration. Fig. 3, the dashed line indicates the engine torque or power reduced by conventional control at a predetermined rate determined by taking into account vibrations and noises from gear rattles, and the solid line indicates the engine torque or power reduced in a first control mode at a rate lower than the predetermined rate of the conventional control determined by taking into account exhaust emission levels. In the following explanation, the above-mentioned conventional control is referred to as "low-power mode."

[0035] As it is in Fig. 3, in the conventional low-output mode shown by the dashed line, the engine torque or engine power is reduced when the accelerator pedal is released at the relatively larger rate when decelerating the vehicle Ve. In contrast, in the first control mode shown by the solid line, the engine torque or engine power is reduced when the accelerator pedal is released at the relatively smaller rate so as not to increase pollutant emissions. That is, although deceleration of the vehicle is started when the accelerator pedal is released, the internal combustion engine 1 is controlled independently of an operation of the accelerator pedal, such that the engine torque or engine power is gradually reduced.During deceleration of the vehicle Ve, an engine speed is controlled by the first motor 2, and a regenerative torque of the second motor 3 is transmitted as a braking torque to the drive wheels 5. Consequently, the battery 6 is charged with the electricity regenerated by the second motor 3.

[0036] Furthermore, in the first control mode, the internal combustion engine 1 is controlled to reduce fuel consumption. Specifically, the torque and speed of the internal combustion engine 1 are controlled for optimal fuel economy with reference to the map installed in the ECU 21. Fig. 4 is a map for determining an operating point of the internal combustion engine 1, which is regulated by a torque and a rotational speed of the internal combustion engine 1 during deceleration of the vehicle Ve in each control mode.

[0037] In the first control mode, a torque and a rotational speed of the internal combustion engine 1 are controlled so that the operating point of the internal combustion engine 1 is shifted along an optimal fuel consumption curve. Specifically, the optimal fuel consumption curve is determined by connecting optimal operating points of the internal combustion engine 1, which were found based on an experimental result, in a map that determines the operating point based on a torque and a rotational speed of the internal combustion engine 1. The internal combustion engine 1 can be operated in an optimal fuel-efficient manner by controlling the torque and the rotational speed of the internal combustion engine 1 to move the operating point of the internal combustion engine 1 to an intersection point between a constant output power curve of the engine power and the optimal fuel consumption curve in the Fig. 4. That is, a target rotational speed and a target torque can be determined based on the operating point at the above-mentioned intersection point. For example, the operating point of the internal combustion engine 1 can be shifted to a desired point by controlling the rotational speed of the internal combustion engine 1 by the first motor 2 while controlling the torque of the internal combustion engine 1 by controlling an opening degree of the throttle valve.

[0038] That is, in the first control mode, the internal combustion engine 1 can be operated in the most efficient manner while optimizing the emission characteristics and fuel efficiency. Accordingly, when the operating conditions of the battery 6, the first motor 2, and the second motor 3 are not restricted, the first control mode is selected to control the internal combustion engine 1. On the other hand, in the low power mode, the torque and speed of the internal combustion engine 1 (i.e., the engine power) are promptly reduced in response to a deceleration request, as shown in Fig. 4 is shown.

[0039] When the vehicle Ve is decelerating, it is advantageous to control the engine 1 in the first control mode. However, in the first control mode, the vehicle Ve is decelerated while maintaining an output power of the engine 1 in order to adjust the operating point of the engine 1 to the optimal fuel consumption curve. In this situation, the second motor 3 is required to generate a braking torque greater than the output torque of the engine 1, and thus, the amount of regenerated energy is increased. That is, if an SOC level of the battery 6 is higher than a predetermined level when controlling the engine 1 in the first control mode, this would result in overcharging of the battery 6. In this situation, an input power (Win) that can be stored in the battery 6 may be limited depending on a state of the battery 6.Furthermore, a power control unit (abbreviated as "PCU") including the inverter 20 and a converter would overheat depending on a condition. To avoid such disadvantages, according to the exemplary embodiment of the present disclosure, the control mode of the internal combustion engine 1 is selected according to the conditions of the battery 6, the first motor 2, and the second motor 3.

[0040] Examples of the routines for selecting the control mode of the internal combustion engine 1 depending on the states of the battery 6, the first motor 2 and the second motor 3 are shown in the Fig. 5A to 8. In particular, the Fig. 5A and Fig. 5B an example of the routine for selecting the control mode of the internal combustion engine 1 depending on a SOC level of the battery 6, show the Fig. 6A to 7C show examples of the routines for selecting the control mode of the internal combustion engine 1 depending on an input power (Win) that can be stored in the battery 6, and Fig. 8 shows an example of the routine for selecting the control mode of the internal combustion engine 1 depending on the states of the first motor 2, the second motor 3, and the PCU. These routines are repeated at predetermined intervals.

[0041] Fig. 5A shows the routine for selecting the control mode of the internal combustion engine 1 depending on an SOC level of the battery 6, and Fig. 5B shows a diagram showing the threshold levels of the SOC level of the battery 6. In step S1, it is determined whether the SOC level of the battery 6 is lower than a first threshold level. As shown in Fig. 5B, in order to limit damage to the battery 6, the SOC level of the battery 6 is controlled to fall between a lower limit level and an upper limit level. As explained further below, the control system according to the exemplary embodiment is configured to select the control mode of the engine 1 a plurality of times until the vehicle speed Ve is reduced to a target speed by repeating the routine for selecting the control mode of the engine 1 while, for example, observing the SOC level of the battery 6. For example, when the current routine is executed for the first time in response to the acceleration demand, it is determined in step S1 whether the SOC level of the battery 6 is lower than the first threshold level when the initially depressed accelerator pedal is released.If the SOC level of the battery 6 is lower than the first threshold level, so that the answer to step S1 is YES, the control system determines that sufficient capacity of the battery 6 is available. In this case, the routine proceeds to step S2 to select the first control mode and thereby control the internal combustion engine 1. Consequently, the internal combustion engine 1 is controlled to optimize the emission characteristics while regenerating energy.

[0042] In contrast, if the SOC level of the battery 6 is higher than the first threshold level, for example, when the accelerator pedal is released, so that the answer of step S1 is NO, the routine proceeds to step S3 to determine whether the SOC level of the battery 6 is lower than a second threshold level. In particular, as shown in Fig. 5B, the second threshold level is set to a level closer to the upper limit level than the first threshold level. If the SOC level of the battery 6 is equal to or higher than the first threshold level but lower than the second threshold level (first threshold level ≦ SOC < second threshold level), so that the answer of step S3 is YES, the routine proceeds to step S4 to select a second control mode for controlling the internal combustion engine 1.

[0043] In the second control mode, the engine 1 is controlled so that, during deceleration of the vehicle Ve, pollutant emissions are reduced while limiting a charge amount of the battery 6 (i.e., a regeneration amount) within a predetermined range, which is smaller than that in the first control mode. Specifically, in the second control mode, a change rate (i.e., a time change rate) of the output power of the engine 1 during deceleration of the vehicle Ve is faster than that in the second control mode, but slower than that in the low power mode. That is, the engine 1 can generate higher power in the first control mode and the second control mode compared to the low power mode. Accordingly, the first control mode and the second control mode correspond to the "high power mode" of the exemplary embodiment.

[0044] As it is in Fig. 4, in the second control mode, a torque and a rotational speed of the internal combustion engine 1 are controlled such that the operating point of the internal combustion engine 1 is shifted within the range enclosed by the dashed line, in which pollutant emissions can be reduced, along the diagonal arrow. It has been found that pollutant emissions are not significantly increased by reducing the rotational speed of the internal combustion engine 1 within the range enclosed by the dashed line, but are considerably increased by reducing the torque of the internal combustion engine 1 within the range enclosed by the dashed line. Therefore, in the second control mode, the torque of the internal combustion engine 1 is reduced at a rate lower than the rate of change in the low-power mode to suppress emissions of gaseous pollutants.In other words, in the second control mode, the torque and speed of the internal combustion engine 1 are controlled so that pollutant emissions are not increased. In the second control mode shown in . Fig. 4, the output of the engine 1 is reduced by reducing the rotational speed of the engine 1, thereby reducing the regeneration amount. Specifically, in the second control mode, the torque of the engine 1 is reduced at a substantially similar rate to the first control mode, but the rotational speed of the engine 1 is reduced at a greater rate than the rate of change in the first control mode. Therefore, in the second control mode, the regeneration amount can fall within the desired range while suppressing emissions of gaseous pollutants. As described above, in the second control mode, the output of the engine 1 is reduced during deceleration of the vehicle Ve at a smaller rate than the rate of change in the low-power mode.

[0045] Specifically, in the second control mode, the operating point of the internal combustion engine 1 is shifted in response to the deceleration operation so as to pass through a lowest point (ie, point B in Fig. 4). As described above, the control system is designed to select the control mode of the internal combustion engine 1 several times until the speed of the vehicle Ve is reduced to a target speed by repeating the routine for selecting the control mode of the internal combustion engine 1 while observing, for example, the SOC level of the battery 6. For example, in the Fig. 4, the operating point of the internal combustion engine 1 is at point A when the accelerator pedal is released. In this situation, if the SOC level of the battery 6 is between the first threshold level and the second threshold level, so that the second control mode is selected, during the first routine, the operating point of the internal combustion engine 1 is shifted from point A to the above-mentioned point B. Likewise, during the second or subsequent routine(s), the operating point of the internal combustion engine 1 is shifted within a further range further down (not shown), where pollutant emissions may also be reduced, while passing through the lowest point in a further range.

[0046] Otherwise, if the SOC level of the battery 6 is higher than the second threshold level, for example, when the accelerator pedal is released, so that the answer of step S3 is NO, the routine proceeds to step S5 to select the low power mode to control the engine 1. In this case, the SOC level of the battery 6 is close to the upper limit level, thereby promptly reducing the torque and speed of the engine 1 in the low power mode.

[0047] The following is an example of selecting the control mode of the internal combustion engine 1 based on an input power (Win) that can be stored in the battery 6, with reference to Fig. 6A and Fig. 6B explains.

[0048] Fig. 6A shows the routine for selecting the control mode of the internal combustion engine 1 depending on an acceptable value of the input power for the battery 6, where the input power (Win) can be calculated based on a SOC level and a temperature of the battery 6. For example, if the SOC level of the battery 6 is significantly high at a significantly low temperature or a significantly high temperature of the battery 6, an acceptable value of the input power (Win) for the battery 6 can be limited. Furthermore, lithium deposition can be caused if the battery 6 is charged in a state in which an electrolysis solution has coagulated locally in the battery 6. To prevent such lithium deposition, the acceptable value of the input power (Win) for the battery 6 can also be limited. The acceptable values ​​of the input power (Win) for the battery 6 are shown in Fig. 6B. As shown in Fig. As can be seen in Figure 6B, a first acceptable value is set when the input power (Win) for the battery 6 is limited, but the acceptable value of the input power (Win) for the battery 6 is relatively large. Conversely, a second acceptable value is set when the input power (Win) for the battery 6 is limited to a value smaller than the first acceptable value.

[0049] In the Fig. In the routine shown in Figure 6A, it is determined in step S10 whether the acceptable input power (Win) for the battery 6, for example, when the accelerator pedal is released, is greater than a first acceptable value. If the acceptable value of the input power (Win) for the battery 6 is greater than the first acceptable value, so that the answer of step S10 is YES, the control system determines that sufficient free capacity of the battery 6 is available. In this case, therefore, the routine proceeds to step S11 to select the first control mode for controlling the internal combustion engine 1.

[0050] In contrast, if the acceptable value of the input power (Win) for the battery 6 is less than the first acceptable value, so that the answer of step S10 is NO, the routine proceeds to step S12 to determine whether the acceptable value of the input power (Win) for the battery 6 is greater than the second acceptable value. If the acceptable value of the input power (Win) for the battery 6 is less than the first acceptable value but greater than the second acceptable value, so that the answer of step S12 is YES, the routine proceeds to step S13 to select the second control mode for controlling the internal combustion engine 1. In this case, the internal combustion engine 1 is controlled so that the regeneration amount is within the desired range while suppressing emissions of gaseous pollutants.

[0051] In contrast, if the acceptable value of input power (Win) for battery 6 is smaller than the second acceptable value, so that the answer of step S12 is NO, the routine proceeds to step S14 to select the low-power mode for controlling engine 1. In this case, the torque and speed of engine 1 are promptly reduced in the low-power mode because the acceptable value of input power (Win) for battery 6 is very small.

[0052] As described above, in the first control mode, the torque and speed of the internal combustion engine 1 are controlled to optimize fuel consumption. When the condition for selecting the first control mode is not permitted, it is advantageous to control the internal combustion engine 1 in the second control mode. Therefore, it is advantageous to select the first control mode or the second control mode preferably according to the currently acceptable value of the input power (Win) for the battery 6.

[0053] An example of the routine for selecting the control mode of the internal combustion engine 1 in accordance with the currently acceptable value of the input power (Win) for the battery 6 is shown in Fig. 7A. In step S20, it is determined whether the input power (Win) to the battery 6 when the operating point of the internal combustion engine 1 is set to the optimal fuel consumption curve in the first control mode is less than the currently acceptable value of the input power (Win) to the battery 6. As described above, the currently acceptable value of the input power (Win) to the battery 6 can be determined based on the temperature and the SOC level of the battery 6. If the input power (Win) to the battery 6 is less than the currently acceptable value of the input power (Win) to the battery 6 when controlling the internal combustion engine 1 in the first control mode, so that the answer of step S20 is YES, the control system determines that the internal combustion engine 1 can be controlled in the first control mode.In this case, therefore, the routine proceeds to step S21 to select the first control mode for controlling the internal combustion engine 1.

[0054] In contrast, if the input power (Win) to the battery 6 is greater than the currently acceptable value of the input power (Win) to the battery 6 when the engine 1 is controlled in the first control mode, so that the answer of step S20 is NO, the routine proceeds to step S22 to determine whether the input power (Win) to the battery 6 is less than the currently acceptable value of the input power (Win) to the battery 6 when the engine 1 is controlled in the second control mode. If the input power (Win) to the battery 6 is less than the currently acceptable value of the input power (Win) to the battery 6 when the engine 1 is controlled in the second control mode, so that the answer of step S22 is YES, the routine proceeds to step S23 to select the second control mode for controlling the engine 1.

[0055] In contrast, if the input power (Win) to the battery 6 is greater than the currently acceptable value of the input power (Win) to the battery 6 when controlling the engine 1 in the second control mode, so that the answer of step S22 is NO, the engine 1 cannot be controlled in either the first control mode or the second control mode. In this case, the routine proceeds to step S24 to select the low-power mode for controlling the engine 1. Consequently, in the low-power mode, the torque and speed of the engine 1 are promptly reduced.

[0056] Fig. Figure 7B shows an example of changes in the acceptable value of the input power (Win) for the battery 6 and the output power of the combustion engine 1 during the Fig. 7A is executed three times. In the Fig. In the example shown in Fig. 7B, the engine 1 is controlled in the first control mode during the execution of the first and second routines, and in the second control mode during the execution of the third routine. When the accelerator pedal is released at point t1, the first control mode is started to control the engine 1. Consequently, the battery 6 is charged by the electric power regenerated by operating the engine 1 in the first control mode, so that the acceptable value of the input power (Win) for the battery 6 is reduced. Specifically, a difference between the acceptable value of the input power (Win) for the battery 6, shown by the solid line, and the electric power regenerated by the output power of the engine 1, shown by the dashed line, is reduced at point t2.Finally, at point t3, the solid line representing the acceptable value of the input power (Win) for the battery 6 overlaps the dashed line representing the electric power regenerated by the output power of the internal combustion engine 1. Consequently, the control mode of the internal combustion engine 1 is shifted to the second control mode at point t3.

[0057] Fig. 7C shows a map similar to that shown in Fig. 4. As shown in Fig. 7C, when the accelerator pedal is released, the operating point of the engine 1 is shifted from point "a" toward point "b" within the range enclosed by the dashed line. Specifically, during the execution of the first routine, the first control mode is selected, so that the operating point is shifted along the optimal fuel consumption curve. Likewise, during the execution of the second routine, the operating point of the engine 1 is shifted from point "b" toward point "c" along the optimal fuel consumption curve. Eventually, the battery 6 is charged to the currently acceptable value, and the engine 1 can no longer be controlled in the first control mode, so the control mode is shifted to the second control mode.Consequently, the internal combustion engine 1 is controlled so that the operating point passes through the point "d" as a lowest point in the range corresponding to the third routine and enclosed by the dashed line. In this situation, when a required output of the internal combustion engine 1 cannot be achieved at the lowest point in the range corresponding to the third routine, the low-power mode is selected in the third routine. Furthermore, in order to prevent overcharging of the battery 6, it is advantageous to control the internal combustion engine 1 based on the acceptable value of the input power Win·(α<1) to the battery 6, which is calculated by multiplying the acceptable value by a predetermined safety factor.

[0058] The following explains an example of controlling the internal combustion engine 1 according to the states of the first motor 2, the second motor 3, the inverter 20, and so on. For example, if excessive current is supplied to only a specific phase or element of the inverter 20, the first motor 2 and the second motor 3 may be heated and thermally damaged. This limits the output power of the first motor 2 and the second motor 3. In this situation, for example, the second motor 3 cannot generate the required braking torque even if the first control mode is selected to control the internal combustion engine 1. In the powertrain of the vehicle Ve, an output shaft torque Tp can be expressed by the following equation of motion: Tp=Tm⋅Grm+1 / (1+ρ)⋅Te and an engine torque Te can be expressed as: Te=−(1+ρ) / ρ⋅Tg where Tg is a torque of the first motor 2, Tm is a torque of the second motor, ρ is a gear ratio between the sun gear 7 and the ring gear 8 of the power split mechanism 4, and Grm is a gear ratio of the second motor 3.

[0059] To decelerate the vehicle Ve, the torque Tp of the output shaft 1a must be reduced by less than zero. As described above, in the first control mode, the vehicle Ve is decelerated by the second motor 3 while the output power of the internal combustion engine 1 is maintained at a predetermined power. For this purpose, the second motor 3 must generate a braking torque that is greater than the torque Te of the internal combustion engine 1. An example of the routine for selecting the control mode of the internal combustion engine 1 depending on the state of the second motor 3 is shown in Fig. 8. In step S30, it is determined whether the second motor 3 is capable of generating the torque Tm that can satisfy the following inequality: Tm⋅Grm←1 / (1+ρ)⋅Te

[0060] For example, such a determination in step S30 may be made based on a temperature of the second motor 3 (or the first motor 2) and a state of the PCU. If the second motor 3 can generate the torque Tm that can satisfy inequality (3), so that the answer of step S30 is YES, the routine proceeds to step S31 to select the first control mode.

[0061] In this case, the vehicle Ve may be decelerated while energy is being regenerated. Therefore, if the answer of step S30 is YES, it is also possible to select the second control mode. In contrast, if the second motor 3 cannot generate the torque Tm that can satisfy inequality (3), so the answer of step S30 is NO, the routine proceeds to step S32 to select the low-power mode. In this case, the torque and speed of the engine 1 are promptly reduced.

[0062] For example, the second motor 3 cannot generate the torque Tm required to satisfy inequality (3) if the temperature of the second motor 3 is outside the predetermined range, the temperature of the PCU is too high, or a current supplied to the inverter 20 is too high. Therefore, the determination in step S30 can also be made based on the temperature of, for example, the second motor 3.

[0063] Thus, according to the exemplary embodiment, the control system is configured to select the first control mode to control the internal combustion engine 1 when the battery 6 can sufficiently receive the input power and the second motor 3 can generate a required torque. As described above, in the first control mode, the operating point of the internal combustion engine 1 is shifted along the optimal fuel consumption curve, and the air intake to the internal combustion engine 1 is gradually reduced compared to the low-power mode in which the speed and torque of the internal combustion engine 1 are promptly reduced. Therefore, the air intake for controlling an air / fuel ratio can be accurately estimated. For this reason, emissions of gaseous pollutants can be reduced.The control system is further configured to select the second control mode when the SOC level of the battery 6 is equal to or higher than the first threshold level but lower than the second threshold level, thereby limiting a charge amount within a desired range, and to select the low-power mode when the SOC level of the battery 6 is higher than the second threshold level, thereby reducing the output power of the internal combustion engine 1 to reduce regenerative energy. Therefore, overcharging of the battery 6 can be prevented, thus limiting damage to the battery 6.

[0064] Overcharging of the battery 6 can also be prevented by selecting the control mode of the internal combustion engine 1 in accordance with the acceptable input power (Win) for the battery 6.

[0065] The control system is further configured to select the control mode of the internal combustion engine 1 based on the fact that the second motor 3 is in a state where generation of the braking torque for decelerating the vehicle Ve is possible while maintaining the output torque of the internal combustion engine 1. For this reason, the control mode of the internal combustion engine 1 can be appropriately selected to reduce the emissions of gaseous pollutants and protect the battery 6 depending on the state of the second motor 3.

[0066] The control system according to the exemplary embodiment is further configured to select the control mode of the internal combustion engine 1 based on a required deceleration for reducing the speed of the vehicle Ve. Examples of routines for selecting the control mode of the internal combustion engine 1 in accordance with the required deceleration are described below with reference to Fig. 9A to 13B explained.

[0067] Fig. 9A shows an example of the routine for selecting the control mode of the internal combustion engine 1 in accordance with the required deceleration of the vehicle Ve in a driving range (hereinafter abbreviated as "D range"). In step S40, it is determined whether the required deceleration for reducing the speed of the vehicle Ve is less than a first threshold value. As shown in Fig. 9B, the first threshold is set to a relatively smaller value. Accordingly, if the required deceleration is less than the first threshold, so that the answer of step S40 is YES, the first control mode in which the torque and speed of the engine 1 are reduced relatively slowly can be selected. In this case, therefore, the first control mode selection routine proceeds to step S41.

[0068] In contrast, if the required deceleration is greater than the first threshold, so that the answer of step S40 is NO, the routine proceeds to step S42 to determine whether the required deceleration is less than a second threshold set to a value between the first threshold and a maximum deceleration. If the required deceleration is greater than the first threshold but less than the second threshold, so that the answer of step S42 is YES, it is necessary to decelerate the vehicle at a relatively greater rate, but it is beneficial to reduce emissions of gaseous pollutants. In this case, therefore, the routine proceeds to step S43 to select the second control mode.

[0069] In contrast, when the required deceleration is greater than the second threshold so that the answer of step S42 is NO, the routine proceeds to step S44 to select the low power mode, thereby promptly reducing the torque and speed of the engine 1.

[0070] Fig. 10 shows an example of the routine for selecting the control mode of the engine 1 depending on whether a so-called "B range" is selected. In the B range, for example, engine braking force generated by pumping loss of the engine 1 can be transmitted to the drive wheels 5. Therefore, when the accelerator pedal is released in the B range, a larger braking force is applied to the vehicle Ve compared to the D range. In this situation, therefore, the output of the engine 1 must be limited to a lower output during deceleration of the vehicle Ve, even if the first control mode or the second control mode is selected.For this reason, if the B range is currently selected to drive the vehicle Ve so that the answer of step S50 is YES, the routine proceeds to step S51 to select the low power mode and thereby promptly reduce the torque and speed of the engine 1.

[0071] In contrast, if the B range is not selected, so the answer of step S50 is NO, the routine proceeds to step S52 to select the first control mode or the second control mode in accordance with the above-explained parameter, such as the SOC level of the battery 6, etc. Alternatively, if the answer of step S50 is NO, it is also possible to select the control mode of the internal combustion engine 1 from the first control mode and the second control mode in accordance with the required deceleration.

[0072] The Fig. 11A and Fig. 11B is an example of the routine for selecting the control mode of the internal combustion engine 1 in accordance with an operation amount (i.e., one operation) of the brake pedal. When the brake pedal is operated by the driver, it means that the driver intends to generate a larger braking force to decelerate the vehicle Ve. In this situation, it is advantageous to stop the internal combustion engine 1 immediately. However, the driver may decelerate the vehicle Ve while changing an operation of the brake pedal to adjust a vehicle speed. Therefore, the control system according to the exemplary embodiment is further configured to select the first control mode or the second control mode to charge the battery 6 or reduce emissions when an operation of the brake pedal is less than a threshold.

[0073] In the Fig. 11A, it is determined in step S60 whether an operation amount Bs of the brake pedal is greater than a threshold value TBs. As shown in Fig. 11B, the threshold value TBs is set to a value that makes it possible to determine whether the driver intends to immediately stop the engine 1. If the brake pedal depression amount Bs is greater than the threshold value TBs, so that the answer of step S60 is YES, the routine proceeds to step S60 to select the low power mode, thereby promptly reducing the torque and speed of the engine 1.

[0074] In contrast, if the brake pedal depression amount Bs is less than the threshold TBs, so that the answer of step S60 is NO, the routine proceeds to step S60 to select the first control mode or the second control mode in accordance with the above-explained parameter, such as the SOC level of the battery 6, etc. Optionally, in addition to the threshold TBs for selecting the low-power mode, another threshold for selecting the second control mode may also be set.

[0075] A one-pedal mode in which the vehicle Ve is accelerated and decelerated by operating a predetermined pedal may be available in the vehicle Ve to which the control system according to the exemplary embodiment is applied. Fig. 12A and Fig. 12B shows an example of the routine for selecting the control mode of the internal combustion engine 1 depending on whether the one-pedal mode is selected. In the one-pedal mode, a required deceleration or deceleration jerk is regulated by a pedal release speed Vpr. Therefore, it is advantageous to select the control mode of the internal combustion engine 1 based on the pedal release speed Vpr. In the Fig. In the routine shown in Figure 12A, it is determined in step S70 whether the one-pedal mode is selected. For example, such a determination in step S70 may be made depending on whether a switch for selecting the one-pedal mode is closed. If the one-pedal mode is not selected, so that the answer of step S70 is NO, the routine proceeds to step S71 to maintain a normal pedal mode and thereby accelerate and decelerate the vehicle Ve using the accelerator pedal and the brake pedal.

[0076] Otherwise, if the one-pedal mode is selected so that the answer of step S70 is YES, the routine proceeds to step S72 to determine whether the pedal release speed Vpr is lower than a first threshold value TVpr1. As shown in Fig. 12B, the first threshold value TVpr1 is set to a relatively lower level. That is, when the pedal release speed Vpr is lower than the first threshold value TVpr1, so that the answer of step S72 is YES, a required deceleration is relatively small, so that the internal combustion engine 1 can be controlled so that the operating point is shifted along the optimal fuel consumption curve. In this case, therefore, the routine proceeds to step S73 to select the first control mode.

[0077] In contrast, when the pedal release speed Vpr is higher than the first threshold TVpr1, so that the answer of step S72 is NO, the routine proceeds to step S74 to determine whether the pedal release speed Vpr is lower than a second threshold TVpr2. Specifically, the second threshold TVpr2 is set to a higher level than the first threshold TVpr1. That is, when the pedal release speed Vpr is higher than the first threshold TVpr1 but lower than the second threshold TVpr2, so that the answer of step S74 is YES, a required deceleration is small enough to decelerate the vehicle Ve relatively slowly while reducing emissions of gaseous pollutants. In this case, therefore, the routine proceeds to step S75 to select the second control mode.In contrast, when the pedal release speed Vpr is higher than the second threshold TVpr2 so that the answer of step S74 is NO, the routine proceeds to step S76 to select the low power mode and thereby promptly reduce the torque and speed of the engine 1.

[0078] The Fig. 13A and Fig. 13B show an example of the routine for selecting the control mode of the internal combustion engine 1 in accordance with a downward slope θ with respect to a flat road. In the Fig. 13A, it is determined in step S80 whether the downward slope θ is greater than a first threshold slope Tθ1. As shown in Fig. As can be seen from Fig. 13B, the first threshold slope Tθ1 is set to a relatively larger negative value because the first threshold slope Tθ1 is a threshold of the downhill slope θ. When the downhill slope θ is greater than the first threshold slope Tθ1, so that the answer of step S80 is YES, the gradient of the road is relatively moderate, so that the internal combustion engine 1 can be controlled so that the operating point is shifted along the optimal fuel consumption curve. In this case, therefore, the routine proceeds to step S81 to select the first control mode.

[0079] In contrast, if the downhill slope θ is smaller than the first threshold slope Tθ1, so that the answer of step S80 is NO, the routine proceeds to step S82 to determine whether the downhill slope θ is greater than a second threshold slope Tθ2. Specifically, the second threshold slope Tθ2 is set to a smaller value than the first threshold slope Tθ1. That is, if the downhill slope θ is smaller than the first threshold slope Tθ1 but greater than the second threshold slope Tθ2, so that the answer of step S82 is YES, an expected deceleration of the vehicle Ve is still small enough to decelerate the vehicle Ve relatively slowly while reducing emissions of gaseous pollutants. In this case, therefore, the routine proceeds to step S83 to select the second control mode.In contrast, when the downward slope θ is smaller than the second threshold slope Tθ2 so that the answer of step S82 is NO, the routine proceeds to step S84 to select the low power mode and thereby promptly reduce the torque and speed of the engine 1.

[0080] For example, the downward slope θ can be expressed as a percentage (%) calculated based on a drop of the road in 100 m.

[0081] Thus, according to the exemplary embodiment, in the vehicle Ve, the control mode of the internal combustion engine 1 can also be selected in accordance with the required deceleration. Therefore, according to the exemplary embodiment, the internal combustion engine 1 can be controlled to reduce gaseous pollutant emissions and charge the battery 6 in the first control mode or the second control mode while the vehicle Ve is decelerating in accordance with the required deceleration.

[0082] Otherwise, when the torque and speed of the internal combustion engine 1 need to be reduced immediately, the low power mode is selected to reduce the torque and speed of the internal combustion engine 1 immediately.

[0083] Although the exemplary embodiments of the present disclosure are described above, it will be clear to those skilled in the art that the present disclosure is not limited to the exemplary embodiments described above, but various changes and modifications can be made within the scope of the present disclosure. For example, the control system according to the exemplary embodiment can also be applied to a Fig. 14 series hybrid vehicle. As shown in Fig. 14, a drive machine of the series hybrid vehicle Ve comprises an internal combustion engine (in Fig. 14 referred to as ENG) 23 as an internal combustion engine, a first engine (in Fig. 14 designated as MG1) 24 and a second engine (in Fig. 14 referred to as MG2) 25. The series hybrid vehicle Ve further includes the drive wheels 5, the battery 6, and the ECU 21. The first motor 24 may be not only a generator but also a motor generator, and the second motor 25 may be a motor generator. In the series hybrid vehicle Ve, the engine 23 is connected to the first motor 24 so that the first motor 24 can be driven as a generator to generate electricity. The second motor 25 is connected to the drive wheels 5, and the first motor 24 and the second motor 25 are electrically connected to each other through the battery 6. Therefore, the electricity generated by the first motor 24 can be supplied not only to the second motor 25 to drive the second motor 25 as a motor, but also to the battery 6 to charge the battery 6.

[0084] Fig. 15 shows an example of the routine for selecting the control mode of the internal combustion engine 23 of the series hybrid vehicle Ve depending on the states of the first motor 24, the second motor 25, and the PCU. In the series hybrid vehicle Ve, the motor torque Te supplied to the drive wheels 5 is zero, so that the series hybrid vehicle Ve can be decelerated by generating a regenerative torque Tm less than zero by the second motor 25. Accordingly, in step S90, it is determined whether the second motor 25 is allowed to generate the torque Tm less than zero when the first control mode or the second control mode is selected. If the answer of step S90 is YES, the routine proceeds to step S91 to select the first control mode or the second control mode in accordance with, for example, the SOC level of the battery 6.In this case, the torque and speed of the engine 23 are reduced while electricity is being regenerated. In contrast, if the answer to step S90 is NO, the routine proceeds to step S92 to select the low power mode, thereby promptly reducing the torque and speed of the engine 23.

[0085] Furthermore, the first control mode may also be selected to control the engine 1 when the vehicle Ve is accelerated. When the vehicle Ve is accelerated in a conventional manner, the speed and torque of the engine 1 are promptly increased in response to an operation of the accelerator pedal, as shown by the dashed line in Fig. 16. In contrast, when the vehicle Ve is accelerated while the engine 1 is controlled in the first control mode, the speed and torque of the engine 1 are increased relatively slowly, as shown by the solid line in Fig. 16. In this case, a deficit in driving force is compensated by reducing the increase rates of speed and torque of the internal combustion engine 1 by operating the second motor 3 as a single motor. Consequently, the vehicle Ve can be accelerated in an optimal fuel-efficient manner while reducing emissions of gaseous pollutants.

Claims

[1] Control system for a hybrid vehicle (Ve), comprising: an internal combustion engine (1); a first motor (2) which controls a rotational speed of the internal combustion engine (1); a second motor (3) which applies a braking torque to drive wheels (5) when energy is regenerated; and an electrical storage device (6) electrically connected to the first motor (2) and the second motor (3), wherein the control system is designed to decelerate the hybrid vehicle (Ve) by controlling the second motor (3) to generate the braking torque and controlling the first motor (2) to reduce the speed of the internal combustion engine (1), characterized by , that: the control system comprises a control device (21) which controls the internal combustion engine (1), the control device (21) is designed to select a control mode of the internal combustion engine (1) from: a low-power mode in which the hybrid vehicle (Ve) is decelerated in response to a deceleration operation by reducing a torque and a power of the internal combustion engine (1) at a predetermined rate and simultaneously generating the braking torque by the second motor (3); and a high-power mode in which the hybrid vehicle (Ve) is decelerated in response to a deceleration operation by reducing the torque and power of the internal combustion engine (1) at a rate lower than the predetermined rate of the low-power mode and simultaneously generating the braking torque by the second motor (3). [2] A control system for the hybrid vehicle (Ve) according to claim 1, wherein the high-performance mode comprises: a first control mode in which the hybrid vehicle (Ve) is decelerated while the torque and the speed of the internal combustion engine (1) are reduced so that an operating point of the internal combustion engine (1) is shifted along an optimal fuel consumption curve; and a second control mode in which the hybrid vehicle (Ve) is decelerated while reducing a torque of the engine (1) at a same rate as in the first control mode, reducing the speed of the engine (1) at a greater rate than in the first control mode, and reducing the power of the engine (1) at a smaller rate than in the low power mode, so as to reduce emissions. [3] A control system for the hybrid vehicle (Ve) according to claim 2, wherein the control device (21) is further configured to select the control mode of the internal combustion engine (1) based on a charge level of the electrical storage device (6) or an acceptable value of input power (Win) for the electrical storage device (6) when the vehicle (Ve) is decelerated. [4] Control system for the hybrid vehicle (Ve) according to claim 3, wherein the control device (21) is further designed to to select the first control mode when the charge level of the electrical storage device (6) is lower than a first threshold level, to select the second control mode when the charge level of the electrical storage device (6) is higher than the first threshold level but lower than a second threshold level, and to select the low power mode when the charge level of the electrical storage device (6) is higher than the second threshold level. [5] Control system for the hybrid vehicle (Ve) according to claim 3, wherein the control device (21) is further designed to to select the first control mode when the acceptable value of the input power (Win) for the electrical storage device (6) is greater than a first acceptable value, to select the second control mode when the acceptable value of the input power (Win) for the electrical storage device (6) is less than the first acceptable value but greater than a second acceptable value, and to select the low power mode when the acceptable value of the input power (Win) for the electrical storage device (6) is less than the second acceptable value. [6] Control system for the hybrid vehicle (Ve) according to claim 3, wherein the control device (21) is further designed to to determine whether the input power (Win) for the electrical storage device (6) is less than a currently acceptable value of the input power (Win) for the electrical storage device (6) when the internal combustion engine (1) is controlled in the first control mode, to determine whether the input power (Win) for the electrical storage device (6) is less than a currently acceptable value of the input power (Win) for the electrical storage device (6) when the internal combustion engine (1) is controlled in the second control mode, to select the first control mode when the input power (Win) for the electrical storage device (6) is less than the currently acceptable value of the input power (Win) for the electrical storage device (6) and the internal combustion engine (1) is controlled in the first control mode, to select the second control mode when the input power (Win) for the electrical storage device (6) is greater than the currently acceptable value of the input power (Win) for the electrical storage device (6) and the internal combustion engine (1) is controlled in the first control mode, but is less than the input power (Win) for the electrical storage device (6) when the internal combustion engine (1) is controlled in the second control mode, and to select the low power mode when the input power (Win) for the electrical storage device (6) is greater than the currently acceptable value of the input power (Win) for the electrical storage device (6) and the internal combustion engine (1) is controlled in the second control mode. [7] A control system for the hybrid vehicle (Ve) according to any one of claims 1 to 6, wherein the control device (21) is further configured to determine whether the vehicle (Ve) can be decelerated in the high-power mode in response to the deceleration operation using an equation of motion in which a torque (Tm) of the second motor (3) and a torque (Te) of the internal combustion engine (1) are used as parameters. [8] Control system for the hybrid vehicle (Ve) according to one of claims 3 to 7, wherein the control device (21) is further designed to can select the control mode of the internal combustion engine (1) based on a required deceleration including a shift range, an operation amount (Bs) of a brake pedal, an operation speed of a predetermined pedal in a one-pedal mode, and a road gradient with respect to a flat road, to select the first control mode or the second control mode when a predetermined condition of the required deceleration is met, and to select the low power mode when the predetermined condition of the required deceleration is not met. [9] Control system for the hybrid vehicle (Ve) according to one of claims 1 to 8, wherein the hybrid vehicle (Ve) further comprises a power split mechanism (4) which splits an output power of the internal combustion engine (1) between an output element (12) and the first motor (2), the power split mechanism (4) comprises a planetary gear unit having an input element (9) connected to the internal combustion engine (1), a reaction element (7) connected to the first motor (2), and an output element (8) connected to the output element (12), and the second motor (3) is connected to a power transmission path between the drive wheels (5) and the output element (12).

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