Hybrid vehicles

Abstract

To enable an engine to perform the fundamental thermal efficiency and performance of the engine quickly and sufficiently when changing an operating state during an operation mode to travel on engine drive force.SOLUTION: In a hybrid vehicle having an engine 10 for supplying drive force for travel and rotary electric machines 30, 40 for supplying drive force for travel, the engine 10 is an auxiliary chamber-type engine, and includes, as transition control when changing an operation state from a first operating point to a second operating point during an operation mode to travel on drive force of the engine 10: a firing stop step to stop ignition and fuel injection of the engine 10 while operating at the first operating point; a motoring step to reach the second operating point as target by drive force of the rotary electric machines 30, 40; and a firing start step to start firing on the engine 10 with an air volume and a fuel volume corresponding to the second operating point. Further, in the transition control, a fuel injection volume from a direct injection-type fuel injection device is decreased than in starting the engine.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to hybrid vehicles. [Background technology]

[0002] Lean-burn engines have been proposed in the past, which burn a mixture with a leaner fuel ratio (excess air relative to fuel) than the stoichiometric air-fuel ratio. To achieve better combustion of this lean mixture, a pre-chamber engine has been proposed, which has a main combustion chamber and a pre-chamber as combustion chambers. In a pre-chamber engine, a communication passage is provided in the partition wall separating the main and pre-chambers. A mixture formed by fuel injected into the main combustion chamber is supplied to the pre-chamber through the communication passage and ignited by a spark plug in the pre-chamber. When a flame is formed in the pre-chamber, the flame propagates to the main combustion chamber through the communication passage and ignites the mixture in the main combustion chamber. This allows the engine to operate at a leaner air-fuel ratio, which is believed to improve fuel economy (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4389777 [Patent Document 2] International Publication No. 2020 / 196206 Summary of the Invention [Problem to be solved by the invention]

[0004] In engine control of a hybrid vehicle, for example, consider a situation where the operating state is changed during a driving mode in which the vehicle is driven by the engine's driving force. That is, the current operating state of the engine speed and engine load (referred to as a first operating point) is transitioned to another operating state of the engine speed and engine load (referred to as a second operating point). While the engine remains firing, various parameters, such as ignition control, fuel injection control, variable valve timing control, and exhaust gas recirculation control, are simultaneously adjusted to approach the target operating point. Such control to change the operating point (transient control) involves numerous maps and control conditions, resulting in various physical delays (time lags) during each process. This results in a problem in that the engine's inherent thermal efficiency and performance cannot be fully utilized during transient control.

[0005] Therefore, the object of this invention is to enable a hybrid vehicle to quickly and fully demonstrate the engine's inherent thermal efficiency and performance when changing the operating state during an operating mode in which the vehicle runs using the engine's driving force. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a hybrid vehicle equipped with an engine that supplies driving force for running and a rotating electric machine that supplies driving force for running, wherein the engine comprises a main chamber that is surrounded by the inner circumferential surface of a cylinder, the inner surface of a cylinder head, and the top surface of a piston, an auxiliary chamber that is separated from the main chamber and is formed at an end of the main chamber on the cylinder head side, a combustion chamber equipped with a communication passage that communicates the main chamber with the auxiliary chamber, an injection device that supplies fuel to the combustion chamber, an ignition device that ignites the air-fuel mixture in the auxiliary chamber, and a direct injection fuel injection device that supplies fuel into the auxiliary chamber, and the vehicle runs by the driving force of the engine. The hybrid vehicle includes, as transient control when changing the operating state from a first operating point to a second operating point different from the first operating point during an operating mode in which the engine is operated at the first operating point, a firing stop process for stopping ignition and fuel injection of the engine operating at the first operating point, a motoring process for reaching the target second operating point by the driving force of the rotating electric machine, and a firing start process for starting firing of the engine with an air amount and a fuel amount corresponding to the second operating point, and during the transient control, the amount of fuel injected by the direct injection fuel injection device is reduced compared to when the engine was started.

[0007] In addition, the firing start stroke can be configured to adjust the opening of a throttle valve provided in the intake passage of the engine to a predetermined opening corresponding to the second operating point, and based on the adjusted air amount, inject an amount of fuel corresponding to the second operating point and ignite the fuel using an ignition device.

[0008] The system may also include an accelerator position detection means for detecting the amount of accelerator depression and a battery remaining capacity detection means for detecting the remaining capacity of the electricity stored in the battery, and as the second operating point, if the remaining capacity of the battery is equal to or greater than a predetermined value and the amount of accelerator depression is equal to or greater than a predetermined amount, a maximum thermal efficiency point is selected from among pre-calibrated operating points, and if the amount of electricity consumed per unit time of motoring corresponding to the maximum thermal efficiency point in the motoring stroke is greater than a predetermined amount, or if the engine output in the firing start stroke is insufficient at the maximum thermal efficiency point, another operating point having a higher rotation speed or load than the maximum thermal efficiency point may be selected as the second operating point.

[0009] Further, when the engine is in a cold state, a configuration can be adopted in which an operating point at which the motoring rotation speed in the motoring stroke is less than a predetermined rotation speed is set as the second operating point.

[0010] In each of these aspects, a configuration can be adopted in which, during the firing start stroke, fuel increase control is performed to increase the amount of fuel injected by the direct injection fuel injection device within a predetermined number of cycles from the initial explosion, the higher the engine speed.

[0011] In addition, during the firing start stroke, a configuration can be adopted in which the higher the engine speed, the more increased the ignition energy per ignition is for a predetermined number of cycles from the initial explosion, or ignition is strengthened by performing multiple ignitions during one combustion cycle.

[0012] An exhaust passage extending from the combustion chamber is provided with an exhaust purification device that purifies harmful components in the exhaust gas, and if, during the firing start stroke, the temperature of the exhaust purification device is lower than a predetermined temperature and the purification performance of the exhaust purification device is insufficient, ignition timing retard control is performed to retard the ignition timing of the ignition device, and ignition enhancement control is performed to increase the ignition energy per ignition or to perform ignition multiple times during one combustion cycle. [Effects of the Invention]

[0013] According to the present invention, when the operating state of a hybrid vehicle is changed during an operating mode in which the vehicle runs using the driving force of the engine, the engine's inherent thermal efficiency and performance can be exhibited early and sufficiently. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a longitudinal cross-sectional view of a pre-combustion chamber engine. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Figure 3A] FIG. 2 is a vertical cross-sectional view showing the combustion state of a pre-combustion chamber engine. [Figure 3B] FIG. 2 is a vertical cross-sectional view showing the combustion state of a pre-combustion chamber engine. [Figure 3C] FIG. 2 is a vertical cross-sectional view showing the combustion state of a pre-combustion chamber engine. [Figure 4] FIG. 4 is a graph showing the control of the present invention. [Figure 5] FIG. 4 is a graph showing the control of the present invention. [Figure 6] 3 is a flowchart showing the control of the present invention. [Figure 7] 1 is a schematic diagram showing an example of a hybrid vehicle according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described with reference to the drawings. This embodiment is a hybrid vehicle 60 (hereinafter simply referred to as vehicle 60). The main parts of an engine 10 mounted on vehicle 60 are shown in FIGS.

[0016] The vehicle 60 includes a battery 50 that is used primarily as a power source for traveling, and two rotating electric machines 30, 40. One of the rotating electric machines 30 (hereinafter referred to as the first rotating electric machine 30) functions as a starter, and the engine 10 starts when the first rotating electric machine 30 operates. The other rotating electric machine 40 (hereinafter referred to as the second rotating electric machine 40) is a motor that supplies driving force for traveling. The first rotating electric machine 30 also functions as a generator that generates electricity using the driving force of the engine 10 (see FIG. 7).

[0017] The vehicle 60 is a hybrid vehicle that has three drive modes: an electric drive mode (EV mode), a series drive mode, and a parallel drive mode. An electronic control unit (ECU) 20 provided in the vehicle 60 selects the optimum drive mode depending on the current state and drive condition of the vehicle 60, the driver's request, etc. The engine 10, the first rotating electric machine 30, the second rotating electric machine 40, etc. are controlled depending on the selected drive mode. In the embodiment, the vehicle 60 is assumed to be a plug-in hybrid car that can charge the battery 50 directly (external charging) using a plug from a household outlet or the like.

[0018] The first rotating electric machine 30 is a motor-generator that functions both as an electric motor (motor) and as a generator. When starting the engine 10, the first rotating electric machine 30 functions as a starter electric motor. At this time, the first rotating electric machine 30 uses electric power from the battery 50 or a separately installed auxiliary battery. Furthermore, when the engine 10 is running, the first rotating electric machine 30 generates electric power using the driving force of the engine 10. The electric power generated by the first rotating electric machine 30 is supplied to the second rotating electric machine 40, the battery 50, etc. The rotating shaft of the first rotating electric machine 30 is connected to the crankshaft of the engine 10 via an endless member such as a belt, gears, etc. During operation of the engine 10, the first rotating electric machine 30 is normally rotated in conjunction with the rotation of the crankshaft.

[0019] The second rotating electric machine 40 is provided as a drive source for propelling the vehicle 60. The second rotating electric machine 40 is driven using electric power stored in the battery 50 and electric power generated by the first rotating electric machine 30. As shown in FIG. 7 , there are examples in which only one second rotating electric machine 40 is disposed on the front side (front motor example), and examples in which one is disposed on the front side and one on the rear side, and the number and locations of the second rotating electric machine 40 vary. The second rotating electric machine 40 also functions as a generator that generates regenerative electric power mainly during coasting. The second rotating electric machine 40 is a high-output motor, and powerfully drives the vehicle 60 using a large-capacity battery 50 or the like as a power source.

[0020] A control unit (not shown) including an inverter that converts DC current and AC current is provided between the first rotating electric machine 30, the second rotating electric machine 40 and the electronic control unit 20. The rotation speeds of the first rotating electric machine 30 and the second rotating electric machine 40 when they are driven are controlled by the electronic control unit 20 via the inverter.

[0021] The engine 10 is a gasoline engine. Depending on the driving mode, the rotation of the crankshaft of the engine 10 is switched between a state in which it is transmitted to the drive wheels via a torque converter, a continuously variable transmission, a clutch, a differential, etc., and a state in which the transmission is cut off.

[0022] The battery 50 is a high-voltage power supply that can store (charge) the electric power generated by the first rotating electric machine 30 and the electric power regenerated by the second rotating electric machine 40, and can discharge the stored electric power. The battery 50 is used mainly as a power supply that supplies electric power for traveling. In this embodiment, the battery 50 is compatible with a plug-in hybrid car and can be charged (normal charging) from an external power source to the vehicle, for example, a household AC power source, or from a high-voltage DC power source (rapid charging).

[0023] The vehicle 60 is equipped with a steering wheel, a brake pedal, an accelerator pedal, and the like, which are operated by the driver. The brake pedal is provided with a brake sensor that detects the force with which the driver presses the brake pedal. The accelerator pedal is also provided with an accelerator position sensor (accelerator position detection means) that detects the amount of accelerator depression by the driver. Brake information detected by the brake sensor and accelerator information detected by the accelerator position sensor are sent to the electronic control unit 20. The vehicle 60 is also equipped with a vehicle speed sensor that is provided on the axle or the like and detects the traveling speed of the vehicle 60. Vehicle speed information detected by the vehicle speed sensor is also sent to the electronic control unit 20.

[0024] The vehicle 60 is also provided with an engine speed sensor that detects the speed of the engine 10, speed sensors that detect the speeds of the first rotating electric machine 30 and the second rotating electric machine 40, a voltage sensor that detects the cell voltage of the battery 50, and a current sensor that detects the current of the battery 50. The vehicle 60 is also provided with a water temperature sensor that detects the temperature of the coolant for the engine 10 and an oil temperature sensor that detects the temperature of the engine oil. Information from these sensors is also sent to the electronic control unit 20.

[0025] The electronic control unit 20 includes an engine control unit 21 that mainly controls the engine 10, and a vehicle control unit 22 that controls the operation of the entire hybrid vehicle. The electronic control unit 20 is a collection of electronic control devices (computers) that control various devices equipped in the vehicle 60. Inside it are built-in interfaces, processors, memories, etc., which are connected to each other via a bus. The contents of the controls executed by the engine control unit 21 and the vehicle control unit 22 are stored in advance in the memory, and new data is stored as the control progresses, and this data is used for subsequent control.

[0026] Among the driving modes set in the electronic control unit 20, the electric driving mode is a driving mode in which the vehicle 60 is operated (traveled) solely by the driving force of the second electric rotating machine 40, while the engine 10 and the first electric rotating machine 30 are stopped. Conditions for selecting the electric driving mode include, for example, when the amount of electric power stored in the battery 50 is equal to or greater than a predetermined value and the speed (vehicle speed) of the vehicle 60 is less than a predetermined speed. When the electric driving mode is selected, the engine 10 and the first electric rotating machine (motor-generator) 30 are not operating, and the clutch between the crankshaft of the engine 10 and the power transmission path leading to the drive wheels is disengaged. The electric power stored in the battery 50 is evaluated, for example, by the "state of charge," which is the percentage of the battery remaining after subtracting the amount of discharged electricity from the fully charged state of the battery. This remaining battery capacity, "state of charge," is calculated by "remaining capacity (Ah) / fully charged capacity (Ah) × 100." As described above, the electronic control unit 20 includes a remaining battery capacity detection means for detecting the remaining capacity of the electric power stored in the battery, that is, the remaining battery capacity.

[0027] The series traveling mode is a traveling mode in which the first rotating electric machine 30 is operated by the driving force of the engine 10 to generate electricity, and the generated electricity is used to operate (travel) the vehicle 60 with the second rotating electric machine (front motor) 40. At this time, in addition to the electricity generated by the first rotating electric machine (motor-generator) 30, electricity from the battery 50 may also be used. Conditions for selecting the series traveling mode include, for example, when the amount of electricity stored in the battery 50 is less than a predetermined value and when the vehicle speed is less than a predetermined vehicle speed. When the series traveling mode is selected, the engine 10 and the first rotating electric machine (motor-generator) 30 operate, but the clutch between the crankshaft of the engine 10 and the power transmission path leading to the drive wheels is disengaged.

[0028] The parallel driving mode is a driving mode in which the vehicle 60 is operated (driven) by the driving force of the engine 10, and the second rotating electric machine (front motor) 40 assists in the operation (driving) of the vehicle 60 as needed. The parallel driving mode is set at a vehicle speed at which energy can be extracted from the engine 10 with high efficiency, i.e., when the vehicle is mainly traveling at high speeds. In the parallel driving mode, the engine 10 is fired, and the vehicle 60 is driven mainly by the driving force of the engine 10, while supplementarily using the driving force of the second rotating electric machine (front motor) 40. Conditions for selecting the parallel driving mode include, for example, the vehicle speed being equal to or higher than a predetermined vehicle speed, the driver performing a sudden acceleration operation, or an increase in the load on the air conditioner or other auxiliary equipment. The parallel driving mode is selected when any of these conditions is met.

[0029] If the engine 10 is stopped (not in operation) when switching from electric driving mode to series driving mode or from electric driving mode to parallel driving mode, the stopped engine 10 will be started (operated). In other words, in such cases, switching from electric driving mode to series driving mode or from electric driving mode to parallel driving mode is performed after passing through engine start mode.

[0030] The engine 10 equipped in the vehicle 60 of this embodiment is an engine with a pre-combustion chamber. FIGS. 1 and 2 show the main parts of one cylinder 2 of the engine 10. The engine 10 is equipped with an intake passage (intake port) 5 that sends air into the combustion chamber C, an exhaust passage (exhaust port) 6 that is led out from the combustion chamber C, and an injector 9 that supplies fuel to the combustion chamber C. An opening 5a of the intake passage 5 to the combustion chamber C is opened and closed by an intake valve 7. An opening 6a of the exhaust passage 6 to the combustion chamber C is opened and closed by an exhaust valve 8. In this embodiment, the injector 9 is equipped with both a direct injection fuel injector 9a that injects fuel directly into the combustion chamber C to supply fuel to the pre-combustion chamber 11, and a port injection fuel injector 9b that injects fuel into the intake passage 5 to supply fuel to the main combustion chamber 1. The figures show only components and means directly related to the present invention, and other components are omitted. The number of cylinders provided in engine 10 can be freely set according to the specifications of vehicle 60 and engine 10, and may be, for example, three cylinders, four cylinders, or any other number of cylinders.

[0031] As shown in Figure 1, combustion chamber C includes a main chamber 1, which is surrounded by the inner peripheral surface 2a of cylinder (cylinder block) 2, the inner surface (lower surface) of cylinder head 13, and the top surface 3a of piston 3; an auxiliary chamber 11, which is separated from the main chamber 1 and is formed at the end of main chamber 1 on the cylinder head 13 side; a partition wall 14 separating main chamber 1 from auxiliary chamber 11; and a communication passage 12 consisting of a small hole that penetrates partition wall 14. This communication passage 12 connects the space of main chamber 1 to the space of auxiliary chamber 11. In addition, an ignition device 4 is provided in auxiliary chamber 11, which ignites the air-fuel mixture in auxiliary chamber 11 by generating an electric spark.

[0032] To explain the operating state of the engine 10, first, as shown in FIG. 3A, air is introduced into the main combustion chamber 1 through the intake passage 5, and a lean mixture is formed in the main combustion chamber 1 by the injection of fuel from the injector 9. As shown in FIG. 3B, the lean mixture is forced from the main combustion chamber 1 into the auxiliary combustion chamber 11 during the compression stroke in which the piston 3 rises. Then, as shown in FIG. 3C, a spark is generated at the electrode 4a of the ignition device 4, igniting the mixture introduced into the auxiliary combustion chamber 11. When the mixture is ignited in the auxiliary combustion chamber 11, the resulting flame is injected into the main combustion chamber 1 through the connecting passage 12, creating a high-speed flame. This flame promotes combustion even when the mixture is lean (including when a large amount of exhaust gas recirculation gas is introduced). The burned gas is discharged to the outside through the exhaust passage 6 leading from the combustion chamber C. The exhaust passage 6 leads to an exhaust pipe 15 extending toward the rear of the vehicle body, and the exhaust pipe 15 is provided with an exhaust purification device 16 that purifies harmful components in the exhaust gas, and a muffler 17 (see FIG. 7). Before and after the exhaust purification device 16, sensors that detect the amounts and ratios of various components contained in the exhaust gas and a sensor (temperature sensor) that detects the temperature of the exhaust purification device 16 are provided as necessary. Information obtained by these sensors is sent to an electronic control unit 20.

[0033] The engine 10 is controlled to achieve a full lean burn across the entire operating range, based on a lean mixture with a lower fuel ratio (lean fuel) than the theoretical air-fuel ratio (A / F = 14.7). The air-fuel ratio is the air / fuel ratio, and is expressed as a dimensionless quantity obtained by dividing the air mass by the fuel mass. The electronic control unit 20 has the function of detecting or estimating the air-fuel ratio in the auxiliary combustion chamber 11 and the air-fuel ratio of the entire combustion chamber C, based on information from sensors around the engine 10.

[0034] Next, transient control will be described.

[0035] Transient control is a transition control that changes the operating state during a driving mode in which the vehicle travels using the driving force of the engine 10. The transient control controls a transition from a current operating state of the engine speed and engine load (referred to as a first operating point) to another operating state of the engine speed and engine load (referred to as a second operating point). Conventional transient control controls the engine 10 to approach a target operating point by simultaneously adjusting various parameters while the engine 10 is firing, resulting in a physical delay (time lag) in the control. For example, as shown in FIG. 4, when transitioning from operating point A to operating point C, the transition is first performed gradually over time from operating point A to operating point B, and then from operating point B to operating point C. This is because, for example, when controlling a variable valve timing mechanism, there is an upper limit to the degree of change in crank angle per unit time, and also when controlling ignition timing, there is an upper limit to the degree of change in crank angle per unit time. For this reason, although it is originally desired to shift to an operating point where the engine 10 has the highest thermal efficiency, there are cases where it is necessary to shift to another operating point that does not reach the highest thermal efficiency point.

[0036] However, in the present invention, calibration is performed on the vehicle 60 around anticipated operating points in advance, and the behavior of the engine 10 at those operating points is examined to pre-store the optimal control parameters for each operating point. During transient control from one operating point to another, a method is adopted in which firing of the engine 10 is temporarily stopped, the load on the engine 10 is reduced, and the engine 10 is assisted by motoring to reach the target operating point, and then firing of the engine 10 is restarted with the preset optimal control parameters. This eliminates the time lag during the processing of conventional transient control, and immediately after transient control, the engine 10 can maximize its inherent thermal efficiency and performance.

[0037] Transient control when shifting from operating point A (corresponding to the first operating point) to operating point B (corresponding to the second operating point) shown in FIG. 5 will be described. When a command to change from operating point A to operating point B is received, the control proceeds from step S1 to step S2 shown in FIG. 6, where ignition and fuel injection of the engine 10 are stopped (firing is stopped). Stopping firing of the engine 10 reduces the engine load, and at the same time, the engine 10 is driven to the target operating point B by the driving force of the second rotating electric machine (front motor) 40. During this time, the crankshaft of the engine 10 continues to rotate (driven by the second rotating electric machine 40) as the vehicle travels, but firing is stopped (step S3). Thereafter, the throttle opening is adjusted to a predetermined opening corresponding to operating point B by control of the engine 10 (step S4). Based on the adjusted air amount, a fuel amount corresponding to operating point B is injected, and firing of the engine 10 is started at an air-fuel ratio corresponding to operating point B (step S5). The same applies to transient control when transitioning from operating point B (corresponding to the first operating point) to operating point C (corresponding to the second operating point). Furthermore, transient control from operating point C (corresponding to the first operating point) to operating point B (corresponding to the second operating point) and from operating point B (corresponding to the first operating point) to operating point A (corresponding to the second operating point) can be performed in the same manner as above. These controls are performed by control means provided in electronic control unit 20.

[0038] Here, the firing start process is performed by adjusting the opening of the throttle valve 18 (see Figure 1) provided in the intake passage 5 of the engine 10 to a predetermined opening corresponding to the second operating point, and then injecting the amount of fuel corresponding to the second operating point based on the adjusted air amount, and igniting the fuel by the ignition device.

[0039] By implementing such control, it is no longer necessary to change the operating point while simultaneously adjusting various parameters, such as ignition control, fuel injection control, variable valve timing mechanism control, and exhaust gas recirculation control. This eliminates the need to consider the connection between operating points, allowing the engine's inherent thermal efficiency and performance to be fully utilized. This improves robustness, i.e., the ability to maintain stable performance under various operating conditions. This effect is particularly pronounced when the vehicle 60 is equipped with a high-output motor, such as the plug-in hybrid car of the embodiment, and an engine that performs full-range lean burn (performing lean burn throughout the entire operating range) without using an exhaust gas recirculation device, particularly a hybrid vehicle 60 equipped with a pre-chamber engine.

[0040] During this transient control, an optimal operating point is selected as a target point from among the operating points whose information was stored in advance through calibration, depending on the remaining battery capacity and accelerator depression (required torque) at that time. The optimal operating point is basically the maximum thermal efficiency point or a point close to it. However, if the maximum thermal efficiency point or a point close to it is unfavorable in terms of conditions other than thermal efficiency, such as high electricity consumption during motoring or insufficient torque (output) after firing of the engine 10, an operating point with a higher engine speed or load than the maximum thermal efficiency point will be selected instead of the maximum thermal efficiency point.

[0041] In this transient control, the second operating point is assumed to be a case where the remaining battery capacity, as obtained by the remaining battery capacity detection means, is equal to or greater than a predetermined value, and the accelerator depression amount, as obtained by the accelerator position detection means, is equal to or greater than a predetermined depression amount. In such a case, control is performed with priority given to the thermal efficiency of the engine 10. That is, an operating point corresponding to the accelerator depression amount (required torque) is extracted from operating points calibrated in advance, and the highest thermal efficiency point, which has the best thermal efficiency, is selected as the second operating point.

[0042] However, if the operating point selected as the maximum thermal efficiency point consumes more electricity per unit time during the motoring stroke (corresponding to the maximum thermal efficiency point) than a predetermined amount, or if the maximum thermal efficiency point provides insufficient engine output during the firing stroke, the maximum thermal efficiency point is not selected as the second operating point. In this case, another operating point with a higher engine speed or load than the maximum thermal efficiency point is selected as the second operating point. Whether to adopt an operating point with a higher engine speed or a higher load than the maximum thermal efficiency point is determined based on the vehicle speed and accelerator depression amount at that time. For example, if the vehicle speed is above a predetermined speed, priority is given to the engine 10 engine speed, and control is performed to prioritize securing power generation and maintaining vehicle speed. Also, for example, if the accelerator depression amount is above a predetermined amount, priority is given to the engine 10 load, and control is performed to prioritize maintaining torque.

[0043] Furthermore, during this transient control, the amount of fuel injected by the direct fuel injection device can be controlled to be less than when starting the engine 10 in a cold state. Unless the engine 10 is in a cold state, the combustion chamber C and ports of the engine 10 are warmed to a predetermined temperature or higher, creating a warm environment in which fuel is more likely to vaporize. When starting the engine 10 in such a warm state, the amount of fuel injected can be reduced more than when the engine 10 is started in a cold state and then immediately shifted to a target operating point. This reduces the total amount of harmful substances contained in the exhaust gas. This is because fuel injected from a direct fuel injection device tends to be relatively resistant to vaporization.

[0044] Furthermore, when the engine 10 is in a cold state, a second operating point can be set at which the motoring rotation speed during the motoring stroke is less than a predetermined rotation speed, thereby suppressing the rotation speed of the engine 10 (at the second operating point) during the subsequent firing start stroke, thereby protecting the equipment during the cold state.

[0045] Here, the term "cold state of engine 10" generally refers to a state in which engine 10 is at the same temperature as or colder than the ambient temperature of the environment in which engine 10 is placed. In an actual vehicle, the cold state can be established, for example, when the temperature of engine coolant is below a predetermined temperature (e.g., 40°C) or when the temperature of engine oil is below a predetermined temperature (e.g., 60°C).

[0046] Furthermore, during this transient control, the higher the engine speed during the firing start stroke, the more ignition energy per spark can be increased within a predetermined number of cycles from the initial combustion, or the more sparks can be ignited during one combustion cycle. Alternatively, the higher the engine speed during the firing start stroke, the more fuel can be increased by increasing the total amount of fuel injected within a predetermined number of cycles from the initial combustion. These ignition enhancement and fuel increase controls can stabilize the combustion state immediately after startup. This is because when the engine 10 speed is high during startup (e.g., starting at 5,000 rpm or higher), the airflow within the combustion chamber C is intense, making the pre-combustion chamber 11 prone to becoming lean. Regarding fuel increase control, particularly when the injector 9 includes both a direct injection fuel injector 9a and a port injection fuel injector 9b, increasing the amount of fuel injected by the direct injection fuel injector 9a can easily prevent the pre-combustion chamber 11 from becoming lean. The predetermined number of cycles may be, for example, 10 rotations, 20 rotations, or the like.

[0047] Further, as an example of ignition enhancement control, there is a control to increase the ignition energy per combustion cycle by increasing the ignition energy per spark. Conventionally, the ignition energy was constant regardless of the ignition timing (crank angle), but by increasing the ignition energy in this way, it is possible to ensure stable, good combustion from the first combustion even when the engine speed is high. However, if the ignition energy is constantly increased, it is possible that the ignition device 4 (spark plug) will melt or that the thermal efficiency of the engine 10 will decrease due to the use of a lot of electricity. For this reason, when increasing the ignition energy, it is necessary to limit the energy increase to the minimum necessary.

[0048] Specifically, the ignition energy after the energy increase (referred to as the second ignition energy) is higher than the normal ignition energy (referred to as the first ignition energy). (Second ignition energy) = (First ignition energy) × α In this case, α>1, and the value of α can be set to, for example, 1.1, 1.2, 1.3, 1.4, . . . , or the like, to the minimum required value according to the operating state.

[0049] Further, ignition enhancement control includes, for example, control for increasing ignition energy per combustion cycle by changing the ignition pattern. Examples of changing the ignition pattern include a method for promoting ignition by performing ignition multiple times during one combustion cycle, a method for overlapping sparks by performing re-discharge using another coil after one discharge during one combustion cycle (boost), and a method for promoting ignition by creating a state with a higher current value by shortening the discharge time in the ignition device 4.

[0050] Furthermore, during this transient control, if the purification performance of the exhaust purification device 16 is insufficient because the temperature of the exhaust purification device 16 is lower than a predetermined temperature during the firing start stroke, ignition timing retard control is performed to retard the ignition timing of the ignition device 4, and ignition strengthening control can be performed to increase the ignition energy per ignition or to perform ignition multiple times during one combustion cycle. This strengthens the combustion state of the engine 10 immediately after firing starts and increases the temperature of the exhaust gas, allowing the temperature of the exhaust purification device 16 to increase early and improve exhaust purification performance.

[0051] In the above embodiment, both a direct injection fuel injection device and a port injection fuel injection device are provided as the injector 9, but a specification in which only a direct injection fuel injection device is provided as the injector 9 is also considered. Furthermore, in the above embodiment, the location of the direct injection fuel injection device within the combustion chamber C is not specified, but it is sufficient if fuel can be supplied to the auxiliary chamber 11, and it is considered that the direct injection fuel injection device be provided within the main combustion chamber 1 or the auxiliary combustion chamber 11. That is, it is possible to supply fuel to the auxiliary combustion chamber 11 from an injector (injection device) provided within the main combustion chamber 1, or to supply fuel to the auxiliary combustion chamber 11 from an injector (injection device) provided within the auxiliary combustion chamber 11. Furthermore, in the above embodiment, a plug-in hybrid car having at least three driving modes, namely, an electric driving mode, a series driving mode, and a parallel driving mode, is used as the vehicle 60, but the present invention can also be applied to other types of hybrid vehicles having at least a driving mode in which the vehicle runs using the driving force of the engine 10. [Explanation of symbols]

[0052] 1 Main room 2 cylinders 3 pistons 4 Ignition device 10 Engine 11 Antechamber 12 Communication path 20 Electronic Control Unit 30 First Rotating Electric Machine 40 Second rotating electric machine (rotating electric machine) 50 Battery 60 Hybrid Vehicles (Vehicles) C. Combustion chamber

Claims

1. In a hybrid vehicle equipped with an engine that supplies driving force for running and a rotating electric machine that supplies driving force for running, The engine comprises a main chamber formed by an inner peripheral surface of a cylinder, an inner surface of a cylinder head, and a top surface of a piston, an auxiliary chamber separated from the main chamber and formed at an end of the main chamber on the cylinder head side, a combustion chamber provided with a communication passage connecting the main chamber and the auxiliary chamber, an injection device that supplies fuel to the combustion chamber, and an ignition device that ignites the air-fuel mixture in the auxiliary chamber, the injection device includes at least a direct injection fuel injection device that forms an air-fuel mixture in the auxiliary chamber by injecting fuel directly into the main chamber, or that forms an air-fuel mixture in the auxiliary chamber by injecting fuel directly into the auxiliary chamber, As a transient control when changing an operating state from a first operating point to a second operating point different from the first operating point during an operating mode in which the vehicle travels by driving force of the engine, a firing stop process for stopping ignition and fuel injection of the engine operating at the first operating point, a motoring process for reaching the target second operating point by the driving force of the rotating electric machine, and a firing start process for starting firing of the engine with an air amount and a fuel amount corresponding to the second operating point, A hybrid vehicle in which, during the transient control, the amount of fuel injected by the direct fuel injection device is reduced compared to when the engine is cold started.

2. 2. The hybrid vehicle according to claim 1, wherein the firing start process adjusts the opening of a throttle valve provided in an intake passage of the engine to a predetermined opening corresponding to the second operating point, and then injects a fuel amount corresponding to the second operating point based on the adjusted air amount, and ignites the fuel by an ignition device.

3. an accelerator position detection means for detecting an accelerator depression amount; and a battery remaining capacity detection means for detecting a remaining capacity of electric power stored in a battery that supplies electric power to the rotating electric machine, 3. The hybrid vehicle according to claim 1, wherein, as the second operating point, a maximum thermal efficiency point is selected from among pre-calibrated operating points when the remaining capacity of the battery is equal to or greater than a predetermined value and the accelerator depression amount is equal to or greater than a predetermined depression amount, and when the amount of electricity consumed per unit time of motoring corresponding to the maximum thermal efficiency point in the motoring stroke is greater than a predetermined consumption amount, or when the engine output in the firing start stroke is insufficient at the maximum thermal efficiency point, another operating point having a higher rotation speed or load than the maximum thermal efficiency point is selected as the second operating point.

4. 4. The hybrid vehicle according to claim 1, wherein when the engine is cold, the second operating point is set to an operating point at which the motoring rotation speed during the motoring stroke is less than a predetermined rotation speed.

5. 5. The hybrid vehicle according to claim 1, wherein, during the firing start stroke, a fuel increase control is performed to increase the amount of fuel injected by the direct fuel injection device within a predetermined number of cycles from the initial combustion as the engine speed increases.

6. 6. The hybrid vehicle according to claim 1, wherein in the firing start stroke, ignition energy per ignition is increased for a predetermined number of cycles from the first combustion as the engine speed increases, or ignition is strengthened by performing ignition multiple times during one combustion cycle.

7. an exhaust gas purification device that purifies harmful components in exhaust gases in an exhaust passage extending from the combustion chamber; 7. A hybrid vehicle according to any one of claims 1 to 6, wherein, during the firing start process, if the temperature of the exhaust purification device is lower than a predetermined temperature and the purification performance of the exhaust purification device is insufficient, ignition timing retard control is performed to retard the ignition timing of the ignition device, and ignition enhancement control is performed to increase the ignition energy per ignition or to perform ignition multiple times during one combustion cycle.

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