Engine systems and series hybrid vehicles

Abstract

To form a homogeneous air-fuel mixture in a working chamber even when the engine rotation speed is low.SOLUTION: An engine system 12 comprises: a rotary engine 14 having a rotor housing 16, side housings 18, a rotor 20 that is housed in a rotor accommodation chamber surrounded by the rotor housing and the side housings and forms three working chambers 24, and an injector 54 for injecting fuel into one of the working chambers; an eccentric shaft angle sensor 58 for detecting an engine rotation speed of the rotary engine; and an ECM 70 configured to control fuel injection by the injector. When the engine rotation speed is equal to or lower than a first rotation speed, the ECM controls the injector such that the number of times of fuel injection in one combustion cycle of each of the working chambers is greater and the end timing of a last fuel injection is retarder than those when the engine rotation speed is higher than the first rotation speed.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an engine system and a series hybrid vehicle, and more particularly to an engine system and a series hybrid vehicle equipped with a rotary engine. [Background technology]

[0002] A conventional rotary engine has a rotor housed in a rotor chamber surrounded by a rotor housing, a side housing, and a rotor. For example, Patent Document 1 discloses that in a rotary engine, the injection direction of a fuel injection valve is set on the retard side of the rotor in an intake working chamber in the first half of the intake stroke in order to ensure time for fuel to vaporize and promote mixing of the fuel and fresh air. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-053332 Summary of the Invention [Problem to be solved by the invention]

[0004] In a rotary engine, fuel injected into the working chamber mixes with fresh air flowing in from the intake port and flows through the working chamber to form an air-fuel mixture. However, when the engine speed is relatively low, i.e., when the rotor rotation speed is low, the airflow, such as the squish flow generated by the rotor rotation from the trailing side (lagging side, i.e., the rear side in the rotor rotation direction) of the working chamber to the leading side (leading side, i.e., the front side in the rotor rotation direction), weakens, preventing the fuel from flowing sufficiently back from the leading side to the trailing side. As a result, the fuel is not distributed evenly throughout the working chamber and instead remains on the leading side. In other words, the distribution of fuel within the working chamber is uneven, resulting in a shortage of air in fuel-rich regions, which increases unburned fuel and leads to poor fuel economy and emissions.

[0005] The present invention has been made to solve these problems, and aims to provide an engine system and a series hybrid vehicle equipped with a rotary engine that can form a homogeneous mixture in the working chamber even when the engine speed is low. [Means for solving the problem]

[0006] In order to achieve the above object, an engine system according to the present invention includes a rotary engine having a rotor housing, a side housing, a rotor accommodated in a rotor accommodating chamber surrounded by the rotor housing and the side housing and forming three working chambers, and an injector for injecting fuel into one of the working chambers; a rotation speed sensor for detecting an engine speed of the rotary engine; and a controller configured to control fuel injection by the injector, wherein when the engine speed is equal to or lower than a first rotation speed, the controller controls the injector so that the number of fuel injections in one combustion cycle of each working chamber is greater and the end timing of the final fuel injection is retarded compared to when the engine speed is higher than the first rotation speed. When the engine speed is equal to or lower than the first speed, the controller controls the injector so that the ratio of the first fuel injection amount in one combustion cycle of each working chamber increases as the load of the rotary engine increases at the same engine speed. do. According to the present invention configured in this manner, when the engine speed is relatively low, i.e., when the airflow in the working chamber is relatively weak, the number of fuel injections in one combustion cycle of each working chamber is increased and the end timing of the final fuel injection is retarded, thereby making it possible to distribute fuel evenly from the leading side to the trailing side even when the airflow in the working chamber is weak, and to obtain a homogeneous mixture. Also, at the same engine speed, the higher the engine load, the greater the amount of fresh air flowing into the working chamber and the stronger the airflow toward the leading side. However, by increasing the proportion of the first fuel injection amount and increasing the amount of fuel injected toward the leading side as the engine load increases, it is possible to promote mixing of the fresh air flowing toward the leading side with the fuel and obtain a homogeneous mixture.

[0007] In the present invention, preferably, the controller is configured to: for , engine speed First rotation speed or less and The injectors are controlled so that the number of fuel injections in one combustion cycle for each working chamber is greater than when the rotation speed is higher than the second rotation speed, and the injection end timing of the last fuel injection is retarded. According to the present invention configured in this manner, the lower the engine speed is relatively, i.e., the weaker the airflow in the working chamber, the more the number of fuel injections in one combustion cycle of each working chamber is increased and the end timing of the final fuel injection is retarded. This makes it possible to distribute fuel evenly from the leading side to the trailing side even when the airflow in the working chamber is weak, and to obtain a homogeneous mixture.

[0009] In another aspect, the present invention is a series hybrid vehicle having an electric motor as a driving force source and a generator capable of supplying power to the electric motor, and the vehicle is equipped with the above-mentioned engine system, and the rotary engine drives the generator. In series hybrid vehicles, where the driving force of the rotary engine is used only to drive a generator, the rotary engine tends to be operated in a region of high thermal efficiency, i.e., a region where the engine speed is relatively low and the airflow in the working chamber is weak. Therefore, the engine system of the present invention, which can obtain a homogeneous air-fuel mixture even in a region where the engine speed is relatively low and the airflow in the working chamber is weak, is suitable for series hybrid vehicles. [Effects of the Invention]

[0010] According to the engine system and series hybrid vehicle of the present invention, a homogeneous air-fuel mixture can be formed in the working chamber even when the engine speed is low. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a configuration diagram of a series hybrid vehicle according to an embodiment of the present invention. [Figure 2] 1 is a configuration diagram of an engine system according to an embodiment of the present invention. [Figure 3] 1 is a control block diagram of a series hybrid vehicle according to an embodiment of the present invention. [Figure 4] 3 is a flowchart of an engine control process according to an embodiment of the present invention. [Figure 5] 3 is a flowchart of an engine start control process according to an embodiment of the present invention. [Figure 6] 4 is a map showing the relationship between water temperature and required rotation speed in engine start control according to an embodiment of the present invention. [Figure 7] 4 is a map showing the relationship between water temperature and rotation increase rate in engine start control according to an embodiment of the present invention. [Figure 8] 4 is a map showing the relationship between water temperature and the amount of oil introduced at startup in engine startup control according to an embodiment of the present invention. [Figure 9] 4 is a flowchart of a combustion control process according to an embodiment of the present invention. [Figure 10] 4 is a chart illustrating an example of a pattern of fuel injection timing according to engine speed in combustion control according to an embodiment of the present invention. [Figure 11] 4 is a table showing the relationship between engine speed and the number of fuel injections in combustion control according to an embodiment of the present invention. [Figure 12] 4 is a map showing the relationship between engine speed and fuel injection end timing in combustion control according to an embodiment of the present invention. [Figure 13] 4 is a map showing the relationship between the engine load and the split ratio of the fuel injection amount in combustion control according to an embodiment of the present invention. [Figure 14] 1 is a graph showing the relationship between the eccentric shaft angle and the heat release rate in a rotary engine. [Figure 15] 1 is a graph showing the relationship between the EGR rate and the proportion of second-stage combustion in a rotary engine. [Figure 16] 4 is a map showing the relationship between engine load and EGR rate in combustion control according to an embodiment of the present invention. [Figure 17] 4 is a map showing the relationship between engine speed and EGR rate in combustion control according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0013] <System configuration> First, the configuration of the series hybrid vehicle and engine system according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a configuration diagram of the series hybrid vehicle, and Figure 2 is a configuration diagram of the engine system.

[0014] 1, the series hybrid vehicle 1 includes an electric motor 6, which is a driving force source that drives drive wheels 4 (front wheels in the illustrated example) via a reduction gear 2, and a battery 8 and starter generator 10 that can supply electric power to the electric motor 6. The series hybrid vehicle 1 also includes an engine system 12 that has a rotary engine 14. The starter generator 10 is driven by the rotary engine 14 to generate electric power and supply the electric power to the electric motor 6 and the battery 8, and when the rotary engine 14 is started, the starter generator 10 drives the rotary engine 14 using the electric power supplied from the battery 8.

[0015] 2, the engine system 12 includes a rotary engine 14. The rotary engine 14 includes a rotor housing 16 having a trochoidal inner peripheral surface, side housings 18 each having a flat inner surface and disposed on either side of the rotor housing 16, and a rotor 20 housed in a rotor housing chamber surrounded by the rotor housing 16 and the side housings 18.

[0016] The rotor 20 is supported by an eccentric shaft 22 inside the rotor 20 and rotates eccentrically together with the eccentric shaft 22. Three working chambers 24 are formed around the rotor 20 and are surrounded by the rotor housing 16, the side housing 18, and the rotor 20. The volume of each working chamber 24 changes with the eccentric rotation of the rotor 20. A series of strokes of intake, compression, expansion (combustion), and exhaust in the working chambers 24 rotates the rotor 20 and the eccentric shaft 22, and the rotational force is output as power from the eccentric shaft 22 to the starter generator 10 via a drive shaft (not shown) or the like.

[0017] As shown in Figure 2, an ignition plug 26 is attached to the rotor housing 16, and an intake port 28 and an exhaust port 30 are formed in the side housing 18. An intake passage 32 is connected to the intake port 28, and air is introduced into the working chamber 24 via the intake passage 32. An exhaust passage 34 is connected to the exhaust port 30, and exhaust gas is discharged from the working chamber 24 via the exhaust passage 34. The rotor 20 rotates clockwise in Figure 2, and in the state shown in Figure 2, a compression stroke is taking place in the working chamber 24 on the upper right of the rotor 20, and an expansion (explosion) stroke is taking place in the working chamber 24 on the lower right. In the example of Figure 2, the rotor 20 rotates clockwise, so the leading side (advancing side) of the working chamber 24 is the clockwise side of the working chamber 24 (i.e., the lower right side in the upper right working chamber 24 of the rotor 20, and the lower left side in the lower right working chamber 24), and the trailing side (lagging side) is the counterclockwise side of the working chamber 24 (i.e., the upper left side in the upper right working chamber 24 of the rotor 20, and the upper right side in the lower right working chamber 24).

[0018] 2, a throttle valve 36, a throttle opening sensor 38, and an airflow sensor 40 are provided upstream of the intake passage 32, and an air cleaner 42 is provided further upstream thereof. In addition, an EGR device 44 for recirculating a portion of the exhaust gas in the exhaust passage 34 to the intake passage 32, an exhaust gas purification catalyst (not shown), and the like are provided downstream of the exhaust passage 34. The EGR device 44 has an EGR passage 46 connecting the exhaust passage 34 and the intake passage 32, an EGR cooler 48 for cooling the recirculated exhaust gas in the EGR passage 46 to increase its density, and an EGR valve 50 and an EGR valve opening sensor 52 for controlling the EGR rate (the ratio of the amount of burned gas to the total amount of gas flowing into the working chamber 24 during the intake stroke).

[0019] Also attached to the rotor housing 16 are an injector 54 that injects fuel into the working chamber 24 and a metering oil pump 56 that injects oil onto the inner circumferential surface of the rotor housing 16. The injector 54 is connected to a fuel tank via a fuel supply passage (neither of which are shown), and is supplied with fuel from the fuel tank. The metering oil pump 56 is, for example, an electromagnetically operated oil pump that measures oil taken from an oil gallery (not shown) and injects the required amount of oil onto the inner circumferential surface of the rotor housing 16 from an oil nozzle (not shown).

[0020] The rotary engine 14 is also equipped with an eccentric shaft angle sensor 58 that detects the rotation angle of the eccentric shaft 22. The rotation speed of the eccentric shaft 22, i.e., the engine rotation speed of the rotary engine 14, can be detected from the rotation angle detected by the eccentric shaft angle sensor 58. Therefore, the eccentric shaft angle sensor 58 corresponds to the "rotation speed sensor" in this invention. The intake passage 32 is also provided with an intake pressure sensor 60 that detects the intake air pressure in the intake passage 32 and an intake air temperature sensor 62 that detects the intake air temperature. Although not shown in FIG. 2, the rotary engine 14 is also equipped with a water temperature sensor 64 that detects the temperature of the engine coolant (water temperature).

[0021] The engine system 12 includes an ECM (Electronic Control Module) 70 that serves as a computing device and control device for controlling the rotary engine 14. The ECM 70 is a controller based on a well-known microcomputer. The ECM 70 is configured by a computer that includes one or more processors (typically, a CPU) 72, a storage unit (ROM, RAM, etc.) 74 that stores various programs, and the like. The ECM 70 corresponds to an example of a "controller" in the present invention.

[0022] The ECM 70 calculates control variables for each device of the rotary engine 14, such as the spark plugs 26, injectors 54, metering oil pump 56, throttle valve 36, and EGR valve 50, based on signals input from the various sensors 38, 40, 52, 58, 60, 62, and 64 described above and a PCM (Powertrain Control Module) 84 (described later), and outputs electrical signals corresponding to the calculated control variables to those devices. The PCM 84 is a controller that controls the entire power system of the series hybrid vehicle 1, including the electric motor 6, starter generator 10, engine system 12, reduction gear 2, battery 8, and the like, and is configured by a computer equipped with one or more processors (typically a CPU), a memory unit (ROM, RAM, etc.) that stores various programs, and the like. The PCM 84 corresponds to an example of a "controller" in the present invention.

[0023] <Outline of engine control> Next, an overview of engine control in the series hybrid vehicle 1 according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a control block diagram of the series hybrid vehicle according to this embodiment.

[0024] The battery 8 of the series hybrid vehicle 1 is provided with a voltage sensor 76 that detects the output voltage of the battery 8 and a current sensor 78 that detects the output current of the battery 8. These voltage sensor 76 and current sensor 78 output electric signals corresponding to their respective detected values ​​to a BCM (Battery Control Module) 80. The BCM 80 is a controller that mainly controls the charging and discharging of the battery 8, and is configured by a computer that includes one or more processors (typically a CPU), a storage unit (ROM, RAM, etc.) that stores various programs, and the like.

[0025] The BCM 80 estimates the SOC (State of Charge) of the battery 8 from the voltage value and current value of the battery 8 input from the voltage sensor 76 and the current sensor 78, and outputs the SOC to the PCM 84. The PCM 84 calculates the rotation speed (required engine rotation speed) and load (required engine load) of the rotary engine 14 required to obtain a desired engine output based on the SOC input from the BCM 80 and the accelerator opening input from an accelerator opening sensor 82 that detects the opening of an accelerator pedal (not shown) of the series hybrid vehicle 1, and outputs the calculated values ​​to the ECM 70.

[0026] Furthermore, when starting the rotary engine 14, the PCM 84 calculates the rotation speed (required rotation speed) and the rate of increase in the rotation speed (rotation increase rate) when the eccentric shaft 22 of the rotary engine 14 is rotated by the starter generator 10 based on the water temperature of the rotary engine 14 input from the ECM 70, and outputs the results to an SGCM (Starter Generator Control Module) 86. The SGCM 86 is a controller that mainly controls the starter generator 10, and is configured by a computer including one or more processors (typically a CPU), a storage unit (ROM, RAM, etc.) that stores various programs, and the like. The SGCM 86 corresponds to an example of a "controller" in the present invention.

[0027] The ECM 70 calculates the control variables for each device of the rotary engine 14, such as the metering oil pump 56, injectors 54, spark plugs 26, EGR valve 50, and throttle valve 36, based on the required engine speed and required engine load input from the PCM 84, and outputs electrical signals corresponding to the calculated control variables to those devices. Furthermore, when starting the rotary engine 14, the SGCM 86 calculates the control variable for the starter generator 10 based on the required engine speed and rotation increase rate input from the PCM 84, and outputs an electrical signal corresponding to the calculated control variable to the starter generator 10.

[0028] <Engine control processing> Next, the flow of engine control processing according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a flowchart of engine control processing according to this embodiment.

[0029] The engine control process shown in FIG. 4 is repeatedly executed at predetermined intervals by the PCM 84, the ECM 70, and the SGCM 86 while the rotary engine 14 is stopped.

[0030] First, in step S101, the PCM 84 acquires various pieces of information relating to the state of the series hybrid vehicle 1 from the ECM 70, the BCM 80, the accelerator position sensor 82, etc. Specifically, for example, the PCM 84 acquires the SOC input from the BCM 80, the accelerator position input from the accelerator position sensor 82, the water temperature of the rotary engine 14 input from the ECM 70, as well as the vehicle speed and motor rotation speed. Thereafter, the PCM 84 continues to acquire these pieces of information while the engine control process is being executed.

[0031] Next, in step S102, the PCM 84 calculates the torque (required motor torque) to be output by the electric motor 6 based on the information acquired in step S101. Specifically, the PCM 84 refers to a map or a calculation formula (pre-set and stored) that defines the relationship between the accelerator opening and the required motor torque, and calculates the required motor torque corresponding to the accelerator opening acquired in step S101.

[0032] Next, in step S103, the PCM 84 determines whether the SOC acquired in step S101 is equal to or less than a predetermined threshold value (for example, a pre-set and stored allowable lower limit value of the SOC). If the SOC is not equal to or less than the threshold value (step S103: No), that is, if the SOC is greater than the threshold value and there is no need to start the rotary engine 14 to charge the battery 8 with the starter generator 10, the process proceeds to step S104.

[0033] In step S104, the PCM 84 determines whether the required motor torque calculated in step S102 is greater than the torque that can be output by the electric motor 6 (outputtable motor torque). The outputtable motor torque is the torque that the electric motor 6 can output using only the power supplied from, for example, the battery 8, and maps and calculation formulas that define the relationship between the SOC, motor rotation speed, and outputtable motor torque are set and stored in advance. The PCM 84 refers to these maps and calculation formulas to obtain the outputtable motor torque that corresponds to the SOC, motor rotation speed, etc. obtained in step S101, and compares it with the required motor torque.

[0034] If the result of the determination in step S104 is that the required motor torque is not greater than the outputtable motor torque (step S104: No), that is, if the required motor torque is equal to or less than the outputtable motor torque and there is no need to start the rotary engine 14 to supply power from the starter generator 10 to the electric motor 6, the PCM 84 ends the engine control process without starting the rotary engine 14.

[0035] On the other hand, if the result of the determination in step S103 is that the SOC is equal to or lower than the threshold value (step S103: Yes), that is, if it is necessary to start the rotary engine 14 in order to charge the battery 8 using the starter generator 10, or if the result of the determination in step S104 is that the required motor torque is greater than the outputtable motor torque (step S104: Yes), that is, if it is necessary to start the rotary engine 14 in order to supply power from the starter generator 10 to the electric motor 6, the process proceeds to step S105, where the PCM 84, ECM 70, and SGCM 86 execute engine start control to start the rotary engine 14. Details of this engine start control will be described later.

[0036] After the rotary engine 14 is started by the engine start control in step S105, in step S106, the PCM 84 and ECM 70 execute combustion control to operate the rotary engine 14 at a required output. Details of this combustion control will be described later.

[0037] Next, in step S107, the PCM 84 determines whether the SOC most recently acquired from the BCM 80 is equal to or greater than a target value (for example, a preset and stored upper allowable limit value of the SOC). If the result shows that the SOC is not equal to or greater than the target value (step S107: No), that is, if the SOC is lower than the target value and it is necessary to continue charging the battery 8 by the starter generator 10, the PCM 84 returns to step S106 and continues combustion control of the rotary engine 14.

[0038] On the other hand, if the result of the determination in step S107 is that the SOC is equal to or greater than the target value (step S107: Yes), that is, if there is no need to charge the battery 8 by the starter generator 10, the process proceeds to step S108.

[0039] In step S108, the PCM 84 determines whether the required motor torque is equal to or less than the available motor torque. If the required motor torque is not equal to or less than the available motor torque (step S108: No), that is, if the required motor torque is greater than the available motor torque and it is necessary to continue supplying power from the starter generator 10 to the electric motor 6, the process returns to step S106 and the combustion control of the rotary engine 14 continues.

[0040] On the other hand, if the result of the determination in step S108 is that the required motor torque is equal to or less than the outputtable motor torque (step S108: Yes), that is, if there is no need to supply power from the starter generator 10 to the electric motor 6, the process proceeds to step S109, where the PCM 84 stops the rotary engine 14 and terminates the engine control process.

[0041] <Engine start control process> Next, the flow of engine start control according to this embodiment will be described with reference to Figures 5 to 8. Figure 5 is a flowchart of the engine start control process according to this embodiment, Figure 6 is a map showing the relationship between water temperature and required rotation speed in engine start control, Figure 7 is a map showing the relationship between water temperature and rotation increase rate in engine start control, and Figure 8 is a map showing the relationship between water temperature and amount of oil introduced at start-up in engine start control.

[0042] As shown in FIG. 5, when engine start control is started, first, in step S201, the PCM 84 determines the rotation speed (requested rotation speed) at which the eccentric shaft 22 of the rotary engine 14 is rotated by the starter generator 10 and ignition is initiated by the spark plug 26, based on the water temperature of the rotary engine 14 acquired in step S101 of the engine control process. )of The PCM 84 sets the required rotation speed corresponding to the water temperature acquired in step S101 and outputs it to the SGCM 86. Specifically, the PCM 84 references a map (preset and stored) that defines the relationship between the water temperature and the required rotation speed, as shown in FIG. 6, for example, and sets the required rotation speed corresponding to the water temperature acquired in step S101. In the map shown in FIG. 6, the horizontal axis represents the water temperature and the vertical axis represents the required rotation speed. According to the map of FIG. 6, when the water temperature is below Tr (°C), the required rotation speed is set to Rr1 (rpm), and when the water temperature is Tr (°C) or higher, the required rotation speed is set to Rr2 (rpm), which is larger than Rr1. The water temperature Tr and the required rotation speeds Rr1 and Rr2 can be, for example, Tr = -5°C, Rr1 = 1200 rpm, and Rr2 = 2000 rpm, but other appropriate values ​​can be set depending on the rotary engine 14.

[0043] In this way, when the water temperature at engine start is relatively low, i.e., during cold start when the clearance between the rotor housing 16 and the rotor 20 is large and it is difficult for oil to be present, by setting the required rotation speed lower than when the water temperature is relatively high, the airflow in the working chamber 24 weakens until ignition of the rotary engine 14 begins, thereby preventing the introduced oil from being blown away by the airflow before ignition of the rotary engine 14 begins.

[0044] Next, in step S202, based on the water temperature of the rotary engine 14 obtained in step S101 of the engine control process, the PCM 84 sets the rate of increase in the rotational speed (rotation increase rate) when rotating the eccentric shaft 22 of the rotary engine 14 by the starter generator 10, and outputs it to the SGCM 86. Specifically, the PCM 84 refers to a map (preset and stored in advance) that defines the relationship between the water temperature and the rotation increase rate, as shown in FIG. 7 for example, and sets the rotation increase rate corresponding to the water temperature obtained in step S101. In the map illustrated in FIG. 7, the horizontal axis represents the water temperature and the vertical axis represents the rotation increase rate. According to this map of FIG. 7, when the water temperature is less than Ti1 (°C), the rotation increase rate is set to Ir1 (rpm / s); when the water temperature is Ti1 (°C) or more and less than Ti2 (°C), the rotation increase rate is set to Ir2 (rpm / s); when the water temperature is Ti2 (°C) or more and less than Ti3 (°C), the rotation increase rate is set to Ir3 (rpm / s); when the water temperature is Ti3 (°C) or more and less than Ti4 (°C), the rotation increase rate is set to Ir4 (rpm / s); when the water temperature is Ti4 (°C) or more, the rotation increase rate is set to Ir5 (rpm / s). Here, the magnitude relationship of the rotation increase rates is Ir1 < Ir2 < Ir3 < Ir4 < Ir5. The water temperature and the rotation increase rate can be, for example, water temperature Ti1 = -5°C, Ti2 = 5°C, Ti3 = 15°C, Ti4 = 25°C, and rotation increase rates Ir1 = 1500 rpm / s, Ir2 = 2100 rpm / s, Ir3 = 2600 rpm / s, Ir4 = 3200 rpm / s, Ir5 = 3600 rpm / s, but other appropriate values can be set according to the rotary engine 14.

[0045] Thus, when the water temperature at engine startup is relatively low, that is, at cold startup when the clearance between the rotor housing 16 and the rotor 20 is large and it is difficult to interpose oil, by setting the rotation increase rate lower compared to when the water temperature is relatively high, the rate of increase in the strength of the airflow in the working chamber 24 becomes gentle, so it is possible to prevent the oil introduced into the rotor housing 16 from being blown away by the airflow before it sufficiently spreads between the rotor housing 16 and the rotor 20.

[0046] Next, in step S203, the ECM 70 sets the amount of oil to be introduced into the rotor housing 16 by the metering oil pump 56 when the rotary engine 14 is started (start-up oil introduction amount) based on the water temperature of the rotary engine 14 acquired in step S101 of the engine control processing. Specifically, the ECM 70 references a map (pre-set and stored) that defines the relationship between the water temperature and the start-up oil introduction amount, as shown in FIG. 8, for example, and sets the start-up oil introduction amount corresponding to the water temperature acquired in step S101. In the map shown in FIG. 8, the horizontal axis represents the water temperature, and the vertical axis represents the start-up oil introduction amount. According to the map in FIG. 8, the higher the water temperature, the smaller the start-up oil introduction amount (l / min).

[0047] In this way, when the water temperature at engine start is relatively low, i.e., during cold start when the clearance between the rotor housing 16 and the rotor 20 is large and it is difficult for oil to intervene, the amount of oil introduced at start-up is set to be larger than when the water temperature is relatively high, thereby ensuring that oil is distributed between the rotor housing 16 and the rotor 20.

[0048] Next, in step S204, the ECM 70 and the SGCM 86 start the rotary engine 14. Specifically, the SGCM 86 drives the starter generator 10 to rotate the eccentric shaft 22 of the rotary engine 14 in accordance with the required rotational speed and rotation increase rate input from the PCM 84 in steps S201 and S202. The ECM 70 also causes the metering oil pump 56 to introduce the start-time oil introduction amount set in step S203 into the rotor housing 16, and when the rotational speed of the eccentric shaft 22 reaches the required rotational speed, starts fuel injection by the injector 54 and ignition by the spark plug 26. After starting the rotary engine 14 in step S204, the PCM 84 ends the engine start control and returns to the engine control shown in FIG. 4.

[0049] <Combustion control processing> Next, the flow of combustion control for a rotary engine according to this embodiment will be described with reference to Figures 9 to 17. Figure 9 is a flowchart of the combustion control process according to this embodiment, Figure 10 is a chart illustrating an example of a pattern of fuel injection timing according to engine speed in combustion control, Figure 11 is a table showing the relationship between engine speed and the number of fuel injections in combustion control, Figure 12 is a map showing the relationship between engine speed and fuel injection end timing in combustion control, Figure 13 is a map showing the relationship between engine load and the split ratio of the fuel injection amount in combustion control, Figure 14 is a graph showing the relationship between the eccentric shaft angle and the heat release rate in a rotary engine, Figure 15 is a graph showing the relationship between the EGR rate and the proportion of second-stage combustion in a rotary engine, Figure 16 is a map showing the relationship between engine load and the EGR rate in combustion control, and Figure 17 is a map showing the relationship between engine speed and the EGR rate in combustion control.

[0050] 9, when combustion control is started, first in step S301, the PCM 84 calculates the output of the rotor housing 16 (required engine output) required to cause the starter generator 10 to generate desired electric power based on the SOC input from the BCM 80 and the accelerator opening input from the accelerator opening sensor 82. Specifically, the PCM 84 refers to a map (pre-set and stored) that defines the relationship between the SOC, accelerator opening, vehicle speed, and required engine output, and calculates the required engine output corresponding to the most recently acquired SOC, accelerator opening, and vehicle speed. The map is set so that, for example, the required engine output increases as the vehicle speed increases or the accelerator opening increases.

[0051] Next, in step S302, the PCM 84 calculates the rotation speed (required engine rotation speed) and load (required engine load) of the rotary engine 14 required to obtain the required engine output calculated in step S301, and outputs them to the ECM 70. Specifically, the PCM 84 refers to a map (pre-set and stored) that defines the relationship between the required engine output, the required engine rotation speed, and the required engine load, and calculates the required engine rotation speed and required engine load corresponding to the required engine output calculated in step S301. In the map, for example, the required engine load is set to be approximately constant, and the required engine rotation speed increases as the required engine output increases.

[0052] Next, in step S303, the ECM 70 sets the number of times (number of fuel injections) that the injector 54 injects fuel in one combustion cycle for each working chamber 24, the timing (injection timing) at which the fuel is injected, and the amount of fuel to be injected (injection amount) in order to operate the rotary engine 14 at the required engine speed and required engine load input from the PCM 84.

[0053] 10 illustrates an example of a pattern of fuel injection timing set by the ECM 70 in accordance with the engine speed detected by the eccentric shaft angle sensor 58. In this Fig. 10, the horizontal axis represents the injection timing represented by the eccentric shaft angle (EA), with the upper row representing the case where the engine speed R is greater than a first speed R1, the middle row representing the case where the engine speed R is equal to or less than the first speed R1 and greater than a second speed R2, and the lower row representing the case where the engine speed R is equal to or less than the second speed R2. As illustrated in this Fig. 10, the ECM 70 controls the injector 54 so that the number of fuel injections in one combustion cycle of each working chamber 24 increases and the end timing of the final fuel injection is retarded as the engine speed R becomes relatively lower.

[0054] Specifically, the ECM 70 refers to a table (pre-set and stored) that defines the relationship between the engine speed and the number of fuel injections, as shown in FIG. 11 for example, and sets the number of fuel injections corresponding to the engine speed detected by the eccentric shaft angle sensor 58. In the table shown in FIG. 11, when the engine speed R is higher than the first speed R1 (for example, 4000 rpm) (R1 < R), the number of fuel injections is set to one. When the engine speed R is less than or equal to the first speed R1 and higher than the second speed R2 (for example, 3000 rpm) (R2 < R ≦ R1), the number of fuel injections is set to two. When the engine speed R is less than or equal to the second speed R2 (R ≦ R2), the number of fuel injections is set to three. That is, when the engine speed R is less than or equal to the first speed R1, the ECM 70 increases the number of fuel injections in each combustion cycle of the working chamber 24 compared to when the engine speed R is higher than the first speed R1. Also, when the engine speed R is less than or equal to the second speed R2, which is lower than the first speed R1, the ECM 70 increases the number of fuel injections in each combustion cycle of the working chamber 24 compared to when the engine speed R is higher than the second speed R2, and sets the number of fuel injections.

[0055] Thus, the lower the engine speed R is, that is, the weaker the air flow in the working chamber 24 is, the more the number of fuel injections in each combustion cycle of the working chamber 24 is increased. By doing so, even if the air flow in the working chamber 24 is weak, the fuel can be evenly distributed from the leading side to the trailing side, and a homogeneous air-fuel mixture can be obtained.

[0056] Further, the ECM 70 refers to a map (pre-set and stored) that defines the relationship between the engine speed and the fuel injection end time, as shown in FIG. 12 for example, and sets the fuel injection end time corresponding to the engine speed detected by the eccentric shaft angle sensor 58. In the map shown in FIG. 12, the horizontal axis represents the engine speed and the vertical axis represents the fuel injection end time. The end time of the first fuel injection is represented by a solid line, the end time of the second fuel injection is represented by a dashed line, and the end time of the third fuel injection is represented by a dotted line.

[0057] As described above, when the engine speed R is higher than the first speed R1, the number of fuel injections is set to 1, and the end timing of the first injection becomes the end timing of the last fuel injection in one combustion cycle. Also, when the engine speed R is equal to or lower than the first speed R1 and higher than the second speed R2, the number of fuel injections is set to 2, and the end timing of the second injection becomes the end timing of the last fuel injection in one combustion cycle. Also, when the engine speed R is equal to or lower than the second speed R2, the number of fuel injections is set to 3, and the end timing of the third injection becomes the end timing of the last fuel injection in one combustion cycle. In the map shown in FIG. 12, when the engine speed R is equal to or lower than the first speed R1 (when the number of fuel injections is 2 or 3), the end timing of the last fuel injection (the end timing of the second or third fuel injection) is delayed more than when the engine speed R is higher than the first speed R1 (when the number of fuel injections is 1). Furthermore, when the engine speed R is equal to or less than the second speed R2 (when the number of fuel injections is three), the end timing of the last fuel injection (the end timing of the third fuel injection) is retarded more than when the engine speed R is higher than the second speed R2 (when the number of fuel injections is two). In other words, the ECM 70 sets the fuel injection amount so that when the engine speed R is equal to or less than the first speed R1, the end timing of the last fuel injection in one combustion cycle of each working chamber 24 is retarded more than when the engine speed R is higher than the first speed R1, and so that when the engine speed R is equal to or less than the second speed R2 that is lower than the first speed R1, the end timing of the last fuel injection in one combustion cycle of each working chamber 24 is retarded more than when the engine speed R is higher than the second speed R2.

[0058] In this way, the lower the engine speed R is, i.e., the weaker the airflow in the working chamber 24, the more retarded the end timing of the final fuel injection in one combustion cycle of each working chamber 24. This makes it possible to distribute fuel evenly from the leading side to the trailing side even if the airflow in the working chamber 24 is weak, thereby obtaining a homogeneous mixture.

[0059] The ECM 70 also references a map (pre-set and stored) that defines the relationship between the fuel injection amount (total fuel injection amount) per combustion cycle of each working chamber 24 and the engine load (charging efficiency) to obtain the total fuel injection amount corresponding to the required engine load input from the PCM 84 in step S302. Furthermore, the ECM 70 references a map (pre-set and stored) that defines the relationship between the engine load (charging efficiency) and the fuel injection amount split ratio, as shown in FIG. 13, for example, to obtain the split ratio corresponding to the required engine load. The ECM 70 then divides the total fuel injection amount by the obtained split ratio to set the fuel injection amount for each injection. FIG. 13 is a map that defines the fuel injection amount split ratio when the engine speed R is equal to or lower than the second speed R2 (when the number of fuel injections is three), with the horizontal axis representing the engine load and the vertical axis representing the fuel injection amount split ratio. In FIG. 13, the split ratio for the first fuel injection is represented by a solid line, the split ratio for the second fuel injection by a dashed line, and the split ratio for the third fuel injection by a dashed line. 13, the fuel injection amount split ratio is set so that the proportion of the injection amount for the first fuel injection increases and the proportions of the injection amounts for the second and third injections decrease as the engine load increases. Also, although not shown, a map that defines the fuel injection amount split ratio when the engine speed R is higher than the second rotation speed R2 and equal to or less than the first rotation speed R1 (when the number of fuel injections is two) sets the fuel injection amount split ratio so that the proportion of the injection amount for the first fuel injection increases and the proportion of the injection amount for the second injection decreases as the engine load increases. In other words, when the engine speed R is equal to or less than the first rotation speed R1, the ECM 70 sets the fuel injection amount so that the proportion of the first fuel injection amount in one combustion cycle of each working chamber 24 increases as the engine load increases for the same engine speed.

[0060] At the same rotation speed, the higher the engine load, the greater the amount of fresh air flowing into the working chamber 24 and the stronger the airflow toward the leading side. Therefore, by increasing the proportion of the first fuel injection amount and increasing the amount of fuel injected toward the leading side, it is possible to promote mixing of the fresh air flowing toward the leading side with the fuel, thereby obtaining a homogeneous mixture.

[0061] Next, in step S304, the ECM 70 sets the opening of the EGR valve 50 based on the engine speed detected by the eccentric shaft angle sensor 58 and the required engine load input from the PCM 84.

[0062] In the rotary engine 14, due to the rotation of the rotor 20, a squish flow occurs in the working chamber 24 during the combustion stroke, flowing from the trailing side (rear side in the rotor rotation direction) to the leading side (front side in the rotor rotation direction). Due to this squish flow, the flame generated by ignition of the spark plug 26 easily propagates toward the leading side of the spark plug 26 but does not easily propagate toward the trailing side. Therefore, when the spark plug 26 ignites, the air-fuel mixture present on the trailing side of the spark plug 26 does not begin to burn until it moves toward the leading side of the spark plug 26 as the rotor 20 rotates, resulting in a two-stage heat generation process during the combustion stroke. That is, as illustrated in the graph of Figure 14, in the combustion stroke of the rotary engine 14, first, main combustion (i) occurs by combustion of the mixture in the working chamber 24 in the range from near the ignition plug 26 to the leading end of the working chamber 24, and then second-stage combustion (ii) occurs by combustion of the mixture in the working chamber 24 on the trailing side of the ignition plug 26.

[0063] As a result of research, the inventors of the present invention found that when exhaust gas is introduced into the intake air of a rotary engine by an EGR device, the proportion of second-stage combustion in heat generation during the combustion stroke varies depending on the EGR rate. The graph in Figure 15 shows the relationship between the EGR rate and the proportion of second-stage combustion in heat generation during the combustion stroke. As shown in Figure 15, when exhaust gas is introduced into the intake air of a rotary engine by an EGR device, the proportion of second-stage combustion in heat generation during the combustion stroke increases as the EGR rate increases. The combustion control of this embodiment utilizes this relationship between the EGR rate and the proportion of second-stage combustion to set the EGR rate according to the engine speed and engine load, thereby achieving both reduced cooling loss and reduced exhaust loss in the rotary engine 14.

[0064] Specifically, the ECM 84 refers to a map (predetermined and stored) that defines the relationship between the engine load (charging efficiency) and the EGR rate, as shown in Fig. 16, for example, and acquires the EGR rate that corresponds to the required engine load input from the PCM 84 in step S302. The map in Fig. 16 illustrates the relationship between the engine load and the EGR rate when the engine speed R is constant, with the horizontal axis representing the engine load and the vertical axis representing the EGR rate. According to the map in Fig. 16, the higher the engine load, the higher the EGR rate and the smaller the rate of increase in the EGR rate.

[0065] When the engine load is relatively high, the pressure rise due to the main combustion occurring on the leading side of the working chamber 24 becomes steeper, which tends to increase the cooling loss relatively. Therefore, as described above, when the engine load is relatively high, the EGR rate is set higher to increase the proportion of second-stage combustion compared to when the engine load is relatively low, thereby making it possible to moderate the pressure rise due to the main combustion and reduce the cooling loss. Furthermore, by decreasing the rate of increase in the EGR rate in response to an increase in the engine load as the engine load increases, the exhaust loss caused by the second-stage combustion, which has a delayed combustion timing, can be prevented from becoming excessive.

[0066] Furthermore, when the engine load is relatively low, the cooling loss due to the main combustion is small, so the impact of exhaust loss due to the second-stage combustion occurring later than the main combustion becomes relatively large. Therefore, when the engine load is relatively low, the EGR rate can be set lower than when the engine load is relatively high, thereby reducing the proportion of second-stage combustion and reducing exhaust loss due to second-stage combustion.

[0067] Furthermore, the ECM 84 references a map (predetermined and stored) that defines the relationship between engine speed and EGR rate, such as that shown in Fig. 17, and acquires the EGR rate corresponding to the engine speed detected by the eccentric shaft angle sensor 58. The map in Fig. 17 illustrates the relationship between engine speed and EGR rate when the engine load is constant, with the horizontal axis representing engine speed and the vertical axis representing the EGR rate. According to the map in Fig. 17, the higher the engine speed, the lower the EGR rate and the smaller the rate of decrease in the EGR rate.

[0068] When the engine speed is relatively low, the squish flow flowing from the trailing side to the leading side within the working chamber 24 during the combustion stroke is relatively weak, and flame propagation is slow. This causes the unburned mixture remaining on the trailing side of the working chamber 24 to self-ignite earlier than the main combustion flame propagates, making knocking more likely to occur. Therefore, when the engine speed is relatively low, the EGR rate is set higher than when the engine speed is relatively high to increase the proportion of second-stage combustion, i.e., to reduce the proportion of main combustion. This makes it possible to slow the pressure rise due to main combustion and suppress knocking. On the other hand, when the engine speed is relatively high and knocking is unlikely to occur, the EGR rate is set lower to reduce the proportion of second-stage combustion, making it possible to reduce exhaust losses due to second-stage combustion, which has a delayed combustion timing.

[0069] As described above, the ECM 70 acquires the EGR rate corresponding to the engine speed and the required engine load, and sets the opening of the EGR valve 50 corresponding to the acquired EGR rate based on a map or a calculation formula (pre-set and stored) that defines the relationship between the EGR rate and the opening of the EGR valve 50.

[0070] Next, in step S305, the ECM 70 sets the ignition timing of the spark plug 26 based on the engine speed detected by the eccentric shaft angle sensor 58 and the required engine load input from the PCM 84. Specifically, the ECM 70 references a map (predetermined and stored) that defines the relationship between the ignition timing of the spark plug 26 and the engine speed and engine load (charging efficiency), and sets the ignition timing that corresponds to the engine speed detected by the eccentric shaft angle sensor 58 and the required engine load input from the PCM 84 in step S302.

[0071] Next, in step S306, the PCM 84 calculates control variables for various devices of the rotary engine 14, such as the injectors 54, spark plugs 26, EGR valve 50, and throttle valve 36, so as to achieve the number of fuel injections, fuel injection timing, and fuel injection amount set in step S303, the EGR valve opening set in step S304, and the ignition timing set in step S305, and outputs electrical signals corresponding to the calculated control variables to those devices. This control of various devices continues until the rotary engine 14 is operated at the required engine speed and required engine load input from the PCM 84. After step S306, the PCM 84 ends combustion control and returns to the engine control shown in FIG. 4.

[0072] <Modification> Although the embodiments of the present invention have been described above, the specific configurations and means of the present invention can be modified and improved as desired within the scope of the technical ideas of the inventions set forth in the claims. Such modifications will be described below.

[0073] First, the problems that the invention aims to solve and the effects of the invention are not limited to those described above, and the present invention may solve problems that are not described or achieve effects that are not described, or may solve only some of the problems that are described or achieve only some of the effects that are described.

[0074] In the above-described embodiment, the rotary engine 14 is mounted on a series hybrid vehicle 1, but the combustion control of this embodiment can also be applied to rotary engines mounted on parallel hybrid vehicles, split hybrid vehicles, and non-hybrid vehicles.

[0075] <Action and effect> Next, the effects of the series hybrid vehicle 1 and the engine system 12 of this embodiment will be described.

[0076] In this embodiment, when the engine speed R is equal to or less than the first speed R1, the ECM 70 controls the injector 54 so that the number of fuel injections in one combustion cycle of each working chamber 24 is greater and the end timing of the final fuel injection is retarded compared to when the engine speed R is higher than the first speed R1.

[0077] As a result, when the engine speed R is relatively low, i.e., when the airflow in the working chamber 24 is relatively weak, by increasing the number of fuel injections in one combustion cycle of each working chamber 24 and retarding the end timing of the final fuel injection, it is possible to distribute fuel evenly from the leading side to the trailing side even if the airflow in the working chamber 24 is weak, and a homogeneous mixture can be obtained.

[0078] Furthermore, when the engine speed R is equal to or less than a second speed R2 that is lower than the first speed R1, the ECM 70 controls the injectors 54 so that the number of fuel injections in one combustion cycle of each working chamber 24 is greater and the injection end timing of the final fuel injection is retarded, compared to when the engine speed R is higher than the second speed R2. As a result, the lower the engine speed R is, i.e., the weaker the airflow in the working chambers 24, the more the number of fuel injections in one combustion cycle of each working chamber 24 is increased and the more retarded the injection end timing of the final fuel injection is, thereby making it possible to distribute fuel evenly from the leading side to the trailing side even when the airflow in the working chambers 24 is weak, and to obtain a homogeneous mixture.

[0079] Furthermore, when the engine speed R is equal to or lower than the first speed R1, the ECM 70 controls the injector 54 so that the proportion of the first fuel injection amount in one combustion cycle of each working chamber 24 increases as the engine load increases at the same engine speed. At the same engine speed, the higher the engine load, the greater the amount of fresh air flowing into the working chamber 24 and the stronger the airflow toward the leading side. However, by increasing the proportion of the first fuel injection amount and increasing the amount of fuel injected toward the leading side as the engine load increases, it is possible to promote mixing of the fresh air flowing toward the leading side with the fuel and obtain a homogeneous mixture.

[0080] In particular, in a series hybrid vehicle 1 in which the driving force of the rotary engine 14 is used only to drive the starter generator 10, the rotary engine 14 tends to be operated in a region of high thermal efficiency, that is, a region in which the engine speed R is relatively low and the airflow in the working chamber 24 is weak. Therefore, the engine system 12 of this embodiment, which can obtain a homogeneous air-fuel mixture even in a region in which the engine speed R is relatively low and the airflow in the working chamber 24 is weak, is suitable for the series hybrid vehicle 1. [Explanation of symbols]

[0081] 1 Series Hybrid vehicle 2 Reducer 4 drive wheels 6 electric motor 8 Battery 10 Starter generator 12 Engine System 14 Rotary engine 16 rotor housing 18 Side housing 20 rotors 22 Eccentric shaft 24 Working chamber 26 Spark plug 28 Intake port 30 Exhaust port 32 Intake passage 34 Exhaust passage 36 Throttle valve 38 Throttle opening sensor 40 Airflow sensor 42 Air cleaner 44 EGR device 46 EGR passage 48 EGR cooler 50 EGR valve 52 EGR valve opening sensor 54 Injector 56 Metering oil pump 58 Eccentric shaft angle sensor 60 Intake pressure sensor 62 Intake air temperature sensor 64 Water temperature sensor 70 ECM 72 processors 74 Memory section 76 Voltage Sensor 78 Current Sensor 80 BCM 82 Accelerator opening sensor 84 PCM 86 SGCM

Claims

1. a rotary engine including a rotor housing, a side housing, a rotor accommodated in a rotor accommodating chamber surrounded by the rotor housing and the side housing and forming three working chambers, and an injector that injects fuel into one of the working chambers; a rotation speed sensor for detecting an engine rotation speed of the rotary engine; a controller configured to control fuel injection by the injector; the controller controls the injectors so that, when the engine speed is equal to or lower than a first speed, the number of fuel injections in one combustion cycle for each of the working chambers is greater and the end timing of the final fuel injection is retarded compared to when the engine speed is higher than the first speed; when the engine speed is equal to or lower than the first speed, the controller controls the injector so that the proportion of the first fuel injection amount in one combustion cycle of each of the working chambers increases as the load of the rotary engine increases at the same engine speed. Engine system.

2. When the engine speed is equal to or lower than a second speed that is lower than the first speed, the controller controls the injector so that the number of fuel injections in one combustion cycle of each of the working chambers is greater and the injection end timing of the last fuel injection is retarded, compared to when the engine speed is equal to or lower than the first speed and higher than the second speed. The engine system of claim 1 .

3. A series hybrid vehicle including an electric motor as a driving force source and a generator capable of supplying electric power to the electric motor, The engine system according to claim 1 or 2, The rotary engine drives the generator. Series hybrid vehicle.

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