Vehicle control system

Abstract

To achieve request output of a vehicle at the time of operating an engine when an air-fuel ratio of the engine is a threshold value or more.SOLUTION: A controller 90 comprises the steps of: calculating, as a basic processing, an engine basic value which is a basic value of request output of the engine 20 to obtain the request output of the vehicle 10 under a driving condition of the engine where the air-fuel ratio is not restricted when an engine 20 is operated while an air-fuel ratio of the engine 20 is a threshold value or more and an electric motor basic value which is a basic value of MG40 request output; and decreasing, as a change processing, when the engine basic value is larger than a maximum value of output the engine 20 can achieve in a case that the engine 20 operates at a target air-fuel ratio, the request output of the engine 20 from the engine basic value to an engine correction value that is the maximum value or less, and increasing the MG40 request output from the electric motor basic value to an electric motor correction value by a decreased amount of the request output of the engine 20.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a control device for a vehicle.

Background Art

[0002] The vehicle disclosed in Patent Document 1 includes an engine, a first electric motor, a torque converter, a second electric motor, drive wheels, and a control device. The first electric motor, the torque converter, and the second electric motor are arranged in this order along the power transmission path from the engine to the drive wheels. The control device calculates the output that the engine should bear in driving the vehicle as the required output of the engine. Then, the control device determines an operating point that satisfies the required torque of this engine, that is, a combination of the torque and rotational speed of the engine. Further, the control device adjusts the torque of the first electric motor and the torque of the second electric motor, so that the first electric motor, the torque converter, and the second electric motor function as a continuously variable transmission as a whole.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a vehicle such as that of Patent Document 1, an engine fueled by hydrogen may be employed. In an engine fueled by hydrogen, water is generated in the cylinder due to the combustion of the air-fuel mixture containing hydrogen in the cylinder. Therefore, from the viewpoint of preventing an excessive amount of water from remaining in the engine, it is necessary to suppress the amount of water generated in the cylinder. And in suppressing the amount of water generated in the cylinder, it is conceivable to limit the air-fuel ratio in the cylinder to a predetermined value or more. However, when such a restriction is imposed on the air-fuel ratio, the output of the engine is restricted. Along with that, there is a possibility that the required output of the engine cannot be satisfied. [Means for solving the problem]

[0005] A vehicle control device for solving the above problems comprises a hydrogen-fueled engine and an electric motor located on the power transmission path from the engine to the drive wheels, and is configured such that the sum of the engine output and the electric motor output is transmitted to the drive wheels. The control device is capable of performing lean combustion control to operate the engine with an air-fuel ratio greater than or equal to a predetermined threshold, and during the execution of the lean combustion control, it performs a setting process to set the target air-fuel ratio of the engine to a value greater than or equal to the threshold, and operates the engine under predetermined conditions without air-fuel ratio restrictions. The system performs a basic process to calculate an engine base value, which is the base value of the engine's requested output, and an electric motor base value, which is the base value of the electric motor's requested output, so that the vehicle's requested output can be obtained. If the engine base value is greater than the maximum output that the engine can achieve when the engine is operated at the target air-fuel ratio, the system performs a modification process to reduce the engine's requested output from the engine base value to an engine correction value that is less than or equal to the maximum value, and to change the electric motor's requested output from the electric motor base value to an electric motor correction value that is increased by the same amount as the absolute value of the reduction. [Effects of the Invention]

[0006] With the above configuration, the required output for the vehicle can be achieved even when the engine is operated with an air-fuel ratio above the threshold. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of the vehicle's configuration. [Figure 2] This is a flowchart illustrating the processing procedure for lean combustion control. [Figure 3] This diagram shows the operation lines for each gear in relation to the equal output lines. [Figure 4] This diagram shows the operating curves for each air-fuel ratio in relation to the equal power curve. [Figure 5] This diagram explains the method for calculating engine correction values. [Modes for carrying out the invention]

[0008] Hereinafter, one embodiment of the vehicle control device will be described with reference to the drawings. As shown in Figure 1, the vehicle 10 includes an engine 20, a motor generator (hereinafter referred to as MG40), a clutch mechanism 30, a transmission unit 50, a differential 71, and drive wheels 11.

[0009] The engine 20 is the power source for the vehicle 10. The engine 20 is equipped with a crankshaft 24. Details of the engine 20 will be described later. The MG40 is also a power source for the vehicle 10. The MG40 has the functions of both an electric motor and a generator. The MG40 is equipped with an output shaft 43 that rotates integrally with the rotor 42. The MG40 is an example of an electric motor. The clutch mechanism 30 is interposed between the crankshaft 24 and the output shaft 43 of the MG40. The clutch mechanism 30 connects the crankshaft 24 and the output shaft 43, or disconnects them, depending on the hydraulic pressure from a hydraulic mechanism (not shown).

[0010] The transmission unit 50 includes a torque converter 51 and a transmission mechanism 56. The torque converter 51 includes a pump impeller 52, a turbine impeller 53, and a lock-up clutch 54. The torque converter 51 is a fluid coupling with a torque amplification function. The pump impeller 52 rotates integrally with the output shaft 43 of the MG 40. The turbine impeller 53 rotates integrally with the input shaft 57 of the transmission mechanism 56. The lock-up clutch 54 directly connects the pump impeller 52 and the turbine impeller 53 according to the hydraulic pressure from the hydraulic mechanism. In this embodiment, the lock-up clutch 54 is assumed to keep both impellers directly connected at all times while the vehicle 10 is running. The transmission mechanism 56 is a multi-stage type in which the gear ratio is switched in multiple stages by switching gears. The transmission mechanism 56 changes the rotational motion of the input shaft 57 in the transmission mechanism 56 according to the currently selected gear stage and outputs it from the output shaft 58. The gear ratio is the ratio that indicates the number of rotations of the input shaft 57 when the output shaft 58 rotates once. The output shaft 58 is connected to the left and right drive wheels 11 via the differential 71.

[0011] As described above, in the drivetrain of the vehicle 10, the MG40 is located in the power transmission path from the engine 20 to the drive wheels 11. In this drivetrain, when the clutch mechanism 30 is engaged, the sum of the output of the engine 20 and the output of the MG40 is transmitted to the drive wheels 11.

[0012] Vehicle 10 is equipped with a battery 81 and an inverter 82. The battery 81 is electrically connected to the MG40 via the inverter 82. The battery 81 supplies power to the MG40 and stores the power generated by the MG40. The inverter 82 converts DC to AC. When the MG40 functions as an electric motor, the torque of the MG40 (hereinafter referred to as motor torque) is a positive value. When the MG40 functions as a generator, the motor torque is a negative value.

[0013] The engine 20 will now be described in detail. The engine 20 comprises multiple cylinders 21, multiple injection valves 22, multiple spark plugs 23, and the crankshaft 24. Each cylinder 21 is a space for burning a mixture of fuel and intake air. An injection valve 22 is provided for each cylinder 21. The injection valve 22 injects hydrogen as fuel for the engine 20. For example, the injection valve 22 directly injects hydrogen into the cylinder 21. A spark plug 23 is provided for each cylinder 21. The spark plug 23 ignites the mixture in the cylinder 21. The crankshaft 24 rotates using the power generated by the combustion of the mixture in the multiple cylinders 21.

[0014] The engine 20 includes an intake passage 25 and a throttle valve 26. The intake passage 25 is a passage for introducing intake air into each cylinder 21. The intake passage 25 is connected to each cylinder 21. The throttle valve 26 is located in the middle of the intake passage 25. The throttle valve 26's opening degree is adjustable. The flow rate of intake air in the intake passage 25 changes according to the opening degree of the throttle valve 26.

[0015] The engine 20 is equipped with an exhaust passage 27 and a catalytic converter 28. The exhaust passage 27 is a passage for discharging exhaust gas from each cylinder 21. The exhaust passage 27 is connected to each cylinder 21. The catalytic converter 28 is located in the middle of the exhaust passage 27. The catalytic converter 28 purifies NOx contained in the exhaust gas flowing through the exhaust passage 27.

[0016] Vehicle 10 is equipped with various sensors. These sensors include a crank angle sensor 101, a temperature sensor 102, an airflow meter 103, an atmospheric pressure sensor 104, an accelerator sensor 105, a vehicle speed sensor 106, and a battery sensor 107. The crank angle sensor 101 detects the rotation angle of the crankshaft 24. The airflow meter 103 detects the flow rate of intake air in the intake passage 25. The temperature sensor 102 detects the temperature T of the catalyst 28. These three sensors 101-103 constitute part of the engine 20. The atmospheric pressure sensor 104 detects the atmospheric pressure P. The accelerator sensor 105 detects the accelerator opening AC, which is the amount of accelerator pedal operation by the driver of vehicle 10. The vehicle speed sensor 106 detects the vehicle speed V, which is the driving speed of vehicle 10. The battery sensor 107 detects battery information such as the temperature, voltage, and current of the battery 81. Each sensor repeatedly outputs a signal corresponding to the information it has detected to the control device 90, which will be described later.

[0017] Vehicle 10 is equipped with an operating unit 15 that the driver operates when selecting a driving mode for vehicle 10. The operating unit 15 outputs a signal corresponding to the driving mode selected by the driver to the control device 90, which will be described later. There are two pre-configured driving modes for vehicle 10: a normal mode and a sport mode. Sport mode is a mode that increases the responsiveness of the vehicle 10's acceleration when the driver operates the accelerator pedal compared to when normal mode is selected.

[0018] Vehicle 10 includes a control device 90. The control device 90 includes a CPU 91 and a memory 92. The memory 92 stores in advance various programs in which processes to be executed by the CPU 91 are described, and various data necessary for the execution of the programs. The CPU 91 sequentially calculates necessary parameters based on signals received from various sensors. For example, the CPU 91 calculates the engine speed, which is the rotation speed of the crankshaft 24, based on the rotation angle of the crankshaft 24. Further, the CPU 91 calculates a charge rate G, which is the ratio of the remaining capacity to the full charge capacity of the battery 81, based on the battery information. The CPU 91 controls the engine 20, the MG 40, the transmission unit 50, the clutch mechanism 30, etc. based on signals received from the operation unit 15 and various sensors, information calculated therefrom, etc. For example, the CPU 91 switches the gear stage of the transmission mechanism 56 based on the accelerator opening AC and the vehicle speed V.

[0019] The CPU 91 can cause the vehicle 10 to perform hybrid driving or battery driving. When causing the vehicle 10 to perform hybrid driving, the CPU 91 controls the engine 20 and the MG 40 after putting the clutch mechanism 30 in the connected state. When causing the vehicle 10 to perform battery driving, the CPU 91 controls the MG 40 after putting the clutch mechanism 30 in the disconnected state.

[0020] The following describes in detail the processing performed by the CPU 91 when the vehicle 10 is to perform hybrid driving. When the vehicle 10 is to perform hybrid driving, the CPU 91 performs either normal control or lean combustion control. The CPU 91 selects which of these control to perform depending on the operating state of the engine 20. The CPU 91 selects lean combustion control if certain conditions are met, such as the requirement to suppress the generation of water in cylinder 21, and selects normal control otherwise. Normal control is a control that operates the engine 20 without imposing any restrictions on the air-fuel ratio λ. Lean combustion control is a control that operates the engine 20 with the air-fuel ratio λ of the engine 20 set to a value within a predetermined allowable range λR. The lower limit threshold λR1 of the allowable range λR is a value greater than the stoichiometric air-fuel ratio, that is, a value leaner than the stoichiometric air-fuel ratio. Therefore, when lean combustion control is performed, the combustion of the engine 20 becomes lean combustion at an air-fuel ratio λ that is leaner than the stoichiometric air-fuel ratio. The lower threshold λR1 is predetermined, for example through experiments, as a value that keeps the amount of water generated in cylinder 21 below an acceptable level. When lean combustion is performed in engine 20, the output of engine 20 decreases. Taking this into consideration, the upper threshold λR2 of the acceptable range λR is predetermined, for example through experiments, as a value that ensures a certain level of output from engine 20 even when lean combustion is performed. The CPU 91 can estimate the amount of water accumulating in engine 20 based on the fuel injection amount and intake air flow rate. The CPU 91 determines that there is a need to suppress water generation if such water amount exceeds a predetermined standard value.

[0021] When specific conditions are met, the CPU 91 repeats lean combustion control in a predetermined control cycle. Hereinafter, a series of processes of lean combustion control will be described. As shown in FIG. 2, when starting the lean combustion control, the CPU 91 first executes the process of step S10. In step S10, the CPU 91 calculates the output required for driving the vehicle 10 (hereinafter referred to as the required output Y of the vehicle 10). The CPU 91 calculates the required output Y of the vehicle 10 based on the vehicle speed V, the accelerator opening AC, the charge rate G of the battery 81, and the like. The control device 90 calculates the required output Y of the vehicle 10 as a larger value as the accelerator opening AC is larger. When the CPU 91 calculates the required output Y of the vehicle 10, the process proceeds to step S20. As is well known, the output is a parameter representing the product of the rotational speed and the torque.

[0022] In step S20, the CPU 91 calculates the engine base value E1 and the motor base value M1. The engine base value E1 is the base value of the engine 20's requested output EY. The motor base value M1 is the base value of the MG 40's requested output MY. In calculating the engine base value E1 and the motor base value M1, the CPU 91 distributes the vehicle 10's requested output Y, calculated in step S10, to the engine base value E1 and the motor base value M1. Here, the sum of engine torque and motor torque is referred to as system torque. The engine speed is also referred to as system speed. Note that during hybrid driving, the engine speed and the speed of the output shaft 43 of the MG 40 (hereinafter referred to as motor speed) are the same. The CPU 91 distributes the vehicle 10's requested output Y to the engine base value E1 and the motor base value M1, for example, as follows. The CPU 91 calculates a reference operating point for the combination of system torque and system rotational speed that satisfies the vehicle 10's requested output Y, specifically the combination corresponding to the currently selected gear. When calculating the reference operating point, the CPU 91 uses a first map, such as the one shown in Figure 3. The first map represents operating lines for each gear and multiple equal-output lines in a Cartesian coordinate system with system rotational speed on the X-axis and system torque on the Y-axis. Figure 3 illustrates two operating lines and two equal-output lines. The operating lines show the relationship between system rotational speed and system torque at a specific gear. As shown by the solid line in Figure 3, the operating lines have the characteristic that system torque increases as system rotational speed increases. As shown by the dashed line in Figure 3, the equal-output lines are inverse proportion curves. Using the first map, the CPU 91 identifies the intersection point W between the equal-output line corresponding to the requested output Y calculated in step S10 and the operating line corresponding to the currently selected gear. The CPU 91 then calculates the combination of system rotational speed and system torque at this intersection W as the reference operating point. Once the CPU 91 has calculated the reference operating point, it distributes the system torque at the reference operating point between the required engine torque and the required MG torque. At this time, the CPU 91 sets the required engine torque to the following value without limiting the air-fuel ratio λ of the engine 20.In other words, the CPU 91 sets the requested engine torque to the value that provides the best fuel efficiency for engine 20 at the system rotational speed of the reference operating point. Then, the CPU 91 sets the requested MG torque to the value obtained by subtracting the requested engine torque from the system torque. The requested MG torque may also be negative. The CPU 91 may readjust the torque distribution thus allocated, taking into account the charge rate G of battery 81. For example, this would occur if the amount of power generated by MG40 is insufficient to meet the charge demand of battery 81. Due to the readjustment of the torque distribution, the requested engine torque may deviate slightly from the value that provides the best fuel efficiency at the system rotational speed of the reference operating point. Based on the information obtained through the above processing, the CPU 91 sets the basic operating points for engine 20 and MG40, respectively. In other words, the CPU 91 sets the combination of the requested engine torque and the system rotational speed of the reference operating point as the basic operating point for engine 20. The CPU 91 also sets the combination of the requested MG torque and the system rotational speed of the reference operating point as the basic operating point for MG40.

[0023] The CPU 91 calculates the basic operating points for engine 20 and MG40, and then calculates the engine base value E1 and the motor base value M1. Specifically, the CPU 91 defines the engine base value E1 as the product of the engine speed and engine torque, which are the basic operating points for engine 20. Similarly, the CPU 91 defines the motor base value M1 as the product of the motor speed and motor torque, which are the basic operating points for MG40. Once the CPU 91 calculates the engine base value E1, it provisionally sets this engine base value E1 as the requested output EY for engine 20. Furthermore, once the CPU 91 calculates the motor base value M1, it provisionally sets this motor base value M1 as the requested output MY for MG40. After this, as shown in Figure 2, the CPU 91 proceeds to step S30. Note that the processing in step S20 is basic processing. As described above, in this basic processing, the operating condition for engine 20 used to calculate the engine base value E1 and motor base value M1 is predetermined to be that fuel efficiency is optimal or close to it. The CPU 91 then calculates the engine base value E1 and the electric motor base value M1 so that the vehicle 10 can obtain the required output Y under operating conditions where there is no air-fuel ratio restriction and the engine 20 achieves the best fuel efficiency. "Best fuel efficiency" means the state in which the torque of the engine 20 per unit amount of fuel is maximized.

[0024] Now, in step S30, the CPU 91 calculates the target air-fuel ratio λS for the engine 20. In calculating the target air-fuel ratio λS, the CPU 91 first calculates the air-fuel ratio reference value λB. The CPU 91 calculates the air-fuel ratio reference value λB as a value within the above-mentioned allowable range λR. The CPU 91 calculates the air-fuel ratio reference value λB considering the water reduction target and emissions in the engine 20. After calculating the air-fuel ratio reference value λB, the CPU 91 corrects this air-fuel ratio reference value λB using the following (Equation 1). Then, the CPU 91 sets the corrected value as the target air-fuel ratio λS.

[0025] (Formula 1) λS=λB×α1×α2×α3×α4 The CPU 91 applies the following positive values ​​to each coefficient α1 to α4 in (Equation 1): The CPU 91 sets the first coefficient α1 to a smaller value as the rate of increase of the accelerator opening AC increases. That is, the CPU 91 sets the target air-fuel ratio λS to a smaller value as the rate of increase of the accelerator opening AC increases. When sport mode is selected, the CPU 91 sets the second coefficient α2 to a smaller value compared to when normal mode is selected. That is, when sport mode is selected, the CPU 91 sets the target air-fuel ratio λS to a smaller value compared to when normal mode is selected. The CPU 91 sets the third coefficient α3 to a smaller value as the atmospheric pressure P is lower. That is, the CPU 91 sets the target air-fuel ratio λS to a smaller value as the atmospheric pressure P is lower. The CPU 91 sets the fourth coefficient α4 to a smaller value as the temperature T of the catalyst 28 is higher. That is, the CPU 91 sets the target air-fuel ratio λS to a smaller value as the temperature T of the catalyst 28 is higher. The CPU 91 sets each coefficient based on the latest information regarding parameters related to each coefficient, such as the temperature T of the catalyst 28. If the target air-fuel ratio λS calculated using (Equation 1) is smaller than the lower limit threshold λR1 of the allowable range λR, the CPU 91 replaces the target air-fuel ratio λS with the lower limit threshold λR1 from the value calculated using (Equation 1). If the target air-fuel ratio λS calculated using (Equation 1) is larger than the upper limit threshold λR2 of the allowable range λR, the CPU 91 replaces the target air-fuel ratio λS with the upper limit threshold λR2 from the value calculated using (Equation 1). By calculating the target air-fuel ratio λS in this way, the CPU 91 sets the target air-fuel ratio λS to a value within the allowable range λR. Once the CPU 91 has calculated the target air-fuel ratio λS, it proceeds to step S40. The processing in step S30 is a setting process.

[0026] In step S40, the CPU 91 calculates the maximum output EQ, which is the maximum output that the engine 20 can achieve when it is operated at the target air-fuel ratio λS calculated in step S30. As a prerequisite for the processing in step S40, the second map shown in Figure 4 will be explained. The second map shows the operating lines for each air-fuel ratio λ and multiple equal-output lines in a Cartesian coordinate system with engine speed on the X axis and engine torque on the Y axis. In Figure 4, the operating lines are shown as solid lines and the equal-output lines are shown as dashed lines. The operating lines show the relationship between engine speed and engine torque when the engine 20 is operated with a constant air-fuel ratio λ. The four air-fuel ratios λ exemplified in Figure 4 have the relationship "stoichiometric air-fuel ratio < 1st air-fuel ratio λ1 < 2nd air-fuel ratio λ2 < 3rd air-fuel ratio λ3 < 4th air-fuel ratio λ4". Also, the three equal-output lines exemplified in Figure 4 have the relationship "1st output L1 < 2nd output L2 < 3rd output L3". As shown in Figure 4, for a given engine speed, the larger the air-fuel ratio λ, that is, the leaner the air-fuel ratio λ, the smaller the engine torque. In relation to this, the maximum output that engine 20 can achieve decreases as the air-fuel ratio λ increases. Now, in step S40, CPU 91 uses, for example, the second map shown in Figure 4 to calculate the maximum output EQ. That is, CPU 91 identifies the operating line corresponding to the target air-fuel ratio λS and calculates the maximum output of engine 20 on this operating line as the maximum output EQ. As shown in Figure 2, once CPU 91 has calculated the maximum output EQ, it proceeds to step S50.

[0027] In step S50, the CPU 91 determines whether the engine base value E1 calculated in step S20 is greater than the maximum output EQ calculated in step S40. If the engine base value E1 is less than or equal to the maximum output EQ (step S50: NO), the CPU 91 proceeds to step S80. On the other hand, if the engine base value E1 is greater than the maximum output EQ (step S50: YES), the CPU 91 proceeds to step S60.

[0028] In step S60, the CPU 91 calculates the engine correction value E2. Specifically, the CPU 91 calculates the value that best optimizes the fuel efficiency of the engine 20 among the output of the engine 20 that can be achieved at the target air-fuel ratio λS as the engine correction value E2. Although not shown in Figure 4, the second map, for example, also shows isofuel ratio lines, as illustrated by the dashed line in Figure 5. The isofuel ratio lines are distributed in a concentric circle pattern centered on the point with the best fuel efficiency. Note that the distribution of isofuel ratio lines shown in Figure 5 is just an example and does not necessarily match the actual distribution. In such a map, the CPU 91 identifies the engine correction value E2 as follows: That is, on the operating line corresponding to the target air-fuel ratio λS shown by the solid line in Figure 5, the CPU 91 identifies the combination of engine torque and engine speed that best optimizes fuel efficiency and satisfies the specified condition as the correction operating point WB. The specified condition is that the product of engine torque and engine speed is less than or equal to the maximum output EQ calculated in step S40. Once the CPU 91 identifies the correction operating point WB, it calculates the product of the engine torque and engine speed at the correction operating point WB as the engine correction value E2. After calculating the engine correction value E2, the CPU 91 resets this engine correction value E2 as the requested output EY of the engine 20. That is, as illustrated by arrow N in Figure 4, the CPU 91 reduces the requested output EY of the engine 20 from the engine base value E1 to the engine correction value E2. The CPU 91 changes the operating point corresponding to the requested output EY of the engine 20 from the base operating point WA to the correction operating point WB. As shown in Figure 2, after performing the above processing, the CPU 91 proceeds to step S70. Regarding step S60, if there is insufficient margin in the charge level G of the battery 81, the CPU 91 adjusts the engine correction value E2 so that the motor correction value M2, described later, becomes a value that can be achieved with the current charge level G. Even in this case, the CPU 91 sets the engine correction value E2 to the output that can be achieved with the target air-fuel ratio λS. In other words, the CPU 91 sets the engine correction value E2 to a value less than or equal to the maximum output EQ calculated in step S40. Due to this adjustment, the engine correction value E2 may deviate slightly from the value that provides the best fuel efficiency among the output of the engine 20 that can be achieved at the target air-fuel ratio λS.

[0029] In step S70, the CPU 91 calculates the motor correction value M2. Specifically, the CPU 91 calculates the difference value ΔE by subtracting the engine correction value E2 calculated in step S60 from the engine base value E1 calculated in step S20. The CPU 91 then adds this difference value ΔE to the motor base value M1 calculated in step S20. The CPU 91 then sets the resulting value as the motor correction value M2. Thus, the motor correction value M2 is a value that is increased from the motor base value M1 by the amount of the difference value ΔE. Once the CPU 91 calculates the motor correction value M2, it resets this motor correction value M2 as the requested output MY of the MG40. That is, the CPU 91 changes the requested output MY of the MG40 from the motor base value M1 to the motor correction value M2. When the CPU 91 sets the requested output MY for the MG40, it calculates the combination of motor speed and motor torque that satisfies this requested output MY as the correction operating point for the MG40. The motor speed at this correction operating point is the same as the engine speed at the correction operating point of the engine 20. Also, the motor torque at the correction operating point is obtained by dividing the requested output MY of the MG40 by the motor speed at the correction operating point. After performing the above processing, the CPU 91 proceeds to step S80. Note that the processing in steps S60 and S70 is modification processing.

[0030] In step S80, the CPU 91 controls the engine 20 based on the currently set engine 20 request output EY. If the CPU 91 skips steps S60 and S70 and proceeds to step S80, it controls the engine 20 at its basic operating point. On the other hand, if the CPU 91 proceeds through steps S60 and S70 to reach step S80, it controls the engine 20 at its correction operating point. In either case, the CPU 91 controls the engine 20 while adjusting the fuel injection amount and other parameters to achieve the target air-fuel ratio λS. In parallel with controlling the engine 20, the CPU 91 controls the MG40 based on the MG40 request output MY. If the CPU 91 controls the engine 20 at its basic operating point, it controls the MG40 at that basic operating point. If the CPU 91 controls the engine 20 at its correction operating point, it controls the MG40 at that correction operating point. After executing the process in step S80 for a predetermined period of time, the CPU 91 terminates the series of lean combustion control processes. Then, CPU91 executes the process of step S10 again.

[0031] This embodiment provides the following effects. (1) If the CPU 91 cannot achieve the engine base value E1 when the engine 20 is operated with an air-fuel ratio λ set to a target air-fuel ratio λS that is equal to or greater than the lower threshold λR1, it reduces the engine 20's requested output EY from the engine base value E1 to the engine correction value E2. Then, it increases the motor 40's requested output MY from the motor base value M1 to the motor correction value M2. By changing both the engine 20's requested output EY and the MG40's requested output MY in this way, the vehicle 10's requested output Y can be achieved even while lean combustion control is being performed.

[0032] (2) In lean combustion control, where the air-fuel ratio λ of engine 20 is limited to above the lower threshold λR1, the torque and consequently the output of engine 20 tend to be small. Although both engine 20 and MG40 supply the output of vehicle 10, it is preferable to maximize the output of engine 20 when the user requests acceleration. Therefore, when the rate of increase of the accelerator opening AC is large, the CPU 91 reduces the target air-fuel ratio λS. Consequently, when the rate of increase of the accelerator opening AC is large, the requested output EY of engine 20 can be set to a large value. This improves the responsiveness of the vehicle 10's acceleration. Therefore, in the above configuration, even when lean combustion control is being performed, acceleration in response to the user's request can be achieved.

[0033] (3) When sport mode is selected, the CPU 91 reduces the target air-fuel ratio λS compared to when normal mode is selected. Therefore, as explained above in relation to the accelerator opening AC, the acceleration responsiveness of the vehicle 10 is increased in sport mode. Thus, with the above configuration, even when lean combustion control is being performed, acceleration responsiveness according to the driving mode selected by the user can be achieved.

[0034] (4) When atmospheric pressure P is low, the output of the engine 20 decreases in relation to the amount of oxygen contained in the atmosphere. Therefore, the CPU 91 reduces the target air-fuel ratio λS when atmospheric pressure P is low. This makes it possible to set the required output EY of the engine 20 as high as possible, even when performing lean combustion control in an environment with low atmospheric pressure P.

[0035] (5) In the range of air-fuel ratio λ where the degree of leanness is relatively high, such as when lean combustion control is performed, reducing the air-fuel ratio λ tends to increase the amount of NOx produced. Taking this into consideration, the CPU 91 sets the target air-fuel ratio λS to a small value when the temperature T of the catalyst 28 is high and the exhaust purification performance by the catalyst 28 is high. This makes it possible to set the required output EY of the engine 20 as high as possible while suppressing the deterioration of emissions.

[0036] The above embodiment can be modified as follows. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically. The engine operating conditions assumed when calculating the engine base value E1 are not limited to those that result in the best fuel efficiency. For example, operating conditions that take into account the acceleration responsiveness and emissions of vehicle 10 may be predetermined. The assumed operating conditions may also be changed depending on the driving conditions of vehicle 10.

[0037] The calculation method for the engine base value E1 and the electric motor base value M1 is not limited to the example of the above embodiment. Any method that can calculate the engine base value E1 and the electric motor base value M1 so that the required output Y of the vehicle 10 can be obtained under the operating conditions of the engine 20 without air-fuel ratio restrictions is acceptable.

[0038] • When calculating the engine correction value E2, it is not essential to achieve optimal fuel efficiency. The engine correction value E2 may be calculated considering other requirements. The engine correction value E2 should be less than or equal to the maximum output EQ, which is the maximum output that engine 20 can achieve when operating engine 20 at the target air-fuel ratio λS.

[0039] The calculation method for the engine correction value E2 and the motor correction value M2 is not limited to the example of the above embodiment. It is sufficient to calculate the engine correction value E2 as a value less than or equal to the maximum output EQ, and to calculate the motor correction value M2 by increasing the motor base value M1 by the same amount as the absolute value of the decrease from the engine base value E1 to the engine correction value E2.

[0040] The method for determining the first coefficient α1 is not limited to the example of the above embodiment. If the first coefficient α1 is determined so that the target air-fuel ratio λS can be set to a smaller value when the rate of increase of the accelerator opening AC is at the first speed compared to the case where the rate of increase of the accelerator opening AC is at the second speed which is smaller than the first speed, then the effect of (2) above can be enjoyed.

[0041] The method for determining the third coefficient α3 is not limited to the example of the above embodiment. If the third coefficient α3 is determined so that the target air-fuel ratio λS can be set to a smaller value when atmospheric pressure P is 1 atmosphere compared to when atmospheric pressure P is 2 atmosphere, which is higher than 1 atmosphere, then the effect of (4) above can be enjoyed.

[0042] The method for determining the fourth coefficient α4 is not limited to the example of the above embodiment. If the fourth coefficient α4 is determined so that the target air-fuel ratio λS can be set to a smaller value when the temperature T of the catalyst 28 is the first temperature compared to when the temperature T is a second temperature which is smaller than the first temperature, then the effect of (5) above can be enjoyed.

[0043] The method for calculating the target air-fuel ratio λS is not limited to the examples of the above embodiment. The target air-fuel ratio λS may be calculated based on only some of the parameters among the accelerator opening AC, atmospheric pressure P, catalyst temperature T, and the driving mode of the vehicle 10. For example, one of the products of the air-fuel ratio reference value λB and the first coefficient α1, the product of the air-fuel ratio reference value λB and the second coefficient α2, the product of the air-fuel ratio reference value λB and the third coefficient α3, and the product of the air-fuel ratio reference value λB and the fourth coefficient α4 may be selected, and the selected value may be calculated as the target air-fuel ratio λS. The target air-fuel ratio λS may also be set independently of the accelerator opening AC, atmospheric pressure P, catalyst temperature T, and the driving mode of the vehicle 10. The target air-fuel ratio λS only needs to be set to a value within the allowable range λR.

[0044] The method for determining the lower threshold λR1 is not limited to the example of the above embodiment. The lower threshold λR1 may be determined as appropriate according to the requirements to be achieved, such as suppressing the amount of water generated in the engine 20. The method for determining the upper threshold λR2 is not limited to the example of the above embodiment. Furthermore, setting the upper threshold λR2 is not mandatory. Even if the required output EY of the engine 20 becomes considerably smaller due to the elimination of the upper threshold λR2, the required output Y of the vehicle 10 can be achieved by the output of the MG40, provided that the charge level G of the battery 81 is sufficient.

[0045] The overall configuration of the vehicle 10 is not limited to the examples of the above embodiment. A continuously variable transmission may be used in the transmission unit 50. The engine 20 may be one that uses hydrogen as fuel. [Explanation of symbols]

[0046] 10...Vehicle 11...Drive wheels 20...Engine 40...MG 90...Control unit

Claims

1. The vehicle being controlled is a vehicle comprising a hydrogen-fueled engine and an electric motor located on the power transmission path from the engine to the drive wheels, wherein the sum of the output of the engine and the output of the electric motor is transmitted to the drive wheels, and the vehicle is provided with two driving modes: a normal mode and a sport mode which increases the acceleration responsiveness of the vehicle compared to when the normal mode is selected. Lean combustion control can be performed to operate the engine with the air-fuel ratio of the engine set to a predetermined threshold or higher. During the execution of the lean combustion control, A setting process to set the target air-fuel ratio of the engine to a value equal to or greater than the threshold, A basic process for calculating the engine base value, which is the basic value of the engine's required output, and the motor base value, which is the basic value of the motor's required output, so that the vehicle's required output can be obtained under predetermined operating conditions of the engine without any restrictions on the air-fuel ratio, If the engine base value is greater than the maximum output that the engine can achieve when the engine is operated at the target air-fuel ratio, the engine's requested output is reduced from the engine base value to an engine correction value less than or equal to the maximum value, and the motor's requested output is changed from the motor's base value to a motor correction value increased by the same absolute value as the reduction, and this modification process is performed. In the setting process described above, when the sport mode is selected, the target air-fuel ratio is set to a smaller value compared to when the normal mode is selected. Vehicle control system.

2. The vehicle to be controlled is one that comprises a hydrogen-fueled engine and an electric motor located on the power transmission path from the engine to the drive wheels, and is configured such that the sum of the output of the engine and the output of the electric motor is transmitted to the drive wheels. Lean combustion control can be performed to operate the engine with the air-fuel ratio of the engine set to a predetermined threshold or higher. During the execution of the lean combustion control, A setting process to set the target air-fuel ratio of the engine to a value equal to or greater than the threshold, A basic process for calculating the engine base value, which is the basic value of the engine's required output, and the motor base value, which is the basic value of the motor's required output, so that the vehicle's required output can be obtained under predetermined operating conditions of the engine without any restrictions on the air-fuel ratio, If the engine base value is greater than the maximum output that the engine can achieve when the engine is operated at the target air-fuel ratio, the engine's requested output is reduced from the engine base value to an engine correction value less than or equal to the maximum value, and the motor's requested output is changed from the motor's base value to a motor correction value increased by the same absolute value as the reduction, and this modification process is performed. In the setting process described above, when the atmospheric pressure is 1 atmosphere, the target air-fuel ratio is set to a smaller value compared to when the atmospheric pressure is 2 atmosphere, which is higher than 1 atmosphere. Vehicle control system.

3. The control target is a vehicle comprising: an engine that uses hydrogen as fuel and is equipped with a catalyst for purifying exhaust gas flowing through an exhaust passage; and an electric motor located on a power transmission path from the engine to the drive wheels, wherein the sum of the output of the engine and the output of the electric motor is transmitted to the drive wheels, Lean combustion control can be performed to operate the engine with the air-fuel ratio of the engine set to a predetermined threshold or higher. During the execution of the lean combustion control, A setting process to set the target air-fuel ratio of the engine to a value equal to or greater than the threshold, A basic process for calculating the engine base value, which is the basic value of the engine's required output, and the motor base value, which is the basic value of the motor's required output, so that the vehicle's required output can be obtained under predetermined operating conditions of the engine without any restrictions on the air-fuel ratio, If the engine base value is greater than the maximum output that the engine can achieve when the engine is operated at the target air-fuel ratio, the engine's requested output is reduced from the engine base value to an engine correction value less than or equal to the maximum value, and the motor's requested output is changed from the motor's base value to a motor correction value increased by the same absolute value as the reduction, and this modification process is performed. In the setting process described above, when the catalyst temperature is at a first temperature, the target air-fuel ratio is set to a smaller value compared to when the temperature is at a second temperature which is lower than the first temperature. Vehicle control system.

Images