Hybrid vehicle control method and hybrid vehicle control device

Abstract

To enhance fuel consumption of a hybrid vehicle which continues fuel supply to an internal combustion engine when fuel cut is executable.SOLUTION: A hybrid vehicle has an operation mode that allows for: independently executing electric power generation using an internal combustion engine 10; and driving of drive wheels. The hybrid vehicle alters operation points of the internal combustion engine 10 according to an SOC of a battery and continues fuel supply to the internal combustion engine 10 when a fuel cut permission condition is satisfied during the operation mode with a temperature of a manifold catalyst 44 being prescribed temperature or more. In addition, the hybrid vehicle stops the fuel supply to the internal combustion engine 10 when the fuel cut permission condition is satisfied during the operation mode with the temperature of the manifold catalyst 44 being below the prescribed temperature.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control method for a hybrid vehicle and a control device for a hybrid vehicle. [Background technology]

[0002] For example, Patent Document 1 discloses a hybrid vehicle that, when a braking request is made while driving with the internal combustion engine in operation, performs one of the following control operations depending on the temperature of a catalyst that purifies the exhaust gas of the internal combustion engine and the battery's state of charge (SOC): catalyst deterioration suppression control, which continues the fuel supply to the internal combustion engine; fuel cut control, which stops the fuel supply to the internal combustion engine; or catalytic odor suppression control, which stops the fuel supply to the internal combustion engine and increases the amount of intake air compared to fuel cut control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-62021 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 merely determines whether or not to implement a so-called fuel cut in a hybrid vehicle, and does not determine subsequent operating conditions based on the temperature of the battery or catalyst. The catalyst degradation suppression control in Patent Document 1, for example, operates the internal combustion engine autonomously at an idle speed or a speed slightly higher than the idle speed, and does not take fuel economy into consideration. In other words, in hybrid vehicles, there is room for further improvement in fuel economy when fuel supply to the internal combustion engine is continued without implementing a fuel cut when a so-called fuel cut is possible. [Means for solving the problem]

[0005] The hybrid vehicle of the present invention has an operation mode in which power generation using an internal combustion engine and driving of drive wheels can be performed independently, and when a predetermined fuel cut permission condition is met while the temperature of an exhaust purification catalyst of the internal combustion engine is equal to or higher than a predetermined temperature during the operation mode, the operating point of the internal combustion engine is changed according to the SOC of a battery to continue fuel supply to the internal combustion engine. Also, when the fuel cut permission condition is met while the temperature of the catalyst is equal to or higher than a predetermined temperature during the operation mode, the operating point of the internal combustion engine is changed so that a higher output can be obtained as the SOC of the battery decreases. Furthermore, the operating point of the internal combustion engine that is set when the fuel cut permission condition is met while the temperature of the catalyst is at or above a predetermined temperature during the operating mode is determined taking into account the amount of power generation during the transition from the previous operating point of the internal combustion engine. [Effects of the Invention]

[0006] In the hybrid vehicle of the present invention, even when the fuel cut permission condition is met, the internal combustion engine can still output power depending on the state of the battery, so it is possible to efficiently cool the manifold catalyst 44 at an operating point with good fuel economy. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an explanatory diagram that schematically illustrates an outline of a drive system of a hybrid vehicle to which the present invention is applied; [Figure 2] 1 is an explanatory diagram showing a schematic system configuration of an internal combustion engine mounted on a hybrid vehicle to which the present invention is applied; [Figure 3] FIG. 2 is an explanatory diagram schematically showing a situation when an operating point of an internal combustion engine is changed. [Figure 4] 10 is a calculation table for calculating an output that is permitted when the internal combustion engine continues to operate when a fuel cut permission condition is met. [Figure 5] 10 is a rotation speed threshold calculation table. [Figure 6] 1 is a block diagram showing a control flow of a hybrid vehicle to which the present invention is applied; DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the present invention will be described in detail below with reference to the drawings.

[0009] FIG. 1 is an explanatory diagram that schematically shows an outline of a drive system of a hybrid vehicle 1 to which the present invention is applied.

[0010] The hybrid vehicle 1 has a drive unit 3 that drives drive wheels 2 and a power generation unit 4 that generates electric power for driving the drive wheels 2.

[0011] The drive unit 3 has a drive motor 5 that drives the drive wheels 2 to rotate, and a first gear train 6 and a differential gear 7 that transmit the driving force of the drive motor 5 to the drive wheels 2. The drive motor 5 is supplied with power from a battery 8 that is charged with electricity generated by the power generation unit 4, etc.

[0012] The power generation unit 4 has a generator 9 as a motor generator that generates electricity to be supplied to the drive motor 5, an internal combustion engine 10 that can drive the generator 9, and a second gear train 11 that transmits the rotation of the internal combustion engine 10 to the generator 9.

[0013] The hybrid vehicle 1 is a so-called series hybrid vehicle that does not use the internal combustion engine 10 as a power source. That is, the hybrid vehicle 1 runs with the internal combustion engine 10 dedicated to generating electricity and the drive motor 5 driving the drive wheels 2. For example, when the remaining battery charge of the battery 8 becomes low, the hybrid vehicle 1 drives the internal combustion engine 10 to generate electricity with the generator 9 in order to charge the battery 8. That is, the hybrid vehicle 1 has a running mode in which it runs using only the driving force of the drive motor 5.

[0014] The drive motor 5 is a direct drive source for the hybrid vehicle 1, and drives the hybrid vehicle 1 by converting DC power from the battery 8, for example, into AC power using an inverter or the like. The drive motor 5 is, for example, a synchronous motor that uses a permanent magnet in the rotor.

[0015] The drive motor 5 also functions as a generator when the hybrid vehicle 1 decelerates. That is, the drive motor 5 is a generator motor that can charge the battery 8 with regenerative energy generated when the vehicle decelerates as electric power.

[0016] The first gear train 6 reduces the rotation speed of the drive motor 5 and increases the motor torque to ensure sufficient drive torque for traveling.

[0017] The first gear train 6 is, for example, a two-stage reduction gear train, and has a motor shaft 14 equipped with a drive unit first gear 13, and a first idler shaft 17 equipped with a drive unit second gear 15 and a drive unit third gear 16. The motor shaft 14 is the rotation shaft of the drive motor 5.

[0018] The drive unit first gear 13 is meshed with the drive unit second gear 15. The drive unit third gear 16 is meshed with an input side gear 18 provided on the input side of the differential gear 7.

[0019] The differential gear 7 transmits the drive torque input from the first gear train 6 via the input gear 18 to the left and right drive wheels 2, 2 via left and right drive shafts 19, 19. The differential gear 7 can transmit the same drive torque to the left and right drive wheels 2, 2 while allowing for a difference in rotation speed between the left and right drive wheels 2, 2.

[0020] The generator 9 is, for example, a synchronous motor using a permanent magnet in its rotor. The generator 9 converts rotational energy generated in the internal combustion engine 10 into electrical energy and charges, for example, the battery 8. The generator 9 also functions as an electric motor that drives the internal combustion engine 10, and functions as a starter motor when the internal combustion engine 10 is started. In other words, the generator 9 is a generator motor that can supply generated electric power to the battery 8 and can be rotationally driven by electric power from the battery 8.

[0021] The electric power generated by the generator 9 may be supplied directly to the drive motor 5, depending on the operating state, instead of charging the battery 8. The internal combustion engine 10 may also be started by a dedicated starter motor different from the generator 9, for example.

[0022] The second gear train 11 is a gear train that connects the internal combustion engine 10 and the generator 9. The second gear train 11 has an engine shaft 24 equipped with a power generation unit first gear 23, a second idler shaft 26 equipped with a power generation unit second gear 25, and a generator input shaft 28 equipped with a power generation unit third gear 27.

[0023] During power generation operation, the second gear train 11 increases the rotation speed of the internal combustion engine 10 to transmit the engine torque required for the generator 9. When the generator 9 functions as a starter, the second gear train 11 reduces the rotation speed of the generator 9 to transmit the motor torque required for the internal combustion engine 10.

[0024] The engine shaft 24 rotates synchronously with a crankshaft 30 (see FIG. 2 described later) of the internal combustion engine 10. The generator input shaft 28 rotates synchronously with a rotor (not shown) of the generator 9.

[0025] The power generation unit first gear 23 is meshed with the power generation unit second gear 25. The power generation unit third gear 27 is meshed with the power generation unit second gear 25. In other words, the power generation unit first gear 23 and the power generation unit third gear 27 are meshed with the power generation unit second gear 25.

[0026] The internal combustion engine 10 is capable of transmitting the rotation of a crankshaft 30 to a rotor of a generator 9. The internal combustion engine 10 is, for example, a gasoline engine arranged in an engine room located on the front side of the hybrid vehicle 1.

[0027] FIG. 2 is an explanatory diagram that schematically shows the system configuration of the internal combustion engine 10. As shown in FIG.

[0028] The internal combustion engine 10 is a so-called reciprocating internal combustion engine that converts the reciprocating linear motion of a piston 31 into the rotational motion of a crankshaft 30 and extracts the power.

[0029] The internal combustion engine 10 has an intake passage 32 and an exhaust passage 33. The intake passage 32 is connected to a combustion chamber 35 via an intake valve 34. The exhaust passage 33 is connected to the combustion chamber 35 via an exhaust valve 36.

[0030] The internal combustion engine 10 has a fuel injection valve 37 that directly injects fuel (gasoline) into a combustion chamber 35. The fuel injected from the fuel injection valve 37 is ignited by a spark plug 39 in the combustion chamber 35. Note that the internal combustion engine 10 may also inject fuel into the intake port of each cylinder.

[0031] The intake passage 32 is provided with an air cleaner 40 that collects foreign matter in the intake air, an air flow meter 41 that detects the amount of intake air, and an electric throttle valve 43 whose opening is controlled by a control signal from a control unit 42.

[0032] The air flow meter 41 is disposed upstream of the throttle valve 43. The air flow meter 41 has a built-in temperature sensor and is capable of detecting the intake air temperature at the intake inlet. The air cleaner 40 is disposed upstream of the air flow meter 41.

[0033] A manifold catalyst 44 and an underfloor catalyst 45 are provided in the exhaust passage 33. The manifold catalyst 44 is provided relatively close to the combustion chamber 35, for example, directly downstream of the exhaust manifold assembly. The underfloor catalyst 45, which has a larger capacity than the manifold catalyst 44, is located downstream of the manifold catalyst 44. The manifold catalyst 44 and the underfloor catalyst 45 are exhaust purification catalysts made up of, for example, a three-way catalyst.

[0034] The internal combustion engine 10 also has an exhaust turbine type supercharger (turbocharger) 48 that includes a compressor 46 provided in the intake passage 32 and an exhaust turbine 47 provided in the exhaust passage 33, which are coaxially arranged. The compressor 46 is disposed upstream of the throttle valve 43 and downstream of the air flow meter 41. The exhaust turbine 47 is disposed upstream of the manifold catalyst 44.

[0035] A recirculation passage 49 is connected to the intake passage 32. One end of the recirculation passage 49 is connected to the intake passage 32 upstream of the compressor 46, and the other end is connected to the intake passage 32 downstream of the compressor 46.

[0036] An electric recirculation valve 50 is disposed in this recirculation passage 49, and is capable of releasing the boost pressure from the downstream side of the compressor 46 to the upstream side of the compressor 46. Note that the recirculation valve 50 may be a so-called check valve that opens only when the pressure downstream of the compressor 46 reaches or exceeds a predetermined pressure.

[0037] An intercooler 51 is provided in the intake passage 32 downstream of the compressor 46 to improve charging efficiency by cooling the intake air compressed (pressurized) by the compressor 46. The intercooler 51 is located downstream of the downstream end of the recirculation passage 49 and upstream of the throttle valve 43.

[0038] An exhaust bypass passage 52 is connected to the exhaust passage 33, bypassing the exhaust turbine 47 and connecting the upstream and downstream sides of the exhaust turbine 47. The downstream end of the exhaust bypass passage 52 is connected to the exhaust passage 33 at a position upstream of the manifold catalyst 44. An electric wastegate valve 53 is disposed in the exhaust bypass passage 52, which controls the exhaust flow rate in the exhaust bypass passage 52. The wastegate valve 53 is capable of bypassing a portion of the exhaust gas guided to the exhaust turbine 47 to the downstream side of the exhaust turbine 47, and is capable of controlling the boost pressure of the internal combustion engine 10.

[0039] The internal combustion engine 10 is also capable of exhaust gas recirculation (EGR), which introduces (recirculates) a portion of the exhaust gas from the exhaust passage 33 into the intake passage 32 as EGR gas, and has an EGR passage 54 branching off from the exhaust passage 33 and connected to the intake passage 32. One end of the EGR passage 54 is connected to the exhaust passage 33 at a position between the manifold catalyst 44 and the underfloor catalyst 45, and the other end is connected to the intake passage 32 at a position downstream of the air flow meter 41 and upstream of the compressor 46. The EGR passage 54 is provided with an electric EGR valve 55 that controls the flow rate of EGR gas in the EGR passage 54, and an EGR cooler 56 that can cool the EGR gas.

[0040] 1 denotes a collector portion of the intake passage 32. If the internal combustion engine 10 is a multi-cylinder internal combustion engine, the intake passage 32 branches off for each cylinder as an intake manifold downstream of the collector portion 57.

[0041] The control unit 42 is a well-known digital computer equipped with a CPU, a ROM, a RAM, and an input / output interface.

[0042] In addition to the detection signal of the air flow meter 41 described above, detection signals from various sensors such as a vehicle speed sensor 61 that detects the vehicle speed, a crank angle sensor 62 that detects the crank angle of the crankshaft 30, an accelerator opening sensor 63 that detects the amount of depression of the accelerator pedal, and a catalyst temperature sensor 64 that detects the temperature of the manifold catalyst 44 are input to the control unit 42.

[0043] The crank angle sensor 62 is capable of detecting the engine rotation speed of the internal combustion engine 10. The accelerator opening sensor 63 is capable of detecting the accelerator opening, which is the amount of accelerator pedal operation, as well as the accelerator pedal change speed, which is the accelerator pedal operation speed.

[0044] The control unit 42 as a control section optimally controls the amount and timing of fuel injected from the fuel injection valve 37, the ignition timing of the internal combustion engine 10 (spark plug 39), the amount of intake air, etc. based on detection signals from various sensors, and also controls the air-fuel ratio of the internal combustion engine 10.

[0045] The control unit 42 uses the detection value of the accelerator opening sensor 63 to calculate the required load of the internal combustion engine 10 (the load of the internal combustion engine 10).

[0046] The control unit 42 is also capable of detecting the SOC (State Of Charge), which is the ratio of the remaining charge to the charge capacity of the battery 8.

[0047] The hybrid vehicle 1 of the above-described embodiment is a so-called series hybrid vehicle that runs by driving the drive motor 5 with electric power from the generator 9 driven by the internal combustion engine 10 and electric power from the battery 8. In other words, the hybrid vehicle 1 has a battery 8 that is charged with electric power generated using the internal combustion engine 10, and has a driving mode that allows for independent generation of electric power using the internal combustion engine 10 and driving of the drive wheels 2 by the drive motor 5. When the SOC of the battery 8 becomes low while the series hybrid vehicle is running, the internal combustion engine 10 is driven to charge the battery 8.

[0048] Furthermore, when a predetermined fuel cut permission condition is met while the internal combustion engine 10 is operating, the control unit 42 implements a fuel cut to stop the supply of fuel to the internal combustion engine 10 under certain conditions. The fuel cut permission condition is met, for example, when the engine speed after warming up of the internal combustion engine 10 is equal to or higher than a predetermined fuel cut rotation speed, and the accelerator opening is equal to or lower than a predetermined opening (for example, the accelerator is off), or the required torque (required output) of the internal combustion engine 10 is equal to or lower than a predetermined value. Here, the above-mentioned certain condition is, for example, when the temperature of the manifold catalyst 44 is lower than a predetermined temperature (first predetermined temperature).

[0049] More specifically, when the fuel cut permission condition is met while the temperature of the manifold catalyst 44 is at or above a predetermined temperature (first predetermined temperature), the control unit 42 changes the operating point (operating conditions) of the internal combustion engine 10 in accordance with the SOC of the battery 8, and continues the supply of fuel to the internal combustion engine 10. The operating point of the internal combustion engine 10 is determined by the torque and engine speed of the internal combustion engine 10.

[0050] Furthermore, when the fuel cut permission condition is met while the temperature of the manifold catalyst 44 is below a predetermined temperature (first predetermined temperature), the control unit 42 stops the supply of fuel to the internal combustion engine 10. Here, the first predetermined temperature is, for example, a temperature at which the manifold catalyst 44 may deteriorate if fuel is cut.

[0051] When a predetermined fuel cut recovery permission condition is met during fuel cut of the internal combustion engine 10, the control unit 42 resumes fuel supply to the internal combustion engine 10. The fuel cut recovery condition is met, for example, when the accelerator opening becomes larger than a predetermined opening, or when the engine speed becomes equal to or lower than a predetermined fuel cut recovery speed without the accelerator pedal being depressed.

[0052] When fuel cut is performed on the manifold catalyst 44 from a high temperature state, the oxygen concentration in the exhaust gas supplied increases, causing aggregation of the catalytic precious metals and resulting in a decrease in catalytic function (catalyst deterioration). In other words, the amount of precious metals supported on the manifold catalyst 44 must be set taking into consideration such catalyst deterioration.

[0053] Therefore, when it is expected that the catalyst will deteriorate significantly, the amount of precious metal carried by the manifold catalyst 44 in a new state will be excessive, resulting in higher costs.

[0054] Therefore, when it is predicted that fuel cutoff will cause deterioration of the manifold catalyst 44, the hybrid vehicle 1 prohibits stopping the fuel supply to the internal combustion engine 10 (fuel cutoff) even if the fuel cutoff permission condition is met.

[0055] In more detail, when the internal combustion engine 10 is operating at an operating point in a region where there is a risk of thermal degradation of the manifold catalyst 44 if fuel is cut, the hybrid vehicle 1 does not perform fuel cut even if the fuel cut permission condition is met, but changes the operating point of the internal combustion engine 10 to an operating point in a region where there is no risk of thermal degradation of the manifold catalyst 44 in accordance with the SOC of the battery 8, and continues to supply fuel to the internal combustion engine 10, as shown in FIG.

[0056] 3 is an explanatory diagram that schematically shows a situation in which fuel supply to the internal combustion engine 10 is continued by changing the operating point of the internal combustion engine 10 according to the SOC of the battery 8 when a fuel cut permission condition is met. The dashed line L1 in FIG. 3 is a catalyst degradation temperature criterion (threshold value) that separates an operating region A, which indicates an operating region in which fuel cut may cause thermal degradation of the manifold catalyst 44, from an operating region B, which indicates an operating region in which fuel cut does not cause thermal degradation of the manifold catalyst 44. In other words, region A is an operating point of the internal combustion engine 10 at which the temperature of the manifold catalyst 44 is equal to or higher than a predetermined temperature (first predetermined temperature).

[0057] Operating point P in FIG. 3 is an operating point within region A. Operating point Q1 in FIG. 3 is an operating point within region B, which provides a relatively high output (high torque) within region B. Operating point Q1 is, for example, the best fuel economy point of internal combustion engine 10. Operating point Q2 in FIG. 3 is an operating point within region B, which provides a relatively medium output (torque) within region B. Operating point Q3 in FIG. 3 is an operating point within region B, which provides a relatively low output (low torque) within region B. Operating point Q3 is, for example, an operating point at which torque equivalent to the friction of internal combustion engine 10 is obtained. Furthermore, dashed dotted line L2 in FIG. 3 indicates an example of a rotation speed threshold value, which will be described later.

[0058] The control unit 42, while operating the internal combustion engine 10 at an operating point within the region A, When the fuel cut permission condition is met, when changing the operating point of the internal combustion engine 10 to an operating point within region B, it is determined which operating point within region B to change to depending on the SOC of the battery 8.

[0059] For example, if the SOC of the battery 8 has a sufficient margin, the operating point is changed to operating point Q1, which is the best fuel economy point. If the SOC of the battery 8 has a sufficient margin, charging the battery 8 with power generated during catalyst cooling operation at operating point Q1 will not result in overcharging, and the energy (fuel) consumed during catalyst cooling operation can be recovered as power, thereby suppressing deterioration in fuel economy. Also, for example, if the SOC of the battery 8 does not have a sufficient margin, the operating point is changed to operating point Q2, which has a lower torque than the best fuel economy point. For example, if the SOC of the battery 8 is high and there is no margin for charging the battery 8, the operating point is changed to operating point Q3, which has a lower torque, so that charging of the battery 8 does not occur. In this case, the energy (fuel) consumed during catalyst cooling operation is wasted, but overcharging of the battery 8 can be avoided.

[0060] This allows the internal combustion engine 10 to output power depending on the state of the battery 8, making it possible to efficiently cool the manifold catalyst 44 at an operating point with good fuel economy.

[0061] Furthermore, the manifold catalyst 44, which is in a high temperature state, is cooled by continuing to operate the internal combustion engine 10. In other words, it is possible to suppress deterioration of the manifold catalyst 44 that occurs when the catalyst is in a high temperature state. By continuing to operate the internal combustion engine 10, the manifold catalyst 44 is cooled, and when the temperature of the manifold catalyst 44 falls below a predetermined temperature, there is no longer any risk of deterioration, and if the fuel cut condition continues, a fuel cut is implemented.

[0062] Therefore, the amount of precious metal carried by the manifold catalyst 44 can be reduced, and the cost of the manifold catalyst 44 can be reduced.

[0063] When the fuel cut permission condition is met while the temperature of the manifold catalyst 44 is at or above a predetermined temperature (first predetermined temperature), the control unit 42 operates the internal combustion engine 10 at an operating point that provides a higher output as the SOC of the battery 8 decreases.

[0064] When the fuel cut permission condition is met with the temperature of the manifold catalyst 44 being equal to or higher than a predetermined temperature (first predetermined temperature), the control unit 42 is able to change the operating point of the internal combustion engine 10 to an operating point that provides the best fuel economy when the SOC of the battery 8 becomes equal to or lower than a predetermined first threshold. That is, when the fuel cut permission condition is met with the temperature of the manifold catalyst 44 being equal to or higher than a predetermined temperature (first predetermined temperature), the control unit 42 is able to change the operating point of the internal combustion engine 10 within a range whose upper limit is the output T1 (torque T1) that is obtained at the operating point that provides the best fuel economy when the SOC of the battery 8 becomes equal to or lower than the predetermined first threshold. At this time, the internal combustion engine 10 does not require a torque greater than the torque T1 that is obtained at the best fuel economy point, and therefore, in order to suppress deterioration of fuel economy, the internal combustion engine 10 is operated with the output that is obtained at the best fuel economy point when the SOC of the battery 8 is equal to or lower than the first threshold as its upper limit.

[0065] When the fuel cut permission condition is met with the temperature of the manifold catalyst 44 being equal to or higher than a predetermined temperature (first predetermined temperature), the control unit 42 can change the operating point of the internal combustion engine 10 to an operating point at which an output T2 (torque T2) corresponding to the friction of the internal combustion engine 10 is obtained when the SOC of the battery 8 is equal to or higher than a predetermined second threshold, as shown in Fig. 4. That is, when the fuel cut permission condition is met with the temperature of the manifold catalyst 44 being equal to or higher than a predetermined temperature (first predetermined temperature), the control unit 42 can change the operating point of the internal combustion engine 10 within a range up to the torque T2 (output T2) corresponding to the friction of the internal combustion engine 10 when the SOC of the battery 8 is equal to or higher than the predetermined second threshold. At this time, the internal combustion engine 10 cannot charge the battery 8 with power even if it generates power (the amount of power that can be charged to the battery 8 is small), and therefore no torque for power generation is required. Therefore, the internal combustion engine 10 is operated so as to obtain an output corresponding to the output T2 (torque T2) corresponding to the friction of the internal combustion engine 10 when the SOC of the battery 8 is equal to or higher than the second threshold.

[0066] Furthermore, when the fuel cut permission condition is met when the temperature of the manifold catalyst 44 is equal to or higher than a predetermined temperature (first predetermined temperature), as shown in FIG. 4, if the SOC of the battery 8 is greater than a first threshold value and less than a second threshold value, the control unit 42 operates the internal combustion engine 10 at an operating point that provides a higher output (higher torque) as the SOC of the battery 8 decreases.

[0067] When the fuel cut permission condition is satisfied while the temperature of the manifold catalyst 44 is equal to or higher than a predetermined temperature (first predetermined temperature), the rotation speed is limited so that the operating point of the internal combustion engine 10 is equal to or lower than the rotation speed threshold determined according to the vehicle speed. That is, when the fuel cut permission condition is satisfied while the internal combustion engine 10 is operating at an operating point in region A, the control unit 42 changes the operating point of the internal combustion engine 10 so that the engine rotation speed of the internal combustion engine 10 is equal to or lower than the rotation speed threshold. The rotation speed threshold is calculated using, for example, a rotation speed threshold calculation table such as that shown in FIG. 5. The rotation speed threshold increases as the vehicle speed of the hybrid vehicle 1 increases. That is, when the vehicle speed of the hybrid vehicle 1 is low and the rotation speed threshold is lower than the engine rotation speed at the best fuel economy point as shown by the dashed dotted line L2 in FIG. 3, the internal combustion engine 10 is operated at an operating point (for example, operating point Q2) that has a lower output than the best fuel economy point.

[0068] In addition, the operating point of the internal combustion engine 10 that is set when the fuel cut permission condition is met while the temperature of the manifold catalyst 44 is at or above a predetermined temperature (first predetermined temperature) may be determined taking into consideration the amount of power generated during the transition from the previous operating point of the internal combustion engine 10.

[0069] The operating point of the internal combustion engine 10 that is set when the fuel cut permission condition is met when the temperature of the manifold catalyst 44 is at or above a predetermined temperature (first predetermined temperature) may be determined so as to reduce the fuel consumption of the internal combustion engine 10.

[0070] When the fuel cut permission condition is met while the temperature of the manifold catalyst 44 is equal to or higher than a predetermined temperature (first predetermined temperature), fuel supply to the internal combustion engine 10 is continued for a predetermined time so that the temperature of the manifold catalyst 44 will not reach or exceed a predetermined thermal degradation temperature threshold and thermal degradation of the manifold catalyst 44 is suppressed even if fuel supply to the internal combustion engine 10 is stopped. The duration of fuel supply to the internal combustion engine 10 at this time may be determined according to, for example, the temperature of the manifold catalyst 44, the operating point of the internal combustion engine 10, and the SOC of the battery 8.

[0071] FIG. 6 is a block diagram showing the flow of control of the hybrid vehicle 1 described above.

[0072] In step S1, the temperature of the manifold catalyst 44 and the required output of the internal combustion engine 10 are used to determine whether or not the fuel cut permission condition is met when the temperature of the manifold catalyst 44 is equal to or higher than a predetermined temperature (first predetermined temperature). The temperature of the manifold catalyst 44 can also be estimated, for example, from the operating history of the internal combustion engine 10. The required output of the internal combustion engine 10 is calculated, for example, using the detection signal of the accelerator opening sensor 63.

[0073] In step S2, the required output of the internal combustion engine 10 and the vehicle speed of the hybrid vehicle 1 are used to calculate the above-mentioned rotation speed threshold value.

[0074] In step S3, the allowable output (allowable output) of the internal combustion engine 10 is calculated using the SOC of the battery 8 and the current operating point of the internal combustion engine 10. The current operating point of the internal combustion engine 10 is the operating point at the time when the fuel cut permission condition is met while the temperature of the manifold catalyst 44 is equal to or higher than a predetermined temperature (first predetermined temperature). The allowable output (torque) of the internal combustion engine 10 is calculated, for example, using the calculation table shown in FIG. 4 described above.

[0075] In step S4, the operation point of the internal combustion engine 10 is determined when the fuel cut permission condition is met with the temperature of the manifold catalyst 44 being equal to or higher than a predetermined temperature (first predetermined temperature), using the determination result of step S1, the rotational speed threshold calculated in step S2, the output of the internal combustion engine 10 calculated in step S3, and information from a fuel efficiency map of the internal combustion engine 10. The fuel efficiency map is, for example, a map in which fuel efficiency at each operation point of the internal combustion engine 10 is allocated.

[0076] In step S4, the duration of fuel supply to the internal combustion engine 10 that will continue when the fuel cut permission condition is met while the temperature of the manifold catalyst 44 is at or above a predetermined temperature (first predetermined temperature) and the amount of electricity generated during this duration are also calculated.

[0077] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0078] Although the hybrid vehicle 1 in the above-described embodiment is a series hybrid vehicle, the present invention is also applicable to hybrid vehicles having an operating mode that can independently realize power generation by the internal combustion engine and driving of the drive wheels.

[0079] Hybrid vehicles having driving modes that can independently generate electricity using an internal combustion engine and drive the drive wheels include series hybrid vehicles such as hybrid vehicle 1, as well as parallel hybrid vehicles and series-parallel hybrid vehicles.

[0080] When the present invention is applied to a parallel hybrid vehicle or a series-parallel hybrid vehicle, it may be applied during an operation mode in which power generation by the internal combustion engine and driving of the drive wheels can be achieved independently.

[0081] Furthermore, even if the temperature of the manifold catalyst 44 is below a predetermined temperature, if the temperature of the underfloor catalyst 45 is equal to or higher than a predetermined temperature (for example, a second predetermined temperature), when the fuel cut permission condition is met, the operating point of the internal combustion engine 10 may be changed according to the SOC of the battery 8, and fuel supply to the internal combustion engine 10 may be continued. Note that the second predetermined temperature is, for example, a temperature at which the underfloor catalyst 45 may deteriorate if fuel is cut.

[0082] The present invention can also be applied to a catalyst as a target, such as the underfloor catalyst 45. That is, if it is predicted that the temperature of the underfloor catalyst 45 will become high (for example, a second predetermined temperature) when fuel is cut, the hybrid vehicle 1 may prohibit stopping the fuel supply to the internal combustion engine 10 (fuel cut) even if the fuel cut permission condition is met. That is, the present invention can be applied to a catalyst provided in an exhaust passage.

[0083] Furthermore, when a fuel cut condition that takes priority over preventing catalyst deterioration is met, the above catalyst cooling control may not be performed, and fuel may be cut immediately.

[0084] The above-described embodiments relate to a control method for a hybrid vehicle and a control device for a hybrid vehicle. [Explanation of symbols]

[0085] 1...Vehicle 2...Drive wheels 5...Drive motor 8...Battery 9...Generator 10...Internal combustion engine 42...Control unit 44...Manifold catalyst

Claims

1. A control method for a hybrid vehicle having a battery that is charged with electric power generated by an internal combustion engine, and having an operation mode in which electric power generation by the internal combustion engine and driving of drive wheels can be performed independently, comprising: When a predetermined fuel cut permission condition for permitting the stop of fuel supply to the internal combustion engine is established while the temperature of an exhaust gas purification catalyst of the internal combustion engine is equal to or higher than a predetermined temperature during the operation mode, an operating point of the internal combustion engine is changed in accordance with an SOC of the battery, and fuel supply to the internal combustion engine is continued, A control method for a hybrid vehicle, wherein, when the fuel cut permission condition is met while the temperature of the catalyst is at or above a predetermined temperature during the operation mode, the operating point of the internal combustion engine is changed to an operating point at which higher output can be obtained as the SOC of the battery becomes smaller, and the operating point of the internal combustion engine that is set when the fuel cut permission condition is met while the temperature of the catalyst is at or above a predetermined temperature during the operation mode is determined taking into account the amount of power generated during the movement from the previous operating point of the internal combustion engine.

2. 2. The method for controlling a hybrid vehicle according to claim 1, wherein the operating point is changed to continue fuel supply to the internal combustion engine, and then a fuel cut is implemented after the temperature of the catalyst falls below the predetermined temperature.

3. 3. A control method for a hybrid vehicle as described in claim 1 or 2, wherein, when the fuel cut permission condition is met with the temperature of the catalyst being equal to or higher than a predetermined temperature during the driving mode, the operating point of the internal combustion engine can be changed to an operating point that provides the best fuel economy when the SOC of the battery is equal to or lower than a predetermined first threshold.

4. 4. A control method for a hybrid vehicle according to claim 1, wherein, when the fuel cut permission condition is met with the temperature of the catalyst being equal to or higher than a predetermined temperature during the driving mode, when the SOC of the battery is equal to or higher than a predetermined second threshold, the operating point of the internal combustion engine can be changed to an operating point at which torque equivalent to the friction of the internal combustion engine can be obtained.

5. an operating point of the internal combustion engine is determined by a torque of the internal combustion engine and an engine speed of the internal combustion engine; 5. A control method for a hybrid vehicle according to claim 1, wherein when the fuel cut permission condition is met while the temperature of the catalyst is at or above a predetermined temperature during the driving mode, the rotation speed of the internal combustion engine is limited so that the operating point of the internal combustion engine is equal to or less than a predetermined rotation speed threshold determined according to the vehicle speed.

6. 6. A control method for a hybrid vehicle according to claim 1, wherein the operating point of the internal combustion engine, which is set when the fuel cut permission condition is met with the temperature of the catalyst being equal to or higher than a predetermined temperature during the operating mode, is determined so as to reduce fuel consumption of the internal combustion engine.

7. A control method for a hybrid vehicle as described in any one of claims 1 to 6, wherein, when the fuel cut permission condition is met while the temperature of the catalyst is at or above a predetermined temperature during the operating mode, fuel supply to the internal combustion engine is continued for a predetermined time so that thermal deterioration of the catalyst is suppressed even if fuel supply to the internal combustion engine is stopped.

8. A control device for a hybrid vehicle having a battery that is charged with electric power generated by an internal combustion engine, and having a driving mode in which electric power generation by the internal combustion engine and driving of drive wheels can be performed independently, a control unit that, when a predetermined fuel cut permission condition for permitting the stop of fuel supply to the internal combustion engine is established in a state in which the temperature of an exhaust gas purification catalyst of the internal combustion engine is equal to or higher than a predetermined temperature during the operation mode, changes an operating point of the internal combustion engine in accordance with an SOC of the battery and continues fuel supply to the internal combustion engine, The control unit changes the operating point of the internal combustion engine to an operating point that provides higher output as the SOC of the battery decreases when the fuel cut permission condition is met while the temperature of the catalyst is at or above a predetermined temperature during the operating mode, and the operating point of the internal combustion engine that is set when the fuel cut permission condition is met while the temperature of the catalyst is at or above a predetermined temperature during the operating mode is determined taking into account the amount of power generated during the transition from the previous operating point of the internal combustion engine.

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