Hybrid vehicle control device

Abstract

To optimize execution time of fuel cut at the time of strong brake to prevent overspeed and overcharge of a power generator motor.SOLUTION: When strong brake is done on a hybrid vehicle in which an engine 10, a first motor generator 71, and a drive shaft 45 of a wheel 62 are connected respectively to three rotation elements of a first planetary gear mechanism 40, an electronic control unit 100 executes strong brake fuel cut processing of executing fuel cut of the engine 10 and return processing of ending the fuel cut when a rate of decrease in rotational speed of the drive shaft 45 becomes equal to or larger than a default return determination value during execution of fuel cut by the strong brake fuel cut processing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a known control device for a hybrid vehicle in which an engine, a generator motor, and a wheel drive shaft are connected to three rotating elements of a planetary gear mechanism. When the brake pedal is pressed hard while the hybrid vehicle is running, the rotation speed of the wheel drive shaft drops sharply. If the engine rotation speed does not drop quickly enough, the rotation speed of the generator motor increases, which can lead to over-rotation and overcharging.

[0003] In response to this, the control device for a hybrid vehicle described in Patent Document 1 executes a fuel cut to the engine when the brake pedal is pressed hard, thereby quickly reducing the engine rotation speed and suppressing an increase in the rotation speed of the generator motor, thereby suppressing over-revving and overcharging. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-235809 Summary of the Invention [Problem to be solved by the invention]

[0005] Some engines are equipped with a filter that captures particulate matter (PM) in the exhaust. When fuel is cut off, the exhaust gas flowing into the filter is replaced with fresh air. Therefore, if fuel is cut off when a large amount of PM has accumulated on the filter, oxygen is supplied to the filter, causing the PM to burn, and the filter temperature rises. If fuel is cut off for a long period of time, there is a risk that the filter's function will be impaired due to excessive temperature rise. As such, continuing fuel cut for a long period of time may not be desirable.

[0006] On the other hand, the fuel cut during heavy braking as described above may continue for a long time depending on the brake pedal operation of the driver. Therefore, depending on the situation, there is a risk of adverse effects such as excessive temperature rise of the filter due to the long-term fuel cut. [Means for solving the problem]

[0007] The control device for solving the above problem is applied to a hybrid vehicle in which an engine, a generator motor, and a drive shaft of a wheel are respectively connected to three rotating elements of a planetary gear mechanism. The control device includes a heavy braking fuel cut process for cutting fuel to the engine when heavy braking is applied, and a control device for controlling the rotation speed of the drive shaft when the rate of decrease in the rotation speed of the drive shaft during fuel cut by the heavy braking fuel cut process is greater than a predetermined return judgment value. below Status continued for a specified period of time When this occurs, a recovery process is performed to end the fuel cut.

[0008] When the brake pedal is pressed hard to apply a strong braking force to the wheels, the rotational speed of the wheel drive shaft drops suddenly. At this time, if the rate of decrease in engine rotational speed is low, the rotational speed of the generator-motor may increase excessively. On the other hand, if fuel is cut, the rate of decrease in engine rotational speed can be made greater than if combustion were maintained. Therefore, by cutting fuel during heavy braking, the increase in rotational speed of the generator-motor can be suppressed, preventing the generator-motor from over-rotating and overcharging the battery due to the generator-motor.

[0009] In addition, if the rate of decrease in the rotation speed of the drive shaft of the wheels is smaller than a certain level, even if the rate of decrease in the engine rotation speed is achievable while maintaining combustion, the increase in the rotation speed of the generator motor can be kept within a range that can avoid the above-mentioned over-revving and overcharging. In the control device for the hybrid vehicle, when the rate of decrease in the rotation speed of the drive shaft during fuel cut due to the heavy braking fuel cut process is smaller than a predetermined return judgment value, below Status continued for a specified period of time Therefore, the duration of fuel cut during heavy braking can be shortened to the extent that over-speed of the generator motor and overcharging by the generator motor can be avoided. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram schematically illustrating the configuration of a drive system and a control system of a hybrid vehicle to which an embodiment of a control device is applied; [Figure 2] 4 is a flowchart showing the procedure of a fuel cut process during heavy braking executed by the control device. [Figure 3] 10 is a graph showing a setting manner of an overspeed risk region. [Figure 4] 4 is a flowchart showing the procedure of a process for determining convergence of a rate of decrease executed by the control device. [Figure 5] FIG. 10 is a nomographic diagram showing changes in the rotation speeds of the engine, the first motor generator, and the drive shaft during heavy braking. [Figure 6] This is a time chart showing the changes in vehicle speed (A), brake torque (B), motor rotation speed reduction rate (C), convergence counter value (D), and FC request flag status (E) when fuel is cut off due to heavy braking fuel cut processing. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of a control device for a hybrid vehicle will be described in detail below with reference to FIGS. <Hybrid vehicle drivetrain> First, with reference to FIG. 1, the configuration of a hybrid vehicle to which the control device of this embodiment is applied will be described.

[0012] As shown in Fig. 1, a hybrid vehicle to which the control device of this embodiment is applied has three drive sources: an engine 10, a first motor generator 71, and a second motor generator 72. The engine 10 is an internal combustion engine that generates power by burning fuel. The first motor generator 71 and the second motor generator 72 are generator motors that function as both a motor and a generator.

[0013] The hybrid vehicle is further provided with a battery 77, a first inverter 75, and a second inverter 76. The battery 77 stores the electric power generated by the first motor generator 71 and the second motor generator 72 when they function as generators. Furthermore, the battery 77 supplies the stored electric power to the first motor generator 71 and the second motor generator 72 when they function as motors. The first inverter 75 adjusts the amount of electric power exchanged between the first motor generator 71 and the battery 77, and the second inverter 76 adjusts the amount of electric power exchanged between the second motor generator 72 and the battery 77.

[0014] The engine 10 has multiple cylinders 11 that combust an air-fuel mixture. The engine 10 is also provided with an intake passage 15, which serves as a passage through which air is introduced into each cylinder 11. The intake passage 15 is provided with a throttle valve 16, which is a valve for adjusting the amount of intake air. The portion of the intake passage 15 downstream of the throttle valve 16 branches off for each cylinder. Each branch of the intake passage 15 for each cylinder is provided with a fuel injection valve 17. Meanwhile, each cylinder 11 is provided with an ignition device 18 that ignites the air-fuel mixture introduced into the cylinder 11 by spark discharge. The engine 10 is also provided with an exhaust passage 21, which serves as a passage through which exhaust gas generated by the combustion of the air-fuel mixture in each cylinder 11 is discharged. A three-way catalytic converter 22 is provided in the exhaust passage 21 to purify the exhaust gas. Furthermore, a filter device 23 that collects PM in the exhaust gas is provided downstream of the three-way catalytic converter 22 in the exhaust passage 21.

[0015] An air-fuel mixture containing fuel injected by a fuel injection valve 17 is introduced into each cylinder 11 of the engine 10 through an intake passage 15. When an ignition device 18 ignites this air-fuel mixture, combustion occurs in the cylinder 11. Exhaust gas produced by this combustion is discharged from the cylinder 11 into an exhaust passage 21. In this engine 10, a three-way catalytic device 22 oxidizes HC and CO in the exhaust gas and reduces NOx, and a filter device 23 collects particulate matter in the exhaust, thereby purifying the exhaust gas.

[0016] On the other hand, the hybrid vehicle is provided with a first planetary gear mechanism 40. The first planetary gear mechanism 40 has a sun gear 41, which is an external gear, and a ring gear 42, which is an internal gear, arranged coaxially with the sun gear 41. A plurality of pinion gears 43 are arranged between the sun gear 41 and the ring gear 42, and mesh with both the sun gear 41 and the ring gear 42. Each pinion gear 43 is supported by a carrier 44 in a state in which it can freely rotate and revolve. The sun gear 41, the ring gear 42, and the carrier 44 constitute three rotating elements of the first planetary gear mechanism 40. The carrier 44 of the first planetary gear mechanism 40 is connected to the crankshaft 14, which is the output shaft of the engine 10, and the sun gear 41 is connected to a first motor-generator 71. A drive shaft 45 is connected to the ring gear 42. Wheels 62 are connected to the drive shaft 45 via a reduction mechanism 60, a differential mechanism 61, and wheel axles 63. That is, the drive shaft 45 is a shaft for extracting power to the wheels 62. The first planetary gear mechanism 40 functions as a power split mechanism that splits the power of the engine 10 between the first motor generator 71 and the drive shaft 45.

[0017] Each wheel 62 is provided with a brake mechanism 64. The brake mechanism 64 is configured to generate a braking force that slows down the rotation of the wheel 62 in response to the driver's depression of the brake pedal.

[0018] A second motor-generator 72 is connected to the drive shaft 45 via a second planetary gear mechanism 50. The second planetary gear mechanism 50 has a sun gear 51, which is an external gear, and a ring gear 52, which is an internal gear, arranged coaxially with the sun gear 51. A plurality of pinion gears 53 are arranged between the sun gear 51 and the ring gear 52, and mesh with both the sun gear 51 and the ring gear 52. Each pinion gear 53 is rotatable on its own axis but is unable to revolve. The ring gear 52 of the second planetary gear mechanism 50 is connected to the drive shaft 45, and the second motor-generator 72 is connected to the sun gear 51. The second planetary gear mechanism 50 functions as a reduction mechanism that reduces the rotation speed of the second motor-generator 72 and transmits it to the drive shaft 45.

[0019] <Hybrid vehicle control system> Next, the configuration of the control system of the hybrid vehicle will be described with reference to FIG. The hybrid vehicle is equipped with an electronic control unit 100 as a control device for the hybrid vehicle. Detection signals from an accelerator pedal sensor 80, a vehicle speed sensor 81, and a brake pedal sensor 87 are input to the electronic control unit 100. The accelerator pedal sensor 80 is a sensor that detects an accelerator pedal opening angle ACC, which is the amount of depression of the accelerator pedal by the driver. The vehicle speed sensor 81 is a sensor that detects a vehicle speed V, which is the traveling speed of the vehicle. The brake pedal sensor 87 is a sensor that detects the amount of operation or operating force of the brake pedal by the driver. The electronic control unit 100 also acquires the battery charge amount, which is the amount of power stored in the battery 77.

[0020] Furthermore, the electronic control unit 100 receives detection signals from various sensors installed in the engine 10. The engine 10 is equipped with sensors such as an air flow meter 82, an air-fuel ratio sensor 83, a catalyst outlet gas temperature sensor 84, a crank angle sensor 85, and a water temperature sensor 86. The air flow meter 82 is installed in the intake passage 15 upstream of the throttle valve 16 and detects the flow rate of intake air flowing through the intake passage 15. The air-fuel ratio sensor 83 is installed in the exhaust passage 21 upstream of the three-way catalyst device 22 and detects the oxygen concentration in the gas flowing through the exhaust passage 21, i.e., the air-fuel ratio of the mixture. The catalyst outlet gas temperature sensor 84 is installed in the exhaust passage 21 between the three-way catalyst device 22 and the filter device 23 and detects the temperature of the gas flowing out of the three-way catalyst device 22. The crank angle sensor 85 is installed near the crankshaft 14 and detects the rotational phase of the crankshaft 14. The water temperature sensor 86 detects the temperature of the coolant for the engine 10.

[0021] The electronic control unit 100 configured as described above calculates the required torque, which is a required value of the torque to be output to the drive shaft 45, based on the accelerator pedal opening ACC and the vehicle speed V. The electronic control unit 100 also determines the torque distribution among the engine 10, the first motor generator 71, and the second motor generator 72, depending on the required torque, the amount of electricity stored in the battery, etc. Then, the electronic control unit 100 controls the output torque of the engine 10 and the power running / regenerative torque of the first motor generator 71 and the second motor generator 72 in accordance with the determined torque distribution.

[0022] The electronic control unit 100 obtains the rotational speed of the crankshaft 14 of the engine 10 from the detection signal of the crank angle sensor 85. In the following description, the rotational speed of the crankshaft 14 of the engine 10 will be referred to as engine rotational speed NE. In the following description, the rotational speed of the first motor-generator 71 will be referred to as generator rotational speed NG, and the rotational speed of the second motor-generator 72 will be referred to as motor rotational speed NM. In the following description, the rotational speed of the drive shaft 45 will be referred to as drive shaft rotational speed NP. The engine rotational speed NE matches the rotational speed of the carrier 44 of the first planetary gear mechanism 40, the generator rotational speed NG matches the rotational speed of the sun gear 41 of the first planetary gear mechanism 40, and the drive shaft rotational speed NP matches the rotational speed of the ring gear 42 of the first planetary gear mechanism 40, respectively.

[0023] As described above, the second motor-generator 72 is connected to the drive shaft 45 via the second planetary gear mechanism 50, which functions as a speed reduction mechanism. Therefore, the motor rotation speed NM and the drive shaft rotation speed NP are proportional to each other. The electronic control unit 100 uses the motor rotation speed NM as an index value for the drive shaft rotation speed NP.

[0024] <Fuel cut-off during heavy braking> The electronic control unit 100 performs a heavy braking fuel cut process as part of the control of the hybrid vehicle. The heavy braking fuel cut process is a process for cutting fuel to the engine 10 when heavy braking is applied.

[0025] A flowchart of the fuel cut process during heavy braking is shown in Fig. 2. The electronic control unit 100 repeatedly executes the process of Fig. 2 at each predetermined control cycle. When this process starts, the electronic control unit 100 first determines in step S100 whether or not the FC request flag is set. The FC request flag is a flag that indicates whether or not a fuel cut is being requested for the engine 10 through this process. The electronic control unit 100 cuts fuel for the engine 10 while the FC request flag is set.

[0026] If the FC request flag is not set (S100: NO), the electronic control unit 100 determines whether to set the FC request flag in steps S110 to S130. Specifically, if all of the following requirements (A) to (C) are met, the electronic control unit 100 sets the FC request flag in step S140 and executes a fuel cut for the engine 10.

[0027] Requirement (i) is that the hybrid vehicle is traveling (S110: YES). In this embodiment, it is determined that the hybrid vehicle is traveling when the vehicle speed V exceeds a predetermined stop determination value.

[0028] Requirement (ii) is that the engine speed NE is within the overspeed risk region (S120: YES). The overspeed risk region represents the range of engine speed NE within which the first motor-generator 71 may overspeed as a result of a sudden deceleration of the drive shaft speed NP due to heavy braking.

[0029] Fig. 3 shows how the overspeed risk region is set in this embodiment. In this embodiment, the overspeed risk region is set based on the motor rotation speed NM. Specifically, the lower limit of the range of engine rotation speed NE, which becomes the overspeed risk region, is set as a value that decreases as the motor rotation speed NM decreases.

[0030] Requirement (c) is that heavy braking is being performed (S130: YES). In this embodiment, it is determined that heavy braking is being performed when the brake torque generated by the brake mechanism 64 is equal to or greater than a predetermined heavy braking determination value. The electronic control unit 100 calculates the brake torque based on the detection result of the brake pedal sensor 87.

[0031] On the other hand, if the FC request flag is set (S100: YES), the electronic control unit 100 determines whether to clear the FC request flag in steps S150 to S180. Specifically, if one or more of the following four requirements (iv) to (vii) are met, the electronic control unit 100 clears the FC request flag in step S190 and ends the fuel cut of the engine 10. In this embodiment, the processing of steps S150 to S190 corresponds to the return processing.

[0032] Requirement (iv) is that the hybrid vehicle is stopped (S150: YES). In this embodiment, it is determined that the hybrid vehicle is stopped when the vehicle speed V is equal to or less than the above-mentioned stop determination value.

[0033] Requirement (e) is that the engine rotation speed NE is equal to or less than a predetermined overspeed safe determination value. The overspeed safe determination value is set as the upper limit of the range of engine rotation speed NE at which overspeed of the first motor-generator 71 does not occur even if the drive shaft rotation speed NP continues to decrease.

[0034] Requirement (f) is that the hard braking is released (S170: YES). In this embodiment, the hard braking is determined to be released when the brake torque falls below a predetermined release determination value. The release determination value is set to a value smaller than the above-mentioned hard braking determination value.

[0035] The requirement (G) is that the rate of decrease in the drive shaft rotation speed NP is equal to or less than a predetermined return determination value (S180: YES). In this embodiment, whether the requirement (G) is met is determined based on the rate of decrease ΔNM of the motor rotation speed NM, which is proportional to the drive shaft rotation speed NP.

[0036] <Decrease rate convergence determination process> Next, the details of the decrease rate convergence determination process, which is a process for determining whether the decrease rate of the drive shaft rotation speed NP has decreased to or below a predetermined return determination value, will be described with reference to Fig. 4. Fig. 4 shows a flowchart of the decrease rate convergence determination process. The electronic control unit 100 repeatedly executes the process of Fig. 4 at every predetermined control cycle.

[0037] In the process of determining whether the rate of decrease has converged, the electronic control unit 100 first determines whether the FC request flag is set in step S200. If the FC request flag is not set (NO), the electronic control unit 100 resets the value of the convergence counter C to "0" in step S210, and then ends the process of determining whether the rate of decrease has converged in the current control cycle.

[0038] On the other hand, if the FC request flag is set (S200: YES), the electronic control unit 100 determines in step S220 whether the decrease rate ΔNM of the motor rotation speed NM is equal to or less than a predetermined return determination value. The decrease rate ΔNM represents the amount of decrease in the motor rotation speed NM per unit time. The electronic control unit 100 calculates the decrease rate ΔNM by subtracting the current motor rotation speed NM from the motor rotation speed NM from the unit time before. If the decrease rate ΔNM exceeds the return determination value (NO), the electronic control unit 100 resets the value of the convergence counter C to "0" in the above-mentioned step S210 and then terminates the decrease rate convergence determination process for the current control cycle. On the other hand, if the decrease rate ΔNM is equal to or less than the return determination value (YES), the electronic control unit 100 proceeds to step S230.

[0039] When the process proceeds to step S230, the electronic control unit 100 increments the value of the convergence counter C in step S230. Then, in the following step S240, the electronic control unit 100 determines whether the incremented value of the convergence counter C is equal to or greater than a predetermined convergence determination value. If the value of the convergence counter C is less than the convergence determination value (NO), the electronic control unit 100 terminates the decline rate convergence determination process for the current control cycle. On the other hand, if the value of the convergence counter C is equal to or greater than the convergence determination value (YES), the electronic control unit 100 performs a convergence determination in step S250 and then terminates the decline rate convergence determination process for the current control cycle. The convergence determination is a determination that the decline rate of the drive shaft rotation speed NP has decreased to or below a predetermined return determination value. The electronic control unit 100 determines that the above-mentioned requirement (G) is satisfied when the convergence determination is made. That is, the determination in step S180 of the heavy braking fuel cutoff process in FIG. 2 is made based on whether the convergence determination is successful.

[0040] The electronic control unit 100 also executes fuel cut when the generator rotation speed NG is equal to or greater than a predetermined forced FC determination value. The forced FC determination value is set to a rotation speed value that is slightly smaller than the upper limit of the allowable generator rotation speed NG. The electronic control unit 100 executes fuel cut processing based on the generator rotation speed NG in priority over fuel cut processing during heavy braking.

[0041] <Effects of the embodiment> The operation and effects of this embodiment will be described. As described above, the hybrid vehicle of this embodiment is configured such that the engine 10, the first motor generator 71, and the drive shaft 45 are connected via the first planetary gear mechanism 40. In such a hybrid vehicle, if strong braking is applied while the engine 10 is running at high speed, there is a possibility that the first motor generator 71 will over-revolve.

[0042] A straight line L1 in FIG. 5 is a collinear diagram showing the relationship between the generator rotation speed NG, the engine rotation speed NE, and the drive shaft rotation speed NP when the hybrid vehicle is running with the engine 10 operating at high speed.

[0043] If heavy braking is applied in this state, the drive shaft rotation speed NP drops sharply. The straight line L2 in FIG. 5 shows a nomographic chart for the case where combustion in the engine 10 is maintained even after heavy braking. If combustion in the engine 10 continues, the engine rotation speed NE does not drop immediately. Therefore, if combustion in the engine 10 continues after heavy braking, the generator rotation speed NG rises sharply. In the example shown in FIG. 5, the drive shaft rotation speed NP drops from "np1" to "np2" due to heavy braking, while the engine rotation speed NE is maintained at "ne1." Therefore, the generator rotation speed NG rises from "ng1" to "ng2." Thus, during heavy braking, the generator rotation speed NG may exceed its allowable upper limit, which could result in overspeeding of the first motor-generator 71. To prevent such overspeeding, it is conceivable to suppress the increase in generator rotation speed NG by regeneratively driving the first motor-generator 71. However, in this case, a large regenerative torque is required to suppress the increase in generator rotation speed NG, which may result in overcharging of the battery 77.

[0044] In response to this, the electronic control unit 100 cuts fuel to the engine 10 during heavy braking, quickly reducing the engine speed NE. The straight line L3 in FIG. 5 shows a nomographic diagram in which fuel cut is performed after heavy braking. In this case, the drive shaft speed NP drops from "np1" to "np2" due to heavy braking, while the engine speed NE also drops from "ne1" to "ne3." Therefore, the increase in the generator speed NG after heavy braking in this case is limited to between "ng1" and "ng3." Therefore, by cutting fuel to the engine 10 during deceleration of the hybrid vehicle due to heavy braking, it is possible to prevent the first motor-generator 71 from over-revving and the battery 77 from overcharging.

[0045] Note that once the hybrid vehicle comes to a stop, the drive shaft rotation speed NP approaches "0" and stops decreasing. Furthermore, once the heavy braking is released, the sudden decrease in the drive shaft rotation speed NP ends. Therefore, in these cases, the hybrid vehicle has escaped a state in which overspeed or overcharging may occur. Furthermore, in this embodiment, the upper limit of the range of engine rotation speed NE, at which the first motor-generator 71 does not overspeed even if the decrease in drive shaft rotation speed NP continues, is set as the overspeed safe determination value. Therefore, when any of the above requirements (d), (e), and (f) is met, the risk of overspeed or overcharging is eliminated. Therefore, when any of the above requirements (d), (e), and (f) is met, the electronic control unit 100 ends the fuel cut during heavy braking.

[0046] During fuel cut, the exhaust gas from the engine 10 is replaced with fresh air, and oxygen is supplied to the filter device 23. Then, PM trapped in the filter device 23 is burned, causing the temperature of the filter device 23 to rise. Therefore, if fuel cut continues for a long period of time, there is a risk that the filter device 23 will overheat. In addition, there is a risk that prolonged fuel cut will accelerate deterioration of the three-way catalytic device 22. On the other hand, depending on the situation, it may take time for the above requirements (d) to (f) to be met, and in such cases, there is a risk that fuel cut will continue for a long period of time.

[0047] In contrast, the electronic control unit 100 also ends fuel cutoff during heavy braking when the rate of decrease ΔNM of the motor rotation speed NM falls below the return judgment value. The rate of decrease ΔNM of the motor rotation speed NM is proportional to the rate of decrease of the drive shaft rotation speed NP. When heavy braking is applied while the hybrid vehicle is running, the drive shaft rotation speed NP drops sharply. As the hybrid vehicle approaches a stop, the decrease in the drive shaft rotation speed NP gradually subsides. Therefore, even if the rate of decrease in the drive shaft rotation speed NP converges to a certain value or below after the start of fuel cutoff during heavy braking, it is considered that the risk of over-revving or overcharging has been eliminated.

[0048] Figure 6 shows an example of an implementation of the fuel cut-off process during heavy braking in this embodiment. In detail, Figures 6(A) to 6(E) show the transitions of the following values ​​during deceleration of a hybrid vehicle due to heavy braking. That is, Figure 6(A) shows the transitions of vehicle speed V, Figure 6(B) shows the transitions of brake torque, Figure 6(C) shows the transitions of the reduction rate ΔNM of motor rotation speed NM, Figure 6(D) shows the transitions of the value of convergence counter C, and Figure 6(E) shows the state of the FC request flag.

[0049] In the example of FIG. 6, at time t1, the brake torque exceeds the hard braking determination value, and the FC request flag is set. The electronic control unit 100 starts fuel cut of the engine 10 at this time t1. After the hard braking starts, the reduction rate ΔNM of the motor rotation speed NM increases significantly once, and then gradually converges to "0." Depending on the state of grip of the wheels 62 on the road surface, the reduction rate ΔNM may repeatedly fluctuate during this convergence process.

[0050] In this embodiment, the electronic control unit 100 increments the value of the convergence counter C when the FC request flag is set and the decrease rate ΔNM is equal to or less than the return judgment value. On the other hand, the electronic control unit 100 resets the value of the convergence counter C to "0" when the FC request flag is cleared or when the decrease rate ΔNM exceeds the return judgment value. Therefore, the value of the convergence counter C represents the duration of the state in which the decrease rate ΔNM is equal to or less than the return judgment value during fuel cut during heavy braking. Then, when the convergence counter C is equal to or greater than the convergence judgment value, the electronic control unit 100 determines that the decrease rate of the drive shaft rotation speed NP has converged to a certain value or less.

[0051] 6, there is a period before time t2 when the decrease rate ΔNM is temporarily equal to or less than the restoration judgment value, but the electronic control unit 100 does not perform a convergence judgment at that time and keeps the FC request flag set. Then, after time t2, when the decrease rate ΔNM remains equal to or less than the restoration judgment value and the convergence counter C reaches the convergence judgment value at time t3, the electronic control unit 100 clears the FC request flag and ends the fuel cut.

[0052] According to the control device for a hybrid vehicle of the present embodiment described above, the following effects can be achieved. (1) The duration of fuel cutoff during heavy braking can be set to an appropriate time that is not too long and that can prevent over-revving and overcharging.

[0053] (2) It is possible to suppress excessive temperature rise of the filter device 23 and progression of deterioration of the three-way catalyst device 22 due to a long period of fuel cut. (3) If the rate of decrease ΔNM remains below the recovery threshold for a certain period of time, it is determined that the decrease in the drive shaft rotation speed NP has converged. This prevents a temporary decrease in the rate of decrease ΔNM from being mistakenly determined as a decrease in the drive shaft rotation speed NP.

[0054] This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility. As long as it is possible to appropriately determine that the decrease in the drive shaft rotation speed NP has converged, the convergence determination by the decrease rate convergence determination process may be performed in a manner different from that of the above embodiment.

[0055] In the above embodiment, the motor rotation speed NM was used as an index value for the drive shaft rotation speed NP in the heavy braking fuel cut process and the process for determining whether the rate of decrease has converged. However, the drive shaft rotation speed NP may be detected, and the detected value may be used to perform the heavy braking fuel cut process and the process for determining whether the rate of decrease has converged.

[0056] The conditions for executing fuel cut during the heavy braking fuel cut process may be different from those in the above embodiment. Also, the conditions for ending fuel cut during the heavy braking fuel cut process may be different from those in the above embodiment as long as they include the above requirement (G). [Explanation of symbols]

[0057] 10...Engine 11...cylinder 14...Crankshaft 15...Intake passage 16...Throttle valve 17...Fuel injection valve 18...Ignition device 21...Exhaust passage 22…Three-way catalyst device 23...Filter device 40...First planetary gear mechanism 41,51...Sun gear 42,52...Ring gear 43,53...Pinion gear 44...Career 45...Ring gear shaft 50...Second planetary gear mechanism 60…Reduction mechanism 61...Differential mechanism 62...Wheel 63...Drive wheels 64...Brake mechanism 71...First motor generator (generator motor) 72...Second motor generator 75...First inverter 76...Second inverter 77...Battery 80...Accelerator pedal sensor 81...Vehicle speed sensor 82...Air flow meter 83...Air-fuel ratio sensor 84...Catalyst outlet gas temperature sensor 85...Crank angle sensor 86...Water temperature sensor 87...Brake pedal sensor 100...Electronic control unit

Claims

[Claim 1] a fuel cut process during heavy braking that cuts fuel to the engine when heavy braking is applied to a hybrid vehicle in which an engine, a generator motor, and a drive shaft of a wheel are connected to three rotating elements of a planetary gear mechanism, respectively, and the engine speed is within an overspeed risk region; a return process for ending the fuel cut when a state in which a rate of decrease in the rotational speed of the drive shaft is equal to or less than a predetermined return determination value continues for a predetermined time during the fuel cut performed by the heavy braking fuel cut process; Run The lower limit of the overspeed risk region is set to a value that decreases as the rotation speed of the drive shaft decreases. A control device for a hybrid vehicle.

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