JP7704057B2 - Control System - Google Patents

Description

This disclosure relates to a control system used in a hybrid vehicle equipped with a reduction catalyst for purifying nitrogen oxides (NOx).

Among hybrid vehicles equipped with an engine and a motor generator, there is known a hybrid vehicle equipped with a NOx purification device for purifying nitrogen oxides (NOx) emitted from the engine. The NOx purification device includes, for example, a NOx storage reduction catalyst, and purifies the NOx emitted from the engine by reducing it to nitrogen gas.

JP 2014-227005 A (Patent Document 1) discloses a control method for a hybrid vehicle equipped with a NOx storage reduction catalyst, which drives a motor generator according to the catalyst temperature. The hybrid vehicle of Patent Document 1 determines whether to drive the motor generator based on the NOx storage reduction catalyst temperature and the driving load requested by the user.

More specifically, in the hybrid vehicle of Patent Document 1, when the activation temperature is below the lower limit and the driving demand is low load, the travel motor is used as a generator and engine torque is increased. If the exhaust gas temperature rises due to the increase in engine torque, the temperature of the NOx storage reduction type catalyst rises. In addition, in the hybrid vehicle of Patent Document 1, when the activation temperature is below the lower limit and the driving demand is high load, the travel motor is rotated and the engine torque is reduced. The reduction in engine torque reduces the amount of NOx emitted from the engine.

JP 2014-227005 A

In Patent Document 1, when the activation temperature falls below the lower limit and the driving demand is low load, the driving motor is used as a generator to raise the activation temperature. By bringing the NOx storage reduction catalyst within the activation temperature range, the NOx purification rate is improved.

However, the NOx purification rate is affected not only by the catalyst temperature but also by the exhaust flow rate. Even if the catalyst temperature is raised to within the activation temperature range, the exhaust flow rate passing through the NOx storage reduction catalyst may not be small enough to ensure the reduction reaction time, and it may be possible that the NOx purification rate cannot be improved efficiently.

This disclosure has been made to solve the above-mentioned problems, and its purpose is to efficiently improve the NOx purification rate when the motor generator is driven.

(1) The control system according to the present disclosure is used in a hybrid vehicle that runs using at least one of the power sources of a motor generator and an engine. The control system includes an exhaust passage, a NOx purification catalyst, and a control device. The exhaust passage is connected to the engine and exhaust generated in the engine flows through it. The NOx purification catalyst is disposed in the exhaust passage and purifies NOx contained in the exhaust. The control device controls the motor generator. While the engine is running, the control device obtains the flow rate of exhaust passing through the NOx purification catalyst, calculates the NOx purification rate of the NOx purification catalyst using the ratio between the capacity of the NOx purification catalyst and the exhaust flow rate, and uses the NOx purification rate to decide whether to drive the motor generator.

According to the above configuration, if the ratio between the capacity of the NOx purification catalyst and the exhaust flow rate is large, the exhaust flow rate becomes excessive and the NOx purification rate decreases. Therefore, by using the ratio between the capacity of the NOx purification catalyst and the exhaust flow rate to calculate the NOx purification rate and determine whether or not to drive the motor generator, the NOx purification rate can be efficiently improved when the motor generator is driven.

(2) In one embodiment, the control device calculates the increase in the NOx purification rate due to the operation of the motor generator, and drives the motor generator if the increase exceeds a threshold value.

(3) In one embodiment, the control device estimates the amount of NOx emitted from the engine and determines the threshold value using at least one of the amount of NOx emitted from the engine after the motor generator is driven and the charge storage rate of the power storage device that supplies power to the motor generator.

(4) In one aspect, the control system further includes a flow sensor and a temperature sensor. The flow sensor detects the flow rate of the intake air of the engine. The temperature sensor detects the temperature of the exhaust. The control device calculates the exhaust flow rate using the detection values of the flow sensor, the detection values of the temperature sensor, and the exhaust pressure.

(5) In one embodiment, the engine is a turbocharged engine. After receiving a driving request from the user, the control device drives the motor generator as a turbocharger assist during a transitional period until the engine state becomes a turbocharged state.

According to the present disclosure, the NOx purification rate can be efficiently improved when the motor generator is driven.

1 is a diagram showing an example of the overall configuration of a control system used in a hybrid vehicle according to an embodiment of the present invention. FIG. 4 is a diagram showing an example of a correspondence relationship between an S/V ratio and a NOx purification rate. 5 is a flowchart showing an example of a purification rate assistance process performed by an ECU; 4 is a flowchart showing an example of a processing procedure of step S12 in FIG. 3 . 4 is a flowchart showing an example of a processing procedure of step S13 in FIG. 3 . FIG. 11 is a diagram illustrating an example of a method for calculating a purification rate assist determination threshold value. 4 is a diagram showing an example of changes in various parameters when the processing procedure shown in FIG. 3 is executed;

The following describes in detail the embodiments of the present disclosure with reference to the drawings. Note that the same or corresponding parts in the drawings are given the same reference numerals and their description will not be repeated.

Figure 1 is a diagram showing an example of the overall configuration of a control system 100 used in a hybrid vehicle according to this embodiment. The control system 100 includes an engine 10, a motor generator 20, an exhaust purification device 30, drive wheels 40, and an ECU (Electronic Control Unit) 50. The control system 100 further includes an air flow meter 11, an injector 12, an engine speed sensor 13, a turbocharger 14, a low-voltage battery 15, a clutch 16, a DC/DC converter 17, a high-voltage battery 18, an inverter 19, and an exhaust temperature sensor 31.

Engine 10 is a diesel engine having multiple cylinders. However, engine 10 may be a gasoline engine. The crankshaft of engine 10 and the rotating shaft of motor generator 20 are connected via clutch 16. However, engine 10 may have only one cylinder.

The high-voltage battery 18 is a power storage device that stores the power supplied to the motor generator 20. The output voltage of the high-voltage battery 18 is set to a voltage (e.g., several hundred volts) higher than the output voltage of the low-voltage battery 15 (e.g., about 12 volts) and the output voltage used for low-voltage auxiliary devices (not shown). Examples of low-voltage auxiliary devices include an electric pump and glow plugs.

The motor generator 20 is, for example, a three-phase AC rotating electric machine. The rotating shaft of the motor generator 20 is disposed between the crankshaft of the engine 10 and the drive wheels 40. An automatic transmission may be disposed between the rotating shaft of the motor generator 20 and the drive wheels 40.

The inverter 19 performs power conversion between the motor generator 20 and the high-voltage battery 18. Specifically, the inverter 19 converts the DC power of the high-voltage battery 18 into three-phase AC power and supplies it to the motor generator 20. The motor generator 20 is driven by the power supplied from the high-voltage battery 18 via the inverter 19.

The inverter 19 also converts the three-phase AC power generated by the motor generator 20 into DC power and supplies it to the high-voltage battery 18. The high-voltage battery 18 is charged by the power supplied from the motor generator 20 via the inverter 19. A voltage converter (step-up/step-down converter) may be provided between the motor generator 20 and the inverter 19.

The DC/DC converter 17 is provided between the high-voltage battery 18 and the low-voltage battery 15 and low-voltage auxiliary devices, and converts the high-voltage DC power from the high-voltage battery 18 into low-voltage DC power and supplies it to the low-voltage battery 15 and low-voltage auxiliary devices.

The power of at least one of the engine 10 and the motor generator 20 is transmitted to the drive wheels 40. A hybrid vehicle using the control system 100 of this embodiment can switch the driving mode to any one of EV driving, assisted driving, charging driving, and regenerative driving.

During EV driving, a hybrid vehicle using the control system 100 runs on the power of the motor generator 20 with the clutch 16 in a disengaged state and the engine 10 stopped. During assisted driving, a hybrid vehicle using the control system 100 runs on the power of both the engine 10 and the motor generator 20 with the clutch 16 in an engaged state. Therefore, during EV driving and assisted driving, the power stored in the high-voltage battery 18 is discharged to the motor generator 20.

During charging running, the hybrid vehicle using the control system 100 runs using part of the power of the engine 10 with the clutch 16 engaged, and charges the high-voltage battery 18 with electricity generated by the motor generator 20 using surplus energy (energy not used for running) of the engine 10. During regenerative running, the hybrid vehicle using the control system 100 runs at a reduced speed, and charges the high-voltage battery 18 with electricity generated by the motor generator 20 using the deceleration energy of the hybrid vehicle using the control system 100. Therefore, during charging running and regenerative running, the high-voltage battery 18 is charged with electricity generated by the motor generator 20.

The ECU 50 controls the overall running of the hybrid vehicle. Specifically, the ECU 50 controls the engine 10 and the motor generator 20. The ECU 50 drives the motor generator 20 by controlling the inverter 19. The ECU 50 includes a CPU 51 (Central Processing Unit), a memory 52, and a storage device (not shown). The memory 52 is, for example, a working memory, such as a RAM (Random Access Memory). The storage device is, for example, a storage device, such as a ROM (Read Only Memory). The storage device may be a rewritable non-volatile memory, such as an EEPROM. Note that although the ECU 50 is shown as a single unit in FIG. 1, the engine ECU that controls the engine and the motor generator ECU that controls the motor generator 20 may be provided as separate units.

The ECU 50 controls each device based on signals from each sensor and device, as well as programs stored in the memory 52. Note that the various controls are not limited to processing by software, and can also be processed by dedicated hardware (electronic circuits).

The air flow meter 11 detects the flow rate (intake air volume) Qi of the intake air introduced into the intake pipe IP. The air flow meter 11 transmits a signal indicating the detected intake air volume Qi to the ECU 50. The air flow meter 11 is an example of a "flow sensor" in this disclosure.

Each cylinder in the engine is provided with an injector 12 that injects fuel into the combustion chamber. When the engine 10 is driven, the ECU 50 generates a command including the fuel injection amount FJ for each cylinder according to the user's required power, etc., and outputs the command to the injector 12 of each cylinder. As a result, fuel according to the fuel injection amount FJ is injected from the injector 12 in each cylinder.

The engine speed sensor 13 detects the rotation speed of the crankshaft of the engine 10 as the engine speed NE. The engine speed sensor 13 transmits a signal indicating the detected engine speed NE to the ECU 50.

The turbocharger 14 includes a compressor and a turbine. Air flowing through the intake pipe IP is drawn into the compressor of the turbocharger 14 and compressed. The air compressed by the compressor is introduced into the combustion chamber of the engine 10 through the intake pipe IP. The engine 10 generates driving force by burning a mixture of air and fuel in the combustion chamber. The burned mixture, i.e., exhaust, passes through the turbine of the turbocharger 14 and is then discharged outside the vehicle through the exhaust pipe EP. That is, the exhaust pipe EP is connected to the engine 10, and the exhaust generated within the engine 10 flows through it.

After receiving a driving request from the user, during the transitional period until the engine state is supercharged by the supercharger 14, the engine 10 is in a state where so-called turbo lag occurs. The ECU 50 drives the motor generator 20 to reduce the turbo lag. Hereinafter, the driving of the motor generator 20 to reduce this turbo lag is referred to as "supercharging assist."

The exhaust temperature sensor 31 is provided in the exhaust pipe EP and detects the temperature HE of the exhaust gas discharged from the engine 10. The exhaust temperature sensor 31 transmits a signal indicating the detected exhaust gas temperature HE to the ECU 50.

An exhaust purification device 30 is provided on the exhaust pipe EP. The exhaust purification device 30 has the function of purifying NOx in the exhaust. The exhaust purification device 30 is, for example, a catalyst that reduces NOx in the exhaust using a reducing agent. More specifically, the exhaust purification device 30 is, for example, an NSR (NOx Storage Reduction) catalyst. The catalyst in the exhaust purification device 30 stores NOx in the exhaust when the exhaust air-fuel ratio is lean, and releases NOx when the exhaust air-fuel ratio is rich. The catalyst capacity included in the exhaust purification device 30 is stored by a storage device in the ECU 50.

The ECU 50 calculates the NOx purification rate using a data map showing the correspondence between the S/V ratio and the NOx purification rate, which will be described later. The NOx purification rate (%) is the ratio of the amount of NOx in the exhaust downstream of the exhaust purification device 30 to the amount of NOx in the exhaust upstream of the exhaust purification device 30. In other words, the NOx purification rate is an index showing the amount of NOx purified by the exhaust purification device 30. Hereinafter, the amount of NOx in the exhaust upstream of the exhaust purification device 30 may be referred to as the "engine discharge NOx amount," and the amount of NOx in the exhaust downstream of the exhaust purification device 30 may be referred to as the "post-catalyst NOx amount."

[Correspondence between S/V ratio and NOx purification rate]
Fig. 2 is a diagram showing an example of the correspondence relationship between the S/V ratio and the NOx purification rate. The vertical axis of the graph shown in Fig. 2 indicates the NOx purification rate, and the horizontal axis indicates the S/V ratio. As shown in Fig. 2, the S/V ratio (Surface Volume) is the ratio of the exhaust flow rate (liters/hour) to the catalyst volume (liters) of the exhaust purification device 30. The catalyst volume is constant for each exhaust purification device 30. The catalyst volume is stored by the ECU 50. The catalyst volume means the volume of the catalyst that contributes to NOx purification.

While the catalyst capacity is constant for each exhaust purification device 30, the exhaust flow rate varies depending on the intake air volume Qi, fuel injection volume FJ, etc. The exhaust flow rate is the flow rate of the exhaust passing through the exhaust purification device 30. As the exhaust flow rate for a given catalyst capacity increases, the proportion of the amount of NOx that cannot be treated by the exhaust purification device 30 increases. On the other hand, as the exhaust flow rate for a given catalyst capacity decreases, the proportion of the amount of NOx that cannot be treated by the exhaust purification device 30 decreases. In other words, as the S/V ratio increases, the NOx purification rate decreases, and as the S/V ratio decreases, the NOx purification rate increases. Therefore, as shown in FIG. 2, the NOx purification rate decreases monotonically as the S/V ratio increases.

The NOx purification rate decreases monotonically as the S/V ratio increases, but the rate of decrease is not constant and varies depending on the S/V ratio. In other words, as shown in FIG. 2, the slope of the curve showing the correspondence relationship between the NOx purification rate and the S/V ratio varies depending on the S/V ratio. In the example shown in FIG. 2, when the S/V ratio is divided into low, medium, and high regions, the slope of the curve in the medium region is the largest among the low, medium, and high regions. Compared to the slope of the curve in the medium region, the slope of the curve in the low and high regions is smaller.

In other words, when the S/V ratio is reduced in the middle region where the slope is steep, the increase in the NOx purification rate is more likely to be greater than when the S/V ratio is reduced in the low or high region where the slope is shallow. More specifically, when the ratio BsZ, which is the S/V ratio in the high region shown in Figure 2, is reduced by ΔSV to become ratio AsZ, the NOx purification rate increases by ΔRZ. In other words, the increase in the NOx purification rate when the S/V ratio is reduced by ΔSV in the high region is ΔRZ.

On the other hand, when the ratio Bs, which is the S/V ratio in the middle region, is reduced by ΔSV to become ratio As, the NOx purification rate increases by ΔR. In other words, the increase in the NOx purification rate when the S/V ratio is reduced by ΔSV in the middle region is ΔR. As shown in FIG. 2, the increase ΔR is greater than the increase ΔRZ. In this way, when the S/V ratio is reduced by the same reduction amount ΔSV, the increase in the NOx purification rate is greater when the S/V ratio is reduced in a region with a larger rate of reduction (slope of the curve).

The correspondence between the NOx purification rate and the S/V ratio shown in FIG. 2 is stored as a data map in the storage device in the ECU 50. In the control system 100 of this embodiment, the ECU 50 controls the driving of the motor generator 20 using the data map shown in FIG. 2. Hereinafter, the driving of the motor generator 20 using the data map shown in FIG. 2 is referred to as "purification rate assist." A constant power value is stored in the storage device in the ECU 50 as the power to be supplied when the purification rate assist is executed. The ECU 50 may change the power to be supplied depending on the load requested by the user, the vehicle speed, etc. when the purification rate assist is executed.

[Processing procedure for purification rate assistance]
The procedure for the purification rate assist will be described below. The ECU 50 in this embodiment uses the data map shown in Fig. 2 to calculate the increase in the NOx purification rate, and determines whether or not to execute purification rate assist depending on the increase. Fig. 3 is a flowchart showing an example of the procedure for the purification rate assist by the ECU 50. This flowchart is repeatedly executed at regular calculation intervals.

The CPU 51 determines whether or not a driving request has been received from the user (step S10). The driving request in step S10 is a driving request to drive the engine 10, and does not include an EV driving request. That is, the process shown below is a process that is executed while the engine 10 is running. If a driving request has not been received (NO in step S10), the CPU 51 ends the process. If a driving request has been received (YES in step S10), the CPU 51 determines whether or not the catalyst temperature is within the activation temperature range (step S11). The activation temperature is the temperature at which the catalyst of the exhaust purification device 30 is activated, and if it is within the activation temperature range, the NOx purification rate increases. If the catalyst temperature of the exhaust purification device 30 is not within the activation temperature range, the NOx purification rate drops significantly, and the correspondence between the NOx purification rate and the S/V ratio becomes a correspondence different from that shown in FIG. 2.

In step S11, the CPU 51 calculates the catalyst temperature of the exhaust purification device 30 based on the exhaust temperature HE obtained from the exhaust temperature sensor 31. A data map showing the correspondence between the exhaust temperature HE and the catalyst temperature of the exhaust purification device 30 is stored in the storage device in the ECU 50. The catalyst temperature of the exhaust purification device 30 may be calculated based on the detection value of a new temperature sensor provided near the catalyst in the exhaust purification device 30. If the catalyst temperature is not within the activation temperature range (NO in step S11), the CPU 51 ends the process without performing purification rate assistance regarding the correspondence between the NOx purification rate and the S/V ratio.

If the catalyst temperature is within the activation temperature range (YES in step S11), the CPU 51 acquires the current S/V ratio and calculates the current NOx purification rate (step S12). The current S/V ratio and the current NOx purification rate refer to the actual S/V ratio and NOx purification rate when the processing of step S12 is being performed. The processing content of step S12 in FIG. 3 will be specifically explained below using the flowchart of FIG. 4. FIG. 4 is a flowchart showing an example of the processing procedure of step S12 in FIG. 3.

The CPU 51 acquires the intake air volume Qi from the air flow meter 11 (step S121). Next, the CPU 51 acquires the exhaust temperature HE from the exhaust temperature sensor 31 (step S122). The CPU 51 acquires the exhaust pressure PE (step S123).

The exhaust pressure PE is the pressure of the exhaust gas discharged from the engine 10. For example, the CPU 51 estimates the exhaust pressure PE using the engine speed NE and the fuel injection amount FJ. At this time, the CPU 51 estimates the exhaust pressure PE using a data map that shows the correspondence between the engine speed NE and the fuel injection amount FJ and the exhaust pressure PE. Note that if a pressure sensor is provided in the exhaust pipe EP, the detection value of the pressure sensor in the exhaust pipe EP may be used as the exhaust pressure PE.

The CPU 51 calculates the exhaust flow rate using the intake air amount Qi obtained from the air flow meter 11, the exhaust temperature HE obtained from the exhaust temperature sensor 31, and the exhaust pressure PE obtained in step S123 (step S124). The CPU 51 calculates the exhaust flow rate using the intake air amount Qi before it is compressed by the engine 10, and the exhaust temperature HE and exhaust pressure PE after it is compressed by the engine 10. For example, the CPU 51 sets the detection value of a temperature sensor (not shown) that detects the temperature of the atmosphere as the temperature of the intake air amount Qi, and calculates the exhaust flow rate (liters/hour) by using a PV diagram.

The CPU 51 calculates the S/V ratio from the catalyst volume stored in the ECU 50 and the exhaust flow rate calculated in step S124 (step S125). This allows the CPU 51 to obtain the current S/V ratio. Finally, the CPU 51 calculates the current NOx purification rate using the correspondence equation between the NOx purification rate and the S/V ratio shown in FIG. 2 and the S/V ratio calculated in step S125 (step S126). That is, the CPU 51 identifies the NOx purification rate corresponding to the current S/V ratio by referring to the correspondence shown in FIG. 2, and sets the identified NOx purification rate as the current purification rate. This allows the CPU 51 to obtain the actual NOx purification rate when performing the process of step S12 in FIG. 3.

Returning to FIG. 3, the CPU 51 advances the process from step S12 to step S13. In step S13, the CPU 51 calculates the S/V ratio and the NOx purification rate after the purification rate assist is executed. As with step S12, the process of step S13 will be specifically described below with reference to the flowchart of FIG. 5. FIG. 5 is a flowchart showing an example of the process procedure of step S13 in FIG. 3.

The CPU 51 acquires the supply power supplied from the high-voltage battery 18 to the motor generator 20 when performing purification rate assistance. The CPU 101 calculates the amount of reduction in torque generated in the engine 10 when the motor generator 20 is driven by the supply power (step S130). In this embodiment, the ECU 50 reduces the torque generated in the engine 10 by the amount of driving force generated by driving the motor generator 20.

The CPU 51 executes steps S131 to S136 based on the amount of engine torque reduction calculated in step S130. Steps S131 to S136 correspond to steps S121 to S126 in FIG. 4.

The CPU 51 estimates the intake air volume Qi when the engine torque is reduced (step S131). Next, the CPU 51 estimates the exhaust temperature HE when the engine torque is reduced (step S132).

The CPU 51 estimates the exhaust pressure PE when the engine torque is reduced using the estimated engine speed NE and the fuel injection amount FJ estimated in step S134 (step S133). The CPU 51 calculates the exhaust flow rate using the intake air amount Qi, exhaust temperature HE, and exhaust pressure PE when the engine torque is reduced (step S134).

The CPU 51 calculates the S/V ratio when the engine torque is reduced from the catalyst capacity and the exhaust flow rate estimated in step S135 (step S135). The CPU 51 calculates the NOx purification rate after purification rate assistance using the correspondence relationship between the NOx purification rate and the S/V ratio shown in FIG. 2 and the S/V ratio calculated in step S135 (step S136). This allows the CPU 51 to estimate the NOx purification rate after the motor generator 20 is driven by the purification rate assistance.

Returning to FIG. 3, the CPU 51 compares the current NOx purification rate with the NOx purification rate after purification rate assistance, and calculates the increase in the NOx purification rate when purification rate assistance is performed (step S14). That is, it calculates the increase in the NOx purification rate described in FIG. 2.

Then, in steps S15 and S16, the CPU 51 calculates a "purification rate assist determination threshold" which is a threshold for comparison with the increase calculated in step S14. Specifically, the CPU 51 estimates the engine exhaust NOx amount after purification rate assistance (step S15). As described above, the engine exhaust NOx amount is the amount of NOx in the exhaust upstream of the exhaust purification device 30. In other words, it is the amount of NOx in the exhaust emitted from the engine 10 before it is purified by the catalyst.

The CPU 51 estimates the amount of engine exhaust NOx after purification rate assistance using the engine 10 rotation speed and fuel injection amount FJ. Since the amount of engine exhaust NOx depends on the fuel injection amount and the engine rotation speed, it can be estimated using a data map determined by experiment or simulation.

The CPU 51 calculates a purification rate assist determination threshold based on the amount of NOx exhausted from the engine estimated in step S16 and the state of charge (SOC) of the high-voltage battery 18 (step S16). The purification rate assist determination threshold is a threshold for comparison with the increase amount calculated in step S14. The CPU 51 determines whether or not to perform purification rate assistance based on the result of comparing the increase amount with the purification rate assist determination threshold.

The CPU 51 acquires the charge rate of the high voltage battery 18 based on the detected values of the input/output current and/or voltage of the high voltage battery 18. The CPU 51 detects the input/output current and/or voltage based on a sensor (not shown). The calculation method of the purification rate assist determination threshold will be described below with reference to FIG. 6. FIG. 6 is a diagram showing an example of the calculation method of the purification rate assist determination threshold.

The vertical axis of the graph shown in FIG. 6 indicates the purification rate assist determination threshold, and the horizontal axis indicates the amount of engine exhaust NOx. Lines Ln1 to Ln3 indicate the correspondence relationship between the purification rate assist determination threshold and the amount of engine exhaust NOx. The CPU 51 selects one of the correspondence relationship from lines Ln1 to Ln3 based on the charge rate of the high-voltage battery 18. Specifically, when the charge rate of the high-voltage battery 18 is greater than a predetermined threshold ThH, the CPU 51 selects line Ln1. Furthermore, when the charge rate of the high-voltage battery 18 is greater than or equal to a predetermined threshold ThL and less than or equal to the threshold ThH, the CPU 51 selects line Ln2. Furthermore, when the charge rate of the high-voltage battery 18 is less than the predetermined threshold ThL, the CPU 51 selects line Ln3.

The correspondence equations shown by lines Ln1 to Ln3 are correspondence equations that monotonically decrease when the amount of engine exhaust NOx is in the medium range, and have a constant assist determination threshold in the high and low ranges. That is, the CPU 51 first calculates the charge rate of the high-voltage battery 18, and selects a correspondence equation from lines Ln1 to Ln3. The CPU 51 then uses the selected correspondence equation to identify the purification rate assist determination threshold that corresponds to the estimated amount of engine exhaust NOx.

In this way, if the charge rate of the high-voltage battery 18 is low, the purification rate assist judgment threshold will be high. Also, if the amount of engine exhaust NOx is low, the purification rate assist judgment threshold will be high. Returning to FIG. 3, the CPU 51 determines whether the increase amount is greater than the calculated purification rate assist judgment threshold (step S17). If the increase amount exceeds the purification rate assist judgment threshold (YES in step S17), the CPU 51 executes purification rate assist (step S18) and ends the process. Note that the CPU 51 may execute purification rate assist when the increase amount is equal to or greater than the purification rate assist judgment threshold.

If the increase is equal to or less than the purification rate assist determination threshold (NO in step S17), the CPU 51 determines whether the supercharging assist condition is satisfied (step S19). As described above, supercharging assist is the driving of the motor generator 20 for the purpose of reducing turbo lag. After receiving a driving request from the user, the CPU 51 determines whether or not the vehicle is in a transitional period until the supercharger 14 is in a supercharged state, and if the vehicle is in the transitional period, the CPU 51 drives the motor generator 20 to perform supercharging assist (step S20).

The power supplied from the high-voltage battery 18 to the motor generator 20 during supercharging assist is greater than the power supplied from the high-voltage battery 18 to the motor generator 20 during purification rate assist. If the supercharging assist condition is not met (NO in step S19), the CPU 51 does not execute supercharging assist and ends the process. This allows a hybrid vehicle equipped with the control system 100 to use purification rate assist and supercharging assist selectively at the appropriate time.

In this way, the control system 100 uses the S/V ratio to obtain the increase amount, which is the difference between the NOx purification rate after the purification rate assist is executed and the current NOx purification rate, and if the increase amount is greater than the purification rate assist judgment threshold, the purification rate assist is executed. As a result, in the control system 100, if the increase amount of the NOx purification rate due to the execution of the purification rate assist is equal to or less than the purification rate assist judgment threshold, it is possible to prioritize improvement of fuel efficiency, and if the increase amount of the NOx purification rate due to the execution of the purification rate assist is greater than the purification rate assist judgment threshold, it is possible to execute the purification rate assist. In other words, if the ratio between the capacity of the NOx purification catalyst and the exhaust flow rate is large, the exhaust flow rate becomes excessive and the NOx purification rate is reduced. Therefore, in the control system 100, the ratio between the capacity of the NOx purification catalyst and the exhaust flow rate is used to calculate the NOx purification rate and determine whether or not to drive the motor generator 20, so that the NOx purification rate can be efficiently improved when the motor generator 20 is driven.

In addition, by calculating the purification rate assist determination threshold value using the method described in FIG. 6, when the charge rate of the high-voltage battery 18 is low, the control system 100 makes it difficult to execute the purification rate assist. As a result, even if the charge rate of the high-voltage battery 18 is low, the purification rate assist is executed, and an excessive decrease in the charge rate of the high-voltage battery 18 can be suppressed. Furthermore, when the amount of engine exhaust NOx is small, the control system 100 makes it difficult to execute the purification rate assist. As a result, even if the increase amount is high, if the amount of NOx to be purified is small, the execution of the purification rate assist can be suppressed, and fuel efficiency can be improved. In the example of FIG. 6, an example was described in which the purification rate assist determination threshold value is determined using both the charge rate of the high-voltage battery 18 and the amount of engine exhaust NOx, but the CPU 51 may determine the purification rate assist determination threshold value using only one of the charge rate of the high-voltage battery 18 or the amount of engine exhaust NOx.

[Experimental Results]
Fig. 7 is a diagram showing an example of the transition of various parameters when the processing procedure shown in Fig. 3 is executed. Eight parameters are shown on the same time axis (horizontal axis) in Fig. 7. The parameters shown in Fig. 7 are (A) the increase amount of NOx purification rate, (B) purification rate assist determination, (C) power supplied to the motor generator 20, (D) S/V ratio, (E) NOx purification rate, (F) engine exhaust NOx amount, (G) post-catalyst NOx amount, and (H) vehicle speed. The timings Tm1 to Tm6 are shown at the bottom of Fig. 7.

In (D) to (G), the solid lines indicate the parameter values when the processing procedure in this embodiment is executed, and the dashed and dotted lines indicate the parameter values when the drive wheels 40 are driven by the power of the engine 10 alone, without driving the motor generator 20. In other words, the dashed and dotted lines are a comparative example.

During the period from timing Tm1 to Tm2, as shown in (A), the increase in the NOx purification rate is smaller than the purification rate assist judgment threshold. Therefore, as shown in (B), during the period from timing Tm1 to Tm2, the purification rate assist judgment is in the OFF state. On the other hand, as shown in (C), electric power is supplied to the motor generator 20 during supercharging assistance. As shown in (H), the period from timing Tm1 to Tm2 is the period immediately after a driving request is received from the user, so the supercharging assistance condition is met.

As shown in (D), the engine torque or engine 10 speed is reduced by performing supercharging assistance, and the S/V ratio is reduced. As the S/V ratio is reduced, the NOx purification rate is improved, as shown in (E). In addition, the amount of NOx discharged from the engine and the amount of NOx after the catalyst are reduced, as shown in (F) and (G).

In the example of FIG. 7, at timing Tm2, the supercharging assist condition is not satisfied, and the increase amount exceeds the purification rate assist determination threshold, as shown in (A). Therefore, as shown in (B), the CPU 51 executes the purification rate assist, and as shown in (C), power is supplied to the motor generator 20 during the purification rate assist.

During the period from timing Tm2 to Tm3, the purification rate assist is executed, thereby decreasing the S/V ratio shown in (D) and improving the NOx purification rate shown in (E). Furthermore, the engine exhaust NOx amount and post-catalyst NOx amount shown in (F) and (G) decrease. This allows the CPU 51 to drive the motor generator 20 at a timing when the increase in the NOx purification rate is not reduced when driving the motor generator 20 for NOx purification.

The period from timing Tm3 to Tm4 is a period in which neither the purification rate assist nor the supercharger assist is performed, and the drive wheels 40 are driven only by the power of the engine 10. The period from timing Tm4 to Tm5 is a period in which the supercharger assist is performed, similar to the period from timing Tm1 to timing Tm2. The period from timing Tm5 to Tm6 is a period in which the purification rate assist is performed, similar to the period from timing Tm2 to timing Tm3.
[Modification]
In the above embodiment, an example (FIG. 5) has been described in which the NOx purification rate is estimated when the motor generator 20 is driven in order to calculate the increase amount of the NOx purification rate.

However, the CPU 51 may determine whether to perform purification rate assist using only the slope of the curve shown in FIG. 2 without estimating the NOx purification rate after purification rate assist is performed. Specifically, when the CPU 51 calculates the current S/V ratio in step S12 of FIG. 3, it acquires the slope of the curve corresponding to the current S/V ratio. If the current S/V ratio is calculated as the ratio Bs shown in FIG. 2, the CPU 51 acquires the slope of the curve at the ratio Bs shown in FIG. 2. Also, if the current S/V ratio is calculated as the ratio BsZ shown in FIG. 2, the CPU 51 acquires the slope of the curve at the ratio BsZ shown in FIG. 2.

In step S17 in FIG. 3, the CPU 51 compares the obtained slope with the purification rate assist determination threshold. The purification rate assist determination threshold in the modified example is a threshold for comparing with the slope. As a result, when the slope is large, such as the ratio Bs, purification rate assist is more likely to be performed, and when the slope is small, such as the ratio BsZ, purification rate assist is less likely to be performed. Therefore, even in the control system 100 in the modified example, when the motor generator 20 is driven to purify NOx, the S/V ratio is used to determine whether or not to drive the motor generator 20, thereby making it possible to efficiently improve the NOx purification rate when the motor generator 20 is driven.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims.

10 engine, 11 air flow meter, 12 injector, 13 engine speed sensor, 14 turbocharger, 15 low voltage battery, 16 clutch, 17 converter, 18 high voltage battery, 19 inverter, 20 motor generator, 30 exhaust purification device, 31 exhaust temperature sensor, 40 drive wheels, 52 memory, 100 control system, As, AsZ, Bs, BsZ ratio, EP exhaust pipe, FJ fuel injection amount, HE exhaust temperature, IP intake pipe, Ln1 to Ln3 lines, NE engine speed, PE exhaust pressure, Qi intake air volume.

Claims (5)

A control system for a hybrid vehicle that runs using at least one of a motor generator and an engine,
an exhaust passage connected to the engine and through which exhaust gas generated within the engine flows;
a NOx purification catalyst disposed in the exhaust passage for purifying NOx contained in the exhaust gas;
A control device for controlling the motor generator,
The control device, while the engine is running,
A flow rate of the exhaust gas passing through the NOx purification catalyst is obtained;
Calculating a NOx purification rate of the NOx purification catalyst using a ratio between a capacity of the NOx purification catalyst and a flow rate of the exhaust gas;
A control system that uses the NOx purification rate to determine whether or not to drive the motor generator. The control device includes:
Calculating an increase in the NOx purification rate due to driving of the motor generator;
The control system according to claim 1 , further comprising: a step of driving the motor generator when the increase amount exceeds a threshold value. The control device estimates an amount of NOx emitted from the engine,
3. The control system according to claim 2, wherein the threshold value is determined using at least one of an amount of NOx discharged from the engine after the motor generator is driven and a charge rate of an electric storage device that supplies electric power to the motor generator. a flow rate sensor that detects the flow rate of intake air of the engine;
A temperature sensor for detecting the temperature of the exhaust gas is further provided.
The control system according to any one of claims 1 to 3, wherein the control device calculates the flow rate of the exhaust gas using the detection value of the flow rate sensor, the detection value of the temperature sensor, and the pressure of the exhaust gas. The engine is a turbocharged engine,
The control system according to claim 1 , wherein the control device drives the motor generator as a supercharging assist during a transitional period until the engine state becomes a supercharged state after receiving a driving request from a user.

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