Control system

Abstract

To efficiently improve a NOx purification rate when a motor generator is driven.SOLUTION: Provided is a control system (100) used in a hybrid vehicle that travels using power of at least one of a motor generator (20) and an engine (10). The control system (100) includes a NOx purification catalyst (30) that purifies NOx contained in exhaust gas, and a control device (50). The control device (50) acquires an exhaust gas flow rate during drive of the engine (10) (S124), a NOx purification rate of the NOx purification catalyst is calculated using a ratio of a volume of the NOx purification catalyst and the exhaust gas flow rate (S126), and whether the motor generator (20) is driven using the NOx purification rate is determined (S17, 18).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a control system used in a hybrid vehicle including a reduction catalyst for purifying nitrogen oxides (NOx).

Background Art

[0002] In a hybrid vehicle including an engine and a motor generator, a hybrid vehicle including a NOx purification device for purifying nitrogen oxides (NOx) discharged from the engine is known. The NOx purification device includes, for example, a NOx storage reduction type catalyst, and purifies the NOx discharged from the engine by reducing it to nitrogen gas.

[0003] Japanese Unexamined Patent Application Publication No. 2014-227005 (Patent Document 1) discloses a control method for a hybrid vehicle including a NOx storage reduction type catalyst and driving 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 temperature of the NOx storage reduction type catalyst and the driving request load from the user.

[0004] More specifically, when the hybrid vehicle of Patent Document 1 is below the lower limit value of the activation temperature and the driving request is a low load, the driving motor is used as a generator to increase the engine torque. If the temperature of the exhaust gas rises due to the increase in the engine torque, the temperature of the NOx storage reduction type catalyst rises. Further, when the hybrid vehicle of Patent Document 1 is below the lower limit value of the activation temperature and the driving request is a high load, the driving motor is rotationally driven to reduce the engine torque. Due to the decrease in the engine torque, the generation amount of NOx discharged from the engine decreases.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In Patent Document 1, when the running requirement is low load and the temperature is below the lower limit value of the activation temperature, the running motor is used as a generator to increase the activation temperature. By bringing the NOx storage reduction type catalyst within the activation temperature range, the NOx purification rate is improved.

[0007] However, the NOx purification rate is affected not only by the catalyst temperature but also by the exhaust gas flow rate. Even if the catalyst temperature is raised to within the activation temperature range, the exhaust gas flow rate passing through the NOx storage reduction type catalyst may not be small enough to ensure the reduction reaction time, and it can be assumed that the NOx purification rate cannot be efficiently improved.

[0008] The present disclosure has been made to solve the above problems, and an object thereof is to efficiently improve the NOx purification rate when driving a motor generator.

Means for Solving the Problems

[0009] (1) The control system according to the present disclosure is used in a hybrid vehicle that travels using the power of at least one 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 the exhaust gas generated in the engine flows through it. The NOx purification catalyst is disposed in the exhaust passage and purifies NOx contained in the exhaust gas. The control device controls the motor generator. The control device acquires the flow rate of the exhaust gas passing through the NOx purification catalyst during the driving of the engine, calculates the NOx purification rate of the NOx purification catalyst using the ratio of the capacity of the NOx purification catalyst to the flow rate of the exhaust gas, and determines whether to drive the motor generator using the NOx purification rate.

[0010] According to the above configuration, if the ratio of the capacity of the NOx purification catalyst to the exhaust gas flow rate is large, the exhaust gas flow rate becomes excessive and the NOx purification rate decreases. Therefore, by calculating the NOx purification rate using the ratio of the capacity of the NOx purification catalyst to the exhaust gas flow rate and determining whether to drive the motor generator, it is possible to efficiently improve the NOx purification rate when the motor generator is driven.

[0011] (2) In one aspect, the control device calculates the increase amount of the NOx purification rate due to the drive of the motor generator, and drives the motor generator when the increase amount exceeds the threshold value.

[0012] (3) In one aspect, the control device estimates the amount of NOx discharged from the engine, and determines the threshold value using at least one of the amount of NOx discharged from the engine after driving the motor generator and the state of charge of the power storage device that supplies power to the motor generator.

[0013] (4) In one aspect, the control system further includes a flow rate sensor and a temperature sensor. The flow rate sensor detects the flow rate of the intake air of the engine. The temperature sensor detects the temperature of the exhaust gas. 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.

[0014] (5) In one aspect, the engine is a supercharged engine. After receiving a driving request from the user, the control device drives the motor generator as supercharging assist during the transient period until the state of the engine becomes a supercharged state.

Effect of the Invention

[0015] According to the present disclosure, it is to efficiently improve the NOx purification rate when the motor generator is driven.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0018] FIG. 1 is a diagram showing an example of the overall configuration of a control system 100 used in a hybrid vehicle according to the present 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. Further, the control system 100 includes an air flow meter 11, an injector 12, an engine speed sensor 13, a supercharger 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.

[0019] The engine 10 is a diesel engine having a plurality of cylinders. Note that the engine 10 may be a gasoline engine. The crankshaft of the engine 10 and the rotating shaft of the motor generator 20 are connected with a clutch 16 interposed therebetween. Note that the number of cylinders the engine 10 has may be one.

[0020] The high-voltage battery 18 is a power storage device that stores electric power supplied to the motor generator 20. The output voltage of the high-voltage battery 18 is set to a voltage (for example, about several hundred volts) higher than the output voltage of the low-voltage battery 15 (for example, about 12 volts) and the output voltage used for an accessory device of a low-voltage system (not shown). The accessory device of the low-voltage system is, for example, an electric pump, a glow plug, or the like.

[0021] 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.

[0022] 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 electric power supplied from the high-voltage battery 18 via the inverter 19.

[0023] Also, the inverter 19 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 electric power supplied from the motor generator 20 via the inverter 19. Note that a voltage converter (step-up / step-down converter) may be provided between the motor generator 20 and the inverter 19.

[0024] The DC / DC converter 17 is provided between the high-voltage battery 18, the low-voltage battery 15, and the low-voltage auxiliary equipment. It 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 the low-voltage auxiliary equipment.

[0025] The driving wheels 40 are transmitted with the power of at least one of the engine 10 and the motor generator 20. The hybrid vehicle using the control system 100 in the present embodiment can switch the driving mode to any one of EV driving, assist driving, charging driving, and regenerative driving.

[0026] During EV driving, the hybrid vehicle using the control system 100 runs with the power of the motor generator 20 while disengaging the clutch 16 and stopping the engine 10. During assist driving, the hybrid vehicle using the control system 100 runs using the power of both the engine 10 and the motor generator 20 with the clutch 16 engaged. Therefore, during EV driving and assist driving, the power stored in the high-voltage battery 18 is discharged to the motor generator 20.

[0027] During charging driving, the hybrid vehicle using the control system 100 runs using a part of the power of the engine 10 with the clutch 16 engaged, and charges the high-voltage battery 18 with the power generated by the motor generator 20 using the surplus energy (energy not used for running) of the engine 10. During regenerative driving, the hybrid vehicle using the control system 100 decelerates while running, and charges the high-voltage battery 18 with the power generated by the motor generator 20 using the deceleration energy of the hybrid vehicle using the control system 100. Therefore, during charging driving and regenerative driving, the high-voltage battery 18 is charged with the power generated by the motor generator 20.

[0028] 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 and is a RAM (Random Access Memory). The storage device is, for example, a storage for preservation and is a ROM (Read Only Memory). The storage device may be a rewritable non-volatile memory such as an EEPROM. Although the ECU 50 is described as one 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.

[0029] 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 various controls are not limited to software processing, and can also be processed by dedicated hardware (electronic circuits).

[0030] The air flow meter 11 detects the flow rate (intake air amount) Qi of the intake air introduced into the intake pipe IP. The air flow meter 11 transmits a signal indicating the detected intake air amount Qi to the ECU 50. The air flow meter 11 is an example of the "flow rate sensor" in the present disclosure.

[0031] An injector 12 for injecting fuel into the combustion chamber is arranged in each cylinder included in the engine. When driving the engine 10, the ECU 50 generates a command including the fuel injection amount FJ to each cylinder according to the user's required power and the like, and outputs it to the injector 12 of each cylinder. Thereby, in each cylinder, fuel corresponding to the fuel injection amount FJ is injected from the injector 12.

[0032] The engine speed sensor 13 detects the rotational 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.

[0033] The supercharger 14 includes a compressor and a turbine. The air flowing through the intake pipe IP is sucked into and compressed by the compressor of the supercharger 14. The air compressed by the compressor is introduced into the combustion chamber of the engine 10 through the intake pipe IP. When the air-fuel mixture in the combustion chamber burns, the engine 10 generates driving force. The exhaust gas after combustion, that is, the exhaust, passes through the turbine of the supercharger 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 gas generated in the engine 10 flows through it.

[0034] After receiving a driving request from the user, during the transient period until the state of the engine becomes a supercharged state 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 mitigate the turbo lag. Hereinafter, the driving of the motor generator 20 to mitigate this turbo lag is referred to as "supercharging assist".

[0035] The exhaust temperature sensor 31 is provided in the exhaust pipe EP and detects the exhaust temperature HE discharged from the engine 10. The exhaust temperature sensor 31 transmits a signal indicating the detected exhaust temperature HE to the ECU 50.

[0036] An exhaust gas purification device 30 is provided on the exhaust pipe EP. The exhaust gas purification device 30 has a function of purifying NOx in the exhaust gas. The exhaust gas purification device 30 is, for example, a catalyst that reduces NOx in the exhaust gas using a reducing agent. More specifically, the exhaust gas purification device 30 is, for example, an NSR (NOx Storage Reduction) catalyst. The catalyst in the exhaust gas purification device 30 stores NOx in the exhaust gas 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 gas purification device 30 is stored by the storage device in the ECU 50.

[0037] The ECU 50 calculates the NOx purification rate based on 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 gas on the downstream side of the exhaust gas purification device 30 to the amount of NOx in the exhaust gas on the upstream side of the exhaust gas purification device 30. That is, the NOx purification rate is an index indicating the amount of NOx purified by the exhaust gas purification device 30. Hereinafter, the amount of NOx in the exhaust gas on the upstream side of the exhaust gas purification device 30 may be referred to as the "engine exhaust NOx amount", and the amount of NOx in the exhaust gas on the downstream side of the exhaust gas purification device 30 may be referred to as the "post-catalyst NOx amount".

[0038] [Correspondence between S / V ratio and NOx purification rate] FIG. 2 is a diagram showing an example of the correspondence 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. The S / V ratio (Surface Volume) is, as shown in FIG. 2, the ratio of the exhaust gas flow rate (liters / hour) to the catalyst capacity (liters) of the exhaust gas purification device 30. The catalyst capacity is constant for each exhaust gas purification device 30. The catalyst capacity is stored by the ECU 50. The catalyst capacity means the volume of the catalyst contributing to NOx purification.

[0039] While the catalyst capacity is constant for each exhaust gas purification device 30, the exhaust gas flow rate varies depending on the intake air amount Qi, the fuel injection amount FJ, etc. The exhaust gas flow rate is the flow rate of the exhaust gas passing through the exhaust gas purification device 30. When the exhaust gas flow rate for a certain catalyst capacity increases, the proportion of the amount of NOx that cannot be processed by the exhaust gas purification device 30 increases. On the other hand, when the exhaust gas flow rate for a certain catalyst capacity decreases, the proportion of the amount of NOx that cannot be processed by the exhaust gas purification device 30 decreases. That is, 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 monotonically decreases as the S / V ratio increases.

[0040] The NOx purification rate monotonically decreases as the S / V ratio increases, but the rate of decrease is not constant and varies depending on the magnitude of the S / V ratio. In other words, as shown in Figure 2, the slope of the curve showing the correspondence between the NOx purification rate and the S / V ratio varies depending on the magnitude of the S / V ratio. In the example shown in Figure 2, when the magnitude of the S / V ratio is divided into a low region, a middle region, and a high region, among the low region, the middle region, and the high region, the slope of the curve in the middle region is the largest. Compared with the slope of the curve in the middle region, the slopes of the curves in the low region and the high region are small.

[0041] That is, when reducing the S / V ratio in the middle region with a large slope, the increase in the NOx purification rate is more likely to be larger than when reducing the S / V ratio in the low region or the high region with a small slope. More specifically, when the ratio BsZ, which is the S / V ratio in the high region shown in Figure 2, is decreased by ΔSV to become the ratio AsZ, the NOx purification rate increases by ΔRZ. That is, when the S / V ratio in the high region is decreased by ΔSV, the increase in the NOx purification rate is ΔRZ.

[0042] On the other hand, when the ratio Bs, which is the S / V ratio in the middle region, is decreased by ΔSV to become the ratio As, the NOx purification rate increases by ΔR. That is, when the S / V ratio in the middle region is decreased by ΔSV, the increase in the NOx purification rate is ΔR. As shown in Figure 2, the increase amount ΔR is larger than the increase amount ΔRZ. Thus, when the S / V ratio is decreased by the same reduction amount ΔSV, decreasing the S / V ratio in the region with a large reduction rate (the slope of the curve) results in a higher increase in the NOx purification rate.

[0043] The correspondence relationship between the NOx purification rate and the S / V ratio shown in FIG. 2 is stored as a data map in the storage device within the ECU 50. In the control system 100 of the present 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". In the storage device within the ECU 50, a certain power value is stored as the supply power when the purification rate assist is executed. Note that the ECU 50 may change the supply power according to the required load from the user, vehicle speed, etc. when executing the purification rate assist.

[0044] [Processing Procedure of Purification Rate Assist] Hereinafter, the processing procedure of the purification rate assist will be described. The ECU 50 in the present embodiment uses the data map shown in FIG. 2 to calculate the increase amount of the NOx purification rate, and determines whether to execute the purification rate assist according to the increase amount. FIG. 3 is a flowchart showing an example of the processing procedure of the purification rate assist by the ECU 50. This flowchart is repeatedly executed at regular calculation cycles.

[0045] The CPU 51 determines whether it has received a driving request 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 following processing is executed during the driving of the engine 10. If the driving request has not been received (NO in step S10), the CPU 51 ends the processing. If the driving request has been received (YES in step S10), the CPU 51 determines whether 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 becomes active. When within the activation temperature range, the NOx purification rate increases. When the catalyst temperature of the exhaust purification device 30 is not within the activation temperature range, the NOx purification rate greatly decreases, and the correspondence relationship between the NOx purification rate and the S / V ratio becomes a correspondence relationship different from the correspondence relationship shown in FIG. 2.

[0046] In step S11, the CPU 51 calculates the catalyst temperature of the exhaust gas purification device 30 based on the exhaust gas temperature HE acquired from the exhaust gas temperature sensor 31. In the storage device within the ECU 50, a data map showing the correspondence between the exhaust gas temperature HE and the catalyst temperature of the exhaust gas purification device 30 is stored. Note that the catalyst temperature of the exhaust gas purification device 30 may be calculated based on the detection value of a newly provided temperature sensor near the catalyst within the exhaust gas purification device 30. If the catalyst temperature is not within the activation temperature range (NO in step S11), for the correspondence between the NOx purification rate and the S / V ratio, the CPU 51 ends the process without executing the purification rate assist.

[0047] 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 mean the actual S / V ratio and NOx purification rate when the process of step S12 is being performed. Hereinafter, the processing content of step S12 in FIG. 3 will be specifically described using the flowchart of FIG. 4. FIG. 4 is a flowchart showing an example of the processing procedure of step S12 in FIG. 3.

[0048] The CPU 51 acquires the intake air amount Qi from the air flow meter 11 (step S121). Subsequently, the CPU 51 acquires the exhaust gas temperature HE from the exhaust gas temperature sensor 31 (step S122). The CPU 51 acquires the exhaust gas pressure PE (step S123).

[0049] The exhaust gas pressure PE is the pressure of the exhaust gas discharged from the engine 10. For example, the CPU 51 estimates the exhaust gas pressure PE using the engine speed NE and the fuel injection amount FJ. At this time, the CPU 51 estimates the exhaust gas pressure PE using a data map showing the correspondence between the engine speed NE, the fuel injection amount FJ, and the exhaust gas pressure PE. Note that when 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 gas pressure PE.

[0050] The CPU 51 calculates the exhaust gas flow rate using the intake air amount Qi acquired from the air flow meter 11, the exhaust gas temperature HE acquired from the exhaust gas temperature sensor 31, and the exhaust gas pressure PE acquired in step S123 (step S124). The CPU 51 calculates the exhaust gas flow rate using the intake air amount Qi before being compressed by the engine 10, the exhaust gas temperature HE after being compressed by the engine 10, and the exhaust gas pressure PE. For example, the CPU 51 sets the detected 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 gas flow rate (liters / hour) by using a PV diagram.

[0051] The CPU 51 calculates the S / V ratio from the catalyst capacity stored in the ECU 50 and the exhaust gas flow rate calculated in step S124 (step S125). Thereby, the CPU 51 can obtain the current S / V ratio. Finally, the CPU 51 calculates the current NOx purification rate by using the relational expression 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 specifies the NOx purification rate corresponding to the current S / V ratio with reference to the correspondence shown in FIG. 2, and sets the specified NOx purification rate as the current purification rate. Thereby, the CPU 51 can obtain the actual NOx purification rate when performing the process of step S12 in FIG. 3.

[0052] Returning to FIG. 3, the CPU 51 proceeds with 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 executing the purification rate assist. Hereinafter, similar to step S12, the processing content of step S13 will be specifically described with reference to the flowchart of FIG. 5. FIG. 5 is a flowchart showing an example of the processing procedure of step S13 in FIG. 3.

[0053] When the CPU 51 executes the purification rate assist, it obtains the supply power supplied from the high-voltage battery 18 to the motor generator 20. The CPU 101 calculates the amount of decrease in the torque generated in the engine 10 when the motor generator 20 is driven by the supply power (step S130). In the present embodiment, the ECU 50 reduces the torque generated in the engine 10 by the amount of the driving force generated by the driving of the motor generator 20.

[0054] Based on the amount of decrease in the engine torque calculated in step S130, the CPU 51 executes the processes from step S131 to S136. The processes from step S131 to S136 correspond to the processes from step S121 to S126 in FIG. 4.

[0055] The CPU 51 estimates the intake air amount Qi when the engine torque decreases (step S131). Subsequently, the CPU 51 estimates the exhaust temperature HE when the engine torque decreases (step S132).

[0056] The CPU 51 estimates the exhaust pressure PE when the engine torque decreases by using the estimated engine speed NE and the fuel injection amount FJ estimated in step S134 (step S133). The CPU 51 calculates the exhaust gas flow rate by using the intake air amount Qi, the exhaust temperature HE, and the exhaust pressure PE when the engine torque decreases (step S134).

[0057] The CPU 51 calculates the S / V ratio when the engine torque decreases from the catalyst capacity and the exhaust gas flow rate estimated in step S135 (step S135). The CPU 51 calculates the NOx purification rate after the purification rate assist by using the correspondence relationship between the NOx purification rate shown in FIG. 2 and the S / V ratio and the S / V ratio calculated in step S135 (step S136). Thereby, the CPU 51 can estimate the NOx purification rate after the motor generator 20 is driven by the purification rate assist.

[0058] Returning to FIG. 3, the CPU 51 compares the current NOx purification rate with the NOx purification rate after the purification rate assist, and calculates the increase in the NOx purification rate when the purification rate assist is executed (step S14). That is, the increase in the NOx purification rate described with reference to FIG. 2 is calculated.

[0059] Subsequently, the CPU 51 calculates a “purification rate assist determination threshold value”, which is a threshold value for comparison with the increase calculated in step S14, in steps S15 and S16. Specifically, the CPU 51 estimates the engine exhaust NOx amount after the purification rate assist (step S15). As described above, the engine exhaust NOx amount is the amount of NOx in the exhaust gas on the upstream side of the exhaust purification device 30. That is, it is the amount of NOx in the exhaust gas discharged from the engine 10 before being purified by the catalyst.

[0060] The CPU 51 estimates the engine exhaust NOx amount after the purification rate assist using the engine speed of the engine 10 and the fuel injection amount FJ. Since the engine exhaust NOx amount depends on the fuel injection amount and the engine speed, it can be estimated by a data map determined by experiments or simulations.

[0061] The CPU 51 calculates a purification rate assist determination threshold value based on the engine exhaust NOx amount estimated in step S16 and the state of charge (SOC) of the high-voltage battery 18 (step S16). The purification rate assist determination threshold value is a threshold value for comparison with the increase calculated in step S14. The CPU 51 determines whether to execute the purification rate assist based on the result of comparing the increase with the purification rate assist determination threshold value.

[0062] The CPU 51 obtains the state of charge 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). Hereinafter, the calculation method of the purification rate assist determination threshold value will be described with reference to FIG. 6. FIG. 6 is a diagram showing an example of the calculation method of the purification rate assist determination threshold value.

[0063] The vertical axis of the graph shown in FIG. 6 indicates the purification rate assist determination threshold value, and the horizontal axis indicates the engine exhaust NOx amount. Lines Ln1 to Ln3 indicate the correspondence relationship formula between the purification rate assist determination threshold value and the engine exhaust NOx amount. The CPU 51 selects one correspondence relationship formula from among lines Ln1 to Ln3 based on the state of charge of the high-voltage battery 18. Specifically, when the state of charge of the high-voltage battery 18 is greater than a predetermined threshold value ThH, the CPU 51 selects line Ln1. Also, when the state of charge of the high-voltage battery 18 is equal to or greater than a predetermined threshold value ThL and equal to or less than the threshold value ThH, the CPU 51 selects line Ln2. Further, when the state of charge of the high-voltage battery 18 is less than a predetermined threshold value ThL, the CPU 51 selects line Ln3.

[0064] The correspondence relationship formula indicated by lines Ln1 to Ln3 is a formula that monotonically decreases when the magnitude of the engine exhaust NOx amount is in the middle range and has a constant assist determination threshold value in the high range and the low range. That is, the CPU 51 first calculates the state of charge of the high-voltage battery 18 and selects a correspondence relationship formula from among lines Ln1 to Ln3. Thereafter, the CPU 51 uses the selected correspondence relationship formula to specify the purification rate assist determination threshold value corresponding to the estimated engine exhaust NOx amount.

[0065] In this way, if the state of charge of the high-voltage battery 18 is small, the purification rate assist determination threshold value becomes high. Also, if the engine exhaust NOx amount is small, the purification rate assist determination threshold value becomes high. Returning to FIG. 3, the CPU 51 determines whether or not the increase amount is greater than the calculated purification rate assist determination threshold value (step S17). When the increase amount exceeds the purification rate assist determination threshold value (YES in step S17), the CPU 51 executes the purification rate assist (step S18) and ends the process. Note that the CPU 51 may execute the purification rate assist when the increase amount is equal to or greater than the purification rate assist determination threshold value.

[0066] When the increase amount is less than or equal to 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, the supercharging assist is the driving of the motor generator 20 for the purpose of alleviating the turbo lag. After receiving a driving request from the user, the CPU 51 determines whether it is a transient period until the supercharger 14 enters a supercharged state. If it is the transient period, the motor generator 20 is driven to execute the supercharging assist (step S20).

[0067] The power supplied from the high-voltage battery 18 to the motor generator 20 during the supercharging assist is greater than the power supplied from the high-voltage battery 18 to the motor generator 20 during the purification rate assist. When the supercharging assist condition is not satisfied (NO in step S19), the CPU 51 does not execute the supercharging assist and ends the process. Thereby, in the hybrid vehicle equipped with the control system 100, the purification rate assist and the supercharging assist can be appropriately used separately at the right time.

[0068] As described above, in the control system 100, the increase amount, which is the difference between the NOx purification rate after executing the purification rate assist using the S / V ratio and the current NOx purification rate, is obtained. If the increase amount is greater than the purification rate assist determination threshold, the purification rate assist is executed. Thereby, in the control system 100, when the increase amount of the NOx purification rate due to the execution of the purification rate assist is less than or equal to the purification rate assist determination threshold, it is possible to prioritize the improvement of fuel efficiency. When the increase amount of the NOx purification rate due to the execution of the purification rate assist is greater than the purification rate assist determination threshold, the purification rate assist can be executed. That is, when the ratio of the capacity of the NOx purification catalyst to the exhaust gas flow rate is large, the exhaust gas flow rate becomes excessive and the NOx purification rate decreases. Therefore, in the control system 100, by using the ratio of the capacity of the NOx purification catalyst to the exhaust gas flow rate to calculate the NOx purification rate and determine whether to drive the motor generator 20, the NOx purification rate can be efficiently improved when the motor generator 20 is driven.

[0069] Also, by calculating the purification rate assist determination threshold value by the method described with reference to FIG. 6, when the state of charge 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 when the state of charge of the high-voltage battery 18 is low, it is possible to suppress an excessive decrease in the state of charge of the high-voltage battery 18 due to the execution of the purification rate assist. Further, when the amount of NOx discharged from the engine is small, the control system 100 makes it difficult to execute the purification rate assist. Thereby, even when the increase amount is high, when the amount of NOx to be purified itself is small, it is possible to suppress the execution of the purification rate assist and improve the fuel efficiency. In the example of FIG. 6, an example of determining the purification rate assist determination threshold value using both the state of charge of the high-voltage battery 18 and the amount of NOx discharged from the engine has been described. However, the CPU 51 may determine the purification rate assist determination threshold value using only either the state of charge of the high-voltage battery 18 or the amount of NOx discharged from the engine.

[0070] [Experimental Results] FIG. 7 is a diagram showing an example of transitions of various parameters when the processing procedure shown in FIG. 3 is executed. FIG. 7 shows eight parameters on the same time axis (horizontal axis). In FIG. 7, (A) the increase amount of the NOx purification rate, (B) the purification rate assist determination, (C) the power supplied to the motor generator 20, (D) the S / V ratio, (E) the NOx purification rate, (F) the amount of NOx discharged from the engine, (G) the amount of NOx after the catalyst, and (H) the vehicle speed are shown as parameters. Timings Tm1 to Tm6 are shown at the bottom of FIG. 7.

[0071] In (D) to (G), the solid line indicates the parameter value when the processing procedure in the present embodiment is executed, and the dashed-dotted line indicates the parameter value when the drive wheels 40 are driven only by the power of the engine 10 without driving the motor generator 20. That is, the dashed-dotted line is a comparative example.

[0072] During the period from timing Tm1 to Tm2, as shown in (A), the increase in NOx purification rate is smaller than the purification rate assist determination threshold. Therefore, as shown in (B), during the period from timing Tm1 to Tm2, the purification rate assist determination is in the OFF state. On the other hand, as shown in (C), power during supercharging assist is supplied to the motor generator 20. As shown in (H), since the period from timing Tm1 to Tm2 is the period immediately after receiving a driving request from the user, the supercharging assist condition is satisfied.

[0073] As shown in (D), when supercharging assist is executed, the engine torque or the rotational speed of the engine 10 decreases, and the S / V ratio decreases. When the S / V ratio decreases, as shown in (E), the NOx purification rate improves. Also, as shown in (F) and (G), the engine exhaust NOx amount and the post-catalyst NOx amount decrease.

[0074] In the example of FIG. 7, at timing Tm2, the supercharging assist condition becomes not satisfied, and as shown in (A), the increase amount exceeds the purification rate assist determination threshold. Therefore, as shown in (B), the CPU 51 executes purification rate assist, and as shown in (C), power during purification rate assist is supplied to the motor generator 20.

[0075] During the period from timing Tm2 to Tm3, when purification rate assist is executed, the S / V ratio shown in (D) decreases, and the NOx purification rate shown in (E) improves. Furthermore, the engine exhaust NOx amount and the post-catalyst NOx amount shown in (F) and (G) decrease. Thereby, when the CPU 51 drives the motor generator 20 for NOx purification, the motor generator 20 can be driven at a timing when the increase amount of the NOx purification rate is not reduced.

[0076] Timings Tm3 to Tm4 are periods during which neither the purification rate assist nor the supercharger assist is executed, 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 during which the supercharging assist is executed in the same manner as from timing Tm1 to timing Tm2. The period from timing Tm5 to Tm6 is a period during which the purification rate assist is executed in the same manner as from timing Tm2 to timing Tm3. [Modification Example] In the above-described embodiment, an example (FIG. 5) of estimating the NOx purification rate when driving the motor generator 20 in order to calculate the increase amount of the NOx purification rate has been described.

[0077] However, the CPU 51 may determine whether to execute the purification rate assist using only the slope of the curve shown in FIG. 2 without estimating the NOx purification rate after the execution of the purification rate assist. Specifically, when the CPU 51 calculates the current S / V ratio in step S12 of FIG. 3, the CPU 51 acquires the slope of the curve corresponding to the current S / V ratio. When the current S / V ratio is calculated as the ratio Bs shown in FIG. 2, the CPU 51 acquires the slope at the ratio Bs of the curve shown in FIG. 2. Also, when the current S / V ratio is calculated as the ratio BsZ shown in FIG. 2, the CPU 51 acquires the slope at the ratio BsZ of the curve shown in FIG. 2.

[0078] In step S17 in FIG. 3, the CPU 51 compares the acquired slope with the purification rate assist determination threshold value. The purification rate assist determination threshold value in the modification example is a threshold value for comparison with the slope. Thus, when the slope is large like the ratio Bs, the purification rate assist is likely to be executed, and when the slope is small like the ratio BsZ, the purification rate assist is less likely to be executed. Therefore, also in the control system 100 in the modification example, when driving the motor generator 20 for NOx purification, by determining whether to drive the motor generator 20 using the S / V ratio, the NOx purification rate can be efficiently improved when the motor generator 20 is driven.

[0079] The embodiments disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present disclosure is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Description of Reference Numerals

[0080] 10 Engine, 11 Airflow meter, 12 Injector, 13 Engine speed sensor, 14 Supercharger, 15 Low-voltage battery, 16 Clutch, 17 Converter, 18 High-voltage battery, 19 Inverter, 20 Motor generator, 30 Exhaust gas purification device, 31 Exhaust temperature sensor, 40 Driving wheel, 52 Memory, 100 Control system, As, AsZ, Bs, BsZ ratios, 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

1. A control system for a hybrid vehicle that travels using the power of at least one of a motor generator and an engine, an exhaust passage that is connected to the engine and through which exhaust generated in the engine flows, a NOx purification catalyst disposed in the exhaust passage for purifying NOx contained in the exhaust, and a control device for controlling the motor generator, wherein the control device, during driving of the engine, acquires the flow rate of the exhaust passing through the NOx purification catalyst, calculates the NOx purification rate of the NOx purification catalyst using the ratio of the capacity of the NOx purification catalyst to the flow rate of the exhaust, and determines whether to drive the motor generator using the NOx purification rate. A control system.

2. The control device, calculates the increase amount of the NOx purification rate due to the driving of the motor generator, and when the increase amount exceeds a threshold value, drives the motor generator. The control system according to claim 1.

3. The control device estimates the amount of NOx discharged from the engine, and determines the threshold value using at least one of the amount of NOx discharged from the engine after driving the motor generator and the state of charge of a power storage device that supplies power to the motor generator. The control system according to claim 2.

4. further comprising a flow rate sensor for detecting the flow rate of the intake air of the engine, and a temperature sensor for detecting the temperature of the exhaust, wherein the control device calculates the flow rate of the exhaust using the detection value of the flow rate sensor, the detection value of the temperature sensor, and the pressure of the exhaust. The control system according to any one of claims 1 to 3.

5. The engine is a supercharged engine, and the control device drives the motor generator as supercharging assist during a transient period until the state of the engine becomes a supercharged state after receiving a driving request from the user. The control system according to claim 1.

Images