JP2019173685A - Exhaust emission control system for internal combustion engine and exhaust emission control method for internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control system for an internal combustion engine that includes a NOx purification device in an exhaust passage for an internal combustion engine, and to provide an exhaust emission control method for an internal combustion engine.SOLUTION: In an internal combustion engine that includes an SCR device 24 in an exhaust passage 22 for the internal combustion engine 10, an alternator 31 reduces or stops power generation when temperature Tg of an exhaust gas G flowing into the SCR device 24 becomes equal to or more than set temperature Tc which is preliminarily set.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to an exhaust gas purification system for an internal combustion engine that purifies exhaust gas discharged from the internal combustion engine and an exhaust gas purification method for the internal combustion engine.

  In an internal combustion engine such as a diesel engine or a lean-burn gasoline engine, an exhaust gas turbine is provided upstream of the catalyst disposed in the exhaust passage to purify harmful components in the exhaust, and the exhaust temperature or the catalyst temperature exceeds the set temperature. At this time, by driving the generator with this exhaust gas turbine and supplying it to the battery, the temperature of the exhaust gas flowing into the catalyst is lowered, and the temperature of the catalyst is maintained within a good range of the NOx purification rate. Therefore, the NOx purification function is improved (see, for example, Patent Document 1).

JP 05-263628 A

  By the way, in such an exhaust gas purification system, when the charge amount of the battery is saturated, the thermal energy of the exhaust gas is wasted.

  An object of the present disclosure is to provide an exhaust gas purification system for an internal combustion engine and an internal combustion engine capable of improving a NOx purification rate in an exhaust gas purification system for an internal combustion engine provided with a NOx purification catalyst device in an exhaust passage of the internal combustion engine. An exhaust gas purification method is provided.

  To achieve the above object, an exhaust gas purification system for an internal combustion engine according to an aspect of the present invention is an exhaust gas purification system for an internal combustion engine in which an NOx purification catalyst device is provided in an exhaust passage of the internal combustion engine. And a control device configured to perform load reduction control for reducing or stopping power generation of the alternator when the temperature of the exhaust gas flowing into the exhaust gas becomes equal to or higher than a preset temperature.

  An exhaust gas purification method for an internal combustion engine according to an aspect of the present invention for achieving the above object is the exhaust gas purification method for an internal combustion engine in which an NOx purification catalyst device is provided in the exhaust passage of the internal combustion engine. This is a method characterized in that when the temperature of the exhaust gas flowing into the catalyst device becomes equal to or higher than a preset temperature, the power generation of the alternator is reduced or stopped.

  According to the exhaust gas purification system for an internal combustion engine and the exhaust gas purification method for the internal combustion engine of the aspect of the present invention, in the exhaust gas purification system for an internal combustion engine in which the NOx purification catalyst device is provided in the exhaust passage of the internal combustion engine, the NOx purification rate Can be improved.

It is a figure which shows typically the structure of the exhaust-gas purification system of the internal combustion engine of embodiment of this invention. It is a figure which shows typically the structure of the control apparatus of the exhaust-gas purification system of the internal combustion engine of embodiment of this invention. It is a figure which shows an example of the control flow for enforcing the exhaust-gas purification method of the internal combustion engine of embodiment of this invention. It is a figure which illustrates the relationship between an engine exit temperature and a NOx purification rate in an SCR catalyst and an LNT catalyst.

  Hereinafter, an exhaust gas purification system for an internal combustion engine and an exhaust gas purification method for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, an exhaust gas purification system (hereinafter referred to as an exhaust gas purification system) 1 for an internal combustion engine according to an embodiment of the present invention includes intake air (EGR gas) in an intake manifold 12 of an engine body 11 of an engine (internal combustion engine) 10. An intake passage 13 for supplying A is provided, and a compressor 14a and an intercooler 15 for the hybrid turbo 14 are provided in this intake passage 13 in order from the upstream side. Further, an exhaust passage 22 for exhausting exhaust gas G from the exhaust manifold 21 is provided, and in this exhaust passage 22 in order from the upstream side, the exhaust turbine 14b of the hybrid turbo 14, the urea water supply device 23, and the SCR (SCR: Selective Catalytic). A reduction (selective reduction catalyst) device 24 is provided.

  The crankshaft 11a of the engine 10 is provided with an alternator (ACG: Alternating Current Generator) 31 driven by a power transmission mechanism 11b composed of a pulley and a belt, and AC power E generated by the alternator 31 is provided. Is converted into DC power E and the battery 32 is charged. The power generation amount of the alternator 31 is controlled by a control device 40 described later, and the load on the engine 10 can be reduced by controlling the power generation amount to be reduced. Furthermore, a clutch may be provided in the power transmission mechanism 11b, and the alternator 31 may be stopped when the clutch is disengaged.

  Further, the hybrid turbo 14 is provided with a motor generator 33, and the electric power E generated by the motor generator 33 is also charged in the battery 32. Further, a drive assist device (drive assist device) 34 such as a starter for driving the crankshaft 11a is provided.

  Here, in order to simplify the description, a filter device that collects particulate matter (PM) in the exhaust gas G that is not directly related to the present invention is omitted.

  The hybrid turbo 14 incorporates a motor generator 33 into a turbocharger that compresses the intake air A to increase the pressure, and drives the motor generator 33 with the driving force of the exhaust turbine 14b to generate power. This is a device that improves the transient response delay (turbo lag) by driving the compressor 14a with the driving force of the motor generator 33 to assist (assist) supercharging. In the hybrid turbo 14, the compressor 14 a and / or the motor generator 33 is driven by the exhaust turbine 14 b driven by the exhaust gas G. The intercooler 15 is a heat exchanger that cools the intake air A that has been compressed by the supercharging of the hybrid turbo 14 and has risen in temperature.

  The urea water supply device 23 in the exhaust passage 22 is an injection device for supplying urea water U supplied from a urea water tank (not shown) via the urea water supply pipe 23a to the SCR device 24, and is a control device. 40, the presence / absence of the injection of the urea water U and the injection amount U1 thereof are adjusted and controlled.

As shown in FIG. 4, the SCR device 24 is a NOx purification catalyst device having an upper limit in the temperature range Ra in which the NOx purification rate is good. The SCR device 24 is configured to carry, for example, a urea selective reduction catalyst that reacts with NOx in the exhaust gas G with generated NH ₃ to react with NOx in the exhaust gas G, using urea water as a reducing agent U, to form nitrogen and water. As the urea selective reduction catalyst, include zeolite catalyst such as iron ion exchange aluminosilicate and copper ion-exchanged aluminosilicate, adsorbs NH _3, has a function to reduce and purify NOx in NH ₃ was the suction ing. By using this SCR device 24, instead of directly using NH ₃ , urea water is injected into the exhaust gas G, and NH ₃ generated by hydrolysis from urea water reacts with NOx. Detoxify NOx.

  That is, the exhaust gas purification system 1 is configured by providing the SCR device 24 in the exhaust passage 22 of the engine 10. Moreover, the control apparatus 40 for controlling this exhaust gas purification system 1 is provided.

  The SCR device 24 is a NOx purification catalyst device having an upper limit in the temperature range Ra where the NOx purification rate is good. Here, the SCR device 24 is exemplified, but a catalyst device that supports a NOx storage reduction catalyst (LNT catalyst, LNT: Lean NOx Trap) or the like may be used. This NOx occlusion reduction type catalyst is composed of a molded body carrying a NOx occlusion material formed of a noble metal catalyst such as platinum and an alkaline earth metal such as barium on a catalyst carrier. Then, when NOx in the exhaust gas is in a lean state, the NOx storage material is temporarily stored, and the exhaust gas is made into a rich air-fuel ratio state by NOx purge control before the NOx storage amount is saturated, so that the NOx storage material NOx occluded in the catalyst is released and reduced by the three-way function of the noble metal catalyst. As shown in FIG. 4, this LNT catalyst also has an upper limit in the temperature range Rb where the NOx purification rate is good.

  The control device 40 is usually incorporated in a control device called an engine control unit (ECU) that performs overall control of the engine 10, but may be a separate control device. Further, regarding the temperature sensor in the sensor group arranged in the exhaust passage 22, the exhaust gas temperature sensor 35 for detecting the temperature (SCR inlet temperature) Tg of the exhaust gas G flowing into the SCR device 24 is the SCR device 24. It is provided on the entrance side. In addition, the sensor group includes a NOx sensor for detecting the NOx concentration in the exhaust gas G, and a lambda sensor (air-fuel ratio sensor: oxygen concentration sensor) for detecting the air-fuel ratio (λ) of the exhaust gas G. However, these are omitted for the sake of simplicity.

  Detection values of these various sensors are input to the control device 40, and the control device 40 performs various calculations based on these input data and outputs a control command to the engine 10. At the same time, a control command is output to the urea water supply device 23 to perform urea water supply control for adjusting and controlling the injection amount U1 of the reducing agent U injected from the urea water supply device 23.

  As shown in FIG. 2, in addition to the urea water supply control means 41 that performs the urea water supply control, the control device 40 includes a load reduction control means 51, a power generation auxiliary control means 52, and a driving force auxiliary control means. 53 is provided.

  The load reduction control means 51 reduces or stops power generation in the alternator 31 provided in the engine 10 when the temperature Tg of the exhaust gas G flowing into the SCR device 24 is equal to or higher than a preset temperature Tc. Then, by reducing the friction in the engine 10 and reducing the load on the engine 10, the fuel injection amount is reduced and the load reduction control for reducing the temperature Tg of the exhaust gas G flowing into the SCR device 24 is performed. Means.

  By reducing and stopping the power generation in the alternator 31, the friction for power generation in the alternator 31 in the engine 10 is reduced, and the output that can be taken out from the crankshaft 11b to the same output is maintained with a small amount of fuel. be able to.

This set temperature Tc is a relationship between the NOx purification rate and the engine outlet temperature illustrated in FIG. 4, and the NOx purification rate is low and the consumption rate of occluded NH ₃ is reduced so that there is a temperature at which the NOx purification rate becomes low in SCR. For example, about 400 ° C. That is, the temperature of the catalyst of the SCR device 24 is set to a temperature close to the upper limit of the temperature range Ra with a good NOx purification rate.

By this load reduction control, it is avoided that the temperature Tg of the exhaust gas G becomes equal to or higher than the set temperature Tc, and the catalyst temperature of the SCR device 24 is set within a temperature range Ra with a good NOx purification rate ( depending on the type of catalyst). For example, the NOx purification rate is maintained at a high level by maintaining the temperature at 300 ° C. to 400 ° C.). At the same time, the amount of fuel injected to the engine 10 is reduced to reduce the fuel consumption. In addition, by controlling the increase in the temperature Tg of the exhaust gas G, the released ammonia in the ammonia storage control in the SCR device 24 is suppressed, the consumption amount of urea water is suppressed, and the effective utilization rate of urea water is increased. In other words, the ammonia adsorbed on the SCR device 24 has the property of releasing adsorbed ammonia (ammonia slip) when it encounters a rapid temperature rise, but this can be avoided.

  The effect of this load reduction control is that the exhaust gas purification system 1 of the internal combustion engine includes a filter device that collects particulate matter (PM) in the exhaust gas G, and during regeneration of this filter, The temperature becomes higher when the temperature Tg of the exhaust gas G is high, the high-temperature oxidation performance of the catalyst of the SCR device 24 becomes strong, and the NOx purification rate by the SCR device 24 decreases.

  The power generation auxiliary control means 52 is means for performing power generation auxiliary control for generating electric power by driving the motor generator 33 of the hybrid turbo 14 by the exhaust turbine 14b when performing load reduction control. Thereby, after reducing or stopping the power generation by the alternator 31, the power is generated instead of the alternator 31 to charge the battery 32 to supplement the power generation amount, and the exhaust turbine 14b absorbs the energy of the exhaust gas G, The temperature Tg of the exhaust gas G is lowered. That is, by using the motor generator 33 of the hybrid turbo 14, the amount of power generated by the alternator 31 is supplemented, the required torque generated by the engine 10 is reduced, and the heat of the exhaust gas from the exhaust turbine 14 b is converted into electric power. Thus, an increase in the temperature Tg of the exhaust gas G is suppressed. Thereby, the catalyst temperature of the SCR device 24 can be easily maintained in the temperature range Ra with a good NOx purification rate, and the purification performance of the SCR device 24 can be enhanced.

  Further, the driving force auxiliary control means 53 is configured to use the driving auxiliary device 34 to assist the driving force of the engine 10 or to use the alternator 31 as an electric motor when performing load reduction control. In this case, for example, when an ACG starter in which ACG and a starter are integrated is used as the drive assist device 34, the alternator 31 is used as an electric motor to assist the drive force of the engine 10. That is, when the temperature Tg of the exhaust gas G is high, the shaft output from the drive assist device 34 or the electric motor is added to the crankshaft 11b. As a result, the driving force generated in the engine 10 can be reduced by the assisting driving force, so that the fuel injection amount in the engine 10 can be reduced and the temperature of the exhaust gas G can be lowered.

  An exhaust gas purification method for an internal combustion engine (hereinafter referred to as an exhaust gas purification method) according to an embodiment of the present invention is an exhaust gas purification method for an internal combustion engine in which an SCR device 24 is provided in the exhaust passage 22 of the engine 10. In this method, the power generation of the alternator 31 is reduced or stopped when the temperature Tg of the exhaust gas G flowing into the SCR device 24 becomes equal to or higher than a preset temperature Tc.

  In this exhaust gas purification method, it is preferable that when the operation for reducing the load is further performed, the motor generator 33 is driven by the exhaust turbine 14b to generate power, or the drive assist device 34 is used. When the alternator 31 is configured to be usable as an electric motor, the alternator 31 is used as an electric motor to assist the driving force of the engine 10.

  The above control can be performed by an example control flow as shown in FIG. The control flow of FIG. 3 is called from the advanced control flow when the internal combustion engine starts operation, and is executed in parallel with the operation control flow of the other exhaust gas purification system 1, and when the operation of the internal combustion engine ends. Shows that an interrupt occurs, returns to the advanced control flow, and ends with this advanced control flow.

  When the control flow of FIG. 3 is called from the upper control flow and started, the temperature (SCR inlet temperature) Tg of the exhaust gas G flowing into the SCR device 24 is input in “Input of SCR inlet temperature (Tg)” in step S11. To do. In the next “temperature check” in step S12, it is determined whether or not the SCR inlet temperature Tg is equal to or higher than a preset temperature Tc. If the SCR inlet temperature Tg is not equal to or higher than the set temperature Tc in the “temperature check” in step S12 (NO), the process returns to step S11 after a preset control time has elapsed.

  On the other hand, if the SCR inlet temperature Tg is equal to or higher than the set temperature Tc in the “temperature check” in step S12 (YES), the process goes to “load reduction control” in step S13.

  In the “load reduction control” in step S13, the power generation in the alternator 31 provided in the engine 10 is reduced or stopped. Then, by reducing the load on the engine 10, the fuel injection amount is reduced, and the temperature Tg of the exhaust gas G flowing into the SCR device 24 is lowered. Thus, the temperature Tg of the exhaust gas G is prevented from becoming higher than the set temperature Tc, the catalyst temperature of the SCR device 24 is maintained within the temperature range Ra with a good NOx purification rate, and the NOx purification rate is high. To maintain. At the same time, the amount of fuel injected to the engine 10 is reduced to reduce the fuel consumption.

  In the “load reduction control” in step S13, preferably, the motor generator 33 of the hybrid turbo 14 is driven by the exhaust turbine 14b to generate electric power. Specifically, after the power generation in the alternator 31 is reduced or stopped, and before the power generation in the alternator 31 before the power generation in the alternator 31 starts, the motor generator 33 of the hybrid turbo 14 is exhausted from the exhaust turbine. It drives with 14b and generates electric power. That is, after the control to reduce or stop the power generation in the alternator 31 and reduce the load on the engine 10, in other words, the power generation assist control and the driving force assist control are performed while the alternator 31 is off. With respect to the electric power consumed while the charging capacity is saturated, the electric power generated by the electric power generation assist control can be charged into the battery 32, and the waste of the energy of the exhaust gas G can be reduced.

  Thereby, in response to reducing or stopping the power generation by the alternator 31, power is generated instead of the alternator 31 to supplement the amount of power generation, and the exhaust turbine 14b absorbs the energy of the exhaust gas G, and the exhaust gas The temperature Tg of G is lowered. This makes it easier to maintain the catalyst temperature of the SCR device 24 within the temperature range Ra with a good NOx purification rate.

  Furthermore, preferably, when the drive assisting device 34 is used to assist the driving force of the engine 10 or the alternator 31 can be used as an electric motor, for example, an ACG and a starter are used as the drive assisting device 34. When the integrated ACG starter is used, the alternator 31 is used as an electric motor to assist the driving force of the engine 10. As a result, the driving force generated in the engine 10 can be reduced by the assisting driving force, so that the fuel injection amount in the engine 10 can be reduced and the temperature of the exhaust gas G can be lowered.

  When the power generation assist control and the driving force assist control are performed, if the exhaust gas temperature is equal to or lower than a predetermined temperature set in advance, “(power to be generated)> (power to assist driving)”. Driving assist control is performed, and when the temperature is equal to or higher than the predetermined temperature, driving assist control is performed so that “(power to be generated) <(power to assist driving)”. As a result, the NOx purification rate can be improved while ensuring the charge capacity of the battery 32.

  After performing the “load reduction control” in step S13 for a preset time, the temperature of the exhaust gas G (SCR inlet) flowing into the SCR device 24 in “input of SCR inlet temperature (Tg)” in the next step S14. Enter the temperature (Tg). In the next “temperature check” in step S15, it is determined whether or not the SCR inlet temperature Tg is equal to or lower than a preset end temperature Tt. If the SCR inlet temperature Tg is not equal to or lower than the end temperature Tt in the “temperature check” in step S15 (NO), the process returns to step S13.

  On the other hand, if the SCR inlet temperature Tg is equal to or lower than the end temperature Tt in the “temperature check” in step S15 (YES), the process proceeds to “end load reduction control” in step S16. And it returns to step S11 and repeats step S11-step S16.

  If the operation of the internal combustion engine is terminated in the middle of the control flow of FIG. 3, an interrupt is performed to perform necessary control termination processing (not shown), and then return to the upper control flow. It ends with the control flow.

  As described above, according to the exhaust gas purification system 1 for an internal combustion engine and the exhaust gas purification method for the internal combustion engine of this embodiment, the exhaust gas purification of the internal combustion engine in which the SCR device 24 is provided in the exhaust passage 22 of the engine 10. In the system, the NOx purification rate can be improved.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification system of internal combustion engine 10 Engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 11 Engine main body 12 Intake manifold 13 Intake passage 14 Hybrid turbo 14a Compressor 14b Exhaust turbine 15 Intercooler 21 Exhaust manifold 22 Exhaust passage 23 Urea water supply device 24 SCR device (NOx purification catalyst device)
31 Alternator 32 Battery 33 Motor Generator 34 Drive Auxiliary Device 40 Control Device 41 Urea Water Supply Control Unit 51 Load Reduction Control Unit 52 Power Generation Auxiliary Control Unit 53 Driving Force Auxiliary Control Unit A Intake G Exhaust Gas U Urea Water (Reducing Agent)

Claims (5)

In an exhaust gas purification system for an internal combustion engine in which an NOx purification catalyst device is provided in the exhaust passage of the internal combustion engine,
A control device configured to perform load reduction control to reduce or stop the power generation of the alternator when the temperature of the exhaust gas flowing into the NOx purification catalyst device becomes equal to or higher than a preset temperature. An exhaust gas purification system for an internal combustion engine. The exhaust passage includes a hybrid turbo having an exhaust turbine, a compressor, and a motor generator,
The control device is configured to perform power generation auxiliary control for generating power by driving the motor generator with the exhaust turbine after reducing or stopping power generation of the alternator by the load reduction control. The exhaust gas purification system for an internal combustion engine according to claim 1.   The control device is configured to perform driving force assist control for assisting the driving force of the internal combustion engine using a drive assist device after reducing or stopping power generation of the alternator by the load reduction control. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2. While configuring the alternator to be usable as an electric motor,
The control device is configured to perform driving force assist control for assisting the driving force of the internal combustion engine using the alternator as an electric motor after reducing or stopping the power generation of the alternator by the load reduction control. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2. In an exhaust gas purification method for an internal combustion engine in which an NOx purification catalyst device is provided in an exhaust passage of the internal combustion engine,
An exhaust gas purification method for an internal combustion engine, comprising: reducing or stopping power generation of an alternator when a temperature of exhaust gas flowing into the NOx purification catalyst device is equal to or higher than a preset temperature.

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