JP2012233414A - Method and device for controlling operation of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for controlling operation of an internal combustion engine using both an SCR system and an EGR system in which overheat of the internal combustion engine can be prevented while keeping an NOamount in exhaust gas at or below a reference value.SOLUTION: In the device, there included are cooling water circulation paths 42a, 42b circulating cooling water between a radiator 40 and an engine block 12, and a branch cooling water circulation path 48 branched off from the cooling water circulation path 42b and connected to an EGR cooler 46 provided in an EGR path 44. When temperature t of the cooling water is not more than a threshold value T0, the operation is transitioned to a normal operation control mode by a controller 60. When the temperature t of the cooling water exceeds the threshold value T0 and an SCR catalyst 36 is at an active temperature, an EGR amount is reduced and the operation is transitioned to a first operation control mode to increase an additive amount of urea water. When the temperature t of the cooling water exceeds the threshold value T0 and the SCR catalyst 36 is not at the active temperature, the operation is transitioned to a second operation control mode to reduce engine power.

Description

The present invention relates to an operation control method and operation control for an internal combustion engine capable of preventing overheating while maintaining the amount of NO _X in exhaust gas below a reference value in an internal combustion engine having a NO _X purification device and an exhaust gas recirculation path. Relates to the device.

  In large vehicles equipped with diesel engines such as trucks and buses, SCR (Selective Catalytic Reduction) catalysts using urea as a reducing agent are used as exhaust gas purifiers to purify nitrogen oxides (NOx) in exhaust gases. A selective catalytic reduction (SCR) system has been put into practical use. An exhaust gas purification apparatus using an SCR catalyst is provided with an SCR catalyst having the property of selectively reacting nitrogen oxide (NOx) in exhaust gas with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe for exhaust gas discharge. , NOx in the exhaust gas is selectively cleaned by the SCR catalyst.

  In this purification method, urea water is injected into the exhaust passage upstream of the SCR catalyst, and urea in the urea water is hydrolyzed to generate ammonia as a reducing agent. The generated ammonia is supplied to the SCR catalyst, the NOx adsorbed on the SCR catalyst is reduced, decomposed into nitrogen and water, and discharged to the outside, so that the NOx emission concentration is reduced below the reference value.

Another means of reducing the amount of NO _X in the exhaust gas, is introduced a portion of the exhaust after combustion air supply path, there is an exhaust gas recirculation (EGR) system to supply again. This reduces the oxygen concentration of the air supply, by lowering the combustion temperature, thereby reducing the NO _X generation amount. In order to comply with exhaust gas regulations that will be further strengthened in the future and strict exhaust gas regulations already in effect in other countries, it is necessary to simultaneously implement the SCR method and the EGR method.
Patent Documents 1 to 3 disclose an internal combustion engine that uses both the SCR system and the EGR system at the same time.

JP-A-9-122447 JP 2003-314254 A JP 2009-270549 A

  In the EGR system provided with a cooler that cools the exhaust gas flowing through the recirculation path with cooling water, the heat retained in the cooling water is radiated by the radiator. If the vehicle continues to be heavily loaded and overheated in an intense heat that exceeds expectations, it becomes difficult to operate the vehicle at the same speed, and it is necessary to limit the output of the internal combustion engine. Especially in the case of large vehicles, if the speed is reduced, there is a risk of obstructing the flow of surrounding traffic, and it is not easy to secure a stopping place for large vehicles even when stopping temporarily to eliminate overheating. .

In the cooling system in which the cooling water circulates between the radiator and the cooler provided in the cylinder block and the exhaust gas recirculation path, the cooling water temperature is reduced by reducing the amount of heat taken from the exhaust gas flowing through the recirculation path. The rise can be prevented and overheating of the internal combustion engine can be prevented. However, when performing this operation, there is a problem that _the amount of NO _X held in the low level by the EGR system is increased. Patent Documents 1 to 3 do not disclose a solution for solving such a problem.

The present invention is, in the conventional view of the art problems, SCR system and EGR system combination with an internal combustion engine, while retaining the amount of NO _X in the exhaust gas below the reference value, the enabling preventing overheating of the internal combustion engine Objective.

  In order to achieve such an object, an operation control method for an internal combustion engine according to the present invention circulates cooling water between a radiator and an engine block and a cooler provided in an exhaust gas recirculation path. A cooling process for cooling, a detection process for detecting the temperature of cooling water flowing into the engine block, and a recirculation exhaust amount when the temperature of the cooling water is higher than a threshold value and the exhaust temperature is the activation temperature of the denitration catalyst When the temperature of the cooling water is higher than the threshold value and the exhaust gas temperature is not the activation temperature of the denitration catalyst. And a second operation step for reducing the output of the engine.

In the method of the present invention, normal operation is performed when the cooling water temperature does not exceed the threshold value. That is, while maintaining below the reference value of the exhaust gas amount of NO _X, performs operation the consumption of fuel and the reducing agent is minimized. (Fuel + urea water) Reduce operating costs by minimizing consumption. When the cooling water temperature exceeds the threshold, if the exhaust temperature is the activation temperature of the denitration catalyst, the exhaust gas recirculation amount is suppressed to be equal to or less than the overheat limit value of the internal combustion engine, thereby preventing overheating of the internal combustion engine and reducing agent addition amount is increased, the increase of the NO _X purification action of NO x removal catalyst so as to compensate for the decrease in the NOx purification capability due to suppressed the exhaust gas recirculation amount, holds the exhaust amount of NO _X to less than the reference value .

  If the exhaust water temperature does not reach the activation temperature of the denitration catalyst when the cooling water temperature exceeds the threshold value, the output of the internal combustion engine is reduced and overheating is prevented.

The outline of the method of the present invention will be described with reference to FIG. 4, during normal operation the cooling water temperature t is the threshold value T ₀ or less, the recirculation exhaust gas amount (EGR amount) is set to reduce possible A quantity exhaust amount of NO _X. The amount of EGR uniquely corresponds to the amount of heat that the cooling water takes away from the recirculated exhaust. That is, if the EGR amount increases, the amount of heat taken away also increases, and if the amount of EGR decreases, the amount of heat removed also decreases. In response to the EGR quantity A, NO _X amount in the exhaust gas so that more than the reference value, to adjust the urea water addition amount of the exhaust gas purification apparatus using the SCR catalyst C amount.

When the cooling water temperature t exceeds the threshold T ₀ , the EGR amount is reduced to the B amount, and the amount of heat that the cooling water takes away from the recirculated exhaust gas is reduced to prevent overheating of the internal combustion engine. Reducing the EGR amount to the amount of B, since the amount of NO _X in the exhaust gas is increased, increasing the urea water addition amount to the amount of D, and to suppress the exhaust amount of NO _X to less than the reference value.
By performing such an operation, while maintaining the exhaust amount of NO _X than the reference value, to prevent overheating of the internal combustion engine.

  The internal combustion engine operation control apparatus of the present invention that can be directly used for carrying out the method of the present invention includes a cooling water path for circulating cooling water between a radiator and an engine block and a cooler provided in an exhaust gas recirculation path. A temperature sensor for detecting the temperature of the cooling water flowing into the engine block; and when the temperature of the cooling water is higher than a threshold value and the exhaust temperature is the activation temperature of the denitration catalyst, the recirculated exhaust amount is overheated in the internal combustion engine. A controller that reduces the output of the internal combustion engine when the temperature of the cooling water is higher than a threshold value and the exhaust gas temperature is not the activation temperature of the denitration catalyst, while reducing below the limit value and increasing the reducing agent addition amount; It has.

In the device of the present invention, the internal combustion engine is detected by detecting the cooling water temperature on the inlet side of the internal combustion engine and reducing the exhaust gas recirculation amount if the exhaust water temperature is the activation temperature of the denitration catalyst when the cooling water temperature exceeds a threshold value. Prevent overheating. At the same time, the NO _X purification action of the denitration catalyst, the NO _X amount exhausted from the exhaust passage to less than the reference value.

  Further, when the cooling water temperature is higher than the threshold and the exhaust temperature is not the activation temperature of the denitration catalyst, the output of the internal combustion engine is reduced. In this way, by suppressing the recirculation amount of the exhaust, the amount of heat that the cooling water takes away from the recirculation exhaust is reduced, and overheating of the internal combustion engine is prevented. Moreover, the overheating of the internal combustion engine is prevented by reducing the output of the internal combustion engine.

In the present invention apparatus, the controller, when the coolant temperature is equal to or less than the threshold, while the exhaust amount of NO _X to less than the reference value, a normal operation control means for minimizing the consumption of fuel and reducing agent, cooling water When the temperature of the engine is higher than the threshold value and the exhaust temperature is the activation temperature of the denitration catalyst, the first operation control for reducing the recirculated exhaust amount to be equal to or less than the overheat limit value of the internal combustion engine and increasing the reducing agent addition amount And a second operation control means for reducing the output of the engine when the temperature of the cooling water is higher than the threshold and the exhaust temperature is not the activation temperature of the denitration catalyst.

During normal operation when the cooling water temperature does not exceed the threshold value, operation based on normal operation control means minimizes fuel and reducing agent consumption, thereby minimizing operating costs. . When the coolant temperature exceeds the threshold value, the internal combustion engine is operated by the first operation control means or the second operation control means. Thus, the exhaust amount of NO _X while maintaining below the reference value, it is possible to prevent overheating of the internal combustion engine.

According to the method invention, the NO _X purification step of adding a reducing agent to the exhaust gas of the internal combustion engine, and purifying NO _X in the exhaust gas with the reducing agent and the denitration catalyst, and the exhaust gas for recirculating a part of the exhaust gas to the air supply passage In the internal combustion engine operation control method for performing the recirculation step, the cooling step of circulating the cooling water between the radiator and the engine block and the cooler provided in the exhaust gas recirculation path to cool the engine block and the recirculated exhaust gas. And a detecting step for detecting the temperature of the cooling water flowing into the engine block, and when the temperature of the cooling water is higher than the threshold and the exhaust temperature is the activation temperature of the denitration catalyst, A first operation step in which the temperature is reduced to an overheat limit value and the reducing agent addition amount is increased, and when the temperature of the cooling water is higher than the threshold value and the exhaust temperature is not the activation temperature of the denitration catalyst, A second operation step of reducing the force, since from the exhaust amount of NO _X while keeping below the reference value, it is possible to prevent overheating of the internal combustion engine. Therefore, in any environment, the output of the internal combustion engine can be secured and the operation of the vehicle can be continued quickly.

According to the apparatus invention, the NO _X purification device consisting of a reducing agent addition device for adding a reducing agent to the upstream side exhaust passage of the denitration catalyst and the denitration catalyst in an exhaust passage of an internal combustion engine, a part of the exhaust air supply passage In an internal combustion engine operation control device comprising an exhaust gas recirculation path for recirculation, a cooling water path for circulating cooling water between a radiator, an engine block and a cooler provided in the exhaust gas recirculation path, and an engine block A temperature sensor that detects the temperature of the cooling water flowing into the engine, and when the cooling water temperature is higher than the threshold value and the exhaust temperature is the activation temperature of the denitration catalyst, the recirculation exhaust amount is less than the overheat limit value of the internal combustion engine A controller for reducing the output of the internal combustion engine when the temperature of the cooling water is higher than a threshold and the exhaust temperature is not the activation temperature of the denitration catalyst, Therefore, the same effects as those of the above-described method invention can be obtained.

1 is a system diagram of an internal combustion engine according to an embodiment of the present invention. It is a flowchart which shows the operation control of the said embodiment. It is a diagram which shows the operation control map of the said embodiment. It is explanatory drawing which shows the outline of this invention.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

  An embodiment of the method and apparatus of the present invention will be described with reference to FIGS. First, the configuration of the diesel engine 10 of the present embodiment will be described with reference to FIG. In FIG. 1, an air supply manifold 14 and an exhaust manifold 16 are connected to an engine block 12 in which a plurality of cylinders 26 are built. An air supply pipe 18 is connected to the air supply manifold 14, and an exhaust pipe 20 is connected to the exhaust manifold 16.

  A supercharger 22 is provided across the air supply pipe 18 and the exhaust pipe 20. The supercharger 22 includes a compressor 22a provided in the air supply pipe 18 and an exhaust turbine 22b provided in the exhaust pipe 20, and the compressor 22a and the exhaust turbine 22b are integrally coupled by a shaft. By rotating the exhaust turbine 22b by the exhaust e, the compressor 22a rotates and feeds the air supply a into the air supply pipe 18.

  An intercooler 24 is provided in the air supply pipe 18 on the downstream side of the compressor 22a, and the air supply pipe 18 is cooled by the intercooler 24 to have a high density in order to improve the operation efficiency. The supply air a cooled by the intercooler 24 is supplied to the plurality of cylinders 26 through the supply manifold 14. In the cylinder 26, fuel (for example, light oil) and the supply air a are mixed, and these are compressed and burned. The exhaust e is exhausted to the exhaust pipe 20 through the exhaust manifold 16.

An exhaust gas purification device 32 in which a front-stage oxidation catalyst 28 and a DPF filter 30 are combined is provided in the exhaust gas passage 20 on the downstream side of the exhaust turbine 22b. The exhaust gas purifying apparatus 32 captures particulate matter in exhaust by DPF filter 30, the exhaust NO _X in the high state of NO ₂ in the upstream side oxidation catalyst 28, particulate was captured by strong oxidizing action of NO ₂ It burns substances.

  A urea water injection nozzle 34 is provided on the downstream side of the exhaust gas purification device 32, and an SCR catalyst 36 is provided on the downstream side of the urea water injection nozzle 34. The urea water n is injected from the urea water injection nozzle 34 by a pump (not shown) provided in the urea water supply pipe 35. The urea in the urea water is hydrolyzed by the heat of the exhaust e to produce ammonia as a reducing agent. The produced ammonia is supplied to the SCR catalyst 36, NOx adsorbed on the SCR catalyst is reduced, decomposed into nitrogen and water, and discharged to the outside. The post-stage oxidation catalyst 38 provided on the downstream side of the SCR catalyst 36 removes remaining ammonia, carbon monoxide, hydrocarbons, and the like.

  Cooling water circulation paths 42 a and 42 b that connect between the radiator 40 and the engine block 12 are provided. Further, an exhaust gas recirculation path (EGR path) 44 branched from the exhaust manifold 16 and connected to the air supply manifold 14 is provided. An EGR cooler 46 is interposed in the EGR path 44. The EGR cooler 46 is connected to a branch cooling water circulation path 48 that branches from the cooling water circulation path 42b, is connected to the EGR cooler 46, and joins the cooling water circulation path 42b again. The exhaust gas e (EGR gas) flowing through the EGR path 44 is cooled by exchanging heat with cooling water in the EGR cooler 46. A flow rate adjustment valve 50 is provided in the EGR path 44.

  On the inlet side of the engine block 12 (a position suitable for grasping the overheat state of the diesel engine 10), a temperature sensor 52 is provided in the cooling water circulation path 42a to detect the engine block inlet side cooling water temperature t. Further, a temperature sensor 54 is provided in the inlet side exhaust pipe 20 of the exhaust gas purification device 32, and a temperature sensor 56 is provided in the inlet side exhaust pipe 20 of the SCR catalyst 36. Detection signals from these temperature sensors are sent to an ECU (Engine Control Unit) 60 that controls the operation of the diesel engine 10.

  The ECU 60 controls the opening degree of the flow rate adjustment valve 50 based on these detected values and adjusts the amount of cooling water flowing through the EGR cooler 46. Further, the ECU 60 controls the opening degree of the flow rate adjustment valve 58 provided in the urea water supply pipe 35 to adjust the urea water addition amount. The ECU 60 includes a storage unit 62, normal operation control means 64, first operation control means 66, and second operation control means 68. The storage unit 62 incorporates a normal operation control map, a first operation control map, and a second operation control map. The normal operation control means 64 executes the normal operation control mode based on the normal operation control map, the first operation control means 66 executes the first operation control mode based on the first operation control map, and the second operation control. The means 68 executes the second operation control mode based on the second operation control map.

In such a configuration, operation control of the diesel engine 10 will be described with reference to FIG. 2, to start the operation of the diesel engine 10 (S10), when the cooling water temperature t does not exceed the threshold value _{T 0} (S12), the normal operation control unit 64 shifts to the normal operation control mode (S14). FIG. 3 shows an operation control map. Curve E in FIG. 3 is a graph showing the relationship between the exhaust amount of NO _X (the diesel + urea water) consumption. The running cost is proportional to (light oil + urea water) consumption. The NO _X purification amount and the urea water consumption amount corresponding to the NO _X purification amount are uniquely determined by the chemical reaction equation when the NO _X and urea water chemically react.

Curve F in Figure 3, showing the relationship between the heat radiation amount in the exhaust amount of NO _X and the radiator 40. The radiator heat release amount is equal to the heat amount equivalent to the sum of the heat absorption amount of the cooling water in the engine block 12 and the heat absorption amount of the cooling water in the EGR cooler 46. To reduce the engine outlet exhaust gas amount of NO _X, increasing the recirculated exhaust amount (EGR gas amount), heat absorption amount of the cooling water in the EGR cooler 46 is increased, therefore, radiator heat radiation amount increases.

To the NO _X amount exhausted from the exhaust pipe 20 to the outside than the reference value, (diesel + urea water) Total cost when the adjusting two parameters, increasing or decreasing the increase or decrease and the urea water adding amount of the EGR gas amount , as shown by the curve E, becomes minimum when a certain engine outlet _the amount of NO _X a0. As described above, the urea water consumption is uniquely determined by the chemical reaction formula when the NO _X and urea water chemically react, and in addition to that, from the relationship between the engine outlet NO _X amount and fuel consumption, The amount of outlet NOX is determined by the total cost of (light oil + urea water). During normal operation, the total cost (light oil + urea water) is set to be minimum. That is, the exhaust gas in _the amount of NO _X into the exhaust gas purification device 32 at this time the exhaust pipe 20 (the engine outlet NOx amount) and a0.

In the first operation control mode, for reducing the EGR gas amount, the engine outlet _the amount of NO _X increases from a0 to a1. On the other hand, carried away heat from the EGR cooler 46 is reduced from _{R 0} to _{R 1.} Thereby, overheating of the diesel engine 10 is avoided. At this time, the engine outlet _the amount of NO _X increases with reducing the amount of EGR gas to increasing the urea water addition amount so as to purify the SCR catalyst 36. First place when the engine outlet _the amount of NO _X is a0, but (light oil + aqueous urea) total cost is the smallest, shifts to the first operation control mode, if reducing the EGR gas amount, but diesel consumption is reduced, Since the urea water consumption increases, the total cost (light oil + urea water) deteriorates from b0 to b1.

2, when the cooling water temperature t exceeds the threshold value _{T 0} (S12), if the exhaust e is an active temperature of SCR catalyst 36 (S16), by the first operation control unit 66, shifts to the first operation control mode (S18). In the figure, T ₁ is a lower limit value of the activation temperature of the SCR catalyst 36, and T ₂ is an upper limit value of the activation temperature of the SCR catalyst 36. The first operation control map for executing the first operation control mode reduces the EGR amount and increases the urea water addition amount in order to prevent overheating of the diesel engine 10. By reducing the amount of EGR gas, the amount of heat taken away from the cooling water is reduced, thereby preventing overheating of the diesel engine 10. Compensate for the amount of decrease in the EGR gas amount by increasing the urea water addition amount, can be performed operation held below the reference value in the outlet exhaust gas amount of NO _X in the exhaust pipe 20 when.

2, when the cooling water temperature t exceeds the threshold value _{T 0} (S12), if the exhaust e is not active temperature of SCR catalyst 36 (S16), it shifts to the second operation control mode (S20). In the second operation control mode, the output of the diesel engine 10 is reduced. As a result, it is possible to reduce the output of the diesel engine 10 and perform an operation that prevents the diesel engine 10 from overheating.

According to this embodiment, the normal operation control mode, the first operation control mode, or the second operation control mode is shifted according to the cooling water temperature t and the temperature of the exhaust e entering the SCR catalyst 36, and the EGR amount, urea water since so as to adjust the amount or the engine output, it is possible to perform the operation to prevent overheating of the diesel engine 10, and was held exit _the amount of NO _X in the exhaust pipe 20 below the reference value. Therefore, the engine output of large vehicles such as buses and trucks equipped with the diesel engine 10 can be secured and the operation can be continued without any trouble.

According to the present invention, it is possible to perform the operation to prevent overheating of the internal combustion engine, and holding the exhaust amount of NO _X to less than the reference value. Therefore, in any environment, the output of the internal combustion engine can be secured and the operation of the vehicle can be continued.

DESCRIPTION OF SYMBOLS 10 Diesel engine 12 Engine block 14 Supply manifold 16 Exhaust manifold 18 Supply pipe 20 Exhaust pipe 22 Supercharger 22a Compressor 22b Exhaust turbine 24 Intercooler 26 Cylinder 28 Pre-stage oxidation catalyst 30 DPF filter 32 Exhaust gas purification device 34 Urea water injection nozzle 36 SCR catalyst (denitration catalyst)
38 Rear-stage oxidation catalyst 40 Radiators 42a, 42b Cooling water circulation path 44 EGR path 46 EGR cooler (cooler)
48 Branch cooling water circulation path 50, 58 Flow rate adjustment valve 52, 54, 56 Temperature sensor 60 ECU
62 storage unit 64 normal operation control means 66 first operation control means 68 second operation control means T ₁ lower limit of activation temperature T ₂ upper limit of activation temperature a supply air e exhaust n urea water

Claims (3)

A NO _X purification step of adding a reducing agent to the exhaust gas of the internal combustion engine and purifying NO _X in the exhaust gas with the reducing agent and the denitration catalyst, and an exhaust gas recirculation step of returning a part of the exhaust gas to the air supply path In an operation control method for an internal combustion engine,
A cooling step of circulating cooling water between the radiator and the cooler provided in the engine block and the exhaust gas recirculation path to cool the engine block and the recirculated exhaust gas;
A detection step for detecting the temperature of the cooling water flowing into the engine block;
When the temperature of the cooling water is higher than the threshold value and the exhaust temperature is the activation temperature of the denitration catalyst, the recirculation exhaust amount is reduced below the overheat limit value of the internal combustion engine, and the reducing agent addition amount is increased. 1 operation process,
An internal combustion engine operation control method comprising: a second operation step of reducing the output of the internal combustion engine when the temperature of the cooling water is higher than a threshold value and the exhaust gas temperature is not the activation temperature of the denitration catalyst. . And NO _X purifying device comprising the reducing agent addition device for adding a reducing agent to the upstream side exhaust passage of the denitration catalyst and the denitration catalyst in an exhaust passage of an internal combustion engine, exhaust gas recirculation for recirculating part of exhaust into the air supply path An internal combustion engine operation control device comprising:
A cooling water path for circulating cooling water between the radiator and the cooler provided in the engine block and the exhaust gas recirculation path;
A temperature sensor for detecting the temperature of the cooling water flowing into the engine block;
When the temperature of the cooling water is higher than the threshold value and the exhaust temperature is the activation temperature of the denitration catalyst, the recirculation exhaust amount is reduced below the overheat limit value of the internal combustion engine, and the reducing agent addition amount is increased. And a controller that reduces the output of the internal combustion engine when the temperature of the cooling water is higher than a threshold value and the exhaust temperature is not the activation temperature of the denitration catalyst. Said controller, when the coolant temperature is equal to or less than the threshold, while the exhaust amount of NO _X to less than the reference value, a normal operation control means for minimizing the consumption of fuel and reducing agent, the temperature of the cooling water is the threshold A first operation control means for reducing the recirculation exhaust amount to be equal to or lower than the overheat limit value of the internal combustion engine and increasing the reducing agent addition amount when the exhaust gas temperature is the activation temperature of the denitration catalyst, and the cooling water; And a second operation control means for reducing the output of the internal combustion engine when the temperature of the engine is higher than a threshold value and the exhaust temperature is not the activation temperature of the denitration catalyst. An operation control device for an internal combustion engine.

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