EP3036413A1

EP3036413A1 - Additive supply device for internal combustion engine

Info

Publication number: EP3036413A1
Application number: EP14780556.8A
Authority: EP
Inventors: Hirohiko Ota
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2013-08-20
Filing date: 2014-08-14
Publication date: 2016-06-29
Also published as: AU2014330864B2; AU2014330864A1; WO2015049557A1; JP2015040480A

Abstract

This device is equipped with a urea addition valve that injects urea water to an exhaust passage of an engine, an NOx purification catalyst that purifies NOx through the addition of an additive from the urea addition valve, and a control unit that executes injection of the additive from the urea addition valve when a temperature of exhaust gas in the exhaust passage in a region upstream of the urea addition valve in an exhaust gas flow direction is equal to or higher than a predetermined temperature. The urea addition valve has a heat radiation fm that radiates heat through the exchange of heat with outside air. The control unit reduces an injection amount of urea water (a target cooling injection amount TQc) as an outside air temperature THout is low.

Description

ADDITIVE SUPPLY DEVICE FOR INTERNAL COMBUSTION ENGINE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to an additive supply device for an internal combustion engine.

2. Description of Related Art

[0002] There is known a device that supplies an additive to an exhaust passage in order to purify exhaust gas in an internal combustion engine. For example, a device described in Japanese Patent Application Publication No. 2009-103013 (JP-2009-103013 A) supplies urea water into an exhaust passage in order to reduce and purify nitrogen oxides (NOx) in exhaust gas by a catalyst.

[0003] Besides, the device of Japanese Patent Application Publication No. 2009-103013 (JP-2009-103013 A) supplies an additive to the interior of an addition valve in order to protect the addition valve from a heat damage resulting from high-temperature exhaust gas. In this device, since the additive vaporizes inside the addition valve or inside a supply passage through which the additive is supplied to the addition valve, the addition valve is cooled through the use of heat of the vaporization.

SUMMARY OF THE INVENTION

[0004] In the device of Japanese Patent Application Publication No. 2009-103013 (JP-2009-103013 A), it is necessary to inject the additive from the addition valve in cooling the addition valve. In thus injecting the additive in order to cool the addition valve, there is not only a possibility of the addition amount failing to become an amount suited for the purification of NOx in the catalyst, but there is also a possibility of the additive being injected in a situation unsuited for the purification of NOx. In this case, the injection of the additive for cooling the addition valve contributes toward incurring an increase in the consumption of the additive.

[0005] The invention provides an additive supply device for an internal combustion engine that makes it possible to reduce the consumption of an additive.

[0006] In an additive supply device for an internal combustion engine according to one aspect of the invention, the internal combustion engine includes an addition valve that injects an additive to an exhaust passage of the internal combustion engine, and an NOx purification catalyst that is provided in the exhaust passage downstream of the addition valve in an exhaust gas flow direction, and purifies NOx through addition of the additive from the addition valve. The addition valve has a heat radiation fin that radiates heat through exchange of heat with outside air. The additive supply device includes a control unit configured to execute injection of the additive from the addition valve when a temperature of exhaust gas in the exhaust passage in a region upstream of the addition valve in the exhaust gas flow direction is equal to or higher than a predetermined temperature. The control unit is configured to reduce an injection amount of the additive as a temperature of outside air decreases.

[0007] According to the aforementioned device, although the temperature of the addition valve becomes high due to the reception of heat from exhaust gas in the internal combustion engine, the addition valve is cooled through the exchange of heat with outside air in the heat radiation fin. Therefore, the temperature of the addition valve can be restrained from rising correspondingly. Moreover, in the aforementioned device, the injection amount of the additive at the time when the temperature of exhaust gas in the exhaust passage in the region upstream of the addition valve in the exhaust gas flow direction is equal to or higher than the predetermined temperature can be reduced as the temperature of outside air decreases, namely, as the temperature of the addition valve falls due to a large amount of heat exchange in the heat radiation fin. Thus, the injection amount of the additive for cooling the addition valve can be reduced. Therefore, the consumption of the additive can be reduced while restraining the temperature of the addition valve from rising.

[0008] In the aforementioned device, the internal combustion engine may be mounted on a vehicle, and the control unit may reduce the injection amount of the additive as a traveling speed of the vehicle increases. In the aforementioned device, as the traveling speed of the vehicle increases, the air volume of traveling wind increases, so the amount of heat exchange in the heat radiation fin increases, and the temperature of the addition valve falls. According to the aforementioned device, the injection amount of the additive for cooling the addition valve can be reduced in accordance with such a relationship between the traveling speed of the vehicle and the amount of heat exchange in the heat radiation fin. Therefore, the consumption of the additive can be favorably reduced.

[0009] In the aforementioned device, the control unit may reduce the injection amount of the additive as the temperature of exhaust gas in the internal combustion engine decreases. As the temperature of exhaust gas in the internal combustion engine decreases, the amount of heat received by the addition valve from exhaust gas decreases, so the temperature of the addition valve becomes likely to be low. According to the aforementioned device, the injection amount of the additive for cooling the addition valve can be reduced as the temperature of exhaust gas decreases and as the temperature of the addition valve becomes likely to be low. Therefore, the consumption of the additive can be favorably reduced.

[0010] In the aforementioned device, the control unit may reduce the injection amount of the additive as a flow rate of exhaust gas in the exhaust passage decreases. As the flow rate of exhaust gas in the internal combustion engine decreases, the amount of heat received by the addition valve from exhaust gas decreases, so the temperature of the addition valve becomes likely to be low. According to the aforementioned device, the injection amount of the additive for cooling the addition valve can be reduced as the flow rate of exhaust gas decreases and as the temperature of the addition valve becomes likely to be low. Therefore, the consumption of the additive can be favorably reduced.

[0011] In the aforementioned device, the control unit may calculate a first additive injection amount for cooling the addition valve, and a second additive injection amount for purifying NOx in the NOx purification catalyst, and the control unit may execute injection of the additive from the addition valve based on the first additive injection amount when the first additive injection amount is larger than the second additive injection amount, and may execute injection of the additive from the addition valve based on the second additive injection amount when the first additive injection amount is equal to or smaller than the second additive injection amount.

[0012] In the aforementioned device, the injection amount needed to cool the addition valve (the first additive injection amount) and the injection amount needed to purify NOx in the NOx purification catalyst (the second additive injection amount) are separately calculated, and the injection of the additive from the addition valve is executed based on the larger of the injection amounts. Thus, if the first additive injection amount is larger than the second additive injection amount, it is assumed that the temperature of the addition valve cannot be held low simply by injecting the amount of the additive needed to purify NOx, so the amount of the additive needed to cool the addition valve, which is larger than this amount of the additive needed to purify NOx, is injected. Therefore, at this time, the amount of the additive that is sufficient to purify NOx and suited for the cooling of the addition valve can be injected. Moreover, if the first additive injection amount is equal to or smaller than the second additive injection amount, it is assumed that the temperature of the addition valve can be held low by injecting the amount of the additive needed to purify NOx, so the amount of the additive needed to purify NOx is injected. At this time, the amount of the additive that is suited for the purification of NOx and sufficient to cool the addition valve can be injected from the addition valve. In consequence, according to the aforementioned device, the consumption of the additive can be reduced while satisfying both the function of cooling the addition valve and the function of purifying NOx.

[0013] In the aforementioned device, the control unit may set the second additive injection amount to a positive value when a condition for carrying out injection of the additive for purifying the NOx is fulfilled, and may set the second additive injection amount to zero when the condition for carrying out injection is not fulfilled.

[0014] In the aforementioned device, while the injection of the additive from the addition valve is executed through the use of the second additive injection amount when the condition for executing injection is fulfilled, the injection of the additive from the addition valve is executed based on the first additive injection amount without the use of the second additive injection amount when the condition for executing injection is not fulfilled. Thus, according to the aforementioned device, the injection of the additive from the addition valve can be executed depending on whether or not it is necessary to inject the additive to purify NOx.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Features, advantages, and technical and industrial significance of an exemplary embodiment of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic view showing an overall configuration of one embodiment of an additive supply device for an internal combustion engine;

FIG. 2 is a flowchart showing a procedure of performing an injection amount calculation process;

FIG. 3 is a conceptual view showing a relationship between an outside air temperature and a correction value Al ;

FIG. 4 is a conceptual view showing a relationship between a vehicle speed and a correction value B 1 ;

FIG. 5 is a conceptual view showing a relationship between a second exhaust gas temperature and a correction value CI ;

FIG. 6 is a conceptual view showing a relationship between an exhaust gas flow rate and a correction value D 1 ;

FIG. 7 is a conceptual view showing a relationship among an engine load, an engine rotational speed and a base cooling injection amount; and FIG. 8 is a conceptual view showing a relationship among the engine load, the engine rotational speed and a target purification injection amount.

DETAILED DESCRIPTION OF EMBODIMENT

, [0016] One embodiment of the invention as a concretization of an additive supply device for an internal combustion engine will be described hereinafter. FIG. 1 is a schematic view showing an overall configuration of a diesel engine (hereinafter referred to simply as "an engine") to which the additive supply device according to this embodiment of the invention is applied, and a peripheral configuration thereof.

[0017] An engine 1 is provided with a plurality of cylinders #1 to #4. A plurality of fuel injection valves 4a to 4d are attached to a cylinder head 2. These fuel injection valves 4a to 4d inject fuel into combustion chambers of the cylinders #1 to #4 respectively. Besides, the cylinder head 2 is provided with intake ports for introducing fresh air into the cylinders, and exhaust ports 6a to 6d for discharging combustion gas to the outside of the cylinders, in such a manner as to correspond to the cylinders #1 to #4 respectively.

[0018] The fuel injection valves 4a to 4d are connected to a common rail 9 in which high-pressure fuel is accumulated. The common rail 9 is connected to a supply pump 10. The supply pump 10 sucks in the fuel in a fuel tank, and supplies high-pressure fuel to the common rail 9. The high-pressure fuel supplied to the common rail 9 is injected from the fuel injection valves 4a to 4d into the cylinders respectively, when the fuel injection valves 4a to 4d are opened respectively.

[0019] An intake manifold 7 is connected to the intake ports. The intake manifold 7 is connected to an intake passage 3. An intake throttle valve 16 for adjusting the amount of intake air is provided in this intake passage 3.

[0020] An exhaust manifold 8 is connected to the exhaust ports 6a to 6d. The exhaust manifold 8 is connected to an exhaust passage 26. A turbocharger 11 that supercharges the intake air introduced into the cylinders through the use of an exhaust pressure is provided in the exhaust passage 26 between both ends thereof. An intercooler 18 is provided in the intake passage 3 between an intake-side compressor of the turbocharger 11 and the intake throttle valve 16. This intercooler 18 is designed to cool the intake air whose temperature has risen by being supercharged by the turbocharger 11.

[0021] Besides, a first purification member 30 that purifies exhaust gas is provided in the exhaust passage 26 between both ends thereof, downstream of an exhaust-side turbine of the turbocharger 11 with respect to exhaust gas. An oxidation catalyst 31 and a filter 32 are disposed in series with respect to an exhaust gas flow direction, inside this first purification member 30.

[0022] A catalyst that subjects the HC in exhaust gas to an oxidation treatment is supported by the oxidation catalyst 31. Besides, the filter 32 is a member that collects PM (particulate matter) in exhaust gas, and is configured from a porous ceramic. A catalyst for promoting the oxidation of PM is supported by this filter 32. The PM in exhaust gas is collected when passing through a porous wall of the filter 32.

[0023] Besides, a fuel addition valve 5 for supplying fuel as an additive to the oxidation catalyst 31 and the filter 32 is provided in the vicinity of a confluence portion of the exhaust manifold 8. This fuel addition valve 5 is connected to the supply pump 10 via a fuel supply pipe 27. Incidentally, the position where the fuel addition valve 5 is disposed can also be changed as appropriate, as long as the fuel addition valve 5 is located in an exhaust system upstream of the first purification member 30.

[0024] If the amount of the PM collected by the filter 32 becomes larger than a predetermined value, a regeneration treatment of the filter 32 is started, and fuel is injected from the fuel addition valve 5 toward the interior of the exhaust manifold 8. The fuel injected from this fuel addition valve 5 is burned upon reaching the oxidation catalyst 31. Thus, the temperature of exhaust gas is raised. Then, the exhaust gas whose temperature has been raised in the oxidation catalyst 31 flows into the filter 32, and the temperature of the filter 32 is thereby raised. Thus, the PM deposited in the filter 32 is subjected to the oxidation treatment, so the filter 32 is regenerated.

[0025] Besides, a second purification member 40 that purifies exhaust gas is provided in the exhaust passage 26 between both ends thereof, downstream of the first purification member 30 with respect to exhaust gas. A selective reduction-type NOx catalyst (hereinafter referred to as "an SCR catalyst") 41 that reduces and purifies the NOx in exhaust gas through the use of a reducing agent is disposed inside the second purification member 40.

[0026] Furthermore, a third purification member 50 that purifies exhaust gas is provided in the exhaust passage 26 between both ends thereof, downstream of the second purification member 40 with respect to exhaust gas. An ammonia oxidation catalyst 51 that purifies the ammonia in exhaust gas is disposed inside the third purification member 50.

[0027] The engine 1 is provided with a urea water supply mechanism 200 that supplies a reducing agent to the aforementioned SCR catalyst 41. The urea water supply mechanism 200 is constituted of a tank 210 that stores urea water, a urea addition valve 230 that injects and supplies urea water into the exhaust passage 26, a supply passage 240 that connects the urea addition valve 230 and the tank 210 to each other, and a pump 220 that is provided in the supply passage 240 except at both ends thereof.

[0028] The urea addition valve 230 is provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40, and an injection hole of the urea addition valve 230 is directed toward the SCR catalyst 41. When this urea addition valve 230 is opened, urea water is injected and supplied into the exhaust passage 26 via the supply passage 240.

[0029] The urea addition valve 230 is attached to the exhaust passage 26 via a heat radiation member 231. A plurality of heat radiation fins 232 are integrally formed on an outer surface of this heat radiation member 231. Since this heat radiation member 23 is provided, heat exchange between the urea addition valve 230 and outside air is promoted, and the urea addition valve 230 is cooled. Incidentally, when urea water is injected from the urea addition valve 230, the urea addition valve 230 is cooled through the exchange of heat with relatively low-temperature urea water that is supplied from the tank 210.

[0030] The pump 220 is a motor pump, and delivers urea water from the tank 210 toward the urea addition valve 230 during normal rotation. On the other hand, the pump 220 delivers urea water from the urea addition valve 230 toward the tank 210 during reverse rotation. That is, during reverse rotation of the pump 220, urea water is recovered from the urea addition valve 230 and the supply passage 240 to be returned to the tank 210.

[0031] Besides, a dispersion plate 60 that disperses the urea water injected from the urea addition valve 230 to promote atomization of the urea water is provided in the exhaust passage 26 between the urea addition valve 230 and the SCR catalyst 41.

[0032] The urea water injected from the urea addition valve 230 is hydrolyzed by the heat of exhaust gas, and turns into ammonia. This ammonia is then supplied to the SCR catalyst 41 as a reducing agent for NOx, The ammonia supplied to the SCR catalyst 41 is occluded by the SCR catalyst 41, and is utilized to reduce NOx. Incidentally, part of the hydrolyzed ammonia is directly utilized to reduce NOx before being occluded by the SCR catalyst 41.

[0033] In addition, the engine 1 is equipped with an exhaust gas recirculation device (hereinafter referred to as "an EGR device"). This EGR device is a device that introduces part of exhaust gas (so-called EGR gas) into intake air to thereby lower the combustion temperature in the cylinders and reduce the generation amount of NOx. This EGR device is constituted of an EGR passage 13 that establishes communication between the intake passage 3 and the exhaust manifold 8, an EGR valve 15 that is provided in the EGR passage 13, an EGR cooler 14, and the like. The opening degree of the EGR valve 15 is adjusted, whereby the amount of exhaust gas recirculated to be introduced into the intake passage 3 from the exhaust passage 26, namely, the amount of EGR is regulated. Besides, the temperature of exhaust gas flowing in the EGR passage 13 is lowered by the EGR cooler 14. In this embodiment of the invention, the introduction of EGR gas by the EGR device is carried out only in an engine operation region where an engine load KL (a fuel injection amount from the fuel injection valves 4a to 4d in this embodiment of the invention) is relatively small and an engine rotational speed NE is relatively low. That is, the introduction of EGR gas by the EGR device is not carried out in an engine operation region where the engine load KL is large or an engine operation region where the engine rotational speed NE is high.

[0034] The engine 1 is fitted with various sensors for detecting an engine operation state. For example, an airflow mater 19 detects an intake air amount GA in the intake passage 3. A throttle valve opening degree sensor 20 detects an opening degree of the intake throttle valve 16. An engine rotational speed sensor 21 detects a rotational speed of the crankshaft, namely, the engine rotational speed NE. An accelerator sensor 22 detects a depression amount of an accelerator pedal, namely, an accelerator operation amount ACCR An outside air temperature sensor 23 detects an outside air temperature THout. A vehicle speed sensor 24 detects a traveling speed of a vehicle that is mounted with the engine 1, namely, a vehicle speed SPD. An ignition switch 25 detects start operation and stop operation of the engine 1 by a driver of the vehicle.

[0035] Besides, a first exhaust gas temperature sensor 100 that is provided upstream of the oxidation catalyst 31 with respect to exhaust gas detects a first exhaust gas temperature THl as a temperature of exhaust gas that has not flowed into the oxidation catalyst 31. A differential pressure sensor 110 detects a pressure difference ΔΡ between an exhaust pressure upstream of the filter 32 with respect to exhaust gas and an exhaust pressure downstream of the filter 32 with respect to exhaust gas.

[0036] A second exhaust gas temperature sensor 120 and a first NOx sensor 130 are provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40, upstream of the urea addition valve 230 with respect to exhaust gas. The second exhaust gas temperature sensor 120 detects a second exhaust gas temperature TH2 as a temperature of exhaust gas that has not flowed into the SCR catalyst 41. The first NOx sensor 130 detects a first NOx concentration Nl as a concentration of NOx in exhaust gas that has not flowed into the SCR catalyst 41.

[0037] A second NOx sensor 140 that detects a second NOx concentration N2 as a concentration of NOx in exhaust gas that has been purified by the SCR catalyst 41 is provided in the exhaust passage 26 downstream of the third purification member 50 with respect to exhaust gas.

[0038] Outputs of these various sensors and the like are input to a control unit 80. This control unit 80 is mainly configured as a microcomputer that is equipped with a central processing unit (a CPU), a read only memory (a ROM) that stores in advance various programs, maps and the like, a random access memory (a RAM) that temporarily stores a calculation result and the like of the CPU, an input interface, an output interface and the like. Incidentally, the CPU and the aforementioned various sensors are supplied with electric power from a battery.

[0039] Then, the control unit 80 performs various kinds of control for the engine 1, for example, fuel injection amount control/fuel injection timing control for the fuel injection valves 4a to 4d and the fuel addition valve 5, discharge pressure control for the supply pump 10, drive amount control for an actuator 17 that opens/closes the intake throttle valve 16, opening degree control for the EGR valve 15 and the like. Besides, the control unit 80 also performs various kinds of exhaust gas purification control such as the aforementioned regeneration treatment for burning the PM collected by the aforementioned filter 32 and the like.

[0040] Besides, the control unit 80 performs addition control of an additive by the aforementioned urea addition valve 230, as one kind of exhaust gas purification control. In this addition control, the injection of urea water for purifying NOx in the SCR catalyst 41 (hereinafter referred to as purification injection) and the injection of urea water for cooling the urea addition valve 230 (hereinafter referred to as cooling injection) are carried out.

[0041] Purification injection is basically carried out as follows. That is, an injection amount of urea water (a target purification injection amount TQn) that is neither too large nor too small to subject the NOx discharged from the engine 1 to a reduction treatment is calculated on the basis of an engine operation state (the engine load KL and the engine rotational speed NE). Then, the valve-open state of the urea addition valve 230 is controlled such that the same amount of urea water as this target purification injection amount TQn is injected from the urea addition valve 230. Incidentally, in this embodiment of the invention, this target purification injection amount TQn is equivalent to the second additive injection amount.

[0042] Besides, cooling injection is basically carried out as follows. That is, an injection amount of urea water (a target cooling injection amount TQc) that is neither too large nor too small to hold the temperature of the urea addition valve 230, which is exposed to high-temperature exhaust gas, lower than an upper-limit temperature in a temperature compensation range is calculated on the basis of an engine operation state (the engine load KL and the engine rotational speed NE). Then, the valve-open state of the urea addition valve 230 is controlled such that the same amount of urea water as the target cooling injection amount TQc is injected from the urea addition valve 230. In this embodiment of the invention, this target cooling injection amount TQc is equivalent to the first additive injection amount. Incidentally, it can be determined that the injection of urea water from the urea addition valve 230 contributes toward cooling the urea addition valve 230, if the second exhaust gas temperature TH2 is equal to or higher than a predetermined temperature (more specifically, a temperature that makes the temperature in the vicinity of the injection hole of the urea addition valve 230 equal to or higher than a boiling point of urea water). In this case, since urea water vaporizes inside the urea addition valve 230, the urea addition valve 230 is cooled by the heat of vaporization. Besides, if the concentration of NOx in exhaust gas that has not flowed into the SCR catalyst 41 (the first NOx concentration Nl) and the concentration of NOx in exhaust gas that has been purified by the SCR catalyst 41 (the second NOx concentration N2) are not very much different from each other when the second exhaust gas temperature TH2 is equal to or higher than the predetermined temperature, it is possible to conclude that urea water hardly contributes toward purifying NOx, and that the injection of urea water contributes toward cooling the urea addition valve 230.

[0043] By the way, in cooling injection, the injection amount is not always an amount suited to purify NOx in the SCR catalyst 41. In addition, urea water may be injected in a situation unsuited for the purification of NOx, for example, when the bed temperature of the SCR catalyst 41 is excessively high etc. In such a case, cooling injection plays a role in incurring an increase in the consumption of urea water.

[0044] Thus, in this embodiment of the invention, a value corrected on the basis of the outside air temperature THout, the vehicle speed SPD, the second exhaust gas temperature TH2, and the flow rate of exhaust gas is calculated as the target cooling injection amount TQc.

[0045] The procedure of performing a process that includes this calculation of the target cooling injection amount TQc and is designed to calculate an injection amount of urea water from the urea addition valve 230 (an injection amount calculation process) will be described hereinafter in detail.

[0046] FIG. 2 shows the procedure of performing the aforementioned injection amount calculation process. A series of processing steps shown in a flowchart of FIG. 2 are performed by the control unit 80 as interrupt handling on a predetermined cycle. As shown in FIG. 2, in this process, it is first determined whether or not the following addition condition is fulfilled (step SI 01).

[0047] [Addition Condition]

The addition condition requires that the bed temperature of the SCR catalyst 41 be equal to or higher than an activation temperature. Concretely, the addition condition requires that the second exhaust gas temperature TH2 be equal to or higher than a predetermined temperature (e.g., 200°C). If this addition condition is not fulfilled (step SI 01 : NO), the present process is temporarily ended without performing the following processing steps.

[0048] If the addition condition is fulfilled (step SI 01 : YES), a correction value Al is calculated on the basis of the outside air temperature THout (step SI 02). FIG. 3 shows a relationship between the outside air temperature THout and the correction value Al . As shown in FIG. 3, the correction value Al (N.B., 0 < Al < "1.0") is calculated as a value that decreases as the outside air temperature THout falls. The target cooling injection amount TQc is reduced as this correction value Al decreases. Therefore, in the present process, the target cooling injection amount TQc decreases as the outside air temperature THout falls.

[0049] In this embodiment of the invention, although the temperature of the urea addition valve 230 becomes high due to the reception of heat from exhaust gas, the urea addition valve 230 is cooled through the exchange of heat with outside air in the heat radiation fins 232, so the temperature of the urea addition valve 230 is restrained from rising correspondingly. Moreover, the target cooling injection amount TQc can be reduced as the outside air temperature THout falls, namely, as the temperature of the urea addition valve 230 falls due to a large amount of heat exchange (a large amount of heat radiation) in the heat radiation fins 232. Thus, by carrying out cooling injection on the basis of the target cooling injection amount TQc, the consumption of urea water can be reduced while suitably restraining the temperature of the urea addition valve 230 from rising.

[0050] Besides, a correction value Bl is calculated on the basis of the vehicle speed SPD (step SI 03 in FIG. 2). FIG. 4 shows a relationship between the vehicle speed SPD and the correction value Bl . As shown in FIG. 4, the correction value Bl (N.B., 0 < Bl < "1.0") is calculated as a value that decreases as the vehicle speed SPD increases. The target cooling injection amount TQc is reduced as this correction value Bl decreases. Therefore, the target cooling injection amount TQc decreases as the vehicle speed SPD increases.

[0051] As the vehicle speed SPD increases, the air volume of a traveling wind increases, so the amount of heat exchange (the amount of heat radiation) in the heat radiation fins 232 increases, and the temperature of the urea addition valve 230 falls. In the present process, the target cooling injection amount TQc can be reduced when the vehicle speed SPD is high, in accordance with such a relationship between the vehicle speed SPD and the amount of heat exchange in the heat radiation fins 232. Therefore, by carrying out cooling injection on the basis of the target cooling injection amount TQc, the consumption of urea water can be reduced while suitably restraining the temperature of the urea addition valve 230 from rising.

[0052] Furthermore, a correction value CI is calculated on the basis of the second exhaust gas temperature TH2 (step SI 04 in FIG. 2). FIG. 5 shows a relationship between the second exhaust gas temperature TH2 and the correction Value CI . As shown in FIG. 5, the correction value CI (N.B., 0 < CI < "1.0") is calculated as a value that decreases as the second exhaust gas temperature TH2 falls. The target cooling injection amount TQc is reduced as the correction value CI decreases. Therefore, the target cooling injection amount TQc decreases as the second exhaust gas temperature TH2 falls.

[0053] As the temperature of exhaust gas in the engine 1 falls, the amount of heat received by the urea addition valve 230 from exhaust gas decreases, so the temperature of the urea addition valve 230 becomes likely to be low. In the present process, the target cooling injection amount TQc can be reduced as the second exhaust gas temperature TH2 falls, and as the temperature of the urea addition valve 230 becomes likely to be low. Therefore, by carrying out cooling injection on the basis of the target cooling injection amount TQc, the consumption of urea water can be reduced while suitably restraining the temperature of the urea addition valve 230 from rising.

[0054] Besides, a correction value Dl is calculated on the basis of the flow rate of exhaust gas in the engine 1 (concretely, the intake air amount GA as an index value thereof) (step SI 05 in FIG. 2). FIG. 6 shows a relationship between the flow rate of exhaust gas and the correction value Dl . As shown in FIG. 6, the correction value Dl (N.B., 0 < Dl < "1/0") is calculated as a value that decreases as the flow rate of exhaust gas decreases. The target cooling injection amount TQc is reduced as the correction value Dl decreases. Therefore, the target cooling injection amount TQc decreases as the flow rate of exhaust gas decreases.

[0055] As the flow rate of exhaust gas decreases, the amount of heat received by the urea addition valve 230 from exhaust gas decreases, so the temperature of the urea addition valve 230 becomes likely to be low. In the present process, the target cooling injection amount TQc can be reduced as the flow rate of exhaust gas in the engine 1 decreases, and as the temperature of the urea addition valve 230 becomes likely to be low. Therefore, by carrying out cooling injection on the basis of the target cooling injection amount TQc, the consumption of urea water can be reduced while suitably restraining the temperature of the urea addition valve 230 from rising.

[0056] After the respective correction values Al, Bl, CI, and Dl are thus calculated (steps SI 02 to SI 05 in FIG. 2), a control basic value of the injection amount for cooling injection (a base cooling injection amount Qcb) is calculated on the basis of the engine load KL and the engine rotational speed NE (step SI 06).

[0057] The temperature of exhaust gas rises as the engine load KL increases, and the flow rate of exhaust gas increases as the engine rotational speed NE increases. Therefore, the amount of heat received by the urea addition valve 230 from exhaust gas increases, and the temperature of the urea addition valve 230 becomes likely to be high. In the present process, with a view to holding the temperature of the urea addition valve 230 lower than the upper-limit temperature of the temperature compensation range in accordance with this tendency, a relationship among the engine load KL, the engine rotational speed NE and the base cooling injection amount Qcb is determined in advance and stored in the control unit 80. In the processing step of step SI 06, as shown in FIG. 7, the base cooling injection amount Qcb is calculated as an amount that increases as the engine load KL increases and as the engine rotational speed NE increases.

[0058] Then, a value (QcbxAl BlxClxDl) obtained by multiplying this base cooling injection amount Qcb by the respective correction values Al, Bl, CI and Dl is calculated as the target cooling injection amount TQc (step SI 07 in FIG. 2).

[0059] After that, an injection amount of urea water in purification injection (the target purification injection amount TQn) is calculated on the basis of the engine load KL and the engine rotational speed NE (step SI 08). FIG. 8 shows a relationship among the engine load KL, the engine rotational speed NE, and the target purification injection amount TQn. As shown in FIG. 8, "a positive value" is set as the target purification injection amount TQn in an engine operation region where the introduction of EGR gas by the EGR device is carried out (an EGR region). In this embodiment of the invention, a condition for carrying out purification injection is assumed to be fulfilled in the EGR region, and purification injection is carried out. In this EGR region, the amount of NOx in exhaust gas increases as the engine load KL increases and as the engine rotational speed NE increases. Therefore, a large amount is calculated as the target purification injection amount TQn. On the other hand, in an engine operation region where the introduction of EGR gas by the EGR device is not carried out (a non-EGR region), "0" is set as the target purification injection amount TQn. In this non-EGR region, the condition for carrying out purification injection is assumed not to be fulfilled, and the injection is not carried out. Incidentally, a border between the EGR region and the non-EGR region is indicated by an alternate long and short dash line in FIGS. 7 and 8.

[0060] After that, the target cooling injection amount TQc and the target purification injection amount TQn are compared with each other, and the larger of the injection amounts is calculated as a final injection amount Qf (step SI 09 in FIG. 2). After that, the present process is temporarily ended.

[0061] Then, in addition control according to this embodiment of the invention, the valve-open state of the urea addition valve 230 is controlled such that the same amount of urea water as this final injection amount Qf is injected from the urea addition valve 230. The operation of this calculation of the final injection amount Qf will be described hereinafter.

[0062] In this embodiment of the invention, the injection amount needed to cool the urea addition valve 230 (the target cooling injection amount TQc) and the injection amount needed to purify NOx in the SCR catalyst 41 (the target purification injection amount TQn) are separately calculated, and the injection of urea water from the urea addition valve 230 is carried out on the basis of the larger of the injection amounts (the final injection amount Qf).

[0063] Thus, if the target cooling injection amount TQc is larger than the target purification injection amount TQn, it is assumed that the temperature of the urea addition valve 230 cannot be suitably held low simply by injecting an amount of urea water that is neither too large nor too small to subject NOx to the reduction treatment, and hence, an amount of urea water larger than this, namely, an amount of urea water that is neither too large nor too small to hold the temperature of the urea addition valve 230 lower than the upper-limit temperature is injected. Therefore, at this time, an amount of urea water that is sufficient to purify NOx in the SCR catalyst 41 and neither too large nor too small to hold the temperature of the urea addition valve 230 lower than the upper-limit temperature can be injected.

[0064] Moreover, if the target cooling injection amount TQc is equal to or smaller than the target purification injection amount TQn, it is assumed that the temperature of the urea addition valve 230 can be suitably held low by injecting an amount of urea water that is neither too large nor too small to subject NOx to the reduction treatment, and an amount of urea water that is needed to purify NOx is injected on the basis of the target purification injection amount TQn. At this time, an amount of the additive that is neither too large nor too small to subject NOx to the reduction treatment and sufficient to cool the urea addition valve 230 can be injected from the urea addition valve 230.

[0065] In consequence, according to this embodiment of the invention, regardless of whether the target cooling injection amount TQc is larger than the target purification injection amount TQn or equal to or smaller than the target purification injection amount TQn, both the function of cooling the urea addition valve 230 and the function of purifying NOx in the SCR catalyst 41 can be favorably satisfied.

[0066] Besides, in this embodiment of the invention, the target cooling injection amount TQc and the target purification injection amount TQn are separately calculated. Therefore, the target cooling injection amount TQc can be adequately corrected in accordance with the amount of heat radiation of the urea addition valve 230 by the heat radiation fins 232 (more specifically, the outside air temperature THout and the vehicle speed SPD as index values thereof) and the amount of heat received by the urea addition valve 230 from exhaust gas (more specifically, the second exhaust gas temperature TH2 and the flow rate of exhaust gas as index values thereof), without correcting the target purification injection amount TQn unnecessarily. Thus, an injection amount of urea water that is neither too large nor too small to subject the NOx discharged from the engine 1 to the reduction treatment can be accurately calculated as the target purification injection amount TQn. Besides, an injection amount of urea water that is neither too large nor too small to hold the temperature of the urea addition valve 230 lower than the upper-limit temperature in the temperature compensation range can be accurately calculated as the target cooling injection amount TQc. Accordingly, the injection amount of urea water can be suitably reduced in such a manner as to correspond to the amount of heat radiation of the urea addition valve 230 by the heat radiation fins 232 and the amount of heat received by the urea addition valve 230 from exhaust gas, so the consumption of urea water can be favorably reduced.

[0067] Besides, in this embodiment of the invention, while "a positive value" is set as the target purification injection amount TQn to carry out purification injection in the EGR region, "0" is set as the target purification injection amount TQn to refrain from carrying out purification injection in the non-EGR region. Thus, while the injection of urea water from the urea addition valve 230 is carried out through the use of the target purification injection amount TQn if the condition for carrying out injection is fulfilled, the injection of urea water from the urea addition valve 230 is carried out on the basis of the target cooling injection amount TQc without the use of the target purification injection amount TQn if the condition for carrying out injection is not fulfilled. In this manner, according to this embodiment of the invention, the injection of urea water from the urea addition valve 230 can be carried out depending on whether or not purification injection is necessary.

[0068] As described above, according to this embodiment of the invention, the effects described below are obtained. (1) The urea addition valve 230 is provided with the heat radiation fins 232, and the target cooling injection amount TQc is reduced as the outside air temperature THout falls. Therefore, the target cooling injection amount TQc can be reduced in such a manner as to correspond to the amount of heat radiation in the heat radiation fins 232. By carrying out cooling injection on the basis of this target cooling injection amount TQc, the consumption of urea water can be reduced while suitably restraining the temperature of the urea addition valve 230 from rising.

[0069] (2) The target cooling injection amount TQc is reduced as the vehicle speed SPD increases. Therefore, the consumption of urea water can be favorably reduced while suitably restraining the temperature of the urea addition valve 230 from rising, in accordance with the relationship between the vehicle speed SPD and the amount of heat exchange in the heat radiation fins 232.

[0070] (3) The target cooling injection amount TQc is reduced as the second exhaust gas temperature TH2 falls. Thus, the target cooling injection amount TQc can be reduced in such a manner as to correspond to the relationship between the temperature of exhaust gas in the engine 1 and the amount of heat received by the urea addition valve 230. Therefore, the consumption of urea water can be favorably reduced while suitably restraining the temperature of the urea addition valve 230 from rising.

[0071] (4) The target cooling injection amount TQc is reduced as the flow rate of exhaust gas decreases. Thus, the target cooling injection amount TQc can be reduced in such a manner as to correspond to the relationship between the flow rate of exhaust gas and the amount of heat received by the urea addition valve 230 from exhaust gas. Therefore, the consumption of urea water can be reduced while suitably restraining the temperature of the urea addition valve 230 from rising.

[0072] (5) The target cooling injection amount TQc and the target purification injection amount TQn are separately calculated. The larger of the injection amounts is set as the final injection amount Qf, and the injection of urea water from the urea addition valve 230 is carried out on the basis of the final injection amount Qf. Therefore, both the function of cooling the urea addition valve 230 and the function of purifying NOx in the SCR catalyst 41 can be favorably satisfied. Moreover, the injection amount of urea water that is neither too large nor too small to hold the temperature of the urea addition valve 230 lower than the upper-limit temperature in the temperature compensation range can be accurately calculated as the target cooling injection amount TQc. Therefore, the consumption of urea water can be favorably reduced.

[0073] (6) In the EGR region where the condition for carrying out purification injection, "a positive value" is set as the target purification injection amount TQn. On the other hand, in the non-EGR region where the condition for carrying out purification injection is not fulfilled, "0" is set as the target purification injection amount TQn. Therefore, the injection of urea water from the urea addition valve 230 can be carried out depending on whether or not purification injection is necessary.

[0074] Incidentally, the aforementioned embodiment of the invention may be carried out after being modified as follows. As the engine load KL, it is possible to use an arbitrary value such as a value obtained by dividing the fuel injection amount from the fuel injection valves 4a to 4d by the engine rotational speed NE (the fuel injection amount / NE), the accelerator operation amount ACCP, or the like, instead of using the fuel injection amount.

[0075] As the respective correction values Al, Bl, CI and Dl of the injection amount calculation process (FIG. 2), it is also acceptable to calculate values by which the base cooling injection amount Qcb is divided, values that are added to the base cooling injection amount Qcb, or values that are subtracted from the base cooling injection amount Qcb, in addition to calculating values by which the base cooling injection amount Qcb is multiplied.

[0076] One, two or three of the processing step of calculating the correction value Al (step S102), the processing step of calculating the correction value Bl (step S103), the processing step of calculating the correction value CI (step SI 04), and the processing step of calculating the correction value Dl (step SI 05) in the injection amount calculation process (FIG. 2) may be omitted.

[0077] The base cooling injection amount Qcb can be corrected using a value other than the outside air temperature THout and the vehicle speed SPD (an intake air temperature or the like) as a correction parameter, as long as the value is an index value of the amount of heat radiation of the urea addition valve 230 by the heat radiation fins 232. In this device, a value that makes the target cooling injection amount TQc decrease as the amount of heat radiation by the heat radiation fins 232 increases may be calculated as a correction value.

[0078] The base cooling injection amount Qcb can be corrected using a value other than the second exhaust gas temperature TH2 and the flow rate of exhaust gas (the first exhaust gas temperature TH1 or the like) as a correction parameter, as long as the value is an index value of the amount of heat received from exhaust gas. In this device, a value that makes the target cooling injection amount TQc decrease as the amount of heat received by the urea addition valve 230 from exhaust gas decreases may be calculated as a correction value.

[0079] The device according to the aforementioned embodiment of the invention is also applicable to a device in which purification injection is carried out in the EG region. The processing step of calculating the target purification injection amount TQ (step SI 08) and the processing step of calculating the larger of the target cooling injection amount TQc and the target purification injection amount TQn as the final injection amount Qf (step SI 09) in the injection amount calculation process (FIG. 2) may be omitted. In this device, it is appropriate to control the valve-open state of the urea addition valve 230 such that the same amount of urea water as the target cooling injection amount TQc is injected from the urea addition valve 230, on the condition that the condition for carrying out cooling injection be fulfilled. This device also makes it possible to reduce the consumption of urea water while suitably restraining the temperature of the urea addition valve 230 from rising, in comparison with a device in which no correction is made on the basis of the outside air temperature THout, the vehicle speed SPD, the second exhaust gas temperature TH2, and the flow rate of exhaust gas. Incidentally, it is possible to determine that the condition for carrying out cooling injection is fulfilled, for example, on the basis of the engine operation region (the engine load KL and the engine rotational speed NE), or if the second exhaust gas temperature TH2 is equal to or higher than a predetermined temperature or if the temperature of the urea addition valve 230 is equal to or higher than a predetermined temperature. In addition to being directly detected by a temperature sensor, the temperature of the urea addition valve 230 can also be estimated on the basis of a vehicle driving state (the fuel injection amount, the intake air amount GA, the engine rotational speed NE, the temperature of exhaust gas, the outside air temperature THout, the vehicle speed SPD and the like).

[0080] Although urea water is used as the additive, it is acceptable to use other additives.

Claims

1. An additive supply device for an internal combustion engine, the internal combustion engine including

an addition valve injecting an additive to an exhaust passage of the internal■ combustion engine, the addition valve having a heat radiation fin that radiates heat through exchange of heat with outside air, and

an NOx purification catalyst provided in the exhaust passage downstream of the addition valve in an exhaust gas flow direction, and purifying NOx through addition of the additive from the addition valve,

the additive supply device comprising:

a control unit configured to execute injection of the additive from the addition valve when a temperature of exhaust gas in the exhaust passage in a region upstream of the addition valve in the exhaust gas flow direction is equal to or higher than a predetermined temperature, and

the control unit being configured to reduce an injection amount of the additive as a temperature of outside air decreases.

2. The additive supply device for the internal combustion engine according to claim 1, wherein

the internal combustion engine is mounted on a vehicle, and

the control unit is configured to reduce the injection amount of the additive as a traveling speed of the vehicle increases.

3. The additive supply device for the internal combustion engine according to claim 1 or 2, wherein

the control unit is configured to reduce the injection amount of the additive as the temperature of exhaust gas in the internal combustion engine decreases.

4. The additive supply device for the internal combustion engine according to any one of claims 1 to 3, wherein

the control unit is configured to reduce the injection amount of the additive as a flow rate of exhaust gas in the exhaust passage decreases.

5. The additive supply device for the internal combustion engine according to any one of claims 1 to 4, wherein

the control unit is configured to calculate a first additive injection amount for cooling the addition valve, and a second additive injection amount for purifying NOx in the NOx purification catalyst,

the control unit is configured to execute injection of the additive from the addition valve based on the first additive injection amount when the first additive injection amount is larger than the second additive injection amount, and

the control unit is configured to execute injection of the additive from the addition valve based on the second additive injection amount when the first additive injection amount is equal to or smaller than the second additive injection amount.

6. The additive supply device for the internal combustion engine according to claim 5, wherein

the control unit is configured to set the second additive injection amount to a positive value when a condition for executing injection of the additive for purifying the NOx is fulfilled, and

the control unit is configured to set the second additive injection amount to zero when the condition for executing injection is not fulfilled.