Control device for internal combustion engines

Abstract

This invention provides a control device for internal combustion engines that can simultaneously purify NOx emissions and regenerate filters. [Solution] A control device for an internal combustion engine, wherein the exhaust pipe of the internal combustion engine is provided with a filter, a first catalyst, a second catalyst, a first urea water supply unit, and a second urea water supply unit, the first catalyst is coated on the filter or provided upstream of the filter in the exhaust pipe, the second catalyst is provided downstream of the filter in the exhaust pipe, the first urea water supply unit supplies urea water to the first catalyst, the second urea water supply unit supplies urea water to the second catalyst, the control device comprises an acquisition unit for acquiring the temperature of the filter during filter regeneration, a first control unit for controlling the first urea water supply unit, and a second control unit for controlling the second urea water supply unit, and during filter regeneration, if the temperature is below a predetermined value, the first control unit stops supplying urea water from the first urea water supply unit, and the second control unit supplies urea water from the second urea water supply unit.

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine.

Background Art

[0002] In order to purify the exhaust gas of an internal combustion engine, a technique has been developed in which two SCR catalysts (selective reduction type catalysts, SCR: Selective Catalytic Reduction), a filter, and an aqueous urea injection device are provided in an exhaust pipe (for example, Patent Document 1, etc.).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] SCR reduces nitrogen oxides (NOx) to nitrogen and water using aqueous urea as a reducing agent. The filter collects particulate matter (PM) in the exhaust gas. The filter can be regenerated by burning the PM deposited on the filter. However, depending on operating conditions and the like, it may be difficult to achieve both NOx purification and filter regeneration. Therefore, an object is to provide a control device for an internal combustion engine that can achieve both NOx purification and filter regeneration.

Means for Solving the Problems

[0005] The above objective can be achieved by a control device for an internal combustion engine, wherein the exhaust pipe of the internal combustion engine is provided with a filter, a first catalyst, a second catalyst, a first urea water supply unit, and a second urea water supply unit, the first catalyst is coated on the filter or provided upstream of the filter in the exhaust pipe, the second catalyst is provided downstream of the filter in the exhaust pipe, the first urea water supply unit supplies urea water to the first catalyst, the second urea water supply unit supplies urea water to the second catalyst, and the control device comprises an acquisition unit for acquiring the temperature of the filter during regeneration of the filter, a first control unit for controlling the first urea water supply unit, and a second control unit for controlling the second urea water supply unit, wherein during regeneration of the filter, if the temperature is below a predetermined value, the first control unit stops supplying urea water from the first urea water supply unit, and the second control unit supplies urea water from the second urea water supply unit. [Effects of the Invention]

[0006] We can provide an internal combustion engine control system that can achieve both NOx purification and filter regeneration. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram of the internal combustion engine according to this embodiment. [Figure 2] Figure 2 is a flowchart illustrating the process in the embodiment. [Figure 3] Figures 3(a) and 3(b) illustrate modified examples. [Modes for carrying out the invention]

[0008] The control device for the internal combustion engine of this embodiment will be described below with reference to the drawings. Figure 1 is a schematic diagram of the internal combustion engine according to this embodiment. An exhaust pipe 12 is connected to the internal combustion engine 10. The exhaust pipe 12 is equipped with an oxidation catalyst (DOC; Diesel Oxidation Catalyst) 14, a selective reduction catalyst (SCR) 16 (first catalyst), an SCR 18, a filter 20, and an SCR 22 (second catalyst). The ECU (Electronic Control Unit) 40 is a control device for the internal combustion engine.

[0009] An oxidation catalyst 14, SCR 16, filter 20, and SCR 22 are provided from the upstream to the downstream side of the exhaust pipe 12. SCR 18 is coated onto the filter 20. SCR 22 includes SCR 22a and SCR 22b. Of the SCR 22, SCR 22a is located on the upstream side and SCR 22b is located on the downstream side.

[0010] The exhaust pipe 12 is equipped with a urea water injection valve 24 (first urea water supply unit), a urea water injection valve 26 (second urea water supply unit), a pressure sensor 27, and a pressure sensor 28. The urea water injection valve 24 is located downstream of the oxidation catalyst 14 and upstream of the SCR 16. The urea water injection valve 26 is located downstream of the filter 20 and upstream of the SCR 22. The pressure sensor 27 is located downstream of the SCR 16 and upstream of the filter 20. The pressure sensor 28 is located downstream of the filter 20 and upstream of the urea water injection valve 26. Differential pressure sensors may be provided instead of pressure sensors 27 and 28. A member (such as a plate) for dispersing urea water may be provided between the urea water injection valve 24 and the SCR 16. A plate or the like may also be provided between the urea water injection valve 26 and the SCR 22.

[0011] Air is introduced into the internal combustion engine 10 from an intake manifold (not shown), and fuel is supplied from a fuel injection valve 11. A mixture of air and fuel is formed. When this mixture burns in the internal combustion engine 10, driving force is output and exhaust gas is generated. The exhaust gas is discharged from the internal combustion engine 10 into an exhaust pipe 12, flows through the exhaust pipe 12, and is discharged outside the vehicle. The exhaust gas contains nitrogen oxides (NOx) and particulate matter (PM), etc. The oxidation catalyst 14, SCR 16 and 22, and filter 20 purify the exhaust gas.

[0012] The oxidation catalyst 14 oxidizes hydrocarbons (HC) in the exhaust gas to carbon dioxide and water. The oxidation catalyst 14 also oxidizes nitric oxide (NO) to nitrogen dioxide (NO2).

[0013] Urea solution injection valves 24 and 26 inject urea solution into the exhaust pipe 12. The urea solution flows from upstream to downstream along with the exhaust. Urea solution injected from urea solution injection valve 24 is supplied to SCR 16 and 18. Urea solution injected mainly from urea solution injection valve 26 is supplied to SCR 22. Ammonia (NH3) is generated when the urea solution is hydrolyzed. SCR 16, 18 and 22 adsorb the ammonia and use the ammonia as a reducing agent to reduce NOx in the exhaust. NOx in the exhaust is purified by reduction.

[0014] Filter 20 is, for example, a DPF (Diesel Particulate Filter) and is made of porous ceramic or the like. The inlet and outlet of filter 20 are alternately closed. Filter 20 captures PM in the exhaust. SCR18 coated on filter 20 purifies NOx, similar to SCR16.

[0015] Pressure sensor 27 detects the pressure upstream of filter 20. Pressure sensor 28 detects the pressure downstream of filter 20. Pressure sensors 27 and 28 form a differential pressure sensor and detect the differential pressure between the upstream and downstream of filter 20.

[0016] The temperature sensor 30 detects the temperature of the filter 20. The temperature sensor 32 detects the temperature of the SCR 22. Also, the ECU 40 may estimate the temperatures of the filter 20 and the SCR 22.

[0017] The ECU 40 includes an arithmetic unit such as a CPU (Central Processing Unit), and storage devices such as a RAM (Random Access Memory) and a ROM (Read Only Memory). The ECU 40 performs various controls by executing programs stored in the ROM or the storage device.

[0018] The ECU 40 acquires the flow rate of the air introduced into the internal combustion engine 10 from an air flow meter (not shown). The ECU 40 acquires the vehicle speed. The ECU 40 controls the fuel injection amount and injection timing from the fuel injection valve 11, etc.

[0019] The ECU 40 functions as an acquisition unit 42, a first control unit 44, and a second control unit 46. The acquisition unit 42 acquires the pressure from the pressure sensors 27 and 28, and acquires the differential pressure between the upstream side and the downstream side of the filter 20. The acquisition unit 42 acquires the temperature from the temperature sensor 30 and the temperature sensor 32.

[0020] The first control unit 44 controls the urea water addition valve 24, and performs injection and stop of the urea water, control of the injection amount, etc. The second control unit 46 controls the urea water addition valve 26, and performs injection and stop of the urea water, control of the injection amount, etc.

[0021] When the differential pressure becomes equal to or greater than a predetermined value, the ECU 40 performs a filter regeneration process. In the filter regeneration, for example, the fuel injection amount and injection frequency from the fuel injection valve 11 are controlled to increase the exhaust temperature. The high-temperature exhaust flows into the filter 20, and the PM deposited on the filter 20 burns.

[0022] The oxidation rate of PM depends on the temperature of the filter 20 and the atmosphere around the filter 20. For example, when the temperature is 600 °C and the exhaust gas contains a large amount of oxygen (O2 atmosphere), the oxidation rate increases. When the temperature is between 450 °C and 550 °C and in an O2 atmosphere, the oxidation rate decreases. When the temperature is between 450 °C and 550 °C and the exhaust gas contains a large amount of NOx (NO2 atmosphere), the oxidation rate increases.

[0023] When the vehicle speed is low, etc., the exhaust gas temperature may not easily rise. Even if a large amount of oxygen is supplied to the filter 20, since the oxidation rate of PM is slow, efficient filter regeneration is difficult. At such temperatures, to increase the oxidation rate and promote filter regeneration, NO2 may be supplied to the filter 20. On the other hand, it is also important to purify NOx in the exhaust gas. However, by purifying NOx by the SCR 16, the NO2 supplied to the filter 20 decreases. In the embodiment, filter regeneration and NOx purification are made compatible.

[0024] Figure 2 is a flowchart illustrating the processing in the embodiment. The ECU 40 determines whether there is a request for filter regeneration (step S10). The acquisition unit 42 acquires the differential pressure between the upstream side and the downstream side of the filter 20. If the differential pressure is less than a predetermined value, there is no regeneration request, and it is a negative determination (No). If the differential pressure is greater than or equal to the predetermined value, there is a regeneration request, and it is an affirmative determination (Yes). Also, in addition to the differential pressure, PM emission amount estimated integration, driving distance, etc. may be used for the determination of the regeneration request. If the estimated integrated amount of PM is above a certain amount or the driving distance is above a predetermined distance, it is considered that there is a regeneration request.

[0025] If the determination in step S10 is positive, the ECU 40 determines whether the temperature Tf of the filter 20 is less than or equal to a predetermined value Tth (step S12). At temperatures higher than the predetermined temperature Tth, the PM oxidation rate in the O2 atmosphere is high. Below Tth, the PM oxidation rate in the O2 atmosphere decreases. If the determination in step S12 is positive, the ECU 40 determines whether the temperature Ts of the SCR 22 is greater than or equal to a predetermined value (activation temperature) Ta (step S14). If all of steps S10 to S14 are positive, the first control unit 44 stops the addition of urea solution from the urea solution addition valve 24. The second control unit 46 continues the addition from the urea solution addition valve 26 (step S16).

[0026] If a negative result is obtained in any of steps S10 to S14, normal urea solution addition control is performed (step S18). Depending on the amount of PM accumulation, temperature, etc., urea solution is added from one or both of the urea solution addition valves 24 and 26. The process ends in step S16 or after S16.

[0027] According to this embodiment, the ECU 40 regenerates the filter 20. When the temperature Tf of the filter 20 is below a predetermined temperature Tth, the first control unit 44 stops adding urea water from the urea water addition valve 24 (step S16). The amount of urea water supplied to SCR 16 and 18 decreases, making it more difficult for NOx to be reduced in SCR 16 and 18. The amount of NOx supplied to the filter 20 increases. PM deposited on the filter 20 is oxidized by NO2. The filter 20 is regenerated.

[0028] The second control unit 46 adds urea solution from the urea solution addition valve 26 (step S16). Since urea solution is supplied to the SCR22, NOx is purified in the SCR22. It is possible to achieve both NOx purification and filter regeneration simultaneously.

[0029] When the temperature Ts of SCR22 is above the activation temperature Ta, the second control unit 46 adds urea solution from the urea solution addition valve 26. Because SCR22 is activated, NOx can be efficiently purified.

[0030] If the temperature Ts of SCR22 is below the activation temperature Ta, urea solution is added to SCR16 from the urea solution addition valve 24 (step S18). NOx can be purified by SCR16 and 18.

[0031] If the temperature Tf of filter 20 is higher than Tth, urea solution may be added from both urea solution addition valves 24 and 26 (step S18). If the temperature Tf is higher than Tth, the PM oxidation rate in the O2 atmosphere is high, so filter regeneration is possible by supplying oxygen to filter 20. Even if NOx is purified in SCR 16 and 18, the effect on filter regeneration is small. In other words, PM can be oxidized by oxygen in filter 20, and NOx can be purified by SCR 16, 18 and 22.

[0032] Figures 3(a) and 3(b) illustrate modified examples and illustrate the exhaust pipe 12. The same configuration as in the embodiment is omitted from the explanation. The ECU 40 and other components are omitted, but they are included in the configuration as in Figure 1.

[0033] In the modified example 1 shown in Figure 3(a), SCR16 is not provided. The urea solution addition valve 24 is located upstream of the filter 20 and adds urea solution to the filter 20. The SCR18 coated on the filter 20 reduces NOx using urea solution as a reducing agent.

[0034] In the modified example 2 shown in Figure 3(b), the oxidation catalyst 14 is located between the SCR 16 and the filter 20. The SCR 16 is located upstream of the oxidation catalyst 14. The urea water injection valve 24 is located upstream of the SCR 16.

[0035] In the examples shown in Figures 3(a) and 3(b), similar to the embodiment, the ECU 40 can supply NOx to the filter 20 by stopping the addition from the urea water addition valve 24 upstream of the filter 20. Filter regeneration is possible. NOx can be purified in the SCR 22 by adding urea water from the urea water addition valve 26 downstream of the filter 20.

[0036] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. [Explanation of Symbols]

[0037] 10 Internal combustion engine, 11 Fuel injection valve, 12 Exhaust pipe, 14 Oxidation catalyst, 16, 18, 22, 22a, 22b SCR, 20 Filter, 24, 26 Urea water injection valve, 27, 28 Pressure sensor, 30, 32 Temperature sensor, 40 ECU, 42 Acquisition unit, 44 First control unit, 46 Second control unit

Claims

[Claim 1] A control device for an internal combustion engine, The exhaust pipe of the internal combustion engine is provided with a filter, a first catalyst, a second catalyst, a first urea solution supply unit, and a second urea solution supply unit. The first catalyst is coated on the filter, or is provided in the exhaust pipe upstream of the filter. The second catalyst is provided downstream of the filter in the exhaust pipe. The first urea water supply unit supplies urea water to the first catalyst, The second urea water supply unit supplies urea water to the second catalyst. The control device is An acquisition unit that acquires the temperature of the filter during the regeneration of the filter, A first control unit that controls the first urea water supply unit, The system comprises a second control unit that controls the second urea water supply unit, A control device for an internal combustion engine, wherein, during the regeneration of the filter, if the temperature is below a predetermined value, the first control unit stops supplying the urea water from the first urea water supply unit, and the second control unit supplies the urea water from the second urea water supply unit.

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