WO2012168793A1

WO2012168793A1 - Control unit and control method for internal combustion engine

Info

Publication number: WO2012168793A1
Application number: PCT/IB2012/001224
Authority: WO
Inventors: Ryo Michikawauchi
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2011-06-10
Filing date: 2012-06-08
Publication date: 2012-12-13
Also published as: JP2012255423A

Abstract

A control unit (100) for an internal combustion engine in which diesel fuel and alcohol are used singly or in combination as engine fuel, includes: an alcohol concentration detection unit (420) that detects an alcohol concentration in the engine fuel; an after-injection control unit (440) that executes a control for performing an after-injection after a main injection of the engine fuel; and an after-injection amount determination unit (430) that determines an amount of fuel injected by the after-injection such that the lower the alcohol concentration in the engine fuel is, the smaller the amount is.

Description

CONTROL UNIT AND CONTROL METHOD FOR INTERNAL COMBUSTION

ENGINE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a control unit and a control method for an internal combustion _¾ engine in which diesel fuel and alcohol are used singly or in combination as engine fuel.

2. Description of Related Art

[0002] As an internal combustion engine of the above-mentioned type, there is known an internal combustion engine in which a blended fuel obtained by blending multiple types of fuels together (e.g., a blend of diesel fuel and alcohol) is used. The blend ratio of the blended fuel may be made variable, for example, by storing the fuels in different fuel tanks and blending the fuels from the respective fuel tanks together. In this case, the blend ratio of the blended fuel is determined as appropriate depending on various conditions such as the operating condition of the internal combustion engine. For example, Japanese Patent Application Publication No. 06-307307 (JP 06-307307 A) describes a technique of controlling a diesel fuel supply amount depending on the amount of diesel fuel remaining in a fuel injection valve. JP 06-307307 A describes that the technique makes it possible to avoid the situation where only one of the fuels is excessively injected to such an extent that the exhaust gas property deteriorates. Japanese Patent Application Publication No. 2003-161178 (JP 2003-161178 A) describes a technique in which after the duration of a main injection using diesel fuel reaches a predetermined duration, alcohol-blended fuel is injected. Japanese Patent Application Publication No. 59-108844 (JP 59-108844 A) describes a technique of performing a three-step injection in which diesel fuel is injected in a first step, a blend of diesel fuel and alcohol is injected in a second step, and only diesel fuel is injected in a third step. [0003] Japanese Patent Application Publication No. 2007-187149 (JP 2007-187149 A) and Japanese Patent Application Publication No. 2003-278587 (JP 2003-278587 A) each describe a technique in which, in an internal combustion engine where diesel fuel is used, after a main injection that is performed mainly for fuel supply to the engine, an after-injection is performed to inject a small amount of fuel. JP 2007-187149 A and JP 2003-278587 A describe that, with the after-injection, particulate matter (PM) generated by the main injection is burned, which reduces the amount of PM emissions.

[0004] With the after-injection described above, the PM is burned. However, the after-injection itself also generates PM. Therefore, if an excessive amount of fuel is injected by the after-injection, the amount of PM may be increased, conversely.

[0005] Specifically, when a blend of diesel fuel and alcohol is used, as the ratio of alcohol in the blended fuel decreases, the amount of PM generated by the after- injection increases, resulting in increases in the amount of PM emissions.

[0006] JP 06-307307 A, JP 2003-161178 A, and JP 59-108844 A have description regarding a blend of diesel fuel and alcohol but does not have any description regarding an after-injection. In JP 2007-187149 A and JP 2003-278587 A, description regarding an after injection is provided, but using a blend of diesel fuel and alcohol is not taken into account at all. Therefore, according to the techniques described above, if an after-injection is performed using an alcohol-blended fuel, the amount of PM emissions may not be reliably reduced.

SUMMARY OF THE INVENTION

[0007] The invention provides a control unit and a control method for an internal combustion engine in which an alcohol-blended fuel is used, the control unit making it possible to reduce the amount of PM emissions.

[0008] A first aspect of the invention relates to a control unit for an internal combustion engine in which diesel fuel and alcohol are used singly or in combination as engine fuel. The control unit includes: an alcohol concentration detection unit that detects an alcohol concentration in the engine fuel; an after- injection control unit that performs an after-injection after a main injection of the engine fuel; and an after-injection amount determination unit that determines an amount of fuel injected by the after-injection such that the lower the alcohol concentration in the engine fuel is, the smaller the amount is.

[0009] A second aspect of the invention relates to a control method for an internal combustion engine in which diesel fuel and alcohol are used singly or in combination as engine fuel. The control method includes: detecting an alcohol concentration in the engine fuel; controlling an injector , which is included in the internal combustion engine, so as to perform an after- injection after a main injection of the engine fuel; and determining an amount of fuel injected by the after-injection such that the lower the alcohol concentration in the engine fuel is, the smaller the amount is.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Features, advantages, and technical and industrial significance of exemplary embodiments 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 diagram that shows the overall configuration of an engine system;

FIG. 2 is a block diagram that shows the configuration of an electronic control unit (ECU);

FIG. 3 is a flowchart that shows an after-injection control process performed by a control unit for an internal combustion engine according to an embodiment of the invention; and .

FIG. 4 is a graph that shows the correlation between an alcohol concentration and an after-injection amount.

DETAILED DESCRIPTION OF EMBODIMENTS

[0011] An internal combustion engine according to the invention is, for example, an internal combustion engine mounted in a vehicle. In the internal combustion engine, power generated by combustion of fuel in a combustion chamber inside a cylinder is , extracted as drive power via physical or mechanical transmission means such as a piston, a connecting rod, and a crankshaft.

[0012] Hereafter, an embodiment of the invention will be described with reference to the accompanying drawings.

[0013] First, the overall configuration of an engine system according to the embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram that shows the overall configuration of the engine system. Note that, for ease of description, FIG. 1 shows only elements that are selected from among elements that constitute the engine system and that are closely associated with the embodiment, and the other elements are omitted in FIG. 1.

[0014] As shown in FIG. 1, the engine system according to the embodiment mainly includes an ECU 100, a compressor 110, a turbine 120, an engine 200, and a fuel tank 300.

[0015] The ECU 100 may function as a control unit for an internal combustion engine according to the invention. The ECU 100 includes, for example, a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). That is, the ECU 100 is an electronic control unit that controls the overall operation of the engine system. The ECU 100 executes various controls in accordance with control programs stored in the ROM, for example. The specific configuration of the ECU 100 will be described in more detail later.

[0016] The compressor 110 compresses the supplied air, and the compressed air is supplied downstream of the compressor 110. The turbine 120 is rotated by the exhaust gas supplied from the engine 200 through an exhaust pipe 215. The turbine 120 +is connected to the compressor 110 via a shaft, and rotates together with the compressor 110. That is, the turbine 120 and the compressor 110 function as a turbocharger.

[0017] The engine 200 is a diesel engine that serves as a power source of a vehicle such as an automobile, and may function as the internal combustion engine in the invention. The engine 200 is, for example, an in-line four-cylinder engine in which four cylinders 201 are arranged in a line inside a cylinder block.

[0018] An air cleaner 101, an intake control valve 103, the compressor 110, an intercooler 113, and a throttle valve 208 are provided on an intake side of the engine 200 (i.e., upstream of the cylinders 201).

[0019] The air cleaner 101 purifies air taken in from the outside, and supplies the purified air to the compressor 110 through an intake pipe 102. The amount of air that is supplied from the air cleaner 101 is controlled by the intake control valve 103. The intercooler 1 13 provided downstream of the compressor 110 cools the intake air to increase the air supercharging efficiency.

[0020] The throttle valve 208 is provided downstream of the intercooler 113. The drive state of the throttle valve 208 is controlled by a throttle valve motor 209 that is electrically connected to the ECU 100. The ECU 100 controls the throttle valve motor 209 so as to achieve a throttle opening degree that corresponds to an operation amount of an accelerator pedal (not shown). Alternatively, the throttle opening degree may be adjusted without depending on a driver's intention, by controlling the throttle valve motor 209 independently of the operation amount of the accelerator pedal. That is, the throttle valve 208 may be configured as a type of electronically-controlled throttle valve.

[0021] The air-fuel mixture introduced into each cylinder 201 from the intake side of the engine 200 is ignited by compression ignition, whereby a power stroke is performed in the cylinder 201. After the power stroke, the burned air-fuel mixture (partially containing unburned air-fuel mixture) is discharged to an exhaust port (not shown) in an exhaust stroke subsequent to the power stroke. The exhaust gas discharged to the exhaust port is introduced into the exhaust pipe 215.

[0022] An EGR pipe 117, an EGR control valve 118, the turbine 120, and an exhaust gas control catalyst 122 are provided on an exhaust side of the engine 200 (i.e., downstream of the cylinders 201). Here, the EGR control valve 118 functions as a high pressure loop EGR control valve that returns an exhaust pressure higher than an intake pressure to the intake side of the engine 200. [0023] The exhaust gas discharged from the engine 200 to the exhaust pipe 215 may return to an intake pipe 207 on the intake side of the engine 200 through the EGR pipe 117. The EGR pipe 117 is provided with the EGR control valve 118 so that the amount of exhaust gas (EGR gas) that is returned to the intake pipe 207 is adjusted. The EGR control valve 118 may be an electromagnetic on-off valve that is placed in any one of two states, which are a fully-open state and a fully-closed state, for example. The EGR control valve 118 is electrically connected to the ECU 100, and the on-off state of the EGR control valve 118 is controlled by the ECU 100.

[0024] The exhaust gas control catalyst 122 is provided in an exhaust pipe 121. The exhaust gas control catalyst 122 removes hydrocarbon (HC), carbon dioxide (C0₂), and nitrogen oxide (NOx) contained in the exhaust gas that has passed through the turbine 120.

[0025] The fuel tank 300 stores a blend of diesel fuel and alcohol, which is the fuel used in the engine 200. The fuel stored in the fuel tank 300 is supplied to injectors 210 through a fuel supply pipe 310. Each injector 210 injects the supplied fuel into the corresponding cylinder 201. Note that a fuel injection pressure of each injector 210 is variable and controlled by the ECU 100.

[0026] The amount of fuel stored in the' fuel tank 300 is detected by a fuel sensor 320. Information regarding the amount of fuel stored in the fuel tank 300 (stored fuel amount information) is transmitted to the ECU 100. In addition, the alcohol concentration in the fuel is detected by an alcohol concentration sensor 330. Information regarding the alcohol concentration (alcohol concentration information) is transmitted to the ECU 100. Note that the alcohol concentration in the fuel may be detected, for example, in the fuel supply pipe 310, instead of being detected in the fuel tank 300.

[0027] Next, the specific configuration of the ECU 100, which is the control unit for an internal combustion engine according to the embodiment, will be described with reference to FIG. 2. FIG. 2 is a block diagram that shows the configuration of the ECU 100. [0028] As shown in FIG. 2, the ECU 100 includes a fuel supply detection unit 410, an alcohol concentration detection unit 420, an after- injection amount determination unit 430, and an after-injection control unit 440.

[0029] The fuel supply detection unit 410 detects refueling of the fuel tank 300. Specifically, the fuel supply detection unit 410 detects the amount of fuel remaining in the fuel tank 300 using the fuel sensor 320. Based on information regarding the remaining fuel amount (remaining fuel amount information), the fuel supply detection unit 410 determines that refueling has been performed if the remaining fuel amount has increased. The information that refueling has been detected by the fuel supply detection unit 410 is transmitted to the alcohol concentration detection unit 420.

[0030] The alcohol concentration detection unit 420 detects the alcohol concentration in the fuel stored in the fuel tank 300. Specifically, the alcohol concentration detection unit 420 detects the alcohol concentration in the fuel based on the alcohol concentration information obtained by the alcohol concentration sensor 330 provided at the fuel tank 300. Note that the alcohol concentration may be an indirectly obtained value through calculation (i.e., estimated value) instead of a value detected directly based on the alcohol concentration information. The detected alcohol concentration is transmitted to the after-injection amount determination unit 430.

[0031] The after-injection amount determination unit 430 determines the amount of fuel that is injected from each injector 210 in an after-injection (referred to as "after-injection amount" below as appropriate). In other words, the after-injection amount determination unit 430 adjusts the after-injection amount. Specifically, the after- injection amount determination unit 430 determines the after-injection amount depending on the alcohol concentration in the fuel, which is detected by the alcohol concentration detection unit 420. Note that the after-injection amount determination unit 430 may determine the after-injection amount using other parameters in addition to the alcohol concentration. Alternatively, the after-injection amount determination unit 430 may store a plurality of after- injection amount control maps respectively set for different degrees of alcohol concentration, and determine the after-injection amount by switching the control map among the plurality of control maps depending on the detected alcohol concentration.

[0032] After a main injection that is performed mainly for fuel supply to the engine 200, the after-injection control unit 440 controls various portions of the engine 200 so as to perform an after-injection for burning PM generated by the main injection. The injection amount for the main injection is determined depending on the loads on the internal combustion engine (i.e., the throttle opening degree and the operation amount of an accelerator pedal, for example). Meanwhile, a relatively small amount of fuel is injected by the after-injection to burn the PM generated by the main injection, and the after-injection is perforrried after the main injection. Performing the after- injection reduces the amount of PM emissions.

[0033] The ECU 100 configured to include the various control units described above is a single electronic control unit. The operations of the various control units are all executed by the ECU 100. However, the physical, mechanical, and electrical configurations of the various control units according to the invention are not limited to the configurations described above. For example, the control units may be configured as various computer systems, such as a plurality of ECUs, various processing units, various controllers, or microcomputer devices. The ECU may include a micro processing unit (MPU), various processors and various controllers, in addition to at least one CPU, at least one ROM, and at least one RAM. Alternatively, the ECU may further include, as appropriate, various storage means such as a buffer memory and a flash memory.

[0034] Next, a process performed by the ECU 100, which is the control unit for an internal combustion engine according to the embodiment, and effects thereof will be described with reference to FIGS. 3 and 4. FIG. 3 is a flowchart that shows an after- injection control process performed by the control Unit for an internal combustion engine according to the embodiment. FIG. 4 is a graph that shows the correlation between an alcohol concentration and an after- injection amount.

[0035] As shown in FIG. 3, when the control unit for an internal combustion engine according to the embodiment is operated, first, the fuel supply detection unit 410 determines whether refueling has been performed (step SI 01 ). If refueling is not detected (step SlOl : No), steps SI 02 and SI 03 described below are skipped, and step SI 04 is executed.

[0036] If the fuel supply detection unit 410 determines that refueling has been performed (step S101 : Yes), the alcohol concentration detection unit 420 detects the alcohol concentration in the fuel (step SI 02). The alcohol concentration in the blended fuel stored in the fuel tank 300 changes if the fuel tank 300 is supplied with a blended fuel with a blend ratio different from that of the blended fuel that has been stored in the fuel tank 300. In other words, it is considered that the alcohol concentration in the blended fuel does not significantly change unless refueling is performed. Therefore, if the alcohol concentration is detected when refueling is detected, detection of the alcohol concentration is efficiently performed at a timing at which the alcohol concentration changes. That is, the alcohol concentration is detected when refueling is detected (specifically, after refueling is completed) instead of being detected constantly or periodically. In other words, refueling of the fuel tank 300 in the embodiment described above is monitored by the fuel supply detection unit 410.

[0037] After detection of the alcohol concentration, the after- injection amount determination unit 430 changes the control map for determining the after-injection amount based on the detected alcohol concentration (step SI 03). Specifically, the after-injection amount determination unit 430 stores a plurality of control maps that are respectively set for different degrees of alcohol concentration and used to determine the after-injection amount. The after-injection amount determination unit 430 selects the control map among the plurality of control maps, which corresponds to the detected alcohol concentration.

[0038] In the after-injections that are performed after the control map is changed, the after-injection amount determination unit 430 determines the after-injection amount based on the post-change control map. Each injector 210 is controlled by the after-injection control unit 440 so as to inject the fuel in the determined after-injection amount. Accordingly, the control unit for an internal combustion engine according to the embodiment executes the after-injection control based on alcohol concentration.

[0039] The above-described control maps for determining the after-injection amount are set such that the lower the alcohol concentration is, the smaller the after-injection amount is. Thus, the correlation between the alcohol concentration and the after- injection amount is as shown in FIG. 4, for example.

[0040] Alcohol contains oxygen in its molecules, and has a lower cetane number than that of diesel fuel. Therefore, as compared with diesel fuel, alcohol has the properties that the time required for alcohol to be ignited is long, alcohol is quickly vaporized because the boiling point of alcohol is low, and sprayed alcohol is easily atomized and vaporized because the kinetic viscosity and surface tension of alcohol are low. Thus, if the ratio of alcohol (i.e., alcohol concentration) in the blended fuel increases, the amount of PM generated by the after-injection decreases. Conversely, if the ratio of alcohol in the blended fuel decreases, the amount of PM generated by the after- injection increases.

[0041] Therefore, according to the embodiment, the after- injection amount is reduced when the alcohol concentration becomes lower, as described above. It is therefore possible to suppress an increase in the amount of PM generation due to a decrease in alcohol concentration. In other words, even if PM is more likely to be generated due to a change in the fuel property, the fuel injection amount is reduced accordingly to offset an increase in the PM. Accordingly, it is possible to reduce or maintain the amount of PM emissions as a whole.

[0042] · As described above, with the control unit for an internal combustion engine according to the embodiment, it is possible to reduce the amount of PM emissions in an internal combustion engine in which an alcohol-blended fuel is used.

[0043] In the above embodiment, a method of selecting a control map for the after-injection amount based on the alcohol concentration is described. However, any other method may be employed as long as the method is configured to set the smaller after injection amount as the alcohol concentration becomes lower. In other words, the concrete method for determining the after-injection amount is not particularly limited.

[0044] The invention is not limited to the embodiment described above. Various modifications may be made without departing from the spirit and scope of the invention as interpreted from the claims and the specification overall. A control unit and a control method for an internal combustion engine accompanying any such modification are obviously included in the technical scope of the invention.

Claims

CLAIMS:

1. _A control unit (100) for an internal combustion engine (200) in which diesel fuel and alcohol are used singly or in combination as engine fuel, the control unit comprising: an alcohol concentration detection unit (420). that detects an alcohol concentration in the engine fuel;

an after-injection control unit (440) that performs an after-injection after a main injection of the engine fuel; and

an after- injection amount determination unit (430) that determines an amount of fuel injected by the after- injection such that the lower the alcohol concentration in the engine fuel is, the smaller the amount is.

2. The control unit (100) for the internal combustion engine (200) according to claim 1, further comprising:

a fuel supply detection unit (410) that detects refueling a fuel tank (300) that stores the engine fuel,

wherein the alcohol concentration detection unit (420) detects the alcohol concentration in the engine fuel each time refueling is detected.

3. The control unit (100) for the internal combustion engine (200) according to claim 1 or 2, wherein the internal combustion engine (200) includes an injector (210) and the after-injection control unit (440) controls the injector (210) so as to perform the main injection and the after-injection.

4. A control method for an internal combustion engine (200) in which diesel fuel and alcohol are used singly or in combination as engine fuel comprising:

detecting an alcohol concentration in the engine fuel;

performing an after-injection of the engine fuel after a main injection of the engine fuel; and determining an amount of fuel injected by the after-injection such that the lower the alcohol concentration in the engine fuel is, the smaller the amount is.