Engine starting control device

Abstract

To achieve stable combustion over a wide air-fuel ratio.SOLUTION: A start control device for an engine, in which fuel containing alcohol is directly injected into a cylinder, changes fuel injection setting in accordance with a cooling water temperature. At the cooling water temperature of equal to or higher than B°C, the start control device for the engine performs collective injection in an intake stroke, and at the cooling water temperature of lower than B°C, the start control device for the engine performs injection in the former stage of a compression stroke when performing multi-stage injection in the compression stroke.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an engine starting control device.

Background Art

[0002] In recent years, FFV (Flexible Fuel Vehicle) and the like that can use a fuel obtained by mixing a conventional fuel such as gasoline or light oil and an alternative fuel such as ethanol at an arbitrary ratio have become widespread. In an FFV, for example, fuels such as E85 (a mixed fuel of 85% ethanol and 15% gasoline) and E100 (a fuel of 100% ethanol) are used.

[0003] Since ethanol has a higher flash point temperature than gasoline, when using a mixed fuel with a high ethanol concentration or an ethanol fuel, if the temperature in the combustion chamber of the cylinder (engine temperature) is low, the injected fuel becomes difficult to vaporize, and combustion cannot be properly performed.

[0004] Therefore, a technique is known in which fuel is injected in the later stages of the compression stroke to take advantage of adiabatic compression in the cylinder and promote fuel vaporization. For example, a technique is known in which, when the alcohol concentration of the fuel is above a predetermined value and the engine temperature, etc., is below a predetermined value, the fuel injection termination time of the fuel injector is set to the compression stroke during the starting of the internal combustion engine and / or for a predetermined period after starting. In addition, a technique is known in which, when the temperature state of the engine body is below a predetermined temperature and the load state of the engine body is above a predetermined load, the fuel is supplied into the cylinder within the range from the intake stroke to the compression stroke, and when the concentration of the special fuel in the fuel is higher than predetermined, the amount of fuel injected by the fuel injector during the compression stroke is greater than the amount of fuel injected during the intake stroke. Furthermore, in a direct injection engine in which alcohol-containing fuel is directly injected into the cylinder, a technique is known in which, when the direct injection engine is cold-started from a state where the engine temperature is below a predetermined temperature, the first fuel injection is performed into the cylinder after the start of cranking and during the latter half of the compression stroke, and the timing of the fuel injection performed after combustion in the cylinder is advanced compared to the timing of the first fuel injection. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-037968 [Patent Document 2] Japanese Patent Publication No. 2014-206117 [Patent Document 3] Japanese Patent Publication No. 2013-224621 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Furthermore, it is known that increasing the air-fuel ratio improves fuel efficiency. However, when fuel injection is performed in the later stages of the compression stroke, misfires may be more likely to occur when the air-fuel ratio is increased.

[0007] The objective of the present invention is to provide an engine starting control device that can achieve stable combustion over a wide range of air-fuel ratios. [Means for solving the problem]

[0008] In one embodiment, the engine starting control device is an engine starting control device in which an alcohol-containing fuel is directly injected into the cylinder, and the fuel injection setting is changed according to the coolant temperature. When the coolant temperature is B°C or higher, the engine starting control device performs a single injection during the intake stroke, and when the coolant temperature is below B°C, it performs multi-stage injection during the compression stroke, and injects in the stage before the compression stroke.

[0009] According to one embodiment, stable combustion can be achieved over a wide range of air-fuel ratios. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a longitudinal cross-sectional view showing an example of the configuration of an engine cylinder and starting control device. [Figure 2] Figure 2 is a functional block diagram showing an example of the functional configuration of an ECU (Engine Control Unit) for engine starting control. [Figure 3] Figure 3 shows an example of the relationship between temperature, fuel alcohol concentration, and engine starting control. [Figure 4] Figure 4 is a graph showing the changes in engine speed over time. [Figure 5] Figure 5 is a flowchart showing an example of the processing flow performed by the ECU of the engine start control device. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following, coordinate axes may be shown with the direction in which the piston 12 of the engine 1, which will be described later, slides as the Z-axis direction. First, the schematic configuration of the engine in an embodiment of the present invention will be described using Figure 1. Figure 1 is a longitudinal cross-sectional view showing an example of the configuration of the engine cylinders and starting control device. The engine 1 is mounted in a vehicle such as a four-wheeled automobile.

[0012] As shown in Figure 1, the engine 1 comprises a cylinder consisting of a cylinder 10 having a bore wall 22 and a cylinder head 23, and a piston 12. The cylinder head 23, piston 12, and bore wall 22 constitute a combustion chamber 13. The engine 1 is a direct injection engine that injects fuel directly into the combustion chamber 13. The engine 1 may have multiple cylinders.

[0013] The cylinder head 23 includes an intake valve 15 and an exhaust valve 17. The intake valve 15 introduces air flowing through the intake port 14 into the combustion chamber 13. The exhaust valve 17 exhausts the combustion gases generated in the combustion chamber 13 through the exhaust port 16. Note that there may be multiple intake valves 15 and exhaust valves 17.

[0014] An injector 19 and a spark plug 18 are installed in the cylinder head 23, facing into the combustion chamber 13. The injector 19 forms a fuel-air mixture by injecting fuel supplied from the fuel pipe 11 into the combustion chamber 13, into which air is introduced from the intake port 14. The spark plug 18 is installed directly above the combustion chamber 13, between the intake valve 15 and the exhaust valve 17, and ignites the fuel-air mixture in the combustion chamber 13.

[0015] During the intake stroke, when the intake valve 15 opens and the piston 12 moves downward in the negative Z-axis direction, air is drawn into the combustion chamber 13 from the intake port 14. Subsequently, during the compression stroke following the intake stroke, as the piston 12 moves upward in the positive Z-axis direction, the air drawn into the combustion chamber 13 is compressed.

[0016] The piston 12 is installed below the combustion chamber 13 and slides along the bore wall surface 22 of the combustion chamber 13. The other end of the connecting rod 20 connected below the piston 12 is connected to the crankshaft 21.

[0017] The explosion force of the air-fuel mixture generated in the combustion chamber 13 generates the vertical movement of the piston 12. The vertical movement of the piston 12 is converted into the rotational movement of the crankshaft 21 to generate the driving force of the vehicle on which the engine is mounted. The crankshaft 21 transmits the driving force to a driving wheel (not shown) via a speed reducer (not shown), for example.

[0018] The crank angle sensor 31 measures the rotational angle of the crankshaft 21. The crank angle sensor 31 is installed in the vicinity of the crankshaft 21. The crank angle sensor 31 measures, for example, the rotational angle of a disk provided with slits around it and rotating together with the crankshaft 21 installed around the crankshaft 21 by an optical element such as a phototransistor or an electromagnetic pickup.

[0019] The air-fuel ratio sensor 32 measures the oxygen concentration in the exhaust gas. The air-fuel ratio sensor 32 is installed, for example, in the exhaust port 16. As the air-fuel ratio sensor 32, for example, an O2 sensor, an A / F sensor, or the like is used.

[0020] The water thermometer 33 measures the water temperature of the cooling water of the engine 1.

[0021] The alcohol concentration sensor 34 detects the concentration of alcohol in the fuel in the fuel pipe 11.

[0022] Note that the engine 1 may be provided with other sensors such as a cylinder pressure sensor that measures the pressure fluctuation in the combustion chamber 13.

[0023] Engine 1 is controlled by an ECU 25 (Electronic Control Unit). The ECU 25 is equipped with a microcontroller (microcomputer), which includes, for example, a CPU, non-volatile memory such as flash memory, and volatile memory such as DRAM (Dynamic Random Access Memory). Various sensors, such as the crank angle sensor 31, air-fuel ratio sensor 32, water temperature gauge 33, and alcohol concentration sensor 34 shown in Figure 1, are connected to the ECU 25, and detection signals from these connected sensors are input to it. By working in conjunction with these sensors, the ECU 25 functions as a starting control device in this embodiment.

[0024] The ECU 25 implements the temperature acquisition unit 41, concentration acquisition unit 42, determination unit 43, injection control unit 44, and crank angle detection unit 45 shown in Figure 2 by loading a control program stored in ROM (Read Only Memory) or the like into RAM (Random Access Memory) and operating it. Figure 2 is a functional block diagram showing an example of the functional configuration of the ECU of an engine start control device. Note that some or all of these functional units may be implemented by dedicated hardware.

[0025] The temperature acquisition unit 41 acquires the coolant temperature from, for example, the water thermometer 33 shown in Figure 1. The temperature acquisition unit 41 substitutes the acquired coolant temperature X for the engine temperature inside the cylinder 10. The temperature acquisition unit 41 may also use the temperature acquired by another temperature sensor as the engine temperature.

[0026] The concentration acquisition unit 42 acquires the alcohol concentration of the fuel in the fuel pipe 11 from, for example, the alcohol concentration sensor 34 shown in Figure 1.

[0027] The determination unit 43 determines the fuel injection timing and fuel pressure based on the water temperature obtained by the temperature acquisition unit 41 and the alcohol concentration obtained by the concentration acquisition unit 42. Specifically, the determination unit 43 determines the timing for fuel injection by the injector 19 based on the relationship between the coolant temperature, the fuel alcohol concentration, and the fuel injection angle, as shown in Figure 3. Figure 3 is a diagram showing an example of the relationship between temperature, fuel alcohol concentration, and engine start control. The information showing the correspondence between water temperature, fuel alcohol concentration, and engine start control, as shown in Figure 3, is stored in, for example, ROM or RAM.

[0028] The injection control unit 44 instructs the injector 19 on the timing, injection ratio, and fuel pressure of fuel injection based on the determination result from the determination unit 43. At that time, the injection control unit 44 instructs fuel injection at the timing determined based on the crank angle detected by the crank angle detection unit 45.

[0029] The crank angle detection unit 45 detects the current crank angle or detects that the engine 1 has started, for example, based on changes in crank angle information acquired from the crank angle sensor 31.

[0030] Next, the determination contents of the determination unit 43 will be explained using Figure 3. For example, if the water temperature X is 90°C or higher, stable combustion is possible even with single injection (bulk injection) during the intake stroke, regardless of the alcohol concentration. In this case, the determination unit 43 decides to perform single injection when the crank angle is 200°. Note that a water temperature of 90°C is an example of the second threshold B°C, which will be explained later.

[0031] If the water temperature X is below 90°C, the ECU 25 determines that fuel injection will occur during the compression stroke so that the air-fuel mixture is formed by utilizing the adiabatic compression action within the combustion chamber 13 during the compression stroke. In particular, with fuels containing alcohol such as ethanol, the latent heat of vaporization of ethanol is high, so in order to suppress the temperature drop in the combustion chamber 13 due to the heat of vaporization, the ECU 25 determines that fuel will be injected in segments (multi-injection).

[0032] For example, if the water temperature X is 40°C or higher but less than 90°C, the determination unit 43 determines that fuel will be injected in two stages: once when the crank angle is 160° and again when the crank angle is 120°. In this case, the fuel injection ratio will be, for example, 5-5, with the same amount of fuel injected in the first and second stages. Note that a water temperature of 40°C is an example of the first threshold A°C, which will be explained later. Furthermore, if the alcohol concentration in the fuel is low, for example, if the ethanol concentration is less than 22%, the control may be such that split injection is not performed, or fuel injection is performed during the intake stroke.

[0033] In the process described above, the determination unit 43 determines the timing and injection ratio of fuel injection regardless of the alcohol concentration of the fuel. On the other hand, if the water temperature X is lower than 40°C, the determination unit 43 may change the injection timing, etc., according to the alcohol concentration of the fuel.

[0034] For example, if the water temperature X is between 15°C and 40°C, the determination unit 43 decides to increase the number of injections from two to three, and to perform fuel injection in the later stages of the compression stroke as well. Note that a water temperature of 15°C is an example of the third threshold d°C, which will be explained later.

[0035] In this case, the fuel injection ratio will be, for example, 4:4:2. That is, the ratio of the amount of fuel injected before the compression stroke to the amount of fuel injected after the compression stroke will be 8:2.

[0036] In this process, the determination unit 43 determines the timing of the third fuel injection according to the alcohol concentration Y of the fuel. For example, if the alcohol concentration Y of the fuel is 60% or higher, such as with E100 fuel, the determination unit 43 determines that the third fuel injection will occur on the retarded side of the later stages of the compression stroke, for example, when the crank angle is 30°. Note that an alcohol concentration of 60% is an example of a threshold e%, which will be explained later.

[0037] On the other hand, if the fuel alcohol concentration Y is less than 60%, such as with E22 fuel, the determination unit 43 determines that the third injection will be performed on the advanced side of the later stages of the compression stroke, for example, when the crank angle is 80°.

[0038] Furthermore, when the water temperature X is even lower than 15°C, and the fuel alcohol concentration Y is 60% or higher, such as in the E100, it is necessary to inject fuel near top dead center. In this case, if the ECU25 determines, for example, that the fuel alcohol concentration Y is 60% or higher, it decides to inject fuel at a position even closer to top dead center than when the water temperature X is 15°C or higher, for example, when the crank angle is 15°.

[0039] Furthermore, near top dead center of compression, the pressure inside the combustion chamber 13 increases, so the fuel pressure when injecting fuel from the injector 19 also needs to be increased. In this case, the ECU 25 determines that the fuel pressure should be 20 MPa.

[0040] In this process, by injecting fuel in stages prior to the compression stroke (when the crank angle is 160° and 120°), the airflow generated by the piston's upward movement suppresses fuel adhesion to the bore wall 22, thereby promoting premixing of fuel and air. This suppresses misfires.

[0041] In a lean-burn state with an improved air-fuel ratio, misfires are more likely to occur when fuel is injected near top dead center, as shown in Figure 4. Figure 4 is a graph showing the change in engine speed.

[0042] In Figure 4, the solid line P shows the change in engine speed when fuel is injected near top dead center of compression in a non-lean burn state. The dashed line Q shows the change in engine speed when fuel is injected near top dead center of compression in a lean burn state. As shown in Figure 4, in a lean burn state, when fuel is injected all at once, misfires are more likely to occur after the initial combustion, resulting in larger fluctuations in engine speed.

[0043] On the other hand, in Figure 4, the graph indicated by the dashed line R shows the change in engine speed when fuel is injected in a split manner under lean-burn conditions. The timing of the split fuel injection is when the crank angle is 160°, 120°, and 15°, respectively, and the fuel injection ratio is 1:1:8.

[0044] When fuel is injected in segments, misfires are less likely to occur compared to when it is injected all at once. In this case, as shown in Figure 4, the fluctuation in engine speed becomes smaller, so it approaches the trend of engine speed when not in a lean-burn state.

[0045] Furthermore, the split injection ratio when the water temperature X is below 15°C may be appropriately changed depending on the water temperature X and alcohol concentration Y. For example, when the water temperature X is 0°C or higher, the fuel injection ratio at each crank angle may be set to 2:2:6, as shown in Figure 3. In this case, the ratio of the fuel injection amount before the compression stroke to the fuel injection amount after the compression stroke will be 4:6.

[0046] On the other hand, if the fuel injection ratio in the pre-compression stroke is further reduced, for example to 0.5:0.5:9, the premix becomes significantly leaner, making misfires more likely. Therefore, even when the split injection ratio in the post-compression stroke is increased, it is preferable to keep the ratio of fuel injection amount in the pre-compression stroke to fuel injection amount in the post-compression stroke at 2:8 or less.

[0047] Furthermore, when the water temperature X is less than 15°C and the fuel alcohol concentration Y is low, for example, when the ethanol concentration is less than 60%, the ECU 25 decides to perform split injection in the later stages of the compression stroke, injecting fuel on the advance side rather than near top dead center. In this case, fuel injection in the later stages of the compression stroke is performed at the timing when the crank angle is 80°, for example, as in the case when the water temperature X is 15°C or more and less than 40°C. Note that on the advance side, the pressure in the combustion chamber 13 is lower than near top dead center, so the setting may be such that the fuel pressure is not increased beyond 10 MPa. Also, the timing of fuel injection in the earlier stages of the compression stroke and the fuel injection ratio may be the same as in the case when the fuel alcohol concentration Y is 60% or more, as shown in Figure 3.

[0048] (Process flow performed by the startup control device) Figure 5 illustrates the processing flow of the engine start control device. Figure 5 is a flowchart showing an example of the processing flow performed by the ECU of the engine start control device.

[0049] The crank angle detection unit 45 detects engine starting, for example, based on a change in crank angle information (step S101). Next, the temperature acquisition unit 41 acquires the coolant water temperature X (step S102).

[0050] The determination unit 43 then determines whether the cooling water temperature X is less than the first threshold A°C (step S110). If it is determined that the water temperature X is less than A°C (step S110: Yes), the process proceeds to step S111. On the other hand, if it is determined that the water temperature X is A°C or greater (step S110: No), the process proceeds to step S120. The first threshold A°C for the water temperature X is, for example, 20°C to 60°C, and preferably 40°C as shown in Figure 3, but the specific threshold is just an example and is not limited to this. The same applies to the second threshold B°C and the third threshold d°C for the water temperature X, and the threshold e% for the alcohol concentration Y, which will be described below.

[0051] In step S110, if it is determined that the water temperature X is less than A°C, the determination unit 43 decides to perform multi-injection in the pre-compression stage and the post-compression stage (step S111). Then, the process proceeds to step S130.

[0052] In step S110, if it is determined that the water temperature X is A°C or higher, it is determined whether the water temperature X is less than a second threshold B°C (step S120). In step S120, if it is determined that the water temperature X is less than B°C (step S120: Yes), the determination unit 43 decides to perform multi-injection in the preceding stage of the compression stroke (step S121) and proceeds to step S160. On the other hand, in step S120, if it is determined that the water temperature X is B°C or higher (step S120: No), the determination unit 43 decides to perform single injection in the intake stroke (step S122) and proceeds to step S160.

[0053] In step S130, the determination unit 43 determines whether the cooling water temperature X is less than the third threshold d°C. If it is determined that the water temperature X is less than the third threshold d°C (step S130: Yes), the process proceeds to step S131. On the other hand, if it is determined that the water temperature X is greater than or equal to the third threshold d°C (step S130: No), the process proceeds to step S133.

[0054] In step S130, if it is determined that the water temperature X is less than d°C, the determination unit 43 decides to increase the injection ratio in the later stages of the compression stroke among the multi-injection (step S131). Then, the concentration acquisition unit 42 acquires the alcohol concentration Y (step S132), and the process proceeds to step S140.

[0055] In step S130, if it is determined that the water temperature X is d°C or higher, the determination unit 43 decides to reduce the injection ratio in the later stages of the compression stroke among the multi-injection (step S133). Then, the concentration acquisition unit 42 acquires the alcohol concentration Y (step S134), and the process proceeds to step S150.

[0056] In step S140, the determination unit 43 determines whether the alcohol concentration Y of the fuel in the fuel pipe 11 is equal to or greater than the threshold e%. If it is determined that the alcohol concentration Y is equal to or greater than the threshold e% (step S140: Yes), the process proceeds to step S141. On the other hand, if it is determined that the alcohol concentration Y is less than the threshold e% (step S140: No), the process proceeds to step S143.

[0057] In step S140, if it is determined that the alcohol concentration Y is e% or greater, the determination unit 43 decides to increase the fuel pressure to, for example, 20 MPa (step S141). The determination unit 43 then decides to retard the injection timing in the later stage of the compression stroke among the multi-injection injections, for example, to 15° (step S142), and proceeds to step S160.

[0058] In step S140, if it is determined that the alcohol concentration Y is less than e%, the determination unit 43 decides to reduce the fuel pressure to, for example, 10 MPa (step S143). The determination unit 43 then decides to advance the injection timing in the later stage of the compression stroke in the multi-injection process, for example, to 80° (step S144), and proceeds to step S160.

[0059] Returning to step S150, the determination unit 43 determines whether the alcohol concentration Y of the fuel in the fuel pipe 11 is greater than or equal to the threshold e% (step S150). If it is determined to be greater than or equal to the threshold e% (step S150: Yes), the process proceeds to step S151. On the other hand, if it is determined to be less than the threshold e% (step S150: No), the process proceeds to step S152.

[0060] In step S150, if it is determined that the alcohol concentration Y is e% or greater, the determination unit 43 decides to set the injection timing in the later stage of the compression stroke in the multi-injection to the retarded side, for example, 30° (step S151), and proceeds to step S160.

[0061] In step S150, if it is determined that the alcohol concentration Y is less than e%, the determination unit 43 decides to advance the injection timing in the later stage of the compression stroke among the multi-injection injections, for example to 80° (step S152), and proceeds to step S160.

[0062] The injection control unit 44 then controls the injector 19 to inject fuel at the fuel pressure, injection ratio, and injection timing determined by the determination unit 43 (step S160). Note that the fuel injection timing for the second and subsequent injections may be set to remain unchanged from the first injection if, for example, there is no change in the water temperature X or alcohol concentration Y.

[0063] As described above, the engine starting control device in the embodiment is an engine starting control device in which an alcohol-containing fuel is directly injected into the cylinder, and the fuel injection setting is changed according to the coolant temperature. When the coolant temperature is above B°C, the engine starting control device performs a single injection during the intake stroke, and when the coolant temperature is below B°C, it performs injection in the preceding stage of the compression stroke when performing multi-stage injection during the compression stroke. With this control, stable combustion can be achieved over a wide range of temperatures and fuel alcohol concentrations without the need for a temperature control device or variable valve timing mechanism.

[0064] The injection timings, fuel pressures, and injection ratios described above are merely examples and are not limited to those shown. For example, in the relationship between water temperature, alcohol concentration, and fuel injection as shown in Figure 3, a configuration that smoothly changes the injection timing or injection ratio by linear interpolation may be used in the E20-E60 range (alcohol concentration between 20% and 60%).

[0065] Furthermore, the determination unit 43 may be configured to perform only some of the branching determinations shown in Figure 5. For example, the determination unit 43 may be configured to omit the temperature-based determination shown in step S120 of Figure 5, or it may be configured not to perform the alcohol concentration-based determination shown in step S150.

[0066] Although the above configuration is described as an FFV, the technology disclosed herein can be broadly applied to vehicles equipped with engines that are supplied with alcohol-containing fuel, such as hybrid vehicles equipped with electric motors, even if they are not FFVs.

[0067] While embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms. Furthermore, various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment is included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0068] 1 Engine 10 cylinders 11 Fuel pipe 12 pistons 13 Combustion chamber 14 Intake Ports 15 Intake valve 16 exhaust ports 17 Exhaust valve 18 Spark plugs 19 Injectors 20 Connecting Rods 21 Crankshaft 22 Bore wall 23 Cylinder head 25 ECU 31 Crank angle sensor 32. Air-fuel ratio sensor 33 Water temperature gauge 34. Alcohol concentration sensor 41 Temperature acquisition section 42 Concentration acquisition section 43 Judgment section 44 Injection Control Unit 45 Crank angle detection unit

Claims

1. An engine starting control device in which an alcohol-containing fuel is directly injected into the cylinder, This system changes the fuel injection settings according to the coolant temperature. If the coolant temperature is above B°C, a single injection is performed during the intake stroke. When the coolant temperature is between A°C and B°C, during multi-stage injection in the compression stroke, the injection ratio between the pre-compression and post-compression stages is varied within the range of 8:2 to 10:0 according to the temperature from the high-temperature side to the low-temperature side. When the cooling water temperature is below A°C, during multi-stage injection in the compression stroke, the injection ratio between the pre-compression and post-compression stages is varied within a range of 4:6 to 2:8, depending on the temperature from the high-temperature side to the low-temperature side. A°C is a lower temperature than B°C. Engine starting control device.

2. This system changes the fuel injection settings according to the alcohol concentration. If it is determined that the alcohol concentration is above a predetermined threshold, during multi-stage injection in the compression stroke, the fuel pressure is increased and injection is performed, and the subsequent injection is performed at a retarded ignition timing in the later stages of the compression stroke. The engine starting control device according to claim 1.

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