Fuel injection control device for internal combustion engine

Abstract

To execute fuel injection so as to suppress unburned fuel flowing into a catalyst in an exhaust system to the extent possible while securing combustion stability at low temperature in a fuel direct injection type internal combustion engine that uses fuel containing a component difficult to vaporize.SOLUTION: In a fuel injection control device 10, injection operation control means is configured to in the case where an injection finish time point that is a time point from fuel injection start timing until after passage of an injection period length is a time point after ignition timing, delay injection of fuel to be injected from the ignition timing to the injection finish time point until after start of a next compression stroke.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine, and more particularly to a fuel injection control device for an internal combustion engine in which fuel is supplied in a direct injection manner.

Background Art

[0002] When an alcohol-containing fuel is used as the fuel of an internal combustion engine, since the fuel is difficult to vaporize, in a fuel direct injection type internal combustion engine, fuel injection control in a mode different from that when using gasoline fuel conventionally used has been variously proposed. For example, in Patent Document 1, in an internal combustion engine after cold start, in order to ensure a more stable and good combustion state, according to the engine temperature parameter, alcohol concentration, and the load of the internal combustion engine, fuel is injected in the intake stroke. It has been proposed to select one of the intake stroke injection and the compression stroke injection in which fuel is injected in the compression stroke.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, in a fuel injection type internal combustion engine, in order to improve combustion stability and to improve fuel vaporization, it is preferable to start fuel injection under the condition that the in-cylinder temperature exceeds the boiling point of the fuel components. In this regard, when using a fuel containing components that are difficult to vaporize, such as alcohol-containing fuel, particularly at low temperatures such as during engine startup, it is effective to start injection immediately before top dead center of the compression stroke where the in-cylinder temperature reaches the maximum temperature. However, due to fluctuations in the operating conditions of the internal combustion engine (engine speed, load factor, fuel pressure, etc.), the injection period may become longer than intended, and the injection end time may be after the ignition time. In that case, most of the fuel injected after the ignition time will flow into the exhaust system as unburned fuel and adhere to the catalyst. Then, since combustion does not occur in the cylinder during fuel injection cut-off, the unburned fuel adhering to the catalyst will undergo an oxidation reaction due to the oxygen flowing into the catalyst, and the catalyst temperature may reach a high temperature and cause melting of the catalyst. In order to avoid such a situation, for example, it is conceivable to execute fuel injection so that the fuel portion that will be injected after the ignition time is burned in the cylinder in the next combustion cycle.

[0005] Thus, the main problem of the present invention is to provide a control device for an internal combustion engine that executes fuel injection so as to suppress unburned fuel flowing into the catalyst of the exhaust system as much as possible while ensuring combustion stability even at low temperatures in a fuel injection type internal combustion engine using a fuel containing components that are difficult to vaporize.

Means for Solving the Problems

[0006] According to the present invention, the above problem is a fuel injection control device for a direct injection type internal combustion engine in which fuel is injected into the cylinder, fuel injection amount determining means for determining the fuel injection amount to be injected for one combustion stroke, injection period length determining means for determining the length of the injection period required to inject the fuel injection amount, injection start time determining means for determining the injection start time of the fuel, ignition time acquisition means for acquiring the ignition time, injection operation control means for controlling the operation of a fuel injector that injects the fuel into the cylinder including when the injection end time, which is the time point after the elapse of the injection period length from the injection start time of the fuel, is after the ignition time, the injection of the fuel to be injected from after the ignition time to the injection end time is achieved by a device configured to delay it until after the start of the next compression stroke.

[0007] In the above configuration, the internal combustion engine may be an internal combustion engine mounted on a vehicle such as an automobile. In particular, in the present invention, as the fuel, a fuel containing a component that is difficult to vaporize, such as an alcohol-containing fuel such as ethanol fuel, may be used. The "fuel injection amount", "length of the injection period", "injection start time", and "ignition time" to be injected for one combustion stroke may be appropriately set based on the engine speed, in-cylinder temperature, required load, time required for fuel vaporization, fuel injection pressure, etc. The "fuel injector" may be a device that opens a valve at a controlled injection start time and injects fuel into the cylinder in a normal mode adopted in this field. Note that each of the above means may be realized by an operation according to a program by a computer device.

[0008] In the fuel injection control of the direct injection type internal combustion engine targeted by the present invention described above, the "injection start time" is set at a stage when the in-cylinder temperature has risen so that the fuel can be vaporized well. Therefore, the lower the in-cylinder temperature, the closer the injection start time is set to the top dead center of compression (that is, the higher the in-cylinder temperature, the farther the injection start time is set from the top dead center of compression). In this regard, particularly in the case of a fuel containing a component that is difficult to vaporize, since it is necessary to set the injection start time at a time when the temperature in the cylinder, which is the combustion chamber, reaches a higher temperature, the injection start time is set closer to the top dead center of compression. However, if so, as already mentioned, there may be a case where the ignition time arrives before the injection of the fuel to be supplied in one combustion stroke ends. When the fuel is injected after the ignition time, the amount of unburned fuel flowing out to the exhaust system increases. This situation occurs particularly during cold start when the in-cylinder temperature is low.

[0009] Therefore, in the device of the present invention, as described above, the injection start timing, the length of the injection period, and the ignition timing are determined in the normal manner. In particular, when, during low-temperature operation, the injection end point after the elapse of the length of the injection period from the injection start timing occurs after the ignition timing, the fuel to be injected from after the ignition timing until the injection end point is injected after the start of the next compression stroke. That is, in the present invention, fuel injection starts at the injection start timing, but the injection is once stopped at the ignition timing, and the remaining fuel out of the fuel injection amount to be injected for one combustion stroke, which was not injected from the injection start timing until the ignition timing, is injected into the cylinder after the start of the next compression stroke, that is, after the passage of the next bottom dead center of compression. According to such a configuration, the injection start timing is set to the time when the fuel injected during one compression stroke is sufficiently vaporized. It is expected that the fuel injected from the injection start timing until the ignition timing will be vaporized well. Also, the fuel that was not injected from the injection start timing until the ignition timing is injected during the next compression stroke and thus will be burned during the next combustion stroke, suppressing the outflow amount of unburned fuel to the exhaust system. Further, since the amount of fuel supplied per cycle of the internal combustion engine substantially matches the amount of fuel to be injected for one combustion stroke, the internal combustion engine will output the driving force as required.

[0010] In the configuration of the present invention described above, when injecting, after the start of the next compression stroke, the portion of the fuel amount to be injected during one compression stroke that was not injected until the ignition timing, the timing to start the injection may be any time after the start of the next compression stroke. However, so that the fuel is supplied into the cylinder as early as possible and its vaporization progresses, it may be immediately after the start of the next compression stroke. Note that the injection end point of the portion of the fuel amount to be injected during one compression stroke that was not injected until the ignition timing is set so as not to occur after the next injection start timing, and it is preferable that the fuel injected at such next injection start timing is vaporized well.

Advantages of the Invention

[0011] According to the configuration of the fuel injection control according to the present invention described above, the injection start timing is set so that the fuel injected from that point is vaporized well, ensuring combustion stability even at low temperatures. On the other hand, the fuel portion that will be injected after the ignition timing is injected into the cylinder after the next compression stroke and burned in the next combustion stroke, suppressing the inflow and adhesion to the exhaust system catalyst as unburned fuel, and avoiding the melting of the catalyst. The device of the present invention is advantageously used for fuel injection control of internal combustion engines of vehicles such as automobiles, and may also be used for internal combustion engines for other uses of vehicles. Further, the configuration of the present invention is advantageously used for fuel injection control of internal combustion engines using fuels not derived from fossil fuels such as alcohol fuels, and thus can be used for the control of internal combustion engines that achieve carbon neutrality.

[0012] Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Explanation of Signs

[0014] 5…Fuel injector, 10…Control device,

Best Mode for Carrying Out the Invention

[0015] The present invention will be described in detail below with reference to the accompanying drawings in several preferred embodiments. In the drawings, the same reference numerals indicate the same parts.

[0016] Configuration of the control device The control device according to the present embodiment is for an internal combustion engine (not shown) for driving a vehicle such as an automobile or operating a mechanical device other than a vehicle, and is applied to the fuel injection control of an internal combustion engine in a form in which fuel is directly injected from an injector into a cylinder. As shown in FIG. 1, the control device 10 of the present embodiment, in a normal mode, based on the required load on the internal combustion engine, the in-cylinder temperature, the engine speed, etc., determines the fuel injection amount per cycle, the period during which fuel is injected from the injector, and the injection start timing, respectively, and has an injector operation control means for operating the fuel injector 5 so that fuel is injected into the cylinder at the injection start timing and injection period determined by those means. Further, in the present embodiment, as will be described later, since the mode of fuel injection control is changed according to the relationship between the end of fuel injection and the ignition timing, the injector operation control means is further configured to refer to the ignition timing that may be determined in a normal mode. Note that the control device 10 may be a normal computer device, and each means may be realized by the operation according to the program of the computer device.

[0017] The fuel injection control by the control device 10 of the present embodiment is particularly advantageously applied to an internal combustion engine using a fuel that is less likely to vaporize compared to conventional gasoline fuels such as alcohol-containing fuels, but is not limited thereto.

[0018] Regarding the relationship between the end of the injection period and the ignition timing Referring to Fig. 2(A), in a general direct injection internal combustion engine, fuel injection and ignition are generally carried out in the vicinity where the crank angle in the compression stroke of the engine reaches the top dead center. More specifically, the ignition timing is appropriately set by taking into account the balance between the vaporization time of the injected fuel and the combustion speed. The fuel injection period is determined as it goes according to the fuel injection amount (in one engine cycle) that is determined moment by moment according to the required load and the fuel discharge pressure of the injector. The injection start timing is appropriately set in consideration of the balance between the in-cylinder temperature and the fuel vaporization time so that the fuel vaporization rate is maximized. In this regard, in order to obtain combustion stability, it is preferable that the injection start timing is set when the in-cylinder temperature is higher than the temperature at which the fuel is rapidly and favorably vaporized after injection into the cylinder. As depicted in Fig. 2(B), the in-cylinder temperature increases as the crank angle of the compression stroke approaches the top dead center. Therefore, in the case of a fuel that is more difficult to vaporize compared to conventional gasoline fuels such as alcohol-containing fuels like ethanol fuel, it is preferable that the injection start timing is set at a time closer to the top dead center of the compression stroke and when the in-cylinder temperature is sufficiently high compared to the case of conventional gasoline fuels.

[0019] However, since the fuel injection period is determined according to the fuel injection amount and the fuel discharge pressure as described above, when the injection start timing is close to the ignition timing, as schematically depicted in Fig. 2(A), the end of the injection period may be after the ignition timing. In that case, most of the fuel R injected into the cylinder after the ignition timing may remain unburned and flow out into the exhaust system and reach and adhere to the catalyst. If unburned fuel adheres to the catalyst in such a way, when the air inhaled at the time of fuel injection cut reaches the catalyst without combustion, the unburned fuel may undergo an oxidation reaction, and there is a possibility that the catalyst becomes hot and melts. Such a situation is likely to occur during cold start of an engine with a low in-cylinder temperature.

[0020] Improvements in the fuel injection mode according to this embodiment Therefore, in the present embodiment, the injection start timing is set near the top dead center of the compression stroke when the in-cylinder temperature is sufficiently high. While maintaining combustion stability, in order to suppress the outflow of unburned fuel to the exhaust system, when the ignition timing arrives before the end of the fuel injection period, if the injection of fuel is once stopped at the ignition timing and a part of the fuel amount to be supplied in one engine cycle remains un-injected, the injection of the remaining fuel is delayed until after the start of the next compression stroke (hereinafter, the injection after the start of the next compression stroke is referred to as "additional injection"). According to such a configuration, even at the time of cold start of the engine, the fuel injected at the injection start timing set near the top dead center of the compression stroke where the in-cylinder temperature is sufficiently high is vaporized well, maintaining combustion stability. Also, the fuel supplied into the cylinder by the additional injection executed after the ignition timing is burned in the combustion stroke after the next compression stroke, so that the outflow of unburned fuel to the exhaust system can be suppressed. Further, the total amount of fuel supplied into the cylinder per cycle is the sum of the amount not injected in the previous compression stroke and the amount injected from the current injection start timing to the ignition timing, and generally coincides with the fuel amount determined according to the required load. Therefore, the output of the internal combustion engine also generally follows the requirement.

[0021] Figures 3(A) to (C) show, as described above, an example of the temporal changes in the engine speed, fuel injection quantity, injection start timing, and ignition timing during the transition from the start to the running state of an internal combustion engine in a configuration where, when the ignition timing arrives before the end of the fuel injection period, the fuel injection is temporarily stopped immediately before the ignition timing and additional injection is executed after the start of the next compression stroke. In the figures, in (B) and (C), the direction in which the crank angle advances is taken downward. As can be understood from the figure, in the initial stage of starting the internal combustion engine, since the rotational speed is low and the in-cylinder temperature is low, the injection start timing and the ignition timing are set at positions closer to the compression top dead center, and as the rotational speed and the in-cylinder temperature increase, they shift toward the compression bottom dead center side (advance angle side). At that time, as shown in the figure, the ignition timing is basically set appropriately before the compression top dead center, but since the fuel injection period is determined by the fuel injection quantity and the fuel discharge pressure as already described, as shown in Fig. 3(B), in the initial stage of starting, if left as it is, the injection end time may be after the passage of the ignition timing. Therefore, in the present embodiment, as exemplified in Fig. 3(C), the fuel injection executed at the injection start timing determined based on the required load, in-cylinder temperature, rotational speed, etc. is temporarily stopped once the ignition timing arrives, even if there is still fuel to be injected. Then, the remaining fuel (R) that was not injected is injected into the cylinder with a delay after the next compression bottom dead center as additional injection (or late injection) and is burned in the next combustion stroke.

[0022] In the configuration of the present embodiment described above, the execution of the additional injection may be at an arbitrary time after the start of the next compression stroke. However, if the additional injection overlaps with the fuel injection executed before the next ignition timing, the vaporization rate of the fuel injected before the ignition timing will decrease. Therefore, as schematically depicted in the right figure of Fig. 3(C), the additional injection is executed such that its end time is sufficiently before the start time of the fuel injection executed before the next ignition timing. Typically, the additional injection may be executed immediately after the start of the next compression stroke (in that case, the time for the fuel supplied into the cylinder by the additional injection to vaporize sufficiently becomes longer, which is advantageous).

[0023] Operation of the control device Fuel injection by the control device according to the present embodiment may be executed as in the flowchart illustrated in FIG. 4. In operation, as illustrated, in each compression stroke, before the crank angle reaches top dead center, the amount of fuel to be burned in the combustion stroke, that is, the fuel injection amount to be injected in the compression stroke, is determined according to the required load (step 1), the fuel injection period is determined based on the fuel injection amount, the discharge pressure in the injector, etc. (step 2), the fuel injection start timing is determined based on the predicted value of the in-cylinder temperature, the fuel vaporization rate, etc. (step 3), the fuel injection period is added to the injection start timing, and the fuel injection end time is calculated (step 4). Also. In the present embodiment, since the ignition timing is referred to in fuel injection control, the ignition timing is appropriately determined based on the in-cylinder temperature and the rotational speed, or the ignition timing determined by another ignition timing control device is acquired (step 5). Thereafter, when the fuel injection start timing arrives (step 6), fuel injection is started. When the previously calculated fuel injection end time is earlier than the ignition timing (step 7), the fuel injection is executed over the previously determined fuel injection period (step 8). On the other hand, when the previously calculated fuel injection end time is later than the ignition timing (step 7), the fuel injection is executed until the ignition timing and then once stopped (step 9), waits for the start of the next compression stroke (step 10), and additional injection of the remaining fuel amount (delayed injection amount) is executed (step 11). As understood from FIGS. 3(A) to 3(C), usually, steps 9 to 11 are executed from the start period to the idle period of the internal combustion engine. When the rotational speed increases and the in-cylinder temperature rises to the running state of the internal combustion engine, step 8 is executed.

[0024] Thus, according to the above-described present embodiment, the injection start timing is set so that the fuel injected from that point is vaporized well, and the fuel portion that will be injected after the ignition timing is injected into the cylinder after the next compression stroke and burned in the next combustion stroke, so that it is suppressed from flowing into and adhering to the catalyst in the exhaust system as unburned fuel. As a result, combustion stability is ensured even at low temperatures such as at the start of the internal combustion engine, while problems such as melting of the catalyst due to a substantial amount of unburned fuel reaching the catalyst can be avoided. The effects of the configuration of the above-described present embodiment are achieved particularly even when using a fuel that is not derived from fossil fuels such as alcohol fuel but is difficult to vaporize. Therefore, the present embodiment is a configuration that is advantageously adopted for realizing carbon neutrality.

[0025] The above description has been made in relation to embodiments of the present invention, but many modifications and changes are easily possible for those skilled in the art, and the present invention is not limited to only the embodiments illustrated above, and it will be apparent that the present invention can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A fuel injection control device for a direct injection type internal combustion engine in which fuel is injected into a cylinder, A fuel injection amount determination means for determining a fuel injection amount to be injected for one combustion stroke; an injection period length determining means for determining the length of an injection period required to inject the fuel injection amount; an injection start timing determination means for determining a timing for starting injection of the fuel; An ignition timing acquisition means for acquiring an ignition timing; an injection operation control means for controlling the operation of a fuel injector that injects the fuel into the cylinder; Including, The device is configured such that, when the injection end point, which is the point in time after the injection start timing of the fuel and the injection period length has elapsed, is after the ignition timing, the injection of fuel that should be injected from after the ignition timing to the injection end point is delayed until after the start of the next compression stroke.

Images