JP2010180725A - Start control device of internal combustion engine - Google Patents

Abstract

A start control device that suppresses a decrease in startability of an in-cylinder direct injection internal combustion engine is provided.
A fuel injection valve for directly injecting fuel into a cylinder of an internal combustion engine, temperature acquisition means for acquiring the temperature of the internal combustion engine or the temperature of intake air taken into the cylinder, and at the time of starting the internal combustion engine Cranking speed variable means for making the cranking speed variable, and fuel in the cylinder after the start of cranking based on the temperature acquired by the temperature acquisition means when performing cranking at the start of the internal combustion engine The cranking speed is variable so as to reduce the cranking speed of at least the first cycle of the cranking when it is determined whether there is a possibility of self-ignition. Control means for controlling the means.
[Selection] Figure 3

Description

  The present invention relates to a start control device for an internal combustion engine.

  During the warm start of the internal combustion engine, when the rotational speed of the internal combustion engine is low immediately after the start of cranking, fuel self-ignition occurs before compression top dead center, making it difficult to start. As a technique for preventing this, Patent Document 1 describes an invention in which fuel supply is stopped until the rotational speed of the internal combustion engine increases to a rotational speed at which the intake pressure decreases to a predetermined pressure during the cranking period.

  As a technique related to the present invention, Patent Document 2 describes a technique in which a motor that applies a driving force to a piston of an internal combustion engine is provided and the piston speed is reduced by the driving force of the motor in an expansion stroke.

JP 2007-292061 A JP 2007-21650 A

  In an internal combustion engine provided with a fuel injection valve that directly injects fuel into a cylinder, when the stop period of the internal combustion engine becomes longer, fuel may exist in the cylinder at the next start due to fuel leakage from the fuel injection valve. At the time of warm start, there is a possibility that the fuel existing in the cylinder due to this fuel leakage is self-ignited to cause a decrease in startability.

  The present invention has been made in view of such problems, and an object thereof is to suppress a decrease in startability of a direct injection internal combustion engine.

In order to solve the above problems, an internal combustion engine start control device according to the present invention includes:
A fuel injection valve for directly injecting fuel into the cylinder of the internal combustion engine;
Temperature acquisition means for acquiring the temperature of the internal combustion engine or the temperature of intake air taken into the cylinder;
Cranking speed variable means for variable cranking speed at the start of the internal combustion engine;
When performing cranking at the time of starting the internal combustion engine, it is determined whether there is a possibility that the fuel in the cylinder self-ignites after the cranking starts based on the temperature acquired by the temperature acquisition means, and self-ignition Control means for controlling the cranking speed variable means so as to reduce the cranking speed of at least the first cycle of the cranking,
It is characterized by providing.

In a direct injection type internal combustion engine having a fuel injection valve that directly injects fuel into a cylinder, fuel may leak from the fuel injection valve while the internal combustion engine is stopped. When the in-cylinder temperature at the next start is high, the fuel leaked during the engine stop may self-ignite after the start of cranking at the start. If such in-cylinder fuel self-ignition occurs in the compression stroke of the first cycle of cranking, it may cause a decrease in startability and noise generation. Such in-cylinder fuel self-ignition tends to occur when the in-cylinder temperature during cranking is high. The in-cylinder temperature at the start is related to the temperature of the internal combustion engine and the intake air temperature at the start.

  According to the present invention, when it is determined that there is a possibility of such self-ignition based on the engine temperature or the intake air temperature at the start, the cranking speed of at least the first cycle of the cranking at the start is determined. Reduced. By reducing the cranking speed, the in-cylinder temperature after the start of cranking can be prevented from rising to a high temperature at which self-ignition of the fuel existing in the cylinder can occur. Therefore, even when the fuel leaked from the fuel injection valve while the internal combustion engine is stopped is present in the cylinder at the start of cranking at the start, the fuel self-ignites after the start of cranking at the start. Can be suppressed. As a result, it is possible to suitably suppress startability deterioration and noise generation during warm start of the direct injection type internal combustion engine.

  In the present invention, the control means includes an estimation means for estimating a compression end temperature of the cylinder after the start of the cranking based on the temperature acquired by the temperature acquisition means when the internal combustion engine is started. When the compression end temperature estimated by the estimation means is higher than the upper limit value of the compression end temperature at which it can be determined that the fuel in the cylinder does not self-ignite, the cranking speed of at least the first cycle of the cranking is The cranking speed variable means may be controlled so that the compression end temperature of the cylinder in the cranking becomes a cranking speed that is not more than the upper limit value.

  When the cranking speed is changed by the cranking speed variable means and the cranking is started at the default cranking speed, the estimating means determines the compression end temperature to be realized as the cranking speed and the engine temperature or the intake air. It is a means to estimate based on temperature. The compression end temperature is accurate for determining whether or not the in-cylinder temperature may reach a temperature at which the fuel existing in the cylinder can self-ignite in the compression stroke of the first cycle of cranking at the start. It becomes an indicator.

  According to the above configuration, when the estimated value of the compression end temperature when cranking is started at the default cranking speed is higher than the predetermined upper limit value of the compression end temperature at which it can be determined that the fuel in the cylinder does not self-ignite In addition, control for reducing the cranking speed is performed. Then, the cranking speed can be varied so that the compression end temperature in the first cycle of cranking at start-up becomes the upper limit value of the compression end temperature at which it can be determined that the fuel existing in the cylinder does not self-ignite or a temperature close thereto. The cranking speed can be controlled by the means.

  As a result, if it is determined that there is a possibility that the fuel in the cylinder will self-ignite after the start of cranking at the time of starting, the cranking speed may be excessively decreased to reduce the starting performance, and conversely In addition, it is possible to suppress that the amount of decrease in the cranking speed is insufficient and the occurrence of self-ignition cannot be suitably suppressed, and it is possible to more suitably suppress the decrease in startability at the time of warm start.

  The amount of fuel that leaks from the fuel injection valve while the internal combustion engine is stopped increases as the stop period of the internal combustion engine increases. Therefore, when the stop period of the internal combustion engine is short, only a small amount of fuel exists in the cylinder at the next start. When the amount of fuel present in the cylinder is small, even if the in-cylinder temperature in the compression stroke of the first cycle of cranking at the time of start-up increases, self-ignition does not occur.

  Therefore, in the present invention, when the start of the internal combustion engine is a start within a predetermined period from the stop of the internal combustion engine immediately before, the control means controls the cranking speed variable means at the start of the internal combustion engine. The control for reducing the cranking speed may not be performed.

  The “predetermined period” means that the amount of fuel leaking from the fuel injection valve is less than or equal to the upper limit of the amount of fuel that does not cause self-ignition regardless of the in-cylinder temperature in the compression stroke of the first cycle of cranking at the start This is the stop period of the internal combustion engine. If the period from the previous stop of the internal combustion engine to the start of the internal combustion engine is within this predetermined period, self-ignition occurs even if control for reducing the cranking speed is not performed in the first cranking cycle. It can be judged that there is nothing. According to the above configuration, since the start is performed at the default cranking speed under the condition that there is no possibility of such self-ignition and it is not necessary to perform control to reduce the cranking speed, the cranking speed The useless operation of the variable means can be suppressed, and good startability can be realized.

  The amount of fuel that leaks from the fuel injection valve while the internal combustion engine is stopped varies depending on the fuel injection valve usage history (such as the number of injections) and the fuel pressure during the stop of the internal combustion engine.

  Therefore, in the present invention, the control means starts to leak from the fuel injection valve into the cylinder during the stop of the internal combustion engine based on the use history of the fuel injection valve or the fuel pressure during the stop of the internal combustion engine. Sometimes it is possible to estimate the amount of fuel present in the cylinder and to determine that the estimated amount of fuel will not cause auto-ignition regardless of the in-cylinder temperature in the compression stroke of the first cranking cycle at start-up If the fuel amount is less than or equal to the upper limit value of the fuel amount, control for lowering the cranking speed by the cranking speed variable means may not be performed when the internal combustion engine is started.

  According to this configuration, it is possible to accurately estimate the amount of fuel that leaks from the fuel injection valve into the cylinder while the internal combustion engine is stopped. Therefore, the self-ignition of the fuel in the cylinder can occur during cranking at the start. It is possible to estimate whether or not there is a certainty with higher accuracy. Therefore, it is possible to more accurately determine the necessity of the control for reducing the cranking speed at the start by the cranking speed variable means, it is possible to suppress the wasteful operation of the cranking speed variable means, Startability can be realized.

  According to the present invention, in a direct injection type internal combustion engine that directly injects fuel into a cylinder, the fuel that leaks into the cylinder from the fuel injection valve while the engine is stopped is self-ignited during cranking at the start. A decrease in startability can be suitably suppressed.

1 is a diagram schematically illustrating a schematic configuration of an internal combustion engine according to a first embodiment. It is a figure which shows the relationship between a cranking speed and the compression end temperature at the time of cranking. 3 is a flowchart showing processing contents of start control of the internal combustion engine according to the first embodiment. It is a figure which shows the relationship between a cranking speed and the compression end temperature at the time of cranking. 6 is a flowchart showing processing contents of start control of an internal combustion engine according to a second embodiment. It is a figure which shows the relationship between the compression end temperature at the time of cranking, the amount of fuel which exists in a cylinder at the time of cranking start, and the presence or absence of the possibility of the fuel in a cylinder self-igniting. It is a figure which shows the relationship between the elapsed time after an internal combustion engine stops, and the fuel amount which leaks from a fuel injection valve when the said internal combustion engine stops. 7 is a flowchart showing the contents of a start control process for an internal combustion engine according to a third embodiment. It is a figure which shows the relationship between the cooling water temperature of an internal combustion engine, and the estimated value of the compression end temperature when cranking is started at the default cranking speed. It is a figure which shows the relationship between the frequency | count of injection of a fuel injection valve, and the fuel amount which leaks from a fuel injection valve per unit time when an internal combustion engine stops. It is a figure which shows the relationship between the fuel pressure in the time of a stop of an internal combustion engine, and the fuel amount which leaks from a fuel injection valve per unit time at the time of a stop of an internal combustion engine. 12 is a flowchart showing the processing content of start control of an internal combustion engine according to a fourth embodiment.

  Hereinafter, embodiments of the present invention will be described in detail. The dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the present embodiment are not intended to limit the technical scope of the invention only to those unless otherwise specified.

  FIG. 1 is a diagram schematically illustrating a schematic configuration of an internal combustion engine according to the present embodiment.

  An internal combustion engine 1 shown in FIG. 1 is an in-cylinder direct-injection spark ignition gasoline engine having four cylinders 2. A piston 3 is slidably inserted into the cylinder 2. The reciprocating motion of the piston 3 in the cylinder 2 is converted into the rotational motion of the crankshaft 17 through the connecting rod 16. A combustion chamber 12 is formed between the upper part of the cylinder 2 and the top part of the piston 3. The cylinder 2 is connected to an intake port 4 for communicating a combustion chamber 12 with an intake passage (not shown). The intake port 4 is provided with an intake air temperature sensor 13 that measures the temperature of air taken into the combustion chamber 12 via the intake port 4. The cylinder 2 is connected to an exhaust port 5 for communicating the combustion chamber 12 with an exhaust passage (not shown). A fuel injection valve 6 that directly injects fuel into the cylinder 2 is provided in the vicinity of the connection portion of the intake port 4 in the cylinder 2. A spark plug 7 for igniting an air-fuel mixture formed by fuel injected from the fuel injection valve 6 and air taken into the combustion chamber 12 from the intake port 4 is provided at the top of the cylinder 2. The internal combustion engine 1 is provided with an intake valve 8 that opens and closes an intake port 4. Although an exhaust valve for opening and closing the exhaust port 5 is also provided, it is not shown in FIG. 1 in order to avoid complexity of the drawing. The internal combustion engine 1 is provided with a motor 15, and the power of the motor 15 is transmitted to the crankshaft 17 through the gear mechanism 18. The path for transmitting the power of the motor 15 to the crankshaft 17 need not be limited to the gear mechanism. Further, the power source for generating the power to be transmitted to the crankshaft 17 is not necessarily limited to the motor.

  The internal combustion engine 1 is provided with a water temperature sensor 14 that measures the cooling water temperature of the internal combustion engine 1 and a fuel pressure sensor 19 that measures the fuel pressure of the fuel for injection supplied to the fuel injection valve 6. Measurement data from these sensors and the intake air temperature sensor 13 described above is supplied to an ECU 10 that is a computer unit that controls the operation of the internal combustion engine 1. The ECU 10 outputs a signal for controlling the operation of the fuel injection valve 6, the spark plug 7, and the motor 15 based on the data acquired from these various sensors.

  In a direct injection type internal combustion engine having the above-described configuration, fuel may leak from the fuel injection valve 6 while the internal combustion engine 1 is stopped. If the in-cylinder temperature rises after the start of cranking at the next start, the fuel that leaks while the engine is stopped may self-ignite after the cranking starts. If such in-cylinder fuel self-ignition occurs in the compression stroke of the first cycle of cranking, it may cause a decrease in startability and noise generation.

The in-cylinder temperature after the start of cranking is related to the cooling water temperature of the internal combustion engine 1 at the start. Therefore, in this embodiment, the cooling water temperature of the internal combustion engine 1 is measured by the cooling water temperature sensor 14 at the start, and when the measured cooling water temperature is higher than a predetermined reference temperature Twth, the cranking speed at the start is reduced. To do. In this embodiment, the cranking speed is decreased by applying a driving force in the direction opposite to the cranking rotation direction to the crankshaft 17 by the motor 15.

  The reference value Twth for the cooling water temperature is determined based on the upper limit value of the cooling water temperature at which it can be determined that the fuel in the cylinder does not self-ignite when cranking is started at the default cranking speed. The default cranking speed is the cranking speed when the driving force is not applied to the crankshaft 17 by the motor 15.

  As the cranking speed increases, the cylinder temperature during cranking tends to increase. FIG. 2 is a diagram illustrating the relationship between the cranking speed and the compression end temperature during cranking. Here, the compression end temperature is the in-cylinder temperature when the piston position reaches the compression top dead center, and is the maximum value of the in-cylinder temperature during cranking. Therefore, the compression end temperature at the time of cranking is an accurate index of the in-cylinder temperature at the time of cranking. As shown in FIG. 2, by reducing the cranking speed, the compression end temperature at the time of cranking can be lowered. Therefore, even when the cooling water temperature is higher than the reference temperature Twth, Can be prevented from rising to a temperature at which the fuel in the cylinder self-ignites. Accordingly, it is possible to suppress the self-ignition of the fuel in the cylinder after the start of cranking at the time of warm start, and it is possible to suitably suppress the deterioration of startability and the generation of noise at the time of warm start.

  The start control of the internal combustion engine 1 according to the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing the processing contents of the start control of the internal combustion engine 1 of the present embodiment. The process shown in the flowchart of FIG. 3 is executed by the ECU 10 when the internal combustion engine 1 is started.

  When the processing of the flowchart of FIG. 3 is started, the ECU 10 first acquires the cooling water temperature Tw of the internal combustion engine 1 based on the measurement data by the cooling water temperature sensor 14 in step S101, and the acquired cooling water temperature Tw is the reference temperature. It is determined whether it is higher than Twth. When the coolant temperature Tw of the internal combustion engine 1 is higher than the reference temperature Twth (Tw> Twth), the ECU 10 proceeds to the process of step S102, and applies a driving force in the direction opposite to the cranking rotation direction to the crankshaft 17 by the motor 15. Start cranking. As a result, cranking is performed at a low speed, so that the increase in the in-cylinder temperature during cranking is reduced. As a result, the cylinder temperature is prevented from rising to a temperature at which the fuel in the cylinder can self-ignite after the cranking starts, and the fuel in the cylinder at the time of cranking can be restrained from self-igniting.

  On the other hand, in step S101, when the coolant temperature Tw of the internal combustion engine 1 is not higher than the reference temperature Twth (Tw ≦ Twth), the ECU 10 proceeds to the process of step S103 and applies the driving force to the crankshaft 17 by the motor 15. Instead, start cranking at the default cranking speed. In this case, since the temperature in the cylinder of the internal combustion engine 1 is low, even if cranking is performed at the default cranking speed, the possibility that the fuel in the cylinder self-ignites is low.

  The in-cylinder temperature at the time of cranking is also related to the temperature of air taken into the cylinder 2 from the intake port 4. Therefore, the possibility of self-ignition of the fuel in the cylinder after the start of cranking may be determined based on the intake air temperature measured by the intake air temperature sensor 13. In that case, when cranking is started at the default cranking speed, the reference temperature Tath of the intake air temperature is determined based on the upper limit value of the intake air temperature at which it can be determined that the fuel in the cylinder does not self-ignite, and the internal combustion engine 1 When the intake air temperature Ta measured by the intake air temperature sensor 13 is higher than the reference temperature Tath, the cranking speed can be reduced by the motor 15.

In this embodiment, the cooling water temperature sensor 14 corresponds to the temperature acquisition means in the present invention. The motor 15 corresponds to the cranking speed varying means in the present invention. Moreover, ECU10 which performs the process of step S101-102 corresponds to the control means in this invention.

  The compression end temperature at the time of cranking can be used as an index of the in-cylinder temperature at the time of cranking. The compression end temperature at the time of cranking can be estimated based on the cranking speed and the cooling water temperature of the internal combustion engine 1 at the time of starting.

  Therefore, this embodiment is realized when cranking is started at the default cranking speed based on the measured value Tw of the cooling water temperature of the internal combustion engine 1 at the start and the default cranking speed Ne0. When the estimated compression end temperature is estimated and the estimated compression end temperature is higher than a predetermined reference temperature Tcylth, the cranking speed at the start is reduced, and the compression end temperature at the time of cranking becomes the reference temperature Tcylth or less. The application of driving force to the crankshaft 17 by the motor 15 is controlled so as to reduce the cranking speed.

  The reference value Tcylth of the compression end temperature is determined based on the upper limit value of the compression end temperature when the in-cylinder temperature at the time of cranking becomes a temperature at which the fuel in the cylinder does not self-ignite.

  FIG. 4 is a diagram illustrating the relationship between the cranking speed and the compression end temperature during cranking. The relationship between the cranking speed and the compression end temperature varies depending on the cooling water temperature of the internal combustion engine 1 at the time of starting. The graph shown in FIG. 4 shows the relationship between the cranking speed and the compression end temperature when the coolant temperature of the internal combustion engine 1 at the start is the coolant temperature Tw measured by the coolant temperature sensor 14 at the start. As shown in FIG. 4, when the estimated value Tcyl of the compression end temperature when starting the cranking at the default cranking speed Ne0 when the cooling water temperature is Tw is higher than the reference temperature Tcylth, the cranking speed is When the water temperature is Tw, actual cranking is started while the driving force is applied to the crankshaft 17 by the motor 15 so that the compression end temperature is equal to or lower than the cranking speed Neth at which the reference temperature Tcylth is reached. .

  As a result, the cranking speed can be more reliably lowered to the cranking speed at which the fuel in the cylinder does not self-ignite. Therefore, it is possible to preferably avoid that the amount of decrease in the cranking speed is insufficient and the occurrence of self-ignition cannot be suitably suppressed.

  Further, if the cranking speed is reduced to a cranking speed Neth corresponding to the reference temperature Tcylth or a speed slower than the cranking speed Neth but close to the cranking speed Neth, the cranking speed is excessively increased. It is also possible to avoid a decrease in startability due to the decrease.

  The start control of the internal combustion engine 1 according to the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing the processing contents of the start control of the internal combustion engine 1 of the present embodiment. The process shown in the flowchart of FIG. 5 is executed by the ECU 10 when the internal combustion engine 1 is started.

  When the processing of the flowchart of FIG. 5 is started, the ECU 10 first acquires the cooling water temperature Tw of the internal combustion engine 1 based on the measurement data by the cooling water temperature sensor 14 in step S201, and the acquired cooling water temperature Tw and the default The compression end temperature Tcyl that will be realized when cranking is started at the default cranking speed Ne0 is estimated based on the cranking speed Ne0. Then, it is determined whether or not the estimated compression end temperature Tcyl is higher than the reference temperature Tcylth.

When the estimated value Tcyl of the compression end temperature is higher than the reference temperature Tcylth (Tcyl> Tcy)
lth), the ECU 10 proceeds to the process of step S202, and calculates a cranking speed Neth at which the compression end temperature at the time of cranking becomes the reference temperature Tcylth under the condition that the cooling water temperature is Tw. Then, cranking is started while a driving force opposite to the cranking rotation direction is applied to the crankshaft 17 by the motor 15 so that the cranking speed becomes Neth. As a result, cranking is performed at the upper limit value of the cranking speed at which the fuel in the cylinder does not self-ignite or at a speed close thereto. Therefore, it is possible to suppress the self-ignition of the fuel in the cylinder after the cranking is started.

  On the other hand, when the estimated value Tcyl of the compression end temperature estimated in step S201 is equal to or lower than the reference temperature Tcylth (Tcyl ≦ Tcylth), the ECU 10 proceeds to the process of step S203 and applies the driving force to the crankshaft 17 by the motor 15. Without performing, cranking is started at the default cranking speed Ne0. In this case, since the compression end temperature is unlikely to be higher than the reference temperature Tcylth, even if cranking is performed at the default cranking speed Ne0, the possibility that the fuel in the cylinder self-ignites is low.

  Note that the compression end temperature at the time of cranking can also be estimated based on the intake air temperature measured by the intake air temperature sensor 13 and the cranking speed. Therefore, based on the measured value of the intake air temperature at the time of starting and the default cranking speed, the compression end temperature realized when the cranking is started under the intake air temperature condition is estimated, and the estimated When the compression end temperature is higher than the reference temperature Tcylth, the motor 15 is configured so that the cranking speed is reduced to a cranking speed at which the compression end temperature is equal to or lower than the reference temperature Tcylth when cranking is started under the condition of the intake air temperature. Thus, the driving force applied to the crankshaft 17 may be controlled.

  In this embodiment, the compression end temperature Tcyl realized when cranking is started at the default cranking speed Ne0 based on the coolant temperature Tw of the internal combustion engine 1 and the default cranking speed Ne0 in step S201. ECU10 which performs the process which estimates this corresponds to the estimation means in this invention. Further, the ECU 10 that executes the process of step S202 when the estimated value Tcyl of the compression end temperature is higher than the reference temperature Tcylth in step S201 corresponds to the control means in the present invention.

  Whether the fuel in the cylinder self-ignites after the start of cranking depends on the amount of fuel present in the cylinder at the start of cranking. FIG. 6 is a diagram showing the relationship between the compression end temperature at the time of cranking and the amount of fuel present in the cylinder at the start of cranking and the presence or absence of the possibility that the fuel in the cylinder self-ignites. The horizontal axis in FIG. 6 represents the compression end temperature, and the vertical axis represents the amount of fuel in the cylinder. The hatched area in FIG. 2 represents an area in which it can be determined that the fuel in the cylinder may self-ignite after cranking starts.

  As described above, when the compression end temperature at the time of cranking is higher than the reference temperature Tcylth, the fuel in the cylinder may self-ignite, but as shown in FIG. 6, it exists in the cylinder at the start of cranking. When the fuel amount is equal to or less than the predetermined reference amount Qlth, it can be determined that the fuel in the cylinder does not reach self-ignition regardless of the compression end temperature. The reference value Qlth of the fuel amount existing in the cylinder is determined based on the upper limit value of the fuel amount in the cylinder that can be determined that the fuel in the cylinder does not self-ignite after the cranking starts regardless of the compression end temperature.

  Even if it is estimated that the compression end temperature at the time of cranking becomes higher than the reference temperature Tcylth, if the amount of fuel present in the cylinder at the start of cranking is less than the reference amount Qlth, the cranking speed Even if control for lowering the engine speed from the default cranking speed Ne0 is not performed, the possibility that the fuel in the cylinder self-ignites after the start of cranking is low.

  Here, the amount of fuel existing in the cylinder at the start of cranking is substantially equal to the amount of fuel leaking from the fuel injection valve 6 while the internal combustion engine 1 is stopped. The amount of fuel that leaks from the fuel injection valve 6 while the internal combustion engine 1 is stopped is related to the elapsed time since the internal combustion engine 1 stopped. FIG. 7 is a diagram showing the relationship between the elapsed time since the internal combustion engine 1 stopped and the amount of fuel leaking from the fuel injection valve 6 while the internal combustion engine 1 is stopped. The horizontal axis in FIG. 7 represents the stop period of the internal combustion engine 1, and the vertical axis represents the amount of fuel leaking from the fuel injection valve 6. As shown in FIG. 7, the longer the stop period of the internal combustion engine 1, the greater the amount of fuel leaking from the fuel injection valve 6.

  Therefore, in this embodiment, when the start of the internal combustion engine 1 is a start within a predetermined reference stop period Δth from the stop of the internal combustion engine 1, the compression when the cranking is started at the default cranking speed Ne0. Even when the end temperature is estimated to be higher than the reference temperature Tcylth, the control for reducing the cranking speed is not performed.

  The reference value Δth of the stop period of the internal combustion engine 1 is a stop period of the internal combustion engine 1 such that the amount of fuel leaking from the fuel injection valve 6 becomes the reference amount Qlth. If the stop period of the internal combustion engine 1 is within the reference stop period Δth, the amount of fuel present in the cylinder at the start of cranking is equal to or less than the reference amount Qlth. It is unlikely that the fuel will self-ignite. In such a case, unnecessary driving of the motor 15 can be avoided by not performing the control for reducing the cranking speed.

  The start control of the internal combustion engine 1 according to the present embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing the processing contents of the start control of the internal combustion engine 1 of the present embodiment. The process shown in the flowchart of FIG. 8 is executed by the ECU 10 when the internal combustion engine 1 is started.

  When the processing of the flowchart of FIG. 8 is started, the ECU 10 first acquires the cooling water temperature Tw of the internal combustion engine 1 based on the measurement data by the cooling water temperature sensor 14 in step S301, and the acquired cooling water temperature Tw is a predetermined value. It is determined whether or not the temperature is higher than the reference temperature Twth. Here, in this embodiment, the cooling water temperature at which the estimated value of the compression end temperature when cranking is started at the default cranking speed Ne0 becomes the reference temperature Tcylth is determined as the reference value Twth of the cooling water temperature. That is, in the relationship between the cooling water temperature of the internal combustion engine 1 as shown in FIG. 9 and the estimated value of the compression end temperature when cranking is started at the default cranking speed Ne0, the reference value Tcylth of the compression end temperature is obtained. The corresponding cooling water temperature Twth is adopted as the determination criterion in step S301.

  When the cooling water temperature Tw of the internal combustion engine 1 is higher than the reference temperature Twth (Tw> Twth), it can be determined that the fuel existing in the cylinder may self-ignite when cranking is started at the default cranking speed Ne0. The ECU 10 proceeds to the process of step S302, and determines whether or not the stop period Δ of the internal combustion engine 1 exceeds the reference stop period Δth. Information on the stop period Δ of the internal combustion engine 1 is acquired based on the information about the stop / start of the internal combustion engine 1 stored in the storage device of the ECU 10.

  When the stop period Δ of the internal combustion engine 1 exceeds the reference stop period Δth (Δ> Δth), it can be determined that the amount of fuel present in the cylinder is a fuel amount that can be ignited, so the ECU 10 performs the process of step S303. The cranking is started while the driving force applied in the direction opposite to the cranking rotation direction is applied to the crankshaft 17 by the motor 15. As a result, cranking is performed at a low speed, so that the increase in the in-cylinder temperature at the time of cranking is reduced, and it is possible to suppress the self-ignition of the fuel in the cylinder after the cranking starts. Note that the amount of decrease in the cranking speed may be determined by the method described in the second embodiment.

  If the stop period Δ of the internal combustion engine 1 is within the reference stop period Δth (Δ ≦ Δth), it can be determined that the amount of fuel present in the cylinder is less than the amount of fuel that can be ignited, so the ECU 10 performs the process of step S304. The cranking is started at the default cranking speed Ne0 without applying the driving force to the crankshaft 17 by the motor 15. In this case, although the compression end temperature at the time of cranking becomes higher than the reference temperature Tcylth, the amount of fuel present in the cylinder is small, so that the fuel does not reach self-ignition.

  In step S301, when the coolant temperature Tw of the internal combustion engine 1 is not higher than the reference temperature Twth (Tw ≦ Twth), the ECU 10 proceeds to the process of step S304 and starts cranking at the default cranking speed Ne0. In this case, since the compression end temperature at the time of cranking is equal to or lower than the reference temperature Tcylth, self-ignition does not occur regardless of the amount of fuel present in the cylinder.

  In this embodiment, the ECU 10 that executes the processes of steps S301 to S303 corresponds to the control means in the present invention.

  The amount of fuel leaking from the fuel injection valve 6 into the cylinder while the internal combustion engine 1 is stopped is also related to the history of use of the fuel injection valve 6 up to that point and the fuel pressure during the stop of the internal combustion engine 1.

  FIG. 10 is a diagram showing the relationship between the number of injections of the fuel injection valve 6 so far and the amount of fuel leaking from the fuel injection valve 6 per unit time when the internal combustion engine 1 is stopped. The horizontal axis in FIG. 10 represents the number of injections of the fuel injection valve 6, and the vertical axis represents the amount of fuel leaking from the fuel injection valve 6 per unit time. As shown in FIG. 10, as the number of injections of the fuel injection valve 6 increases, the amount of fuel leaking from the fuel injection valve 6 per unit time when the internal combustion engine 1 is stopped tends to decrease.

  FIG. 11 is a diagram showing the relationship between the fuel pressure when the internal combustion engine 1 is stopped and the amount of fuel leaking from the fuel injection valve 6 per unit time when the internal combustion engine 1 is stopped. The horizontal axis in FIG. 11 represents the fuel pressure, and the vertical axis represents the amount of fuel leaking from the fuel injection valve 6 per unit time. As shown in FIG. 11, when the fuel pressure is low and high, the amount of fuel leaking from the fuel injection valve 6 is relatively small, and when the fuel pressure is medium, the amount of fuel leaking from the fuel injection valve 6 is compared. There is a tendency to increase.

  In consideration of such a tendency, in the present embodiment, the amount of fuel existing in the cylinder at the start of cranking of the internal combustion engine 1 is determined by the length of the stop period of the internal combustion engine 1 and the injection of the fuel injection valve 6 until that time. Based on the number of times and the fuel pressure during the stop of the internal combustion engine 1, the estimated fuel amount in the cylinder is the reference value Qlth of the fuel amount existing in the cylinder at the start of cranking described in the third embodiment. When the number is larger, control is performed to reduce the cranking speed. Since it is possible to accurately estimate the amount of fuel present in the cylinder at the start of cranking, it is necessary to perform control to reduce the cranking speed in the warm start condition where the compression end temperature at the time of cranking exceeds the reference temperature Tcylth It becomes possible to more accurately determine the presence or absence of sex.

  The start control of the internal combustion engine 1 according to the present embodiment will be described with reference to FIG. FIG. 12 is a flowchart showing the processing contents of the start control of the internal combustion engine 1 of the present embodiment. The process shown in the flowchart of FIG. 12 is executed by the ECU 10 when the internal combustion engine 1 is started.

When the processing of the flowchart of FIG. 12 is started, the ECU 10 first acquires the cooling water temperature Tw of the internal combustion engine 1 based on the measurement data by the cooling water temperature sensor 14 in step S401, and the acquired cooling water temperature Tw is a predetermined value. It is determined whether the temperature is higher than the reference temperature Twth. The reference temperature Twth is the same as that described in the third embodiment. When the cooling water temperature Tw of the internal combustion engine 1 is higher than the reference temperature Twth (Tw> Twth), it can be determined that the fuel existing in the cylinder may self-ignite when cranking is started at the default cranking speed Ne0. The ECU 10 proceeds to the process of step S402, and estimates the fuel amount Ql leaked from the fuel injection valve 6 during the stop period of the internal combustion engine 1. In this embodiment, the amount of fuel leaking from the fuel injection valve 6 based on the stop period Δ of the internal combustion engine 1, the fuel pressure P while the internal combustion engine 1 is stopped, and the number of injections N of the fuel injection valve 6 so far. Ql is estimated.

  In step S403, it is determined whether or not the fuel amount Ql estimated in step S402 is larger than the reference amount Qlth. The reference amount Qlth is the same as that described in the third embodiment. When the estimated fuel amount Ql is larger than the reference amount Qlth, if cranking is started at the default cranking speed Ne0, it can be determined that the fuel in the cylinder may self-ignite after the cranking starts. Proceeding to S404, cranking is started while applying a driving force in the direction opposite to the cranking rotation direction to the crankshaft 17 by the motor 15. As a result, cranking is performed at a low speed, so that the in-cylinder temperature at the time of cranking can be prevented from rising to a temperature at which the fuel in the cylinder self-ignites. Therefore, it is possible to suppress the self-ignition of the fuel in the cylinder after the cranking starts.

  On the other hand, if the fuel amount Ql estimated in step S402 is less than or equal to the reference amount Qlth, there is no possibility that the fuel in the cylinder will self-ignite after cranking starts even if cranking is started at the default cranking speed Ne0. Since the determination can be made, the ECU 10 proceeds to the process of step S405 and starts cranking at the default cranking speed Ne0 without applying the driving force to the crankshaft 17 by the motor 15. In this case, the in-cylinder temperature at the time of cranking rises above the temperature at which the fuel in the cylinder can self-ignite, but the amount of fuel leaked into the cylinder from the fuel injection valve 6 during the stop period of the internal combustion engine 1 Therefore, the fuel does not reach self-ignition.

  In step S401, when the coolant temperature Tw of the internal combustion engine 1 is not higher than the reference temperature Twth (Tw ≦ Twth), the ECU 10 proceeds to the process of step S405 and starts cranking at the default cranking speed Ne0. In this case, the in-cylinder temperature at the time of cranking does not rise to a temperature at which the fuel in the cylinder self-ignites, so that self-ignition does not occur regardless of the amount of fuel present in the cylinder.

  In this embodiment, the ECU 10 that executes the processes of steps S401 to S404 corresponds to the control means in the present invention.

  Each embodiment described above is an example for explaining the present invention. Each embodiment may be changed or combined within a range not departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Piston 4 Intake port 5 Exhaust port 6 Fuel injection valve 7 Spark plug 8 Intake valve 10 ECU
12 Combustion chamber 13 Intake air temperature sensor 14 Cooling water temperature sensor 15 Motor 16 Connecting rod 17 Crankshaft 18 Gear mechanism

Claims (4)

A fuel injection valve for directly injecting fuel into the cylinder of the internal combustion engine;
Temperature acquisition means for acquiring the temperature of the internal combustion engine or the temperature of intake air taken into the cylinder;
Cranking speed variable means for variable cranking speed at the start of the internal combustion engine;
When performing cranking at the time of starting the internal combustion engine, it is determined whether there is a possibility that the fuel in the cylinder self-ignites after the cranking starts based on the temperature acquired by the temperature acquisition means, and self-ignition A control means for controlling the cranking speed variable means so as to reduce the cranking speed of at least the first cycle of the cranking,
A start control device for an internal combustion engine, comprising: In claim 1,
The control means includes
An estimation means for estimating the compression end temperature of the cylinder after the start of the cranking based on the temperature acquired by the temperature acquisition means when the internal combustion engine is started;
When the compression end temperature estimated by the estimation means is higher than the upper limit value of the compression end temperature at which it can be determined that the fuel in the cylinder does not self-ignite, the cranking speed of at least the first cycle of the cranking is An internal combustion engine start control device, characterized in that the cranking speed variable means is controlled such that a compression end temperature of the cylinder in the cranking becomes a cranking speed that is not more than the upper limit value. In claim 1 or 2,
When the start of the internal combustion engine is a start within a predetermined period from the stop of the internal combustion engine immediately before, the control means reduces the cranking speed by the cranking speed variable means at the start of the internal combustion engine. An internal combustion engine start control device characterized by not performing control. In claim 1 or 2,
The control means leaks from the fuel injection valve into the cylinder while the internal combustion engine is stopped, based on the use history of the fuel injection valve or the fuel pressure during the stop of the internal combustion engine, and is present in the cylinder at the start. The upper limit of the amount of fuel that can be determined that self-ignition does not occur regardless of the in-cylinder temperature in the compression stroke of the first cranking cycle when starting In the following cases, the internal combustion engine start control device is characterized in that the control for reducing the cranking speed by the cranking speed variable means is not performed when the internal combustion engine is started.

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