JP2006233814A - Fuel cooling device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for suppressing generation of vapor in a fuel pipe, in a fuel cooling device for an internal combustion engine. <P>SOLUTION: The fuel cooling device for an internal combustion engine 1 having a means 4 for cooling the fuel, comprises: a fuel pressure detection means 7 detecting pressure of the fuel; a fuel temperature detection means 8 detecting a temperature of the fuel; and a vapor generation temperature estimation means 16 estimating a fuel temperature where the vapor may be generated. When the internal combustion engine 1 is stopped and the temperature detected by the fuel temperature detection means 8 is higher than the fuel temperature estimated by the vapor generation temperature estimation means 16, the fuel is cooled. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cooling device for an internal combustion engine.

  In a direct-injection gasoline engine, the fuel pressure is rapidly increased when the engine is started, and high-pressure fuel is injected in the compression stroke of each cylinder to atomize the fuel, thereby reducing the required injection amount and reducing the HC at the time of engine start. A technique for reducing the discharge amount (startup boost control) is known.

  However, fuel injection cannot be performed until the fuel pressure rises, and there is a possibility that the time required to complete the start-up becomes longer. In particular, when vapor is generated in the fuel pipe when the engine is stopped, it takes time for the vapor to disappear or be compressed at the start, and as a result, the time until the start is completed may be longer. The amount of vapor generated varies depending on fuel properties, fuel temperature from engine stop to start, fuel pressure, and the like.

  Further, the pressure in the fuel pipe near the injector is maintained at a high pressure even when the engine is stopped by a check valve or the like. However, fuel may leak from the check valve or the like due to aging of the check valve or the like. In this case, immediately after the engine is stopped, the fuel in the fuel pipe near the injector is in a high temperature and low pressure state, the amount of vapor generated increases, and the time until the completion of the start becomes longer at the next engine start.

On the other hand, a technique is known in which when it is determined that vapor is generated, a radiator fan is operated to lower the fuel temperature (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 8-218872 JP-A-9-256926 JP-A-6-280709 Japanese Patent No. 2795020 No. 7-54597

  However, even if the fuel temperature is lowered after the vapor is generated, if the engine is stopped after the warm-up is completed and then restarted immediately, there may be a restart request before the vapor disappears. In this case, it takes a long time to complete the start-up.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of suppressing the generation of vapor in a fuel pipe in a fuel cooling device for an internal combustion engine.

In order to achieve the above object, the internal combustion engine fuel cooling apparatus according to the present invention employs the following means. That is,
In a fuel cooling device for an internal combustion engine comprising means for cooling fuel,
Fuel pressure detection means for detecting the pressure of the fuel;
Fuel temperature detection means for detecting the temperature of the fuel;
Vapor generation temperature estimation means for estimating a fuel temperature at which vapor may be generated from the fuel pressure detected by the fuel pressure detection means;
With
The fuel is cooled when the internal combustion engine is stopped and the temperature detected by the fuel temperature detecting means is higher than the fuel temperature estimated by the vapor generation temperature estimating means. .

  For example, when the internal combustion engine is stopped after the warming-up is completed, the fuel temperature is high and the fuel pressure is high. If the fuel pressure is kept high, vapor is unlikely to be generated even if the fuel temperature is high. However, when the fuel flows out from the check valve or the like, the fuel pressure is reduced and only the fuel temperature is in a high temperature state. If it does so, fuel will evaporate and it will become a bubble, or the air melt | dissolved in the fuel will become a bubble. These bubbles are called vapor. Thus, vapor is more likely to occur as the temperature of the fuel is higher and the pressure of the fuel is lower. The relationship between the fuel temperature at which vapor is generated and the fuel pressure can be obtained for each fuel property. Based on these, the vapor generation temperature estimation means estimates the fuel temperature at which vapor may be generated.

  That is, if the fuel pressure is detected by the fuel pressure detecting means, the fuel temperature at which vapor is likely to be generated at that pressure is known. The generation of vapor can be suppressed by cooling the fuel so that the fuel temperature is maintained at a temperature lower than the fuel temperature at which this vapor may occur.

  In the present invention, the fuel cooling conditions can be determined by the fuel properties.

  That is, since the relationship between the temperature and pressure at which vapor is generated varies depending on the difference in fuel properties, the vapor generation temperature estimating means changes the estimated value of the temperature at which vapor is likely to be generated due to this difference in fuel properties. This makes it possible to suppress the generation of vapor even if the fuel changes.

  In the fuel cooling device for an internal combustion engine according to the present invention, the generation of vapor in the fuel pipe can be suppressed in the fuel cooling device for the internal combustion engine, and the time until the start of the internal combustion engine can be shortened. Further, the fuel can be cooled only when the fuel needs to be cooled.

  Hereinafter, specific embodiments of a fuel cooling device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a fuel cooling device for an internal combustion engine according to the present embodiment.

  The internal combustion engine 1 includes four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 for injecting fuel into the cylinder 2. Each fuel injection valve 3 is connected to a delivery pipe 4. The delivery pipe 4 is connected to an inflow pipe 5 into which fuel from the fuel tank flows and an outflow pipe 6 to return the fuel to the fuel tank.

  A fuel pressure sensor 7 for outputting a signal corresponding to the fuel pressure in the delivery pipe 4 and a fuel temperature sensor 8 for outputting a signal corresponding to the fuel temperature in the delivery pipe 4 are attached to the delivery pipe 4.

The inflow pipe 5 is connected to the fuel tank 20. A feed pump 21 that discharges fuel at a low pressure is provided in the fuel tank 20, and the feed pump 21 is connected to the inflow pipe 5. A high-pressure pump 22 that discharges fuel at a high pressure is attached in the middle of the inflow pipe 5. A check valve 9 is provided between the high-pressure pump 22 and the delivery pipe 4 to prevent back flow of fuel.

  The fuel in the fuel tank 20 is discharged at a low pressure by the feed pump 21 and flows to the high pressure pump 22. Then, after the fuel pressure is increased by the high-pressure pump 22, this high-pressure fuel is supplied to the delivery pipe 4.

  Further, a regulator 10 that opens when the fuel pressure in the delivery pipe 4 becomes equal to or higher than a predetermined pressure is attached to a connection portion between the delivery pipe 4 and the outflow pipe 6. The outflow pipe 6 is connected to the fuel tank 20, and the fuel flowing out from the delivery pipe 4 is returned to the fuel tank 20.

  The delivery pipe 4 is stored inside the fuel cooling device 11. The fuel cooling device 11 is connected to the radiator 12 via a cooling water passage 13. An electric water pump 14 for circulating cooling water is provided in the middle of the cooling water passage 13. The radiator 12 and the cooling water passage 13 are also connected to a cylinder block or the like other than the fuel cooling device 11, but the passages are not shown.

  A radiator fan 15 that blows air to the radiator 12 is attached to the radiator 12.

  The fuel cooling device 11 may simply be a cooling water passage for flowing cooling water to the cylinder head around the delivery pipe 4.

  The internal combustion engine 1 configured as described above is provided with an ECU 16 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 16 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  A fuel pressure sensor 7 and a fuel temperature sensor 8 are connected to the ECU 16 via electric wiring, and output signals from these sensors are input to the ECU 16.

  The electric water pump 14 and the radiator fan 15 are connected to the ECU 16 via electric wiring, and these are controlled by the ECU 8.

  Here, when the internal combustion engine 1 is stopped after the warm-up of the internal combustion engine 1 is completed, the cooling water of the internal combustion engine 1 is stopped, so that the temperature of the internal combustion engine 1 temporarily rises. Thereby, the temperature of the delivery pipe 4 rises, and the fuel temperature in the delivery pipe 4 also rises. At this time, since the volume of the fuel expands, the fuel pressure in the delivery pipe 4 increases. However, when the fuel leaks from the check valve 9 or the regulator 10, the fuel pressure in the delivery pipe 4 does not increase so much and only the fuel temperature. Rises. Depending on the relationship between the fuel temperature and the fuel pressure at that time, vapor may be generated in the delivery pipe 4.

  On the other hand, in this embodiment, the fuel is cooled so that no vapor is generated according to the fuel pressure at that time.

  FIG. 2 is a diagram showing the relationship between the fuel temperature and the total vapor pressure in the delivery pipe. The total vapor pressure is the sum of the partial pressure of the gas dissolved in the fuel and the partial pressure of the fuel vapor, and may be the fuel pressure.

An alternate long and short dash line A indicates a vapor pressure curve, and vapor begins to be generated on the alternate long and short dash line A. When the total vapor pressure becomes lower than the one-dot chain line A or when the fuel temperature becomes higher, vapor is generated. That is, vapor is generated in a region below the alternate long and short dash line A.

  A one-dot chain line B indicates a state where vapor may be generated. In this embodiment, when the total vapor pressure is lower than the one-dot chain line B or when the fuel temperature is high, vapor is generated. Is considered to be. That is, it is considered that vapor is generated in a region below the alternate long and short dash line B. For example, the alternate long and short dash line B may be a value obtained by increasing the total vapor pressure by a predetermined value β as compared with the alternate long and short dash line A.

  An alternate long and short dash line C indicates a state in which the fuel needs to be cooled. In this embodiment, the electric water pump 14 is operated when the fuel pressure is lower than the alternate long and short dash line C or when the fuel temperature is higher than the alternate long and short dash line C. To lower the fuel temperature. That is, the fuel is cooled in a region below the alternate long and short dash line C. The one-dot chain line C may be a value obtained by increasing the total vapor pressure by a predetermined value α, for example, compared with the one-dot chain line A.

  A solid line X indicates changes in the fuel pressure and the total vapor pressure when the fuel is not cooled and the amount of fuel leaking from the check valve 9 or the regulator 10 is large, that is, when the fuel pressure is greatly reduced. After the internal combustion engine 1 is stopped, the fuel state changes in the direction of the arrow. In this case, due to fuel leakage, the total vapor pressure quickly decreases while the fuel temperature is high, and the one-dot chain line C, the one-dot chain line B, and the one-dot chain line A cross in order. And since it reaches the area | region below the dashed-dotted line A, the vapor | steam has generate | occur | produced.

  The solid line Y indicates the transition of the fuel pressure and the total vapor pressure when the fuel is not cooled but the amount of fuel leaking from the check valve 9 or the regulator 10 is small, that is, when the decrease in the fuel pressure is small. In this case, compared with the case of the solid line X, the total vapor pressure decreases more slowly. Therefore, it becomes difficult to generate vapor. However, as the fuel temperature decreases, the total vapor pressure also decreases. Therefore, vapor is generated in a region below the alternate long and short dash line A.

  A solid line Z indicates changes in the fuel pressure and the total vapor pressure when the fuel is cooled according to this embodiment. By cooling the fuel, it is suppressed that the total vapor pressure is low and the fuel temperature is high. Thereby, it is suppressed that the state of a fuel becomes the area | region below the dashed-dotted line A, and generation | occurrence | production of vapor | steam is suppressed.

  Next, a flow for suppressing the occurrence of vapor according to the present embodiment will be described.

  FIG. 3 is a flowchart for determining whether or not to perform fuel cooling. This routine is repeatedly executed every predetermined time.

  In step S101, it is determined whether the internal combustion engine 1 is stopped and the fuel pressure PR is greater than or equal to a predetermined value a.

  If the internal combustion engine 1 is in operation, the fuel is not cooled according to this embodiment. Further, even when the fuel pressure PR is smaller than the fuel pressure required at the time of starting (for example, 4 MPa), the fuel is not cooled. In this step, unnecessary fuel cooling is suppressed.

  If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S102, a change amount dPR per unit time of the fuel pressure PR and a change amount dTP per unit time of the fuel temperature TP are calculated.

  A value obtained by storing the fuel pressure PR obtained from the fuel pressure sensor 7 and the fuel temperature TP obtained from the fuel temperature sensor 8 every predetermined time, and dividing the value obtained by subtracting the current detected value from the previous stored value by the predetermined time. Can be obtained as

  In step S103, it is determined whether or not the fuel pressure change amount dPR is larger than a predetermined value Cp and the fuel temperature change amount dTP is larger than a predetermined value Ct.

  Here, it is determined whether or not vapor generation can be suppressed by cooling the fuel. That is, if the fuel pressure change amount dPR or the fuel temperature change amount dTP is too large, vapor may be generated before the electric water pump 14 is operated and the fuel temperature decreases. In this case, the fuel is not cooled, and the pressure increase time (pre-feed execution time) before starting the engine is maximized.

  If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, the process proceeds to step S105.

  In step S104, the cooling execution flag XC is turned ON. The cooling execution flag XC is a flag that is turned on when vapor generation can be suppressed by cooling the fuel.

  In step S105, the cooling execution flag XC is turned OFF, and the prefeed execution time PF is set to the maximum value b. In this case, since there is a high possibility that vapor has occurred, the pre-feed execution time is made as long as possible to eliminate the vapor.

  Next, the flow of fuel cooling control will be described. For example, the maximum value b is between 500 ms and 700 ms.

  FIG. 4 is a flowchart showing a flow of fuel cooling control. This routine is repeatedly executed every predetermined time.

  In step S201, it is determined whether the cooling execution flag XC is ON. That is, it is determined whether or not vapor generation can be suppressed by cooling the fuel.

  If an affirmative determination is made in step S201, the process proceeds to step S202. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S202, the vapor pressure y generated by vapor is calculated based on the fuel temperature. That is, the vapor pressure y is obtained by substituting the fuel temperature obtained from the fuel temperature sensor 8 into the alternate long and short dash line A in FIG. For example, an approximate expression of the alternate long and short dash line A may be obtained in advance, and the fuel pressure may be substituted into this approximate expression to obtain the vapor pressure y.

  In step S203, it is determined whether or not the fuel pressure PR obtained from the fuel pressure sensor 7 is smaller than the required fuel pressure for cooling. The fuel pressure required for cooling is a vapor pressure indicated by a one-dot chain line C in FIG. 2, and is a vapor pressure obtained by adding a predetermined value α to the vapor pressure y generated by vapor.

  If an affirmative determination is made in step S203, the process proceeds to step S204. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S204, the radiator fan 15 is turned on and the electric water pump 14 is turned on. That is, they are activated. Thereby, fuel temperature falls and generation | occurrence | production of vapor | steam is suppressed.

  In step S205, it is determined whether or not the fuel pressure PR obtained from the fuel pressure sensor 7 is smaller than the vapor generation vapor pressure. The vapor generation vapor pressure is a vapor pressure indicated by a one-dot chain line B in FIG. 2 and is a vapor pressure obtained by adding a predetermined value β to the vapor pressure y generated by the vapor. That is, in this step, it is determined whether or not vapor can be considered.

  If an affirmative determination is made in step S205, the process proceeds to step S206. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S206, the vapor generation amount BP is calculated. The vapor generation amount BP is obtained by adding the vapor generated from the previous time to the current time to the previously calculated vapor generation amount BP, and is calculated by the following equation.

  BP = BP + (y−PR) × γ

  Here, γ is a coefficient for converting the difference between the vapor pressure y generated by the vapor and the fuel pressure PR obtained from the fuel pressure sensor 7 into a vapor generation amount, and is obtained and set in advance through experiments or the like.

  Next, the flow of pre-feed control that is performed when the internal combustion engine 1 is started will be described.

  FIG. 5 is a flowchart showing a flow of pre-feed control performed when the internal combustion engine 1 is started. This routine is repeatedly executed every predetermined time. Further, the pre-feed control is performed by operating the feed pump 21 prior to start-up pressure increase control by the high-pressure pump 22. That is, the fuel pressure is raised to some extent by the feed pump 21 before the start-up pressure increase control.

  In step S301, it is determined whether the vapor generation amount BP is larger than 0, that is, whether vapor is generated. When no vapor is generated, normal pre-feed control is performed.

  If an affirmative determination is made in step S301, the process proceeds to step S302. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S302, it is determined whether the pre-feed execution time is larger than 0, that is, whether the pre-feed execution time has already been set. For example, if the pre-feed execution time is set to the maximum value b in step S105, an affirmative determination is made.

  If an affirmative determination is made in step S302, the process proceeds to step S304, whereas if a negative determination is made, the process proceeds to step S303.

In step S303, the required pre-feed execution time PF is calculated based on the vapor generation amount BP. The pre-feed execution time PF calculated at this time is a time required to eliminate the generated vapor. The vapor that disappears at this time is mainly fuel vapor. The relationship between the pre-feed execution time PF and the vapor generation amount BP is obtained in advance through experiments or the like and mapped.

  In step S304, it is determined whether or not the internal combustion engine 1 is started. For example, it is determined that the internal combustion engine 1 is started when the ignition switch is turned on.

  If an affirmative determination is made in step S304, the process proceeds to step S305. On the other hand, if a negative determination is made, this routine is temporarily terminated.

  In step S305, the pre-feed is executed for the pre-feed execution time PF.

  Then, after the pre-feed control is finished, start-up pressure increase control is executed.

  The vapor pressure when vapor is generated varies depending on the fuel properties. This fuel property can be judged from the increase value of the fuel pressure when the fuel is pumped once from the fuel pump, for example, when the fuel pressure is increased. In this way, by grasping the fuel properties and switching the map and coefficient, it becomes possible to suppress the vapor according to the fuel properties.

  As described above, according to this embodiment, even when there is a risk of vapor generation when the internal combustion engine 1 is stopped, generation of vapor can be suppressed by cooling the fuel. Even if vapor is generated, the vapor is extinguished by extending the prefeed execution time, so that the fuel pressure increase time during the start pressure increase control can be shortened. In this way, the time required to complete the start of the internal combustion engine 1 can be shortened, and the amount of HC discharged when the internal combustion engine 1 is started can be reduced.

  Moreover, since the electric water pump 14 and the radiator fan 15 are operated only when vapor is likely to be generated, it is possible to reduce power consumption and operating noise.

It is a figure which shows schematic structure of the fuel cooling device of the internal combustion engine which concerns on an Example. It is the figure which showed the relationship between fuel temperature and the total vapor pressure in a delivery pipe. It is a flowchart for determining whether cooling of a fuel is performed. It is the flowchart which showed the flow of fuel cooling control. It is the flowchart which showed the flow of the pre-feed control performed at the time of starting of an internal combustion engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Delivery pipe 5 Inflow piping 6 Outflow piping 7 Fuel pressure sensor 8 Fuel temperature sensor 9 Check valve 10 Regulator 11 Fuel cooling device 12 Radiator 13 Cooling water passage 14 Electric water pump 15 Radiator fan 16 ECU
20 Fuel tank 21 Feed pump 22 High pressure pump

Claims (2)

In a fuel cooling device for an internal combustion engine comprising means for cooling fuel,
Fuel pressure detection means for detecting the pressure of the fuel;
Fuel temperature detection means for detecting the temperature of the fuel;
Vapor generation temperature estimation means for estimating a fuel temperature at which vapor may be generated from the fuel pressure detected by the fuel pressure detection means;
With
The fuel is cooled when the internal combustion engine is stopped and the temperature detected by the fuel temperature detecting means is higher than the fuel temperature estimated by the vapor generation temperature estimating means. A fuel cooling device for an internal combustion engine.   2. The fuel cooling device for an internal combustion engine according to claim 1, wherein the fuel cooling condition is determined by the fuel property.

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