JP2015161297A - Fuel supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel supply device which can exactly determine the necessity of control for improving startability in a low-temperature environment and combustion stability after start.SOLUTION: The fuel supply device includes: a fuel injection valve 7 which injects liquid fuel into a cylinder of an internal combustion engine 1; a common rail 5 to which the fuel injection valve 7 is attached; a low-pressure fuel pump 3 which sucks up the liquid fuel from a fuel tank 2; a high-pressure fuel pump 4 which is driven by the internal combustion engine 1, increases pressure of the liquid fuel sucked by the low-pressure fuel pump 3 and supplies the liquid fuel to the common rail 5; a common rail pressure sensor 6 which detects pressure in the common rail 5; a controller 8 which controls the pressure in the common rail 5 by controlling a discharge amount of the high-pressure fuel pump 4; and a water temperature sensor 9 which detects a temperature of the cooling water of the internal combustion engine 1. Then, the controller 8 lowers the pressure in the common rail 5 in a low-temperature state in which the temperature of the cooling water is a prescribed value or below.

Description

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

  In the internal combustion engine, the friction increases as the temperature decreases, so that the startability and the combustion stability after start-up deteriorate as the outside air temperature decreases. On the other hand, Patent Document 1 discloses a fuel supply device that executes control to reduce the fuel pressure (fuel pressure) applied to the fuel injection valve if the outside air temperature is an extremely low temperature that is not more than a predetermined value when the internal combustion engine is stopped. ing. According to this fuel supply device, the force required to open the fuel injection valve is reduced by lowering the fuel pressure, so that the fuel injection valve opens quickly and the startability is improved. Further, since the force required to open the fuel injection valve is reduced, the combustion stability in a low temperature state where the friction is large is also improved. In the above document, the temperature detected by the intake air temperature sensor, that is, the intake air temperature is used as the outside air temperature.

Japanese Patent Laid-Open No. 2000-274312

  By the way, the friction of the internal combustion engine depends on the temperatures of the internal combustion engine body and parts, and the above-mentioned document uses the intake air temperature as a temperature correlated with these temperatures to determine whether or not the control for reducing the fuel pressure is necessary. .

  However, since the detected value of the intake air temperature sensor is easily influenced by traveling wind, the value varies depending on the traveling condition even if the temperature of the internal combustion engine body is the same. For this reason, after the start of traveling, it is impossible to accurately determine whether or not the control for reducing the fuel pressure is required by the determination method described in the above document. For example, even if the component temperature has risen to such an extent that control for lowering the fuel pressure is not required due to idling after the engine is started, the control value for lowering the fuel pressure is necessary because the detected value of the intake air temperature sensor has decreased due to the start of traveling. There is a risk that it will be judged.

  Therefore, in the present invention, a fuel that supplies fuel to an internal combustion engine for a vehicle that can improve the startability in a low temperature environment and can accurately determine the necessity of control for improving the combustion stability after the start. An object is to provide a supply device.

  According to an aspect of the present invention, a fuel injection valve that injects liquid fuel into a cylinder of an internal combustion engine, a common rail to which the fuel injection valve is attached, a low-pressure fuel pump that sucks liquid fuel from a fuel tank, and a drive to the internal combustion engine And a high-pressure fuel pump that boosts the liquid fuel sucked up by the low-pressure fuel pump and supplies it to the common rail. The fuel supply device includes a common rail pressure sensor that detects the pressure in the common rail, a controller that controls the pressure in the common rail by controlling the discharge amount of the high-pressure fuel pump, a water temperature sensor that detects the cooling water temperature of the internal combustion engine, Are further included. And a controller reduces the pressure in a common rail in the low temperature state whose cooling water temperature is below a predetermined value.

  According to the above aspect, whether or not to execute the control for reducing the pressure in the common rail, which is effective in improving the startability and the combustion stability after the start, is determined based on the coolant temperature correlated with the friction of the internal combustion engine. Therefore, it is possible to accurately determine whether the control needs to be executed.

FIG. 1 is a schematic configuration diagram of a fuel supply apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing the configuration of the high-pressure fuel pump. FIG. 3 is a diagram illustrating an example of a normal fuel pressure map. FIG. 4 is a flowchart showing a fuel pressure control routine. FIG. 5 is a diagram illustrating an example of a low-temperature fuel pressure map. FIG. 6 is a diagram showing the correlation between the coolant temperature, the fuel temperature, and the temperature of the internal combustion engine body.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of a fuel supply device and its peripheral devices according to an embodiment. The fuel supply device supplies liquid fuel to the internal combustion engine 1. The internal combustion engine 1 is mounted on a vehicle and functions as a drive source for the vehicle. Although FIG. 1 shows an in-line four-cylinder internal combustion engine 1, this embodiment can be similarly applied to other types such as an in-line three-cylinder and a V-type six-cylinder.

  The fuel supply device includes a common rail 5 attached to the internal combustion engine 1, a fuel injection valve 7, and a high-pressure fuel pump 4, and a fuel tank 2 disposed in a lower portion of a vehicle trunk, a rear seat or the like. The

  The fuel tank 2 includes a low-pressure fuel pump 3, a fuel filter 12 that filters fuel on the discharge side of the low-pressure fuel pump 3, and a low-pressure pressure regulator 13 that adjusts the pressure of the low-pressure fuel line 10. The low pressure regulator 13 adjusts the low pressure fuel line 10 to a constant pressure, for example, about 0.3 to 0.5 MPa, by returning a part of the fuel discharged from the low pressure fuel pump 3 to the fuel tank 2. The low pressure fuel pump 3 is driven by an electric motor (not shown).

  The fuel pumped by the low pressure fuel pump 3 is supplied to the high pressure fuel pump 4 via the low pressure fuel line 10.

  The cooling water for cooling the internal combustion engine 1 also circulates in the heater core 14.

  FIG. 2 is a diagram showing a detailed configuration of the high-pressure fuel pump 4. The high-pressure fuel pump 4 is mainly composed of a plunger pump 20. The plunger pump 20 changes the volume of the pump chamber 29 by reciprocating the plunger 25 against the biasing force of the spring 28 by a cam 24 provided on the exhaust camshaft of the internal combustion engine 1. In the intake stroke of the plunger 25, fuel is sucked into the pump chamber 29 via the intake-side one-way valve 23, and in the discharge stroke in which the plunger 25 rises through the bottom dead center, the discharge-side one-way valve 26 is used. The fuel in the pump chamber 29 is discharged.

  The discharge side of the high-pressure fuel pump 4 is connected to a common rail 5 as a pressure accumulation chamber via a high-pressure fuel line 11. A fuel injection valve 7 facing the combustion chamber of each cylinder of the internal combustion engine 1 is connected to the common rail 5. Therefore, the fuel discharged from the high-pressure fuel pump 4 flows into the common rail 5 and is then injected into the cylinder through the fuel injection valve 7 provided in each cylinder of the internal combustion engine 1. A common rail pressure sensor 6 that detects the pressure (fuel pressure) in the common rail 5 is attached to the common rail 5. The detection signal of the common rail pressure sensor 6 is read into the controller 8 and converted into a pressure value by the controller 8.

  In addition to the common rail pressure sensor 6, the controller 8 reads various detection signals such as a water temperature sensor 9 that detects the cooling water temperature of the internal combustion engine 1, a crank angle sensor (not shown), a throttle position sensor, an accelerator opening sensor, and a battery sensor. It is. The controller 8 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). It is also possible to configure the controller 8 with a plurality of microcomputers.

  The high pressure fuel pump 4 further includes a solenoid 22. The solenoid 22 is provided on the opposite side of the plunger pump 20 with the suction-side one-way valve 23 interposed therebetween, and opens the suction-side one-way valve 23 by an electromagnetic force generated by energization regardless of the pressure in the pump chamber 29. The valve state can be maintained. Accordingly, the start timing of the discharge operation of the plunger pump 20, that is, the discharge amount can be controlled depending on at which timing of the discharge stroke of the plunger pump 20 the controller 8 ends the energization of the solenoid 22.

  Further, the high-pressure fuel line 11 between the discharge-side one-way valve 26 and the common rail 5 branches to become a return pipe 31. The return pipe 31 is provided with a relief valve 27. When the pressure of the high-pressure fuel line 11 exceeds a predetermined pressure of, for example, about 15 MPa, the relief valve 27 is opened, and a part of the fuel is exchanged with the fuel damper 21. Return to the solenoid 22. Thereby, it is possible to prevent the pressure in the common rail 5 from exceeding a desired pressure. That is, the upper limit value of the fuel pressure can be limited.

  Here, the pressure control (fuel pressure control) in the common rail 5 will be described.

  The controller 8 controls the discharge end of the high-pressure fuel pump 4 by controlling the end timing of energization of the solenoid 22, that is, the closing timing of the suction side one-way valve 23 in the discharge stroke, thereby matching the fuel pressure with the target fuel pressure. . Specifically, the pump discharge amount is feedback-controlled so that the difference between the detected value of the common rail pressure sensor 6 and the target fuel pressure is eliminated during the operation with the fuel injection amount corresponding to the operation state.

  The target fuel pressure is set by the controller 8 according to the operating conditions, that is, the engine speed and the load. The controller 8 stores in advance a map in which the target fuel pressure is set higher as the load of the internal combustion engine 1 becomes higher and the engine speed becomes higher, as shown in FIG. 3, for example. Set with.

  The “load” in the map of FIG. 3 may be replaced with a basic fuel injection amount or a basic fuel injection pulse.

  The target value (target fuel injection amount) of the fuel injection amount from the fuel injection valve 7 is set by the controller 8 according to the operating conditions. Then, the controller 8 calculates an injection time for injecting the target fuel injection amount under the target fuel pressure, and controls the valve opening time of the fuel injection valve 7 according to the calculated injection time. For example, even if the target fuel injection amount is the same, the higher the target fuel pressure, the shorter the injection time, and conversely, the lower the target fuel pressure, the longer the injection time.

  Next, control of the fuel supply device at the time of cold start will be described.

  In the internal combustion engine 1, the clearance of each part such as the crankshaft, the camshaft, the piston, the high-pressure fuel pump 4 and the like becomes narrower as the temperature becomes lower, and the viscosity of the lubricating oil becomes higher as the temperature becomes lower. For this reason, the friction required for driving the internal combustion engine 1 (hereinafter also simply referred to as “friction”) is greater at the time of cold start than at the start of warm-up. In addition, since the atomization characteristics of the fuel deteriorate as the temperature becomes lower, the desired combustion state cannot be obtained and the generated torque decreases. Such an increase in friction and a decrease in generated torque cause a decrease in startability and a decrease in combustion stability after the start.

  In the present embodiment, the fuel pressure, that is, the common rail pressure is reduced in order to reduce friction. This is due to the fact that when the common rail pressure is lowered, the discharge amount of the plunger pump 20 is reduced and the drive friction of the high-pressure fuel pump 4 is reduced. This reduces friction.

  However, the lower the fuel pressure, the larger the particle size of the fuel injected from the fuel injection valve 7 and the more difficult the atomization of the fuel, and the weaker the penetration of the injected fuel and the homogeneity of the fuel spray in the cylinder Decreases. The deterioration of the atomization characteristics and the decrease in homogeneity lead to a decrease in startability and combustion stability of the internal combustion engine 1. Further, when the fuel atomization characteristics deteriorate, the amount of fuel adhering to the cylinder wall surface increases, so the amount of fuel flowing into the oil pan below the cylinder block increases, and so-called oil dilution is promoted.

  Therefore, when reducing the fuel pressure, the effect of the decrease in the drive friction of the high-pressure fuel pump 4 is compared with the degree of deterioration in the fuel atomization characteristics and the decrease in homogeneity, so that the startability of the internal combustion engine 1 can be reduced. In addition, it is necessary to set a fuel pressure that improves combustion stability.

  By the way, the atomization characteristic of the fuel also changes depending on the fuel temperature, and even when the fuel pressure is the same, the atomization characteristic becomes more difficult as the fuel temperature becomes lower. That is, when lowering the fuel pressure, it is necessary to consider the fuel temperature.

  Further, since the fuel temperature has a correlation with the temperature of the main body of the internal combustion engine 1, it can be determined based on the fuel temperature whether or not the fuel pressure is reduced.

  As described above, using the fuel temperature, it is possible to determine whether or not the fuel pressure needs to be decreased in order to suppress the decrease in startability and combustion stability, and to set the fuel pressure when the fuel pressure is decreased. it can. However, sensors for detecting the fuel temperature are often not mounted on existing vehicles. In addition, there is a temperature of the fuel injection valve 7 as a temperature that can be equated with the fuel temperature, but a sensor for detecting the temperature is often not mounted on an existing vehicle. Therefore, in order to detect the fuel temperature or the temperature of the fuel injection valve 7, a new sensor is provided, which increases the cost.

  Therefore, the controller 8 executes the control described below in order to improve the startability at the cold start and improve the combustion stability after the start without detecting the fuel temperature or the fuel injection valve temperature. .

  FIG. 4 is a flowchart showing a control routine of fuel pressure control executed by the controller 8. This routine is repeatedly executed at a short interval of, for example, about 10 milliseconds after the ignition switch is turned on. Hereinafter, it demonstrates according to a step.

  The controller 8 reads the cooling water temperature detected by the water temperature sensor 9 in step S100, and determines whether or not the cooling water temperature is −30 ° C. or lower in step S110.

  As a result of the determination, the controller 8 executes the process of step S120 if the cooling water temperature is −30 ° C. or lower, and executes the process of step S130 if the cooling water temperature is higher than −30 ° C. When this process is finished, this routine is finished.

  Step S110 determines whether or not the fuel pressure needs to be reduced, that is, whether or not the internal combustion engine 1 is in an extremely low temperature state where the startability and the like deteriorate. As described above, it is desirable to make the determination based on the fuel temperature. However, if a new sensor is provided to detect the fuel temperature, the cost increases. Therefore, in the present embodiment, the determination is performed based on the cooling water temperature. The fuel temperature has a correlation with the temperature of the main body of the internal combustion engine 1, and the coolant temperature also has a correlation with the temperature of the main body of the internal combustion engine 1. Therefore, since there is also a correlation between the cooling water temperature and the fuel temperature, whether or not the fuel pressure needs to be reduced based on the cooling water temperature can be determined by examining the correlation between the cooling water temperature and the fuel temperature in advance. It can be judged accurately. Note that the threshold value for determination of −30 ° C. is merely an example, and for example, a higher temperature may be used.

  In step S120, the controller 8 executes fuel pressure control using a low-temperature fuel pressure map (also referred to as low-temperature fuel pressure map control). In step S130, the controller 8 performs fuel pressure control using a normal fuel pressure map (also referred to as normal fuel pressure map control). Run.

  The normal fuel pressure map is a fuel pressure map used when the internal combustion engine 1 is not in an extremely low temperature state. As shown in FIG. 3 described above, a higher fuel pressure is set as the load becomes higher and the rotation speed is higher.

  On the other hand, the low-temperature fuel pressure map is a fuel pressure map used when the internal combustion engine 1 is in an extremely low temperature state, and a fuel pressure lower than the fuel pressure under the same operating conditions in the normal fuel pressure map is set. Yes.

  FIG. 5 is an example of a low-temperature fuel pressure map, and a constant value is set regardless of the load and the engine speed. Here, the “constant value” is a value smaller than the minimum fuel pressure in the normal fuel pressure map. Note that the fuel pressure upper limit value may be provided for each operating condition without setting the fuel pressure for all operating conditions to a constant value.

  According to the control routine described above, the drive friction of the high-pressure fuel pump 4 is reduced by the low-temperature fuel pressure map control when the engine is started at a very low temperature. Even after the engine is started, the low-temperature fuel pressure map control is executed while the internal combustion engine 1 is in an extremely low temperature state. When the internal combustion engine 1 leaves the extremely low temperature state as the operation time elapses, the control is switched to the normal fuel pressure up control.

  In the control routine of the present embodiment, the low-pressure fuel pressure control is executed at an extremely low temperature (for example, −30 ° C. or lower), in which the effect of reducing the fuel pressure is particularly large. Even in a state (for example, about 0 ° C.), the effect of reducing the fuel pressure can be obtained. Therefore, the threshold used for the determination in step S110 may be a value higher than −30 ° C. (for example, about 0 to 5 ° C.).

  FIG. 6 is a diagram showing a correlation between the above-described cooling water temperature, fuel temperature, and temperature of the internal combustion engine 1 main body. For comparison, the change in intake air temperature is also shown.

  In FIG. 6, the vehicle starts the engine at timing T0, the cooling water temperature reaches −30 ° C. at timing T1, starts running at timing T2, accelerates to timing T3, travels at a constant speed from timing T3 to timing T4, The vehicle decelerates from timing T4 to timing T6. Note that the “oil dilution limit” in the figure is the lower limit temperature within which the degree of oil dilution is acceptable.

  The cooling water temperature, the fuel temperature, and the temperature of the internal combustion engine 1 all start rising after the engine is started. The reason why the cooling water temperature rises is that the temperature of the internal combustion engine 1 body rises as the engine starts, and the cooling water flowing inside the internal combustion engine 1 receives heat from the internal combustion engine 1. The fuel temperature rises because the temperature of the common rail 5 attached to the internal combustion engine 1 rises by receiving heat from the internal combustion engine 1, and the fuel in the common rail 5 is warmed. Even after the start of traveling, the cooling water temperature and the fuel temperature rise as the temperature of the internal combustion engine 1 body rises. In FIG. 6, since the coolant temperature has reached −30 ° C. at the timing T1, the low-temperature fuel pressure map control is executed before the timing T1, and the normal fuel pressure map control is switched after the timing T1. The same applies to the determination of the necessity of low-temperature fuel pressure map control using the fuel temperature.

  On the other hand, the intake air temperature rises due to the temperature rise in the engine room as the engine starts, but once the vehicle starts to travel, it greatly decreases once due to the influence of the traveling wind. For this reason, at the timing T1, the determination threshold value is reached and the low-temperature fuel pressure map control is switched to the normal fuel pressure map control. However, when it falls below the determination threshold value due to the influence of traveling wind, the low-temperature fuel pressure map control is switched again. .

  Further, the intake air temperature once decreases and then rises again. However, during the constant vehicle speed, the slope of the rise is smaller than when the vehicle is stopped, and when the vehicle starts decelerating, the slope of the temperature rise becomes larger than when the vehicle speed is constant. That is, the intake air temperature is weakly correlated with the temperature of the main body of the internal combustion engine 1 as compared with the coolant temperature and the fuel temperature. The intake air temperature reaches the determination threshold again at timing T5.

  As described above, when it is determined whether or not the low-temperature fuel pressure map control is necessary using the intake air temperature, the low-temperature fuel pressure map control is executed even when the low-temperature fuel pressure map control is unnecessary. On the other hand, if the necessity of low-temperature fuel pressure map control is determined using the coolant temperature as in the present embodiment, a more accurate determination can be made than when the intake air temperature is used for the determination.

  In addition, when a sensor for detecting the fuel temperature or the temperature of the fuel injection valve 7 is mounted, or when it can be allowed to be newly mounted for other reasons such as using the detected value for other control, The determination in S110 of FIG. 4 may be performed based on the fuel temperature or the temperature of the fuel injection valve 7.

  In addition to the coolant temperature, the temperature correlated with the fuel temperature includes the temperature of the internal combustion engine 1 (cylinder head, cylinder block), the temperature of the common rail 5, and the heater core temperature. Sensors that detect these temperatures are often not installed in existing vehicles, but if they are installed or if it is allowed to be newly installed, either of these temperatures will be used. Based on this, the determination in S110 of FIG. 4 may be performed.

  Next, effects of executing the above-described control routine will be described.

(1) In this embodiment, it is determined based on the coolant temperature whether or not the temperature is extremely low, that is, whether the normal fuel pressure map control or the low temperature fuel pressure map control is executed. Thereby, since it is possible to accurately determine whether or not the low-temperature fuel pressure map control is required without providing a new sensor, startability and combustion stability can be improved at low cost.

(2) In this embodiment, whether the normal fuel pressure map control or the low temperature fuel pressure map control is executed is any one of the fuel temperature, the temperature of the fuel injection valve, the cylinder head temperature, the cylinder block temperature, or the heater core temperature. You may determine based on. Also in this case, it is possible to accurately determine whether or not the low-temperature fuel pressure map control is necessary, and to improve the startability and the combustion stability. In addition, when a sensor for detecting each temperature is provided, or when it is allowed to be newly installed for other reasons such as use in other controls, there is no problem of cost increase.

(3) In this embodiment, the controller 8 stores the low-temperature fuel pressure map and the normal fuel pressure map in advance, and switches the map used for fuel pressure control according to the determination result as to whether or not the temperature is extremely low. For this reason, startability and combustion stability can be improved by simple control.

  In addition, when creating a low-temperature fuel pressure map, control is performed to improve startability and combustion stability by setting a fuel pressure that takes into account the effects of deterioration in atomization characteristics and reduction in homogeneity. The promotion of oil dilution can be suppressed.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Fuel tank 3 Low pressure fuel pump 4 High pressure fuel pump 5 Common rail 6 Common rail pressure sensor 7 Fuel injection valve 8 Controller 9 Water temperature sensor 14 Heater core 20 Plunger pump 25 Plunger

Claims (3)

A fuel injection valve for injecting liquid fuel into the cylinder of the internal combustion engine;
A common rail to which the fuel injection valve is attached;
A low-pressure fuel pump for sucking up the liquid fuel from a fuel tank;
A high-pressure fuel pump that is driven by the internal combustion engine and pressurizes the liquid fuel sucked up by the low-pressure fuel pump and supplies the liquid fuel to the common rail;
A common rail pressure sensor for detecting the pressure in the common rail;
A controller for controlling the pressure in the common rail by controlling the discharge amount of the high-pressure fuel pump;
A water temperature sensor for detecting a cooling water temperature of the internal combustion engine;
In a fuel supply device comprising:
The controller uses the cooling water temperature as a temperature for determination, and lowers the pressure in the common rail in a low temperature state where the cooling water temperature is equal to or lower than a predetermined value compared to when the cooling water temperature is higher than a predetermined value. A fuel supply device. A fuel injection valve for injecting liquid fuel into the cylinder of the internal combustion engine;
A common rail to which the fuel injection valve is attached;
A low-pressure fuel pump for sucking up the liquid fuel from a fuel tank;
A high-pressure fuel pump that is driven by the internal combustion engine and pressurizes the liquid fuel sucked up by the low-pressure fuel pump and supplies the liquid fuel to the common rail;
A common rail pressure sensor for detecting the pressure in the common rail;
A controller for controlling the pressure in the common rail by controlling the discharge amount of the high-pressure fuel pump;
Means for detecting or estimating the cooling water temperature of the internal combustion engine, the cylinder head temperature of the internal combustion engine, the cylinder block temperature of the internal combustion engine, the temperature in the common rail, the temperature of the fuel injection valve, or the temperature of the heater core;
In a fuel supply device comprising:
The controller uses the cooling water temperature, the cylinder head temperature, the cylinder block temperature, the temperature in the common rail, the temperature of the fuel injection valve, or the temperature of the heater core as the temperature for determination. The fuel supply device, wherein the pressure in the common rail is reduced in a low temperature state where the temperature for use is lower than a predetermined value for determination. The fuel supply device according to claim 1 or 2,
The controller includes a low-temperature fuel pressure map in which a pressure in the common rail is set when the determination temperature is equal to or less than the predetermined value for determination, and the common rail in the case where the determination temperature is higher than the predetermined value for determination. A normal fuel pressure map in which the pressure is set in advance, and the low temperature fuel pressure map or the normal fuel pressure map of the low temperature fuel pressure map is determined according to a determination result of whether the determination temperature is equal to or less than the determination predetermined value. A fuel supply device that determines which one to use.

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