JP2004245103A - Direct injection diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct injection diesel engine capable of improving exhaust gas performance by enabling compression ratio to be reduced without damaging low-temperature startability. <P>SOLUTION: The common-rail type direct injection diesel engine 1 comprises a fuel injection valves 2a-2d for directly injecting fuel into a combustion chamber of the engine 1, a fuel pressure adjusting means 5 formed of a fuel supply pump 5a for adjusting pressure of the fuel supplied to the fuel injection valves and a solenoid valve 5b, and a start control section of an electronic control unit 3 for controlling the fuel injection valves and the fuel pressure adjusting means at a starting time of the engine. When the temperature at the starting time of the engine is not higher than a predetermined temperature, the start control section controls the fuel injection valves 2a-2d to perform pilot injection prior to a main injection, and controls the fuel pressure adjusting means 5 to adjust the pressure of the fuel to be higher than that when the the temperature exceeds the predetermined temperature. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a direct-injection diesel engine capable of achieving a low compression ratio and improving exhaust gas performance.
[0002]
[Prior Art and Problems to be Solved by the Invention]
Generally, in a direct injection diesel engine provided with a fuel injection valve for directly injecting fuel into a combustion chamber of an engine, when the compression ratio is reduced (for example, a compression ratio of 17 to 18.5 → a compression ratio of 16.0), the combustion temperature is reduced. It is well known that, while the generation of NOx (nitrogen oxide) and soot is suppressed and the exhaust gas performance is improved due to the decrease in the temperature, the low-temperature startability in a low-temperature environment is deteriorated.
[0003]
It is considered that the deterioration of the low-temperature startability is originally caused by the fuel injection characteristics at the low-temperature start of the low-compression ratio direct injection diesel engine in which the air-fuel mixture hardly reaches the self-ignition temperature due to the low compression ratio. That is, as shown in FIG. 6, since the injection pressure at a low temperature was set at a relatively low level of about 20 MPa, atomization of the injected fuel was not sufficiently promoted. However, since only the control of the injection amount and the injection start timing is performed, it is difficult to easily achieve the self-ignition atmosphere at a low temperature.
[0004]
Incidentally, in order to improve startability in high altitudes such as mountainous areas, start control of a common rail diesel engine that controls a common rail pressure (ie, injection pressure) at the time of engine start and executes pilot injection and main injection (main injection). Patent Literature 1 discloses a technique for controlling the common rail pressure to be lower as the atmospheric pressure is lower and to advance the main injection start timing. Further, Patent Document 1 discloses a technique of increasing the pilot injection amount (and / or the main injection amount) as the engine temperature is lower.
[0005]
However, Patent Literature 1 discloses a technique of controlling the common rail pressure at the time of low-temperature start and executing pilot injection prior to main injection as described above, but reducing the compression ratio without impairing low-temperature startability. There is no disclosure of a technology that makes this possible.
[0006]
[Patent Document 1]
JP 2001-12277 A
SUMMARY OF THE INVENTION It is an object of the present invention to provide a direct injection diesel engine capable of achieving a low compression ratio without deteriorating low-temperature startability and improving exhaust gas performance.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a direct injection diesel engine according to claim 1 of the present invention controls a fuel injection valve for directly injecting fuel into a combustion chamber of the engine, and regulates a pressure of fuel supplied to the fuel injection valve. A direct-injection diesel engine, comprising: a fuel pressure adjusting unit that controls the fuel injection valve and the fuel pressure adjusting unit at the time of starting the engine. When the temperature is equal to or lower than the predetermined temperature, the fuel injection valve is controlled to execute the pilot injection prior to the main injection, and the fuel pressure adjusting means is controlled so as to adjust the pressure of the fuel to a higher pressure than when the temperature exceeds the predetermined temperature. It is characterized by the following.
[0009]
As a result, atomization of the injected fuel is sufficiently promoted (by increasing the fuel pressure), and an atmosphere in which the main injection is easily ignited can be easily made (by split injection of fuel). As a result, in the direct injection diesel engine, the compression ratio can be reduced without impairing the low temperature startability, and the exhaust gas performance can be improved.
[0010]
A direct injection diesel engine according to claim 2, wherein a fuel injection valve that injects fuel directly into a combustion chamber of the engine, a fuel pressure adjustment unit that adjusts a pressure of fuel supplied to the fuel injection valve, and when the engine is started. In a direct-injection diesel engine including the fuel injection valve and a start control device that controls the fuel pressure adjusting unit, the start control device performs, prior to main injection, when a temperature at the time of starting the engine is equal to or lower than a predetermined temperature. And controlling the fuel injection valve to execute pilot injection and controlling the fuel pressure adjusting means to adjust the pressure of the fuel to 40 MPa or more.
[0011]
Thereby, the same operation and effect as the first aspect can be obtained.
[0012]
The direct injection diesel engine according to claim 3 is characterized in that the compression ratio of the engine is 16.5 or less.
[0013]
Thereby, the exhaust gas performance is further improved by lowering the compression ratio.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the direct injection diesel engine according to the present invention will be described in detail with reference to the drawings.
[0015]
[Example]
FIG. 1 is a system configuration diagram of a direct injection diesel engine showing an embodiment of the present invention, FIG. 2 is an explanatory view of a split injection pattern, and FIG. 3 is a graph showing the relationship between engine coolant temperature and injection pressure (control fuel pressure) at startup. FIG. 4 is a graph illustrating the comparison of the injection pressure, and FIG. 5 is a graph similarly illustrating the relationship between the injection pressure and the complete explosion time at a low temperature start.
[0016]
As shown in FIG. 1, fuel injection valves 2a to 2d are provided for each cylinder of a common rail direct injection diesel engine (hereinafter, referred to as an engine) 1 mounted on a vehicle such as a truck or a bus (four cylinders in the figure). An example is shown), and the electromagnetic valves (not shown) mounted on the fuel injection valves 2a to 2d are turned on / off by an electronic control unit (hereinafter referred to as ECU) 3 composed of a microcomputer or the like, so that the fuel injection is performed. (Fuel injection amount, injection timing, etc.) are controlled according to the operating state of the engine 1.
[0017]
Fuel of a predetermined pressure stored in a common rail 4 is constantly supplied to the fuel injection valves 2a to 2d. A fuel tank (not shown) is supplied to the common rail 4 by a fuel supply pump 5a constituting a fuel pressure adjusting means 5. Fuel is supplied.
[0018]
The ECU 3 receives a pressure signal from an injection pressure sensor (common rail pressure sensor) 6 attached to the common rail 4 and adjusts the valve opening of the solenoid valve 5b constituting the fuel pressure adjusting means 5 by duty control. The fuel pressure of the common rail 4 (that is, the injection pressure of the fuel injection valves 2a to 2d) is feedback-controlled according to the operating state of the engine 1.
[0019]
The ECU 3 includes a water temperature sensor for detecting an engine cooling water temperature, a starter switch for detecting whether or not the engine is cranking, and an engine rotation sensor for detecting an engine rotation speed, as means for detecting an operation state of the engine 1. And various detection signals such as an accelerator opening sensor for detecting an engine load state.
[0020]
In this embodiment, when the engine 1 is started (this is detected by a starter switch), the fuel injection valves 2a to 2d and the fuel pressure adjusting means 5 are controlled by a start control unit (start control device) provided in the ECU 3. When the starting temperature of the engine 1 (which is detected by a water temperature sensor) is equal to or lower than a predetermined temperature, one pilot injection is executed prior to the main injection as shown in FIG. As shown in FIG. 3 (A) and FIG. 4, the injection pressure (control fuel pressure) of the fuel injection valves 2a to 2d is adjusted to a higher pressure than when the temperature exceeds the predetermined temperature. As shown in FIG. 3B, the injection pressure (control fuel pressure) may be adjusted to a high pressure in a stepwise manner in a region where the engine cooling water temperature at the time of starting is equal to or lower than a predetermined value.
[0021]
The injection amount of the pilot injection is preferably about 10% of the entire injection amount, and the divided injection interval between the end time of the pilot injection and the start time of the main injection is preferably about 5 ° in crank angle (FIG. 2).
[0022]
The injection pressure has a limit in order to reduce the load on the engine 1, but it is preferable to increase the injection pressure from the conventional 20 MPa to about 60 MPa (see FIG. 4).
[0023]
As described above, in the present embodiment, when the starting temperature of the engine 1 is equal to or lower than the predetermined temperature, the injection pressure of the fuel injection valves 2a to 2d is adjusted to a higher pressure than when the temperature exceeds the predetermined temperature. Atomization can be sufficiently promoted, and the execution of the pilot injection prior to the main injection can easily create an atmosphere in which the main injection is easily ignited.
[0024]
As a result, as shown in FIG. 5, in the common rail type direct injection diesel engine 1, a low compression ratio (for example, a compression ratio of 16.5 or less) can be achieved without impairing the low temperature startability, and the exhaust gas performance can be improved.
[0025]
From FIG. 5, it can be seen that the complete explosion time at the time of low temperature start (the time required to increase from the start of cranking to the idling speed) is reduced from about 9 seconds to about 2 seconds in the related art. It can also be seen that a sufficient effect is obtained even when the injection pressure is 40 MPa or more.
[0026]
It is needless to say that the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention. For example, other detection means such as an atmospheric temperature sensor may be used instead of the water temperature sensor as a means for detecting the engine start temperature. Further, the split injection may be executed when the temperature at the time of starting the engine 1 exceeds a predetermined temperature, or even at times other than the starting time.
[0027]
【The invention's effect】
As described above, according to the first aspect of the present invention, the start control device that controls the fuel injection valve and the fuel pressure adjusting means at the time of starting the engine performs the main injection when the engine start temperature is equal to or lower than the predetermined temperature. Since the fuel injection valve is controlled to execute pilot injection in advance and the fuel pressure adjusting means is controlled to adjust the pressure of the fuel to a higher pressure than when the temperature exceeds the predetermined temperature, atomization of the injected fuel is sufficient. Therefore, the direct injection diesel engine can have a low compression ratio without impairing the low-temperature startability, thereby improving exhaust gas performance.
[0028]
According to the invention of claim 2, the start control device that controls the fuel injection valve and the fuel pressure adjusting means at the time of starting the engine performs the pilot injection prior to the main injection when the temperature at the time of starting the engine is equal to or lower than a predetermined temperature. Since the fuel injection valve is controlled to be executed and the fuel pressure adjusting means is controlled to adjust the pressure of the fuel to 40 MPa or more, the same operation and effect as the first aspect of the invention can be obtained.
[0029]
According to the invention of claim 3, since the compression ratio of the engine is 16.5 or less, the exhaust gas performance is further improved by lowering the compression ratio.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a direct injection diesel engine showing one embodiment of the present invention.
FIG. 2 is an explanatory view of a divided injection pattern.
FIG. 3 is a graph showing a relationship between an engine cooling water temperature and an injection pressure (control fuel pressure) at the time of starting.
FIG. 4 is a graph similarly illustrating a comparison of injection pressures.
FIG. 5 is a graph showing the relationship between the injection pressure and the complete explosion time at the time of low temperature startup.
FIG. 6 is an explanatory diagram showing injection characteristics at the time of a conventional low-temperature start.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Common rail type direct injection diesel engine 2a-2d Fuel injection valve 3 Electronic control unit (ECU)
4 common rail 5 fuel pressure adjusting means 5a fuel supply pump 5b solenoid valve 6 injection pressure sensor (common rail pressure sensor)

Claims (3)

A fuel injection valve that injects fuel directly into the combustion chamber of the engine;
Fuel pressure adjusting means for adjusting the pressure of the fuel supplied to the fuel injection valve;
A start control device that controls the fuel injection valve and the fuel pressure adjusting means when the engine is started;
In a direct injection diesel engine with
The start control device includes:
When the starting temperature of the engine is equal to or lower than a predetermined temperature, the fuel injection valve is controlled to execute pilot injection prior to the main injection, and the pressure of the fuel is adjusted to a higher pressure than when the temperature exceeds the predetermined temperature. A direct-injection diesel engine, which controls the fuel pressure adjusting means. A fuel injection valve that injects fuel directly into the combustion chamber of the engine;
Fuel pressure adjusting means for adjusting the pressure of the fuel supplied to the fuel injection valve;
A start control device that controls the fuel injection valve and the fuel pressure adjusting means when the engine is started;
In a direct injection diesel engine with
The start control device includes:
When the temperature at the time of starting the engine is equal to or lower than a predetermined temperature, the fuel injection valve is controlled to execute a pilot injection prior to the main injection, and the fuel pressure adjusting means is controlled to adjust the pressure of the fuel to 40 MPa or more. Direct injection diesel engine. 3. The direct injection diesel engine according to claim 1, wherein a compression ratio of the engine is 16.5 or less.

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