JP2000130284A - Fuel injector of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize higher injection pressure without increasing supply pressure from a pressure accumulating chamber. SOLUTION: This fuel injector is provided with a pressure accumulating chamber 1 for accumulating high-pressure fuel, a nozzle hole 13 provided on an oil storage chamber 5 into which fuel from the pressure accumulating chamber 1 is to be introduced through an oil passage 4, a needle valve 6 for opening and closing the nozzle hole 13, a driving means for lifting the needle valve 6, an opening and closing valve 14 interposed in the oil passage 4, and a control means 15 for opening the opening and closing valve 14 before the needle valve 6 is opened and for closing the opening and closing valve 14 after the needle valve 6 is closed. Therefore, dynamic pressure of high-pressure fuel is generated in the oil storage chamber 5 before fuel injection, and high injection pressure is maintained by making use of dynamic pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection device for a diesel engine.

[0002]

2. Description of the Related Art A common rail fuel injection device is known as a fuel injection device for a diesel engine. In this method, high-pressure fuel is temporarily stored in the common rail, and high-pressure fuel is injected directly into the combustion chamber by controlling the opening and closing of an electromagnetically-actuated fuel injection valve. There is an advantage that can be controlled.

As this fuel injection valve, Japanese Patent Application Laid-Open No. 9-158
No. 811 proposes a construction as shown in FIG. 6. The high-pressure fuel in the accumulator 1 in a common rail into which high-pressure fuel is fed by a pump (not shown) is supplied through a high-pressure pipe 2 to a fuel injector. It is guided to a nozzle oil reservoir 5 via an oil passage 4 inside 3 and to a hydraulic chamber 8 of a hydraulic piston 7 connected to a needle valve 6 via a filling orifice 9.

When the fuel is not injected, the solenoid valve 10 is closed, whereby the hydraulic piston 7 is pushed by the high pressure of the hydraulic chamber 8 and the needle valve 6 is seated and closed. When injecting fuel, the solenoid valve 10 is opened, and the pressure in the hydraulic chamber 8 is released to the low pressure side through the discharge orifice 11, and the needle valve 6 lifts while pushing up the hydraulic piston 7 by the oil pressure in the nozzle oil reservoir 5. Then, the injection hole 13 is opened, and the fuel is injected.

[0005] When the same fuel pressure is acting, the pressing force of the hydraulic piston 7 is larger than the lifting force applied to the needle valve 6 due to the difference in the pressure receiving area.
Is closed. When the engine is stopped, the needle valve 6 is closed and held by the return spring 12 so that the fuel in the nozzle oil reservoir 5 does not leak.

[0006]

In such a fuel injection device, before the fuel injection, the pressure in the oil reservoir 5 is increased.
However, the pressure in the oil reservoir 5 decreases with the start of fuel injection, and the actual injection pressure becomes lower than the set pressure in the pressure accumulator 1. This means that even if the fuel corresponding to the fuel injected from the nozzle oil reservoir 5 through the injection hole 13 is supplied from the accumulator 1, the speed is reduced to the speed of the pressure wave propagating through the high-pressure pipe 2 and the internal oil passage 4. This is because the speed is limited and a delay in fuel supply occurs.

For this reason, under high engine speed and high load operating conditions where a high injection pressure is required for suppressing smoke emission, the pressure corresponding to the oil reservoir chamber 5 is reduced in consideration of the pressure drop in the oil storage chamber 5 and the pressure is further increased. It is necessary to increase the supply pressure of the chamber 1.

When the pressure is increased in this manner, new problems such as an increase in the required pump driving force, a decrease in efficiency, a loss due to fuel leakage, a pressure resistance of the piping, and an increase in the required driving force of the solenoid valve are caused. .

The present invention has been proposed to solve such a problem, and has as its object to realize a higher injection pressure without increasing the supply pressure from the pressure accumulating chamber.

[0010]

According to a first aspect of the present invention, there is provided a pressure accumulation chamber for storing high-pressure fuel, an injection hole provided in an oil reservoir through which fuel from the pressure accumulation chamber is guided through an oil passage, and an injection hole. A needle valve for opening and closing, a driving means for lifting the needle valve, an opening / closing valve interposed in the oil passage, and a control means for opening the opening / closing valve before opening the needle valve and closing the opening / closing valve after closing.

According to a second aspect, in the first aspect, the driving means comprises a hydraulic piston connected to a needle valve for opening and closing the injection hole, a hydraulic chamber in which the hydraulic piston slides, and a pressure in the hydraulic chamber. Pressure control means for closing the needle valve via the hydraulic piston by raising it and opening the needle valve by reducing the pressure.

In a third aspect based on the second aspect, the control means opens the on-off valve a predetermined time before fuel injection, and the predetermined time sets the length of the oil passage from the on-off valve to the oil reservoir. The time is set to be substantially equal to or slightly longer than the value divided by the transmission speed of the fuel pressure.

According to a fourth aspect, in the third aspect, a pressure reducing means for leaking the pressure in the oil reservoir after the on-off valve is closed is provided.

In a fifth aspect based on the fourth aspect, the pressure reducing means reduces the pressure in the hydraulic chamber within a range in which the needle valve is not opened by the pressure control means.

In a sixth aspect based on the fifth aspect, the pressure reducing means performs the pressure releasing operation for an extremely short time only once or a plurality of times.

In a seventh aspect based on the first to sixth aspects, the control means for the on-off valve keeps the on-off valve open in an operation region in which pilot injection is performed prior to main injection of fuel. .

In an eighth aspect based on the first to sixth aspects, the control means for the on-off valve comprises: an injection mode in which the on-off valve is always kept open in accordance with an operating condition; Switch to.

[0018]

According to the first or second aspect of the present invention,
When the on-off valve opens the oil passage for conducting high-pressure fuel before fuel is injected, the fuel pressure from the accumulator is guided accordingly, and the fuel pressure in the oil reservoir rises. When the fuel injection is started by opening the injection hole, the fuel injection is performed using the dynamic pressure generated in the oil reservoir. Therefore, a high fuel injection pressure is maintained during the injection period, and the initial fuel injection rate is also increased. Thereby, the discharge of smoke can be reduced. In addition, since the fuel pressure in the accumulator to obtain the same injection pressure can be reduced, the driving force of the pump that supplies fuel to the accumulator decreases,
In addition, the pump efficiency is increased, the fuel efficiency of the engine is improved, and the pressure resistance condition is relaxed, so that the pressure-resistant parts can be reduced in size and weight.

According to the third aspect of the present invention, the time from the opening of the on-off valve to the arrival of the pressure wave of the fuel can be appropriately set in relation to the start timing of the fuel injection. It can be injection pressure.

In the fourth to sixth aspects of the present invention, the fuel pressure in the oil reservoir when fuel injection is not being performed is reduced. Therefore, when the on-off valve is opened next time, the fuel pressure from the accumulator is increased by a large differential pressure. And a dynamic pressure is reliably applied, and a high fuel injection pressure can be maintained using the dynamic pressure.

In the seventh aspect of the invention, in the pilot injection operation region, the on-off valve is kept open and the initial injection rate is suppressed from rising rapidly, and the injection amount control accuracy of the pilot injection is increased, thereby improving the combustion characteristics. In addition, the exhaust characteristics can be improved.

According to the eighth aspect of the present invention, similarly to the above, when the occurrence of smoke is originally small due to operating conditions, for example, in a low rotation speed and low load range, the on-off valve is kept open and the initial injection rate rises sharply. Prevention and reduction of combustion noise.

[0023]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, 1 is an accumulator, 2 is a high pressure pipe, 3 is an injector, 4 is an internal oil passage, 5 is a nozzle oil reservoir, 6 is a needle valve, 7 is a hydraulic piston, 8 is a hydraulic chamber, 9 Is a filling orifice, 10 is a solenoid valve, 11 is a discharge orifice,
Reference numeral 12 denotes a return spring, and 13 denotes an injection hole, which are substantially the same as those in FIG.

According to the present invention, the pressure accumulating chamber 1 and the injector 3
A second solenoid valve (open / close valve) 14 in the middle of the high pressure pipe 2
Is interposed. This solenoid valve 14 is connected to a controller 15
This opens and closes the flow path of the high-pressure fuel guided to the oil passage 4 in response to a signal from the controller, thereby using the dynamic pressure of the supplied fuel to prevent a decrease in the injection pressure. The first solenoid valve 10 is also opened and closed by a signal from the controller 15, and the fuel injection amount and the injection timing are controlled.

The operation will be described with reference to FIGS.

First, the principle of operation will be described with reference to FIG. 2. If the second solenoid valve 14 is closed before fuel injection, high-pressure fuel leaks from the sliding gap between the needle valve 6 and the hydraulic piston 7, so that The fuel pressure Pn of the nozzle oil reservoir 5 becomes lower than that of the conventional one that communicates with the pressure accumulator 1.

When the solenoid valve 14 is opened immediately before fuel injection, a high pressure is supplied from the pressure accumulating chamber 1, so that the fuel pressure Pn in the oil reservoir 5 increases. When the fuel pressure Pn has increased to some extent, the first solenoid valve 10 is opened to lift the needle valve 6 and perform fuel injection. At this time, the fuel pressure P in the oil reservoir 5
n becomes higher than before. This is because a flow of fuel is generated from the pressure accumulating chamber 1 toward the oil storage chamber 5 from a stage before the needle valve 6 is lifted, and the dynamic pressure is converted into static pressure in the oil storage chamber 5 accordingly.

At this point, if the fuel flow from the pressure accumulating chamber 1 occurs only after the needle valve 6 is lifted, a delay will occur by that much, and the recovery of the pressure in the oil reservoir 5 will be delayed. is there.

Here, the timing of opening the second solenoid valve 14 is determined by the pressure accumulating chamber 1 generated by opening the solenoid valve 14.
The fuel injection is started so that the pressure wave from the (electromagnetic valve 14) reaches the oil reservoir 5 and the fuel pressure Pn is high, but before the fuel pressure Pn reaches the maximum pressure. That is, the time tp from the opening of the second electromagnetic valve 14 to the start of fuel injection is determined by the length of the oil passage from the electromagnetic valve 14 to the oil reservoir 5 by the transmission speed (sound speed) of the pressure wave of the high-pressure fuel. Set so that it is approximately equal to or slightly longer than the divided value.

FIG. 3 shows the fuel injection period and the second solenoid valve 14.
The second solenoid valve 14 opens at a predetermined timing immediately before fuel injection, and closes without delay when fuel injection ends. The fuel injection starts when the first solenoid valve 10 is opened and ends when the first solenoid valve 10 is closed. After the fuel has been injected, when the second solenoid valve 14 is closed, the pressure in the nozzle oil reservoir 5 decreases due to leak before the next injection, and the solenoid valve 14 is opened immediately before the next fuel injection, When the pressure in the nozzle oil reservoir 5 starts to rise, the first solenoid valve 10 is opened and fuel injection is started before the pressure reaches the maximum pressure, so that the dynamic pressure acting on the oil reservoir 5 can be effectively used. As a result, a high injection pressure can be maintained.

As a result, even if the supply pressure of the accumulator 1 is the same,
A high injection pressure can be obtained, and the initial injection rate of the fuel can be increased. In particular, the emission of smoke can be effectively suppressed by the high injection pressure in a high engine speed and high load region. Since there is no need to increase the pressure of the pressure accumulating chamber 1, the driving horsepower of the pump is reduced, the pump efficiency is increased, and the pressure resistance of the fuel pipe and the like is improved, so that the size and weight can be reduced. Reduce.

Next, another embodiment shown in FIG. 4 will be described. Here, the first solenoid valve 10 is opened a plurality of times only for a very short time after the fuel injection is completed.

However, this valve opening time is a short time in a range where fuel injection is not performed, and is extremely short.
When the valve 0 is opened, the pressure in the hydraulic chamber 8 is reduced, although not so much as to lift the needle valve 6, so that the fuel pressure P in the oil reservoir 5 is reduced.
n can be reliably reduced, so that the next time the second solenoid valve 14 is opened, the differential pressure with the pressure accumulating chamber 1 increases, and preparations for using the dynamic pressure can be made more reliably. Become. The lower the pressure of the oil reservoir 5 before the second solenoid valve 14 is opened, the greater the pressure rise when the oil reservoir is opened. This dynamic pressure prevents a decrease in the pressure of the oil reservoir 5 at the time of fuel injection. The injection pressure can be maintained.

In this manner, even when the engine speed is high and the interval between the injections is short, or under the condition that the fuel leak from the sliding parts such as the needle valve 6 and the hydraulic piston 7 of the injector 3 is small, the following conditions can be obtained. Nozzle oil reservoir 5 before injection
The fuel pressure can be reduced, and the dynamic pressure can be reliably used.

Next, as shown in FIG. 5, when the pilot injection is performed according to the operating conditions, the second solenoid valve 14 is kept open in the pilot injection region, and the electromagnetic valve is opened only in the region where the pilot injection is not performed. The valve 14 is opened and closed.

The fuel injection is divided into two parts in a region other than the high-speed, high-load region, and a small amount of pilot injection is performed before the main injection, so that the combustion characteristics are moderated and noise and vibration are suppressed. Further, the exhaust composition can be improved. However, in this case, if the second solenoid valve 14 is opened immediately before the pilot injection, the initial injection rate rises sharply, which makes it difficult to accurately inject a small amount of fuel. It is preferable that the initial injection rate be low when a small amount of fuel is injected. Therefore, in the operation region where the pilot injection is performed, the opening and closing operation of the second solenoid valve 14 is stopped and is kept open.

Further, regardless of the presence or absence of the pilot injection, a region in which the opening and closing operation of the second solenoid valve 14 is stopped may be determined depending on the operation region. The combustion noise may be reduced by making the initial injection rate gradual. In this case, the second solenoid valve 14 is opened and closed in a high rotation and high load region, a high injection pressure is maintained, and smoke is reduced.

It should be noted that the present invention is not limited to the above-described embodiment, and it is apparent that various modifications can be made within the scope of the technical idea of the present invention.

For example, although the first solenoid valve 10 is a two-way valve, it may be a three-way valve.
Instead of using a valve that opens and closes with a piezo element, and further uses the pressure change of the hydraulic chamber 8 to drive the needle valve 6, the needle valve 6 is directly driven by an electromagnetic actuator.
May be driven.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a waveform diagram of a fuel pressure.

FIG. 3 is a characteristic diagram showing a relationship between an opening / closing timing of a solenoid valve and a fuel injection pressure.

FIG. 4 is a characteristic diagram showing a relationship between an opening / closing timing of an electromagnetic valve and a fuel injection pressure in another embodiment.

FIG. 5 is an explanatory diagram showing an operation region in which pilot injection is performed.

FIG. 6 is a sectional view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Accumulation chamber 3 Injector 4 Oil passage 5 Oil reservoir 6 Needle valve 7 Hydraulic piston 8 Hydraulic chamber 10 First solenoid valve 13 Injection hole 14 Second solenoid valve (open / close valve) 15 Controller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G066 AA07 AB02 AC09 AD12 BA05 BA17 BA22 BA24 BA46 BA63 BA67 CB01 CB08U CB12 CC06T CC08T CC14 CC26 CC61 CC64T CC66 CC67 CC68U CC70 CD26 CE13 CE22 DA09 DA13 DA14 DB08 DB09 DB12 DB13

Claims (8)

[Claims] 1. An accumulator for storing high-pressure fuel, an injection hole provided in an oil reservoir through which fuel from the accumulator is guided through an oil passage,
A needle valve for opening and closing the injection hole, a driving means for lifting the needle valve,
A fuel injection device for a diesel engine, comprising: an on-off valve interposed in the oil passage; and control means for opening the on-off valve before opening the needle valve and closing it after closing. 2. A hydraulic valve, comprising: a hydraulic piston connected to a needle valve for opening and closing the injection hole; a hydraulic chamber in which the hydraulic piston slides; and a needle valve through a hydraulic piston by increasing the pressure in the hydraulic chamber. 2. The fuel injection device for a diesel engine according to claim 1, further comprising pressure control means for closing the valve and opening the needle valve by reducing the pressure. 3. The control means opens the on-off valve a predetermined time before fuel injection, and the predetermined time is a value obtained by dividing the length of the oil passage from the on-off valve to the oil reservoir by the transmission speed of the fuel pressure. 3. The fuel injection device for a diesel engine according to claim 2, wherein the time is set to be substantially equal to or slightly longer than that. 4. The diesel engine fuel injection device according to claim 3, further comprising pressure reducing means for leaking the pressure in the oil reservoir after the on-off valve is closed. 5. The pressure reducing means reduces the pressure in a hydraulic chamber within a range where the needle valve is not opened by the pressure control means.
A fuel injection device for a diesel engine according to claim 1. 6. A fuel injection device for a diesel engine according to claim 5, wherein said pressure reducing means performs a pressure releasing operation once or a plurality of times for an extremely short time. 7. The on-off valve according to claim 1, wherein said on-off valve control means keeps said on-off valve open in an operation region in which pilot injection is performed prior to main injection of fuel. Fuel injection device for diesel engines. 8. The fuel supply system according to claim 1, wherein the control means for the on-off valve switches between an injection mode in which the on-off valve is always kept open and an injection mode in which the on-off valve is opened and closed according to operating conditions. A fuel injection device for a diesel engine as described.