JP2007071082A - Fuel injector of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of preventing propagation of pressure pulsation between two common rails in a fuel injector of an internal combustion engine having the two common rails different in pressure accumulating force. <P>SOLUTION: This invention has a fuel pump for boosting and delivering fuel, the two common rails different in the pressure accumulating force, and a switching means for conducting the fuel pump only to one of the two common rails in a partial period of an effective delivery stroke of the fuel pump and conducting the fuel pump only to the other of the two common rails in a residual period of the effective delivery stroke for solving the above problem. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel injection device including a plurality of common rails.

In a fuel injection device for an internal combustion engine comprising two fuel injection valves having different injection pressures and two common rails for supplying fuel to each of the two fuel injection valves, the fuel discharged from a single fuel pump A configuration for supplying serial data to two common rails has been proposed (see, for example, Patent Document 1).
JP 2004-232599 A JP 2002-539374 A JP 2003-148275 A JP 2003-148220 A

  By the way, when two common rails are connected in series, pressure pulsation in one common rail propagates to the other common rail, and thus the accumulated pressure in the two common rails may become unstable. If the accumulated pressure of each common rail becomes unstable, the fuel injection pressure and the injection amount may fluctuate irregularly.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to propagate pressure pulsation between two common rails in a fuel injection device for an internal combustion engine having two common rails having different accumulated pressures. It is to provide a preventable technique.

  In order to solve the above-described problems, the present invention is configured to selectively supply the fuel discharged from a single fuel pump to one of the two common rails, thereby reducing the pressure pulsation of one common rail. Propagation to the other common rail was prevented.

  In detail, the fuel injection device for an internal combustion engine according to the present invention selectively selects one of the two common rails, a fuel pump that boosts and discharges fuel, two common rails having different accumulated pressures, and the fuel. And switching means for conducting with the pump.

  Among the two common rails having different accumulated pressures, the pressure pulsation is likely to increase in the common rail having a high accumulated pressure (hereinafter referred to as a high-pressure common rail) compared to the common rail having a low accumulated pressure (hereinafter referred to as a low-pressure common rail).

  For this reason, if the high-pressure common rail and the low-pressure common rail are in communication with each other, the pressure pulsation of the high-pressure common rail may propagate to the low-pressure common rail and the accumulated pressure on the low-pressure common rail and high-pressure common rail may become unstable. was there.

  As a method for solving such a problem, the fuel injection device is divided into two systems by independently providing a fuel pump for supplying fuel to the high pressure common rail and a fuel pump for supplying fuel to the low pressure common rail. Can be considered. However, the increase in fuel pumps and piping may lead to cost increase and deterioration in in-vehicle performance.

On the other hand, if the fuel pump is configured to selectively conduct with only one of the two common rails, the high-pressure common rail and the low-pressure common rail do not conduct with each other. Propagation to the low pressure common rail can be prevented.

  As a result, it is possible to stabilize the accumulated pressure of the high pressure common rail and the low pressure common rail without unnecessarily increasing the number of fuel pumps and piping.

  The switching means according to the present invention includes a fuel supply path for transporting fuel discharged from a fuel pump, two fuel branch paths branched from the fuel supply path and connected to two common rails, and two fuel supply paths. A three-way switching valve arranged at a portion branching to the fuel branch passage and a fuel branch pipe (hereinafter referred to as a high-pressure fuel branch pipe) connected to the high-pressure common rail among the two fuel branch pipes. And a check valve for preventing a back flow of the high-pressure fuel branch passage.

  According to such a configuration, when the fuel is supplied to the high pressure common rail, the three-way switching valve connects the high pressure common rail and the fuel pump, and shuts off the low pressure common rail. It will not be propagated to the common rail.

  Also, when fuel is supplied to the low-pressure common rail, the three-way selector valve connects the low-pressure common rail and the fuel pump, and shuts off the high-pressure common rail, preventing pressure propagation between the high-pressure common rail and the low-pressure common rail. Is done.

  By the way, when the three-way switching valve performs the switching operation, the low pressure common rail and the high pressure common rail are temporarily connected. In this case, the high-pressure common rail fuel may flow back through the fuel branch pipe and flow out to the low-pressure common rail, or the pressure pulsation of the high-pressure common rail may propagate to the low-pressure common rail. Since the stop valve is provided, the fuel in the high pressure common rail is also prevented from flowing out to the low pressure common rail.

  Therefore, when the switching means is configured as described above, it is possible to stabilize the accumulated pressure of the high pressure common rail and the low pressure common rail while suppressing an increase in fuel pumps and piping.

  According to the present invention, in a fuel injection device for an internal combustion engine having two common rails having different accumulator pressures, it is possible to prevent propagation of pressure pulsations between the two common rails while suppressing an increase in the number of fuel pumps and complicated piping. Is possible.

  Hereinafter, specific embodiments of a fuel injection 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 an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) provided with two injectors per cylinder.

  In the cylinder head 2 of the internal combustion engine 1, a center injector 4 is disposed substantially at the center of the surface facing the top surface of the piston 3. A side injector 5 is disposed at the edge of the surface of the cylinder head 2 facing the top surface of the piston 3.

  The center injector 4 communicates with the high-pressure common rail 7 through the first fuel pipe 6. The high-pressure common rail 7 is connected to a three-way switching valve 9 via a high-pressure fuel branch pipe 8. In the middle of the high-pressure fuel branch pipe 8, a check valve (check valve) 10 that suppresses the back flow of fuel is disposed.

  The side injector 5 communicates with the low pressure common rail 12 via the second fuel pipe 11. The low pressure common rail 12 is connected to the three-way switching valve 9 via a low pressure fuel branch pipe 13.

  In addition to the high-pressure fuel branch pipe 8 and the low-pressure fuel branch pipe 13, a fuel supply pipe 14 is connected to the three-way switching valve 9. The three-way switching valve 9 is a valve that selectively connects one of the high-pressure fuel branch pipe 8 and the low-pressure fuel branch pipe 13 to the fuel supply pipe 14.

  The fuel supply pipe 14 is connected to the fuel pump 15. The fuel pump 15 is a pump that boosts and discharges fuel pumped from a fuel tank (not shown). FIG. 2 is a diagram showing a schematic configuration of the fuel pump 15.

  In FIG. 2, the fuel pump 15 includes a cylinder 150, a plunger 151 fitted into the cylinder 150 so as to be slidable in the axial direction, and a spring 152 that urges the plunger 151 downward (downward in FIG. 2). And a pump camshaft 153 for pressing the plunger 151 in the upward direction (upward in FIG. 2).

  The pump camshaft 153 is provided with a first cam 154 and a second cam 155 for pressing the plunger 151 in the upward direction. The first cam 154 and the second cam 155 have the same cam profile and are different in rotational phase by 180 degrees. The pump camshaft 153 configured as described above rotates in synchronization with the camshaft of the internal combustion engine 1 (one rotation every time the crankshaft rotates twice), so that the plunger 151 is rotated every time the crankshaft rotates once. Is raised once (one reciprocation). That is, the pump camshaft 153 raises the plunger 151 twice (two reciprocations) per cycle of the internal combustion engine 1.

  Also, the cylinder 150 has a suction hole 156 that guides the fuel sucked up from the fuel tank into the cylinder 150 and a discharge that discharges the fuel in the cylinder 150 that has been pressurized by the rise of the plunger 151 to the fuel supply pipe 14. A hole 157 is formed.

  The suction hole 156 is provided with a suction valve 158 that is opened and closed by the ECU 16. The discharge hole 157 is opened when the fuel pressure in the cylinder 150 becomes higher than the fuel pressure in the fuel supply pipe 14, and in the cylinder 150 as compared with the fuel pressure in the fuel supply pipe 14. A check valve 159 that closes when the fuel pressure becomes low is provided.

  In the fuel pump 15 configured as described above, when the intake valve 158 is opened while the plunger 151 is in the stroke (intake stroke) by the first cam 154 and the second cam 155, fuel is supplied into the cylinder 150. Inhaled.

  The valve opening period (effective intake stroke) of the intake valve 158 is determined based on the fuel injection amount required for the internal combustion engine 1. For example, in the fuel pump 15 shown in FIG. 2, the pump camshaft 153 raises the plunger 151 twice (two reciprocations) per cycle of the internal combustion engine 1, so that fuel injection for two cylinders is performed in one effective intake stroke. The valve opening period may be determined so that the amount can be sucked into the cylinder 150.

When the intake valve 158 is closed and the plunger 151 moves from a lowering stroke to a rising stroke (discharge stroke), the fuel in the cylinder 150 is boosted as the plunger 151 moves up. When the fuel pressure in the cylinder 150 becomes higher than the pressure in the fuel supply pipe 14, the check valve 159 is opened and high pressure fuel in the cylinder 150 is discharged to the fuel supply pipe 14 (effective discharge). Process). The high-pressure fuel discharged from the cylinder 150 to the fuel supply pipe 14 is supplied to the high-pressure common rail 7 or the low-pressure common rail 12 via the high-pressure fuel branch pipe 8 or the low-pressure fuel branch pipe 13.

  Here, referring back to FIG. 1, the internal combustion engine 1 is provided with an ECU 16. The ECU 16 is an arithmetic logic circuit that includes a CPU, a ROM, a RAM, a backup RAM, and the like. Various sensors such as a crank position sensor 17 and an accelerator position sensor 18 are electrically connected to the ECU 16, and output signals from these various sensors can be input.

  The ECU 16 electrically controls the center injector 4, the side injector 5, the three-way switching valve 9, and the fuel pump 15 using the output signals of the various sensors described above as parameters.

  For example, when the internal combustion engine 1 includes four cylinders, the ECU 16 causes the intake stroke top dead center for each of the first cylinder (# 1) to the fourth cylinder (# 4) as shown in FIG. In the vicinity of (for example, 400 ° CA to 300 ° CA before the compression stroke top dead center), the fuel is injected from the center injector 4 (bi-rubber injection), and then from the beginning to the middle of the compression stroke (eg, before the compression stroke top dead center). By performing (premixed injection) from the side injector 5 at 150 ° CA to 60 ° CA), a premixed gas is formed in the cylinder, and the premixed gas is compressed by raising the piston 3 to ignite and burn. Let

  At that time, the ECU 16 may suppress ignition delay by injecting fuel from the center injector 4 again in the vicinity of the compression stroke top dead center as necessary.

  By the way, when fuel is injected from both the center injector 4 and the side injector 5 as shown in FIG. 2, the fuel discharged from the fuel pump 15 is supplied to both the high-pressure common rail 7 and the low-pressure common rail 12. There is a need.

  However, if the fuel supply pipe 14 communicates with both the high-pressure fuel branch pipe 8 and the low-pressure fuel branch pipe 13 at the same time, the pressure pulsation in one common rail may propagate to the other common rail. In particular, since the high pressure common rail 7 is likely to generate a large pressure pulsation as compared with the low pressure common rail 12, the pressure pulsation of the high pressure common rail 7 propagates to the low pressure common rail 12, and the injection pressure and injection amount from the side injector 5 are increased. May fluctuate.

  In contrast, when the ECU 16 supplies the fuel discharged from the fuel pump 15 to the high-pressure common rail 7 and the low-pressure common rail 12, the fuel pump 15 (fuel supply pipe 14) has the high-pressure common rail 7 and the low-pressure common rail 12. The three-way switching valve 9 is controlled so as to be electrically connected to only one of them.

  Hereinafter, the control procedure of the three-way switching valve 9 by the ECU 16 will be described with reference to FIG. FIG. 4 is a timing chart showing the control procedure of the three-way switching valve 9.

  The ECU 16 performs an effective discharge stroke (in FIG. 4, when the first cam 154 or the second cam 155 raises the plunger 151, and the fuel pressure in the cylinder 150 is changed to the fuel pressure P in the fuel supply pipe 14. The three-way switching valve 9 is connected so that the fuel supply pipe 14 and the low-pressure fuel branch pipe 13 are electrically connected only during a part of the higher period), and the fuel supply pipe 14 is electrically connected to the high-pressure fuel branch pipe 8 in the other periods. To control.

For example, in the example shown in FIG. 4, the ECU 16 communicates with the low-pressure fuel branch pipe 13 from the middle of the effective discharge stroke until the end of the effective discharge stroke, and from the end of the effective discharge stroke. The three-way switching valve 9 is controlled so that the fuel supply pipe 14 communicates with the high-pressure fuel branch pipe 8 during the period until the middle of the next effective discharge stroke.

  When the three-way switching valve 9 is controlled in this way, the fuel supply pipe 14 communicates only with the high-pressure fuel branch pipe 8 in the first half of the effective discharge stroke, and the fuel supply pipe 14 communicates with the low-pressure fuel branch in the second half of the effective discharge stroke. Only the tube 13 will be communicated.

  Therefore, according to the present embodiment, when the fuel is supplied to the high-pressure common rail 7, the three-way switching valve 9 connects the high-pressure common rail 7 and the fuel pump 15 and shuts off the low-pressure common rail 12. Propagation of pressure pulsation between 7 and the low pressure common rail 12 is prevented.

  When the fuel is supplied to the low-pressure common rail 12, the three-way switching valve 9 connects the low-pressure common rail 12 and the fuel pump 15 and shuts off the high-pressure common rail 7, so that the high-pressure common rail 7 and the low-pressure common rail 12 Propagation of pressure pulsations between the two is prevented.

  By the way, when the three-way switching valve 9 is switched, the high-pressure fuel branch pipe 8 and the low-pressure fuel branch pipe 13 temporarily communicate with each other, so that the fuel in the high-pressure common rail 7 flows back through the high-pressure fuel branch pipe 8. May flow into the low-pressure fuel branch pipe 13 and the low-pressure common rail 12. However, in the fuel injection device for the internal combustion engine according to the present embodiment, the check valve 10 is arranged in the middle of the high-pressure fuel branch pipe 8, so that the high-pressure fuel branch pipe 8 and the low-pressure fuel branch pipe 8 are switched when the three-way switching valve 9 is switched. Even if the fuel branch pipe 13 is conducted, it is possible to prevent the fuel in the high-pressure common rail 7 from flowing into the low-pressure common rail 12.

  According to the embodiment described above, in a fuel injection device for an internal combustion engine including the high-pressure common rail 7 and the low-pressure common rail 12, the propagation of pressure pulsation between two common rails is prevented using a single fuel pump 15. It becomes possible. As a result, it is possible to stabilize the accumulated pressure of each common rail while suppressing a decrease in in-vehicle performance and an increase in cost.

It is a figure which shows schematic structure of the internal combustion engine in an Example. It is a figure which shows schematic structure of a fuel pump. It is a timing chart which shows the control procedure of a fuel injection valve. It is a timing chart which shows the control procedure of a three-way selector valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Center injector 5 ... Side injector 6 ... 1st fuel pipe 7 ... Common rail for high pressure 8 ... High pressure Fuel branch pipe 9 ... Three-way switching valve (switching means)
10. Check valve (check valve)
11 .... Second fuel pipe 12 .... Low pressure common rail 13 .... Low pressure fuel branch pipe 14 .... Fuel supply pipe (fuel supply path)
15 ... Fuel pump 16 ... ECU

Claims (2)

A fuel pump for boosting and discharging the fuel;
Two common rails with different accumulated pressures,
Switching means for selectively conducting either one of the two common rails with the fuel pump;
A fuel injection device for an internal combustion engine, comprising: In Claim 1, the switching means includes a fuel supply path for transporting the fuel discharged from the fuel pump, two fuel branch paths branched from the fuel supply path and connected to the two common rails, A three-way switching valve disposed at a portion branched from the fuel supply passage to the fuel branch passage, and a fuel branch passage connected to a common rail on the high pressure side of the two common rails. A fuel injection device for an internal combustion engine, comprising: a check valve for preventing.

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