JP2000161173A - Accumulator type fuel injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance fuel consumption and exhaust gas characteristic by optimizing injection pressure at the initial stage of main injection by use of an accumulator fuel injection device which executes auxiliary injection prior to the main injection to prevent the delay of ignition. SOLUTION: A controller 8 forms in a fuel passage downstream of an injection rate changing selector valve 5 fuel pressure higher than auxiliary injection pressure and lower than main injection pressure by opening the selector valve 5 for a short time between auxiliary injection and main injection, the selector valve 5 controlling the supply of high pressure fuel from a high pressure accumulator 3 to the fuel passage 10a downstream of a check valve 32. Under this condition, the main injection is started by opening a selector valve 7 for controlling injection timing, so that the injection pressure at the initial stage of the main injection attains the appropriate pressure higher than the auxiliary injection pressure and lower than subsequent main injection pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accumulator type fuel injection device.

[0002]

2. Description of the Related Art There is known a pressure-accumulation type fuel injection device capable of stably supplying high-pressure fuel stored in an accumulator to each cylinder of a diesel engine to improve engine performance in a wide operating range. However, even when such a fuel injection device is used, if the fuel injection rate immediately after the start of fuel injection is excessive, that is, if the amount of fuel injected during the ignition delay period is large, rapid explosive combustion occurs at the beginning of combustion. As a result, not only the engine operation noise increases, but also the NOx in the exhaust gas increases.

As one of the measures for solving such a problem, there is a case where an auxiliary injection is performed prior to a main injection in each fuel injection cycle. In this case, since the ignition delay period is shortened, the amount of fuel injected in the main injection stroke during the ignition delay period is reduced, so that rapid combustion is prevented,
Operation noise and NOx emission can be reduced. However, in the case of a device configuration in which high-pressure injection is performed from the start of main injection following auxiliary injection, operation noise and NOx emission may not be sufficiently reduced. In addition, in the auxiliary injection, it is desirable to inject the minimum amount of fuel to obtain the ignition delay reducing effect. However, in the case of a device configuration in which the auxiliary injection is performed at a relatively high injection pressure, the fuel injection amount is suppressed to the required minimum amount. To do so, the auxiliary injection time must be shortened, and the required control accuracy increases. If the required control accuracy is not obtained, the fuel injection amount in the auxiliary injection becomes too small or too large, so that the original effect of the auxiliary injection is not obtained, and the exhaust gas and the fuel consumption are rather deteriorated.

[0004] As another measure for reducing operating noise and NOx emission, a pressure-accumulation type fuel injection device which injects fuel at a low fuel injection rate in an initial stage of fuel injection in each fuel injection cycle is provided. Proposed. The device according to this proposal selectively connects, for example, a low-pressure accumulator for storing low-pressure fuel, a high-pressure accumulator for storing high-pressure fuel, and a low-pressure accumulator or a high-pressure accumulator to an injector (fuel injection nozzle). A switching valve for switching the injection rate, and an opening / closing valve for controlling the injection start / end timing by communicating / cutting off the control chamber of the injector and the fuel tank.

An accumulator type fuel injection device of this type, for example, disclosed in International Publication WO98 / 09068, controls the opening / closing timing of an opening / closing valve for controlling the injection timing and a switching valve for switching the injection rate, thereby controlling each opening / closing timing. Only the main injection is performed or the main injection and the auxiliary injection are performed for each fuel injection cycle. Further, there is disclosed a technique of performing high-pressure injection after performing low-pressure injection in an initial stage of main injection.

In connection with the present invention, in the apparatus described in the above publication, low-pressure auxiliary injection is performed for a short time, and main injection is started when a predetermined time has elapsed since the end of auxiliary injection. In the initial stage, the low-pressure injection may be performed, and the high-pressure injection may be performed over the remaining period of the main injection.
In this case, by closing the on-off valve for controlling the injection timing and the switching valve for switching the injection rate, the fuel passage connecting the switching valve and the fuel chamber of the injector is filled with low-pressure fuel and the injector is controlled to communicate with the fuel passage. The fuel is supplied to the chamber to keep the injector closed, and when the auxiliary injection start time comes, the on-off valve is opened to discharge the fuel in the control chamber to the fuel tank, thereby opening the injector to reduce the low pressure. , And the on-off valve is closed when the auxiliary injection time has elapsed. When the main injection start timing comes after a predetermined time has elapsed from the end of the auxiliary injection, the on-off valve is opened again to start low-pressure main injection, and further, the switching valve is opened during the main injection to open the high-pressure accumulator. The high-pressure fuel from the nozzle is injected from a nozzle to perform high-pressure injection.

As described above, the fuel consumption and exhaust gas characteristics of the engine are improved by performing the low-pressure auxiliary injection and the main injection including the low-pressure injection and the high-pressure injection in each fuel injection cycle. However, there is a demand for further improvement in fuel efficiency and exhaust gas characteristics.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a pressure accumulator which can further improve the fuel efficiency and exhaust gas characteristics by optimizing the injection pressure in the initial stage of the main injection performed after the low pressure auxiliary injection. It is an object of the present invention to provide a fuel injection device.

[0009]

SUMMARY OF THE INVENTION An accumulator type fuel injection device according to the present invention has a first accumulator for storing high-pressure fuel, and a control for controlling discharge of high-pressure fuel in the first accumulator to a downstream side of a fuel passage. A valve, a second accumulator connected to a fuel passage downstream of the control valve for storing low-pressure fuel, and a main injection and a low-pressure auxiliary injection preceding the fuel injection nozzle connected to the fuel injection nozzle connected to the fuel passage. A fuel control means for opening the control valve between the auxiliary injection and the main injection for a short time, opening the valve in the middle of the main injection, and closing the valve at the end of the main injection. It is characterized by.

According to this pressure accumulating fuel injection device, when the control valve is opened for a short time after the low pressure auxiliary injection is performed, the high pressure fuel from the first pressure accumulator is supplied to the fuel passage for a short time,
The fuel pressure in the fuel passage becomes higher than the auxiliary injection pressure. Therefore, in the initial stage of the main injection by the fuel injection nozzle,
Fuel injection is performed at an intermediate pressure higher than the auxiliary injection pressure and lower than the main injection pressure. When the control valve is opened during the main injection, high-pressure fuel is supplied to the fuel injection nozzle via the fuel passage, and high-pressure injection is performed.

As described above, when the medium-pressure injection is performed in the initial stage of the main injection following the low-pressure auxiliary injection, compared to the case where the low-pressure injection is performed in the initial stage of the main injection, the initial injection of the main injection is performed. Is increased, the amount of fuel to be injected in the remaining period of the main injection is reduced by the increase in the injection amount in the initial stage, and the main injection time is shortened as a whole. As described above, when an appropriate amount of fuel is injected at the initial stage of the main injection and the main injection time is shortened, the fuel injection is terminated early, and the fuel efficiency is improved. In addition, excessive fuel supply is prevented from being performed before ignition as in the case where high-pressure injection is started from the initial stage of main injection, and operation noise and NOx emissions are reduced.

In addition, when the auxiliary injection is performed at a low pressure, the required accuracy related to the auxiliary injection time control is reduced as compared with the case where the auxiliary injection is performed at a high pressure. The amount can be controlled to contribute to improving fuel efficiency. Further, the fuel control means may control the opening / closing timing of, for example, a valve for controlling the injection timing and a valve for switching the injection rate, and the configuration of the apparatus is not particularly complicated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an accumulator type fuel injection device according to an embodiment of the present invention will be described. The accumulator type fuel injection device is, for example, an in-line six-cylinder diesel engine (not shown).
The high pressure pump 1 is provided as shown in FIGS. The high-pressure pump 1 is driven by the engine to pump up and pressurize fuel in the fuel tank 17, and is composed of, for example, a positive displacement plunger pump, and the fuel discharge pressure can be adjusted by adjusting the effective section of the pressure feeding stroke. ing. The pumping stroke adjustment is performed, for example, by adjusting the closing timing of a solenoid valve (not shown), and the pumping operation is disabled while the solenoid valve is open. The high-pressure pump 1 in the device of the present embodiment relating to a six-cylinder engine has a
With two plungers. Each plunger is associated with three cylinders and is adapted to perform three pumping strokes from each plunger during one revolution of the high pressure pump shaft.

[0014] The controller (EC
U) 8 is an engine speed Ne detected by the engine speed sensor 8a and an accelerator pedal depression amount (accelerator opening) detected by an accelerator opening sensor (not shown).
The pumping stroke of the pump 1 is variably adjusted in accordance with ACC, and the pumping stroke (fuel) is further adjusted in accordance with the actual pressure PHP in the high-pressure accumulator (first accumulator) 3 detected by the pressure sensor 3a (FIG. 2). Pressure) is feedback-controlled to obtain high-pressure fuel suitable for the operating state of the engine.

The fuel pressurized by the pump 1 is stored in the high-pressure accumulator 3. This high-pressure accumulator 3 is common to each cylinder and communicates with the fuel passage 10a. In the middle of the fuel passage 10a, a switching valve (control valve) 5 for switching the fuel injection rate, for example, comprising a two-way solenoid valve is provided for each cylinder, and in the fuel passage 10a, immediately downstream of the switching valve 5 A check valve 32 is provided.

A low-pressure accumulator (second accumulator) common to each cylinder is connected to the fuel passage 10a via a fuel passage 10b branched from the fuel passage 10a downstream of the check valve 32. A check valve 6 is provided in the middle of the fuel passage 10 b, and the check valve 6 is connected to the fuel passage 1 on the side of the low-pressure accumulator 4.
The fuel pressure in the fuel passage 10b on the downstream side of the check valve 32
The valve is opened when the fuel pressure is higher than the fuel pressure in a. The fuel passage 10b is provided with a bypass fuel passage that bypasses the check valve 6, and the bypass fuel passage is provided with an orifice 6a. When the fuel pressure in the fuel passage 10a is higher than that in the fuel passage 10b,
The fuel in the fuel passage 10a flows into the fuel passage 10b through the orifice 6a, and further flows into the low-pressure accumulator 4.
Between the low-pressure accumulator 4 and the fuel tank 17, a mechanical pressure control valve 34 (FIG. 1) that opens when the fuel pressure in the low-pressure accumulator 4 reaches a predetermined pressure is provided.

Instead of the pressure control valve 34 in FIG. 1, a pressure control valve 34 (FIG. 2) for adjusting the fuel pressure in the low-pressure accumulator 4 to a predetermined pressure under the control of the controller 8 may be used. A fuel injection device including the pressure control valve 34 shown in FIG. 2 will be described. In FIG. 2, reference numeral 4a denotes a pressure sensor for detecting the fuel pressure PLP in the low-pressure accumulator 4. The controller 8 detects the fuel pressure in the low-pressure accumulator 4 by the pressure sensor 4a (FIG. 2) so that the fuel pressure in the low-pressure accumulator 4 becomes a pressure suitable for the engine operation state represented by the engine speed Ne and the accelerator pedal depression amount ACC. The pressure control valve 34 is controlled based on the actual fuel pressure PLP thus obtained.

An injector (fuel injection nozzle) 9 for each cylinder of the engine has a control chamber 11 and a fuel chamber 12 connected to a fuel passage 10a. The control chamber 11 is connected to a fuel tank via a fuel return passage 10c. 17. Reference numerals 15 and 16 represent orifices. Reference numeral 7 denotes an on-off valve for controlling the injection timing, which is arranged in the middle of the fuel return passage 10c and includes, for example, a two-way solenoid valve. Note that the on-off valve 7 may be incorporated in the injector.

The injector 9 has a needle valve 13 that can move in a direction to open the nozzle hole by receiving the fuel pressure supplied into the fuel chamber 12 and a nozzle hole that receives the fuel pressure supplied into the control chamber 11. It has a hydraulic piston 14 that can move in the closing direction and a spring (not shown) that urges the needle valve in the direction that closes the nozzle hole. Therefore, when fuel of the same pressure is supplied to the control chamber 11 and the fuel chamber 12 from the fuel passage 10a and the on-off valve 7 for controlling the injection timing is closed, the action force due to the fuel pressure applied to the hydraulic piston 14 is reduced. The resultant force with the acting force of the spring exceeds the acting force due to the fuel pressure applied to the needle valve 13, and the nozzle hole is closed by the needle valve 13.
On the other hand, when the fuel in the control chamber 11 is discharged to the fuel tank 17 side by opening the on-off valve 7, the acting force applied to the hydraulic piston 14 decreases or disappears, and the needle valve 13 pushes up the hydraulic piston 14 to push up the nozzle hole. Is opened, and the fuel in the fuel chamber 12 is injected into the combustion chamber (not shown) of the engine.

The accumulator type fuel injection device according to the present embodiment executes a main injection and an auxiliary injection preceding the main injection.
It is intended mainly to shorten the main injection time without excessively increasing the injection pressure in the initial stage of the main injection, particularly the injection pressure until ignition, and to prevent the ignition delay of the fuel supplied by the main injection. The aim is to supply the required minimum amount of fuel by auxiliary injection, thereby simultaneously improving fuel efficiency and reducing engine operation noise and NOx emissions.

Specifically, as shown in the uppermost part of FIG. 3, the fuel injection device is configured such that in each fuel injection cycle, when a predetermined time has elapsed from completion of the low-pressure auxiliary injection, the medium-pressure main injection is performed. The injection is started, and the injection pressure is switched from the medium pressure to the high pressure in the middle of the main injection. In connection with the above-described fuel injection control, the controller 8 determines the engine operating state based on, for example, the engine speed Ne and the accelerator pedal depression amount Acc, and according to the determined engine operating state, the electromagnetic for adjusting the pumping stroke. The pumping stroke of the high-pressure pump 1 is adjusted by controlling the opening / closing timing of a valve (not shown), whereby the fuel pressure in the high-pressure accumulator 3 is controlled to match the engine operating state. , The operation of the pressure control valve 34 is controlled to control the fuel pressure in the low-pressure accumulator 4 to a value suitable for the operating state of the engine. Then, the controller 8 determines the value of the injection control parameter according to the engine operating state, for example, based on a map (not shown). As shown in FIG. 3, the injection control parameters include, for example, the auxiliary injection start timing t1, the auxiliary injection time Δ
TL (= t2−t1), high pressure fuel introduction start timing t3 for medium pressure formation, high pressure fuel introduction time ΔTm (= t4−t)
3), main injection start timing t5, medium pressure injection time ΔTM (= t
6-t5) and main injection time ΔTMH (= t7−t6)
including. Further, the controller 8 controls the injector drive signal ON timing t based on the injection control parameter value.
1, t5 and injector drive signal off timing t2,
It is configured to determine t7, switching valve drive signal on timings t3, t6, and switching valve drive signal off timings t4, t8.

Hereinafter, the operation of the fuel injection device having the above configuration will be described. During operation of the engine, a fuel pressure control routine (not shown) and an injector / switching valve control routine shown in FIG. 4 are executed by the controller 8 in parallel and periodically. Both control routines are started each time it is determined that the start of the fuel injection cycle in each cylinder has been reached based on, for example, a cylinder discrimination signal (not shown) or a time elapsed from the rise of the crankshaft rotation position signal.

For convenience of illustration and description, the control routine of FIG. 4 shows only the control procedure for one cylinder. Note that a part of the control procedure, for example, the determination of the engine operation state may be performed once in one fuel injection cycle in common to all cylinders. In the fuel pressure control routine, the opening / closing timing and valve opening of the solenoid valve for adjusting the pressure feeding stroke and the pressure control valve are controlled in accordance with the determined engine operating state, and the fuel pressure in the accumulators 3 and 4 is changed to the engine operating state. It is controlled to the appropriate target pressure.

The injector / switching valve control routine shown in FIG. 4 is started each time the start point of each fuel injection cycle is reached. At this time, for example, a timer (not shown) built in the controller 8 is started, and the elapsed time from the start of the fuel injection cycle is measured. In the control routine of FIG. 4, the engine speed Ne and the accelerator pedal depression amount ACC
Is read, and the engine operating state is determined (step S1). Then, the respective values of the auxiliary injection start time t1, the auxiliary injection time ΔTL, the high pressure fuel introduction start time t3, the high pressure fuel introduction time ΔTm, the main injection start time t5, the medium pressure injection time ΔTM, and the main injection time ΔTMH are determined in step S
A determination is made from a map (not shown) based on the engine operation state determined in step 1, and further, injector / switch valve drive signal on / off timings t1 to t8 are determined based on these injection control parameter values (step S2).

It is determined whether or not the auxiliary injection start timing t1 has arrived based on the elapsed time from the start of the fuel injection cycle. As shown in FIG. 3, the switching valve 5 and the on-off valve 7 are both closed until the auxiliary injection start timing t1 arrives, and the low-pressure accumulator 4 supplies the low-pressure fuel to the fuel passage 10a downstream of the switching valve 5. Is supplied to the control chamber 1
1 and the fuel chamber 12. Since the on-off valve 7 is closed, the hydraulic piston 1 is controlled by the fuel pressure in the control chamber 11.
The combined force of the acting force on the needle 4 and the acting force of the spring on the needle valve exceeds the acting force on the needle valve 13 due to the fuel pressure in the fuel chamber 12, and the needle valve 13 closes the nozzle hole of the injector 9.

At this time, the fuel pressure (injector inlet pressure) in the fuel chamber 12 is maintained at substantially the same pressure as the low-pressure fuel in the low-pressure accumulator 4. That is, when the fuel pressure in the fuel passage 10a downstream of the check valve 32 becomes lower than the pressure of the low-pressure fuel, the check valve 6 in the fuel passage 10b opens, and the low-pressure fuel flows from the low-pressure accumulator 4 to the fuel passage 10a. On the other hand, when the fuel pressure in the downstream fuel passage 10a exceeds the pressure of the low-pressure fuel, the fuel in the fuel passage 10a is supplied to the orifice 6a.
Flows into the low-pressure accumulator 4 via the

When the auxiliary injection start timing t1 arrives, the injector drive signal is turned on and only the on-off valve 7 is opened (step S3), and the low-pressure fuel in the control chamber 11 drains through the orifice 16 and the fuel return passage 10c. And
When the combined force of the acting force applied to the hydraulic piston 14 and the acting force of the spring on the needle valve becomes smaller than the acting force applied to the needle valve 13, the needle valve 13 rises, the nozzle hole is opened, and the low-pressure fuel is injected into the injector 9. Injected from. Auxiliary injection is started at a relatively low injection pressure, that is, at a relatively low fuel injection rate (fuel injection amount per unit time).

Thereafter, when the auxiliary injection time .DELTA.TL elapses from the auxiliary injection start time t1 and the auxiliary injection end time t2 arrives, the injector drive signal is turned off, the on-off valve 7 is closed (step S3), and the needle valve 13 controls the nozzle. The hole is closed. As a result, the auxiliary injection at low pressure ends.
The fuel injected into the combustion chamber of the engine in this way
Although not necessarily burning immediately, chemical activation proceeds and facilitates ignition of the fuel supplied to the engine by the subsequent main injection. That is, the ignition delay is reduced. The auxiliary injection time ΔTL is set so as to supply a minimum amount of fuel necessary for preventing ignition delay, thereby improving fuel efficiency.

When the auxiliary injection is performed at a low pressure as described above, the required accuracy of the auxiliary injection time control is reduced as compared with the case where the auxiliary injection is performed at a high pressure. It can be precisely controlled to the minimum required
Contributes to improved fuel efficiency. Next, the medium-pressure fuel supplied to the medium-pressure injection in the initial stage of the main injection is supplied to the fuel chamber 12 of the injector 9.
And a high pressure fuel for medium pressure formation from the high pressure accumulator 3 to the fuel passage 10a so as to fill the downstream portion of the fuel passage 10a.
into the downstream part of a.

Specifically, when the high-pressure fuel introduction start time t3 determined in step S2 arrives, the switching valve drive signal is turned on. As a result, the switching valve 5 for switching the injection rate is opened (step S4), and the high-pressure fuel from the high-pressure accumulator 3 opens the check valve 32 and flows into the downstream portion of the fuel passage 10a. 9 flows into the control chamber 11 and the fuel chamber 12. As a result, as shown in the lowermost part of FIG. 3, the injector inlet pressure increases from the injection pressure (low pressure) in the auxiliary injection.

Thereafter, when the high-pressure fuel introduction time ΔTm elapses from the high-pressure fuel introduction start time t3 and the high-pressure fuel introduction end time t4 arrives, it is determined that the intermediate pressure formation in the fuel chamber 12 and the downstream portion of the fuel passage 10a has been completed. The switching valve drive signal is turned off and the switching valve 5 is closed (step S4), and the introduction of the high-pressure fuel for forming the medium pressure is completed.

Part of the medium-pressure fuel in the fuel chamber 12 and the downstream portion of the fuel passage 10a then gradually flows into the low-pressure accumulator 4 via the orifice 6a. It gradually decreases slightly as shown.
Then, when the main injection start timing t5 comes, the injector drive signal is turned on, the on-off valve 7 for injection timing control is opened (step S5), the nozzle hole of the injector 9 is opened, and the fuel chamber 12 is filled. The medium pressure fuel is injected into the engine combustion chamber. Since the main injection fuel is supplied in a state where the fuel related to the auxiliary injection is activated, the ignition of the main injection fuel is quickly performed. Typically, ignition occurs at the time of transition from medium-pressure injection to high-pressure injection or before or after the transition. Therefore, by changing the injection pressure at the time of the medium-pressure main injection in accordance with the operating conditions of the engine, it is possible to optimize the combustion speed of the main injection fuel at the initial combustion stage.

As described above, when the medium pressure injection is performed as shown by the solid line in FIGS. 3 and 5 in the initial stage of the main injection following the low pressure auxiliary injection, the low pressure injection is performed in the initial stage of the main injection ( (Indicated by a broken line in FIG. 5), the fuel injection amount in the initial stage of the main injection is increased, and the fuel amount to be injected in the remaining period of the main injection is reduced by the increased injection amount in the initial stage. The main injection time is shortened as a whole.
Therefore, fuel injection ends early and fuel efficiency is improved. In addition, excessive fuel supply is prevented from being performed before ignition as in the case where high-pressure injection is started immediately from the initial stage of main injection, and engine operation noise and NOx emissions are reduced. Furthermore, since the medium pressure injection can be performed only by opening and closing the switching valve 5 for switching the injection rate between the auxiliary injection and the main injection, the configuration of the apparatus is not particularly complicated.

Thereafter, the intermediate pressure injection time ΔTM has elapsed since the main injection start timing t5, and the switching valve drive signal ON timing t
When the valve 6 arrives, the switching valve 5 for switching the injection rate is turned on and opened while the on-off valve 7 for controlling the injection timing is maintained in the open state (step S6), and the high-pressure accumulates via the fuel passage 10a. High-pressure fuel is supplied from the injector 3 to the combustion chamber 12, and high-pressure fuel is injected from the injector 9 (FIGS. 3 and 5). That is, fuel injection (high-pressure main injection) is performed at an injection rate larger than the fuel injection rate in medium-pressure injection.

When the main injection time .DELTA.TMH has elapsed from the main injection start time t5 and the fuel injection end time t7 has arrived, the injector drive signal is turned off and the on-off valve 7 for injection timing control is closed (step S7). ). As a result, the hydraulic piston 14 using the high-pressure fuel supplied to the control chamber 11
When the combined force of the force acting on the needle valve 13 and the force acting on the needle valve exceeds the force acting on the needle valve 13 in the fuel chamber 12, the needle valve 13 closes the nozzle hole, and the main injection ends.

If the cross-sectional area of the flow passage of the orifice 16 is relatively large, the fuel injection rate falls rapidly at the end point t7 of the fuel injection, and the amount of black smoke and particulates discharged from the engine is reduced. Contribute. Further, the switching valve 5 for switching the injection rate is closed at a time point t8 when a predetermined time has elapsed from the fuel injection timing end time point t7 (step S8).
The switching valve 5 may be closed at time t7.

After the closing time t8 of the switching valve 5, a considerable portion of the high-pressure fuel in the fuel passage 10a downstream of the check valve 32 passes through the low-pressure accumulator through the bypass fuel passage provided with the orifice 6a. And flows into the low-pressure accumulator 4 to form low-pressure fuel.
It flows into the inside or leaks from around the control chamber 11 to the fuel tank 17 side. As a result, as shown in FIG. 3, the downstream portion of the fuel passage 10a and the injector inlet pressure decrease to a low pressure as time elapses before the auxiliary injection in the next fuel injection cycle is started.

The present invention is not limited to the above embodiment, but can be variously modified. For example, in the above-described embodiment, in each fuel injection cycle, the medium pressure injection is always performed at the initial stage of the main injection following the low pressure auxiliary injection as shown by a solid line in FIG. 5. It is not essential that the combination with the medium pressure / high pressure main injection is always performed in each fuel injection cycle. That is, one of the combination of the low-pressure auxiliary injection and the medium-pressure / high-pressure main injection shown by the solid line in FIG. 5 or the combination of the low-pressure auxiliary injection and the low-pressure / high-pressure main injection shown by the broken line in FIG. Alternatively, it may be selectively implemented.

[0039]

According to the pressure accumulating type fuel injection device of the present invention, when the fuel injection nozzle connected to the fuel passage performs the main injection and the low pressure auxiliary injection preceding the main injection, the high pressure fuel is supplied downstream of the fuel passage. The control valve for controlling the discharge to the side is opened for a short time between the auxiliary injection and the main injection, so that the fuel pressure higher than the auxiliary injection pressure and lower than the main injection pressure is provided in the fuel passage downstream of the control valve. Is formed, and the fuel injection is performed at a pressure higher than the auxiliary injection pressure and lower than the subsequent main injection pressure in the initial stage of the main injection, so that the injection pressure in the initial stage of the main injection can be optimized. Therefore, the fuel efficiency and exhaust gas characteristics of the engine can be improved, and the engine operation noise can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a pressure accumulating fuel injection device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing connection between main elements of the fuel injection device shown in FIG. 1 and injectors of each cylinder of the engine.

FIG. 3 shows the injection waveform in one fuel injection cycle implemented in the fuel injection device shown in FIGS. 1 and 2 together with the ON / OFF state of the injector drive signal and the switching valve drive signal and the change over time of the injector inlet pressure. FIG.

FIG. 4 is a flowchart of an injector / switching valve control routine executed by the controller shown in FIGS. 1 and 2;

FIG. 5 is a diagram showing a main injection time shortening effect when a medium-pressure / high-pressure main injection is performed following a low-pressure auxiliary injection.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 High-pressure pump 8 Controller 8a Engine speed sensor 3 High-pressure accumulator (first accumulator) 3a, 4a Pressure sensor 4 Low-pressure accumulator (second accumulator) 5 Switching valve for switching low-pressure / high-pressure accumulator (injection rate) (Control valve) 9 Injector 10a, 10b Fuel passage

Continued on the front page F term (reference) 3G066 AA07 AB02 AC09 AD12 BA14 BA17 BA22 BA24 BA25 CB07U CB09 CB11 CB12 CC06T CC14 CC64T CC67 CC68U CC70 CE22 DA06 DA09 DA11 DA14 DA16 DC04 DC09 DC18

Claims (1)

[Claims] A first pressure accumulator for storing high-pressure fuel pressurized by a pump; a fuel injection nozzle connected to the first pressure accumulator via a fuel passage for injecting fuel into a combustion chamber of the engine; A control valve for controlling discharge of the high-pressure fuel in the first pressure accumulator to a downstream side of the fuel passage; and a high pressure in the first pressure accumulator connected to the fuel passage downstream of the control valve via a branch passage. A second pressure accumulator for storing fuel at a lower pressure than the fuel; and a control valve for causing the fuel injection nozzle to perform main injection and a short auxiliary injection preceding the main injection at intervals. A fuel control means for opening the valve for a short time between the auxiliary injection and the main injection, opening the valve in the middle of the main injection, and closing the valve at the end of the main injection. Fuel injection device.