JPH1162682A - Fuel injection device of pressure accumulating type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the fuel injecting pressure accurately with good responsiveness. SOLUTION: From a high pressure fuel supply pump 5, fuel is supplied to an aux. pressure accumulation chamber 33 inside a common rail 3, and high pressure fuel is stored in the aux. pressure accumulation chamber. A control circuit (ECU) 20 detects the intra-aux. chamber fuel pressure using a sensor 23 and controls the intra-aux. chamber fuel pressure to the predetermined value by controlling the pressure feed amount of fuel of the fuel supply pump 5. The aux. chamber is connected with the main pressure accumulating chamber 31 through a solenoid valve 25, and the solenoid valve 25 is opened each time a fuel injection valve 10 connected with the main chamber injects the fuel into the main chamber, and the fuel is supplied from the aux. to the main chamber. The ECU detects the fuel pressure in the main chamber using a sensor 21 and controls the opening time of the solenoid valve 25 so that the internal pressure of the main chamber becomes the set pressure in accordance with the engine load conditions. Because the internal pressure of the aux. chamber is controlled to constant value, the controllability for the internal pressure of the main chamber (fuel injection pressure) is enhanced.

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 for storing pressurized fuel in an accumulator and injecting the fuel in the accumulator into an internal combustion engine via a fuel injection valve.

[0002]

2. Description of the Related Art Fuel is supplied from a high-pressure fuel pump to a common accumulator (common rail), and a fuel injection valve for each cylinder is connected to the accumulator to supply high-pressure fuel stored in the accumulator to each cylinder of the internal combustion engine. 2. Description of the Related Art There is known a so-called pressure accumulation type (common rail type) fuel injection device that injects fuel into a fuel cell.

In an accumulator type fuel injection device, the injection rate of a fuel injection valve is controlled by the fuel pressure in a common rail, and the fuel injection amount is controlled by both the fuel pressure in the common rail and the valve opening (fuel injection) time of the fuel injection valve. Is done. Therefore, in the accumulator type fuel injection device, it is necessary to control the injection rate (pressure in the common rail) according to the engine load condition, and it is necessary to control the fuel pressure in the common rail with good responsiveness according to the change in the engine load condition. Become.

[0004] An example of a pressure-accumulation type fuel injection device which controls the fuel pressure in the common rail with good responsiveness is disclosed in, for example, JP-A-8-68368. The device disclosed in the publication includes a pressure control common rail to which a fuel injection valve is connected, a pressure holding common rail connected to the pressure control common rail and a communication state switching means such as a solenoid valve, and a pressure holding common rail. And a fuel supply pump for pumping high pressure fuel.

In the device disclosed in the publication, the fuel in the pressure control common rail can be rapidly reduced by injecting the fuel in the pressure control common rail with the fuel injection valve while the solenoid valve is closed. In addition, by opening the solenoid valve to guide the fuel in the pressure holding common rail into the pressure control common rail, and by pumping the fuel from the fuel supply pump, the fuel pressure in the pressure control common rail can be rapidly increased. It has become.

[0006]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. 8-
In the pressure accumulating fuel injection device described in Japanese Patent No. 68368, the fuel pressure in the pressure control common rail is controlled only by opening and closing a solenoid valve that connects the pressure holding common rail and the pressure control common rail.
There is a problem that the control of the injection pressure is complicated and the stability of the pressure control is reduced.

That is, in the apparatus disclosed in the publication, the fuel pressure in the pressure holding common rail is determined by the amount of fuel pumped from the fuel supply pump and the fuel injection amount (the amount of fuel supplied from the pressure holding common rail to the pressure control common rail). Is not kept constant because it is determined by the balance with In general,
As a high-pressure fuel supply pump that supplies fuel to the common rail, a positive displacement pump such as a plunger pump is used. However, a positive displacement pump cannot supply fuel continuously. And the pumping of the fuel to the common rail is performed intermittently at a cycle corresponding to the pump rotation speed. For this reason, in the device of the above publication, the fuel pressure in the pressure holding common rail greatly increases each time fuel is pumped from the pump. Conversely, when the solenoid valve is opened and fuel is supplied from the pressure holding common rail to the pressure control common rail, the fuel pressure of the pressure holding common rail decreases. For this reason, the fuel pressure in the pressure holding common rail repeatedly increases and decreases when the fuel is pumped, and decreases when the solenoid valve is opened. For this reason, the pressure in the common rail for maintaining pressure when the solenoid valve is opened greatly fluctuates between the maximum pressure at the time of fuel pumping and the minimum pressure at the time of the previous solenoid valve opening even if the fuel injection amount is the same. In addition, the solenoid valve opening time required to control the fuel pressure in the pressure control common rail to the set pressure greatly changes. For this reason, in the device disclosed in the above publication, it may be difficult to control the fuel pressure in the pressure control common rail accurately and with good responsiveness.

This problem can also be solved theoretically by making the volume of the pressure holding common rail sufficiently large so that the pressure fluctuations caused by fuel pumping and solenoid valve opening become relatively small. However, in order to suppress the above-mentioned pressure fluctuation within an allowable range, it is necessary to set the volume of the pressure holding common rail to be extremely large as compared with the fuel pumping amount and the fuel injection amount, which makes mounting on an engine difficult. There are cases.

Further, even when the common rail volume is made sufficiently large, the fuel injection amount, that is, the amount of fuel supplied from the pressure holding common rail to the pressure control common rail greatly varies depending on the engine load condition. Unless the amount of fuel pumped from the pump and the amount of fuel injected are constantly balanced, the fuel pressure in the pressure holding common rail gradually increases or decreases, and the pressure in the pressure holding common rail is not constant. For this reason, in the device of the above publication, the required valve opening time of the solenoid valve is greatly different between the case where the pressure in the pressure holding common rail is high and the case where the pressure is low, and the opening and closing control of the solenoid valve becomes complicated, and the pressure is increased. In some cases, it is difficult to accurately and responsively control the fuel pressure (fuel injection pressure) in the control common rail.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a pressure-accumulation type fuel injection device capable of controlling the fuel injection pressure accurately and responsively according to engine load conditions without greatly increasing the common rail volume. I have.

[0011]

According to the first aspect of the present invention, there is provided a fuel injection valve for injecting fuel into an internal combustion engine at a predetermined timing, and a pressurized fuel connected to the fuel injection valve. A main accumulator, a sub-accumulator connected to the main accumulator via a fuel control valve for storing fuel higher in pressure than the fuel in the main accumulator, and a fuel supply for pumping fuel to the sub-accumulator. A pump, injection pressure control means for controlling the fuel pressure in the main accumulator to a predetermined value by controlling the valve opening state of the control valve, and a preset value for controlling the fuel pressure in the sub-accumulator. And a fuel pressure control means for controlling the pressure.

That is, in the first aspect of the invention, the fuel pressure in the sub-accumulation chamber is controlled to a predetermined set pressure by the fuel pressure control means. The set pressure may be a pressure set according to the engine load state, or may be a constant value higher than the fuel in the main accumulator. As described above, since the sub-accumulation chamber pressure is maintained at a stable value by controlling the sub-accumulation chamber pressure, the control valve can accurately and responsively control the fuel pressure in the main accumulation chamber. Becomes

According to the second aspect of the present invention, the fuel pressure control means includes a fuel pressure sensor for detecting a fuel pressure in the sub-accumulation chamber, and a sub-accumulation pressure from the fuel supply pump based on an output of the sensor. A pressure-accumulation fuel injection device according to claim 1, further comprising: a pumping amount control unit that controls an amount of fuel pumped into the chamber. That is, in the second aspect of the present invention, the fuel pressure control means of the first aspect controls the fuel pumping amount from the fuel supply pump based on the actual fuel pressure in the sub-accumulation chamber so that the pressure in the sub-accumulation chamber becomes a set value. Is provided. Therefore, the fuel pressure in the sub-accumulation chamber is stably maintained at a desired value, for example, a value set according to the engine load state or a constant value.

According to a third aspect of the present invention, the fuel pressure control means discharges fuel from the sub-accumulation chamber when the fuel pressure in the sub-accumulation chamber exceeds the set value, and controls the fuel pressure in the sub-accumulation chamber. The pressure accumulating fuel injection device according to claim 1, further comprising a pressure regulating valve that maintains a pressure at the set value. That is, according to the third aspect of the present invention, in the fuel pressure control means of the first aspect, when the fuel pressure in the sub-accumulation chamber exceeds a set value, the fuel in the sub-accumulation chamber is discharged by the pressure regulating valve. The pressure will always be kept at the set value.
Note that a pressure control valve that automatically opens when the fuel pressure in the sub-accumulation chamber exceeds a set value can be used as the pressure control valve. The pressure in the accumulator may be detected using a pressure sensor, and the solenoid valve may be opened when the pressure in the sub-accumulator exceeds a set value.

According to a fourth aspect of the present invention, the injection pressure control means controls the opening and closing of the control valve each time the fuel injection operation of each fuel injection valve is performed.
A pressure accumulating fuel injection device according to the item is provided. That is, in the invention of claim 4, since the control valve is opened and closed each time the fuel injection operation of each fuel injection valve is executed, high-pressure fuel is supplied from the sub-accumulator to the main accumulator each time the fuel injection operation is executed.
This prevents the fuel pressure in the main accumulator from fluctuating due to fuel injection from each fuel injection valve. Further, since the fuel once stored in the sub-accumulation chamber is supplied to the main pressure-accumulation chamber, the fuel can be supplied to the main pressure accumulation chamber regardless of the timing of pumping the fuel from the pump to the sub-accumulation chamber. For example, when a plunger-type high-pressure pump is used, the fuel pumping time from the pump is determined by the number of plungers and cannot be arbitrarily selected. For this reason, when performing fuel pumping from the fuel supply pump directly to the main accumulator, it is necessary to set the number of plungers so that fuel pumping is performed for each fuel injection operation. It is necessary to correspond to the number of plungers. However, according to the present invention, since the high-pressure fuel is temporarily stored in the sub-accumulation chamber and then supplied to the main pressure-accumulation chamber, a pump having a capacity sufficient to maintain the sub-accumulation chamber at a high pressure has a number of cylinders. It is not always necessary to correspond to the number of pump plungers. In other words, pumping fuel from the pump is stored in the sub-accumulation chamber, and fuel is supplied from the sub-accumulation chamber to the main accumulator for each fuel injection, so that pumps having the same number of plungers are used for engines having different numbers of cylinders. It is possible to do.

According to the fifth aspect of the present invention, further,
4. A low-pressure chamber for storing fuel at a lower pressure than the main accumulator, connected to the main accumulator through an injection pressure control valve that is opened and closed by the injection pressure controller. The pressure accumulating fuel injection device according to claim 1 is provided. That is, in the invention of claim 5, since the fuel in the main pressure accumulating chamber can be discharged to the low pressure chamber by opening the injection pressure control valve, the pressure in the main pressure accumulating chamber can be rapidly reduced. Therefore, control responsiveness when the injection pressure needs to be rapidly reduced is improved. Also,
In order to discharge the fuel in the main accumulator into the low-pressure chamber with a certain capacity, it is possible to discharge a large amount of fuel at a time compared to returning the fuel in the main accumulator to the fuel tank using a small-capacity pipe. Therefore, the response of the pressure control becomes extremely good.

According to the sixth aspect of the present invention, further,
The pressure accumulating fuel injection device according to claim 3, further comprising a low-pressure chamber connected to the sub-accumulation chamber via the pressure regulating valve and configured to store fuel at a lower pressure than the main accumulator. That is, in the invention of claim 6, fuel in the sub-accumulation chamber is discharged to the low-pressure chamber via the pressure regulating valve. For this reason, a large amount of fuel can be discharged from the sub-accumulation chamber at a time as compared with the case where the fuel in the sub-accumulation chamber is returned to the fuel tank using a small capacity pipe or the like. Accordingly, control responsiveness when controlling the pressure in the sub-accumulation chamber using the pressure regulating valve is extremely improved.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment of the accumulator type fuel injection device of the present invention. FIG.
Numeral 10 denotes a fuel injection valve for directly injecting fuel into each cylinder of the internal combustion engine 1 (a four-cylinder diesel engine in this embodiment), and 3 denotes a common fuel injection valve to which each fuel injection valve 1 is connected. Shows the accumulator (common rail). The common rail 3 has a function of storing pressurized fuel supplied from a high-pressure fuel supply pump 5 described later and distributing the pressurized fuel to each fuel injection valve 1. Further, as described later, in the present embodiment, three independent sections of a main pressure accumulation chamber (main common rail) 31, a sub-accumulation chamber (sub-common rail) 33, and a low-pressure chamber 35 are formed in the common rail 3. Each section in the common rail 3 will be described later in detail.

In FIG. 1, reference numeral 7 denotes a fuel tank for storing fuel (light oil in this embodiment) of the engine 1. During operation of the engine, the fuel in the tank 7 is pressurized by the high-pressure fuel supply pump 5, supplied to the sub-accumulator chamber 33 in the common rail 3, and from the main accumulator chamber 31 via each fuel injection valve 1 to the internal combustion engine. It is injected into the cylinder. As described above, in the present embodiment, the main accumulator chamber 31 and the sub-accumulator chamber 3 are provided in the common rail 3.
3. Three independent sections of the low-pressure chamber 35 are formed. In addition, the main pressure accumulating chamber 31 is controlled by the solenoid valve 25 to the auxiliary pressure accumulating chamber 3.
3 and the low pressure chamber 35 are connected to each other by the solenoid valve 27, and can be communicated with the sub-accumulation chamber 33 and the low pressure chamber 35 by opening the solenoid valves 25 and 27.

The main accumulator 31 is connected to the fuel injectors 1 of each cylinder of the engine 1, and the high-pressure fuel in the main accumulator 31 is directly injected into each cylinder through the fuel injectors 1. Also,
The sub-accumulation chamber 33 is connected to the high-pressure fuel supply pump 5. That is, in the present embodiment, the fuel pressure-fed from the high-pressure fuel supply pump 5 first flows into the sub-accumulation chamber 33 and is stored in the sub-accumulation chamber 33. When the solenoid valve 25 is opened, the fuel stored in the sub-accumulation chamber 33 is released from the main accumulation chamber 31.
And is injected from the fuel injection valve 10 into each cylinder.

In the present embodiment, the main pressure accumulating chamber 31 and the auxiliary pressure accumulating chamber 33 each have a pressure sensor 2 for detecting a fuel pressure.
1 and 23 are provided. In FIG. 1, reference numeral 20 denotes an engine control circuit (ECU) for controlling the engine. E
The CU 20 includes a read only memory (ROM), a random access memory (RAM), and a microprocessor (CP
U), it is configured as a microcomputer having a known configuration in which input / output ports are connected by a bidirectional bus.

In the present embodiment, the ECU 20 controls the discharge amount of the high-pressure fuel supply pump 5 to control the fuel pressure in the sub-accumulation chamber 33 to a predetermined value as described later. Further, the ECU 20 controls the solenoid valves 25 and 27 to perform injection pressure control for controlling the fuel pressure (fuel injection pressure) in the main pressure accumulating chamber 31 in accordance with the engine load, the number of revolutions, and the like, and adjusts the injection rate of the fuel injection valve. The fuel injection control is performed in accordance with the engine load, the number of revolutions, and the like, while controlling the valve opening time of the fuel injection valve 1 to control the amount of fuel injected into the cylinder.

For the above control, an input port of the ECU 20 is connected to the main pressure accumulation chamber 31 and the sub pressure accumulation chamber 33 by the fuel pressure sensor 21 provided in the main pressure accumulation chamber 31 and the fuel pressure sensor 23 provided in the sub pressure accumulation chamber 33, respectively. A voltage signal corresponding to the internal fuel pressure is input via an AD converter (not shown).
An output port of the ECU 20 is connected to each fuel injection valve 1 via a drive circuit (not shown), controls the operation of each fuel injection valve 1, and is connected to the high-pressure fuel supply pump 5 via a drive circuit. Thus, the discharge amount of the pump 5 is controlled. In the present embodiment, the output port of the ECU 20 is connected to solenoid valves 25 and 27 via a drive circuit (not shown), and controls the opening and closing of these solenoid valves.

In this embodiment, the high-pressure fuel supply pump 5
Is in the form of a plunger pump having a plurality of plungers, for example. The plunger in each cylinder of the pump 5 is reciprocated in the cylinder by being pressed by a cam formed on a plunger drive shaft in the pump. In addition, a suction valve that is opened and closed by a solenoid actuator is provided at a suction port of each cylinder. The plunger drive shaft is driven by the crankshaft of the engine 1 and rotates in synchronization with the crankshaft. For this reason, the sub-accumulation chamber 33 is output from the pump 5 a number of times that is proportional to the number of plungers of the pump in each stroke cycle (720 ° rotation of the crankshaft) of the engine 1.
The fuel is pumped to.

The ECU 20 controls the discharge flow rate of the fuel oil from the pump by changing the closing timing of the above-mentioned suction valve in the ascent (pressure feed) stroke of the plunger of each cylinder of the pump. That is, the ECU 20 stops energizing the solenoid actuator during the plunger descending stroke (suction stroke) of each cylinder and for a predetermined period after the start of the plunger ascent stroke (discharge stroke), and maintains the suction valve in the open state. Thus, even if the plunger enters the discharge stroke in each cylinder, the fuel in the cylinder flows back from the suction valve to the tank, and the fuel pressure in the cylinder does not increase. And
After the elapse of the period, the ECU 20 energizes the solenoid actuator of the suction valve to close the suction valve. As a result, the pressure in the cylinder increases with the rise of the pump plunger,
Fuel is pumped from the cylinder to the sub-accumulation chamber 33. That is, the ECU 20 changes the effective stroke of the plunger of the pump 5 to control the amount of fuel to be pumped to the common rail 3 by adjusting the closing time of the suction valve of each cylinder of the pump 5 (the energizing time to the solenoid actuator). I have.

Next, the fuel pressure control of the main pressure accumulating chamber 31 and the sub pressure accumulating chamber 33 according to the present embodiment will be described. In the present embodiment, the ECU 20 stores the ROM in advance according to the engine load and the number of revolutions.
Then, the pressure (injection pressure) in the main pressure accumulating chamber 31 and the fuel injection amount (opening time of the fuel injection valve 1) are set based on the relationship stored in. When the pressure in the main accumulator chamber 31 detected by the fuel pressure sensor 21 is lower than the injection pressure set as described above, the ECU 20 opens the solenoid valve 25 so that the pressure detected by the sensor 21 becomes the set injection pressure. By controlling the valve time, high-pressure fuel flows from the sub-accumulator 33 into the main accumulator 31,
The pressure in the main accumulator is increased to the set injection pressure. If the set injection pressure becomes lower than the internal pressure of the main pressure accumulating chamber 31 detected by the sensor 21 due to a sudden change in the operating state, etc.
U20 opens the solenoid valve 27 and discharges the fuel in the main storage chamber to the low-pressure chamber 35 through the solenoid valve 27 until the pressure in the main storage chamber detected by the sensor 21 becomes equal to the set injection pressure. Thereby, the fuel pressure in the main pressure accumulating chamber 31 is controlled to the injection pressure set according to the engine load condition.

Further, in this embodiment, the ECU 20 further controls the fuel pumping amount of the fuel pump 5 so that the fuel pressure in the sub-accumulation chamber 33 detected by the fuel pressure sensor 23 becomes a predetermined set pressure. That is, the ECU 20 can control the amount of fuel pumped from the fuel pump 5 to the sub-accumulation chamber by changing the closing timing of the suction valve of the pump 5 as described above. Therefore, in the present embodiment, by changing the closing timing of the suction valve of the pump 5 based on the output of the fuel pressure sensor 23, the fuel pressure in the sub-accumulation chamber 33 becomes the pressure set according to the engine load condition. It will be controlled stably. In the present embodiment, the set pressure of the sub-accumulation chamber is set to a constant value sufficiently larger than the maximum value of the set pressure of the main accumulator. If the pressure set value is changed so that the pressure difference between the main accumulator and the sub-accumulator becomes substantially constant, the controllability of the pressure in the main accumulator further improves.

FIG. 2 is a timing diagram showing changes in fuel pressure in the main pressure accumulating chamber 31 and the sub pressure accumulating chamber 33 when the fuel pressure control of the sub pressure accumulating chamber of this embodiment is performed. In FIG. 2, (a) shows a change in the amount of fuel pumped from the fuel supply pump 5,
(B) shows a change in fuel pressure in the sub-accumulation chamber 33, and (c) shows a change in fuel pressure in the main accumulation chamber 31. The dotted line in FIG. 2A indicates the maximum pumping amount of the fuel supply pump 5 (the pumping amount when the pumping amount control by the suction valve is not performed).

As shown in FIG. 2C, the pressure in the main accumulator decreases every time the fuel injection is performed (see FIG. 2C).
Point), the solenoid valve 25 is opened each time fuel injection is completed, and fuel is supplied from the sub-accumulation chamber 33, so that the pressure in the main pressure accumulation chamber immediately returns to the set value immediately after the end of injection. On the other hand, the pressure in the sub-accumulation chamber 33 (FIG. 2B) decreases slightly each time the solenoid valve 25 is opened and the fuel in the sub-accumulation chamber is supplied to the main accumulator (FIG. 2B). In the example of FIG. 2, every time the fuel is supplied to the main pressure accumulating chamber, the pump 5 pumps an amount of fuel enough to return the pressure in the sub-accumulating chamber to the set value (FIG. 2 (a)). ), III point) The pressure in the sub-accumulator also returns to the set value immediately after the fuel is supplied to the main accumulator. FIG. 2 shows a case where the fuel injection amount is relatively small, and as shown in FIG. 2A, the pump 5 corresponds to a part of the maximum pumping amount (shown by a dotted line in FIG. 2A). Only the amount of fuel is pumped into the sub-accumulator.

On the other hand, FIG. 3 is a view similar to FIG. 2 showing a change when the pressure in the sub-accumulation chamber is not controlled. In this case, as shown in FIG. 3A, the pump 5 always feeds a constant amount (in FIG. 3, the maximum pumping amount) of fuel to the sub-accumulation chamber. In this case, since the pumping amount from the pump 5 is larger than the fuel injection amount, the fuel pressure in the sub-accumulation chamber 33 is
(Indicated by a dotted line in FIG. 3 (b)). Moreover, in this state, a large amount of fuel is continuously supplied compared to the fuel injection amount, so that the maximum value of the pressure fluctuation (point IV in FIG. 3B) increases with time, and the pressure of the sub-accumulation chamber increases with time. It changes along with and is not constant. For this reason, even when the fuel injection amount is constant, the pressure in the sub-accumulation chamber when the solenoid valve 25 is opened changes with time, so that the pressure in the main accumulation chamber 31 is accurately maintained at the set value. It is necessary to greatly change the valve opening time of the solenoid valve 25 every time the valve is opened. In the above description, the case where the fuel injection amount is constant has been described. However, if the fuel injection amount changes, the pressure in the sub-accumulation chamber naturally changes greatly accordingly, and the control of the solenoid valve 25 becomes more complicated. Occurs.

On the other hand, in the case of the present embodiment shown in FIG. 2, when the solenoid valve 25 is opened, the sub-accumulation chamber pressure is always constant regardless of the fuel injection amount. Is simplified, and the accuracy of the main pressure accumulating chamber pressure control is improved. 2 and 3
In the figure, a case is shown in which the fuel pumping from the pump 5 is performed each time the solenoid valve 25 is opened (that is, every fuel injection operation). In order to perform the fuel pumping from the pump 5 every fuel injection as described above, The number of pump plungers and the number of engine cylinders need to correspond. That is, in the present embodiment, the pump 5 rotates in synchronization with the rotation of the crankshaft. On the other hand, since fuel is discharged from the pump 5 when each plunger is in the pressure feeding stroke, the number of times fuel is pumped per one rotation of the engine from the pump 5 is the number of plungers × the number of plunger drive cam ridges, It becomes an integral multiple. For this reason, the number of plungers must be a number corresponding to the number of cylinders in order to pump fuel to the sub-accumulation chamber for each fuel injection.

For this reason, in a conventional pressure-accumulation type fuel injection device in which fuel is directly supplied to the main pressure accumulator without providing the sub-accumulator, the fuel pressure in the main pressure accumulator is maintained at a set value in every fuel injection operation. Since it is necessary to pump fuel to the main accumulator, the number of pump plungers and the number of engine cylinders need to correspond exactly, and it is generally difficult to apply the same pump to engines of different cylinders. It is.

However, as in the present embodiment, if the sub-accumulation chamber is provided, the high-pressure fuel is temporarily stored in the sub-accumulation chamber, and the stored fuel is supplied to the main accumulator for each fuel injection. It is not necessary to make the number of pump plungers exactly correspond to the number of cylinders of the engine, and the same pump can be shared by engines having different numbers of cylinders. That is, since fuel at a higher pressure than the main accumulator is always stored in the sub-accumulator, fuel is supplied to the main accumulator by opening the solenoid valve 25 irrespective of fuel pumping timing from the pump. It has become possible.

However, even when a pump having a plunger number not corresponding to the number of engine cylinders is used, a problem arises when the fuel pressure control in the sub-accumulation chamber is not performed as shown in FIG. That is, when the number of pump plungers and the number of engine cylinders do not correspond to each other, fuel pressure feeding to the sub-accumulation chamber may not be performed for each fuel supply operation to the main accumulation chamber (opening operation of the solenoid valve 25). Occurs. For example, when the number of cylinders corresponds to the number of plungers, the fuel is pumped from the pump to the sub-accumulator once every time fuel is supplied to the main accumulator.
However, when the number of cylinders and the number of plungers do not correspond to each other, the timing of fuel pumping is shifted, so that the fuel is pumped once after the fuel is supplied to the main accumulator once as described above. The case where the fuel is pumped from the pump after the fuel is supplied to the main accumulator twice (or more times) may be mixed and repeated. in this case,
When the pressure control of the sub-accumulation chamber is not performed, when the solenoid valve 25 is opened, the fuel pressure in the sub-accumulation chamber is, for example, at the maximum value indicated by MAX in FIG. 3B (after the last time the solenoid valve 25 was opened). The case where the fuel pumping is performed from the pump) and the case where the fuel pumping is not performed after the previous time when the solenoid valve 25 is opened (the case where the fuel pumping is not performed) occur at the minimum value indicated by MIN. Will be. That is, in this case, the pressure of the sub-accumulation chamber when the solenoid valve 25 is opened fluctuates at the maximum within the range indicated by ΔP in FIG. 3B, and it becomes difficult to control the pressure of the main and sub-accumulation chambers. Occurs.

On the other hand, when the pressure in the sub-accumulation chamber is controlled to a constant value as shown in FIG. 2, even if the number of cylinders and the number of pump plungers do not correspond to each other, at most, FIG. It changes only in the range indicated by ΔP ₀ in b). That is, since the pressure in the sub-accumulation chamber is controlled to a constant value, the pressure fluctuation width is kept small, and in this case also, there is an advantage that the controllability of the pressure in the main accumulation chamber is improved.

As described above, according to the present embodiment, by controlling the pressure in the sub-accumulation chamber to a predetermined value, the responsiveness of the pressure control in the main accumulation chamber without greatly increasing the volume of the sub-accumulation chamber. And control stability can be improved. Next, another embodiment of the present invention will be described. FIG. 4 is a view similar to FIG. 1 showing a schematic configuration of another embodiment of the accumulator type fuel injection device of the present embodiment. 4, the same reference numerals as those in FIG. 1 represent the same elements as those in FIG.

In this embodiment, unlike the embodiment of FIG. 1, the pressure sensor 23 for detecting the fuel pressure in the sub-accumulation chamber 33 is used.
(FIG. 1) is not provided, and the pumping amount control of the pump 5 based on the fuel pressure in the sub-accumulation chamber 33 is not performed. In the present embodiment, the sub-accumulation chamber 33 and the low-pressure chamber 35 are
1 is different from the embodiment of FIG. As the pressure regulating valve of the present embodiment, for example, a mechanical safety valve or a pressure control valve is used, and the valve is opened when the pressure in the sub-accumulation chamber 33 exceeds a predetermined set pressure, and the fuel in the sub-accumulation chamber 33 is opened. To the low-pressure chamber 35. That is, in this embodiment, since the pumping amount control of the pump 5 is not performed, the pumping amount of the pump 5 is always maintained at a constant value (for example, an amount corresponding to the maximum fuel injection amount). However, when the pressure in sub-accumulation chamber 33 rises above a predetermined set value, pressure regulating valve 29 is opened and the pressure in sub-accumulation chamber 33 is maintained at the set value. Also in the present embodiment, since the pressure in the sub-accumulation chamber 33 is maintained at a constant value, the same effect as in the embodiment of FIG. 1 can be obtained. In this embodiment, the pressure in the sub-accumulation chamber 33 is controlled only by the pressure regulating valve 29.
There is no need to provide the pressure sensor 23 to control the fuel pumping amount of the pump 5 as in the embodiment, and there is an advantage that the pressure control is simplified.

In the embodiments shown in FIGS. 1 and 4, fuel is supplied from the main pressure accumulating chamber 31 to the low pressure chamber 35 via the solenoid valve 27, and in the embodiment shown in FIG. I try to discharge. For example, when returning fuel from the solenoid valve 27 or the pressure regulating valve 29 to the fuel tank 7 through a pipe directly, a large amount of fuel cannot flow at one time due to the small capacity of the pipe, and the fuel in the main pressure accumulating chamber and the sub-pressure accumulating chamber cannot be used. The pressure decreasing speed may be limited, and the responsiveness of the pressure control may be reduced. However, in this embodiment, the fuel is once discharged into the low-pressure chamber having a certain capacity, and the fuel is returned from the low-pressure chamber to the fuel tank 7 via the pipe. The situation where the response of the pressure control of 33 is limited by the pipe capacity does not occur. In the above embodiment, the main pressure accumulating chamber 31, the sub pressure accumulating chamber 33,
It is preferable that the volume of the main pressure accumulating chamber 31 of the low-pressure chamber 35 is minimized, the volume of the sub-pressure accumulating chamber 33 is maximized, and the volume of the low-pressure chamber 35 is intermediate between the two.

[0039]

According to the present invention, high-pressure fuel is temporarily stored in the sub-accumulation chamber, and the fuel pressure in the sub-accumulation chamber is controlled to a predetermined value. By supplying the fuel to the accumulator, a common effect is achieved in that the fuel injection pressure can be accurately controlled with good responsiveness without greatly increasing the volume of the sub-accumulator.

[Brief description of the drawings]

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

FIG. 2 is a timing diagram showing a pressure change of each part of the common rail of FIG. 1;

FIG. 3 is a diagram similar to FIG. 2 for explaining the effect of the present invention.

FIG. 4 is a view similar to FIG. 1, showing a schematic configuration of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Common rail 5 ... High pressure fuel supply pump 10 ... Fuel injection valve 20 ... Control circuit (ECU) 25, 27 ... Solenoid valve 29 ... Pressure regulating valve 31 ... Main pressure accumulating chamber 33 ... Sub-pressure accumulating chamber 35 ... Low pressure chamber

Claims (6)

[Claims] 1. A fuel injection valve for injecting fuel into an internal combustion engine at a predetermined timing, a main pressure accumulating chamber connected to the fuel injection valve for storing pressurized fuel, and a fuel control valve in the main pressure accumulating chamber. A sub-accumulator that stores fuel higher in pressure than the fuel in the main accumulator, a fuel supply pump that pumps fuel to the sub-accumulator, and an open state of the control valve. An injection pressure control means for controlling the fuel pressure in the main accumulator to a predetermined value; and a fuel pressure control means for controlling the fuel pressure in the sub-accumulator to a predetermined value. Injection device. 2. The fuel pressure control means controls a fuel pressure sensor for detecting a fuel pressure in the sub-accumulation chamber, and controls an amount of fuel pumped from the fuel supply pump to the sub-accumulation chamber based on an output of the sensor. The pressure accumulating fuel injection device according to claim 1, further comprising: 3. The fuel pressure control means for discharging fuel from the sub-accumulation chamber when the fuel pressure in the sub-accumulation chamber exceeds the set value and maintaining the fuel pressure in the sub-accumulation chamber at the set value. The pressure accumulating fuel injection device according to claim 1, further comprising a pressure valve. 4. The accumulator type fuel injection device according to claim 1, wherein the injection pressure control means controls the opening and closing of the control valve each time the fuel injection operation of each fuel injection valve is performed. 5. A low-pressure chamber connected to the main accumulator through an injection pressure control valve that is opened and closed by the injection pressure control means and configured to store fuel at a lower pressure than the main accumulator. Item 4. An accumulator-type fuel injection device according to any one of Items 1 to 3. 6. The pressure-accumulation fuel injection device according to claim 3, further comprising a low-pressure chamber connected to the sub-accumulation chamber via the pressure regulating valve, for storing fuel at a lower pressure than the main pressure-accumulation chamber.