JP3812620B2 - Accumulated fuel injection system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an accumulator fuel injection device that forms fuel pressure in a low-pressure accumulator using high-pressure fuel in a high-pressure accumulator, and in particular, stabilizes the low-pressure fuel in the low-pressure accumulator at an appropriate pressure in a wide rotation range. It is related with the pressure-accumulation type fuel-injection apparatus made to maintain.
[0002]
[Related background]
2. Description of the Related Art An accumulator fuel injection device is known in which high-pressure fuel stored in an accumulator is stably supplied to each cylinder of a diesel engine so that engine performance can be improved 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, rapid explosion combustion occurs at the beginning of combustion, which not only increases engine operating noise. NOx in the exhaust gas increases.
[0003]
In order to solve such a problem, an accumulator fuel injection apparatus that injects fuel at a lower fuel injection rate in the initial stage of each fuel injection cycle has been proposed. In this type of accumulator fuel injection device, a low-pressure accumulator that stores low-pressure fuel or a high-pressure accumulator that stores high-pressure fuel is selectively connected to an injector (fuel injection nozzle) to switch an injection rate; Some cylinders have an open / close valve for controlling the injection timing by connecting / blocking the injector control chamber and the fuel tank for each cylinder, and using the high pressure fuel in the high pressure accumulator to obtain the low pressure fuel in the low pressure accumulator (International Publication WO 98/09068).
[0004]
In the accumulator fuel injection device described in this publication, the fuel passage connecting the switching valve and the fuel chamber of the injector is filled with low-pressure fuel by closing the switching valve for injection timing control and the switching valve for switching the injection rate. At the same time, low pressure fuel is supplied to the control chamber of the injector communicating with the fuel passage to hold the injector in a closed state, and when the injection start time comes, the on-off valve is opened to discharge the low pressure fuel in the control chamber to the fuel tank. Thus, the injector is opened to perform low-pressure initial injection (hereinafter referred to as low-pressure injection), and when the low-pressure injection period has elapsed, the switching valve is opened to inject high-pressure fuel from the high-pressure accumulator from the nozzle. High-pressure main injection (hereinafter referred to as high-pressure injection) is performed, and the switching valve is closed when the injection end time comes.
[0005]
The fuel pressures in the high-pressure accumulator and in the low-pressure accumulator are variably adjusted according to the engine operating state in order to properly perform the low-pressure injection and the high-pressure injection. Regarding pressure adjustment for low-pressure fuel, when the fuel pressure in the low-pressure accumulator exceeds the target pressure set according to engine operating conditions, the pressure control valve arranged in the fuel discharge passage of the low-pressure accumulator is opened. Thus, part of the fuel in the low pressure accumulator is discharged to reduce the pressure of the low pressure fuel.
[0006]
[Problems to be solved by the invention]
In the accumulator type fuel injection device that forms the fuel pressure in the low pressure accumulator using the high pressure fuel in the high pressure accumulator as described above, one corresponding to the switching valve is opened over the high pressure injection period for each cylinder of the engine. The high pressure fuel is supplied to the corresponding fuel passage. After the fuel injection period elapses, the fuel pressure in the fuel passage gradually decreases due to, for example, the formation of fuel pressure in the low pressure accumulator, but this fuel pressure drop characteristic (injector inlet pressure reduction time shown in FIG. 9) Correspondence) is determined by the specifications of the fuel injection device, particularly the specifications around the fuel passage, regardless of the engine speed.
[0007]
On the other hand, as the engine speed increases, the valve opening time interval when the plurality of switching valves provided for each cylinder sequentially open becomes shorter, and the fuel in the fuel passage corresponding to a certain switching valve is reduced. Before the pressure drops sufficiently, the switching valve of another cylinder opens to supply high-pressure fuel to another fuel passage, and the supply of high-pressure fuel to the fuel passage is overlapped as a whole. (See FIG. 10). Since all of the multiple fuel passages are connected to the low-pressure accumulator, the amount of high-pressure fuel used for fuel pressure formation in the low-pressure accumulator increases in the high rotation range, and the low-pressure fuel in the low-pressure accumulator The pressure tends to increase. When the low-pressure fuel exceeds the target pressure, the pressure control valve provided on the fuel discharge side of the low-pressure accumulator is opened to discharge part of the fuel and the fuel pressure is reduced. If it is set lower than the valve opening ratio corresponding to high rotation, the pressure of the low-pressure fuel in the low-pressure accumulator is higher than the low-pressure initial injection pressure set according to the operating state and the injection amount increases, and the combustion noise increases. And increase in NOx generation amount.
[0008]
On the other hand, as the engine speed decreases, the pressure of the high-pressure fuel in the high-pressure accumulator is generally controlled in a decreasing direction, and the time interval until the switching valve of each cylinder is sequentially opened becomes longer and enters the fuel passage. The high-pressure fuel is intermittently supplied (see FIG. 10). Therefore, in the low speed range, the actual pressure of the low-pressure fuel in the low-pressure accumulator tends to decrease, but immediately after a certain first control valve is closed, the fuel pressure in the corresponding fuel passage is The actual pressure of the low-pressure fuel in the low-pressure accumulator is at a high level, and the actual pressure of the low-pressure fuel may exceed the target pressure.
[0009]
In this case, in the conventional accumulator fuel injection device, the degree of opening of the pressure control valve is increased to control the low pressure fuel to the target pressure, and as a result, the actual pressure of the low pressure fuel may be excessively reduced. In the low speed range, the time interval until the switching valve of each cylinder opens sequentially is long, so once the pressure of the low pressure fuel drops, another switching valve opens and high pressure fuel begins to be supplied to the fuel passage. For a while, the low-pressure fuel pressure does not increase (see FIG. 11). For this reason, the actual pressure of the low-pressure fuel may be significantly lower than the target pressure, making it impossible to perform low-pressure injection.
[0010]
Accordingly, an object of the present invention is to provide an accumulator fuel injection device that can stably perform low-pressure injection by stably maintaining low-pressure fuel at an appropriate pressure over a wide rotation range.
[0011]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an accumulator fuel injection device comprising: a first accumulator that stores high-pressure fuel pressurized by a pump; and a plurality of fuel passages that extend between the first accumulator and a plurality of fuel injection nozzles. A plurality of first control valves arranged to control discharge of high-pressure fuel from the first pressure accumulator to the plurality of fuel passages, and connected to the plurality of fuel passages downstream of the plurality of first control valves to store low-pressure fuel The second pressure accumulator, the second control valve for variably adjusting the discharge of the low pressure fuel from the second pressure accumulator, and the difference between the target pressure and the actual pressure of the low pressure fuel , And engine speed Pre-separated engine speed range Based on Correct the operation of the second control valve when the engine speed is in the high engine speed range so that the actual pressure of the low-pressure fuel approaches the target pressure. do it Ensure that the actual pressure of the low-pressure fuel approaches the target pressure and Second Fuel pressure control means for variably controlling the degree of opening of the second control valve so as to suppress discharge of low-pressure fuel from the two pressure accumulators.
[0012]
According to the conventional accumulator fuel injection device that controls the opening degree of the second control valve (pressure control valve) only with the pressure of the low pressure fuel approaching the target pressure, the low pressure fuel pressure is excessively low in the low rotation range. In the present invention, the degree of opening of the second control valve in the low rotation range is suppressed more than in the rotation range other than the low rotation range (hereinafter sometimes referred to as the high rotation range). An excessive pressure drop of the low-pressure fuel is prevented in advance. For this reason, the low-pressure fuel is stably maintained at an appropriate pressure even in a low rotation range, and the low-pressure injection is appropriately performed, which contributes to improvement of fuel consumption and exhaust gas characteristics.
[0013]
In the present invention, preferably, the fuel pressure control means sets a reference valve opening degree suitable for pressure control in a rotation range other than the low rotation range if the engine is operated in a rotation range other than the low rotation range. The opening degree of the second control valve is controlled to the reference opening degree. If the engine is operating in a low rotation range, a correction valve opening degree that is suitable for pressure control in the low rotation range and smaller than the reference valve opening degree is set, and the opening degree of the second control valve is corrected. Control the degree of valve opening.
[0014]
For example, the calculation of the reference valve opening degree is performed according to a first arithmetic expression that expresses a valve opening degree suitable for pressure control in a rotation range other than the low rotation range as a function of a difference between the target pressure and the actual pressure of the low-pressure fuel. Is called. The corrected valve opening degree is calculated according to the second arithmetic expression that represents the degree of valve opening suitable for pressure control in the low rotation range as a function of the difference. According to this preferred embodiment, the valve opening degree suitable for the low rotation range can be appropriately calculated according to the second calculation formula different from the first calculation formula used for calculating the valve opening degree suitable for the high rotation range.
[0015]
Preferably, the correction valve opening degree is calculated by multiplying the reference valve opening degree by a correction coefficient smaller than the value 1. According to this preferred embodiment, the corrected valve opening degree suitable for the low rotation range can be obtained relatively easily.
More preferably, the fuel pressure control means variably controls the valve opening duty ratio of the second control valve. According to such duty ratio control, the average opening degree of the second control valve and thus the degree of valve opening can be variably adjusted accurately and with good responsiveness even with a device having a relatively simple configuration. In this preferred embodiment, the fuel pressure control means has a valve opening duty ratio suitable for pressure control in a rotational range other than the low rotational range in a rotational range other than the low rotational range, and the difference between the target pressure and the actual pressure of the low pressure fuel. A reference valve opening duty ratio is obtained from a first map set in advance as a function of, and the second control valve is opened at the reference valve opening duty ratio. In the low rotation range, a corrected valve opening duty ratio is obtained from the second map in which the valve opening duty ratio suitable for pressure control in the low rotation range is set in advance as a function of the above difference, and the second control valve is corrected. The valve is opened at the valve opening duty ratio. According to this preferred embodiment, the valve opening degree suitable for each of the low rotation range and the high rotation range can be obtained more easily and more quickly.
[0016]
In the pressure accumulation type fuel injection device according to claim 2, the degree of opening of the second control valve is variably controlled according to the engine load so that the discharge of the low pressure fuel from the second pressure accumulator is suppressed in the low load range. The
In the low load range, the pressure of the high pressure fuel in the first pressure accumulator is generally controlled in a decreasing direction, and the fuel pressure used for forming the fuel pressure in the second pressure accumulator becomes low, which causes the pressure drop of the low pressure fuel. Become. Therefore, immediately after the closing of a certain first control valve, the pressure of the low-pressure fuel is brought close to the target pressure even when the fuel pressure in the fuel passage and thus the pressure of the low-pressure fuel in the second accumulator is at a high level. If only the degree of opening of the second control valve is increased with only this in mind, the amount of fuel discharged from the second control valve exceeds the amount of fuel supplied into the second accumulator, and the pressure of the low-pressure fuel becomes the target. The pressure may be excessively reduced and the low pressure injection may not be performed.
[0017]
Therefore, in the invention of claim 2, by suppressing the degree of opening of the second control valve in the low load region, the pressure of the low pressure fuel is prevented from excessively decreasing, and proper low pressure injection is performed. .
According to the preferred embodiment of the invention of claim 2, the valve opening degree and the valve opening duty ratio suitable for the pressure control in the rotation / load region other than the low rotation / low load region are set between the target pressure and the actual pressure of the low pressure fuel. The reference valve opening degree and the reference valve opening duty ratio are obtained from the first arithmetic expression represented by the difference function and the first map. Further, the degree of valve opening and the valve opening duty ratio suitable for the pressure control in the low rotation / low load range are obtained from the second arithmetic expression and the second map that are expressed as a function of the above difference. In this case, the setting of the degree of opening of the second control valve suitable for the engine rotation / load range is simplified.
[0018]
In the pressure accumulation type fuel injection device according to claim 3, the second control valve is configured such that the discharge of the low pressure fuel from the second pressure accumulator is suppressed in a low differential pressure range where the difference between the target pressure and the actual pressure of the low pressure fuel is small. Control the degree of valve opening.
A small difference between the target pressure and the actual pressure indicates that the amount of fuel supplied from the fuel passage is decreasing due to the formation of the fuel pressure in the second pressure accumulator. Therefore, if the degree of opening of the second control valve is increased with only the pressure of the low pressure fuel approaching the target pressure, the amount of fuel discharged from the second control valve is supplied to the second pressure accumulator. The pressure of the low-pressure fuel in the second pressure accumulator may be excessively reduced with respect to the target value, making it impossible to perform low-pressure injection.
[0019]
Therefore, in the invention of claim 3, by suppressing the degree of opening of the second control valve in the low differential pressure region, the pressure of the low pressure fuel in the second pressure accumulator is prevented from excessively decreasing, and proper low pressure injection is performed. To implement.
Preferably, when the engine is operated in a low speed range or a low load range, the degree of opening of the second control valve in the low differential pressure range is suppressed. Although the degree of valve opening is suppressed in the low rotation range and low load range, if the differential pressure related to low pressure fuel pressure control is small in the low rotation range and low load range where low pressure fuel tends to drop, (2) It is useful to prevent the pressure drop of the low-pressure fuel by further suppressing the degree of opening of the control valve.
[0020]
For this reason, for example, the magnitude of the reduction correction (for example, the correction coefficient) when obtaining the corrected valve opening degree from the reference valve opening degree is made small in the low differential pressure range, whereby the second control valve in the low differential pressure range. The degree of valve opening becomes smaller.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an accumulator fuel injection device according to an embodiment of the present invention will be described.
The accumulator fuel injection device is mounted on, for example, an inline 6-cylinder diesel engine (not shown), and includes a high-pressure pump 1 as shown in FIGS. 1 and 2. The high-pressure pump 1 is driven by an engine and pumps and pressurizes the fuel in the fuel tank 17. The high-pressure pump 1 is composed of a positive displacement plunger pump, for example, and the fuel discharge pressure can be adjusted by adjusting the effective section of the pumping stroke. ing. The pressure feed stroke adjustment is performed, for example, by adjusting the closing timing of a solenoid valve (not shown), and the pressure feed operation is disabled while the solenoid valve is open. The high-pressure pump in the apparatus according to the present embodiment relating to a 6-cylinder engine includes, for example, two plungers. Each plunger is associated with three cylinders, and performs three pumping strokes during one rotation of the high-pressure pump shaft.
[0022]
The controller 8 of the accumulator fuel injection device is responsive to the engine speed Ne detected by the engine speed sensor 8a and the accelerator pedal depression amount (accelerator opening) ACC detected by the accelerator opening sensor (not shown). The pumping stroke of the pump 1 is variably adjusted, and further, the pumping stroke (fuel pressure) is feedback controlled according to the actual pressure PHP in the high pressure accumulator (first accumulator) 3 detected by the pressure sensor 3a (FIG. 2). By doing so, a high-pressure fuel suitable for the engine operating condition is obtained. The engine speed sensor 8a and the accelerator opening sensor constitute engine operating state detecting means.
[0023]
The fuel pressurized by the pump 1 is stored in the high pressure accumulator 3. The high pressure accumulator 3 is common to each cylinder and communicates with a plurality of fuel passages 10a provided for each cylinder. In the middle of the fuel passage 10a, for example, a switching valve (first control valve) 5 for switching the fuel injection rate composed of a two-way solenoid valve is provided for each cylinder. A check valve 32 is provided downstream.
[0024]
A low pressure accumulator (second accumulator) 4 common to each cylinder is connected to each fuel passage 10a through 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 10b, and a bypass fuel passage for bypassing the check valve 6 is attached to the fuel passage 10b, and an orifice 6a is provided in the bypass fuel passage. 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. A pressure control valve (second control valve) 34 that operates under the control of the controller 8 is provided between the low pressure accumulator 4 and the fuel tank 17. In FIG. 2, reference numeral 4 a represents a pressure sensor (fuel pressure detecting means) for detecting the fuel pressure (actual pressure) PLP in the low pressure accumulator 4.
[0025]
The controller (fuel pressure control means) 8 obtains a command pressure (target pressure) suitable for the engine operating state represented by the engine speed Ne and the accelerator pedal depression amount ACC from, for example, a map (not shown), and the inside of the low pressure accumulator 4 The pressure control valve 34 is controlled on the basis of the actual pressure PLP detected by the pressure sensor 4a so that the fuel pressure becomes the indicated pressure.
[0026]
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, and the control chamber 11 is connected to a fuel tank 17 via a fuel return passage 10c. Has been. Reference numerals 15 and 16 denote orifices. Reference numeral 7 denotes an on-off valve for injection timing control, which is arranged in the middle of the fuel return passage 10c and is composed of, for example, a two-way electromagnetic valve. The on-off valve 7 may be incorporated in the injector.
[0027]
The injector 9 has a needle valve 13 that opens and closes its nozzle hole and a hydraulic piston 14 that is movably disposed in the control chamber 11. The needle valve 13 is urged toward the nozzle hole by a spring (not shown). Yes. When fuel is supplied from the fuel passage 10 a to the control chamber 11 and the fuel chamber 12 and the on-off valve 7 for controlling the injection timing is closed, the resultant force of the spring force of the spring and the fuel pressure is applied to the needle valve 13. The needle valve 13 closes the nozzle hole against the fuel pressure in the fuel chamber 12. On the other hand, when the opening / closing valve 7 is opened and the fuel in the control chamber 11 is discharged to the fuel tank 17 side, the needle valve 13 moves toward the hydraulic piston 14 against the spring force of the spring by the fuel pressure in the fuel chamber 12. The nozzle hole is moved and the fuel in the fuel chamber 12 is injected into the combustion chamber (not shown) of the engine.
[0028]
Hereinafter, the basic operation of the fuel injection device having the above configuration will be described.
Under the control of the controller 8, the fuel pressure in the high pressure accumulator 3 and the fuel pressure in the low pressure accumulator 4 are controlled so as to match the engine operating state, and the engine operating state (engine speed, accelerator pedal depression amount). ), A fuel injection period (fuel injection start / end timing) and a low pressure injection period are set.
[0029]
As shown in FIG. 3, the switching valve 5 and the on-off valve 7 are both closed until the fuel injection start timing arrives, and the low-pressure fuel is supplied from the low-pressure accumulator 4 to the fuel passage 10 a on the downstream side of the switching valve 5. This low pressure fuel is supplied to the control chamber 11 and the fuel chamber 12. Since the on-off valve 7 is closed, the fuel pressure supplied into the control chamber 11 is applied to the needle valve 13 via the hydraulic piston 14, and the nozzle hole of the injector 9 is closed by the needle valve.
[0030]
At the fuel injection start timing, only the on-off valve 7 is opened, the low-pressure fuel in the control chamber 11 is drained through the orifice 16 and the fuel return passage 10c, and the fuel pressure applied to the needle valve 13 through the hydraulic piston 14 When the resultant force with the spring force of the spring becomes smaller than the fuel pressure in the fuel chamber 12 acting to push up the needle valve 13, the needle valve 13 rises to open the nozzle hole, and low pressure fuel is injected from the injector 9. Is done. That is, low-pressure initial injection is performed at a relatively small fuel injection rate (fuel injection amount per unit time). Due to this low pressure injection, the amount of fuel before ignition is reduced and the premixed combustion amount is reduced, so that combustion in the initial stage of the fuel injection period is performed relatively slowly, which contributes to the reduction of the NOx amount in the exhaust gas.
[0031]
When a predetermined time elapses after the low pressure injection is started, the switching valve 5 for switching the injection rate is opened while the on / off valve 7 for controlling the injection timing is kept open, and the high pressure fuel is supplied to the fuel chamber 12. Is supplied and high pressure fuel is injected from the injector 9. That is, fuel injection (high pressure main injection) is performed at an injection rate larger than the fuel injection rate in low pressure injection.
[0032]
When the fuel injection end timing is reached, the injection timing control on-off valve 7 is closed, the high-pressure fuel supplied to the control chamber 11 acts on the needle valve 13 via the hydraulic piston 14, and the needle valve 13 becomes the injector. 9 nozzle holes are closed. At the end of fuel injection, the fuel injection rate falls rapidly, contributing to the reduction of black smoke (smoke) and particulate (PM) emissions from the engine. The switching valve 5 for switching the injection rate is closed when a predetermined time (indicated by symbol ΔTe in FIG. 9) elapses from the closing timing of the on-off valve 7, that is, the fuel injection timing end timing.
[0033]
As shown in FIG. 9, the fuel pressure (injector inlet pressure) in the fuel passage 10a between the injector 9 and the switching valve 5 for switching the injection rate is determined from the time when the fuel injection in each fuel injection cycle is completed. Decrease gradually until the fuel injection in the next fuel injection cycle is started, the fuel pressure is reduced to the low pressure injection and stabilized, and the injection pressure in the next low pressure injection, that is, the injection rate becomes the required one. .
[0034]
In the present embodiment, the diameter of the orifice 6a related to the fuel pressure formation in the low pressure accumulator 4 is set to a value that falls within the optimum range shown in FIG. The amount of high-pressure fuel flowing from the fuel passage 10a to the low-pressure accumulator 4 through the bypass fuel passage provided with the orifice 6a increases as the orifice diameter increases. For this reason, when the orifice diameter exceeds the upper limit value of the optimum range shown in FIG. 8, the inflow amount of the high-pressure fuel into the low-pressure accumulator 4 exceeds the inflow amount necessary to maintain the pressure of the low-pressure fuel at a suitable value, In order to obtain a suitable pressure, the pressure control valve 34 must be opened to discharge the fuel in the low pressure accumulator 4 to the fuel tank 17. That is, if the orifice diameter is excessive, wasteful fuel discharge is performed. On the other hand, when the orifice diameter is less than the lower limit value of the optimum range shown in FIG. 8, the amount of high-pressure fuel flowing into the low-pressure accumulator 4 is from the next fuel injection start timing in the engine operating state at the maximum rotational speed. However, the fuel flow (injector inlet pressure) in the fuel passage 10a is less than the inflow amount required to reduce the pressure to the pressure suitable for the low pressure injection by the time before the margin time. For this reason, if the orifice diameter is too small, the next low-pressure injection cannot be performed properly at the maximum speed operation.
[0035]
The orifice 6a of the present embodiment has an orifice diameter that falls within the optimum range shown in FIG. 8, and stably maintains the pressure of the low-pressure fuel in an appropriate range in a wide rotation range, thereby preventing wasteful fuel discharge and the following. The low-pressure injection can be performed properly, and the fuel consumption and exhaust gas characteristics are improved.
Further, in the accumulator fuel injection device of the present invention, in order to maintain the fuel pressure in the low pressure accumulator 4 more appropriately and more stably, the valve control operation of the pressure control valve 34 is optimized to perform appropriate low pressure injection. It can be implemented stably.
[0036]
In the present embodiment, during engine operation, the controller 8 executes the low-pressure fuel pressure control routine shown in FIG. 4 at a predetermined cycle.
In this control routine, the engine speed sensor output and the accelerator pedal depression amount sensor output are read, and the engine speed Ne and the accelerator pedal depression amount ACC (more generally, the engine load) are detected as the engine operating state (step S1). ). Next, referring to a map (not shown), a target pressure (indicated pressure) of the low-pressure fuel according to the engine speed and the accelerator pedal depression amount is determined (step S2). Further, the output of the pressure sensor 4a is read, and the fuel pressure (actual pressure) PLP in the low pressure accumulator 4 is detected (step S3). Then, the differential pressure ΔP is calculated by subtracting the target pressure determined in step S2 from the actual pressure detected in step S3 (step S4). Here, if the sign of the differential pressure ΔP is negative, the differential pressure ΔP is set to the value 0.
[0037]
Next, with reference to a map indicated by a solid line in FIG. 6, a reference valve opening duty ratio corresponding to the differential pressure ΔP detected in step S4 is determined (step S5). In the map shown by the solid line in FIG. 6, the valve opening duty ratio suitable for the low pressure fuel pressure control in the rotation / load region other than the low rotation / low load region shown in FIG. It is preset as a function. In the solid line map of FIG. 6, the reference valve opening duty ratio is set to increase linearly from 0% to 100% as the differential pressure ΔP increases in the differential pressure range where the differential pressure ΔP is equal to or less than the predetermined differential pressure ΔP1. In the high differential pressure region exceeding the predetermined differential pressure ΔP1, it is set to 100% regardless of the differential pressure ΔP.
[0038]
Then, referring to the map shown in FIG. 5, whether or not the engine is operating in a low rotation / low load range is determined based on the engine speed and the accelerator pedal depression amount detected in step S1 ( Step S6). As shown in FIG. 5, in the low rotation range that forms part of the low rotation / low load range, the engine load changes from low load to high load, and the low load range that forms the remainder of the low rotation / low load range Then, the engine speed changes from a low speed to a middle speed Ne1.
[0039]
If the determination result in step S6 is negative (No), that is, if it is not in the low rotation / low load range, the reference valve opening duty ratio determined in step S5 is used for valve opening control of the pressure control valve 34. (Step S7). On the other hand, if it is determined in step S6 that the engine is operating in the low rotation / low load range, a correction corresponding to the differential pressure ΔP detected in step S4 is performed with reference to the map indicated by the broken line in FIG. A valve opening duty ratio is determined (step S8), and this corrected valve opening duty ratio is set as a valve opening duty ratio used for valve opening control of the pressure control valve 34 (step S9).
[0040]
In the map indicated by a broken line in FIG. 6, a valve opening duty ratio that is suitable for the pressure control in the low rotation / low load range shown in FIG. 5, that is, a corrected valve opening duty ratio is preset as a function of the differential pressure ΔP. The corrected valve opening duty ratio is necessarily smaller than the reference valve opening duty ratio if the differential pressure ΔP is the same over the entire differential pressure range. That is, the degree of opening of the pressure control valve 34 in a low rotation / low load range is suppressed.
[0041]
FIG. 7 represents the ratio (≦ 1) of the corrected valve opening duty ratio indicated by the broken line in FIG. 6 to the reference valve opening duty ratio indicated by the solid line in FIG. 6 as a function of the differential pressure ΔP. In FIG. 7, this ratio is referred to as a correction coefficient. The corrected valve opening duty ratio corresponds to a value obtained by multiplying the reference valve opening duty ratio by this correction coefficient.
As shown in FIG. 6, the corrected valve opening duty ratio is linear with a small gradient from 0% to the predetermined duty ratio D2% as the differential pressure ΔP increases in the low differential pressure range where the differential pressure ΔP is up to the predetermined differential pressure ΔP2. Change. That is, the degree of opening of the pressure control valve 34 in the low differential pressure region is suppressed. Further, in the differential pressure region of the predetermined differential pressure ΔP2 or more, it linearly changes with a large gradient from the predetermined duty ratio D2% to 100% as the differential pressure ΔP increases.
[0042]
Finally, the pressure control valve 34 is duty controlled with the valve opening duty ratio set in step S7 or step S9 (step S10). As a result, the pressure control valve 34 opens at a valve opening duty ratio that matches the difference between the target pressure and the actual pressure of the low pressure fuel (differential pressure ΔP), and fuels a part of the low pressure fuel in the low pressure accumulator 4. The pressure is discharged to the tank 17, and the actual pressure of the low-pressure fuel approaches the target pressure. Further, if the engine is operated in a low rotation / low load range, the valve opening duty ratio of the pressure control valve 34 is suppressed as compared with the other rotation ranges, and a low pressure that is likely to occur in the low rotation / low load range. An excessive pressure drop of the fuel is prevented. As a result, in combination with the configuration in which the orifice diameter of the orifice 6a interposed between the fuel passage 10a and the low pressure accumulator 4 is set to fall within the optimum range shown in FIG. Is stably maintained at an appropriate pressure, whereby an appropriate low-pressure injection is performed, and fuel consumption and exhaust gas characteristics are improved.
[0043]
The present invention is not limited to the above embodiment, and can be variously modified.
For example, in the embodiment, the entire engine operation region is divided into two regions, ie, a low rotation / low load region and other rotation / load regions, but the method of dividing the operation region is not limited to this. For example, the entire engine operation range may be divided into a low rotation range and the other two, or may be divided into three or more operation ranges depending on the engine speed alone or the engine speed and the engine load. . Here, the degree of opening of the pressure control valve in each engine operating range is set according to the difference between the target pressure of the low-pressure fuel and the actual pressure (differential pressure ΔP), and is opened in the low rotation range and low load range. The degree of valve is set to be smaller than that in other operating ranges.
[0044]
In the embodiment, the reference valve opening duty ratio suitable for pressure control in the rotation / load range other than the low rotation / low load range and the corrected valve opening duty ratio suitable for pressure control in the low rotation / low load range are obtained from the map. Although it is obtained, it may be calculated according to arithmetic expressions respectively corresponding to the bent straight lines shown by the solid line and the broken line in FIG. In this case, the corrected valve opening duty ratio may be obtained by multiplying the reference valve opening duty ratio by the correction coefficient shown in FIG.
[0045]
In addition, it is not essential to variably adjust the average opening by duty-controlling the pressure control valve as in the embodiment, and the actual opening of the pressure control valve is adjusted according to the engine operating range and the differential pressure. It can be configured as follows.
In addition, various modifications are possible within the scope of the present invention.
[0046]
【The invention's effect】
A pressure accumulation fuel injection device according to the present invention includes a second pressure accumulator connected to a plurality of fuel passages downstream of a plurality of first control valves for controlling discharge of high pressure fuel from the first pressure accumulator to the plurality of fuel passages. Between target pressure and actual pressure of low-pressure fuel stored in water , And engine speed Pre-separated engine speed range Based on Correct the operation of the second control valve when the engine speed is in the high engine speed range so that the actual pressure of the low-pressure fuel approaches the target pressure. do it Ensure that the actual pressure of the low-pressure fuel approaches the target pressure and Second 2 The degree of opening of the second control valve that adjusts the discharge of the low pressure fuel from the second pressure accumulator is variably controlled so that the discharge of the low pressure fuel from the pressure accumulator is suppressed. Can be stably maintained at an appropriate pressure, and an appropriate low-pressure injection can be carried out, thereby improving fuel consumption and exhaust gas characteristics.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a pressure accumulation type fuel injection device according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing a connection between main elements of the fuel injection device shown in FIG. 1 and injectors of respective cylinders of the engine.
FIG. 3 is a diagram showing a change in injection rate over time and a change in opening / closing states of a switching valve for switching the injection rate and an on / off valve for controlling the injection timing in one fuel injection cycle.
4 is a flowchart of a low-pressure fuel pressure control routine executed by the electronic control unit shown in FIG.
5 is a diagram exemplifying an engine speed, an accelerator pedal depression amount, and an operation region map used for discrimination of a low rotation / low load region in the low pressure fuel pressure control routine of FIG. 4;
6 is a diagram illustrating a differential pressure / valve opening duty ratio map used for setting a reference valve opening duty ratio and a corrected valve opening duty ratio in the low pressure fuel pressure control routine of FIG. 4; FIG.
7 is a diagram showing a ratio (correction coefficient) of a corrected valve opening duty ratio with respect to a reference valve opening duty ratio shown in FIG. 6. FIG.
FIG. 8 is a diagram showing an optimum range of the diameter of an orifice that is one element of the pressure accumulation type fuel injection device shown in FIG.
FIG. 9 is a diagram illustrating an injector inlet pressure reduction characteristic of the accumulator fuel injection device.
FIG. 10 is a diagram showing changes in injector inlet pressure of the accumulator type fuel injection device in a high rotation region and a low rotation region as a function of a crank angle.
FIG. 11 is a diagram illustrating an example of a case where the low pressure fuel pressure excessively decreases the pressure in the fuel passage, the amount of fuel flowing into the low pressure accumulator, the amount of fuel discharged from the low pressure accumulator, and the temporal change in the low pressure fuel pressure. .
[Explanation of symbols]
1 High pressure pump
8 Controller (fuel injection control means, fuel pressure control means)
3 High pressure accumulator (first accumulator)
3a, 4a Pressure sensor (fuel pressure detection means)
4 Low pressure accumulator (second accumulator)
5 Switching valve (first control valve) for switching accumulator (injection rate)
8a Engine speed sensor (engine operating state detection means)
9 Injector (fuel injection nozzle)
10a, 10b Fuel passage

Claims (3)

A first accumulator for storing high-pressure fuel pressurized by a pump;
A plurality of fuel injection nozzles for injecting fuel into a combustion chamber for each cylinder of the engine;
A plurality of fuel passages extending between the first pressure accumulator and the plurality of fuel injection nozzles;
A plurality of first control valves disposed in each of the plurality of fuel passages to control discharge of high-pressure fuel from the first pressure accumulator to the downstream side of the plurality of fuel passages;
A second accumulator connected to the plurality of fuel passages via branch passages on the downstream side of the plurality of first control valves and storing fuel having a pressure lower than that of the high pressure fuel in the first accumulator;
Fuel pressure detecting means for detecting the actual pressure of the low-pressure fuel in the second pressure accumulator;
A second control valve for variably adjusting the discharge of low-pressure fuel from the second pressure accumulator;
Fuel injection control means for controlling fuel injection from the plurality of fuel injection nozzles by controlling opening and closing of the plurality of fuel injection nozzles and the plurality of first control valves;
Engine operating state detecting means for detecting the engine operating state including the engine speed;
A difference between a target pressure of the low-pressure fuel in the second pressure accumulator determined according to the engine operating state detected by the engine operating state detecting unit and the actual pressure detected by the fuel pressure detecting unit , and the engine Based on a predetermined engine speed range in which the engine speed detected by the operating state detection means exists, the operation of the second control valve is controlled by the low pressure when the speed is in a high speed range. When the rotational speed is in the low rotation range so that the actual pressure of the fuel approaches the target pressure, the operation of the second control valve is corrected so that the actual pressure of the low-pressure fuel approaches the target pressure. as the discharge of low pressure fuel from且one top Symbol second accumulator is prevented, accumulator fuel injection, characterized in that it comprises a fuel pressure control means for variably controlling the valve opening degree of the second control valve apparatus. The engine operating state detecting means detects an engine load,
The fuel pressure control means controls the second control valve according to the engine load detected by the engine operating state detection means so that the discharge of low-pressure fuel from the second accumulator is suppressed in a low load range. The pressure accumulation type fuel injection device according to claim 1, wherein the valve opening degree is variably controlled.   The fuel pressure control means includes the target pressure, the actual pressure, and the actual pressure so that discharge of low-pressure fuel from the second pressure accumulator is suppressed in a low differential pressure range where a difference between the target pressure and the actual pressure is small. 2. The accumulator fuel injection device according to claim 1, wherein the degree of opening of the second control valve is variably controlled according to the difference between the two.

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