GB2459018A

GB2459018A - Common-Rail Pressure Control on Engine Start up.

Info

Publication number: GB2459018A
Application number: GB0905187A
Authority: GB
Inventors: Seiichi Yoshida
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2008-04-10
Filing date: 2009-03-25
Publication date: 2009-10-14
Anticipated expiration: 2029-03-25
Also published as: JP4572950B2; DE102009002099A1; DE102009002099B4; GB2459018B; JP2009250192A; GB0905187D0

Abstract

A common rail pressure control apparatus and method; the apparatus comprises an injection valve 30 which injects fuel accumulated in the common rail 20 to an internal combustion engine 2. An opening control unit (S308, S310, fig.6) controls an electric current supplied to a metering valve 16 for manipulating an opening of the metering valve to meter fuel supplied from the supply pump 14 to the common rail and control pressure in the common rail. The opening control unit first sets the opening of the metering valve at a substantially full open state in a starting operation of the internal combustion engine. The opening control unit subsequently switches the opening of the metering valve from the substantially full open state to a predetermined opening, which is smaller than the opening in the substantially full open state, in response to a determination that the switching condition is satisfied. Preferably water and fuel temperatures are taken into consideration for determining a predetermined common-rail pressure which is used for the switching condition.

Description

COMMON-RAIL PRESSURE CONTROL APPARATUS AND

FUEL INJECTION SYSTEM HAVING THE SAME

Description

The present invention relates to a common-rail pressure control apparatus for controlling pressure in a common rail by metering fuel supplied from a fuel supply pump. The present invention further relates to a fuel injection system having the common-rail pressure control apparatus. The present invention further relates to a method for controlling pressure in the common rail.

For example, JP-A-6-207548 discloses a pressure-accumulation fuel injection system having a common rail for accumulating fuel supplied from a fuel supply pump and injecting fuel accumulated in the common rail through a fuel injection valve into a cylinder of an internal combustion engine. In JP-A-6-207548, a solenoid valve controls communication between a pump chamber of the fuel supply pump, which draws and pressurizes fuel, and a low-pressure passage of a fuel inlet.

In JP-A-6-207548, pressurization of fuel is started in response to closing of the solenoid valve in a compression stroke of a plunger. Fuel supplied from the fuel supply pump is metered according to a time point, at which the solenoid valve is closed in the compression stroke of the plunger. In JP-A-6-207548, in a starting operation of an internal combustion engine, the solenoid valve is opened in a suction stroke of the plunger, and the solenoid valve is closed in the compression stroke of the plunger. Thereby, in the starting operation of the internal combustion engine, a large amount of fuel can be supplied. In the starting operation of the internal combustion engine, a large amount of fuel is fed to the common rail, and thereby pressure in the common rail can be quickly increased.

However, in the starting operation of the internal combustion engine, when excessive amount of fuel is supplied from the fuel supply pump to the common rail, pressure (common rail pressure) in the common rail may be excessively increased, and consequently the common rail pressure may overshoot. When the common rail pressure is excessively increased in the starting operation of the engine, combustion noise and emission of NOx may be increased.

In view of the foregoing and other problems, it is an object of the present invention to produce a common-rail pressure control apparatus capable of quickly increasing common rail pressure in a starting operation of an internal combustion engine, while restricting excessive increasing in common rail pressure. It is another object of the present invention to produce a fuel injection system having the common-rail pressure control apparatus. It is another object of the present invention to produce a method for controlling pressure in the common rail for an internal combustion engine.

According to one aspect of the present invention, a common-rail pressure control apparatus for a fuel injection system, which includes a fuel supply pump for supplying fuel to a common rail and a fuel injection valve for injecting fuel accumulated in the common rail to a cylinder of an internal combustion engine, the common-rail pressure control apparatus configured to manipulate a metering valve for metering fuel supplied from the fuel supply pump so as to control pressure in the common rail, the common-rail pressure control apparatus comprises switching condition determination means for determining whether a switching condition is satisfied. The common-rail pressure control apparatus further comprises opening control means for controlling an electric current supplied to the metering valve for manipulating an opening of the metering valve. The opening control means first sets the opening of the metering valve at a substantially full open state in a starting operation of the internal combustion engine. The opening control means subsequently switches the opening of the metering valve from the substantially full open state to a predetermined opening, which is smaller than the opening in the substantially full open state, in response to a determination of the switching condition determination means that the switching condition is satisfied.

According to another aspect of the present invention, a method for controlling pressure in a common rail for an internal combustion engine, the method comprises setting an opening of a metering valve at a substantially full open state in a starting operation of the internal combustion engine so as to control an amount of fuel, which is supplied from a fuel supply pump, metered through the metering valve, and accumulated in the common rail. The method further comprises switching the opening of the metering valve from the substantially full open state to a predetermined opening, which is smaller than the opening in the substantially full open state, when the switching condition is satisfied.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: FIG. us a schematic diagram showing a fuel injection system according to a first embodiment; FIG. 2 is a graph showing a relationship between an electric current supplied to a metering valve and fuel flow amount; FIG. 3 is a graph showing a relationship between an opening of the metering valve and common rail pressure in a starting operation of an engine; FIG. 4 is a graph showing a relationship between fuel temperature and a predetermihed opening of the metering valve; FIG. 5A is a graph showing the relationship and change in common rail pressure according to the fuel temperature, and FIG 58 is a graph showing a relationship between fuel temperature and predetermined pressure; FIG 6 is a flow chart showing a common-rail-pressure control processing in the starting operation of the engine; and FIG. 7 is a graph showing the relationship and change in common rail pressure in the starting operation of the engine, according to a second embodiment.

(First Embodiment) (Fuel Injection System) FIG. I depicts a fuel injection system according to the present first embodiment. For example, a fuel injection system 10 supplies fuel to a 4-cylinder diesel engine 2 of an automobile. The fuel injection system 10 includes a high-pressure pump 14, a common rail 20, a fuel injection valve 30, and an electronic control unit (ECU) 40. The high-pressure pump 14 supplies high-pressure fuel to the common rail 20. The common rail 20 accumulates the high-pressure fuel supplied from the high-pressure pump 14. The fuel injection valve 30 injects the high-pressure fuel, which is supplied from the common rail 20, into each cylinder of the engine 2. The electronic control unit (ECU) 40 controls the fuel injection system 10. The high-pressure pump 14 includes a feed pump for pumping fuel from a fuel tank I 2. The high-pressure pump 14 as a fuel supply pump has a generally known structure and includes plungers, each moving back and forth in response to rotation of a cam of a camshaft of the engine for pressurizing fuel drawn into a compression chamber of the high-pressure pump 14. In the high-pressure pump 14, multiple plungers are arranged around one cam. A metering valve 16 as a metering actuator is provided at the side of an inlet of the high-pressure pump 14. The metering valve 16 is supplied with electric current, and the electric current is controlled so as to meter fuel drawn into the high-pressure pump 14 in a suction stroke of the high-pressure pump 14. As shown in FIG 2, the metering valve 16 is a normally open valve, which is substantially full open when the electric current supplied to the metering valve 16 is zero. An amount of fuel pres-fed from the high-pressure pump 14 can be controlled by metering fuel drawn into the high-pressure pump 14.

The common rail 20 is provided with a pressure sensor 22 and a pressure limiter 24. The pressure sensor 22 detects pressure (common rail pressure) of fuel in the pressure sensor 22. The pressure limiter 24 opens to return fuel to the fuel tank 12, thereby reducing the common rail pressure when the common rail pressure excessively increases. The pressure sensor 22 is equivalent to fuel pressure detection means. The engine 2 is provided with a crank sensor 32 and a cam sensor 34 for detecting an operation state of the engine 2. The crank sensor 32 detects a crank angle of the engine 2. The cam sensor 34 determines a combustion state of a cylinder of the four cylinders, for example. The ECU 40 detects the crank angle based on an output signal of the crank sensor 32, thereby obtaining a rotation speed of the engine 2. The fuel injection system 10 further includes other sensors for detecting an operation state of the engine 2. For example, the fuel injection system 10 further includes an accelerator sensor, which detects an accelerator position (ACCP) corresponding a manipulation of an accelerator, a temperature sensor, which detects temperature (intake-air temperature) of intake air, temperature (water temperature) of cooling water, and temperature (fuel temperature) of fuel, and the like.

The fuel injection valve 30 is a solenoid valve having a generally known structure in which a lift of a nozzle needle for opening and closing a nozzle hole is controlled according to pressure in a control chamber, for example. When the fuel injection valve 30 injects fuel, the control chamber is communicated with a low-pressure component, and thereby high-pressure fuel supplied from the common rail to the control chamber is partially returned to the low-pressure component. In the present operation, fuel pressure in the control chamber decreases, and thereby the nozzle needle is lifted. Fuel is returned from the control chamber of the fuel injection valve 30 to the low-pressure component such as the fuel tank 12 at a low-pressure side.

The ECU 40 of the common-rail pressure control apparatus includes a microcomputer having a CPU, a ROM, a RAM, a flash memory, and the like. The ECU 40 receives detection signals from various sensors including the pressure sensor 22, the crank sensor 32, and the cam sensor 34, thereby controlling the engine operation state. For example, the ECU 40 controls an amount of fuel press-fed from the high-pressure pump 14, fuel injection from the fuel injection valve 30, a fuel injection timing, a pattern of a multi-stage injection, and the like. In the multi-stage injection, for example, a main injection, pilot injection before the main injection, a post-injection after the main injection, and the like are performed. The ECU 40 controls an electric current supplied to the metering valve 16 by pulse width modulation (PWM) control so as to meter fuel press-fed from the high-pressure pump 14, thereby controlling the common rail pressure. The electric current supplied to the metering valve 16 increases in response to increase in duty ratio of the PWM control. The metering valve 16 is a normally open valve. Therefore, as shown in FIG 2, when the duty ratio of the PWM control is set at zero to reduce the electric current to zero, the metering valve 16 is substantially in the full open state, and thereby the flow amount of fuel increases to the maximum. Alternatively, when the duty ratio of the PWM control is raised so as to increase the electric current, the metering valve 16 gradually closes from the full open state, and thereby the flow amount of fuel decreases. The common rail pressure increases in response to opening of the metering valve 16 and increase in flow amount of fuel, which is press-fed from the high-pressure pump 14. On the contrary, the common rail pressure decreases in response to closing of the metering valve 16 and decrease in flow amount of fuel, which is press-fed from the high-pressure pump 14. In the present structure, the ECU 40 controls the common rail pressure by manipulating the metering valve 16 so as to meter the flow amount of fuel, which is press-fed from the high-pressure pump 14.

In FIG. 2, a dotted line 200 indicates the maximum flow characteristic for the electric current supplied to the metering valve 16 in consideration of an individual difference, a variation caused by aging, and the like. A solid line 210 indicates the median of the flow characteristic. The ECU 40 controls the metering valve 16 in consideration of the maximum flow characteristic indicated by the dotted line 200.

The ECU 40 operates as the following means by executing a control program stored by the ROM or the flash memory, for example.

(Pressure Determination Means) The ECU 40 obtains the common rail pressure from the output signal of the pressure sensor 22. The ECU 40 determines whether the common rail pressure is increased to predetermined pressure (kinjpc) after the engine 2 starts.

(Switching Condition Determination Means) When the pressure determination means determines that the common rail pressure is increased to the predetermined pressure kinjpc after the engine 2 is started, the ECU 40 determines that a switching condition (selecting condition} is satisfied. When the switching condition is satisfied, the ECU 40 manipulates the metering valve 16 at a predetermined opening, which is smaller than the opening of the passage area thereof in the full open state, after manipulating the metering valve 16 at the full open state in the starting operation of the engine 2. According to the present operation, it is determined whether the switching condition, in which the opening of the metering valve 16 is manipulated from the full open state to the predetermined opening, is satisfied based on the common rail pressure, which is obtained from the output signal of the pressure sensor 22. Therefore, a time point (switching time point), at which the opening of the metering valve 16 is selected and switched to the predetermined opening, can be determined with high accuracy in the starting operation of the engine 2. Thus, the common rail pressure can be controlled with high accuracy.

(Opening Control Means) Preferably, as indicated by a solid line 220 in FIG 3, the common rail pressure is quickly increased to a target pressure in the starting operation of the engine 2 so as to promptly inject fuel from the fuel injection valve 30. According to the present operation, when an ignition device is activated by, for example, rotating an ignition key to a start position, the ECU 40 first controls the duty ratio of the PWM control at substantially zero so -as to control the electric current supplied to the metering valve 16 at substantially zero. Thereby, the metering valve 16 is manipulated at the full open state, and the maximum flow of fuel is drawn from the metering valve 16 into the compression chamber of the high-pressure pump 14.

Thus, as indicated by a solid Hne 230, the common rail pressure increases. In the present condition, when the metering valve 16 is maintained at the full open state, the common rail pressure increases to be larger than the target pressure. Consequently, as indicted by the solid line 230, the common rail pressure overshoots the target pressure.

Therefore, when the pressure determination means determines that the common rail pressure, which is obtained based on the output signal of the pressure sensor 22, increases to the predetermined pressure (kinjpc), the ECU 40 increase the duty ratio of the PWM control so as to increase the electric current supplied to the metering valve 16 from zero. Thus, the ECU 40 controls the metering valve 16 at the predetermined opening, which is smaller than the opening at the full open state.

Thus, the amount of fuel flowing into the high-pressure pump 14 decreases, and thereby the amount of fuel press-fed from the high-pressure pump 14 decreases.

Therefore, as indicated by the dotted line 240, an increase rate of the common rail pressure is reduced compared with the increase rate indicated by the solid line 230 at the full open state.

In FIG 3, a time delay t occurs subsequent to a time point, at which the metering valve 16 is supplied with the electric current and controlled at the predetermined opening from the full open state, and in advance of a time point at which the increase rate of the common rail pressure starts decreasing. As defined by the following formula (1), the time delay t is mainly determined by three factors (dta, dtb, dtc).

t=dta+dtb+dtc (1) The term dta is a time period elapsed for drawing fuel from the metering valve 16 into the compression chamber. The term dtb is a time period elapsed for pressurizing fuel and press-feeding the fuel after drawing the fuel into the compression chamber. The term dtc is a time period elapsed for the fuel flowing from the high-pressure pump 14 to the common rail 20. As time delay Lit, is obtained by conducting an experiment or the like in advance. The predetermined pressure (kinjpc), at which the opening of the metering valve 16 is selected and switched, is determined based on the time lag t in the formula (1), water temperature, and the like.

(Opening Setting Means) The ECU 40 determines and sets the predetermined opening, to which the ECU 40 selects and switches the opening of the metering valve 16 from the full open state, based on water temperature or fuel temperature in the starting operation of the engine 2. As the water temperature becomes high, the fuel temperature becomes high, and thereby the viscosity of fuel decreases. When the viscosity of fuel decreases, for example, quantity of fuel leaking from a high-pressure component to the low-pressure component through a sliding portion between the plunger of the high-pressure pump 14 and the cylinder increases. Consequently, as the fuel temperature becomes high, the amount of fuel press-fed from the high-pressure pump 14 decreases on a precondition that the opening of the metering valve 16 is constant. Therefore, as shown in FIG. 4, as the fuel temperature (water temperature) becomes high, the predetermined opening, to which the opening of the metering valve 16 is selected and switched from the full open state, is increased.

Thereby, reduction in amount of fuel, which is press-fed from the high-pressure pump 14, caused by increase in fuel temperature can be restricted.

The ECU 40 may estimate the fuel temperature based on the water temperature. Alternatively, the ECU 40 may detect the fuel temperature and may set the predetermined opening based on the detected fuel temperature.

(Pressure Setting Means) The ECU 40 determines and sets the predetermined pressure (kinjpc), at which the ECU 40 selects and switches the opening of the metering valve 16 from the full open state to the predetermined opening, based on the water temperature or the fuel temperature in the starting operation of the engine 2. As the fuel temperature becomes high, and thereby the viscosity of fuel decreases, the amount of fuel press-fed from the high-pressure pump 14 decreases. Thus, the increase rate of the common rail pressure decreases in response to reduction in amount of fuel press-fed from the high-pressure pump 14. Therefore, as shown in FIG 5A, on a precondition that the predetermined pressure (kinjpc), when the opening of the metering valve 16 is switched from the full open state to the predetermined opening, is constant regardless of the fuel temperature, an increasing characteristic of the common rail pressure indicated by the dotted line 240 in an ambient temperature state becomes a characteristic indicated by a dashed dotted line 250 in response to increase in fuel temperature. Consequently, the time period elapsed for the common rail pressure to increase to the target pressure becomes large.

Therefore, as shown in FIG 5B, the ECU 40 sets the predetermined pressure (kinjpc) at a higher pressure when the fuel temperature of the water temperature becomes high. According to the present operation, as indicated by a two-dot chain line 252 in FIG 5A, the common rail pressure can be significantly increased in the condition where the metering valve 16 is in the full open state such that the common rail pressure does not overshoot in the starting operation of the engine 2. Consequently, reduction in increase rate of the common rail pressure, which is caused by increase in fuel temperature, can be compensated, and thereby the common rail pressure can be promptly increased to the target pressure.

(Common Rail Pressure Control in Starting Operation) In a common-rail-pressure control, the metering valve 16 is manipulated so as to control the common rail pressure in the stating operation of the engine 2. A common-rail-pressure control routine will be described with reference to FIG 6. The common-rail-pressure control is executed in the starting operation of the engine 2.

(Common-Rail-Pressure Control Processing) At S300 in FIG 6, when the ignition key is manipulated to the start position, for example, the ECU 40 rotates a starter device to start a clanking operation of the engine 2. At S302, the ECU 40 determines whether sensor signals of the crank sensor and the cam sensor are properly outputted and synchronized. When the sensor signals of the crank sensor and the cam sensor are synchronized, a positive determination is made at S302. In this case, at S304, the ECU 40 performs a normal control of the opening of the metering valve 16 so as to feedback control the common rail pressure in accordance with the difference between the actual common rail pressure, which the pressure sensor 22 detects, and the target common rail pressure. When the sensor signals of the crank sensor and the cam sensor are not synchronized, a negative determination is made at S302. In this case, at S306, the ECU 40 determines whether the actual common rail pressure (RP), which the pressure sensor 22 detects, is larger than the predetermined pressure (kinjpc).

When the actual common rail pressure (RP) is less than the predetermined pressure (kinjpc), a negative determination is made at S306. In this case, at S308, the ECU sets the electric current supplied to the metering valve 16 at a full-open electric current by which the metering valve 16 is controlled at the full open state. The metering valve 16 according to the present embodiment is the normally open valve, and therefore the full-open electric current, by which the metering valve 16 is at the full open state, is substantially zero. Thus, the processing of the ECU 40 returns to step S302. When the actual common rail pressure (RP) is equal to or greater than the predetermined pressure (kinjpc), a positive determination is made at S306. In this case, at S310, the ECU 40 obtains the electric current, which is supplied to the metering valve 16, from a data map or the like in accordance with the predetermined opening and the water temperature. Thus, the processing of the ECU 40 returns to step S302.

(Second Embodiment) According to the present second embodiment, the ECU 40 includes pressure increase rate detection means and switching time point setting means for determining the switching time point, at which the ECU 40 selects and switches the opening of the metering valve 16 from the full open state to the predetermined opening.

(Pressure Increase Rate Detection Means) As shown in FIG 7, in the starting operation of the engine 2, the ECU 40 starts the clanking operation of the engine 2 while controlling the metering valve 16 at the full open state. Subsequently, the ECU 40 calculates and detects the increase rate (p1/TI) of the common the rail pressure in accordance with the common rail pressure p1, which increases in a predetermined periods TI.

(Switching Time Point Setting Means) The ECU 40 calculates a time 1, which the common rail pressure needs to increase to a target pressure p2 of the common rail pressure in the condition where the metering valve 16 is in the full open state, from the following formula (2) by using the increase rate (p1/TI).

Tp21(plITI)=p2x(T1/pI)...(2) The predetermined pressure (kinjpc), at which the opening of the metering valve 16 is switched from the full open state to the predetermined opening such that the common rail pressure does not overshoot, is determined to satisfy the following formula (3). The predetermined pressure (kinjpc) is determined in consideration of the time lag At, which the common rail pressure needs to change after the switching of the opening of the metering valve 16.

I -At > kinjpc x (TI / p1) p2x(T1 /pl)-At>kinjpcx(T1 Ipl) p2.-Atx(pl /T1)>kinjpc... (3) The ECU 40 determines the predetermined pressure (kinjpc) within a limit, which satisfies the formula (3), on the basis of a safety factor, a prediction increase rate of the common rail pressure when the opening of the metering valve 16 is reduced from the full open state to the predetermined opening, and the like. The safety factor is determined such that the common rail pressure does not to overshoot.

The predetermined pressure (kinjpc) relates to a switching time point at which the opening of the metering valve is switched from the full open to the predetermined opening. The predetermined pressure (kinjpc) is determined based on the increase rate (p1/TI) of the common rail pressure calculated based on the output signal of the pressure sensor 22. Therefore, the predetermined pressure (kinjpc) is determined in consideration of change in flow characteristic of the high-pressure pump 14 caused by change in fuel temperature, an individual difference of the metering valve 16, aging, and the like. In the present structure, the opening of the metering valve 16 can be suitably switched from the full open state to the predetermined opening according to a feeding state of the high-pressure pump 14.

According to the present second embodiment, the opening of the metering valve 16 is first controlled at the full open state so as to feed the total amount of fuel from the high-pressure pump 14 to the common rail 20 in the starting operation of the engine 2. Thus, the common rail pressure quickly increases in the starting operation of the engine 2. When the common rail pressure increases to the predetermined pressure (kinjpc), the metering valve 16 is set at the predetermined opening, which is smaller than the opening at the full open state. Thus, the increase rate of the common rail pressure can be reduced. Consequently, the common rail pressure can be restricted from overshooting the target pressure.

(Other Embodiment) According to the first embodiment, the predetermined pressure (kinjpc), at which the opening of the metering valve 16 is switched from the full open state to the predetermined opening in the starting operation of the engine 2, and the predetermined opening are determined based on the water temperature and/or the fuel temperature. Alternatively, at least one of the predetermined pressure (kinjpc) and the predetermined opening may be a constant value regardless of the water temperature and the fuel temperature.

According to the above embodiments, the metering valve 16 is provided to the inlet of the high-pressure pump 14 for metering fuel fed from the high-pressure pump 14 according to the opening thereof by metering fuel drawn into the high- pressure pump 14. It suffices that the metering valve meters fuel fed from the high-pressure pump 14 according to the opening thereof. Therefore, the metering valve may be provided to the outlet of the high-pressure pump to meter fuel fed from the high-pressure pump.

According to the above embodiments, the metering valve 16 is first controlled at the full open state in the starting operation of the engine 2. Thereafter, the switching condition is determined to be satisfied when the common rail pressure increases to the predetermined pressure (kinjpc), and thereby the metering valve 16 is switched from the full open state to the predetermined opening. Alternatively, for example, the switching condition may be determined to be satisfied and the metering valve 16 may be switched from the full open state to the predetermined opening after a predetermined time period elapses in the starting operation of the engine 2.

According to the above embodiments, the ECU 40 includes the switching condition determination means, the opening control means, the opening setting means, the pressure determination means, the pressure setting means, the pressure increase rate detection means, and the switching time point selling means, each defined by the control program. Alternatively, at least a part of the function of the means may be produced by a hardware including electronic circuits.

In this manner, the invention is not limited to the embodiments described above but is applicable to various embodiments within a scope not departing from the gist thereof.

The above processings such as calculations and determinations are not limited being executed by the ECU 40. The control unit may have various structures including the ECU 40 shown as an example. The functions of the means (units) may be produced using a hardware resource having functions specified by a construction thereof, a hardware resource having functions specified by a program, or a combination of the hardware resources. The above embodiments are not limited to an analog circuitry including analog signal handling equipments configured to perform the processings such as the comparison, the amplification, and other operations by using analog quantities. For example, at least part of the signals in the circuit structures in the above embodiments may be converted to digital signals, and substantially the same processings such as the comparison, the amplification, and other operations may be performed using the converted digital signals by employing a microcomputer, a programmable logic circuit, and the like. For example, the above processings such as calculations and determinations may be performed by any one or any combinations of software, an electric circuit, a mechanical device, and the like. The software may be stored in a storage medium, and may be transmitted via a transmission device such as a network device. The electric circuit may be an integrated circuit, and may be a discrete circuit such as a hardware logic configured with electric or electronic elements or the like. The elements producing the above processings may be discrete elements and may be partially or entirely integrated.

It should be appreciated that while the processes of the embodiments of the present invention have been described herein as including a specific sequence of steps, further alternative embodiments including various other sequences of these steps and/or additional steps not disclosed herein are intended to be within the steps of the present invention.

The above structures of the embodiments can be combined as appropriate.

Various modifications and alternations may be diversely made to the above embodiments without departing from the spirit of the present invention.

Claims

Claims: 1. A common-rail pressure control apparatus for a fuel injection system, which includes a fuel supply pump for supplying fuel to a common rail and a fuel injection valve for injecting fuel accumulated in the common rail to a cylinder of an internal combustion engine, the common-rail pressure control apparatus configured to manipulate a metering valve for metering fuel supplied from the fuel supply pump so as to control pressure in the common rail, the common-rail pressure control apparatus comprising: switching condition determination means for determining whether a switching condition is satisfied; and opening control means for controlling an electric current supplied to the metering valve for manipulating an opening of the metering valve, wherein the opening control means first sets the opening of the metering valve at a substantially full open state in a starting operation of the internal combustion engine, and the opening control means subsequently switches the opening of the metering valve from the substantially full open state to a predetermined opening, which is smaller than the opening in the substantially full open state, in response to a determination of the switching condition determination means that the switching condition is satisfied.
2. The common-rail pressure control apparatus according to claim 1, further comprising: opening setting means for setting the predetermined opening on the basis of at least one of water temperature and fuel temperature.
3. The common-rail pressure control apparatus according to claim 1 or 2, further comprising: pressure determination means for determining whether pressure in the common rail increases to predetermined pressure, wherein the switching condition determination means determines that the switching condition is satisfied in response to determination of the pressure determination means that the pressure in the common rail increases to the predetermined pressure.
4. The common-rail pressure control apparatus according to claim 3, further comprising: pressure setting means for setting the predetermined pressure on the basis of at least one of water temperature and fuel temperature.
5. The common-rail pressure control apparatus according to claim I or 2, further comprising: pressure increase rate detection means for detecting a rate of increase in pressure in the common rail per unit time when the metering valve is in the substantially full open state in the starting operation of the internal combustion engine; and switching time point setting means for setting a switching time point, at which the opening of the metering valve is switched from the substantially full open state to the predetermined opening, on the basis of the rate of increase in pressure and a time delay between a time point, at which the opening of the metering valve is switched from the substantially full open state to the predetermined opening, and a time point, at which the pressure in the common rail changes, wherein the switching condition determination means determines that the switching condition is satisfied at the switching time point subsequent to starting of the internal combustion engine.
6. A fuel injection system comprising: the common-rail pressure control apparatus according to any one of claims lto5; the fuel supply pump for pressurizing and supplying fuel; the metering valve for metering fuel supplied from the fuel supply pump; the common rail for accumulating fuel supplied from the fuel supply pump; the fuel injection valve for injecting fuel, which is accumulated in the common rail, to each cylinder of the internal combustion engine.
7. A method for controlling pressure in a common rail for an internal combustion engine, the method comprising: setting an opening of a metering valve at a substantially full open state in a starting operation of the internal combustion engine so as to control an amount of fuel, which is supplied from a fuel supply pump, metered through the metering valve, and accumulated in the common rail; and switching the opening of the metering valve from the substantially full open state to a predetermined opening, which is smaller than the opening in the substantially full open state, when the switching condition is satisfied.
8. The method according to claim 7, further comprising: determining the switching condition to be satisfied in response to increase in pressure in the common rail to predetermined pressure.
9. The method according to claim 8, further comprising: setting the predetermined pressure on the basis of at least one of water temperature and fuel temperature.
10. The method according to claim 7, further comprising: detecting a rate of increase in pressure in the common rail per unit time when the metering valve is in the substantially full open state; setting a switching time point, at which the opening of the metering valve is switched from the substantially full open state to the predetermined opening, on the basis of the rate of increase in pressure and a time delay between a time point, at which the opening of the metering valve is switched from the substantially full open state to the predetermined opening, and a time point, at which the pressure in the common rail changes; and determining the switching condition to be satisfied at the switching time point subsequent to starting of the internal combustion engine.
11. Apparatus substantially as hereinbefore described.
12. A method substantially as hereinbefore described.