JP4556881B2 - Common rail fuel injection system - Google Patents

Description

  The present invention relates to a common rail fuel injection device including a piezo injector equipped with a piezo stack that injects fuel by pressurizing a hydraulic chamber filled with low-pressure fuel, and more particularly to a countermeasure technique when air enters the hydraulic chamber. .

A common rail type fuel injection device equipped with a piezo injector is known.
Specific examples of piezo injectors include: (1) The switching valve (three-way switching valve) is driven by varying the pressure in the hydraulic chamber (displacement expansion chamber) by the piezo stack, and the pressure in the back pressure chamber of the needle is controlled by the switching valve. A switching valve type (see FIG. 2) that drives the needle by switching, (2) a control chamber that lifts the intermediate piston that urges the needle in the seating direction by varying the pressure of the hydraulic chamber (hydraulic converter) by the piezo stack An intermediate piston type is known in which the pressure is varied and the needle is driven by the movement of the intermediate piston.

  In addition to the common rail fuel injection device, the fuel injection device may have air mixed into the system due to a lack of gas. When air enters the piezo injector, it takes time from the start of cranking to the start (complete explosion) of the engine when the internal combustion engine (hereinafter referred to as the engine) is started. For this reason, the problem that the comfort at the time of engine starting is impaired arises.

The technique of Patent Document 1 is known as a technique for improving the startability of an engine after a gas shortage. The common rail fuel injection device of Patent Document 1 is equipped with an electromagnetic injector that drives a needle by moving a command piston that urges the needle in the seating direction by varying the pressure in the control chamber by an electromagnetic valve. There is a technology for improving engine startability by discharging air between the common rail and the electromagnetic injector by driving the electromagnetic valve while the engine is stopped.
However, when air is mixed into the hydraulic chamber of the piezo injector, the air is compressed in the hydraulic chamber and the increase in hydraulic pressure is suppressed {see FIG. 3 (a)}. However, the comfort (shortening of the cranking time) when starting the engine cannot be obtained.
JP-A-11-343946

The present invention has been made in view of the above-described problems, and the object thereof is to provide air in the hydraulic chamber of a piezo injector due to a lack of gas or the like due to a lack of gas or the like due to an easy and reliable configuration that is easy to ensure reliability. The present invention provides a common rail type fuel injection device that can shorten the time from cranking start to engine start (complete explosion) even if mixed.

[Means of claim 1]
The common rail type fuel injection device adopting the means of claim 1 uses the fuel pressure discharged from the priming means for guiding the fuel in the fuel tank to the supply pump to increase the pressure on the low pressure side of the piezo injector when the engine is started. Is.
When air is mixed into the hydraulic chamber of the piezo injector due to lack of gas, etc., the air mixed into the hydraulic chamber of the piezo injector is compressed by increasing the pressure on the low pressure side of the piezo injector by the priming means, and the volume of the hydraulic chamber is increased. The volume ratio occupied by air is reduced.
As a result, air compression in the hydraulic chamber is suppressed when the piezo stack is operated, and the time from the start of cranking to the start of the engine (complete explosion) can be shortened.
Moreover, since the fuel pressure discharged from the priming means, that is, the priming pressure to the supply pump is much lower than the fuel pressure from the supply pump to the common rail, the configuration of piping and valves to be added is also reliable. Can be easily secured, and the structure is inexpensive and simple.

[Means of claim 2]
In the common rail fuel injection apparatus employing the means of claim 2, the pressure on the low-pressure side of the piezo injector, which is increased when the engine is started by the priming means, is a substantial air elimination pressure at which the piezo injector can perform an injection operation by the operation of the piezo stack. is there.

[Means of claim 3]
The common rail type fuel injection device employing the means of claim 3 uses the fuel pressure discharged from the overflow portion of the supply pump that pumps high pressure fuel to the common rail to increase the pressure on the low pressure side of the piezo injector when starting the engine. Is.
When air is mixed into the hydraulic chamber of the piezo injector due to lack of gas, etc., it is mixed into the hydraulic chamber of the piezo injector by increasing the pressure on the low pressure side of the piezo injector using the fuel pressure discharged from the overflow part of the supply pump. Air is compressed, and the volume ratio of the air in the volume of the hydraulic chamber is reduced.
As a result, air compression in the hydraulic chamber is suppressed when the piezo stack is operated, and the time from the start of cranking to the start of the engine (complete explosion) can be shortened.
In addition, since the fuel pressure discharged from the overflow portion of the supply pump, that is, the overflow pressure from the supply pump is also low as in the means of claim 1, the reliability of the configuration of pipes and valves to be added is also reliable. Can be easily secured, and the structure is inexpensive and simple.

[Means of claim 4]
5. A common rail fuel injection apparatus employing the means of claim 4, wherein the pressure on the low pressure side of the piezo injector, which is increased when the engine is started by the fuel pressure discharged from the overflow portion of the supply pump, is controlled by the operation of the piezo stack. This is the air substantial disappearance pressure at which the injection operation becomes possible.

Common rail fuel injectors
A common rail for accumulating high-pressure fuel,
A supply pump that supplies high pressure fuel to the common rail;
Low pressure piping to return fuel to the fuel tank;
A high-pressure part that receives high-pressure fuel from a common rail and a low-pressure part that communicates with low-pressure piping, and a hydraulic chamber filled with low-pressure fuel (an oil chamber that converts expansion and contraction of a piezo stack into hydraulic pressure: for example, displacement expansion that drives a switching valve Chamber, a piston that can pressurize the intermediate piston, etc., and a piezo stack that pressurizes the hydraulic chamber by driving the piston when it is energized. And a piezo injector for injecting high-pressure fuel supplied from the common rail by the change.
This piezo injector includes low-pressure fuel supply means (such as a check valve) that guides the low-pressure side fuel only to the hydraulic chamber.
Further, the common rail fuel injection device includes a back pressure check valve for setting the low pressure fuel pressure on the piezoelectric injector side to a predetermined pressure in the middle of the low pressure pipe.
Furthermore, the common rail fuel injection device includes low pressure boosting means for increasing the pressure on the low pressure side of the piezo injector when the engine is started.

The low pressure boosting means of the best mode 1 is
Priming means for guiding the fuel in the fuel tank to the supply pump, a back pressure check valve for setting the low pressure fuel pressure on the piezo injector side to a predetermined pressure, and low pressure fuel supply for guiding the low pressure side fuel to the hydraulic chamber only in the piezo injector And a fuel path switching unit that switches the fuel discharged from the priming unit from the supply pump to the low-pressure pipe on the piezo injector side from the back pressure check valve.
Further, the low pressure boosting means of the best mode 2 includes low pressure fuel supply means (such as a check valve) for guiding the low pressure side fuel only to the hydraulic chamber in the piezo injector, and fuel discharged from the overflow portion of the supply pump, It comprises fuel path switching means that switches from the back pressure check valve to the low pressure piping on the piezo injector side.

In the first embodiment, the configuration of the common rail fuel injection device will be described first, and then the features of the first embodiment will be described.
[Description of common rail fuel injection system]
A common rail fuel injection device will be described with reference to FIG.
The common rail type fuel injection device is a system that injects fuel into each cylinder of an engine (for example, a diesel engine: not shown), and includes a common rail 1, a piezo injector 2, a supply pump 3, a priming means 4, a control device 5, and the like. Is done. The control device 5 includes an ECU (engine control unit) 5a and an EDU (drive unit) 5b, and the EDU 5b may be built in a case of the ECU 5a.

(Description of common rail 1)
The common rail 1 is a pressure accumulating container for accumulating high-pressure fuel supplied to the piezo injector 2, and discharge of a supply pump 3 that pumps high-pressure fuel through a high-pressure pump pipe so that the common rail pressure corresponding to the fuel injection pressure is accumulated. In addition to being connected to the outlet, a plurality of injector pipes 6 for supplying high-pressure fuel to each piezo injector 2 are connected.

A pressure reducing valve 7 also serving as a pressure limiter is attached to one end of the common rail 1. The pressure reducing valve 7 is opened by a valve opening instruction signal given from the control device 5 and rapidly reduces the common rail pressure via a reflux pipe (low pressure pipe) 8. In this way, by mounting the pressure reducing valve 7 on the common rail 1, the control device 5 can quickly control the common rail pressure to a pressure corresponding to the vehicle running state.
A common rail pressure sensor 9 is attached to the other end of the common rail 1 so that the common rail pressure to be accumulated can be detected by the ECU 5a.

(Description of piezo injector 2)
The piezo injector 2 is mounted in each cylinder of the engine and supplies fuel into each cylinder. The piezo injector 2 is connected to the downstream ends of a plurality of injector pipes 6 branched from the common rail 1 and accumulated in the common rail 1. The high pressure fuel is injected and supplied into each cylinder, and its specific configuration will be described later.
The low-pressure leaked fuel leaked from the piezo injector 2 is led to the return pipe 8 through the back pressure check valve 11 and returned to the fuel tank 12. The back pressure check valve 11 is a means that opens at a predetermined pressure (for example, 200 kPa) or more and maintains the leak fuel pressure of the piezo injector 2 at a predetermined pressure during engine operation.

(Description of supply pump 3)
The supply pump 3 includes a high-pressure pump that pumps high-pressure fuel to the common rail 1 and a feed pump that supplies the fuel in the fuel tank 12 to the high-pressure pump through the fuel filter 13. The supply pump 3 supplies the fuel sucked up by the feed pump. Compressed to high pressure with a high-pressure pump and pumped to the common rail 1. The feed pump and the high pressure pump are driven by a common camshaft 14. The camshaft 14 is rotationally driven by the engine.

  The supply pump 3 is equipped with an SCV (suction metering valve) 15 for adjusting the degree of opening of the fuel flow path in a fuel flow path that guides the fuel into a pressurizing chamber that pressurizes the fuel to a high pressure. . The SCV 15 is a metering valve that adjusts the amount of fuel sucked into the pressurizing chamber and changes the amount of fuel pumped to the common rail 1 by being controlled by a pump drive signal from the control device 5. Yes, the common rail pressure is adjusted by adjusting the discharge amount of fuel pumped to the common rail 1. That is, the ECU 5a can control the common rail pressure to a pressure corresponding to the vehicle running state by controlling the SCV 15.

  The inside of the supply pump 3 is filled with fuel for lubrication. Specifically, a part of the fuel discharged from the feed pump in the supply pump 3 is provided so as to fill the supply pump 3, and the fuel overflowing from the supply pump 3 overflows from the overflow part 3 a of the supply pump 3. It is led to the return pipe 8 through the pipe 16 and returned to the fuel tank 12.

(Description of priming means 4)
The priming means 4 is operated when the supply pipe 17 that leads the fuel from the fuel tank 12 to the supply pump 3 is empty and the supply pump 3 cannot suck the fuel at the time of shipment or when the gas runs out. The common rail fuel injection device is an electric pump (electric priming) 4a mounted in the fuel tank 12, or a manual pump (manual priming) mounted on the fuel filter 13. At least one of 4b is mounted.
The fuel supply pressure by the manual pump (manual priming) 4b can be about 200 kPa.

[Description of Piezo Injector 2]
An example of the piezo injector 2 will be described with reference to FIG. In the following description, the upper side in FIG. 2 is referred to as the upper side, and the lower side in FIG. 2 is referred to as the lower side.
The piezo injector 2 includes a nozzle portion 21, a three-way switching valve 22, a displacement enlarging means 23, and a piezo stack 24 from bottom to top.

(Description of nozzle portion 21)
The nozzle unit 21 switches between injection and stop of high-pressure fuel, and includes a needle 26 that is slidably supported in the axial direction in a housing 25 (specifically, a nozzle holder).
The needle 26 has a large-diameter portion 27 provided at an upper portion thereof slidably supported in the housing 25, and a lower end conical portion 28 of the needle 26 is formed on an annular sheet 29 formed on the inner side of the lower end of the housing 25. Sit or leave. High-pressure fuel is introduced into the outer peripheral space 31 below the needle 26 via a high-pressure fuel passage 32 (a fuel passage communicating with the injector pipe 6) formed in the housing 25, and the injection hole 33 is formed when the needle 26 is seated. Fuel is injected from. The high-pressure fuel supplied to the outer peripheral space 31 below the needle 26 acts on the step surface 27 a on the lower surface of the large-diameter portion 27 to generate an upward force (separating direction) on the needle 26.

On the other hand, on the upper side of the large diameter portion 27, a pressure control chamber 34 for generating a downward (sitting direction) force on the needle 26 by the pressure of the fuel is formed. High pressure fuel is supplied to the pressure control chamber 34 from the high pressure fuel passage 32 through the in-orifice 35, and the high pressure fuel supplied to the pressure control chamber 34 acts on the upper surface 27 b of the large diameter portion 27, so that the needle The needle 26 is pressed downward together with the spring 36 (sitting direction).
The internal pressure of the pressure control chamber 34 is controlled to be switched between a high pressure state and a low pressure state by the three-way switching valve 22. (1) The pressure control chamber 34 becomes a low pressure, and the downward force of the needle 26 (sitting direction) When the upward force (separating direction) of the needle 26 exceeds, the needle 26 is lifted and high-pressure fuel is injected from the injection hole 33. (2) The pressure control chamber 34 becomes high pressure and the needle 26 is upward (separated). When the downward force (sitting direction) of the needle 26 exceeds the force in the seating direction), the needle 26 is lifted down and fuel injection from the injection hole 33 is stopped.

(Description of the three-way switching valve 22)
The three-way switching valve 22 is a hydraulic switching valve that switches the internal pressure of the pressure control chamber 34 by switching the valve chamber 37 communicating with the pressure control chamber 34 to one of the high pressure fuel passage 32 and the low pressure fuel passage 39 by the switching valve 38. . The low-pressure fuel passage 39 is a fuel passage formed in the housing 25 and communicating with the recirculation pipe 8.
A low pressure side valve seat 41 communicating with the inside of the valve chamber 37 and the low pressure fuel passage 39 is formed at the upper portion of the valve chamber 37, and the high pressure fuel passage 32 inside the valve chamber 37 and the high pressure side is provided at the lower portion of the valve chamber 37. A high-pressure side valve seat 42 that communicates is formed.
The switching valve 38 is supported by a small-diameter piston 43 described later so as to be movable in the vertical direction in the valve chamber 37.

Then, the switching valve 38 is displaced downward to open the low pressure side valve seat 41 and close the high pressure side valve seat 42, whereby the valve chamber 37 and the pressure control chamber 34 are switched to low pressure (injection operation).
Conversely, the switching valve 38 is displaced upward, the high pressure side valve seat 42 is opened, and the low pressure side valve seat 41 is closed, whereby the valve chamber 37 and the pressure control chamber 34 are switched to high pressure (injection stop operation).

(Explanation of displacement enlarging means 23)
The displacement enlarging means 23 increases the expansion / contraction displacement amount (change amount in the stacking direction, that is, change amount in the vertical direction) of the piezo stack 24 and transmits it to the switching valve 38 of the three-way switching valve 22. A small-diameter piston (valve piston) 43 connected to the piezo stack 24, a large-diameter piston (piezo-piston) 44 driven directly by the piezo stack 24, and a fuel formed between the upper surface of the small-diameter piston 43 and the lower surface of the large-diameter piston 44. The displacement expansion chamber (an example of a hydraulic chamber) 45 is filled.

The large diameter piston 44 is supported inside the housing 25 so as to be slidable in the axial direction. The large-diameter piston 44 is pressed against the piezo stack 24 by a disc spring (piezo spring) 46 disposed in the displacement expansion chamber 45, and is displaced in the vertical direction by the same amount as the expansion and contraction of the piezo stack 24.
Here, the large-diameter piston 44 is formed with a communication passage 47 that allows the displacement expansion chamber 45 and the low-pressure fuel passage 39 to communicate with each other, and a check valve 48 that can open and close the communication passage 47 is incorporated therein. The check valve 48 opens when fuel is replenished in the closed space including the displacement expansion chamber 45. That is, the closed space is filled with fuel. For example, when the fuel in the displacement expansion chamber 45 is pressurized by the large-diameter piston 44, the fuel gradually leaks from the sliding gap of the large-diameter piston 44. To do. For this reason, it is necessary to replenish the closed space with fuel. Therefore, when the pressure in the displacement expansion chamber 45 becomes lower than the pressure in the low-pressure fuel passage 39 (low-pressure side fuel pressure set by the back pressure check valve 11) due to fuel leakage, the check valve 48 opens. Thus, the displacement expansion chamber 45 is automatically refilled with fuel. That is, even when the operation of the piezo injector 2 is stopped, the pressure in the displacement expansion chamber 45 is set to the pressure in the low pressure fuel passage 39.

The small diameter piston 43 is slidably supported in the axial direction inside the housing 25. The small diameter piston 43 is displaced in the vertical direction integrally with the switching valve 38.
Here, the diameter of the upper end of the small-diameter piston 43 facing in the displacement expansion chamber 45 is set smaller than the diameter of the lower end of the large-diameter piston 44, and the axial displacement of the large-diameter piston 44 expands to the small-diameter piston 43. Is transmitted.

The piezoelectric stack 24 extends in the stacking direction, the large-diameter piston 44 moves downward, and the switching valve 38 is displaced downward together with the small-diameter piston 43, whereby the low-pressure side valve seat 41 is opened and the high-pressure side valve seat 42 is moved. The valve chamber 37 and the pressure control chamber 34 are switched to low pressure (injection operation).
Conversely, when the piezo stack 24 contracts in the stacking direction and the large-diameter piston 44 moves upward by the disc spring 46, the small-diameter piston 43 is sucked upward by the displacement expansion chamber 45, and the switching valve 38 is moved together with the small-diameter piston 43. By displacing upward, the high pressure side valve seat 42 is opened, the low pressure side valve seat 41 is closed, and the valve chamber 37 and the pressure control chamber 34 are switched to high pressure (injection stop operation).

(Description of piezo stack 24)
The piezo stack 24 has a well-known configuration, and an example thereof will be described.
The piezo stack 24 is formed by laminating a large number of plate-like piezo elements that expand in the thickness direction when charged. Each piezo element includes a piezoelectric body having a substantially disk shape and internal electrodes formed on both surfaces of the piezoelectric body, and a piezo stack 24 is formed by stacking a large number of piezo elements in the thickness direction.

In addition, two side electrodes are provided on the side surface of the piezo stack 24. One side electrode is electrically connected to one internal electrode of the piezoelectric body, and the other side electrode is electrically connected to the other internal electrode of the piezoelectric body. The two side electrodes are connected to an external connector exposed to the outside of the piezo injector 2. The external connector is connected to the control device 5 (specifically, EDU 5b), and charge / discharge control of the piezo stack 24 is performed from the control device 5 via the external connector.
The piezo stack 24 is provided in the piezo injector 2 so as not to come into contact with fuel.

(Description of the control device 5)
As described above, the control device 5 includes the ECU 5a and the EDU 5b.
The ECU 5a is a well-known structure including a CPU that performs control processing and arithmetic processing, a storage device (memory such as ROM, RAM, SRAM, and EEPROM) that stores various programs and data, an input circuit, an output circuit, and a power supply circuit. Of computers.
The ECU 5a performs various arithmetic processes based on the read sensor signals (engine parameters: signals corresponding to the operating state of the occupant and the operating state of the engine).
The ECU 5a includes, as sensors for detecting engine parameters, an accelerator sensor for detecting an accelerator opening, a rotation speed sensor for detecting an engine speed and a crank angle, a water temperature sensor for detecting an engine cooling water temperature, a common rail pressure, and the like. Various sensors such as a common rail pressure sensor 9 for detecting the above are connected.

The ECU 5 a is equipped with a “charge / discharge control function (piezo injector 2 control function)” for performing injection control of the piezo injector 2, an “SCV control function” for controlling the opening degree of the SCV 15, and the like.
The charge / discharge control function is a function for controlling the charge / discharge of the piezo stack 24 at a timing according to the current operating state, and includes a program installed in advance and signals (engine parameters) of various sensors read into the ECU 5a. Based on the above, the "injection form" such as single injection and multi-injection, "injection start time" for each injection, and "injection period (injection amount)" for each injection are calculated, and the calculated injection form and injection start time The charging and discharging of the piezo stack 24 are controlled based on the injection period (injection amount).
The SCV control function is a control program that calculates a target common rail pressure corresponding to the current operating state and calculates an SCV opening at which the actual common rail pressure detected by the common rail pressure sensor 9 becomes the target common rail pressure. "Valve signal (for example, PWM signal)" is output to SCV15.

[Features of Example 1]
Next, a problem peculiar to the common rail type fuel injection device adopting the piezo injector 2 and a solution to the problem will be described.
(Background of Example 1)
Air may enter the system due to lack of gas. When air is mixed into the piezo injector 2, it takes time from the start of cranking to the start (complete explosion) of the engine at the start of the engine, thereby impairing the comfort at the start.

This starting failure mechanism will be described with reference to FIGS.
As shown in FIG. 3A, when air (bubbles: indicated by circles in the figure) is mixed in the displacement expansion chamber 45 due to a lack of gas or the like, the piezo stack 24 extends to cause the large-diameter piston 44 to move. Even if it is displaced downward, air is compressed in the displacement expansion chamber 45 and the increase in hydraulic pressure in the displacement expansion chamber 45 is suppressed, so that the driving force of the piezo stack 24 is not properly transmitted to the small-diameter piston 43. The valve 38 cannot be properly separated from the low-pressure side valve seat 41. For this reason, the operation of switching the valve chamber 37 and the pressure control chamber 34 to a low pressure is hindered, and the needle 26 cannot be lifted.

The air mixed in the displacement expansion chamber 45 tends to stay in the displacement expansion chamber 45 for a long time even when fuel is supplied from the common rail 1 to the piezo injector 2 through the injector pipe 6 after the fuel tank 12 is filled with fuel. There is.
Here, even if air mixed in the displacement expansion chamber 45 remains, the fuel pressure in the low pressure fuel passage 39 increases due to the function of the back pressure check valve 11 during engine operation, and the fuel pressure in the displacement expansion chamber 45 increases. Thus, as shown in FIG. 3B, the volume of the mixed air is reduced, and the ratio of the air compression absorbing the driving force of the piezo stack 24 is reduced, thereby enabling injection.
That is, even if mixed air remains in the displacement expansion chamber 45, the fuel pressure in the low-pressure fuel passage 39 increases to a pressure P1 (for example, 100 kPa: reference, see FIG. 4) or more, so that the injection by the piezo injector 2 is performed. It becomes possible.

Fuel supply from the low pressure fuel passage 39 to the displacement expansion chamber 45 is performed by operation of a check valve 48 provided in the large diameter piston 44. In order to supply fuel from the low pressure fuel passage 39 to the displacement expansion chamber 45, the fuel in the low pressure fuel passage 39 needs to be pressurized to some extent.
The reason why the fuel in the low pressure fuel passage 39 is pressurized is that the fuel in the high pressure fuel passage 32 leaks to the low pressure side through the clearance between the switching valve 38 and the low pressure side valve seat 41. It takes a long time for the fuel in the low-pressure fuel passage 39 to be pressurized by (hereinafter referred to as a switching valve leak for the sake of explanation).

This will be described with reference to FIG.
Since the fuel pressure rise in the high-pressure fuel passage 32 due to the switching valve leak is moderate as shown by the solid line A, the pressure P1 is reached after the cranking start T0 at the time T1, and the injector operation (T1) starts from the cranking start T0. Requires a long time ΔT1, impairing the comfort at the start.

In particular, when the temperature is low, the viscosity of the fuel increases, so the switching valve leak tends to decrease, the time required for pressurization of the low-pressure fuel passage 39 becomes longer, and the time until the function of the piezo injector 2 is restored. It will be longer.
Assuming that a piezo injector 2 free from static leak (leak due to mechanical gaps) has been developed as a future technology, the low pressure fuel passage 39 cannot be expected to rise due to static leak. If air is mixed in, the malfunction of the piezo injector 2 due to air compression cannot be avoided.

(Solutions for problems)
In order to solve the above problems, the common rail fuel injection device is displaced via the check valve 48 by increasing the pressure in the low pressure fuel passage 39 of the piezo injector 2 at the time of engine start (including immediately before starting). Low pressure boosting means for increasing the pressure in the expansion chamber 45 is provided.
The low pressure boosting means of the first embodiment includes a priming means 4 that can obtain a fuel supply pressure of about 200 kPa, a back pressure check valve 11 that sets the internal pressure of the low pressure fuel passage 39 to about 200 kPa in the return pipe (low pressure pipe), The check valve 48 guides the fuel in the low-pressure fuel passage 39 to the displacement expansion chamber 45, and a fuel path switching means 51 described below.
The priming means 4, the back pressure check valve 11, and the check valve 48 are those conventionally mounted by a common rail fuel injection device. The main additional parts are the fuel path switching means 51 and the fuel path switching means 51. Only the boosted fuel transport pipe 52 that connects the switching means 51 and the reflux pipe 8 on the piezo injector side of the back pressure check valve 11 is provided.

  The fuel path switching means 51 (1) The supply destination of the fuel discharged from the priming means 4 is supplied from the supply pump 3 to the back pressure check valve 11 only when “pressure increase of the low pressure fuel passage 39 is performed by air mixing”. It may be a three-way switching valve that switches to the return pipe 8 (low pressure fuel passage 39 side) on the piezo injector side, or (2) boosted fuel transport only when “pressurization of the low pressure fuel passage 39 is performed by air mixing” The pipe 52 may be opened, and a part of the fuel discharged from the priming means 4 may be supplied from the back pressure check valve 11 to the return pipe 8 on the piezo injector side (low pressure fuel passage 39 side).

The fuel path switching means 51 may be an electric switching valve driven by an electric actuator (for example, an electromagnetic actuator) or a manual switching valve that is switched manually.
When the fuel path switching means 51 is constituted by an electric switching valve, (1) when the priming means 4 (mainly electric priming) is operated, the switching of the fuel path switching means 51 is controlled by the ECU 5a, and the discharge of the priming means 4 is performed. It may be provided so as to send fuel to the low pressure fuel passage 39, or (2) a manual changeover switch is provided on the operation panel near the driver's seat, and the fuel path switching means 51 is switched by the operation of the occupant changeover switch. It may be provided as follows. Further, when the fuel path switching means 51 is constituted by a manual switching valve, the operation contents are clearly described in the vicinity of the manual and the priming means 4 (mainly manual priming), and the operation of the fuel path switching means 51 is performed by a driver or the like. Switching is performed.

Here, the pressure of the low-pressure fuel passage 39 of the piezo injector 2 that is increased by the priming means 4 when the engine is started is the pressure at which the piezo injector 2 can perform an injection operation by the operation of the piezo stack 24, that is, the air in the displacement expansion chamber 45. It is desirable that the pressure can be substantially disappeared (air substantial disappearance pressure) P1 or more.
However, as shown in FIG. 4, it is assumed that the pressure of the low pressure fuel passage 39 of the piezo injector 2 that is raised by the priming means 4 when the engine is started does not reach P1, for example, pressure P2 (P2> P0: P0 is atmospheric pressure). However, the time when the pressure in the low pressure fuel passage 39 reaches P1 due to the switching valve leak is shortened from time T1 to time T2.
That is, by using the priming means 4 to increase the pressure of the low-pressure fuel passage 39 to P2, cranking starts even if the fuel pressure rise in the high-pressure fuel passage 32 due to the switching valve leak is gradual as shown by the solid line B. The pressure P1 from T0 is reached at time T2, and the injector operation (T2) time from cranking start T0 can be shortened to ΔT2.

(Effect of Example 1)
As described above, in the common rail fuel injection device according to the first embodiment, when air is mixed into the displacement expansion chamber 45 of the piezo injector 2 due to a lack of gas or the like, the priming means 4 is used to start the operation in the fuel tank 12 when starting the engine. The fuel is sent to the low pressure fuel passage 39 of the piezo injector 2 to increase the pressure in the low pressure fuel passage 39.
Thereby, the air mixed in the displacement expansion chamber 45 of the piezo injector 2 is compressed, and the volume ratio occupied by the air in the displacement expansion chamber 45 is reduced. Then, the piezo injector 2 can be operated by boosting the low pressure fuel passage 39 to the pressure P1 by the priming means 4.
Even when the pressure of the low pressure fuel passage 39 by the priming means 4 is a pressure P2 lower than P1, the time for the pressure of the low pressure fuel passage 39 to reach P1 due to the switching valve leak is shortened. Time to start (complete explosion) can be shortened compared to the conventional method.

A second embodiment will be described with reference to FIG. In the second embodiment, the same reference numerals as those in the first embodiment denote the same functional objects.
The low pressure boosting means of the first embodiment boosts the pressure of the low pressure fuel passage 39 by the priming means 4 when starting the engine after the gas runs out.
On the other hand, the low-pressure pressurizing means of the second embodiment starts the engine after the gas runs out due to the fuel discharged from the overflow portion 3a of the supply pump 3 (a part of the fuel discharged from the feed pump in the supply pump 3). In some cases, the pressure in the low pressure fuel passage 39 is increased.

Specifically, in the second embodiment, the fuel path switching means 51 and the boosted fuel transport pipe 52 shown in the first embodiment are provided on the downstream side (fuel tank 12 side) of the connection portion between the overflow pipe 16 and the reflux pipe 8. The pressure in the low pressure fuel passage 39 is increased by the fuel discharged from the overflow portion 3a when the engine is started after the gas runs out.
Note that the pressure in the low-pressure fuel passage 39, which is increased when the engine is started by the fuel discharged from the overflow portion 3a of the supply pump 3, is a pressure (air substantial disappearance pressure) P1 at which the air in the displacement expansion chamber 45 can be substantially eliminated. However, as in the first embodiment, the pressure P2 may be lower than the pressure P1.
Even if the second embodiment is adopted, the same effect as the first embodiment can be obtained.

[Modification]
In the above embodiment, the piezo injector 2 in which the switching valve 38 is displaced in the axial direction is illustrated, but a piezo injector in which the internal pressure of the pressure control chamber 34 is changed by the rotational displacement of the switching valve 38 may be used.
In the above-described embodiment, the switching valve type piezo injector 2 that drives the three-way switching valve 22 with the piezo stack 24 is illustrated. However, by changing the pressure in the hydraulic chamber (hydraulic converter) by the piezo stack 24, the needle 26 An intermediate piston type piezo injector that varies the pressure in the control chamber that lifts the intermediate piston that urges the piston in the seating direction and drives the needle 26 by the movement of the intermediate piston may be used.

1 is a schematic view of a common rail fuel injection device (Example 1). FIG. (Example 1) which is a schematic sectional drawing of a piezo injector. It is a schematic diagram for operation | movement description (Example 1). It is a time chart for operation | movement description (Example 1). (Example 2) which is the schematic of a common rail type fuel injection device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Common rail 2 Piezo injector 3 Supply pump 3a Overflow part 4 Priming means 12 Fuel tank 24 Piezo stack 45 Displacement expansion chamber (hydraulic chamber)
51 Fuel path switching means 52 Boosted fuel transport pipe

Claims (4)

In a common rail fuel injection device comprising a piezo injector equipped with a piezo stack that injects fuel by pressurizing a hydraulic chamber filled with low pressure fuel, and a supply pump that pumps high pressure fuel to the piezo injector to the common rail.
This common rail fuel injection device
Priming means for guiding the fuel in the fuel tank to the supply pump ;
A fuel path switching means provided in a fuel path from the priming means to the supply pump, and capable of supplying fuel discharged from the priming means to the low pressure side of the piezo injector when an internal combustion engine is started,
Using the fuel pressure discharged from the priming means, a common rail fuel injection apparatus characterized by increasing the pressure of the low pressure side of the piezo injector at the start of the internal combustion engine. In the common rail fuel injection device according to claim 1,
The common rail fuel injection device, wherein the pressure on the low pressure side of the piezo injector, which is increased when the internal combustion engine is started by the priming means, is a substantially air elimination pressure that enables an injection operation by the operation of the piezo stack. . In a common rail fuel injection device comprising a piezo injector equipped with a piezo stack that injects fuel by pressurizing a hydraulic chamber filled with low pressure fuel, and a supply pump that pumps high pressure fuel to the piezo injector to the common rail.
This common rail fuel injection device
Fuel path switching means provided in the fuel path from the overflow part of the supply pump to the fuel tank, and capable of supplying the fuel discharged from the overflow part of the supply pump to the low pressure side of the piezo injector when the internal combustion engine is started With
Using said fuel pressure discharged from the overflow portion of the supply pump, a common rail fuel injection apparatus characterized by increasing the pressure of the low pressure side of the piezo injector at the start of the internal combustion engine. In the common rail type fuel injection device according to claim 3,
The pressure on the low-pressure side of the piezo injector, which is increased when the internal combustion engine is started by the fuel pressure discharged from the overflow portion of the supply pump, is a substantial air elimination pressure that enables an injection operation by the operation of the piezo stack. A common rail type fuel injection device characterized by the above.

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