JP2009257215A - Fuel injection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain favorable restarting performance of an engine after fuel is supplied even when the fuel runs out with a relatively simple structure, in a fuel injection device using a piezo-injector 6. <P>SOLUTION: The fuel injection device includes the piezo-injector 6 that conducts fuel injection by adding pressure to a pressure chamber 43 mounted on the engine and filled with low-pressure fuel, an accumulating pipe 5 for retaining high-pressure fuel for supplying into the piezo-injector 6, a high-pressure pump 4 that pressure feeds high-pressure fuel into the accumulating pipe 5, and an accumulating tank 18 that keeps the pressure of a low-pressure fuel passage 27 connected with the pressure chamber 43. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel injection device mounted on an engine, and more particularly to a device including a piezo injector that performs a fuel injection operation by pressurizing a pressure chamber filled with low-pressure fuel.

  2. Description of the Related Art Conventionally, for example, in a diesel engine or an in-cylinder direct injection gasoline engine, an accumulator fuel injection device using an accumulator pipe (common rail) is used (see, for example, Patent Document 1).

  This pressure accumulation type fuel injection device is configured such that fuel is taken out from a fuel tank by a supply pump, is made high pressure and accumulated in a common rail, and the high pressure fuel in the common rail is injected from each injector into a combustion chamber of the engine. It has become.

  The fuel that has been pumped to the injector and not injected into the combustion chamber is returned to the fuel tank via the reflux pipe.

  As for this injector, a piezo injector has been used in recent years.

  The needle drive system of this piezo injector is provided between a large-diameter piston that displaces as the piezo stack expands and contracts, a small-diameter piston that is arranged coaxially with the large-diameter piston, and the small-diameter piston and the large-diameter piston facing each other. In addition, it has a displacement expansion chamber that is filled with fuel and that expands and retracts the displacement of the large diameter piston and transmits it to the small diameter piston. Then, by changing the internal pressure of the displacement expansion chamber with the piezo stack, the pressure applied to the needle is increased or decreased to switch between fuel injection and fuel injection stop.

  The displacement expansion chamber is connected to the return pipe via a slight clearance on the sliding surface between the large diameter piston and the cylinder of the injector body and a slight clearance on the sliding surface between the small diameter piston and the cylinder of the injector body. Yes. For this reason, when the displacement expansion chamber is compressed, fuel in the displacement expansion chamber may leak from the clearance, but when the displacement expansion chamber is expanded, the low-pressure fuel in the return pipe is sucked into the displacement expansion chamber. It is to be compensated.

  In such a configuration, when the engine is stopped due to, for example, the fuel tank being emptied and the engine is stopped, the supply pipe that leads the fuel from the fuel tank to the supply pump is emptied and the low-pressure fuel in the return pipe However, it gradually leaks from the valve seat clearance of the back pressure check valve and returns to the fuel tank. For this reason, bubbles enter the displacement expansion chamber of the injector.

  In such a situation, even if cranking to restart the engine after filling the fuel in the fuel tank, the air in the displacement expansion chamber cannot be immediately replaced with fuel, so the fuel injection by the piezo injector Operation cannot be performed normally. For this reason, there is a concern that the restartability of the engine may be deteriorated, for example, it takes time until the engine starts (complete explosion) after cranking.

  In other words, even if fuel is supplied to the fuel tank, power cannot be transmitted from the large-diameter piston to the small-diameter piston until the air in the displacement expansion chamber is replaced with fuel due to the presence of air in the displacement expansion chamber. As a result, fuel cannot be injected into the engine. In this way, if the fuel runs out, the engine cannot be restarted immediately even if fuel is replenished.

  For this reason, in the fuel injection device disclosed in Patent Document 1, in order to improve the restartability of the engine after running out of fuel, a priming means (electric pump or manual pump) is provided in the fuel tank. The fuel path switching means is provided to switch the discharge side of the means between the state where the discharge side is connected to the fuel supply pipe side and the state where the discharge side is connected to the return pipe side.

In this configuration, when the engine is started after the fuel is replenished due to fuel exhaustion, first the fuel from the fuel tank is sucked up by the priming means and supplied to the return pipe side. Fuel is supplied into the displacement expansion chamber of the piezo type fuel injection valve, and the needle of the injector can be raised and lowered. As a result, the engine can be started relatively early.
JP 2007-205330 A

  In the conventional example according to Patent Document 1, a feed pump is built in the supply pump. However, in addition to the feed pump, a priming means (an electric pump or a manual pump) is further provided. The cost has been forced up.

  In addition, for reference, although it is a configuration that does not use a piezo injector, for example, as shown in Japanese Patent Laid-Open No. 2-61361, when the engine stops due to running out of fuel, The engine can be restarted after running out of fuel by forcibly supplying the fuel to the fuel introduction system with an electromagnetic fuel pump to expel the air in the fuel introduction system from the air vent line to the fuel tank. Is considered.

  Since this reference does not use a piezo injector provided with a needle drive system with a displacement expansion chamber, it is impossible to eliminate the problems associated with fuel shortage in the conventional example according to Patent Document 1. In addition, since the above-mentioned reference is provided with an electromagnetic fuel pump and an air vent line in the fuel introduction system, the equipment cost is high, and when the storage voltage of a battery or the like is insufficient, the electromagnetic type Inconveniences such as inability to drive the fuel pump are pointed out.

  An object of the present invention is to improve the restartability of an engine after fuel replenishment even when a fuel shortage occurs in a fuel injection device using a piezo injector, even though the configuration is relatively simple.

  A fuel injection device according to the present invention includes a piezo injector that performs a fuel injection operation by pressurizing a pressure chamber that is mounted on an engine and is filled with low-pressure fuel, and a pressure accumulator that stores high-pressure fuel to be supplied to the piezo injector. And a high-pressure pump that pumps high-pressure fuel to the pressure-accumulation pipe, and a pressure-accumulation tank that holds the pressure of the low-pressure fuel passage that communicates with the pressure chamber.

  In this configuration, for example, even if the fuel to be supplied to the piezo injector is depleted and the engine is stopped, the pressure in the low pressure fuel passage and the pressure chamber is held by the pressure accumulating tank.

  Thus, for example, when the engine is restarted after replenishing the fuel after the fuel has run out, if the pressure chamber held by the pressure accumulating tank is pressurized, the fuel injection operation by the piezo injector will be immediately normal. You can do it. Therefore, the engine startability after running out of fuel is improved.

  In addition, since only the pressure accumulating tank is provided, it is advantageous in simplifying the configuration and reducing the cost as compared with the conventional example.

  Preferably, the fuel tank further includes a feed pump that supplies fuel in a fuel tank to the high-pressure pump, and the pressure accumulation tank is supplied with low-pressure fuel from the feed pump and is held at a predetermined pressure.

  This configuration is advantageous in simplifying the configuration and reducing the cost as compared with the case where a dedicated pump for supplying low-pressure fuel to the pressure accumulation tank is added. However, a configuration using this dedicated pump is also included in the present invention.

  Preferably, the piezo injector includes a needle that opens and closes a nozzle hole provided at a tip of the injector body, a piezo stack, a needle drive system that displaces the needle using an expansion and contraction operation of the piezo stack, and a high pressure in the nozzle hole. It can be set as the structure which has a high-pressure fuel channel which guides fuel. The needle drive system includes a large-diameter piston that is moved forward and backward by the piezo stack, a small-diameter piston that is arranged coaxially with the large-diameter piston, and the pressure chamber between the small-diameter piston and the large-diameter piston. A displacement expansion chamber that is provided and is supplied with low pressure fuel from the low pressure fuel passage and expands the displacement of the large diameter piston and transmits the displacement to the small diameter piston, and controls the pressure applied to the needle in accordance with the displacement of the small diameter piston. And an applied pressure control means for displacing the needle and a fuel replenishing means for replenishing the displacement expansion chamber with the low pressure fuel from the low pressure fuel passage when the displacement expansion chamber is expanded.

  Here, the configuration of the piezo injector is specifically specified, and this specification makes it possible to easily embody the embodiment of the present invention.

  Further, in this specified configuration, even if the fuel in the displacement expansion chamber leaks to the low pressure fuel passage due to the forward / backward displacement of the large diameter piston, the fuel compensation means passes from the low pressure fuel passage where the pressure is held in the pressure accumulation tank. This makes it possible to quickly fill the displacement expansion chamber with fuel, which is advantageous in keeping the internal pressure of the displacement expansion chamber stable.

  Preferably, the applied pressure control means switches the internal pressure of a pressure control chamber provided on the pressure application side of the needle between a high pressure state and a low pressure state, and controls the high pressure fuel passage, the low pressure fuel passage, and the pressure control. A valve chamber communicated with each of the chambers, and a flow path switching valve element that is connected to a lower end of the small-diameter piston and can be moved up and down in the valve chamber, and the flow path switching valve element is lowered. The pressure control chamber and the low-pressure fuel passage are in communication with each other via the valve chamber, and when the flow path switching valve body is raised, The high pressure fuel passage may be in a communication state.

  In this configuration, the configuration of the applied pressure control unit is specifically specified, and this specification makes it possible to easily embody the embodiment of the present invention. Since the low-pressure fuel passage communicates with the valve chamber of the applied pressure control means, it becomes possible to quickly supply high-pressure fuel and low-pressure fuel to the pressure control chamber when the engine is restarted after the fuel runs out. .

  Preferably, the fuel replenishing means is provided inside the large-diameter piston so as to communicate the displacement expansion chamber and the low-pressure fuel passage, and provided in the middle of the communication passage and from the displacement expansion chamber side. A check valve that prevents fuel from flowing out to the low-pressure fuel passage side while allowing only fuel flow from the low-pressure fuel passage side to the displacement expansion chamber side can be provided.

  In this configuration, the configuration of the fuel compensation means is specifically specified, and this specification makes it possible to easily embody the embodiment of the present invention. Since the communication path of the fuel compensation means communicates with the low pressure fuel path, the pressure of the communication path is also maintained by maintaining the pressure in the low pressure fuel path with the pressure accumulation tank. As a result, fuel can be quickly supplied to the displacement expansion chamber when the engine is restarted after running out of fuel.

  According to the present invention, the fuel injection device using a piezo injector has a relatively simple configuration, but it is possible to improve the restartability of the engine after refueling even if fuel shortage occurs.

  Hereinafter, the best embodiment of the present invention will be described in detail with reference to the drawings. 1 and 2 show an embodiment of the present invention.

  First, a schematic configuration of a fuel injection device according to the present invention will be described with reference to FIG. The fuel injection device shown in FIG. 1 mainly includes a fuel tank 1, a fuel filter 2, a feed pump 3, a supply pump 4, a common rail 5 as a pressure accumulation tube, a piezo injector 6, and the like.

  The number of piezo injectors 6 is the same as the number of engine cylinders, that is, for example, four in the case of a four-cylinder engine and six in the case of a six-cylinder engine.

  In short, this fuel injection device takes out the fuel in the fuel tank 1 by the feed pump 3, makes it high pressure by the supply pump 4 and accumulates it in the common rail 5, and if necessary, supplies the high pressure fuel in the common rail 5. Each piezo injector 6 is configured to inject into a combustion chamber or intake port of an engine (not shown). Reference numeral 7 denotes an upstream fuel supply passage from the fuel tank 1 to the common rail 5, and reference numeral 8 denotes a downstream fuel supply passage from the common rail 5 to each piezo injector 6.

  The fuel that was sent to the supply pump 4 but not pumped to the common rail 5 passes through the overflow passage 9, and the fuel that was sent to the common rail 5 but not sent to the piezo injector 6 passes through the return passage 10, Further, the surplus fuel that is not injected into the combustion chamber while being pumped to the piezo injector 6 is returned to the fuel tank 1 via the leak passage 11.

  The return passage 10 from the common rail 5 and the leak passage 11 from the piezo injector 6 are connected to a back pressure check valve 12. The back pressure check valve 12 is a means that opens at a predetermined pressure or higher and keeps the leaked fuel pressure of the piezo injector 6 at a predetermined pressure during engine operation.

  The feed pump 3 is a low-pressure pump that introduces fuel from the fuel tank 1 to the supply pump 4. The supply pump 4 is a high-pressure pump that compresses the low-pressure fuel introduced by the feed pump 3 to a high pressure and pumps it to the common rail 5. Although not shown, the feed pump 3 and the supply pump 4 are driven using engine power, for example.

  The supply pump 4 is equipped with an SCV (suction metering valve) for adjusting the opening degree of the flow path for guiding the fuel into the pressurizing chamber for pressurizing the fuel to a high pressure. By controlling this SCV by the control device 15, it is possible to adjust the discharge amount of fuel pumped to the common rail 5, and to control the common rail pressure to a pressure corresponding to the vehicle running state.

  The common rail 5 is a pressure accumulating pipe for accumulating high pressure fuel supplied to the piezo injector 6, and supplies the high pressure fuel via the upstream fuel supply passage 7 so that a common rail pressure corresponding to the fuel injection pressure is accumulated. A discharge port of the pump 4 is connected, and is connected to each piezo injector 6 via a downstream fuel supply passage 8.

  A pressure reducing valve 13 that also serves as a pressure limiter is attached to one end of the common rail 5. The pressure reducing valve 13 is opened by a valve opening instruction signal given from the control device 15 and rapidly reduces the common rail pressure via the return passage 10. In this way, by mounting the pressure reducing valve 13 on the common rail 5, the control device 15 can quickly control the common rail pressure to a pressure corresponding to the vehicle running state.

  Each operation in such a fuel injection device is controlled by the control device 15. The control device 15 includes an ECU 16 and an EDU 17. The EDU 17 may be built in the case of the ECU 16.

  Although not shown in detail, the ECU 16 is 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 And so on.

  The ECU 16 performs various arithmetic processes based on the read signals of various sensors (engine parameters: signals corresponding to the occupant operating state and the engine operating state).

  In addition, as various sensors, as sensors for detecting engine parameters, an accelerator sensor for detecting an accelerator opening, a rotational speed sensor for detecting an engine speed and a crank angle, a water temperature sensor for detecting an engine coolant temperature And common rail pressure sensor 14 for detecting the common rail pressure.

  The ECU 16 gives at least a timing signal for starting and stopping fuel injection by the piezo injector 6 to the EDU 17, and the EDU 17 applies a drive voltage to at least the piezo stack 23 of the piezo injector 6 based on the timing signal.

  Next, the configuration and operation of the piezo injector 6 illustrated in this embodiment will be described with reference to FIG.

  The piezo injector 6 mainly has a configuration in which a needle 22, a piezo stack 23, and a needle drive system 24 are provided in an injector body 21.

  In short, in the piezo injector 6, when the needle 22 is raised by the piezo stack 23 and the needle drive system 24, the injection hole 25 provided at the tip of the injector body 21 is opened to inject high-pressure fuel to the outside. When the needle 22 is lowered, the injection hole 25 is closed and the injection of high-pressure fuel is stopped.

  First, the injector body 21 is provided with a high-pressure fuel passage 26 for introducing fuel and a low-pressure fuel passage 27 for returning fuel.

  The high-pressure fuel passage 26 guides high-pressure fuel from the common rail 5 to the injection hole 25, and the low-pressure fuel passage 27 guides surplus fuel inside the piezo injector 6 to the leak passage 11.

  The needle 22 is accommodated in the needle cylinder 21a of the injector body 21 so as to be movable up and down. In the needle cylinder 21 a, the space above the needle 22 is a pressure control chamber 28, and the space below the needle 22 is a fuel reservoir 29.

  In the pressure control chamber 28, a coil spring 30 is housed in a compressed state that presses the needle 22 against the tip seat surface of the injector body 21 and urges the nozzle hole 25 to close. Further, a high pressure fuel passage 26 is communicated with the pressure control chamber 28 via an in-orifice 31.

  The in-orifice 31 eases the pressure drop in the pressure control chamber 28 at the start of fuel injection and gently opens the needle 22, while promoting the pressure increase in the pressure control chamber 28 at the end of injection. 22 has the effect of closing valve 22 quickly.

  When the pressure in the pressure control chamber 28 above the needle cylinder 21a is high, the needle 22 is lowered with the expansion restoring force of the coil spring 30 taken into consideration, so that the needle 22 is brought into pressure contact with the tip seat surface of the injector body 21 and the injection hole 25. However, when the pressure in the pressure control chamber 28 is low, it is raised against the urging force of the coil spring 30 so as to be brought into pressure contact with the upper end seating surface of the needle cylinder 21a to open the nozzle hole 25.

  The piezo stack 23 is a power source that generates power to drive the needle 22 up and down, and is disposed on the upper portion of the injector body 21 so as not to come into contact with fuel. As is well known, the piezo stack 23 has a structure in which a large number of piezoelectric bodies (or electrostrictive elements) that are elongated by charge injection and contract by charge discharge are stacked.

  The needle drive system 24 amplifies the expansion and contraction displacement of the piezo stack 23 and transmits it to the needle 22 to drive the needle 22 up and down. The needle drive system 24 mainly includes a displacement enlarging means 40, an applied pressure control means 50, and fuel compensation. And means 60.

  The displacement enlarging means 40 increases the expansion / contraction displacement amount (change amount in the stacking direction, that is, change amount in the vertical direction) of the piezo stack 23 and transmits it to the flow path switching valve body 52 of the applied pressure control means 50. The large-diameter piston 41, the small-diameter piston 42, and the displacement expansion chamber 43 are configured.

  The large-diameter piston 41 and the small-diameter piston 42 are accommodated in a large and small two-stage stepped cylinder 21b provided in the injector body 21 so as to be slidable on the same axis.

  The large-diameter piston 41 is directly driven by the piezo stack 23, and is pressed against the piezo stack 23 by an extension restoring force of a spring (for example, a disc spring) 44 disposed in a compressed state in the displacement expansion chamber 43. It is displaced in the vertical direction by the same amount as the expansion / contraction amount of the piezo stack 23.

  The small-diameter piston 42 is connected to the upper surface of the flow path switching valve body 52 of the applied pressure control means 50 and is displaced in the vertical direction integrally with the flow path switching valve body 52.

  The displacement expansion chamber 43 is a space provided between the large-diameter piston 41 and the small-diameter piston 42 facing each other. The displacement expansion chamber 43 corresponds to an example of a pressure chamber described in the claims.

  The displacement expansion chamber 43 converts the expansion and contraction displacement of the piezo stack 23 into a hydraulic pressure, expands it according to the outer diameter difference between the large diameter piston 41 and the small diameter piston 42, and transmits it to the small diameter piston 42. That is, the outer diameter of the small diameter piston 42 is set smaller than the outer diameter of the large diameter piston 41, and the axial displacement of the large diameter piston 41 is enlarged and transmitted to the small diameter piston 42.

  The small diameter portion of the stepped cylinder 21 b is connected to the leak passage 11 through a low pressure fuel passage 27.

  The applied pressure control means 50 controls to switch the internal pressure of the pressure control chamber 28 provided above the needle cylinder 21a between a high pressure state and a low pressure state, and mainly includes a valve chamber 51, a flow path switching valve body 52, and the like. It is comprised including.

  The valve chamber 51 is provided so as to communicate with the lower end of the stepped cylinder 21b, and communicates with the high pressure fuel passage 26, the low pressure fuel passage 27, and the pressure control chamber 28, respectively.

  The flow path switching valve body 52 is connected to the lower end of the small-diameter piston 42 and can be moved up and down in the valve chamber 51. When the flow path switching valve body 52 is lowered and pressed against the lower valve seat 53 of the valve chamber 51, the pressure control chamber 28 and the low pressure fuel passage 27 are brought into communication with each other through the valve chamber 51 and the communication passage 32. On the other hand, when the flow path switching valve body 52 is raised and brought into pressure contact with the upper valve seat 54 of the valve chamber 51, the pressure control chamber 28 and the high pressure fuel passage 26 are connected through the valve chamber 51, the communication passage 32, and the high pressure communication passage 33. Communicate.

  The fuel filling means 60 causes the fuel in the displacement expansion chamber 43 to leak from the sliding surfaces of the large diameter piston 41 and the small diameter piston 42 to the low pressure fuel passage 27 when the displacement expansion chamber 43 is compressed as the large diameter piston 41 descends. In consideration of this, the fuel in the low pressure fuel passage 27 and the leak passage 11 is sucked into the displacement expansion chamber 43 when the displacement expansion chamber 43 expands as the large-diameter piston 41 rises.

  Although not shown in the drawing, a sealing member is used so that even if fuel leaks from the sliding surfaces of the large-diameter piston 41 and the small-diameter piston 42, this fuel is guided to the low-pressure fuel passage 27 and does not enter the arrangement space of the piezoelectric stack 23. Is provided.

  The fuel replenishing means 60 mainly includes a communication passage 61 and a check valve 62.

  The communication passage 61 is provided inside the large-diameter piston 41 so as to connect the displacement expansion chamber 43 and the low-pressure fuel passage 27 of the injector body 21 in communication.

  The check valve 62 is provided in the middle of the communication passage 61, and prevents displacement of fuel from the displacement expansion chamber 43 side to the low pressure fuel passage 27 side, while increasing displacement from the leak passage 11 and the low pressure fuel passage 27 side. Only the fuel flow to the chamber 43 side is allowed.

  The check valve 62 has a configuration in which a ball valve body 64 is disposed in the valve chamber 63 of the communication passage 61, and is communicated from the valve chamber 63 to the displacement expansion chamber 43 through a plurality of through holes 65. .

  As for the operation of the check valve 62, when the pressure in the displacement expansion chamber 43 becomes lower than the pressure in the low pressure fuel passage 27 (low pressure fuel pressure set by the back pressure check valve 12), the check valve 62 opens. Since the valve, that is, the ball valve body 64 is slightly lowered and a gap is formed between the valve and the conical seat surface, the fuel in the leak passage 11 and the low pressure fuel passage 27 flows into the displacement expansion chamber 43 through the through hole 65. Thereby, even when the operation of the piezo injector 6 is stopped, the pressure in the displacement expansion chamber 43 is kept at the pressure in the low-pressure fuel passage 27.

  Next, the operation of the above-described piezo injector 6 will be described.

  First, a drive voltage is applied from the EDU 17 to the piezo stack 23 in response to a fuel injection start command from the ECU 16.

  The piezo stack 23 is expanded and displaced in proportion to the voltage, and the large-diameter piston 41 integrated therewith is displaced downward to compress the displacement expansion chamber 43.

  The small-diameter piston 42 is lowered by the increase in internal pressure accompanying the compression of the displacement expansion chamber 43, and the flow path switching valve body 52 is pushed down to be pressed against the lower valve seat 54 of the valve chamber 51. At this time, the lift amount of the flow path switching valve body 52 is increased according to the area ratio of the large diameter piston 41 and the small diameter piston 42 with respect to the displacement of the piezo stack 23.

  As a result, the pressure control chamber 28 communicates with the low pressure fuel passage 27 through the communication passage 32 and the valve chamber 51, so that the inside of the pressure control chamber 28 becomes low pressure, and the needle 22 is moved by the pressure of the high pressure fuel in the fuel reservoir 29. The force to be pushed up exceeds the force to push down the needle 22 by the internal pressure of the pressure control chamber 28 and the coil spring 30. As a result, the needle 22 is lifted to open the nozzle hole 25, and fuel injection is started.

  In order to stop the fuel injection, the application of the drive voltage from the EDU 17 to the piezo stack 23 may be stopped in response to the fuel injection stop command from the ECU 16 to release the electric charge. That is, while the electrification is released, the piezo stack 23 contracts by the amount of displacement at the time of voltage application and returns to the original length, and the large-diameter piston 41 is caused by the elastic urging force accompanying the expansion and restoration of the coil spring 30. And small diameter piston 42 goes up.

  When the flow path switching valve body 52 is brought into pressure contact with the upper valve seat 54 with this rise, high pressure fuel is introduced from the high pressure fuel passage 26 into the pressure control chamber 28 via the valve chamber 51 and the flow passage 32, and high pressure fuel. The high-pressure fuel in the passage 26 flows into the pressure control chamber 28 through the in-orifice 31.

  In this way, the internal pressure of the pressure control chamber 28 is recovered, and the needle 22 is pushed down by the internal pressure of the pressure control chamber 28 and the coil spring 30 rather than the force to push up the needle 22 by the pressure of the high-pressure fuel in the fuel reservoir 29. The power of As a result, the needle 22 lifts down, closes the nozzle hole 25, and stops fuel injection.

  As the operation repeats, the fuel in the displacement expansion chamber 43 decreases due to a slight leak, but the check valve 62 sucks and supplements the fuel in the low pressure fuel passage 27 into the displacement expansion chamber 43. It has become.

  By the way, in the fuel injection device having the above-described configuration, as described in the section of the conventional example, when the fuel in the fuel tank 1 is empty during engine operation, that is, when the engine stops due to running out of fuel, the back pressure is reduced. Since the low-pressure fuel in the low-pressure fuel passage 27 and the leak passage 11 leaks from the valve seat clearance of the check valve 12 to the fuel tank 1 side, bubbles are mixed into the displacement expansion chamber 43 in the piezo injector 6. The engine cannot be restarted immediately after refueling.

  This is because if air bubbles are mixed in the displacement expansion chamber 43, even if the large-diameter piston 41 is displaced downward by extending the piezo stack 23, the air is compressed and displaced in the displacement expansion chamber 43. Since the increase in the hydraulic pressure in the expansion chamber 43 is suppressed, the driving force of the piezo stack 23 is not properly transmitted to the small-diameter piston 42, and the flow path switching valve body 52 cannot be lowered. That is, since it becomes impossible to perform the operation of switching the valve chamber 51 and the pressure control chamber 28 to a low pressure, the needle 22 cannot be lifted.

  Therefore, in this embodiment, even when the fuel shortage as described above occurs, in order to improve the restartability of the engine after the fuel is filled in the fuel tank 1, the pressure accumulation tank 18 is provided. This will be described in detail below.

  As shown in FIG. 1, the pressure accumulating tank 18 holds the pressure of the leak passage 11, the low pressure fuel passage 27 of the piezo injector 6, and the displacement expansion chamber 43 even when the operation of the piezo injector 6 is stopped.

  The accumulator tank 18 is supplied with low-pressure fuel discharged from the feed pump 3, and maintains the pressure of the low-pressure fuel stored in the accumulator tank 18 for a certain period of time after the engine is stopped. It is configured.

  The pressure accumulating tank 18 is connected in the middle of a leak passage 11 that communicates the low pressure fuel passage 27 of the piezo injector 6 and the back pressure check valve 12, whereby the leak passage 11 and the low pressure fuel passage 27 of the piezo injector 6 are connected. By filling the low pressure fuel to the inside, the passages 11 and 27 are kept at a predetermined pressure.

  The internal pressure of the pressure accumulating tank 18 is set to be smaller than the valve opening pressure of the back pressure check valve 12 for maintaining the pressure of the leak passage 11 and the low pressure fuel passage 27 during engine operation. As a result, the back pressure check valve 12 is prevented from opening due to the pressure of the pressure accumulating tank 18.

  According to such a configuration, even when the fuel in the fuel tank 1 is empty during engine operation, that is, even if the engine is stopped due to running out of fuel, the pressure accumulation tank 18 causes the leak passage 11 and the low-pressure fuel passage 27 to pass through a predetermined pressure. Can be kept in. Thereby, it becomes possible to prevent bubbles from being mixed into the displacement expansion chamber 43 of the piezo injector 6 as in the conventional example.

  Therefore, if the fuel is filled in the fuel tank 1 and the engine is cranked, the expansion / contraction operation of the piezo stack 23 of the piezo injector 6 is normally transmitted to the flow path switching valve body 52 to control the pressure in the pressure control chamber 28. Since it becomes possible to carry out promptly, the needle 22 can be normally displaced. As a result, the fuel injection operation by the piezo injector 6 can be normally performed immediately after cranking the engine, so that the engine can be started (complete explosion). Thus, the restartability of the engine after running out of fuel can be improved.

  Moreover, as described above, in this embodiment, only the pressure accumulating tank 18 is provided, which is advantageous in terms of simplification of configuration and cost reduction compared to the conventional example.

  In addition, this invention is not limited only to the said embodiment, All the deformation | transformation and application included in the range equivalent to the claim and the said range are possible. Examples are given below.

  (1) In the above embodiment, the low pressure fuel is supplied from the existing feed pump 3 to the pressure accumulating tank 18, but a dedicated pump may be used instead of the feed pump 3.

  (2) The detailed configuration of the piezo injector 6 shown in the above embodiment is not particularly limited. For example, the applied pressure control means 50 of the piezo injector 6 is not limited to the three-way switching valve, and the pressure control chamber 28 is made to communicate with either the high-pressure fuel passage 26 or the low-pressure fuel passage 27 by combining two-way valves. It can be configured to switch states.

It is a lineblock diagram showing typically one embodiment of a fuel injection device concerning the present invention. It is sectional drawing which expands and shows the piezo injector in FIG.

Explanation of symbols

1 Fuel tank
3 Feed pump
4 Supply pump
5 Common rail
6 Piezo injector 11 Leak passage from the piezo injector 18 Accumulation tank 21 Injector body 22 Needle 23 Piezo stack 24 Needle drive system 25 Injection hole 26 High pressure fuel passage 27 Low pressure fuel passage 28 Pressure control chamber 40 Displacement expansion means 41 Large diameter piston 42 Small diameter Piston 43 Displacement expansion chamber 50 Applied pressure control means 51 Valve chamber 52 Flow path switching valve body 60 Fuel compensation means 61 Communication path 62 Check valve

Claims (5)

  A piezo injector that performs a fuel injection operation by pressurizing a pressure chamber that is mounted on the engine and is filled with low pressure fuel, a pressure accumulator that stores high pressure fuel to be supplied to the piezo injector, and a high pressure fuel that is stored in the pressure accumulator A fuel injection device comprising: a high-pressure pump that pumps pressure; and a pressure accumulation tank that holds a pressure of a low-pressure fuel passage communicated with the pressure chamber. The fuel injection device according to claim 1,
The fuel injection device further comprising a feed pump for supplying fuel in a fuel tank to the high pressure pump, wherein the pressure accumulation tank is supplied with low pressure fuel from the feed pump and is maintained at a predetermined pressure. The fuel injection device according to claim 1 or 2,
The piezo injector includes a needle that opens and closes a nozzle hole provided at the tip of the injector body, a piezo stack, a needle drive system that displaces the needle using the expansion and contraction of the piezo stack, and guides high-pressure fuel to the nozzle hole. A high-pressure fuel passage,
The needle drive system is provided as the pressure chamber between a large-diameter piston moved forward and backward by the piezo stack, a small-diameter piston arranged coaxially with the large-diameter piston, and the small-diameter piston and the large-diameter piston facing each other. And a low-pressure fuel is supplied from the low-pressure fuel passage and the displacement of the large-diameter piston is expanded and transmitted to the small-diameter piston, and the pressure applied to the needle is controlled in accordance with the displacement of the small-diameter piston. Fuel having an applied pressure control means for displacing the needle, and fuel filling means for filling low pressure fuel from the low pressure fuel passage into the displacement expansion chamber when the displacement expansion chamber is expanded. Injection device. The fuel injection device according to claim 3, wherein
The applied pressure control means controls the internal pressure of a pressure control chamber provided on the pressure application side of the needle to be switched between a high pressure state and a low pressure state, and includes a high pressure fuel passage, a low pressure fuel passage, and a pressure control chamber. Each having a valve chamber communicated with, and a flow path switching valve body connected to the lower end of the small-diameter piston and capable of moving up and down in the valve chamber,
When the flow path switching valve body is lowered, the pressure control chamber and the low pressure fuel passage are communicated with each other through the valve chamber, while the flow path switching valve body is lifted. The fuel injection device, wherein the pressure control chamber and the high-pressure fuel passage are in communication with each other through the valve chamber. The fuel injection device according to claim 3 or 4,
The fuel replenishing means includes a communication passage provided inside the large-diameter piston so as to communicate the displacement expansion chamber and the low pressure fuel passage, and a low pressure fuel passage provided in the middle of the communication passage and from the displacement expansion chamber side. A fuel injection device comprising: a check valve that prevents fuel from flowing out to the side, and allows only fuel flow from the low-pressure fuel passage side to the displacement expansion chamber side.

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