JP4552834B2 - Fuel injection device - Google Patents

Description

  The present invention relates to a fuel injection device that injects a predetermined amount of fuel at a high pressure.

  Conventionally, there has been a fuel injection device in which fuel pressurized to a feed pressure by a low pressure feed pump is boosted by a high pressure pump and supplied to a delivery pipe, and high pressure fuel supplied from the delivery pipe is injected from a fuel injection valve To do. For example, this type of fuel injection device is disclosed in Patent Document 1 below.

  The fuel injection device disclosed in Patent Document 1 includes a relief valve (safety valve) that is opened when the delivery pipe reaches a predetermined fuel pressure or higher in order to avoid an abnormal increase in fuel pressure of the delivery pipe. Have deployed. In this fuel injection device, the fuel discharged when the relief valve is opened is returned to the suction port of the high-pressure pump and the fuel tank via a return pipe. Further, in the fuel injection device disclosed in Patent Document 1, a fuel leakage mechanism (notch) that connects the discharge port of the high-pressure pump and the delivery pipe to the check valve on the discharge side of the high-pressure pump even when the valve is closed. ) Is provided.

  In the fuel injection device disclosed in Patent Document 1, a high-pressure pump is used to reduce the fuel pressure of the delivery pipe to a predetermined fuel pressure so that the fuel injection amount does not cause a large torque shock when returning from the fuel cut. A leak passage is provided for communicating the discharge side and the suction side.

  Further, in Patent Document 2 below, in a fuel injection device that supplies high-pressure fuel from a high-pressure pump to a delivery pipe, a discharge check valve and a suction check valve respectively provided in a discharge-side passage and a suction-side passage of the high-pressure pump. And a pressure regulator that functions as a safety valve is disclosed. In the fuel injection device disclosed in Patent Document 2, when a fuel pressure higher than a predetermined pressure is applied to the pressure regulator from the discharge side passage of the high pressure pump, the fuel is discharged to check the intake in the suction side passage. It flows into the upstream of the valve through the return passage.

Japanese Patent Laid-Open No. 2003-184697 International Publication No. 01/007779 Pamphlet

  However, in the above-described conventional fuel injection device, a return pipe (return passage) must be provided separately in order to provide a safety valve, thereby increasing the cost associated with an increase in the number of parts and increasing the size of the device. As a result, the inconvenience of deterioration in mountability in the engine compartment occurs.

  Further, in the fuel injection device disclosed in Patent Document 1, since the safety valve is provided downstream (delivery pipe) from the discharge port of the high-pressure pump, the fuel pressure in the delivery pipe is reduced due to opening / closing hysteresis when the safety valve is activated. There is a risk that it will drop significantly below the set valve opening pressure of the safety valve. As a result, it takes time to raise the fuel pressure in the delivery pipe to the desired fuel pressure immediately after the safety valve is closed, so that the controllability of the fuel pressure by the high-pressure pump is deteriorated.

  Accordingly, the present invention provides a fuel injection device that improves the disadvantages of the conventional example and can suppress an abnormal increase in fuel pressure in the delivery pipe without sacrificing cost and mountability in the engine compartment. The second object is to provide a fuel injection device that is excellent in controllability of the fuel pressure by the high-pressure pump after the abnormal increase in fuel pressure is suppressed.

In order to achieve the above object, according to the first aspect of the present invention, there is provided a high pressure pump comprising a suction chamber into which fuel supplied from a low pressure feed pump flows and a plunger chamber for pumping fuel from the suction chamber by reciprocating movement of the plunger. And a delivery pipe to which fuel discharged from the high-pressure pump is supplied, and a fuel injection valve to which fuel is supplied from the delivery pipe. preparative passage of the fuel which communicates provided only one as a fuel supply passage for communicating the interior of the plunger chamber and the delivery pipe, the interior of the high-pressure pump, plunger when the fuel pressure in the delivery pipe exceeds a predetermined pressure Fuel pressure lowering means for lowering the fuel pressure of the delivery pipe by lowering the fuel pressure in the chamber is provided.

  According to the fuel injection device of the first aspect, since the fuel pressure lowering means that is conventionally provided on the downstream side of the discharge port of the high pressure pump is provided in the high pressure pump, the return as in the conventional fuel injection device is possible. Piping is no longer required, the overall physique of the device can be reduced to improve the mountability in the engine compartment, and the cost can be reduced.

  In order to achieve the above object, according to a second aspect of the present invention, in the fuel injection device according to the first aspect, the fuel pressure reducing means includes a communication passage for communicating the suction chamber and the plunger chamber, and the plunger chamber. And a relief valve that opens when the pressure becomes equal to or higher than the predetermined pressure, and causes the fuel in the plunger chamber to flow out to the suction chamber via the communication path.

  According to the fuel injection device of the second aspect, in addition to the same effect as that of the first aspect of the invention, fuel is supplied from the plunger chamber to the delivery pipe before the relief valve is delayed. Therefore, it is possible to suppress a drop in the fuel pressure of the delivery pipe during the operation of the relief valve, and it is possible to improve the controllability of the fuel pressure by the high-pressure pump immediately after the relief valve is closed.

  In order to achieve the above object, according to a third aspect of the present invention, in the fuel injection device according to the first aspect, the fuel pressure reducing means can move the plunger relative to the plunger main body on the plunger chamber side and the plunger main body. A plunger main body holding portion that is held by the plunger main body, and when the plunger chamber reaches or exceeds the predetermined pressure between the plunger main body and the plunger main body holding portion, An elastic member that relatively moves the plunger main body holding portion is arranged.

  According to the fuel injection device of the third aspect, in addition to the same effect as the first aspect of the invention, even if the return of the plunger main body (movement of the plunger chamber in the direction of reducing the volume) is delayed, Since the fuel is supplied from the plunger chamber to the delivery pipe, it is possible to suppress a drop in the fuel pressure of the delivery pipe when the plunger safety valve function is activated, and the fuel pressure is controlled by the high pressure pump immediately after the plunger main body returns. Can be improved.

  In order to achieve the above object, according to a fourth aspect of the present invention, in the fuel injection device according to the first aspect, the fuel pressure reducing means is configured by increasing the waste volume of the plunger chamber.

  The fuel injection device according to claim 4 can suppress an abnormal increase in fuel pressure in the plunger chamber or in the delivery pipe by increasing the waste volume of the plunger chamber. Therefore, according to this fuel injection device, in addition to the same effect as that of the first aspect of the invention, it is possible to suppress the drop in fuel pressure of the delivery pipe by optimizing the capacity of the waste volume. The controllability of the fuel pressure by the high-pressure pump can be improved.

  In the fuel injection device according to the present invention, the fuel pressure reducing means is provided in the high-pressure pump, so that no external parts such as a return pipe are required. For this reason, according to this fuel injection device, the fuel pressure lowering means suppresses an abnormal increase in fuel pressure in the delivery pipe, while reducing the overall size of the suppression device and improving the mountability in the engine compartment. In addition, the cost can be reduced. Further, by configuring the fuel pressure reducing means as in claims 2 to 4, the controllability of the fuel pressure by the high pressure pump can be improved even after the abnormal increase in fuel pressure is suppressed.

  Embodiments of a fuel injection device according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the embodiments.

  A fuel injection device according to a first embodiment of the present invention will be described with reference to FIG.

  First, the configuration of the fuel injection device according to the first embodiment will be described.

  As shown in FIG. 1, the fuel injection device of the first embodiment includes a fuel injection valve 10 that directly injects fuel into a combustion chamber of an internal combustion engine (not shown), and a delivery pipe 20 that supplies high-pressure fuel to the fuel injection valve 10. It has. Here, an example of a fuel injection device that supplies fuel to an internal combustion engine having four combustion chambers will be described. Therefore, this fuel injection device includes four fuel injection valves 10. The delivery pipe 20 is provided with a pressure sensor 21 for detecting the internal fuel pressure, and an electronic control unit (ECU) (not shown) monitors the fuel pressure in the delivery pipe 20 based on the detection signal. Yes.

  Further, in the fuel injection device of the first embodiment, the low pressure feed pump 40 that sucks the fuel in the fuel tank 30 and pressurizes it to the feed pressure, and pressurizes the fuel discharged from the low pressure feed pump 40 to deliver the delivery pipe. There is provided a high-pressure pump 50 that maintains the fuel pressure in 20 at a desired high-pressure state.

  The low-pressure feed pump 40 is an electric pump driven by a battery, for example, and is disposed in the fuel tank 30, and the discharge side thereof is connected to the suction port 50 a of the high-pressure pump 50 via the low-pressure passage 61. The fuel tank 30 is provided with a return passage 62 communicating with the low pressure passage 61 and a pressure regulating valve 41 provided on the return passage 62. When the low pressure passage 61 reaches a predetermined pressure, Then, the pressure regulating valve 41 is opened, and the fuel in the low pressure passage 61 is returned to the fuel tank 30.

  On the other hand, the discharge port 50 b of the high pressure pump 50 is connected to the delivery pipe 20 via the high pressure passage 63. The high-pressure pump 50 is configured as follows.

  First, in the high-pressure pump 50, a suction chamber Ri and a plunger chamber Rp are formed in a housing 51. The suction chamber Ri is a chamber for storing fuel sent from the low-pressure feed pump 40 through the suction port 50a. The plunger chamber Rp is a chamber to which fuel stored in the suction chamber Ri is supplied at a predetermined timing, and the high-pressure pump 50 supplies fuel from the plunger chamber Rp to the delivery pipe 20.

  Here, the suction chamber Ri and the plunger chamber Rp communicate with each other via a first communication passage 51a formed in the housing 51. The high-pressure pump 50 is connected to the plunger from the suction chamber Ri on the first communication passage 51a. A fuel metering valve 52 for adjusting the flow rate of the fuel to the chamber Rp is provided.

  The fuel metering valve 52 illustrated here includes a valve body 52a that opens and closes the first communication passage 51a, an elastic member 52b such as a coiled spring that biases the valve body 52a in the valve opening direction, and the valve body 52a. This is a so-called solenoid valve provided with an electromagnet 52c that urges the elastic member 52b against the pressing force of the elastic member 52b in the valve closing direction. The electromagnet 52c is controlled to be energized or de-energized by an electronic control device, and switched between an excited state and a non-excited state.

  In the fuel metering valve 52, the electromagnet 52c is energized when fuel injection is not required when the engine is stopped or the fuel is cut, and the electromagnetic force at that time overcomes the pressing force of the elastic member 52b. The body 52a blocks the first communication path 51a. On the other hand, in the suction stroke in which the low pressure feed pump 40 is driven, the electromagnet 52c is brought into a non-excited state, and the fuel metering valve 52 is opened by the pressing force of the elastic member 52b. Therefore, the fuel in the suction chamber Ri is sent to the plunger chamber Rp when the fuel metering valve 52 is opened.

  Further, the high-pressure pump 50 is provided with a fuel pumping means 53 that pumps the fuel supplied to the plunger chamber Rp to the delivery pipe 20. The fuel pumping means 53 includes a plunger 53a that slides in the plunger chamber Rp in the axial direction, and an elastic member such as a string-wound spring that biases the plunger 53a so as to expand a space in which fuel is supplied in the plunger chamber Rp. 53b and a cam 53c that urges the plunger 53a against the pressing force of the elastic member 53b to reduce the space.

  Here, the cam 53c is configured to rotate in conjunction with a crankshaft (not shown) of the internal combustion engine, and the plunger 53a is reciprocated according to the cam shape to deliver fuel in the plunger chamber Rp to the delivery pipe. 20 is pumped. That is, the high-pressure pump 50 of the first embodiment is a mechanically driven pump that is driven as the crankshaft rotates.

  Further, the high-pressure pump 50 is provided with a check valve 54 on a discharge passage 64 that guides fuel in the plunger chamber Rp to the high-pressure passage 63. The check valve 54 is for preventing fuel from flowing backward from the delivery pipe 20 side to the plunger chamber Rp side due to pressure pulsation generated during driving, and a valve body 54a for opening and closing the discharge passage 64; An elastic member 54b such as a string-wound spring for biasing the valve body 54a in the valve closing direction is provided. Here, the elastic member 54b of the check valve 54 is set so that the valve element 54a opens when a slight pressure difference is generated between the plunger chamber Rp side and the high pressure passage 63 side.

  Furthermore, fuel pressure lowering means for preventing the fuel pressure in the delivery pipe 20 from exceeding a predetermined upper limit pressure is provided inside the high pressure pump 50. In the first embodiment, a relief valve 55 is provided as the fuel pressure lowering means.

  Here, the abnormal increase in the fuel pressure in the delivery pipe 20 can occur during the pressure feeding of the fuel from the high-pressure pump 50 to the delivery pipe 20, and in this case, the check valve 54 described above is activated. Since the valve is open, the plunger chamber Rp of the high-pressure pump 50 is at a pressure equivalent to the fuel pressure in the delivery pipe 20. Therefore, if the fuel pressure in the plunger chamber Rp can be lowered, the fuel pressure in the delivery pipe 20 can be lowered accordingly.

  Therefore, in the first embodiment, when such an abnormal increase in fuel pressure occurs, in order to reduce the fuel pressure in the plunger chamber Rp, on the upstream side of the check valve 54 (on the plunger chamber Rp side). A relief valve 55 is arranged. Specifically, the relief valve 55 according to the first embodiment is provided on the second communication path 51b by providing the housing 51 with a second communication path 51b that allows the suction chamber Ri and the plunger chamber Rp to communicate with each other. That is, the fuel pressure lowering means of the first embodiment is constituted by the relief valve 55 and the second communication passage 51b.

  The relief valve 55 includes a valve body 55a that opens and closes the second communication passage 51b, and an elastic member 55b such as a coiled spring that biases the valve body 55a in the valve closing direction. In the relief valve 55, the spring constant of the elastic member 55b is set so that the valve body 55a is operated in the valve opening direction when the fuel pressure in the plunger chamber Rp or the delivery pipe 20 reaches the set upper limit pressure. Has been.

  Here, since the fuel is also supplied to the suction chamber Ri, the fuel pressure (feed pressure) in the direction opposite to the fuel pressure in the plunger chamber Rp is applied from the suction chamber Ri to the valve body 55a. Therefore, the elastic member 55b is set so that the total force of the pressing force and the fuel pressure in the suction chamber Ri is lower than the set upper limit pressure by the fuel in the plunger chamber Rp. Thereby, in the high pressure pump 50, when the fuel pressure in the plunger chamber Rp reaches the set upper limit pressure, the fuel pressure overcomes the total force of the pressing force of the elastic member 55b and the fuel pressure in the suction chamber Ri. The body 55a is actuated in the valve opening direction, and the fuel in the plunger chamber Rp is sent to the suction chamber Ri.

  Therefore, when the fuel pressure in the plunger chamber Rp or the delivery pipe 20 is abnormally increased by the relief valve 55, the fuel pressure in the plunger chamber Rp can be lowered. The overpressure of the fuel is prevented, and damage to the high-pressure pump 50 and the delivery pipe 20 due to an abnormal increase in fuel pressure can be avoided.

  Further, the fuel in the suction chamber Ri that flows in along with the opening of the relief valve 55 may be stored in the suction chamber Ri depending on the fuel pressure in the suction chamber Ri at that time, or the suction port 50a. May be sent to the low-pressure passage 61 via. In the latter case, the pressure regulating valve 41 is opened by the fuel pressure in the low pressure passage 61, so that the fuel in the low pressure passage 61 is returned to the fuel tank 30.

  Thus, by providing the relief valve 55 upstream of the check valve 54 and between the suction chamber Ri and the plunger chamber Rp, the fuel sent when the relief valve 55 is opened is returned to the fuel tank 30. There is no need to provide a separate return pipe. Thereby, the number of parts can be reduced and the structure can be simplified as compared with the conventional fuel injection device in which such a return pipe is provided outside the high-pressure pump 50 and the delivery pipe 20. . Therefore, according to the fuel injection device of the first embodiment, the physique can be reduced and the cost can be reduced.

  Further, by arranging the relief valve 55 as in the first embodiment, even if the relief valve 55 is delayed due to hysteresis at the time of opening, the check valve 54 is opened before the relief valve 55 is closed, and the plunger is opened. Fuel is pumped from the chamber Rp to the delivery pipe 20. For this reason, according to the fuel injection device of the first embodiment, the required pressure in the delivery pipe 20 required for fuel injection can be maintained without significantly reducing the fuel pressure in the delivery pipe 20. Deterioration of fuel pressure controllability (a drop in fuel pressure) during operation of the relief valve 55 in the pipe 20 can be suppressed.

  By the way, when the relief valve 55 is provided upstream of the check valve 54 in the high-pressure pump 50 and between the suction chamber Ri and the plunger chamber Rp as in the first embodiment, the interior of the delivery pipe 20 is the check valve. Since it is sealed between 54 and the fuel injection valve 10, the following inconvenience may occur.

  For example, when the engine is stopped during the warm-up process, the temperature of the internal combustion engine is higher than that of the delivery pipe 20, and the delivery pipe 20 is heated by the atmospheric heat of the internal combustion engine. In general, since the thermal expansion coefficient of the liquid is larger than the thermal expansion coefficient of the solid, even if the volume is increased with the thermal expansion of the delivery pipe 20, the fuel is further thermally expanded and the delivery pipe 20 is further expanded. Will increase the internal pressure. For example, if the delivery pipe 20 and the fuel inside the delivery pipe 20 rise by 1 ° C. due to the atmospheric heat of the internal combustion engine, the internal pressure of the delivery pipe 20 causes a pressure rise of about 0.5 MPa. Therefore, when the engine is stopped during the warm-up process, the delivery pipe 20 may be ruptured due to the increase in the internal pressure.

  Therefore, in the first embodiment, a minute gap is provided between the delivery pipe 20 and the plunger chamber Rp to avoid an increase in internal pressure of the delivery pipe 20 in the above case.

Specifically, in the first embodiment, the delivery pipe 20 and the plunger chamber Rp are in communication with the valve body 54a of the check valve 54 disposed between the delivery pipe 20 and the plunger chamber Rp. A passage 54a ₁ is formed.

As a result, even if the minute passage 54a ₁ functions to reduce the internal pressure of the delivery pipe 20, and even if the internal pressure of the delivery pipe 20 can rise abnormally, the fuel in the delivery pipe 20 causes the minute passage 54a _{1 to} flow. Since it flows into the plunger chamber Rp via the, the delivery pipe 20 can be prevented from being damaged.

Further, since the internal pressure of the delivery pipe 20 by the pressure reducing function of the small passage 54a ₁ it can be stabilized, it is possible to maintain the fuel flow accuracy in re-injection through the fuel cut during deceleration.

Further, the pressure reducing function of the minute passage 54a ₁ reduces the internal pressure of the delivery pipe 20 to the feed pressure when the engine is stopped, and can keep the feed pressure, so that oil tight leakage can be reduced.

On the other hand, such a when a small passage 54a ₁ is provided on the valve body 54a of the check valve 54, the delivery pipe from the small passage 54a ₁ in magnitude whether the passage area determined by its passage diameters small passage 54a ₁ in the normal driving There is a possibility that the fuel leaks to 20 and the check valve 54 does not operate properly, leading to a decrease in pump efficiency of the high-pressure pump 50. For this reason, in order to avoid such an inconvenience, the passage area of the minute passage 54a ₁ is set to an appropriate size that can suppress a decrease in pump efficiency, for example, by performing a simulation or a test using an actual machine.

Here, the fuel that has flowed into the plunger chamber Rp through the micro passage 54a ₁ is sent to the suction chamber Ri side because the fuel metering valve 52 is open when the engine is stopped. Is done. Therefore, the pressure of the fuel flow path from the low pressure passage 61 to the delivery pipe 20 after the engine is stopped is held at the set pressure of the pressure regulating valve 41 on the low pressure feed pump 40 side.

  Note that the minute gap between the delivery pipe 20 and the plunger chamber Rp may be, for example, the notch disclosed in Patent Document 1 described above.

As described above, according to the fuel injection device of the first embodiment, the safety valve (relief valve 55) that has been conventionally provided on the downstream side of the discharge port of the high-pressure pump is moved into the high-pressure pump 50. This eliminates the need for a return pipe such as the fuel injection apparatus, and makes it possible to reduce the overall size of the apparatus and reduce the cost. And the mountability to an engine compartment improves by having made the physique of the whole apparatus small. In the fuel injection device according to the first embodiment, the check valve 54 opens before the relief valve 55 is delayed (that is, fuel is supplied from the plunger chamber Rp to the delivery pipe 20). Therefore, a drop in the fuel pressure of the delivery pipe 20 during the operation of the relief valve 55 can be suppressed, and the controllability of the fuel pressure by the high-pressure pump 50 immediately after the relief valve 55 is closed is improved. Further, in the fuel injection system of the first embodiment, it is possible to avoid an abnormal rise in the internal pressure of the delivery pipe 20 by pressure reducing function of the small passage 54a _1.

  Next, a second embodiment of the fuel injection device according to the present invention will be described with reference to FIGS.

  In the fuel injection device of the second embodiment, the relief valve 55 is removed from the fuel injection device of the first embodiment, while a fuel pressure lowering means that performs the same safety valve function is provided on the plunger of the fuel pressure feeding means. Specifically, a high-pressure pump 150 is prepared in which the plunger itself of the fuel pressure feeding means is configured as a fuel pressure lowering means so that the plunger has the same function as the relief valve. The high-pressure pump 150 is obtained by changing the fuel pumping means as follows with respect to the high-pressure pump 50 of the first embodiment.

  Reference numeral 153 in FIG. 2 indicates the fuel pressure feeding means of the second embodiment. As shown in FIG. 2, the fuel pumping unit 153 includes an elastic member 53b and a cam 53c similar to those of the fuel pumping unit 53 of the first embodiment, and a plunger 153a configured as follows.

As shown in FIG. 3, the plunger 153a has a split structure including a plunger main body 153a ₁ on the plunger chamber Rp side and a plunger main body holding portion 153a _{2 for} holding the plunger main body 153a ₁ from the elastic member 53b side. Yes. In the second embodiment, the plunger main body 153a ₁ is formed into a cylindrical body whose one end (plunger chamber Rp side) is closed, and the plunger main body holding portion 153a ₂ is formed into a stepped shape, and the plunger main body holding portion The plunger main body 153a ₁ is inserted into the narrow portion of 153a ₂ from the opening at the other end.

The plunger main body 153a ₁ and the plunger main body holding portion 153a ₂ are held together by a pin 153a ₃ inserted in a direction orthogonal to the axis. Here, the narrow portion of the plunger main body holding portion 153a ₂ is formed with a long hole 153a ₂₁ shown in FIG. 4 into which the pin 153a ₃ is inserted. Therefore, the plunger main body 153a ₁ and the plunger main body holding portion 153a are formed. ₂ are integrated so as to be relatively movable in the axial direction (the same direction as the reciprocating sliding direction of the plunger 153a).

Further, in the plunger 153a, coiled elastic members 153a ₄ such as a spring is disposed between the distal end of the inner wall surface and the narrow portion of the plunger main body holding portion 153a ₂ in the axial direction of the plunger main body 153a _1. When the fuel pressure in the plunger chamber Rp becomes equal to or higher than a predetermined pressure (the same upper limit pressure of the fuel pressure in the plunger chamber Rp or the delivery pipe 20 as in the first embodiment), the elastic member 153a ₄ In order to increase the volume of the plunger chamber Rp, the plunger main body 153a ₁ and the plunger main body holding portion 153a ₂ are set to move relative to each other. For this reason, in a normal fuel pressure state, the plunger main body 153a ₁ is held at the position farthest from the plunger main body holding portion 153a ₂ by the elastic force of the elastic member 153a ₄ .

Therefore, when the fuel pressure in the plunger chamber Rp is lower than a predetermined pressure, the plunger 153a is cammed without causing the plunger main body 153a ₁ and the plunger main body holding portion 153a ₂ to move relative to each other in the axial direction as shown in FIG. Reciprocally slides with the rotation of 53c.

On the other hand, the plunger main body holding portion 153a ₂ is always restricted from moving downward by the cam 53c. Therefore, when the fuel pressure in the plunger chamber Rp becomes equal to or higher than a predetermined pressure, the plunger main body 153a ₁ resists the pressing force of the elastic member 153a ₄ by the fuel pressure as shown in FIG. 153a _{2 is} pushed down. As a result, when the fuel pressure in the plunger chamber Rp or the delivery pipe 20 abnormally increases, the fuel pressure in the plunger chamber Rp or the like can be reduced, so that excess fuel from the high-pressure pump 50 to the delivery pipe 20 can be reduced. Pumping is prevented, and damage to the high-pressure pump 50 and the delivery pipe 20 due to an abnormal increase in fuel pressure can be avoided.

The plunger main body 153a ₁ is pushed back by the elastic force of the elastic member 153a _{4 when} the fuel pressure in the plunger chamber Rp later becomes lower than a predetermined pressure.

As described above, according to the fuel injection device of the second embodiment, since the safety valve function is provided in the high-pressure pump 50 as in the first embodiment, a return pipe like the conventional fuel injection device is provided. This eliminates the need to reduce the overall physique of the device, improve the mounting property in the engine compartment, and further reduce the cost. Moreover, since the fuel injection device of the second embodiment can construct a safety valve function with the simple structure as described above, further cost reduction can be achieved. Further, even in the fuel injection device of the second embodiment, the check valve 54 opens before the return of the plunger main body 153a ₁ is delayed. Therefore, the fuel of the delivery pipe 20 when the safety valve function of the plunger 153a is activated. The pressure drop can be suppressed, and the controllability of the fuel pressure by the high-pressure pump 50 immediately after the return of the plunger main body 153a ₁ is improved. Furthermore, in the fuel injection system of the second embodiment, it is possible to avoid an abnormal increase in the internal pressure in the delivery pipe 20 by pressure reducing function of the small passage 54a _1.

  Next, a third embodiment of the fuel injection device according to the present invention will be described with reference to FIGS.

  In the fuel injection device of the third embodiment, the relief valve 55 is removed from the fuel injection device of the first embodiment. On the other hand, fuel pressure reducing means that performs the same safety valve function is provided in the high-pressure pump as in the first embodiment. Is. Specifically, a high-pressure pump 250 is prepared in which the waste volume Vd of the plunger chamber Rp is enlarged to have the same function as the relief valve. The high-pressure pump 250 is obtained by changing the fuel pumping means as follows with respect to the high-pressure pump 50 of the first embodiment.

  Reference numeral 253 in FIG. 7 indicates the fuel pressure feeding means of the third embodiment. As shown in FIG. 7, the fuel pumping means 253 of the third embodiment includes an elastic member 53b and a cam 53c similar to the fuel pumping means 53 of the first embodiment, and a plunger 253a formed as follows. Yes.

  The plunger 253a is obtained by reducing the longitudinal direction of the plunger 53a of the first embodiment in order to increase the useless volume Vd of the plunger chamber Rp. As shown in FIG. 8, the waste volume Vd is a volume of a space formed between the tip of the plunger 253a and the inner wall surface of the plunger chamber Rp when the plunger 253a reaches the lift top dead center. Say. As described above, by increasing the capacity of the waste volume Vd as in the third embodiment, it is possible to suppress an abnormal increase in fuel pressure in the plunger chamber Rp or the delivery pipe 20.

  Here, the waste volume Vd affects the fuel pressure increase amount ΔPf (MPa) when the plunger 253a is raised, and the relationship of the following formula 1 is established. In this equation 1, “Kf” represents the bulk modulus (MPa) of the fuel, “Vl” represents the lift volume of the plunger 253a, and “Vt” represents the total volume of the plunger chamber Rp. The lift volume Vl is a volume of a space formed between the lift top dead center and the lift bottom dead center of the plunger 253a in the plunger chamber Rp, and the total volume Vt of the plunger chamber Rp is the lift of the plunger 253a. The volume of the space formed between the tip of the plunger 253a and the inner wall surface of the plunger chamber Rp when located at the bottom dead center.

  ΔPf = Kf × Vl / Vt = Kf × Vl / (Vl + Vd) (1)

  According to Equation 1, it can be seen that the pressure increase amount ΔPf of the fuel decreases as the waste volume Vd increases. For example, FIG. 9 shows the relationship with the fuel pressure increase amount ΔPf when the waste volume Vd is changed. Here, a waste volume (hereinafter referred to as “basic waste volume”) Vt1 formed by the plunger 53a of the first embodiment, and waste volumes Vt2 and Vt5 obtained by doubling, 5 times, and 7 times this basic waste volume Vt1. , Vt7 is compared.

  Therefore, if the waste volume Vd is increased more than necessary, the fuel pressure increase ΔPf in the plunger chamber Rp is significantly reduced and the pump efficiency is lowered, so that the fuel pressure required in the delivery pipe 20 is ensured. Can not do.

  Therefore, the capacity of the waste volume Vd is set to an optimum value for each fuel injection device so that the boost amount ΔPf is sufficient to ensure the fuel pressure of the delivery pipe 20 required as the performance of the fuel injection device.

As described above, according to the fuel injection device of the third embodiment, since the safety valve function is provided in the high-pressure pump 50 as in the first embodiment, a return pipe like the conventional fuel injection device is provided. It becomes unnecessary, and the physique of the whole apparatus can be reduced and the mountability to the engine compartment can be improved, thereby reducing the cost. Further, the fuel injection device according to the third embodiment can construct a safety valve function with a simple structure that does not increase the number of parts as in the first and second embodiments, so that the cost can be further reduced. be able to. Furthermore, in the fuel injection device according to the third embodiment, the fuel pressure drop of the delivery pipe 20 can be suppressed by optimizing the capacity of the waste volume Vd. Will improve. Furthermore, in the fuel injection device of the third embodiment, it is possible to avoid an abnormal increase in the internal pressure in the delivery pipe 20 by pressure reducing function of the small passage 54a _1.

  As described above, the fuel injection device according to the present invention is a technology that can obtain the effect of suppressing the abnormal increase in fuel pressure in the delivery pipe at a low cost and without sacrificing the mountability in the engine compartment. Useful.

It is a figure which shows the structure of Example 1 of the fuel-injection apparatus which concerns on this invention. It is a figure which shows the structure of Example 2 of the fuel-injection apparatus which concerns on this invention. It is a figure which shows the specific structure of the plunger of Example 2. FIG. It is the figure which looked at the plunger shown in FIG. 3 from the side surface. It is a figure which shows operation | movement of the plunger at the normal time in Example 2. FIG. It is a figure which shows operation | movement of the plunger at the time of the abnormal raise of the fuel pressure in Example 2. FIG. It is a figure which shows the structure of Example 3 of the fuel-injection apparatus which concerns on this invention. It is a figure explaining the relationship between the total volume of plunger chamber Rp, a waste volume, and a lift volume. It is the figure which contrasted the relationship between the capacity | capacitance of a useless volume, and the pressure | voltage rise amount of a fuel according to the magnitude | size of a useless volume.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel injection valve 20 Delivery pipe 40 Low pressure feed pump 50 High pressure pump 50a Suction port 50b Discharge port 51 Housing 51a 1st communication path 51b 2nd communication path 53 Fuel pressure feeding means 53a Plunger 53b Elastic member 53c Cam 54 Check valve 54a Valve body 54a ₁ Minute passage 54b Elastic member 55 Relief valve 55a Valve body 55b Elastic member 61 Low pressure passage 63 High pressure passage 64 Discharge passage 150 High pressure pump 153 Fuel pumping means 153a Plunger 153a ₁ Plunger main body 153a ₂ Plunger main body holding portion 153a ₂₁ Long hole 153a ₃ Pin 153a ₄ Elastic member 250 High pressure pump 253 Fuel pumping means 253a Plunger Ri Suction chamber Rp Plunger chamber Vd Waste volume

Claims (4)

A high-pressure pump including a suction chamber into which fuel supplied from a low-pressure feed pump flows in and a plunger chamber that pumps fuel from the suction chamber by reciprocating movement of the plunger, and a delivery to which fuel discharged from the high-pressure pump is supplied In a fuel injection device comprising a pipe and a fuel injection valve to which fuel is supplied from the delivery pipe,
Only one fuel passage that communicates the inside of the high-pressure pump and the inside of the delivery pipe is provided as a fuel supply passage that communicates the plunger chamber and the inside of the delivery pipe, and the delivery passage is provided inside the high-pressure pump. A fuel injection device comprising fuel pressure lowering means for lowering the fuel pressure in the delivery pipe by lowering the fuel pressure in the plunger chamber when the fuel pressure in the pipe exceeds a predetermined pressure.   The fuel pressure lowering means opens the communication passage for communicating the suction chamber and the plunger chamber, and opens the valve when the plunger chamber becomes the predetermined pressure or higher, and transfers the fuel in the plunger chamber to the suction chamber. The fuel injection device according to claim 1, further comprising a relief valve that flows out through the communication passage.   The fuel pressure reducing means has a structure in which the plunger is divided into a plunger main body on the plunger chamber side and a plunger main body holding portion that holds the plunger main body so as to be relatively movable, and between the plunger main body and the plunger main body holding portion. An elastic member is disposed to relatively move the plunger main body and the plunger main body holding portion so as to increase the volume of the plunger chamber when the plunger chamber becomes equal to or higher than the predetermined pressure. 1. The fuel injection device according to 1.   2. The fuel injection device according to claim 1, wherein the fuel pressure lowering means is configured by increasing a waste volume of the plunger chamber.

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