Fuel injection pump having reduced reflux pulsation effects

Abstract: To provide a fuel injection pump which can sufficiently and stably supply fuel to a fuel pressurization chamber during a fuel intake stroke, a plunger chamber (23), a spill port (29) and a spill passage (33) are mutually communicable, while a reflux passage (34), an intake gallery (15), an intake passage (31), an intake port (27) and the plunger chamber (23) are mutually communicable. A reflux passage (34) communicates with a damping chamber (35) through a communication passage (35a). The spill passage (33) and the reflux passage (34) communicate with each other, and when a spill valve (40) opens, high-pressure fuel within the plunger chamber (23) spills from the spill valve (40) and into the intake gallery (15) through the reflux passage (34), causing pulsation having a pressure level difference to the spill fuel. When the pulsation wave passes through the damping chamber (35), as the level difference in the pulsation wave is reduced, a sufficient quantity of fuel can stably be supplied from the intake gallery (15) to the plunger chamber (23).

Description: The present invention generally relates to a fuel injection pump according to the preamble of claim 1. Some prior art fuel injection systems include a fuel injection pump which uses a solenoid control valve as a spill valve and which controls fuel injection timing by spilling high-pressure fuel from a fuel pressurization chamber by opening and closing the spill valve, in which the spill fuel is refluxed to an intake gallery when fuel injection terminates and thereby the fuel supply rate to a plunger chamber for the next fuel intake stroke is secured to prevent a shortage in fuel supply to the plunger chamber. However, using this method of refluxing spill fuel to the intake gallery, a level difference in the fuel pressure within the intake gallery is created due to pulsation caused by the high-pressure spill fuel as illustrated by graph line 301 in FIG.13. If the intake gallery pressure is high, the inner wall composing the intake gallery may be damaged; if the intake gallery pressure is low, a sufficient quantity of fuel can not be fed out into the plunger chamber. For these reasons, it is possible that fuel can not be supplied to the plunger chamber in a stable manner. Furthermore, even if the rotational pump speed rises, that is, even if the rotational engine speed rises, the level difference in the intake gallery pressure should preferably be within an allowable range as illustrated by graph line 302 in FIG. 14. However, since the level difference in the intake gallery pressure due to pulsation increases as the rotational engine speed increases as illustrated by the graph line 303 in FIG. 14, fuel injection characteristics falls particularly drastically at the high rotational engine speed range. In order to solve the above problems, it is conceivable that a check valve is provided in a reflux passage through which fuel is refluxed from the spill valve to the fuel gallery and fuel flow is possible only in the direction from the intake gallery to the spill valve. In this arrangement, even if the pulsation is transmitted to the fuel within the intake gallery, when the fuel pressure is high, the check valve opens and the fuel flows to the spill valve, and when the fuel pressure is low, the check valve closes and the reflux of the fuel from the spill valve can be prevented, so that the fuel pressure within the intake gallery can be smoothed. However, the conventional fuel injection pump provided with a check valve as described above cannot sufficiently flux the spill fuel to the intake gallery due to the check valve, and as a result, when the fuel is taken into the plunger chamber, the pressure within the intake gallery instantaneously falls and the fuel can not stably be supplied to the plunger chamber. A generic fuel injection pump is known from the EP-A-0 303 237. An intake gallery receives pressurized fuel from the pump via a fuel pipe connected thereto. A fuel pressurizing part press feeds fuel taken in from an intake passage located downstream of the intake gallery via an intake port and includes a rotatably displaceable distributing rotor within a plunger chamber and a plunger for pressurizing and depressurizing fuel within the plunger chamber by rotating integrally with the distributing rotor while reciprocating. A spill valve is provided for opening to spill fuel from the fuel pressurizing part through a spill passage after termination of the fuel injection through an injection nozzle. When the spill valve is open, the fuel is refluxed through a reflux passage to the intake gallery. The reflux passage can be regarded as having a pulsation reducing function for reducing pulsation of refluxed fuel. The distribution rotor includes a distribution port which communicates with the distribution passage leading to the injection nozzle when fuel is pressurized, wherein the intake port communicates with the intake passage when fuel is depressurized. Furthermore, the distributing rotor includes a spill port communicating with the spill passage when the fuel injection is terminated. The reflux passage and the fuel pipe partly overlap. A further fuel injection pump having a spill valve and a fuel pressurizing part is known from the DE-A-3 928 612. According to this reference, a ring channel as well as a channel leading from an intake gallery to the ring channel act as both an intake passage and a reflux passage of the spill valve. It is an object of the present invention to further develop a fuel injection pump according to the preamble of claim 1, such that a sufficient and stable fuel supply to a fuel pressurization chamber during a fuel intake stroke can be achieved. This object is achieved by the features of claim 1. Advantageous further developments are set out in the dependent claims. The pulsation reducing device may be a pulsation reduction chamber communicating with the reflux passage through a communication passage. Moreover, the pulsation reducing device may be a pulsation reduction passage, where the cross-sectional area of the pulsation reduction passage is larger than that of upstream and downstream portions of the reflux passage proximate to the pulsation reduction passage. The length of the pulsation reduction passage, the upstream side of the reflux passage proximate to the pulsation reduction passage, and the downstream side of the reflux passage proximate to the pulsation reduction passage may preferably be formed at a preset ratio. Also, the pulsation reducing device may include a check valve which closes in the direction opposite to a flow of fuel from the fuel pressurization chamber to the spill valve, and it may additionally or alternatively include an orifice. Furthermore, the pulsation reducing device may include a pulsation reducing valve composed of a check valve and an orifice which can pass fuel therethrough from the fuel pressurization chamber to the spill valve even if the check valve closes. The check valve may be provided on the upstream side or downstream side of the reflux passage proximate to the pulsation reduction passage. Additionally, the orifice may be disposed in similar locations. The object as well as advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which: FIG. 1 is a compositional view illustrating a fuel injection pump according to a first embodiment of the present invention; FIG. 2 is representative diagram illustrating a pulsation reducing device according to the first embodiment of the present invention; FIG. 3 is a graph illustrating the characteristics of the fuel intake stroke and fuel press feed stroke according to the first embodiment of the present invention; FIG. 4 is a characteristic diagram illustrating the relationship between the intake gallery pressure and time in a fuel injection pump according to the first embodiment, a first prior art system and a second prior art system; FIG. 5 is a graph illustrating the relationship between the rotational pump speed and intake gallery pulsation pressure according to the first embodiment of the present invention; FIG. 6 is a representative view illustrating a pulsation reducing device for a fuel injection pump according to a second embodiment of the present invention; FIG. 7 is a descriptive view illustrating the pulsation reducing process of the pulsation reducing device according to the second embodiment of the present invention; FIG. 8 is a descriptive view illustrating the pulsation reducing process of a pulsation reducing device according to a third embodiment of the present invention; FIG. 9 is a descriptive view illustrating the pulsation reducing process of a pulsation reducing device according to a fourth embodiment of the present invention; FIG. 10 is a descriptive view illustrating the pulsation reducing process of a pulsation reducing device according to a fifth embodiment of the present invention; FIG. 11 is a descriptive view illustrating the pulsation reducing process of a pulsation reducing device according to a sixth embodiment of the present invention; FIG. 12 is a descriptive view illustrating the pulsation reducing process of a pulsation reducing device according to a seventh embodiment of the present invention; FIG. 13 is a characteristic diagram illustrating the relation between the intake gallery pressure and time in a conventional fuel injection pump; and FIG. 14 is a graph illustrating the relationship between the intake gallery pressure and time in a conventional fuel injection pump. The preferred embodiments according to the present invention will now be described referring to the appended drawings. A fuel injection pump according to a first embodiment of the present invention is illustrated in FIG. 1. In this Figure, a vane-type feed pump 11 of an injection pump 10 rotates in synchronization with a drive shaft 12 driven by an engine (not shown) and pressurizes fuel taken in from a fuel tank 61. The pressurized fuel is accumulated within a feed gallery 13 and supplied to an intake gallery 15 through a fuel pipe 14. A regulating valve 16 regulates the fuel feed pressure of the vane-type feed pump 11 so that the fuel feed pressure can rise in proportion to the rotational speed of the vane-type feed pump 11. The intake gallery 15 is annularly formed around a distributing rotor 21. The distributing rotor 21 is connected to the drive shaft 12 in the axial direction and rotates integrally with this drive shaft 12. The distributing rotor 21 includes a pair of sliding holes 21a intersecting at right angles. The inner walls of the distributing rotor 21 forming the pair of sliding holes 21a oiltightly and slidably support a pair of plungers 22 respectively. The inner walls of the distributing rotor 21 forming the inner end surfaces of the pair of plungers 22 and sliding holes 21a respectively also sectionally form a plunger changer 23. A shoe 24 is disposed at the outside end part of each plunger 22, and each shoe 24 rotatably holds a roller 25. A cam surface with a plurality of cam peaks on the inner periphery thereof is formed on an inner cam ring (not shown) disposed on the outside of the roller. Accordingly, when the roller 25 slides on the cam surface provided on the inner periphery of the inner cam ring according to the rotation of the distributing rotor 21, the roller 25 reciprocates along the cam surface in the radial direction of the inner cam ring, and this reciprocation is transmitted to the above plunger 22 through the shoe 24. A stroke of this plunger 22 to move to the outside in the radial direction of the distributing rotor 21 is a fuel intake stroke, and a stroke of the plunger 22 to move to the inside in the radial direction of the distributing rotor 21 is a fuel press feed stroke. During the fuel press feed stroke driven by the reciprocation of the plunger 22, surplus fuel is returned to the fuel tank 61 through a fuel return pipe 62 by a cam overflow valve 26. The distributing rotor 21 includes an intake port 27 communicating with the plunger chamber 23, a distribution port 28 and a spill port 29 which can communicate with an intake passage 31, a distribution passage 32 and a spill passage 33 respectively according to the rotation of the distributing rotor 21. In the case of a 6-cylinder engine, for example, the intake port 27 communicates with the intake passage 31 for a period occurring every 60° of the rotation of rotor 21. The spill valve 40 is disposed in the far end of the spill passage 33. The spill valve 40 selectively establishes a communication passage between the spill passage 33 and a reflux passage 34 and closes the same passage during the fuel press feed stroke, and controls the fuel injection rate by controlling the delivery timing and spill timing of the pressurized fuel. When an excitation coil 41 is energized and excitation current is supplied thereto, a valve plunger 42 against the return force of a compression coil spring 43 and thereby the spill valve 40 is closed. When the power to excitation coil 41 is terminated, the valve plunger 42 lifts and communication between the spill passage 33 and the reflux passage 34 is established so that the fuel within the plunger chamber 23 refluxes to the intake gallery 15. A damper chamber 35 functioning as a pulsation reducing device for the spill fuel communicates with the reflux passage 34 through a communication passage 35a. The reflux passage 34 is partially connected to an overflow valve 45. A delivery valve 50 is connected to the distribution passage 32. When the fuel pressurized within the plunger chamber 23 exceeds a preset pressure level, the delivery valve 50 opens to feed the high-pressure fuel to an injection nozzle 52 through an injection pipe 51. Next, the operation of the injection pump 10 will be described based on FIGS. 1 and 3. The communication of the intake port 27 with the intake passage 31 is set to the period when the plunger 22 moves from the top dead center to the bottom dead center. During this period, the fuel is taken in from the intake gallery 15 to the plunger chamber 23. When exciting current is supplied to the exciting coil 41 when the plunger 22 reaches the bottom dead center and then moves to the top dead center, the valve 42 lowers against the return force of the compression coil spring 43 and the spill valve 40 is closed. Concurrently, the distribution port 28 communicates with the distribution passage 32. When the fuel pressure within the plunger chamber 23 exceeds a preset pressure level, the delivery valve 50 opens, and the fuel is press fed from the injection pipe 51 to the injection nozzle 52 and injected therefrom into a combustion chamber of each engine cylinder (not shown). When the fuel injection rate reaches a preset value, the electric energization of the spill valve 40 is terminated and the spill valve 40 opens. When the spill valve 40 opens, the spill passage 33 and the reflux passage 34 communicate with each other, and the high-pressure fuel flows from the reflux passage 34 into the intake gallery 15. The operation of the damper chamber 35 in the event of fuel spill will now be described. As illustrated in FIG. 2, pulsation pressure is caused immediately in front of the damper chamber 35 due to the fuel spilled into the reflux passage 34, and the pulsation pressure moves toward to the intake gallery 15. When a high-pressure wave of the pulsation pressure reaches the damper chamber 35, the energy of the high-pressure wave is absorbed into the damper chamber 35, and as a result, the pressure within the damper chamber 35 rises and the pressure of the spill fuel within the reflux passage 34 falls. Next, when a low-pressure wave of the pulsation pressure reaches the damper chamber 35, the energy of the high-pressure wave absorbed into the damper chamber 35 is transferred to the low-pressure wave, and thereby the pressure of the spill fuel within the reflux passage 34 rises. As a result, the pulsation pressure of the spill fuel refluxing from the reflux passage 34 to the intake gallery 15 is smoothed and becomes lower than the upper pressure limit of the intake gallery 15 and higher than the minimum pressure required for fuel supply to the plunger chamber 23. Therefore, a sufficient quantity of fuel can be supplied to the plunger chamber 23 stably. Here, the relations between the elapsed time t and the intake gallery pressure P G according to the first embodiment, first and second prior art systems are illustrated in FIG. 4. The first prior art system is a typical system in which the spill fuel is directly refluxed to the intake gallery 15, and the second prior art system in a typical system in which the spill fuel is not directly refluxed to the intake gallery 15 (see, e.g., Japanese Unexamined Patent Publication No. Hei. 2-169858). According to the first embodiment of the present invention, as illustrated by graph line 101, a slight pulsation is created after the fuel spill. Then, the fuel is supplied from the intake gallery 15 into the plunger chamber 23 during the fuel intake period and the intake gallery pressure P G gradually falls. However, since the intake gallery pressure P G is regulated within the proper range a between the minimum required pressure for reliable fuel supply to the plunger chamber 23 and the maximum permissible pressure for operation of the intake gallery 15, a sufficient quantity of fuel can be supplied into the plunger chamber 23 stably. According to the first prior art system, the pulsation of the spill fuel directly induces the pulsation of the pressure of the intake gallery 15. Therefore, as illustrated by the graph line 102, the pressure of the intake gallery 15 is outside the proper range a on both sides of the minimum required pressure and the maximum permissible pressure due to the pulsation after the fuel spill. Consequently, a sufficient quantity of the fuel cannot be supplied to the intake gallery 15 and the intake gallery pressure P G may fall below the minimum required pressure during the fuel intake period. As a result, the quantity of fuel to be supplied to the plunger chamber 23 is not sufficient, and stable fuel injection can not be maintained. According to the second prior art system represented by graph line 103, since the spill fuel is not directly refluxed to the intake gallery 15, the pressure within the intake gallery 15 does not rise even after the fuel spill and is much lower than the minimum required value during the fuel intake period. For this reason, the quantity of the fuel supply to the plunger chamber 23 is far below the minimally sufficient level, and stable fuel injection can not be maintained. The effect of this embodiment will now be verified using the transmission loss TL of the damper chamber 35. The transmission loss TL of the damper chamber 35 can be obtained from Equations 1A-1C: f 0 = C 2π C 0 V C 0 = S d +0.8 S 0 where C is the velocity of sound, f 0 is the resonance frequency of the damper chamber 35, f is the pulsation frequency, S is the cross-sectional area of the reflux passage, S 0 is the cross-sectional area of the communication passage, d is the length of the communication passage, and V is the volume of damper chamber. When the difference between the pulsation frequency f and the resonance frequency f 0 is reduced, the transmission loss TL increases, and the level difference in the pulsation pressure can be reduced. The effect of reducing the level difference in the pulsation pressure of the damper chamber 35 according to the first embodiment can be confirmed by noting that the reduction in sound energy could be accomplished as a means to counter the noise. The transmission loss TL of sound can be obtained from Equation 2: where I is the energy of transmitted sound in watts per square meter and I 0 is the energy of injected sound in watts per square meter. The transmission loss TL indicates the difference between the transmission sound energy I and the injection sound energy I 0 expressed in decibels. Furthermore, since there is a relationship between the transmission sound energy I and the injection sound energy I 0 is expressed by the following Equation 3, Equation 2 can be replaced by Equation 4. I = P 2 ρ C where ρ is the medium density, C is the velocity of sound, P is the transmission sound pressure in microbars, and P 0 is the injection sound pressure in microbars. Here, since the transmission sound pressure P is equivalent to the pulsation pressure ΔP G of the intake gallery 15 and the injection sound pressure P 0 is equivalent to the spill pulsation pressure ΔP SPV due to the spill fuel, the equation 4 can be expressed by the following equation 5, where the pulsation pressure ΔP G indicates waves in the pulsation pressure within the intake gallery 15, and the spill pulsation pressure ΔP SPV indicates the level difference in the spill pulsation pressure within the spill valve 40. Δ P G = Δ P SPV 10 TL 20 Here, the rotational pump speed N p and intake gallery pulsation pressure ΔP G according to the first embodiment indicate the characteristics illustrated in FIG. 5. The measurement results illustrated in FIG. 5 were obtained by adjusting the pressure pulsation frequency at the maximum rotational pump speed of 2500 rpm and the resonance frequency of the damper chamber 35 to be equal and fixing the spill pulsation pressure ΔP SPV before measurement. The intake gallery pulsation pressure ΔP G within the low rotational pump speed range does not fall. In actuality, however, since the absolute value of the spill pulsation pressure ΔP SPV is smaller than the measurement condition value within the low rotational pump speed range and the intake gallery pulsation pressure ΔP G also falls, there is no problem. From these measurement results, as the level difference in the pulsation pressure of the spill pulsation waves is reduced by the pulsation reducing effect of the damper chamber 35, the spill fuel pressure to be refluxed to the intake gallery 15 is smoothed, and the fuel can stably be supplied to the plunger chamber 23. A pulsation reducing device according to the second embodiment of the present invention is illustrated in FIG. 6. In this embodiment, a damping valve 70 as a pulsation reducing valve is provided on the upstream side of the spill fuel between the damper chamber 35 and the spill valve 40. The damping valve 70 permits fuel flow in the direction of arrow A as viewed in FIG. 6 with no interruption, while fuel flow in the direction of arrow B as viewed in FIG. 6 is possible only through the orifice, since the damping valve 70 is closed. For this structure, the damping valve 70 can prevent further fluctuations in the pulsation pressure of the spill fuel due to the reflected wave in the direction of arrow B as viewed in FIG. 6 caused by the reflection of the fuel on the intake gallery 15 after passing through the damping valve 70. When passing through the damping valve 70, the spill fuel in a reflux position 34a within the reflux passage 34 having the pulsation pressure illustrated by graph line 104 in FIG. 7 can improve the pulsation damping characteristics as illustrated by graph line 105 in FIG. 7. In this way, in a point 34c at which point the pulsation pressure waves having high damping characteristics have passed through the damping chamber 35, as illustrated by graph line 106 in FIG. 7, the pulsation pressure is smoothed in the same way as is in the first embodiment, and fuel having a more stable pressure than that of the first embodiment is refluxed to the intake gallery 15 and fills the same. In the second embodiment, the damping valve 70 as a pulsation reducing valve having the functions of a check valve and an orifice is provided on the upstream side of the damper chamber 35. In the present invention, however, it is possible to provide only a check valve or an orifice on the upstream side of the damper chamber 35. Furthermore, in the present invention, even if the damper chamber 35 as a pulsation reducing chamber is not provided and only the damping valve 70 as a pulsation reducing valve is provided in the reflux passage 34, the pulsation reducing effect can be obtained to some degree. Moreover, even if only the check valve or orifice part is provided in the reflux passage 34, the pulsation reducing effect can be obtained to some degree. A pulsation reducing device according to the third embodiment of the present invention is illustrated in FIG. 8. In this embodiment, the damping valve 70 is provided on the downstream side of the spill fuel from the damping chamber 35. In this embodiment, the pulsation pressure of the damping chamber 35 is smoothed, and then the pulsation damping characteristics are improved by the damping valve 70, but fuel having stable pressure is refluxed to the intake gallery 15 in the same way as in the second embodiment. In the third embodiment, the damping valve 70 as a pulsation reducing valve having the functions of a check valve and an orifice is provided on the downstream side from the damper chamber 35. In the present invention, however, it is possible to provide only a check valve or an orifice on the downstream side of the damper chamber 35. A pulsation reducing device according to the fourth embodiment of the present invention is illustrated in FIG. 9. In this embodiment, instead of the damper chamber 35 communicating with the reflux passage 34 through the communication passage 35a, an accumulation chamber 36 is provided as a part of the reflux passage 34. It is readily apparent that the accumulation chamber 36 has a cross-sectional area larger than that of the portions of the reflux passage 34 upstream and downstream of the accumulation chamber 36. The transmission loss TL of the accumulation chamber 36 can be obtained from Equations 6A-6C: m = S 2 S 1 K = 2π f C where C is the velocity of sound, f is the pulsation frequency, S 1 is the cross-sectional area of the reflux passage, S 2 is the cross-sectional area of the accumulation chamber, and L is the length of the accumulation chamber. When sin 2 KL = 1 , TL is largest, that is, when L = C/4f, TL is the largest, and the level difference in the pulsation pressure is reduced. A pulsation reducing means according to the fifth embodiment of the present invention is illustrated in FIG. 10. In this embodiment, the pulsation pressure is caused not only by the pulsation due to the spill fuel but also by the delivery pulsation due to the residual delivery pressure from the plunger chamber 35 after the fuel spill. In order to smooth the respective pulsation pressures, an accumulation chamber having dimensions in accordance with the respective pulsation frequencies should be provided. For this reason, in the fifth embodiment, two accumulation chambers 36 and 37 are provided in the reflux passage 34. In the fifth embodiment, two accumulation chambers 36 and 37 are provided as parts of the reflux passage 34. It is possible to provide three or more accumulation chambers to reduce pulsation pressures from other sources as well. A pulsation reducing device according to the sixth embodiment of the present invention is illustrated in FIG. 11. Either the damper chamber or the accumulation chamber is provided in the first embodiment through fifth embodiments described above. In the sixth embodiment, however, an accumulation chamber 81 is provided as a part of the reflux passage 34, and a damper chamber 82 is provided is communicating with the accumulation chamber 81 through a communication passage 82a. Furthermore, damper chambers 83 and 84 communicating with the upstream side and downstream side of the spill fuel from the accumulation chamber 81 through communication passages 83a and 84a respectively. The purpose of providing the accumulation chamber 81 and the damper chambers 82, 83 and 84 is to smooth the pulsation pressure resulting from a plurality of concurrent causes in the same way as in the fifth embodiment. According to the present invention, fuel having more stable pressure can be refluxed to the intake gallery 15 by optimally combining the accumulation chamber 81 and damper chambers 82, 83 and 84. A pulsation reducing device according to the seventh embodiment of the present invention is illustrated in FIG. 12. In FIG. 12, S 1 is the cross-sectional area of the intake passage, S 2 is the cross-sectional area of the intake gallery, S 3 is the cross-sectional area of the reflux passage, L 1 is the length of the intake passage, L 2 is the length of the intake gallery, and L 3 is the length of the reflux passage. If there is no space available for the installation of the damper chamber 35 and the accumulation chambers 82, 83 and 84, the intake gallery 15 may be used as an accumulation chamber according to the seventh embodiment. Nevertheless, if the cross-sectional area S 2 of the intake gallery 15 large enough to smooth the pulsation pressure can not be secured, a part of the pulsation pressure wave is transmitted to the intake passage 31 through the intake gallery 15. However, if the dimensions L 1 , L 2 and L 3 are set at a 1 : 1 : 1 ratio, the pulsation pressure can be smoothed as described below. The spill fuel which is the pulsation pressure wave caused by the opening of the spill valve 40 has a pressure wave 201. This pressure wave 201 refluxes to the reflux passage 34 and becomes an input wave 202 having almost the same energy as that of the pressure wave 201. When the input wave 202 reaches the intake gallery 15, a part thereof becomes a transmission wave 203 and the other part becomes a reflection wave 204 having negative energy according to the ratio of the cross-sectional area S 3 of the reflux passage 34 to the cross-sectional area S 2 of the intake gallery 15. The reflection wave 204 collides against the spill valve 40, becomes a reflection wave 205 having negative energy, and advances to the intake gallery 15. When flowing from the intake gallery 15 into the intake passage 31, the transmission wave 203 becomes a transmission wave 206 and a reflection wave 207 according to the ratio of the cross-sectional area S 2 of the intake gallery 15 to the cross-sectional area S 1 of the intake passage 31. The reflection wave 207 collides against the reflection wave 205, the positive pulsation energy and the negative pulsation energy interfere with each other in the position C, and the level difference in the pulsation pressure is reduced. The transmission wave 206 collides against the outer wall of the distributing rotor 21 and becomes a reflection wave 208 until the intake passage 31 and the intake port 27 formed in the distributing rotor 21 communicate with each other. When is reaches the intake gallery 15 from the intake passage 31, the reflection wave 208 becomes a transmission wave 209 and a reflection wave 210. When reaching the reflex passage 34 from the intake gallery 15, the transmission wave 209 becomes a transmission wave (not shown) and a reflection wave 211. The reflection wave 210 collides against the outer wall of the distributing rotor 21 and becomes a reflection wave 212, and then collides against the reflection wave 211 at position D, whereby the positive pulsation energy and the negative pulsation energy interfere with each other and the level difference in the pulsation pressure is reduced. For this reason, even if a sufficiently large cross-sectional area of the intake gallery 15 can not be provided, the level difference in the pulsation pressure is reduced during the period until the intake passage 31 communicates with the intake port 27, and the pulsation pressure can be smoothed. In the seventh embodiment, the pulsation pressure is smoothed by setting L 1 , L 2 and L 3 to the ratio 1 : 1 : 1. In the present invention, however, it is possible to set the values including the cross-sectional area S 1 of the intake passage 31, the cross-sectional area S 2 of the intake gallery 15 and the cross-sectional area S 3 of the reflux passage 34 are set so that the pulsation pressure can be smoothed optimally. To provide a fuel injection pump which can sufficiently and stably supply fuel to a fuel pressurization chamber during a fuel intake stroke, a plunger chamber (23), a spill port (29) and a spill passage (33) are mutually communicable, while a reflux passage (34), an intake gallery (15), an intake passage (31), an intake port (27) and the plunger chamber (23) are mutually communicable. A reflux passage (34) communicates with a damping chamber (35) through a communication passage (35a). The spill passage (33) and the reflux passage (34) communicate with each other, and when a spill valve (40) opens, high-pressure fuel within the plunger chamber (23) spills from the spill valve (40) and into the intake gallery (15) through the reflux passage (34), causing pulsation having a pressure level difference to the spill fuel. When the pulsation wave passes through the damping chamber (35), as the level difference in the pulsation wave is reduced, a sufficient quantity of fuel can stably be supplied from the intake gallery (15) to the plunger chamber (23).

Claims: A fuel injection pump comprising: a pressurizing feed pump (11) for pressurizing fuel from a fuel tank (61); an intake gallery (15) downstream from said pressurizing feed pump (11) for receiving pressurized fuel from said pump (11) via a fuel pipe (14) connected to said intake gallery (15); a fuel pressurizing part (12, 21-26) for press feeding fuel which, via an intake port (27) of said fuel pressurizing part (12, 21-26), is taken in from an intake passage (31) connected to said intake gallery (15) at its downstream end, said fuel pressurizing part including a rotatably displaceable distributing rotor (21) within a plunger chamber (23) and a plunger (22) for pressurizing and depressurizing fuel within said plunger chamber (23) by rotating integrally with said distributing rotor (21) and reciprocating; an injection nozzle (52) for injecting fuel press fed from the fuel pressurizing part (12, 21-26) through a distribution passage (32); a spill valve (40) for opening to spill fuel from said fuel pressurizing part (12, 21-26) through a spill passage (33) when fuel injection is terminated; a reflux passage (34) for refluxing fuel to said intake gallery (15) when said spill valve (40) opens; and a pulsation reducing means (35-37, 70, 81-84) in said reflux passage (34) for reducing pulsation of fuel refluxed to said intake gallery (15), wherein said distributing rotor (21) includes a distribution port (28) communicating with said distribution passage (32) when fuel within said plunger chamber (23) is pressurized, said intake port (27) communicating with said intake passage (31) when fuel within said plunger chamber (23) is depressurized, and a spill port (29) communicating with said spill passage (33) when fuel injection is terminated; characterized in that said reflux passage (34) is connected to said intake gallery (15) at a location other than said intake passage (31) and said fuel pipe (14). A fuel injection pump according to claim 1, characterized in that said pulsation reducing means (35, 82-84) includes a pulsation reduction chamber (35, 82-84) communicating with said reflux passage (34) through a communication passage (35a, 82a-84a). A fuel injection pump according to claim 1, characterized in that said pulsation reducing means (35, 82-84) includes a plurality of pulsation reduction chambers (35, 82-84) communicating with said reflux passage (34) through respective communication passages. A fuel injection pump according to claim 1, characterized in that said pulsation reducing means (36, 37, 81) includes a pulsation reduction passage (36, 37, 81) in said reflux passage (34), a cross-sectional area of said pulsation reduction passage (36, 37, 81) being larger than at cross-sectional area of at least one of a portion of said reflux passage (34) upstream of said pulsation reduction passage (36, 37, 81) and a portion of said reflux passage (34) downstream of said pulsation reduction passage (36, 37, 81). A fuel injection pump according to claim 4, characterized in that a length of said pulsation reduction passage (36, 37, 81), a length of a portion of said reflux passage (34) upstream of said pulsation reduction passage (36, 37, 81) and a length of a portion of said reflux passage (34) downstream of said pulsation reduction passage (36, 37, 81) satisfy at a preset ratio. A fuel injection pump according to claim 4, characterized in that said pulsation reducing means (81, 82) further includes a pulsation reduction chamber (82) communicating with said pulsation reduction passage (81) through a communication passage (82a). A fuel injection pump according to claim 1, characterized in that said pulsation reducing means (36, 37) includes a plurality of pulsation reduction passages (36, 37) in said reflux passage (34), a cross-sectional area of each of said pulsation reduction passages (36, 37) being larger than a cross-sectional area of at least one of a corresponding portion of said reflux passage (34) upstream of that pulsation reduction passage (36, 37) and a corresponding portion of the reflux passage (34) downstream of that pulsation reduction passage (36, 37). A fuel injection pump according to claim 1, characterized in that said pulsation reducing means (70) includes a check valve (70) which closes in a direction opposite to a flow of fuel from said pressurizing feed pump (11) to said spill valve (40). A fuel injection pump according to claim 8, characterized in that said check valve (70) is on one of an upstream side and a downstream side of a pulsation reduction passage (36). A fuel injection pump according to claim 1, characterized in that said pulsation reducing means (70) includes an orifice (70). A fuel injection pump according to claim 10, characterized in that said orifice (70) is on one of an upstream side and a downstream side of a pulsation reduction passage (36). A fuel injection pump according to claim 1, characterized in that said pulsation reducing means includes a pulsation reducing valve (70) composed of a check valve and an orifice capable of passing fuel from said pressurizing feed pump (11) to said spill valve (40) even when said check valve closes. A fuel injection pump according to claim 12, characterized in that said pulsation reducing valve (70) is provided on one of an upstream side and a downstream side of a pulsation reduction passage (36).

Inventors: KATO MASAAKI, OKAJIMA MASAHIRO, KATO, MASAAKI, OKAJIMA, MASAHIRO
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1995
Main classification: F02M41
IPC codes: F02M55, F02M41, F02M59