FUEL INJECTION PUMP

Abstract

 A fuel injection pump for a diesel engine for attaining a specially excellent combustion performance, specifically comprising a notch part (20) formed in the retraction collar (16) of a delivery valve (3), in addition to an Angleich cut(17), to increase the communicating area of a fuel path (18) between a high pressure chamber (7) and a force-feed chamber (11) according to the lift of the delivery valve (3) so as to suppress the retraction effect of the delivery valve (3) in order to prevent a residual pressure in the high pressure chamber (7) from excessively reducing particularly during high idling. An annular groove (54) communicating with a lower lead (52) is formed in the outer peripheral surface of a plunger (50), and a part of fuel inside the force-feed chamber (11) is returned, during force-feed process, to a fuel feed port (13) through the annular groove (54) so as to increase the length of an injection period in low and medium speed ranges to reduce combustion noises, and to delay the injection timing under low idle condition to reduce the emission of blue white smoke.

Description

Field of the Invention

[0001] This invention relates to a fuel injection pump of a diesel engine, more particularly to a structure thereof which is capable of realizing a particularly favorable combustion performance.

Background of the Invention

[0002] Fig. 17 and Fig. 18 show a conventional fuel injection pump. As shown in these drawings, a valve seat 2 is mounted in an upper portion of a pump body 1 and a delivery valve 3 which is accommodated in the valve seat 2 is always biased in a valve closing direction by means of a spring 4. A high pressure chamber 7 is formed in the inside of a valve holder 6 which fixedly secures the valve seat 2 to the pump body 1 and a fuel high pressure tube 8 is connected to the valve holder 6 such that the high pressure tube 8 is communicated with the high pressure chamber 7.

[0003] On the other hand, in a lower portion of the pump body 1, a plunger 10 which is driven by a cam not shown in the drawings is slidably accommodated, while a force-feed chamber 11 is formed between an upper portion of the plunger 10 and the delivery valve 3. A lower lead 12 which is inclined in an oblique direction is formed in an outer peripheral surface of the plunger 10 and the lower lead 12 is communicated with the force-feed chamber 11.

[0004] In the above-mentioned constitution, as shown in Fig. 18, when the plunger 10 is moved upwardly by a cam so as to make the outer peripheral surface of the plunger 10 close a fuel feed port 13 which opens toward the force-feed chamber 11, fuel in the force-feed chamber 11 is compressed and pushes up the delivery valve 3 against the biasing force of the spring 4. Accordingly, the high pressure chamber 7 and the force-feed chamber 11 are communicated with each other and hence, the fuel flows in the inside of the high pressure chamber 7 so as to increase the pressure in the inside of the high pressure chamber 7. When the pressure in the inside of the high pressure chamber 7 becomes equal to or more than the valve opening pressure of an injection nozzle, the fuel is injected from the injection nozzle.

[0005] Then, when the plunger 10 is further moved upwardly so as to make the lower lead 12 release the fuel feed port 13, the fuel in the inside of the force-feed chamber 11 is returned to the fuel feed port 13 through the lower lead 12 thus rapidly reducing the pressure of the force-feed chamber 11. Accordingly, the delivery valve 3 is pushed down by the biasing force of the spring 4 and a conical-shaped valve portion 14 of the upper portion of the delivery valve 3 is hermetically brought into contact with a seat surface of the valve seat 2 thus completing the injection.

[0006] Here, with an action of a retraction collar 16 disposed below the valve portion 14 of the delivery valve 3, the fuel in the inside of the high pressure chamber 7 is retracted to reduce the residual pressure so that the injection cut-off is enhanced and the post-sagging can be prevented.

[0007] However, the retracting action of such a delivery valve 3 gives rise to a problem that a negative pressure is generated at the fuel high pressure tube 8 side in a low speed range so that a fuel injection amount becomes unstable. To cope with such a problem, an Angleich cut 17 is formed in a slide surface of the retraction collar 16 so as to ensure a certain level of residual pressure of the high pressure chamber 7 in the low speed range by suppressing the retraction effect, whereby the characteristics of the fuel injection amount relative to the rotational speed, that is, the N-Q characteristics are improved.

[0008] Further, in the above-mentioned fuel injection pump, control of the fuel injection amount is performed such that the plunger 10 is rotated in a circumferential direction so as to change an operable region, that is, the effective stroke within a range of the lower lead 12 so that the cutting timing of the fuel injection performed by means of the lower lead 12 can be controlled. For example, at the time of low load, the shallow lead position is employed so as to reduce the injection amount, while at the time of high load, the deep lead position is employed so as to increase the injection amount.

[0009] However, the above-mentioned conventional fuel injection pump has a following drawback. In general, the force to push up the plunger generated by the cam is weak in the low speed range and hence, the elevation amount (hereinafter called "lift amount") of the delivery valve becomes small, whereas the force to push up the plunger generated by the cam is strong in the high speed range and hence, the lift amount of the delivery valve caused by this dynamic effect becomes large. When the lift amount of the delivery valve is large, the retraction effect is increased so that the residual pressure in the inside of the high pressure chamber is reduced. That is, as the speed approaches the high speed range, the residual pressure in the inside of the high pressure chamber is reduced correspondingly.

[0010] Such a tendency has existed even in the past. That is, if the residual pressure in the high pressure chamber 7 is to be held low in the low speed range, particularly at the time of high idling condition with small injection amount at the high speed, the residual pressure in the inside of the high pressure chamber 7 is excessively reduced so that the rise of injection at the time of the force-feed process, that is, the dynamic injection timing is delayed. In this case, the misfire occurs at the time of starting in a cold atmosphere and drawbacks such as misfire which generates blue white smoke are liable to occur.

[0011] On the other hand, by preventing the residual pressure from becoming excessively low in the high idling condition, the residual pressure in the low pressure range is increased coupled with ensuring of the pressure performed by the Angleich cut 17 and hence, the injection period becomes short so that the forming of mixture gas and the combustion are performed rapidly and the combustion noise is liable to be generated.

[0012] That is, it has been difficult to maintain the favorable combustion performance by preventing the residual pressure in the inside of the pressure chamber 7 from becoming excessively low in the high idling condition while maintaining the residual pressure in the inside of the pressure chamber 7 low in the low speed range.

[0013] Further, a two-way delivery valve may be used to maintain the residual pressure in the low speed range at a low level to a certain degree. In this case, however, the spill rate in the high speed loading range is reduced thus deteriorating injection cut-off and giving rise to the deterioration of the combustion performance.

[0014] Further, conventionally, in the force-feed process performed by the plunger 10, the pressure in the inside of the force-feed chamber 11 is continuously increased and hence, the injection pressure is also continuously increased so that the injection period becomes short and the mixing gas forming speed is rapidly increased thus bringing about a rapid explosion combustion. As a result, there has been a drawback that a large combustion noise is generated. The generation of such a large noise is particularly apparent in low and middle speed ranges. Further, in the low idling condition with small injection amount, the injection timing becomes early so that there has been a drawback that the combustion is deteriorated thus generating blue white smoke.

[0015] Then, to solve such drawbacks, various kinds of fuel injection pumps which can increase the length of the injection period or can vary the injection timing have been proposed, wherein each fuel injection pump is constituted such that a groove which is communicated with the lower lead is formed in the vicinity of the upper portion of the plunger and the fuel in the inside of the force-feed chamber is partially returned to the fuel feed port through the groove during the force-feed process performed by the plunger so as to moderate the pressure increase in the inside of the force-feed chamber particularly in low and middle speed ranges.

[0016] However, in any one of these proposals, the groove formed in the outer peripheral surface of the plunger is formed of a partial groove which has one end thereof communicated with the lower lead. The reason for forming the groove in such a place is as follows. That is, although it is necessary to increase the effective stroke to make the injection amount maximum by making use of the deepest part of the lower lead particularly at the time of starting, the starting performance is deteriorated if the fuel is to be returned even at the time of starting,. Accordingly, the groove is formed while avoiding the deepest position of the lead.

[0017] In forming such a partial groove in the outer peripheral surface of the plunger by using a cutting machine, a highly accurate positioning of the plunger is required with respect to how far the groove is to be cut and control of the distance from the upper end surface of the plunger to the groove becomes also extremely difficult. Accordingly, the groove machining of the plunger becomes extremely cumbersome and pushes up a manufacturing cost.

[0018] Further, when the plunger is rotated so as to change the injection amount, the relative position between the fuel teed port and the partial groove is changed and hence, the total length of the fuel discharge path is changed thus giving rise to a drawback that the pressure control in the inside of the force-feed chamber cannot be performed with a high accuracy.

[0019] It is an object of the present invention to provide a fuel injection pump which can solve these drawbacks and can realize a favorable fuel combustion performance by preventing the residual pressure in the inside of the high pressure chamber in the high speed range (particularly in the high idling condition) from becoming excessively low while maintaining the residual pressure in the high pressure chamber in the low speed range at a certain low level.

[0020] It is a further object of the present invention to provide a fuel injection pump which enables the reduction of the combustion noise in low and middle speed ranges and the reduction of the generation of blue white smoke in the low idling condition by favorably discharging a part of fuel in a force-feed chamber during the force-feed process and can perform the groove machining of a plunger necessary for the above purpose with extreme easiness.

Disclosure of the Invention

[0021] The present invention is characterized in that a fuel injection pump slidably disposing a delivery valve having a fuel retraction in a fuel path which makes a high pressure chamber connected to an injection nozzle or the like and a force-teed chamber communicated with each other, the improvement being characterized in that an Angleich cut is formed in a retraction collar of the delivery valve and in a stage before the communication area of the fuel path becomes maximum, in addition to the enlargement of the communication area of the fuel path by the Angleich but, communication area enlargement means which enlarges the communication area of the fuel path according to the movement of the delivery valve is provided.

[0022] Due to such a constitution, in the high idling condition with a small injection amount, the whole fuel to be fed to the high pressure chamber can be fed to the high pressure chamber through the fuel path whose area is enlarged by merely slightly lifting the delivery valve. Accordingly, the lift amount of the delivery valve which originally should take a large value can be suppressed to a small value and hence, the retraction effect can be suppressed thus ensuring the residual pressure in the inside of the high pressure chamber in a more stable manner compared to the conventional fuel injection pump. As a result, even when the residual pressure in the inside of the high pressure chamber is set low to a certain degree in the low speed range, the residual pressure in the inside of the high pressure chamber in the high idling condition can be prevented from becoming excessively low.

[0023] On the other hand, in the high speed and high load range, since the injection amount is large, the delivery valve in the inside of the high pressure chamber is lifted to a sufficient height with inertial force thereof and hence, a sufficient retraction effect can be obtained thus sufficiently reducing the residual pressure in the inside of the high pressure chamber.

[0024] Accordingly, the length of the injection period in the low speed range can be increased and the forming of mixture gas and the combustion can be moderated and hence, the rapid generation of heat can be suppressed thus reducing combustion noise and simultaneously the delay of the injection timing in the high idling condition can be eliminated thus remarkably enhancing the combustion performance. Further, in spite of suppressing the reduction of the residual pressure in the high idling condition, in the high speed and high load range, the residual pressure can be held at a sufficiently low value by the sufficient retraction effect thus realizing the favorable combustion performance with the favorable injection cut-off.

[0025] Further, the above-mentioned communication area enlargement means is constituted by a notch part formed in at least one of wall surfaces of the retraction collar of the delivery valve and the fuel path. Due to such a notch part, the above-mentioned effects can be achieved with an extremely simple structure.

[0026] Further, the notch part may be formed by cutting the slide surface of the retraction collar in a stepped shape or in a tapered oblique shape. Still further, by forming the notch by cutting a portion of the retraction collar where the Angleich cut is formed, the Angleich cut and the notch part can be simultaneously formed with one cutting operation and hence, the manufacturing process can be simplified.

[0027] Further, the present invention is directed to a fuel injection pump in which a plunger with a lower lead formed in an outer peripheral portion thereof is slidably inserted into a force-feed chamber and fuel in the inside of a force-feed chamber is force-fed during a force-feed process from a point of time that the fuel feed port which is opened toward the force-feed chamber is clogged by a distal end of the plunger to a point of time that the fuel feed port is released to the lower lead, wherein an annular groove which is communicated with the lower lead is formed in the outer peripheral surface of the plunger so as to return a part of the fuel in the inside of the force-feed chamber to the fuel feed port through the annular groove during the force-feed process.

[0028] The annular groove has the same cross section over the entire circumference thereof and the groove width thereof is set smaller than the diameter of the fuel feed port.

[0029] Due to such a constitution, in the force-teed process, in low and middle speed ranges where the moving speed of the plunger is low, the period in which the fuel feed port and the annular groove are communicated with each other is prolonged, a large amount of fuel is discharged and hence, the force-feed ability is sufficiently reduced so that the pressure rise in the force-feed chamber is moderated and the length of the injection period can be increased, whereby the combustion noise can be reduced. Further, the injection timing in the low idling condition can be delayed so that the generation of blue white smoke can be reduced.

[0030] On the other hand, in the high speed and high load range, the moving speed of the plunger is fast and the period in which the fuel feed port and the annular groove are communicated with each other becomes short and hence, the discharge amount of fuel is small and the force-feed ability is not substantially reduced. Accordingly, although the injection period becomes long in low and middle speed ranges, the injection period in the high speed and high load range, the injection period can be made short so that the favorable combustion performance with a sharp injection cut-off can be maintained.

[0031] Further, by adopting the annular groove having the same cross section, the groove machining of the plunger with the use of a cutting machine can be performed with extreme easiness compared to forming of a conventional partial groove so that the manufacturing cost can be reduced.

[0032] Further, in case the annular groove is formed in the outer peripheral surface of the plunger, communicating portions are formed at two positions with respect to the lower lead and the fuel feed port respectively so that two fuel discharge paths can be obtained with one groove thus enhancing the fuel discharge efficiency.

[0033] Still further, although the relative positions of the fuel feed port and the annular groove are changed when the plunger is rotated in a horizontal direction for changing the injection amount, the total length of the fuel discharge path is always equal to the entire length of the annular groove and hence is not changed. Accordingly, irrespective of the rotational position of the plunger, the fuel discharge condition can be always held constant and hence, the fuel control in the force-feed chamber can be performed with a high accuracy.

Brief Explanation of the Drawings

[0034] Fig. 1 is a longitudinal cross-sectional view of a fuel injection pump of an embodiment of the present invention, Fig. 2 is a longitudinal cross-sectional view of a delivery valve portion of the fuel injection pump, Fig. 3 is a longitudinal cross-sectional view of the delivery valve portion in a condition that the communication area of a fuel path is enlarged, Fig. 4 is a perspective view showing a notch part of the delivery valve, Fig. 5 is a view showing the relationship between the lift amount of the delivery valve and the communication area of the fuel path, Fig. 6 is a front view of the delivery valve in which an oblique tapered notch part is formed, Fig. 7 is a front view of the delivery valve which forms a notch part in a portion where an Angleich cut is formed, Fig. 8 is a front view of the delivery valve which forms a notch part in a portion where an Angleich cut is formed, Fig. 9 is a longitudinal cross-sectional view showing the condition that a notch part is formed in a valve seat, Fig. 10 is a longitudinal view showing the condition that notches are formed on both of a delivery valve and a valve seat, Fig. 11 is a perspective view of a plunger, Fig. 12 is a side view showing the positional relationship between a plunger and a force-feed port during the force-feed process, Fig. 13 is a side view of a plunger provided with a pair of upper and lower annular grooves, Fig. 14 is a side view of a plunger which makes a lower lead and an annular groove communicated with each other through a notch part, Fig. 15 is a side view of a plunger which makes a lower lead and an annular groove communicated with each other through a notch part, Fig. 16 is a perspective view of other plunger in which an annular groove is formed, Fig. 17 is a longitudinal cross-sectional view of a conventional fuel injection pump, and Fig. 18 is a longitudinal cross-sectional view of the fuel injection pump during the force-feed process.

Best Mode for Carrying out the Invention

[0035] The fuel injection pump according to an embodiment of the present invention is capable of improving the combustion performance by devising the structure of a delivery valve and a plunger and the structure of other parts is substantially as same as the structure of conventional fuel injection pump. Members which have the same functions as those of conventional fuel injection pump are denoted by same symbols.

[0036] In this fuel injection pump, a delivery valve 3 is upwardly and downwardly disposed in a slidable manner in a fuel path 18 formed in a valve seat 2 which makes a high pressure chamber 7 and a force-feed chamber 11 communicated with each other. An Angleich cut 17 which is similar to a conventional Angleich cut is formed in a retraction collar 16 of the delivery valve 3. Then, in a stage before the communication area of the fuel path 18 becomes maximum, in addition to the enlargement of the communication area of the fuel path 18 by the Angleich cut 17, communication area enlargement means which enlarges the communication area of the fuel path 18 according to the movement of the delivery valve 3 in a valve opening direction, that is, the lift of the delivery valve 3 is provided.

[0037] As shown in Fig. 2 to Fig. 4, the communication area enlargement means is constituted by a notch part 20 formed in the retraction collar 16 of the delivery valve 3. The notch part 20 is formed by cutting a portion of a slide surface of the retraction collar 16 which is disposed opposite to a portion of the slide surface where the Angleich cut 17 is formed in such a manner that the portion extending from a center of the slide surface slightly close to the upper end of the slide surface to the lower surface is cut in a stepped shape.

[0038] Due to such a constitution, when the delivery valve 3 is pushed up, first of all, the communication area of the fuel path 18 is slightly enlarged by the Angleich cut 17. As shown in Fig. 3, when an upper end portion 21 of the notch part 20 of the delivery valve 3 is positioned above a lower end portion of seat surface 15 of the valve seat 2, an opening is formed between the notch part 20 and the seat surface 15 so that the communication area of the fuel path 18 is further enlarged. Then, when the delivery valve 3 is further pushed up and the lower end portion 22 of the notch part 20, that is, when a lower surface of the retraction collar 16 is positioned above the lower end portion of the seat surface 15, the communication area of the fuel path 18 is further enhanced and reaches the maximum communication area.

[0039] Fig. 5 shows the relationship between the lift amount of the delivery valve 3 and the communication area of the fuel path 18. In the drawing, a solid line indicates a case in which the delivery valve of the present invention which further forms the notch part 20 in addition to forming of the Angleich cut 17 is used and a dotted line indicates a case in which a conventional delivery valve which forms only the Angleich cut 17 is used. As apparent from this drawing, in the conventional delivery valve, the communication area is held constant from a point of time that the communication area is enlarged by the Angleich cut 17 right after pushing up the delivery valve 3 to a point of time that the delivery valve 3 is completely opened, whereas, in the present invention, the communication area is enlarged by the notch part 20 from a point of time that the communication area is enlarged by the Angleich cut 17 to a point of time that the fuel path 18 reaches the maximum communication area, that is, the delivery valve 3 is completely opened.

[0040] In this manner, according to the delivery valve structure of this embodiment, when the lift amount of the delivery valve 3 is smaller compared to the conventional delivery valve, the fuel in the inside of the force-feed chamber 11 can be force-fed to the high pressure chamber 7 while ensuring a sufficient communication area by the notch part 20.

[0041] Accordingly, in the high idling condition which provides high speed driving with a small injection amount, the whole fuel to be fed to the inside of the high pressure chamber 7 can be fed by merely lifting the delivery valve 3 slightly and hence, the lift amount of the delivery valve 3 which originally should be large can be suppressed small so that the retraction effect can be suppressed. On the other hand, in the high speed and high load range with a large injection amount, the delivery valve 3 disposed in the inside of the high pressure chamber 7 is lifted to a high position with inertial force so that a sufficient retraction effect can be obtained.

[0042] Accordingly, even when the residual pressure in the inside of the high pressure chamber 7 in the low speed range is set low to a certain degree, the residual pressure in the inside of the high pressure chamber 7 in the high idling condition is prevented from becoming excessively low and hence, the length of the injection period in the low speed range can be prolonged thus reducing the combustion noise and simultaneously eliminating the delay of injection timing in the high idling condition. Further, in spite of suppressing the reducing of the residual pressure in the high idling condition, the residual pressure can be sufficiently reduced by the sufficient retraction effect in the high speed and high load range so that the improved combustion performance with the sharp injection cut-off can be realized.

[0043] The delivery valve structure which can achieve the above-mentioned operation and effects is not limited to the above-mentioned delivery valve structure and other delivery valve structures are explained hereinafter.

[0044] For example, as shown in Fig. 6, in place of the notch part 20 formed in a stepped shape, the communication area enlargement means may be constituted by a notch part 30 which is formed by cutting a portion of the slide surface of the retraction collar 16 which extends from a center of the slide surface slightly close to the upper end to a lower surface of the retraction collar 16 downwardly and obliquely in a tapered form. In this case, compared to the notch part 20 in a stepped shape which enlarges the communication area of the fuel path 18 in a stepped manner, the communication area can be enlarged gradually and hence, the force-feed of the fuel can be performed smoothly thus realizing the improved combustion performance.

[0045] Further, the portion where the notch part is formed is not necessarily a portion of the slide surface of the retraction collar 16 which is disposed opposite to a portion of the slide surface where the Angleich cut 17 is formed. For example, as shown in Fig. 7 and Fig. 8, notch parts 31, 32 may be formed in portions where the Angleich cuts 17 are formed. In Fig. 7, the notch part 31 is formed by cutting the side portion of the retraction collar 16 from the upper surface to the lower surface including the Angleich cut 17 downwardly and obliquely in a tapered form. The notch part 32 shown in Fig. 8 is formed by, first of all, cutting the side portion of the retraction collar 16 in a flat form in a sliding direction as in the case of forming the Angleich cut 17 and then cutting the side portion in an downwardly extending tapered form. In these cases, the Angleich cut 17 and notch parts 31, 32 are simultaneously formed in one cutting operation so that the manufacturing process can be simplified.

[0046] Further, a plurality of above-mentioned notch parts may be formed on the side portion of the retraction collar 16 of the delivery valve 3 or an inclined or oblique notch part may be formed by continuously connecting tapers which are different in inclination angles.

[0047] Still further, a notch part may be formed in the wall surface of the fuel path 18, that is, in the inner side surface of the valve seat 2 so as to enlarge the communication area according to the lift of the delivery valve 3 in the same manner as the above-mentioned cases. For example, as shown in Fig. 9, a notch part 40 which is disposed above the retraction collar 16 of the delivery valve 3 in a valve closed condition can be formed by cutting the entire circumference of a corner portion of a seat surface 15 in the valve seat 2 in a stepped shape. In this case, when the lower surface of the retraction collar 16 reaches a position above the lower surface of the notch part 40 upon pushing up of the delivery valve 3, an opening is formed between the notch part 40 and the retraction collar 16 so that the communication area of the fuel path 18 can be enlarged.

[0048] Furthermore, as shown in Fig. 10, the above-mentioned notch parts 30, 40 may be formed in both the inner side surfaces of the retraction collar 16 of the delivery valve 3 and the valve seat 2. In this case, when the upper end portion of the notch part 30 is positioned above the lower surface of the notch portion 40 of the valve seat 2, an opening is formed between both notch parts 30,40 so that the communication area of the fuel path 18 can be enlarged thus extremely reducing the lift amount of the delivery valve 3 necessary for enlarging the communication area. A stepped notch part may be adopted as the notch part of the delivery valve 3 side and a tapered notch may be adopted as the notch part of the valve seat 2 side. The number of notch parts and portions where notch parts are formed can be suitably changed.

[0049] On the other hand, as shown in Fig. 11, a longitudinal groove 51 which has a circular cross section and extends downwardly from the center of the upper end surface is formed in the plunger 50. A lower lead 52 is formed in the outer peripheral surface of the plunger 50 in such a manner that the lower lead 52 extends in an oblique direction substantially over the half circumference from a position in the vicinity of the upper end of the outer peripheral surface. The lower end portion of the longitudinal groove 51 is communicated with the central portion of the lower lead 52 through a lateral groove 53.

[0050] Further, in the vicinity of the upper end of the outer peripheral surface of the plunger 50, an annular groove 54 which intersects and is communicated with the upper portion of the lower lead 52 is formed over the entire circumference. This annular groove 54 is disposed in parallel to the upper end surface of the plunger 50 and has the same cross section over the entire circumference. The groove width of the annular groove 54 is set smaller than the diameter of the fuel feed port 13.

[0051] The cross-sectional shape of the annular groove 54 is not limited to a rectangular shape and may be a semicircular shape or a wedge shape.

[0052] In forming such an annular groove 54 by using a cutting machine, the machining position of the annular groove 54, that is, the cutting operation can be performed by merely determining the distance from the upper end surface of the plunger 50, bringing a cutting edge of the cutting machine into pressure contact with this portion by pushing, and then rotating the cutting edge in a horizontal direction while fixing the plunger 50. Accordingly, the highly accurate positioning of the plunger and the difficult distance control of distance from the upper end surface of the plunger which are required in machining the conventional partial groove become no more necessary so that the groove machining work can be extremely simplified and the manufacturing cost can be reduced.

[0053] Fig. 12 shows the positional relationship between the plunger 50 and the fuel feed port 13 in the course of the force-feed process. As shown in the drawing, when the plunger 50 is moved upwardly and the upper end surface of the plunger 50 reaches a position where the surface is as high as the upper end of the fuel feed port 13, the force-feed of the fuel in the force-feed chamber 11 is started. In this force-feed starting condition, the fuel feed port 13 and the annular groove 54 are communicated with each other and hence, the fuel in the inside of the force-feed chamber 11 is discharged into the fuel feed port 13 side through the longitudinal and lateral grooves 51, 53, the lower lead 52 and the annular groove 54. Here, the annular groove 54 is communicated with the fuel feed port 13 at two positions 55, 56 and is communicated with the lower lead 52 at two positions 57, 58 as shown in Fig. 11 so that two fuel discharge paths which reach the fuel feed port 13 from the lower lead 52 are present in one annular groove 54 whereby the fuel can be efficiently discharged. This fuel discharge is continued until the plunger 50 further moves upwardly and the annular groove 54 is positioned above the fuel feed port 13. Then, when the lower lead 52 is communicated with the fuel feed port 13, the injection is completed.

[0054] In this force-feed process, in low and middle speed ranges where the moving speed of the plunger 50 is slow, the period that the fuel feed port 13 and the annular groove 54 are communicated with each other is long and hence, a large amount of fuel is discharged so that the force-feed ability is sufficiently reduced, the pressure rise in the force-feed chamber 11 becomes moderate and the injection time is prolonged, whereby the combustion noise can be reduced.

[0055] On the other hand, in the high speed and high load range, the moving speed of the plunger 50 is fast and the period in which the fuel feed port 13 and the annular groove 54 are communicated with each other is short and hence, a fuel discharge amount is small and the force-feed ability is not reduced substantially. Accordingly, although the injection period becomes long in low and middle speed range, in the high speed and high load range, the injection period becomes short and hence, the combustion performance with sharp injection cut-off can be maintained.

[0056] Further, in controlling the injection amount, the plunger 50 is rotated in a horizontal direction so as to change the effective stroke. In this case, although the relative positions of the fuel feed port 13 and the annular groove 54 are changed, the total length of the fuel discharge path, that is, the length of the combined path formed of the above-mentioned two fuel discharge paths becomes always equal to the entire length of the annular groove 54 and hence is not changed. Accordingly, irrespective of the rotational position of the plunger 50, the fuel discharge condition can be always set constant so that the fuel control in the force-feed chamber 11 can be performed with a high accuracy.

[0057] In case the groove which returns a part of the fuel in the inside of the force-feed chamber 11 to the fuel feed port 13 in the course of the force-teed process is constituted by the annular groove 54 formed over the entire circumference on the outer peripheral surface of the above-mentioned plunger 50, the groove is present even at the deepest position of the lower lead 52. Accordingly, even at the time of starting which is required to maximize the injection amount, the fuel in the inside of the force-feed chamber 11 is discharged. However, the deterioration of the starting performance caused by this fuel discharge can be solved by adjusting the cam speed or by changing the size and shape of each groove.

[0058] The plunger structure which can achieve the above-mentioned operation and effects is not limited to the above-mentioned structure and other plunger structures are explained hereinafter.

[0059] For example, as shown in Fig. 13, a pair of upper and lower annular grooves 54 which are disposed in parallel to each other may be formed on the outer peripheral surface of the plunger 50. In this case, four fuel discharge paths in total can be formed so that the fuel discharge efficiency can be remarkably enhanced.

[0060] Further, in the plunger 50 having a large effective stroke, a case that the annular groove 54 and the upper end portion of the lower lead 52 do not intersect each other arises. In such a case, as shown in Fig. 14 and Fig. 15, a notch part 60, 61 which makes the annular groove 54 and the lower lead 52 communicated with each other is formed on the outer peripheral surface of the plunger 50. The notch part 60 shown in Fig. 14 is formed by cutting a portion in the vicinity of the upper end of the outer peripheral surface of the plunger 50 in a stepped shape, while the notch part 61 shown in Fig. 15 is formed by cutting a portion in the vicinity of the upper end of the outer peripheral surface of the plunger 50 in a tapered form.

[0061] Further, the plunger 50 is not limited to a plunger which forms the longitudinal groove 51 in the central portion thereof and many plungers which form longitudinal grooves which make the force-feed chambers 11 communicated with the lower leads 52 on the outer surfaces of the plungers are known. In such a plunger, in case the annular groove 54 is formed as shown in Fig. 16, the annular groove 54 is inevitably communicated with the lower lead 52 through the longitudinal groove 62 so that it is no more necessary to form the lateral groove which make the longitudinal groove and the lower lead communicated with each other or the above-mentioned notch part.

Claims

1. A fuel injection pump slidably disposing a delivery valve having a fuel retraction in a fuel path which makes a high pressure chamber connected to an injection nozzle or the like and a force-feed chamber communicated with each other, the improvement being characterized in that an Angleich cut is formed in a retraction collar of the delivery valve and in a stage before the communication area of the fuel path becomes maximum, in addition to the enlargement of the communication area of the fuel path by the Angleich cut, communication area enlargement means which enlarges the communication area of the fuel path according to the movement of the delivery valve is provided.

2. A fuel injection pump according to claim 1, wherein the communication area enlargement means is constituted by a notch part formed in at least either one of a wall surface of a retraction collar of the delivery valve and a wall surface of the fuel path.

3. A fuel injection pump according to claim 2, wherein the notch part is formed by cutting a slide surface of the retraction collar in a stepped shape.

4. A fuel injection pump according to claim 2, wherein the notch part is formed by cutting a slide surface of the retraction collar in an oblique tapered shape.

5. A fuel injection pump according to any one of preceding claims 2 to 4, wherein the notch part is formed by cutting a portion of the retraction collar where the Angleich cut is formed.

6. A fuel injection pump slidably inserting a plunger which forms a lower lead in an outer peripheral surface thereof into a force-feed chamber and force-feeding fuel in the inside of the force-feed chamber during a period from a point of time that a fuel feed port which opens toward the force-feed chamber is clogged by a distal end of the plunger to a point of time that the fuel feed port is released by the lower lead, the improvement being characterized in that an annular groove which is communicated with the lower lead is formed in the outer peripheral surface of the plunger so as to return a part of fuel in the inside of the force-feed chamber to the fuel feed port through the annular groove during the force-feed process.

7. A fuel injection pump according to claim 6, wherein the annular groove has the same cross section over the entire circumference.

8. A fuel injection pump according to claim 6 or 7, wherein the groove width of the annular groove is smaller than the diameter of the fuel feed port.

Drawing