GB2311336A

GB2311336A - Distributor type fuel injection pump

Info

Publication number: GB2311336A
Application number: GB9606121A
Authority: GB
Inventors: Yukihiro Shinohara; Kouichi Nagaya; Yoshinori Akiyama; Takao Naganuma; Hiroyuki Nishimura; Hiroyasu Kanamori
Original assignee: NipponDenso Co Ltd
Current assignee: Denso Corp
Priority date: 1995-03-22
Filing date: 1996-03-22
Publication date: 1997-09-24
Anticipated expiration: 2016-03-22
Also published as: GB2311336B; GB9606121D0; GB2311336A8

Abstract

A distributor type fuel injection pump for internal combustion engines includes a spill valve 50 for returning fuel in a fuel pressure chamber 21 formed in a distributor rotor 13 to a fuel tank when the supply of fuel to an injector is to end. The spill valve includes a needle 52 slidably disposed in a cylinder 12 supporting therein the distributor rotor to selectively establish and block fluid communication between a first spill path 17, 15, 55 connected to the fuel pressure chamber 21 and a second spill path including a fuel gallery 14 located around the cylinder and connected to the outside through a pump housing 4. The spill valve is disposed in a plane perpendicular to the axis of the rotor and controls the connection of the chamber 55 to the gallery 14.

Description

SPECIFICATION DISTRIBUTOR TYPE FUEL INJECTION PUMP The present invention relates generally to a distributor type fuel injection pump for internal combustion engines. More particularly, the invention is directed to an improved structure of a valve of a distributor type fuel injection pump.

Japanese Patent First Publication No. 3-179159 discloses, as one example, a conventional distributor type fuel injection pump which includes a spill valve mounted on a distributor head having disposed therein a cylinder which supports a distributor rotor rotatably along with a housing. A valve seat is formed on the distributor head on which a needle of the spill valve is seated. In this structure, a flow path extending from a fuel pressure chamber to the spill is relatively long so that a fuel pressurizing volume is great. resulting in a lowering of efficiency of fuel pressurizing using pump plungers. Additionally, the long flow path from the fuel pressure chamber to the spill valve causes a pressure loss to be increased, resulting in a decrease in amount of fuel discharged from the spill valve per unit time. This leads to deterioration in cut-off of injection.

It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.

It is another object of the present invention to provide an improved structure of a spill valve employed in a distributor type fuel injection pump for internal combustion engines.

According to one aspect of the present invention, there is provided a distributor type fuel injection pump for an internal combustion engine which comprises (a) a pump housing, (b) a cylindrical member having formed therein fuel outlet paths, (c) a distributor rotor disposed within the cylindrical member rotatably about a given axis of rotation in synchronism with rotation of the internal combustion engine for selectively delivering fuel to cylinders of the internal combustion engine through the fuel outlet paths of the cylindrical member, (d) a fuel pressure chamber formed in the distributor rotor, (e) a pressurizing means for introducing fuel into the fuel pressure chamber and pressuring the introduced fuel according to a cam profile of a cam member, (f) a first fuel spill path formed in the cylindrical member, communicating with the fuel pressure chamber, (g) a second fuel spill path communicating with a spill outlet formed in the pump housing for discharging the fuel outside the pump housing, (h) a third fuel spill path defined around an outer peripheral surface of the distributor rotor, communicating between the first and second fuel spill paths, (i) a spill valve having a valve member movable in a valve bore formed in the cylindrical member along a given travel path for selectively establishing and blocking communication between the second and third fuel spill paths, and (j) a fourth fuel spill path communicating between the third fuel spill path and the valve bore, extending in a direction substantially perpendicular both to the given travel path of the valve member of the spill valve and to the axis of rotation of the distributor rotor.

In the preferred mode of the invention, the given travel path of the valve member is defined on a plane extending perpendicular to the axis of rotation of the distributor rotor.

The given travel path of the valve member is away from the axis of rotation of the distributor rotor at a given distance.

A fuel gallery is formed between the pump housing and the cylindrical member which establishes communication between the second fuel spill path and the spill outlet. The spill valve establishes the communication between the second and third fuel spill paths to discharge the fuel in the fuel pressure chamber through the spill outlet.

The cylindrical member includes a support member having formed therein the valve seat and a cylinder body supporting the support member.

The spill valve includes a solenoid valve and a valve mounting member. The valve mounting member is urged into engagement with the cylindrical member.

The cylindrical member has formed therein a bore in which the distributor rotor is disposed. The third fuel spill path is defined by an annular groove formed in an inner wall of the cylindrical member defining the bore.

The fuel is introduced into the fuel pressure chamber through a portion of a fuel flow path consisting of the first, second. third.

and fourth fuel spill paths.

The valve member of the spill valve may be designed to have a first pressure-energized surface and a second pressure-energized surface. The first pressure-energized surface receives thereon pressure of the fuel in the fuel gallery to urge the valve member for establishing the communication between the second and third fuel spill paths. The second pressure-energized surface receives thereon the pressure of the fuel in the fuel gallery to urge the valve member for blocking the communication between the second and third fuel spill paths. The valve member is disposed within the fuel gallery.

A low pressure chamber may be provided which communicates with the fuel gallery through a restrictor. The spill valve includes an armature connected to the valve member for moving the valve member along the given travel path. The armature is disposed within an armature chamber communicating with the low pressure chamber through a path.

The cylindrical member may have formed therein a hole substantially extending perpendicular to the axis of rotation of the distributor rotor. A cylindrical support member which supports therein the valve member of the spill valve slidably is inserted into the hole of the cylindrical member.

The cylindrical support member is disposed within the hole of the cylindrical member with a given clearance.

A pressing member and an urging member are provided. The pressing member mounts the spill valve in the pump housing so as to press the cylindrical support member in a first direction. The urging member urges the cylindrical support member in a second direction opposite the first direction.

The cylindrical support member may engage at its end an inner wall of the pump housing.

An accumulator is provided for absorbing pressure pulsation generated in the fuel gallery.

The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to limit the invention to the specific embodiment but are for explanation and understanding only.

In the drawings: Fig. 1 is a cross sectional view which shows a distributor type fuel injection pump according to a first embodiment; Fig. 2 is a cross sectional view taken along the line I-I in Fig.

1; Fig. 3 is a transverse cross sectional view which shows a distributor type fuel injection pump according to a second embodiment; Fig. 4 is a transverse cross sectional view which shows a distributor type fuel injection pump according to a third embodiment; Fig. 5 is a transverse cross sectional view which shows a distributor type fuel injection pump according to a fourth embodiment; Fig. 6 is a cross sectional view which shows a distributor type fuel injection pump according to a fifth embodiment; Fig. 7 is a cross sectional view taken along the line I-I in Fig.

6; Fig. 8 is a cross sectional view taken along the line II-II in Fig.

7; Fig. 9 is a time chart which shows the relation among operations of a spill valve and plungers, an injection pressure, and a rate of injection; Fig. 10 is a graph which shows variations in pressure in an upper needle chamber, a lower needle chamber, and an armature chamber; Fig. 11(a) is a time chart which shows movement of a needle of a spill valve according to the present invention; Fig. 11(b) is a time chart which shows movement of a needle of a spill valve of a conventional fuel injection pump; and Fig. 12 is a cross sectional view which shows a distributor type fuel injection pump according to a sixth embodiment.

Referring now to the drawings, particularly to Figs. 1 and 2, there is shown a distributor type fuel injection pump 10 according to a first embodiment of the invention.

The fuel injection pump 10 includes, as shown in Fig. 1, a drive shaft 1 which is rotatably supported in a pump housing 4 through a bearing 2 and a journal 3 and driven in synchronism with rotation of an internal combustion engine (not shown). A vane type feed pump 5 is rotated together with the drive shaft 1 to suck fuel out of a fuel tank (not shown) through a fuel inlet 6 and an intake port 7 and to pressurize the fuel. The pressurized fuel is then discharged from an outlet port 8 to a fuel gallery 14 through a fuel pipe (not shown). The intake port 7 and the outlet port 8 of the vane type feed pump 5 are connected through a pressure regulator valve (not shown) for regulating the fuel pressure discharged from the outlet port 8. The fuel gallery 14 is defined by an annular groove formed in an outer wall of a cylinder 12.

The first embodiment, as will be described later in detail, has a structure wherein a needle 52 of a spill valve 50 is disposed in the cylinder 12 so as to be movable along a given path into engagement with and disengagement from a valve seat 12a. This allows the length of a fuel flow path extending from a fuel pressure chamber 21 to the spill valve 50 to be minimized regardless of the diameter of the cylinder 12. Thus, the diameter of the cylinder 12 may be increased for providing a large volume of the fuel gallery 14.

The cylinder 12 is disposed in a distributor head 11 in engagement with an inner wall. A distributor rotor 13 is inserted at one end into the cylinder 12 and at the other end connected to the drive shaft 1 in alignment therewith so as to be rotatable along with the drive shaft.

The distributor rotor 13 has formed therein a pair of sliding bores 13a extending perpendicular to each other. In each sliding bore 13a, a pair of plungers 20 is slidably supported in fluid tight engagement with an inner wall of the sliding bore 13a. The fuel pressure chamber 21 is defined by opposite end surfaces of the plungers 20 and the inner wall of the sliding bore 13a.

A shoe 22 is attached to an outer end of each of the plungers 20. A roller 23 is rotatably retained by each of the shoes 22. An inner cam ring 24 is disposed rotatably in the pump housing 4, and an angular position thereof is adjusted by a timer device 40. The inner cam ring 24 has formed on its inner wall a cam surface on which cam protrusions of a number corresponding to the number of cylinders of the engine are formed. The rollers 23 engage the cam surface of the inner cam ring 24. The rotation of the distributor rotor 13 causes the rollers 23 to follow the cam protrusions of the inner cam ring 24 so that the rollers 23 reciprocate in a radius direction of the inner cam ring 24. The reciprocating motion of the rollers 23 is transmitted to the plungers 20 through the shoes 22 so that the plungers 20 move in a radius direction of the distributor rotor 13. When the plungers 20 move outward. the volume of the fuel pressure chamber 21 is increased to suck the fuel, while when the plungers 20 move inward, the volume of the fuel pressure chamber 21 is decreased to pressurize the fuel.

The fuel pressure chamber 21 communicates with a fuel path 15 and a delivery path 16 through a common path 17. Delivery paths 25 of a number corresponding to the number of the cylinders of the engine are formed in the cylinder 12. The delivery path 16 selectively communicates with one of the delivery paths 25 according to rotation of the distributor rotor 13. The delivery paths 25 communicate with delivery paths 26 formed in the distributor head 11 at all times, respectively, for supplying the pressurized fuel to injectors (not shown) through delivery valves 30.

The spill valve 50 has a valve casing 51 mounted on the pump housing 4. The needle 52 is, as described above, movable in the radius direction of the cylinder 12 into engagement with and disengagement from the valve seat 12a. The spill valve 50 is provided with a solenoid valve. When a solenoid 54 is deenergized, the needle 52 is urged by a compression spring 53 into disengagement from the valve seat 12a to establish fluid communication between the fuel gallery 14 and the fuel pressure chamber 21. Alternatively, when the solenoid 54 is energized, it will cause the needle 52 to be brought into engagement with the valve seat 12a against the spring force of the compression spring 53 to block the fluid communication between the fuel gallery 14 and the fuel pressure chamber 21.

A pulser 41 is disposed on an outer wall of the drive shaft 1 which has formed thereon protrusions 41a at regular intervals. An angular position sensor 42 is secured on the inner cam ring 24 which converts passage of the protrusions 41 a into pulse signals indicative of an angular position of the drive shaft 1 relative to the inner cam ring 24, that is, an angular position of the distributor rotor 13 relative to the inner cam ring 24.

An overflow valve 62 is installed in the distributor head 11 which reduces the pressure of the fuel flowing into a flow path 63 from the fuel gallery 14 and returns it to the fuel tank.

The spill valve 50 is, as shown in Fig. 2, mounted in the pump housing 4 so that a longitudinal center line C (i.e., a travel path) of the needle 52 may extend perpendicular to a longitudinal center line (i.e., an axis of rotation) of the distributor rotor 13 at a given interval away from each other. The cylinder 12 has formed in its inner wall an annular groove 12b define an annular gallery 18 together with an outer wall of the distributor rotor 13. A chamber is formed in the cylinder 12 to define an annular high pressure chamber 55 around a peripheral surface of the needle 52 which communicates with the fuel pressure chamber 21 through a fuel path 61, the annular gallery 18, the fuel path 15. and the common path 17 at all times. The fuel path 61 extends from the annular gallery 18 to the high pressure chamber 55 in a direction substantially perpendicular both to the center line C of the spill valve 50 and to the longitudinal center line of the distributor rotor 13. When the needle 52 is in a position away from the valve seat 12a, the fuel gallery 14 communicates with the annular gallery 18 through the fuel path 27 and the high pressure chamber 55.

Although in a transverse section of Fig. 2, the fuel gallery 14 is illustrated as being divided into two parts. these two parts practically communicate with each other through an annular path formed in another transverse section.

Operations of the fuel injection pump 10 will be described below.

FUEL SUCTION OPERATION When the spill valve 50 is in an Off position, the needle 52 is away from the valve seat 12a to establish fluid communication between the fuel path 27 and the high pressure chamber 55. When the plungers 20 are moved outward of the distributor rotor 13 according to rotation of the distributor rotor 13, the volume of the fuel pressure chamber 21 is increased to decrease the pressure therein. This causes the fuel in the fuel gallery 14 to be drawn into the fuel pressure chamber 21 through a fuel intake path consisting of the fuel path 27, the high pressure chamber 55, the annular gallery 18, the fuel path 15, and the common path 17. The communication between the delivery paths 25 and the delivery path 16 is blocked by the outer wall of the distributor rotor 13.

FUEL PRESSURIZING OPERATION When the distributor rotor 13 is further rotated, and the rollers 23 are pushed by the cam protrusions of the inner cam ring 24 to move the plungers 20 inward, the solenoid 54 of the spill valve 50 is energized to move the needle 52 toward the valve seat 12a against the spring force of the compression spring 53. Upon engagement of the needle 52 with the valve seat 12a, the communication between the fuel path 27 and the high pressure chamber 55 is blocked. The inward movement of the plungers 20 then pressurizes the fuel in the fuel pressure chamber 21. When the fuel pressure in the fuel pressure chamber 21 is elevated above a given level and when the communication between the delivery path 16 and one of the delivery paths 25 is established, the pressurized fuel in the fuel pressure chamber 21 is discharged from a corresponding one of the delivery valves 30 to the injector through the common path 17 and the delivery paths 16, 25. and 26. As described above, since the needle 52 of the spill valve 50 is supported in the cylinder 12 so as to be movable into engagement with and disengagement from the valve seat 12a formed in the cylinder 12. the length of the fuel path extending from the fuel pressure chamber 21 to the high pressure chamber 55 is shorter than that of a conventional fuel injection pump, resulting in a decrease in volume of fuel to be pressurized. The efficiency of pressurizing the fuel through the plungers 20 is thus greatly improved.

FUEL SPILLING OPERATION When the solenoid 54 of the spill valve 50 is turned off during the pressurizing operation, the needle 52 is moved out of engagement with the valve seat 12a with aid of the spring force of the compression spring 53 to establish the communication between the fuel path 27 and the high pressure chamber 55. The pressurized fuel in the fuel pressure chamber 21 then flows into the fuel gallery 14 through a fuel spill path consisting of the common path 17, the fuel path 15, the annular gallery 18, the high pressure chamber 55, and the fuel path 27. The fuel introduced into the fuel gallery 14 is returned to the fuel tank through the overflow valve 62.

When the fuel in the fuel pressure chamber 21 is discharged therefrom, the fuel pressure in the fuel pressure chamber 21 and the delivery path 26 is decreased to close the delivery valves 30 so that a fuel supply to the injectors is stopped to terminate a fuel injection operation. In this embodiment, the fuel path extending from the fuel pressure chamber 21 to the high pressure chamber 55 is, as already mentioned, shorter than that of a conventional fuel injection pump, thereby resulting in a decreased length of the spill path from the fuel pressure chamber 21 to the fuel gallery 14. This allows the supply of fuel to the injectors to be cut off quickly.

The control of the amount of fuel to be injected and injection timing is achieved by performing the above fuel suction, fuel pressurizing, and fuel spilling operations.

Usually, the pressure pulsation occurs upon fuel flow to the fuel gallery 14 when the spill valve 50 is opened, but it is greatly absorbed because the volume of the fuel gallery 14 is greater than that of the conventional fuel injection pump. Further, since the groove 12b is formed in the cylinder 12 to define the annular gallery 18, the variation in flow direction of the fuel caused by rotation of the distributor rotor 13 is small as compared with a structure wherein a groove is formed in a distributor rotor to define a fuel gallery.

Fig. 3 shows the fuel injection pump according to a second embodiment of the invention. The same reference numbers refer to the same parts. and explanation thereof in detail will be omitted here.

The fuel injection pump includes a cylinder assembly 70 consisting of two separate parts: a cylinder body 71 and a support member 72. The support member 72 slidably supports the needle 52 and defines therein a high pressure chamber 74 communicating with the annular gallery 18. The support member 72 is made of a cylindrical member having formed on an end portion threads and on the other end portion a flange 76 extending outward in a radius direction. The support member 72 is inserted into a bore 72a formed in the cylinder body 71 until the flange 76 is seated on an outer wall of the cylinder body 71 and secured by tightening a lock nut 77 on the threads of the support member 72. The outside diameter of the support member 72 is slightly smaller than the inside diameter of the bore 72a for preventing the support member 72 from being deformed upon insertion into the bore 72a. The bore 72a has formed on an inner wall a valve seat 73. When the needle 52 is seated on the valve seat 73, it blocks fluid communication between the high pressure chamber 74 defined around the needle 52 and a fuel path 75 formed in the support member 72.

The cylinder body 71 and the support member 72 are. as described above, made of separate members, thereby facilitating the formation of the valve seat 73 in the support member 72.

The support member 72 may be pressed into the bore 72a and secured on the cylinder body 71 with a screw. In this case, the support member 72 may be deformed upon insertion into the bore 72a. It is, therefore, advisable that the valve seat 73 be machined again after the support member 72 is pressed into the bore 72a.

Fig. 4 shows the fuel injection pump according to a third embodiment of the invention.

The fuel injection pump includes a cylinder assembly 80 and a spill valve 90. The cylinder assembly 80 consists of two separate parts: a cylinder body 81 and a cylindrical support member 82. The spill valve 90 includes a valve member 91 consisting of a plunger 92 and a valve head 93. The plunger 92 and the valve head 93 are slidably supported in the support member 82. A compression spring 94 urges the valve head 82 so as to bring the plunger 92 into disengagement from a valve seat 82a formed on an inner wall of the support member 82. A valve casing 95 is disposed above the support member 82 through a spacer 83. The valve casing 95 is pressed against the support member 82 by a cover 96 engaging a pump housing 4 in a screw fashion.

In operation, when a coil 97 is energized. it will cause an armature 98 to be drawn downward, as viewed in the drawing. the plunger 92 being seated on the valve seat 82a against a spring force of the compression coil spring 94 to block the fluid communication between the high pressure chamber 84 and the fuel path 85.

When the coil 97 is deenergized and the plunger 92 leaves the valve seat 82a to establish the fluid communication between the high pressure chamber 84 and the fuel path 85, the fuel gallery 14 communicates with the fuel pressure chamber (i.e., the fuel pressure chamber 21 in Fig. 1). When the plunger 92 leaves the valve seat 82a during the fuel pressurizing operation, the high pressure fuel is discharged from the high pressure chamber 84 to the fuel path 85. During the discharge of the high pressure fuel. the pressure of the fuel with pressure pulsation acts on opposite surfaces of the plunger 92 and the valve seat 82a so that the pressure acting on the plunger 92 is substantially canceled by the pressure acting on the valve seat 82a. This achieves stable movement of the plunger 91 in a valve opening direction.

In the third embodiment, since the spacer 83 and the valve casing 95 are disposed above the support member 82, and the cover presses the valve casing 95 toward the support member 82, it is easy to adjust an air gap defined between opposite surfaces of a stator around which the coil 97 is wound and the armature 98 to a given interval as compared with, for example, a structure wherein the support member 82 is mounted in the cylinder body 81, and the valve casing 95 is installed on the pump housing 4. This decreases the inevitable variation in air gap between individual fuel injection pumps.

Fig. 5 shows the fuel injection pump according to a fourth embodiment of the invention.

The fuel injection pump includes a cylinder assembly 100 and an accumulator 102. The cylinder assembly 100 includes a cylinder body 101 and a cylindrical support member 72. The accumulator 102 serves to damp pressure pulsation occurring during the fuel spilling operation of the fuel injection pump. The accumulator 102 includes a housing 103 secured on the pump housing 4 in screw fashion, a piston 104 exposed to the fuel gallery 14, and a compression coil spring 105 disposed between an inner wall of the housing 103 and the piston 104. The piston 104 is supported in the pump housing 4 to be movable in a vertical direction, as viewed in the drawing.

In operation, when the solenoid 54 of the spill valve 50 is turned off during the fuel pressurizing operation, the needle 52 leaves the valve seat 73 so that the high pressure fuel is discharged from the high pressure chamber 74 to the fuel gallery 14. The pressure pulsation is then generated in the fuel gallery 14 and transmitted to the piston 104 of the accumulator 102. As the pressure pulsation acting on the piston 104 is increased above a given level, the piston 104 is lifted upward against a spring force of the compression coil spring 105, while as the pressure pulsation is decreased below the given level, the piston 104 is moved downward, thereby damping the pressure pulsation well.

Figs. 6 to 8 show the fuel injection pump according to a fifth embodiment of the invention. The same reference numbers as employed in the above embodiments refer to the same parts. and explanation thereof in detail will be omitted here.

The pump housing 4 has formed therein a cam chamber 28 serving as a low pressure chamber which communicates with the fuel gallery 14 through a restrictor or orifice 29 for damping pressure pulsation generated in the fuel gallery 14 during the fuel spilling operation to maintain the pressure in the cam chamber 28 at a desired lower level without variation in pressure.

Figs. 7 and 8 show a structure of the spill valve 50. Fig. 7 is a cross sectional view taken along the line I-I in Fig. 6. Fig. 8 is a cross sectional view taken along the line II-II in Fig. 7.

The spill valve 50 is provided with a normally open solenoid valve which includes a solenoid portion 141 and a flow regulating portion 142. The solenoid portion 141 is secured on the pump housing 4. The flow regulating portion 142 is disposed within the cylinder 12.

The solenoid portion 141 includes a cylindrical solenoid housing 143 engaging a threaded hole 104a formed in the pump housing 4. On the bottom of the threaded hole 104a, a stop ring 155 is disposed to support the bottom of the solenoid housing 143.

A lift stopper 156 is mounted in a lower portion of the solenoid housing 143.

The solenoid housing 143 has disposed therein a stator 144 having formed therein an annular groove 145 within which a coil 146 is disposed. The stator 144 has formed in its central portion a through hole 147 into which a very hard bush 148 is pressed. A rod 150 connected to an armature 149 is slidably supported in the bush 148.

A cover 151 tightly engages an inner wall of the solenoid housing 143 to define an armature chamber 152 within which the armature 149 is disposed. A stopper 153 is disposed in a central portion of the cover 151 for restricting a vertical movement of the armature 149. Signal input terminals 54 are inserted into the cover 151 and the armature 149 and electrically connected to the coil 146 through lead wires. The armature chamber 152, as shown in Fig. 8, communicates with the cam chamber 28 through a path 70 at all times.

The flow regulating portion 142 includes a cylindrical needle body 158 which is inserted into a through hole 112 with a given clearance of the order of several um. The through hole 112 is formed in the cylinder 12 and extends perpendicular to an axis of rotation of the distributor rotor 13. The needle body 158 engages at its upper end the lift stopper 156. The needle body 158 has formed therein a sliding bore 160 supporting the needle 159 slidably. The sliding bore 160 communicates with an annular high pressure chamber 161. The needle body 158 has also formed therein fuel paths 162a and 162b communicating with the high pressure chamber 161. The needle 159 is connected to a lower end of the rod 150 and constantly urged by a compression coil spring 163 against the lift stopper 156 in a valve opening direction (i.e., an upward direction as viewed in the drawing). Thus, even if an interval between the pump housing 4 and the cylinder 12 is changed due to a difference in temperature characteristic between material (e.g., aluminum) of the pump housing 4 and material (e.g., iron) of the cylinder 12, that is, a difference in coefficient of thermal expansion, the needle 159 is kept engaging the lift stopper 156. In other words, even if the dimension of the pump housing 4 or the cylinder 12 is changed due to a change in ambient temperature, the needle 158 is moved as part of the structure of the spill valve 50 without distortion being generated in the cylinder 12.

This maintains a constant stroke of the needle 158.

The lift stopper 156 has formed therein a plurality of cut-out portions 156a establishing fluid communication between the fuel gallery 14 and an upper needle chamber 177 defined above the needle 159. The needle 159 has a small-diameter portion 159a to define a lower needle chamber 178 which communicates with the fuel gallery 14 at all times through the fuel path 162b so that the pressure in the fuel gallery 14 is transmitted to the lower needle chamber 178. Thus, the pressure in the fuel gallery 14 acts on an upper end surface 159b of the needle 159 so as to block the fluid communication between the fuel paths 162a and 162b and also acts on a lower end surface 159c of the needle 159 so as to establish the fluid communication between the fuel paths 162a and 162b. Fig. 7 shows the spill valve 40 being turned off with the needle 159 being away from the valve seat 158a formed in the needle body 158.

A longitudinal center line of the needle 159, as apparent from Fig. 7, extends perpendicular to a longitudinal center line of the distributor rotor 13 at a given interval away from each other. The cylinder 12 has formed therein an annular groove 12b to define the annular gallery 18 along with a circumferential wall of the distributor rotor 13. The cylinder 12 has also formed therein a path 169 connecting the annular gallery 18 and the fuel path 162a of the needle body 158. Specifically, the high pressure chamber 161 communicates with the fuel pressure chamber 21 at all times through the fuel path 162a, the path 169, the annular gallery 168, the fuel path 15, and the common path 17. A flow path from the path 169 of the cylinder 12 to the fuel path 162a of the needle body 158 is inclined at a given angle relative to a travel path of the needle 159. but it may be oriented at right angles relative to the travel path of the needle 159, as shown in Fig. 2 in the first embodiment, for minimizing the length of the flow path.

When the spill valve 50 is in an Off position. a given air gap is.

as shown in Fig. 7. formed between the upper surface of the stator 144 and the lower surface of the armature 149 so that the needle 159 is in a valve opening position. Specifically, the needle 159 is away from the valve seat 158a of the needle body 158. The fuel gallery 14, as shown in Figs. 6 and 7, communicates with the fuel pressure chamber 21 through the fuel paths 162a and 162b, the high pressure chamber 161, the path 169, the annular gallery 168, the fuel path 15, and the common path 17.

When the coil 146 is energized, it will cause the armature 149 to be drawn to the stator 144 so that the needle 159 is moved to a valve closing position and then seated on the valve seat 158a to block the fluid communication between the fuel gallery 14 and the fuel pressure chamber 21.

A spring retainer 165 is fixed on an inner wall of the pump housing 4. A compression coil spring 164 is disposed between the spring retainer 165 and a lower end surface of the needle body 158 and has a spring constant producing a spring load greater than the sum of a magnetic force generated upon energization of the coil 146 and a spring force of the compression coil spring 163. A coil chamber 166 within which the compression coil spring 163 is disposed communicates with the fuel gallery 14 through a path 167.

An accumulator 171 is mounted on the pump housing 4 which damps pressure pulsation generated during the fuel spilling operation of the fuel injection pump 10. The accumulator 171 includes a housing 172, a piston 173, a cover 174, and a compression coil spring 175. The housing 172 is integrally formed with the pump housing 4. The coil spring 175 is disposed between the piston 173 and the cover 174. The piston 173 is exposed to the fuel gallery 14 so as to move vertically according to variation in pressure in the fuel gallery 14 to damp it.

Operations of the fuel injection pump 10 of this embodiment will be discussed with reference to a time chart in Fig. 9.

FUEL SUCTION OPERATION When the solenoid 141 of the spill valve 50 is turned off, the needle 159 leaves the valve seat 158a of the needle body 158 with the aid of the spring force of the compression coil spring 163, thereby establishing the fluid communication between the fuel gallery 14 and the high pressure chamber 161. When the plungers 20 are then moved outward of the distributor rotor 13 according to rotation of the distributor rotor 13, the volume of the fuel pressure chamber 21 is increased to decrease the pressure therein. This causes the fuel in the fuel gallery 14 to be drawn into the fuel pressure chamber 21 through a clearance between the needle 159 and the valve seat 1 58a and a fuel intake path consisting of the fuel path 162a, the path 169, the annular gallery 18, the fuel path 15 and the common path 17. The communication between the delivery paths 25 and the delivery path 16 is blocked by the outer wall of the distributor rotor 13.

FUEL PRESSURIZING OPERATION When the distributor rotor 13 is further rotated, and the solenoid 141 of the spill valve 50 is turned on with a given timing, the needle 159 is moved to the valve closing position against the spring force of the compression spring 163 to block the fluid communication between the fuel gallery 14 and the high pressure chamber 161. When the rollers 23 are moved inward by the inner cam ring 24 according to the rotation of the distributor rotor 13 to displace the plungers 20, it will cause the fuel in the fuel pressure chamber 21 to be pressurized. When the fuel pressure in the fuel pressure chamber 21 is elevated above a given level and when the communication between the delivery path 16 and one of the delivery paths 25 is established, the pressurized fuel in the fuel pressure chamber 21 is supplied from a corresponding one of the delivery valves 30 to the injector through the common path 17 and the delivery paths 16, 25, and 26 and then injected under injection pressure at a rate of injection, as shown in Fig. 9.

FUEL SPILLING OPERATION When the solenoid 141 of the spill valve 50 is turned off during the pressurizing operation, the needle 159 is moved out of engagement with the valve seat 158a with the aid of the spring force of the compression coil spring 163 to establish the communication between the fuel gallery 14 and the high pressure chamber 161.

The pressurized fuel then spills from the fuel pressure chamber 21 and flows into the fuel gallery 14 through the clearance between the needle 159 and the valve seat 1 58a and a fuel spill path consisting of the common path 17, the fuel path 15, the annular gallery 18, the path 169, and the fuel path 162a. The fuel spill path is the same as the fuel intake path as discussed above, but it may be formed as a separate path from the fuel intake path.

The fuel introduced into the fuel gallery 14 is then returned to the fuel tank through the overflow valve 62. When the fuel in the fuel pressure chamber 21 is discharged therefrom, the fuel pressure in the fuel pressure chamber 21 and the delivery path 26 is decreased to close the delivery valves 30 so that a fuel supply to the injectors is stopped to terminate a fuel injection operation.

As discussed above, the needle body 158 is inserted into the through hole 112 formed in the cylinder 12. The needle 159 is slidably disposed within the needle body 158. The needle body 158 and the needle 159 are exposed to the fuel in the fuel gallery 14.

The upper needle chamber 177 and the lower needle chamber 178 are so designed that the fuel pressure in the fuel gallery 14 equally acts on the upper needle chamber 177 and the lower needle chamber 178. Therefore, when pressure pulsation of the fuel is generated during the fuel spilling operation, it is transmitted to both the upper needle chamber 177 and the lower needle chamber 178 without any delay, thereby achieving stable valve opening and closing movement of the needle 159. Specifically, the fuel pressures acting on the needle 159 to urge it to the valve opening position and to the valve closing position are equal to each other.

Fig. 10 represents experimentally measured variations in fuel pressure in the upper needle chamber 177 and the lower needle chamber 178. The graph shows that a time lag T between the pressure variation of the upper needle chamber 177 and the pressure variation of the lower needle chamber 178 is substantially zero so that the fuel pressures acting on the needle 159 upward and downward are balanced with each other.

Fig. 11(a) is a time chart representing movement of the needle 159 of the spill valve 50 over a range from the valve opening position to the valve closing position. Similarly, Fig. 1 lib) is a time chart representing movement of a needle of a conventional spill valve wherein pressures acting on the needle upward and downward are different from each other. It is to be noted that the needle 159 of the invention is moved to the valve closing position quickly (T1 < T2). and bouncing vibrations of the needle 159 is greatly damped as compared with the conventional spill valve.

The cam chamber 28, as discussed above, communicates with the armature chamber 152 through the path 70 for maintaining the pressure in the armature chamber 152 at a lower level and decreasing pressure pulsation in the armature chamber 152. The variation in pressure in the armature chamber 152 is shown by a two-dot chain line in Fig. 10. It will be noted that bouncing vibrations urging the armature 149 in the valve closing direction, caused by the pressure pulsation in the armature chamber 152 are dampened early.

Fig. 12 shows a sixth embodiment which is different from the fifth embodiment only in structure of the needle body 158. Other arrangements are the same, and explanation thereof in detail will be omitted here.

The needle body 158 is mounted at its lower end surface on a flat surface 181 formed on an inner wall of the pump housing 4 without use of the compression coil spring 164 for transmitting clamping forces acting on the solenoid housing 143 and the lift stopper 156 directly to the pump housing 4 through the needle body 158.

While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate a better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modification to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.

For example, in the above embodiments, the spill valve is turned on before the plungers 20 are moved, but it is possible to provide pre-strokes of the plungers 20 and to turn on the spill valve after the plungers 20 are moved. This achieves stable movement of the needle both in the valve opening and closing positions so that the amount of fuel to be injected can be adjusted with high accuracy.

Further, the above embodiments refer to the inner cam type fuel injection pump, but the present invention may be used with a face cam type fuel injection pump such as that taught in U. S. P. No.

5.273,017.

Claims

1. A distributor type fuel injection pump for an internal combustion engine comprising: a pump housing; a cylindrical member having formed therein fuel outlet paths; a distributor rotor disposed within said cylindrical member rotatably about a given axis of rotation in synchronism with rotation of the internal combustion engine for selectively delivering fuel to cylinders of the internal combustion engine through the fuel outlet paths of said cylindrical member; a fuel pressure chamber formed in said distributor rotor; pressurizing means for introducing fuel into said fuel pressure chamber and pressuring the introduced fuel according to a cam profile of a cam member; a first fuel spill path formed in said cylindrical member, communicating with said fuel pressure chamber; a second fuel spill path communicating with a spill outlet formed in said pump housing for discharging the fuel outside said pump housing; a third fuel spill path defined around an outer peripheral surface of said distributor rotor, communicating between said first and second fuel spill paths; a spill valve having a valve member movable in a valve bore formed in said cylindrical member along a given travel path for selectively establishing and blocking communication between said second and third fuel spill paths; and a fourth fuel spill path communicating between said third fuel spill path and the valve bore, extending in a direction substantially perpendicular both to the given travel path of the valve member of said spill valve and to the axis of rotation of said distributor rotor.

2. A distributor type fuel injection pump as claimed in claim 1, wherein the given travel path of the valve member is defined on a plane extending perpendicular to the axis of rotation of said distributor rotor.

3. A distributor type fuel injection pump as claimed in claim 2, wherein the given travel path of the valve member is away from the axis of rotation of said distributor rotor at a given distance.

4. A distributor type fuel injection pump as claimed in any one of claims 1 to 3, further comprising a fuel gallery formed between said pump housing and said cylindrical member, establishing communication between said second fuel spill path and the spill outlet. said spill valve establishing the communication between said second and third fuel spill paths to discharge the fuel in said fuel pressure chamber through the spill outlet.

5. A distributor type fuel injection pump as claimed in any one of claims 1 to 4, wherein said cylindrical member includes a support member having formed therein the valve seat and a cylinder body supporting the support member.

6. A distributor type fuel injection pump as claimed in any one of claims 1 to 5, wherein said spill valve includes a solenoid valve and a valve mounting member, the valve mounting member being urged into engagement with said cylindrical member.

7. A distributor type fuel injection pump as claimed in any one of claims 1 to 6, wherein said cylindrical member having formed therein a bore in which said distributor rotor is disposed, said third fuel spill path being defined by an annular groove formed in an inner wall of said cylindrical member defining the bore.

8. A distributor type fuel injection pump as claimed in any one of claims 4 to 7, wherein the fuel is introduced into said fuel pressure chamber through a portion of a fuel flow path consisting of said first.

second, third, and fourth fuel spill paths.

9. A distributor type fuel injection pump as claimed in claim 4, wherein the valve member of said spill valve has a first pressureenergized surface and a second pressure-energized surface, the first pressure-energized surface receiving thereon pressure of the fuel in said fuel gallery to urge the valve member for establishing the communication between said second and third fuel spill paths. the second pressure-energized surface receiving thereon the pressure of the fuel in said fuel gallery to urge the valve member for blocking the communication between said second and third fuel spill paths.

10. A distributor type fuel injection pump as claimed in claim 9, wherein the valve member is disposed within said fuel gallery.

11. A distributor type fuel injection pump as claimed in any one of claims 4, 9. and 10, further comprising a low pressure chamber communicating with said fuel gallery through a restrictor, and wherein said spill valve includes a solenoid valve having an armature connected to the valve member for moving the valve member along the given travel path. the armature being disposed within an armature chamber communicating with said low pressure chamber through a path.

12. A distributor type fuel injection pump as claimed in any one of claims 1 to 11, wherein said cylindrical member has formed therein a hole substantially extending perpendicular to the axis of rotation of said distributor rotor, and wherein a cylindrical support member which supports therein the valve member of said spill valve slid ably is inserted into the hole of said cylindrical member.

13. A distributor type fuel injection pump as claimed in claim 12.

wherein said cylindrical support member is disposed within the hole of said cylindrical member with a given clearance.

14. A distributor type fuel injection pump as claimed in claim 12 or 13, further comprising a pressing member and an urging member, the pressing member mounting said spill valve in said pump housing so as to press said cylindrical support member in a first direction, the urging member urging said cylindrical support member in a second direction opposite the first direction.

15. A distributor type fuel injection pump as claimed in claim 13, wherein said cylindrical support member engages at its end an inner wall of said pump housing.

16. A distributor type fuel injection pump as claimed in claim 4, further comprising an accumulator for absorbing pressure pulsation generated in said fuel gallery.

17. A distributor type fuel injection pump substantially as described herein with reference to the accompanying drawings.