GB2098673A

GB2098673A - Fuel injection device for internal combustion engine

Info

Publication number: GB2098673A
Application number: GB8209719A
Authority: GB
Original assignee: Yanmar Diesel Engine Co Ltd
Current assignee: Yanmar Co Ltd
Priority date: 1981-04-02
Filing date: 1982-04-01
Publication date: 1982-11-24
Also published as: DE3212010A1; IT1191181B; GB2098673B; IT8267432A0

Abstract

A fuel injection device for internal combustion engines having a plunger (59) of a comparatively small diameter, a servo piston (60) having a comparatively large diameter and adapted to actuate the plunger thereby to pressurize the fuel, and an injection nozzle (30) adapted to inject the fuel pressurized by the plunger. The fuel inlet port (77) to the servo piston chamber (76) and the outlet port 87 therefrom are opened and closed by a fluid-actuated valve member (61), the fluid actuation of the valve 61 in turn being controlled by a solenoid valve (111). A controller 20 determines when the solenoid valve is energised and de-energised whereby the rate and timing of the fuel injection are optimized over a wide range of engine operation. <IMAGE>

Description

SPECIFICATION Fuel injection device for internal combustion engine The present invention relates to a fuel injection device for internal combustion engines and, more particularly, to a fuel injection device having a plunger operatively connected to a servo piston having a diameter greater than that of the plunger, the servo piston being controlled by a solenoid valve to drive the plunger to pressurize a fuel to a high pressure thereby to inject the fuel through an injection nozzle.

Japanese Patent Publication Nos. 35254/1979 and 26651/1979 disclose fuel injection devices of the type mentioned above. These known fuel injection devices, however, sufferthefollowing disadvantages.

Namely, in the fuel injection device disclosed in the first-mentioned Patent Publication, the fuel inlet port and the fuel outlet ports of a servo piston chamber are opened and closed by means of a slide valve, and the hydraulic pressure acting on the end surface of the slide valve is controlled by opening and closing a spherical movable valve operatively connected to a solenoid valve. This fuel injection device, therefore, requires a solenoid of a large power as will be described later. In addition, this fuel injection device has inferior durability due to a rapid wear of the movable valve.

On the other hand, the fuel injection device disclosed in the second-mentioned Patent Publication has two valves operatively connected to a solenoid valve and adapted to directly control the fuel inlet and outlet of the servo piston chamber and, therefore, is not suited for injecting a large amount of fuel at a high pressure in a short period of time.

In view of the above-described problems of the known fuel injection devices, the present invention aims as its major object at providing a simple, small-sized and light-weight fuel injection device for internal combustion engine, in which, thanks to the use of a conical valve adapted to be controlled by a solenoid valve so as to open and close the fuel inlet to the servo piston chamber, the rate and timing of the fuel injection, as well as the engine speed, are controlled optimumlyovera wide range of engine operation and the injection of fuel art a high pressure is facilitated.

To this end, according to the invention, there is provided a fuel injection device for internal combustion engine comprising: a pump nozzle including a pump section, an injection nozzle section and a control section, the pump section having a servo piston of a comparatively large diameter and adapted to be driven by a part of the supplied fuel and a plunger of a comparatively small diameter and adapted to be driven by the servo piston to move reciprocatingly as a unit with the latter thereby to plunge the fuel, the injection nozzle section having a nozzle valve adapted to inject the fuel pressurized by the pump section, the control section having a solenoid valve for controlling the servo piston; a fuel supply pump for supplying the pump nozzle with the fuel; and a controller adapted to open and close the solenoid valve of the pump nozzle, so that a part of the supplied fuel is introduced into the servo piston chamber by the opening and closing operation of the solenoid valve under the control of the controller, whereby the servo piston is driven by the pressure of the fuel introduced into the servo piston chamber to permit a fuel injection from the injection nozzle section, wherein the improvementcomprises:: a servo piston chamber formed in the pump nozzle and adapted to receive the servo piston, the servo piston chamber having a servo piston chamber inlet port for introducing thereinto a part of the supplied fuel which acts as a working fluid for operating the servo piston and a servo piston chamber outlet port through which the supplied fuel is discharged from the servo piston chamber; a conical valve disposed to oppose to the servo piston chamber inlet port so as to open and close the latter; and a conical valve chamber accomodating the conical valve and having a fuel introduction port and a fuel discharge port so that the conical valve is driven in accordance with the introduction and discharge of the fuel into the conical valve chamber thereby to open and close the servo piston chamber inlet port, the introduction and discharge of the fuel into and out of the conical valve chamber being made by the solenoid valve.

By way of example only, certain illustrative embodiments of the invention will now be described with reference to the accompanying drawings in which: Fig. lisa sectional view of an essential part of an internal combustion engine incorporating a fuel injection device in accordance with a first embodiment of the invention; Fig. 2 is a vertical sectional view of a pump nozzle of the fuel injection device in accordance with the invention; Fig. 3 is an enlarged view of a portion Ill shown in Fig.2; Fig. 4 is an enlarged view of a portion IV shown in Fig. 2; Fig. 5 is a sectional view of an essential part taken along the line V-V of Fig. 2; Fig. 6 is an illustration of the essential part shown in Fig. 5 as viewed in the direction of an arrow VI;; Fig. 7 is a vertical sectional view taken along the lineVII-VII of Fig. 6; Fig. 8 is a cross-sectional view taken along the line VIII-VIII of Fig. 3; Fig. 9 is a partly-sectioned perspective view of a conical valve incorporated in the pump nozzle shown in Fig. 2; Figs. 10 and 11 illustrate the operation of the conical valve shown in Fig. 9; Fig. 12 is an enlarged perspective view of the solenoid valve seat shown in Fig. 2; Fig. 13 is a diagram showing the operation characteristics of a solenoid coil incorporated in the pump nozzle shown in Fig. 2; Figs. 14 and 15 are illustration of operation of the pump nozzle shown in Fig. 2; Fig. 16 is a vertical sectional view of a pump nozzle in accordance with a second embodiment of the invention;; Fig. 17 is an enlarged view of a portion XVII of Fig.

16; Figs. 18 and 19 are illustrations of operation of the pump nozzle shown in Fig. 16; Fig. 20 is a detailed illustration of the valve head portion of a modification of the conical valve of the pump nozzle shown in Fig. 2; Fig. 21 is a diagram showing the change in the opening area of the servo piston chamber in relation to the lift ofthe conical valve shown in Fig. 20; Figs. 22 and 23 are illustrations of construction and operation of a pump nozzle in accordance with a third embodiment of the invention; Figs. 24 and 25 are illustrations of construction and operation of a pump nozzle in accordance with a fourth embodiment of the invention; Fig. 26 is a partial sectional view of the pump nozzle of a conventional fuel injection pump; and Fig. 27 is a partial sectional view of another con ventional fuel injection pump.

Before turning to the detailed description of the preferred embodiments, a description will be made hereinunder asto the drawbacks ofthe prior arts disclosed in Japanese Patent Publication Nos.

35254/1979 and 26651/1979.

(1) Namely, the fuel injection device disclosed in Japanese Patent Publication No. 35254/1 979 shown in Fig. 26 has the following features. The fuel inlet port 211 and the fuel outlet port 212 of the servo piston chamber 207 are adapted to be opened and closed by means of a slide valve 202. The slide valve 202 is adapted to be operated by changing the hydraulic pressure acting on the end surface 206 thereof, through opening and closing the outlet port 204 and the inlet port 205 of a spherical movable valve 203 adapted to be operated by a solenoid valve 201.

When the areas of the outlet and inlet ports of the movable valve 203 are large, the masses of the mov able parts 201,202 are made correspondingly large, so that it is necessary to employ a solenoid 211 having a large capacityto achieve sufficiently vigorous operation of the movable parts. In addition, since the pressure-receiving area of the movable valve 203 is large, it is necessaryto use a pressure-balance type valve as the solenoid valve 201. In consequence, the construction of the fuel injection device itself is complicated impractically. In addition, this type of fuel injection device suffered the problem of lack of durability. Namely, the surface of the movable part 203 is worn rapidlyto rotate to deteriorate the oiltightness.In addition, the diameter of the valve seat is changed due to wear so that the balance of pres sure is deteriorated.

(2) Since a single control bore 208 is used for con trolling both of the inlet port 211 and outlet port 212 of the servo piston chamber 207, a conical projection 210, which is formed on the servo piston 209 for controlling the injection pattern in the injecting stroke adversely affect also the charging stroke.

On the other hand, in the fuel injection device dis closed in Japanese Patent Publication No.

26651/1979 shown in Fig. 27, the inlet port 303 and the outlet port 302 of the servo piston chamber 304 are directly opened and closed by valves 301 and 306 operatively connected to the solenoid valve 305.

Therefore, the size of the inlet port 303 and outlet port 302 of the servo piston chamber 304 are limited by the load received by the solenoid valve 305 and the attracting force of the solenoid 307, so that it is extremely difficult to pressurize a large amount of fuel to a high pressure in a short period of time and to discharge the same at the high pressure.

These problems, however, are overcome by the present invention as will be understood from the following description of the preferred embodiments. A fuel injection device of the first embodiment of the invention will be described hereinunderwith reference to Figs. 1 to 15. Referringfirstto Fig. 1,there is shown a fuel injection device Z of the first embodiment mounted on the cylinder head of a diesel engine Y. The fuel injection device Z has a pump nozzleX mounted in a pump nozzle receiving hole 6 formed in the cylinder head 2 and retained by a nozzle retainer 13 in such a manner that the nozzle attached to the end thereof projects into a working chamber4 defined on the piston 5 in the cylinder block 1.The fuel injection device further includes a fuel supply pump disposed at the outside of the diesel engine Y, and a controller 20 which controls a solenoid valve (described later) incorporated in the pump nozzle. The arrangement is such that the fuel is supplied into the pump nozzle X through a fuel pipe 10 and a fuel supply pipe 11 from a fuel tank 19 by the fuel supply pump 18, and the rate of injection of fuel into the working chamber4 is adjausted by controlling the solenoid valve of the pump nozzle X by means of a controller 20 in accordance with the input signal delivered by a sensor 21 which operates upon detect of the state of operation of the engine.In addition, the pressure at which the fuel is supplied to the pump nozzles is adjusted by means of a restriction valve 26 which is controlled by a controller 20' in accordance with the amount of fuel injection.

The construction of the pump nozzleX will be described in detail hereinunder.

As will be seen from Fig. 2, the pump nozzle X has an injection nozzle section 30 having a nozzle valve 32, a pump section 55 having a plunger 59 and a servo piston 60 for driving the plunger 59, and a control section 105 having a solenoid valve 111 adapted to control a servo piston 60 of the pump section 55, the sections being connected in series coaxially.

As will be seen from Figs. 2,4 and 7, the injection nozzle section 30 is composed of a nozzle body 31 slidably receiving the nozzle valve 32, a nozzle stop spacer 33 in the form of a short shaft and an injector cage 34. A nozzle spring seat 39 having a spring 36 for normally biasing the nozzle valve 32 in the closing direction is received by a nonle spring seat receiving hole40 formed continuously in the nozzle stop spacer 33 and the injector cage 34. The nozzle body 31, nozzle stop spacer 33 and the injector cage 34 are integrally attached to the end of a latermentioned plunger body 58 by means of a nozzle mounting nut 35. The end surface 33a of the nozzle stop spacer 33 adjacent to the nozzle stop spacer 33 abuts the upper end surface 32a of the nozzle valve 32 to limitthe upper end of the stroke of the nozzle valve 32.

A radial recess or groove 41 formed in the upper end surface of the injector cage 34 provides a communication between the plunger chamber 67 of a later-mentioned plunger body 58 and a feed valve chamber 68. Furthermore, the radial groove 41 is communicated with a fuel well chamber 38 formed in the end of the nozzle body, through a vertical bore 42 in the injector cage 34, inclined bore 43 of the nozzle stop spacer 33, and annular recess 44 and an inclined bore 45 formed in the nozzle body 31. The fuel pressurized to a high pressure is introduced into the fuel well chamber 38 through the fuel passage 46 between the groove 41 and the chamber 38. This passage, therefore, will be referred to as highpressure fuel passage 46, hereinafter.

Besides the groove 41, an inclined bore47 is formed in the upper end surface of the injector cage 34 so as to provide a communication between the nozzle spring seat receiving hole 40 and an inclined bore 83 of a later-mentioned plunger body 58, as will be seen from Fig. 7. A reference numeral 37 denotes a sim for adjusting the spring 36, while numeral 48 denotes parallel pins for circumferentially locating the plunger body 58, injector cage 34 and the nozzle stop spacer 33. A reference numeral 49 denotes a nozzle port.

As will be seen from Figs. 2,5 and 7, the pump section 55 has a plunger body 58 having a plunger chamber 67 for receiving a plunger 59, a servo piston body 57 having a servo piston chamber 76 for accomodating a servo piston 60, the servo piston body 57 cooperating with the plunger body 58 in constituting a pump body A, and a conical valve body 59 having a conical valve chamber 84 for accomodating a later-mentioned conical valve 61.

The plunger body 58, servo piston body 57 and the conical valve body 56 are connected in series coaxially by means of bolts 85,85, as will be seen from Fig. 5.

The servo piston chamber76 formed to axially penetrate the servo piston body 57 is coaxially communicated with the plunger chamber 67 formed axially through the plunger body 58. The servo piston chamber 76 and the plunger chamber 67 slidably receive the servo piston 60 of a larger diameter and a plunger 59 of a smaller diameter, respectively. The servo piston 60 and the plunger 59 are adapted to be driven as a unit reciprocatingly in accordance with the pressures of the fuel introduced into the servo piston chamber 76 and the plunger chamber 67.

Thus, the fuel injection pressure is determined by the ratio of cross-sectional area between the servo piston 60 and the plunger 59. The servo piston chamber 76 and the plunger chamber 67 are offset from the common axis of the servo piston body 57 and the plunger body 58, i.e. the pump body A, by a suitable distance S. A later-mentioned fuel charging passage 70 and a feed valve chamber 68 for accomodating a feed valve 62 are formed in the thick-wall portion 57a, 58a of the servo piston body 57 and the plunger body 58 presented as a result of the radial offset of the chambers.

The conical valve body 56 has a horizontal bore 71 of a suitable depth in the radial direction from one side thereof. The aforementioned fuel supply pipe 11 is screwed to the outer end portion of the horizontal bore 71. The horizontal bore 71 constitutes a passage for receiving the fuel which comes from the aforementioned fuel supply pump 18. This horizontal bore 71, therefore, will be referred to as "supplied fuel passage 71", hereinafter. The conical valve chamber 84 and a servo piston inlet port 77 are formed coaxially in the conical valve body 56 along the axis of the latter, so as to communicate with and cross the supplied fuel passage 71 at a right angle.

The servo piston chamber inlet port 77 is formed so as to make visible the top surface of the servo piston 60 which has been inserted into the servo piston chamber 76 through the servo piston chamber inlet port 77. The open end surface of the servo piston chamber inlet port 77 adjacent to the supplied fuel passage 71 serves as a valve seat 79 for a latermentioned conical valve 61. On the other hand, the conical valve chamber 84 extends from the upper end surface of the conical valve body 56 towards the supplied fuel passage 71, and the conical valve chamber 84 receives the conical valve 61 axially slidably.

The conical valve 61 has a bottom-equipped cylin drical form with its end adjacent to the supplied fuel passage 71 being closed, and is adapted to be moved up and down by the control of the back pressure in the conical valve chamber 84, with its end seated on or spaced from the valve seat 79 on the servo piston chamber inlet port 77, thereby to open and close the latter. The conical valve 61 is biased by a suitable force exerted by the spring 65 fitted therein towards the conical valve seat 79.

A disc-shaped solenoid valve seat 106 is attached to the portion of the conical valve chamber 84 close to the outer end surface of the latter. The lower end surface of the solenoid valve seat 106 closes one end of the conical valve chamber 84. As will be seen from Fig. 12, the solenoid valve seat 106 is constituted by a disc-shaped member of a suitable thickness. The lower end surface 106d of the solenoid valve seat 106 serves as the member which limits the lift of the conical valve 61. Namely, the open end surface 61 a of the conical valve 61 abuts the solenoid valve seat 106 when the conical valve 61 opens.

The solenoid valve seat 106 has a peripheral surface 106a of a large diameter and a peripheral surface 106b of a small diameter. The solenoid valve seat 106 is received by a solenoid valve seat receiving hole 56a formed in the upper end of the conical valve body 56 coaxially with the conical valve chamber 84, with the end surface 106d closertothe small-diameter peripheral surface 106b facing the conical valve chamber 84. In this state, an annular groove 140 of a suitable width is formed between the small-diameter peripheral surface 106b and the peripheral wall ofthe solneoid valve seat receiving bore 56a. The other end surface 106c adjacent to the large-diameter peripheral surface 1 06a confronts the through bore 146 of the solenoid spacer 107 which serves as a part of the conical valve chamber outlet passage 165 which will be explained later in connection with Fig. 3. The space 170 formed by the through bore 146 of the solenoid spacer 107 is intended for receiving one 136 of the valve bodies of the solenoid valve which will be described later. This space, therefore, is referred to as solenoid valve chamber 170. The solenoid valve seat 106 has a radial horizontal bore 141 of a suitable size opening in the small-diameter peripheral surface thereof.The horizontal bore 141 is made to communicate with the solenoid valve chamber 170 through a small aperture 142 formed in the axial part of the solenoid valve seat 106, and is communicated, through the aforementioned annular groove 140, with an inclined bore 97 formed in the conical valve body 56 and having one end opening to the aforementioned supplied fuel passage 71. The small aperture 142 serves as an introduction port for introducing the fuel into the conical valve chamber. This aperture 142, therefore, will be referred to as a fuel introduction port 142.

Thus, the solenoid valve chamber 170 and the supplied fuel passage 71 are communicated with each other through a fuel introduction port 142, horizontal bore 141, annular bore 140 and the inclined bore 97. Therefore, the fuel introduction port 142 formed in the solenoid valve seat 106 and the annular groove 140 in combination will be referred to as a "fuel supply passage 180". A reference numeral 143 designates a valve seat for the solenoid valve 111, formed on the end of the fuel introduction port 142 adjacent to the solenoid valve chamber 170.

The fuel supply passage 180, therefore, is opened and closed by the solenoid valve 111 which clears and rests on the valve seat 143 selectively. Four axial bores 144 are formed in the axial direction of the solenoid valve seat 106 around the fuel introduction port 142. These through bores 144 provide comminication between the solenoid valve chamber 170 and the conical valve chamber 84, and serves as a fuel passage through which the fuel introduced into the solenoid valve chamber 170 is supplied into the conical valve chamber 84 or, alternatively, the fuel in the conical valve chamber 84 is discharged to the solenoid valve chamber 170. The through bore 144, fuel passage 180 and an inclined bore 97 of the conical valve body 56, which are connected in series, serve as a fuel passage for introducing the fuel from the supplied fuel passage 71 into the conical valve chamber 84.These passages, therefore, will be referred to as conical valve chamber fuel introduction passage 139 (See Fig. 3). Therefore, when the fuel introduction port 142 is kept opened, the fuel in the supplied fuel passage 71 is introduced into the conical valve chamber 84 through the conical valve chamber fuel introduction passage 139. To the contrary, when the fuel introduction port 142 is closed, the fuel received by the conical valve chamber 84 is introduced into the through bore 145 of the solenoid spacer 107, via the through bores 144, and further into a fuel return pipe 124 thorugh a fuel passage 152 formed in a static core 110 o,'the control section 105 which will be detailed later.

On the other hand an annular groove 80 of a suitable width is formed in the sliding surface of the conical valve 61 opposing to the wall of the conical valve chamber 84. As will be seen from Fig. 5, this annular groove 80 communicates, when the conical valve 61 is closed, with an oil relief port 88 which is formed radially through the conical valve chamber 84. However, when the conical valve 61 is kept opened, the annular groove 80 does not communi cate with the oil relief port 88. This selective com munication is achieved by a suitable selection of the axial position of the annular groove 80.The oil relief port 88 is communicated at its one end with the servo piston chamber 76 through the servo piston chamber outlet port 87 and connected at its other end to an external fuel tank 19 through the orifice 89 and a groove 90 formed in the lower end surface of the conical valve body 56. A series of fuel circuit constituted by the servo piston outlet chamber 87, annular groove 80, oil relief port 88 and the groove 90 will be referred to as "working oil relief passage 94", hereinunder. The groove 90 is communicated with the back-pressure side of the servo piston 60 through the inclined bore 93 formed in the plunger body 58 and the vertical bore 92 formed in the servo piston body 57. The leak oil from the servo piston 60 is discharged to the fuel tank 19 via the vertical bore 92 and the inclined bore 93.Therefore, when the conical valve 61 is opened, the servo piston chamber outlet port 87 is closed so that the fuel introduced from the servo piston chamber inlet port 77 into the servo piston chamber76 acts to displace the servo piston 60 downwardly, whereas, when the conical valve 61 is closed, the servo piston chamber outlet port 87 is opened so that the servo piston 60 is moved upwardly by the pressure of the fuel introduced into the plunger pump chamber 67 through a later-mentioned feed valve 69.

Furthermore, a feed valve chamber 68 is formed in the lower end of the plunger body 58, such that its one end opens to the groove 41 formed in the injector cage 34. The feed valve chamber 68 is communicated with the plunger chamber 67 through the groove 41. The upper end of the feed valve chamber 68 is communicated with the aforementioned supplied fuel passage 71 through the inclined bore 74 of the plunger body 58, the vertical bore 73 of the servo piston body 57 and the vertical bore 72 of the conical valve body 56. A feed valve 62 having small apertures 69,69 is fitted in the feed valve chamber 68.

The feed valve 62 is normally biased in the closing direction by the force of the spring 64. The series of fuel passages 70 leading from the supplied fuel passage 71 to the feed valve chamber 68 is for charging the plunger chamber 67 with the fuel and, therefore, will be referred to as a "fuel charging passage" and designated at a numeral 70.

As will be clearly seen from Fig. 7, a passage 86 is formed to provide a direct communication between the supplied fuel passage 71 and the nozzle spring seat receiving bore 40 formed in the injector cage 34.

The passage 86 is constituted by the inclined bore 81 in the conical valve body 56, vertical bore 82 in the servo piston body 57, the inclined bore 83 of the plunger body 58 and the inclined bore 47 in the injector cage 34, as will be seen from Fig. 7. This passage serves as a passage for introducing the fuel into the nozzle spring seat receiving bore 40 for producing a back pressure acting on the nozzle valve 32. Since the opening pressure of the nozzle valve 32 is determined by the sum of the load imposed by the nozzle spring 36 and the back pressure acting on the nozzle valve 32, the passage 86 will be referred to as "noz zle valve biasing fuel passage 86", hereinafter.A reference numeral 63 designates parallel pins for cir cumferentially locating the conical valve body 56, servo piston body 57 and the plunger body 58 with respect to one another.

The control section 105 is constituted, as shown in Figs. 2 and 3, the solenoid coil 116 the exciting tim ing and exciting period of which are determined by the controller 20, and a solenoid valve 111 which is driven to open and close by the attracting force of the solenoid coil 116.

The solenoid valve 111 is formed of a four-way slide rod provided at its both ends with needle-like valve members 135, 136 (ora rod provided at both ends with grooves communicating with each other).

A disc-shaped flange 137 is formed adjacent to one 135 ofthe valve members. The valve member 136 having long four-way sliding portion is inserted into a straight cylindrical active core 112 having a step ped inner peripheral surface from the large-diameter side of the latter, such that the flange 137 abuts the axial end surface 1 12a of a step formed on the inner peripheral surface of the active core 112. A flangeequipped elongated cylindrical stator core 110 is placed at the same side of the active core 112 as the valve body 136 projecting downwardly from the lower end surface of the active core 112, such that a lower spring 113 is interposed between the stator core 110 and the active core 112. The stator core 110 and the active core 112 are received by a core receiving bore 162 in a flange-equipped elongated cylindrical core guide 109.The upper portion of the core guide 109 is a thread hole 164 of a small diameter communicated with a core receiving hole 162. An upper seat 119 provided with an axial fuel relief port 148 therein is received by the threaded hole 164. The core guide 109 is fastened, together with the flange of the stator core 110, to the aforementioned solenoid spacer 107 by means of a lower support 115 screwed to the conical valve body 56.

Between the upper seat 119 and the flange of the solenoid valve 111, disposed is an upper spring 114 having a smaller spring constant and smaller initial load than the lower spring 113. The upper valve member 135 of the solenoid valve 111 and the lower valve member 136 of the same are positioned to oppose to the valve seat 149 of the upper seat 119 and the valve seat 143 of the aforementioned solenoid valve seat 106 so as to be able to contact these valve seats. The solenoid valve 111 is normally biased together with the active core 112 towards the upper seat 119 by the difference of force between the upper spring 114 and the lower spring 113, so as to close the fuel relief port 148.

The lift H ofthe solenoid valve 111 (See Fig. 3) is selected to be smaller than the lift H of the conical valve 61. This is to actuate the solenoid valve 111 rapidly and effectively within the stroke range of large horizontal attracting force, by making use of the characteristics of the solenoid coil 116 that the horizontal attracting force is increased as the stroke of the solenoid valve 111 is decreased. The oil relief port 148 in the upper seat 119 is communicated with the through bores 144 of the solenoid valve seat 106, through the communication bores 147, 147 of the active core 112, and through a communication bore 152 (see Fig. 8) formed between the solenoid valve receiving bore 151 and the four-way sliding portion of the solenoid valve.A series of passage including the through bore 144 of the solenoid valve seat 106, internal space of an upper support 118 screwed to the outside of the upper seat 119 and the passage leading from the internal space 150 to a single-end pipe joint 123 will be referred to as "conical valve chamber outlet passage 165, hereinafter. In this case, the valve seat 149 of the upper seat 119 serves as a discharge port for discharging the fuel from the conical valve chamber 84. The valve seat 149, therefore, will be referred to as a "fuel discharge port 149", hereinafter.

As will be seen from Fig. 3, the support 115 has a large-diameter portion 115b having a threaded inner peripheral surface and a small-diameter portion 115c provided with a smooth inner peripheral surface.

The open end of the small-diameter portion 115c is closed by a bottom plate 115f. Thus, the support 115 as a whole has a bottom-equipped cylindrical form.

A support cap mount 115e of small diameter having a threaded outer peripheral surface for engaging a support cap 118 is formed on the bottom plate 115f.

A core guide receiving bore 1159 for receiving the aforementioned core guide 109 is formed in the central axis portion of the support cap mount 1 15e so as to extend through the bottom plate 115f. The core guide receiving bore 1159 receives the core guide 109 having a flange 109a which is retained by a step surface 115d formed between the large-diameter portion 11 sub and small-diameter portion 11 sic of the support 115, while the other end 1 09b of the core guide 109 is projected outwardly from the upper end surface of the aforementioned support cap mount 115e. A nut member 120 is screwed to the end 109b of the core guide 109 projected outwardly. The core guide 109 and the support 115 are coupled axially and detachably to each other by tightening this nut 120.An annular space 115a of a suitable size is formed between the small-diameter inner peripheral surface of the support 115 and the outer peripheral surface of the core guide 109. Furthermore, the aforementioned solenoid coil 116 is accomodated by the annular space 11 spa. By arranging such that the solenoid coil 116 is accomodated by the annular space between the support 115 and the core guide 109 which are coupled to each other in the axial direction by the nut 120, the tightening force of the nut 120 acts between the step surface 1 15d and the flange 109a of the core guide 109 but does not directly act on the solenoid coil 116, so that the undesirable breakdown of the solenoid coil due to excessive tightening of the nut 120 is completely avoided. In addition, the support 115 and the core guide 109 are easily connected to and disconnected from each other without rotating these members relatively to each other, simply by screwing the nut 120 of a small diameter. Therefore, the undesirable damaging of the leads 11 6a of the solenoid coil 116, attributable to the contact with the edges of the lead ports 115h formed in the support 115, is avoided perfectly. The solenoid core 116, in combination with the support 115 and the core guide 109, constitute a block which is detachably screwed to the upper end opening 56a of the conical valve body 56 together with the support 115 and the core guide 109.

As shown in Figs. 1 and 4, the portion 56b of the pump nonle X above the upper end surface of the conical valve body 56, i.e. the portion adjacent to the support 115, is projected to the outside of the pump nozzle mounting hole 6 of the engine body. Therefore, as the support 115 is detached from the conical valve body 56 together with the solenoid coil 116 and the core guide 109, the solenoid valve 111, active coil 112 and the stator core 110 are exposed to the outside. Furthermore, as the solenoid spacer 107 and the solenoid valve seat 106 are removed, the conical valve 61 can easily be withdrawn from the conical valve chamber 84.

On the other hand, the axial center of the solenoid coil 116 is positioned belowthe level ofthe axial center of the active core 112, so that the solenoid coil 116 may attract the active core 112 downwardly when the solenoid coil 116 is energized. Thus, when the solenoid coil 116 is energized, the solenoid valve 111 is lowered together with the active core 112 by the attracting force of the solenoid coil 116, so that the lower valve member 136 closes the fuel introduction port 143 of the conical valve chamber 84 while opening the fuel discharge port 149.To the contrary, as the solenoid coil 116 is de-energized, the attracting force is dismissed to perm it the solenoid valve 111 to be raised again upwardly by the difference of force between the lower spring 113 and the upper spring 114, so that the fuel introduction port 143 of the conical valve chamber 84 is opened while the fuel discharge port 149 is closed. By rotating the upper seat 119 to change the axial position of the upper seat relatively to the solenoid valve 111, it is possible to suitably adjust the opening degree and the stroke of the solenoid valve 111. Reference numerals 10, 10a, Ob and 10c denote fuel pipes for respective cylinders in the case of a multi-cylinder engine.In Fig. 3, numeral 117 denote a yoke, while a reference numeral 121 denotes a lock nut for the upper seat 119, while numeral 122 in Fig. 2 denotes pipe joint bolts. Numerals 124, 124a, 124b and 124c denote fuel returning pipes for respective cylinders, while a numeral 126 denotes a connection terminal of the solenoid coil 116.

In Fig. 1, a relief valve 26 the pressure of which is controlled by a controller 20' shunts from and connected to an intermediate portion (fuel pipe 10) of the fuel supply passage P leading from the fuel supply pump 18 to the fuel inlet port71 ofthe pump nozzle X. The controller 20' operates in response to the changes in the fuel injection rate of the pump nozzle X and the engine speed so as to vary the opening of the fuel relief valve seat in the relief valve 26 thereby to control the fuel injection pressure in accordance with the fuel injection rate and the engine speed. Thus, the relief valve 26 and the controller20' in combination constitutes a pressure reg ulator Q forthe fuel supply passage P.

The operation and the effect of the fuel injection device in accordance with the first embodiment of the invention will be described with reference to Fig.

14 and Fig. 15 which schematically show the fuel injection device described hereinbefore. In operation, the fuel supply pump 18, driven by the engine Y, supplies the fuel from the fuel tank 19 to the pump nozzle, and the solenoid valve 111 in the pump nozzle X is suitably controlled by the controller20 in adcordance with a signal from a sensor 21 attached to the fly-wheel 22 of the engine Y, in synchronism with the operation of the engine Y.

On the other hand, the fuel relief valve seat in the relief valve 26 attached tithe fuel pipe 10 is controlled to open and close by the controller 20' in accordance with the change in the rate of fuel injection and the engine speed in such a manner as to permit a part of the fuel to be returned to the fuel tank 19 thereby to adjust the pressure of the fuel supplied to the pump nozzle. An accumulator 25 functions to absorb the pulsation of pressure of the fuel discharged from the fuel supply pump 18.

The operation of the pump noale X when the solenoid coil 116 is energized will be explained first with reference to Fig. 14. The solenoid coil 116 is energized as it is supplied with electric power by the controller 20, to produce an attracting force to attract the solenoid valve 111 downwardly, so that the fuel introduction port 143 is closed while the fuel discharge port 149 is opened in the conical valve chamber 84. Then, the fuel in the conical valve chamber 84 is returned to the fuel tank 19 through the conical valve chamber fuel discharge passage 165 and then through the fuel return pipe 124.As the fuel is discharged from the conical valve chamber 84, a pressure difference is established across the conical valve 61, so that the conical valve 61 is moved upward by the fuel pressure in the supplied fuel passage 71 thereby to open the inlet port 77 of the servo piston chamber 76. The fuel in the supplied fuel passage 71 is introduced into the servo piston chamber76 as the servo piston chamber inlet port 77 is opened. At this time, since the servo piston chamber outlet port 87 is blocked by the sliding surface of the conical valve 61, the servo piston 60 is depressed by the fuel downwardly. As the servo piston 60 is depressed downwardly, the plunger 59 is depressed downwardly and, in consequence, the fuel in the plunger chamber 67 is pressurized to a level high enough to open the feed valve 62.Simultaneously with the opening of the feed valve 62, the fuel pressure in the fuel well chamber 38 is increased drastically to open the nozzle valve 32, so that the fuel in the plunger chamber 67 is successively injected into the working chamber 4 via the highpressure fuel passage 46 and through the nozzle ports 49. Then, as the plunger 59 comes down to the lower iimit position of the lift, the fuel pressure in the nozzle fuel well chamber 38 is lowered so that the nozzle valve 32 is closed by the force of the spring 36 acting on the nozzle valve 32 and by the pressure of the fuel introduced into the nozzle spring receiving hole 40 through the nozzle valve biasing fuel passage 86, thereby to terminate the injection of the fuel.

Then, the operation of the pump nozzle performed when the solenoid coil 116 is de-energized will be explained with reference to Fig. 15. As the solenoid coil 116 is de-energized, the attracting force on the solenoid valve 111 is dismissed so that the solenoid valve 111 is moved upward by the force of the spring, thereby to open the fuel introduction port 143 of the conical valve chamber 84 while closing the fuel discharge port 149 of the same.As the fuel introduction port 143 is opened, the fuel in the supplied fuel passage 71 is allowed to flow from the conical valve chamber introduction passage 139 into the conical valve chamber 84, so that the fuel pressure across the conical valve 61 is balanced so that the conical valve 61 is moved downwardly by the force of the spring 65, thereby to close the servo piston chamber inlet port 77. As the conical valve 61 moves downward, the annular groove 80 formed in the sliding surface thereof is brought into communication with the oil relief port 88, so that the servo piston chamber outlet 87 is opened to permit the fuel to be returned from the servo piston chamber 76 into the fuel tank 19 through the fuel relief passage 94. In consequence, the fuel pressure in the servo piston chamber 76 is lowered to lower also the pressure in the plunger chamber 67.In consequence, the highpressure fuel in the fuel charging passage 70 flows into the plunger chamber 67 forcibly opening the feed valve 62. The plunger 59 and the servo piston 60 are moved upwardly by the pressure of the fuel.

The internal combustion engine Y operates continuously, by a cyclic repetition of the injection stroke illustrated in Fig. 14 and the charging stroke illustrated in Fig. 15.

The rate of injection of fuel from the pump nozzle Xis determined by the time length of charging of the fuel, i.e. by the length of return stroke of the plunger 59. The time length of charging can be adjusted by suitably selecting the time length of energization of the solenoid coil 116, while the return speed of the servo piston 60 is adjusted by suitably restricting the flow of fuel from the servo piston chamber 76 by means of an orifice 89 disposed in the fuel relief passage 94, and by varying the initial load of the spring 64.

Hereinafter, a fuel injection device in accordance with the second embodiment of the invention will be explained in connection with Figs. 16 to 19. As will be seen from Fig. 16, in the fuel injection device of the second embodiment, the servo piston 60 is driven through opening and closing the servo piston chamber inlet port 77 by means of a conical valve 61 which is under the control of the solenoid valve 111, thereby to inject the fuel art a high pressure from the injection nozzle 30, as in the case of the first embodiment Also, the arrangement of control members such as solenoid coil 116 in relation to the conical valve is substantially equal to that in the first embodiment.This second embodiment, however, has a different method of control of the back pressure of the conical valve 61 and the method of forming the conical valve chamber outlet passage 165 from those of the first embodiment.

Namely, in this second embodiment, a small through bore 156 is formed in the side wall of the upstream side portion of the end of the conical valve 61 exposed to the supplied fuel passage 71, so as to provide a communication between the inside and outside of the conical valve 61. This through bore 156 serves as the fuel introduction port 156 of the conical valve chamber 84. A fuel discharge port 155 from the conical valve chamber 84, having a greater diameter than the aforementioned fuel introduction port 156, is formed in the solenoid valve seat 128 which is secured to close the upper open end of the conical valve chamber 84. Only the fuel discharge port 155 out ofthe ports 155 and 156 is opened and closed by the valve member 136 of the solenoid valve 111 which is integrally connected to the active core 131 which is driven up and down by the attracting force of the solenoid coil 116.Namely, in this second embodiment, the back pressure of the conical valve 61 is controlled by suitably opening and closing the fuel discharge port 155 of the conical valve chamber 84 by the operation of the solenoid valve 111. The conical valve 61 is moved back and forth by the controlled back pressure thereby to open and close the servo piston chamber inlet port 77. The fuel coming out from the fuel discharge port 155 is discharged to a fuel return pipe 124 through a communication port 148 formed in the stator core 133 attached to the axial portion of the solenoid coil 116 as shown in Fig. 16.

In this pump nozzle, as the solenoid coil 116 is energized, the solenoid valve 111 is moved upward through the active core 131 by the attracting force of the solenoid coil 116asshown in Fig. 18, so thatthe fuel discharge port 155 of the conical valve chamber 84 is opened to permit the fuel to be discharged from the conical valve chamber 84 through the fuel discharge port 155. Simultaneously, the fuel in the supplied fuel passage 71 flows into the conical valve chamber 84 through the fuel introduction port 156.In this case, since the cross-sectional area of the fuel introduction port 156 is selected to be smaller than that of the fuel discharge port 155, the fuel pressure in the conical valve chamber 84 becomes lower than the fuel pressure in the supplied fuel passage 71, so that the conical valve 61 is moved upward by this pressure differential thereby to open the servo piston chamber inlet port 77.

On the other hand, as the solenoid coil 116 is deenergized as shown in Fig. 19, the active core 131 is relieved from the attracting force exerted by the solenoid coil 116, so that the solenoid valve 111 is depressed downwardly by the force of the spring 132 to close the fuel discharge port 155 of the conical valve chamber 84. As a result of the closing of the fuel discharge port 155, the fuel pressure is balanced across the conical valve 61, so that the conical valve 111 is moved downward by the force of the spring 65 thereby to close the servo piston chamber inlet 77.

The manners of operation of respective parts of the pump nozzle, after the opening or closing of the servo piston chamber inlet 77 by the conical valve 61, are not described here because they are materially identical to those in the first embodiment.

In Fig. 16, a reference numeral 130 denotes a core guide, while 133 denotes a stator core. All other parts or members are designated at the same refer ence numerals as those in the first embodiment.

In the pump nozzlesX of the first and second embodiments, the servo piston chamber inlet port 77 is opened and closed by the conical valve 61, so that it is possible to preserve a large diameter of the servo piston inlet port 77. In addition, since the valve seat 79 of the conical valve 61 is disposed in the close proximity of the servo piston chamber 76, it is possible to promptly introduce the fuel into the servo piston chamber 76 to permit an injection of fuel at a high pressure in a short period of time.

In addition, since a part of the fuel is introduced directly into the nozzle spring seat receiving bore 40, it is possible to reduce the size of the mounting portion ofthe nozzle spring 36 which determines the opening pressure of the nozzle valve 32.

Furthermore, by making the fuel coming out from the conical valve chamber 84 flow through the conical valve chamber discharge passage 165 formed in the axial portion of the solenoid coil 116, the solenoid coil 116 can effectively be cooled by the fuel coming out of the solenoid valve chamber 84 to make it possible to avoid any deterioration of the attracting performance of the solenoid coil due to heating and to make sure of the safe operation of the solenoid valve 111.

The conical valve 61, solenoid valve 111, solenoid coil 116, active cores 112,131 and the stator cores 112,113 are positioned in the close proximity of one another, and there is no movable member which would impede the attracting operation by the solenoid coil 116 for driving the active cores 112, 113. It is, therefore, possible to make an efficient use of the magnetic force exerted by the solenoid coil.

Furthermore, since the conical chamber outlet passage 165 is formed to extend linearly from the conical valve chamber 84 through the axial part of the control section, the fuel coming out from the conical valve chamber 84 can flow smoothly through the conical valve chamber outlet passage 165 to ensure the rapid and safe operation of the solenoid valve 111 or the conical valve 61.

Fig. 20 shows a modification of the conical valve of the pump nozzle in the first and second embodiments described heretofore. This conical valve is provided on its head portion with a projection of a suitable size. This projection suitably varies the area of the passage of the fuel flowing into the servo piston chamber thereby to optimize the rates of fuel injection in the pre-injection period and the main injection period to achieve an improvement in the fuel injection characteristics of the pump nozzle.

As shown in Fig. 20, the conical valve 61 has a bottom-equipped cylindrical form closed at its one side adjacent to the supplied fuel passage 71, and is adapted to be moved up and down along the wall of the conical valve chamber 84 by a control of the back pressure in the conical valve chamber 84 to position the tapered surface on the valve head 61 e thereof in contact with or apart from the valve seat 79 of the servo piston chamber inlet port 77 to close and open the latter. The valve head 61 e of this conical valve 61 is provided with a projection 61a of a suitable size, formed integrally therewith.As the conical valve 61 moves to open and close the inlet port77, the projection 61 a is moved in the axial direction back and forth to suitably vary the area of the fuel flowing from the supplied fuel passage 71 into the servo piston chamber 76 in the beginning period of opening of the conical valve 61. More specifically, the projection 61 a is composed of a first throttle portion 61 b of a diameter slightly smallerthan the inside diameter of the servo piston chamber inlet port 77, a second throttle portion 65d of a diameter smaller than that of the firstthrottle portion 51 band a tapered shaft portion 61 c formed between the first throttle portion 61 b and the second throttle portion 61 d.Although the second throttle portion 61 d is illustrated by full line in Fig. 20 to have a straight shaft-like form, this can have such a taper that its diameter is gradually increased towards the end thereof as shown by chain line 61d' or that its diameter is gradually decreased towards the end as shown by chain line 61d". By suitably selecting the form of the second throttle portion 61d, it is possible to vary the fuel throttling characteristics in the beginning period of the opening of the conical valve 61 and, hence, the initial fuel injection characteristics.

In this modification, the fuel introduced into the servo piston chamber 76 in the beginning period of opening of the conical valve 61 is restricted by the projection 61 a formed on the valve head portion of the conical valve 61, so that the rate of change of the opening area A of the inlet port 77 in relation to the valve lift of the conical valve 61, i.e. the speed of lowering of the servo piston 60, is changed in a stepped manner from the state of full opening as shown by broken line L in Fig. 24. For information, when the conical valve 61 does not have any projection on its head as in the case of the second embodiment, the rate of changing of the opening area A is changed in a substantially linear manner as shown by full line Lo in Fig. 11.In consequence, the rate of change of the injection amount in relation to time, i.e. the fuel injection rate, is changed in proportion to the speed of lowering of the servo piston 60. In consequence, by suitably selecting the shape and size of the projection 61 a on the conical valve 61 so as to vary the opening area A of the inlet port 77, it is possible to change the fuel injection rate in the begining period of opening of the conical valve 61, i.e. the fuel injection rate in the pre-injection period, in relation to the fuel injection rate in the full-open state of the conical valve 61, i.e. the injection rate in the main injection period.

In Fig. 21,the one-dot-and-dash line L2 shows how the opening area A of the servo piston chamber inlet port 77 is changed in relation to the valve lift of the conical valve 61, when the second throttle portion 61d of the projection 61a is tapered such that the diameter is decreased towardsthe end as shown by chain line 61 d". Similarly, two-dot-and-dash line L3 shows the change of the opening area A of the servo piston chamber inlet port 77 when the second throttle portion 61 d is tapered such that its diameter is gradually increased towards the end as shown by chain line 61 d'. Thus, it is possible to obtain pump nozzles having different transient patterns of fuel injection in the pre-injection period, simply by selecting the shape of the second throttle portion 61 d suitably, without changing other portions at all.

Figs. 22 and 23 show a pump nozzle in the fuel injection device of a third embodiment ofthe inven tion. In this case, the nozzle spring seat receiving bore formed at the back-pressure side of the nozzle valve is communicated, through the servo piston back-pressure chamber formed at the back-pressure side of the servo piston, with the working fuel relief passage for discharging the working fuel from the servo piston back pressure chamber into the fuel tank, thereby to make efficient and concentrated use of the fuel passage formed in the pump nozzle to reduce the size and weight of the pump nozzle.

The pump nozzle of this embodiment will be described in more detail with reference to Figs. 22 and 23.

The fuel injection device Z of this embodiment is constituted by a pump nozzle X mounted on the cylinder head ofthe engine Y, a fuel supply pump 18 for supplying the pump noale X with a fuel, and a controller 20 adapted to control the solenoid valve 111 incorporated in the pump nozzle X in accordance with a signal derived from a sensor 21 attached to the fly-wheel 22 of the engine Y. This fuel injection device Z is adapted to inject the fuel at a suitable rate into the working chamber of the engine Y, thorugh controlling the fuel supplied by the pump 18 into the pump nozzle X by means of the solenoid valve 111.

The pump nozzle X has a pump section 55 for pressurizing the fuel supplied by the fuel supply pump 18, injection nozzle section 30 for injecting the pressurized fuel, and a control section 105 for controlling the injection nozzle section 30 and the pump section 55.

The pump section 55 has a servo piston 60 of a large diameter, a plunger 59 of a small diameter and adapted to reciprocate as a unit with the servo piston 60, and a conical valve 61 adapted to control the servo piston 60. The servo piston 60 is accomodated by a servo piston chamber 76 which is provided with a servo piston chamber inlet port 77 opposing to the top of the servo piston 60 and adapted to introduce the fuel into the servo piston chamber76 and a servo piston chamber outlet port 87 through which the fuel is discharged from the servo piston chamber 76. The servo piston chamber inlet port 77 is communicated with the supplied fuel passage 71 which constitutes an inlet for the fuel supplied by the fuel supply pump 18.The servo piston chamber inlet port 77 is adapted to be opened and closed by the conical valve 61 received by the conical valve chamber 84 and opposing to the servo piston chamber inlet port 77. The conical valve 61 is adapted to be moved back and forth as its back pressure is controlled by opening and closing the fuel introduction port 143 and the fuel discharge port 149 by the solenoid valve 111 of the controller 105 which will be detailed later, thereby to open and close the servo piston chamber inlet port 77. On the other hand, the servo piston chamber outlet port 87 is connected so as to be brought into and out of communication with the working oil relief passage 94 through the conical valve chamber 84.The arrangement is such that the servo piston chamber outlet port 87 communicates through the annular groove 80 formed in the sliding surface of the conical valve 61, only when the annular groove 80 communicates with the open end of the working oil relief passage 94. A reference numeral 89 designates an orifice provided in the working oil relief passage 94, and is adapted to restrict the fuel discharged from the servo piston chamber 76 thereby to adjust the return stroke of the servo piston 60. A reference numeral 65 denotes a spring mounted on the back-pressure side of the conical valve 61 and is adapted to bias the conical valve 61 towards the servo piston chamber inlet port 77.

The plunger chamber 67 is formed coaxially with the servo piston chamber 76 and is communicated with the open end of the latter. The plunger chamber 67 accomodates the plunger 59 adapted to be reciprocatingly moved as a unit with the servo piston 60.

The plunger chamber 67 is communicated with the supplied fuel passage 71 through the fuel charging passage 70 and is communicated also with the fuel well chamber 38 of the injection nozzle section 30 which will be mentioned later, through the highpressure fuel passage 46. The space 100 in the servo piston chamber 76 at the back-pressure side of the servo piston 60 (referred to as servo piston backpressure chamber, hereinunder) is communicated through the fuel passage 86 at the back-pressure side of the nozzle valve with a nozzle valve seat receiving bore 40 of the nozzle section 30 which will be detailed later.

The feed valve chamber 68 formed in the fuel charging passage 70 slidably receives a feed valve 62 which is adapted to open the fuel charging passage 70 by the pressure of the supplied fuel in the charging stroke and to close the same 70 in the plunging stroke by the force of the pressurized fuel and the force exerted by the spring 64.

The control section 105 includes a solenoid coil 116 adapted to be excited under the control of the controller 20 and a solenoid valve 111 adapted to be driven by the attracting force exerted by the solenoid coil 116. The solenoid valve 111 is clamped by a pair of springs 114 and 113 disposed at the upper and lower sides thereof, and is normally biased by the difference of the force between these springs 114, 113 upwardly to close the fuel discharge port 149 of the conical valve chamber 84 while opening the fuel introduction port 143 of the same. As the solenoid coil 116 is energized, the solenoid valve 111 is driven downwardly by the attracting force of the solenoid coil, thereby to open the fuel discharge port 149 while closing the fuel introduction port 143.

The injection nozzle section 30 is opened by the pressure of the fuel pressurized by the plunger 59 and discharges the pressurized fuel through injection ports 49 formed in a nozzle valve 32 thereof. The opening pressure of the nozzle valve 32 is controlled by the force of the spring 36 fitted in the nozzle spring seat receiving bore 4d and the pressure of the discharged fuel which is introduced into the nozzle spring seat receiving bore 40 through the fuel passage 86 behind the nozzle valve.

This fuel injection device operates and provides an effect as explained hereinunder. In this fuel injection device Z, the fuel is supplied from the fuel tank 19 into the pump nozzle X by the fuel supply pump 18 which is driven by the internal combustion engine Y, and the solenoid valve 111 in the pump nozzle X is suitably controlled by the controller 20 in accordance with the signal coming from the sensor 21 attached to the fiy-wheel 22 of the engine, in synchronism with the operation of the engine Y. The supplied fuel pressure is suitably regulated by a pressure regulator valve 24, while the pulsation of the pressure is absorbed by the accumulator 25. The operation of the pump nozzles performed when the solenoid coil 116 is energized will be described hereinunder with reference to Fig. 22.The solenoid coil 116 is energized as it is supplied with electric power by the con troller 20, to exert an attracting force to lower the solenoid valve 111, thereby to close the fuel introduction port 143 of the conical valve chamber 84 while opening the fuel discharge port 149 of the same. In consequence, the fuel in the conical valve chamber 84 is discharged to the fuel tank 19 through the fuel return pipe 124. As the fuel flows out of the conical valve chamber 84, a pressure difference is established across the conical valve 61, so that the conical valve 61 is moved upward by the pressure of the fuel in the supplied fuel passage 71 thereby to open the servo piston chamber inlet port 77, so that the fuel is introduced from the supplied fuel passage 71 into the servo piston chamber 76.At this moment, the servo piston chamber outlet port 87 is closed by the sliding surface of the conical valve 61,so that the servo piston 60 is depressed downwardly by the pressure of the fuel. As the servo piston 60 is pressed downwardly, the plunger 59 is lowered also to pressurize the fuel in the plunger chamber 67 so that the feed valve 62 is closed by the force of the pressurized fuel. At the same time, the fuel pressure in the nozzle fuel well is increased drastically to open the nozzle valve 32, so that the fuel is injected from the plunger chamber 67 into the working chamber of the engine through the high-pressure fuel passage 46 and the nozzle ports 49.As the plunger 59 reaches the lower end of its stroke, the fuel pressure in the nozzle fuel well 38 is lowered so that the nozzle valve 32 is closed to terminate the fuel injection by the force of the spring 36 acting on the nozzle valve 32 and by the force generated by the pressure of the discharged fuel which is introduced through the fuel passage 86 behind the nozzle valve into the nozzle spring seat receiving bore 40.

Then, the operation of the pump nozzle X performed when the solenoid coil 116 is de-energized will be explained in connection with Fig. 23. As the solenoid coil 116 is de-energized, the solenoid valve 111 is relieved from the attracting force so that the solenoid valve 111 is moved upward by the force of the spring to open the fuel introduction port 143 of the conical valve chamber 84 while closing the fuel discharge port 149 of the same. In consequence, the fuel in the supplied fuel passage 71 is introduced into the conical valve chamber 84 through the coni cal valve chamber introduction passage 143, so that the balance of pressure is established across the conical valve 61 to permit the latter to be moved downwardly by the force of the spring 65 thereby to open the servo piston chamber inlet port 77.As the conical valve 61 moves downward, the annular groove 80 formed in the sliding surface of the conical valve 61 is brought into communication with the working oil relief passage 94 so that the servo piston chamber outlet port 87 is opened to permit the fuel to flow from the servo piston chamber 76 into the fuel tank 19 through the working oil relief passage 94, so that the pressure in the servo piston chamber 76 is lowered followed by a reduction in the pressure within the plunger chamber 67. Therefore, the highpressure fuel in the fuel charging passage 70 flows into the plunger chamber 67 forcibly opening the feed valve 62 by its pressure and charged the chamber 67 so as to move the plunger 59 and the servo piston 60 upward.

The internal combustion engine operates continuously as the injection stroke illustrated in Fig. 22 and the charging stroke illustrated in Fig. 23 are performed alternatingly and repeatedly.

In this pump nozzle, the rate of fuel injection is determined by the time length of the charging, i.e. by the length of the return stroke of the plunger 59. The charging time can be adjusted by suitably setting the time lengths of energization and de-energization of the solenoid coil 116. At the same time, the speed of return stroke of the servo piston 60 can be adjusted by suitably restricting the fuel discharged from the servo piston chamber 76, by means of an orifice 89 disposed in the fuel relief passage 94, and by varying the initial load of the spring 64.

In the pump noale X of this embodiment, the servo piston chamber inlet port77 is opened and closed by the conical valve 61,so that it is possible to preserve a large diameter of the servo piston chamber inlet port 77. In addition, since the conical valve 61 is disposed in the close proximity of the servo piston chamber 76, it is possible to promptly introduce the fuel into the servo piston chamber 76 and to inject the fuel at a high pressure in quite a short period of time.

Furthermore, since the fuel passage 86 behind the nozzle valve and the working oil relief passage 94 are communicated with each other through the servo piston back-pressure chamber 100 formed behind the servo piston 60, the fuel leaked into the nozzle valve seat receiving bore 40 through the sliding portion of the nozzle valve 32 and the fuel leaked through the sliding portion between the servo piston 60 and the plunger 59 are collected in the servo piston back-pressure chamber 100 and is returned to the fuel tank 19 together with the fuel which is discharged from the servo piston chamber 76 through the end portion of the working fuel relief passage 94.

Namely, the servo piston back-pressure chamber 100 serves as the discharge passageforthe fuel which is discharged from the fuel passage 86 behind the nozzle valve communicating with the nozzle valve seat receiving bore 40. In addition, the end portion 94a of the working fuel relief passage 94 serves as the discharge passage of the working fuel from the servo piston chamber 76 and also as a passage for discharging the leaked fuel collected in the servo piston back-pressure chamber 100. In consequence, the numberofthe passagesto be formed in the pump nozzle is reduced and the length of the same is shortened.

Figs. 24 and 25 show a pump nozzle incorporated in the fuel injection device of the fourth embodiment of the invention.

This fourth embodiment differs from the first embodiment shown in Figs. 14 and 15 only in the points described hereinunder. The construction and operation of other portions than mentioned below are materially identical to those of the first embodiment, so that the detailed description of such identical portions is omitted.

In this pump nozzleX, the servo piston chamber inlet port 77 is formed substantially in an inversed U-like form, and is provided at its bent portion adjacent to the supplied fuel passage 71 with a valve seat 79 for seating the conical valve 61.

The conical valve 61 is disposed in the servo piston chamber inlet passage 77 in such a manner that the end surface 61 a thereof adjacent to the valve member opposes to the direction of flow of the fuel in the servo piston chamber inlet passage 77 so that the pressure of the fuel is applied to the abovementioned end surface 61a of the conical valve.

Thus, the conical valve 61 is displaced axially by the difference oftheforce between the back pressure acting on the conical valve 61 and the fuel pressure acting on the end surface 61a, thereby to open and close the servo piston chamber inlet passage 77. It is, therefore, possible to preserve a large diameter of the conical valve 61 thereby to increase the opening pressure thereof easily. In addition, it is possible to reduce the required lift of the conical valve 61 by increasing the opening area of the same. Furthermore, it is possible to quickly open the conical valve 61 to introduce a large amount of fuel into the servo piston chamber 76 in quite a short period of time.

Therefore, the rate of compression of the fuel by the servo piston 60 is increased to permit an injection of the fuel at a high pressure and in a short period of time.

Hereinafter, the effect of the fuel injection device of the present invention will be explained. In the fuel injection device of the invention, the back pressure of the conical valve controlling the operation of the servo piston is adjusted by the solenoid valve which is adapted to be opened and closed by the solenoid coil. It is, therefore, possible to reduce the area of the valve seat of the solenoid valve to permit the use of solenoid coil having a smaller attracting capacity and, hence, to reduce the size and weight of the solenoid portion.

In addition, since the inlet port of the servo piston chamber is adapted to be opened and closed by the conical valve, it is possible to adopt a sufficiently large diameter ofthe servo piston chamber inlet port to permit a rapid introduction of the fuel into the servo piston chamber, which in turn permits a fuel injection at a high pressure and in a short period of time.

In opening and closing the inlet port of the servo piston chamber by the conical valve, the fuel introduction port and the fuel discharge port are provided in the conical valve chamber separately and are opened and closed alternatively and simultaneously, so that the introduction of the fuel into the conical valve chamber is made in quite a smooth manner to make sure of smooth and quick operation of the conical valve, thereby to ensure a higher characteristics for following up the change in the engine speed to permit the engine to operate at a high speed.

Furthermore, since the inlet port of the servo piston chamber is opened and closed by the conical valve which is disposed to oppose to the inlet port, the ratio dAldL between the change dA of opening area of the servo piston inlet port to the change dL of the valve lift L is greater than the ratio dAldS between the change dA of the opening area of the servo piston inlet port to the change dS is the slide valve stroke in the conventional fuel injection device in which the servo piston chamber inlet port is opened and closed by the slide valve, as will be seen from Fig. 26. This means that the fuel can be introduced into the servo piston chamber promptly to permit the fuel injection at a higher pressure and in a shorter period of time.

Furthermore, in the described embodiment of the invention, the end portion of the conical valve moved back and forth in the conical valve chamber constitutes a valve member for opening and closing the servo piston chamber inlet port. At the same time, the sliding surface of the conical valve which makes sliding contact with the wall of the conical valve chamber is provided with an annular groove, the sliding surface having the annular groove functions as a valve member for opening and closing the servo piston chamber outlet port. Therefore, the opening and closing of the servo piston chamber inlet port and the servo piston chamber outlet port are made always in synchronism, in accordance with the movement of the conical valve back and forth.

Thus, the conical valve serves as a valve member for opening and closing the servo piston chamber outlet port, so that it is not necessary to employ any specific valve mechanism for opening and closing the servo piston outlet port. As a result, the number of parts is decreased and the construction of the pump nozzle is simplified, to contribute to the reduction in size and weight.

Furthermore, since the servo piston chamber outlet port for discharging the working oil from the servo piston chamber is adapted to be opened and closed by the annular groove formed in the side surface of the conical valve for opening and closing the servo piston chamber inlet port, in accordance with the opening and closing of the servo piston chamber inlet achieved by the conical valve, it is possible to operate the servo piston without failure to further improve the injection performance of the pump nozzle.

In addition, since the fuel injection rate in the preinjection period and the fuel injection rate in the main injection period are optimized by suitably changing the area of the passage for the fuel flowing into the servo piston chamber by a projection formed on the head portion of the conical valve, it is possible to reduce the amount of fuel injected in the period of the ignition time lag, i.e. in the beginning period of the injection, thereby to suppress the tendency of the knowcking of the engine and to improve the combustion characteristics of the internal combustion engine.

Moreover, since the rate of fuel injection in the pre-injection period and the rate of fuel injection in the main injection period are automaticaliy regu lated by the projection formed on the valve head portion of the conical valve, it is not necessary to provide separate nozzle ports for the pre-injection of the fuel, so thatthe construction of the nozzle portion is simplified considerably.

It is also to be pointed out that, since the valve lift of the solenoid valve is selected to be sufficiently small to permit the solenoid valve effectively operate within the stroke range of large attracting force exerted by the solenoid coil, it is possible to obtain the required attracting force with a solenoid coil having a smaller size to further contribute to the reduction in size and weight of the pump nozzle.

Furthermore, since the solenoid coil is disposed in the annular space between the support and the core guide which are connected to each other in the axial direction, the undesirable damaging of the solenoid coil due to collision with other parts during assembling and disassembling is completely eliminated to further improve the durability of the solenoid coil.

In addition, the coupling between the support and the core guide is made such that the flange of the core guide contacts the step surface of the support in the axial direction to maintain a constant axial length of the annular space formed between the support and the core guide, the undesirable collapse or breakdown of the solenoid coil due to excessive tightening of the member for coupling the support and the core guide is completely eliminated and, at the same time, the work for coupling these members, i.e. the work for mounting the solenoid coil therebetween, is considerably facilitated.

In the described embodiments of the invention, the fuel passage behind the nozzle valve, communicating with the nozzle valve seat receiving bore formed at the back side of the nozzle valve, is communicated through the servo piston back pressure chamber formed at the back-pressure side of the servo piston with the working fuel relief passage through which the working fuel is discharged from the servo piston chamber, so that it becomes unnecessaryto form a specific fuel discharge passage for the fuel discharged from the nozzle valve seat receiving bore, thereby to make efficient and concentrated use of the fuel passage. In consequence, the number and length of the fuel passages formed in the pump nozzle body are decreased to contribute to the reduction in size and weight of the pump nozzle.At the same time, the internal construction of the pump nozzle is very much simplified to remarkably reduce the cost of the mechanical processing such as boring.

Furthermore, the small-diameter disc-shaped solenoid valve seat having fuel passages for introducing and discharging the fuel into and from the conical valve chamber, as well as valve seats for solenoid valve adapted to open and close these passages, is disposed between the solenoid valve and the conical valve which are disposed coaxiaily in the close proximity of each other. Thanks to the use of the member having a plurality of functions, the construction of the pump nozzle is simplified and made compact.

By arranging the conical valve, solenoid valve, solenoid coil, active core and the stator core coaxially and in the close proximity of one another, it is possible to make an efficient use of the magnetic force excited by the solenoid coil, so that the flow of the working fuel for controlling the conical valve is smoothed to improve the operation characteristics of the solenoid valve, as well as the injection characteristics of the pump nozzle.

The solenoid valve is disposed between a pair of springs arranged at both sides thereof and having different spring force, such that the solenoid valve is biased by the difference of force of the spring to close the fuel discharge port of the conical valve chamber and to open the fuel introduction of the same when the solenoid coil is de-energized and, when the solenoid coil is energized, to open and close the fuel discharge port and fuel introduction port, respectively. This makes it possible to reduce the volume of the fuel chamber in the conical valve chamber 84 which in turn permits a reduction in the sizes of the fuel introduction port 142 and the fuel discharge port 148. Consequently, the sizes of the solenoid valve 111 and the active core 112 can be decreased advantageously. It is also possible to reduce the size and weight of the conical valve 61.In consequence, it is possible to increase the speed of operation of the valves.

The servo piston and the plunger are disposed at an offset from the axis of the pump nozzle to provide a thick-walled portion of the pump nozzle in which formed are a feed valve chamber for accomodating the feed pump and a fuel charging passage for supplying the fuel into the feed valve chamber, so that the outside dimension of the pump nozzle is decreased considerably. In consequence, the pump nozzle as a whole can have a smaller diameter to suit for use in internal combustion engines having smaller bore diameters.

According to the invention, the conical valve chamber and the fuel passages such as supplied fuel passage, servo piston chamber inlet port, working oil relief passage and so forth are formed in the conical valve body by radial and axial boring which is comparatively easy to perform. In consequence, the processing of the conical valve body is facilitated and, moreover, pump nozzles of different specifications are produced easily by suitably selecting the kinds of the conical valve body, thanks to the fact that the conical valve body is formed as an independent member and clamped between the control section and the pump body section.

In addition, since the seat member of the solenoid valve seat and the conical valve controlled by the solenoid valve is disposed in the axial direction and in the close proximity of each other, so that the conical valve can operate following up the opening and closing operation of the conical valve with a good response. In consequence, the speed of operation of the servo piston is increased to improve the injection characteristics of the pump nozzle.

In addition, since a fuel supply pressure regulator is provided in the fuel supply passage to regulate the fuel pressure upon detect of a reduction in the fuel injection rate, it is possible to maintain the fuel injection pressure when the fuel injection rate is small at the same level as that attained when the fuel injec tion rate is large.

Furthermore, since the volume of the fuel chamber for the working fuel formed on the top of the servo piston is made as small as possible, it is possible to promptly operate the servo piston without any time lag to increase the rate of pressure increase in the plunger chamber. In consequence, the fuel injection pressure is further increased and the fuel injection time is further shortened to improve the injection characteristics of the pump nozzle.

It is also to be pointed out that, since the conical valve is disposed to oppose to the top surface of the servo piston in the close proximity of the latter and the volume of the fuel chamber for the working fuel formed on the top of the servo piston is made as small as possible, the servo piston can operate with a good response by the working fuel introduced into the servo piston chamber when the servo piston chamber inlet port is opened. In consequence, the rate of fuel pressure increase in the nozzle valve is enhanced to further increase the injection pressure and to shorten the injection time.

Bn the embodiment in which only the fuel discharge port of the conical valve chamber is opened and closed while the fuel introduction port of the conical valve chamber is opened continuously, it suffices only to polish-finish the valve seat on the discharge port and cooperating portion of the solenoid valve. In consequence, it is possible to reduce the cost of production through reduction in number of the steps of the production process.

Finally, by forming the fuel introduction port of the conical valve chamber in the conical valve itself as in the case of the illustrated embodiment, the processing of the inlet port is facilitated and the number of steps of the production process is decreased thereby to simplify the construction of the conical valve portion.

Claims

1. A fuel injection device for internal combustion engine comprising: a pump nozzle including a pump section, an injection nozzle section and a control section, said pump section having a servo piston of a comparatively large diameter and adapted to be driven by a part of the supplied fuel and a plunger of a comparatively small diameter and adapted to be driven by said servo piston to move reciprocatingly as a unit with the latter thereby to plunge the fuel, said injection nozzle section having a nozzle valve adapted to inject the fuel pressurized by said pump section, said control section having a solenoid valve for controlling said servo piston; a fuel supply pump for supplying said pump nozzle with said fuel; and a controller adapted to open and close said solenoid valve of said pump nozzle, so that a part of the supplied fuel is introduced into said servo piston chamber by the opening and closing operation of said solenoid valve under the control of said controller, whereby said servo piston is driven by the pressure of said fuel introduced into said servo piston chamberto permit a fuel injection from said injection nozzle section, wherein the improvement comprises: a servo piston chamber formed in said pump nozzle and adapted to receive said servo piston, said servo piston chamber having a servo piston chamber inlet port for introducing thereinto a part of the supplied fuel which acts as a working fluid for operating said servo piston and a servo piston chamber outlet portthrough which said supplied fuel is discharged from said servo piston chamber; a conical valve disposed to oppose to said servo piston chamber inlet port so as to open and close the latter; and a conical valve chamber accomodating said conical valve and having a fuel introduction port and a fuel discharge port so that said conical valve is driven in accordance with the introduction and discharge of the fuel into said conical valve chamber thereby to open and close said servo piston chamber inlet port, the introduction and discharge of said fuel into and out of said conical valve chamber being made by said solenoid valve.

2. A fuel injection device as claimed in claim 1, wherein the fuel back pressure acting on said conical valve is controlled by alternatingly opening and closing said fuel introduction port and said fuel discharge port of said conical valve chamber.

3. A fuel injection device as claimed in claim 1, wherein the top surface of said conical valve opposing to said servo piston chamber inlet port constitutes a valve member for opening and closing said servo piston chamber inlet port, said conical valve being provided in its sliding surface making sliding contact with the wall of said conical valve chamber with an annular groove which is adapted to be brought, as said conical valve is moved reciprocatingly, into and out of communication with a working fuel relief passage 94 extending through said conical valve chamber in the radial direction and having one end communicating with said servo piston chamber outlet port, said annular groove being adapted to be brought into and out olF communication with said servo piston chamber outlet port when said solenoid coil is energized, after said servo piston chamber inlet port is opened by the valve member of said conical valve, whereas, when said solenoid coil is de-energized, said annular groove is brought into communication with said servo piston chamber outlet port when said servo piston chamber inlet port is closed by said valve member.

4. Afuel injection device as claimed in Claim 1, wherein said servo piston chamber outlet port is communicated with one end of a working fuel relief passage extending through the conical valve chamber in the radial direction and opened to the outside at its other end, said conical valve being provided in the intermediate portion of said sliding surface with an annular groove of a suitable size, said annular groove communicating, when said servo piston chamber inlet port is closed by said conical valve, with the open end of said working fuel relief passage opening to said inner peripheral surface of said conical valve chambertherebyto communicate said servo piston chamber outlet port to the outside, whereas, when said conical valve is positioned to open said servo piston chamber inlet port, said open end of said working oil relief passage is closed by said sliding surface of said conical valve thereby to close said servo piston chamber discharge port.

5. Afuel injection device for internal combustion engine as claimed in claim 1, wherein said conical valve is provided on its valve head portion with a projection which can suitably vary the opening area of said servo piston chamber inlet port while said conical valve is moved from the fully closed position to the maximum lift position.

6. A fuel injection device for internal combustion engine as claimed in claim 1, wherein the lift of said solenoid valve is smaller than the lift of said conical valve.

7. A fuel injection device for internal combustion engine as claimed in claim 1, wherein a solenoid coil is disposed in a substantially cylindrical support adapted to be detachably screwed to a conical valve body in which said conical valve chamber is formed, said solenoid coil receiving a core guide which in turn receives a stator core and an active core opposing to each other, said active core being adapted to be attracted and driven by said solenoid coil, so that said solenoid valve is reciprocatable in the axial direction together with said active core to control the introduction and discharge of the fuel into and out of said conical valve chamber by means of said solenoid valve, said support having a stepped bottomequipped cylindrical form constituted by a smalldiameter portion, large-diameter portion and a bottom plate closing the bottom, said core guide having a flange-equipped tubular form with a flange provided at its one end thereof, said core guide being inserted into said support with said solenoid coil received by the annular space of a suitable size formed between the inner surface of said support and the outer surface of said core guide, said core guide having one end projected to the outside through said bottom plate of said support, said sup port and said core guide being coupled to each other by a suitable fastening member attached to one end of said core guide projected from the bottom of said support, with said flange contacting the step surface formed between said large-diameter portion and small-diameter portion of said support.

8. A fuel injection device for internal combustion engines as claimed in claim 1, wherein the fuel pressurized by said plunger is injected from said nozzle ports in accordance with the opening operation of said nozzle valve which is normally biased in the closing direction by a spring received by the nozzle spring seat receiving bore, said nozzle spring seat receiving bore being communicated with said working fuel relieving passage through a servo piston back-pressure chamber formed atthe back-pressure side of said servo piston in said servo piston chamber.

9. Afuel injection device for internal combustion engine as claimed in claim 1, wherein said solenoid valve is disposed in a solenoid valve chamber formed to oppose to said conical valve chamber coaxially with said conical valve, such that the introduction and discharge of the fuel to and form said conical valve chamber are controlled by said solenoid valve, and the fuel pressurized by said plunger is discharged from the nozzle port of said nozzle valve, and wherein a small-diameter disc-shaped solenoid valve seat is placed between said conical valve chamber and said solenoid valve chamber, said solenoid valve seat having a fuel passage for introducing a part of the fuel in the fuel inlet port into said solenoid valve chamber, a valve seat adapted be selectively engaged by said solenoid valve to open and close said fuel supply passage, and a through bore providing a communication between said solenoid valve chamber and said conical valve chamber.

10. Afuel injection device for internal combustion engine as claimed in claim 1, wherein a solenoid coil is disposed above said conical valve chamber and a stator core and an active core are disposed in said solenoid coil so as to oppose to each other, said active core being movable reciprocatingly in the axial direction as a unit with said solenoid valve, said solenoid valve controlling the introduction and discharge of the fuel into and out of said conical valve chamber, said conical valve, active core, stator core and said solenoid coil being disposed coaxially and in the close proximity of one another.

11. Afuel injection device for internal combustion engine as claimed in claim 1, wherein said solenoid valve is resiliently supported between an upper spring and a lower spring disposed at the upper and lower sides thereof, respectively, said springs having different spring forces such that, when said solenoid coil is de-energized, said solenoid valve is biased by the difference of force between said upper and lower spring to the position where said solenoid valve closes said fuel discharge port and opens said fuel introduction port, whereas, when said solenoid coil is energized, said solenoid valve is moved towards said fuel introduction port by the attracting force of said solenoid coil thereby to open said fuel discharge port and to close said fuel introduction port.

12. Afuel injection device for internal combustion engines as claimed in claim 1, wherein said servo piston and said plunger are disposed along the axis of said pump nozzle and an offset from the same, so as to present a thick-walled portion of said pump nozzle in which formed are a feed valve chamber for accomodating said feed valve and a fuel charging passage for charging said feed valve chamber with said fuel.

13. Afuel injection device for internal combustion engine as claimed in claim 1, wherein said pump nozzle includes a pump body having said plunger chamber accomodating said plunger and a servo piston chamber accomodating said servo piston, said pump body being provided at its end with said nozzle valve; a conical valve body having a conical valve chamber accomodating said conical valve; and a control section having said solenoid valve and said solenoid coil; said pump body, said conical valve body and said control section being constructed as separate parts and said conical valve body being clamped between said pump body and said control section, wherein, in said conical valve body, said conical valve chamber, said servo piston chamber inlet port and said servo piston chamber outlet port are formed in axial direction, said conical valve body having a radial relief port communicating with said servo piston chamber outlet portthrough said conical valve chamber and a radial fuel inlet port extend ing through said conical valve chamber, said conical valve being further provided in its sliding surface with an annular groove, whereby said servo piston chamber outlet port is closed by the outer peripheral surface of said conical valve in accordance with the operation of said conical valve adapted to open and close said servo piston chamber inlet port and or said servo piston chamber outlet port is brought into communication with said relief port through said annular groove.

14. Afuel injection device for internal combustion engines as claimed in claim 1, wherein said conical valve is disposed such that the end surface forming a valve member thereof opposes to the flow of the fuel flowing in said servo piston chamber inlet passage, so that the pressure of the fuel iscontinu- ously applied to said end surface of said conical valve.

15. A fuel injection device for internal combustion engine as claimed in claim 1, wherein said solenoid valve and said conical valve are disposed in the axial direction in the close proximity of each anther, whereih the lift of said conical valve is limited by a valve seat member of said solenoid valve.

16. A fuel injection device for internal combustion engine as claimed in claim 1, characterized by a fuel supply pressure regulator disposed in the intermediate portion of the fuel supply passage leading to said fuel inlet port, said regulator being adapted to increase the pressure of fuel supplied to said fuel inlet when the rate of injection of fuel is decreased.

17. Afuel injection device for internal combustion engine as claimed in claim 1, wherein a conical valve body having a conical valve chamber and a servo piston body having said servo piston chamber are arranged in the close proximity of each other, such that the end surface of said conical valve body is directly opposed by the top surface of said servo piston, said conical valve body having said servo piston chamber inlet port so as to directly oppose to the top surface of said servo piston.

18. Afuel injection device for internal combustion engines as claimed in claim 1, wherein said servo piston chamber inlet port is formed along the axis of said servo piston so as to oppose to the top surface of said servo piston, and the valve seat of said conical valve is formed so as to oppose to the top surface of said servo piston in the close prnxim- ity of said top surface of said servo piston.

19. A fuel injection device for internal combus Lion engines as claimed in claim 1, wherein the fuel introduction port for introducing the fuel into said conical valve chamber is normally opened and said fuel discharge port of said conical valve chamber has a large area than said fuel introduction port, the fuel back pressure acting on said conical valve being controlled by opening and closing said fuel discharge port by means of said solenoid valve.