Three-way electromagnetic valve

Abstract: A three-way electromagnetic valve provided with a valve body (2), a movable member (12) slidably disposed in the valve body, an actuator (21) for driving the movable member, an opening-closing mechanism (14, 18) provided in an internal passage (17) formed in the movable member. A clearance reducing portion (32) is formed to reduce a gap created by a pressurized fluid entering the slide section or by the force of fastening and fixing the valve body, thereby limiting the leakage of the pressurized fluid.

Description: BACKGROUND OF THE INVENTION This invention relates to a three-way electromagnetic valve according to the preamble of claims 1, 5 and 14, respectively, suitable for use in a system for controlling a high pressure fluid, for example, a diesel fuel injection system. In a diesel engine fuel injection system such as the one disclosed in the Japanese Patent Laid-Open No. 59-165858, a three-way electromagnetic valve is used to control the injection timing and the injection rate. This three-way electromagnetic valve operates in such a manner that a fuel supplied at a high pressure from a pressure fuel feed pump is led from a fuel passage to a supply port and is supplied to a chamber formed in a moving piston and to a control port via an annular recess and a plurality of fuel passages formed in the moving piston and communicating with the recess. A high pressure is applied to the valve body at the annular recess outward in the radial direction by the effect of the high pressure fuel led to the recess, thereby increasing the clearance of the slide section formed between the slide bore and the moving piston. The high pressure fuel therefore leaks and enters the increased clearance and presses not only the recess but also the whole of the bore wall, and further increases the clearances of upper and lower slide sections defined above and below the annular recess, resulting in an increase in the leakage of the high pressure fuel. A solenoid, the valve body and a control chamber are integrally fixed by fastening to construct the three-way valve while maintaining the desired pressure at which contact surfaces of the valve body and the control chamber are pressed against each other. Since in this construction a spacer in the form of a ring is interposed between the solenoid and the valve body, the fastening force acts toward the outer periphery of the valve body at the upper surface thereof and causes the bore edge of the slide bore to be deformed outward. The clearances of the slide sections between the slide bore and the moving piston are thereby increased toward the bore edge, resulting in a further increase in the leakage of the high pressure fuel. As described above, if the clearances of the slide sections are increased, the leakage of the high pressure liquid through these clearances becomes large. This three-way electromagnetic valve therefore entails the problem of loss of the driving torque of the pressure fuel feed pump, the problem of a reduction in the fuel injection pressure, and so on. Further, the document DE-A-2 051 944 forming the preamble of claims 1, 5 and 14, respectively, discloses a three-way electromagnetic valve comprising a valve body which has a supply port through which a pressurized fluid flows, a control port, a discharge port, a slide bore formed with the ports so as to communicate with the same, and a valve seat formed between the supply port and the discharge port. A movable member is slidably disposed in the slide bore and capable of contacting and moving away from the valve seat. The movable member has an internal passage formed in its body to enable the supply and control ports or the control and discharge ports to communicate with each other. Furthermore, the three-way electromagnetic valve comprises an actuator for driving the movable member, and opening-closing means which are disposed in the internal passage of the movable member and operable to open the internal passage when the movable member is seated on the valve seat. Moreover, a fixing means for fastening and fixing one end surface of the valve body to the actuator may be provided. According to this state of the art, the three-way electromagnetic valve is incorporated in a pressure accumulating unit injector of a nozzle back pressure control type in which a nozzle and a spool valve are improved by recognizing the fact that a leakage is developed at an instance when two seats open simultaneously when the three-way electomagnetic valve is operated, whereby a leakage of high pressure fuel which is supplied from an injector may be reduced. However, this state of the art suffers from the fact that a leakage of the pressurized fluid is developed constantly in a sliding clearance between the movable members of the three-way electromagnetic valve, as well. Finally, the document EP-A-0 319 371 shows a three-way electromagnetic valve whose structure is quite similar to that described above. Additionally, an annular chamber is formed in the valve body which utilizes an inward deformation of a thin wall portion of the valve body. For forming such a chamber either the valve body is to be divided in two halves or the chamber is to be closed by a cap. As a result, problems as to leakage of the high pressure fuel may occur at the sealing necessary at the division or the cap, as well. Summarily, one particular disadvantage of the aforementioned state of the art is that, due to the high pressure fuel introduced into the valve, the clearances of the slide sections of the valve are increased, thereby resulting in a large leakage of the high pressure fuel through these clearances, whereby the known three-way electromagnetic valves entail the problems of e.g. loss of driving torque of the pressure fuel feed pump and reduction in the fuel injection pressure. SUMMARY OF THE INVENTION Accordingly, the object of the present invention is to provide a three-way electromagnetic valve in which the leakage of high pressure fuel is limited. This object is solved by the features indicated in the independent claims 1, 5 and 14, respectively. Advantageously developed embodiments of the invention are subject-matter of the dependent claims 2 to 4, 6 to 13 and 15 to 17. The invention will become more apparent upon a consideration of the following description of the preferred embodiments of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 to 3 show a first embodiment of the present invention, wherein Fig. 1 is a cross-sectional view thereof; Fig. 2 is a cross-sectional view of a modification of the first embodiment; Fig. 3 is a diagram of the extent of deformation; Figs. 4 to 7 show a second embodiment of the present invention, wherein Fig. 4 is a cross-sectional view thereof; Fig. 5 is a cross-sectional view taken along the line V - V of Fig. 4; Fig. 6 is a diagram of a state of application of pressures; Fig. 7 is a graph showing reductions in the leakage; Figs. 8 to 10B show a third embodiment of the present invention, wherein Fig. 8 is a cross-sectional view thereof; Fig. 9 is a cross-sectional view taken along the line IX - IX of Fig. 8; Figs. 10A and 10B are diagrams of the extents of deformations, wherein Fig. 10A relates to a case of a conventional valve where no pressure accumulating chamber is provided; Fig. 10B relates to the case of the present invention where a pressure accumulating chamber is provided; Figs. 11 to 14 show a fourth embodiment of the present invention, wherein Fig. 11 is a cross-sectional view thereof; Fig. 12 is a cross-sectional view of essential portions thereof; Fig. 13 is a diagram of comparison between the extents of deformations of slide sections depending upon the existence of an annular groove; Fig. 14 is a graph showing the relationship between the depth of the annular groove and the leakage; and Fig. 15 is a cross-sectional view of a conventional three-way electromagnetic valve. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below together with the conventional art with reference to the accompanying drawings. In the diesel engine fuel injection system disclosed in the Japanese Patent Laid-Open No.59-165858, a three-way electromagnetic valve is used to control the injection timing and the injection rate. This electromagnetic valve has a structure such as that illustrated in Fig. 15. Referring to Fig. 15, a slide bore 3 is formed in a valve body 2 of the three-way electromagnetic valve 1 at the center thereof. A supply port 4 through which a high pressure fuel which is a pressurized fluid is supplied, is formed in a portion of the bore wall defining the slide bore 3. A control port 5 and a discharge port 6 are also formed in the valve body 2; the control port 5 opens into the slide bore 3 in the direction of the axis thereof, and the discharge port 6 laterally opens into the slide bore 3. A chamber 7 is formed between the ports 5 and 6. In the valve body 2 are also formed an annular recess 8 which communicates with the supply port 4 and an inlet passage 9 through which the high pressure fuel is introduced into the supply port 4. A discharge passage 10 is formed so as to extend from the discharge port 6. One end of a branch passage 11 branching off at the other end from the discharge passage 10 opens in an upper surface of the valve body 2. A moving piston 12 is slidably disposed in the slide bore 3. The moving piston 12 has a poppet portion 12c which is formed at its one end and which can be brought into contact with and moved apart from a valve seat 5a formed at an edge of the control port 5. The moving piston 12 also has an armature 13 formed at its other end so as to face a later-mentioned electromagnetic coil 21. A fitting bore 15 in which a free piston 14 is fitted is formed in the moving piston 12. A chamber 16 is formed continuously with the fitting bore 15. The fitting bore 15 communicates with the control port 5 via the chamber 16 and a passage 17. A valve seat 18 is formed between the chamber 16 and the passage 17. A poppet portion 14a of the free piston 14 can be brought into contact with and moved apart from the valve seat 18. A plurality of fuel passages 19 for introducing the high pressure fuel into the chamber 16 are formed in the moving piston 12 while being arranged in the circumferential direction at equal angular intervals at positions corresponding to the annular recess 8 formed in the slide bore 3. The valve body 2 is integrally and fixedly connected by fastening with fastening bolts 25 or the like to a solenoid 22 in which the electromagnetic coil 21 is wound and to a control chamber 24 having a passage 23 communicating with the control port 5, with a spacer 20 in the form of a ring being interposed between the solenoid 22 and the valve body 2, thus constructing the three-way electromagnetic valve 1. A spring 26 is set between the solenoid 22 and the moving piston 12 to press the poppet portion 12 c of the moving piston 12 against the valve seat 5a. The thus-constructed conventional three-way electromagnetic valve 1 operates as described below. As is well known, two states of the valve are alternately established: one in which the moving piston 12 is moved upward by energizing the electromagnetic coil 21 to provide communication between the control port 5 and the discharge port 6, while the poppet portion 14a of the free piston 14 is seated on the valve seat 18 to stop the supply of the high pressure fuel from the supply port 4 to the control port 5; and one in which the electromagnetic coil 21 is not energized, the moving piston 12 is moved downward and seated on the valve seat 5a to stop communication between the control port 5 and the discharge port 6, and the free piston 14 is moved apart from the valve seat 18 to provide communication between the supply port 4 and the control port 5, thereby supplying the high pressure fuel to the control chamber 24. In the three-way electromagnetic valve 1 based on the above-described construction and operation, the fuel supplied from the pressure fuel feed pump at a high pressure is introduced into the supply port 4 via the fuel passage 9 and is supplied to the chamber 16 and to the control port 5 via the annular recess 8 and the plurality of fuel passages 19 communicating with the recess 8. The high pressure fuel introduced into the annular recess 8 applies a high pressure to the valve body 2 at the recess 8 outward in the radial direction so that the valve body 2 is deformed outwardly, thereby increasing the clearances of slide sections between the slide bore 3 and the moving piston 12. The high pressure fuel therefore leaks out of the recess 8 into the increased clearances and pressurizes not only the inner surface of the recess 8 but also the whole of the wall surface of the slide bore 3, and acts to further increase the clearances of the slide sections defined above and below the annular recess 8, thereby increasing the leakage of the high pressure fuel. The three-way electromagnetic valve 1 is assembled by integrally and fixedly connecting the solenoid 22, the valve body 2 and the control chamber 24 by fastening in order to maintain the desired pressure at the contact surfaces of the valve body 2 and the control chamber 24. However, since the spacer 20 in the form of a ring is interposed between the solenoid 22 and the valve body 2, the fastening force acts in the direction of the outer periphery of the valve body 2 at the upper surface of the same and causes the bore edge at the opening of the slide bore 3 to be bent outwardly and deformed. The clearances of the slide sections between the slide bore 3 and the moving piston 12 are increased toward the bore edge of the slide bore 3, thereby increasing the leakage of the high pressure fuel. As described above, as the clearances of the slide sections increase, the rate at which the high pressure fuel leaks out therethrough is increased, resulting in an increase in the loss of the driving torque of the pressure fuel feed pump for pressure-feeding the high pressure fluid as well as a reduction in the fuel injection pressure. Next, a first embodiment of the present invention will be described below with reference to Fig. 1. As shown in Fig. 1, a valve body 2 of a three-way electromagnetic valve 1 is formed of a bearing steel (SUJ2), and a slide bore 3 is formed in the valve body 2 at the center thereof. In the bore wall of the slide bore 3 are formed a supply port 4, a control port 5 which opens into the slide bore 3 in the direction of the axis thereof, and a discharge port 6 which laterally opens into the slide bore 3. A valve seat 5a is formed on an inlet portion of the control port 5. A chamber 7 is formed between the control port 5 and the discharge port 6. In the valve body 2 are also formed an annular recess 8 which communicates with the supply port 4, and an inlet passage 9 through which a high pressure fuel is introduced into the supply port 4. A discharge passage 10 is formed so as to extend from the discharge port 6. One end of a branch passage 11 branching off at the other end from the discharge passage 10 opens in an upper surface of the valve body 2. A moving piston 12 provided as a movable member is slidably disposed in the slide bore 3. The clearance between the moving piston 12 and the slide bore 3 is set to 2 to 3 µm. The moving piston 12 has a slide portion 12a which is formed of a cemented steel (SCM415), and a flange portion 12b which is formed of a silicon steel (3LSS) and fixed to the slide portion 12a. The moving piston 12 has a poppet portion 12c formed at its end opposite to the flange portion 12b. The poppet portion 12c can be brought into contact with and moved apart from the valve seat 5a. The flange portion 12b faces an electromagnetic coil 21. A fitting bore 15 in which a free piston 14 formed of a bearing steel (SUJ2) is fitted is formed in the moving piston 12. A chamber is formed continuously with the fitting bore 15. A larger-diameter bore 31 which defines a later-mentioned pressure accumulating chamber 32 is formed with the fitting bore 15. The larger-diameter bore 31 communicates with the control port 5 via an internal passage 17. A valve seat 18 is formed between the larger-diameter bore 31 and the passage 17. A poppet portion 14a of the free piston 14 can be brought into contact with and moved apart from the valve seat 18. A plurality of fuel passages 19 for introducing the high pressure fuel into the larger-diameter bore 31 are formed in the moving piston 12 while being arranged in the circumferential direction at equal angular intervals at positions corresponding to the annular recess 8 formed in the slide bore 3. The upper end of the larger diameter bore 31 is positioned at a distance L₁ from the supply port 4 which is about 20 to 40 % of the distance L from the supply port 4 at which the extent of outward deformation in the radial direction of the valve body 2 caused by the high pressure fuel forcibly entering the gap between the outer peripheral surface of the free piston 14 and the slide bore 3 is zero, that is, the distance between the supply port 4 and the upper end surface of the valve body 2. The pressure accumulating chamber 32 is thus defined in which the high pressure fuel introduced from the fuel passage 19 communicating with the supply port 4 is accumulated. In the illustrated state of this embodiment, the side wall of the pressure accumulating chamber 32 symmetrically faces upper and lower slide sections 33 and 34 defined above and below the supply port 4 between the slide bore 3 and the moving piston 12. However, the pressure accumulating chamber 32 may be formed so that its side wall faces the upper slide section 33 alone, as illustrated in Fig. 2. The valve body 2 is integrally and fixedly connected by fastening with fastening bolts (not shown) to a solenoid 22 in which the electromagnetic coil 21 is wound and to a control chamber 24 having a passage 23 communicating with the control port 5, with a spacer 20 in the form of a ring being interposed between the solenoid 22 and the valve body 2. A spring 26 is set between the solenoid 22 and the moving piston 12 to press the poppet portion 12c of the moving piston 12 against the valve seat 5a. The operation of three-way electromagnetic valve 1 in accordance with this embodiment is the same as that of the conventional type and will not be described again. The effects of the high pressure fuel accumulated in the pressure accumulating chamber 32 shown in Fig. 1 will be described below. Ordinarily, if an internal pressure P₁ and an external pressure P₂ are simultaneously applied to a hollow cylinder formed of a thick wall and having an inside radius a and an outside radius b, the extent of deformation in the radial direction at a point of a radius r is calculated by the equation: where E (modulus of elasticity) = 21,000 kg/mm², and 1/m ( Poisson's ratio) = 0.3. It is assumed that the pressure P₂ in the slide sections between the valve body 2 and the moving piston 12 is proportional to the distance from the position at which the supply port is disposed (hereinafter referred to as "central position") such that the pressure P₂ has a maximum value of 10 kg/mm² equal to the pressure P₁ of the high pressure fuel at the annular recess 8 communicating with the supply port 4, and is zero at the upper end of the upper slide section 33 and at the lower end of the lower slide section 34. The outside radius b is set to 3.37 mm and the inside radius a is set to a value closer to that of the outside radius, i.e, to 3 mm to make the extent of deformation of the moving piston 12 due to the pressure difference (between P₁ and P₂). On this condition, the extent of deformation U₁ of the moving piston 12 at a point of r = b = 3.75 mm is obtained by the equation (i). On the other hand, the extent of deformation of the valve body 2, i.e., the extent of deformation U₂ of the slide bore 3 is calculated by assuming that the internal pressure is P₂ and that only the internal pressure acts on the slide bore 3. Since the pressure P₂ linearly decreases from the central position toward the end of each of the upper and lower slide sections 33 and 34, the extents of the above-mentioned deformations also change linearly according to the distance from the central position. Fig. 3 shows calculated values of these deformations. As shown in Fig. 3, when the distance L₁ from the supply port 3 is L₁ = 0.4L, the extent of deformation U₁ of the moving piston 12 is U₁ = 1.8 µm, and the extent of deformation U₂ of the valve body 2 is U₂ = 1.5 µm. Thus, the extents of these deformations are generally equal to each other and the increase in the clearance is therefore limited, thereby reducing the leakage of the high pressure fuel. Positioning the upper end of the pressure accumulating chamber 32 at the distance L₁ = 0.4L ensures that the leakage characteristics are optimum in terms of maintenance of the clearance for sliding of the slide bore 3 and the moving piston 12, the problem of leakage of the high pressure fuel through the slide section between the fitting bore 15 and the free-piston 14 due to deformation of the moving piston 12, and so on. However, the value of the distance L₁ slightly varies depending on changes in the set internal and external pressures, the slide length of the slide section between the fitting bore 15 and the free piston 14, the material of the valve body 2, the material of the moving piston 12 and so on. In the arrangement shown in Fig. 2, the pressure accumulating chamber 32 is formed so that its side wall faces the upper slide section 33 alone. This arrangement ensures that the increase in the clearance of the upper slide section 33 is limited by the effect of the pressure of the high pressure fuel accumulated in the pressure accumulating chamber 32, thereby reducing the leakage of the high pressure fuel through the slide section. Referring next to Fig. 4, a second embodiment of the present invention is illustrated in section. Three introduction passages 9 are provided through which the high pressure fuel is introduced into supply ports 4. The introduction passages 9 are formed so as to extend in parallel to the slide bore 3 formed in the valve body 2 while being arranged in the circumferential direction at equal angular intervals of 120°, as shown in Fig. 5 in transverse cross section. The supply ports 4 are bored laterally from the outside of the valve body 2 so as to be perpendicular to the introduction passages 9 and to communicate with the slide bore 3. Openings of the supply ports 4 in the valve body 2 are closed by screw plugs 41. In this embodiment, no annular recess is provided for communication with the supply port 4 while the supply ports 4 and the introduction passages 9 are disposed at three positions. Three fuel passage 19 are formed in the moving piston 12 at three positions in the circumferential direction so as to coincide with the supply ports 4, thereby enabling the high pressure fuel to be supplied to the control port 5 via a chamber 16 and the passage 17. The introduction passages 9 intersecting the supply ports 4 at right angles further extend in parallel to the slide bore 3, and extension portions 42 have a length L₂. The pressure of the high pressure fuel introduced and accumulated in the extension portions 42 acts toward the center in the radial direction to limit the displacement of the valve body 2 created in the opposite direction by the pressure of the high pressure fuel leaking and entering the clearance of a slide section 43 between the slide bore 3 and the moving piston 12 (refer to Fig. 6). Since no annular recess is provided, there is no possibility that the pressure of the high pressure fuel acts over the whole periphery. Fig. 7 shows a graph of the relationship between the ratio of the length L₂ of the extension portions 42 of the introduction passages 9 to the depth L to the position of the supply ports 4 and the leakage of the high pressure fuel through the slide section 43, when the inside diameter of the slide bore 3 is 10 mm, the inside diameter of each of the supply ports 4 and the introduction passages 9 is 2 mm, and the distance X between the supply ports 4 and the introduction passages 9 is 2 mm. In this case, the pressure of the high pressure fuel is set to 100 Mpa and the leakage exhibited in the case in which the extensions 42 are not provided is set to 100. In this graph, the tendency of reduction in the leakage can be recognized at L₂/L = 0.4 , and the reduction is about 10 % at L₂/L = 0.7 and about 50 % at L₂/L = 0.9 . It is therefore preferable to set the length L₂ of the extension portions 42 to a longer possible length at least not less than half the depth L to the position of the supply ports 4 so that the extension portions 42 are brought closer to the upper surface of the valve body 2. However, the length L₂ is set to about 90 % of L in consideration of the pressure of the high pressure fuel, the accuracy with which the extension portions 42 are worked, and so on. The positions in which the supply ports 4, the introduction passages 9 and the extension portions 42 are placed in association with each other is not limited to those in the described embodiment spaced apart from each other in the circumferential direction by 120°. Referring to Fig. 8, a third embodiment of the present invention is illustrated in section. Three supply ports 4 are bored from the outside of the valve body 2 in the direction perpendicular to the slide bore 3 generally at the middle point of a slide section 71 defined between the slide bore 3 and the moving piston 12 so as to open into the slide bore 3. The supply ports 4 are arranged in the circumferential direction at equal angular intervals of 120°, as shown in Fig. 9 in transverse section. Pressure accumulating chambers 72 having a larger diameter are also formed in the valve body 2 with the supply ports 4. The opening of each pressure accumulating chamber 72 on the outside of the valve body 2 is closed by a screw plug 73. Introduction passages 9 through which the high pressure fuel is introduced are formed in the valve body 2 so as to respectively communicate with the pressure accumulating chamber 72, thereby enabling the high pressure fuel to be supplied to the supply ports 4 while being accumulated in the pressure accumulating chambers 72. Fuel passages 19 are formed in the moving piston 12 so as to coincide with the supply ports 4, thereby enabling the high pressure fuel to be supplied to the control port 5 via the chamber 16 and the passage 17. The pressure of the high pressure fuel introduced and accumulated in each pressure accumulating chamber 72 acts to radially inwardly press a portion encircling the supply port 4 over the area defined as the difference between the cross-sectional areas of the supply ports 4 and the pressure accumulating chambers 72, i.e., to press a larger-diameter step portion 72a. In each of Figs. 10A and 10B, the extent of outward deformation of the valve body 2 is indicated with a broken line which deformation is caused by the pressure of the high pressure fuel leaking out of the supply port 4 into the clearance of the slide section 71 between the slide bore 3 formed in the valve body 2, and the moving piston 12. Fig. 10A relates to a case of the conventional arrangement in which the pressure accumulating chamber 72 is not provided, and Fig. 10B relates to a case in which the pressure accumulating chamber 72 is provided. The pressure of the high pressure fuel is set to 300 MPa. In the construction of Fig. 10B, the position B at which the larger-diameter step portion 72a of the pressure accumulating chamber 72 is formed is at a distance of 1 mm from the slide bore 3, and the ratio D/d of the inside diameter D of the pressure accumulating chamber 72 to the inside diameter of the supply port 4 is 5. As a result of the provision of the pressure accumulating chamber 72, in the construction of Fig. 10B, the extent of deformation of the portion of the wall of the slide bore 3 corresponding to the larger-diameter step portion 72a of the pressure accumulating chamber 72 is limited to approximately zero. Accordingly, this embodiment is substantially free from the problem of any increase in the clearance of the slide section 71 caused by the pressure of the high pressure fluid leaking out of the supply port 4 into the clearance of the slide section 71 as in the case of the conventional valve and, hence, from the problem of any increase in the leakage of the high pressure fuel, thus achieving a remarkable reduction in the leakage of the high pressure fuel. The ratio of the inside diameter D of the pressure accumulating chamber 72 and the inside diameter d of the supply port 4 is not limited to the above-mentioned value, and the positions of the supply ports 4, the introduction passages 9 and the pressure accumulating chambers 72 are not limited to those mentioned above. Referring then to Fig. 11, a fourth embodiment of the present invention is illustrated in section. The valve body 2 is integrally and fixedly connected by fastening with fastening bolts 25 to the solenoid 22 and to the control chamber 24 having a passage 23 communicating with the control port 5, with a spacer 20 in the form of a ring being interposed between the solenoid 22 and the valve body 2. An annular groove 61 is formed in the upper surface of the valve body 2 on the outside of the slide bore 3. The annular groove 61 serves to interrupt, when the valve body 2 is fastened in this manner, transmission of the fastening force acting toward the outer periphery of the valve body 2 and to thereby prevent an upper slide section 62 of the slide bore 3 at an upper portion of the valve body 2 from being displaced outward. The leakage Q L through the slide section is calculated by Q L = k·ε₁²·ε₂²/(ε₁ + ε₂) where ε₁: a clearance at the slide section inlet, ε₂: a clearance at the slide section outlet, and k: a constant determined by the internal pressure, the passage length, the inside diameter and the viscosity coefficient. Q L is therefore maximized when ε₁ = ε₂ and can be reduced by making ε₂ smaller than ε₁ (refer to Fig. 12). Fig. 13 shows the results of measurements of the extents of deformations of the upper slide section 62 and a lower slide section 63 conducted as described below. The valve body 2 is provided in which the inside diameter of the slide bore 3 is 7.5 mm, both the lengths of the upper slide section 62 and the lower slide section 63 with the annular recess 8 interposed therebetween are 8 mm, and the depth of the annular groove 61 is 8 mm. The bottom of the valve body 2 is fixed, and a fastening load of 8.6 kg/mm² is applied to an outer peripheral portion of the upper end surface of the valve body 2 while an internal pressure of 10 kg/mm² is applied. Fig. 13 also shows the extents of deformations in the case in which no annular groove is provided in the upper surface of the valve body 2. As can be understood from Fig. 13, the outward displacement of the upper half of the upper slide section 62 is effectively limited; the displacement of the slide bore edge is smaller than that in the case in which no annular groove is provided by about 1 mm, and the clearance ε₂ at the slide section outlet in the equation for calculation the leakage is correspondingly smaller, resulting in a reduction in the leakage through each slide section. Fig. 14 shows the relationship between the depth L₃ (mm) of the annular groove 61 and the leakages (cc/min.) of the high pressure fuel through the slide sections in the valve body 2 specified above. In Fig. 14, a line a indicates changes in the leakage through the lower slide section 63, a line b indicates changes in the leakage through the upper slide section 62, and a line c indicates the sum of these leakages. As shown in Fig. 14, when the groove depth L₂ = 8 mm, i.e., it is equal to the length of the upper and lower slide sections 62 and 63, the leakage is minimized, i.e., it is reduced by 15 % from the leakage in the case in which no annular groove is provided. Even if the depth of the annular groove is further increased, the leakage is not reduced although it is maintained at the minimum level. This is because when the depth of the annular groove 61 exceeds the length (depth) of the upper slide section 62, the leakage through the lower slide section 63 increases and cancels out the reduction in the leakage through the upper slide section 62. In this embodiment, the minimum value of the leakage is obtained, i.e., the optimum leakage characteristics are exhibited when the depth L₃ is equal to the length of the upper slide section 62. However, the above values slightly vary by changes in the measurement conditions, e.g., the internal pressure and the viscosity. The phenomenon of increase in the leakage based on the increase in the clearance of the slide section between the slide bore 3 of the valve body 2 and the moving piston 12 caused by the pressure of the high pressure fuel leaking and entering this clearance is different from the phenomenon of increase in the leakage based on the increase in the clearance of the slide section caused by the fastening force. The fourth embodiment can therefore be combined with each of the first to third embodiments to cope with the problem of increase in the leakage in respective cases, thereby enabling the leakage to be further reduced. In accordance with the present invention, as described above, gaps formed between the slide bore and the outer peripheral surface of the movable member can be reduced by suitable reduction means. It is thereby possible to reduce the leakage and, hence, to effect fluid control with improved accuracy.

Claims: A three-way electromagnetic valve comprising a valve body (2) having a supply port (4) through which a pressurized fluid flows, a control port (5), a discharge port (6), a slide bore (3) formed with said ports so as to communicate with the same, and a valve seat (5a) formed between said supply port and said discharge port, a movable member (12) slidably disposed in said slide bore and capable of contacting and moving away from said valve seat, said movable member having an internal passage (17) formed in its body to enable said supply and control ports or said control and discharge ports to communicate with each other, an actuator (21) for driving said movable member, and opening-closing means (14, 18) disposed in said internal passage of said movable member and operable to open said internal passage when said movable member is seated on said valve seat, characterized by a pressure accumulating chamber (32) formed in said internal passage (17) of said movable member (12) to enable the pressurized fluid to deform said movable member by pressing the same outward in a radial direction from the interior thereof for reducing a gap between said slide bore and the outer peripheral surface of said movable member. A three-way electromagnetic valve according to claim 1, wherein said gap formed between said slide bore (3) and the outer peripheral surface of said movable member (12) is created by penetration of the pressurized fluid between said slide bore and said movable member. A three-way electromagnetic valve according to claim 1 or 2, wherein the distance between said supply port (4) and an end of said pressure accumulating chamber (32) is set such that the extent of the radial outward deformation of said movable member (12) caused by the pressurized fluid in said pressure accumulating chamber is generally equal to the extent of the radial outward deformation of said valve body (2) caused by penetration of the pressurized fluid between said slide bore (3) and the outer peripheral surface of said movable member. A three-way electromagnetic valve according to one of the preceding claims, wherein the distance (L₁) between said supply port (4) and an end of said pressure accumulating chamber (32) is about 20 to 40% of the distance (L) between said supply port and a point at which the extent of the radial outward deformation of said movable member (12) is zero, namely the distance (L) between said supply port and an upper end surface of said valve body (2), said deformation being caused by the pressurized fluid penetrating between said slide bore (3) and the outer peripheral surface of said movable member. A three-way electromagnetic valve according to the preamble portion of claim 1, characterized in that said supply port (4) consists of a plurality of ports surrounding said slide bore (3), wherein a plurality of pressure accumulating chambers (9, 42, 72) are circumferentially distributed in said valve body (2) surrounding said slide bore to enable the pressurized fluid to deform said valve body by pressing the same toward said slide bore, said chambers communicating with said supply ports. A three-way electromagnetic valve according to claim 5, wherein said pressure accumulating chambers are high pressure fluid passages (9, 42) formed in said valve body (2) along a slide section between said slide bore (3) and said movable member (12) in the axial direction, a high pressure fuel being supplied through said high pressure fluid passages. A three-way electromagnetic valve according to claim 6, wherein said supply ports (4) are formed in said valve body (2), and a plurality of fuel passages (19) facing said supply ports are formed in said movable member (12) as part of said internal passage (17) so as to extend in radial directions. A three-way electromagnetic valve according to claim 6 or 7, wherein the distance (L₂) between said supply port (4) and an end of said high pressure fluid passages (9, 42) is not smaller than about 50% of the distance (L) between said supply port and a point at which the extent of the radial outward deformation of said movable member (12) is zero, namely the distance (L) between said supply port and an upper end surface of said valve body (2), said deformation being caused by the high pressure fluid penetrating between said slide bore (3) and the outer peripheral surface of said movable member. A three-way electromagnetic valve according to one of the claims 6 to 8, wherein the distance (L₂) between said supply port (4) and an end of said high pressure fluid passages (9, 42) is not larger than about 90% of the distance (L) between said supply port and a point at which the extent of the radial outward deformation of said movable member (12) is zero, namely the distance (L) between said supply port and an upper end surface of said valve body (2), said deformation being caused by the high pressure fluid penetrating between said slide bore (3) and the outer peripheral surface of said movable member. A three-way electromagnetic valve according to claim 5, wherein said pressure accumulating chambers (72) are adapted to communicate with said supply port (4). A three-way electromagnetic valve according to claim 10, wherein said ports of said supply port (4) are formed in said valve body (2), and said pressure accumulating chambers (72) are adapted to face said ports in radial directions. A three-way electromagnetic valve according to claim 10 or 11, wherein the diameter (D) of said pressure accumulating chamber (72) is about 5 times larger than the diameter (d) of said supply port (4). A three-way electromagnetic valve according to one of the preceding claims, wherein said pressure accumulation chambers (9, 32, 42, 72) are adapted to maintain a part of the pressurized fluid for balancing the pressure deformation caused by penetration of the pressurized fluid between said slide bore (3) and the outer peripheral surface of said movable member (12) when said movable member is seated on said valve seat (5a). A three-way electromagnetic valve according to the preamble portion of claim 1, further comprising a fixing means (25) for fastening and fixing one end surface of said valve body (2) to said actuator (21), characterized by an annular groove (61) formed in said valve body (2) around said slide bore (3), said annular groove (61) extending from an upper surface of said valve body (2) and having a depth (L₃) from said upper surface of said valve body (2) which is less than or equal to the distance (L) between said upper surface of said valve body (2) and said supply port (4), so as to interrupt the transmission of the fastening force of said fixing means (25) towards said slide bore (3), thereby preventing an upper slide section (62) of said slide bore (3) at an upper portion of said valve body (2) from being displaced outwards. A three-way electromagnetic valve according to claim 14, wherein an outer peripheral portion of said upper surface of said valve body (2) is integrally fixed to said actuator (21) by means of said fixing means (25), said fixing creating a gap between said slide bore (3) and the outer peripheral surface of said movable member (12). A three-way electromagnetic valve according to claim 14 or 15, wherein said depth (L₃) of said annular groove (61) from said upper surface of said valve body (2) is about 30 to 100% of said distance (L) between said upper surface of said valve body (2) and said supply port (4). A three-way electromagnetic valve according to one of the claims 14 to 16, further comprising a pressure accumulation chamber means which is adapted to maintain a part of the pressurized fluid for balancing the pressure deformation caused by penetration of the pressurized fluid between said slide bore (3) and the outer peripheral surface of said movable member (12) when said movable member is seated on said valve seat (5a).

Inventors: KABAI KOICHI, TAMAI KATSUYUKI, KABAI, KOICHI, TAMAI, KATSUYUKI
Applicants: NIPPON DENSO CO, NIPPONDENSO CO., LTD.
Application year: 1989
Main classification: F16K31
IPC codes: F16K31, F02M51, F02M59, F02M47, F16K11