Control valve

Abstract

The present invention relates to a control valve for a fuel injector. The control valve has a control valve body which defines a supply passage for high pressure fuel. A control chamber and a pressure compensating chamber are provided in the control valve. The control chamber and the pressure compensating chamber are both in fluid communication with the supply passage. A control valve member is provided for controlling fuel pressure in the control chamber. The pressure compensating chamber is spaced radially outwardly from the control chamber. The invention also relates to a control valve member having a pressure compensating cavity.

Claims

1. A control valve for a fuel injector, the control valve comprising: a control valve body; a supply passage for high pressure fuel; a control chamber and a pressure compensating chamber, the control chamber and the pressure compensating chamber both being in fluid communication with the supply passage such that the supply passage communicates high pressure fuel to the control chamber and to the pressure compensating chamber; a low pressure fuel return line; and a control valve member mounted in the control chamber which selectively prevents fluid communication between the control chamber and the fuel return line and between the pressure compensating chamber and the low pressure fuel return line and which selectively permits fluid communication between the control chamber and the fuel return line and between the pressure compensating chamber and the low pressure fuel return line for controlling fuel pressure in the control chamber; wherein the pressure compensating chamber is spaced radially outwardly from the control chamber.

2. A control valve as claimed in claim 1, wherein the pressure compensating chamber comprises an annular chamber.

3. A control valve as claimed in claim 1, wherein the control chamber and the pressure compensating chamber are arranged concentrically.

4. A control valve as claimed in claim 1, wherein the control chamber is in fluid communication with the supply passage via the pressure compensating chamber.

5. A control valve as claimed in claim 1 further comprising a sleeve located in the control valve body, the pressure compensating chamber being formed between an outer surface of the sleeve and the control valve body.

6. A control valve as claimed in claim 5, wherein the sleeve is a restriction fit in the control valve body; and/or at least one high pressure seal is formed between the sleeve and the control valve body.

7. A control valve as claimed in claim 5, wherein an inner surface of the sleeve forms a seal with the control valve member.

8. A fuel injector comprising a control valve as claimed in claim 1.

9. A control valve as claimed in claim 1, wherein the control chamber and the pressure compensating chamber are both in fluid communication with the supply passage when the control valve member is closed.

10. A control valve as claimed in claim 1, wherein the control chamber and the pressure compensating chamber are both in fluid communication with the supply passage regardless of the position of the control valve member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

(2) FIG. 1 shows a prior art fuel injector;

(3) FIGS. 2A and 2B illustrate the pressure force gradients created in a control valve of the prior art fuel injector shown in FIG. 1;

(4) FIG. 3 shows the operating clearance between the control valve body and the control valve member of the control valve shown in FIG. 2;

(5) FIG. 4 shows a fuel injector according to a first embodiment of the present invention;

(6) FIG. 5 shows a pressure compensating control valve according to the present invention;

(7) FIG. 6 shows the operating clearance between the control valve body and the control valve member of the control valve according to the present invention;

(8) FIG. 7 shows a first modified version of the control valve according to the present invention shown in FIG. 5;

(9) FIG. 8 shows a second modified version of the control valve according to the present invention shown in FIG. 5;

(10) FIG. 9 shows a modified pressure compensating control valve member according to the present invention; and

(11) FIG. 10 shows a modified version of the injector nozzle according to the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

(12) A fuel injector 101 in accordance with the present invention will now be described with reference to FIGS. 4 to 6. The fuel injector 101 has particular application in diesel fuel injector systems. The operation of the fuel injector 101 is generally the same as the prior art fuel injector 1 described herein and the description will focus on the pressure compensating features which are the subject of the present invention.

(13) The fuel injector 101 comprises an injector body 103 (also referred to as a nozzle holder body), a nozzle body 104, an injector nozzle 105 and a movably mounted injector needle 107. The injector nozzle 105 comprises a plurality of nozzle holes (not shown) which can be selectively opened and closed by the injector needle 107 to inject fuel into a combustion chamber (not shown). A spring 109 is provided in a spring chamber 111 for biasing the injector needle 107 towards a seated position in which the nozzle holes are closed.

(14) The fuel injector 101 further comprises a control valve 113, as illustrated in FIG. 5. The control valve 113 comprises a control valve body 115; and a control valve member 117 mounted in a cylindrical control chamber 119. The control valve member 117 comprises a guide barrel 121, a stem 122 and a conical valve 123. An electro-mechanical solenoid 125 actuates the control valve member 117 and, thereby, controls communication between a high pressure fuel passage 133 (which is in fluid communication with a fuel supply line 131) and a low pressure fuel return line 127.

(15) The sidewall of the control chamber 119 is defined by a cylindrical insert 135 which is located in a bore 137 formed in the control valve body 115. The top of the cylindrical insert 135 also defines a valve seat 124 for receiving the conical valve 123 of the control valve member 117. When the conical valve 123 is seated in the valve seat 124, the control valve 113 is closed and fluid communication between the control chamber 119 and the low pressure return line 127 is inhibited.

(16) An outer annular recess 139 is formed in an outer surface 141 of the insert 135 to form a pressure compensating chamber 143 which remains in fluid communication with the high pressure fuel passage 133. The outer annular recess 139 defines top and bottom flanges 145, 147 which are a restriction fit in the bore 137 to sealing mount the insert 135. An inner annular recess 149 is formed in an inner surface 151 of the insert 135 coincident with the stem 122 of the control valve member 117 to form the control chamber 119. An aperture 153 is formed in the insert 135 to maintain fluid communication between the pressure compensating chamber 143 and the control chamber 119. In the present embodiment, the aperture 153 is inclined relative to a longitudinal axis of the insert 135 to form a continuation of the high pressure fuel passage 133.

(17) The pressure compensating chamber 143 and the control chamber 119 are arranged concentrically, with the pressure compensating chamber 143 spaced radially outwardly of the control chamber 119. The pressure compensating chamber 143 is in direct fluid communication with the high pressure fuel passage 133. The control chamber 119 is in indirect fluid communication with the high pressure fuel passage 133 via the aperture 153 formed in the insert 135.

(18) The aperture 153 maintains fluid communication with the result that the pressure is uniform between the control chamber 119 and the pressure compensating chamber 143. In use, the forces resulting from the high pressures in the control chamber 119 are balanced by the forces generated in the pressure compensating chamber 143. The pressure force gradient generated in the control chamber 119 is represented by a third plot P.sub.3 in FIG. 4. The corresponding pressure force gradient generated in the pressure compensating chamber 143 is represented by a fourth plot P.sub.4. The pressure compensating chamber 143 thereby serves to reduce distortion of the control valve member 117 and the control chamber 119. The static leaks from the control valve 113 according to the first embodiment can be reduced.

(19) A graph showing the relative distortion of the control valve body 115, the stem 123 and the insert 135 along their length (mm) for a constant operating pressure of 2200 bar is shown in FIG. 6. The distortion of the control valve body 115 is represented by a first distortion plot D.sub.1; the distortion of the stem 123 is represented by a second distortion plot D.sub.2; and the distortion of the insert 135 is represented by a third distortion plot D.sub.3.

(20) A manufacturing clearance C.sub.M is specified between the control valve body 115 and the stem 123 when the control valve 113 is not pressurised. In the prior art control valve 13 (which does not include a pressure compensating chamber 143), under normal operating conditions the introduction of high pressure fuel causes the diameter of the bore in the control valve body 15 to increase by a first clearance C.sub.1 and the diameter of the stem 23 to decrease by a second clearance C.sub.2. Under operating conditions, the total clearance C.sub.T between the control valve body 15 and the stem 23 is given by the equation C.sub.T=C.sub.M+C.sub.1+C.sub.2. In contrast, with the compensating chamber 143, changes in the diameter of the bore in the control valve body 115 do not alter the clearance with the stem 123. Moreover, the introduction of high pressure fuel into the pressure compensating chamber 143 decreases the diameter of the insert 135 by a third clearance C.sub.3. Accordingly, under operating conditions, the total clearance C.sub.T between the stem 123 and the insert 135 is given by the equation C.sub.T=C.sub.M+C.sub.2C.sub.3. In practice, the third clearance C.sub.3 may be approximately the same as the manufacturing clearance C.sub.M so that the total clearance C.sub.T is substantially equal to the reduction in diameter of the stem 123. It will be appreciated that increasing the operating pressure of the fuel will reduce the total clearance C.sub.T between the stem 123 and the insert 135. It will be appreciated that the operation of the fuel injector 101 is the same as that of the prior art fuel injector 1 described herein.

(21) A first modified version of the control valve 113 according to the first embodiment of the present invention is illustrated in FIG. 7. Like reference numerals are used for like components, albeit suffixed with a modifier letter prime for clarity.

(22) The control valve 113 comprises a modified insert 135 located in the bore 137 formed in the control valve body 115. Rather than form an interference fit between the top and bottom flanges 145, 147 and the control valve body 115, top and bottom high pressure annular seals 155, 157 are formed to sealingly mount the insert 135. Furthermore, the aperture 153 in the modified insert 135 extends radially to maintain fluid communication between the control chamber 119 and the pressure compensating chamber 143.

(23) The operation of the first modified control valve 113 is unchanged from that of the first embodiment described above. The pressure force gradient generated in the pressure compensating chamber 143 is represented by a fifth plot P.sub.5 in FIG. 7.

(24) A second modified version of the control valve 113 according to the first embodiment of the present invention is illustrated in FIG. 8. Like reference numerals are again used for like components, albeit suffixed with two modifier letter primes for clarity.

(25) The control valve 113 comprises an insert 135 located in a bore 137 formed in a control valve body 115; and a control valve member 117 movably mounted within the insert 135. The insert 135 is a cylindrical sleeve which forms a control chamber 119. In the present arrangement, the insert 135 has an outer surface 141. The control valve member 117 comprises a guide barrel 121, a stem 122 and a conical valve 123. The stem 122 has a smaller diameter than the guide barrel 121. An inner annular recess 149 is formed in an inner surface 151 of the insert 135, coincident with the stem 122 of the control valve member 117, to form an annular region between the control valve member 117 and the insert 135. The operation of the control valve member 117 is unchanged from that of the first embodiment described herein.

(26) A pressure compensating chamber 143 is formed concentrically around the insert 135 and is maintained in fluid communication a high pressure fuel passage 133. First and second apertures 153 are formed in the insert 135 coincident with the annular region formed between the control valve member 117 and the stem 122 of the insert 135. The first and second apertures 153 maintain fluid communication between the pressure compensating chamber 143 and the control chamber 119. Thus, the control chamber 119 is maintained in fluid communication with the high pressure fuel passage 133 via the pressure compensating chamber 143. In use, the fuel pressure is the same in both the control chamber 119 and the pressure compensating chamber 143, thereby balancing pressure forces acting on the insert 135.

(27) A first (top) bearing surface 167 and a second (bottom) bearing surface 169 are formed in the bore 137. The first and second bearing surfaces 167, 169 are annular projections which extend radially inwardly. The insert 135 is an interference fit with the first and second annular bearing surfaces 167, 169. The first and second bearing surfaces 167, 169 secure the insert 143 in position axially by virtue of friction and said interference fit. Moreover, the first and second bearing surfaces 167, 169 define the top and bottom respectively of the pressure compensating chamber 143. The first and second bearing surfaces 167, 169 sealingly engage the outer surface 141 of the insert 135 to seal the pressure compensating chamber 143. A gluing and/or bonding operation can optionally also be performed to enhance the seal and/or fixed mounting of the insert 143.

(28) To facilitate assembly of the control valve 113, the diameter of a bottom seal formed between the insert 135 and the control valve body 115 can be smaller than the diameter of a top seal formed between the insert 135 and the control valve body 115. In this arrangement, the first and second bearing surfaces 167, 169 have different diameters. The first bearing surface 167 has a larger diameter than the second bearing surface 169 to facilitate insertion of the insert 135. This arrangement facilitates location of the insert 135 in the control valve body 114 without causing damage to the first bearing surface 167. The outer surface 141 of the insert 135 can be profiled to match the different diameters of the first and second bearing surfaces 167, 169. For example, the outer surface 141 of the insert 135 can be tapered towards its bottom end to form a conical profile. Alternatively, the outer surface 141 could comprise third and fourth bearing surfaces (not shown) for engaging the first and second bearing surfaces 167, 169.

(29) The operation of the second modified control valve 113 is the same as the first embodiment described above.

(30) The second modified version of the control valve 113 has been described as having first and second apertures 153 to maintain fluid communication between the pressure compensating chamber 143 and the control chamber 119. It will be appreciated that a single aperture 153 could be provided or more than two apertures 153 provided. For example, up to ten (10) of said apertures 153 could be provided to maintain fluid communication.

(31) The pressure compensating technique described herein for offsetting the pressure applied to the control valve body 115 can also be employed in the control valve member 117. A modified control valve member 117 is illustrated in FIG. 9. A pressure compensating cavity 159 is formed inside the control valve member 117 for communicating with the control chamber 119 via an inlet passage 161. The pressure compensating cavity 159 extends along a longitudinal axis X of the control valve member 117 and the inlet passage 161 extends transversely. The pressure compensating cavity 159 can be formed by drilling the control valve member 117 and inserting a plug (not shown). Alternatively, the control valve member 117 could comprise a hollow cylinder fitted onto the control valve stem 123.

(32) In use, high pressure fuel enters the control chamber 119 from the high pressure fuel passage 133 and fills the pressure compensating cavity 159, as illustrated by the arrows A. The resulting pressure force within the control valve member 117 acts radially outwardly to balance the pressure force applied on an exterior of the control valve member 117. The pressure compensating cavity 159 can thereby help to reduce distortion of the control valve member 117. The pressure compensating cavity 159 is placed in fluid communication with the low pressure return line 127 only when the control valve 113; 113 is open.

(33) Although the pressure balancing cavity has been illustrated as extending downwardly through the guide barrel 121 of the control valve member 117, it could also extend upwardly to the conical valve 123 of the control valve member 117.

(34) The control valve 113 and the control valve member 117 have been described with reference to a particular type of fuel injector 101, but it will be understood that they could be provided in combination or independently in other types of fuel injector.

(35) The pressure compensating techniques described herein could have other applications. For example, a pressure compensating chamber could be provided in the injector nozzle 105. A modified version of the fuel injector 101 according to the first embodiment of the present invention is shown in FIG. 10. Like reference numerals will be used for like components, again suffixed with a modifier letter prime to aid clarity.

(36) A cylindrical nozzle insert 163 is provided in the injector nozzle 105 to define a nozzle pressure compensating chamber 165. The nozzle insert 163 is arranged concentrically with the injector needle 107 and forms a seal around the injector needle 107. The nozzle pressure compensating chamber 165 is located between the nozzle insert 163 and the nozzle body 104 and remains in fluid communication with the fuel supply line 131. The nozzle pressure compensating chamber 165 thereby reduces deformation of the nozzle body 104 around the injector needle 107. The seal around the injector needle 107 can be maintained during normal operating conditions. The nozzle insert 163 can also provide improved guidance of the injector needle 107 as it travels within the injector nozzle 105.

(37) Alternatively, or in addition, a pressure compensating cavity could be provided in an injector needle 107. These modifications (separately or in combination) could improve guiding of the injector needle 107 under pressure and reduce floating of the injector needle 107 when it reaches the seat.

(38) It will be appreciated that various changes and modifications can be made to the control valve and the control valve member described herein without departing from the scope of the present invention.