Coil assembly

Abstract

A coil assembly in a fuel injector includes a magnetic core and; a winding wound around the core, the winding being overmoulded and forming a cylindrical overmoulding. An axial blind hole extends towards the interior of the coil assembly from a first surface to a distal end, the blind hole being suitable for housing at least one spring for loading a magnetic armature. The coil assembly is provided with a degassing hole passing through the core and the overmoulding from the blind axial hole to an axial outer cylindrical surface, the degassing hole being provided in the magnetic core and having a restriction that is arranged in a first section that is proximal to the blind axial hole.

Claims

1. A coil assembly of an electromagnetic actuator in a fuel injector, the coil assembly comprising: a magnetic core extending along a principal axis; a winding wound around the magnetic core, the winding being overmolded to form a cylindrical overmolding and extending axially from a transverse first face to a second surface; an axial blind hole extending toward an interior of the coil assembly from the transverse first face at a distal end, the axial blind hole being adapted to house at least one spring which loads a magnetic armature; and a degassing hole passing through the magnetic core and the cylindrical overmolding from the axial blind hole to an axial external cylindrical surface, the degassing hole formed in the magnetic core and having a restriction in a first section that is proximal to the axial blind hole and in which the first section has a first diameter and a first length wherein the first length divided by the first diameter is greater than 1 and is less than 8.

2. The coil assembly as claimed in claim 1, wherein the first length divided by the first diameter is 6.

3. The coil assembly as claimed in claim 1, wherein: the degassing hole has a second section with a second diameter at a proximal end of a return circuit and a second length; the first diameter divided by the second diameter is greater than 0.02 and is less than 0.06; and the first length divided by the second length is greater than or equal to 0.15 and is less than 0.3.

4. The coil assembly as claimed in claim 3, wherein the first diameter divided by the second diameter is 0.04.

5. The coil assembly as claimed in claim 3, wherein the first length divided by the second length is 0.15.

6. The coil assembly as claimed in claim 1, wherein the degassing hole is disposed proximally to the distal end of the axial blind hole.

7. The coil assembly as claimed in claim 1, wherein a diameter of the axial blind hole is less than a mean diameter of the axial blind hole with which the first section of the degassing hole communicates.

8. The coil assembly as claimed in claim 1, wherein the degassing hole is at an angle to the principal axis between 80 degrees and 120 degrees inclusive.

9. The coil assembly as claimed in claim 8, wherein the angle is 90 degrees.

10. A fuel injector comprising: a coil assembly comprising: a magnetic core extending along a principal axis; a winding wound around the magnetic core, the winding being overmolded to form a cylindrical overmolding and extending axially from a transverse first face to a second surface; an axial blind hole extending toward an interior of the coil assembly from the transverse first surface at a distal end, the axial blind hole being adapted to house at least one spring which loads a magnetic armature; and a degassing hole passing through the magnetic core and the cylindrical overmolding from the axial blind hole to an axial external cylindrical surface, the degassing hole formed in the magnetic core and having a restriction in a first section that is proximal to the axial blind hole and in which the first section has a first diameter and a first length wherein the first length divided by the first diameter is greater than 1 and is less than 8.

11. A method of manufacturing the coil assembly as defined in claim 3, comprising the following steps: winding electric wire onto a subassembly, then; winding the electric wire at one end of terminals, then; fitting caps to a lower end of the terminals and welding the caps, then; overmolding the coil assembly and thereafter; producing the first section of the degassing hole in the magnetic core, then; producing the second section of the degassing hole in the overmolding of the coil assembly.

12. The method as defined in claim 11, in which the degassing hole is produced using an attached part during the overmolding of the electric wire.

13. The coil assembly as claimed in claim 1, wherein: the degassing hole has a second section with a second diameter and a second length; the first section is located between said axial blind hole and said second section; and the first diameter is smaller than the second diameter.

14. The fuel injector as claimed in claim 10, wherein: the degassing hole has a second section with a second diameter and a second length; the first section is located between said axial blind hole and said second section; and the first diameter is smaller than the second diameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features, aims and advantages of the invention will become apparent on reading the following detailed description with reference to the appended drawings provided by way of nonlimiting example:

(2) FIG. 1 is a partial section of an injector.

(3) FIG. 2 is an isometric view of a coil subassembly.

(4) FIG. 3 is an isometric view of a coil assembly.

(5) FIG. 4 is a section of the degassing hole.

DESCRIPTION OF PREFERRED EMBODIMENTS

(6) To facilitate and clarify the following description, the top to bottom orientation is chosen arbitrarily and words and expressions such as “hereinabove, below, above, below, top, bottom . . . ” may be used without any intention of limiting the invention.

(7) The injector 10 extends along a longitudinal axis X and comprises, from bottom to top in the conventional and nonlimiting direction of the figures, a nozzle assembly 12 comprising a valve element 14 or as it is commonly called a needle 14 arranged in a nozzle body 16, a control stem 34 arranged in a valve body 20, an actuator 22 arranged in an actuator body 24. The needle 14 is arranged to slide axially in a cylindrical longitudinal bore 26 in the nozzle body between a closed position in which the needle 14 is in contact with a nozzle body seat (not shown) and an open position in which the needle 14 is moved away from the seat (not shown).

(8) As described in FIG. 1, the injector 10 is provided with a fuel circulation circuit that enables high-pressure fuel to be fed via a high-pressure circuit from an inlet orifice arranged in a top part of the injector 10 to the injection holes (not shown) arranged in a bottom part of the injector 10.

(9) A first embodiment is described now with reference to FIGS. 1, 2 and 3. The electromagnetic actuator 22 comprises an electric coil assembly 28, a mobile magnetic armature 30 fixed and fastened to a valve element 31 and commonly called a control stem 34 moving toward the coil assembly 28 when the latter is electrically energized and an elastic device 32 pushing the magnetic armature 30 at all times toward a position away from the coil assembly 28. The coil assembly 28 comprises a cylindrical overmolding 42 and a coil subassembly 43 comprising two ends 36, a core 38 and a winding 40 wound around the core 38. The two ends 36 extend along the principal X toward an upper end of the subassembly 43. The winding 40 is overmolded to form the cylindrical overmolding 42. The winding 40 extends axially from a transverse first face 46 extending axially as far as a second surface 48. The overmolded coil assembly 28 further comprises an axial blind hole 50 extending toward the interior of the coil assembly 28 from a first end 51 to a second end 52. The blind hole 50 is adapted to house at least two springs 54, 56 for loading the magnetic armature 30. The coil assembly 28 is further provided with a degassing hole 58 passing through the overmolding 42 from the axial blind hole 50 to an axial external cylindrical surface 60. The degassing hole 58 has a restriction arranged in a first section 62 that is proximal to the axial blind hole 50. The restriction is a reduction in the diameter of the hole such that, placed in the flow of the moving fluid, it limits its flow rate or modifies the pressure in the first portion 62 of the degassing hole. The restriction also produces necessary head losses of the pressurized fluid in a leak return circuit 61.

(10) The degassing hole 58 has a first section 62 having a first diameter D62 and a first length L62 with the following characteristics: 1<L62/D62<8, preferably 6.

(11) The choice of these dimensions enables complete reduction of the return waves of the fluid in the axial blind hole 50.

(12) The degassing hole 58 has a second section 64 with a second diameter D64 between the first section 62 and the exterior transverse surface 60 proximal to the leak return circuit 61 and a second length L64: −0.02<D62/D64<0.06, preferably D62/D64=0.04; −0.15≤L62/L64<0.3, preferably L62/L64=0.15.

(13) Similarly the choice of the dimensions of the two sections 62, 64 enables less turbulent flow toward the leak return circuit 61.

(14) The degassing hole 58 is disposed proximally to the distal second end 52. In other alternatives not shown the degassing hole 58 may be proximal to the first end 51 of the blind hole. The degassing hole 58 is at an angle of 90° to the principal axis X. In an alternative embodiment not shown the degassing hole 58 may be at an angle to the principal axis X between 80 degrees and 120 degrees inclusive.

(15) The blind hole 50 extends along the longitudinal axis X. The blind hole 50 has a first diameter D50a and a second diameter D50b. The first diameter D50a is the mean diameter of the hole 50. The second diameter D50b is less than the mean or first diameter D50a of the hole.

(16) The elastic device 32 comprises two coil springs 54, 56 separated by a separator member 66 or pin 66. In other alternatives of the elastic device 32 may comprise a single spring 54, 56. The elastic device 32 is arranged in the axial blind hole 50. In FIG. 1, the first spring 54 is compressed between the first face 68 of the pin 66 and the second end 52 of the hole. The second spring 56 is compressed between the second face 69 of the pin and the electric armature 30.

(17) The method of manufacturing the coil assembly 28 comprises the following steps: winding electric wire 44 onto a subassembly 43, then; winding the wire 44 at one end of the terminals 36, then; fitting caps 74 to the lower end of the terminals 74 and welding the caps 74, then; overmolding the coil assembly 28 and thereafter; producing the first section 62 of the degassing hole 58 in the magnetic core 38, then; producing the second section 64 of the degassing hole in the overmolding 42 of the coil assembly 28.

(18) The calibrated degassing hole 58 is therefore formed in the magnetic part 38. The degassing hole 58 may be produced by laser technology or by any other means. The shape of the degassing hole 58 may be round, square or conical or any other shape.

(19) In this chapter we are going to describe the operation of the injector 10. As described in FIG. 1, when the actuator 22 is electrically energized the two springs 54, 56 of the actuator are compressed by the pressure with which they are loaded by the armature 30 and the pressure in the axial blind hole 50 increases. During the opening phase of the control stem 34, the length of the springs 54, 56 is reduced so that the volume of the axial hole 50 is reduced so that the pressure increases. The armature 30, moving upward, pushes on the fluid in the axial blind hole 50 and the wave created in the fluid moves downward toward the armature 30. The wave created in the fluid therefore disturbs the control stem 34. The raised pressure in the axial hole 50 is eliminated via the degassing hole 58 which is in fluid communication with the axial blind hole 50 via the first section 62 of the degassing hole and via the second section 64 arranged in line with the first section 62 between the first section 62 and a low-pressure zone that communicates with the leak return circuit 61.

(20) The following references have been used in the description: 10 injector 12 nozzle assembly 14 needle 16 nozzle body 20 valve body 22 actuator 24 actuator body 26 blind hole 28 coil assembly 30 armature 31 valve element 32 elastic device 34 control stem 36 end 38 core 40 winding 42 overmolding 43 winding subassembly 44 winding wires 46 first winding surface 48 second winding surface 50 axial blind hole 51 first end 52 second end 54 first spring 56 second spring 58 degassing hole 60 transverse exterior surface 61 return circuit 62 first section 64 second section 66 separator member/pin 68 first pin face 69 second pin face 74 cap X longitudinal axis