GB2098004A - An electromagnetic device for controlling the movement of an injector valve of a fuel injector - Google Patents

Abstract

An electromagnetic device comprises an armature having a thin plate (8), and a winding arrangement (7) arranged in an electromagnet body (1) in at least three slots (2, 3, 4) which are disposed symmetrically about the centre of the armature plate. This feature leads to a reduced armature mass, a short magnetic flux path and a low leakage flux. The electromagnet device is therefore suitable for rapid reciprocation. <IMAGE>

Description

SPECIFICATION An electromagnetic device for controlling the movement of an injector valve of a fuel injector The invention relates to an electromagnetic device for controlling the movement of an injector valve of a fuel injector for a diesel engine, the electromagnet device having a body carrying an electrical winding arrangement, and an armature movable relatively to the body.

In a known device of this kind the body takes the form of a cylindrical member whose surface is formed with saw-tooth cross-section two-start helical slots which receive the electrical windings.

The inside surface of a cylindrical armature around the body is formed with similiar slots. The result is two helical air gaps bounded by surface portions which extend at right-angles to the common axis of the body and armature. The path of the magnetic flux therefore extends by way of two air gaps and the body and armature material which bounds the saw-tooth grooves. In this device, therefore, the path for the magnetic flux is relatively iarge and the armature mass is relatively substantial. Also, the leakage flux near the air gaps is relatively large.

It is an object of the invention to provide a reciprocating electromagnet device which has a reduced armature mass, a shorter path for the magnetic flux and reduced leakage flux and which is therefore suitable for rapid movements making it suitable for the purpose discussed.

Accordingly the present invention provides an electromagnet device, for controlling the movement of an injector valve of a fuel injector for a diesel engine comprising an electromagnet body carrying an electrical winding arrangement and an armature movable relatively to the body, the armature comprising a thin plane plate and the winding arrangement being arranged in a pattern extending parallel to the surface of the body facing the armature in at least two slots in the body, which are distributed symmetrically about the centre of the armature plate.

The resulting device has a very light armature plate, since the cross-section to carry the magnetic flux has to be suitable for only a small proportion of the total flux-i.e., for half the total flux in the case of two slots and for one-third of the total flux in the case of three slots. Leakage flux occurs only near the outermost and/or innermost slot. Iron losses are minimal because of the very short flux paths. The plane armature plate in accordance with the invention is much simpler to manufacture than the armature formed with helical slots in its inside surface. Also, minimal armature distances can be achieved more accurately with the plate. Consequently, the magnet in accordance with the invention is suitable for very rapid reciprocations such as occur in the control of the injector valves of fuel injectors of diesel engines.

In order to promote a fuller understanding of the above and other aspects of the present invention, some embodiments will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a fuel injector whose injector valve is controlled by an electromagnet device; Figure 2 is an axial section through an electromagnet device of circular contour; Figure 3 is a simplified view of the body of the device of Figure 1, looking from the armature side; Figures 4 and 5 are views similiar to Figure 3 of bodies with different kinds of slot; Figure 6 shows the slots in a body for a rectangular-contour device, and Figure 7 is an axial section through an alternative form of electromagnet device.

Figure 1, shows in schematic outline a fuel injector 50 disposed in a cylinder head 51 (not shown in greater detail) of a diesel engine, which has in its body 52 a fuel supply duct 53 which extends to a chamber 54. Disposed in the body 52 is an injector valve 55 which has at its lower end 49 a sealing surface to cooperate with a seat surface in the valve body 52. Joining the chamber 54 below the injector valve end 49 in Figure 1 is a central duct 48 which merges at its bottom end into a number of orifices 47 which are distributed over the periphery of the body 52 and through which, when the valve 55 is open, fuel is injected in finely divided form into a combustion chamber 46.

At its top end the injector valve 55 has a piston 56 arranged to reciprocate in a cylinder chamber 57; connected to the chamber 57 is a hydraulic line 58 through which hydraulic medium is supplied from a source (not shown) to control the actuation of the injector valve 55. A line 59 branches off line 58 and has a valve 60 controlled by means of an electromagnet device 61 the construction of which is shown in greater detail in Figure 2. With the valve 60 in the position shown, the force applied to the piston 56 by the pressure medium supplied through the line 58 is such that the injector valve 55 remains closed.To cause fuel to be injected into the combustion chamber 46, the electromagnet 61 is activated to disengage valve 60 from its seat in line 59, so that the hydraulic pressure in the cylinder 57 decreases and the pressure of the fuel in the chamber or "gallery" 54 may force the injector valve 55 upwards, with the result that the fuel is free to flow through the central duct 48 and the orifices 47. This injection step terminates when, as a result of the valve 60 closing, the force acting on the piston 56 increases and exceeds the opposite force deriving from the fuel in the gallery 54, so that the injector valve 55 returns to its closed position shown in Figure 1.

Referring to Figure 2, the electromagnetic device 61 has a body 1 of magnetic material, which is substantially discoid and of circular contour. The body 1 is formed, on its face which is downwards in Figure 2, with three concentric downwardly open slots 2, 3 and 4 which have an undercut cross-section and which are adapted to receive an electrical winding arrangement. As can be gathered from Figure 3, the slots 2,3 and 4 are interconnected by two radial slots 5, 6. The winding arrangement 7, whose path is shown in chain lines in Figure 3, extends from the outside by way of the outer part of the radial slot 5, then passes a number of times around the slot 4 over the entire periphery thereof, then go through the central part of slot 5 into slot 3, around which it also passes a number of times over the entire periphery of the slot.The winding arrangement then passes by way of the innermost part of the radial slot 5 into slot 2, and then issues therefrom to be led out of the body through slots 5. The arrows in Figure 3 indicate the direction of current flow in the winding arrangement.

Disposed below the three slots 2, 3 and 4 is a thin plane armature plate 8 in the form of an annular disc which is embedded in a disc-shaped support member 9. The plate 8 is formed with two rows of apertures 10 which are arranged in circular patterns between the slots 2 and 3 and between the slots 3 and 4. The diameter of the apertures 10 is at most 20% of the pitch or distance between the centre lines of the slots 2, 3 and 4. The member 9 is formed with apertures 11 registering with the apertures 10 but of greater diameter than the latter. The disc 9 is made of light metal and has a land 1 2 adjacent the inner edge of the armature plate 8 and a land 13 adjacent the outer edge of the armature plate 8.

The two lands 12, 13 extend beyond the armature plate 8 and form an abutment to limit armature movement towards the body 1. When the two lands abut the underside of the body 1; between such underside and the top of the plate 8 there remains a gap of a few hundredths of a millimetre, the gap having the reference s infigure 2. The gap s prevents the armature from sticking in the upward position as seen in the drawings.

Distributed over the periphery of the edges 12, 1 3 are a number of apertures in the form of radial incisions 14, 1 5 respectively which cooperate with the orifices 10, 11 for venting purposes when the armature drops from the upward position.

The body 1 is formed at its centre with a bore 16 through which a boss 17 of the member 9 extends. The member 9 also has a downwardly extending boss 18. A screwthreaded rod 1 9 extends through the bosses 1 7 and 18. A spring spider 20 engages the end face of boss 1 7 and a spring spider 21 engages the end face of boss 1 8, each such spider having a number of radial arms.

The spiders 20, 21 are rigidly connected to the member 9 by means of nuts screwed on the rod 19. The outer ends of the arms of the top spring 20 bear on the body 1 and are retained thereon by means of an intermediate ring 22 and circlip 23.

The outer ends of the bottom spider 21 are received in an annular groove 24 in a spacer ring 25 which extends around the support member 9 and is secured in an annular groove 26 in the periphery of body 1. This resilient suspension of the support member 9 and, therefore, of the armature plate 8, eliminates sliding friction. The top spring 20 also serves as an abutment for limiting downward armature movement. Such downward movement is indicated with the reference h in Figure 2. The springs 20, 21 are made of a non-magnetic substance such as nonrusting steel or beryllium bronze. The moving member of the valve 60 (Figure 1) is directly connected to the rod 19, but this arrangement is not shown here in greater detail.

Since the armature plate 8 is embedded in the support member 9, the thin plate armature cannot be deformed by the magnetic forces. The apertures 10 in the armature plate are disposed centrally between two adjacent slots and are of relatively reduced diameter. This means there is little disturbance of the magnetic flux, more particularly because the flux is insignificant at the centre region anyway.

Referring to Figure 4, which shows an alternative embodiment in which the slots, instead of being concentric, can extend in two spirals in the body 1. In this case the innermost ends of the two slots are interconnected by a radial slot 30.

The manner in which the winding arrangement 7 extends is indicated by a chain line and the arrows show the direction of currentflow.

Another arrangement is shown in Figure 5, in which there are two circular slots.

A further arrangement is with the slots parallel to one another, is shown in Figure 6. This arrangement is suitable for a rectangular contour magnet arrangement. The winding arrangement, starting from the outermost slot, extends seriatim through the other slots.

An important consideration concerning the path of the conductors in all the embodiments is that the current flows in adjacent slots must be oppositely directed.

Figure 7 shows a further embodiment in which the magnet has an armature plate 8 without a support member. The slots 2, 3 and 4 in the body 1' are arranged as in Figure 2 and receive the winding arrangement 7. The body 1' is formed at its centre with a blind bore 30 receiving a spring 31 which, with the winding arrangement 7 de energised, forces the armature plate 8 away from the body 1. In the embodiment shown in Figure 7, two stop rings 32, 33 correspond to the edges 12, 13 of the support member 9 of Figure 2. The rings 32, 33 are received in annular grooves in the body 1 ' and are formed with downwardly open radial slots 34, 35 respectively for venting. The screwthreaded rod 1 9' of this embodiment has its top end secured at the centre of the armature plate 8, (for example by riveting over) and extends through a central guide bore 36 in a housing 37 which, like the spacer ring 25 of Figure 2, is secured to the body 1 '. The housing 37 is formed with a number of bores 38 which extend parallel to the guide bore 36, and terminate at their top end in a shallow annular recess 39 and, like the slots 34, 35, cooperate with the apertures 10 in the plate 8 for ventilation purposes. The slots in the body 1' can be of the kinds shown in Figures 4 and 5 or, if the body is of polygonal contour, of the kind shown in Figure 6 and receive the winding arrangement 7. The housing 37 is made of nonmagnetic material. Thus for practical purposes the magnet shown in Figure 7 also has a support for the armature plate which will not be distorted by the magnetic flux.

In all the embodiments shown the maximum number of slots receiving electrical winding arrangements, as seen from the centre of the armature in a direction transversely of the slots, is six-i.e. a total of six annular slots in round magnets and a total of twelve slots in rectangular magnets.

Claims (9)

1. An electromagnet device, for controlling the movement of an injector valve of a fuel injector for a diesel engine comprising an electromagnet body carrying an electrical winding arrangement and an armature movable relatively to the body, the armature comprising a thin plate and the winding arrangement being arranged in a pattern extending parallel to the surface of the body facing the armature in at least two slots in the body, which are distributed symmetrically about the centre of the armature plate.

2. An electromagnet device as claimed in Claim 1 in which the armature plate is attached to a light metal support member.

3. An electromagnet device as claimed in Claim 2 in which the support member has a land at least outside the periphery of the armature which extends beyond the armature plate and limits the movement thereof towards the body.

4. An electromagnet device as claimed in Claim 3 in which the support member land is formed with at least one aperture for the passage of air.

5. An electromagnet device as claimed in any one of Claims 1 to 4 in which the armature plate is formed with a number of apertures through it disposed between the body slots, which apertures are continued through the support member when it is used.

6. An electromagnet device as claimed in Claim 5 in which the diameter of the apertures in the armature plate is at most 20% of body slot pitch.

7. An electromagnet device as claimed in any one of Claims 2 to 6 in which the support member has on either face at its centre a boss one of which extends through the body, the outer end of each boss being attached to a respective spring spider having a number of radial arms, the spiders bearing on the body by way of the outer ends of the arms.

8. An electromagnet device as claimed in Claim 7 in which the spring spiders are made of a nonmagnetic material.

9. An electromagnet device as claimed in any one of Claims 1 to 8 in which the armature plate is circular and the slots in the body extend concentrically with the armature.

1 0. An electromagnet substantially as specifically described herein with reference to the accompanying drawings.