GB2201039A

GB2201039A - A solenoid valve for a fuel injection pump of an internal combustion engine

Info

Publication number: GB2201039A
Application number: GB08803133A
Authority: GB
Inventors: Nestor Rodriguez-Amaya; Alfred Schmitt; Friedrich Weiss
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1987-02-13
Filing date: 1988-02-11
Publication date: 1988-08-17
Also published as: DE3704579A1; JPS63203981A; GB8803133D0

Abstract

In order to obtain extremely short valve switching times, at least a part of the magnetic circuit of the electromagnet 19 is laminated in that it comprises a plurality of thin sheet metal layers, which extend in the direction of magnetic flux therein, are contiguous one another and are electrically insulated with respect to one another. Lamination is preferably restricted to the magnet pot 23 which forms the magnet core and the yoke for completing the magnetic path. The laminations comprise wedge shaped segments or planar sheets and reduce the effect of eddy currents. <IMAGE>

Description

DESCRIPTION A SOLENOID VALVE FOR A FUEL INJECTION PUMP OF AN INTERNAL COMBUSTION ENGINE The present invention relates to a solenoid valve for a fuel injection pump of an internal combustion engine.

In known diesel fuel injection pumps, which, as a pumping nozzle for diesel engines, are mounted directly in the cylinder head of the internal combustion engine and which enclose the associated injection nozzle i-n a common housing or which, as distributortype fuel injection pumps, meter a predetermined quantity of fuel to separate injection nozzles in the cylinder heads of the internal combustion engine, the quantity of injected fuel expelled from the pump working chamber to the injection nozzle during the delivery stroke of the pump piston is determined by the "on period" of a solenoid valve which is open when no current flows therethrough and which functions as a two-port, two-position valve, inserted in an overflow passage connecting the pump working chamber to a low-pressure chamber.

The time taken for the valve switch over is an important factor in controlling the precise quantity of fuel injected, particularly when so-called preinjection is provided, that is, when the quantity of fuel to be metered per delivery stroke of the pump piston is divided into a smaller pre-injection quantity and a larger main injection quantity. As such, two triggering pulses are applied to the solenoid valve in quick succession and short valve switching times are required for opening and closing the valve so that the co-ordination of pre-injection and main injection are freely selectable and that the valve needle stroke may fully develop when the valve opens for pre-injection and subsequently closes for main injection. Such full development of the valve needle stroke is of considerable importance in avoiding variations in the metering of the main injection quantity.

In such a solenoid valve disclosed in German Offenlengungrsschrift No. 35 23 536, the magnetic flux path of the electromagnet, which actuates the valve needle, comprises homogeneous magnetic materials having high electrical conductivity. The magnetic core and yoke which completes the magnetic path of the electromagnet, are provided in one piece and form the magnet pot, which is seated by way of an inner cyli.nder wall of a porti.on of the valve housi.ng which forms a guide sleeve for the valve needle and has an annular chamber defined by the inner cylinder wall and an outer cyli.nder wall for accommodating a cylindrical magnetic winding.The magnet pot is closed off b.y an annular pole disc, disposed opposite a magnet armature and forming an outer air gap between them. An annular projection on the magnet armature passes through the pole disc and is disposed opposite the annular end face of the inner cylinder wall of the magnet pot forming an inner air gap therebetween. The magnet armature is connected to the valve needle, which is substantially hollow for the purpose of reducing mass in order to achieve short valve switching times.

In accordance with the present invention there is provided a solenoid valve for a fuel injection pump in an internal combustion engine, said valve having a valve needle for controlling a valve flow-through port, and an electromagnet for actuating the valve needle, which electromagnet includes a magnet winding and a magnetic flux path comprising a magnet core, a magnet armature connected to the valve needle, and located opposite the core so as the form an air gap between the armature and the core, and a yoke for completing the magnetic path, wherein at least part of the magnetic flux path is laminated in that it comprises thin, contiguous, sheet metal layers which extend in the direction of magnetic flux incident therein and are electrically insulated with respect to one another.

The solenoid valve according to the invention has the advantage that lamination of the magnetic circuit substantially reduces the effect of electrical eddy-currents which act so as to delay the build-up and reduction of the magnetic flux when the solenoid valve is switched on and off, and hence prevent fast switching. As a result of the mutually electrically insulated sheet metal layers, no closed eddy-current paths can affect the entire magnetic flux. The weakening effect, of the individual eddy-current circuits developed in the thin sheet metal layers, on the magnetic field is substantially less than that in a magnetic circuit made of homogeneous magnetic material.

In known solenoid valves of the type described above- and having a magnetic circuit comprising -a magnet pot, pole disc, armature and inner and outer annular air gaps, the difficulty of providing total lamination of the magnetic circuit results from the small dimension of the armature and pole disc. Since the greater part of the iron path length of the magnetic circuit is apportioned to the magnet pot, lamination of the magnet- pot has a particularly advantageous effect on shortening valve switching times.

Preferably, the present invention provides ideal conditions with respect to the distribution of magnetic flux in the magnet pot, pole disc and annular air gaps such that it corresponds to that of a conventional magnetic circuit of rotationally symmetrical solenoid valves, with the advantage of a large degree of suppression of eddies, and hence recognisably shorter switching times.

Preferably, the sheet metal layers are in the form of planar, parallel sheet metal laminations combined to form a magnet pot having a flat surface at its base region and at diametrically opposite outer walls disposed adjacent part of the outer surface of the inner cylinder wall of the magnet pot. Although these measures provide for technically simple manufacture of the laminated magnet pot, they also result in inhomogeneous magnet fields and losses in magnetic flux and force.

Advantageously, measures are provided which enable the magnet pot to be manufactured simply, with a symmetrical structure and good magnetic flux distribution in the solenoid pot, pole disc and annular air gaps.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a longitudinal section through one embodiment of a solenoid valve in accordance with the present invention, for a fuel injection pump in the form of a pump nozzle for a diesel engine; Fig. 2 is a longitudinal section through one embodiment of a magnet pot of the solenoid valve of Fig. 1; Fig. 3 is a plan-view of the magnet pot of Fig. 2; Fig. 4 is a perspective representation of a sheet metal segment of the magnet pot of Figs. 2 and 3; Fig. 5 is a perspective representation of a portion of the magnet pot of Figs. 2 and 3; Fig. 6 is a longitudinal section through another embodiment of a magnet pot; Fig. 7 is a plan view of the magnet pot of Fig. 6; Fig. 8 is a longitudinal section through a further embodiment of a magnet pot; and Fig. 9 is a plan view of the magnet pot of Fig. 8.

The solenoid valve shown in longitudianl section in Fig. 1 and operating as a two-port, two-position valve, is inserted in an aver flow passage of a fuel injection pump in the form of a pump nozzle described in detail in German Offenlengungsschrift No. 35 23 536.

The overflow passage connects the pump working chamber of a fuel injection pump to a low-pressure chamber and, following connection of the solenoid valve to the housing of the fuel injection pump by means of a union nut 10, it has a first passage segment 11 connected to the pump working chamber, and a second passage segment 12 connected to the low-pressure chamber, both of which passage segments are in a housing 13 of the solenoid valve. The passage segments 11, 12 are separated from one another by a flow-through port 14 surrounded by a valve seat 15. The valve seat 15 co-operates with a valve needle 16 acted upon by a valve spring 17 so as to open and close the flowthrough port 14. The end of the valve needle 16, remote from the valve seat 15 is connected to an armature 18 of an electromagnet 19.A stroke stop 20, fixed to the housing, is provided to limit the stroke of the valve needle.

The electromagnet 19 has a magnet winding 21 and a closed magnetic circuit 22 which comprises an armature 18, a magnetic core which lies opposite the armature 18 leaving an air gap therebetween, and a yoke which completes the magnetic path. The core and the yoke are formed by a pot 23, which is in one piece, and has an outer cylinder wall 24 and an inner cylinder wall 25 connected to one another by way of a base 26. The inner surface 24a and outer surface 25a (Fig. 2) of the two cylinder walls 24,25 define an annular chamber 27, in which the winding 21 is disposed.The magnet pot 23 is seated by way of its inner cylinder wall 25 on a portion 13a of the valve housing 13, which wall 25 forms a guide sleeve for the valve needle 16, and the opening of the magnetic pot is covered by an annular pole d is c 28 located opposite the armature 18 such that an outer annular air gap 29 is formed therebetween in the axial direction. The armature 18 is integral with a cylindrical protrusion 30 which is located through the pole disc 28, is disposed opposite the annular end face of the inner cylinder wall 24 and forms an inner air gap 31 therebetween. The two ends of the winding 21 are connected electrically to two attachment plugs 32,33.If the winding 21 is excited, the armature 18 is moved against the return force of the valve compression spring 17, towards the pole disc 28 and pot 23 so as to reduce the air gaps 29,31 until the valve needle 16 presses onto the valve seat 15 and prevents further movement of the armature 18.

To obtain short valve switching times, the magnet pot 23 is laminated by a plurality of thin, contiguous layers of sheet metal extending in the direction of magnetic flux and electrically insulated from one another. The embodiments of the pot shown in Figs. 4 to 9 show different possible types of lamination of the- pot.

In the case of the magnet pot 23 shown in various views in Figs. 2 to 5, the sheet metal layers are in the form of wedge-shaped sheet metal segments 34, which taper radially towards the centre of the pot.

One sheet metal segment 34 is shown in persepctive in Fig. 4. This segment 34 has an outer member 341 and an inner member 342, parallel to one another and connected by way of a base member 343, which is at right angles thereto and tapers in a wedge-shape from the outer member 341- to the inner member 342.

The two members 341 and 342 have an annular segmental cross section. The magnetic flux which forms in the sheet metal segment 34 when the winding 21 is excited is indicated in Fig. 4 by arrows 35, and the electrical eddy-currents caused by the magnetic flux are indicated by arrows 36. A plurality of such sheet metal segments 34 are combined to form the rotationally symmetric magnet pot 23, as shown in perspective in Fig. 5 and as a plan view in Fig. 3.

The plurality of outer members 341 form the outer cylinder wall 24, the plurality of inner members 342 form the inner cylinder wall 25 and the plurality of base members 343 form the base 26 of the magnet pot 23. To manufacture the magnet pot 23, wedgeshaped rectangular sheet metal pieces, from which the U-shaped members 341 and 343 in Fig. 4 have not yet been worked, are combined in a device and contacted, thus producing a solid cylinder block. By working, e.g., eroding or grinding, the solid cylinder block appropriately, a magnet pot 23 with two cylinder walls 24,25 and base 26 can be produced. Such a rotationally symmetrical pot 23, which is laminated in the radial direction, has ideal magnetic flux distribution, such as can be found in conventional rotationally symmetrical pots made of homogeneous magnetic material.

In the magnet pot 123 shown in the embodiment in Figs. 6 and 7, the sheet metal layers are in the form of planar, parallel sheet metal laminations 137 located parallel to the diameter of the magnet pot.

The shaded part in Fig. 6 represents the end contour of the middle sheet metal lamination 137, whose longitudinal axis coincides with the diameter of the magnet pot 123. A plurality of such parallel, adjacently disposed sheet metal laminations 137 form the magnet pot 123, having a flat surface at its base region and at diametrically opposite outer walls 124 disposed adjacent part of the outer surface 125a of the inner cylinder wall 125. The asymmetrical shape of the magnet pot 123 which results from this lateral flattening can be seen particularly clearly in the plan view of the pot 123 shown in Fig. 7. In manufacture, a plurality of planar, rectangular sheet metal laminations 137 are glued or welded together to form a stack of laminations, whose thickness is the same as the diameter of the outer surface 125a of the inner cylinder wall 125 of the pot 123.The shape of the pot 123 as shown in Figs. 6 and 7 is produced by eroding or grinding the stack of laminations.

For reasons of clarity, the pattern of the parallel sheet metal lam-inations 137 is shown in Fig. 7 in part only.

In the embodiment of a magnet pot 223 shown in Figs. 8 and 9, the sheet metal layers are again in the form of planar, parallel sheet metal laminations 238, which are combined to form four pot segments 239, which are disposed crosswise. The pot segments 239 are radially aligned with respect to one another and are staggered by an angle of 900. The end face portions 240 of the segments 239, which are inclined by 450, meet at the centre region of the pot. Each pot segment 239 has an inner cylinder wall portion 225' and an outer cylinder wall portion 224', which are connected, as one piece, to one another by way of a pot base portion 226'. All the segments have the same width, which corresponds to the diameter of the outer surface 225a of the inner cylinder wall 225 of the pot 223. As a result of the crosswise arrangement of the pot segments'239, the four inner cylinder wall portions 225' , which meet in the middle of the pot, form the closed inne-r cylinder wall 225 of the pot 223. In manufacture, each pot segment 239 is formed by means of .erosion or grinding from a rectangular bundle of laminations, whose thickness is the same as the diameter of the outer surface 225a of the inner cylinder wall 225 of the pot 223. The individual stacks of laminations are again made by welding or sticking together planar, rectangular sheet metal laminations 238.

Claims

1. A solenoid valve for a fuel injection pump in an internal combustion engine, said valve having a valve needle for controlling a valve flow-through port, and an electromagnet for actuating the valve needle, which electromagnet includes a magnet winding and a magnetic flux path comprising a magnet core, a magnet armature connected to the valve needle,-and located opposite the core so as to form an air gap between the armature and the core, and a yoke for completing the magnetic path, wherein at least part of the magnetic flux path is laminated in that it comprises thin, contiguous, sheet metal layers which extend in the direction of magnetic flux incident therein and are electrically insulated with respect to one another.

2. A valve as claimed in claim 1, wherein the magnet core and yoke are laminated.

3. A valve as claimed in claim 2, wherein the magnet core and the yoke are in one piece and form a magnet pot having an outer and an inner cylinder wall interconnected by way of a pot base, the magnet winding, in the form of a bobbin, being enclosed in an annular chamber formed by the outer surface of the inner cylinder wall and the inner surface of the outer cylinder wall.

4. A valve as claimed in claim 3, wherein the sheet metal layers are in the form of wedge-shaped sheet metal segments tapering radially towards the middle of the magnet-pot and combined to form a rotationally symmetrical magnet pot.

5. A valve as claimed in claim 3, wherein the sheet metal layers are in the form of planar, parallel sheet metal laminations combined to form a magnet pot having a flat surface at its base region and at diametrically opposite outer walls disposed adjacent part of the outer surface of the inner cylinder wall of the magnet pot.

6. A valve as claimed in claim 5, wherein the laterally flat magnet pot is formed from a stack of laminations, whose thickness corresponds to the diameter of the outer surface of the inner cylinder wall of the magnet pot.

7. A valve as claimed in claim 3, wherein the sheet metal layers are in the form of planar, parallel sheet metal laminations combined to form four crosswise disposed pot segments whose end face portions, which are inclined at 450, abut at the centre region of the magnet pot and wherein each pot segment has an inner cylinder wall portion and an outer cylinder wall port ion mutually connected by way of a pot base portion having the same width as each pot segment, whereby the inner cylinder wall portions-of the four pot segments form the closed inner cylinder wall of the magnet pot.

8. A valve as claimed in claim 7, wherein each pot segment is formed from a stack of laminations, whose thickness is the same as the diameter of the outer surface of the inner cylinder wall of the cylinder pot.

9. A valve as claimed in claim 6 or 8, wherein the pot is formed by eroding or grinding the bundle of laminations.

10. A solenoid valve for a fuel injection pump in an internal combustion engine substantially as hereinbefore described with reference td and as illustrated in the accompanying drawings.