[0001] This invention relates to a fuel injector for an internal combustion engine.
[0002] In a previously proposed fuel injector the injector body has therein a fuel flow
passage terminating at one end in a shaped orifice through which, in use, fuel issues
into the inlet manifold of the internal combustion engine. Within the body the fuel
flow to the orifice is controlled by a valve including a valve closure member movable
relative to a valve seat. Movement of the closure member in one direction to engage
the seat, and thus cut off the flow of fuel through the injector, is generated by
a spring, and movement in the opposite direction to open the valve is generated by
energisation of an electromagnet. In the previously proposed injector the closure
member is in the form of a circular disc the peripheral edge of which defines a cylindrical
surface. The disc is guided for movement in the direction of the axis of said cylindrical
edge surface by a corresponding internal circular cylindrical surface of the injector
body.
[0003] The use of a closure member having a cylindrical edge surface supported as a sliding
fit in a corresponding cylindrical part of the injector body gives rise in particular
to
/problems. Firstly it is found to be difficult to assemble the closure member to the
body owing to the similarity of the diameters of the closure member and the region
of the body within which the closure member is received, and secondly when the closure
member is assembled within the body, the presence, in use, of fuel in the bearing
defined by the cylindrical surface of the closure member and the internal cylindrical
surface of the body impedes the movement; of the closure member. It is believed that
this latter problem results from "fluid" or "viscous" drag exhibited by the thin film
of fuel in the bearing when subjected to shear forces during movement of the closure
member relative to the body. It is an object of the present invention to provide an
injector of the kind wherein a disc-like closure member is slidably received in the
injector body, in which the aforementioned problems are minimised.
[0004] A fuel injector according to the invention includes a body having therein a fuel
flow path, a valve in said fuel flow path, said valve including a disc-like closure
member guided by an internal circular cylindrical surface of the body for movement
relative to the body in a direction parallel to the axis of said cylindrical surface,
between a closed position wherein the member engages a mating valve seat to prevent
fuel flowing through said path, and an open position wherein thenember is spaced from
said seat to permit fuel flow along said path, the peripheral surface of said closure
member, which co-operates with said internal cylindrical surface, being so shaped
that considering the member and said cylindrical surface in axial-section (as opposed
to cross-section) the peripheral edge of the member includes a region which is curved,
with the straight line defined by the axial-section of said cylindrical surface tangential
thereto, the peripheral surface of the closure member thus having a peripheral, substantially,
line-contact, at its region of greatest diameter, with said internal cylindrical surface.
[0005] Conveniently said region of the peripheral surface of said closure member is part-spherical.
[0006] Preferably the whole of the peripheral surface of said closure member is part-spherical.
[0007] Desirably the centre of curvature of said part spherical surface of the closure member
coincides with the centre point of the region of the closure member bounded by said
part-spherical surface.
[0008] The accompanying drawing is an axial sectional view of part of an injector in accordance
with one example of the pres t invention.
[0009] Referring to the drawing the injector includes a multi-part body 11 including a main
body 12, an annular bearing plate 13, and a nozzle assembly 14. A fuel flow path 15
extends through the body 11 from an inlet union (not shown) to an outlet orifice 16
defined by the nozzle assembly 14. The bearing plate 13 is interposed between the
nozzle assembly 14 and the main body part 12, and the portion of the fuel flow path
15 defined within the main body part 12 communicates with the orifice l6 by way of
the central aperture of the annular bearing plate 13. However, within the central
aperture of the bearing plate 13 is supported a circular, disc-like valve closure
member 17.
[0010] The outlet end of the portion of the fuel flow path within the main body part 12
is defined by an annular aperture 18 which is aligned with the central aperture of
the plate 13. The orifice 16 of the nozzle assembly 14 is disposed on the axis of
the injector, and surrounding the orifice 16 is a raised valve seat 19 against which
the closure member 17 is urged by a compression spring 21. The valve closure member
17 is formed with a circular row of through bores 22 which communicate at one end
with the annular outlet 18 of the main body part 12. The circular row of through bores
22 lies radially outwardly from the valve seat 19, and thus when the central solid
part of the closure member 17 engages the valve seat 19 then flow of fuel from the
bores 22 to the orifice 16 is prevented. However, when the closure member 17 is raised
from the valve seat 19 fuel can flow from the outlet 18 of the main body part 12,
through the bores 22, between the lower face of the closure member 17 and the seat
19, and through the orifice 16 into the inlet tract of the internal combustion engine
utilizing the injector.
[0011] As previously mentioned the valve defined by the closure member 17 and the seat 19
is closed by the action of the spring 21 which urges the closure member 17 firmly
against the seat 19. The valve is opened by energisation of an electromagnet the fixed
inner pole of which is defined by a centrally disposed hollow spigot 12a of the main
body part 12,and the movable armature of which is defined by the closure member 17.
As will be apparent from the drawing the spring 21 is housed within the hollow spigot
12a. The electromagnet winding (which is not shown in the drawing) encircles the spigot
l2รข,and when the winding is energised the closure member 17 which is formed from ferro-magnetic
material, is moved towards the lower end of the spigot 12a against the action of the
spring 21 to open the valve.
[0012] The wall 23 of the central aperture in the plate 13 is cylindrical, and is of circular
cross-section, the axis of the cylindrical surface 23 being coincident with the axis
of the spigot 12a. The peripheral, outer surface 24 of the closure member 17, for
which the surface 23 constitutes a bearing, is part spherical, having its centre of
curvature coincident with the centre point of the closure member. Thus the region
of the closure member 17 of greatest diameter is on the median plane of the closure
member 17 and makes substantially line contact, around the periphery of the closure
member 17, with the surface 23. When considered in axial section, (as shown in the
drawing) the peripheral edge of the closure member is part circular, and the line
defined by the axial section of the cylindrical surface 23 is tangential thereto.
It should be noted that in the interests of clarity no contact is shown in the drawing
between the surface 24 and the surface 23. In practice however bearing contact can
occur and by virtue of the curved nature of the surface 24 the contact between the
surface 24 and the surface 23 is restricted to a peripheral, substantially line contact.
It will be recognised therefore that on either side of the line of contact between
the surface 24 and the surface 23 the closure member is in effect relieved to provide
a clearance between the surfaces 23 and 24. This clearance facilitates insertion of
the closure member 17 into the aperture of the bearing plate 13 during assembly of
the injector, and also minimizes the "fluid" or "viscous" drag on the closure member
17 resulting from the presence of liquid fuel in the bearing defined between the closure
member 17 and the bearing plate 13, by comparison with the drag which would be exhibited
by the fuel film in the bearing if the outer peripheral surface of the closure member
17 were cylindrical and a sliding fit in the bearing plate 13.
[0013] While it is preferable for the surface 24 of the closure member 17 to be part spherical,
having its centre of curvature coincident with the centre of the closure member 17,
it is to be understood that it is not essential that the surface 24 is part spherical,
and it is not essential that even if the surface 24 is part spherical then its centre
of curvature is coincident with the actual centre point of the closure member. For
example, it would be possible to produce the closure member 17 having the surface
24 part spherical, but with the centre of curvature of the surface 24 coincident with
the centre of one or other of the axial end faces of the closure member 17. In such
an arrangement of course the region of greatest diameter of the closure member would
be at one or other of the axial ends of the closure member, and all of the clearance
between the surface 24 and the surface 23 would be to one side of the peripheral line
of contact between the surface 24 and the surface 23. Equally of course the surface
24 may if desired by part elipsoidal or the like rather than part spherical. Nevertheless,
it is preferable for the surface 24 to be part spherical having its centre of curvature
coincident with the actual centre of the closure member so that misalignment of the
closure member within the plate 13 can be accommodated in use. It will be recognised
that in such an arrangement the closure member and plate 13 will act in the manner
of a ball and cup joint and the effects of any misalignment will be minimal.
1. A fuel injector including a body having therein a fuel flow path, a valve in said
fuel flow path, said valve including a disc-like closure member guided by an internal
circular cylindrical surface of the body for movement relative to the body in a direction
parallel to the axis of said cylindrical surface between a closed position wherein
said member engages a mating valve seat to prevent fuel flow along said path, and
an open position wherein the member is spaced from said seat to permit fuel to flow
along said path characterized in that the peripheral surface 24 of said closure member
17, which co-operates with said internal cylindrical surface 23, being so shaped that
considering the member 17 and said cylindrical surface 23 in axial section the peripheral edge of said member
17 includes a region which is curved, with the straight line defined by the axial
section of said cylindrical surface 23 tangential thereto, the peripheral surface
24 of the member 17 thus having a peripheral substantially line contact, at its region
of greatest diameter, with said internal cylindrical surface 23.
2. An injector as claimed in claim 1 characterized in that said region of the peripheral
surface 24 of the member 17 is part-spherical.
3. An injector as claimed in claim 2 characterized in that the whole of the peripheral
surface 23 of the member 17 is part-spherical.
4. An injector as claimed in claim 2 or claim 3 wherein the centre of curvature of
said part spherical surface 24 of the member 17 coincides with the centre point of
the region of the member 17 bounded by said part spherical surface 24.
