Injector and injector assembly

An injector assembly comprising an injector (3) and a wall (1) having an inner surface (2) defining a cavity receiving the injector (3). A peripheral surface portion of the injector (3) and a corresponding portion of the cavity inner surface (2) are configured to inter-engage such that force applied to the injector (3) in a predetermined direction causes mutually oppositely directed reaction forces perpendicular to the applied force which tend to laterally compress the injector (3), for relieving lateral stress within the injector (3). Additionally, an injector (3) for fitting in a cavity of an injector assembly, the injector (3) including an axially extending portion (10) comprising at least two peripheral irregularities in an otherwise substantially regular lateral cross-section.

This invention relates to an injector assembly comprising an injector and a
 wall having an inner surface defining a cavity receiving the injector. The
 invention also relates to an injector for fitting in a cavity. The
 invention is applicable particularly, but not exclusively, to fuel
 injectors and injector assemblies for internal combustion engines.
 In a known type of fuel injector assembly, an injector having an axially
 extending portion of substantially circular cross-section is closely
 fitted in a cavity within a cylinder head, the cavity having an inner
 surface of correspondingly circular cross-section. A connector feeds fuel
 from a high pressure line into a fuel passageway in the injector. The
 passageway's inlet opens to the lateral periphery of the axially extending
 portion of the injector. When the connector is tightly fitted so as to
 seal against the inlet, lateral force is exerted on the injector. The
 lateral force causes an equal and opposite reaction force where the
 substantially concentric surfaces of the injector and cavity meet, in a
 region diametrically opposite the injector inlet.
 Whilst such assemblies have hitherto provided acceptable performance at
 commonly used levels of fuel pressure, a problem has arisen with such
 assemblies due to stress concentrations within the injector at a region of
 intersection of a generally laterally extending drilling and a generally
 axially extending drilling which together form the fuel passageway. The
 problem is exacerbated when increased fuel injection pressures are used.
 Such stress concentrations tend to produce tensile forces acting
 substantially perpendicularly to the applied force, outwardly of the
 injector, which may limit the pressure which the injector is able to
 withstand.
 The invention seeks to overcome or mitigate the above-mentioned problem.
 SUMMARY OF THE INVENTION
 Accordingly, the invention provides an injector assembly comprising an
 injector and a wall having an inner surface defining a cavity receiving
 the injector, a peripheral surface portion of the injector and a
 corresponding portion of the cavity inner surface being configured to
 inter-engage such that force applied to the injector in a predetermined
 direction causes mutually oppositely directed reaction forces
 perpendicular to the applied force which tend to laterally compress the
 injector, for relieving lateral stress within the injector. This can
 conveniently be achieved by providing a space between the wall's inner
 surface and a region of the peripheral surface portion of the injector
 lying opposite a point of application of the applied force.
 The injector and cavity are preferably configured such that reaction forces
 having two mutually equal and opposite components are caused perpendicular
 to the applied force.
 Where the injector includes a passageway for carrying high pressure fluid
 leading from the lateral periphery of the injector to an axial end of the
 injector, the applied force being applied laterally by a connector
 supplying fluid to the passageway, and the passageway comprises a
 primarily laterally extending portion and a primarily axially extending
 portion, the injector and cavity surfaces may conveniently be arranged to
 direct the mutually opposite reaction forces through a region of the
 injector where the passageway portions intersect.
 Advantageously, an axially extending portion of the injector which includes
 the above-mentioned peripheral surface portion thereof is part circular in
 lateral cross-section. Preferably, this axially extending portion is
 configured such that the part circular portion of its periphery would
 provide a close matching fit with the substantially circular corresponding
 portion of the cavity inner surface, but for a relieved segment of the
 axially extending portion having an eccentrically disposed peripheral
 curve with a larger radius of curvature, thereby providing two regions of
 inter-engagement of the injector and the cavity inner surface for
 respectively providing the reaction forces.
 Alternatively, the injector may comprise an axially extending portion which
 is substantially circular in lateral cross-section, two irregularities
 extending radially inwardly from the cavity inner surface, which is
 otherwise correspondingly circular in cross-section, thereby providing two
 regions of inter-engagement between the injector and the cavity inner
 surface for respectively providing the reaction forces.
 The connector conveniently applies lateral force in a direction along the
 primarily laterally extending portion of the passageway midway between the
 regions of engagement, thereby bisecting the injector.
 The wall may comprise a body portion having a bore receiving a sleeve, the
 inner surface of which defines said cavity.
 The invention also includes an injector for fitting in a cavity, the
 injector having an axially extending portion comprising at least two
 peripheral irregularities in an otherwise substantially regular lateral
 cross-section. The axially extending portion may be part circular in
 lateral cross-section, one segment of this portion having an eccentrically
 disposed peripheral curve with a large radius of curvature, thereby
 providing two peripheral irregularities for engaging a cavity inner
 surface having a substantially circular cross-section.
 In order that the invention may be well understood, an example thereof,
 which is given by way of example only, will now be described with
 reference to the accompanying drawings, in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring to the figures, the cylinder head of an internal combustion
 engine includes a wall 1 having an inner surface 2 defining a cavity
 receiving an injector 3 for injecting fuel into a cylinder (not shown) of
 the engine. The injector 3 has a drilling 4 extending primarily laterally
 from its inlet 5 which opens to the lateral periphery of the injector 3,
 to an intersection 11 with another drilling 6. The drilling 6 extends
 primarily axially within the injector 3 from the intersection 11 to
 connect the first mentioned drilling 4 with an outlet 7. The two drillings
 4, 6, together form a passageway for carrying high pressure fuel.
 In use, fuel from a high pressure pump is fed through a pipe 8 through a
 connector 9 into the inlet 5 and is injected into the cylinder through the
 fuel passageway 4, 6. To provide an effective seal between the inlet 5 of
 the fuel passageway 4, 6 and the outlet end of the connector 9, the
 connector 9 is securely fastened to the wall 1 by a screw fastening 9a to
 provide the necessary sealing force. Whilst the exemplary arrangement
 shows a connector 9 having its axis substantially perpendicular to the
 axis of the injector 3, it is to be understood that the invention is
 equally applicable to arrangements where the connector axis is oblique to
 the injector axis, thereby providing a sealing force having a substantial
 component in the direction of the axis of the injector in addition to a
 lateral component.
 An axially extending portion 10 of the injector 3, which portion includes
 the inlet 5, is closely fitted within a corresponding axially extending
 portion of the cavity having a substantially circular lateral
 cross-section. As best shown in FIG. 2, disregarding the irregularity
 formed by the inlet 5, the portion 10 is not circular in lateral
 cross-section. Rather, a portion 10 of regular circular cross-section has
 been relieved over a region diametrically opposite the inlet 5, this
 relieved segment having an eccentrically disposed periphery with a larger
 radius of curvature. Thus, with the injector 3 fitted in the cavity and
 lateral force F applied by the connector 9, the axially extending portion
 10 of the injector 3 engages the inner surface 2 of the cavity at two
 points equidistant the line of action of the applied force, which acts
 along the fuel passageway 4, 6, causing two resultant reaction forces
 F.sub.R one to either side of the line of action of the applied force F.
 Each reaction force F.sub.R has a component acting perpendicularly to the
 direction of the applied force F and passing through the intersection 11
 of the drillings 4, 6. A compressive force is thus provided which tends to
 counteract stress concentrations at the intersection 11 generated by high
 pressure fuel in the passageway 4, 6, which tend to act in a direction
 perpendicular to the applied force F. Clearly , this arrangement also
 avoids the increase in such stress concentration which results from a
 single reaction force, equal and opposite to the applied force F, acting
 through the intersection 11.
 The applied clamping force F, the location of the engagement points between
 the injector and cavity surfaces, and the angle .theta. between the
 reaction forces F.sub.R in the exemplary embodiment are selected to
 provide a small compressive stress at the intersection 11 when no high
 pressure fuel is flowing in the passageway 4, 6. In operation, with
 fluctuating fuel pressure in the passageway 4, 6, peak and mean stresses
 experienced at the intersection 11 can be significantly reduced.
 Clearly, many other ways of causing reaction forces having compressive
 components perpendicular to the applied force will be apparent to the
 skilled man. For example, irregularities may be provided on the inner
 surface of the cavity offset to either side of the line of the applied
 force, whereby suitable compressive forces can be obtained using an
 injector having a substantially circular cross-section. Such
 irregularities may be formed on the inner surface of a sleeve which is
 then inserted into a bore in the wall.
 Although in the description hereinbefore the applied force results from the
 action of the inlet connector, it will be appreciated that the invention
 is also applicable where other applied forces result in the formation of
 stress concentrations in the injector.