Internal combustion engine fuel injector

An internal combustion engine fuel injector has a casing defining a nozzle; and a shutter pin having an axis, and housed in axially sliding manner inside the casing to close the nozzle by virtue of a control rod. The pin and the control rod are connected by a connecting device, which has an axial seat carried by the pin, and a head interposed between the axial seat and the control rod, and which engages the axial seat to transmit to the pin a resultant of forces directed solely along the pin axis.

The present invention relates to an internal combustion engine fuel injector.

BACKGROUND OF THE INVENTION

Fuel injectors are known which comprise an inlet connected to a fuel supply pump; a nozzle communicating with the inlet to inject fuel into the engine; and a shutter pin, which is moved axially, to open and close the nozzle, by the opposite axial thrusts exerted by the pressure of the injected fuel, on one side, and by a positioning spring and a control rod, on the other.

The control rod is located along the axis of the pin, on the opposite side to the nozzle, is activated by an electromagnetic metering valve forming part of the injector, and is connected to the pin with the axial interposition of a cylindrical spacer body.

The spacer body is defined by two opposite flat surfaces crosswise to the axis and resting on the flat ends of the control rod and pin respectively, and is of an axial height calibrated according to given classes, and which is selected as a function of the desired maximum lift or axial stroke of the pin.

Known injectors of the above type are not always satisfactory, owing to the resultant of the contact pressures between the spacer body and the pin being applied at a normally indefinite point, and normally generating on the pin undesired transverse forces crosswise to the axis.

The pressures exerted by the spacer body on the pin, in fact, are not always distributed evenly over the mutually contacting surfaces, mainly on account of inevitable flatness and roughness tolerances, so that the resultant of the pressures sometimes generates on the pin rotation torques about a direction perpendicular to the pin axis.

Said transverse forces are sometimes also generated by the mutually contacting surfaces of the spacer body and pin not being perfectly perpendicular to the pin axis.

Such transverse forces produce relatively severe friction forces along the seat in which the pin slides, thus resulting in an anomalous increase in wear and, therefore, in the radial clearance between the pin and seat. This in turn results in an undesired increase in leakage of the unused fuel, which flows out of the injector through a recirculating outlet.

The increase in leakage and, therefore, in the amount of fuel recirculated may result in the pump being unable to supply the injectors in all engine operating conditions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an internal combustion engine injector designed to provide a straightforward, low-cost solution to the above drawbacks.

According to the present invention, there is provided a fuel injector for an internal combustion engine; the injector comprising a casing defining a nozzle for injecting fuel into said engine; a shutter having an axis and housed in axially sliding manner inside said casing to open and close said nozzle; control means for pushing said shutter towards said nozzle to close the nozzle; and connecting means for connecting said shutter to said control means; characterized in that said connecting means comprise an axial seat carried by one of said shutter and said control means; and a head interposed between said axial seat and the other of said shutter and said control means, and engaging said axial seat so as to transmit to said shutter a resultant of forces directed solely along said axis of said shutter.

DETAILED DESCRIPTION OF THE INVENTION

Number1inFIG. 1indicates a fuel injector for an internal combustion engine, in particular a diesel engine (not shown). Injector1comprises a hollow outer structure or casing2extending along an axis3, and having a lateral inlet5for connection to a pump forming part of a fuel supply system (not shown), and an end nozzle7communicating with inlet5to inject fuel into a relative cylinder of the engine.

Casing2comprises an intermediate axial portion8, and two opposite end portions9,10. Portion9is located on the opposite side to nozzle7, and houses a known electromagnetic metering valve12(not described in detail) having an outlet13for recirculating back to the supply system tank (not shown) the portion of fuel “consumed” by valve12, and the portion of fuel leaking through the internal components of injector1, and which is fed to valve12along an inner conduit14.

Portion10is a so-called atomizer, and defines a cylindrical axial chamber15housing a shutter pin16, and comprising a channel17terminating in nozzle7, and a guide seat18.

Pin16has an axis19coincident with axis3, and comprises a rod20housed in channel17; and a cylindrical head portion21, which is slid axially with relatively little clearance inside seat18, to allow the tip of rod20to open and close nozzle7, by the opposite axial thrusts exerted, on one side, by the pressure of the fuel in channel17, and, on the other, by a positioning spring22and an axial control rod23.

Rod23is activated by valve12to slide axially inside portion8, and is subjected, in particular, to the opposite axial thrusts of the reaction of pin16and the pressure of the fuel inside an axial control chamber24communicating with inlet5and controlled by valve12. Chamber24is defined by a tubular body25, which has a cylindrical axial guide seat26communicating with chamber24and engaged in sliding manner and with relatively little radial clearance by an end portion28of rod23.

With reference toFIG. 1, rod23comprises two opposite portions30,31. Portion30faces valve12and terminates with portion28; while portion31is smaller in diameter than portion30, and is surrounded by spring22, which is interposed between two spacer rings32,33resting axially on a shoulder34of portion8and on portion21respectively.

Portion21is connected to portion31by a connecting device35for transmitting from rod23to pin16a resultant of forces A directed solely along axis19.

Device35comprises a cavity36formed, coaxially with axis19, in portion21and defined by a conical surface37; and a spherical spacer body39interposed between pin16and rod23, and engaging cavity36. Body39is defined by a spherical surface40resting, on one side, on the flat end of portion31, at a point of contact42along axis19, and, on the other side, on conical surface37, along a circular line of contact43(shown by a dash line inFIGS. 1,2and3).

The diameter of body39is calibrated according to given classes, and is selected as a function of the desired maximum lift or axial stroke of pin16.

TheFIG. 2embodiment relates to a fuel injector51, the component parts of which are indicated, where possible, using the same reference numbers as for injector1. Injector51is a so-called “virtual lift” type, i.e. comprises a pin16, which slides axially inside seat15to open nozzle7without ever reaching a predetermined axial limit position, and which therefore has no fixed maximum lift value.

Injector51differs from injector1substantially by having no body39. Instead of device35, injector51therefore comprises a connecting device55, in turn comprising cavity36, and a hemispherical head59integral with rod23and defining the axial end of portion31. Head59engages cavity36, and is defined by a spherical surface60having the same curvature as surface40, and resting on conical surface37along contact line43.

Device55also comprises a weakened portion of rod23, defined by a circumferential groove61formed in an intermediate portion63of portion30, outside seat26, and which allows portion31a relatively limited amount of freedom to flex with respect to portion28in a direction crosswise to axis3, so as to center head59automatically inside cavity36, i.e. to position spherical surface60perfectly coaxial with conical surface37.

In injector1, body39is also, obviously, centered automatically inside cavity36, by being movable crosswise to rod23at point of contact42.

In theFIG. 3variation, to simplify production, spring22is replaced by a spring64resting, on one side, on spacer ring32, and, on the other, on a flat surface65defining portion21directly, without ring33. The same variation may also be applied to injector1.

In theFIG. 4variation, to simplify production, hemispherical head59is replaced by a conical head69resting on conical surface37along a line of contact73defined by the circular edge connecting head69to the rest of portion31.

In actual use, rod23exerts an axial thrust F, which is transmitted along line of contact43,73in a direction perpendicular to conical surface37to move pin16towards, and so close, nozzle7. Given a generic diametric section, as shown in the larger-scale details inFIGS. 1 and 2, diametrically opposite points P1and P2along line of contact43are subjected to respective forces F1and F2of equal modulus, by thrust F being directed coaxially with conical surface37.

If each force F1, F2is divided into a respective component A1, A2directed parallel to axis19, and a respective component T1, T2directed perpendicularly to axis19, components T1and T2are equal and opposite, and therefore give rise to a zero resultant; whereas components A1and A2, being equal and concordant and applied at respective points P1, P2symmetrical with respect to axis19, give rise to a resultant of forces A acting on pin16and directed solely along axis19.

As a result of microdeformations in body39and heads59,69along relative lines of contact43,73, lines of contact43,73are in fact defined by annular areas of contact, which, however, are so small as to have no effect on the above resolution of forces.

Devices35,55connecting pin16to rod23therefore provide for reducing the increase in wear and, therefore, radial clearance between seat18and portion21, by pin16receiving from rod23a resultant of forces A having no component crosswise to axis19.

Moreover, devices35,55are relatively straightforward, by comprising a fairly small number of components, and by only requiring precision machining to ensure surface37is coaxial with the cylindrical lateral surface of portion21sliding inside seat18; and, unlike known solutions, surface65of portion21need not be perfectly flat and perpendicular to axis19.

Since, in the case of “virtual lift” injectors, the lift of pin16need not be calibrated by an appropriately sized spacer body, injector51, as compared with known solutions, is extremely straightforward by comprising no intermediate body between rod23and pin16.

Clearly, changes may be made to injectors1,51as described and illustrated herein without, however, departing from the scope of the present invention.

In particular, cavity36, head59,69and/or body39may be defined by contacting surfaces other than surfaces37,40,60, but still interacting with one another to transmit from rod23to pin16a resultant of forces A directed solely along axis19.

Also, cavity36may be formed axially in the end of rod23, and head59,69may be carried by pin16.