Patent Description:
A direct injection system comprises a plurality of injectors, a common rail which feeds the fuel under pressure to the injectors, a high-pressure fuel pump, which feeds the fuel to the common rail by means of a high-pressure feeding duct and is provided with a flow rate adjustment device, and a control unit which controls the flow rate adjustment device for maintaining the pressure of the fuel inside the common rail equal to an intended value generally variable over time depending on the operation conditions of the engine.

The high-pressure fuel pump described in patent application <CIT> comprises: a main body, a pumping chamber made in the main body and inside which a piston slides with reciprocating motion, an intake duct adjusted by an intake valve for feeding the fuel at a low pressure inside the pumping chamber, and a delivery duct adjusted by a delivery valve for feeding the fuel at a high pressure outside of the pumping chamber and towards the common rail.

The intake valve is normally pressure operated and in the absence of external interventions the intake valve is closed when the pressure of the fuel in the pumping chamber is greater than the pressure of the fuel in the intake channel and is open when the pressure of the fuel in the pumping chamber is less than the pressure of the fuel in the intake channel. The flow rate adjustment device is mechanically coupled to the intake valve for maintaining, when necessary, the intake valve open during the pumping step of the piston and thus enabling a flow of fuel to come out of the pumping chamber through the intake channel. In particular, the flow rate adjustment device comprises a control rod, which is coupled to the intake valve and is movable between a passive position, in which it allows the intake valve to close, and an active position, in which it does not allow the intake valve to close. The flow rate adjustment device further comprises an electromagnetic actuator, which is coupled to the control rod for moving the control rod between the active position and the passive position. The electromagnetic actuator comprises a spring which maintains the control rod in the active position, and an electromagnet which is adapted to move the control rod in the passive position magnetically attracting a ferromagnetic keeper integral with the control rod against a fixed magnetic armature.

The flow rate adjustment device is normally housed in a metal bottom which is laser welded to a side wall of the main body in the area of the intake duct.

It has been noted that a small but not entirely negligible percentage of the high-pressure fuel pumps of the type described above are faulty particularly due to the absence of operation or for the irregular operation of the flow rate adjustment device.

Patent applications <CIT> and <CIT> describe a high-pressure fuel pump for a direct injection system and comprising a flow rate adjustment device provided with a control rod which is coupled to the intake valve and with an electromagnetic actuator configured to axially move the control rod.

The object of the present invention is to provide a fuel pump for a direct injection system, said fuel pump having greater reliability (i.e. reduced faultiness) and, simultaneously, being easy and quick to produce.

According to the present invention, a fuel pump for a direct injection system is provided, according to what claimed in the appended claims.

The claims describe preferred embodiments of the present invention forming integral part of the present description.

The present invention will now be described with reference to the accompanying drawings, which illustrate a non-limiting example embodiment thereof, wherein:.

In <FIG>, reference numeral <NUM> indicates, as a whole, a high-pressure fuel pump for a direct fuel injection system of common rail type in an internal combustion engine; preferably, the direct injection system is used in an internal combustion engine having a controlled ignition and thus fed with petrol or similar fuels.

The high-pressure pump <NUM> comprises a main body <NUM> which has a longitudinal axis <NUM> and defines therein a pumping chamber <NUM> having a cylindrical shape. On the inside of the pumping chamber <NUM>, a piston <NUM> is mounted in a sliding manner which, by moving with reciprocating motion along the longitudinal axis <NUM>, causes a cyclical variation of the volume of the pumping chamber <NUM>. A lower portion of the piston <NUM> is coupled on one side to a spring <NUM> which tends to push the piston <NUM> towards a position of maximum value of the pumping chamber <NUM> and is coupled on the other side to an eccentric (not illustrated) which is driven into rotation by a driving shaft of the internal combustion engine for cyclically moving the piston <NUM> upwards compressing the spring <NUM>.

From a side wall of the pumping chamber <NUM> an intake duct <NUM> originates which is adjusted by an intake valve <NUM> arranged in the area of the pumping chamber <NUM>. From a side wall of the pumping chamber <NUM> and from the opposite side with respect to the intake duct <NUM>, a delivery duct <NUM> originates which is adjusted by a mono-directional delivery valve (not illustrated) which is arranged in the area of the pumping chamber <NUM> and only allows a flow of fuel to exit the pumping chamber <NUM>.

The high-pressure pump <NUM> comprises a flow rate adjustment device <NUM> which is coupled to the intake valve <NUM> (i.e. acts on the intake valve <NUM>). The flow rate adjustment device <NUM> comprises a control rod <NUM>, which is coupled to the intake valve <NUM> and is movable between a passive position, in which it allows the intake valve <NUM> to close, and an active position, in which it does not allow the intake valve <NUM> to close. The flow rate adjustment device <NUM> further comprises an electromagnetic actuator <NUM>, which is coupled to the control rod <NUM> for moving the control rod <NUM> between the active position and the passive position.

According to what is illustrated in <FIG>, the electromagnetic actuator <NUM> comprises a spring <NUM> which maintains the control rod <NUM> in the active position, and an electromagnet which is adapted to move the control rod <NUM> in the passive position magnetically attracting a ferromagnetic keeper <NUM> integral with the control rod <NUM>. When the electromagnet <NUM> is excited, the control rod <NUM> is called back into the passive position and the communication between the intake duct <NUM> and the pumping chamber <NUM> can be interrupted by the closing of the intake valve <NUM>. The electromagnet <NUM> comprises a fixed magnetic armature <NUM> which is surrounded by a coil <NUM>; when passed through by an electric current, the coil <NUM> generates a magnetic field which magnetically attracts the keeper <NUM> towards the magnetic armature <NUM>. The control rod <NUM> and the keeper <NUM> together form a mobile equipment of the flow rate adjustment device <NUM> which axially moves between the active position and the passive position under the control of the electromagnetic actuator <NUM>. The keeper <NUM> and the magnetic armature <NUM> have an annular shape centrally holed so as to have an empty central space in which the spring <NUM> is housed.

The electromagnetic actuator <NUM> comprises a one-way hydraulic brake <NUM> which is integral with the control rod <NUM> and slows down the movement of the mobile equipment (i.e. of the control rod <NUM> and of the keeper <NUM>) only when the mobile equipment moves towards the active position (i.e. the hydraulic brake <NUM> does not slow down the movement of the mobile equipment when the mobile equipment moves towards the passive position).

The adjustment device <NUM> comprises a cup-shaped cylindrical metallic containing element <NUM> and thus having a closed end <NUM> and an open end <NUM> opposite the closed end <NUM>. The containing element <NUM> is connected to the main body <NUM> through an annular weld <NUM> obtained through laser; the annular weld <NUM> has the function of both establishing a stable mechanical connection between the containing element <NUM> and the main body <NUM>, and of creating a hydraulic seal around the containing element <NUM>. In particular, the main body <NUM> has a cylindrical hole <NUM> which is in direct communication with the intake duct <NUM>, is coaxial to the intake valve <NUM> and is sealingly engaged by the containing element <NUM>.

According to what is illustrated in <FIG>, the containing element <NUM> comprises a (inner) cylindrical wall <NUM> inside which the electromagnetic actuator <NUM> is arranged which is in direct contact with the (inner) cylindrical wall <NUM>; i.e. the (inner) cylindrical wall <NUM> defines a housing of the containing element <NUM> in which the electromagnetic actuator <NUM> is inserted without appreciable clearance. Furthermore, the containing element <NUM> comprises a (outer) cylindrical wall <NUM> which is coaxial to the (inner) cylindrical wall <NUM>, has a diameter greater than a diameter of the (inner) cylindrical wall <NUM>, is arranged around the (inner) cylindrical wall <NUM> at a non-null distance from the (inner) cylindrical wall <NUM>, and is connected to the (inner) cylindrical wall <NUM> by means of a discoidal wall <NUM> having an outer circular rim integral with the (outer) cylindrical wall <NUM> and an inner circular rim integral with the (inner) cylindrical wall <NUM>. The assembly of the (inner) cylindrical wall <NUM>, of the (outer) cylindrical wall <NUM> and of the discoidal wall <NUM> constitutes a "U"-shaped rim <NUM> of the containing element <NUM> which is arranged in the area of the open end <NUM>. The annular weld <NUM> is obtained between the main body <NUM> and the (outer) cylindrical wall <NUM> of the containing element <NUM>.

In other words, the containing element <NUM> ends with the "U"-shaped rim <NUM> which is arranged in the area of the open end <NUM> and has on the outside the cylindrical wall <NUM> (i.e. an outer ring) arranged around the cylindrical wall <NUM> and at a given distance from the cylindrical wall <NUM>. The annular weld <NUM> is obtained between the main body <NUM> and the outer ring (i.e. the cylindrical wall <NUM>) of the "U"-shaped rim <NUM> of the containing element <NUM>.

In particular, an inner diameter of the cylindrical hole <NUM> of the main body <NUM> is (substantially) equal to an outer diameter of the cylindrical wall <NUM> (i. e of the outer ring of the "U"-shaped rim <NUM>) of the containing element <NUM> so that the cylindrical wall <NUM> engages the cylindrical hole <NUM> substantially without appreciable clearance.

According to a preferred embodiment, the upper edges of the "U"-shaped rim <NUM> of the containing element <NUM> are rounded; in this manner the "U"-shaped rim <NUM> of the containing element <NUM> has a countersunk shape (thus self-centring) which eases the insertion of the "U"-shaped rim <NUM> of the containing element <NUM> inside the cylindrical hole <NUM> of the main body <NUM>.

The fuel pump <NUM> described above has numerous advantages.

Firstly, the fuel pump <NUM> described above has a high reliability (i.e. a reduced faultiness). This result is obtained thanks to the fact that the annular weld <NUM> is not obtained directly between the main body <NUM> and a wall of the containing element <NUM>, but is obtained between the main body <NUM> and the cylindrical wall <NUM> (i.e. the outer ring of the "U"-shaped rim <NUM>), it is thus obtained at a given distance from the cylindrical wall <NUM> of the containing element <NUM>; in this manner, the possible deposits which accidentally form during the making of the annular weld <NUM> do not enter the containing element <NUM> but remain on the outside of the containing element <NUM>.

In other words, during the execution through laser of the annular weld <NUM>, melted metal spatters can originate which, when cooling, form small deposits; but such small deposits do not manage to enter the containing element <NUM> since the annular weld <NUM> is not obtained directly between the main body <NUM> and the cylindrical wall <NUM> of the containing element <NUM>, but is obtained between the main body <NUM> and the cylindrical wall <NUM> (i.e. the outer ring of the "U"-shaped rim <NUM>), it is thus obtained at a given distance from the cylindrical wall <NUM> which constitutes the containing element <NUM>.

The absence of possible deposits generated by a weld inside the containing element <NUM> allows reducing in a substantial manner the faultiness in particular of the flow rate adjustment device <NUM>, since these small deposits, if present, could migrate, for example, towards the ferromagnetic keeper <NUM> blocking or anyway altering its sliding ability or reducing its stroke.

Furthermore, the thickness of the cylindrical wall <NUM> of the containing element <NUM> can be contained (i.e. the thickness of the cylindrical wall <NUM> of the containing element <NUM> can be particularly thin), all to the advantage of the reduction in the magnetic flows dispersed in the electromagnetic actuator <NUM> (thus ensuring a high energy efficiency of the electromagnetic actuator <NUM>). In fact, the thickness of the cylindrical wall <NUM> of the containing element <NUM> can be contained since the wall of the containing element <NUM> does not necessarily have to resist the breaching which can occur during the laser welding for obtaining the annular weld <NUM>, because also in case of breaching during the laser welding, the deposits generated by the breaching remain anyway distant from the electromagnetic actuator <NUM>.

Claim 1:
A fuel pump (<NUM>) for a direct injection system and comprising:
a main body (<NUM>);
a pumping chamber (<NUM>) defined in the main body (<NUM>);
a piston (<NUM>), which is mounted in a sliding manner on the inside of the pumping chamber (<NUM>) so as to cyclically vary the volume of the pumping chamber (<NUM>);
an intake duct (<NUM>), which ends in the pumping chamber (<NUM>);
an intake valve (<NUM>), which is arranged along the intake duct (<NUM>); and
a flow rate adjustment device (<NUM>) provided with a control rod (<NUM>), which is coupled to the intake valve (<NUM>), and with an electromagnetic actuator (<NUM>), which is configured to axially move the control rod (<NUM>);
wherein the flow rate adjustment device (<NUM>) comprises a containing element (<NUM>), which houses the electromagnetic actuator (<NUM>), has an open end (<NUM>) facing the intake valve (<NUM>), and is connected to the main body (<NUM>) by means of an annular weld (<NUM>); and
wherein the containing element (<NUM>) comprises a first cylindrical wall (<NUM>) inside which the electromagnetic actuator (<NUM>) is arranged, which is in direct contact with the first cylindrical wall (<NUM>);
the fuel pump (<NUM>) is characterized in that:
the containing element (<NUM>) comprises a second cylindrical wall (<NUM>), which is coaxial to the first cylindrical wall (<NUM>), has a diameter greater than a diameter of the first cylindrical wall (<NUM>), is arranged around the first cylindrical wall (<NUM>) at a non-null distance from the first cylindrical wall (<NUM>), and is connected to the first cylindrical wall (<NUM>) by means of a discoidal wall (<NUM>) having an outer circular rim integral with the second cylindrical wall (<NUM>) and an inner circular rim integral with the first cylindrical wall (<NUM>); and
the annular weld (<NUM>) is obtained between the main body (<NUM>) and the second cylindrical wall (<NUM>) of the containing element (<NUM>).