Patent Description:
The present invention relates to a fuel pump for a direct injection system.

A direct injection system comprises a plurality of injectors, a common rail that supplies pressurized fuel to the injectors, a high-pressure fuel pump, which supplies fuel to the common rail via a high-pressure supply duct and is provided with a flow rate adjusting device, and a control unit that controls the flow rate adjusting device to maintain the fuel pressure inside the common rail at a desired value which can generally vary over time depending on the engine operating conditions.

The high-pressure pump described in patent application <CIT> comprises a main body which defines a cylindrical pumping chamber inside which a piston slides with reciprocating motion; an inlet duct regulated by an inlet valve is provided to supply low-pressure fuel into the pumping chamber, as well as an outlet duct regulated by an outlet valve (also designated as "OCV - Outlet Closing Valve") to supply high-pressure fuel out of the pumping chamber and towards the common rail through the supply duct. There is also a one-way maximum pressure valve (also designated as "PRV" -Pressure Relief Valve) which only allows fuel to flow from the outlet duct to the pumping chamber. The function of the pressure relief valve is to allow fuel to escape if the fuel pressure in the common rail exceeds a maximum value set during design time (for example, in the event of control errors by the control unit or in the event of an injector failure); in other words, the pressure relief valve is calibrated to open automatically when the pressure drop at its ends is above a threshold value set during design time and thus prevent the fuel pressure in the common rail from exceeding the maximum value set during design time.

To simplify the construction of the fuel pump, the outlet closing and pressure relief valves are both arranged coaxially in the outlet channel and are integrated together into a single valve assembly.

The object of the present invention is to provide a fuel pump for a direct injection system, which fuel pump is compact and quick to mount, and at the same time, easy and inexpensive to manufacture.

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

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

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

In <FIG>, the numeral <NUM> indicates, as a whole, a high-pressure fuel pump which is part of a common rail-type direct fuel injection system for an internal combustion heat engine.

The high-pressure pump <NUM> comprises a main body <NUM> which has a longitudinal axis <NUM> and defines, on the inside, a cylindrical pumping chamber <NUM>. A piston (not shown) is slidably mounted inside the pumping chamber <NUM> and, by moving with reciprocating motion along the longitudinal axis <NUM>, causes a cyclical change in the volume of the pumping chamber <NUM>.

An inlet channel <NUM> originates directly from a side wall of the pumping chamber <NUM> and, in use, is connected to a low-pressure pump and regulated by a one-way inlet valve (not shown) arranged in the area of the pumping chamber <NUM>. An outlet channel <NUM> originates directly from a side wall of the pumping chamber <NUM>, on the side opposite the inlet channel <NUM>, and is connected to a common rail and engaged by a valve assembly <NUM> (detailed in <FIG> and <FIG>). That is, the inlet channel <NUM> originates directly from one side of the pumping chamber <NUM>, whereas the outlet channel <NUM> originates directly from the opposite side of the pumping chamber <NUM>.

The valve assembly <NUM> is arranged in the area of (near) the pumping chamber <NUM> and integrates together both a one-way outlet valve <NUM> (also designated as "OCV - Outlet Closing Valve") which only allows fuel to flow out of the pumping chamber <NUM> through the outlet channel <NUM>, and a one-way maximum pressure valve <NUM> (also designated as "PRV" -Pressure Relief Valve) which only allows fuel to flow into the pumping chamber <NUM> through the outlet channel <NUM>. In other words, the pressure relief valve <NUM> is arranged together and coaxially with the outlet closing valve <NUM>, thereby forming a single integrated assembly (the valve assembly <NUM>) with the outlet closing valve <NUM>: the one-way outlet closing valve <NUM> only allows fuel to flow out of the pumping chamber <NUM> through the outlet channel <NUM>, whereas the one-way pressure relief valve <NUM> opens when the fuel pressure downstream of the pressure relief valve <NUM> exceeds a threshold value, only allowing fuel to flow into the pumping chamber <NUM> through the outlet channel <NUM>.

During normal operation of the high-pressure pump <NUM>, the outlet closing valve <NUM> opens and closes with each pumping cycle: the outlet closing valve <NUM> is pressure controlled, in particular, the outlet closing valve <NUM> is open when the fuel pressure in the pumping chamber <NUM> (i.e., upstream of the outlet closing valve <NUM>) is sufficiently higher than the fuel pressure downstream of the outlet closing valve <NUM> (i.e., when the piston is in the pumping phase and is decreasing the volume of the pumping chamber <NUM>) and is closed when the fuel pressure in the pumping chamber <NUM> (i.e., upstream of the outlet closing valve <NUM>) is lower than the fuel pressure downstream of the outlet closing valve <NUM> (i.e., when the piston is in the intake phase and is increasing the volume of the pumping chamber <NUM>).

The function of the pressure relief valve <NUM> is to allow fuel to escape if the fuel pressure in the common rail (i.e., downstream of the valve assembly <NUM>) exceeds a maximum value set during design time (for example, in the event of control errors by a control unit or in the event of failure of an injector connected to the common rail); in other words, the pressure relief valve <NUM> is calibrated to open automatically when the pressure drop at its ends is above a threshold value set during design time and thus prevent the fuel pressure in the common rail (i.e., downstream of the valve assembly <NUM>) from exceeding the maximum value set during design time. Obviously, the pressure relief valve <NUM> can only open (in case of excessive fuel pressure in the common rail) when the piston is in the intake phase and is increasing the volume of the pumping chamber <NUM>, not when the piston is in the pumping phase and is decreasing the volume of the pumping chamber <NUM>.

The fuel pump <NUM> has a cylindrical and internally threaded containing cavity <NUM> which is coaxial with the outlet channel <NUM>, communicates directly with the outlet channel <NUM> (i.e., it is immediately adjacent to the outlet channel <NUM> and constitutes the natural continuation of the outlet channel <NUM>), and is arranged downstream of the outlet channel <NUM> relative to the pumping chamber <NUM>; in addition, the valve assembly <NUM> comprises a cylindrical and externally threaded connector <NUM> which is screwed into the containing cavity <NUM> and is designed to connect the outlet channel <NUM> to a subsequent fuel supply duct; typically, the fuel supply duct is screwed around a spout of the connector <NUM>.

Preferably, a sealing gasket <NUM> is also interposed between the connector <NUM> and the containing cavity <NUM>.

As shown in <FIG> and <FIG>, the connector <NUM> has a housing <NUM> facing the main body <NUM> of the fuel pump <NUM>, i.e., it faces the pumping chamber <NUM>. In other words, the cylindrical-shaped connector <NUM> is inserted in the containing cavity <NUM> and has a housing <NUM> on the inside having one end proximal to the pumping chamber <NUM> that is open, is coaxial with the outlet channel <NUM>, and faces the outlet channel <NUM> in order to receive the axially flowing fuel directly from the outlet channel <NUM> and thus to let the fuel axially enter the housing <NUM>.

The valve assembly <NUM> comprises a valve disc <NUM> which is arranged in the housing <NUM> of the connector <NUM> (i.e., it engages the housing <NUM> of the connector <NUM>) and has a circular wall <NUM>, which faces the pumping chamber <NUM>, and a circular wall <NUM>, which is parallel to and opposite the circular wall <NUM>, faces the side opposite the pumping chamber <NUM> and rests against an annular abutment <NUM> of the housing <NUM>. Preferably, the valve disc <NUM> is interference-fitted into the housing <NUM> until it abuts against the abutment <NUM>; in addition, once the valve disc <NUM> has been interference-fitted until it abuts against the abutment <NUM>, a caulking is made (close to the wall <NUM>) to create a sealing ring (edging) on the wall of the housing <NUM> that axially locks the valve disc <NUM>.

The valve disc <NUM> has a series of through outlet holes <NUM> (in particular, three through outlet holes <NUM> symmetrically arranged around a longitudinal axis of the valve disc <NUM>) through which fuel can flow, and which are part of the outlet closing valve <NUM>, that is, they are only used by the outlet closing valve <NUM>; each outlet hole <NUM> is provided with a valve seat <NUM> obtained in the area of the wall <NUM> of the valve disc <NUM>. In addition, the valve disc <NUM> has a single through relief hole <NUM> (arranged centrally) through which fuel can flow and which is part of the pressure relief valve <NUM>, i.e., it is only used by the pressure relief valve <NUM>; the relief hole <NUM> is provided with a valve seat <NUM> obtained in the area of the wall <NUM> of the valve disc <NUM>.

In the embodiment shown in the accompanying figures, the valve disc <NUM> has a single, centrally arranged relief hole <NUM> and a plurality of outlet holes <NUM> (e.g., three outlet holes <NUM> symmetrically arranged around a longitudinal axis of the valve disc <NUM>) arranged around the relief hole <NUM> along an imaginary circumference centred on the relief hole <NUM>. In particular, in the embodiment shown in the accompanying figures, the valve disc <NUM> has three outlet holes <NUM> symmetrically arranged around a longitudinal and central axis of the valve disc <NUM>, however, according to other embodiments, not shown, the number and/or arrangement of the outlet holes <NUM> may be different.

The outlet closing valve <NUM> further comprises a circular flexible sheet <NUM> (as better shown in <FIG> and <FIG>) which rests against the wall <NUM> of the valve disc <NUM>, closing the passage through the outlet holes <NUM>; in particular, the flexible sheet <NUM> is permanently connected (welded) at certain points (relatively far from the outlet holes <NUM>) to the wall <NUM> of the valve disc <NUM> so that it is fixed to the valve disc <NUM> next to the outlet holes <NUM>. The flexible sheet <NUM>, which constitutes a shutter of the outlet closing valve <NUM>, and also incorporates the respective elastic element, engages the valve seats <NUM> of the outlet holes <NUM> and is movable so as to detach itself from the valve seats <NUM> when the fuel pressure downstream of the valve disc <NUM> is smaller than the fuel pressure upstream of the valve disc <NUM>.

The outlet closing valve <NUM> is pressure controlled and the outlet closing valve <NUM> is closed when the fuel pressure upstream of the valve disc <NUM> (i.e., in the pumping chamber <NUM>) is lower than the fuel pressure downstream of the valve disc <NUM> and is open when the fuel pressure upstream of the valve disc <NUM> (i.e., in the pumping chamber <NUM>) is (sufficiently) higher than the fuel pressure downstream of the valve disc <NUM>. In particular, when the fuel flows from the pumping chamber <NUM> into the outlet channel <NUM>, the flexible sheet <NUM> deforms away from the valve disc <NUM> under the pressure of the fuel allowing fuel to pass through the through outlet holes <NUM>; on the other hand, when the fuel attempts to flow from the outlet channel <NUM> to the pumping chamber <NUM>, the flexible sheet <NUM> presses against the valve disc <NUM> sealing the outlet holes <NUM> and thus preventing fuel from flowing through the outlet holes <NUM>.

As shown in <FIG>, the flexible sheet <NUM> comprises three shutting portions <NUM> (i.e., three "petals"), each of which has a circular shape, is arranged at a valve seat <NUM> of a corresponding outlet hole <NUM>, and is configured to prevent fuel from flowing through the corresponding outlet hole <NUM> when the outlet closing valve <NUM> is closed. Therefore, the three shutting portions <NUM> are symmetrically arranged around a longitudinal axis of the valve disc <NUM> being coaxial with the corresponding outlet holes <NUM>.

In addition, the flexible sheet <NUM> comprises a central mounting portion <NUM> which is arranged at the centre and centrally perforated (i.e., it has a through hole at the centre) so as not to obstruct the relief hole <NUM>; in other words, the central mounting portion <NUM> has an annular shape to encircle the relief hole <NUM> (without obstructing it). The flexible sheet <NUM> comprises an annular peripheral mounting portion <NUM> arranged laterally (i.e., along the outer edge of the valve disc <NUM>). The peripheral mounting portion <NUM> is rigidly connected (in particular welded) to the valve disc <NUM> at certain points; the central mounting portion <NUM> may be rigidly connected (in particular welded) to the valve disc <NUM> or, alternatively, may also be completely disconnected from the valve disc <NUM>.

The flexible sheet <NUM> comprises three outer connection portions <NUM>, each of which has the shape of a semicircle and connects the peripheral mounting portion <NUM> to a corresponding shutting portion <NUM>; that is, each outer connection portion <NUM> originates from the peripheral mounting portion <NUM> and ends at a corresponding shutting portion <NUM>. The flexible sheet <NUM> comprises three inner connection portions <NUM>, each of which is "U"-shaped and connects the central mounting portion <NUM> to a corresponding shutting portion <NUM>; that is, each inner connection portion <NUM> originates from the central mounting portion <NUM> and ends at a corresponding shutting portion <NUM> on the side opposite the corresponding outer connection portion <NUM>. In other words, the two connection portions <NUM> and <NUM> of a same shutting portion <NUM> are arranged on the opposite sides of the shutting portion <NUM>.

As shown in <FIG>, the sheet <NUM> comprises a corresponding outer connection portion <NUM> for each shutting portion <NUM> so that each shutting portion <NUM> is always connected to one and only one outer connection portion <NUM>, and vice versa, that is, each outer connection portion <NUM> is always connected to one and only one shutting portion <NUM>. Similarly, the sheet <NUM> comprises a plurality of inner connection portions <NUM>, each connecting the central mounting portion <NUM> to a corresponding shutting portion <NUM> so that each shutting portion <NUM> is connected to one and only one inner connection portion <NUM>, and vice versa, that is, each inner connection portion <NUM> is always connected to one and only one shutting portion <NUM>.

As shown in <FIG>, each shutting portion <NUM> is supported exclusively by a single outer connection portion <NUM> and a single inner connection portion <NUM> and has no other connection than the corresponding outer connection portion <NUM> and the corresponding inner connection portion <NUM>; as a result, each shutting portion <NUM> is in no way directly connected to another shutting portion <NUM> (i.e., with a single element originating from a shutting portion <NUM> and ending at an adjacent shutting portion <NUM>).

According to a preferred embodiment, the flexible sheet <NUM> is pre-deformed so that, in the absence of external stresses (i.e., in the absence of hydraulic forces generated by the pressurized fuel), it presses against the valve seats <NUM> of the outlet holes <NUM> with a pre-load force other than zero; generally, this pre-load force is greater than <NUM> Newton and comprised between <NUM> and <NUM> Newtons. In particular, the connection portions <NUM> and <NUM> of the flexible sheet <NUM> are plastically pre-deformed so that, in the absence of external stresses and constraints, the shutting portions <NUM> are parallel and spaced from the mounting portions <NUM> and <NUM>; when the flexible sheet <NUM> is fixed to the wall <NUM> of the valve disc <NUM> it is necessary to apply the pre-load force to the flexible sheet <NUM> to make the mounting portions <NUM> and <NUM> coplanar with the shutting portions <NUM>, thus causing elastic deformation of the connection portions <NUM> and <NUM>.

The above-described conformation of the sheet <NUM> allows the sheet <NUM> to have high torsional strength and therefore allows the shutting portions <NUM> of the sheet <NUM> to always move parallel to each other (thus parallel to the wall <NUM> of the valve disc <NUM>), both when opening and when closing, ensuring optimum dynamics of the outlet closing valve <NUM> (i.e., the outlet closing valve <NUM> opens and closes quickly and without uncertainty).

According to the (non-limiting) embodiment shown in <FIG>, the connector <NUM> has an annular abutment <NUM>, which is arranged radially more inwards than the annular abutment <NUM>, is axially displaced with respect to the annular abutment <NUM>, is located near the wall <NUM> of the valve disc <NUM> (facing the wall <NUM> of the valve disc <NUM>) and at a certain distance from the flexible sheet <NUM>, and is designed to limit (contain) the maximum deformation of the flexible sheet <NUM> (i.e., of the shutting portions <NUM> of the flexible sheet <NUM>). In other words, when the shutting portions <NUM> of the flexible sheet <NUM> deform under the pressure of the fuel they cannot move far away from the wall <NUM> of the valve disc <NUM> because at some point they impact against the annular abutment <NUM> of the connector <NUM>, which therefore limits the maximum deformation thereof.

That is, the annular abutment <NUM> of the connector <NUM> is a limit stop for the shutting portions <NUM> of the flexible sheet <NUM>, which sets the maximum distance from the wall <NUM> of the disc <NUM> that the shutting portions <NUM> of the flexible sheet <NUM> can reach when they deform under the pressure of the fuel.

Due to the fact that the limit stop of the shutting portions <NUM> of the flexible sheet <NUM> is integrated in the connector <NUM> (i.e., it consists of the annular abutment <NUM> of the connector <NUM>), it is possible to eliminate the additional component that was added (welded) to carry out the same function and therefore simplify the mounting of the valve assembly <NUM>.

The pressure relief valve <NUM> comprises a spherical shutter <NUM>, which is designed to engage the valve seat <NUM> of the relief hole <NUM> and is movable so as to detach from the valve seat <NUM> when the difference between the pressure downstream of the valve disc <NUM> and the fuel pressure upstream of the valve disc <NUM> (i.e., in the pumping chamber <NUM>) exceeds a predetermined intervention threshold. The shutter <NUM> may be made of metal (typically steel) or ceramic material. The pressure relief valve <NUM> comprises a calibrated spring <NUM> which pushes the shutter <NUM> towards a fluid-tight engagement position of the valve seat <NUM>. In the preferred embodiment shown in the attached figures, the shutter <NUM> has a spherical shape and, as a result, the valve seat <NUM> has a conical shape which can be coupled in a fluid-tight manner to the shutter <NUM>. According to other embodiments, not shown, the shutter <NUM> (and consequently the valve seat <NUM> that must be coupled to the shutter <NUM>) has a different shape, for example a more or less flat shape.

According to a preferred embodiment shown in the attached figures, the pressure relief valve <NUM> comprises a connection element <NUM>, which is interposed between the shutter <NUM> and the spring <NUM>; that is, on one side the connection element <NUM> has a seat <NUM> (as shown in <FIG>) designed to partially contain the spherical shutter <NUM>, and on the other side the connection element <NUM> is shaped to be coupled to the spring <NUM>.

The valve assembly <NUM> comprises an annular body <NUM>, which is arranged in the housing <NUM> of the connector <NUM>, engages the housing <NUM> without clearance (i.e., an outer wall of the annular body <NUM> is in contact with an inner wall of the housing <NUM>), is arranged between the valve disc <NUM> and the main body <NUM>, and has a cylindrical, central through hole <NUM> which allows fuel coming directly and axially from the outlet channel <NUM> to flow axially towards the valve disc <NUM>. The annular body <NUM> is interference-fitted in the housing <NUM> of the connector <NUM> and pushes the valve disc <NUM> against the annular abutment <NUM> of the connector <NUM>.

The spring <NUM> of the pressure relief valve <NUM> is arranged in the central hole <NUM> of the annular body <NUM>; it is important to note that the connection element <NUM> is shaped and sized so as not to completely engage the central hole <NUM> so that fuel can flow along the central hole <NUM> passing through the connection element <NUM>. As shown in <FIG>, the connection element <NUM> comprises a central pin <NUM>, which is shaped to fit inside the spring <NUM> (i.e., the spring <NUM> surrounds the central pin <NUM>) and ends with a cup <NUM> (wider than the central pin <NUM> and narrower than the central hole <NUM> of the annular body <NUM>) in which the seat <NUM> of the shutter <NUM> is obtained; that is, the cup <NUM> is integral with the central pin <NUM>. Furthermore, the connection element <NUM> comprises a guide ring <NUM> which has an outer side wall which is in contact with a wall of the central hole <NUM> of the annular body <NUM> in order to guide the sliding of the connection element <NUM> within the central hole <NUM>; in this way, the connection element <NUM> can only slide axially (i.e., without tilting in any way) along the central hole <NUM> of the annular body <NUM>. The guide ring <NUM> is connected to the cup <NUM> by four spokes <NUM> between which there are four passages <NUM> allowing fuel to flow towards the valve disc <NUM>; it is important to note that the passages <NUM> are wide (i.e., the spokes <NUM> are narrow) and thus allow fuel to flow towards the valve disc <NUM> without obstacles, i.e., without appreciable load loss.

In the wall of the central hole <NUM> of the annular body <NUM> there is an annular protuberance <NUM> (as better shown in <FIG>) which projects from the wall of the central hole <NUM> and constitutes a limit stop limiting the travel of the connection element <NUM> (i.e., of the shutter <NUM> carried by the connection element <NUM>). In other words, when the pressure relief valve <NUM> opens under the fuel pressure downstream of the valve disc <NUM>, the spring <NUM> is compressed and the shutter <NUM> moves axially away (together with the connection element <NUM>) from the obtained valve seat <NUM> of the valve disc <NUM>; this opening movement of the shutter <NUM> is limited by the presence of the annular protuberance <NUM> against which the axial sliding of the connection element <NUM> is blocked. In particular, the annular protuberance <NUM> of the central hole <NUM> of the annular body <NUM> contacts the guide ring <NUM> of the connection element <NUM>.

The presence of the annular protuberance <NUM> which limits the opening travel of the shutter <NUM> ensures that the excursion of the opening travel of the shutter <NUM> (thus the flow rate of the fuel flowing through the open pressure relief valve <NUM>) is always constant and equal to a desired design value regardless of the relevant construction and mounting tolerances of the spring <NUM>. That is, in the absence of the annular protuberance <NUM>, the opening travel of the shutter <NUM> would only stop when the spring <NUM> packs itself and would therefore have a much more uncertain excursion as it is affected by the relevant construction and mounting tolerances of the spring <NUM>. Keeping the opening travel of the shutter <NUM> (relatively) small (due to the presence of the annular protuberance <NUM>) also reduces the rebound of the shutter <NUM> against the valve seat <NUM> when the pressure relief valve <NUM> closes.

According to a preferred embodiment, a striker body <NUM> is interference-fitted along the central hole <NUM> of the annular body <NUM>, said striker body <NUM> being preferably cup-shaped (in substance it is a "cup") to contain, on the inside, one end of the spring <NUM> of the pressure relief valve <NUM> and providing support for the spring <NUM>; as a result, the spring <NUM> of the pressure relief valve <NUM> is compressed between the shutter <NUM> (normally resting against the valve seat <NUM> of the relief hole <NUM> formed in the wall <NUM> of the valve disc <NUM>) and the striker body <NUM>. The cup-shaped striker body <NUM> houses, on the inside, one end of the spring <NUM>, has a centrally perforated base wall against which the spring <NUM> rests, is arranged in the central hole <NUM> of the annular body <NUM>, and is fixed (interference-fitted) inside the annular body <NUM>.

Changing the position of the striker body <NUM> along the central hole <NUM> of the annular body <NUM> (i.e., pushing the striker body <NUM> more or less into the central hole <NUM> of the annular body <NUM>) changes the distance of the striker body <NUM> from the valve disc <NUM> and therefore accordingly changes the degree of compression of the spring <NUM> and the elastic force generated by the spring <NUM> (however, the opening travel of the shutter <NUM>, which is determined by the annular protuberance <NUM>, shall not change).

When mounting the fuel pump <NUM>, it is possible to measure the actual elastic constant of the spring <NUM> (net of construction tolerances) and thus select the position of the striker body <NUM> along the central hole <NUM> of the annular body <NUM> according to the actual elastic constant of the spring <NUM> so that the intervention threshold of the pressure relief valve <NUM> (i.e., the pressure threshold above which the pressure relief valve <NUM> opens) is as close as possible to the desired nominal value. When mounting the fuel pump <NUM>, it is also possible to measure the intervention threshold of the pressure relief valve <NUM> and thus correct the position of the striker body <NUM> along the central hole <NUM> of the annular body <NUM> so that the intervention threshold of the pressure relief valve <NUM> is as close as possible to the desired nominal value.

The valve assembly <NUM> (consisting of the outlet closing valve <NUM> and the pressure relief valve <NUM>) is fully assembled in the housing <NUM> of the connector <NUM> before inserting (screwing) the connector <NUM> into the containing cavity <NUM> of the outlet duct. In this way, the valve assembly <NUM> can be tested before inserting (screwing) the connector <NUM> into the containing cavity <NUM> of the outlet duct and therefore, in the event of excessive deviation from the nominal performance, it is possible to correct (modify) the valve assembly <NUM> or, at most, discard the valve assembly <NUM> without having to intervene in the completely assembled fuel pump <NUM> or even without having to discard the completely assembled fuel pump <NUM>.

In particular, when the assembling of the valve assembly <NUM> in the housing <NUM> of the connector <NUM> is completed, the striker body <NUM> is fitted into the housing <NUM> by compressing the spring <NUM>, completing the assembling of the valve assembly <NUM>; at this point it is possible to measure the intervention threshold of the pressure relief valve <NUM> (i.e., the pressure threshold above which the pressure relief valve <NUM> opens), and if the intervention threshold of the pressure relief valve <NUM> is too low (i.e., significantly lower than the desired nominal value), it is possible to act on (push) the striker body <NUM> to move the striker body <NUM> closer to the valve disc <NUM> and thus further compress the spring <NUM> to increase the elastic force generated by the spring <NUM>.

It may therefore be convenient to initially arrange the striker body <NUM> in a position slightly further away from the valve disc <NUM> compared to the nominal position and then, if necessary, correct the position of the striker body <NUM> by moving the striker body <NUM> closer to the valve disc <NUM> after measuring the intervention threshold of the pressure relief valve <NUM> (i.e., the pressure threshold above which the pressure relief valve <NUM> opens).

The embodiments described herein may be combined with each other without departing from the scope of protection of the present invention.

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

Firstly, the valve assembly <NUM> of the fuel pump <NUM> described above allows the construction and mounting tolerances to be compensated for very effectively, ensuring high accuracy and hence compliance with the nominal performance.

In addition, the valve assembly <NUM> of the fuel pump <NUM> described above has optimum dynamics of the outlet closing valve <NUM> (i.e., the outlet closing valve <NUM> opens and closes quickly and without uncertainty).

Claim 1:
A valve assembly (<NUM>) for a fuel pump (<NUM>) and comprising:
a one-way outlet closing valve (<NUM>), which only allows fuel to flow out;
a one-way pressure relief valve (<NUM>), which only allows fuel to flow in;
a connector (<NUM>), which has a housing (<NUM>) on the inside;
a valve disc (<NUM>), which engages the housing (<NUM>) of the connector (<NUM>) and has a plurality of through outlet holes (<NUM>), which are part of the outlet closing valve (<NUM>) and are each provided with a first valve seat (<NUM>) obtained in the area of a first wall (<NUM>) of the valve disc (<NUM>), and a through relief hole (<NUM>), which is part of the pressure relief valve (<NUM>) and is provided with a second valve seat (<NUM>) obtained in the area of a second wall (<NUM>) of the valve disc (<NUM>) parallel to and opposite the first wall (<NUM>);
an annular body (<NUM>), which is arranged in the housing (<NUM>) of the connector (<NUM>), engages the housing (<NUM>) without clearance and has a central through hole (<NUM>) with a cylindrical shape, which allows fuel to axially flow towards the valve disc (<NUM>);
a spring (<NUM>), which is part of the pressure relief valve (<NUM>), is arranged in the central hole (<NUM>) of the annular body (<NUM>) and pushes a shutter (<NUM>) of the pressure relief valve (<NUM>) against the second valve seat (<NUM>);
a striker body (<NUM>), which is cup-shaped so as to contain, on the inside, one end of the spring (<NUM>), has a centrally perforated base wall, against which the spring (<NUM>) rests, is arranged in the central hole (<NUM>) of the annular body (<NUM>) and is fixed inside the annular body (<NUM>); and
a connection element (<NUM>), which is interposed between the shutter (<NUM>) of the pressure relief valve (<NUM>) and the spring (<NUM>);
the valve assembly (<NUM>) is characterized in that the central hole (<NUM>) of the annular body (<NUM>) has an annular protuberance (<NUM>), which projects from a wall of the central hole (<NUM>) and constitutes a limit stop that limits the travel of the connection element (<NUM>).