Pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine

A pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine; the pump unit (1) comprising: a head (4) inside which a cylinder (12) extending along an axis (A1) is formed; a pumping piston (5) extending along the axis (A1) and slidingly coupled with the cylinder (12); a through-hole (13) which extends from the cylinder (12) towards the outside of the pump unit (1); an intake chamber (8) communicating with the cylinder (12) via the hole (13); an intake valve (7) which controls the flow of fuel from the intake chamber (8) to the hole (13); a cap (23; 123; 223) which is connected to the head (4), is arranged on the opposite side to the pumping piston (5) and can be selectively fixed along an outer surface (25) of the head (4) so as to close the intake chamber (8) on one side.

BACKGROUND OF THE INVENTION

The present invention relates to a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine.

In general, a pump unit comprises a pump body; a head assembled on the pump body; a pumping piston housed inside the head; a cylinder which houses the pumping piston; an intake valve having a valve body housed inside a seat formed in the head; and a delivery valve.

The valve body is fixed to the seat by means of threaded means which mate with the inner walls of the seat. In particular, the pump body comprises a connector which has a threaded, outer, side surface and is housed inside the seat after the valve body has been inserted. The connector keeps the valve body in contact with the head. The connector is fixed to the inner side surface of the seat by means of a threaded connection provided with a threaded surface formed on the threaded, outer, side wall of the connector and another threaded surface formed on the inner side wall of the seat.

One of the main drawbacks of the prior art consists in the fact that, in order to form the threaded surface on the inner side wall of the seat, fairly long and costly precision-machining operations are necessary. Moreover, the said threaded surfaces thus formed may give rise to wear and problems of leak-tightness during the working life of the pump because the forces which they must be withstand are high.

SUMMARY OF THE INVENTION

One object of the present invention is that of providing a pump unit of the type described above which limits the abovementioned drawbacks.

According to the present invention a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine is provided; the pump unit comprising:

a head inside which a cylinder extending along an axis is formed;

a pumping piston extending along the axis and slidingly coupled with the cylinder;

a through-hole which extends from the cylinder towards the outside of the pump unit;

an intake chamber communicating with the cylinder via the hole;

an intake valve which controls the flow of fuel from the intake chamber to the hole;

a cap which is connected to the head, is arranged on the opposite side to the pumping piston and can be selectively fixed along an outer surface of the head so as to close the intake chamber on one side.

As a result of the present invention, closure of the head by means of the cap is performed in an efficient and low-cost manner. Owing to fixing along an outer surface of the head, the threaded connection is simpler to realize and less costly. Moreover, fixing along the outer surface of the head results in less wear and a more efficient sealing action. Moreover, the threaded inner surface of the cap may be easily realized. In other words, as a result of the present invention, the threaded connection is provided partly along an inner surface of the cap which ensures an optimum seal, low costs and shorter manufacturing times.

According to a preferred embodiment of the present invention, the head and the cap define the intake chamber into which an intake duct leads.

As a result of the present invention, the intake chamber is located between the head and the cap and has lower manufacturing costs and shorter manufacturing times.

According to another preferred embodiment of the present invention, the outer surface of the head is threaded so that it may be connected to the cap.

Owing to the thread on the outer surface of the head an excellent sealing action and low manufacturing cost are ensured.

According to another preferred embodiment of the present invention, the cap comprises a threaded inner surface which mates with the outer surface of the head.

The threaded inner surface formed on the cap is easy and inexpensive to produce.

According to another preferred embodiment of the present invention, the intake valve comprises a valve body formed inside the head, and a closing member arranged inside the hole; preferably the valve body and the cylinder are formed as a single monobloc.

As a result of the present invention, the friction and wear points inside the pump unit are reduced and the working life of the pump unit increases and the leak-tightness is improved.

According to another embodiment of the present invention, the pump unit comprises a compression chamber formed in the cylinder and communicating with the hole so as to receive fuel through the hole. Moreover, the intake valve comprises a closing member, a resilient element and disc element fixed integrally to the closing member; and wherein the resilient element is arranged between the head and the disc element so as to control the movement of the closing member.

According to another embodiment of the present invention, the cap comprises a cavity inside which the disc element slides so as to dampen the movement of the closing member and wherein a diameter of the cavity has a dimension which is at the most equal to the product of 1.4 times a diameter of the disc element.

As a result of the present invention the wear between the contact point of the closing member and the head is reduced.

According to another embodiment of the present invention, the cap comprises a cover-piece for closing the intake chamber on one side and a ring nut for locking the cover-piece in a given position.

According to another embodiment of the present invention, the cover-piece comprises a collar which protrudes radially with respect to the axis outwards; the ring nut comprises a flange which protrudes radially with respect to the axis inwards and engages with the collar of the cover-piece.

As a result of the present invention, the connection between the cap and the head ensures an optimum seal.

According to another preferred embodiment of the present invention, the collar comprises a first projecting surface; and the ring nut comprises a second projecting surface which makes contact with the first projecting surface.

According to another preferred embodiment of the present invention, the ring nut exerts an axial force on the cover-piece so as to keep the cover-piece in contact with the head.

According to another preferred embodiment of the present invention, the cap is a single piece and comprises a central portion for delimiting on one side the intake chamber and a side portion for engagement with the head.

According to another preferred embodiment of the present invention, the pump unit comprises a sealing element arranged between the cap and the head.

As a result of the present invention the pump unit is low-cost and easy to implement.

According to another preferred embodiment of the present invention, the intake valve is of the mechanical type; preferably the intake valve is operated during opening and closing by the difference in pressure between the cylinder and a compression chamber arranged inside the cylinder.

DETAILED DESCRIPTION

With reference toFIGS. 1 and 2, 1denotes in its entirety, a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine (not shown).

The pump unit1comprises a high-pressure pump2of the pumping piston type designed to feed the fuel to the said internal combustion engine (not shown); and a known gear pump (not shown) designed to feed the fuel to the pump2. The pump2and the gear pump are driven by a shaft (not shown in the attached figures).

The pump2comprises a pump body3; a head4assembled on the pump body2; a cylinder12formed in the head4and extending along an axis A1; a pumping piston5which extends along the axis A1and is slidingly coupled with the cylinder12; an intake duct6formed partly in the head4; an intake valve7communicating with the intake duct6; an intake chamber8arranged between the intake duct6and the intake valve7; a compression chamber9communicating with the intake chamber8via the intake valve7; a delivery duct10formed partly inside the head4and communicating with the compression chamber9; and a delivery valve11for selectively interrupting the fuel along the delivery duct10.

The head4has a through-hole13which is formed in the head4coaxially with the axis A1and communicates with one end of the cylinder12. In particular, the hole13extends from the cylinder12towards the outside of the head4. In greater detail, the hole13extends inside the head4from the intake chamber8to the compression chamber9and houses part of the intake valve7. The head4comprises a seat14which houses the intake chamber8. The seat14and the cylinder12are arranged on opposite sides of the hole13.

The pumping piston5is displaced by an actuating device (not shown in the attached figures) along the cylinder12with an alternating rectilinear movement comprising an intake stroke for drawing the fuel inside the cylinder12and a compression stroke for the fuel contained inside the said cylinder12, i.e. for compressing the fuel drawn into the compression chamber9.

The intake duct6connects the gear pump to the intake valve7.

The intake valve7is of the mechanical type. The intake valve7is designed to control selectively feeding of the fuel inside the cylinder12from the intake chamber8to the compression chamber9along the hole13. The intake valve7extends along the axis A1and comprises a valve body15which is formed inside the head4. In other words, a portion of the head4defines the valve body15of the intake valve7, another portion of the head4defines also the cylinder12. Therefore, the valve body15and the head4are formed as a single monobloc, preferably by means of machining with stock removal.

With reference toFIG. 2, the intake valve7comprises a closing member16movable along the axis A1so as to allow selectively the fuel to pass through; a resilient element17; and a disc element18fixed integrally to the closing member16. The closing member16comprises a stem19and a foot20. The stem19is housed inside the hole13. The foot20, when in use during the compression phase, makes contact with the valve body15in particular with one end of the cylinder12into which the hole13leads. The disc element18is fixed to the stem19of the closing member16and the resilient element17is arranged between the valve body15and the disc element18. In other words, the resilient element17is arranged between the head4and the disc element18. In particular, the resilient element17imparts a resilient force which opposes opening of the closing member16when the pump unit1is in the intake phase. In fact, during the intake phase, the pressure inside the compression chamber9is less than the pressure inside the intake duct6and the closing member16is pushed by the difference in pressure along the axis A1towards the pumping piston5. In this way the closing member16allows the fuel to pass from the intake chamber8to the compression chamber9. Consequently, the intake valve7is of the mechanical type because it operates by means of pressure difference without the aid of an electronic control mechanism acting directly on the closing member16.

During the compression phase, the pumping piston5moves along the axis A1towards the closing member16. The intake valve7during the compression phase is in the closed position and the closing member16is in contact with the head5. In fact, when the intake phase finishes, the resilient element17pushes the closing member16along the axis A1from the opposite side to the pumping piston5. In this case, the foot20of the closing member16makes contact with the valve body15which is defined by the portion of the head5. During the compression phase, the resilient element17keeps the foot20of the closing member16in contact by applying a force along the axis A1to the stem19of the closing member16via the disc element18. In other words, the resilient element17pushes the disc element18along the axis A1in a direction opposite to the cylinder12.

The head4defines a seat21which houses the intake chamber8and into which the intake duct6at least partly formed in the head4leads.

With reference toFIGS. 1 and 2, the head4comprises a cap23connected to the head4and arranged on the opposite to the pumping piston5relative to the hole13. The cap23comprises a cover-piece23aand a ring nut24which fixes the cover-piece23ato the head4. The ring nut24is connected along an outer surface25of the head4. The head4comprises an annular wall26of the seat21. The outer surface25is annular and is defined by the outer surface of the wall26of the seat21. In particular, the wall26is defined by a cylinder portion and the outer surface25is the outer surface of the cylinder portion. The cap23delimits the seat21, closing it sealingly on one side. Moreover, the outer surface25is threaded so as to engage with the ring nut24of the cap23. The ring nut24engages with the cap23aand the head4. In particular, the ring nut24comprises a threaded inner surface27which mates with the outer surface25of the head4. The cover-piece23acomprises a collar30which extends radially with respect to the axis A1outwards and which comprises a projecting surface28which during use faces the ring nut24. The ring nut24comprises a flange32which extends radially with respect to the axis A1inwards and which comprises a projecting surface29which during use faces the head4. During use, the flange32engages with the collar30of the cover-piece23a. Moreover, the projecting surface29makes contact with the projecting surface28. In other words, the ring nut24exerts an axial force on the cover-piece23aso as to keep the cover-piece23ain contact with the head4along an annular contact surface33of the head4and an annular contact surface36of the cover-piece23a. The annular contact surface33of the head4is situated outside the intake chamber8. In greater detail the contact surfaces33and36are situated inside the seat21and are arranged between the inner surface38of the annular wall26.

The cap23delimits on one side the intake chamber8. In greater detail the cap23ahas a cavity31which defines part of the intake chamber8. The cover-piece23aalso houses part of the closing member16, in particular the disc element18and part of the stem19inside the cavity31. The cover-piece23adefines part of the intake chamber8.

Moreover, the pump unit1comprises a sealing ring40arranged inside a cavity41arranged between the cover-piece23aand the head4. In particular, the cover-piece23ahas an annular recess42which extends radially with respect to the axis A1along an outer side surface39and in the vicinity of the contact surface36. The cavity41is defined between the annular recess42and the head4, in particular between the annular recess42and the wall26of the seat21, in particular along a portion of the inner surface38of the wall26.

The sealing ring40may be made of rubber, plastic or metallic material. The sealing ring40is made of a material having a hardness which is less than the hardness of the material of the cover-piece23aand the head4. The sealing ring40is configured to prevent liquid from escaping from the intake chamber8towards the outside of the head4.

With reference toFIG. 1, the pump unit1comprises a resilient element35; in the non-limiting embodiment shown in the attached figures it is a helical spring engaged between a free end36of the pumping piston7and the head4.

The pump unit1comprises a seat36for the delivery valve11and a connector37for keeping the delivery valve11inside the seat36. The delivery valve11is housed along the delivery duct10and is designed to control selectively feeding of the fuel to the said internal combustion engine (not shown).

According to an alternative embodiment shown inFIG. 3, the pump unit1comprises the cap123instead of the cap23. The cap123comprises the cover-piece123ainstead of the cover-piece23a. The cover-piece123adiffers from the cover-piece23aowing to the internal shape of the cavity. The cover-piece123ahas a cavity131with a cylindrical cross-section having a shape the same as the shape of the disc element18. The cavity131has a cylindrical shape like the disc element18, in particular the cavity131has a cylindrical shape with a circular base. The cavity131houses the disc element18inside the cylindrical portion and so that the disc element18is free to move along the axis A1. In greater detail, the cylindrical portion of the cavity131has a diameter D1comparable to a diameter D2of the disc element18so as to produce a damping effect when the disc element18moves inside the cavity131. In greater detail, when the disc element18moves inside the cavity131it propels the fuel which occupies the cavity131. The fuel under the pressure of the disc element18tends to move into a zone of the cavity131where there is less pressure. In greater detail, when the disc element18moves towards the cover-piece123a, the fuel tends to move from the cavity131towards the head4. As a result, the movement of the disc element18is slowed down by the fuel. The diameter D1of the cavity131has a value which is at the most 40% greater than the diameter D2of the disc element18. Owing to the cavity131, the movement of the closing member16is dampened and this causes less wear at the point where the foot20makes contact with the valve body15which in this case is formed directly on the head4.

According to another alternative embodiment shown inFIG. 4, the pump unit1comprises the cap223instead of the cap23. The cap223is composed of a single piece and comprises a central portion223aand a side portion224. The central portion223aextends radially with respect to the axis A1and delimits on one side the intake chamber8. The side portion224extends along the axis A1. The side portion224mates with the head4, in particular with the wall26along the threaded outer surface25of the head4. In particular, the side portion224has a threaded inner surface227for engagement with the head4. The cap223closes the intake chamber8on one side.

The pump unit1comprises a sealing element241arranged between the cap223and the head4. In particular, the head4comprises a contact surface233arranged at one end of the seat21of the head4, in particular between the threaded side surface25and the inner side surface38of the seat21of the head4. In other words, the contact surface233is arranged along a base of the cylindrical portion of the seat21. The cap223comprises a contact surface236which during use faces the contact surface233and is defined by an inner radial shoulder230arranged along the side portion224. The sealing element241is arranged between the contact surface236and the contact surface233. The sealing element241is rigid and may be made of plastic or metallic material. The sealing element241has a hardness factor less than that of the cap223and the head4.

It is moreover evident that the present invention also covers embodiments not described in the detailed description and equivalent embodiments which fall within the scope of protection of the attached claims.