DESCRIPTION

Title

"HIGH-PRESSU RE PUMP"

The present invention relates to a high-pressure pump, in particular for supplying fuel to a common rail of an internal-combustion engine.

As is known, a high-pressure pump comprises a pump body with a compartment able to house a mechanism for actuating at least one pumping member; a shaft rotatable about an axis; a bush which is forced-fitted with interference inside a cylindrical seat of the pump body, has the function of supporting the shaft and forms a passage between an inner surface of the bush and an outer surface of the shaft; and a duct which connects the compartment to the passage in order to supply lubricating liquid to the passage.

In the known high-pressure pumps the duct which connects the compartment to the passage is formed inside the pump body and supplies part of the fuel, usually diesel fuel, which in turn is supplied to the high-pressure pump via a pre-supply pump. The duct comprises three supply holes: two supply holes radial with respect to the axis of the shaft; and a supply hole parallel to the axis of the shaft which intersects the two radial supply holes. Consequently, three different boring operations and two pressing operations for closing the free ends of the radial supply holes are necessary. These operations make the procedure for manufacturing the high-pressure pump complicated and costly.

The object of the present invention is to provide a high-pressure pump which reduces the cost of manufacturing the high-pressure pump.

According to the invention this object is achieved by a high-pressure pump characterized in that the duct comprises a groove arranged between the pump body and the bush and at least one hole formed in the bush and arranged opposite the groove.

The duct is substantially delimited by the pump body and by the bush and boring of the pump body is not required. According to the present invention formation of the groove requires a single chip removal machining operation instead of three boring operations.

Further details, characteristics and advantages of the invention will emerge more clearly from the following description of a non-limiting example of embodiment provided with reference to the accompanying figures in which:

- Figure 1 is a longitudinally sectioned view, with parts removed for the sake of clarity, of a high-pressure pump designed according to the present invention; and

- Figure 2 is a longitudinally sectioned view of a detail of the high-pressure pump shown in Figure 1, overturned with respect to Figure 1, with further parts removed for the sake of clarity.

Figure 1 shows in its entirety a high-pressure pump designed to compress the fuel to pressures in the region of 2000 bar in order to supply, via a common rail, an internal-combustion engine not shown in Figure 1. The high-pressure pump comprises a pump body 1, a compartment 2 able to house an actuating mechanism, not shown in Figure 1; and an actuating shaft 3 which is shown in Figure 1 in broken lines and is rotatable about an axis A. The actuating mechanism is able to actuate at least one pumping member (not shown in Figure 1) which is able to perform an alternating movement in the radial direction with respect to the shaft 3.

In particular, the pump body 1 comprises an annular wall 4 which has three seats 5 for housing respective pumping members (only two seats 5 are shown in Figure 1) and three service openings 6 (only two of which are shown in Figure 1) closed

by respective plugs 7, only one of which shown in Figure 1. The seats 5 for the pumping members are arranged at 120° relative to each other about the axis A.

The pump body 1 comprises a wall 8 of considerable thickness which extends perpendicularly with respect to the axis A, is adjacent to the wall 4 and has an opening 9 along the axis A for housing the shaft 3. The pump body 1 comprises an axial closing plate for the compartment 2, which is arranged on the opposite side of the wall 8 and is not shown in Figure 1.

In the case in question the opening 9 is delimited by a cylindrical seat 10 and by an annular lug 11 of the wall 8. The minimum diameter of the annular lug 11 is smaller than the diameter of the cylindrical seat 10.

The high-pressure pump comprises a bush 12 which is made of material with a low coefficient of friction, usually bronze, and has the function of supporting a portion 13 of the shaft 3 which has a ground outer surface 14. The actuating mechanism, not shown in the accompanying figures, generally comprises a cam which is fixed onto another portion of the shaft 3 inside the compartment 2. The cam is designed to cooperate, in a known manner, with a prismatic ring, of the known type and not shown in the accompanying figures, so as to actuate in sequence the three pumping members not shown in the accompanying figures.

The bush 12 essentially comprises a cylindrical wall which has an outer surface 15 and a ground inner surface 16 rotatably mating with the outer surface 14 of the portion 13 of the shaft 3.

The bush 12 is fixed with interference inside the cylindrical seat 10 of the pump body 1 so that it is fluid-tight with the pump body 1.

The high-pressure pump is coupled in a fluid-tight manner with a portion 18 of the shaft 3 via the annular lug 11.

The portion 18, which has a diameter smaller than that of the portion 13, is connected to the portion 13 by an annular face 19 which is substantially

perpendicular to the axis A and is situated facing the annular lug 11. An annular chamber 20 is defined between the annular lug 11, the face 19, the portion 18 of the shaft 3 and the cylindrical seat 10 of the pump body 1 and communicates with the compartment 2 via a narrow passage 21 which extends between the bush 12 and the portion 13 of the shaft 3, in particular between the inner surface

16 of the bush 12 and the outer surface 14 of the shaft 3.

In order to lubricate and cool the actuating mechanism, the compartment 2 is designed to receive a part of the fuel supplied to the high-pressure pump so as to undergo a compression phase. The fuel supplied to the high-pressure pump is generally provided by a tank (not shown in the accompanying figures) and is first compressed by a pre-supply pump (not shown in the accompanying figures) which compresses the fuel to a relatively low pressure of about 5 bar. Part of the low-pressure fuel which is controlled by special valves, not shown in the accompanying figures, is sent to the compartment 2 via an inlet not shown in the accompanying figures. During operation of the high-pressure pump the fuel fills the compartment 2, lubricating and cooling the actuating mechanism. From the compartment 2 the fuel flows out through an outlet, not visible in the figures, and is discharged into the tank (not shown).

In order to favour exchange of the fluid and correct supplying of the fuel to the passage 21, the high-pressure pump comprises a duct 22 which is formed partly in the bush 12 and partly in the pump body 1 and connects the compartment 2 and the passage 21. The duct 22 consists of a groove 23, formed in the pump body 1 along the cylindrical seat 10 housing the bush 12, and of at least one through-hole 24 passing through the cylindrical wall of the bush 12 and communicating with the groove 23. Therefore, the groove 23 and the hole 24 allow the fuel to pass from the compartment 2 to the passage 21 connecting together the cylindrical seat 10 and the outer surface 15 of the bush 12 via the groove 23 along the cylindrical seat 10.

Advantageously, the groove 23 extends axially and circumferential Iy along the cylindrical seat 10 and has a substantially helical form with a first end 25 in the

region of the compartment 2 and a second end 26 in the region of the annular chamber 20.

The groove 23 has a curved cross-section and extends helically on the outer surface 16 over at least 90°, preferably over at least 180°.

At the first end 25 the groove 23 has a portion 27 with a larger cross-section able to favour supplying of the fuel to the groove 23.

Preferably the groove 23 connects the compartment 2 to the annular chamber 20 so as to cool and lubricate suitably also the zone of the high-pressure pump adjacent to the annular chamber 20.

During operation of the high-pressure pump, the low-pressure fuel is supplied to the compartment 2 and fills this compartment 2, lubricating the actuating mechanism of the high-pressure pump and flows out of the compartment towards a tank not shown in the accompanying figures. Part of this fuel is supplied to the groove 23 in order to lubricate and cool the contact zone between the shaft 3 and the bush 12. In other words, the groove 23 supplies the fuel to the passage 21 via the hole 24 between the outer surface 14 of the portion 13 of the shaft 3 and the inner surface 16 of the bush 12, lubricating and cooling effectively the contact zone between the bush 12 and the shaft 3.

Moreover, the groove 23 also supplies the annular chamber 20 which, in turn, supplies the passage 21 along which the fuel flows back towards the compartment 2.

Essentially the groove 23 and the hole 24 define the delivery path of the fuel, while the passage 21 defines the return path of the fuel.

The above description clearly reveals the advantages of the high-pressure pump according to the invention compared to the prior art.

In particular, the duct 22 is obtained by means of a groove 23 along the cylindrical seat 10 of the pump body 1 and a radial hole 24 in the cylindrical wall of the bush 12. Therefore, machining of the duct 22 is greatly simplified and may be performed before fixing the bush 12 inside the seat 10, so that the high- pressure pump is less costly.

It is understood that various modifications and improvements may be made to the high-pressure pump described without departing from the scope of the claims. For example, the high-pressure pump may have any number of pumping members. Moreover, the shape of the cross-section and the path along which the groove 23 extends may be different from those described. Two or more axially spaced through-holes 24 may also be provided in the bush 12. Finally two or more ducts 22 which are angularly offset relative to each other and/or extend axially in a different manner may be envisaged.

Moreover, in accordance with a variant not shown, the groove 23 may be formed along the outer surface 15 of the bush 12.

According to further variant not shown, the groove 23 may be formed partly along the outer surface 15 of the bush 12 and partly along the cylindrical seat 10 of the pump body 1.