EP2612017B1

EP2612017B1 - Pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine and associated assembly method

Info

Publication number: EP2612017B1
Application number: EP11746265.5A
Authority: EP
Inventors: Gaetano Riglietti
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-09-01
Filing date: 2011-08-24
Publication date: 2014-12-10
Anticipated expiration: 2031-08-24
Also published as: EP2612017A1; KR20130103718A; CN103080530A; WO2012028507A1; CN103080530B; IT1401914B1; RU2013114165A; RU2573434C2; ITMI20101594A1; JP2013540930A; JP5654682B2

Description

The present invention relates to a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine.
In particular, the present invention relates to a pump unit comprising a pump body; a piston pump designed to feed the fuel to an internal combustion engine; and a gear pump designed to feed the fuel to the piston pump.
Such a pump unit with a piston pump is known from the document DE 87 08 761 U1 . The piston pump comprises at least one cylinder which is formed in the pump body; and a piston engaged slidably inside the cylinder so as to perform an intake stroke for drawing the fuel into the cylinder under the thrust of a spring arranged between the pump body and a support plate mounted on the piston and a compression stroke for compressing the fuel contained inside the cylinder under the thrust of an actuating device.
The support plate has an opening, which is formed through the support plate, parallel to a longitudinal axis of the piston, and comprises a seat for inserting the piston through the support plate, a seat for engaging the piston in the support plate, and a communicating section for allowing the piston to pass between the insertion seat and the engaging seat.
Generally, the piston is provided with an annular groove, which is formed on the outer surface of the piston and has a diameter slightly greater than a width of the communicating section; the insertion seat has a substantially circular shape and a diameter slightly greater than a diameter of the piston; and the engaging seat has a substantially circular shape and a diameter slightly greater than the diameter of the annular groove.
Once the piston has been introduced into the insertion seat, the piston and the support plate are firstly displaced axially with respect to each other until the annular groove is radially aligned with the communicating section and are then displaced radially with respect to each other so as to transfer the piston from the insertion seat into the engaging seat by moving the annular groove through the communicating section.
Since the width of the communicating section is smaller than the diameter of the annular groove, the annular groove interferes with the communicating section when the piston is displaced from the insertion seat into the engaging seat. Consequently, the known pump units of the type described above have a number of drawbacks due principally to the fact that assembly of the support plate on the piston may cause damage to the annular groove, separation of metal particles from the piston and, therefore, reduction of the fatigue strength of the piston and seizing of the piston inside the cylinder.
The object of the present invention is to provide a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine, which does not have the drawbacks described above and which is simple and inexpensive to produce.
According to the present invention a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine as claimed in Claims 1 to 12 is provided.
The present invention also relates to a method for assembling a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine.
According to the present invention a method for assembling a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine as claimed in Claims 13 to 17 is provided.
The present invention will now be described with reference to the accompanying drawings which illustrate a non-limiting example of embodiment thereof in which:

Figure 1 is a schematic cross-sectional view, with parts removed for the sake of clarity, of a preferred embodiment of the pump unit according to the present invention;
Figure 2 is a side view of a first detail of Figure 1; and
Figure 3 is a plan view of a second detail of Figure 1.

With reference to Figure 1, 1 denotes, in its entirety, a pump unit for feeding fuel, in particular diesel fuel, to an internal combustion engine (not shown).
The pump unit 1 comprises a pump body 2 provided with a central hole (not shown) having a given longitudinal axis 3; a piston pump 4 designed to feed the fuel to the said internal combustion engine (not shown); and a gear pump, known and not shown, designed to feed the fuel to the pump 4.
The pump 4 comprises a plurality of cylinders 5 (only one of which is shown in Figure 1) which are formed in the pump body 2, are uniformly distributed around the axis 3 and have respective longitudinal axes 6 substantially perpendicular to the axis 3.
Each cylinder 5 is slidably engaged by an associated piston 7 which is mounted inside the cylinder 5 coaxially with the axis 6, has a diameter D1 and is provided with an annular groove 8 (Figure 2) which is formed on an outer surface of the piston 7 at an intermediate point of the piston 7 itself and has a diameter D2 smaller than the diameter D1.
The pistons 7 are displaced with an alternating rectilinear movement along the associated cylinders 5 by an actuating device 9 comprising, in the case in question, a drive shaft (not shown) which extends through the pump body 2 coaxially with the axis 3, is mounted so as to rotate, relative to the pump body 2, about the axis 3 and has an eccentric portion engaged rotatably, via a rolling bearing (not shown), through a sleeve (not shown).
The sleeve (not shown) has a longitudinal axis parallel to the axis 3 and is bounded externally by a cylindrical surface provided with a plurality of flat faces equal in number to the number of cylinders 5 and each facing a respective disk element (not shown) arranged between an associated piston 7 and the flat face itself.
The actuating device 9 furthermore comprises, for each piston 7, a respective spring 10 which is mounted coaxially with the associated axis 6, is arranged between the pump body 2 and a substantially flat support plate 11 mounted on the piston 7, perpendicularly with respect to the associated axis 6, and is designed to displace - and normally keep - the piston 7 itself in contact with the associated disk element (not shown).
Following rotation of the drive shaft (not shown), each piston 7 is displaced by the associated spring 10 during an outward intake stroke for drawing the fuel into the associated cylinder 5 and by the eccentric portion of the drive shaft (not shown), by the sleeve (not shown) and by the associated washer (not shown) during a return compression stroke for compressing the fuel contained inside the said associated cylinder 5.
In accordance with that shown in Figure 3, the plate 11 has an opening 12 which is formed through the plate 11, parallel to the axis 6, has a plane S of symmetry substantially coplanar with the axis 6, is bounded by a shaped side wall 13 and comprises a seat 14 for inserting the piston 7 through the plate 11, a seat 15 for engaging the piston 7 in the plate 11, and a communicating section 16 allowing passage between the seat 14 and the seat 15.
The seat 14 has a substantially circular shape, a centre C1 of curvature different from the axis 6, and a diameter D3 slightly greater than the diameter D1 of the piston 7; and the seat 15 has a substantially circular shape, a centre C2 of curvature substantially arranged along the axis 6, and a diameter D4 which is slightly smaller than the diameter D1 of the piston 7 and slightly greater than the diameter D2 of the groove 8.
It should be pointed out, moreover, that the distance between the centres C1 and C2 is smaller than the sum of the radii of curvature of the two seats 14 and 15.
The communicating section 16 is bounded laterally by two elastically deformable arms 17 which project from the wall 13 inside the opening 12, extend on opposite sides of the plane S and have respective free ends 18 provided, in the case in question, with respective holes 19 formed in the plate 11, parallel to the axis 6.
The arms 17 are arranged, normally, in an initial narrow configuration (Figure 3) where the section 16 has a width L1, measured perpendicularly with respect to the plane S, which is slightly smaller than the diameter D2 of the groove 8 and where each arm 17 has a substantially V-shaped form and cooperates with the other arm 17 so as to define part of the seat 14 and part of the seat 15.
The opening 12 further comprises two recesses 20, which are formed on opposite sides of the plane S and are each bounded by the wall 13 and by an associated arm 17.
In order to assemble the plate 11 on the piston 7:

the piston 7 is inserted into the insertion seat 14;
the plate 11 is displaced axially along the piston 7 so as to align radially the groove 8 with the communicating section 16;
the arms 17 are splayed inside the associated recesses 20, for example by means of a splaying tool (not shown) engaged inside the holes 19, so as to provide the section 16 with a final widened configuration (not shown), where the section 16 has a width L2, measured perpendicularly with respect to the plane S, greater than the width L1 and at least equal to the diameter of the groove 8;
the piston 7 is displaced radially from the seat 14 into the engaging seat 15 so as to move the groove 8 through the section 16; and
the arms 17 are released so as to radially lock the piston 7 inside the seat 15.

Since the groove 8 has, in the case in question, a height H greater than the thickness of the plate 11, the plate 11 is finally displaced axially in contact with the piston 7.
The final widened configuration of the arms 17 allows the piston 7 to be displaced radially from the seat 14 into the seat 15 without interfering with the section 16 and therefore avoids damage to the groove 8, separation of metal particles from the piston 7, reduction in the fatigue strength of the piston 7 and seizing of the piston 7 inside the cylinder 5.

Claims

Pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine, the pump unit comprising a pump body (2); at least one cylinder (5) formed in the pump body (2); a piston (7), which is slideably engaged inside the cylinder (5) and has at least one first diameter (D2); a support plate (11) mounted on the piston (7); a spring (10) arranged between the pump body (2) and the support plate (11) for displacing the piston (7) during an intake stroke for drawing the fuel into the cylinder (5); and an actuating device for displacing the piston (7) during a compression stroke for compressing the fuel contained inside the said cylinder (5); the support plate (11) having an opening (12) which is formed through the support plate (11), parallel to a longitudinal axis (6) of the piston (7), and comprises a seat (14) for inserting the piston (7) through the support plate (11), a seat (15) for engaging the piston (7) in the support plate (11), and a communicating section (16) for allowing the piston (7) to pass between the insertion seat (14) and the engaging seat (15); the communicating section (16) having, in an initial narrow configuration thereof, a first width (L1) which is slightly smaller than the said first diameter (D2); and being characterized in that the communicating section (16) is bounded laterally by two elastically deformable arms (17) each having a respective free end (18).
Pump unit according to Claim 1, wherein the communicating section (16) has, in a final widened configuration thereof following widening of the two arms (17), a second width (L2) at least equal to the said first diameter (D2).
Pump unit according to Claim 2, wherein the arms (17) have respective gripping means (19) designed to allow displacement of the said arms (17) into the final widened configuration.
Pump unit according to Claim 2 or 3, wherein the arms (17) have respective gripping seats (19) designed to be engaged by at least one splaying tool for displacing the arms (17) into the final widened configuration.
Pump unit according to any one of the preceding claims, wherein the insertion seat (14) and the engaging seat (15) are substantially circular.
Pump unit according to Claim 5, wherein the centres of curvature (Cl, C2) of the insertion and engaging seats (14, 15) are arranged at a distance from one another less than the sum of the radii of curvature of the said insertion and engaging seats (14, 15).
Pump unit according to any one of the preceding claims, wherein the said opening (12) has, furthermore, two recesses (20) arranged on opposite sides of the communicating section (16) for receiving the arms (17) following elastic deformation of the said arms (17).
Pump unit according to any one of the preceding claims, wherein the piston (7) has a second diameter (D1) and comprises at least one annular groove (8) which is formed on the outer surface of the piston (7) and has the said first diameter (D2).
Pump unit according to Claim 8, wherein the insertion seat (14) has a third diameter (D3) slightly greater than the second diameter (D1) and the engaging seat (15) has a fourth diameter (D4) slightly greater than the first diameter (D2) and slightly smaller than the second diameter (D1).
Pump unit according to Claim 8 or 9, wherein the annular groove (8) has a height (H), measured parallel to the said axis (6), which is greater than a thickness of the support plate (11).
Pump unit according to any one of the preceding claims, wherein the two arms (17) project inside the opening (12) from a side wall (13) of the said opening (12).
Pump unit according to Claim 11, wherein, at least when the arms (17) are arranged in their initial narrow configuration, each arm (17) has a substantially V-shaped form and cooperates with the other arm (17) so as to define part of the insertion seat (14) and part of the engaging seat (15).
Method for assembling a pump unit for feeding fuel, preferably diesel fuel, to an internal combustion engine, the pump unit comprising a pump body (2); at least one cylinder (5) formed in the pump body (2); a piston (7), which is slidably engaged inside the cylinder (5), extends through a support plate (11) and has at least one first diameter (D2); a spring (10) arranged between the pump body (2) and the support plate (11) for displacing the piston (7) during an intake stroke for drawing the fuel into the cylinder (5); and an actuating device for displacing the piston (7) during a compression stroke for compressing the fuel contained inside the said cylinder (5); the support plate (11) having an opening (12), which is formed through the support plate (11), parallel to a longitudinal axis (6) of the piston (7), and comprises a seat (14) for inserting the piston (7) through the support plate (11), a seat (15) for engaging the piston (7) in the support plate (11), and a communicating section (16) for allowing the piston (7) to pass between the insertion seat (14) and the engaging seat (15); the communicating section (16) being bounded laterally by two elastically deformable arms (17) each having a respective free end (18) and having, in an initial narrow configuration thereof, a first width (L1) which is slightly smaller than the said first diameter (D2), wherein the piston (7) has a second diameter (D1) and comprises at least one annular groove (8) which is formed on the outer surface of the piston (7) and has the said first diameter (D2), and wherein the annular groove (8) is formed at an intermediate point of the piston (7) and has a height (H), measured parallel to the said axis (6), greater than a thickness of the support plate (11); the method comprising the steps of:
introducing the piston (7) into the insertion seat (14);

axially displacing the piston (7) and the support plate (11) with respect to each other through the insertion seat (14) so as to align the annular groove (8) with the communicating section (16);

widening the two arms (17) so as to impart to the communicating section (16) a final widened configuration, where the communicating section (16) has a second width (L2) at least equal to the said first diameter (D2);

displacing the piston (7) and the support plate (11) with respect to each other transversely with respect to the said axis (6) so as to displace the piston (7) from the insertion seat (14) into the engaging seat (15) through the communicating section (16);

radially displacing the piston (7) and the support plate (11) with respect to each other so as to move the annular groove (8) through the communicating section (16);

and axially displacing the piston (7) and the support plate (11) with respect to each other through the engaging seat (15) so as to lock axially the support plate (11) against the said piston (7).
Method according to Claim 13, wherein the piston (7) is displaced from the insertion seat (14) into the engaging seat (15) without interfering with the communicating section (16).
Method according to Claim 13 or 14 and further comprising the step of:
releasing the two arms (17) so as to radially lock the piston (7) inside the engaging seat (15).