WO2017144189A1

WO2017144189A1 - Pumping assembly to feed fuel, preferably diesel fuel, to an internal combustion engine

Info

Publication number: WO2017144189A1
Application number: PCT/EP2017/050150
Authority: WO
Inventors: Adriano SCIUSCO; Chiara MAZZOTTA
Original assignee: Robert Bosch Gmbh
Priority date: 2016-02-26
Filing date: 2017-01-04
Publication date: 2017-08-31
Also published as: ITUB20161107A1

Abstract

A pumping assembly to feed fuel, preferably diesel fuel, to an internal combustion engine is provided with at least one piston (23) which is movable along a cylinder (22) under the thrust of a drive shaft (36), which is engaged in a rotatable manner through a pump body (8) by means of the interposition of at least two support bearings (37, 38), and is coupled in a fluid-tight manner to the pump body (8) by means of the interposition of an annular gasket (51) and of a labyrinth sealing device (53) mounted between the annular gasket (51) and one of the support bearings (37, 38).

Description

DESCRIPTION

Title

PUMPING ASSEMBLY TO FEED FU EL, PREFERABLY DIESEL FU EL, TO AN INTERNAL COMBUSTION ENGINE

The present invention relates to a pumping assembly to feed fuel, preferably diesel fuel, to an internal combustion engine.

In particular, the present invention relates to a pumping assembly of the type comprising a high-pressure pump, in the case in question a piston pump, to feed the fuel to the internal combustion engine; and a pre-feed pump, for example a gear pump, to feed the fuel from a storage tank to the piston pump.

The piston pump comprises a pump body; at least one cylinder formed in the pump body; a piston engaged slidingly in the cylinder; and an actuating device to move the piston with an intake stroke of the fuel into the cylinder and with a compression stroke of the fuel present in said cylinder.

The piston pump further comprises a duct for the intake of the fuel inside the cylinder; an intake valve mounted along the intake duct for selectively controlling the feed of the fuel in the cylinder; a duct for delivering the fuel to the internal combustion engine; and a delivery valve mounted along the delivery duct for selectively controlling the feed of the fuel to the internal combustion engine.

The actuating device comprises a drive shaft mounted through the pump body to rotate about a rotation axis transverse to a longitudinal axis of the cylinder and move the piston with its compression stroke; and a spring interposed between the pump body and the piston to move said piston with its intake stroke. The pump body comprises a containing casing engaged in a rotatable manner by the drive shaft by means of the interposition of at least one first support bearing; and a tubular bush, which is connected to the containing casing and is engaged in a rotatable manner by the drive shaft by means of the interposition of at least one second support bearing.

The tubular bush is delimited by an inner wall comprising a narrower portion defining a housing seat for the second support bearing and a wider portion defining a housing seat for an annular gasket, which is mounted at an end of the wider portion and axially closes a chamber for collecting the fuel seeping between the narrower portion and the drive shaft through the second support bearing.

The pumping assembly moreover comprises a return branch to discharge into the storage tank the amount of fuel exceeding that required for the correct operation of the internal combustion engine.

Since the collection chamber is connected to the return branch by means of a feed duct formed through the pump body, the average pressure inside the collection chamber is substantially the same as the sum total of the pressure of the fuel in the return branch, of the drops in pressure in the feed duct, and of the pressure of the fuel seeping through the second support bearing.

As a result, the known pumping assemblies of the type described above have a number of disadvantages mainly arising from the fact that the pressure of the fuel in the collection chamber is relatively high and causes relatively high losses of fuel through the annular gasket mounted between the tubular bush and the drive shaft.

When the fuel leaking from the pumping assembly drops onto the internal combustion engine, this may result in critical operating conditions of said engine, ultimately leading to a fire. It is an object of the present invention to provide a pumping assembly to feed fuel, preferably diesel fuel, to an internal combustion engine, which does not have the above-described disadvantages and is simple and inexpensive to produce.

According to the present invention, a pumping assembly to feed fuel, preferably diesel fuel, to an internal combustion engine is provided as claimed in the accompanying claims.

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

Figure 1 is a hydraulic diagram of a preferred embodiment of the pumping assembly of the present invention;

Figure 2 is a first schematic sectional view, with parts removed for clarity, of the pumping assembly shown in Figure 1; and

Figure 3 is a second schematic sectional view, with parts removed for clarity, of the pumping assembly shown in Figure 1.

With reference to Figure 1, 1 denotes in its entirety a pumping assembly to feed a liquid fuel, preferably diesel fuel, from a storage tank 2 to an internal combustion engine 3, in the case in question a diesel combustion engine.

The engine 3 comprises a fuel distribution manifold 4, commonly referred to by the term "common rail", and a plurality of injectors 5 connected to the manifold 4 and designed to atomize the fuel inside associated combustion chambers (not shown) of said engine 3.

The pumping assembly 1 comprises a high-pressure pump 6 to feed the fuel to the engine 3, and a low-pressure or pre-feed pump 7, in the case in question an electric pump, to feed the fuel from the tank 2 to the pump 6. According to that shown in Figures 2 and 3, the pump 6 is a piston pump provided with a pump body 8 comprising a containing casing 9, which has a central hole 10 having a longitudinal axis 11 and furthermore has at least one lateral hole 12 (normally a plurality of holes 12 distributed uniformly about the axis 11), which has a longitudinal axis 13 transverse to the axis 11 and extends radially towards the outside of the casing 9 proceeding from said hole 10.

The pump body 8 further comprises a tubular bush 14, which is mounted in the hole 10, projects axially on the outside of the hole 10, and is delimited by an inner wall defining a wider portion 15 and a narrower portion 16 arranged in succession along the axis 11 proceeding from a free end face of said tubular bush 14.

Each hole 12 is closed by a cylinder head 17, which is arranged in contact with the casing 9 and has an extended portion 18 projecting inside the hole 12 coaxially with the axis 13.

The cylinder head 17 has a central hole 19, which is formed through the cylinder head 17 coaxially with the axis 13, and comprises a wider portion 20 and a narrower portion 21 in alignment with one another along said axis 13.

The portion 21 faces towards the hole 10 and defines a cylinder 22 of the piston pump 6.

The cylinder 22 is engaged slidingly by a piston 23, which is movable, under the thrust of an actuating device 24, with an alternate rectilinear movement, comprising an intake stroke of the fuel into the cylinder 22 and a compression stroke of the fuel present inside said cylinder 22.

The device 24 comprises a tubular sleeve 25, which is engaged slidingly on the inside of the hole 12 coaxially with the axis 13, extends about the cylinder 22, and has an inner annular flange 26, which projects radially from an inner surface of the sleeve 25 and divides said sleeve 25 into two cylindrical portions 27, 28, of which the portion 27 faces towards the hole 10. The device 24 further has a tappet 29, comprising a substantially cylindrical coupling block 30, which is blocked by interference on the inside of the portion 27, is arranged in contact with the flange 26, and supports a cam follower 31.

The cam follower 31 projects from the block 30 towards the hole 10 and is coupled in a rotatable manner to the block 30 to rotate, with respect to said block 30, about a longitudinal axis 32 thereof substantially perpendicular to the axis 13.

The flange 26 supports an annular plate 33, which extends about the piston 23, is inserted into the portion 28 of the sleeve 25 coaxially with the axis 13, and has an outer perimetral edge facing axially towards the flange 26 and an inner perimetral edge facing axially towards a head of said piston 23.

The device 24 further comprises a compression spring 34, which is mounted between the extended portion 18 and the sleeve 25 coaxially with the axis 13, and is interposed between the cylinder head 17 and the plate 33 to move, and normally keep, the plate 33 in contact with the flange 26 and the cam follower 31 in contact with a cam 35 formed on an outer surface of an intermediate portion of a drive shaft 36 mounted through the hole 10 to rotate, with respect to the casing 9, about the axis 11.

The shaft 36 is engaged in a rotatable manner through the casing 9 by means of the interposition of a first support bearing 37 and through the tubular bush 14 by means of the interposition of a second support bearing 38 mounted in the narrower portion 16.

The pumping assembly 1 further comprises a hydraulic circuit 39 comprising, in turn, a first branch 40 to connect together the tank 2 and the pump 7; a second branch 41, which connects together the pumps 6 and 7, extends through the pump body 8 to lubricate the actuating device 24, and is connected to the cylinder 22 by means of an intake valve 42; and a third branch 43, which extends between the pump 6 and the manifold 4 and is connected to the cylinder 22 by means of a delivery valve 44. The branch 41 is provided with a metering electrovalve 45, which is mounted upstream of the valve 42 in a direction 46 of feeding of the fuel along the branches 40, 41 and 43, is movable between a closed position and an open position of the branch 41, and is designed to selectively control the instantaneous flow rate of fuel fed to the pump 6 depending on the values of a plurality of operating parameters of the engine 3.

The circuit 39 further comprises a fourth branch 47, which connects the branch 41 upstream of the electrovalve 45 in the direction 46 to the tank 2, extends through an overflow valve 48, and allows at least some of the amount of fuel exceeding that fed through said electrovalve 45 to be discharged into the tank 2.

The circuit 39 further has a fifth branch 49, which extends between the manifold 4 and the branch 47 and allows the amount of fuel exceeding that necessary for the injectors 5 to be discharged into the tank 2.

The circuit 39 further comprises a sixth branch 50 for discharging into the branch 47, and therefore into the tank 2, the fuel fed through the pump body 8 by the branch 41 and seeping through the support bearings 37, 38 of the shaft 36.

The branch 50 is in hydraulic communication with the wider portion 15 of the tubular bush 14 at a shoulder defined between the wider portion 15 and the narrower portion 16 of said tubular bush 14.

The wider portion 15 is closed axially by an annular gasket 51, which is mounted between the tubular bush 14 and the shaft 36 coaxially with the axis 11, and defines, together with the tubular bush 14 and the shaft 36, a chamber 52 for collecting the fuel seeping along the bearing 38.

The chamber 52 houses on its inside a labyrinth sealing device 53 arranged in such a way as to separate the gasket 51 from the bearing 38 and from the branch 50. In the case in question, the device 53 comprises a cylindrical sleeve 54, which is mounted on the inside of the wider portion 15 of the tubular bush 14 coaxially with the axis 11, extends about the shaft 36, and has a plurality of mutually parallel annular discs 55 projecting radially towards said shaft 36.

The discs 55 are arranged at a specific distance from the shaft 36 so as to force the fuel to move axially along a path set up to reduce the pressure peaks generated in the chamber 52 by the fuel seeping along the bearing 38 and by the drops in pressure along the branch 50.

As a result, the reduction in said pressure peaks makes it possible to reduce the losses of fuel through the gasket 51 and therefore to improve the stability, the safety and the service life of the pumping assembly 1.

It goes without saying that the labyrinth sealing device 53 can be produced with configurations which differ from that illustrated in Figure 3.

According to one variant, which is not shown, the electric pump 7 is dispensed with and replaced by a gear pump. In this case, the branch 47 is connected, preferably but not necessarily, to the inlet of the pump 7 and not to the tank 2, so as to perform controlled lubrication of the bearings 37, 38.

Claims

1. Pumping assembly to feed fuel, preferably diesel fuel, to an internal combustion engine, the pumping assembly comprising a pump body (8); at least one cylinder (22) formed in the pump body (8); a piston (23) engaged slidingly in the cylinder (22); an actuating device (24) to move the piston (23) with an intake stroke of the fuel into the cylinder (22) and with a compression stroke of the fuel present in said cylinder (22), the actuating device (24) comprising a drive shaft (36) mounted in a rotatable manner through the pump body (8) by means of the interposition of a first support bearing (37) and of a second support bearing (38); and an annular gasket (51) interposed between the pump body (8) and the drive shaft (36) to avoid fuel leaks from said pump body (8); and being characterized in that it further comprises a labyrinth sealing device (53) interposed between the pump body (8) and the drive shaft (36) and mounted between the annular gasket (51) and the second support bearing (38).

2. Pumping assembly according to Claim 1, wherein the pump body (8) has a central hole (10), which is engaged in a rotatable manner by the drive shaft (36), and comprises a narrower portion (16) defining a housing seat for the second support bearing (38) and a wider portion (15) defining a housing seat for the annular gasket (51).

3. Pumping assembly according to Claim 2 and further comprising a collection chamber (52) formed in said wider portion (15) to collect the fuel seeping along the second support bearing (38); the collection chamber (52) being delimited axially by the annular gasket (51) and housing on its inside the labyrinth sealing device (53).

4. Pumping assembly according to Claim 3 and further comprising a pre-feed pump (7) to feed the fuel from a storage tank (2) to the cylinders (22).

5. Pumping assembly according to Claim 4, wherein the collection chamber (52) is connected to the storage tank (2).

6. Pumping assembly according to Claim 4, wherein the collection chamber (52) is connected to an inlet for the fuel into the pre-feed pump (7).

7. Pumping assembly according to Claim 4 and further comprising a feed duct (50) to connect the collection chamber (52) to the storage tank (2) or to an inlet for the fuel into the pre-feed pump (7).

8. Pumping assembly according to Claim 7, wherein the labyrinth sealing device (53) is mounted between the annular gasket (51) and the assembly defined by the feed duct (50) and by the second support bearing (38).

9. Pumping assembly according to Claim 7 or 8, wherein the feed duct (50) is connected to the collection chamber (52) at a shoulder defined between said wider and narrower portions (15, 16).

10. Pumping assembly according to any one of the preceding claims, wherein the pump body (8) comprises a containing casing (9) engaged in a rotatable manner by the drive shaft (36) by means of the interposition of the first support bearing (37), and a tubular bush (14), which is connected to the containing casing (9) and is engaged in a rotatable manner by the drive shaft (36) by means of the interposition of the second support bearing (38); the annular gasket (51) and the labyrinth sealing device (53) being housed in the tubular bush (14).