GB2266349A

GB2266349A - Fuel-injection pump for internal combustion engines.

Info

Publication number: GB2266349A
Application number: GB9307275A
Authority: GB
Inventors: Jaroslaw Hlousek
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1992-04-10
Filing date: 1993-04-07
Publication date: 1993-10-27
Anticipated expiration: 2013-04-07
Also published as: GB2266349B; JPH0626422A; GB9307275D0; DE4212183A1

Abstract

A fuel-injection pump for delivering a quantity of fuel sub-divided into a pre-injection quantity and a main- injection quantity, has an angularly adjustable piston (7) reciprocating in a cylinder sleeve (3) and defining therewith a pump working chamber (11). The piston (7) has an oblique control edge (38) leading to a first annular groove (42) separated from a second annular groove (46) by a land (44). The boundaries of the land (44) form control edges (48, 50) which cooperate with the control edges (32, 30) of a blind bore recess (25) in the sleeve (3). During part of the delivery stroke of the piston (7), a connection is opened between the chamber (11) and a low pressure chamber (19) via the grooves (42, 46). The high fuel pressure in the chamber (11) is thus momentarily relieved. All control edges on the piston (7) are formed as oblique edges to enable the commencement and termination of delivery of the pre-injection process and of the main-injection process to be varied. <IMAGE>

Description

2266349

DESCRIPTION FUEL-INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES

The invention relates to fuel-injection pumps for internal combustion engines.

In the case of a fuel-injection pump known from EP-Bl 0 020 249, the quantity of injected fuel is divided during the high pressure delivery into a preinjection quantity and a main-injection quantity. By reducing the quantity of fuel introduced into the combustion chamber during retarded ignition, this measure reduces the pressure peaks during the ignition and consequently, as a result. reduces the combustion noise. For this purpose, it is possible in the known fuel-injection pump. wherein a pump piston is axially moveable in a cylinder bore of a cylinder sleeve and can be rotated for the purpose of adjusting the quantity of injected fuel and which defines by its front face a pump working chamber, which can be connected by two control ports in the cylinder sleeve to a low pressure chamber which surrounds the cylinder sleeve and forms an intake chamber, to connect an annular groove, which is on the pump piston below the control recesses and is divided by a land into two parts, to a further control port in the cylinder sleeve. and it is possible, by way of a recess at the land. for the fuel to flow through between the two -2parts of the annular groove and furthermore by way of the control recess to the pump working chamber. The upper annular groove is at the same time connected continuously to the pump working chamber and has for the purpose of controlling the quantity of injected fuel an upper oblique control edge, which cooperates with the two control ports. During a part of the delivery stroke of the pump piston. the land therefore opens the connection between the pump working chamber and the lower control port by way of the lower annular groove, causing the pressure in the pump working chamber to be relieved and as a result of this, the high pressure delivery is interrupted.

At the same time, it is only possible with the known fuel-injection pump to carry out a limited control of the commencement of injection of the preinjection process, which is carried out in accordance with Fig. 9 of EP-B-0020249 by way of a displaceable piston which is connected to a pump working chamber and which closes a relief line of the pump working chamber. This displaceable piston is moved at the same time against a stop by the compressed fuel against the force of the return spring and in this position closes the relief line. The commencement of injection of the pre-injection process is therefore dependent upon the build-up of pressure in the pump -3working chamber, which in turn is determined by the rotational speed of the internal combustion engine.

in order to optimise the combustion characteristic of the internal combustion engine in the entire performance graph of the engine with respect to the combustion noise, the gas emission and the usability of a qualitatively wide fuel spectrum, it is, however, necessary to control the quantity of pre-injection fuel in dependence upon the load and the rotational speed and this facility is not available with the known fuelinjection pump.

The present invention resides in a fuel-injection pump for an internal combustion engine having at least one pump piston, which is guided axially and in a manner so as to be able to rotate and is reciprocatingly driven in a cylinder bore and which defines by its front face a pump working chamber, in which the pump piston has in its periphery a control recess connected to the pump working chamber, this control recess having an oblique control edge which is at a predetermined angle to the axis of the pump piston and which cooperates with a control port in the wall of the cylinder bore, and the control port is connected to a low pressure chamber and issues into a first annular groove in the periphery of the pump piston. the annular groove being connected -4continuously to the pump working chamber and being separated from a second annular groove by a land formed by a part of the piston, and in which the second annular groove is connected during part of the pump piston stroke to a through-opening in the cylinder wall connected to the low pressure chamber, and the land has circumferential boundary edges contiguous to the periphery of the pump piston and these boundary edges form in each case a control edge, of which an upper control edge, towards the pump working chamber, cooperates with an upper control edge,towards the pump working chamber of a recess in the cylinder wall and a lower control edge of the land cooperates with the lower control edge of the recess, the lower control edge of the land having regions with oblique edges.

This has the advantage, that the commencement of injection and the termination of injection of the preinjection process and the maininjection process can be changed by designing the piston control edges in the form of oblique edges in dependence upon the rotational position of the piston and therefore in dependence upon the load. In addition to the possibility of controlling the commencement of fuelinjection and the quantity of injected fuel, this design of the piston control edges also provides a -5possibility in certain regions of the performance graph of the engine to produce only the main-injection process without the pre-injection process.

In order to form a defined flow cross section, which cooperates with the control edges at the land controlling the intermediate pressure relief and which renders it possible for the fuel to flow through from the highly pressurised upper annular groove connected to the pump working chamber to the lower annular groove connected to a pressure relief line. a blind bore is provided in the cylinder wall in an advantageous manner and this blind bore is closed by means of a screw. In addition to its control cross section, which is precisely designed geometrically, the recess formed in this way also has the advantage of being simple to manufacture.

A further advantage is produced by providing an oblique blind bore, which negates the need, when fully functionable, for providing a further bore to connect the lower annular groove to the low pressure chamber. In addition to this, this embodiment of the recess in accordance with the invention does not require the original blind bore to be closed, which reduces both the production costs and also the material expenditure.

The invention is further described. by way of -6example, with reference to the accompanying drawings, in which:- Fig. 1 is a longitudinal sectional view through a part of a first embodiment of a fuel-injection pump in accordance with the invention, having a constant commencement of fuel-injection and a variable termination of injection of the pre-injection process and the main- injection process, showing the position of the pump piston at the commencement of injection of the pre-injection process; Fig. 2 is a developed view of the pump piston illustrated in Fig. 1.

Fig. 3 is a developed view of a pump piston of a second embodiment wherein all the control edges are designed as oblique edges for the purpose of varying the commencement of injection and the termination of injection; and Fig. 4 is a longitudinal section of a third embodiment analogous to the illustration of Fig. 1, in which the recess in the cylinder sleeve is formed by virtue of an oblique blind bore.

In the fuel-injection pump of which only the region relevant to the invention is illustrated in Fig. 1, mostly several cylinder sleeves 3 are installed in line in a pump housing 1. Each cylinder sleeve 3 has a cylinder bore 5, in which a pump piston -77 is moved by a cam drive (not illustrated) axially in a reciprocating manner with its front face 9 defining a pump working chamber 11 and is rotated by way of a control rod, (likewise not illustrated) for the purpose of adjusting the fuel-injection. The pump working chamber 11 is. for its part, connected by way of a fuel-injection line 13 in which is disposed a pressure-equalising delivery valve 15 (illustrated symbolically), to a fuel-injection valve (not illustrated) protruding into a combustion chamber of the internal combustion engine being supplied. Two diametrically opposite control ports 17 are disposed in the cylinder sleeve 3 for the purpose of supplying the pump working chamber 11 with fuel. The two control ports 17 are designed as radial through- going bores and open into a low pressure chamber 19 forming an intake chamber, which for its part is supplied with low pressure fuel by a fuel- delivery pump (not illustrated). The boundary edges of the control ports 17 form in each case two control edges, of which an upper control edge 21 is towards the pump working chamber 11 and a lower control edge 23 is further away from the pump working chamber 11. A radial blind bore 25 is provided in the cylinder sleeve 3 at a predetermined spacing from the control port 17 in the direction away from the pump working chamber 11, in -8such a way that the wall of the cylinder bore 5 is penetrated from the low pressure chamber 19 and terminates in the opposite wall of the cylinder bore 5, wherein it extends at an angle, in the embodiment illustrated in Fig. 1, at 90 offset from the control port 17. The part 26 of the blind bore 25, which is open towards the low pressure chamber 19 and which forms a through-going bore. is closed by a closure screw 28, so that the remaining parts of the blind bore 25 are now only recesses, which form an overflowcross section with the pump piston 7, wherein their lower boundary forms a lower control edge 30 and their upper boundary towards the pump working chamber 11 forms an upper control edge 32 at the cylinder bore 5. An additional radial through-bore 34, adjoins the blind bore 25 and connects the cylinder sleeve 3 (or rather the cylinder bore 5) to the low pressure chamber 19, and is aligned analogously to the control port 17.

The pump piston 7, forms by its front face 9 a first upper control edge 36, which cooperates with the upper control edge 21 of the control opening 17, and has in addition to this, a second lower oblique control edge 38 on its periphery. This second lower oblique control edge 38 cooperates with the lower control edge 23 of the control ports 17 and forms on -9the pump piston 7 an upper boundary edge of a first annular groove 42, which is continuously connected to the pump working chamber 11 by way of a longitudinal groove 40. This first annular groove 42 is separated by a land 44 from a second annular groove 46 on the side of the pump piston 7 remote from the pump working chamber 11. In so doing, the boundaries of the land 44 form in each case an upper third control edge 48 facing the pump working chamber 11 and a lower fourth control edge 50 remote from the pump working chamber 11. The fourth lower control edge 50 comprises oblique regions 52 at the land 44.

The land 44 is designed in the axial longitudinal direction of the pump piston 7 in such a way, that its axial extent is less than the diameter of the blind bore 25, so that it is possible during a part of the pump piston stroke for fuel to flow through from the first annular groove 42 by way of the blind bore 25 into the second annular groove 46. Since the second annular groove 46 is continuously connected by way of the through bore 34 to the low pressure chamber 19 whilst the land 44 crosses over the blind bore 25, a connection is therefore produced between the first annular groove connected to the highly pressurised pump working chamber 11 and the second annular groove 46 connected to the low pressure chamber 19 whilst the -10land 44 crosses over the blind bore 25. This connection is opened by the lower control edge 50 of the land 44 crossing over the lower control edge 30 of the blind bore 25 and closed again by virtue of the upper control edge 48 of the land 44 crossing over the upper control edge 32 of the blind bore 25.

In order to show clearly the position of the control edges on pump piston 7 of Fig. 1, the pump piston 7 in Fig. 2 is illustrated additionally as a developed view corresponding to the first embodiment illustrated in Fig. 1.

As can be seen, the pump piston 7 in this embodiment is designed with two flows, i.e. it is provided with two oblique control edges 38, and two oblique control edges 52 which are precisely symmetrically to each other and which cooperate with corresponding control ports 17, 25 and 34 in the double design.

The second embodiment illustrated in Fig. 3 differs from the first embodiment illustrated in Figs. 1 and 2 merely in the design of the control edges on the pump piston 7, for which reason only a developed view of this is illustrated. In order to be able to vary the control of the commencement of the injection and the termination of injection of the pre-injection process and the main-injection process by means of the -11rotational position of the pump piston, all control edges 36, 38, 48, 50 comprise oblique edges, which, as described with reference to Figs. 1 and 2, cooperate with the control edges in the cylinder sleeve 3.

A third embodiment is illustrated in Fig. 4 analogous to the illustration of Fig. 1. This embodiment differs merely by virtue of a simplified manufacture of the recess in the cylinder sleeve 3 provided by the blind bore 25 and the additional through bore 34, in that these are replaced by a single oblique blind bore 60. The tip 62 of this oblique blind bore 60 forms the recess in the cylinder wall illustrated in Fig. 1 analogous to the blind bore 25 and therefore renders it possible during a part of the pump piston stroke for fuel to flow through from the first upper annular groove 42 to the second lower annular groove 46. The boundaries of the wall of the cylinder bore 5 are formed as control edges, of which the upper control edge 32 cooperates with the upper, third control edge 48 at the land 44 of the pump piston 7 and the lower control edge 30 cooperates with the lower fourth control edge 50 of the pump piston 7. In this embodiment, the part 64 of the oblique bore 60 formed as a through bore to the cylinder bore 5 between the low pressure chamber 19 and the cylinder bore 5 replaces the additional through bore 34 of Fig.

-121 and also completely assumes its function.

The axial spacing of the lower control edge 30 of the tip 62 of the blind bore 60 from the upper control edge 66 of the part 64 of the blind bore 60 forming the through bore is smaller than the axial height of the land 44.

The fuel-injection pump in accordance with the invention functions as follows.

During the intake stroke of the pump piston 7 in the direction towards the bottom dead centre, fuel flows from the low pressure chamber 19 by way of the control port 17 into the pump working chamber 11, wherefrom, fuel flows by way of the longitudinal groove 40 as far as the first annular groove 42 and the blind bore 25, 60. During this time, the lower annular groove 46 is supplied with fuel from the low pressure chamber 19 by way of the through bore 34 andlor the part 64 of the oblique blind bore 60.

During the subsequent delivery stroke of the pump piston 7 in the direction towards the top dead centre, fuel initially flows from the pump working chamber 11 and the volume connected thereto back into the low pressure chamber 19 whilst the fuel located in the second annular groove 46, which is at the identical pressure as that the low pressure chamber 19, is moved simultaneously by reason of its inertia.

Upon the first and second annular groove being sealingly separated from each other by the land 44, the pre-injection process begins when the first upper control edge 36 of the pump piston 7 crosses over the upper control edge 21 (as illustrated in Fig. 1). When the connection between the pump working chamber 11 and the low pressure chamber 19 is thereby interrupted, fuel is compressed in the pump working chamber 11. the fuel- injection pressure is achieved, the pressure-equalising delivery valve 15 is pushed open and the fuel flows by way of the fuel-injection valve for the purpose of fuel-injection. This preinjection of a small quantity of fuel is terminated by virtue of the lower control edge 50 of the land 44 crossing over the lower control edge 30 of the blind bore 25, since the highly pressurised fuel is now relieved by way of the first annular groove 22, the blind bore 25 and the second annular groove 46 into the low pressure chamber 19. At the same time, the fuel pressure in the pump working chamber 11 drops below the fuel-injection pressure, the pressureequalising delivery valve closes and the fuelinjection is interrupted. During the course of the further delivery stroke of the pump piston 7, the upper control edge 48 of the land 44 on the pump piston 7 crosses over the upper control edge 32 of the -14blind bore 25, so that the connection between the two annular grooves is interrupted and it is possible for the pressure required for fuel- injection to build up again in the pump working chamber and the main quantity of fuel continues to be injected as described above.

The termination of the main-injection process is determined in a known manner by virtue of the oblique control edge 38 crossing over the lower control edge 23 of the control port 17 by means of which a connection is reopened between the pump working chamber 11 and the low pressure chamber 19.

By designing all control edges 36. 38, 48, 50 of the pump piston 7 in accordance with the invention as oblique control edges, it is possible at the same time to control the points in time of the commencement of the delivery and the termination of delivery of the pre-injection process and the main-injection process in dependence upon the rotational position of the pump piston 7, whereby in addition to being able to control the point in time of the fuel-injection, it is also possible to control the fuel quantities. In addition to this, it is possible to avoid the preinjection process by disposing the regions 52 of the lower control edge 50 in a lower position, in that these regions are so low, that when the control port 17 is - is- closed by the pump piston 7, the lower control edge 50 has already opened a flow cross section between the second annular groove 46 and the blind bore 25, which is connected to the first annular groove 42, so that it is not possible for high pressure to build up in the pump working chamber 11.

A zero delivery quantity is achieved at the same time during the maininjection process in a known manner by virtue of moving the longitudinal groove 40 of the pump piston 7 over the control port 17.

Claims

-16CLAIMS

1. A fuel-injection pump for an internal combustion engine having at least one pump piston, which is guided axially and in a manner so as to be able to rotate and is reciprocatingly driven in a cylinder bore and which defines by its front face a pump working chamber, in which the pump piston has in its periphery a control recess connected to the pump working chamber. this control recess having an oblique control edge which is at a predetermined angle to the axis of the pump piston and which cooperates with a control port in the wall of the cylinder bore, and the control port is connected to a low pressure chamber and issues into a first annular groove in the periphery of the pump piston, the annular groove being connected continuously to the pump working chamber and being separated from a second annular groove by a land formed by a part of the piston, and in which the second annular groove is connected during part of the pump piston stroke to a through-opening in the cylinder wall connected to the low pressure chamber, the land has circumferential boundary edges contiguous to the periphery of the pump piston and these boundary edges form in each case a control edge, of which an upper control edge, towards thie pump working chamber, cooperates with an upper control edge,towards the pump -17working chamber of a recess in the cylinder wall and a lower control edge of the land cooperates with the lower control edge of the recess. the lower control edge of the land having regions with oblique edges.

2. A fuel-injection pump according to claim 1, in which the axial height of the recess is greater than the axial height of the land, enabling the land to bridge the recess over a predetermined pump piston stroke.

3. A fuel-injection pump according to claim 2, in which the recess in the cylinder wall is formed as a blind bore which radially penetrates the cylinder bore and the end of the blind bore which would be open towards the low pressure chamber is closed off, and in which the piston has two oblique control edges which are disposed symmetrically to each other and which cooperate with the diametrically opposite control ports; and the lower control edge of the land comprises two oblique-sided regions which are allocated in a symmetrical manner and which cooperate with two diametrically opposite recesses.

4. A fuel-injection pump according to claim 1 or 2, in which an oblique blind bore whose axis intersects the axis of the cylinder bore, is provided in such a way that it forms a through bore forming a through opening between the low pressure chamber and the cylinder sleeve and the tip of the blind bore is simultaneously the recess in the cylinder wall. and in which the lower control edge of the recess formed by the tip of the blind bore is spaced axially from the upper control edge of the through bore part of the blind bore and this spacing is smaller than the axial height of the land.

5. A fuel-injection pump according to any of claims 1 to 4, in which the upper control edge of the land comprises regions which have oblique edges.

6. A fuel-injection pump according to claim 3, in which the through bore forming the through opening in the cylinder wall is disposed offset to the blind bore.

7. A fuel-injection pump according to any of claims 1 to 4, in which the front face of the pump piston is formed with an oblique control edge.

8. A fuel-injection pump for an internal combustion engine, constructed and adapted to operate substantially as herein described, with reference to and as illustrated in the accompanying drawings.