GB2394002A

GB2394002A - An injection system operating with pressure intensification

Info

Publication number: GB2394002A
Application number: GB0327914A
Authority: GB
Inventors: Volker Schwarz
Original assignee: DaimlerChrysler AG
Current assignee: Daimler AG
Priority date: 2001-12-03
Filing date: 2002-11-25
Publication date: 2004-04-14
Anticipated expiration: 2022-11-25
Also published as: GB2394001A; GB2394002B; GB0327911D0; GB0327914D0; GB2394001B

Abstract

An injection system operating with pressure intensification comprises an injector 3 supplied with an injection medium from a pressure source and a pressure intensifier 13. The injector 3 has a nozzle needle 5 and action space 7 which controls the movement of the nozzle needle, the action space being connected to the inflow from the pressure source and to a return 11, the inflow side having a non-return. The pressure intensifier 13 comprises pressure receiver 16 and pressure transmitter 17. The receiver 16 has a larger action surface 18 than transmitter 17, and is connected to the inflow to the action space 7 of the injector 3. The pressure receiver has a control space 20 on one side and a spring 47 at the other. The action space 7 and control space 20 are connected to the return 11 by separate valve control, the return from the control space being actuated by control slide 29 via the action of the nozzle needle of the injector.

Description

Injection system operating with pressure intensification The invention

relates to an injection system operating with pressure intensification, in which there is arranged, at the transition from a pressure source, which is formed, in particular, by a pressure accumulator, to an injection injector, a pressure intensifier having a control space, as a function of the pressure level of which the degree of intensification, and consequently the pressure rise in relation to the initial pressure in the pressure accumulator, is to be determined and therefore also the action pressure for the injector is to be fixed, the nozzle needle of the latter being loaded in the closing direction by the action of pressure on an action space assigned on the rear side.

In a known injection system of this type, the control space and also the action space are connected to the return independently of one another, in each case by valve control, so that, by control of the pressure intensifier, the shape of the pressure curve can be fixed and, by the injector activation independent of this, a suitable range of the pressure curve for injection can be selected. The mutually independent activation of the pressure intensifier and of the injector takes place via magnetically actuated 2/2-way valves and, in addition to a space requirement and costs, necessitates a highly accurate coordination in the activation of these, since even small tolerances result in marked differences in the injection behaviour.

In order to arrive at a reduction in the space requirement and the costs, and also at a simplification of activation, along with a breadth of variation sufficient for exerting influence on combustion, a solution according to the invention utilizes the injection injector itself as a control element or control valve, in that a part, involved in action upon the nozzle needle and correspondingly stroke-moveable together with the nozzle needle, of the latter or of a part stroke-moveable together with it is designed as a control slide, thus resulting, by virtue of the design of the control cross section, without any appreciable additional outlay, in a possibility of exerting influence by which, in particular, the rising flank of the pressure profile can be varied in relation to the pressure prevailing at the nozzle-needle seat.

For this process sequence, it is assumed that the closing position of the magnetically activated control valve has corresponding to it a closing position of the nozzle needle, due to the high pressure prevailing in the action space and due to the cut-off of the control space relative to the return, this cut-off being determined via the pressure balance. When the magnetically activated control valve, which is designed, in particular, as a 2/2-way valve, is briefly opened, this leads primarily to a pressure drop in the action space and, with some delay, to a pressure drop in the control space and a lowering of pressure in the action upon the control piston of the pressure balance in the direction of its closing position. In this intermediate phase, however, the nozzle needle is still closed, so that, in the event of the correspondingly brief opening of the control valve, the pressure in the action space is reduced, but not the pressure prevailing on the inflow side, assuming corresponding dimensioning of the throttle cross sections in the inflow and in the outflow to the action space. If, then, the control valve is once again changed over into its opening position, an initial situation with a lowered pressure in the action space, along with the high pressure prevailing on the inflow side, is defined, so that, during the opening of the nozzle needle, a correspondingly steep pressure rise at the nozzle-needle seat, and consequently a steep ramp, is obtained, especially since the previous lowering of pressure as a result of the preceding brief opening of the control valve also causes the pressure acting upon the control slide of the pressure balance in the direction of its closing position to be reduced, so that, when the control valve is once again changed over into its opening position in order to initiate injection, there is a rapid displacement of the control slide of the pressure balance into the opening position connecting the control space to the return.

In a further embodiment, in which the pressure balance is branched off, on the one hand, from the inflow and, on the other hand, from a throttled connection between the inflow and the connection of the control space to the following control valve, when injection is initiated by opening of the control valve, the pressure intensifier is cut in before the injector is released. The result of this is a high pressure prevailing at the injector when the latter responds, this, in turn, entailing a steep, virtually rectangular pressure profile during injection.

Overall, therefore, in the solution according to the invention with only one magnetically activated control valve, a working behaviour is achieved, in which tolerances in the activation behaviour are avoided and the space requirement and control requirement are reduced overall, and in which, irrespective of these simplifications, both preinjection and postinjection are possible and the injection pressure is freely selectable.

Further details and features of the invention may be gathered from the claims. Moreover, embodiments of the invention are explained below in terms of its construction, with reference to the drawings in which: Fig. I shows a diagrammatic illustration of an injection system with pressure intensification, in which the connection of the control space of the pressure intensifier and of the action space of the injector is controlled via a control valve, Fig. 2 shows a diagrammatic illustration of the pressure profile at the nozzle-needle seat over tine, Fig. 3 shows a further embodiment of an injection system with pressure intensification, the stroke movement of the nozzle needle of the injection injector being utilized for controlling the connection of the control space of the pressure intensifier to the return, and Figs 4 and 5 show further solutions for an injection system with pressure intensification, in which the connection of the control space of the pressure intensifier or the connection of the action space of the injection injector to the return are controlled via a pressure balance.

In the figures, reference I designates an injection system which comprises a pressure source 2 in the form of a pressure accumulator, as is customary particularly in common-

rail systems, and an injection injector 3. The injection injector 3 is illustrated merely diagrammatically and has a nozzle-needle bore which runs out onto a nozzle seat 4 with following injection holes and in which is guided a nozzle needle 5 which is spring-loaded in the direction of its closing position, as indicated diagrammatically at 6, and which runs out on the rear side onto an action space 7 which is connected in a throttled manner,

indicated by a diaphragm or throttle 8, to the inflow 9 and which also has a connection 10 to the return 11, a throttle 12, if appropriate also designed as a diaphragm, being provided, in turn, at the transition of the action space 7 to the connection 10.

A pressure intensifier 13 lies at the transition from the pressure source 2 to the injection injector 3, specifically in the bypass to a portion 14 of the inflow 9 which is shut off relative to the pressure source 2 via a non-return valve 15.

The pressure intensifier 13 comprises, in a design in the manner of a step piston, a pressure receiver 16 and a pressure transmitter 17, the pressure receiver 16 having a larger action surface 18 than the pressure transmitter 17, the action surface of which is designated by 19.

In the opposite direction to the action surface 18, the pressure receiver 16 is assigned a control space 20 and a spring 47 which lies in the latter, which control space is connected in a throttled manner, illustrated symbolically by the throttle 21, to the inflow connection 22 between the pressure source 2 and the working space 23 assigned to the action surface 18 of the pressure receiver 16.

The control space 20 has a connection 24 to the return 11, and the connection 24 of the control space 20 to the return 11 is led, combined with the connection 10 of the action space 7 to the return 11, to a control valve 25 which is designed as a magnetically controlled 2/2-way valve and via which the control space 20 and the action space 7 are to be connected to the return 11 or cut off relative to the latter.

In relation to the illustrated initial position of the control valve 25, the connections 10 and 24 are cut off relative to the return 11, with the result that the pressure intensifier 13 is not activated and the nozzle needle 5 is held in its closing position via the pressure prevailing in the action space 7.

When the control valve 25 is opened, the control space 20 and also the action space 7 are simultaneously connected to the return 11 and are consequently relieved of pressure, with the result that the pressure intensifier 13 is activated and the nozzle needle 5 is raised into

the opening position via the injection medium which is present under high pressure. In this case, by the pressure intensifier 13 being interposed, there is a raising of the pressure prevailing on the inlet side via the pressure source 2, so that, depending on the degree of intensification, very high injection pressures are available, the pressure rise being restricted to that fraction of the injection medium which runs via the injection injector 3.

The response times in the connection of the control space 20 to the return 11 or of the action space 7 to the return 11 can be influenced via the respective connection cross sections, as illustrated for the connection 10 by the throttle 12.

Fig. 2 illustrates the profile of the pressure P at the nozzle-needle seat 4 over time t, Pi designating the pressure provided by the pressure source, and P2 designating the pressure which prevails on the inflow side during activation of the pressure intensifier 13. It designates the time point of the opening of the control valve 25 and t2 its subsequent closing time point. The opening-side ramp of the pressure-profile curve is designated by 26 and the ramp occurring during closing is designated by 27. A steeper or flatter profile of the ramps 26, 27 is obtained as a function of the pressure reduction in the action space 7 and of the level of the high pressure prevailing on the inflow side, the aim being to have a steep, preferably virtually rectangular profile particularly on the opening side.

Fig. 3 shows a further embodiment, corresponding parts or connections being given the same reference symbols.

Contrary to the illustration according to Fig. 1, the connection from the control space 20 to the return l 1 is designated by 28 and is led via a control slide 29 which is formed as an integral part in the actuation, emanating from the action space 7, of the nozzle needle 5 by the control piston and which delimits the action space on the nozzle-needle side, the control slide 29 having a control groove 30.

Via the control groove 30 and its position in relation to the connection cross sections of the connection 28 to the injector 3, the control times can be additionally influenced, whilst the control groove 30 may, if appropriate, also form a throttle cross section.

In the solution according to Fig. 4, as in the previous versions, the control valve 25 lies in the connection 10 to the return 11. The connection 31 between the control space 20 and the return 11 is led via a pressure balance 32 containing a control slide 33 which has a control groove 34 and which is loaded in the direction of one end position via a spring 35.

The pressure balance 32 is connected, at the end opposite the spring 35, to the inflow 9, and a throttled connection 36 running via the throttle 37 leads from the inflow 9 to the connection 10 of the action space 7 to the return 11, the connection for that end of the control slide 33 which is acted upon via the spring 35 being branched off from the connection 36. Depending on the action of pressure, the control groove 34 overlaps with the connection 31 of the control space 20 towards the return 11 or cuts off this connection. When the control valve 25 is opened, the pressure in the action space 7 and also the spring-side action of pressure on the control slide 33 of the pressure balance 32 fall, so that the pressure intensifier 13 is activated. The corresponding time sequences can be influenced in a more or less throttling manner by means of appropriate connection cross sections. Corresponding influence is also made possible by the timing of the control valve 25, for example such that the latter is first opened briefly, so that there is some lowering of pressure in the action space 7, but the nozzle needle 5 does not lift off from the nozzle seat 4. When the control valve 25 is reopened after a brief closing phase, an initial position is defined, in which there is a lower action pressure in the action space 7 and therefore the high pressure built up via the pressure intensifier 13 acts upon the nozzle needle 5 against a lower counterpressure, thus leading to a virtually abrupt opening of the nozzle needle 5, along with a correspondingly steep pressure rise in the nozzle seat 4.

In the embodiment according to Fig. 5, once again a pressure balance 38 is used for operation, having a control slide 39 which is loaded towards one end position via a spring 40 and which has a control groove 41.

The control space 20 of the pressure intensifier 13 is connected to the return 11 via the connection 24 running via the control valve 25. The pressure balance 38 lies between the inflow 9 and the connection 24 of the control space 20 to the return 11. The spring-side end of the pressure balance 38 is assigned a connection 42 which runs towards the inflow

9 via a throttle 43 and towards the connection 24 via a throttle 44, the connection 45 to the spring side of the pressure balance 38 being branched off between these throttles 43 and 44. The opposite connection is designated by 46 and is connected, unthrottled, to the inflow 9. In this embodiment, during the opening of the valve 25, the pressure intensifier 13 is first cut in and there is some delay time in the response of the injector 3, so that, at the start of injection, a high pressure becomes effective on the nozzle needle 5 and an approximately rectangular profile of the pressure curve is obtained.

Attention is directed to co-pending Patent Application No. 00271711.7 (published under No. 2384821) from which the present application is divided.

Claims

1. An injection system operating with pressure intensification, which has an injection injector supplied with injection medium from a pressure source, with a nozzle needle and with an action space which lies on the rear side in relation to the nozzle needle and which is connected in a throttling manner to an inflow emanating from the pressure source and to a return, the said injection system having, in a bypass to an inflow portion having non-

return protection relative to the pressure source, a pressure intensifier comprising a pressure receiver and a pressure transmitter of smaller working surface, which is connected to the inflow to the action space of the injection injector and against which is supported counter to spring force the pressure receiver which, with respect to its working surface acted upon in the direction of the pressure transmitter, is connected to the pressure source, from which a throttled connection leads to a control space assigned to the opposite surface of the pressure receiver, the control space and the action space being connected to the return in each case separately by valve control, wherein the valve control for the connection of the control space to the return is formed by a control slide lying in the actuation of the nozzle needle emanating from the action space of the injection injector.

2. An injection system operating with pressure intensification according to Claim 1, wherein the control slide is formed by the control piston of the nozzle-needle control, the said control piston delimiting the action space on the nozzle-needle side.

3. An injection system operating with pressure intensification, in accordance with claim 1 and substantially as described herein, with reference to and as illustrated in, the accompanying drawings.