GB2107802A

GB2107802A - Fuel injection pump, suitable for a diesel engine

Info

Publication number: GB2107802A
Application number: GB08230205A
Authority: GB
Inventors: Wilfried Hofken
Original assignee: LOrange GmbH
Current assignee: LOrange GmbH
Priority date: 1981-10-21
Filing date: 1982-10-21
Publication date: 1983-05-05
Also published as: DE3141653A1; JPS6151664B2; DE3141653C2; GB2107802B; FR2514828A1; IT8223865A0; JPS58131354A; IT1153287B; FR2514828B1

Abstract

A fuel injection pump comprising a piston 3 working in a cylinder body 2a has an inlet bore 5 and at least one axially staggered control bore (9). The control bore or bores is/are selectively operable by a slide (10), the position of the bore which is open, until closed by the piston, determining the start of the actual delivery. The slide is operated by an actuator (30). Thus the timing of the beginning of the injection can be varied by appropriate selection of which bore is effective. <IMAGE>

Description

SPECIFICATION Fuel injection pump, suitable for a diesel engine This invention relates to a fuel injection pump, suitable for a diesel engine.

In known fuel pumps changes in the beginning of supply or in the output are effected by varying the effective stroke of the pump piston. This variation of the effective stroke is achieved by a twisting of the pump piston, which has an overhead slanting control edge which, via a longitudinal groove, is connected with an annular groove positioned below it. In such pump versions the supply begins, when during the working stroke the slanting control edge has run over the control bore and is positioned at the level of the valvesided rim of the inlet bore. The supply is terminated, when the running piston releases the control bore again, because then the pressure space above the piston is again connected with the control bore via the longitudinal groove.Thus the beginning of supply is dependent on a twisting of the pump piston, while the termination of supply remains uncnanged.

Moreover fuel injection pumps are known in which the termination of supply is changed, while the beginning of supply remains unchanged. In these versions the supply of the fuel begins, when the front face of the piston is positioned at the level of the valve-sided rim of the inlet bore, while the termination of supply is affected by a lower control edge.

Thus in both cases the effective stroke is affected by appropriate measures at the supply piston. This requires a relatively complicated mechanism, because an action on the movable piston is necessary.

Moreover so-called fuel-injection adjusting mechanisms are known in which the beginning of fuel injection is put forward with increasing revolutional speed in order to improve the engine output. For this purpose in most cases mechanical governors are used which are able to displace the cam shaft of the fuel injection pump by some angular degrees relative to the crank shaft of the engine. These versions to modify the beginning of fuel injection are also relatively complicated and thus also expensive and, to a certain extent, susceptible to trouble.

The invention is based on the problem of developing a fuel injection pump so as to vary the beginning of fuel injection with means as simple as possible and not susceptible to trouble.

According to the present invention there is provided a fuel injection pump suitable for a diesel engine, comprising a piston movably mounted in a piston guiding body, which piston via at least one inlet bore in the area of the bottom dead centre presses the fuel flowing into the pump chamber during the pressure stroke into a supply pipe via a delivery valve, whereby at the beginning of the effective stroke a control edge on the piston is located at the level of the inlet bore rim facing the valve, wherein the position of the valve-sided rim of the bore affecting the effective stroke is variable by a slide operable by an actuator.

In contrast to known versions, in which the height of the effective stroke is determined by a change in the position of the control edge on the piston, the invention is based on the idea of varying the position of the inlet bore rim affecting the effective stroke. An action on movable parts of the fuel injection pump, namely the piston, is thereby prevented, so that the design can be considerably simplified.

In principle the invention can be realised by a continuously displaceable slide, so that the beginning of the fuel injection can be continuously varied.

A very simple design is realised in a solution including the features of claim 2. In this case the piston guiding body has at least one control bore, which in the axial direction is staggered relative to the inlet bore and opens into the pump chamber and whose rim facing the valve affects the effective stroke and that to the control bore is assigned a slide to be operated via an actuator for opening and closing the control bore. When the control bore is closed the effective stroke is dependent on the position of the valve-sided rim of the inlet bore. When the control bore, however, is open its valve-sided rim affects the effective stroke.

If a multi-step variation of the beginning of fuel injection is required the piston guiding body can be provided with several control bores which in the axial direction are staggered relative to one another. In this case the respective valve-sided rim of the uppermost and open control bore determines the beginning of fuel injection. The control bores opening into the pump chamber in a staggered way can in addition be also staggered in the circumferential direction. In this case a slide can be assigned to each control bore without any difficulty.

In a multi-step version a solution will however be preferred, in which the control bores staggered in the axial direction are arranged along a straight line, preferably a jacket line, so that a common slide can be assigned to all control bores.

The slide can be displaced by an electromagnetic or a hydraulic actuator or by an actuator working in another way in dependence on the revolutional speed and/or on the adjusted load. In this case it is particularly advantageous, that the beginning of fuel injection of otherwise identical fuel injection pumps can be easily varied also by way of addition without having for example to exchange the piston.

In order that the invention can be clearly understood reference wiil now be made to the accompanying drawings in which: Fig. 1 is a partial section through a fuel injection pump with an electromagnetic actuator, according to an embodiment of the invention.

Fig. 2 is a partial section through another embodiment with a hydraulic actuator.

In Fig. 1 the pump housing has the reference numeral 1. In this pump housing a piston guiding body 2 is inserted and held by screws in a known manner. In the piston guiding body slides the piston 3, whose front edge 4 forms a control edge affecting the effective stroke. An annular duct in the pump housing 1, which annular duct is known as such, is connected with the pump chamber via an inlet bore 5. This inlet bore opens into the pump chamber in the area of the bottom dead centre of the piston shown in the drawing. The supply in conventional fuel injection pumps equipped in this manner begins, when the front edge 4 on the piston 3 is positioned at the level of the valve-sided rim 5a of the inlet bore 5. In this case the inlet bore 5 is closed.With the following effective stroke of the piston 3 a pressure valve 6 opens and the fuel is pressed from the pump chamber into the outlet bore 7 and further into a supply pipe not shown in detail.

In the embodiment according to Fig. 1 the piston guiding body 2 is provided with a control bore 9, which also connects the annular duct with the pump chamber, but relative to the inlet bore 5 in the axial direction and in the direction of motion of the piston respectively this control bore is arranged in a staggered way. The drawing shows that the spacing a between the valve-sided rim Sa of the inlet bore 5 and the control edge 4 of the piston is smaller in the bottom dead centre position than the spacing b between the valvesided rim 9a of the control bore 9 and the front edge 4. Thus during the pressure stroke the piston closes the inlet bore 5 earlier than the control bore 9.

The piston guiding body 2 is provided with a guiding bore 8 which intersects the control bore 9 and in which a slide 10 is fitted with the smallest play possible. This slide 10 is connected with an actuating rod 12 also mounted in the guiding bore 8. The connection is effected via 1 a joint 11 which can be a cardanic joint. The guiding bore is also penetrated by a thrust-carrying piece 1 7 which is screwed onto the front side of the piston guiding body 2. A lever 1 3 is articulated to the end of the actuating rod 12. This lever is acted upon by an actuator as a whole designated with the reference numeral 30. In the embodiment according to Fig. 1 this actuator 30 is an electromagnet. In the switching position shown in Fig. 1 the actuator occupies its rest position.The slide 10 thereby closes the control bore 9, so that through this control bore no fuel can flow from the annular duct into the pump chamber. When the magnet of the actuator 30 becomes excited the actuating rod and thus also the slide 10 is displaced in the direction of arrow A, so that the control bore 9 is released. In this case the begin of fuel supply is no longer determined by the position of the valve-sided rim 5a of the inlet bore 5, but by the position of the valve-sided rim 9a of the control bore 9. Thus the difference between the spacings b and a determines the injection lag.

The slide can be well sealed towards the outside by a rubber ring 14 inserted in a groove of the actuating rod. The possible lift of the slide is limited by stops 1 6 and 1 8 on the thrust-carrying piece 17 and the piston guiding body 2 respectively, which co-operate with a stop shoulder 1 5 on the actuating rod 1 2.

The embodiment according to Fig. 2 substantially differs from that of Fig. 1 only by another type of actuator 30. The actuating rod and the slide 10 respectively is provided with a piston 19 upon which acts a spring 22, which is supported on the wall 16 of the thrust-carrying piece via a suitable recess 20. The piston 19 and thus the slide 10 can be displaced in the direction of arrow A against the force of the spring 22, when a liquid is pressed into the piston space through a duct 23. When the piston space is relieved the piston is reset by the pressure spring 22 into its rest position shown in which the control bore 9 is closed. Alternatively Fig. 2 shows an embodiment in which the piston 1 9 is acted upon by a liquid from both sides alternatingly via the ducts 23 or 24.

In order to seal the piston space properly with regard to the liquid streaming into it through the duct 24, a sealing ring 21 is provided which is put onto the recess 20.

In Fig. 2 it is indicated by broken lines that in the axial direction staggered relative to the bore 9 a further bore 29 can be arranged. The valve-sided rim 29a is positioned at a spacing c from the front edge 4 of the piston in its bottom dead centre position. The two bores 9 and 29 are positioned on a straight line and therefore can both be controlled via the slide 10. Further bores can, of course, be arranged staggered in the axial direction, if one wants to vary the beginning of injection in several steps. Moreover it is conceivable to provide in the plane of the control bore 9 or 29 further boes staggered in the circumferential direction, which further bores are closed, for example, a by a ring-shaped slide.

In the embodiments shown the slide is displaced in parallel to the piston guiding axis.

However embodiments are conceivable in which the slide is adjusted at any desired angle to the piston guiding axle, for example also rectangularly to it. However the embodiments shown have the advantage of a smaller overall height.

Claims

1. A fuel injection pump suitable for a diesel engine, comprising a piston movably mounted in a piston guiding body, which piston via at least one inlet bore in the area of the bottom dead centre presses the fuel flowing into the pump chamber during the pressure stroke into a supply pipe via a delivery valve, whereby at the beginning of the effective stroke a control edge on the piston is iocated at the level of the inlet bore rim facing the valve, wherein the position of the valve-sided rim of the bore affecting the effective stroke is variable by a slide operable by an actuator.

2. A fuel injection pump according to claim 1, wherein the piston guiding body has at least one control bore, which in the axial direction is staggered relative to the inlet bore and opens into the pump chamber and whose rim facing the valve affects the effective stroke and that to the control bore is assigned a slide to be operated via an actuator for opening and closing the control bore.

3. A fuel injection pump according to claim 2, wherein several control bores open into the pump chamber and are staggered in the axial direction and possibly in the circumferential direction and a slide is assigned to each control bore.

4. Afuel injection pump according to claim 2, wherein several control bores arranged along a straight line opening into the pump chamber and that the respective control bores are positioned between the upper dead centre of the piston and the effective control bore and can be closed by a slide common for all control bores.

5. A fuel injection pump according to any one of the preceding claims, wherein several control bores are arranged at a plane which is perpendicular to the piston motion, which control bores are closed or opened by a common slide.

6. A fuel injection pump according to any one of the preceding claims, wherein in the piston guiding body a guiding bore is provided which intersects the control bores and in which guiding bore the slide and, preferably articulatedly connected with the slide, an actuating rod are guided upon which the actuator acts.

7. A fuel injection pump according to claim 6, wherein a thrust-carrying piece is screwed onto the front side of the piston guiding body, that the guiding bore also penetrates this thrust-carrying piece and that stops are formed on the piston guiding body and on the thrust-carrying piece for a stop shoulder on the actuating rod.

8. A fuel injection pump according to any one of the preceding claims, wherein the slide is displaceable by an electromagnetic actuator.

9. A fuel injection pump according to any one of claims 1 to 7, wherein the slide is displaceable by a hydraulic actuator.

10. A fuel injection pump according to claim 9, wherein the actuating rod of the slide or slides is itself provided with a displaceable piston and this piston and thus also the slide is displaced against the force of a pressure spring by a liquid streaming into the piston space into a position in which the inlet bore is open.

11. A fuel injection pump according to claim 9, wherein the actuating rod of the slide or slides itself is provided with a displaceable piston and the piston may be alternatingly acted upon from both sides by the pressure of a liquid.

12. A fuel injection pump substantially as hereinbefore described with reference to and as illustrated in Fig. 1 or Fig. 2 of the accompanying drawings.

13. A diesel engine having a fuel injection pump according to any preceding claim.